794 research outputs found
Phi meson production in near threshold proton-nucleus collisions
The cross section for production of Phi mesons in proton-nucleus reactions is
calculated as a function of the target mass. The decay width of the Phi meson
is affected by the change of the masses of the Phi, K+ and K- mesons in the
medium. A strong attractive K- potential leads to a measurable change of the
behavior of the cross section as a function of of the target mass. Comparison
between the kaon and electron decay modes are made.Comment: 4 pages, 1figure, new figure, new reference
Calculating potentials of mean force and diffusion coefficients from nonequilibirum processes without Jarzynski's equality
In general, the direct application of the Jarzynski equality (JE) to
reconstruct potentials of mean force (PMFs) from a small number of
nonequilibrium unidirectional steered molecular dynamics (SMD) paths is
hindered by the lack of sampling of extremely rare paths with negative
dissipative work. Such trajectories, that transiently violate the second law,
are crucial for the validity of JE. As a solution to this daunting problem, we
propose a simple and efficient method, referred to as the FR method, for
calculating simultaneously both the PMF U(z) and the corresponding diffusion
coefficient D(z) along a reaction coordinate z for a classical many particle
system by employing a small number of fast SMD pullings in both forward (F) and
time reverse (R) directions, without invoking JE. By employing Crook's
transient fluctuation theorem (that is more general than JE) and the stiff
spring approximation, we show that: (i) the mean dissipative work W_d in the F
and R pullings are equal, (ii) both U(z) and W_d can be expressed in terms of
the easily calculable mean work of the F and R processes, and (iii) D(z) can be
expressed in terms of the slope of W_d. To test its viability, the FR method is
applied to determine U(z) and D(z) of single-file water molecules in
single-walled carbon nanotubes (SWNTs). The obtained U(z) is found to be in
very good agreement with the results from other PMF calculation methods, e.g.,
umbrella sampling. Finally, U(z) and D(z) are used as input in a stochastic
model, based on the Fokker-Planck equation, for describing water transport
through SWNTs on a mesoscopic time scale that in general is inaccessible to MD
simulations.Comment: ReVTeX4, 13 pages, 6 EPS figures, Submitted to Journal of Chemical
Physic
qBitcoin: A Peer-to-Peer Quantum Cash System
A decentralized online quantum cash system, called qBitcoin, is given. We
design the system which has great benefits of quantization in the following
sense. Firstly, quantum teleportation technology is used for coin transaction,
which prevents from the owner of the coin keeping the original coin data even
after sending the coin to another. This was a main problem in a classical
circuit and a blockchain was introduced to solve this issue. In qBitcoin, the
double-spending problem never happens and its security is guaranteed
theoretically by virtue of quantum information theory. Making a block is time
consuming and the system of qBitcoin is based on a quantum chain, instead of
blocks. Therefore a payment can be completed much faster than Bitcoin. Moreover
we employ quantum digital signature so that it naturally inherits properties of
peer-to-peer (P2P) cash system as originally proposed in Bitcoin.Comment: 11 pages, 2 figure
Size of Fireballs Created in High Energy Lead-Lead Collisions as Inferred from Coulomb Distortions of Pion Spectra
We compute the Coulomb effects produced by an expanding, highly charged
fireball on the momentum distribution of pions. We compare our results to data
on Au+Au at 11.6 A GeV from E866 at the BNL AGS and to data on Pb+Pb at 158 A
GeV from NA44 at the CERN SPS. We conclude that the distortion of the spectra
at low transverse momentum and mid-rapidity can be explained in both
experiments by the effect of the large amount of participating charge in the
central rapidity region. By adjusting the fireball expansion velocity to match
the average transverse momentum of protons, we find a best fit when the
fireball radius is about 10 fm, as determined by the moment when the pions
undergo their last scattering. This value is common to both the AGS and CERN
experiments.Comment: Enlarged discussion, new references added, includes new analysis of
pi-/pi+ at AGS energies. 12 pages 5 figures, uses LaTex and epsfi
Contribution of the nucleon-hyperon reaction channels to K production in proton-nucleus collisions
The cross sections for producing K mesons in nucleon-hyperon elementary
processes are estimated assuming one-pion exchange and using the experimentally
known pion-hyperon cross sections. The results are implemented in a transport
model which is applied to calculation of proton-nucleus collisions. In
significant difference to earlier estimates for heavy-ion collisions the
inclusion of the nucleon-hyperon cross section roughly doubles the K
production in near-threshold proton-nucleus collisions
Kinetic Monte Carlo and Cellular Particle Dynamics Simulations of Multicellular Systems
Computer modeling of multicellular systems has been a valuable tool for
interpreting and guiding in vitro experiments relevant to embryonic
morphogenesis, tumor growth, angiogenesis and, lately, structure formation
following the printing of cell aggregates as bioink particles. Computer
simulations based on Metropolis Monte Carlo (MMC) algorithms were successful in
explaining and predicting the resulting stationary structures (corresponding to
the lowest adhesion energy state). Here we present two alternatives to the MMC
approach for modeling cellular motion and self-assembly: (1) a kinetic Monte
Carlo (KMC), and (2) a cellular particle dynamics (CPD) method. Unlike MMC,
both KMC and CPD methods are capable of simulating the dynamics of the cellular
system in real time. In the KMC approach a transition rate is associated with
possible rearrangements of the cellular system, and the corresponding time
evolution is expressed in terms of these rates. In the CPD approach cells are
modeled as interacting cellular particles (CPs) and the time evolution of the
multicellular system is determined by integrating the equations of motion of
all CPs. The KMC and CPD methods are tested and compared by simulating two
experimentally well known phenomena: (1) cell-sorting within an aggregate
formed by two types of cells with different adhesivities, and (2) fusion of two
spherical aggregates of living cells.Comment: 11 pages, 7 figures; submitted to Phys Rev
Cavitation and bubble collapse in hot asymmetric nuclear matter
The dynamics of embryonic bubbles in overheated, viscous and non-Markovian
nuclear matter is studied. It is shown that the memory and the Fermi surface
distortions significantly affect the hinderance of bubble collapse and
determine a characteristic oscillations of the bubble radius. These
oscillations occur due to the additional elastic force induced by the memory
integral.Comment: Revtex file (10 pages) and 3 figure
Resonance Model of for Kaon Production in Heavy Ion Collisions
The elementary production cross sections
and are needed to describe
kaon production in heavy ion collisions. The reactions
were studied previously by a resonance model. The model can explain the
experimental data quite well \cite{tsu}. In this article, the total cross
sections at intermediate energies (from the kaon
production threshold to3 GeV of center-of-mass energy) are
calculated for the first time using the same resonance model. The resonances,
and for the reactions, and
, and for the reactions are taken into account coherently as
the intermediate states in the calculations. Also t-channel vector meson exchange is included. The results show that
exchange is neglegible for the
reactions, whereas this meson does not contribute to the reactions. Furthemore, the
contributions to kaon production in heavy ion collisions are not only
non-neglegible but also very different from the
reactions. An argument valid for cannot be extended to
reactions. Therefore, cross sections for including correctly the different isospins must beComment: ( Replaced with corrections of printing errors in the Table. ) 15
pages, Latex file with 4 figures, 1 figure is included in the text. A
compressed uuencode file for 3 figures is appended. (A figure file format was
changed.) Also available upon reques
Large scale quantum walks by means of optical fiber cavities
We demonstrate a platform for implementing quantum walks that overcomes many of the barriers associated with photonic implementations. We use coupled fiber-optic cavities to implement time-bin encoded walks in an integrated system. We show that this platform can achieve very low losses combined with high-fidelity operations, enabling an unprecedented large number of steps in a passive system, as required for scenarios with multiple walkers. Furthermore the platform is reconfigurable, enabling variation of the coin, and readily extends to multidimensional lattices. We demonstrate variation of the coin bias experimentally for three different values
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