719 research outputs found
A tunable radiation source by coupling laser-plasma-generated electrons to a periodic structure
Near-infrared radiation around 1000 nm generated from the interaction of a high-density MeV electron beam, obtained by impinging an intense ultrashort laser pulse on a solid target, with a metal grating is observed experimentally. Theoretical modeling and particle-in-cell simulation suggest that the radiation is caused by the Smith-Purcell mechanism. The results here indicate that tunable terahertz radiation with tens GV=m field strength can be achieved by using appropriate grating parameter
A recent rebuilding of most spirals ?
Re-examination of the properties of distant galaxies leads to the evidence
that most present-day spirals have built up half of their stellar masses during
the last 8 Gyr, mostly during several intense phases of star formation during
which they took the appearance of luminous infrared galaxies (LIRGs). Distant
galaxy morphologies encompass all of the expected stages of galaxy merging,
central core formation and disk growth, while their cores are much bluer than
those of present-day bulges. We have tested a spiral rebuilding scenario, for
which 75+/-25% of spirals have experienced their last major merger event less
than 8 Gyr ago. It accounts for the simultaneous decreases, during that period,
of the cosmic star formation density, of the merger rate, of the number
densities of LIRGs and of compact galaxies, while the densities of ellipticals
and large spirals are essentially unaffected.Comment: (1) GEPI, Obs. Meudon, France ;(2)Max-Planck Institut fuer
Astronomie, Germany (3) National Astronomical Observatories, CAS, China. Five
pages, 1 figure. To be published in "Starbursts: From 30 Doradus to Lyman
Break Galaxies", held in Cambridge, ed. R. de Grijs & R. M. Gonzalez Delgado
(Dordrecht: Kluwer
Computational Fluid Dynamics Simulations at Micro-Scale Stenosis for Microfluidic Thrombosis Model Characterization
Platelet aggregation plays a central role in pathological thrombosis, preventing healthy physiological blood flow within the circulatory system. For decades, it was believed that platelet aggregation was primarily driven by soluble agonists such as thrombin, adenosine diphosphate and thromboxane A2. However, recent experimental findings have unveiled an intriguing but complementary biomechanical mechanism—the shear rate gradients generated from flow disturbance occurring at sites of blood vessel narrowing, otherwise known as stenosis, may rapidly trigger platelet recruitment and subsequent aggregation. In our Nature Materials 2019 paper [1], we employed microfluidic devices which incorporated micro-scale stenoses to elucidate the molecular insights underlying the prothrombotic effect of blood flow disturbance. Nevertheless, the rheological mechanisms associated with this stenotic microfluidic device are poorly characterized. To this end, we developed a computational fluid dynamics (CFD) simulation approach to systematically analyze the hemodynamic influence of bulk flow mechanics and flow medium. Grid sensitivity studies were performed to ensure accurate and reliable results. Interestingly, the peak shear rate was significantly reduced with the device thickness, suggesting that fabrication of microfluidic devices should retain thicknesses greater than 50 µm to avoid unexpected hemodynamic aberration, despite thicker devices raising the cost of materials and processing time of photolithography. Overall, as many groups in the field have designed microfluidic devices to recapitulate the effect of shear rate gradients and investigate platelet aggregation, our numerical simulation study serves as a guideline for rigorous design and fabrication of microfluidic thrombosis models
A characterization of Schauder frames which are near-Schauder bases
A basic problem of interest in connection with the study of Schauder frames
in Banach spaces is that of characterizing those Schauder frames which can
essentially be regarded as Schauder bases. In this paper, we give a solution to
this problem using the notion of the minimal-associated sequence spaces and the
minimal-associated reconstruction operators for Schauder frames. We prove that
a Schauder frame is a near-Schauder basis if and only if the kernel of the
minimal-associated reconstruction operator contains no copy of . In
particular, a Schauder frame of a Banach space with no copy of is a
near-Schauder basis if and only if the minimal-associated sequence space
contains no copy of . In these cases, the minimal-associated
reconstruction operator has a finite dimensional kernel and the dimension of
the kernel is exactly the excess of the near-Schauder basis. Using these
results, we make related applications on Besselian frames and near-Riesz bases.Comment: 12 page
Morphologies of AGN host galaxies using HST/ACS in the CDFS-GOODS field
Using HST/ACS images in four bands F435W, F606W, F775W and F850LP, we
identify optical counterparts to the X-ray sources in the Chandra Deep Field
South in the GOODS South field. A detailed study has been made of these sources
to study their morphological types. We use methods like decomposition of galaxy
luminosity profiles, color maps and visual inspection of 192 galaxies which are
identified as possible optical counterparts of Chandra X-ray sources in the
CDFS-GOODS field. We find that most moderate luminosity AGN hosts are bulge
dominated in the redshift range (z \approx 0.4-1.3), but not
merging/interacting galaxies. This implies probable fueling of the moderate
luminosity AGN by mechanisms other than those merger driven.Comment: pdflatex, accepted in ApSS. revisions in tex
Impurity and spin effects on the magneto-spectroscopy of a THz-modulated nanostructure
We present a grid-free DFT model appropriate to explore the time evolution of
electronic states in a semiconductor nanostructure. The model can be used to
investigate both the linear and the nonlinear response of the system to an
external short-time perturbation in the THz regime. We use the model to study
the effects of impurities on the magneto-spectroscopy of a two-dimensional
electron gas in a nanostructure excited by an intense THz radiation. We do
observe a reduction in the binding energy of the impurity with increasing
excitation strength, and at a finite magnetic field we find a slow onset of
collective spin-oscillations that can be made to vanish with a stronger
excitation.Comment: LaTeX,10 pages with 11 embedded postscript figure
A new ghost cell/level set method for moving boundary problems:application to tumor growth
In this paper, we present a ghost cell/level set method for the evolution of interfaces whose normal velocity depend upon the solutions of linear and nonlinear quasi-steady reaction-diffusion equations with curvature-dependent boundary conditions. Our technique includes a ghost cell method that accurately discretizes normal derivative jump boundary conditions without smearing jumps in the tangential derivative; a new iterative method for solving linear and nonlinear quasi-steady reaction-diffusion equations; an adaptive discretization to compute the curvature and normal vectors; and a new discrete approximation to the Heaviside function. We present numerical examples that demonstrate better than 1.5-order convergence for problems where traditional ghost cell methods either fail to converge or attain at best sub-linear accuracy. We apply our techniques to a model of tumor growth in complex, heterogeneous tissues that consists of a nonlinear nutrient equation and a pressure equation with geometry-dependent jump boundary conditions. We simulate the growth of glioblastoma (an aggressive brain tumor) into a large, 1 cm square of brain tissue that includes heterogeneous nutrient delivery and varied biomechanical characteristics (white matter, gray matter, cerebrospinal fluid, and bone), and we observe growth morphologies that are highly dependent upon the variations of the tissue characteristics—an effect observed in real tumor growth
LRRK2 A419V is not associated with Parkinson's disease in different Chinese populations
10.1371/journal.pone.0036123PLoS ONE77
Measurements of the observed cross sections for exclusive light hadron production in e^+e^- annihilation at \sqrt{s}= 3.773 and 3.650 GeV
By analyzing the data sets of 17.3 pb taken at GeV
and 6.5 pb taken at GeV with the BESII detector at the
BEPC collider, we have measured the observed cross sections for 12 exclusive
light hadron final states produced in annihilation at the two energy
points. We have also set the upper limits on the observed cross sections and
the branching fractions for decay to these final states at 90%
C.L.Comment: 8 pages, 5 figur
Search for the Rare Decays J/Psi --> Ds- e+ nu_e, J/Psi --> D- e+ nu_e, and J/Psi --> D0bar e+ e-
We report on a search for the decays J/Psi --> Ds- e+ nu_e + c.c., J/Psi -->
D- e+ nu_e + c.c., and J/Psi --> D0bar e+ e- + c.c. in a sample of 5.8 * 10^7
J/Psi events collected with the BESII detector at the BEPC. No excess of signal
above background is observed, and 90% confidence level upper limits on the
branching fractions are set: B(J/Psi --> Ds- e+ nu_e + c.c.)<4.8*10^-5, B(J/Psi
--> D- e+ nu_e + c.c.) D0bar e+ e- + c.c.)<1.1*10^-5Comment: 10 pages, 4 figure
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