Narrow Portion Research Articles

Thermal transport of glasses via machine learning driven simulations

Accessing the thermal transport properties of glasses is a major issue for the design of production strategies of glass industry, as well as for the plethora of applications and devices where glasses are employed. From the computational standpoint, the chemical and morphological complexity of glasses calls for atomistic simulations where the interatomic potentials are able to capture the variety of local environments, composition, and (dis)order that typically characterize glassy phases. Machine-learning potentials (MLPs) are emerging as a valid alternative to computationally expensive ab initio simulations, inevitably run on very small samples which cannot account for disorder at different scales, as well as to empirical force fields, fast but often reliable only in a narrow portion of the thermodynamic and composition phase diagrams. In this article, we make the point on the use of MLPs to compute the thermal conductivity of glasses, through a review of recent theoretical and computational tools and a series of numerical applications on vitreous silica and vitreous silicon, both pure and intercalated with lithium.

Environmental and geographic low suitability overlapping of geoduck clams in the Pacific Northeast predicted by Ecological Niche Modeling

The known distribution limits of geoduck clams (genus Panopea) remain geographically separated globally. However, in the northeast Pacific, P. generosa is distributed from Alaska to northern Mexico, but approaches, and likely overlaps, the distribution of P. globosa, which is mainly distributed in the Gulf of California. There is incipient evidence that both populations coexist in the central part of the Baja California Peninsula on the Pacific coast. However, knowledge of the biogeographic distribution and environmental conditions for both species is still developing. To address the hypothesis of coexistence in the same geographic space, we developed distribution area models using ecological niche modeling through the maximum entropy algorithm. The algorithm used presence-only records and environmental layers (predictive variables) such as mean surface temperature, mean salinity, mean depth, temperature range, and primary productivity. The results indicate that both species overlap in a narrow portion of the environmental space (Grinnellian ecological niche), which is reflected in a restricted geographic distribution with conditions of low abiotic suitability. Our results contribute to directing new research in the areas of ecology, biogeography, paleontology, and geoduck clam fisheries management.

Preliminary results of a feasibility study of CONFIDENCE: An intervention to reduce financial strain among Latino family caregivers

AbstractBackgroundLatino/Hispanic family caregivers to persons living with Alzheimer’s disease and related dementias (ADRD) spend 47% of their annual income on the out‐of‐pocket costs of caregiving compared to 26% of annual income spent among caregivers of any race or ethnicity.1 This presentation describes the preliminary results of the CONFIDENCE psychoeducational intervention, developed to reduce the out‐of‐pocket care costs and financial strain among ADRD Latino/Hispanic caregivers. Intervention components were designed to build caregiver resourcefulness, posited to help caregivers displace some out‐of‐pocket costs by increasing the use of community resources. CONFIDENCE consists of five, 1.5‐hour group Zoom sessions. To ensure the intervention was culturally tailored, CONFIDENCE was developed with a Community Advisory Council and informed by qualitative interviews with Latino family caregivers.MethodCONFIDENCE has been delivered at a community agency since May 2022. Data reported here are from the first 5 intervention cohorts. Participation in the study was optional. Study participants were asked to complete a self‐administered online baseline survey before the first session, followed by two surveys sent immediately and 2‐months post‐intervention. Eligible caregivers were Latino/Hispanic, cared for someone living with ADRD for at least 6 months, and were aged 50 or older. (See NCT05292248.) All sessions were delivered in English. Spanish delivery will begin in March 2023.ResultCONFIDENCE was delivered to 27 caregivers, although 55 caregivers registered to attend (49.1%). Of those who attended any of the five sessions, participants attended an average of 2.9 of 5 (SD = 1.4) sessions. Among those who attended at least one session, 56.5% expressed an interest in learning more about the research study when they registered. Of those, six caregivers were eligible to participate and enrolled into the study. Despite lower‐than‐expected participation, those who completed the intervention report high satisfaction. All study completers “Agreed” or “Strong Agreed” that they would recommend CONFIDENCE to others.ConclusionInitial findings suggest a 5‐week, Zoom‐delivered financial psychoeducational intervention may only meet the needs of a narrow portion of ADRD Latino family caregivers. To increase participation, researchers intend to explore alternative forms of delivery that require less time commitment.

Thoracic cavity of the Shirazi cats: New insights using computed tomography and magnetic resonance imaging.

Our study provided a comprehensive characterization of the thorax of Shirazi cats by comparing the relevant soft and bone windows of computed tomography (CT) and magnetic resonance imaging (MRI) with cross, sagittal and coronal sectional anatomy. We outlined the mediastinum and its anatomic relationships with the trachea, oesophagus, lungs, heart, cranial and caudal vena cavae, and other thoracic structures using the data series gathered from adult normal Shirazi cats. The cranial mediastinum extended from the thoracic inlet to the 4th intercostal space, the middle mediastinum extended from the 5th and 7th intercostal spaces and was occupied by the heart and large blood vessels and the caudal mediastinum extended as a short and narrow portion from the 8th intercostal space to the diaphragm. The contents of the mediastinum and its relationship with the lungs and diaphragm were clearly presented in coronal-sectional anatomy and CT slices. The diaphragm was clearly observed in the lung windows of the ventral thorax. Sagittal-sectional anatomy and CT clarified the thorax's architecture and its contents, with higher density in the soft windows. The distribution of thoracic vessels on cross- and coronal-contrast CT scans was clearly visible. In addition, MRI scans provided an excellent anatomic reference of the thorax with the help of cross, coronal and sagittal scans, especially in the heart and blood vessels. Our study provides a valuable atlas for the diagnosis of malformations of the thoracic structures and offers better assessments for helping veterinary radiologists and clinicians in diagnostic processes.

Immediate Tooth Replacement in the Esthetic Zone with the Socket Shield Technique and a Novel Body-Shift Implant: A Pilot Study with Up to 3 Years of Follow-up.

Successful rehabilitation of the anterior maxilla remains a challenge, primarily due to postextraction ridge collapse, which can lead to gingival recession and a nonesthetic appearance. The socket shield technique presents a viable alternative for immediate dental implant placement in the esthetic zone. This pilot study aimed to evaluate the survival, complication rates, and marginal bone loss around body-shift implants placed in fresh extraction sockets with the socket shield technique to replace maxillary incisors. After socket shield preparation, 14 hopeless incisors were extracted and immediately replaced by a body-shift implant (Inverta, Southern Implants) at baseline. Patients were followed up for 12 to 39 months (mean: 18.1 ± 8.2 months). The average age was 52.3 ± 16.9 years, and the survival rate was 100%. One socket shield presented minimal internal exposure that was successfully treated with a connective tissue graft. The mean PES score was 12.9 ± 1.2. Mean interproximal marginal bone loss was -0.4 ± 0.5 mm. Body-shift implants can be a promising alternative for immediate tooth replacement combined with the socket shield technique. The superior esthetic outcomes remained stable, suggesting that the extra space created by the narrow cervical portion of the implant is beneficial for preserving the alveolar bone and limiting internal shield exposure.

Assessment of Posterior Pharyngeal Airway Changes After Orthognathic Surgery Using Barium Sulfate.

Obstructive sleep apnea(OSA), caused by airway narrowing, is likely to occur if the mandibular plane to hyoid distance is greater than 15.4 mm and the posterior airway space (PAS) is less than 11 mm. OSA may be caused by mandibular deficit, bimaxillary retrusion, increased lower facial height, extended soft palate, a large tongue base, and a posteroinferiorly positioned hyoid bone. Snoring and drowsiness during exercise are symptoms of OSA, which is a risk factor for high blood pressure, heart disease, and stroke, and these can result in car crashes. However, orthognathic surgery can improve dental occlusion and aesthetics by adjusting facial bone position, shape, and size. When bones move, the position and tension of soft tissues change. These novel soft tissue interactions, especially when anteroposterior, change the face's appearance and PAS dimensions. This study uses barium sulfate paste to enhance lateral cephalograms before and after orthognathic surgery to assess posterior pharyngeal airway changes. Barium sulfate was mixed with water to make a paste for the tongue's dorsum. A preoperative digital lateral cephalogram was obtained, and a postoperative evaluation was conducted six weeks after the procedure. In the cephalostat, the Frankfort horizontal and median planes were aligned parallel to the floor, and a radiograph was taken after the breathing cycle to standardize the hyoid bone location. Preoperative lateral cephalogram analysis using Burstone's hard tissue landmarks confirmed skeletal class II or III deformities. First, the narrowest part of the posterior pharyngeal airway was measured. Second, the narrowest portion between the soft palate and posterior pharyngeal wall parallel to the Frankfort horizontal plane was measured preoperatively, and the procedure was repeated six weeks postop. Complexity characterizes the pharyngeal airway, which, along with the surrounding structures, facilitates the bodily functions of eating, talking, and breathing. The pharyngeal airway is located behind the nose, mouth, and larynx, and adjusting the jaws changes the size and structure of the pharyngeal airway and surrounding soft tissues, which may affect breathing.A statistically significant change is detected in the posterior palatal and posterior lingual airways after different orthognathic operations. After the mandible is moved forward, both the posterior palatal and posterior lingual airways enlarge. Furthermore, the soft palate exhibits slight decreases in length, thickness, and angle. Additionally, there is an anterosuperior displacement of the hyoid bone. Following maxillary superior impaction, mandibular autorotation is seen in a counterclockwise direction, which has the same result as that of mandibular advancement. It is essential to consider these soft tissue changes when planning orthognathic procedures, as alterations in the pharyngeal airway may impact the patient's postoperative breathing and overall health. Patients with OSA or those at risk of developing it should be closely evaluated and managed appropriately during the surgical planning process.

Marine Transgression in Modern Times.

Marine transgression associated with rising sea levels causes coastal erosion, landscape transitions, and displacement of human populations globally. This process takes two general forms. Along open-ocean coasts, active transgression occurs when sediment-delivery rates are unable to keep pace with accommodation creation, leading to wave-driven erosion and/or landward translation of coastal landforms. It is highly visible, rapid, and limited to narrow portions of the coast. In contrast, passive transgression is subtler and slower, and impacts broader areas. It occurs along low-energy, inland marine margins; follows existing upland contours; and is characterized predominantly by the landward translation of coastal ecosystems. The nature and relative rates of transgression along these competing margins lead to expansion and/or contraction of the coastal zone and-particularly under the influence of anthropogenic interventions-will dictate future coastal-ecosystem response to sea-level rise, as well as attendant, often inequitable, impacts on human populations.

On the steady flow of non-newtonian fluid through multi-stenosed elliptical artery: A theoretical model

The study of blood flow through stenotic arteries is more important as the existence and progression of stenosis may lead to severe damage. The current study aims to analyze and understand the non-Newtonian nature of blood flow through the multi-stenosed artery of an elliptical cross-section. The Carreau fluid model accounts for the non-Newtonian nature of blood. The mathematical equations are transformed to dimensionless form, and assumptions of mild stenosis are employed to reduce the non-linearity of the mathematical model. The perturbation method via polynomial technique is utilized to solve the resulting equations by considering We2 as the perturbation parameter. The results of the velocity and wall shear stress are examined graphically. It is found that stenosis severity substantially impacts flow velocity in the narrower portion of the artery. The stenosis growth strongly affects the flow velocity and wall shear stress in the stenotic region. The non-Newtonian effects are found to dominate along the minor axis. This fact assures that the conduit’s narrower cross-section strengthens the fluid’s non-Newtonian behavior. It is observed that the non-Newtonian fluid has a smaller velocity than the Newtonian fluid. Moreover, non-Newtonian fluid has a different nature along the minor and major axes, but Newtonian fluid has the same behavior.

Exponential fitting of spread of excitation response measurements in cochlear implants

BackgroundHearing performance in cochlear implant (CI) users is variable. An objective measure which can allow a prediction of this performance is desirable. Spread of neural excitation (SoE) curves are an objective measure that can be obtained using the fitting software of cochlear implants and might be able to be used as a predictor. A novel method to interpret SoE curves is presented. New MethodSpread of excitation measurements for three recording sites were fitted using two exponential functions. An asymmetric width measure was developed, defined as the distance in mm to the point, where 25% or 50% of peak normalized amplitude was reached, for each half of the SoE separately. Also, a novel population of subjects with MED-EL CIs is used. Furthermore, speech perception (speech reception threshold, SRT) was evaluated using a matrix sentence test in a multi-source noise field. ResultsSoE width was narrowest for the basal recording site and widest for the apical recording site. Fitted SoE exponential functions were most asymmetric for the apical recording site. A significant positive correlation between sentence test SRT and SoE width at the apical recording site was found. Comparison with Existing MethodsThe use of an asymmetric width measure correlated strongly and positively with speech perception for apical recording sites, unlike the symmetric width measure used in previous studies. Presumably, longer electrodes allow stimulation of a more apical part of the cochlear. At the apical part of the cochlea, dendrites from a large region of the basilar membrane map to a narrow portion on the spiral ganglion, which might explain the observed asymmetry. ConclusionsFor subjects implanted with long electrode arrays, an asymmetric width measure correlates positively with apical SoE distance. However, due to lack of a sufficient amount of data, the results are currently less conclusive and need to be consolidated in a larger cohort of subjects.

Novel technologies to improve the treatment of endodontic microbial infections: Inputs from a drug delivery perspective

Endodontic microbial infections are still a challenge for an effective treatment for being biofilm-mediated and very refractory to conventional therapies. Biomechanical preparation and chemical irrigants cannot fully eradicate biofilms due to the anatomic structure of the root canal system. Instruments employed in biomechanical preparation and irrigants solution cannot reach the narrow and deepest portion of root canals, especially the apical thirds. In addition, aside from the dentin surface, biofilms can also infiltrate dentine tubules and periapical tissues, compromising treatment success. Therefore, different technologies have been investigated to achieve a more effective outcome in the control of endodontic infections. However, these technologies continue to face great difficulties in reaching the apical region and eradicating biofilms to avoid the recurrence of infection. Here, we present an overview of the fundamentals of endodontics infections and review technologies currently available for root canal treatment. We discuss them from a drug delivery perspective, highlighting each technology’s strength to envision the best use of these technologies.

A single-arm prospective interventional study to assess the efficacy of continuous bronchial cuff pressure monitoring to detect the displacement of lung isolation devices in elective thoracic surgeries.

During proximal or distal migration of lung isolation device (LID), the bronchial cuff would move into a wider or narrower portion of the bronchus, leading to a decrease or increase in the cuff pressure, respectively. To test this hypothesis, we conducted a study to find out the efficacy of continuous bronchial cuff pressure (BCP) monitoring for detecting the displacement of LID. A single-arm interventional study was conducted including hundred adult patients undergoing elective thoracic surgeries using a left-sided LID. BCP was monitored in a continuous manner using a pressure transducer connected to the bronchial cuff of the LID. The position of the LID was assessed using a paediatric bronchoscope. Changes in the BCP were noted when the LID was moved intentionally in the left main bronchus (part 1) and during the surgery (part 2). Bronchoscopic confirmation was performed at the end of the surgery to note any uncaptured movement of the LID (part 3). During part 1 of the study, BCP consistently decreased on the proximal movement and increased on the distal movement of the LID, although the magnitude of change was not constant. During part 2 of the study, sensitivity, specificity, positive predictive value, negative predictive value and accuracy of continuous BCP monitoring to detect the dislodgement of LIDs (n = 41) during the surgery were 97.6%, 40%, 76.9%, 88.9% and 78.7%, respectively. Continuous BCP monitoring is a useful and sensitive method for monitoring the position of left-sided LIDs in limited-resource settings.

Heat aging effect on tensile behavior at different strain rates of thermoplastic styrene elastomer

Thermoplastic elastomers (TPEs) are a class of polymer materials used for interior, exterior and under the hood automotive applications which have the elastic behavior of elastomeric materials and the processability the same as for thermoplastics. TPEs have become the most rapidly growing segment of polymer industry. This paper focuses on obtaining the tensile test response of a heat aged compared to as delivered state of SEBS/TPS (Styrene-Ethylene-Butylene-Styrene/Thermoplastic Styrene Elastomers). Samples were analyzed before and after aging through thermal analysis and scanning electron microscopy to observe the chemical degradation of the materials.The dumb-bell samples used for the experimental program were prepared according to ISO 37 type 2 (overall length of 75 mm, length of the narrow portion of 25 mm, width of narrow portion: 4 mm). The samples were subjected to heat-aging according to ISO 188 with the following parameters: 168 h at 100 °C. Tensile tests were performed on the as delivered samples and the heat aged samples. Different values of strain rate (5 mm min−1; 50 mm min−1; 500 mm min−1) were used to determine the difference in the response of the thermoplastic elastomer sample.The ultimate tensile strength of the aged samples is higher than the virgin samples values. Displacement values are lower for the aged materials as the elongation at break is reduced due to the stiffening of the material after heat aging. There was no visible structural difference between aged and virgin samples.

Secretory system in Cuphea calophylla (Lythraceae): the bi-compartmentalization of epidermal cells, reclassification of glandular appendages, and the first report of hydathodes

Cuphea calophylla Cham. & Schltdl. is a Lythraceae subshrub that occurs in different environmental conditions. The aerial portions of this plant have medicinal properties and are used for soap production. We assessed the structure, ultrastructure, and histochemistry of the secretory cells and tissues in C. calophylla leaves and stems to further understand its secretory system. Hydathodes with epithem, tracheary elements, and water pores occur at the leaf border and are here described for the first time for a Cuphea species. Glandular appendages occur in leaves and stems and are characterized by a wide basis and a narrower apical portion that exuded sticky material. Ontogenetical analysis showed that these appendages are glandular emergences; phenolic compounds, mucilage, and lipids were produced in their cells which exhibited Golgi bodies, vesicles, smooth endoplasmic reticulum, oil drops, and plastids. The epidermis of the leaf blade has bi-compartmentalized secretory cells divided by a cellulosic septum in their equatorial region. These cells contain phenolic compounds in the upper compartment and mucilage in the lower compartment. Our results shed light on the sites producing bioactive compounds in C. calophylla and expand the knowledge on the secretory system in Lythraceae, promoting a reclassification and an identification of new structures.

Climate driven disruption of transitional alpine bumble bee communities.

Pollinators at high elevations face multiple threats from climate change including heat stress, failure to phenological match advancing flower resources and competitive pressure from range-expanding species of lower elevations. We conducted long-term multi-site surveys of alpine bumble bees to determine how phenology of range-stable and range-expanding species is responding to climate change. We ask whether bumble bee responses generate mismatches with floral resources, and whether these mismatches in turn promote community disruption and potential species replacement. In alpine environments of the central Rocky Mountains, range-stable and range-expanding bumble bees exhibit phenological mismatches with flowering host plants due to earlier flowering of preferred resources under warmer spring temperatures. However, workers of range-stable species are more canalised in their foraging schedules, exploiting a relatively narrow portion of the flowering season. Specifically, range-stable species show less variance in phenology in response to temporally and spatially changing conditions than range-expanding ones. Because flowering duration drives the seasonal abundance of floral resources at the landscape scale, we hypothesize that canalisation of phenology in alpine bumble bees could reduce their access to earlier or later season flowers. Warmer conditions are decreasing abundances of range-stable alpine bumble bees above the timberline, increasing abundance of range-expanding species, and facilitating a novel and more species-diverse bumble bee community. However, this trend is not explained by greater phenological mismatch of range-stable bees. Results suggest that conversion of historic habitats for cold-adapted alpine bumble bee species into refugia for more heat-tolerant congeners is disrupting bumble bee communities at high elevations, though the precise mechanisms accounting for these changes are not yet known. If warming continues, we predict that the transient increase in diversity due to colonization by historically low-elevation species will likely give way to declines of alpine bumble bees in the central Rocky Mountains.

Effect of crooked drill pipe rotation on cuttings transport in horizontal directional drilling using kinetic theory of granular flow – A numerical perspective

Effective cuttings transportation is essential for trenchless horizontal directional drilling (HDD). Inadequate borehole cleaning is one of the major reasons for drilling problems. Due to complicated mechanical effects accompanying the drilling process, the rotating drill pipe inevitably subjects bending deformation, which has a significant influence on the cuttings-drilling mud two-phase flow in the horizontal borehole, especially in the pilot hole drilling stage when the drill pipe is in a state of full rotation. However, there is a lack of research on the cuttings transport in the borehole where the rotating drill pipe is crooked. In this work, considering the bending deformation of the rotating drill pipe, the cuttings transport has been investigated in horizontal directional drilling based on the kinetic theory of granular flow. Using the dynamic mesh method, the crooked drill pipe is modeled as a sinusoidal form and rotates around the borehole axis. Flow behaviors of cuttings and drilling mud are predicted in pilot holes with a concentrically straight pipe, an eccentrically straight pipe, and a crooked pipe. Modeling results display the complex two-phase flow pattern for the horizontal directional drilling. The rotation of the crooked drill pipe enhances the cuttings spiral flow, where the axial velocity core zones of both cuttings and drilling fluid rotate with the drill pipe. The tangential velocities of the two phases originate from the rotating drill pipe wall, and the secondary flow is generated in the region that closes to the borehole inner wall within the annulus narrow portion. The cuttings transport mechanism is revealed by kinetic theory of granular flow. Predicted granular temperatures confirm more intense collisions between cuttings in the moving bed region due to the high shear rates caused by the pipe rotation. The suspension region contributes most of the cuttings transport velocity, and the fixed bed is formed by cuttings deposition. More uniform distributions of cuttings concentration and axial velocity are found in the borehole with a crooked drill pipe, however, it is found that the average torque of the crooked drill pipe is three times higher than that of the straight drill pipe exerted by the liquid–solid mixture.

LB1005 Skin marking for reflectance confocal microscopy

Reflectance confocal microscopy (RCM) generates serial depth images with either 8mm mosaic or 0.6mm field views with the Vivascope 1500 or 3000, respectively. Using 830nm light produces greyscale cellular level images of features that refract light at that narrow portion of the spectrum. Margin mapping for lentigo maligna and lentigo maligna melanoma with RCM can be challenging, especially without clear lesion boundaries or visible markings within confocal images. In some cases, orientation of anatomical direction is important, while in other cases, marking the boundaries of a particular finding is critical.

An Update on the Molecular Mechanism of the Vertebrate Isthmic Organizer Development in the Context of the Neuromeric Model.

A crucial event during the development of the central nervous system (CNS) is the early subdivision of the neural tube along its anterior-to-posterior axis to form neuromeres, morphogenetic units separated by transversal constrictions and programed for particular genetic cascades. The narrower portions observed in the developing neural tube are responsible for relevant cellular and molecular processes, such as clonal restrictions, expression of specific regulatory genes, and differential fate specification, as well as inductive activities. In this developmental context, the gradual formation of the midbrain-hindbrain (MH) constriction has been an excellent model to study the specification of two major subdivisions of the CNS containing the mesencephalic and isthmo-cerebellar primordia. This MH boundary is coincident with the common Otx2-(midbrain)/Gbx2-(hindbrain) expressing border. The early interactions between these two pre-specified areas confer positional identities and induce the generation of specific diffusible morphogenes at this interface, in particular FGF8 and WNT1. These signaling pathways are responsible for the gradual histogenetic specifications and cellular identity acquisitions with in the MH domain. This review is focused on the cellular and molecular mechanisms involved in the specification of the midbrain/hindbrain territory and the formation of the isthmic organizer. Emphasis will be placed on the chick/quail chimeric experiments leading to the acquisition of the first fate mapping and experimental data to, in this way, better understand pioneering morphological studies and innovative gain/loss-of-function analysis.

Capacity and Allocation across Sensory and Short-Term Memories.

Human memory consists of sensory memory (SM), short-term memory (STM), and long-term memory (LTM). SM enables a large capacity, but decays rapidly. STM has limited capacity, but lasts longer. The traditional view of these memory systems resembles a leaky hourglass, the large top and bottom portions representing the large capacities of SM and LTM, whereas the narrow portion in the middle represents the limited capacity of STM. The “leak” in the top part of the hourglass depicts the rapid decay of the contents of SM. However, recently, it was shown that major bottlenecks for motion processing exist prior to STM, and the “leaky hourglass” model was replaced by a “leaky flask” model with a narrower top part to capture bottlenecks prior to STM. The leaky flask model was based on data from one study, and the first goal of the current paper was to test if the leaky flask model would generalize by using a different set of data. The second goal of the paper was to explore various block diagram models for memory systems and determine the one best supported by the data. We expressed these block diagram models in terms of statistical mixture models and, by using the Bayesian information criterion (BIC), found that a model with four components, viz., SM, attention, STM, and guessing, provided the best fit to our data. In summary, we generalized previous findings about early qualitative and quantitative bottlenecks, as expressed in the leaky flask model and showed that a four-process model can provide a good explanation for how visual information is processed and stored in memory.

Enhancing anisotropy of thermal conductivity based on tandem acoustic Bragg reflectors

Thermal metamaterials have emerged as one of the latest research topics in applied science due to breakthrough advantages in modifying conductive heat flux. An acoustic Bragg reflector (ABR), composed of alternating arrays of two materials with contrasting acoustic impedances, is anticipated to coherently manipulate the transport properties of thermally important phonon branches by attaining interface roughness close to the monoatomic scale. However, there is a lack of research on how a narrow portion of the phononic band of a particular ABR can be extended to cover the entire thermal spectrum. Here, we report a modeling study of thermal transport using ABR, representatively based on GaAs/AlAs, GaN/AlN, or HfO2/SiO2 superlattices. Our calculations show that the anisotropy of thermal conductivity in HfO2/SiO2 can be significantly improved by tandemizing four different ABR layers, thus approaching the theoretically anticipated values based on monolayered materials. This work demonstrates how the tandem ABR can expand forbidden phononic bands beyond that occupied by a single ABR and proposes a practical strategy for realizing spectrally functionalized thermal properties from compound semiconductor materials that can be directly integrated into the existing device fabrication processes.

Modeling Complex Systems: A Case Study of Compartmental Models in Epidemiology

Compartmental epidemic models have been widely used for predicting the course of epidemics, from estimating the basic reproduction number to guiding intervention policies. Studies commonly acknowledge these models’ assumptions but less often justify their validity in the specific context in which they are being used. Our purpose is not to argue for specific alternatives or modifications to compartmental models, but rather to show how assumptions can constrain model outcomes to a narrow portion of the wide landscape of potential epidemic behaviors. This concrete examination of well‐known models also serves to illustrate general principles of modeling that can be applied in other contexts.