538 research outputs found
A non-homogeneous constitutive model for human blood. Part 1. Model derivation and steady flow
The earlier constitutive model of Fang & Owens (Biorheology, vol. 43, 2006, p. 637) and Owens (J. Non-Newtonian Fluid Mech. vol. 140, 2006, p. 57) is extended in scope to include non-homogeneous flows of healthy human blood. Application is made to steady axisymmetric flow in rigid-walled tubes. The new model features stress-induced cell migration in narrow tubes and accurately predicts the FĂ„hraeus-Lindqvist effect whereby the apparent viscosity of healthy blood decreases as a function of tube diameter in sufficiently small vessels. That this is due to the development of a slippage layer of cell-depleted fluid near the vessel walls and a decrease in the tube haematocrit is demonstrated from the numerical results. Although clearly influential, the reduction in tube haematocrit observed in small-vessel blood flow (the so-called FĂ„hraeus effect) does not therefore entirely explain the FĂ„hraeus-Lindqvist effec
High Performance Direct Gravitational N-body Simulations on Graphics Processing Units -- II: An implementation in CUDA
We present the results of gravitational direct -body simulations using the
Graphics Processing Unit (GPU) on a commercial NVIDIA GeForce 8800GTX designed
for gaming computers. The force evaluation of the -body problem is
implemented in ``Compute Unified Device Architecture'' (CUDA) using the GPU to
speed-up the calculations. We tested the implementation on three different
-body codes: two direct -body integration codes, using the 4th order
predictor-corrector Hermite integrator with block time-steps, and one
Barnes-Hut treecode, which uses a 2nd order leapfrog integration scheme. The
integration of the equations of motions for all codes is performed on the host
CPU.
We find that for particles the GPU outperforms the GRAPE-6Af, if
some softening in the force calculation is accepted. Without softening and for
very small integration time steps the GRAPE still outperforms the GPU. We
conclude that modern GPUs offer an attractive alternative to GRAPE-6Af special
purpose hardware. Using the same time-step criterion, the total energy of the
-body system was conserved better than to one in on the GPU, only
about an order of magnitude worse than obtained with GRAPE-6Af. For N \apgt
10^5 the 8800GTX outperforms the host CPU by a factor of about 100 and runs at
about the same speed as the GRAPE-6Af.Comment: Accepted for publication in New Astronom
Relative Energy Requirements for an Erythemal Response of Skin to Monochromatic Wave Lengths of Ultraviolet Present in the Solar Spectrum**From the Departments of Dermatology and Pathology, Baylor University College of Medicine, Houston, Texas.
Offshore transport of shelf waters through interaction of vortices with a shelfbreak current
Author Posting. © American Meteorological Society, 2013. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 43 (2013): 905â919, doi:10.1175/JPO-D-12-0150.1.Interactions between vortices and a shelfbreak current are investigated, with particular attention to the exchange of waters between the continental shelf and slope. The nonlinear, three-dimensional interaction between an anticyclonic vortex and the shelfbreak current is studied in the laboratory while varying the ratio Δ of the maximum azimuthal velocity in the vortex to the maximum alongshelf velocity in the shelfbreak current. Strong interactions between the shelfbreak current and the vortex are observed when Δ > 1; weak interactions are found when Δ < 1. When the anticyclonic vortex comes in contact with the shelfbreak front during a strong interaction, a streamer of shelf water is drawn offshore and wraps anticyclonically around the vortex. Measurements of the offshore transport and identification of the particle trajectories in the shelfbreak current drawn offshore from the vortex allow quantification of the fraction of the shelfbreak current that is deflected onto the slope; this fraction increases for increasing values of Δ. Experimental results in the laboratory are strikingly similar to results obtained from observations in the Middle Atlantic Bight (MAB); after proper scaling, measurements of offshore transport and offshore displacement of shelf water for vortices in the MAB that span a range of values of Δ agree well with laboratory predictions.Laboratory work was supported by the
National Science Foundation through Grant OCE-
0081756. Glider observations in MarchâApril 2006 were
supported by the National Science Foundation through
Grant OCE-0220769. Glider observations in Julyâ
October 2007 were supported by a grant from Raytheon.
RET was supported by the Postdoctoral Scholar Program
at the Woods Hole Oceanographic Institution,
with funding provided by the Cooperative Institute for
the North Atlantic Region. The REMUS observations
were funded by the Office of Naval Research. GGG was
supported by the National Science Foundation through
Grant OCE-1129125 for analysis and writing.2013-11-0
Robust Machine Learning Applied to Astronomical Datasets I: Star-Galaxy Classification of the SDSS DR3 Using Decision Trees
We provide classifications for all 143 million non-repeat photometric objects
in the Third Data Release of the Sloan Digital Sky Survey (SDSS) using decision
trees trained on 477,068 objects with SDSS spectroscopic data. We demonstrate
that these star/galaxy classifications are expected to be reliable for
approximately 22 million objects with r < ~20. The general machine learning
environment Data-to-Knowledge and supercomputing resources enabled extensive
investigation of the decision tree parameter space. This work presents the
first public release of objects classified in this way for an entire SDSS data
release. The objects are classified as either galaxy, star or nsng (neither
star nor galaxy), with an associated probability for each class. To demonstrate
how to effectively make use of these classifications, we perform several
important tests. First, we detail selection criteria within the probability
space defined by the three classes to extract samples of stars and galaxies to
a given completeness and efficiency. Second, we investigate the efficacy of the
classifications and the effect of extrapolating from the spectroscopic regime
by performing blind tests on objects in the SDSS, 2dF Galaxy Redshift and 2dF
QSO Redshift (2QZ) surveys. Given the photometric limits of our spectroscopic
training data, we effectively begin to extrapolate past our star-galaxy
training set at r ~ 18. By comparing the number counts of our training sample
with the classified sources, however, we find that our efficiencies appear to
remain robust to r ~ 20. As a result, we expect our classifications to be
accurate for 900,000 galaxies and 6.7 million stars, and remain robust via
extrapolation for a total of 8.0 million galaxies and 13.9 million stars.
[Abridged]Comment: 27 pages, 12 figures, to be published in ApJ, uses emulateapj.cl
Kinetic models for dilute solutions of dumbbells in non-homogeneous flows revisited
We propose a two fluid theory to model a dilute polymer solution assuming
that it consists of two phases, polymer and solvent, with two distinct
macroscopic velocities. The solvent phase velocity is governed by the
macroscopic Navier-Stokes equations with the addition of a force term
describing the interaction between the two phases. The polymer phase is
described on the mesoscopic level using a dumbbell model and its macroscopic
velocity is obtained through averaging. We start by writing down the full
phase-space distribution function for the dumbbells and then obtain the
inertialess limits for the Fokker-Planck equation and for the averaged friction
force acting between the phases from a rigorous asymptotic analysis. The
resulting equations are relevant to the modelling of strongly non-homogeneous
flows, while the standard kinetic model is recovered in the locally homogeneous
case
Plant 4/1 protein: potential player in intracellular, cell-to-cell and long-distance signaling
Originally isolated as a result of its ability to interact with the movement protein of Tomato spotted wilt virus in a yeast two-hybrid system, the 4/1 protein is proving to be an excellent tool for studying intracellular protein trafficking and intercellular communication. Expression of 4/1 in vivo is tightly regulated, first appearing in the veins of the cotyledon and later in the vasculature of the leaf and stem in association with the xylem parenchyma and phloem parenchyma. Structural studies indicate that 4/1 proteins contain as many as five coiledâcoil (CC) domains; indeed, the highest level of sequence identity among 4/1 proteins involves their C-terminal CC domains, suggesting that proteinâprotein interaction is important for biological function. Recent data predict that the tertiary structure of this C-terminal CC domain is strikingly similar to that of yeast protein She2p; furthermore, like She2p, 4/1 protein exhibits RNA-binding activity, and mutational analysis has shown that the C-terminal CC domain is responsible for RNA binding. The 4/1 protein contains a nuclear export signal. Additional microscopy studies involving leptomycin and computer prediction suggest the presence of a nuclear localization signal as well
Tracking along-arc sediment inputs to the Aleutian arc using thallium isotopes.
Sediment transport from the subducted slab to the mantle wedge is an important process in understanding the chemical and physical conditions of arc magma generation. The Aleutian arc offers an excellent opportunity to study sediment transport processes because the subducted sediment flux varies systematically along strike (Kelemen et al., 2003) and many lavas exhibit unambiguous signatures of sediment addition to the sub-arc mantle (Morris et al., 1990). However, the exact sediment contribution to Aleutian lavas and how these sediments are transported from the slab to the surface are still debated. Thallium (Tl) isotope ratios have great potential to distinguish sediment fluxes in subduction zones because pelagic sediments and low-temperature altered oceanic crust are highly enriched in Tl and display heavy and light Tl isotope compositions, respectively, compared with the upper mantle and continental crust.
Here, we investigate the Tl isotope composition of lavas covering almost the entire Aleutian arc a well as sediments outboard of both the eastern (DSDP Sites 178 and 183) and central (ODP Hole 886C) portions of the arc. Sediment Tl isotope compositions change systematically from lighter in the Eastern to heavier in the Central Aleutians reflecting a larger proportion of pelagic sediments when distal from the North American continent. Lavas in the Eastern and Central Aleutians mirror this systematic change to heavier Tl isotope compositions to the west, which shows that the subducted sediment composition is directly translated to the arc east of Kanaga Island. Moreover, quantitative mixing models of Tl and Pb, Sr and Nd isotopes reveal that bulk sediment transfer of âŒ0.6â1.0% by weight in the Eastern Aleutians and âŒ0.2â0.6% by weight in the Central Aleutians can account for all four isotope systems. Bulk mixing models, however, require that fractionation of trace element ratios like Ce/Pb, Cs/Tl, and Sr/Nd in the Central and Eastern Aleutians occurs after the sediment component was mixed with the mantle wedge. Models of Sr and Nd isotopes that involve sediment melting require either high degrees of sediment melting (>50%), in which case trace element ratios like Ce/Pb, Cs/Tl, and Sr/Nd of Aleutian lavas need to be produced after mixing with the mantle, or significant fluid additions from the underlying oceanic crust with Sr and Nd isotope compositions indistinguishable from the mantle wedge as well as high Sr/Nd ratios similar to that of low (<20%) degree sediment melts.
Thallium isotope data from Western Aleutian lavas exhibit compositions slightly lighter than the upper mantle, which implies a negligible sediment flux at this location and probably involvement of low-temperature altered oceanic crust in the generation of these lavas. In general, the lightest Tl isotope compositions are observed for the highest Sr/Y ratios and most unradiogenic Sr and Pb isotope compositions, which is broadly consistent with derivation of these lavas via melting of eclogitized altered oceanic crust
An overview of harms associated with ÎČ-lactam antimicrobials: where do the carbapenems fit in?
The US Institute of Medicine's focus on patient safety has motivated hospital administrators to facilitate a culture of safety. As a result, subcommittees of the pharmacy and therapeutics committee have emerged in many hospitals to focus on adverse events and patient safety. Antimicrobial harms have gained the attention of practicing clinicians and hospital formulary committees, because they top the list of drugs that are associated with adverse events and because of certain serious harms that have ultimately led to the withdrawal of some antimicrobial agents. In the near future, several antimicrobials in the late phase of development will become available for clinical use (ceftobiprole, ceftaroline, and telavancin), and others (doripenem and dalbavancin) have recently joined the armamentarium. Because new antimicrobials will become part of the treatment armamentarium, it is important to discuss our current understanding of antimicrobial harms in general. Although not thought of as traditional adverse events, Clostridium difficile infection and development of resistance during therapy are adverse events that occur as a result of antimicrobial exposure and therefore are discussed. In addition, a distillation of our current understanding of ÎČ-lactam specific adverse events will be provided. Finally, new methods of administration are being evaluated that may influence peak concentration-related antimicrobial adverse events
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