419 research outputs found
Baryon kinetic energy loss in the color flux tube model
This article generalizes Schwinger's mechanism for particles production in
the arbitrary finite field volume. McLerran-Venugopolan(MV) model and iterative
solution of DGLAP equation in the double leading log approximation for small x
gluon distribution function were used to derive the new formula for initial
chromofield energy density. This initial chromofield energy is distributed
among color neutral clusters or strings of different length. This strings are
stretched by receding nucleus. From the proposed mechanism of string
fragmentation or color field decay based on exact solution of Dirac equation in
the different finite volume, the new formulae for esimated baryon kinetic
energy loss and rapidity spectrum of produced partons were derived.Comment: 13 pages, 2 figure
Towards the theory of hardness of materials
Recent studies showed that hardness, a complex property, can be calculated
using very simple approaches or even analytical formulae. These form the basis
for evaluating controversial experimental results (as we illustrate for
TiO2-cotunnite) and enable a systematic search for novel hard materials, for
instance, using global optimization algorithms (as we show on the example of
SiO2 polymorphs)
WLC22-4: Efficient request mechanism usage in IEEE 802.16
IEEE 802.16 protocols for metropolitan broadband wireless access systems have been standardized recently. According to the standard, a subscriber station can deliver bandwidth request messages to a base station by numerous methods. This paper provides both the simulation and analytical models for the investigation of specified random access method, which is compared with centralized polling and station- grouping mechanisms. Based on the assumptions of Bernoulli request arrival process and ideal channel conditions, the mean delay of a request transmission is evaluated for varying number of transmission opportunities and different arrival rates
Use of dynamical coupling for improved quantum state transfer
We propose a method to improve quantum state transfer in transmission lines.
The idea is to localize the information on the last qubit of a transmission
line, by dynamically varying the coupling constants between the first and the
last pair of qubits. The fidelity of state transfer is higher then in a chain
with fixed coupling constants. The effect is stable against small fluctuations
in the system parameters.Comment: 5 pages, 7 figure
Exotic behavior and crystal structures of calcium under pressure
Experimental studies established that calcium undergoes several
counterintuitive transitions under pressure: fcc \rightarrow bcc \rightarrow
simple cubic \rightarrow Ca-IV \rightarrow Ca-V, and becomes a good
superconductor in the simple cubic and higher-pressure phases. Here, using ab
initio evolutionary simulations, we explore the behavior of Ca under pressure
and find a number of new phases. Our structural sequence differs from the
traditional picture for Ca, but is similar to that for Sr. The {\beta}-tin
(I41/amd) structure, rather than simple cubic, is predicted to be the
theoretical ground state at 0 K and 33-71 GPa. This structure can be
represented as a large distortion of the simple cubic structure, just as the
higher-pressure phases stable between 71 and 134 GPa. The structure of Ca-V,
stable above 134 GPa, is a complex host-guest structure. According to our
calculations, the predicted phases are superconductors with Tc increasing under
pressure and reaching ~20 K at 120 GPa, in good agreement with experiment
Role of interference in quantum state transfer through spin chains
We examine the role that interference plays in quantum state transfer through
several types of finite spin chains, including chains with isotropic Heisenberg
interaction between nearest neighbors, chains with reduced coupling constants
to the spins at the end of the chain, and chains with anisotropic coupling
constants. We evaluate quantitatively both the interference corresponding to
the propagation of the entire chain, and the interference in the effective
propagation of the first and last spins only, treating the rest of the chain as
black box. We show that perfect quantum state transfer is possible without
quantum interference, and provide evidence that the spin chains examined
realize interference-free quantum state transfer to a good approximation.Comment: 10 figure
Laser and Diffusion Driven Optimal Discrimination of Similar Quantum Systems in Resonator
A method for solving the problem of efficient population transfer from the
ground to some excited state by available technical means (varying resonator
length) is proposed. We consider a mixture of similar quantum systems
distributed in a stationary gas flow in the resonator with variable resonator
length, which implements tailored laser field close to the optimal one. In
difference from previous works, in this work piezoelectric transducer (PZT; or
actuator) is used as mean of control to manipulate variable resonator length.
The external actions are optimized to selectively prepare different stationary
states of different species which are then separated using their diffusion with
rates which differ due to different masses. This system provides an example of
the general problem of optimizing states of distributed systems with stationary
gas flow with diffusion.Comment: 18 pages, 1 figur
Lie Symmetry Analysis for Cosserat Rods
We consider a subsystem of the Special Cosserat Theory of Rods and construct
an explicit form of its solution that depends on three arbitrary functions in
(s,t) and three arbitrary functions in t. Assuming analyticity of the arbitrary
functions in a domain under consideration, we prove that the obtained solution
is analytic and general. The Special Cosserat Theory of Rods describes the
dynamic equilibrium of 1-dimensional continua, i.e. slender structures like
fibers, by means of a system of partial differential equations.Comment: 12 Pages, 1 Figur
Baryon deceleration by strong chromofields in ultrarelativistic nuclear collisions
It is assumed that strong chromofields are generated at early stages of
ultrarelativistic heavy-ion collisions which give rise to a collective
deceleration of net baryons from colliding nuclei. We have solved classical
equations of motion for baryonic slabs under the action of a time-dependent
longitudinal chromoelectric field. It is demonstrated that the slab final
rapidities are rather sensitive to the strength and decay time of the
chromofield as well as to the back reaction of the produced partonic plasma.
The net-baryon rapidity loss of about 2 units, found for most central Au-Au
collisions at RHIC, can be explained by the action of chromofields with the
initial energy density of about 50 GeV/fm^3. Predictions for the baryon
stopping at the LHC are made.Comment: 10 pages in revtex, 3 eps figure
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