270,140 research outputs found
Expansion Aspect of Color Transparency on the Lattice
The opportunity to observe color transparency (CT) is determined by how
rapidly a small-sized hadronic wave packet expands. Here we use SU(2) lattice
gauge theory with Wilson fermions in the quenched approximation to investigate
the expansion. The wave packet is modeled by a point hadronic source, often
used as an interpolating field in lattice calculations. The procedure is to
determine the Euclidean time (t), pion channel, Bethe-Salpeter amplitude
, and then evaluate . This quantity represents the soft interaction of a small-sized
wave packet with a pion. The time dependence of is fit as a
superposition of three states, which is found sufficient to reproduce a reduced
size wave packet. Using this superposition allows us to make the analytic
continuation required to study the wave packet expansion in real time. We find
that the matrix elements of the soft interaction between the excited
and ground state decrease rapidly with the energy of the excited state.Comment: 19 pages, latex, 4 figure
Spread of wave packets in disordered hierarchical lattices
We consider the spreading of the wave packet in the generalized
Rosenzweig-Porter random matrix ensemble in the region of non-ergodic extended
states . We show that despite non-trivial fractal dimensions characterize wave function statistics in this region, the
wave packet spreading is governed by
the "diffusion" exponent outside the ballistic regime
and in the ballistic regime for
. This demonstrates that the multifractality exhibits itself only
in {\it local} quantities like the wave packet survival probability but not in
the large-distance spreading of the wave packet.Comment: Accepted in EP
Wave packet dynamics in a monolayer graphene
The dynamics of charge particles described by Gaussian wave packet in
monolayer graphene is studied analytically and numerically. We demonstrate that
the shape of wave packet at arbitrary time depends on correlation between the
initial electron amplitudes and on the
sublattices and correspondingly (i.e. pseudospin polarization). For the
transverse pseudospin polarization the motion of the center of wave packet
occurs in the direction perpendicular to the average momentum . Moreover, in this case the initial wave packet splits
into two parts moving with opposite velocities along . If the
initial direction of pseudospin coincides with average momentum the splitting
is absent and the center of wave packet is displaced at along the same
direction. The results of our calculations show that all types of motion
experience {\it zitterbewegung}. Besides, depending on initial polarization the
velocity of the packet center may have the constant component ,
where is the Fermi velocity and is a function of
the parameter ( is the initial width of wave packet). As a result,
the direction of the packet motion is determined not only by the orientation of
the average momentum, but mainly by the phase difference between the up- and
low- components of the wave functions. Similar peculiarities of the dynamics of
2D electron wave packet connected with initial spin polarization should take
place in the semiconductor quantum well under the influence of the Rashba
spin-orbit coupling.Comment: 7 pages, 8 figures, to be published in Phys. Rev.
Wave-packet dynamics at the mobility edge in two- and three-dimensional systems
We study the time evolution of wave packets at the mobility edge of
disordered non-interacting electrons in two and three spatial dimensions. The
results of numerical calculations are found to agree with the predictions of
scaling theory. In particular, we find that the -th moment of the
probability density scales like in dimensions. The
return probability scales like , with the generalized
dimension of the participation ratio . For long times and short distances
the probability density of the wave packet shows power law scaling
. The numerical calculations were performed
on network models defined by a unitary time evolution operator providing an
efficient model for the study of the wave packet dynamics.Comment: 4 pages, RevTeX, 4 figures included, published versio
Buffer Overflow Management with Class Segregation
We consider a new model for buffer management of network switches with
Quality of Service (QoS) requirements. A stream of packets, each attributed
with a value representing its Class of Service (CoS), arrives over time at a
network switch and demands a further transmission. The switch is equipped with
multiple queues of limited capacities, where each queue stores packets of one
value only. The objective is to maximize the total value of the transmitted
packets (i.e., the weighted throughput).
We analyze a natural greedy algorithm, GREEDY, which sends in each time step
a packet with the greatest value. For general packet values , we show that GREEDY is -competitive, where . Furthermore, we show a lower bound of on the competitiveness of any deterministic online algorithm.
In the special case of two packet values (1 and ), GREEDY is shown
to be optimal with a competitive ratio of
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