603 research outputs found
Modelling Load Balancing and Carrier Aggregation in Mobile Networks
In this paper, we study the performance of multicarrier mobile networks.
Specifically, we analyze the flow-level performance of two inter-carrier load
balancing schemes and the gain engendered by Carrier Aggregation (CA). CA is
one of the most important features of HSPA+ and LTE-A networks; it allows
devices to be served simultaneously by several carriers. We propose two load
balancing schemes, namely Join the Fastest Queue (JFQ) and Volume Balancing
(VB), that allow the traffic of CA and non-CA users to be distributed over the
aggregated carriers. We then evaluate the performance of these schemes by means
of analytical modeling. We show that the proposed schemes achieve quasi-ideal
load balancing. We also investigate the impact of mixing traffic of CA and
non-CA users in the same cell and show that performance is practically
insensitive to the traffic mix.Comment: 8 pages, 6 figures, submitted to WiOpt201
Possible triplet superconductivity in MOSFETs
A theory that predicts a spin-triplet, even-parity superconducting ground
state in two-dimensional electron systems is re-analyzed in the light of recent
experiments showing a possible insulator-to-conductor transition in such
systems. It is shown that the observations are consistent with such an exotic
superconductivity mechanism, and predictions are made for experiments that
would further corroborate or refute this proposal.Comment: 4 pp., REVTeX, psfig, 1 eps fig, final version as publishe
Universality at integer quantum Hall transitions
We report in this paper results of experimental and theoretical studies of
transitions between different integer quantum Hall phases, as well as
transition between the insulating phase and quantum Hall phases at high
magnetic fields. We focus mainly on universal properties of the transitions. We
demonstrate that properly defined conductivity tensor is universal at the
transitions. We also present numerical results of a non-interacting electron
model, which suggest that the Thouless conductance is universal at integer
quantum Hall transitions, just like the conductivity tensor. Finite temperature
and system size effects near the transition point are also studied.Comment: 20 pages, 15 figure
On the Theory of Metal-Insulator Transitions in Gated Semiconductors
It is shown that recent experiments indicating a metal-insulator transition
in 2D electron systems can be interpreted in terms of a simple model, in which
the resistivity is controlled by scattering at charged hole traps located in
the oxide layer. The gate voltage changes the number of charged traps which
results in a sharp change in the resistivity. The observed exponential
temperature dependence of the resistivity in the metallic phase of the
transition follows from the temperature dependence of the trap occupation
number. The model naturally describes the experimentally observed scaling
properties of the transition and effects of magnetic and electric fields.Comment: 4 two-column pages, 4 figures (included in the text
Kinetics of the helix-coil transition
Based on the Zimm-Bragg model we study cooperative helix-coil transition
driven by a finite-speed change of temperature. There is an asymmetry between
the coil-to-helix and helix-to-coil transition: the latter is displayed already
for finite speeds, and takes shorter time than the former. This hysteresis
effect has been observed experimentally, and it is explained here via
quantifying system's stability in the vicinity of the critical temperature. A
finite-speed cooling induces a non-equilibrium helical phase with the
correlation length larger than in equilibrium. In this phase the characteristic
length of the coiled domain and the non-equilibrium specific heat can display
an anomalous response to temperature changes. Several pertinent experimental
results on the kinetics helical biopolymers are discussed in detail.Comment: 6 pages, 8 figure
Indication of the ferromagnetic instability in a dilute two-dimensional electron system
The magnetic field B_c, in which the electrons become fully spin-polarized,
is found to be proportional to the deviation of the electron density from the
zero-field metal-insulator transition in a two-dimensional electron system in
silicon. The tendency of B_c to vanish at a finite electron density suggests a
ferromagnetic instability in this strongly correlated electron system.Comment: 4 pages, postscript figures included. Revised versio
Classical versus Quantum Effects in the B=0 Conducting Phase in Two Dimensions
In the dilute two-dimensional electron system in silicon, we show that the
temperature below which Shubnikov-de Haas oscillations become apparent is
approximately the same as the temperature below which an exponential decrease
in resistance is seen in B=0, suggesting that the anomalous behavior in zero
field is observed only when the system is in a degenerate (quantum) state. The
temperature dependence of the resistance is found to be qualitatively similar
in B=0 and at integer Landau level filling factors.Comment: 3 pages, 3 figure
A new semiconducting perovskite alloy system made possible by gas-source molecular beam epitaxy
We demonstrate epitaxial thin film growth of the chalcogenide perovskite
semiconducting alloy system BaZrSSe using gas-source molecular
beam epitaxy (MBE). BaZrS is stable in the perovskite structure in bulk
form, but the pure selenide BaZrSe is not. Here stabilize the full range of
compositions y = 0 ... 3 in the perovskite structure, up to and including
BaZrSe, by growing on BaZrS buffer layers. The alloy grows by
pseudomorphic heteroepitaxy on the sulfide buffer, without interruption in the
reflection high energy electron diffraction (RHEED) pattern. The resulting
films are environmentally stable and the direct band gap (E) varies
strongly with Se content, as predicted by theory, covering the range E =
1.9 ... 1.4 eV for y = 0 ... 3. This creates possibilities for visible and
near-infrared (VIS-NIR) optoelectronics, solid state lighting, and solar cells
using chalcogenide perovskites
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