15,232 research outputs found
On the Evolution of Thermonuclear Flames on Large Scales
The thermonuclear explosion of a massive white dwarf in a Type Ia supernova
explosion is characterized by vastly disparate spatial and temporal scales. The
extreme dynamic range inherent to the problem prevents the use of direct
numerical simulation and forces modelers to resort to subgrid models to
describe physical processes taking place on unresolved scales.
We consider the evolution of a model thermonuclear flame in a constant
gravitational field on a periodic domain. The gravitational acceleration is
aligned with the overall direction of the flame propagation, making the flame
surface subject to the Rayleigh-Taylor instability. The flame evolution is
followed through an extended initial transient phase well into the steady-state
regime. The properties of the evolution of flame surface are examined. We
confirm the form of the governing equation of the evolution suggested by
Khokhlov (1995). The mechanism of vorticity production and the interaction
between vortices and the flame surface are discussed. The results of our
investigation provide the bases for revising and extending previous
subgrid-scale model.Comment: 15 pages, 22 postscript figures. Accepted for publication by the
Astrophysical Journal. High resolution figures can be found at
http://flash.uchicago.edu/~zhang/research_paper.htm
Resonator-Aided Single-Atom Detection on a Microfabricated Chip
We use an optical cavity to detect single atoms magnetically trapped on an
atom chip. We implement the detection using both fluorescence into the cavity
and reduction in cavity transmission due to the presence of atoms. In
fluorescence, we register 2.0(2) photon counts per atom, which allows us to
detect single atoms with 75% efficiency in 250 microseconds. In absorption, we
measure transmission attenuation of 3.3(3)% per atom, which allows us to count
small numbers of atoms with a resolution of about 1 atom.Comment: 4.1 pages, 5 figures, and submitted to Physical Review Letter
Fundamental Differences in Mechanical Behavior between Two Types of Crystals at the Nanoscale
We present differences in the mechanical behavior of nanoscale gold and molybdenum single crystals. A significant strength increase is observed as the size is reduced to 100 nm. Both nanocrystals exhibit discrete strain bursts during plastic deformation. We postulate that they arise from significant differences in the dislocation behavior. Dislocation starvation is the predominant mechanism of plasticity in nanoscale fcc crystals, while junction formation and hardening characterize bcc plasticity. A statistical analysis of strain bursts is performed as a function of size and compared with stochastic models
Production and mixing of scalar mesons in and decays
We briefly discuss how the chiral unitary approach in coupled channels and
symmetry can be used to describe the production of ,
and in the reaction,
recently measured by the BESIII collaboration. In this reaction a very strong
peak for the can be seen in the invariant mass, while
clear signals for the and appear in the one of
. Next, we show the predictions made with the same model for the
analogous decay , which could also be measured
experimentally. We discuss the differences of these two reactions which are
interesting to test the picture where these scalar mesons are dynamically
generated from the interaction of pairs of pseudoscalars. Furthermore, we
comment on a new recent work where the same model was used to study the
mixing in the and
reactions, showing that quantitative
agreement with the experimental measurement of this mixing, also performed by
BESIII, can be obtained, revealing interesting aspects of the dynamics of this
process and the importance of coupled channels.Comment: Talk presented at the XVII International Conference on Hadron
Spectroscopy and Structure - Hadron2017, 25-29 September, 2017, University of
Salamanca, Salamanca, Spain. arXiv admin note: substantial text overlap with
arXiv:1707.0722
Ray and wave chaos in asymmetric resonant optical cavities
Optical resonators are essential components of lasers and other
wavelength-sensitive optical devices. A resonator is characterized by a set of
modes, each with a resonant frequency omega and resonance width Delta
omega=1/tau, where tau is the lifetime of a photon in the mode. In a
cylindrical or spherical dielectric resonator, extremely long-lived resonances
are due to `whispering gallery' modes in which light circulates around the
perimeter trapped by total internal reflection. These resonators emit light
isotropically. Recently, a new category of asymmetric resonant cavities (ARCs)
has been proposed in which substantial shape deformation leads to partially
chaotic ray dynamics. This has been predicted to give rise to a universal,
frequency-independent broadening of the whispering-gallery resonances, and
highly anisotropic emission. Here we present solutions of the wave equation for
ARCs which confirm many aspects of the earlier ray-optics model, but also
reveal interesting frequency-dependent effects characteristic of quantum chaos.
For small deformations the lifetime is controlled by evanescent leakage, the
optical analogue of quantum tunneling. We find that the lifetime is much
shortened by a process known as `chaos-assisted tunneling'. In contrast, for
large deformations (~10%) some resonances are found to have longer lifetimes
than predicted by the ray chaos model due to `dynamical localization'.Comment: 4 pages RevTeX with 7 Postscript figure
Hepatocellular carcinoma: Review of disease and tumor biomarkers.
© The Author(s) 2016.Hepatocellular carcinoma (HCC) is a common malignancy and now the second commonest global cause of cancer death. HCC tumorigenesis is relatively silent and patients experience late symptomatic presentation. As the option for curative treatments is limited to early stage cancers, diagnosis in non-symptomatic individuals is crucial. International guidelines advise regular surveillance of high-risk populations but the current tools lack sufficient sensitivity for early stage tumors on the background of a cirrhotic nodular liver. A number of novel biomarkers have now been suggested in the literature, which may reinforce the current surveillance methods. In addition, recent metabonomic and proteomic discoveries have established specific metabolite expressions in HCC, according to Warburgs phenomenon of altered energy metabolism. With clinical validation, a simple and non-invasive test from the serum or urine may be performed to diagnose HCC, particularly benefiting low resource regions where the burden of HCC is highest
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