2,245 research outputs found
Electron Imaging of Nanoscale Charge Distributions Induced by Femtosecond Light Pulses
Surface charging is a phenomenon ubiquitously observable in in-situ
transmission electron microscopy of non-conducting specimens as a result of
electron-beam/sample interactions or optical stimuli and often limits the
achievable image stability and spatial or spectral resolution. Here, we report
on the electron-optical imaging of surface charging on a nanostructured surface
following femtosecond-multiphoton photoemission. By quantitatively extracting
the light-induced electrostatic potential and studying the charging dynamics on
the relevant timescales, we gain insights into the details of the multi-photon
photoemission process in the presence of a background field. We study the
interaction of the charge distribution with the high-energy electron beam and
secondary electrons and propose a simple model to describe the interplay of
electron- and light-induced processes.Comment: 26 pages; Manuscript with 3 figures and Supporting Information with 1
additional figur
Effects of Homophobic versus Nonhomophobic Victimization on School Commitment and the Moderating Effect of Teacher Attitudes in Brazilian Public Schools
This study investigated homophobic victimization, teacher support, and school commitment in Brazilian schools. Participants were 339 students, ages 11 to 18 years old, in two public schools in Brazil. Data were obtained using the Brazil Preventing School Harassment Survey. Structural equation modeling revealed that both homophobic and nonhomophobic victimization were negatively related to school commitment but that homophobic victimization was a stronger predictor. Results supported the hypothesis that supportive teachers can moderate the relationship between victimization and school commitment. Finally, the moderating effect of teacher support was stronger in instances of frequent homophobic victimization
Lattice dynamics and vibrational spectra of the orthorhombic, tetragonal and cubic phases of methylammonium lead iodide
The hybrid halide perovskite CH3NH3PbI3 exhibits a complex structural
behaviour, with successive transitions between orthorhombic, tetragonal and
cubic polymorphs at ca. 165 K and 327 K. Herein we report first-principles
lattice dynamics (phonon spectrum) for each phase of CH3NH3PbI3. The
equilibrium structures compare well to solutions of temperature-dependent
powder neutron diffraction. By following the normal modes we calculate infrared
and Raman intensities of the vibrations, and compare them to the measurement of
a single crystal where the Raman laser is controlled to avoid degradation of
the sample. Despite a clear separation in energy between low frequency modes
associated with the inorganic PbI3 network and high-frequency modes of the
organic CH3NH3+ cation, significant coupling between them is found, which
emphasises the interplay between molecular orientation and the corner-sharing
octahedral networks in the structural transformations. Soft modes are found at
the boundary of the Brillouin zone of the cubic phase, consistent with
displacive instabilities and anharmonicity involving tilting of the PbI6
octahedra around room temperature.Comment: 9 pages, 4 figure
Quantitative theory for the diffusive dynamics of liquid condensates
Key processes of biological condensates are diffusion and material exchange with their environment. Experimentally, diffusive dynamics are typically probed via fluorescent labels. However, to date, a physics-based, quantitative framework for the dynamics of labeled condensate components is lacking. Here, we derive the corresponding dynamic equations, building on the physics of phase separation, and quantitatively validate the related framework via experiments. We show that by using our framework, we can precisely determine diffusion coefficients inside liquid condensates via a spatio-temporal analysis of fluorescence recovery after photobleaching (FRAP) experiments. We showcase the accuracy and precision of our approach by considering space- and time-resolved data of protein condensates and two different polyelectrolyte-coacervate systems. Interestingly, our theory can also be used to determine a relationship between the diffusion coefficient in the dilute phase and the partition coefficient, without relying on fluorescence measurements in the dilute phase. This enables us to investigate the effect of salt addition on partitioning and bypasses recently described quenching artifacts in the dense phase. Our approach opens new avenues for theoretically describing molecule dynamics in condensates, measuring concentrations based on the dynamics of fluorescence intensities, and quantifying rates of biochemical reactions in liquid condensates
Cultural and economic complementarities of spatial agglomeration in the British television broadcasting industry: Some explorations.
This paper considers the processes supporting agglomeration in the British television broadcasting industry. It compares and contrasts the insights offered by the cultural turn in geography and more conventionally economic approaches. It finds that culture and institutions are fundamental to the constitution of production and exchange relationships and also that they solve fundamental economic problems of coordinating resources under conditions of uncertainty and limited information. Processes at a range of spatial scales are important, from highly local to global, and conventional economics casts some light on which firms are most active and successful
Partisan US News Media Representations of Syrian Refugees
We investigate how representations of Syrian refugees (2011-2021) differ
across US partisan news outlets. We analyze 47,388 articles from the online US
media about Syrian refugees to detail differences in reporting between left-
and right-leaning media. We use various NLP techniques to understand these
differences. Our polarization and question answering results indicated that
left-leaning media tended to represent refugees as child victims, welcome in
the US, and right-leaning media cast refugees as Islamic terrorists. We noted
similar results with our sentiment and offensive speech scores over time, which
detail possibly unfavorable representations of refugees in right-leaning media.
A strength of our work is how the different techniques we have applied validate
each other. Based on our results, we provide several recommendations.
Stakeholders may utilize our findings to intervene around refugee
representations, and design communications campaigns that improve the way
society sees refugees and possibly aid refugee outcomes
Revision total hip replacement: predictors of blood loss, transfusion requirements, and length of hospitalisation
Potential climatic transitions with profound impact on Europe
We discuss potential transitions of six climatic subsystems with large-scale impact on Europe, sometimes denoted as tipping elements. These are the ice sheets on Greenland and West Antarctica, the Atlantic thermohaline circulation, Arctic sea ice, Alpine glaciers and northern hemisphere stratospheric ozone. Each system is represented by co-authors actively publishing in the corresponding field. For each subsystem we summarize the mechanism of a potential transition in a warmer climate along with its impact on Europe and assess the likelihood for such a transition based on published scientific literature. As a summary, the ‘tipping’ potential for each system is provided as a function of global mean temperature increase which required some subjective interpretation of scientific facts by the authors and should be considered as a snapshot of our current understanding. <br/
Burden of respiratory syncytial virus infection in older and high-risk adults: a systematic review and meta-analysis of the evidence from developed countries
BACKGROUND: Respiratory syncytial virus (RSV) significantly impacts the health of older and high-risk adults (those with comorbidities). We aimed to synthesise the evidence on RSV disease burden and RSV-related healthcare utilisation in both populations. METHODS: We searched Embase and MEDLINE for papers published between 2000 and 2019 reporting the burden and clinical presentation of symptomatic RSV infection and the associated healthcare utilisation in developed countries in adults aged ≥60 years or at high risk. We calculated pooled estimates using random-effects inverse variance-weighted meta-analysis. RESULTS: 103 out of 3429 articles met the inclusion criteria. Among older adults, RSV caused 4.66% (95% CI 3.34–6.48%) of symptomatic respiratory infections in annual studies and 7.80% (95% CI 5.77–10.45%) in seasonal studies; RSV-related case fatality proportion (CFP) was 8.18% (95% CI 5.54–11.94%). Among high-risk adults, RSV caused 7.03% (95% CI 5.18–9.48%) of symptomatic respiratory infections in annual studies, and 7.69% (95% CI 6.23–9.46%) in seasonal studies; CFP was 9.88% (95% CI 6.66–14.43%). Data paucity impaired the calculation of estimates on population incidence, clinical presentation, severe outcomes and healthcare-related utilisation. CONCLUSIONS: Older and high-risk adults frequently experience symptomatic RSV infection, with appreciable mortality; however, detailed data are lacking. Increased surveillance and research are needed to quantify population-based disease burden and facilitate RSV treatments and vaccine development
Spatio-temporal Models of Lymphangiogenesis in Wound Healing
Several studies suggest that one possible cause of impaired wound healing is
failed or insufficient lymphangiogenesis, that is the formation of new
lymphatic capillaries. Although many mathematical models have been developed to
describe the formation of blood capillaries (angiogenesis), very few have been
proposed for the regeneration of the lymphatic network. Lymphangiogenesis is a
markedly different process from angiogenesis, occurring at different times and
in response to different chemical stimuli. Two main hypotheses have been
proposed: 1) lymphatic capillaries sprout from existing interrupted ones at the
edge of the wound in analogy to the blood angiogenesis case; 2) lymphatic
endothelial cells first pool in the wound region following the lymph flow and
then, once sufficiently populated, start to form a network. Here we present two
PDE models describing lymphangiogenesis according to these two different
hypotheses. Further, we include the effect of advection due to interstitial
flow and lymph flow coming from open capillaries. The variables represent
different cell densities and growth factor concentrations, and where possible
the parameters are estimated from biological data. The models are then solved
numerically and the results are compared with the available biological
literature.Comment: 29 pages, 9 Figures, 6 Tables (39 figure files in total
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