1,281 research outputs found
Aharonov-Bohm oscillations in a mesoscopic ring with a quantum dot
We present an analysis of the Aharonov-Bohm oscillations for a mesoscopic
ring with a quantum dot inserted in one of its arms. It is shown that
microreversibility demands that the phase of the Aharonov-Bohm oscillations
changes {\it abruptly} when a resonant level crosses the Fermi energy. We use
the Friedel sum rule to discuss the conservation of the parity of the
oscillations at different conductance peaks. Our predictions are illustrated
with the help of a simple one channel model that permits the variation of the
potential landscape along the ring.Comment: 11 pages, Revtex style, 3 figures under request. Submitted to Phys.
Rev. B (rapid communications
Linux kernel compaction through cold code swapping
There is a growing trend to use general-purpose operating systems like Linux in embedded systems. Previous research focused on using compaction and specialization techniques to adapt a general-purpose OS to the memory-constrained environment, presented by most, embedded systems. However, there is still room for improvement: it has been shown that even after application of the aforementioned techniques more than 50% of the kernel code remains unexecuted under normal system operation. We introduce a new technique that reduces the Linux kernel code memory footprint, through on-demand code loading of infrequently executed code, for systems that support virtual memory. In this paper, we describe our general approach, and we study code placement algorithms to minimize the performance impact of the code loading. A code, size reduction of 68% is achieved, with a 2.2% execution speedup of the system-mode execution time, for a case study based on the MediaBench II benchmark suite
Singular Liouville fields and spiky strings in \rr^{1,2} and SL(2,\rr)
The closed string dynamics in \rr^{1,2} and SL(2,\rr) is studied within
the scheme of Pohlmeyer reduction. In both spaces two different classes of
string surfaces are specified by the structure of the fundamental quadratic
forms. The first class in \rr^{1,2} is associated with the standard lightcone
gauge strings and the second class describes spiky strings and their conformal
deformations on the Virasoro coadjoint orbits. These orbits correspond to
singular Liouville fields with the monodromy matrixes . The first class
in SL(2,\rr) is parameterized by the Liouville fields with vanishing chiral
energy functional. Similarly to \rr^{1,2}, the second class in SL(2,\rr)
describes spiky strings, related to the vacuum configurations of the
SL(2,\rr)/U(1) coset model.Comment: 37 p. 6 fi
Searching for Radio Pulsars in 3EG Sources at Urumqi Observatory
Since mid-2005, a pulsar searching system has been operating at 18 cm on the
25-m radio telescope of Urumqi Observatory. Test observations on known pulsars
show that the system can perform the intended task. The prospect of using this
system to observe 3EG sources and other target searching tasks is discussed.Comment: a training project about MSc thesi
Higher spin fields and the problem of cosmological constant
The cosmological evolution of free massless vector or tensor (but not gauge)
fields minimally coupled to gravity is analyzed. It is shown that there are
some unstable solutions for these fields in De Sitter background. The back
reaction of the energy-momentum tensor of such solutions to the original
cosmological constant exactly cancels the latter and the expansion regime
changes from the exponential to the power law one. In contrast to the
adjustment mechanism realized by a scalar field the gravitational coupling
constant in this model is time-independent and the resulting cosmology may
resemble the realistic one.Comment: 15 pages, Latex twic
Spin Glass Behavior in RuSr2Gd1.5Ce0.5Cu2O10
The dynamics of the magnetic properties of polycrystalline
RuSr2Gd1.5Ce0.5Cu2O10 (Ru-1222) have been studied by ac susceptibility and dc
magnetization measurements, including relaxation and ageing studies. Ru-1222 is
a reported magneto-superconductor with Ru spins magnetic ordering at
temperatures near 100 K and superconductivity in Cu-O2 planes below Tc ~ 40 K.
The exact nature of Ru spins magnetic ordering is still debated and no
conclusion has been reached yet. In this work, a frequency-dependent cusp was
observed in ac susceptibility vs. T measurements, which is interpreted as a
spin glass transition. The change in the cusp position with frequency follows
the Vogel-Fulcher law, which is commonly accepted to describe a spin glass with
magnetically interacting clusters. Such interpretation is supported by
themoremanaent magnetization (TRM) measurements at T = 60 K. TRM relaxations
are well described by a stretched exponential relation, and present significant
ageing effects.Comment: 4 pages, 6 figures, submitted to Phys. Rev.
Collisional equilibrium, particle production and the inflationary universe
Particle production processes in the expanding universe are described within
a simple kinetic model. The equilibrium conditions for a Maxwell-Boltzmann gas
with variable particle number are investigated. We find that radiation and
nonrelativistic matter may be in equilibrium at the same temperature provided
the matter particles are created at a rate that is half the expansion rate.
Using the fact that the creation of particles is dynamically equivalent to a
nonvanishing bulk pressure we calculate the backreaction of this process on the
cosmological dynamics. It turns out that the `adiabatic' creation of massive
particles with an equilibrium distribution for the latter necessarily implies
power-law inflation. Exponential inflation in this context is shown to become
inconsistent with the second law of thermodynamics after a time interval of the
order of the Hubble time.Comment: 19 pages, latex, no figures, to appear in Phys.Rev.
Decaying D-branes and Moving Mirrors
We present an exact time-dependent solution to the effective D-brane
world-volume theory which describes an inhomogeneous decay of a brane-antibrane
system. We compute the quantum energy flux induced by the particle creation in
this inhomogeneous and time-dependent background. We find that this calculation
is essentially equivalent to that of the moving mirror system. In the initial
stage, the energy flux turns out to be thermal with the temperature given by
the inverse of the distance between the brane and the antibrane. Later it
changes its sign and becomes a negative energy flux. Our result may be relevant
for the (p)reheating process or/and the evolution of cosmic string network
after stringy brane inflation.Comment: 26pages, 4 figures, Latex, typos correcte
Curvature effects on the surface thickness and tension at the free interface of He systems
The thickness and the surface energy at the free interface of
superfluid He are studied. Results of calculations carried out by using
density functionals for cylindrical and spherical systems are presented in a
unified way, including a comparison with the behavior of planar slabs. It is
found that for large species is independent of the geometry. The obtained
values of are compared with prior theoretical results and experimental
data. Experimental data favor results evaluated by adopting finite range
approaches. The behavior of and exhibit overshoots
similar to that found previously for the central density, the trend of these
observables towards their asymptotic values is examined.Comment: 35 pages, TeX, 5 figures, definitive versio
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