20,191 research outputs found
Compressive sampling for accelerometer signals in structural health monitoring
In structural health monitoring (SHM) of civil structures, data compression is often needed to reduce the cost of data transfer and storage, because of the large volumes of sensor data generated from the monitoring system. The traditional framework for data compression is to first sample the full signal and, then to compress it. Recently, a new data compression method named compressive sampling (CS) that can acquire the data directly in compressed form by using special sensors has been presented. In this article, the potential of CS for data compression of vibration data is investigated using simulation of the CS sensor algorithm. For reconstruction of the signal, both wavelet and Fourier orthogonal bases are examined. The acceleration data collected from the SHM system of Shandong Binzhou Yellow River Highway Bridge is used to analyze the data compression ability of CS. For comparison, both the wavelet-based and Huffman coding methods are employed to compress the data. The results show that the values of compression ratios achieved using CS are not high, because the vibration data used in SHM of civil structures are not naturally sparse in the chosen bases
Triton-3He relative and differential flows and the high density behavior of nuclear symmetry energy
Using a transport model coupled with a phase-space coalescence after-burner
we study the triton-3He relative and differential transverse flows in
semi-central 132Sn+124Sn reactions at a beam energy of 400 MeV/nucleon. We find
that the triton-3He pairs carry interesting information about the density
dependence of the nuclear symmetry energy. The t-3He relative flow can be used
as a particularly powerful probe of the high-density behavior of the nuclear
symmetry energy.Comment: 6 pages, 2 figures, Proceeding of The International Workshop on
Nuclear Dynamics in Heavy-Ion Reactions and the Symmetry Energ
Ultrafast initialization and QND-readout of a spin qubit via control of nanodot-vacuum coupling
Ultrafast initialization enables fault-tolerant processing of quantum
information while QND readout enables scalable quantum computation. By
spatially assembling photon resonators and wave-guides around an n-doped
nanodot and by temporally designing optical pump pulses, an efficient quantum
pathway can be established from an electron spin to a charged exciton to a
cavity photon and finally to a flying photon in the waveguide. Such control of
vacuum-nanodot coupling can be exploited for ultrafast initialization and QND
readout of the spin, which are particularly compatible with the optically
driven spin quantum computers.Comment: 4 pages 3 figure
Quantum control of electron--phonon scatterings in artificial atoms
The phonon-induced dephasing dynamics in optically excited semiconductor
quantum dots is studied within the frameworks of the independent Boson model
and optimal control. We show that appropriate tailoring of laser pulses allows
a complete control of the optical excitation despite the phonon dephasing, a
finding in marked contrast to other environment couplings.Comment: to appear in Phys. Rev. Let
Actomyosin-based Self-organization of cell internalization during C. elegans gastrulation
Background: Gastrulation is a key transition in embryogenesis; it requires self-organized cellular coordination, which has to be both robust to allow efficient development and plastic to provide adaptability. Despite the conservation of gastrulation as a key event in Metazoan embryogenesis, the morphogenetic mechanisms of self-organization (how global order or coordination can arise from local interactions) are poorly understood.
Results: We report a modular structure of cell internalization in Caenorhabditis elegans gastrulation that reveals mechanisms of self-organization. Cells that internalize during gastrulation show apical contractile flows, which are correlated with centripetal extensions from surrounding cells. These extensions converge to seal over the internalizing cells in the form of rosettes. This process represents a distinct mode of monolayer remodeling, with gradual extrusion of the internalizing cells and simultaneous tissue closure without an actin purse-string. We further report that this self-organizing module can adapt to severe topological alterations, providing evidence of scalability and plasticity of actomyosin-based patterning. Finally, we show that globally, the surface cell layer undergoes coplanar division to thin out and spread over the internalizing mass, which resembles epiboly.
Conclusions: The combination of coplanar division-based spreading and recurrent local modules for piecemeal internalization constitutes a system-level solution of gradual volume rearrangement under spatial constraint. Our results suggest that the mode of C. elegans gastrulation can be unified with the general notions of monolayer remodeling and with distinct cellular mechanisms of actomyosin-based morphogenesis
Theory of control of spin/photon interface for quantum networks
A cavity coupling a charged nanodot and a fiber can act as a quantum
interface, through which a stationary spin qubit and a flying photon qubit can
be inter-converted via cavity-assisted Raman process. This Raman process can be
controlled to generate or annihilate an arbitrarily shaped single-photon
wavepacket by pulse-shaping the controlling laser field. This quantum interface
forms the basis for many essential functions of a quantum network, including
sending, receiving, transferring, swapping, and entangling qubits at
distributed quantum nodes as well as a deterministic source and an efficient
detector of a single photon wavepacket with arbitrarily specified shape and
average photon number. Numerical study of noise effects on the operations shows
high fidelity.Comment: 4 pages, 2 figure
Constraining the Skyrme effective interactions and the neutron skin thickness of nuclei using isospin diffusion data from heavy ion collisions
Recent analysis of the isospin diffusion data from heavy-ion collisions based
on an isospin- and momentum-dependent transport model with in-medium
nucleon-nucleon cross sections has led to the extraction of a value of MeV for the slope of the nuclear symmetry energy at saturation density.
This imposes stringent constraints on both the parameters in the Skyrme
effective interactions and the neutron skin thickness of heavy nuclei. Among
the 21 sets of Skyrme interactions commonly used in nuclear structure studies,
the 4 sets SIV, SV, G, and R are found to give values
that are consistent with the extracted one. Further study on the correlations
between the thickness of the neutron skin in finite nuclei and the nuclear
matter symmetry energy in the Skyrme Hartree-Fock approach leads to predicted
thickness of the neutron skin of fm for Pb, fm for Sn, and fm for Sn.Comment: 10 pages, 4 figures, 1 Table, Talk given at 1) International
Conference on Nuclear Structure Physics, Shanghai, 12-17 June, 2006; 2) 11th
China National Nuclear Structure Physics Conference, Changchun, Jilin, 13-18
July, 200
Computing the ground state solution of Bose-Einstein condensates by a normalized gradient flow
In this paper, we prove the energy diminishing of a normalized gradient flow
which provides a mathematical justification of the imaginary time method used
in physical literatures to compute the ground state solution of Bose-Einstein
condensates (BEC). We also investigate the energy diminishing property for the
discretization of the normalized gradient flow. Two numerical methods are
proposed for such discretizations: one is the backward Euler centered finite
difference (BEFD), the other one is an explicit time-splitting sine-spectral
(TSSP) method. Energy diminishing for BEFD and TSSP for linear case, and
monotonicity for BEFD for both linear and nonlinear cases are proven.
Comparison between the two methods and existing methods, e.g. Crank-Nicolson
finite difference (CNFD) or forward Euler finite difference (FEFD), shows that
BEFD and TSSP are much better in terms of preserving energy diminishing
property of the normalized gradient flow. Numerical results in 1d, 2d and 3d
with magnetic trap confinement potential, as well as a potential of a stirrer
corresponding to a far-blue detuned Gaussian laser beam are reported to
demonstrate the effectiveness of BEFD and TSSP methods. Furthermore we observe
that the normalized gradient flow can also be applied directly to compute the
first excited state solution in BEC when the initial data is chosen as an odd
function.Comment: 28 pages, 6 figure
Improved Simulation of the Mass Charging for ASTROD I
The electrostatic charging of the test mass in ASTROD I (Astrodynamical Space
Test of Relativity using Optical Devices I) mission can affect the quality of
the science data as a result of spurious Coulomb and Lorentz forces. To
estimate the size of the resultant disturbances, credible predictions of
charging rates and the charging noise are required. Using the GEANT4 software
toolkit, we present a detailed Monte Carlo simulation of the ASTROD I test mass
charging due to exposure of the spacecraft to galactic cosmic-ray (GCR) protons
and alpha particles (3He, 4He) in the space environment. A positive charging
rate of 33.3 e+/s at solar minimum is obtained. This figure reduces by 50% at
solar maximum. Based on this charging rate and factoring in the contribution of
minor cosmic-ray components, we calculate the acceleration noise and stiffness
associated with charging. We conclude that the acceleration noise arising from
Coulomb and Lorentz effects are well below the ASTROD I acceleration noise
limit at 0.1 mHz both at solar minimum and maximum. The coherent Fourier
components due to charging are investigated, it needs to be studied carefully
in order to ensure that these do not compromise the quality of science data in
the ASTROD I mission.Comment: 20 pages, 14 figures, submitted to International Journal of Modern
Physics
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