721 research outputs found
Remedy for the fermion sign problem in the diffusion Monte Carlo method for few fermions with antisymmetric diffusion process
We suggest an exact approach to help remedy the fermion sign problem in diffusion quantum Monte Carlo simulations. The approach is based on an explicit suppression of symmetric modes in the Schrodinger equation by means of a modified stochastic diffusion process (antisymmetric diffusion process). We introduce this algorithm and illustrate it on potential models in one dimension (1D) and show that there it solves the fermion sign problem exactly and converges to the lowest antisymmetric state of the system. Then, we discuss extensions of this approach to many-dimensional systems on examples of quantum oscillator in 2D-20D and a toy model of three and four fermions on harmonic strings in 2D and 3D. We show that in all these cases our method shows a performance comparable to that of a fixed-node approximation with an exact node
Scattering of plasmons at the intersection of two metallic nanotubes: Implications for tunnelling
We study theoretically the plasmon scattering at the intersection of two
metallic carbon nanotubes. We demonstrate that for a small angle of crossing,
, the transmission coefficient is an oscillatory function of
, where is the interaction parameter of the Luttinger
liquid in an individual nanotube. We calculate the tunnel density of states,
, as a function of energy, , and distance, , from the
intersection. In contrast to a single nanotube, we find that, in the geometry
of crossed nanotubes, conventional "rapid" oscillations in due
to the plasmon scattering acquire an aperiodic "slow-breathing" envelope which
has nodes.Comment: 4 pages, 2 figures (revised version
Higher Fock State Contributions to the Generalized Parton Distribution of Pion
We discuss the higher Fock state (q \bar q g) contributions to the nonzero
value of the pion GPD at the crossover point x = zeta between the DGLAP and
ERBL regions. Using the phenomenological light-front constituent quark model,
we confirm that the higher Fock state contributions indeed give a nonzero value
of the GPD at the crossover point. Iterating the light-front quark model wave
function of the lowest q \bar q Fock state with the Bethe-Salpeter kernel
corresponding to the one-gluon-exchange, we include all possible time-ordered q
\bar q g Fock state contributions and obtain the pion GPD satisfying necessary
sum rules and continuity conditions.Comment: References adde
Using of parallel computing for the quasi-static analysis of microstrip filters topology
An algorithm for calculation of multiconductor microstrip devices implemented on a substrate with slots in the ground plane using a quasistatic
methods has been developed. Analysis of techniques for constructing a parallel algorithm for finding the inverse matrices for quasi-static calculation of microstrip filters was carried ou
Restoring the equivalence between the light-front and manifestly covariant formalisms
We discuss a treacherous point in light-front dynamics (LFD) which should be taken into account to restore complete equivalence with the manifestly covariant formalism. We present examples that require an inclusion of the arc contribution in the light-front energy contour integration in order to achieve the equivalence between the LFD result and the manifestly covariant result
Fast non-negative deconvolution for spike train inference from population calcium imaging
Calcium imaging for observing spiking activity from large populations of
neurons are quickly gaining popularity. While the raw data are fluorescence
movies, the underlying spike trains are of interest. This work presents a fast
non-negative deconvolution filter to infer the approximately most likely spike
train for each neuron, given the fluorescence observations. This algorithm
outperforms optimal linear deconvolution (Wiener filtering) on both simulated
and biological data. The performance gains come from restricting the inferred
spike trains to be positive (using an interior-point method), unlike the Wiener
filter. The algorithm is fast enough that even when imaging over 100 neurons,
inference can be performed on the set of all observed traces faster than
real-time. Performing optimal spatial filtering on the images further refines
the estimates. Importantly, all the parameters required to perform the
inference can be estimated using only the fluorescence data, obviating the need
to perform joint electrophysiological and imaging calibration experiments.Comment: 22 pages, 10 figure
Coulomb drag by small momentum transfer between quantum wires
We demonstrate that in a wide range of temperatures Coulomb drag between two
weakly coupled quantum wires is dominated by processes with a small interwire
momentum transfer. Such processes, not accounted for in the conventional
Luttinger liquid theory, cause drag only because the electron dispersion
relation is not linear. The corresponding contribution to the drag resistance
scales with temperature as T^2 if the wires are identical, and as T^5 if the
wires are different
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