3,143 research outputs found
A canonical ensemble approach to graded-response perceptrons
Perceptrons with graded input-output relations and a limited output precision
are studied within the Gardner-Derrida canonical ensemble approach. Soft non-
negative error measures are introduced allowing for extended retrieval
properties. In particular, the performance of these systems for a linear and
quadratic error measure, corresponding to the perceptron respectively the
adaline learning algorithm, is compared with the performance for a rigid error
measure, simply counting the number of errors. Replica-symmetry-breaking
effects are evaluated.Comment: 26 pages, 10 ps figure
Precise Charm- and Bottom-Quark Masses: Theoretical and Experimental Uncertainties
Recent theoretical and experimental improvements in the determination of
charm and bottom quark masses are discussed. A new and improved evaluation of
the contribution from the gluon condensate to the
charm mass determination and a detailed study of potential uncertainties in the
continuum cross section for production is presented, together with a
study of the parametric uncertainty from the -dependence of our
results. The final results, MeV and
MeV, represent, together with a closely related lattice
determination MeV, the presently most precise
determinations of these two fundamental Standard Model parameters. A critical
analysis of the theoretical and experimental uncertainties is presented.Comment: 12 pages, presented at Quarks~2010, 16th International Seminar of
High Energy Physics, Kolomna, Russia, June 6-12, 2010; v2: references adde
Measuring the Photon Helicity in Radiative B Decays
We propose a way of measuring the photon polarization in radiative B decays
into K resonance states decaying to K\pi\pi, which can test the Standard Model
and probe new physics. The photon polarization is shown to be measured by the
up-down asymmetry of the photon direction relative to the K\pi\pi decay plane
in the K resonance rest frame. The integrated asymmetry in K_1(1400)\to
K\pi\pi, calculated to be 0.34\pm 0.05 in the Standard Model, is measurable at
currently operating B factories.Comment: 4 pages, final version to appear in Physical Review Letter
Laser pump X ray probe experiments with electrons ejected from a Cu 111 target space charge acceleration
A comprehensive investigation of the emission characteristics for electrons induced by X rays of a few hundred eV at grazing incidence angles on an atomically clean Cu 111 sample during laser excitation is presented. Electron energy spectra due to intense infrared laser irradiation are investigated at the BESSY II slicing facility. Furthermore, the influence of the corresponding high degree of target excitation high peak current of photoemission on the properties of Auger and photoelectrons liberated by a probe X ray beam is investigated in time resolved pump and probe measurements. Strong electron energy shifts have been found and assigned to space charge acceleration. The variation of the shift with laser power and electron energy is investigated and discussed on the basis of experimental as well as new theoretical result
Nuclear suppression of heavy quark production at forward rapidities in relativistic heavy ion collisions
We calculate nuclear suppression of heavy quarks produced from the
initial fusion of partons in nucleus-nucleus collisions at RHIC and LHC
energies. We take the shadowing as well as the energy loss suffered by them
while passing through Quark Gluon Plasma into account. We obtain results for
charm and bottom quarks at several rapidities using different mechanisms for
energy loss, to see if we can distinguish between them.Comment: 21 pages including 13 figures. To appear in J. Phys.
Resolution and enhancement in nanoantenna-based fluorescence microscopy
Single gold nanoparticles can act as nanoantennas for enhancing the
fluorescence of emitters in their near-fields. Here we present experimental and
theoretical studies of scanning antenna-based fluorescence microscopy as a
function of the diameter of the gold nanoparticle. We examine the interplay
between fluorescence enhancement and spatial resolution and discuss the
requirements for deciphering single molecules in a dense sample. Resolutions
better than 20 nm and fluorescence enhancement up to 30 times are demonstrated
experimentally. By accounting for the tip shaft and the sample interface in
finite-difference time-domain calculations, we explain why the measured
fluorescence enhancements are higher in the presence of an interface than the
values predicted for a homogeneous environment.Comment: 10 pages, 3 figures. accepted for publication in Nano Letter
The path-integral analysis of an associative memory model storing an infinite number of finite limit cycles
It is shown that an exact solution of the transient dynamics of an
associative memory model storing an infinite number of limit cycles with l
finite steps by means of the path-integral analysis. Assuming the Maxwell
construction ansatz, we have succeeded in deriving the stationary state
equations of the order parameters from the macroscopic recursive equations with
respect to the finite-step sequence processing model which has retarded
self-interactions. We have also derived the stationary state equations by means
of the signal-to-noise analysis (SCSNA). The signal-to-noise analysis must
assume that crosstalk noise of an input to spins obeys a Gaussian distribution.
On the other hand, the path-integral method does not require such a Gaussian
approximation of crosstalk noise. We have found that both the signal-to-noise
analysis and the path-integral analysis give the completely same result with
respect to the stationary state in the case where the dynamics is
deterministic, when we assume the Maxwell construction ansatz.
We have shown the dependence of storage capacity (alpha_c) on the number of
patterns per one limit cycle (l). Storage capacity monotonously increases with
the number of steps, and converges to alpha_c=0.269 at l ~= 10. The original
properties of the finite-step sequence processing model appear as long as the
number of steps of the limit cycle has order l=O(1).Comment: 24 pages, 3 figure
Long-range Energy Transfer and Ionization in Extended Quantum Systems Driven by Ultrashort Spatially Shaped Laser Pulses
The processes of ionization and energy transfer in a quantum system composed
of two distant H atoms with an initial internuclear separation of 100 atomic
units (5.29 nm) have been studied by the numerical solution of the
time-dependent Schr\"odinger equation beyond the Born-Oppenheimer
approximation. Thereby it has been assumed that only one of the two H atoms was
excited by temporally and spatially shaped laser pulses at various laser
carrier frequencies. The quantum dynamics of the extended H-H system, which was
taken to be initially either in an unentangled or an entangled ground state,
has been explored within a linear three-dimensional model, including two z
coordinates of the electrons and the internuclear distance R. An efficient
energy transfer from the laser-excited H atom (atom A) to the other H atom
(atom B) and the ionization of the latter have been found. It has been shown
that the physical mechanisms of the energy transfer as well as of the
ionization of atom B are the Coulomb attraction of the laser driven electron of
atom A by the proton of atom B and a short-range Coulomb repulsion of the two
electrons when their wave functions strongly overlap in the domain of atom B.Comment: 11 pages, 7 figure
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