Probing the superconducting ground state of the rare-earth ternary boride superconductors RRRuB2_2 (RR = Lu,Y) using muon-spin rotation and relaxation

The superconductivity in the rare-earth transition metal ternary borides $R$RuB$_2$ (where $R$ = Lu and Y) has been investigated using muon-spin rotation and relaxation. Measurements made in zero-field suggest that time-reversal symmetry is preserved upon entering the superconducting state in both materials; a small difference in depolarization is observed above and below the superconducting transition in both compounds, however this has been attributed to quasistatic magnetic fluctuations. Transverse-field measurements of the flux-line lattice indicate that the superconductivity in both materials is fully gapped, with a conventional s-wave pairing symmetry and BCS-like magnitudes for the zero-temperature gap energies. The electronic properties of the charge carriers in the superconducting state have been calculated, with effective masses $m^*/ m_\mathrm{e} =$ $9.8\pm0.1$ and $15.0\pm0.1$ in the Lu and Y compounds, respectively, with superconducting carrier densities $n_\mathrm{s} =$ ($2.73\pm0.04$) $\times 10^{28}$ m$^{-3}$ and ($2.17\pm0.02$) $\times 10^{28}$ m$^{-3}$. The materials have been classified according to the Uemura scheme for superconductivity, with values for $T_\mathrm{c}/T_\mathrm{F}$ of $1/(414\pm6)$ and $1/(304\pm3)$, implying that the superconductivity may not be entirely conventional in nature.Comment: 8 pages, 8 figure

Superconducting and normal-state properties of the noncentrosymmetric superconductor Re3Ta

The noncentrosymmetric superconductor, Re3Ta, has been characterized in detail with a combination of magnetization, heat capacity, and electrical resistivity measurements, as well as a microscopic investigation of the internal magnetic fields using muon spin spectroscopy (μSR). In low applied fields, we observe 100% flux expulsion at a temperature of Tc = 4.68 K, which is concomitant with a sudden decrease of the electrical resistivity to zero and a sharp discontinuity in the heat capacity, confirming bulk superconductivity in this material. We find that Re3Ta is a poor metal, with superconductivity occurring in the dirty limit, and in which the disorder in the structure dominates the physical properties. Zero-field μSR shows that the superconducting state preserves time-reversal symmetry, and transverse-field measurements of the superfluid density are well described by an isotropic s-wave model. A careful analysis of the internal field distribution reveals a high level of disorder in the vortex lattice. Furthermore, we have combined the experimental data and calculated the effective mass, carrier density, and electronic mean-free path in this material, and ultimately show that Re3Ta lies close to the unconventional region of the Uemura plot

Unconventional superconductivity in La7Ir3 revealed by muon spin relaxation : introducing a new family of noncentrosymmetric superconductor that breaks time-reversal symmetry

The superconductivity of the noncentrosymmetric compound La7Ir3 has been investigated using muon spin rotation and relaxation (μSR). Zero-field measurements reveal the presence of spontaneous static or quasi-static magnetic fields below the superconducting transition temperature Tc = 2:25 K - a clear indication that the superconducting state breaks time-reversal symmetry. Furthermore, transverse-field rotation measurements suggest that the superconducting gap is isotropic, and that the pairing symmetry of the superconducting electrons is predominantly s-wave with an enhanced binding strength. The results indicate that the superconductivity in La7Ir3 may be unconventional, and paves the way for further studies of this family of materials

Drought-induced biomass burning as a source of black carbon to the central Himalaya since 1781 CE as reconstructed from the Dasuopu ice core

Himalayan glaciers are melting due to atmospheric warming, with the potential to limit access to water for more than 25 % of the global population that resides in these glacier meltwater catchments. Black carbon has been implicated as a factor that is contributing to Himalayan glacier melt, but its sources and mechanisms of delivery to the Himalayas remain controversial. Here, we provide a 211-year ice core record spanning 1781–1992 CE for refractory black carbon (rBC) deposition from the Dasuopu glacier ice core that has to date provided the highest-elevation ice core record (7200 m). We report an average rBC concentration of 1.5 µg L−1 (SD=5.0, n=1628) over the 211-year period. An increase in the frequency and magnitude of rBC deposition occurs after 1877 CE, accompanied by decreased snow accumulation associated with a shift in the North Atlantic Oscillation Index to a positive phase. Typically, rBC is deposited onto Dasuopu glacier during the non-monsoon season, and short-lived increases in rBC concentration are associated with periods of drought within neighboring regions in northwestern India, Afghanistan, and Pakistan. Using a combination of spectral and back-trajectory analyses, as well as a comparison with a concurrent analysis of trace metals at equivalent depths in the same ice core, we show that biomass burning resulting from dry conditions is a source of rBC to the central Himalaya and is responsible for deposition that is up to 60 times higher than the average rBC concentration over the time period analyzed. We suggest that biomass burning is a significant source of rBC to the central Himalaya and that the rBC record can be used to identify periods of drought in nearby regions that are upwind of Dasuopu glacier

PoLAR-FIT: Pliocene Landscapes and Arctic Remains—Frozen in Time

This short summary presents selected results of an ongoing investigation into the feedbacks that contribute to amplified Arctic warming. The consequences of warming for Arctic biodiversity and landscape response to global warmth are currently being interpreted. Arctic North American records of large-scale landscape and paleoenvironmental change during the Pliocene are exquisitely preserved and locked in permafrost, providing an opportunity for paleoenvironmental and faunal reconstruction with unprecedented quality and resolution. During a period of mean global temperatures only ~2.5°C above modern, the Pliocene molecular, isotopic, tree-ring, paleofaunal, and paleofloral records indicate that the high Arctic mean annual temperature was 11°C–19°C above modern values, pointing to a much shallower latitudinal temperature gradient than exists today. It appears that the intense Neogene warming caused thawing and weathering to liberate sediment and create a continuous and thick (>2.5 km in places) clastic wedge from at least Banks Island to Meighen Island to form a coastal plain that provided a highway for camels and other mammals to migrate and evolve in the high Arctic. In this summary we highlight the opportunities that exist for research on these and related topics with the PoLAR-FIT community.RÉSUMÉCe bref résumé présente les résultats choisis d'une enquête en cours sur les déclencheurs qui contribuent à l’amplification du réchauffement de l'Arctique. Les conséquences du réchauffement sur la biodiversité arctique et de la réponse du paysage au réchauffement climatique sont en cours d’être interprété. Des dossiers nord-américains de paysage à grande échelle et le changement paléoenvironnementales durant le Pliocène sont exceptionnellement préservés et scellées dans un état de congélation qui fournissant une occasion pour la reconstruction paléoenvironnementale et faunistique avec une qualité et une résolution sans précédent. Pendent une période de réchauffement global seulement ~2,5°C au-dessus de moderne les dossiers, moléculaire, isotopique, annaux de croissance, paléofaunistique et paléovégétation indiquent que l'Arctique a connu une augmentation de la température annuelle moyenne de 11°C–19°C au-dessus de moderne, en montrant un inferieur gradient de température latitudinal qu'aujourd'hui. Il semble que le réchauffement intense pendent le Néogène a provoqué la décongélation et erosion pour libérer les sédiments et créer une plaine côtière continuel et épaisse (> 2,5 km dans lieux) qui a fourni une route pour les chameaux et autres mammifères pour migrer et évoluer dans l’Haut-Arctique. Dans ce résumé, nous soulignons les opportunités qui existent pour la recherche sur ces sujets et les sujets connexes avec la communauté PoLAR-FIT

Income Tax Avoidance and Evasion: A Narrow Bracketing Approach

We characterize optimal individual tax evasion and avoidance when taxpayers ìnarrow bracketî the joint avoidance/evasion decision by exhausting all gainful methods for legal avoidance before choosing whether or not also to evade illegally. We Önd that (i) evasion is an increasing function of the audit probability when the latter is low enough, yet tax avoidance is always decreasing in the probability of audit; (ii) an analogous Önding to the so-called Yitzhaki puzzle for evasion also holds for tax avoidance ñan increase in the tax rate decreases the level of avoided income and the level of avoided tax; and (iii) that, holding constant the expected return to evasion, it is not always the case that the combined loss of reported income due to avoidance and evasion can be stemmed by increasing the Öne rate and decreasing the audit probability

Hysteresis and hierarchies: dynamics of disorder-driven first-order phase transformations

We use the zero-temperature random-field Ising model to study hysteretic behavior at first-order phase transitions. Sweeping the external field through zero, the model exhibits hysteresis, the return-point memory effect, and avalanche fluctuations. There is a critical value of disorder at which a jump in the magnetization (corresponding to an infinite avalanche) first occurs. We study the universal behavior at this critical point using mean-field theory, and also present preliminary results of numerical simulations in three dimensions.Comment: 12 pages plus 2 appended figures, plain TeX, CU-MSC-747

Suboptimal Activation of Antigen-Specific CD4+ Effector Cells Enables Persistence of M. tuberculosis In Vivo

Adaptive immunity to Mycobacterium tuberculosis controls progressive bacterial growth and disease but does not eradicate infection. Among CD4+ T cells in the lungs of M. tuberculosis-infected mice, we observed that few produced IFN-γ without ex vivo restimulation. Therefore, we hypothesized that one mechanism whereby M. tuberculosis avoids elimination is by limiting activation of CD4+ effector T cells at the site of infection in the lungs. To test this hypothesis, we adoptively transferred Th1-polarized CD4+ effector T cells specific for M. tuberculosis Ag85B peptide 25 (P25TCRTh1 cells), which trafficked to the lungs of infected mice and exhibited antigen-dependent IFN-γ production. During the early phase of infection, ∼10% of P25TCRTh1 cells produced IFN-γ in vivo; this declined to <1% as infection progressed to chronic phase. Bacterial downregulation of fbpB (encoding Ag85B) contributed to the decrease in effector T cell activation in the lungs, as a strain of M. tuberculosis engineered to express fbpB in the chronic phase stimulated P25TCRTh1 effector cells at higher frequencies in vivo, and this resulted in CD4+ T cell-dependent reduction of lung bacterial burdens and prolonged survival of mice. Administration of synthetic peptide 25 alone also increased activation of endogenous antigen-specific effector cells and reduced the bacterial burden in the lungs without apparent host toxicity. These results indicate that CD4+ effector T cells are activated at suboptimal frequencies in tuberculosis, and that increasing effector T cell activation in the lungs by providing one or more epitope peptides may be a successful strategy for TB therapy

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Estimating global injuries morbidity and mortality : methods and data used in the Global Burden of Disease 2017 study

Background: While there is a long history of measuring death and disability from injuries, modern research methods must account for the wide spectrum of disability that can occur in an injury, and must provide estimates with sufficient demographic, geographical and temporal detail to be useful for policy makers. The Global Burden of Disease (GBD) 2017 study used methods to provide highly detailed estimates of global injury burden that meet these criteria. Methods: In this study, we report and discuss the methods used in GBD 2017 for injury morbidity and mortality burden estimation. In summary, these methods included estimating cause-specific mortality for every cause of injury, and then estimating incidence for every cause of injury. Non-fatal disability for each cause is then calculated based on the probabilities of suffering from different types of bodily injury experienced. Results: GBD 2017 produced morbidity and mortality estimates for 38 causes of injury. Estimates were produced in terms of incidence, prevalence, years lived with disability, cause-specific mortality, years of life lost and disability-adjusted life-years for a 28-year period for 22 age groups, 195 countries and both sexes. Conclusions: GBD 2017 demonstrated a complex and sophisticated series of analytical steps using the largest known database of morbidity and mortality data on injuries. GBD 2017 results should be used to help inform injury prevention policy making and resource allocation. We also identify important avenues for improving injury burden estimation in the future