High accuracy measure of atomic polarizability in an optical lattice clock

Despite being a canonical example of quantum mechanical perturbation theory, as well as one of the earliest observed spectroscopic shifts, the Stark effect contributes the largest source of uncertainty in a modern optical atomic clock through blackbody radiation. By employing an ultracold, trapped atomic ensemble and high stability optical clock, we characterize the quadratic Stark effect with unprecedented precision. We report the ytterbium optical clock's sensitivity to electric fields (such as blackbody radiation) as the differential static polarizability of the ground and excited clock levels: 36.2612(7) kHz (kV/cm)^{-2}. The clock's fractional uncertainty due to room temperature blackbody radiation is reduced an order of magnitude to 3 \times 10^{-17}.Comment: 5 pages, 3 figures, 2 table

A Generative-Discriminative Basis Learning Framework to Predict Clinical Severity from Resting State Functional MRI Data

We propose a matrix factorization technique that decomposes the resting state fMRI (rs-fMRI) correlation matrices for a patient population into a sparse set of representative subnetworks, as modeled by rank one outer products. The subnetworks are combined using patient specific non-negative coefficients; these coefficients are also used to model, and subsequently predict the clinical severity of a given patient via a linear regression. Our generative-discriminative framework is able to exploit the structure of rs-fMRI correlation matrices to capture group level effects, while simultaneously accounting for patient variability. We employ ten fold cross validation to demonstrate the predictive power of our model on a cohort of fifty eight patients diagnosed with Autism Spectrum Disorder. Our method outperforms classical semi-supervised frameworks, which perform dimensionality reduction on the correlation features followed by non-linear regression to predict the clinical scores

High-resolution absorption spectroscopy of the circumgalactic medium of the Milky Way

In this article we discuss the importance of high-resolution absorption spectroscopy for our understanding of the distribution and physical nature of the gaseous circumgalactic medium (CGM) that surrounds the Milky Way. Observational and theoretical studies indicate a high complexity of the gas kinematics and an extreme multi-phase nature of the CGM in low-redshift galaxies. High-precision absorption-line measurements of the Milky Way's gas environment thus are essential to explore fundamental parameters of circumgalactic gas in the local Universe, such as mass, chemical composition, and spatial distribution. We shortly review important characteristics of the Milky Way's CGM and discuss recent results from our multi-wavelength observations of the Magellanic Stream. Finally, we discuss the potential of studying the warm-hot phase of the Milky Way's CGM by searching for extremely weak [FeX] l6374.5 and [FeIVX] l5302.9 absorption in optical QSO spectra.Comment: 7 pages, 4 figures; accepted for publication in Astronomical Notes (paper version of a talk presented at the 10th Thinkshop, Potsdam, 2013

A Survey of O VI, C III, and H I in Highly Ionized High-Velocity Clouds

(ABRIDGED) We present a Far-Ultraviolet Spectroscopic Explorer survey of highly ionized high-velocity clouds (HVCs) in 66 extragalactic sight lines. We find a total of 63 high-velocity O VI absorbers, 16 with 21 cm-emitting H I counterparts and 47 ``highly ionized'' absorbers without 21 cm emission. 11 of these high-velocity O VI absorbers are positive-velocity wings (broad O VI features extending asymmetrically to velocities of up to 300 km/s). The highly ionized HVC population is characterized by =38+/-10 km/s and <log N_a(O VI)>=13.83+/-0.36. We find that 81% (30/37) of high-velocity O VI absorbers have clear accompanying C III absorption, and 76% (29/38) have accompanying H I absorption in the Lyman series. The lower average width of the high-velocity H I absorbers implies the H I lines arise in a separate, lower temperature phase than the O VI. We find that the shape of the wing profiles is well reproduced by a radiatively cooling, vertical outflow. However, the outflow has to be patchy and out of ionization equilibrium. An alternative model, consistent with the observations, is one where the highly ionized HVCs represent the low N(H I) tail of the HVC population, with the O VI formed at the interfaces around the embedded H I cores. Though we cannot rule out a Local Group explanation, we favor a Galactic origin. This is based on the recent evidence that both H I HVCs and the million-degree gas detected in X-ray absorption are Galactic phenomena. Since the highly ionized HVCs appear to trace the interface between these two Galactic phases, it follows that highly ionized HVCs are Galactic themselves. However, the non-detection of high-velocity O VI in halo star spectra implies that any Galactic high-velocity O VI exists at z-distances beyond a few kpc.Comment: 36 pages, 14 figures (3 in color), accepted to ApJS. Some figures downgraded to limit file siz

Modeling GRB 050904: Autopsy of a Massive Stellar Explosion at z=6.29

GRB 050904 at redshift z=6.29, discovered and observed by Swift and with spectroscopic redshift from the Subaru telescope, is the first gamma-ray burst to be identified from beyond the epoch of reionization. Since the progenitors of long gamma-ray bursts have been identified as massive stars, this event offers a unique opportunity to investigate star formation environments at this epoch. Apart from its record redshift, the burst is remarkable in two respects: first, it exhibits fast-evolving X-ray and optical flares that peak simultaneously at t~470 s in the observer frame, and may thus originate in the same emission region; and second, its afterglow exhibits an accelerated decay in the near-infrared (NIR) from t~10^4 s to t~3 10^4 s after the burst, coincident with repeated and energetic X-ray flaring activity. We make a complete analysis of available X-ray, NIR, and radio observations, utilizing afterglow models that incorporate a range of physical effects not previously considered for this or any other GRB afterglow, and quantifying our model uncertainties in detail via Markov Chain Monte Carlo analysis. In the process, we explore the possibility that the early optical and X-ray flare is due to synchrotron and inverse Compton emission from the reverse shock regions of the outflow. We suggest that the period of accelerated decay in the NIR may be due to suppression of synchrotron radiation by inverse Compton interaction of X-ray flare photons with electrons in the forward shock; a subsequent interval of slow decay would then be due to a progressive decline in this suppression. The range of acceptable models demonstrates that the kinetic energy and circumburst density of GRB 050904 are well above the typical values found for low-redshift GRBs.Comment: 45 pages, 7 figures, and ApJ accepted. Revised version, minor modifications and 1 extra figur

Clinical aspects and outcomes of patients with malaria at Chris Hani Baragwanath Academic Hospital,Johannesburg, South Africa

Background. South Africa (SA) is currently experiencing a significant increase in malaria cases despite having shifted focus from malaria control towards malaria elimination. The clinical features of malaria are nonspecific, but their relative frequency on presentation are not well described. HIV and malaria are both independently associated with high mortality in sub-Saharan Africa. There are important interactions between HIV and malaria.Objectives. To describe the population characteristics of patients with malaria at Chris Hani Baragwanath Academic Hospital, Johannesburg, SA, clinical and biochemical features of severity, the proportion of patients with HIV infection, management and outcomes.Methods. A prospective observational study was conducted whereby patients with a confirmed laboratory diagnosis of malaria were identified, approached and consented for study inclusion over the time period January 2017 - January 2018. Clinical and biochemical data were collected at the time of consent and later analysed.Results. The mean (standard deviation) age was 35.7 (12.98) years, and 72 (70.6%) of the 102 patients were male. Peak admissions for malaria were in January, with 58 patients (56.9%) admitted during January 2017 and 2018. All malaria cases were imported, with 74.5% associated with travel to Mozambique. The majority of the patients (61.8%) were expatriates living in SA. The most common presenting symptoms were chills (95.1%), weakness (94.1%), fever (91.2%), headache (90.2%) and lethargy (88.2%). The most common clinical signs were dehydration (31.4%), prostration (19.6%) and jaundice (13.7%). Among the 40 patients (39.2%) who had severe malaria, prostration was the most common feature of severity (19.6%), 8 (7.8%) were admitted to an intensive care unit, and 6 (5.9%) required haemodialysis. The median (interquartile range) duration of hospital stay was 5 (3 -6) (range 2 - 35) days. HIV status was known in 83 patients (81.4%), of whom 32 (38.6%) were HIV-positive. Malaria prophylaxis had been taken by only 8 patients. The all-cause mortality rate was 4.9%, and mortality attributable to malaria 3.9%.Conclusions. There was a high proportion of complicated malaria cases, particularly in January. The majority of patients were young expatriate males with a history of travel to southern Mozambique or Limpopo Province, with very few taking malaria prophylaxis. Most clinical signs and symptoms were constitutional and nonspecific. A large number of patients were found to be HIV-positive, and most were newly diagnosed. Mortality was high, at around five times the national average, and may have been an underestimate

Digestion kinetics of dried cereal grains

Grain fermentability largely determines the feed value of grains for ruminants. Our objective was to evaluate the variation in kinetics of gas production of cereal grains and the relationship among gas production, chemical composition and feed value. Eighteen barley, 99 corn, 23 sorghum, and 57 wheat samples were fermented in vitro for 48 h. Gas production was measured with a computerized system and an exponential model was fitted to the data. The impact of the variation in composition and kinetics on the feed value of grains in feedlot rations was assessed with the Cornell Net Carbohydrate and Protein System (CNCPS). Fractional gas rates were significantly different between grains (P\u3c0.001), with a mean and S.D. of 0.24 (0.029) h-1 for barley (n=20), 0.15 (0.026) h-1 for corn (n=98), 0.06 (0.016) h-1 for sorghum (n=23) and 0.26 (0.039) h-1 for wheat (n=57). Fermentation rates were more variable than the chemical components. Fractional rates were poorly correlated with chemical composition within grain with the highest correlations for acid detergent insoluble crude protein (ADICP) (r=-0.31, P\u3c0.01) and ADF (r=-0.27, P\u3c0.01) for corn and neutral detergent insoluble crude protein (NDICP) (r=0.35, P\u3c0.05) for wheat. The impact of the variation in composition and kinetics on the feed value of grains in feedlot rations was assessed. The CNCPS predicted a maximal variation of \u3c2.1 MJ/day and \u3c60 g/day in metabolizable energy (ME) and metabolizable protein (MP) supply from grains, respectively. For sorghum, the fermentation rate was predicted to be a major determinant of the site of starch fermentation. A detailed evaluation of feed values for grains needs to include information on rates of fermentation

Clinical aspects and outcomes of patients with malaria at Chris Hani Baragwanath Academic Hospital, Johannesburg, South Africa

Background. South Africa (SA) is currently experiencing a significant increase in malaria cases despite having shifted focus from malaria control towards malaria elimination. The clinical features of malaria are nonspecific, but their relative frequency on presentation are not well described. HIV and malaria are both independently associated with high mortality in sub-Saharan Africa. There are important interactions between HIV and malaria. Objectives. To describe the population characteristics of patients with malaria at Chris Hani Baragwanath Academic Hospital, Johannesburg, SA, clinical and biochemical features of severity, the proportion of patients with HIV infection, management and outcomes. Methods. A prospective observational study was conducted whereby patients with a confirmed laboratory diagnosis of malaria were identified, approached and consented for study inclusion over the time period January 2017 - January 2018. Clinical and biochemical data were collected at the time of consent and later analysed. Results. The mean (standard deviation) age was 35.7 (12.98) years, and 72 (70.6%) of the 102 patients were male. Peak admissions for malaria were in January, with 58 patients (56.9%) admitted during January 2017 and 2018. All malaria cases were imported, with 74.5% associated with travel to Mozambique. The majority of the patients (61.8%) were expatriates living in SA. The most common presenting symptoms were chills (95.1%), weakness (94.1%), fever (91.2%), headache (90.2%) and lethargy (88.2%). The most common clinical signs were dehydration (31.4%), prostration (19.6%) and jaundice (13.7%). Among the 40 patients (39.2%) who had severe malaria, prostration was the most common feature of severity (19.6%), 8 (7.8%) were admitted to an intensive care unit, and 6 (5.9%) required haemodialysis. The median (interquartile range) duration of hospital stay was 5 (3 -6) (range 2 - 35) days. HIV status was known in 83 patients (81.4%), of whom 32 (38.6%) were HIV-positive. Malaria prophylaxis had been taken by only 8 patients. The all-cause mortality rate was 4.9%, and mortality attributable to malaria 3.9%. Conclusions. There was a high proportion of complicated malaria cases, particularly in January. The majority of patients were young expatriate males with a history of travel to southern Mozambique or Limpopo Province, with very few taking malaria prophylaxis. Most clinical signs and symptoms were constitutional and nonspecific. A large number of patients were found to be HIV-positive, and most were newly diagnosed. Mortality was high, at around five times the national average, and may have been an underestimate