Integration of quasi-two-dimensional (2D) films of metal–chalcogenides in optical microcavities permits new photonic applications of these materials. Here we present tunable microcavities with ...monolayer MoS2 or few monolayer GaSe films. We observe significant modification of spectral and temporal properties of photoluminescence (PL): PL is emitted in spectrally narrow and wavelength-tunable cavity modes with quality factors up to 7400; a 10-fold PL lifetime shortening is achieved, a consequence of Purcell enhancement of the spontaneous emission rate.
Highly nonlinear optical materials with strong effective photon-photon interactions are required for ultrafast and quantum optical signal processing circuitry. Here we report strong Kerr-like ...nonlinearities by employing efficient optical transitions of charged excitons (trions) observed in semiconducting transition metal dichalcogenides (TMDCs). By hybridising trions in monolayer MoSe
at low electron densities with a microcavity mode, we realise trion-polaritons exhibiting significant energy shifts at small photon fluxes due to phase space filling. We find the ratio of trion- to neutral exciton-polariton interaction strength is in the range from 10 to 100 in TMDC materials and that trion-polariton nonlinearity is comparable to that in other polariton systems. The results are in good agreement with a theory accounting for the composite nature of excitons and trions and deviation of their statistics from that of ideal bosons and fermions. Our findings open a way to scalable quantum optics applications with TMDCs.
Context. Very long baseline interferometry (VLBI) imaging of radio emission from extragalactic jets provides a unique probe of physical mechanisms governing the launching, acceleration, and ...collimation of relativistic outflows. Aims. VLBI imaging of the jet in the nearby active galaxy M 87 enables morphological and kinematic studies to be done on linear scales down to ~100 Schwarzschild radii (Rs). Methods. The two-dimensional structure and kinematics of the jet in M 87 (NGC 4486) have been studied by applying the wavelet-based image segmentation and evaluation (WISE) method to 11 images obtained from multi-epoch Very Long Baseline Array (VLBA) observations made in January-August 2007 at 43 GHz (λ = 7 mm). Results. The WISE analysis recovers a detailed two-dimensional velocity field in the jet in M 87 at sub-parsec scales. The observed evolution of the flow velocity with distance from the jet base can be explained in the framework of MHD jet acceleration and Poynting flux conversion. A linear acceleration regime is observed up to zobs ~ 2 mas. The acceleration is reduced at larger scales, which is consistent with saturation of Poynting flux conversion. Stacked cross correlation analysis of the images reveals a pronounced stratification of the flow. The flow consists of a slow, mildly relativistic layer (moving at β ~ 0.5c), associated either with instability pattern speed or an outer wind, and a fast, accelerating stream line (with β ~ 0.92, corresponding to a bulk Lorentz factor γ ~ 2.5). A systematic difference of the apparent speeds in the northern and southern limbs of the jet is detected, providing evidence for jet rotation. The angular velocity of the magnetic field line associated with this rotation suggests that the jet in M 87 is launched in the inner part of the disk, at a distance r0 ~ 5Rs from the central engine. Conclusions. The combined results of the analysis imply that MHD acceleration and conversion of Poynting flux to kinetic energy play the dominant roles in collimation and acceleration of the flow in M 87.
Limited information is available regarding epigenomic events mediating initiation and progression of tobacco-induced lung cancers. In this study, we established an in vitro system to examine ...epigenomic effects of cigarette smoke in respiratory epithelia. Normal human small airway epithelial cells and cdk-4/hTERT-immortalized human bronchial epithelial cells (HBEC) were cultured in normal media with or without cigarette smoke condensate (CSC) for up to 9 months under potentially relevant exposure conditions. Western blot analysis showed that CSC mediated dose- and time-dependent diminution of H4K16Ac and H4K20Me3, while increasing relative levels of H3K27Me3; these histone alterations coincided with decreased DNA methyltransferase 1 (DNMT1) and increased DNMT3b expression. Pyrosequencing and quantitative RT-PCR experiments revealed time-dependent hypomethylation of D4Z4, NBL2, and LINE-1 repetitive DNA sequences; up-regulation of H19, IGF2, MAGE-A1, and MAGE-A3; activation of Wnt signaling; and hypermethylation of tumor suppressor genes such as RASSF1A and RAR-beta, which are frequently silenced in human lung cancers. Array-based DNA methylation profiling identified additional novel DNA methylation targets in soft-agar clones derived from CSC-exposed HBEC; a CSC gene expression signature was also identified in these cells. Progressive genomic hypomethylation and locoregional DNA hypermethylation induced by CSC coincided with a dramatic increase in soft-agar clonogenicity. Collectively, these data indicate that cigarette smoke induces 'cancer-associated' epigenomic alterations in cultured respiratory epithelia. This in vitro model may prove useful for delineating early epigenetic mechanisms regulating gene expression during pulmonary carcinogenesis.
We explore the interplay of electron-electron correlations and spin-orbit coupling in the model Fermi liquidSr2RuO4using laser-based angle-resolved photoemission spectroscopy. Our precise measurement ...of the Fermi surface confirms the importance of spin-orbit coupling in this material and reveals that its effective value is enhanced by a factor of about 2, due to electronic correlations. The self-energies for theβandγsheets are found to display significant angular dependence. By taking into account the multi-orbital composition of quasiparticle states, we determine self-energies associated with each orbital component directly from the experimental data. This analysis demonstrates that the perceived angular dependence does not imply momentum-dependent many-body effects but arises from a substantial orbital mixing induced by spin-orbit coupling. A comparison to single-site dynamical mean-field theory further supports the notion of dominantly local orbital self-energies and provides strong evidence for an electronic origin of the observed nonlinear frequency dependence of the self-energies, leading to “kinks” in the quasiparticle dispersion ofSr2RuO4.
We report an extended family of spin textures of zero-dimensional exciton-polaritons spatially confined in tunable open microcavity structures. The transverse-electric-transverse-magnetic (TE-TM) ...splitting, which is enhanced in the open cavity structures, leads to polariton eigenstates carrying quantized spin vortices. Depending on the strength and anisotropy of the cavity confining potential and of the TE-TM induced splitting, which can be tuned via the excitonic or photonic fractions, the exciton-polariton emissions exhibit either spin-vortex-like patterns or linear polarization, in good agreement with theoretical modeling.
Our review addresses one of the most used, but debated, topics in Ergonomics: Situation Awareness (SA). We examine and elaborate upon key SA models. These models are divided into individual SA, team ...SA and systems SA categories. Despite, or perhaps because of, the debates surrounding SA it remains an enduring theme for research and practice in the domain of Ergonomics, now for over two decades. A contingent approach, which seeks to match different models of SA to different types of ergonomics problem, enables the differences between positions to be revealed and reconciled, and the practitioner guided towards optimum methodological solutions.
Practitioner Summary: Measuring SA in individuals, teams and systems has become a key objective in Ergonomics. One single approach to SA does not fit all problems encountered. This review shows the importance of considering all three types of models and achieving a match between them and the problem at hand.
Abstract
Recent theoretical proposals have argued that cobaltates with edge-sharing octahedral coordination can have significant bond-dependent exchange couplings thus offering a platform in 3
d
ions ...for such physics beyond the much-explored realisations in 4
d
and 5
d
materials. Here we present high-resolution inelastic neutron scattering data within the magnetically ordered phase of the stacked honeycomb magnet CoTiO
3
revealing the presence of a finite energy gap and demonstrate that this implies the presence of bond-dependent anisotropic couplings. We also show through an extensive theoretical analysis that the gap further implies the existence of a quantum order-by-disorder mechanism that, in this material, crucially involves virtual crystal field fluctuations. Our data also provide an experimental observation of a universal winding of the scattering intensity in angular scans around linear band-touching points for both magnons and dispersive spin-orbit excitons, which is directly related to the non-trivial topology of the quasiparticle wavefunction in momentum space near nodal points.
Measuring the seroprevalence of antibodies to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) is central to understanding infection risk and fatality rates. We studied Coronavirus ...Disease 2019 (COVID-19)-antibody seroprevalence in a community sample drawn from Santa Clara County.
On 3 and 4 April 2020, we tested 3328 county residents for immunoglobulin G (IgG) and immunoglobulin M (IgM) antibodies to SARS-CoV-2 using a rapid lateral-flow assay (Premier Biotech). Participants were recruited using advertisements that were targeted to reach county residents that matched the county population by gender, race/ethnicity and zip code of residence. We estimate weights to match our sample to the county by zip, age, sex and race/ethnicity. We report the weighted and unweighted prevalence of antibodies to SARS-CoV-2. We adjust for test-performance characteristics by combining data from 18 independent test-kit assessments: 14 for specificity and 4 for sensitivity.
The raw prevalence of antibodies in our sample was 1.5% exact binomial 95% confidence interval (CI) 1.1-2.0%. Test-performance specificity in our data was 99.5% (95% CI 99.2-99.7%) and sensitivity was 82.8% (95% CI 76.0-88.4%). The unweighted prevalence adjusted for test-performance characteristics was 1.2% (95% CI 0.7-1.8%). After weighting for population demographics, the prevalence was 2.8% (95% CI 1.3-4.2%), using bootstrap to estimate confidence bounds. These prevalence point estimates imply that 53 000 95% CI 26 000 to 82 000 using weighted prevalence; 23 000 (95% CI 14 000-35 000) using unweighted prevalence people were infected in Santa Clara County by late March-many more than the ∼1200 confirmed cases at the time.
The estimated prevalence of SARS-CoV-2 antibodies in Santa Clara County implies that COVID-19 was likely more widespread than indicated by the number of cases in late March, 2020. At the time, low-burden contexts such as Santa Clara County were far from herd-immunity thresholds.
Monolayers of molybdenum and tungsten dichalcogenides are direct bandgap semiconductors, which makes them promising for optoelectronic applications. In particular, van der Waals heterostructures ...consisting of monolayers of MoS2 sandwiched between atomically thin hexagonal boron nitride (hBN) and graphene electrodes allows one to obtain light emitting quantum wells (LEQWs) with low-temperature external quantum efficiency (EQE) of 1%. However, the EQE of MoS2- and MoSe2-based LEQWs shows behavior common for many other materials: it decreases fast from cryogenic conditions to room temperature, undermining their practical applications. Here we compare MoSe2 and WSe2 LEQWs. We show that the EQE of WSe2 devices grows with temperature, with room temperature EQE reaching 5%, which is 250× more than the previous best performance of MoS2 and MoSe2 quantum wells in ambient conditions. We attribute such different temperature dependences to the inverted sign of spin–orbit splitting of conduction band states in tungsten and molybdenum dichalcogenides, which makes the lowest-energy exciton in WSe2 dark.
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