10,747 research outputs found
Linear magnetoresistance on the topological surface
A positive, non-saturating and dominantly linear magnetoresistance is
demonstrated to occur in the surface state of a topological insulator having a
wavevector-linear energy dispersion together with a finite positive Zeeman
energy splitting. This linear magnetoresistance shows up within quite wide
magnetic-field range in a spatially homogenous system of high carrier density
and low mobility in which the conduction electrons are in extended states and
spread over many smeared Landau levels, and is robust against increasing
temperature, in agreement with recent experimental findings in BiSe
nanoribbons.Comment: 7 pages, 4 figure
Generalized Area Spectral Efficiency: An Effective Performance Metric for Green Wireless Communications
Area spectral efficiency (ASE) was introduced as a metric to quantify the
spectral utilization efficiency of cellular systems. Unlike other performance
metrics, ASE takes into account the spatial property of cellular systems. In
this paper, we generalize the concept of ASE to study arbitrary wireless
transmissions. Specifically, we introduce the notion of affected area to
characterize the spatial property of arbitrary wireless transmissions. Based on
the definition of affected area, we define the performance metric, generalized
area spectral efficiency (GASE), to quantify the spatial spectral utilization
efficiency as well as the greenness of wireless transmissions. After
illustrating its evaluation for point-to-point transmission, we analyze the
GASE performance of several different transmission scenarios, including
dual-hop relay transmission, three-node cooperative relay transmission and
underlay cognitive radio transmission. We derive closed-form expressions for
the GASE metric of each transmission scenario under Rayleigh fading environment
whenever possible. Through mathematical analysis and numerical examples, we
show that the GASE metric provides a new perspective on the design and
optimization of wireless transmissions, especially on the transmitting power
selection. We also show that introducing relay nodes can greatly improve the
spatial utilization efficiency of wireless systems. We illustrate that the GASE
metric can help optimize the deployment of underlay cognitive radio systems.Comment: 11 pages, 8 figures, accepted by TCo
Elevated temperature strain gages
One of the goals of the HOST Program is the development of electrical resistance strain gages for static strain measurements at temperatures equal to or greater than 1273 K. Strain gage materials must have a reproducible or predictable response to temperature, time and strain. It is the objective of this research to investigate criteria for the selection of materials for such applications through electrical properties studies. The results of the investigation of two groups of materials, refractory compounds and binary alloy solid solutions are presented
Qubit measurement using a quantum point contact with a quantum Langevin equation approach
We employ a quantum Langevin equation approach to establish non-Markovian
dynamical equations, on a fully microscopic basis, to investigate the
measurement of the state of a coupled quantum dot qubit by a nearby quantum
point contact. The ensuing Bloch equations allow us to examine qubit relaxation
and decoherence induced by measurement, and also the noise spectrum of meter
output current with the help of a quantum regression theorem, at arbitrary
bias-voltage and temperature. Our analyses provide a clear resolution of a
recent debate concerning the occurrence of a quantum oscillation peak in the
noise spectrum.Comment: 5 pages, 3 figures, submitted, published version in Phys. Rev.
Characteristics of events with metric-to-decahectometric type II radio bursts associated with CMEs and flares in relation to SEP events
A gradual solar energetic particle (SEP) event is thought to happen when
particles are accelerated at a shock due to a fast coronal mass ejection (CME).
To quantify what kind of solar eruptions can result in such SEP events, we have
conducted detailed investigations on the characteristics of CMEs, solar flares
and m-to-DH wavelength type II radio bursts (herein after m-to-DH type II
bursts) for SEP-associated and non-SEP-associated events, observed during the
period of 1997-2012. Interestingly, 65% of m-to-DH type II bursts associated
with CMEs and flares produced SEP events. The SEP-associated CMEs have higher
sky-plane mean speed, projection corrected speed, and sky-plane peak speed than
those of non-SEP-associated CMEs respectively by 30%, 39%, and 25%, even though
the two sets of CMEs achieved their sky-plane peak speeds at nearly similar
heights within LASCO field of view. We found Pearson's correlation coefficients
between the speeds of CMEs speeds and logarithmic peak intensity of SEP events
are cc = 0.62 and cc = 0.58, respectively. We also found that the
SEP-associated CMEs are on average of three times more decelerated (-21.52
m/s2) than the non-SEP-associated CMEs (-5.63 m/s2). The SEP-associated m type
II bursts have higher frequency drift rate and associated shock speed than
those of the non-SEP-associated events by 70% and 25% respectively. The average
formation heights of m and DH type II radio bursts for SEP-associated events
are lower than for non-SEP-associated events. 93% of SEP-associated events
originate from the western hemisphere and 65% of SEP-associated events are
associated with interacting CMEs. The obtained results indicate that, at least
for the set of CMEs associated with m-to-DH type II bursts, SEP-associated CMEs
are more energetic than those not associated with SEPs, thus suggesting that
they are effective particle accelerators.Comment: 19 pages, 10 figures, 3 tables, accepted for publication by ApS
Deterministic Brownian motion generated from differential delay equations
This paper addresses the question of how Brownian-like motion can arise from
the solution of a deterministic differential delay equation. To study this we
analytically study the bifurcation properties of an apparently simple
differential delay equation and then numerically investigate the probabilistic
properties of chaotic solutions of the same equation. Our results show that
solutions of the deterministic equation with randomly selected initial
conditions display a Gaussian-like density for long time, but the densities are
supported on an interval of finite measure. Using these chaotic solutions as
velocities, we are able to produce Brownian-like motions, which show
statistical properties akin to those of a classical Brownian motion over both
short and long time scales. Several conjectures are formulated for the
probabilistic properties of the solution of the differential delay equation.
Numerical studies suggest that these conjectures could be "universal" for
similar types of "chaotic" dynamics, but we have been unable to prove this.Comment: 15 pages, 13 figure
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