1,019 research outputs found
Stochastic integral characterizations of semi-selfdecomposable distributions and related Ornstein-Uhlenbeck type processes
In this paper, three topics on semi-selfdecomposable distributions are
studied. The first one is to characterize semi-selfdecomposable distributions
by stochastic integrals with respect to Levy processes. This characterization
defines a mapping from an infinitely divisible distribution with finite
log-moment to a semi-selfdecomposable distribution. The second one is to
introduce and study a Langevin type equation and the corresponding
Ornstein-Uhlenbecktype process whose limiting distribution is
semi-selfdecomposable. Also, semi-stationary Ornstein-Uhlenbeck type processes
with semi-selfdecomposable distributions are constructed. The third one is to
study the iteration of the mapping above. The iterated mapping is expressed as
a single mapping with a different integrand. Also, nested subclasses of the
class of semi-selfdecomposable distributions are considered, andit is shown
that the limit of these nested subclasses is the closure of the class of
semi-stable distributions
Quadrupole-scissors modes and nonlinear mode coupling in trapped two-component Bose-Einstein condensates
We theoretically investigate quadrupolar collective excitations in
two-component Bose-Einstein condensates and their nonlinear dynamics associated
with harmonic generation and mode coupling. Under the Thomas-Fermi
approximation and the quadratic polynomial ansatz for density fluctuations, the
linear analysis of the superfluid hydrodynamic equations predicts excitation
frequencies of three normal modes constituted from monopole and quadrupole
oscillations, and those of three scissors modes. We obtain analytically the
resonance conditions for the second harmonic generation in terms of the trap
aspect ratio and the strength of intercomponent interaction. The numerical
simulation of the coupled Gross-Pitaevskii equations vindicates the validity of
the analytical results and reveals the dynamics of the second harmonic
generation and nonlinear mode coupling that lead to nonlinear oscillations of
the condensate with damping and recurrence reminiscent of the Fermi-Pasta-Ulam
problem.Comment: 10 pages, 5 figures, revtex
Coalition structure generation in cooperative games with compact representations
This paper presents a new way of formalizing the coalition structure generation problem (CSG) so that we can apply constraint optimization techniques to it. Forming effective coalitions is a major research challenge in AI and multi-agent systems. CSG involves partitioning a set of agents into coalitions to maximize social surplus. Traditionally, the input of the CSG problem is a black-box function called a characteristic function, which takes a coalition as input and returns the value of the coalition. As a result, applying constraint optimization techniques to this problem has been infeasible. However, characteristic functions that appear in practice often can be represented concisely by a set of rules, rather than treating the function as a black box. Then we can solve the CSG problem more efficiently by directly applying constraint optimization techniques to this compact representation. We present new formalizations of the CSG problem by utilizing recently developed compact representation schemes for characteristic functions. We first characterize the complexity of CSG under these representation schemes. In this context, the complexity is driven more by the number of rules than by the number of agents. As an initial step toward developing efficient constraint optimization algorithms for solving the CSG problem, we also develop mixed integer programming formulations and show that an off-the-shelf optimization package can perform reasonably well
Single Nuclear Spin Cavity QED
We constructed a cavity QED system with a diamagnetic atom of 171Yb and
performed projective measurements on a single nuclear spin. Since Yb has no
electronic spin and has 1/2 nuclear spin, the procedure of spin polarization
and state verification can be dramatically simplified compared with the pseudo
spin-1/2 system. By enhancing the photon emission rate of the 1S0-3P1
transition, projective measurement is implemented for an atom with the
measurement time of T_meas = 30us. Unwanted spin flip as well as dark counts of
the detector lead to systematic error when the present technique is applied for
the determination of diagonal elements of an unknown spin state, which is
delta|beta|^2 < 2 * 10^-2. Fast measurement on a long-lived qubit is key to the
realization of large-scale one-way quantum computing.Comment: 5 pages, 5 figure
Polyamine depletion induces G1 and S phase arrest in human retinoblastoma Y79 cells
<p>Abstract</p> <p>Background</p> <p>Polyamines and ornithine decarboxylase (ODC) are essential for cell proliferation. DL-α-difluoromethylornithine (DFMO), a synthetic inhibitor of ODC, induces G<sub>1 </sub>arrest through dephosphorylation of retinoblastoma protein (pRb). The effect of DFMO on cell growth of pRb deficient cells is not known. We examined the effects of DFMO on pRb deficient human retinoblastoma Y79 cell proliferation and its molecular mechanism.</p> <p>Methods</p> <p>Using cultured Y79 cells, the effects of DFMO were studied by using polyamine analysis, western blot, gel shift, FACS and promoter analysis.</p> <p>Results</p> <p>DFMO suppressed the proliferation of Y79 cells, which accumulated in the G1 and S phase. DFMO induced p27/Kip1 protein expression, p107 dephosphorylation and accumulation of p107/E2F-4 complex in Y79 cells.</p> <p>Conclusion</p> <p>These results indicate that p107 dephosphorylation and accumulation of p107/E2F-4 complex is involved in G<sub>1 </sub>and S phase arrest of DFMO treated Y79 cells.</p
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