Non-Linear Optics at Twist Interfaces in h-BN/SiC Heterostructures

Understanding the emergent electronic structure in twisted atomically thin layers has led to the exciting field of twistronics. However, practical applications of such systems are challenging since the specific angular correlations between the layers must be precisely controlled and the layers have to be single crystalline with uniform atomic ordering. Here, an alternative, simple, and scalable approach is suggested, where nanocrystallinetwo-dimensional (2D) film on 3D substrates yields twisted-interface-dependent properties. Ultrawide-bandgap hexagonal boron nitride (h-BN) thin films are directly grown on high in-plane lattice mismatched wide-bandgap silicon carbide (4H-SiC) substrates to explore the twist-dependent structure-property correlations. Concurrently, nanocrystalline h-BN thin film shows strong non-linear second-harmonic generation and ultra-low cross-plane thermal conductivity at room temperature, which are attributed to the twisted domain edges between van der Waals stacked nanocrystals with random in-plane orientations. First-principles calculations based on time-dependent density functional theory manifest strong even-order optical nonlinearity in twisted h-BN layers. This work unveils that directly deposited 2D nanocrystalline thin film on 3D substrates could provide easily accessible twist-interfaces, therefore enabling a simple and scalable approach to utilize the 2D-twistronics integrated in 3D material devices for next-generation nanotechnology.

The global distribution of oral and maxillofacial surgeons: a mixed-methods study

Despite its role in treating the most dominant non-communicable diseases worldwide, the global workforce of oral and maxillofacial (OM) surgeons is not well-characterized. To address the current deficit in understanding of the global OM surgeon workforce and to elevate oral and maxillofacial surgery (OMS) in the global health discourse, we join other surgical specialties in evaluating global surgical capacity with a descriptive analysis of the distribution of OM surgeons worldwide. A mixed-methods study was implemented using a combination of literature review, in-country contacts, internet searches, and survey data. The survey was distributed globally from January to June 2022. Data regarding OM surgeon workforce estimates were obtained for 104 of 195 United Nations-recognized countries (53.3%). Among countries with available estimates, the median global workforce density was 0.518 OM surgeons per 100,000 population. Twenty-eight countries (26.9%) were reported to have two or fewer OM surgeons. The median OM surgeon workforce density for low-income countries was 0.015 surgeons per 100,000 population, compared to 1.087 surgeons per 100,000 population in high-income countries. low and middle-income countries countries have the least workforce density as well as the least data coverage. More work is needed to better understand the capacity of the global OM surgeon workforce and access to OMS care.

Phase Stability of Hexagonal/Cubic Boron Nitride Nanocomposites

Boron nitride (BN) is an exceptional material, and among its polymorphs, two-dimensional (2D) hexagonal and three-dimensional (3D) cubic BN (h-BN and c-BN) phases are most common. The phase stability regimes of these BN phases are still under debate, and phase transformations of h-BN/c-BN remain a topic of interest. Here, we investigate the phase stability of 2D/3D h-BN/c-BN nanocomposites and show that the coexistence of two phases can lead to strong nonlinear optical properties and low thermal conductivity at room temperature. Furthermore, spark-plasma sintering of the nanocomposite shows complete phase transformation to 2D h-BN with improved crystalline quality, where 3D c-BN possibly governs the nucleation and growth kinetics. Our demonstration might be insightful in phase engineering of BN polymorph-based nanocomposites with desirable properties for optoelectronics and thermal energy management applications.

Clinical and biologic importance of F-actin autoantibodies in HCV monoinfected and HCV-HIV coinfected patients

The purpose of this study was to evaluate the relationship between serum filamentous (F)-actin antibody titers and severity of hepatitis present in hepatitis C virus (HCV)-infected patients. Liver biopsy samples from 18 HCV monoinfected and 20 HCV-HIV coinfected patients were graded with respect to the degree of hepatitis activity and intensity of plasma cell infiltration using MUM-1 and CD138 immunostains. Of the 38 HCV-infected patients, 6 (16%) had F-actin antibody titers in excess of 30 enzyme-linked immunosorbent assay units. We found a positive trend between serum F-actin antibody levels and the mean number of plasma cells present in the portal tracts of patients with HCV infection (r = 0.31; P = .06) and a significant association between these factors in HCV-HIV coinfected patients (r = 0.64; P = .002). Our data suggest that elevated serum F-actin antibody titers are commonly encountered in HCV-infected patients and may reflect more active inflammation in liver biopsy samples, similar to autoimmune hepatitis.

The number of attentional foci and their precision are dissociated in the posterior parietal cortex

Many everyday tasks require us to track moving objects with attention. The demand for attention increases both when more targets are tracked and when the targets move faster. These 2 aspects of attention-assigning multiple attentional foci (or indices) to targets and monitoring each focus with precision-may tap into different cognitive and brain mechanisms. In this study, we used functional magnetic resonance imaging to quantify the response profile of dorsal attentional areas to variations in the number of attentional foci and their spatiotemporal precision. Subjects were asked to track a specific spoke of either 1 or 2 pinwheels that rotated at various speeds. Their tracking performance declined both when more pinwheels were tracked and when the tracked pinwheels rotated faster. However, posterior parietal activity increased only when subjects tracked more pinwheels but remained flat when they tracked faster moving pinwheels. The frontal eye fields and early visual areas increased activity when there were more targets and when the targets rotated faster. These results suggest that the posterior parietal cortex is specifically involved in indexing independently moving targets with attention but not in monitoring each focus with precision.

The capacity of visual short-term memory is set both by visual information load and by number of objects

Previous research has suggested that visual short-term memory has a fixed capacity of about four objects. However, we found that capacity varied substantially across the five stimulus classes we examined, ranging from 1.6 for shaded cubes to 4.4 for colors (estimated using a change detection task). We also estimated the information load per item in each class, using visual search rate. The changes we measured in memory capacity across classes were almost exactly mirrored by changes in the opposite direction in visual search rate (r2=.992 between search rate and the reciprocal of memory capacity). The greater the information load of each item in a stimulus class (as indicated by a slower search rate), the fewer items from that class one can hold in memory. Extrapolating this linear relationship reveals that there is also an upper bound on capacity of approximately four or five objects. Thus, both the visual information load and number of objects impose capacity limits on visual short-term memory.