Accelerated Springtime Melt of Snow on Tundra Downwind from Northern Alaska River Systems Resulting from Niveo-aeolian Deposition Events

It is well known that light-absorbing particulate matter (PM) enhances absorption of sunlight when deposited on ice and snow. Such increased absorption is due to a reduction in surface albedo, resulting in accelerated melt of frozen surfaces. In isolation, earlier melt enhances Arctic warming since dark surfaces underlying snow and ice are exposed and absorb additional solar energy. Here, we combine various observational tools to demonstrate that aeolian deposition of PM along fluvial features on the North Slope of Alaska resulted in a notable reduction of surface albedo in the spring of 2016, from values typical for snow (~0.8) to around 0.35 on average. This reduction resulted in accelerated snow and ice melt by up to three weeks compared to unaffected areas. This phenomenon was observed to some degree in 12 other years dating back to 2003. Deposition generally was found to occur near particular sections of the rivers, with several areas affected by events in multiple years. In all years, the deposition is attributed to high wind events. The extreme case in 2016 is linked to unusually strong and extraordinarily persistent winds during April. The deposited material is thought to be the natural sediment carried by the rivers, resulting in a seasonally replenished source of PM. These findings indicate a previously unreported impact of both fluvial and atmospheric processes on the seasonal melt of northern Alaska rivers.Il s’agit d’un fait bien connu que la matière particulaire photo-absorbante rehausse l’absorption de la lumière solaire lorsqu’elle est déposée sur la glace et la neige. Cette absorption accrue est attribuable à la réduction de l’albédo de la surface, ce qui se traduit par la fonte accélérée des surfaces glacées. Individuellement, la fonte hâtive augmente le réchauffement de l’Arctique parce que les surfaces sombres se trouvant sous la neige et la glace sont exposées et absorbent l’énergie solaire supplémentaire. Ici, nous recourons à divers outils d’observation pour montrer que le dépôt éolien de matière particulaire le long des caractéristiques fluviales de la North Slope de l’Alaska a entraîné une réduction notable de l’albédo de la surface au printemps de 2016, passant de valeurs typiques pour la neige de (~ 0,8) à environ 0,35 en moyenne. Cette réduction a donné lieu à l’accélération de la fonte de la neige et de la glace dans une mesure de trois semaines comparativement aux endroits qui n’ont pas été touchés par la réduction. Ce phénomène a été observé dans une certaine mesure pendant 12 autres années, remontant en 2003. De manière générale, des dépôts se sont ramassés près de segments particuliers des cours d’eau, et plusieurs des secteurs ont été touchés par des événements au cours de plusieurs années. Dans l’ensemble, les dépôts sont attribués à des vents violents. Le cas extrême de 2016 découle de vents inhabituellement forts et extraordinairement persistants en avril. La matière déposée serait peut-être du sédiment naturel transporté par les cours d’eau, ce qui donne lieu au réapprovisionnement saisonnier de la source de matière particulaire. Ces constatations mènent à une incidence antérieurement non déclarée des processus fluviaux et atmosphériques sur la fonte saisonnière des cours d’eau du nord de l’Alaska

Estimation of grain boundary segregation enthalpy and its role in stable nanocrystalline alloy design

Grain boundary segregation provides a method for stabilization of nanocrystalline metals—an alloying element that will segregate to the boundaries can lower the grain boundary energy, attenuating the driving force for grain growth. The segregation strength relative to the mixing enthalpy of a binary system determines the propensity for segregation stabilization. This relationship has been codified for the design space of positive enthalpy alloys; unfortunately, quantitative values for the grain boundary segregation enthalpy exist in only very few material systems, hampering the prospect of nanocrystalline alloy design. Here we present a Miedema-type model for estimation of grain boundary segregation enthalpy, with which potential nanocrystalline phase-forming alloys can be rapidly screened. Calculations of the necessary enthalpies are made for ~2500 alloys and used to make predictions about nanocrystalline stability.United States. Army Research Office (Contract W911NF-09-1-0422)United States. Dept. of Energy. Office of Science (Solid-State Solar-Thermal Energy Conversion Center DE-SC0001299

Ketone bodies for the failing heart:fuels that can fix the engine?

Accumulating evidence suggests that the failing heart reverts energy metabolism toward increased utilization of ketone bodies. Despite many discrepancies in the literature, evidence from both bench and clinical research demonstrates beneficial effects of ketone bodies in heart failure. Ketone bodies are readily oxidized by cardiomyocytes and can provide ancillary fuel for the energy-starved failing heart. In addition, ketone bodies may help to restore cardiac function by mitigating inflammation, oxidative stress, and cardiac remodeling. In this review, we hypothesize that a therapeutic approach intended to restore cardiac metabolism through ketone bodies could both refuel and ‘repair’ the failing heart

The Chemical Compositions of Non-Variable Red and Blue Field Horizontal Branch Stars

We present a new detailed abundance study of field red horizontal branch (RHB) and blue horizontal branch (BHB) non-variable stars. High resolution and high S/N echelle spectra of 11 RHB and 12 BHB were obtained with the McDonald 2.7 m telescope, and the RHB sample was augmented by reanalysis of spectra of 25 stars from a recent survey. We derived stellar atmospheric parameters based on spectroscopic constraints, and computed relative abundance ratios for 24 species of 19 elements. The species include Si II and Ca II, which have not been previously studied in RHB and BHB (Teff < 9000 K) stars. The abundance ratios are generally consistent with those of similar-metallicity field stars in different evolutionary stages. We estimated the masses of the RHB and BHB stars by comparing their Teff--log g positions with HB model evolutionary tracks. The mass distribution suggests that our program stars possess masses of ~0.5 Msun. Finally, we compared the temperature distributions of field RHB and BHB stars with field RR Lyraes in the metallicity range -0.8 >~ [Fe/H] >~ -2.5. This yielded effective temperatures estimates of 5900K and 7400 K for the red and blue edges of the RR Lyrae instability strip.Comment: Accepted to A

Upside-down fluxes Down Under: CO2 net sink in winter and net source in summer in a temperate evergreen broadleaf forest

Predicting the seasonal dynamics of ecosystem carbon fluxes is challenging in broadleaved evergreen forests because of their moderate climates and subtle changes in canopy phenology. We assessed the climatic and biotic drivers of the seasonality of net ecosystem–atmosphere CO2 exchange (NEE) of a eucalyptus-dominated forest near Sydney, Australia, using the eddy covariance method. The climate is characterised by a mean annual precipitation of 800mm and a mean annual temperature of 18°C, hot summers and mild winters, with highly variable precipitation. In the 4-year study, the ecosystem was a sink each year (−225gCm−2yr−1 on average, with a standard deviation of 108gCm−2yr−1); inter-annual variations were not related to meteorological conditions. Daily net C uptake was always detected during the cooler, drier winter months (June through August), while net C loss occurred during the warmer, wetter summer months (December through February). Gross primary productivity (GPP) seasonality was low, despite longer days with higher light intensity in summer, because vapour pressure deficit (D) and air temperature (Ta) restricted surface conductance during summer while winter temperatures were still high enough to support photosynthesis. Maximum GPP during ideal environmental conditions was significantly correlated with remotely sensed enhanced vegetation index (EVI; r2 = 0.46) and with canopy leaf area index (LAI; r2= 0.29), which increased rapidly after mid-summer rainfall events. Ecosystem respiration (ER) was highest during summer in wet soils and lowest during winter months. ER had larger seasonal amplitude compared to GPP, and therefore drove the seasonal variation of NEE. Because summer carbon uptake may become increasingly limited by atmospheric demand and high temperature, and because ecosystem respiration could be enhanced by rising temperatures, our results suggest the potential for large-scale seasonal shifts in NEE in sclerophyll vegetation under climate change.The Australian Education Investment Fund, Australian Terrestrial Ecosystem Research Network, Australian Research Council and Hawkesbury Institute for the Environment at Western Sydney University supported this work. We thank Jason Beringer, Helen Cleugh, Ray Leuning and Eva van Gorsel for advice and support. Senani Karunaratne provided soil classification details

Determination of the Processes Driving the Acquisition of Immunity to Malaria Using a Mathematical Transmission Model

Acquisition of partially protective immunity is a dominant feature of the epidemiology of malaria among exposed individuals. The processes that determine the acquisition of immunity to clinical disease and to asymptomatic carriage of malaria parasites are poorly understood, in part because of a lack of validated immunological markers of protection. Using mathematical models, we seek to better understand the processes that determine observed epidemiological patterns. We have developed an age-structured mathematical model of malaria transmission in which acquired immunity can act in three ways (“immunity functions”): reducing the probability of clinical disease, speeding the clearance of parasites, and increasing tolerance to subpatent infections. Each immunity function was allowed to vary in efficacy depending on both age and malaria transmission intensity. The results were compared to age patterns of parasite prevalence and clinical disease in endemic settings in northeastern Tanzania and The Gambia. Two types of immune function were required to reproduce the epidemiological age-prevalence curves seen in the empirical data; a form of clinical immunity that reduces susceptibility to clinical disease and develops with age and exposure (with half-life of the order of five years or more) and a form of anti-parasite immunity which results in more rapid clearance of parasitaemia, is acquired later in life and is longer lasting (half-life of >20 y). The development of anti-parasite immunity better reproduced observed epidemiological patterns if it was dominated by age-dependent physiological processes rather than by the magnitude of exposure (provided some exposure occurs). Tolerance to subpatent infections was not required to explain the empirical data. The model comprising immunity to clinical disease which develops early in life and is exposure-dependent, and anti-parasite immunity which develops later in life and is not dependent on the magnitude of exposure, appears to best reproduce the pattern of parasite prevalence and clinical disease by age in different malaria transmission settings. Understanding the effector mechanisms underlying these two immune functions will assist in the design of transmission-reducing interventions against malaria

AAPM medical physics practice guideline 10.a.: Scope of practice for clinical medical physics.

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education, and professional practice of medical physics. The AAPM has more than 8000 members and is the principal organization of medical physicists in the United States. The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner. Each medical physics practice guideline (MPPG) represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiation requires specific training, skills, and techniques as described in each document. As the review of the previous version of AAPM Professional Policy (PP)-17 (Scope of Practice) progressed, the writing group focused on one of the main goals: to have this document accepted by regulatory and accrediting bodies. After much discussion, it was decided that this goal would be better served through a MPPG. To further advance this goal, the text was updated to reflect the rationale and processes by which the activities in the scope of practice were identified and categorized. Lastly, the AAPM Professional Council believes that this document has benefitted from public comment which is part of the MPPG process but not the AAPM Professional Policy approval process. The following terms are used in the AAPM's MPPGs: Must and Must Not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline. Should and Should Not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances

Clutter mitigation, multiple peaks, and high-order spectral moments in 35 GHz vertically pointing radar velocity spectra

This study presents and applies three separate processing methods to improve high-order moments estimated from 35GHz (Ka band) vertically pointing radar Doppler velocity spectra. The first processing method removes Doppler-shifted ground clutter from spectra collected by a US Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) program Ka-band zenith pointing radar (KAZR) deployed at Oliktok Point (OLI), Alaska. Ground clutter resulted from multiple pathways through antenna side lobes and reflections off a rotating scanning radar antenna located 2m away from KAZR, which caused Doppler shifts in ground clutter returns from stationary targets 2.5km away. After removing clutter in the recorded velocity spectra, the second processing method identifies multiple separate and sub-peaks in the spectra and estimates high-order moments for each peak. Multiple peaks and high-order moments were estimated for both original 2 and 15s averaged spectra. The third processing step improves the spectrum variance, skewness, and kurtosis estimates by removing velocity variability due to turbulent broadening during 15s averaging intervals. Applying the multiple peak processing to Doppler velocity spectra during liquid-only clouds can identify cloud and drizzle particles and during mixed-phase clouds can identify liquid cloud and frozen hydrometeors. Consistent with previous studies, this work found that spectrum skewness assuming only a single spectral peak was a good indicator of two hydrometeor populations (for example, cloud and drizzle particles) being present in the radar pulse volume. Yet, after dividing the spectrum into multiple peaks, velocity spectrum skewness for individual peaks is near zero, indicating nearly symmetric peaks. This suggests that future studies should use velocity skewness of single-peak spectra as an indicator of possible multiple hydrometeor populations and then use multiple-peak moments for quantitative studies. Three future activities will continue this work. First, KAZR spectra from several ARM sites have been processed and are available in the ARM archive as a principal investigator (PI) product. ARM programmers are evaluating these processing methods as part of future multiple-peak products generated by ARM. Third, MATLAB code generating the Oliktok Point products has been uploaded as supplemental material for public dissemination

Elevated plasma galectin-3 is associated with near-term rehospitalization in heart failure:A pooled analysis of 3 clinical trials

BackgroundRehospitalization is a major cause for heart failure (HF)–related morbidity and is associated with considerable loss of quality of life and costs. The rate of unplanned rehospitalization in patients with HF is unacceptably high; current risk stratification to identify patients at risk for rehospitalization is inadequate. We evaluated whether measurement of galectin-3 would be helpful in identifying patients at such risk.MethodsWe analyzed pooled data from patients (n = 902) enrolled in 3 cohorts (COACH, n = 592; PRIDE, n = 181; and UMD H-23258, n = 129) originally admitted because of HF. Mean patient age was between 61.6 and 72.9 years across the cohorts, with a wide range of left ventricular ejection fraction. Galectin-3 levels were measured during index admission. We used fixed and random-effects models, as well as continuous and categorical reclassification statistics to assess the association of baseline galectin-3 levels with risk of postdischarge rehospitalization at different time points and the composite end point all-cause mortality and rehospitalization.ResultsCompared with patients with galectin-3 concentrations less than 17.8 ng/mL, those with results exceeding this value were significantly more likely to be rehospitalized for HF at 30, 60, 90, and 120 days after discharge, with odds ratios (ORs) of 2.80 (95% CI 1.41-5.57), 2.61 (95% CI 1.46-4.65), 3.01 (95% CI 1.79-5.05), and 2.79 (95% CI 1.75-4.45), respectively. After adjustment for age, gender, New York Heart Association class, renal function (estimated glomerular filtration rate), left ventricular ejection fraction, and B-type natriuretic peptide, galectin-3 remained an independent predictor of HF rehospitalization. The addition of galectin-3 to risk models significantly reclassified patient risk of postdischarge rehospitalization and fatal event at each time point (continuous net reclassification improvement at 30 days of +42.6% [95% CI +19.9%-65.4%], P < .001).ConclusionsAmong patients hospitalized for HF, plasma galectin-3 concentration is useful for the prediction of near-term rehospitalization

Bubbling AdS Black Holes

We explore the non-BPS analog of `AdS bubbles', which are regular spherically symmetric 1/2 BPS geometries in type IIB supergravity. They have regular horizons and can be thought of as bubbling generalizations of non-extremal AdS black hole solutions in five-dimensional gauged supergravity. Due to the appearance of the Heun equation even at the linearized level, various approximation and numerical methods are needed in order to extract information about this system. We study how the vacuum expectation value and mass of a particular dimension two chiral primary operator depend on the temperature and chemical potential of the thermal Yang-Mills theory. In addition, the mass of the bubbling AdS black holes is computed. As is shown numerically, there are also non-BPS solitonic bubbles which are completely regular and arise from continuous deformations of BPS AdS bubbles.Comment: 37 pages, 2 figure