title: Exciton-phonon interaction calls for a revision of the "exciton" concept

abstract:
  The concept of \textit{optical} exciton - a photo-excited bound electron-hole
pair within a crystal - is routinely used to interpret and model a wealth of
excited-state phenomena in semiconductors. Beside originating sub-band gap
signatures in optical spectra, optical excitons have also been predicted to
condensate, diffuse, recombine, relax. However, all these phenomena are rooted
on a theoretical definition of the excitonic state based on the following
simple picture: "excitons" are actual particles that both appear as peaks in
the linear absorption spectrum and also behave as well-defined quasiparticles.
In this paper we show, instead, that the electron-phonon interaction decomposes
the initial optical excitons into \textit{elemental} excitons, the latter being
a different kind of bound electron-hole pairs lacking the effect caused by the
induced, classical, electric field. This is demonstrated within a many-body
perturbation theory approach starting from the interacting electronic
Hamiltonian including both electron-phonon and electron-hole interactions. We
then apply the results on two realistic systems, monolayer MoS$_2$ (where the
lowest-bound exciton is optically inactive) and monolayer MoSe$_2$ (where it is
optically active), using first-principles methods to compute the exciton-phonon
coupling matrix elements. Among the consequences of optical-elemental
decomposition, we point to a homogeneous broadening of absorption peaks
occurring even for the lowest-bound optical exciton, and we provide a lower
bound for the exciton linewidths. More generally, our findings suggest that the
optical excitons gradually lose their initial structure and evolve as elemental
excitons. These states can be regarded as the real intrinsic excitations of the
interacting system, the ones that survive when the external perturbation and
the induced electric fields have vanished.


title:
Symmetries as the guiding principle for flattening bands of Dirac
  fermions

abstract:
  Since the discovery of magic-angle twisted bilayer graphene (TBG), flat bands
in Dirac materials have become a prominent platform for realizing strong
correlation effects in electronic systems. Here we show that the symmetry group
protecting the Dirac cone in such materials determines whether a Dirac band may
be flattened by the tuning of a small number of parameters. We devise a
criterion that, given a symmetry group, allows for the calculation of the
number of parameters required to make the Dirac velocity vanish. This criterion
is employed to study band flattening in twisted bilayer graphene and in surface
states of 3D topological insulators. Following this discussion, we identify the
symmetries under which the vanishing of the Dirac velocity implies the
emergence of perfectly-flat bands. Our analysis allows us to construct
additional model Hamiltonians that display perfectly-flat bands at certain
points in the space of parameters: the first is a toy model of two coupled 3D
TI surfaces, and the second is a quasi-crystalline generalization of the chiral
model of TBG.


title: Quantum measurement process with an ideal detector array

abstract:
  Any observable with finite eigenvalue spectrum can be measured using a
multiport apparatus realizing an appropriate unitary transformation and an
array of detector instruments, where each detector operates as an indicator of
one possible value of the observable. The study of this setup in the frame of
von Neumann's quantum mechanical measurement process has a remarkable result:
already after the interaction of the measured system with the detector array
without collapse, exactly one detector is indicating a detection. Each single
detector indicates either 0 or 1 detection, and no superposition can be
attributed to it.


title:
Optimization of Mechanical Design Bladeless Wind Turbine for Electricity
  Fulfilment in Nusa Tenggara Timur, Indonesia

abstract:
  The current government's goal is the realization of an even distribution of
the electrification ratio in Indonesia. However, in 2018 the electrification
ratio in Nusa Tenggara Timur (NTT) only reached 62.07%. One of the solutions
offered is the implementation of a Bladeless Wind Turbine (BWT). BWT is a type
of wind power plant that can work optimally in areas with low wind speeds, 3 to
8 m/s, which is still above the NTT average wind speed, 2.3 m/s. This study
aims to optimize the mechanical design of BWT with shape and size parameters
based on the manipulation of the coefficient of friction through computational
fluid dynamic simulations that can work optimally according to wind speed in
NTT. In this study, 3 design variations were used, namely Initial Design,
Modified Design 1, and Modified Design 2. Based on the research that has been
done, MD2 has better results than MD1 and ID, and it can be said that MD2 can
work optimally in wind speed areas. low. So MD2 is a mechanical design model
that is very suitable to be applied in NTT and is expected to be a
recommendation in making masts for BWT-based wind power plants in Indonesia.


title:
A New Perspective on Quantum Field Theory Revealing Possible Existence
  of Another Kind of Fermions Forming Dark Matter

abstract:
  Quantum fields are considered as generators of infinite-dimensional Clifford
algebra $Cl(\infty)$, which can be either orthogonal (in case of fermions) or
symplectic (in case of bosons). A generic quantum state can be expressed as a
superposition of the basis elements of $Cl(\infty)$, the superposition
coefficients being multiparticle complex-valued wave functions. The basis
elements, that are products of the generators of $Cl(\infty)$ in the Witt
basis, act as creation and annihilation operators. They create positive and
negative energy states that include the bare and the Dirac vacuum as special
cases. It is shown that the nonvanishing electric charge arises from an extra
dimension or from doubling the number of creation and annihilation operators,
which brings an extra imaginary unit ${\bar i}$ into the description. A further
extension is to consider the ${\bar i}$ as one of the quaternionic imaginary
units and consider a generic state as having values in the quaternionic algebra
or, equivalently, in the complexified 2-dimensional Clifford algebra,
$Cl(2)\otimes C$.contains two distinct fundamental representations of $SU(2)$,
one associated with the weak isospin oublet $(\nu_e,e^-)$, and the other one
with the doublet of new leptons, denoted $(\epsilon^+,\nu_\epsilon)$, that
together with the new quarks $(u',d')$ can be identified with dark matter.


title: ResBos2 and the CDF W Mass Measurement

abstract:
  The recent CDF $W$ mass measurement of 80,433 $\pm$ 9 MeV is the most precise
direct measurement. However, this result deviates from the Standard Model
predicted mass of 80,359.1 $\pm$ 5.2 MeV by $7\sigma$. The CDF experiment used
an older version of the ResBos code that was only accurate at NNLL+NLO, while
the state-of-the-art ResBos2 code is able to make predictions at N${}^3$LL+NNLO
accuracy. We determine that the data-driven techniques used by CDF capture most
of the higher order corrections, and using higher order corrections would
result in a decrease in the value reported by CDF by at most 10 MeV.


title: The law of entropy increase and the Meissner effect

abstract:
  The law of entropy increase postulates the existence of irreversible
processes in physics: the total entropy of an isolated system can increase but
cannot decrease. The annihilation of an electric current in normal metal with
the generation of Joule heat because of a non-zero resistance is well-known
example of irreversible process. The persistent current, an undamped electric
current observed in a superconductor, annihilates after the transition into the
normal state. Therefore this transition was considered as irreversible
thermodynamic process before 1933. But if this transition is irreversible then
the Meissner effect discovered in 1933 is experimental evidence of a process
reverse to the irreversible process. Belief in the law of entropy increase
forced physicists to change their understanding of the superconducting
transition, which is considered a phase transition after 1933. This change has
resulted to the internal inconsistency of the conventional theory of
superconductivity, which is created within the framework of reversible
thermodynamics but predicts Joule heating. The persistent current annihilates
after the transition into the normal state with the generation of Joule heat
and reappears during the return to the superconducting state according to this
theory and contrary to the law of entropy increase. The success of the
conventional theory of superconductivity forces to consider the validity of
belief in the law of entropy increase.


title:
Characterizing temperature and strain variations with qubit ensembles
  for their robust coherence protection

abstract:
  Solid-state spin defects, especially nuclear spins with potentially
achievable long coherence times, are compelling candidates for quantum memories
and sensors. However, their current performances are still limited by the
decoherence due to the variation of their intrinsic quadrupole and hyperfine
interactions. We propose an \textit{unbalanced echo} to overcome this challenge
by using a second spin to refocus the variation of these interactions, which
preserves the quantum information stored in the free evolution. The unbalanced
echo can be used to probe the temperature and strain distribution in materials.
Experimentally, we demonstrate a 20-fold $T_2^*$ coherence time increase in an
ensemble of $\sim10^{10}$ nuclear spins in diamond. Theoretically, we develop
first-principles methods to predict these interaction variations and reveal
their correlation in large temperature and strain ranges. We numerically show
that our method can refocus stronger noise variations than our current
experiments and achieves a 400-fold coherence improvement for a 25~K
temperature inhomogeneity.


title:
First-principles Calculation of the Temperature-dependent Transition
  Energies in Spin Defects

abstract:
  Spin qubits associated with color centers are promising platforms for various
quantum technologies. However, to be deployed in robust quantum devices, the
variations of their intrinsic properties with the external conditions, and in
particular temperature, should be known with high precision. Unfortunately, a
predictive theory on the temperature dependence of the resonance frequency of
electron and nuclear spin defects in solids remains lacking. In this work, we
develop a first-principles method for the temperature dependence of zero phonon
line, zero-field splitting, hyperfine interaction, and nuclear quadrupole
interaction of color centers. As a testbed, we compare our ab-initio
calculation results with experiments in the Nitrogen-Vacancy (NV) center
finding good agreement. Interestingly, we identify the major origin of
temperature dependence as a second-order effect of phonon vibration. The method
is generally applicable to different color centers and provides a theoretical
tool for designing high-precision quantum sensors.


title: Tournaments, Johnson Graphs, and NC-Teaching

abstract:
  Quite recently a teaching model, called "No-Clash Teaching" or simply
"NC-Teaching", had been suggested that is provably optimal in the following
strong sense. First, it satisfies Goldman and Matthias' collusion-freeness
condition. Second, the NC-teaching dimension (= NCTD) is smaller than or equal
to the teaching dimension with respect to any other collusion-free teaching
model. It has also been shown that any concept class which has NC-teaching
dimension $d$ and is defined over a domain of size $n$ can have at most $2^d
\binom{n}{d}$ concepts. The main results in this paper are as follows. First,
we characterize the maximum concept classes of NC-teaching dimension $1$ as
classes which are induced by tournaments (= complete oriented graphs) in a very
natural way. Second, we show that there exists a family $(\cC_n)_{n\ge1}$ of
concept classes such that the well known recursive teaching dimension (= RTD)
of $\cC_n$ grows logarithmically in $n = |\cC_n|$ while, for every $n\ge1$, the
NC-teaching dimension of $\cC_n$ equals $1$. Since the recursive teaching
dimension of a finite concept class $\cC$ is generally bounded $\log|\cC|$, the
family $(\cC_n)_{n\ge1}$ separates RTD from NCTD in the most striking way. The
proof of existence of the family $(\cC_n)_{n\ge1}$ makes use of the
probabilistic method and random tournaments. Third, we improve the
afore-mentioned upper bound $2^d\binom{n}{d}$ by a factor of order $\sqrt{d}$.
The verification of the superior bound makes use of Johnson graphs and maximum
subgraphs not containing large narrow cliques.


title:
Shashthosheba Dissecting Perception of Bangladeshi People towards
  Telemedicine Apps through the Lens of Features of the Apps

abstract:
  Bangladesh, a developing country with a large and dense population, has
recently seen significant economic as well as technological developments. The
growth of technology has resulted in a dramatic increase in the number of
smartphone users in Bangladesh, and as such, mobile apps have become an
increasingly important part of peoples' life, even encompassing healthcare
services. However, the apps used in healthcare (telemedicine to be specific) in
Bangladesh are yet to be studied from the perspective of their features as per
the voices of the users as well as service providers. Therefore, in this study,
we focus on the features of the telemedicine apps used in Bangladesh. First, we
evaluated the present status of existing telemedicine apps in Bangladesh, as
well as their benefits and drawbacks in the context of HCI. We analyzed
publicly accessible reviews of several Bangladeshi telemedicine apps (N = 14)
to evaluate the user impressions. Additionally, to ascertain the public opinion
of these apps, we performed a survey in which the patients (N = 87)
participated willingly. Our analysis of the collected opinions reveals what
users experience, what they appreciate, and what they are concerned about when
they use telemedicine apps. Additionally, our study demonstrates what users
expect from telemedicine apps, independent of their past experience. Finally,
we explore how to address the issues we discovered and how telemedicine may be
used to effectively offer healthcare services throughout the country. To the
best of our knowledge, this study is the first to analyze the perception of the
people of Bangladesh towards telemedicine apps from the perspective of features
of the apps.


title:
GUP inspired asymptotic safety in the radiation process of thin
  accretion disk around a Schwarzschild-like black hole

abstract:
  We study quantum gravity effects on radiation process of the thin accretion
disks around Schwarzschild like black-hole. The quantum gravity correction is
invoked through the framework of generalization of uncertainty which is
equivalent to renormalization group improved quantum gravity and maintain the
limit of the asymptotically safe preposition of gravity. It admits a free
parameter that encodes the quantum effects on the spacetime geometry. It allows
us to study how the thermal properties of the disk are modified in the quantum
regime. We explicitly make estimations of quantum correction to the
time-averaged energy flux, the temperature of the disk, the differential
luminosity, and the conversion efficiency of accreting mass into radiation. We
observe a conspicuous shifting of the radius of the innermost stable circular
orbit (ISCO) toward small values together with an enhancement of the maximum of
the values of the average thermal radiation and greater conversion efficiency
of accreting mass into radiation compared to the classical gravity scenario.


title: Diversifying Neural Dialogue Generation via Negative Distillation

abstract:
  Generative dialogue models suffer badly from the generic response problem,
limiting their applications to a few toy scenarios. Recently, an interesting
approach, namely negative training, has been proposed to alleviate this problem
by reminding the model not to generate high-frequency responses during
training. However, its performance is hindered by two issues, ignoring
low-frequency but generic responses and bringing low-frequency but meaningless
responses. In this paper, we propose a novel negative training paradigm, called
negative distillation, to keep the model away from the undesirable generic
responses while avoiding the above problems. First, we introduce a negative
teacher model that can produce query-wise generic responses, and then the
student model is required to maximize the distance with multi-level negative
knowledge. Empirical results show that our method outperforms previous negative
training methods significantly.


title:
Confronting the prediction of leptonic Dirac CP-violating phase with
  experiments

abstract:
  We update and improve past efforts to predict the leptonic Dirac CP-violating
phase with models that predict perturbatively modified tribimaximal or
bimaximal mixing. Simple perturbations are applied to both mixing patterns in
the form of rotations between two sectors. By translating these perturbed
mixing matrices to the standard parameterization for the neutrino mixing matrix
we derive relations between the Dirac CP-phase and the oscillation angles. We
use these relations together with current experimental results to constrain the
allowed range for the CP-phase and determine its probability density.
Furthermore, we elaborate on the prospects for future experiments probing on
the perturbations considered in this work. We present a model with $A_4$
modular symmetry that is consistent with one of the described perturbed
scenarios and successfully predicts current oscillation parameter data.


title:
On unorthodox qubits, with an application to the closed timelike curve
  problem

abstract:
  In orthodox quantum theory the observables of spacelike separated quantum
systems commute. I shall call this the commutation constraint. It severely
limits quantum theory's explanatory power. For instance, the constraint cannot
be met in the presence of closed timelike curves, leaving us with no choice but
to rule them out by fiat. It also conflicts with Bekenstein's bound. Here I
investigate a modified quantum theory, unorthodox quantum theory, which is
different from the conventional theory only in its omission of this commutation
constraint. In particular, I describe a system of unorthodox qubits and
demonstrate how they can be used to model systems on closed timelike curves and
how they allow for a solution of the grandfather paradox.


title: Effective poset inequalities

abstract:
  We explore inequalities on linear extensions of posets and make them
effective in different ways. First, we study the Bj\"orner--Wachs inequality
and generalize it to inequalities on order polynomials and their $q$-analogues
via direct injections and FKG inequalities. Second, we give an injective proof
of the Sidorenko inequality with computational complexity significance, namely
that the difference is in $\#P$. Third, we generalize actions of Coxeter groups
on restricted linear extensions, leading to vanishing and uniqueness conditions
for the generalized Stanley inequality. We also establish several new
inequalities on order polynomials, and prove an asymptotic version of Graham's
inequality.


title: Free Core Nutation and its relation to the Spin-Over Mode

abstract:
  The time-varying response of the Earth's and other planets' rotation to
external gravitational torques depends strongly on their internal structure. In
particular, the existence of the mode known as the Free Core Nutation in the
fluid core, is known to amplify the forced nutations in the near-diurnal
retrograde frequency band (as measured in the planetary frame of reference).
Due to their proximity in shape and frequency, this mode is sometimes equated
with the so-called Spin-Over Mode which denotes the free oscillation of a
steadily rotating ellipsoidal fluid core. Through a careful study of the freely
rotating two-layer planetary model with a rigid mantle and an inviscid fluid
core, we show that the Spin-Over Mode frequency corresponds to that where the
sum of the external and internal torques on the mantle are balanced, causing it
to rotate steadily. The presence of dissipation at the Core-Mantle Boundary
causes the Free Core Nutation to become damped and slightly offset its
resonance frequency. We show that this offset, which is $\approx-1$ day for the
Earth, can be interpreted as the result of the proximity of the Free Core
Nutation frequency to that of the Spin-Over Mode, which now corresponds to a
minimum in the magnitude of the transfer function for nutations. We also show
how this proximity leads to a slightly lower Quality factor for the resonance
than that compute from the usual formula. We conclude by discussing possible
implications of this mechanism for Mars, the Moon, and the long-term evolution
of the Earth.


title:
Measures of physical mixing evaluate the economic mobility of the
  typical individual

abstract:
  Measures of economic mobility represent aggregated values for how wealth
ranks of individuals change over time. Therefore, in certain circumstances
mobility measures may not describe the feasibility of the typical individual to
change their wealth ranking. To address this issue, we introduce mixing, a
concept from statistical physics, as a relevant phenomenon for quantifying the
ability of individuals to move across the whole wealth distribution. We display
the relationship between mixing and mobility by studying the relaxation time, a
statistical measure for the degree of mixing, in reallocating geometric
Brownian motion (RGBM). RGBM is an established model of wealth in a growing and
reallocating economy that distinguishes between a mixing and a non-mixing
wealth dynamics regime. We show that measures of mixing are inherently
connected to the concept of economic mobility: while certain individuals can
move across the distribution when wealth is a non-mixing observable, only in
the mixing case every individual is able to move across the whole wealth
distribution. Then, there is also a direct equivalence between measures of
mixing and the magnitude of the standard measures of economic mobility. On the
other hand, the opposite is not true. Wealth dynamics, are however, best
modeled as non-mixing. Hence, measuring mobility using standard measures in a
non-mixing system may lead to misleading conclusions about the extent of
mobility across the whole distribution.


title:
Mode stability for the Teukolsky equations on Kerr-anti-de Sitter
  spacetimes

abstract:
  We prove that there are no non-stationary (with respect to the Hawking
vectorfield) real mode solutions to the Teukolsky equations on all
$(3+1)$-dimensional subextremal Kerr-anti-de Sitter spacetimes. We further
prove that stationary solutions do not exist if the black hole parameters
satisfy the Hawking-Reall bound and
$\left|a\sqrt{-\Lambda}\right|<\frac{\sqrt{3}}{20}$. We conclude with the
statement of mode stability which preludes boundedness and decay estimates for
general solutions which will be proven in a separate paper. Our boundary
conditions are the standard ones which follow from fixing the conformal class
of the metric at infinity and lead to a coupling of the two Teukolsky
equations. The proof relies on combining the Teukolsky-Starobinsky identities
with the coupled boundary conditions. In the stationary case the proof exploits
elliptic estimates which fail if the Hawking-Reall bound is violated. This is
consistent with the superradiant instabilities expected in that regime.


title:
Spatial distribution of two symmetric four-wave mixing signals induced
  by Gaussian beams

abstract:
  We present a theoretical analysis of the spatial shape of two symmetric
signals of degenerate four-wave mixing induced by Gaussian beams in a thin
sample of two-level atoms. Our calculations take into account the full spatial
and spectral dependencies of the relevant nonlinear susceptibilities that
govern the two processes. This reveals two interesting effects. The first one
is that the total power of incident beams affects the transverse profile of the
four-wave mixing signals at the medium exit and their free propagation. The
second one is the influence of the spectral characteristics of the medium on
the longitudinal profile of both generated signals upon free propagation. We
argue that the first effect can be seen as the saturation of the medium in
regions of higher intensity, while the second can be understood as the result
of a nonlinear contribution to the refractive index inside the atomic medium.
These effects can be symmetric between the two signals, with asymmetries
induced by different detunings from resonance of the incident fields.


title:
Development of Interpretable Machine Learning Models to Detect
  Arrhythmia based on ECG Data

abstract:
  The analysis of electrocardiogram (ECG) signals can be time consuming as it
is performed manually by cardiologists. Therefore, automation through machine
learning (ML) classification is being increasingly proposed which would allow
ML models to learn the features of a heartbeat and detect abnormalities. The
lack of interpretability hinders the application of Deep Learning in
healthcare. Through interpretability of these models, we would understand how a
machine learning algorithm makes its decisions and what patterns are being
followed for classification. This thesis builds Convolutional Neural Network
(CNN) and Long Short-Term Memory (LSTM) classifiers based on state-of-the-art
models and compares their performance and interpretability to shallow
classifiers. Here, both global and local interpretability methods are exploited
to understand the interaction between dependent and independent variables
across the entire dataset and to examine model decisions in each sample,
respectively. Partial Dependence Plots, Shapley Additive Explanations,
Permutation Feature Importance, and Gradient Weighted Class Activation Maps
(Grad-Cam) are the four interpretability techniques implemented on time-series
ML models classifying ECG rhythms. In particular, we exploit Grad-Cam, which is
a local interpretability technique and examine whether its interpretability
varies between correctly and incorrectly classified ECG beats within each
class. Furthermore, the classifiers are evaluated using K-Fold cross-validation
and Leave Groups Out techniques, and we use non-parametric statistical testing
to examine whether differences are significant. It was found that Grad-CAM was
the most effective interpretability technique at explaining predictions of
proposed CNN and LSTM models. We concluded that all high performing classifiers
looked at the QRS complex of the ECG rhythm when making predictions.


title:
Further stability results of the functional equation
  $f(2x+y)+f\left(\frac{x+y}{2}\right)
  =\frac{2f(x)f(y)}{f(x)+f(y)}+\frac{2f(x+y)f(y-x)}{3f(y-x)-f(x+y)}$

abstract:
  In this paper, we investigate the generalized Hyers-Ulam stability of the
following reciprocal functional equation
\begin{equation*}f(2x+y)+f\left(\frac{x+y}{2}\right)
=\frac{2f(x)f(y)}{f(x)+f(y)}+\frac{2f(x+y)f(y-x)}{3f(y-x)-f(x+y)}\end{equation*}
in non-Archimedean space using a direct method.


title: Activity Detection in Long Surgical Videos using Spatio-Temporal Models

abstract:
  Automatic activity detection is an important component for developing
technologies that enable next generation surgical devices and workflow
monitoring systems. In many application, the videos of interest are long and
include several activities; hence, the deep models designed for such purposes
consist of a backbone and a temporal sequence modeling architecture. In this
paper, we investigate both the state-of-the-art activity recognition and
temporal models to find the architectures that yield the highest performance.
We first benchmark these models on a large-scale activity recognition dataset
in the operating room with over 800 full-length surgical videos. However, since
most other medical applications lack such a large dataset, we further evaluate
our models on the Cholec80 surgical phase segmentation dataset, consisting of
only 40 training videos. For backbone architectures, we investigate both 3D
ConvNets and most recent transformer-based models; for temporal modeling, we
include temporal ConvNets, RNNs, and transformer models for a comprehensive and
thorough study. We show that even in the case of limited labeled data, we can
outperform the existing work by benefiting from models pre-trained on other
tasks.


title:
Proximity-Induced Superconductivity in Scalable Topological
  Insulator/Graphene/Gallium Heterostructures

abstract:
  The introduction of superconductivity to the Dirac surface states of a
topological insulator leads to a novel state of matter known as a topological
superconductor. A topological superconductor may host Majorana zero modes, the
braiding of which is a cornerstone operation of a topological qubit3. The
development of a scalable material platform is key to the realization of
topological quantum computing. Here we report on the growth and properties of
high-quality (Bi,Sb)2Te3/graphene/gallium heterostructures. Our novel synthetic
approach enables atomically sharp layers at both hetero-interfaces, which in
turn promotes proximity-induced superconductivity that originates in the
gallium film. A lithography-free, van der Waals tunnel junction is developed to
perform transport tunneling spectroscopy. Our results show a robust,
proximity-induced superconducting gap formed in the Dirac surface states in
5-10 quintuple-layer (Bi,Sb)2Te3/graphene/gallium heterostructures. The motion
of a single Abrikosov vortex, where the Majorana zero modes are expected to
reside, manifests in discrete conductance changes. The epitaxial thin-film
(Bi,Sb)2Te3/graphene/gallium platform opens up new avenues for understanding
topological superconductivity and realizing Majorana braiding circuitry.


title: Quantum Extremal Learning

abstract:
  We propose a quantum algorithm for `extremal learning', which is the process
of finding the input to a hidden function that extremizes the function output,
without having direct access to the hidden function, given only partial
input-output (training) data. The algorithm, called quantum extremal learning
(QEL), consists of a parametric quantum circuit that is variationally trained
to model data input-output relationships and where a trainable quantum feature
map, that encodes the input data, is analytically differentiated in order to
find the coordinate that extremizes the model. This enables the combination of
established quantum machine learning modelling with established quantum
optimization, on a single circuit/quantum computer. We have tested our
algorithm on a range of classical datasets based on either discrete or
continuous input variables, both of which are compatible with the algorithm. In
case of discrete variables, we test our algorithm on synthetic problems
formulated based on Max-Cut problem generators and also considering higher
order correlations in the input-output relationships. In case of the continuous
variables, we test our algorithm on synthetic datasets in 1D and simple
ordinary differential functions. We find that the algorithm is able to
successfully find the extremal value of such problems, even when the training
dataset is sparse or a small fraction of the input configuration space. We
additionally show how the algorithm can be used for much more general cases of
higher dimensionality, complex differential equations, and with full
flexibility in the choice of both modeling and optimization ansatz. We envision
that due to its general framework and simple construction, the QEL algorithm
will be able to solve a wide variety of applications in different fields,
opening up areas of further research.


title:
Multiwavelength Observations of the Blazar VER J0521+211 During an
  Elevated TeV Gamma-Ray State

abstract:
  We report on a long-lasting, elevated gamma-ray flux state from VER J0521+211
observed by VERITAS, MAGIC, and Fermi-LAT in 2013 and 2014. The peak integral
flux above 200 GeV measured with the nightly-binned light curve is $(8.8 \pm
0.4) \times 10^{-7} \;\text{ph}\;\text{m}^{-2}\; \text{s}^{-1}$, or ~37% of the
Crab Nebula flux. Multiwavelength observations from X-ray, UV, and optical
instruments are also presented. A moderate correlation between the X-ray and
TeV gamma-ray fluxes was observed, and the X-ray spectrum appeared harder when
the flux was higher. Using the gamma-ray spectrum and four models of the
extragalactic background light (EBL), a conservative 95% confidence upper limit
on the redshift of the source was found to be z<=0.31. Unlike the gamma-ray and
X-ray bands, the optical flux did not increase significantly during the studied
period compared to the archival low-state flux. The spectral variability from
optical to X-ray bands suggests that the synchrotron peak of the spectral
energy distribution (SED) may become broader during flaring states, which can
be adequately described with a one-zone synchrotron self-Compton model varying
the high-energy end of the underlying particle spectrum. The synchrotron peak
frequency of the SED, as well as the radio morphology of the jet from the
MOJAVE program, are consistent with the source being an
intermediate-frequency-peaked BL Lac object.


title:
Classical gravitational spinning-spinless scattering at
  $\mathcal{O}(G^{2} S^{\infty})$

abstract:
  Making use of the recently-derived, all-spin, opposite-helicity Compton
amplitude, we calculate the classical gravitational scattering amplitude for
one spinning and one spinless object at $\mathcal{O}(G^{2})$ and all orders in
spin. By construction, this amplitude exhibits the spin structure that has been
conjectured to describe Kerr black holes. This spin structure alone is not
enough to fix all deformations of the Compton amplitude by contact terms, but
when combined with considerations of the ultrarelativistic limit we can
uniquely assign values to the parameters remaining in the even-in-spin sector.
Once these parameters are determined, much of the spin dependence of the
amplitude resums into hypergeometric functions. Finally, we derive the eikonal
phase for aligned-spin scattering.


title:
The decays $\tau \to a_{1} \pi \nu_\tau$, $\tau \to K_{1} \pi \nu_\tau$
  and $\tau \to K_{1} K \nu_\tau$ in the extended $U(3)\times U(3)$ chiral NJL
  model

abstract:
  The branching fractions of the decays $\tau \to a_{1} \pi \nu_\tau$, $\tau
\to K_{1} \pi \nu_\tau$ and $\tau \to K_{1} K \nu_\tau$ are calculated in the
framework of the extended $U(3)\times U(3)$ chiral Nambu--Jona-Lasinio model.
There are no experimental data for these decays in the present time, thus the
obtained results are considered as predictions. The comparison of these results
to the theoretical results of other authors is carried out.


title: Morphological Wobbling Can Help Robots Learn

abstract:
  We propose to make the physical characteristics of a robot oscillate while it
learns to improve its behavioral performance. We consider quantities such as
mass, actuator strength, and size that are usually fixed in a robot, and show
that when those quantities oscillate at the beginning of the learning process
on a simulated 2D soft robot, the performance on a locomotion task can be
significantly improved. We investigate the dynamics of the phenomenon and
conclude that in our case, surprisingly, a high-frequency oscillation with a
large amplitude for a large portion of the learning duration leads to the
highest performance benefits. Furthermore, we show that morphological wobbling
significantly increases exploration of the search space.


title:
Precursor superconducting effects in the optimally doped
  YBa$_2$Cu$_3$O$_{7-\delta}$ superconductor: the confrontation between
  superconducting fluctuations and percolative effects revisited

abstract:
  The confrontation between the superconducting fluctuations and percolation
effects as the origin of the in-plane paraconductivity in cuprate
superconductors was earlier addressed at a quantitative level in the case of
the optimally doped YBa$_2$Cu$_3$O$_{7-\delta}$ (YBCO) compound. Using in-plane
resistivity data from a high-quality YBCO thin film, we will extend these
analyses to high reduced temperatures, in the case of the
Gaussian-Ginzburg-Landau (GGL) approach for the conventional superconducting
fluctuations, by considering the total energy cutoff. These data will also be
analysed in terms of the mean field-approach of the effective-medium theory, to
probe if emergent percolative effects may account for the resistivity rounding
above $T_c$. Our analyses confirm earlier conclusions: the measured
paraconductivity cannot be explained in terms of emergent percolation
processes, but it may be accounted for in terms of the GGL approach. These
results also call into question alternative scenarios, including a recent
proposal derived from emergent percolative effects.


title:
On a gap in the proof of the generalised quantum Stein's lemma and its
  consequences for the reversibility of quantum resources

abstract:
  We show that the proof of the generalised quantum Stein's lemma [Brand\~ao &
Plenio, Commun. Math. Phys. 295, 791 (2010)] is not correct due to a gap in the
argument leading to Lemma III.9. Hence, the main achievability result of
Brand\~ao & Plenio is not known to hold. This puts into question a number of
established results in the literature, in particular the reversibility of
quantum entanglement [Brand\~ao & Plenio, Commun. Math. Phys. 295, 829 (2010);
Nat. Phys. 4, 873 (2008)] and of general quantum resources [Brand\~ao & Gour,
Phys. Rev. Lett. 115, 070503 (2015)] under asymptotically resource
non-generating operations. We discuss potential ways to recover variants of the
newly unsettled results using other approaches.


title: Quantum Annealing for Jet Clustering with Thrust

abstract:
  Quantum computing holds the promise of substantially speeding up
computationally expensive tasks, such as solving optimization problems over a
large number of elements. In high-energy collider physics, quantum-assisted
algorithms might accelerate the clustering of particles into jets. In this
study, we benchmark quantum annealing strategies for jet clustering based on
optimizing a quantity called "thrust" in electron-positron collision events. We
find that quantum annealing yields similar performance to exact classical
approaches and classical heuristics, but only after tuning the annealing
parameters. Without tuning, comparable performance can be obtained through a
hybrid quantum/classical approach.


title: Cut-Down de Bruijn Sequences

abstract:
  A cut-down de Bruijn sequence is a cyclic string of length $L$, where $1 \leq
L \leq k^n$, such that every substring of length $n$ appears at most once.
Etzion [Theor. Comp. Sci 44 (1986)] gives an algorithm to construct binary
cut-down de Bruijn sequences that requires $o(n)$ simple $n$-bit operations per
symbol generated. In this paper, we simplify the algorithm and improve the
running time to $\mathcal{O}(n)$ time per symbol generated using
$\mathcal{O}(n)$ space. We then provide the first successor-rule approach for
constructing a binary cut-down de Bruijn sequence by leveraging recent ranking
algorithms for fixed-density Lyndon words. Finally, we develop an algorithm to
generate cut-down de Bruijn sequences for $k>2$ that runs in $\mathcal{O}(n)$
time per symbol using $\mathcal{O}(n)$ space after some initialization. While
our $k$-ary algorithm is based on our simplified version of Etzion's binary
algorithm, a number of non-trivial adaptations are required to generalize to
larger alphabets.


title: Antenna Designs for Recent Millimeter and THz Applications

abstract:
  Over the previous few years, the millimetre wave frequency range and sub-THz
range have been received a lot of attention as they include unused frequency
spectrum resources that are appropriate for providing a lot of applications
such as automotive radars, short communication, medical imaging, security, and
5G communications to provide end-user access to Multi-Gbit/s services. On the
other hand and because of the restrictions on the communication systems in
these ranges such as power, path losses, and attenuation, the present RF
antennas can't be used for millimeter and THz applications. The needed antennas
should have low-profile, high-gain, acceptable technology, high efficiency and
low cost to compensate for these ranges restrictions. Although there are some
antenna designs for millimeter and sub THz ranges through the last decay, the
antenna designs in these ranges still under investigation and studies to
complete the vision of the proposed designs for the aforementioned
applications. Thus, they cannot be carried by the optimum response and
efficiency for these applications. This thesis aims to introduce a
comprehensive study of the main applications that occupy these ranges of
frequencies. In addition to introducing efficient antennas for each application
with acceptable technology for it.


title:
Differential $t\bar{t}$ cross-section measurements using boosted top
  quarks in the all-hadronic final state with 139 fb$^{-1}$ of ATLAS data

abstract:
  Measurements of single-, double-, and triple-differential cross-sections are
presented for boosted top-quark pair-production in 13$~\text{TeV}$
proton--proton collisions recorded by the ATLAS detector at the LHC. The top
quarks are observed through their hadronic decay and reconstructed as
large-radius jets with the leading jet having transverse momentum
($p_{\text{T}}$) greater than 500$~$GeV. The observed data are unfolded to
remove detector effects. The particle-level cross-section, multiplied by the
$t\bar{t} \rightarrow W W b \bar{b}$ branching fraction and measured in a
fiducial phase space defined by requiring the leading and second-leading jets
to have $p_{\text{T}} > 500~$GeV and $p_{\text{T}} > 350~$GeV, respectively, is
$331 \pm 3 \text{(stat.)} \pm 39 \text{(syst.)}~$fb. This is approximately 20\%
lower than the prediction of $398^{+48}_{-49}~$fb by Powheg+Pythia$~$8 with
next-to-leading-order (NLO) accuracy but consistent within the theoretical
uncertainties. Results are also presented at the parton level, where the
effects of top-quark decay, parton showering, and hadronization are removed
such that they can be compared with fixed-order next-to-next-to-leading-order
(NNLO) calculations. The parton-level cross-section, measured in a fiducial
phase space similar to that at particle level, is $1.94 \pm 0.02 \text{(stat.)}
\pm 0.25 \text{(syst.)}~$pb. This agrees with the NNLO prediction of
$1.96^{+0.02}_{-0.17}~$pb. Reasonable agreement with the differential
cross-sections is found for most NLO models, while the NNLO calculations are
generally in better agreement with the data. The differential cross-sections
are interpreted using a Standard Model effective field-theory formalism and
limits are set on Wilson coefficients of several four-fermion operators.


title: Generative methods for sampling transition paths in molecular dynamics

abstract:
  Molecular systems often remain trapped for long times around some local
minimum of the potential energy function, before switching to another one -- a
behavior known as metastability. Simulating transition paths linking one
metastable state to another one is difficult by direct numerical methods. In
view of the promises of machine learning techniques, we explore in this work
two approaches to more efficiently generate transition paths: sampling methods
based on generative models such as variational autoencoders, and importance
sampling methods based on reinforcement learning.


title: The J-invariant over splitting fields of Tits algebras

abstract:
  We describe the J-invariant of a semi-simple algebraic group G over a generic
splitting field of a Tits algebra of G in terms of the J-invariant over a base
field.


title: Geometry-induced patterns through mechanochemical coupling

abstract:
  Intracellular protein patterns regulate a variety of vital cellular processes
such as cell division and motility, which often involve dynamic changes of cell
shape. These changes in cell shape may in turn affect the dynamics of
pattern-forming proteins, hence leading to an intricate feedback loop between
cell shape and chemical dynamics. While several computational studies have
examined the resulting rich dynamics, the underlying mechanisms are not yet
fully understood. To elucidate some of these mechanisms, we explore a
conceptual model for cell polarity on a dynamic one-dimensional manifold. Using
concepts from differential geometry, we derive the equations governing
mass-conserving reaction-diffusion systems on time-evolving manifolds.
Analyzing these equations mathematically, we show that dynamic shape changes of
the membrane can induce pattern-forming instabilities in parts of the membrane,
which we refer to as regional instabilities. Deformations of the local membrane
geometry can also (regionally) suppress pattern formation and spatially shift
already existing patterns. We explain our findings by applying and generalizing
the local equilibria theory of mass-conserving reaction-diffusion systems. This
allows us to determine a simple onset criterion for geometry-induced
pattern-forming instabilities, which is linked to the phase-space structure of
the reaction-diffusion system. The feedback loop between membrane shape
deformations and reaction-diffusion dynamics then leads to a surprisingly rich
phenomenology of patterns, including oscillations, traveling waves, and
standing waves that do not occur in systems with a fixed membrane shape. Our
work reveals that the local conformation of the membrane geometry acts as an
important dynamical control parameter for pattern formation in mass-conserving
reaction-diffusion systems.


title:
Photon emissivity of the quark-gluon plasma: a lattice QCD analysis of
  the transverse channel

abstract:
  We present results for the thermal photon emissivity of the quark-gluon
plasma derived from spatially transverse vector correlators computed in lattice
QCD at a temperature of 250 MeV. The analysis of the spectral functions,
performed at fixed spatial momentum, is based on continuum-extrapolated
correlators obtained with two flavours of dynamical Wilson fermions. We compare
the next-to-leading order perturbative QCD correlators, as well as the ${\cal
N}=4$ supersymmetric Yang-Mills correlators at infinite coupling, to the
correlators from lattice QCD and find them to lie within $\sim10\%$ of each
other. We then refine the comparison, performing it at the level of filtered
spectral functions obtained model-independently via the Backus-Gilbert method.
Motivated by these studies, for frequencies $\omega\lesssim2.5\,$GeV we use fit
ans\"atze to the spectral functions that perform well when applied to mock data
generated from the NLO QCD or from the strongly-coupled SYM spectral functions,
while the high-frequency part, $\omega\gtrsim 2.5\,$GeV, is matched to NLO QCD.
We compare our results for the photon emissivity to our previous analysis of a
different vector channel at the same temperature. We obtain the most stringent
constraint at photon momenta around $k\simeq0.8\,$GeV, for which we find a
differential photon emission rate per unit volume of $d\Gamma_\gamma/d^3k =
(\alpha_{\rm em}/(\exp(k/T)-1))\times (2.2 \pm 0.8 ) \times 10^{-3}\,{\rm
GeV}$.


title:
Transient Luminous Events in the lower part of the Atmosphere originated
  in the Peripheral Regions of a Thunderstorm

abstract:
  We present and discuss Transient Luminous Events in the lower atmosphere,
observed during large disturbances of the near-surface electric fields (NSEF)
and coinciding with large enhancements of the particle fluxes.


title: Intrinsic spin Hall torque in a moire Chern magnet

abstract:
  In spin torque magnetic memories, electrically actuated spin currents are
used to switch a magnetic bit. Typically, these require a multilayer geometry
including both a free ferromagnetic layer and a second layer providing spin
injection. For example, spin may be injected by a nonmagnetic layer exhibiting
a large spin Hall effect, a phenomenon known as spin-orbit torque. Here, we
demonstrate a spin-orbit torque magnetic bit in a single two-dimensional system
with intrinsic magnetism and strong Berry curvature. We study AB-stacked
MoTe2/WSe2, which hosts a magnetic Chern insulator at a carrier density of one
hole per moire superlattice site. We observe hysteretic switching of the
resistivity as a function of applied current. Magnetic imaging using a
superconducting quantum interference device reveals that current switches
correspond to reversals of individual magnetic domains. The real space pattern
of domain reversals aligns precisely with spin accumulation measured near the
high-Berry curvature Hubbard band edges. This suggests that intrinsic spin- or
valley-Hall torques drive the observed current-driven magnetic switching in
both MoTe2/WSe2 and other moire materials. The switching current density of
10^3 Amps per square centimeter is significantly less than reported in other
platforms paving the way for efficient control of magnetic order.


title: Rapid Locomotion via Reinforcement Learning

abstract:
  Agile maneuvers such as sprinting and high-speed turning in the wild are
challenging for legged robots. We present an end-to-end learned controller that
achieves record agility for the MIT Mini Cheetah, sustaining speeds up to 3.9
m/s. This system runs and turns fast on natural terrains like grass, ice, and
gravel and responds robustly to disturbances. Our controller is a neural
network trained in simulation via reinforcement learning and transferred to the
real world. The two key components are (i) an adaptive curriculum on velocity
commands and (ii) an online system identification strategy for sim-to-real
transfer leveraged from prior work. Videos of the robot's behaviors are
available at: https://agility.csail.mit.edu/


title:
Dual Octree Graph Networks for Learning Adaptive Volumetric Shape
  Representations

abstract:
  We present an adaptive deep representation of volumetric fields of 3D shapes
and an efficient approach to learn this deep representation for high-quality 3D
shape reconstruction and auto-encoding. Our method encodes the volumetric field
of a 3D shape with an adaptive feature volume organized by an octree and
applies a compact multilayer perceptron network for mapping the features to the
field value at each 3D position. An encoder-decoder network is designed to
learn the adaptive feature volume based on the graph convolutions over the dual
graph of octree nodes. The core of our network is a new graph convolution
operator defined over a regular grid of features fused from irregular
neighboring octree nodes at different levels, which not only reduces the
computational and memory cost of the convolutions over irregular neighboring
octree nodes, but also improves the performance of feature learning. Our method
effectively encodes shape details, enables fast 3D shape reconstruction, and
exhibits good generality for modeling 3D shapes out of training categories. We
evaluate our method on a set of reconstruction tasks of 3D shapes and scenes
and validate its superiority over other existing approaches. Our code, data,
and trained models are available at https://wang-ps.github.io/dualocnn.


title:
Quantum State Preparation and Non-Unitary Evolution with Diagonal
  Operators

abstract:
  Realizing non-unitary transformations on unitary-gate based quantum devices
is critically important for simulating a variety of physical problems including
open quantum systems and subnormalized quantum states. We present a dilation
based algorithm to simulate non-unitary operations using probabilistic quantum
computing with only one ancilla qubit. We utilize the singular-value
decomposition (SVD) to decompose any general quantum operator into a product of
two unitary operators and a diagonal non-unitary operator, which we show can be
implemented by a diagonal unitary operator in a 1-qubit dilated space. While
dilation techniques increase the number of qubits in the calculation, and thus
the gate complexity, our algorithm limits the operations required in the
dilated space to a diagonal unitary operator, which has known circuit
decompositions. We use this algorithm to prepare random sub-normalized
two-level states on a quantum device with high fidelity. Furthermore, we
present the accurate non-unitary dynamics of two-level open quantum systems in
a dephasing channel and an amplitude damping channel computed on a quantum
device. The algorithm presented will be most useful for implementing general
non-unitary operations when the SVD can be readily computed, which is the case
with most operators in the noisy intermediate-scale quantum computing era.


title:
Identifying Cause-and-Effect Relationships of Manufacturing Errors using
  Sequence-to-Sequence Learning

abstract:
  In car-body production the pre-formed sheet metal parts of the body are
assembled on fully-automated production lines. The body passes through multiple
stations in succession, and is processed according to the order requirements.
The timely completion of orders depends on the individual station-based
operations concluding within their scheduled cycle times. If an error occurs in
one station, it can have a knock-on effect, resulting in delays on the
downstream stations. To the best of our knowledge, there exist no methods for
automatically distinguishing between source and knock-on errors in this
setting, as well as establishing a causal relation between them. Utilizing
real-time information about conditions collected by a production data
acquisition system, we propose a novel vehicle manufacturing analysis system,
which uses deep learning to establish a link between source and knock-on
errors. We benchmark three sequence-to-sequence models, and introduce a novel
composite time-weighted action metric for evaluating models in this context. We
evaluate our framework on a real-world car production dataset recorded by
Volkswagen Commercial Vehicles. Surprisingly we find that 71.68% of sequences
contain either a source or knock-on error. With respect to seq2seq model
training, we find that the Transformer demonstrates a better performance
compared to LSTM and GRU in this domain, in particular when the prediction
range with respect to the durations of future actions is increased.


title: Quantum van Est Isomorphism

abstract:
  Motivated by the fact that the Hopf-cyclic (co)homology of the quantized
algebras of functions and quantized universal enveloping algebras are the
correct analogues of the Lie algebra and Lie group (co)homologies, we hereby
construct three van Est type isomorphisms between the Hopf-cyclic
(co)homologies of Lie groups and Lie algebras, and their quantum groups and
corresponding enveloping algebras, both in $h$-adic and $q$-deformation
frameworks.


title:
Foundations for NLP-assisted formative assessment feedback for
  short-answer tasks in large-enrollment classes

abstract:
  Research suggests "write-to-learn" tasks improve learning outcomes, yet
constructed-response methods of formative assessment become unwieldy with large
class sizes. This study evaluates natural language processing algorithms to
assist this aim. Six short-answer tasks completed by 1,935 students were scored
by several human raters, using a detailed rubric, and an algorithm. Results
indicate substantial inter-rater agreement using quadratic weighted kappa for
rater pairs (each QWK > 0.74) and group consensus (Fleiss Kappa = 0.68).
Additionally, intra-rater agreement was estimated for one rater who had scored
178 responses seven years prior (QWK = 0.89). With compelling rater agreement,
the study then pilots cluster analysis of response text toward enabling
instructors to ascribe meaning to clusters as a means for scalable formative
assessment.


title:
Visually plausible human-object interaction capture from wearable
  sensors

abstract:
  In everyday lives, humans naturally modify the surrounding environment
through interactions, e.g., moving a chair to sit on it. To reproduce such
interactions in virtual spaces (e.g., metaverse), we need to be able to capture
and model them, including changes in the scene geometry, ideally from
ego-centric input alone (head camera and body-worn inertial sensors). This is
an extremely hard problem, especially since the object/scene might not be
visible from the head camera (e.g., a human not looking at a chair while
sitting down, or not looking at the door handle while opening a door). In this
paper, we present HOPS, the first method to capture interactions such as
dragging objects and opening doors from ego-centric data alone. Central to our
method is reasoning about human-object interactions, allowing to track objects
even when they are not visible from the head camera. HOPS localizes and
registers both the human and the dynamic object in a pre-scanned static scene.
HOPS is an important first step towards advanced AR/VR applications based on
immersive virtual universes, and can provide human-centric training data to
teach machines to interact with their surroundings. The supplementary video,
data, and code will be available on our project page at
http://virtualhumans.mpi-inf.mpg.de/hops/


title:
The PAndAS View of the Andromeda Satellite System. III. Dwarf galaxy
  detection limits

abstract:
  We determine the detection limits of the search for dwarf galaxies in the
Pan-Andromeda Archaeological Survey (PAndAS) using the algorithm developed by
the PAndAS team. The recovery fractions of artificial dwarf galaxies are, as
expected, a strong function of physical size and luminosity and, to a lesser
extent, distance. We show that these recovery fractions vary strongly with
location in the surveyed area because of varying levels of contamination from
both the Milky Way foreground stars and the stellar halo of Andromeda. We
therefore provide recovery fractions that are a function of size, luminosity,
and location within the survey on a scale of 1 square degree. Overall, the
effective surface brightness for a 50-percent detection rate range between 28
and 30 mag per square arcsecond. This is in line with expectations for a search
that relies on photometric data that are as deep as the PAndAS survey. The
derived detection limits are an essential ingredient on the path to
constraining the global properties of Andromeda's system of satellite dwarf
galaxies and, more broadly, to provide constraints on dwarf galaxy formation
and evolution in a cosmological context.


title: Entity Cloze By Date: What LMs Know About Unseen Entities

abstract:
  Language models (LMs) are typically trained once on a large-scale corpus and
used for years without being updated. However, in a dynamic world, new entities
constantly arise. We propose a framework to analyze what LMs can infer about
new entities that did not exist when the LMs were pretrained. We derive a
dataset of entities indexed by their origination date and paired with their
English Wikipedia articles, from which we can find sentences about each entity.
We evaluate LMs' perplexity on masked spans within these sentences. We show
that models more informed about the entities, such as those with access to a
textual definition of them, achieve lower perplexity on this benchmark. Our
experimental results demonstrate that making inferences about new entities
remains difficult for LMs. Given its wide coverage on entity knowledge and
temporal indexing, our dataset can be used to evaluate LMs and techniques
designed to modify or extend their knowledge. Our automatic data collection
pipeline can be easily used to continually update our benchmark.


title: Cross-view Transformers for real-time Map-view Semantic Segmentation

abstract:
  We present cross-view transformers, an efficient attention-based model for
map-view semantic segmentation from multiple cameras. Our architecture
implicitly learns a mapping from individual camera views into a canonical
map-view representation using a camera-aware cross-view attention mechanism.
Each camera uses positional embeddings that depend on its intrinsic and
extrinsic calibration. These embeddings allow a transformer to learn the
mapping across different views without ever explicitly modeling it
geometrically. The architecture consists of a convolutional image encoder for
each view and cross-view transformer layers to infer a map-view semantic
segmentation. Our model is simple, easily parallelizable, and runs in
real-time. The presented architecture performs at state-of-the-art on the
nuScenes dataset, with 4x faster inference speeds. Code is available at
https://github.com/bradyz/cross_view_transformers.


title:
Fixing Malfunctional Objects With Learned Physical Simulation and
  Functional Prediction

abstract:
  This paper studies the problem of fixing malfunctional 3D objects. While
previous works focus on building passive perception models to learn the
functionality from static 3D objects, we argue that functionality is reckoned
with respect to the physical interactions between the object and the user.
Given a malfunctional object, humans can perform mental simulations to reason
about its functionality and figure out how to fix it. Inspired by this, we
propose FixIt, a dataset that contains about 5k poorly-designed 3D physical
objects paired with choices to fix them. To mimic humans' mental simulation
process, we present FixNet, a novel framework that seamlessly incorporates
perception and physical dynamics. Specifically, FixNet consists of a perception
module to extract the structured representation from the 3D point cloud, a
physical dynamics prediction module to simulate the results of interactions on
3D objects, and a functionality prediction module to evaluate the functionality
and choose the correct fix. Experimental results show that our framework
outperforms baseline models by a large margin, and can generalize well to
objects with similar interaction types.


title:
Contact Points Discovery for Soft-Body Manipulations with Differentiable
  Physics

abstract:
  Differentiable physics has recently been shown as a powerful tool for solving
soft-body manipulation tasks. However, the differentiable physics solver often
gets stuck when the initial contact points of the end effectors are sub-optimal
or when performing multi-stage tasks that require contact point switching,
which often leads to local minima. To address this challenge, we propose a
contact point discovery approach (CPDeform) that guides the stand-alone
differentiable physics solver to deform various soft-body plasticines. The key
idea of our approach is to integrate optimal transport-based contact points
discovery into the differentiable physics solver to overcome the local minima
from initial contact points or contact switching. On single-stage tasks, our
method can automatically find suitable initial contact points based on
transport priorities. On complex multi-stage tasks, we can iteratively switch
the contact points of end-effectors based on transport priorities. To evaluate
the effectiveness of our method, we introduce PlasticineLab-M that extends the
existing differentiable physics benchmark PlasticineLab to seven new
challenging multi-stage soft-body manipulation tasks. Extensive experimental
results suggest that: 1) on multi-stage tasks that are infeasible for the
vanilla differentiable physics solver, our approach discovers contact points
that efficiently guide the solver to completion; 2) on tasks where the vanilla
solver performs sub-optimally or near-optimally, our contact point discovery
method performs better than or on par with the manipulation performance
obtained with handcrafted contact points.


title: Neural 3D Scene Reconstruction with the Manhattan-world Assumption

abstract:
  This paper addresses the challenge of reconstructing 3D indoor scenes from
multi-view images. Many previous works have shown impressive reconstruction
results on textured objects, but they still have difficulty in handling
low-textured planar regions, which are common in indoor scenes. An approach to
solving this issue is to incorporate planer constraints into the depth map
estimation in multi-view stereo-based methods, but the per-view plane
estimation and depth optimization lack both efficiency and multi-view
consistency. In this work, we show that the planar constraints can be
conveniently integrated into the recent implicit neural representation-based
reconstruction methods. Specifically, we use an MLP network to represent the
signed distance function as the scene geometry. Based on the Manhattan-world
assumption, planar constraints are employed to regularize the geometry in floor
and wall regions predicted by a 2D semantic segmentation network. To resolve
the inaccurate segmentation, we encode the semantics of 3D points with another
MLP and design a novel loss that jointly optimizes the scene geometry and
semantics in 3D space. Experiments on ScanNet and 7-Scenes datasets show that
the proposed method outperforms previous methods by a large margin on 3D
reconstruction quality. The code is available at
https://zju3dv.github.io/manhattan_sdf.


title: BlobGAN: Spatially Disentangled Scene Representations

abstract:
  We propose an unsupervised, mid-level representation for a generative model
of scenes. The representation is mid-level in that it is neither per-pixel nor
per-image; rather, scenes are modeled as a collection of spatial, depth-ordered
"blobs" of features. Blobs are differentiably placed onto a feature grid that
is decoded into an image by a generative adversarial network. Due to the
spatial uniformity of blobs and the locality inherent to convolution, our
network learns to associate different blobs with different entities in a scene
and to arrange these blobs to capture scene layout. We demonstrate this
emergent behavior by showing that, despite training without any supervision,
our method enables applications such as easy manipulation of objects within a
scene (e.g., moving, removing, and restyling furniture), creation of feasible
scenes given constraints (e.g., plausible rooms with drawers at a particular
location), and parsing of real-world images into constituent parts. On a
challenging multi-category dataset of indoor scenes, BlobGAN outperforms
StyleGAN2 in image quality as measured by FID. See our project page for video
results and interactive demo: http://www.dave.ml/blobgan


title: Symplectic Computation of Lyapunov Exponents

abstract:
  A recently developed method for the calculation of Lyapunov exponents of
dynamical systems is described. The method is applicable whenever the
linearized dynamics is Hamiltonian. By utilizing the exponential representation
of symplectic matrices, this approach avoids the renormalization and
reorthogonalization procedures necessary in usual techniques. It is also easily
extendible to damped systems. The method is illustrated by considering two
examples of physical interest: a model system that describes the beam halo in
charged particle beams and the driven van der Pol oscillator.


title:
Order $\hbar$ Corrections to the Classical Dynamics of a Particle with
  Intrinsic Spin Moving in a Constant Magnetic Field

abstract:
  $O(\hbar)$ effects that modify the classical orbit of a charged particle are
described for the case of a classical spin-1/2 particle moving in a constant
magnetic field, using a manifestly covariant formalism reported previously. It
is found that the coupling between the momentum and spin gives rise to a shift
in the cyclotron frequency, which is explicitly calculated. In addition the
orbit is found to exhibit $O(\hbar)$ oscillations along the axis of the uniform
static magnetic field whenever the gyromagnetic ratio $g$ of the particle is
not 2. This oscillation is found to occur at a frequency $\propto$ $\frac{g}{2}
- 1$, and is an observable source of electric dipole radiation.


title: Candela Photo-Injector Experimental Results

abstract:
  The CANDELA photo-injector is a two cell S-band photo-injector. The copper
cathode is illuminated by a 500 fs Ti:sapphire laser. This paper presents
energy spectrum measurements of the dark current and intense electron emission
that occurs when the laser power density is very high.


title: High-Brightness Photocathode Electron Sources

abstract:
  Most present and future electron accelerators require bright sources.
Invented less than ten years ago, the photo-injector the principle of which is
briefly recalled, has already demonstrated that it can provide very bright
beams. In this paper, the most advanced photo-injector projects are reviewed,
their specific features are outlined, and their major issues are examined. The
state-of-the-art in photocathode and laser technologies is presented. Beam
dynamics issues are also considered since they are essential in the production
of bright beams. Finally, the question of the maturity of photo-injector
technology is addressed.


title: Finding matched rms envelopes in rf linacs: A Hamiltonian approach

abstract:
  We present a new method for obtaining matched solutions of the rms envelope
equations. In this approach, the envelope equations are first expressed in
Hamiltonian form. The Hamiltonian defines a nonlinear mapping, $\cal M$, and
for periodic transport systems the fixed points of the one-period map are the
matched envelopes. Expanding the Hamiltonian around a fiducial trajectory one
obtains a linear map, $M$, that describes trajectories (rms envelopes) near the
fiducial trajectory. Using $\cal M$ and $M$ we construct a contraction mapping
that can be used to obtain the matched envelopes. The algorithm is
quadratically convergent. Using the zero-current matched parameters as starting
values, the contraction mapping typically converges in a few to several
iterations. Since our approach uses numerical integration to obtain all the
mappings, it includes the effects of nonidealized, $z$-dependent transverse and
longitudinal focusing fields. We present numerical examples including finding a
matched beam in a quadrupole channel with rf bunchers.


title: Coupling Impedances and Heating due to Slots in the KEK B-factory

abstract:
  The longitudinal and transverse coupling impedances produced by the long
slots in the Low Energy Ring of KEK B-factory are calculated. The power
dissipated inside the vacuum chamber due to the fields scattered by the slots
is evaluated using results for the real part of the coupling impedance.
Estimates are made for the power flow through the slots to the pumping chamber.


title:
A Study of Influence of Synchrotron Radiation Quantum Fluctuations on
  the Synchrotron Oscillations of a Single Electron Using Undulator Radiation

abstract:
  A single electron circulating in a storage ring is a very peculiar object.
Synchrotron radiation quantum fluctuation causes stohastic process in the
synchrotron oscillation of an electron. The radiation from a undulator permits
one to obtain discret moments of longitudional electron motion. Experiments
with a single electron on on the VEPP-3 optical klystrons are described.


title: Beam Dynamics problems in a muon collider

abstract:
  We discuss the various beam dynamics problems in muon collider systems,
starting from the proton accelerator needed to generate the muon beams and
proceeding through the muon storage ring.


title: Muon Transverse Ionization Cooling: Stochastic Approach

abstract:
  Transverse ionization cooling of muons is modeled as a Brownian motion of the
muon beam as it traverses a Li or Be rod. A Langevin like equation is written
for the free particle case (no external transverse magnetic field) and for the
case of a harmonically bound beam in the presence of a focusing magnetic field.
We demonstrate that the well known muon cooling equations for short-absorbers
can be extrapolated to the useful case of a long absorber rod with a focusing
magnetic field present.


title: MONTE CARLO SIMULATIONS OF MUON PRODUCTION

abstract:
  Muon production requirements for a muon collider are presented. Production of
muons from pion decay is studied. Lithium lenses and solenoids are considered
for focussing pions from a target, and for matching the pions into a decay
channel. Pion decay channels of alternating quadrupoles and long solenoids are
compared. Monte Carlo simulations are presented for production of $\pi
\rightarrow \mu $ by protons over a wide energy range, and criteria for
choosing the best proton energy are discussed.


title:
A General Approach for Calculating Coupling Impedances of Small
  Discontinuities

abstract:
  A general theory of the beam interaction with small discontinuities of the
vacuum chamber is developed taking into account the reaction of radiated waves
back on the discontinuity. The reactive impedance calculated earlier is
reproduced as the first order, and the resistive one as the second order of a
perturbation theory based on this general approach. The theory also gives, in a
very natural way, the results for the trapped modes due to small
discontinuities obtained earlier by a different method.


title: Trapped Modes in the Vacuum Chamber of an Arbitrary Cross Section

abstract:
  It has been shown that a small discontinuity such as an enlargement or a hole
on circular waveguides can produce trapped electromagnetic modes with
frequencies slightly below the waveguide cutoff. The trapped modes due to
multiple discontinuities can lead to high narrow-band contributions to the
beam-chamber coupling impedance, especially when the wall conductivity is high
enough. To make more reliable estimates of these contributions for real
machines, an analytical theory of the trapped modes is developed in this paper
for a general case of the vacuum chamber with an arbitrary single-connected
cross section. The resonant frequencies and coupling impedances due to trapped
modes are calculated, and simple explicit expressions are given for circular
and rectangular cross sections. The estimates for the LHC are presented.


title:
Polarizabilities of an Annular Cut and Coupling Impedances of
  Button-Type Beam Position Monitors

abstract:
  The longitudinal and transverse coupling impedances of a small discontinuity
on the accelerator chamber wall can be expressed in terms of the electric and
magnetic polarizabilities of the discontinuity. The polarizabilities are
geometrical factors and can be found by solving a static (electric or magnetic)
problem. However, they are known in the explicit analytical form only for a few
simple-shaped discontinuities, for example, for an elliptic hole in a thin
wall. In the present paper the polarizabilities of a ring-shaped cut in the
wall are obtained. The results are applied to calculate the coupling impedances
of button-type beam position monitors.


title: RFQ-DRL MATCHING SOLUTIONS FOR DIFFERENT REQUIREMENTS

abstract:
  The Radio-Frequency Quadrupole (RFQ) has a FODO lattice and Drift-Tube-Linacs
(DTL) in general also have FODO lattices. Therefore the natural solution for
the matching between these is a FODO lattice. For matching in all three planes
one then needs sixteen degrees of freedom. However, different requirements,
depending on the applications, may change this solution. For example, in the
production environment (like medical and industrial applications), one needs
fixed current and fixed beam quality. On the other hand, in the research
environment one not only needs all degrees of freedom, but may also want to
chop of beam pulse. This paper discusses matching solutions for these different
requirements.


title:
Stroboscopic Laser Diagnostics for Detection of Ordering in
  One-Dimensional Ion beam

abstract:
  A novel diagnostic method for detecting ordering in one-dimensional ion beams
is presented. The ions are excited by a pulsed laser at two different positions
along the beam and fluorescence is observed by a group of four
photomultipliers. Correlation in fluorescence signals is firm indication that
the ion beam has an ordered structure.


title:
Normal Mode Tunes for Linear Coupled Motion in Six Dimensional Phase
  Space

abstract:
  The motion of a particle in 6-dimensional phase space in the presence of
linear coupling can be written as the sum of 3 normal modes. A cubic equation
is found for the tune of the normal modes, which allows the normal mode tunes
to be computed from the 6x6 one turn transfer matrix. This result is similar to
the quadratic equation found for the normal mode tunes for the motion of a
particle in 4-dimensional phase space. These results are useful in tracking
programs where the one turn transfer matrix can be computed by multiplying the
transfer matrices of each element of the lattice. The tunes of the 3 normal
modes, for motion in 6-dimensional phase space, can then be found by solving
the cubic equation. Explicit solutions of the cubic equation for the tune are
given in terms of the elements of the 6x6 one turn transfer matrix.


title:
Coaxial Ring Cyclotron as a Perspective Nuclear Power Engineering
  Machine

abstract:
  The circuit arrangement of the proposed coaxial ring cyclotron (CRC) is
described, and its main advantages, such as simple injection technique, several
injected beams summation option, high efficiency, are considered. The proposed
proton accelerator is a perspective machine for the solution of the main
problems of the present day nuclear power engineering as well as for the
next-generation nuclear power plants, representing a combination of subcritical
reactors and particle accelerators. The possibility of installation of CRCs
into ring accelerators with an average diameter from 60 to $100m$, e.g., the
Yerevan electron synchrotron, is considered.


title: Linear Orbit Parameters for the Exact Equations of Motion

abstract:
  This paper defines the beta function and other linear orbit parameters using
the exact equations of motion. The orbit functions are redefined using the
exact equations. Expressions are found for the transfer matrix and the
emittances. Differential equations are found for the beta function and the eta
function. New relationships between the linear orbit parameters are found.


title:
Ultrashort Laser-pulse Diagnostics for Detection of Ordering within an
  Ion beam

abstract:
  A novel diagnostic method to detect ordering within one-dimensional ion beams
in a storage ring is presented. The ions are simultaneously excited by a
ultrashort pulsed laser ($\simeq 1$ ps) at two different locations along the
beam and fluorescence is detected by a group of four photo-multipliers.
Correlation in fluorescence signals is a firm indication that the ion beam has
an ordered structure.


title: Polarizabilities of an Annular Cut in the Wall of an Arbitrary Thickness

abstract:
  The electric and magnetic polarizabilities of an aperture are its important
characteristics in the theory of aperture coupling and diffraction of EM waves.
The beam coupling impedances due to a small discontinuity on the chamber wall
of an accelerator can also be expressed in terms of the polarizabilities of the
discontinuity. The polarizabilities are geometrical factors which can be found
by solving a static (electric or magnetic) problem. However, they are known in
an explicit analytical form only for a few simple-shaped discontinuities, such
as an elliptic hole in a thin wall. In the present paper the polarizabilities
of a ring-shaped cut in the wall of an arbitrary thickness are studied using a
combination of analytical, variational and numerical methods. The results are
applied to estimate the coupling impedances of button-type beam position
monitors.


title:
Full Phase-Space Analysis of Particle Beam Transport in the Thermal Wave
  Model

abstract:
  Within the Thermal Wave Model framework a comparison among Wigner function,
Husimi function, and the phase-space distribution given by a particle tracking
code is made for a particle beam travelling through a linear lens with small
aberrations. The results show that the quantum-like approach seems to be very
promising.


title:
Radiation Damping and Quantum Excitation for Longitudinal Charged
  Particle Dynamics in the Thermal Wave Model

abstract:
  On the basis of the recently proposed {\it Thermal Wave Model (TWM) for
particle beams}, we give a description of the longitudinal charge particle
dynamics in circular accelerating machines by taking into account both
radiation damping and quantum excitation (stochastic effect), in presence of a
RF potential well. The longitudinal dynamics is governed by a 1-D
Schr\"{o}dinger-like equation for a complex wave function whose squared modulus
gives the longitudinal bunch density profile. In this framework, the
appropriate {\it r.m.s. emittance} scaling law, due to the damping effect, is
naturally recovered, and the asymptotic equilibrium condition for the bunch
length, due to the competition between quantum excitation (QE) and radiation
damping (RD), is found. This result opens the possibility to apply the TWM,
already tested for protons, to electrons, for which QE and RD are very
important.


title:
Construction of Nonlinear Symplectic Six-Dimensional Thin-Lens Maps by
  Exponentiation

abstract:
  The aim of this paper is to construct six-dimensional symplectic thin-lens
transport maps for the tracking program SIXTRACK, continuing an earlier report
by using another method which consistes in applying Lie series and
exponentiation as described by W. Groebner and for canonical systems by A.J.
Dragt. We firstly use an approximate Hamiltonian obtained by a series expansion
of the square root. Furthermore, nonlinear crossing terms due to the curvature
in bending magnets are neglected. An improved Hamiltonian, excluding solenoids,
is introduced in Appendix A by using the unexpanded square root mentioned
above, but neglecting again nonlinear crossing terms...


title:
Linear Parameters and the Decoupling Matrix for Linearly Coupled Motion
  in 6 Dimensional Phase Space

abstract:
  It will be shown that starting from a coordinate system where the 6 phase
space coordinates are linearly coupled, one can go to a new coordinate system
where the motion is uncoupled by means of a linear transformation. The original
coupled coordinates and the new uncoupled coordinates are related by a 6x6
matrix, R. R will be called the decoupling matrix. It will be shown that of the
36 elements of the 6x6 decoupling matrix R, only 12 elements are independent.
This may be contrasted with the results for motion in 4-dimensional phase
space, where R has 4 independent elements. A set of equations is given from
which the 12 elements of R can be computed from the one period transfer
matrix.This set of equations also allows the linear parameters for the
uncoupled coordinates to be computed from the one period transfer matrix. An
alternative procedure for computing the linear parameters and the 12
independent elements of the decoupling matrix R is also given which depends on
computing the eigenvectors of the one period transfer matrix. These results can
be used in a tracking program, where the one period transfer matrix can be
computed by multiplying the transfer matrices of all the elements in a period,
to compute the linear parameters and the elements of the decoupling matrix R.


title:
Particle Motion in the Stable Region Near an Edge of a Linear
  Half-Integer Stopband

abstract:
  This paper studies the motion of a particle whose tune is inside and near a
linear half-integer stopband. Results are found for the tune and beta functions
in the stable region close to an edge of the stopband. It is shown that the
eigenvalues and the eigenfunctions of the transfer matrix are real inside the
stopband. All the results found are also valid for small accelerators where the
large accelerator approximation is not used.


title:
Particle Motion in the Stable Region Near an Edge of a Linear Sum
  Resonance Stopband

abstract:
  This paper studies the particle motion when the tune is in the stable region
close to the edge of linear sum resonance stopband. Results are found for the
tune and the beta functions. Results are also found for the two solutions of
the equations of motion. The results found are shown to be also valid for small
accelerators where the large accelerator approximation may not be used.


title: Muon Colliders

abstract:
  Muon Colliders have unique technical and physics advantages and disadvantages
when compared with both hadron and electron machines. They should thus be
regarded as complementary. Parameters are given of 4 TeV and 0.5 TeV high
luminosity \mumu colliders, and of a 0.5 TeV lower luminosity demonstration
machine. We discuss the various systems in such muon colliders, starting from
the proton accelerator needed to generate the muons and proceeding through muon
cooling, acceleration and storage in a collider ring. Problems of detector
background are also discussed.


title:
Diffusion due to the Beam-Beam Interaction and Fluctuating Fields in
  Hadron Colliders

abstract:
  Random fluctuations in the tune, beam offsets and beam size in the presence
of the beam-beam interaction are shown to lead to significant particle
diffusion and emittance growth in hadron colliders. We find that far from
resonances high frequency noise causes the most diffusion while near resonances
low frequency noise is responsible for the large emittance growth observed.
Comparison of different fluctuations shows that offset fluctuations between the
beams causes the largest diffusion for particles in the beam core.


title: Final Focus System for a Muon Collider: A Test Model

abstract:
  The present scenario for a high luminosity 4 TeV on center of mass muon
collider requires a beta function =3 mm at the interaction point. We discuss a
test model of a basic layout which satisfies the requirements although it is
not fully realistic.


title: On the Problem of the Coupled Cavity Chain Characteristic Calculations

abstract:
  This paper presents the results of studies in elaboration of a mathematical
model of the cavity-chain slow wave structures. Considered is the problem of
coupling of an infinitely long cylindrical cavity chain coupled through
centerholes in the dividing walls of finite thickness without the assumption
about smallness of any parameters. On the basis of a rigorous electrodynamic
approach it is shown that the cavity chain can be described by a set of
equations that describe the coupling of an infinite number of similar-type
modes of short-circuit cavities. At the same time the coupling coefficients are
determined by solving the basic sets of linear algebraic equations which
describe the coupling the tangential electric fields on the right and left
cylindrical hole cross-sections of the disks. The results are given of
numerical simulations of the dependence of electrodynamic characteristics on
the number of connections between the modes taken into account. Based on these
calculations for different cavity dimensions, the number of coupling
connections that give the sufficient accuracy of the description was
determined.


title: On Two-cavity Coupling

abstract:
  This work presents research results on a novel analytical model of
electromagnetic systems coupling through small size holes. The key problem
regarding coupling of two cavities through an aperture in separating screen of
finite thickness without making assumption on smallness of any parameters is
considered. We are the first to calculate on the base of rigorous
electromagnetic approach the coupling coefficients of the cylindrical cavities
within the limit of small aperture and infinitely thin separating screen. The
numeric results of electromagnetic characteristic dependencies that have been
impossible to perform on the base of previous models are given.


title: Analytical Solutions in the Two-cavity Coupling Problem

abstract:
  Analytical solution of precise equations that describe the rf-coupling of two
cavities through a co-axial cylindrical hole are given for various limited
cases. For their derivation we have used the method of solution of an infinite
set of linear algebraic equations, based on its transformation into dual
integral equations.


title: Muon Collider Design

abstract:
  Muon Colliders have unique technical and physics advantages and disadvantages
when compared with both hadron and electron machines. They should thus be
regarded as complementary. Parameters are given of 4 TeV and 0.5 TeV high
luminosity \mu^+ \mu^- colliders, and of a 0.5 TeV lower luminosity
demonstration machine. We discuss the various systems in such muon colliders,
starting from the proton accelerator needed to generate the muons and
proceeding through muon cooling, acceleration and storage in a collider ring.
Detector background, polarization, and nonstandard operating conditions are
discussed.


title: Polarized Beams in a Muon Collider

abstract:
  This paper presents a first overview on how to obtain and maintain polarized
beams in a muon-collider


title: Design of the Muon Collider Lattice: Present Status

abstract:
  We discuss a preliminary design for a high luminosity 4 TeV center of mass
$\mu^+\,\mu^-$ collider ring.


title: Approximate Analytical Description of the Underdense Short Plasma Lens

abstract:
  The perturbative approach for describing the underdense
plasma--ultrarelativistic electron bunch system is developed, using the ratio
$\frac{n_0}{n_b}$ as a small parameter ($n_b$--bunch,$n_0$--plasma electron
densities). Focusing of the electron bunch emerged in the first approximation
of the perturbative procedure as a result of the plasma electrons
redistribution. Focusing gradient and strength for ultrarelativistic, flat,
uniform and short bunch are obtained and compared with the previous results.


title:
A tracking algorithm for the stable spin polarization field in storage
  rings using stroboscopic averaging

abstract:
  Polarized protons have never been accelerated to more than about $25$GeV. To
achieve polarized proton beams in RHIC (250GeV), HERA (820GeV), and the
TEVATRON (900GeV), ideas and techniques new to accelerator physics are needed.
In this publication we will stress an important aspect of very high energy
polarized proton beams, namely the fact that the equilibrium polarization
direction can vary substantially across the beam in the interaction region of a
high energy experiment when no countermeasure is taken. Such a divergence of
the polarization direction would not only diminish the average polarization
available to the particle physics experiment, but it would also make the
polarization involved in each collision analyzed in a detector strongly
dependent on the phase space position of the interacting particle. In order to
analyze and compensate this effect, methods for computing the equilibrium
polarization direction are needed. In this paper we introduce the method of
stroboscopic averaging, which computes this direction in a very efficient way.
Since only tracking data is needed, our method can be implemented easily in
existing spin tracking programs. Several examples demonstrate the importance of
the spin divergence and the applicability of stroboscopic averaging.


title: Orbit Dynamics for Unstable Linear Motion

abstract:
  A treatment is given of the orbit dynamics for linear unstable motion that
allows for the zeros in the beta function and makes no assumptions about the
realness of the betatron and phase functions. The phase shift per turn is shown
to be related to the beta function and the number of zeros the beta function
goes through per turn. The solutions of the equations of motion are found in
terms of the beta function.


title:
An Investigation of Stochastic Cooling in the Framework of Control
  Theory

abstract:
  This report provides a description of unbunched beam stochastic cooling in
the framework of control theory. The main interest in the investigation is
concentrated on the beam stability in an active cooling system. A stochastic
cooling system must be considered as a closed-loop, similar to the feedback
systems used to damp collective instabilities. These systems, which are able to
act upon themselves, are potentially unstable.
  The self-consistent solution for the beam motion is derived by means of a
mode analysis of the collective beam motion. This solution yields a criterion
for the stability of each collective mode. The expressions also allow for
overlapping frequency bands in the beam spectrum and thus are valid over the
entire frequency range.
  Having established the boundaries of stability in this way, the Fokker-Planck
equation is used to describe the cooling process. This description does not
include collective effects and thus a stable beam must be assumed. Hence the
predictions about the cooling process following from the Fokker-Planck equation
only make physical sense within the boundaries of beam stability. Finally it is
verified that the parameters of the cooling system which give the best cooling
results are compatible with the stability of the beam.


title:
A Scintillating Fiber Hodoscope for a Bremstrahlung Luminosity Monitor
  at an Electron$-$Positron Collider

abstract:
  The performance of a scintillating fiber (2mm diameter) position sensitive
detector ($4.8 \times 4.8$ cm$^2$ active area) for the single bremstrahlung
luminosity monitor at the VEPP-2M electron-positron collider in Novosibirsk,
Russia is described. Custom electronics is triggered by coincident hits in the
X and Y planes of 24 fibers each, and reduces 64 PMT signals to a 10 bit (X,Y)
address. Hits are accumulated (10 kHz) in memory and display (few Hz) the
VEPP-2M collision vertex. Fitting the strongly peaked distribution ( $\sim$ 3-4
mm at 1.6m from the collision vertex of VEPP-2M ) to the expected QED angular
distribution yields a background in agreement with an independent determination
of the VEPP-2M luminosity.


title:
Calculation of the dynamic aperture in the ANKA storage ring with a
  high-field wavelength shifter

abstract:
  Third order tracking calculations show that a wavelength shifter on the basis
of a commercially available 12 T split-pair solenoid is compatible with the
ANKA storage ring


title: Polarization in a Muon Collider

abstract:
  In this paper the possibility of obtaining polarized beams in a high energy
muon collider is discusssed


title:
Selfacceleration of Electrons in One-dimensional Bunches, Moving in Cold
  Plasma

abstract:
  Nonlinear dynamics of the one-dimensional ultrarelativistic bunch of
electrons,moving in cold plasma,is considered in multiple scales perturbative
approach. A square root of the inverse Lorentz factor of the bunch electrons is
taken as a small parameter. Bunch electrons momenta is changed in the first
approximation.In the underdense plasma and for the model example of the
combined bunch the selfacceleration of the bunch electrons can be remarkable.


title: A High Current Proton Linac with 352 MHz SC Cavities

abstract:
  A proposal for a 10-120 mA proton linac employing superconducting
beta-graded, CERN type, four cell cavities at 352 MHz is presented. The high
energy part (100 MeV-1 GeV) of the machine is split in three beta-graded
sections, and transverse focusing is provided via a periodic doublet array. All
the parameters, like power in the couplers and accelerating fields in the
cavities, are within the state of the art, achieved in operating machines. A
first stage of operation at 30 mA beam current is proposed, while the upgrade
of the machine to 120 mA operation can be obtained increasing the number of
klystrons and couplers per cavity. The additional coupler ports, up to four,
will be integrated in the cavity design. Preliminary calculations indicate that
beam transport is feasible, given the wide aperture of the 352 MHz structures.
A capital cost of less than 100 M$ at 10 mA, reaching up to 280 M$ for the 120
mA extension, has been estimated for the superconducting high energy section
(100 MeV-1 GeV). The high efficiency of the proposed machine, reaching 50% at
15 mA, makes it a good candidate for proposed nuclear waste incineration
facilities and Energy Amplifier studies.


title:
Coupling Impedances of Azimuthally Symmetric Obstacles of
  Semi-Elliptical Shape in a Beam Pipe

abstract:
  The beam coupling impedances of small axisymmetric obstacles having a
semi-elliptical cross section along the beam in the vacuum chamber of an
accelerator are calculated at frequencies for which the wavelength is large
compared to a typical size of the obstacle. Analytical results are obtained for
both the irises and the cavities with such a shape which allow simple estimates
of their broad-band impedances.


title: Beam Coupling Impedances of Obstacles Protruding into Beam Pipe

abstract:
  The beam coupling impedances of small obstacles protruding inside the vacuum
chamber of an accelerator are calculated analytically at frequencies for which
the wavelength is large compared to a typical size of the obstacle. Simple
formulas for a few important particular cases, including both essentially
three-dimensional objects like a post or a mask and axisymmetric irises, are
presented. The analytical results are compared and agree with three-dimensional
computer simulations. These results allow simple practical estimates of the
broad-band impedance contributions from such discontinuities.


title: The length of a typical Huffman codeword

abstract:
  If p is the probability of a letter of a memoryless source, the length l of
the corresponding binary Huffman codeword can be very different from the value
-log p. We show that, nevertheless, for a typical letter, l is approximately
equal to -log p. More precisely, the probability that l differs from -log p by
more than m decreases exponentially with m.


title: Evolution to the Edge of Chaos in Imitation Game

abstract:
  Motivated by the evolution of complex bird songs, an abstract imitation game
is proposed to study the increase of dynamical complexity: Artificial "birds"
display a "song" time series to each other, and those that imitate the other's
song better win the game. With the introduction of population dynamics
according to the score of the game and the mutation of parameters for the song
dynamics, the dynamics is found to evolve towards the borderline between chaos
and a periodic window, after punctuated equilibria. The importance of edge of
chaos with topological chaos for complexity is stressed.