Improvements to 232-thorium, 230-thorium, and 231-protactinium analysis in seawater arising from GEOTRACES intercalibration

The GEOTRACES program requires the analysis of large numbers of seawater samples for ^(232)Th, ^(230)Th, and ^(231)Pa. During the GEOTRACES international intercalibration exercise, we encountered unexpected difficulties with recovery and contamination of these isotopes, ^(232)Th in particular. Experiments were carried out to identify the source of these issues, leading to a more streamlined and efficient procedure. The two particular problems that we identified and corrected were (1) frits in columns supplied by Bio-Rad Laboratories caused loss of Th during column chemistry and (2) new batches of AG1-X8 resin supplied by Bio-Rad Laboratories released more than 100 pg of ^(232)Th during elution of sample. To improve yields and blanks, we implemented a series of changes including switching to Eichrom anion exchange resin (100-200 μm mesh) and Environmental Express columns. All Th and Pa samples were analyzed on a Neptune multi-collector inductively-coupled-plasma mass spectrometer (MC-ICP-MS) using peak hopping of ^(230)Th and ^(229)Th on the central SEM, with either ^(232)Th, ^(236)U (or both) used to monitor for beam intensity. We used in-house laboratory standards to check for machine reproducibility, and the GEOTRACES intercalibration standard to check for accuracy. Over a 1-y period, the 2 s.d. reproducibility on the GEOTRACES SW STD 2010-1 was 2.5% for ^(230)Th, 1.8% for ^(232)Th, and 4% for ^(231)Pa. The lessons learned during this intercalibration process will be of value to those analyzing U-Th-Pa and rare earth elements as part of the GEOTRACES program as well as those using U-series elements in other applications that require high yields and low blanks, such as geochronology

Promising Payment Reform: Risk-Sharing With Accountable Care Organizations

Describes the implementation of shared payer-provider risk payment models at eight private accountable care organizations. Analyzes challenges for providers, purchasers, and payers, including securing the infrastructure for successful risk management

Observation of the critical regime near Anderson localization of light

Diffusive transport is among the most common phenomena in nature [1]. However, as predicted by Anderson [2], diffusion may break down due to interference. This transition from diffusive transport to localization of waves should occur for any type of classical or quantum wave in any media as long as the wavelength becomes comparable to the transport mean free path $\ell^*$ [3]. The signatures of localization and those of absorption, or bound states, can however be similar, such that an unequivocal proof of the existence of wave localization in disordered bulk materials is still lacking. Here we present measurements of time resolved non-classical diffusion of visible light in strongly scattering samples, which cannot be explained by absorption, sample geometry or reduction in transport velocity. Deviations from classical diffusion increase strongly with decreasing $\ell^*$ as expected for a phase transition. This constitutes an experimental realization of the critical regime in the approach to Anderson localization.Comment: 5 pages, 4 figure

Thermodynamic identities and particle number fluctuations in weakly interacting Bose--Einstein condensates

We derive exact thermodynamic identities relating the average number of condensed atoms and the root-mean-square fluctuations determined in different statistical ensembles for the weakly interacting Bose gas confined in a box. This is achieved by introducing the concept of {\it auxiliary partition functions} for model Hamiltonians that do conserve the total number of particles. Exploiting such thermodynamic identities, we provide the first, completely analytical prediction of the microcanonical particle number fluctuations in the weakly interacting Bose gas. Such fluctuations, as a function of the volume V of the box are found to behave normally, at variance with the anomalous scaling behavior V^{4/3} of the fluctuations in the ideal Bose gas.Comment: 5 pages, 1 figur

Resolving the Helium Lyman-α\alpha Forest: Mapping Intergalactic Gas and Ionizing Radiation at z≈3z\approx 3

We present a new, high resolution HST/GHRS spectrum of quasar Q0302-003, and use the HeII Lyman-$\alpha$ absorption, together with a high resolution Keck spectrum of the HI Lyman-$\alpha$ forest, to probe the distribution and ionization state of foreground gas just below the quasar redshift $z\approx 3.3$. The main new conclusions from the current data are: 1. The HeII Lyman-$\alpha$ forest is detected; 2. The ``diffuse'' (redshift-space-filling) medium is also detected, and must have a low density ($\Omega\le 0.01 (h/0.7)^{-3/2}$) consistent with standard primordial nucleosynthesis and models of early gas collapse into protogalaxies; 3. The intergalactic ionizing spectrum is soft ($\eta\ge 100$), although the intergalactic helium is probably mostly doubly ionized by $z=3.3$; 4. The helium abundance is within a factor of a few of standard Big Bang predictions, over a large volume of space at high redshift.Comment: AAS Latex, 3 figures, accepted for publication in the Astronomical Journa

New Fermionic Description of Quantum S = 1/2 Antiferromargnet

A novel approach to S =1/2 antiferromagnets with strong fluctuations based on the representation of spin-1/2 operators as bylinear forms of real (Majorana) fermions is suggested. This representation has the advantage of being irreducible without any constraints on the fermionic Hilbert space. This property allows to derive an effective Hamiltonian for low-lying excitations in the spin liquid state. It is proven that these excitations are S = 1 real fermions.Comment: 4 page

Atmospheric Dust Inputs, Iron Cycling, and Biogeochemical Connections in the South Pacific Ocean from Thorium Isotopes

One of the primary sources of micronutrients to the sea surface in remote ocean regions is the deposition of atmospheric dust. Geographic patterns in biogeochemical processes such as primary production and nitrogen fixation that require micronutrients like iron (Fe) are modulated in part by the spatial distribution of dust supply. Global models of dust deposition rates are poorly calibrated in the open ocean, owing to the difficulty of determining dust fluxes in sparsely sampled regions. We present new estimates of dust and Fe input rates from measurements of dissolved and particulate thorium isotopes ²³⁰Th and ²³²Th on the FS Sonne SO245 section (GEOTRACES process study GPpr09) in the South Pacific. We first discuss high‐resolution upper water column profiles of Th isotopes and the implications for the systematics of dust flux reconstructions from seawater Th measurements. We find dust fluxes in the center of the highly oligotrophic South Pacific Gyre that are the lowest of any mean annual dust input rates measured in the global oceans, but that are 1–2 orders of magnitude higher than those estimated by global dust models. We also determine dust‐borne Fe fluxes and reassess the importance of individual Fe sources to the surface South Pacific Gyre, finding that dust dissolution, not vertical or lateral diffusion, is the primary Fe source. Finally, we combine our estimates of Fe flux in dust with previously published cellular and enzymatic quotas to determine theoretical upper limits on annual average nitrogen fixation rates for a given Fe deposition rate

Atmospheric Dust Inputs, Iron Cycling, and Biogeochemical Connections in the South Pacific Ocean from Thorium Isotopes

One of the primary sources of micronutrients to the sea surface in remote ocean regions is the deposition of atmospheric dust. Geographic patterns in biogeochemical processes such as primary production and nitrogen fixation that require micronutrients like iron (Fe) are modulated in part by the spatial distribution of dust supply. Global models of dust deposition rates are poorly calibrated in the open ocean, owing to the difficulty of determining dust fluxes in sparsely sampled regions. We present new estimates of dust and Fe input rates from measurements of dissolved and particulate thorium isotopes ²³⁰Th and ²³²Th on the FS Sonne SO245 section (GEOTRACES process study GPpr09) in the South Pacific. We first discuss high‐resolution upper water column profiles of Th isotopes and the implications for the systematics of dust flux reconstructions from seawater Th measurements. We find dust fluxes in the center of the highly oligotrophic South Pacific Gyre that are the lowest of any mean annual dust input rates measured in the global oceans, but that are 1–2 orders of magnitude higher than those estimated by global dust models. We also determine dust‐borne Fe fluxes and reassess the importance of individual Fe sources to the surface South Pacific Gyre, finding that dust dissolution, not vertical or lateral diffusion, is the primary Fe source. Finally, we combine our estimates of Fe flux in dust with previously published cellular and enzymatic quotas to determine theoretical upper limits on annual average nitrogen fixation rates for a given Fe deposition rate

Efficient HTTP based I/O on very large datasets for high performance computing with the libdavix library

Remote data access for data analysis in high performance computing is commonly done with specialized data access protocols and storage systems. These protocols are highly optimized for high throughput on very large datasets, multi-streams, high availability, low latency and efficient parallel I/O. The purpose of this paper is to describe how we have adapted a generic protocol, the Hyper Text Transport Protocol (HTTP) to make it a competitive alternative for high performance I/O and data analysis applications in a global computing grid: the Worldwide LHC Computing Grid. In this work, we first analyze the design differences between the HTTP protocol and the most common high performance I/O protocols, pointing out the main performance weaknesses of HTTP. Then, we describe in detail how we solved these issues. Our solutions have been implemented in a toolkit called davix, available through several recent Linux distributions. Finally, we describe the results of our benchmarks where we compare the performance of davix against a HPC specific protocol for a data analysis use case.Comment: Presented at: Very large Data Bases (VLDB) 2014, Hangzho

Generic theory of colloidal transport

We discuss the motion of colloidal particles relative to a two component fluid consisting of solvent and solute. Particle motion can result from (i) net body forces on the particle due to external fields such as gravity; (ii) slip velocities on the particle surface due to surface dissipative phenomena. The perturbations of the hydrodynamic flow field exhibits characteristic differences in cases (i) and (ii) which reflect different patterns of momentum flux corresponding to the existence of net forces, force dipoles or force quadrupoles. In the absence of external fields, gradients of concentration or pressure do not generate net forces on a colloidal particle. Such gradients can nevertheless induce relative motion between particle and fluid. We present a generic description of surface dissipative phenomena based on the linear response of surface fluxes driven by conjugate surface forces. In this framework we discuss different transport scenarios including self-propulsion via surface slip that is induced by active processes on the particle surface. We clarify the nature of force balances in such situations.Comment: 22 pages, 1 figur