Movement of Trace Elements During Residence in the Antarctic Ice: a Laboratory Simulation

Recent work has determined that differences in the trace element distribution between Antarctic eucrites and non-Antarctic eucrites may be due to weathering during residence in the ice, and samples that demonstrate trace element disturbances do not necessarily correspond to eucrites that appear badly weathered to the naked eye. This study constitutes a preliminary test of the idea that long-term residence in the ice is the cause of the trace element disturbances observed in the eucrites. Samples of a non-Antarctic eucrite were leached in water at room temperature conditions. Liquid samples were analyzed for rare earth element abundances using ion chromatography. The results for the short-term study showed little or no evidence that leaching had occurred. However, there were tantalizing hints that something may be happening. The residual solid samples are currently being analyzed for the unleached trace metals using instrumental neutron activation analysis and should show evidence of disturbance if the chromatography clues were real. In addition, another set of samples continues to be intermittently sampled for later analysis. The results should give us information about the movement of trace elements under our conditions and allow us to make some tentative extrapolations to what we observe in actual Antarctic eucrite samples

Observation of a multimode plasma response and its relationship to density pumpout and edge-localized mode suppression

Density pumpout and edge-localized mode (ELM) suppression by applied n=2 magnetic fields in low-collisionality DIII-D plasmas are shown to be correlated with the magnitude of the plasma response driven on the high-field side (HFS) of the magnetic axis but not the low-field side (LFS) midplane. These distinct responses are a direct measurement of a multimodal magnetic plasma response, with each structure preferentially excited by a different n=2 applied spectrum and preferentially detected on the LFS or HFS. Ideal and resistive magneto-hydrodynamic (MHD) calculations find that the LFS measurement is primarily sensitive to the excitation of stable kink modes, while the HFS measurement is primarily sensitive to resonant currents (whether fully shielding or partially penetrated). The resonant currents are themselves strongly modified by kink excitation, with the optimal applied field pitch for pumpout and ELM suppression significantly differing from equilibrium field alignment.This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Fusion Energy Sciences, using the DIII-D National Fusion Facility, a DOE Office of Science user facility, under Awards No. DE-FC02-04ER54698, No. DE-AC02-09CH11466, No. DE-FG02-04ER54761, No. DE-AC05-06OR23100, No. DE-SC0001961, and No. DE-AC05-00OR22725. S. R. H. was supported by AINSE and ANSTO

Arterial stiffness and Vitamin D levels: the Baltimore Longitudinal Study of Aging

CONTEXT: The importance of vitamin D for bone health has long been acknowledged. Recent evidence suggests that vitamin D can also play a role in reducing the risk of several other diseases, including cardiovascular disease. OBJECTIVE: The aim of this study is to test the hypothesis that 25-hydroxyvitamin D (25-OH D) is an independent cross-sectional correlate of central arterial stiffness in a normative aging study population. DESIGN AND SETTINGS: We conducted a cross-sectional analysis. SUBJECTS: We studied 1228 healthy volunteers (50% males; age, 70\ub112 yr) of the Baltimore Longitudinal Study of Aging. MAIN OUTCOME MEASURES: We measured carotid-femoral pulse wave velocity (PWV) and 25-OH D levels. RESULTS: We found a significant inverse association between PWV and 25-OH D levels (adjusted r2=0.27; \u3b2=-0.43; P=0.001). After adjusting for age, gender, ethnicity, season of blood draw, estimated glomerular filtration rate, physical activity level, cardiovascular risk factors score (smoking, visceral obesity, hypercholesterolemia, hypertension, and diabetes), calcium/vitamin D supplementation, serum calcium, and PTH levels, the association between PWV and 25-OH D levels was only slightly reduced and remained statistically significant (adjusted r2=0.34; \u3b2=-0.34; P=0.04). CONCLUSIONS: Vitamin D levels are inversely associated with increased arterial stiffness in a normative aging population, irrespective of traditional risk factor burden. Further research is needed to understand the mechanism of this association and to test the hypothesis that vitamin D supplementation can reduce arterial stiffness

RELICS: The Reionization Lensing Cluster Survey and the Brightest High-z Galaxies

Massive foreground galaxy clusters magnify and distort the light of objects behind them, permitting a view into both the extremely distant and intrinsically faint galaxy populations. We present here the z ~ 6-8 candidate high-redshift galaxies from the Reionization Lensing Cluster Survey (RELICS), a Hubble and Spitzer Space Telescope survey of 41 massive galaxy clusters spanning an area of ≈200 arcmin². These clusters were selected to be excellent lenses, and we find similar high-redshift sample sizes and magnitude distributions as the Cluster Lensing And Supernova survey with Hubble (CLASH). We discover 257, 57, and eight candidate galaxies at z ~ 6, 7, and 8 respectively, (322 in total). The observed (lensed) magnitudes of the z ~ 6 candidates are as bright as AB mag ~23, making them among the brightest known at these redshifts, comparable with discoveries from much wider, blank-field surveys. RELICS demonstrates the efficiency of using strong gravitational lenses to produce high-redshift samples in the epoch of reionization. These brightly observed galaxies are excellent targets for follow-up study with current and future observatories, including the James Webb Space Telescope

Competing Ultrafast Energy Relaxation Pathways in Photoexcited Graphene

For most optoelectronic applications of graphene a thorough understanding of the processes that govern energy relaxation of photoexcited carriers is essential. The ultrafast energy relaxation in graphene occurs through two competing pathways: carrier-carrier scattering -- creating an elevated carrier temperature -- and optical phonon emission. At present, it is not clear what determines the dominating relaxation pathway. Here we reach a unifying picture of the ultrafast energy relaxation by investigating the terahertz photoconductivity, while varying the Fermi energy, photon energy, and fluence over a wide range. We find that sufficiently low fluence ($\lesssim$ 4 $\mu$J/cm$^2$) in conjunction with sufficiently high Fermi energy ($\gtrsim$ 0.1 eV) gives rise to energy relaxation that is dominated by carrier-carrier scattering, which leads to efficient carrier heating. Upon increasing the fluence or decreasing the Fermi energy, the carrier heating efficiency decreases, presumably due to energy relaxation that becomes increasingly dominated by phonon emission. Carrier heating through carrier-carrier scattering accounts for the negative photoconductivity for doped graphene observed at terahertz frequencies. We present a simple model that reproduces the data for a wide range of Fermi levels and excitation energies, and allows us to qualitatively assess how the branching ratio between the two distinct relaxation pathways depends on excitation fluence and Fermi energy.Comment: Nano Letters 201

Search for the disappearance of muon antineutrinos in the NuMI neutrino beam

We report constraints on antineutrino oscillation parameters that were obtained by using the two MINOS detectors to measure the 7% muon antineutrino component of the NuMI neutrino beam. In the Far Detector, we select 130 events in the charged-current muon antineutrino sample, compared to a prediction of 136.4 ± 11.7(stat)^(+10.2)_(-8.9)(syst) events under the assumption │Δm^2│ = 2.32 X 10^(-3) eV^2, sin^2(2θ) = 1.0

New constraints on muon-neutrino to electron-neutrino transitions in MINOS

This paper reports results from a search for ν_μ → ν_e transitions by the MINOS experiment based on a 7×10^(20) protons-on-target exposure. Our observation of 54 candidate ν_e events in the far detector with a background of 49.1±7.0(stat)±2.7(syst) events predicted by the measurements in the near detector requires 2sin^2(2θ_(13))sin^2θ_(23)<0.12(0.20) at the 90% C.L. for the normal (inverted) mass hierarchy at δ_(CP)=0. The experiment sets the tightest limits to date on the value of θ_(13) for nearly all values of δ_(CP) for the normal neutrino mass hierarchy and maximal sin^2(2θ_(23))