*2.1. Study Population and Data*

This was a single-center, retrospective study which was approved by the Institutional Review Board of Yamaguchi University Hospital (H2020-198). Informed consent was obtained from the parents of each patient before their inclusion in the study, and data were collected from patient medical records at our hospital.

Between 1 January 2000 and 31 December 2019, all 62 children with DS born at our hospital or referred to our hospital during the neonatal period were enrolled in this study (Figure 1). Nineteen of the 62 children with DS were excluded from the analysis because they were lost to follow-up. Three children had insufficient data, seven moved shortly after birth, seven were transferred to another hospital for cardiac operations, and two died within the first year of life. Finally, the clinical course of 43 children with DS was followed up for more than 1 year. The DS patients were diagnosed according to chromosomal examinations. FPIES patients were diagnosed according to the criteria of the International Consensus Guidelines for the Diagnosis and Management of FPIES [16]. *Nutrients* **2022**, *14*, x FOR PEER REVIEW 3 of 10

**Figure 1.** Flow diagram of the subject selection process**.** DS, Down syndrome; FPIES, food proteinin both groups. **Figure 1.** Flow diagram of the subject selection process. DS, Down syndrome; FPIES, food proteininduced enterocolitis syndrome.

Outcome measurements included demographic characteristics of the FPIES and non-FPIES groups in children with DS and clinical features of FPIES in children with DS. Demographic characteristics included sex, gestational age, birth weight, delivery type, neonatal asphyxia, neonatal jaundice, nutrition, comorbidities, surgical history, serum total IgE level, and antigen-specific IgE level in those below 12 months of age. Serum total IgE level was detected by IgE-LATEX "SEIKEN" (Denka Seiken, Tokyo, Japan), and antigenspecific IgE level was detected by ImmunoCAP (Thermo Fisher Scientific, Uppsala, Sweden). Clinical features of FPIES included age at onset, diagnosis, tolerance, causative

Demographic characteristics, surgical history, and serum total IgE were summarized using descriptive statistics or contingency tables. The Fisher's exact test or the Mann– Whitney U test was used to compare variables between two groups. Statistical significance was set at *p* < 0.05. Statistical analyses were performed using JMP Pro version 14 (SAS

Among 43 children with DS, five (11.6%) were diagnosed with FPIES (Figure 1). In the FPIES and non-FPIES groups, sex, gestational age, and median birth weight were approximately the same (Table 1). In the FPIES and non-FPIES groups, more than 60% of children were born by vaginal delivery. Neonatal asphyxia was observed in less than onefourth, and neonatal jaundice in approximately half of the children. Neonatal asphyxia in this study was defined as an Apgar score ≤7 at one min after birth, and neonatal jaundice was defined as requiring phototherapy. There were no breast milk-only infants in either group, and mixed feeding infants accounted for approximately 80% of the total children

induced enterocolitis syndrome

*2.2. Outcome Measurements*

*2.3. Statistical Analyses*

Institute, Cary, NC, USA).

**3. Results**

foods, clinical symptoms, and severity.


**1. Introduction**

208 Ultra Wideband – Current Status and Future Trends

1998

2002.

House, Inc. 2001.

[12] D. E.J. Humphrey, V.F. Fusco and S. Drew, "Active Antenna Array Behavior", IEEE Transactions on Microwave Theory and Techniques, Vol. 43, No. 8, August 1995. [13] F. Carrez, R. Stolle, J. Vindevoghel, "Integrated Active Microstrip Antenna for

[14] A. Ramadan, Active Antennas with High Input Impedance Low Noise and Highly

[15] Y. Qian, and T. Itoh, "Progress in Active Integrated Antennas and Their Applications", IEEE Transactions on Microwave Theory and Techniques, Vol. 46, No. 11, November

[16] R. Garg, P. Bhartia, I. Bahl, A. Ittipiboon, Microstrip Antenna Design Handbook, Artech

[17] S.L. Loyka, J.R. Mosig, "Nonlinear Modeling and Simulation of Active Array Antennas",

[18] S. Asadi, "Design and Simulation of UWB Distributed Power Amplifier ". Amirkabir

[19] D. Nezhad Malayeri: "Design, Simulation and Nonlinear Analysis of UWB Active

[20] V. Rizzoli, A. Costanzo and P. Spadoni, "Computer-Aided Design of Ultra Wide band Active Antennas by Means of a New Figure of Merit", IEEE Microwave and Wireless

[21] C.C. Penalosa, "Numerical Stady-State Analysis of Nonlinear Microwave Circuits with Periodic Excitation", IEEE Transactions on Microwave Theory and Techniques, vol.

[22] N. Soveiko, and M. Nakhla, "Wavelet Harmonic Balance", IEEE Microwave and

[23] Y. Zhang, P. Gardner, H. Ghafouri-Shiraz and P.S. Hall, "FDTD Analysis of Microwave Active Integrated Antenna Including Nonlinear Model of FET Transistor", 3rd International Conference on Microwave and Millimiter wave Technology Proceedings,

[24] J. Zhang, Y. Wang, and Y. Chen, "Analysis of Active Antenna by using Piecewise Harmonic Balance Technique and Neural Network", International Journal of Infrared

[25] R. Goyal and V. Veremey, "Application of Neural Networks to efficient Design of

[26] V. Rizzoli, A. Neri, D. Masotti and A. Lipparini, "A New Family of Neural Network-Based Bidirectional and Dispersive Behavioral Models for Nonlinear RF/Microwave

[27] M. Jalali, A. Abdipour, A. Tavakoli, and G. Moradi, "Performance Amelioration of an Active Integrated Spiral Antenna System for UWB Applications", Iranian Journal of

Wireless and RF Circuits and Systems", Xpedion Design Systems, Inc.

Electrical and Computer Engineering, Vol. 7, No. 1, Winter-Spring 2008

Subsystems", (InvitedPaper), Wiley & Sons, Inc., John 2002.

Communication and Identification Applications", IEEE. 1997.

Linear Amplifiers. Universitat der Bundeswehr München, July 2005

5th COST 260 MC & WG Meeting, Wroclaw, Poland, 30 June 1999.

Antenna" Shahid Bahonar university of Kerman. MSc. Thesis, 2009

university of Tehran (Politechniques), MSc. Thesis, 2006

Components Letters, Vol. 18, No. 4, April 2008.

Wireless Components Letters, December 12, 2002.

and Millimeter Waves, Vol. 18., No. 5, 1997.

MTT-31, p. 724-730, Sept. 1983.

UWB is a very promising technology for short-range wireless communications providing the opportunity of high data rate communications. In 2002, the Federal Communication Commission (FCC) regulated the UWB technology utilization for commercial applications in the United States in the frequency range of 3.1–10.6 GHz [1]. Other than the United States, UWB regulations have been issued in Europe, Japan, Korea and Singapore. These regulations did not stipulate the technology type to be used. Later, two distinct techniques were envisaged: the Multi-band Orthogonal Frequency Division Multiplexing (MB-OFDM) and the Impulse-UWB (I-UWB) [2]. The MB-OFDM divides the UWB spectrum in 14 subbands, the utilization of the bands is managed for a code time-frequency exploiting the spatial-temporal diversity [3], while the I-UWB transmits pulses of very short duration that occupy the entire allowable frequency band [4]. UWB has vast array of applications in wireless world. The dominant applications include WBAN, WPAN, RFIDs, sensor networks, radars, etc. The relevant IEEE standards for UWB are: 802.15.3a for high data rate and 802.15.4a for low data rate. Digital communication using Multi-Input Multi-Output (MIMO) processing has emerged as a breakthrough for wireless systems of revolutionary importance. All wireless technologies face the challenges of signal fading, multipath, increasing interference and limited spectrum. MIMO technology exploits multipath to provide higher data throughput, and simultaneous increase in range and reliability all without consuming extra radio frequency. Early studies conducted by Foschini and Gans [5] indicated that capacity increases were possible by using MIMO systems. In a rich scattering environment, Telatar showed that the capacity of system consisting of ܯ transmitter and ܰ receiver antennas is ݉݅݊ሺܯǡ ܰሻ times that of a single transmitter receiver system [6]. MIMO systems exploit the antenna diversity (spatial, polarization or pattern diversity) to increase the strength of the transmitted signals and therefore to improve the Signal Noise Ration

© 2012 Najam et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Najam et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

(SNR). Spatial multiplexing in MIMO systems helps in increasing data rate. Beamforming is used either to increase data rate or to strengthen the signal. The applications of MIMO include digital television (DTV), wireless local area networks (WLANs), metropolitan area networks (MANs), and mobile communications. IEEE standard related to MIMO technology is 802.11n.

Multiple-Input Multiple-Output Antennas for Ultra Wideband Communications 211

systems, and to present a state of art in techniques to be used to reduce mutual coupling and enhance the isolation. This chapter also describes some of our proposed designs and structures of the different types of MIMO antennas for UWB applications exploiting spatial, polarization and pattern diversities, and a solution to enhance the isolation with reduced

The antennas are an essential part of any wireless system. According to the IEEE Standard Definition of terms for Antennas, an antenna is defined as "a means for radiating and receiving radio waves" [9]. In an advanced wireless system, an antenna is usually required to optimize or accentuate the radiation energy in some directions and suppress it in others at certain frequencies. A good design of the antenna can relax system requirements and improve overall system performance. To describe the performance of an antenna, there are several commonly used antenna parameters, including impedance bandwidth, radiation

In UWB systems, the previous fundamental and classical parameters must be considered in designing antennas but there are more challenges to monitor them and some additional

**Bandwidth** - First of all, what distinguishes a UWB antenna from other antennas is its ultra wide frequency bandwidth. According to the FCC's definition, a suitable UWB antenna should be able to yield an absolute bandwidth of not less than 500 MHz or a fractional bandwidth of at least 0.2. Moreover, UWB antenna must be operable and must have stable impedance matching over the entire 3.1-10.6 GHz frequency range in the case of I-UWB following the FCC defined spectral mask. Sometimes, it is also demanded (e.g., in Europe) that the UWB antennas should provide the band-rejected characteristic to coexist with other narrowband devices and services occupying the same operational

**Radiation Pattern** - Directional or omni-directional radiation properties are needed depending on the practical application. Omni-directional patterns are normally desirable in mobile and hand-held systems. For radar systems and other directional systems where high gain is desired, directional radiation characteristics are preferred. High radiation efficiency is usually required for antennas but it is imperative and essential for an ultra wideband antenna because the transmit power spectral density is excessively low. Therefore, any excessive losses incurred by the antenna could potentially compromise the functionality of

**Size and Cost** - A suitable antenna needs to be small and of light weight enough to be compatible to the application. As we are projecting UWB for the applications that include

pattern, directivity, gain, efficiency, and polarization [10].

**2.1. Specific parameters for UWB antennas**

size of antenna.

parameters.

band [11].

the system.

**2. Antenna theory**

Where one says that UWB is a classical solution to the demand of high data rate communications, there arise the questions while thinking of UWB and MIMO together in the wireless systems. Obviously, it can be answered in terms of the reasons rather motivations behind this combination of two technologies. In effect, it is well known that the main applications of UWB technology are found for WPAN and WBAN (Wireless body area network) in indoor environments where the dense multipath propagation leads to generally detrimental Inter Symbol Interference (ISI). Therefore, to turn this drawback into an advantage, multiple antennas or MIMO techniques can be employed to exploit such rich scattering environments. The more important is that the applications of UWB are limited to the short distance communication due to very low transmission power allowed by the FCC. Hence, using MIMO together with UWB helps in extending the communication range as well as offers higher link reliability. The benefits of UWB-MIMO can be summarized as following [7]-[8]: interference mitigation/suppression, higher data rates, improved link quality, extended coverage, reduced analog hardware requirements, and concurrent localization. Apart from these benefits, there are also challenges for the joint implementation of UWB and MIMO. These challenges include: UWB-MIMO signaling trade-offs, UWB-MIMO channel modeling, the optimization of UWB-MIMO modulation schemes, design of compact and suitable UWB antenna arrays, efficient and cost-effective UWB-MIMO RF circuit design, etc. Among these challenges, the design of compact and suitable UWB diversity antennas has appealed many researchers to work on this topic. The significance of antenna in a wireless communication system cannot be avoided. It also becomes a critical element to be miniaturized along with the other circuit elements. The design of antenna faces a lot of challenges itself in this race. As devices are going to be more compact, therefore the antennas must be positioned within the available space. Moreover, MIMO can be implemented by three ways: beamforming, spatial multiplexing and diversity techniques. Diversity techniques, more specifically antenna diversity techniques (i.e., spatial, polarization and pattern), are adopted for MIMO antenna designs. Hence, the implementation of multi-antenna structures becomes more challenging in the very limited space provided by the small terminals. The limitations to exploit the diversity arise when the antennas are placed in close vicinity. So, it is required to decorrelate their patterns, or in other words, mutual coupling should be minimized. Another challenge is the enhancement of isolation between the access ports of MIMO antennas. In the literature, a relative few MIMO antenna designs have been presented for UWB systems. In this context, this chapter presents an overview of MIMO UWB antennas with the main following objectives: to highlight the additional parameters required to characterize the performance of UWB antennas as well as MIMO antennas, to bring a state of the art in MIMO antennas for UWB systems, and to present a state of art in techniques to be used to reduce mutual coupling and enhance the isolation. This chapter also describes some of our proposed designs and structures of the different types of MIMO antennas for UWB applications exploiting spatial, polarization and pattern diversities, and a solution to enhance the isolation with reduced size of antenna.


**4. Discussion**

In this study, for the first time, the changes in NADH fluorescence in epidermal cells have been investigated in highly trained athletes before and after a training period. The main and novel finding is a significant increase in NADH fluorescence after training.

#### *4.1. The E*ff*ect of Training*

In our study, an increase in NADH fluorescence after a 7-week training period in highly trained athletes was observed. It is widely known that physical training induces several adaptations including mitochondrial adaptations [22]. The measurement of NADH fluorescence may be used to indirectly evaluate the mitochondrial function and information about its metabolic status [1,5]. However, the changes in NADH fluorescence alone do not allow us to answer the question of what particular metabolic changes took place. It is known that NAD+ and NADH are in balance (i.e., the more NAD+, the less NADH and vice versa [8]). Therefore, the higher post-training NADH fluorescence shown in our study may indicate increased NAD turnover.

Our participants represented different sport disciplines, but the study was only conducted in the general preparation period of the annual training cycle. The main goal of this period, regardless of sports discipline, was the development of endurance capacity. VO2max did not change after training in our athletes, which is in line with other reports [30,31] that also did not observe such changes in highly trained athletes in an annual training cycle. However, we assume that the changes occurred at the cellular respiration level. The endurance-dominant training in all athletes significantly affected the increase in the NADH fluorescence, which can be reflected by the changes in mitochondrial functions as shown in measured NADH parameters (Bmean, FImax, FRmin). The post-training increase in Bmean, FImax, and FRmin suggests a training-induced increase in the total NAD pool. However, there is a lack of research on training-induced changes in skin mitochondria. We can only compare our findings with those obtained from muscle mitochondria. To the best of our knowledge, the only research on training-related changes in NAD levels was performed on rat muscles. It has been found that NAD levels increased in response to endurance training [16]. There is a lack of studies on NAD changes in trained humans. The training-related changes in mitochondria have been widely described in human muscles [19,21,22,25,32]. The training-related changes in the mitochondria are probably connected with the improvement in mitochondrial biogenesis and the removal of dysfunctional mitochondria [21,22,25,32]. After training, an increase was observed in the levels of proteins related to mitochondrial biogenesis [21,25] and an improvement in mitochondrial respiratory function [19]. It is suggested that the profile of the mitochondrial changes depends on training intensity and volume. Training volume seems to affect mitochondrial content, whereas training intensity is correlated with the improvement in mitochondrial respiration [19]. It must be remembered that exercise does not necessarily imply exactly the same metabolic changes in muscle and skin mitochondria. However, intense physical activity affects mitochondrial activity and induces an increase in NADH fluorescence, which we have shown in our previous study [5]. Therefore, the observed increase in NADH fluorescence after 7-weeks of training may indirectly indicate adaptive changes in skin mitochondria.

#### *4.2. Exercise Response*

In our recent paper [5], we showed that a single bout of exercise until exhaustion induced a significant increase in skin NADH fluorescence. The results of this study are in line with our previous observations. We found that the Imax parameter, related to fluorescence intensity, decreased after exercise and that the Rmin parameter increased after exercise. The likely explanation is that with limited aerobic metabolism, NADH is accumulated and the NAD+ amount decreases because anaerobic metabolism does not allow for restoring NAD+ from NADH to a sufficient extent [33–35].

However, some authors [36] suggest that the decrease in NADH fluorescence intensity during reperfusion not only shows the change in mitochondrial function, but also in microcirculatory and endothelial functions related to the efficiency of blood supply to the skin. Both the skin blood vessels' thermoregulatory [37–39] and endothelial [40] functions improved after training. Our study supports this view and suggests improvements in exercise tolerance based on NADH fluorescence measurement.

#### *4.3. Practical Application*

The FMSF method might be useful to evaluate metabolic adaptations related to mitochondrial function and/or microcirculatory function as the effect of training (training efficiency). This might also be used to observe the recovery after exercise when returning to the resting NADH values.