**2. Materials and methods**

#### **2.1 Tooth preparation**

Tables 1 and 2 list the materials used in this study and the study design, respectively. Twenty four freshly extracted caries and restoration-free permanent human molars stored in distilled water were used. The teeth were embedded in improved stone with the occlusal surface of the crown exposed and parallel to the base of the stone, and the embedded teeth were sectioned at one third of the occlusal surfaces to expose the dentin surface. Each tooth was wet-ground with 320-grit silicon carbide paper and polished with 1200-grit to obtain a flat dentin surface. The specimens were stored in distilled water at 37 °C. The teeth were divided randomly into two groups, control and laser irradiated groups. The control groups without laser irradiation were divided randomly into two subgroups (SE bond and Single bond), and the laser irradiated groups were divided into four subgroups (SE bond with 1.4 W, 2.25 W and Single bond with 1.4W, 2.25W).

#### **2.2 Laser irradiation**

The Er,Cr:YSGG laser (Waterlase, BioLase Technology, Inc., San Clemente, CA) with a 2780 nm wavelength and 20 Hz of power with a sapphire tip was used. Laser irradiation was performed on the dentin surface with either 1.4 W or 2.25 W. The flattened dentin surfaces of the teeth were irradiated at 90° in non-contact mode with a fixed distance of 6 mm away from the laser tip in a sweeping motion to achieve an even surface coverage by overlapping the laser impact. The laser handpiece was attached to a modified surveyor to ensure a consistent energy density, spot size, distance and handpiece angle.

#### **2.3 Bonding procedures**

In all groups, including laser irradiated groups and control groups, the bonding procedures recommended by the manufacturer' instruction were followed strictly. In the single bond

depends on the hybridization of the resin within the exposed collagen mesh as well as to the dentin tubules (Abdalla & Davidson, 1998), creating a micromechanical interlocking of the resin within the exposed collagen fibril scaffold. The second is the "self-etch" adhesives (SEA) which employs acidic monomers that simultaneously condition and prime dentin. The smear layer remains partially but is used to hybridize with the underlying dentin (Perdigao et al., 2000). The last is an all-in-one system, but the stability of the bond strength

According to previous reports, a tiny flake surface formed by the laser irradiation of dentin can be removed with 30-40 % acid etching, but the primer of SEA cannot. This study hypothesized that the primer of SEA cannot improve the free surface energy of irradiated dentin. Therefore, it is unable to make a proper environment for sufficient bond strength. The null hypothesis was that the shear bond strength with "self-etch" adhesives (SEA) did not show a difference from that with the etch-and-rinse (ER) technique after a pretreatment

This study examined the shear bond strength of a hybrid composite resin bonded with two different adhesive systems to the dentin surfaces prepared with Er,Cr:YSGG laser etching, and evaluated the morphologic structure of de-bonded dentin surface after Shear Bond

Tables 1 and 2 list the materials used in this study and the study design, respectively. Twenty four freshly extracted caries and restoration-free permanent human molars stored in distilled water were used. The teeth were embedded in improved stone with the occlusal surface of the crown exposed and parallel to the base of the stone, and the embedded teeth were sectioned at one third of the occlusal surfaces to expose the dentin surface. Each tooth was wet-ground with 320-grit silicon carbide paper and polished with 1200-grit to obtain a flat dentin surface. The specimens were stored in distilled water at 37 °C. The teeth were divided randomly into two groups, control and laser irradiated groups. The control groups without laser irradiation were divided randomly into two subgroups (SE bond and Single bond), and the laser irradiated groups were divided into four subgroups (SE bond with 1.4

The Er,Cr:YSGG laser (Waterlase, BioLase Technology, Inc., San Clemente, CA) with a 2780 nm wavelength and 20 Hz of power with a sapphire tip was used. Laser irradiation was performed on the dentin surface with either 1.4 W or 2.25 W. The flattened dentin surfaces of the teeth were irradiated at 90° in non-contact mode with a fixed distance of 6 mm away from the laser tip in a sweeping motion to achieve an even surface coverage by overlapping the laser impact. The laser handpiece was attached to a modified surveyor to ensure a

In all groups, including laser irradiated groups and control groups, the bonding procedures recommended by the manufacturer' instruction were followed strictly. In the single bond

decreases with time by because it contains many hydrophilic monomers.

Strength (SBS) Test by scanning electron microscopy.

W, 2.25 W and Single bond with 1.4W, 2.25W).

consistent energy density, spot size, distance and handpiece angle.

with a laser in dentin.

**2. Materials and methods**

**2.1 Tooth preparation**

**2.2 Laser irradiation**

**2.3 Bonding procedures**

adhesive system, etching procedures were conducted using 37 % phosphoric acid (3M ESPE, St. Paul, MN, USA) for 15 seconds followed by rinsing with a water spray for 15 seconds, and blot dried, and bonded and light curing for 15 seconds. In the Clearfil SE bond system, a primer was applied to the dentin surface for 10 seconds followed by bonding and light curing, as shown table 1.

After light curing the bonding resin, a Teflon tube (GI tech, Seoul, Korea) with an inner diameter of 2 mm and a height of 2 mm was attached to each dentin surface and filled with A3 Body Shade of the hybrid composite Resin (Filtek Supreme Plus 3 M ESPE, MN, USA) followed by light curing for 40 s. After light curing, the teeth were stored in water at 37°C for 24h before the Shear Bond Strength (SBS) Test.

Table 1. Materials used in this study.

Table 2. Classification of the experimental groups.


**1. Introduction**

According to the most recent scores from the National Assessment of Educational Progress (NAEP), a significant number of fourth- and eighth-grade students in the United States (U.S.) are failing to read at satisfactory levels [1]. Specifically, 32% of all fourth-grade students were found to be reading below basic levels, demonstrating di fficulties with making simple inferences and finding relevant information to support their understanding of a text. This statistic sees an alarming increase among students identified as having learning disabilities, with 68% of struggling fourth graders reading below basic levels. This is hardly surprising considering that di fficulties with reading are commonplace among students identified with learning disabilities [2].

Chall's stages of reading highlight the importance of oral reading fluency as students' decoding develops. Proficient oral reading fluency is one of the main characteristics identifying children moving from stage 2 (learning to read) where the focus is on rapid decoding of words to stage 3 (reading to learn) where students begin to gain new knowledge and ideas through their reading of increasingly complex texts from a variety of di fferent genres [3]. Based on Chall's model, fourth graders should be entering the reading-to-learn phase (stage 3). However, findings of students reading below basic

levels in the fourth grade on the NAEP suggest that many fourth graders in the U.S. have not entered this phase and are still working to master learning to read. Students' difficulties with oral reading fluency may thus be one factor prohibiting students from progressing to the more advanced stages of reading development [3]. This theoretical proposition is well supported in research conducted among students in the U.S. For instance, Daane, Campbell, Grigg, Goodman, and Oranje examined a subsample of fourth-grade students who took the NAEP reading assessment in 2002 and identified 40% of the sample to be "non-fluent" readers who also scored at or below the basic achievement level on the overall NAEP reading assessment [4]. The negative impact of deficits in oral reading fluency extends to many other school subjects that require students to gain understanding through reading [5], further underscoring the importance of oral reading fluency for reading development. Beyond the U.S. context, the importance of fluency for reading is also evident in that reading curricula standards across different countries and languages cite the achievement of fluency in reading words and texts, typically by grade three, as a curricula goal [6]. Deficits in automaticity in reading have also been found to be associated with children identified as having reading disabilities across a range of languages [7,8].

Therefore, in light of the far-reaching effects of difficulties in reading fluency and that fluency is identified as a crucial building block of reading development [5,9], it is essential that fluency interventions be provided for elementary students demonstrating difficulties in reading [5]. An increase in oral reading fluency skills would allow students to read more complex text at more proficient levels. Thus, this synthesis of research will examine the types of interventions which aim to build the oral reading fluency and their impact on reading outcomes in students with reading difficulties.

#### *1.1. Oral Reading Fluency*

Fluent reading is often conceptualized as being synonymous with three aspects, namely, the ability to read texts with accuracy, appropriate rate, and prosody [10], with the ultimate aim of extracting meaning in reading [11]. The multifaceted nature of fluency and the association between fluency and reading comprehension is well-placed in theory and empirical research [11–14]. For one, how rate and accuracy components in reading fluency facilitate reading comprehension is outlined in the model of automatic processing [15]. According to this model, all individuals have limited cognitive capacity which makes it necessary for readers to develop automaticity in lower-level word recognition skills such as grapheme–phoneme correspondences and phonemic awareness in order to dedicate adequate cognitive resources to higher-order tasks involving comprehension of texts [15]. This ability to develop automaticity in word recognition processes is what often differentiates fluent from dysfluent readers. Dysfluent readers likely find their cognitive attention consumed primarily by decoding as they have to intently and laboriously attend to letters, sound-symbol correspondences, and word recognition. The inability to achieve automaticity in lower-order processing places large demands on working memory, leaving few resources available to negotiate meaning making in texts. Considering the centrality of working memory in facilitating the storage and retrieval of information in texts during the process of reading for comprehension [16,17], non-automaticity in decoding hinders reading comprehension [18].

It has also been suggested that fluency aspects of accuracy and rate mediates the association between decoding and reading comprehension, a postulation that has been empirically supported. Silverman, Speece, Harring, and Ritchey measured the contributions of aspects of decoding comprising phonological awareness, word and nonword reading as well as fluency (measured by speed and accuracy in reading words, sentences, and texts) in reading comprehension, controlling for linguistic comprehension [19]. They found that when fluency aspects were not included in the model, there was a significant relation between decoding and reading comprehension. However, this relation was no longer apparent once fluency was accounted for. In addition, students who were good decoders but non-fluent readers were weaker in reading comprehension as compared to those with strong decoding and fluency skills [19]. The finding in Silverman et al. that good decoders could be further classified as fluent or dysfluent readers also supports that of previous research, suggesting that although there

is a strong association between decoding and fluency [20,21], proficiency in the former does not automatically translate into the latter. Rather, explicit instruction that builds up fluency is necessary to facilitate the transition from being able to recognize words accurately to being able to recognize words both accurately and rapidly [19].

The role of prosody in reading comprehension has also been established, although to a lesser extent than accuracy and rate aspects. Prosody, a frequently overlooked component of oral reading fluency [22], is concerned with reading with expression and is associated with the ability to produce appropriate changes in pitch and stress as well as use appropriate phrasing and intonation [14]. Prosodic elements are suggested to be central components of fluency and reading comprehension because reading words in meaningful phrases allows readers to focus on the ideas in the text and students who read without expression are likely not gaining full meaning of texts [9,23]. Empirical research supports this view. For instance, in a study examining the relationship between prosody and reading comprehension in 80 third-grade students [24], students read aloud a passage which targeted specific characteristics of prosodic reading, including (1) basic declarative sentences thought to elicit a decline in pitch, (2) basic quotes intended to elicit pauses in phrasing, (3) yes/no questions designed to elicit an increase in pitch, and (4) phrase-final commas thought to elicit pauses in phrasing. Findings showed that children who demonstrated greater prosodic awareness, where they showed a decline in pitch in declarative sentences and an ascent in pitch with yes/no questions, had higher reading comprehension scores as those who did not.

#### *1.2. Oral Reading Fluency and Reading Di*ffi*culties*

Increasingly, deficits in reading fluency have been acknowledged as an area in which children with reading disabilities struggle [20,25]. This is evident in that oral reading fluency was added to the federal definition of a specific learning disability through the Individuals with Disabilities Education Improvement Act (IDEA) in 2004 [26]. Scientific studies of reading also support this view. For instance, as evidenced in Daane et al. [4], many students with reading di fficulties were dysfluent readers who read slowly and laboriously. These students often struggled with automatic word recognition and had to stop frequently while reading to sound out words or use structural analysis to look for common syllable types or morphemes [27]. In another study, Rasinski and Padak examined the word recognition, oral reading fluency, and reading comprehension abilities of 604 students in second through sixth grade identified as having reading di fficulties [28]. After collecting data from an informal reading assessment (Ekwall Reading Inventory) and routine assessments given by teachers, Rasinski and Padak concluded that di fficulties with reading speed translated into fluency deficits that negatively impacted reading comprehension [28]. In another recent study, Kang and Shin concluded that an estimated 6% of struggling readers in upper elementary grades exhibited early reading di fficulties related to decoding and fluency [29]. Moreover, when combined with students who had issues with basic reading skills, as well as comprehension, more than half of all struggling readers in upper elementary grades displayed deficits in decoding and fluency skills. Their work emphasized that fluency is, in fact, an essential component of reading comprehension, and that fluency, while it overlaps with decoding, is a separate component that makes unique contributions to reading comprehension.

In light of the evidence suggesting the crucial role fluency plays in reading, especially among children with reading disabilities, researchers have pointed to the importance of interventions targeted at raising students' fluency skills. Specifically, researchers have emphasized the need for interventions to target fluency aspects directly rather than indirectly through other related reading skills such as phonological awareness because interventions of the latter nature alone have not been shown to improve fluency skills [5,12,30]. Researchers have put forth that fluency improvements increase reading comprehension among struggling readers indirectly by freeing up limited working memory resources to be used in higher-order processes in reading [15,31,32]. This explanation is tenable considering that research has shown that children with reading di fficulties often exhibit working memory deficits, see [33] for a review.

*Educ. Sci.* **2020**, *10*, 52

However, fluency instruction is often absent from elementary school reading curriculum today, possibly because classroom teachers are rarely provided with any training on instructional strategies to promote oral reading fluency [34]. This lack of attention to fluency in instruction and the consideration that fluency is a skill that has been identified to be di fficult to build up points to the importance of examining the e fficacy of direct interventions of fluency [35,36]. In addition, considering the close association between fluency and reading comprehension, examining the e fficacy of fluency interventions on reading comprehension in addition to fluency outcomes is necessary. In general, previous syntheses and meta-analyses that have examined children with reading disabilities have shown oral reading fluency interventions to be e ffective in improving fluency and/or comprehension outcomes in school-aged children [37–39]. Across these reviews, researchers have also highlighted the importance of considering characteristics including type of intervention, type of interventionist (adult vs. peer), number of times texts were read in the interventions, pre-instructional support, corrective feedback, and number of elements included in interventions in order to assess intervention effectiveness [37–39], although these have not been systematically examined among children with reading di fficulties across reviews. For instance, the systematic review conducted by Therrien found considerable e ffect sizes associated with fluency interventions on fluency and comprehension outcomes for students with and without learning disabilities (LD) and highlighted that interventions that were conducted by an adult typically yielded greater e ffect sizes as compared to those mediated by peers [39]. However, the review focused solely on repeated reading interventions and did not consider the e ffects of other types of interventions. In addition, the characteristics of interventions and their e ffectiveness on reading outcomes for LD children specifically were not discussed. Similarly, only repeated reading interventions were examined in a more recent meta-analysis conducted by Lee and Yoon and the effects of interventions on fluency outcomes only were examined. Transfer e ffects of fluency to reading comprehension outcomes were not examined [37]. Furthermore, although the review conducted by Chard et al. discussed in detail intervention characteristics related to di fferent fluency interventions and the e ffects of interventions on both fluency and comprehension outcomes, e ffect sizes across studies reviewed were not reported [38]. In addition, the number of studies reviewed pertaining to the di fferent intervention characteristics were very small, making it di fficult to draw definite conclusions from these studies. Finally, in the most recent synthesis by Stevens et al. [40], single-case studies figured as the majority which the authors noted could impose limits on the generalizability of findings.

#### *1.3. The Current Study*

In light of these gaps, this paper seeks to systematically examine the e ffects of oral reading fluency interventions on elementary students (i.e., first through fifth grade) identified as having reading di fficulties across a range of experimental studies conducted in school settings. Specifically, we addressed the following objectives: (1) whether oral reading fluency interventions increase the oral reading fluency (i.e., accuracy, rate, and prosody) and reading comprehension of elementary students identified as having reading di fficulties, and (2) the characteristics of e ffective interventions that facilitate these reading outcomes.

In addition to providing a more updated examination of the e ffectiveness of fluency interventions, the current review builds on previous syntheses [37–40] in several ways. First, we expanded our examination of types of fluency interventions to include that other than repeated reading. Second, we examined the magnitude of intervention e ffects on both fluency and comprehension outcomes within the same synthesis to examine the local and transfer e ffects of interventions, respectively, and compared the magnitude of e ffects of interventions on both types of outcomes. Third, our present study only reviewed group-design studies, following Stevens et al.'s point about limitations on generalization of findings with single-case designs [40]. Furthermore, we only included studies that had a control group in order to control for quality of study design and to allow for more definite conclusions to be made about the e ffectiveness of fluency interventions. Finally, although previous syntheses did not examine whether group size influenced the e ffectiveness of interventions, we consider this variable in our present study. This is because intervention studies pertaining to di fferent reading constructs have yielded di fferent findings regarding optimal group size for interventions [41,42]. Thus, it is necessary to examine whether this variable influences intervention outcomes.


**3. Raman spectroscopic variations**

wide range of sample types. Although being recognized as not as specific and sensitive as other metabolomics techniques, several works already demonstrated the potential of Raman applied to health sciences for metabolic fingerprinting because it is possible with only one spectra to simultaneously analyze carbohydrates, amino acids, fatty acids, lipids, proteins, nucleic acids and polysaccharides with a minimum sample preparation. As Raman is a scattering technique

For diagnostic purposes, it is expected that Raman spectra of biological samples result in quantitative data, so it is essential to define some categorical differentiable classes for data by dividing samples in healthy or disease sample classes. For these purposes, chemometric data

Due to Raman spectroscopy features, it is currently widely used in health sciences for spectral imaging of cells and tissues, for the *in-vivo* and *ex-vivo* diagnosis of tissues, where fiber probes can be used, and for biofluid analysis, contributing to a better knowledge of the disease and disease diagnosis at the molecular level. This chapter describes the most relevant application

Raman spectroscopy is an optical technique based on inelastic scattering of light due to the vibration of the molecules that can provide chemical fingerprints of several samples. In health sciences, Raman can be used in DNA analysis, lipids, proteins and amino acids identification, bacteria classification and recognition, cell responses, cancer diagnosis and prognosis, and dental prosthesis, among others. This wide range of application is due to Raman's capabilities that go far beyond of being a noninvasive and nondestructive method that does not require samples preparation. Raman is compatible with aqueous solutions and is also a technique that produces results in a short time, requiring less than a minute to obtain a good quality spectrum, and no sample preparation is needed. This spectroscopic technique is sensitive to identify many different functional groups that produce weak signals in infrared spectroscopy (C═C; S─S; C─S). Besides that, it has a highly selective fingerprint that allows the discrimination of similar molecules and has high spatial resolution that allows single cell analysis and intracellular imaging.

The ability to use advanced optical technologies in the visible or near-infrared spectral range (lasers, microscopes, and optic fibers) is responsible for the growth of Raman spectroscopy in medical diagnostic. As molecular changes in cells, tissues or biofluids can be detected and quantified by Raman spectroscopy, it is possible to use this technique in the diagnosis of

In fact, Raman spectroscopy can offer chemical fingerprints of cells, tissues (*in vivo* or *in-vitro*), or biofluids. A large range of samples can be used for Raman analysis: formalin-fixed and

Whether a sample is a solid, liquid, powder, slurry, or gas, no sample preparation is normally required, and there is no need to dissolution, grinding, glass formation, or pressing in order

diseases and to study the effects of drugs (treatments) in biosystems.

fresh frozen mammalian tissue, fixed cells and biofluids.

and it is not perturbed by aqueous media, it is suitable to analyze biological samples.

processing is a valuable tool.

276 Raman Spectroscopy

of Raman in biomedical field.

**2. Raman features and sampling**

In recent past, Raman spectroscopy was known as a technique with low signals requiring longer acquisition times. However, recent developments were made to overcome this limitation in the last years. Nonlinear optical effects and metallic nanoparticles are currently used to improve Raman signals, fiber-optic Raman probes were introduced and are used for real-time *in-vivo* experiments, and multimodal integration with other optical techniques increased the acquisition speed and spatial accuracy. These advances in the accuracy allow the application of Raman spectroscopy into clinical diagnosis, and time of analysis allows its clinical use.

Surface enhanced Raman spectroscopy (SERS), Tip Enhanced Raman Scattering (TERS) or nano-Raman and resonance effects increase significantly Raman sensitivity to study biological samples. SERS increases Raman intensity compared to the usual and weak Raman scattering. These improvement features are sufficient to allow even single molecule detection using Raman. SERS is useful in trace material analysis, flow cytometry and other applications where the traditional sensitivity/speed of a Raman measurement is insufficient [2]. Resonance Raman spectroscopy is a variant of Raman spectroscopy that instead of using laser excitation at any wavelength to measure Raman scattering of the laser light, the excitation wavelength is used to overlap with an electronic transition. The overlap results in an extraordinary increase in scattering intensities, thus detection limits and measurement times can be significantly decreased. It is also possible to couple Raman to an optical microscope. Raman microspectroscopy uses visible and near-infrared excitation lasers and allows to extract molecular properties of the samples with diffraction-limited spatial resolution. The typical method to obtain Raman spectral images is by scanning the sample with the laser spot and then applying a uni- or multivariate spectral model to each Raman spectrum [3]. In order to decrease the time of analysis, Raman spectral imaging can be based on line-mapping (laser beam is expanded to form a line spot on the sample surface) [4].

TERS is a chemical imaging technique that is label-free and have enhanced-resolution. TERS imaging is performed with a Raman spectrometer, a scanning probe microscope (SPM) integrated with an optical microspectrometer. The scanning probe microscope provides the means for nanoscale imaging and the optical microscope provides the resources to bring the light to a functionalized probe, and the spectrometer is the sensor analyzing the light output providing chemical specificity. It is possible to increase the signal to obtain high-spatial resolution spectral images for large samples using selective-sampling Raman microspectroscopy. In this approach, it is possible to (1) obtain information about sample spatial features by other optical technique [5] or (2) estimate information in real-time from the Raman spectra [6]. When traditional variations of Raman spectroscopy are used to study tissues, the results are not good due to insufficient penetration depth. The advance of spatially offset Raman spectroscopy (SORS) overcame this limitation enabling spectral measurements until 10–20 mm of the sample and, with this modification, the application of Raman in clinical fields increases by collecting the scattered light away from the point of laser illumination [7]. Transmission Raman spectroscopy (TRS) is the term used when the collection and illumination points are on opposite sides of the sample, and it is quite useful to analyze opaque materials. Besides, it was proved to be very useful to read many millimeters of tissues [8]. To increase the resolution of Raman microspectroscopy, it is possible to use Coherent anti-Stokes Raman spectroscopy (CARS) or stimulated Raman spectroscopy (SRS), both based on nonlinear optical effects that upgrade the spatial resolution. Coherent Raman spectroscopy techniques are based on nonlinear effects to increase the speed and spatial resolution of Raman spectroscopy by inducing coherent molecular vibrations in the sample increasing resolution. CARS is used to obtain image from cells and tissues by exciting the CH stretching vibrations of lipids and proteins and SRS allows to obtain high-speed images [9, 10]. Raman spectroscopy is also adaptable for fiber-optic probes, making it valuable for medical diagnosis *in vivo*, for instance in hollow organs. The probe should have very reduced dimensions to permit the access to body cavities, and the spectra acquisition time should be short to allow accurate measurement [11].


3.1.2. Test on Reliability, Validity and Multicollinearity

For the purpose of highly reasonable and effective model training, data pre-processing is crucial in machine learning. As each record is collected by questionnaires, data need to pass both reliability and Bartlett's tests. In particular, the reliability of input second-level indicators (Cronbach's Alpha) is 0.82 above the threshold value of 0.7 [44]. Bartlett's test of those input second-level indicators is 0.81, indicating that feature selection can be done.

Additionally, one common issue in machine learning is that the large regression coefficients cannot be estimated precisely when the features are multicollinear. In accordance to Hair et al., variance inflation factor (VIF) is calculated to determine whether there is multicollinearity among independent variables [44]. In general, when the VIF values are lower than the common cutoff threshold of 10, multicollinearity is not a significant issue. The results of the multicollinearity test for all input second-level indicators are shown in Table 1, and it can be concluded that there is no multicollinearity among them.

\* These codes refer to input second-level indicators, which are shown in Table A1 in Appendix A. For example, the code of 'GC1 refers to the first second-level indicator measuring the variable of goal congruency.


*2.5. Boundary Conditions and Simulations Settings*

Each of the computational domains corresponding to the geometric variants was given homogeneous boundary conditions. The zones defined are inlet, bypass inlet, outlet, wall and symmetry, marked in Figure 5. The inlet boundary condition corresponds to a flow of 90% of the main exhaust stream at a temperature lower than that required for the efficient operation of the SCR reactor. The design inlet type was defined as a mass flow inlet. The main inlet turbulence was specified with the intensity ratio and the hydraulic diameter. Immediately upstream of the design inlet, the boiler has a heat exchanger covering the entire cross-section of the flue gas duct. Therefore, the flue gas flow upstream of the inlet is

relatively uniform and regulated, making it possible to apply the uniform velocity field condition at the domain inlet.

The bypass inlet boundary condition corresponds to the higher temperature flue gases introduced into the main duct. These flue gases are led at 10% of the total amount from the higher temperature boiler part. Mixed with 90% of the flue gases from the main duct, they are supposed to ensure the safe operation of the SCR reactor in the appropriate temperature range. The design type of the bypass flue gas inlet is a mass flow inlet type with a uniform perpendicular velocity field. The uniform velocity field simplification was applied due to the relatively large dimensions of the duct, whose cross-section is almost four square meters. The flow is not laminar, and wall effects are negligible. The turbulence was specified with the intensity ratio and the inlet bypass duct hydraulic diameter.

The domain outlet located just upstream of the SCR reactor was defined as a pressure outlet. The appropriate conditions were applied, such as backflow temperature, exhaust composition and turbulence defined by the intensity and hydraulic outlet diameter.

The remaining boundary conditions are the symmetry condition and the wall condition. The symmetry condition was given on one surface, indicated in Figure 5, and it corresponds to the second, symmetrical part of the boiler, clearly visible in Figure 1. The wall condition was given on all other surfaces of the computational domain, i.e., the external surfaces of the duct as well as all surfaces corresponding to the flow control elements installed in the duct. All walls both inside and outside the channel were modeled as adiabatic. This approach was justified because the walls inside the duct, which are part of the flow control elements, are heated up to the temperature of the flue gases during the continuous boiler operation. Meanwhile, the external duct walls are well insulated, as indicated by modern temperature measurements installed within the examined boiler section.

The key chemical reactions affecting the flue gas composition no longer occur within the investigated boiler section, so the composition was assumed to be homogeneous for the inlets and the outlet. The flue gas composition and other boundary conditions are shown in Table 2. As symmetrical duct operation was simulated, the mass values refer to half of the flow.

**Table 2.** Flue gas composition and the main boundary conditions.

The key applied solver settings in ANSYS Fluent are coupled scheme with second order discretization for all parameters, pseudo-transient mode, convergence criteria: 10-4. In order to properly evaluate the simulation correctness, relevant parameters were monitored: outlet mass flow, mass-weighted outlet temperature, maximum and minimum temperature in the domain, pressure drop across the duct. The accuracy of the monitored parameters was obtained at a level below 0.1%. Simulations were carried out with a computing server and utilization of 60 cores. The time required to run a single simulation was approximately 8 h.

The numerical model was verified by comparing the current boiler geometry modeling results with the empirical values. The calculations were performed for several operational states of the boiler. The obtained results of temperatures, pressure drops and exhaust gas velocity distribution were compared with the current measurement data. The parameters calculated using the numerical model for the existing boiler structure were convergent with the measured parameters.

#### **3. Results and Discussion**

After calculating all geometric variants, and checking the results for correctness through appropriate monitors, the outcomes obtained were evaluated. The most important results testifying the effectiveness of mixing flue gas streams with different temperatures are the temperature fields generated by the calculations carried out. The flue gas temperature distribution for each geometric variant in the plane intersecting the design domain is shown in Figure 6. The right-hand side of Figure 6 also shows the temperature distribution on a plane perpendicular to the direction of flow, intersecting the mixing flap.

**Figure 6.** The flue gas temperature distribution for each geometric variant in the plane intersecting the computational domain (on the left) and in the plane perpendicular to the flow direction intersecting the mixing flap (on the right).

After analyzing the simulation results, it can be concluded that the most uniform temperature distribution was obtained for the G4 geometric variant. The simulation results of G1 variant indicate that the higher temperature exhaust gas is initially led to the lower part of the duct. However, immediately after the mixing flap, through buoyancy forces and the mass-dominant flow of the denser exhaust gas with a lower temperature, the hot exhaust gas is pushed to the upper part of the duct. They are then mixed to a small extent in the further duct section.

In variant G2, where U-profiles are used, mixing the flue gases is slightly better than in variant G1. In that case, however, most of the hot flue gases right after the bypass duct inlet are forced by the stream of denser and cooler flue gases into the spaces between the U-profiles and flush out the hot flue gases from further parts of the U-profiles. Therefore, the U-profiles installed in this way do not fulfill their intended role, not delivering the hot flue gases to the lower main duct section. Immediately after the mixing flap, the flue gases are directed upwards by buoyancy forces and mix to a small extent in the further section of the duct.

Variant G3 shows an improvement in the level of flue gas mixing compared to variants G1 and G2. The application of U-profiles with a flat section at the flap top allows for an appropriate hot flue gas distribution to the lower parts of the U-profiles. The initial flat section prevents hot flue gases from being washed out by the lower temperature main stream. However, as previously mentioned, the dimensions of each flap had to be adapted to the condition of maximum coverage of half the main duct cross-section. Therefore, U-profiles with a total width of two-thirds the width of the duct cannot be longer. Since the U-profile of variant G3 is wide but relatively short, the hot flue gases are not introduced deep enough to mix effectively with the cold flue gases.

The G4 variant represents the final concept developed, which represents a modification of the G3 variant. Similar to variant G3, a flat section is used in the upper flap section followed by three U-profiles. Variant G4 uses U-profiles that are narrower and longer than the profiles used in variant G3. As with G3, the flat section of the flap prevents the hot flue gases from being washed out in the upper duct section and ensures adequate hot flue gas distribution to the U-profiles. Suitably long profiles transport the hot flue gases to the lower part of the main duct. Then, due to the buoyancy forces, the hot flue gases are mixed with the main flue gas stream of higher density and lower temperature. Further downstream, the flue gas temperature is homogenized. Since the plane on which the temperature is displayed follows the curvature of the flue gas duct, clearly visible in Figure 1, the hot flue gas portion in the U-profile is cut off, so the observer cannot see the hot flue gas entering the end of the profile.

Figure 7 shows the temperature distributions at the computational domain outlet, corresponding to the SCR reactor exhaust inlet. The temperature scale has been narrowed to 100 K (from 570 to 670 K). The target temperature of the perfectly mixed exhaust gas is 597 K. The best degree of mixing of flue gases was obtained in the geometrical variant G4, as can be seen in Figure 7. In this case, the maximum flue gas temperature was 616 K, which is only 2.18% of the percentage deviation from the perfectly mixed flue gas temperature of 597 K. The minimum flue gas temperature, in this case, was 573.6, which is a deviation of 3.91% from the target temperature. In the cases G1–G3, the temperature amplitudes are considerably larger. All exceed values of 100 K. Simultaneously, in the lower section of the duct, flue gases with a low temperature (close to the initial temperature of the main stream) are observed, which indicates a complete lack of mixing of the lower layers of flue gases.

**Figure 7.** The temperature distributions at the computational domain outlet for each geometric variant.

Figure 8 shows a plot of the minimum and maximum temperatures found for each geometric variant at the outlet of the computational domain representing the inlet to the SCR reactor. The graph also shows the temperature amplitudes at the domain outlet, indicating the degree of exhaust gas stream mixing.

**Figure 8.** Plot of temperature and amplitude of flue gas temperature at duct outlet for each geometric variant.

The velocity vectors determined on the plane intersecting the computational domain are shown in Figure 9. It can be seen that for variant G1, the velocity of the main flue gas stream increases significantly in the area under the turbulizing flap. Meanwhile, a low-pressure field and backflows are created in the upper part behind the flap. In the G2 variant, the flue gases flow freely through the spaces between the turbulence flap's U-profiles, creating a slight swirl of gas behind the flap. The flow is then stabilized. As in the geometrical variant G1, in the variant G3 with its wide U-profile, the main exhaust flow velocity increases significantly in the area below the flap. Above the flap, a low-pressure field is created together with the backflow. The most uniform velocity field was obtained for variant G4, which is also the most effective in mixing the exhaust gas streams. The main exhaust stream flows gently through the relatively wide spaces between the flap U-profiles. Slight turbulence is created in the upper duct behind the flat part of the turbulence flap.

**Figure 9.** The flue gas velocity distribution for each geometric variant in the plane intersecting the computational domain.

#### **4. Conclusions**

This article presents an innovative method of mixing flue gas streams in a coal boiler using the designed mixing flap. The presented work is concerned with supporting the SCR system operation under low-load conditions of coal-fired boilers, contributing to the flexibility of the operation of these devices. The developed solution was exposed to CFD calculations, in which the distributions of temperature, velocity, density and other key thermodynamic parameters were examined. The results indicate that the invented flap works as intended, causing an adequate mixing of the exhaust gas streams. It results in a uniform gas temperature field before the inlet to the SCR system. The analyses showed that the mixing flap developed by the authors could lower the flue gas amplitude in the desired cross-section from 298 K to 43 K. In the intermediate solutions, amplitudes of 144, 125 and 106 K were obtained. By appropriate mixing, the maximum flue gas temperature was reduced by 251 K. In addition, the developed solution was subjected to computational analyses with regard to its functioning in the case of boiler operation with nominal load. The flap, as previously mentioned, can be folded towards the upper wall of the duct. It allows safe boiler operation in nominal conditions without significant pressure losses in the flue gas duct.

The developed solution entails investment costs and operating costs. However, due to the current energy policy and the need for coexistence of coal-fired boilers with renewable energy sources, such solutions are necessary for these facilities to function. As in the flue gas treatment installation, this type of modernization does not provide direct profits from the implementation but allows the facility to operate in new conditions of the energy system.

It is planned to create a construction design and then install the device on the OP-650 boiler in the longer term. Work will then be carried out to optimize the method. The next steps will involve the application of the method in coal boilers with different power ranges. Although the solution is dedicated to power boilers, it is possible to use the developed concept in other systems requiring mixing gases with different temperatures.

**Author Contributions:** Conceptualization, P.K., M.K.-G. and J.L.; final geometrical concept, P.K.; methodology, P.K. and M.K.-G.; numerical simulation, M.K.-G.; writing—original draft preparation, M.K.-G.; writing—review and editing, M.K.-G.; visualization, M.K.-G.; supervision, P.K. and J.L.; project administration, P.K. and J.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** This research is supported by the National Centre for Research and Development which is co-financed by the European Union in the framework of the Smart Growth Operational Programme and the Power Units 200+ Program. Innovative technology of changing the operating regime of 200 MWe power units.

**Conflicts of Interest:** The authors declare no conflict of interest.


**11. The effect of pregnancy on endometriosis**

Endometriosis during pregnancy presents a variable behavior among different patients and a variable behavior in the same patient during different pregnancies. The endometriotic lesions usually shrink and an amelioration of the symptoms is observed. In early pregnancy the lesions may enlarge and bleed. The endometriotic stromal decidual transformation during pregnancy may cause softening and rupture of the lesion causing acute abdomen and hemoperitoneum.


*Edited by Tao Zhang*

The treatment of waste is highly relevant to human life and is receiving increasing attention from researchers. This volume contains a number of innovative and cuttingedge approaches to waste treatment, which hopefully will provide authors with new ideas for research in the area of waste treatment to contribute to the development of circular economy models.

ISBN 978-1-80355-912-4

The Circular Economy - Recent Advances in Sustainable Waste Management

Published in London, UK © 2022 IntechOpen © saga1966 / iStock


**NEUTRON DIFFRACTION**

Edited by **Irisali Khidirov**

**INTECHOPEN.COM**

http://dx.doi.org/10.5772/2207 Edited by Irisali Khidirov

#### **Contributors**

Tsunehisa Kimura, Fumiko Kimura, Kenji Matsumoto, Metoki Naoto, Nobuo Niimura, Hui Dai, Mahieddine Lahoubi, Guillermo Requena, Gerardo Garcés, Ricardo Fernández, Michael Schöbel, Yuzuru Miyazaki, Honglin Du, Jinbo Yang, William B. Yelon, William James, Xiaodong Zhou, Qingsheng Cai, E-Wen Huang, Wanchuck Woo, Ji-Jung Kai, Maria Helena Braga, Michael J. Wolverton, Maria Sa, Jorge Ferreira, Ramendra Nath Joarder, Xiaohua Cheng, Irisali Khidirov, Javier Dawidowski, Gabriel Cuello, Luis Alberto Rodríguez Palomino

#### **© The Editor(s) and the Author(s) 2012**

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First published in Croatia, 2012 by INTECH d.o.o. eBook (PDF) Published by IN TECH d.o.o. Place and year of publication of eBook (PDF): Rijeka, 2019. IntechOpen is the global imprint of IN TECH d.o.o. Printed in Croatia

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**2. The nature of the conflict**

All activities in educational institutions are aimed at cooperation and cooperation in a team. Bearing in mind that the concepts of developing these competences are based on the norms and principles of social life, the need to create a safe atmosphere based on mutual trust and a sense of interdependence, then it becomes important to recognize conflicts, their sources, their course and the effects that they may entail [11].

The concept of "conflict" is a complex term, which is reflected in various attempts to define the concept. Most of them treat a conflict as *a clash resulting from different attitudes, priorities, methods of proceeding in the face of the actual object or situation* [12] or *a dispute between two or more members or groups resulting from the necessity to share limited resources or work or taking a different position, different goals, values or perceptions* [13].

On the other hand, with regard to interpersonal relations, the conflict may appear as a declared *fight between at least two mutually dependent parties who perceive the incompatibility of goals, the lack of mutual benefits and recognize that the other party creates obstacles in achieving the goal* [14].

In the context of human resource management, conflict is perceived both as an impulse contributing to increased creativity and the cause of many *unfavorable phenomena* [15].

On the basis of the quoted, selected by the authors, definitions of the phenomenon, one can notice the characteristics of conflict situations, such as the presence of at least two mutually dependent parties, and its disclosure takes place when one of the parties notices that its goals, tasks and values are in opposition to the attitudes and behavior of the opposing party. Moreover, it is noticeable that actions are taken to hinder or block the achievement of the goals and tasks of the opposing party. In the nature of conflicts, it is important that they can arise for non-objective reasons and are accompanied by strong emotions [16].

In the context of our research on conflicts and the quality of teacher's work, important are the functions assigned to conflicts - positive (functional, constructive) and negative (dysfunctional, destructive) functions and their etiology.

The positive function of conflicts is reflected in favorable changes, resulting in increased initiative and creativity in the work of teachers, or changes and modifications within the entire organizational structure.

#### *Conflict and the Quality of Teachers' Work DOI: http://dx.doi.org/10.5772/intechopen.111741*

Then, the negative function of conflict situations ultimately leads to a reduction in the effectiveness of the professional work of individual teachers, has a demotivating effect on undertaking innovative activities and, consequently, reduces the quality of work of the entire educational institution.

The etiology of conflicts is conditioned by various factors related to the nature of a man and the place where he performs his professional functions (Więcek-Janka, 2006, p. 116). Ross A. Webber expressed the view that the determinants of conflicts are three factors: incompatibility of goals, community of resources and interdependence of actions [17]. One of the best-known classifications of the sources of conflicts (and at the same time the typology of conflicts) is Christopher Moore's conflict wheel. He divided the sources (and types of conflicts) into the following conflict: data, relations, values, structural and interests. Of these five, the conflict of values is considered to be the most serious, as it arises as a result of world views, hierarchy of values, values of one's "self" (identity), as well as habits and conventions.


**6.5 Rolling**

Water and a combination of water and alcohol are the most common solvents employed in this procedure. The active substance and other components are dissolved in a small amount of aqueous solvent using a high shear processor. Hydrocolloids that are water-soluble are dissolved in water to create a homogeneous viscous solution. The *Thin Films: A Promising Approach for Drug Delivery System DOI: http://dx.doi.org/10.5772/intechopen.103793*

drug-containing solution or suspension is then rolled onto a carrier. After that, the film is cut into the proper shapes and sizes [68].


*Article* **Optimal Coordination of Wind Power and Pumped Hydro Energy Storage**

### **Hussein M. K. Al-Masri 1,\*, Ayman Al-Quraan 1, Ahmad AbuElrub 2 and Mehrdad Ehsani 3**

Received: 29 September 2019; Accepted: 13 November 2019; Published: 19 November 2019

**Abstract:** A study combining wind power with pumped hydro energy storage for the Jordanian utility grid is presented. Three solvers of the Matlab optimization toolbox are used to find the optimal solution for the cost of energy in a combined on-grid system. Genetic algorithm, simulated annealing (SA), and pattern search (PS) solvers are used to find the optimal solution. The GA solution of 0.0955388 \$/kWh is economically feasible. This is 28.7% lower than the electricity purchased from the conventional utility grid. The discounted payback period to recover the total cost is 10.271 years. The suggested configuration is shown to be feasible by comparing it to real measurements for this case and a previous wind-only case. It is shown that the indicators of the optimal solution are improved. For instance, carbon dioxide emissions (ECO2) and conventional grid energy purchases are reduced by 24.69% and 24.68%, respectively. Moreover, it is shown that the benefits of adding hydro storage, combined with increasing the number of wind turbine units, reduces the cost of energy of renewables (COERenewables). Therefore, combining hydro storage with wind power is economically, environmentally, and technically a more efficient alternative to the conventional power generation.

**Keywords:** pumped hydro storage; wind farm; simulated annealing; genetic algorithm; pattern search; Matlab optimization toolbox; economic and environment feasibility


4.5.1. Cells Treatment before and after Exposure to the Extract

The TE671 rhabdomyosarcoma cancer cell line was obtained from the European Collection of cell cultures (ECACC, London, UK). The A172 glioblastoma cell line was obtained from a male patient of 53 years old (ECACC, London, UK, Cat. Nr 88062428). Cells were grown in a cell-culture flask (75 cm2 surface area) in Dulbecco's modified Eagle's Medium (DMEM) (ThermoFisher Scientific Inc. (Gibco), Waltham, MA, USA Cat. Nr. 10566016) enriched with glucose (4500 mg/mL), and 15% fetal bovine serum (FBS) (ThermoFisher Scientific Inc. (Gibco), Waltham, MA, USA Cat. Nr. 26140-079), L-glutamine (2 mM) (ThermoFisher Scientific Inc. (Gibco), Waltham, MA, USA Cat. Nr. A12860-01). A dual antibiotic solution of penicillin G (100IU) and streptomycin (100 μg/mL) was added (ThermoFisher Scientific Inc. (Gibco), Waltham, MA, USA Cat. Nr. 15140-122), in addition to an amphotericin B solution (ThermoFisher Scientific Inc. (Gibco), Waltham, MA, USA Cat. Nr. 14140-122). A Coulter counter apparatus was used to measure the number of cells inoculated in the experimental setup. Cells were seeded in 96-well plates (1.5 × 103 cells/mL) and were allowed to grow for 24 h until reaching ~80% confluence. After 24 h, cells were exposed to successive diluted concentrations of the extract (t = 0 h), ranging from 0.04 to 6.25 mg/mL, derived from the dried extract diluted de novo in DMSO (10% *v*/*v*). The final concentration of DMSO when the extract was added to cell culture was 1% *v*/*v*. A control well with the same concentration of DMSO was used to confirm that no toxic effect was observed. Cells were incubated for 24, 48 and 72 h.

Experiments were performed in 96-well plates (CellStar® Sigma-Aldrich Chemie GmbH, Taufkirchen, DE Cat. Nr. M3687-60EA, Saint Louis, MO, USA). Plate set up was as follows: a column contained only cell culture medium, a column of cell culture and the staining chemical, a column with cultured cells and a column with cultured cells plus the staining chemical. The remaining wells were used for the testing of the extract in various concentrations. As blank were used those wells containing cell culture medium only, cells and no staining agent or drug, whereas as positive control were used those wells with cultured cells without staining agent. All experiments were performed in triplicate.


**1. Introduction**

Despite major progress in the effectiveness and availability of antiretroviral therapy (ART), considerable challenges in the treatment of people living with HIV (PLWH) remain. There are significant gaps in the HIV care continuum, with the greatest deficits seen in retaining individuals in care and achieving viral suppression. Of the 1.1 million individuals living with HIV in the U.S., the Centers for Disease Control and Prevention (CDC)

**Citation:** Traynor, S.M.; Schmidt, R.D.; Gooden, L.K.; Matheson, T.; Haynes, L.; Rodriguez, A.; Mugavero, M.; Jacobs, P.; Mandler, R.; Del Rio, C.; et al. Differential Effects of Patient Navigation across Latent Profiles of Barriers to Care among People Living with HIV and Comorbid Conditions. *J. Clin. Med.* **2023**, *12*, 114. https:// doi.org/10.3390/jcm12010114

Academic Editor: Icro Maremmani

Received: 2 November 2022 Revised: 29 November 2022 Accepted: 10 December 2022 Published: 23 December 2022

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

estimates that only 49% are continuously engaged or retained in HIV care and 53% have reached viral suppression [1]. One population that is particularly difficult to engage in care comprises people living with HIV who report substance use (PLWH-SU). In a 2018 review examining predictors of outcomes along the HIV care continuum, substance use was the most commonly cited risk factor associated with poor retention [2]. Compared to PLWH who report no substance use, those who use substances are less likely to access antiretroviral therapy, less likely to adhere to medication plans, and more likely to fall out of care [3]. Psychiatric comorbidities were also found to be predictors of poor retention in HIV care [4,5], and co-occurring diagnoses or "dual disorders"—the presence of both a substance use disorder and at least one psychiatric disorder [6]—among PLWH further complicate clinical management and deter retention in treatment [7]. This can lead to uncontrolled infection, which contributes to ongoing disease transmission. The need for interventions to improve engagement of this high-risk population in HIV care remains a national public health priority [8].

To understand why PLWH-SU do not engage in care, it is necessary to recognize the challenges they face in accessing care. This requires a thorough examination of multi-level factors, including social determinants of health, associated with access to and retention in HIV care. Data from the 2016 sample of the Medical Monitoring Project, a nationally representative sample of all adults diagnosed with HIV in the U.S., showed that 42% of respondents had household incomes below the federal poverty threshold and 43% were unemployed [9]. These factors have consistently been shown to severely limit the resources available to obtain healthcare [10–12]. Additionally, 22% and 26% of respondents reported symptoms of depression and anxiety, respectively, both of which are associated with lowered healthcare utilization and poor adherence to treatment plans [9,13–15]. Other barriers to HIV treatment identified through both qualitative and quantitative studies include housing instability [11,16–19], food insecurity [16,20,21], transportation [18,22], substance use [2,23,24], intimate partner violence (IPV) [25,26], perceived stigma [23], discrimination [27], clinic location and hours [24], service availability [26], and privacy concerns [24,28]. Self-perceived barriers to care, including financial, structural, and logistical barriers, as well as concerns about personal health or service delivery, have been associated with higher rates of mortality among PLWH [29]. For PLWH-SU, their substance use presents additional barriers to care, such as stigma, incarceration, and difficulty maintaining scheduled treatment regimens [30–33].

One intervention specifically designed to help individuals overcome barriers to care is patient navigation (PN). PN is a patient-centered intervention that identifies strategies to eliminate barriers to care and guides individuals through the healthcare system. It employs a strengths-based case management approach [34] and motivational interviewing [35] to empower individuals to manage their healthcare. Examples of activities involved in PN include helping individuals obtain health insurance, scheduling medical appointments, arranging transportation or childcare services, and providing assistance in applying for social services [36]. Screening for social determinants of health, such as housing, is another critical navigation activity [37]. PN may be combined with other tools such as contingency management (CM), which offers financial incentives for completing various activities of a treatment plan. The use of incentives has been specifically useful for engaging people who use drugs and/or alcohol [38,39]. PN strategies can help individuals with layered and complex mental health and/or addictions overcome barriers to obtaining services from various, and often fragmented, systems [40,41].

Although PN was initially developed to help predominantly underrepresented minority women access breast cancer screening and treatment services, it is now used for a variety of patient populations [42,43]. Among PLWH, results of studies assessing the effect of PN on HIV care have been mixed. Some studies have shown that PN is efficacious for linking individuals to care and improving steps along the HIV care continuum [34,44–46], while others reported no effect [47,48]. These conflicting results have raised questions about the effectiveness of PN and warrant additional research to determine for which

populations and in what circumstances PN is most beneficial [49]. The effectiveness of PN has been difficult to establish, in part because PN is classified as a "complex intervention." This means that it consists of several core components, targets multiple behaviors, and is often tailored to meet specific conditions [50,51]. The many sources of variation make it difficult to determine which aspects of the intervention are most beneficial. In the case of PN, intervention activities are highly dependent on the specific barriers encountered by each individual. Therefore, it is possible that PN works better for certain patients than for others, depending on the type and number of barriers experienced.

It is also possible that the combination of healthcare barriers, stemming from social determinants of health and other individual and interpersonal factors, may influence the effectiveness of an intervention such as PN on HIV care. Because many PLWH face multiple, concurrent barriers, there is a growing number of studies supporting the use of a syndemics framework for describing factors that influence HIV infection. The syndemics approach suggests that there is an overlap of interrelated factors that drives risk for multiple, cooccurring conditions [52]. Previous studies have identified several syndemic conditions known to occur among PLWH; these include mental illness, violence, homelessness, and socioeconomic disadvantage [53,54]. Previous research has shown that PLWH have an average of two to four syndemic conditions, but some may experience as many as eight conditions [55]. Studies have also shown that these concomitant syndemic factors act synergistically to produce poor health outcomes. For example, research on the interplay among psychosocial factors, substance use, and HIV risk-taking suggests that psychological problems and substance use interact to not only negatively impact retention in care [2], but are also associated with increased risky behaviors [56]. The clustering of risk factors creates a syndemic vulnerability that places individuals at increased risk for HIV acquisition, high-risk sexual behaviors, sexually transmitted infections, and more frequent substance use [52,57].

Additional work has been done to examine syndemic vulnerability as it relates to the HIV care continuum. Glynn et al. (2019) found that among PLWH in Miami, Florida, the odds of having low ART adherence (<80%) and unsuppressed viral load increased for every syndemic condition experienced [55]. This finding supported previous work showing that a higher number of syndemic factors is associated with poor medication adherence and lower odds of viral suppression [58,59]. In 2015, Mizuno et al. (2015) examined syndemic factors specifically among persons who inject drugs and found similar results [57]. All outcomes along the HIV care continuum worsened as the number of psychosocial risk factors increased.

Despite the insights of this previous research, it is limited, in that syndemic barriers to care are measured as a sum of the number of syndemic factors an individual experiences. This composite-score approach places equal weight on the influence of each risk factor and suggests that simply minimizing the number of barriers can lead to improved outcomes. It is possible, however, that the pattern of factors an individual faces is more important than simply the number of barriers. Some syndemic factors may be more significant barriers to treatment than others. Some barriers may be more likely to cluster together than other barriers, creating subgroups of individuals characterized by different combinations of healthcare barriers. Thus, examining patterns of experienced barriers and the impact of these patterns on subsequent health outcomes may provide an improved understanding of how individuals respond to interventions designed to address healthcare barriers.

The current study has two main objectives. The first objective is to describe subgroups of PLWH-SU that share common patterns of barriers to care. The second objective is to analyze how subgroup membership influences the association between PN interventions and HIV outcomes. The data for this study come from CTN-0049, a randomized, controlled trial that studied PN in a sample of 801 hospitalized PLWH-SU who had uncontrolled HIV [60]. The trial tested the effect of a 6-month PN intervention, offered with and without CM, on engagement in care and viral suppression at 6 and 12 months. The results showed that the PN and PN+CM interventions were effective for engaging participants in care at 6 months, and PN+CM was effective for viral suppression at 6 months. Although these

effects were not maintained through the 12-month follow-up period, CTN-0049 provides a unique opportunity to explore factors that contributed to the short-term success of the intervention. The data from this study may help characterize the populations likely to benefit from PN; this characterization can inform future adjustments to the intervention, maximize its effectiveness, and result in a more efficient allocation of resources.

#### **2. Materials and Methods**

#### *2.1. CTN-0049 Overview*

The CTN-0049 study was a randomized, controlled trial supported by the National Institute on Drug Abuse's National Drug Abuse Treatment Clinical Trials Network and has been described in detail elsewhere [61]. Briefly, the purpose of CTN-0049 was to determine the effect of a structured PN intervention, delivered with or without CM, on HIV health outcomes among hospitalized PLWH-SU with advanced HIV disease. Participants were recruited between July 2012 and January 2014 from 11 U.S. hospitals with both a high HIV inpatient census and a high prevalence of substance use among patients. Patients were eligible for enrollment if they had a clinical indication that they were out of HIV care and had evidence of substance use in the past 12 months. A total of 801 participants were randomized to one of three treatment groups: (1) PN, (2) PN+CM, or (3) treatment as usual (TAU). Those randomized to one of the PN groups were offered up to 11 PN sessions over a 6-month intervention period. During sessions, navigators used a strengths-based case management approach to assist patients to coordinate care with clinicians, review their health information, address personal challenges, and provide direct psychosocial support. Those in PN+CM also received financial incentives for target behaviors, including session attendance, completion of paperwork, HIV clinic visits, SUD treatment visits, negative substance use specimens, blood draws, and active ART prescriptions. Participants in the TAU group did not interact with the patient navigators, and received the standard treatment provided at their hospital for linking hospitalized patients to outpatient HIV care and substance-use-disorders treatment, which at most hospitals was written referral. Patients were followed up at 6 months (*n* = 761) and 12 months (*n* = 752) post-randomization and assessed for HIV viral load and other outcomes; however, no differences in rates of HIV viral suppression or death among the three groups at 12 months were revealed.