1,641 research outputs found
Advancing time- and angle-resolved photoemission spectroscopy: The role of ultrafast laser development
In the last decade, there has been a proliferation of laser sources for time-
and angle-resolved photoemission spectroscopy (TR-ARPES), building on the
proven capability of this technique to tackle important scientific questions.
In this review, we aim to identify the key motivations and technologies that
spurred the development of various laser sources, from frequency up-conversion
in nonlinear crystals to high-harmonic generation in gases. We begin with a
historical overview of the field in Sec.1, framed by advancements in light
source and electron spectrometer technology. An introduction to the fundamental
aspects of the photoemission process and the observables that can be studied is
given in Sec.2, along with its dependencies on the pump and probe pulse
parameters. The technical aspects of TR-ARPES are discussed in Sec.3. Here,
experimental limitations such as space charge and resultant trade-offs in
source parameters are discussed. Details of various systems and their approach
to these trade-offs are given in Sec.4. Within this discussion, we present a
survey of TR-ARPES laser sources; a meta-analysis of these source parameters
showcases the advancements and trends in modern systems. Lastly, we conclude
with a brief discussion of future directions for TR-ARPES and its capabilities
in elucidating equilibrium and non-equilibrium observables, as well as its
integration with micro-ARPES and spin-resolved ARPES (Sec.5).Comment: 104 pages, 27 figure
Probiotic administration in congenital heart disease: a pilot study.
ObjectiveTo investigate the impact of probiotic Bifidobacterium longum ssp. infantis on the fecal microbiota and plasma cytokines in neonates with congenital heart disease.Study designSixteen infants with congenital heart disease were randomly assigned to receive either B. infantis (4.2 × 10(9) colony-forming units two times daily) or placebo for 8 weeks. Stool specimens from enrolled infants and from six term infants without heart disease were analyzed for microbial composition. Plasma cytokines were analyzed weekly in the infants with heart disease.ResultsHealthy control infants had increased total bacteria, total Bacteroidetes and total bifidobacteria compared to the infants with heart disease, but there were no significant differences between the placebo and probiotic groups. Plasma interleukin (IL)10, interferon (IFN)γ and IL1β levels were transiently higher in the probiotic group.ConclusionCongenital heart disease in infants is associated with dysbiosis. Probiotic B. infantis did not significantly alter the fecal microbiota. Alterations in plasma cytokines were found to be inconsistent
Traffic-related pollution and asthma prevalence in children. Quantification of associations with nitrogen dioxide.
Ambient nitrogen dioxide is a widely available measure of traffic-related air pollution and is inconsistently associated with the prevalence of asthma symptoms in children. The use of this relationship to evaluate the health impact of policies affecting traffic management and traffic emissions is limited by the lack of a concentration-response function based on systematic review and meta-analysis of relevant studies. Using systematic methods, we identified papers containing quantitative estimates for nitrogen dioxide and the 12 month period prevalence of asthma symptoms in children in which the exposure contrast was within-community and dominated by traffic pollution. One estimate was selected from each study according to an a priori algorithm. Odds ratios were standardised to 10 μg/m(3) and summary estimates were obtained using random- and fixed-effects estimates. Eighteen studies were identified. Concentrations of nitrogen dioxide were estimated for the home address (12) and/or school (8) using a range of methods; land use regression (6), study monitors (6), dispersion modelling (4) and interpolation (2). Fourteen studies showed positive associations but only two associations were statistically significant at the 5 % level. There was moderate heterogeneity (I(2) = 32.8 %) and the random-effects estimate for the odds ratio was 1.06 (95 % CI 1.00 to 1.11). There was no evidence of small study bias. Individual studies tended to have only weak positive associations between nitrogen dioxide and asthma prevalence but the summary estimate bordered on statistical significance at the 5 % level. Although small, the potential impact on asthma prevalence could be considerable because of the high level of baseline prevalence in many cities. Whether the association is causal or indicates the effects of a correlated pollutant or other confounders, the estimate obtained by the meta-analysis would be appropriate for estimating impacts of traffic pollution on asthma prevalence
Establishing non-thermal regimes in pump-probe electron-relaxation dynamics
Time- and angle-resolved photoemission spectroscopy (TR-ARPES) accesses the
electronic structure of solids under optical excitation, and is a powerful
technique for studying the coupling between electrons and collective modes. One
approach to infer electron-boson coupling is through the relaxation dynamics of
optically-excited electrons, and the characteristic timescales of energy
redistribution. A common description of electron relaxation dynamics is through
the effective electronic temperature. Such a description requires that
thermodynamic quantities are well-defined, an assumption that is generally
violated at early delays. Additionally, precise estimation of the non-thermal
window -- within which effective temperature models may not be applied -- is
challenging. We perform TR-ARPES on graphite and show that Boltzmann rate
equations can be used to calculate the time-dependent electronic occupation
function, and reproduce experimental features given by non-thermal electron
occupation. Using this model, we define a quantitative measure of non-thermal
electron occupation and use it to define distinct phases of electron relaxation
in the fluence-delay phase space. More generally, this approach can be used to
inform the non-thermal-to-thermal crossover in pump-probe experiments.Comment: 18 pages, 10 figure
Chloroquine and Hydroxychloroquine for the Prevention or Treatment of Novel Coronavirus Disease (COVID-19) in Africa: Caution for Inappropriate Off-Label Use in Healthcare Settings
The novel severe acute respiratory syndrome-coronavirus-2 pandemic has spread to Africa, where nearly all countries have reported laboratory-confirmed cases of novel coronavirus disease (COVID-19). Although there are ongoing clinical trials of repurposed and investigational antiviral and immune-based therapies, there are as yet no scientifically proven, clinically effective pharmacological treatments for COVID-19. Among the repurposed drugs, the commonly used antimalarials chloroquine (CQ) and hydroxychloroquine (HCQ) have become the focus of global scientific, media, and political attention despite a lack of randomized clinical trials supporting their efficacy. Chloroquine has been used worldwide for about 75 years and is listed by the WHO as an essential medicine to treat malaria. Hydroxychloroquine is mainly used as a therapy for autoimmune diseases. However, the efficacy and safety of CQ/HCQ for the treatment of COVID-19 remains to be defined. Indiscriminate promotion and widespread use of CQ/HCQ have led to extensive shortages, self-treatment, and fatal overdoses. Shortages and increased market prices leave all countries vulnerable to substandard and falsified medical products, and safety issues are especially concerning for Africa because of its healthcare system limitations. Much needed in Africa is a cross-continental collaborative network for coordinated production, distribution, and post-marketing surveillance aligned to low-cost distribution of any approved COVID-19 drug; this would ideally be piggybacked on existing global aid efforts. Meanwhile, African countries should strongly consider implementing prescription monitoring schemes to ensure that any off-label CQ/HCQ use is appropriate and beneficial during this pandemic
Potentiality in Biology
We take the potentialities that are studied in the biological sciences (e.g., totipotency) to be an important subtype of biological dispositions. The goal of this paper is twofold: first, we want to provide a detailed understanding of what biological dispositions are. We claim that two features are essential for dispositions in biology: the importance of the manifestation process and the diversity of conditions that need to be satisfied for the disposition to be manifest. Second, we demonstrate that the concept of a disposition (or potentiality) is a very useful tool for the analysis of the explanatory practice in the biological sciences. On the one hand it allows an in-depth analysis of the nature and diversity of the conditions under which biological systems display specific behaviors. On the other hand the concept of a disposition may serve a unificatory role in the philosophy of the natural sciences since it captures not only the explanatory practice of biology, but of all natural sciences. Towards the end we will briefly come back to the notion of a potentiality in biology
Cavity-enhanced high harmonic generation for XUV time-resolved ARPES
With its direct correspondence to electronic structure, angle-resolved
photoemission spectroscopy (ARPES) is a ubiquitous tool for the study of
solids. When extended to the temporal domain, time-resolved (TR)-ARPES offers
the potential to move beyond equilibrium properties, exploring both the
unoccupied electronic structure as well as its dynamical response under
ultrafast perturbation. Historically, ultrafast extreme ultraviolet (XUV)
sources employing high-order harmonic generation (HHG) have required
compromises that make it challenging to achieve a high energy resolution -
which is highly desirable for many TR-ARPES studies - while producing high
photon energies and a high photon flux. We address this challenge by performing
HHG inside a femtosecond enhancement cavity (fsEC), realizing a practical
source for TR-ARPES that achieves a flux of over 10 photons/s delivered
to the sample, operates over a range of 8-40 eV with a repetition rate of 60
MHz. This source enables TR-ARPES studies with a temporal and energy resolution
of 190 fs and 22 meV, respectively. To characterize the system, we perform
ARPES measurements of polycrystalline Au and MoTe, as well as TR-ARPES
studies on graphite.Comment: 11 pages, 5 figure
Straightforward Inference of Ancestry and Admixture Proportions through Ancestry-Informative Insertion Deletion Multiplexing
Ancestry-informative markers (AIMs) show high allele frequency divergence between different ancestral or geographically distant populations. These genetic markers are especially useful in inferring the likely ancestral origin of an individual or estimating the apportionment of ancestry components in admixed individuals or populations. The study of AIMs is of great interest in clinical genetics research, particularly to detect and correct for population substructure effects in case-control association studies, but also in population and forensic genetics studies
Direct determination of mode-projected electron-phonon coupling in the time-domain
Ultrafast spectroscopies have become an important tool for elucidating the
microscopic description and dynamical properties of quantum materials. In
particular, by tracking the dynamics of non-thermal electrons, a material's
dominant scattering processes -- and thus the many-body interactions between
electrons and collective excitations -- can be revealed. Here we present a new
method for extracting the electron-phonon coupling strength in the time domain,
by means of time and angle-resolved photoemission spectroscopy (TR-ARPES). This
method is demonstrated in graphite, where we investigate the dynamics of
photo-injected electrons at the K point, detecting quantized energy-loss
processes that correspond to the emission of strongly-coupled optical phonons.
We show that the observed characteristic timescale for spectral-weight-transfer
mediated by phonon-scattering processes allows for the direct quantitative
extraction of electron-phonon matrix elements, for specific modes, and with
unprecedented sensitivity.Comment: 19 pages, 4 figure
Next-Generation Sequencing Reveals Significant Bacterial Diversity of Botrytized Wine
While wine fermentation has long been known to involve complex microbial communities, the composition and role of bacteria other than a select set of lactic acid bacteria (LAB) has often been assumed either negligible or detrimental. This study served as a pilot study for using barcoded amplicon next-generation sequencing to profile bacterial community structure in wines and grape musts, comparing the taxonomic depth achieved by sequencing two different domains of prokaryotic 16S rDNA (V4 and V5). This study was designed to serve two goals: 1) to empirically determine the most taxonomically informative 16S rDNA target region for barcoded amplicon sequencing of wine, comparing V4 and V5 domains of bacterial 16S rDNA to terminal restriction fragment length polymorphism (TRFLP) of LAB communities; and 2) to explore the bacterial communities of wine fermentation to better understand the biodiversity of wine at a depth previously unattainable using other techniques. Analysis of amplicons from the V4 and V5 provided similar views of the bacterial communities of botrytized wine fermentations, revealing a broad diversity of low-abundance taxa not traditionally associated with wine, as well as atypical LAB communities initially detected by TRFLP. The V4 domain was determined as the more suitable read for wine ecology studies, as it provided greater taxonomic depth for profiling LAB communities. In addition, targeted enrichment was used to isolate two species of Alphaproteobacteria from a finished fermentation. Significant differences in diversity between inoculated and uninoculated samples suggest that Saccharomyces inoculation exerts selective pressure on bacterial diversity in these fermentations, most notably suppressing abundance of acetic acid bacteria. These results determine the bacterial diversity of botrytized wines to be far higher than previously realized, providing further insight into the fermentation dynamics of these wines, and demonstrate the utility of next-generation sequencing for wine ecology studies
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