Hexagonal boron nitride (hBN) has recently emerged as a fascinating platform for room-temperature quantum photonics due to the discovery of robust visible light single-photon emitters. In order to ...utilize these emitters, it is necessary to have a clear understanding of their atomic structure and the associated excitation processes that give rise to this single photon emission. Here, we performed density-functional theory (DFT) and constrained DFT calculations for a range of hBN point defects in order to identify potential emission candidates. By applying a number of criteria on the electronic structure of the ground state and the atomic structure of the excited states of the considered defects, and then calculating the Huang-Rhys (HR) factor, we found that the C
V
defect, in which a carbon atom substitutes a boron atom and the opposite nitrogen atom is removed, is a potential emission source with a HR factor of 1.66, in good agreement with the experimental HR factor. We calculated the photoluminescence (PL) line shape for this defect and found that it reproduces a number of key features in the experimental PL lineshape.
In the present study, we examine competing predictions of stress reaction models and adaptation theories regarding the longitudinal relationship between work-family conflict and subjective ...well-being. Based on data from 432 participants over 3 time points with 2 lags of varying lengths (i.e., 1 month, 6 months), our findings suggest that in the short term, consistent with prior theory and research, work-family conflict is associated with poorer subjective well-being. Counter to traditional work-family predictions but consistent with adaptation theories, after accounting for concurrent levels of work-family conflict as well as past levels of subjective well-being, past exposure to work-family conflict was associated with higher levels of subjective well-being over time. Moreover, evidence was found for reverse causation in that greater subjective well-being at 1 point in time was associated with reduced work-family conflict at a subsequent point in time. Finally, the pattern of results did not vary as a function of using different temporal lags. We discuss the theoretical, research, and practical implications of our findings.
Elastomers embedded with micro- and nanoscale droplets of liquid metal (LM) alloys like eutectic gallium-indium (EGaIn) can exhibit unique combinations of elastic, thermal, and electrical properties ...that are difficult to achieve using rigid filler. For composites with sufficient concentrations of liquid metal, the LM droplets can form percolating networks that conduct electricity and deform with the surrounding elastomer as the composite is stretched. Surprisingly, experimental measurements performed on LM-embedded elastomers (LMEEs) show that the total electrical resistance of the composite increases only slightly even as the elastomer is stretched to several times its natural length. In contrast, Pouillet's law would predict an exponential increase in resistance (
Ω
) with stretch (
λ
) due to the incompressibility of liquid metal and elastomer. In this manuscript, we perform a computational analysis to examine the unique electromechanical properties of conductive LMEE composites. Our analysis suggests that the gauge factor that quantifies electromechanical coupling (
i.e.
= {Δ
Ω
/
Ω
0
}/
λ
) decreases with increasing tortuosity of the conductive pathways formed by the connected LM droplets. A dimensionless parameter for path tortuosity can be used to estimate for statistically homogeneous LMEE composites. These results rationalize experimental observations and provide insight into the influence of liquid metal droplet assembly on the functionality of the composite.
Conductive traces of elastomer embedded with liquid metal droplets exhibit little change in electrical resistance when stretched to large strains. Computational modeling is performed to better understand this remarkable piezoresistive property.
Estimating diet composition is important for understanding interactions between predators and prey and thus illuminating ecosystem function. The diet of many species, however, is difficult to observe ...directly. Genetic analysis of fecal material collected in the field is therefore a useful tool for gaining insight into wild animal diets. In this study, we used high-throughput DNA sequencing to quantitatively estimate the diet composition of an endangered population of wild killer whales (Orcinus orca) in their summer range in the Salish Sea. We combined 175 fecal samples collected between May and September from five years between 2006 and 2011 into 13 sample groups. Two known DNA composition control groups were also created. Each group was sequenced at a ~330bp segment of the 16s gene in the mitochondrial genome using an Illumina MiSeq sequencing system. After several quality controls steps, 4,987,107 individual sequences were aligned to a custom sequence database containing 19 potential fish prey species and the most likely species of each fecal-derived sequence was determined. Based on these alignments, salmonids made up >98.6% of the total sequences and thus of the inferred diet. Of the six salmonid species, Chinook salmon made up 79.5% of the sequences, followed by coho salmon (15%). Over all years, a clear pattern emerged with Chinook salmon dominating the estimated diet early in the summer, and coho salmon contributing an average of >40% of the diet in late summer. Sockeye salmon appeared to be occasionally important, at >18% in some sample groups. Non-salmonids were rarely observed. Our results are consistent with earlier results based on surface prey remains, and confirm the importance of Chinook salmon in this population's summer diet.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A series of copper-promoted iron–chromium oxide catalysts with various copper loadings are investigated for CO2 activation (reverse water–gas shift reaction) to determine the nature of surface oxygen ...intermediates involved in this redox reaction. Using a series of in situ characterizations (XPS, HS-LEIS, DRIFTS, and EXAFS), H2-TPR, and transient kinetic analysis, two reactive surface oxygen species with different reduction characteristics are identified for catalysts during the reaction. The more abundant and more active surface oxygen species are closely related to the surface hydroxyls located at the Cu-Fe3O4 interfacial regions. A direct correlation of the CO2 hydrogenation reaction rate with both the number and reduction kinetics of the more active surface oxygen intermediates is established.
Defect states in 2-D materials present many possible uses but both experimental and computational characterization of their spectroscopic properties is difficult. We provide and compare results from ...13 DFT and ab initio computational methods for up to 25 excited states of a paradigm system, the VNCB defect in hexagonal boron nitride (h-BN). Studied include: (i) potentially catastrophic effects for computational methods arising from the multireference nature of the closed-shell and open-shell states of the defect, which intrinsically involves broken chemical bonds, (ii) differing results from DFT and time-dependent DFT (TDDFT) calculations, (iii) comparison of cluster models to periodic-slab models of the defect, (iv) the starkly differing effects of nuclear relaxation on the various electronic states that control the widths of photoabsorption and photoemission spectra as broken bonds try to heal, (v) the effect of zero-point energy and entropy on free-energy differences, (vi) defect-localized and conduction/valence-band transition natures, and (vii) strategies needed to ensure that the lowest-energy state of a defect can be computationally identified. Averaged state-energy differences of 0.3 eV are found between CCSD(T) and MRCI energies, with thermal effects on free energies sometimes also being of this order. However, DFT-based methods can perform very poorly. Simple generalized-gradient functionals like PBE fail at the most basic level and should never be applied to defect states. Hybrid functionals like HSE06 work very well for excitations within the triplet manifold of the defect, with an accuracy equivalent to or perhaps exceeding the accuracy of the ab initio methods used. However, HSE06 underestimates triplet-state energies by on average of 0.7 eV compared to closed-shell singlet states, while open-shell singlet states are predicted to be too low in energy by 1.0 eV. This leads to misassignment of the ground state of the VNCB defect. Long-range corrected functionals like CAM-B3LYP are shown to work much better and to represent the current entry level for DFT calculations on defects. As significant differences between cluster and periodic-slab models are also found, the widespread implementation of such functionals in periodic codes is in urgent need.
Large numbers of hatchery salmon spawn in wild populations each year. Hatchery fish with multiple generations of hatchery ancestry often have heritably lower reproductive success than wild fish and ...may reduce the fitness of an entire population. Whether this reduced fitness also occurs for hatchery fish created with local‐ and predominantly wild‐origin parents remains controversial. Here, we review recent studies on the reproductive success of such ‘early‐generation’ hatchery fish that spawn in the wild. Combining 51 estimates from six studies on four salmon species, we found that (i) early‐generation hatchery fish averaged only half the reproductive success of their wild‐origin counterparts when spawning in the wild, (ii) the reduction in reproductive success was more severe for males than for females, and (iii) all species showed reduced fitness due to hatchery rearing. We review commonalities among studies that point to possible mechanisms (e.g., environmental versus genetic effects). Furthermore, we illustrate that sample sizes typical of these studies result in low statistical power to detect fitness differences unless the differences are substantial. This review demonstrates that reduced fitness of early‐generation hatchery fish may be a general phenomenon. Future research should focus on determining the causes of those fitness reductions and whether they lead to long‐term reductions in the fitness of wild populations.
Changes in gene regulation have likely played an important role in the evolution of primates. Differences in messenger RNA (mRNA) expression levels across primates have often been documented; ...however, it is not yet known to what extent measurements of divergence in mRNA levels reflect divergence in protein expression levels, which are probably more important in determining phenotypic differences. We used high-resolution, quantitative mass spectrometry to collect protein expression measurements from human, chimpanzee, and rhesus macaque lymphoblastoid cell lines and compared them to transcript expression data from the same samples. We found dozens of genes with significant expression differences between species at the mRNA level yet little or no difference in protein expression. Overall, our data suggest that protein expression levels evolve under stronger evolutionary constraint than mRNA levels.
The reverse water–gas shift (RWGS) reaction is an initial and essential step for CO2 hydrogenation. In this study, Cu- and K-modified iron oxide catalysts were investigated with a series of ...in/ex-situ characterization techniques, including in situ XRD, in situ Raman, in situ DRIFTS quasi in situ XPS, quasi in situ HS-LEIS, H2-TPR, CO2-TPD, and TPSR. The surface structure of the catalyst is found to strongly depend on the presence of Cu and K, leading to diverse reducibility and basicity. Adding K to the iron-based catalyst alters the reaction from a redox pathway that proceeds on surface redox sites to an associative pathway that proceeds on surface redox and basic sites. Metallic Cu facilitates hydrogen dissociation and promotes both mechanisms by either boosting surface vacancy sites or supplying abundant surface hydrogen atoms. These findings would be beneficial for the rational design of CO2 hydrogenation catalysts.
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