52,720 research outputs found
A High Reliability Asymptotic Approach for Packet Inter-Delivery Time Optimization in Cyber-Physical Systems
In cyber-physical systems such as automobiles, measurement data from sensor
nodes should be delivered to other consumer nodes such as actuators in a
regular fashion. But, in practical systems over unreliable media such as
wireless, it is a significant challenge to guarantee small enough
inter-delivery times for different clients with heterogeneous channel
conditions and inter-delivery requirements. In this paper, we design scheduling
policies aiming at satisfying the inter-delivery requirements of such clients.
We formulate the problem as a risk-sensitive Markov Decision Process (MDP).
Although the resulting problem involves an infinite state space, we first prove
that there is an equivalent MDP involving only a finite number of states. Then
we prove the existence of a stationary optimal policy and establish an
algorithm to compute it in a finite number of steps.
However, the bane of this and many similar problems is the resulting
complexity, and, in an attempt to make fundamental progress, we further propose
a new high reliability asymptotic approach. In essence, this approach considers
the scenario when the channel failure probabilities for different clients are
of the same order, and asymptotically approach zero. We thus proceed to
determine the asymptotically optimal policy: in a two-client scenario, we show
that the asymptotically optimal policy is a "modified least time-to-go" policy,
which is intuitively appealing and easily implementable; in the general
multi-client scenario, we are led to an SN policy, and we develop an algorithm
of low computational complexity to obtain it. Simulation results show that the
resulting policies perform well even in the pre-asymptotic regime with moderate
failure probabilities
On the number of contacts of a floating polymer chain cross-linked with a surface adsorbed chain on fractal structures
We study the interaction problem of a linear polymer chain, floating in
fractal containers that belong to the three-dimensional Sierpinski gasket (3D
SG) family of fractals, with a surface-adsorbed linear polymer chain. Each
member of the 3D SG fractal family has a fractal impenetrable 2D adsorbing
surface, which appears to be 2D SG fractal. The two-polymer system is modelled
by two mutually crossing self-avoiding walks. By applying the Monte Carlo
Renormalization Group (MCRG) method, we calculate the critical exponents
, associated with the number of contacts of the 3D SG floating polymer
chain, and the 2D SG adsorbed polymer chain, for a sequence of SG fractals with
. Besides, we propose the codimension additivity (CA) argument
formula for , and compare its predictions with our reliable set of the
MCRG data. We find that monotonically decreases with increasing ,
that is, with increase of the container fractal dimension. Finally, we discuss
the relations between different contact exponents, and analyze their possible
behaviour in the fractal-to-Euclidean crossover region .Comment: 15 pages, 3 figure
On the Limits of Depth Reduction at Depth 3 Over Small Finite Fields
Recently, Gupta et.al. [GKKS2013] proved that over Q any -variate
and -degree polynomial in VP can also be computed by a depth three
circuit of size . Over fixed-size
finite fields, Grigoriev and Karpinski proved that any
circuit that computes (or ) must be of size
[GK1998]. In this paper, we prove that over fixed-size finite fields, any
circuit for computing the iterated matrix multiplication
polynomial of generic matrices of size , must be of size
. The importance of this result is that over fixed-size
fields there is no depth reduction technique that can be used to compute all
the -variate and -degree polynomials in VP by depth 3 circuits of
size . The result [GK1998] can only rule out such a possibility
for depth 3 circuits of size .
We also give an example of an explicit polynomial () in
VNP (not known to be in VP), for which any circuit computing
it (over fixed-size fields) must be of size . The
polynomial we consider is constructed from the combinatorial design. An
interesting feature of this result is that we get the first examples of two
polynomials (one in VP and one in VNP) such that they have provably stronger
circuit size lower bounds than Permanent in a reasonably strong model of
computation.
Next, we prove that any depth 4
circuit computing
(over any field) must be of size . To the best of our knowledge, the polynomial is the
first example of an explicit polynomial in VNP such that it requires
size depth four circuits, but no known matching
upper bound
Thermal conductivity of comets
A value is described for the thermal conductivity of the frost layer and for the water-ice solid debris mixture. The value of the porous structure is discussed as a function of depth only. Graphs show thermal conductivity as a function of depth and temperature at constant porosity and density
Electronic states of PrCoO: X-ray photoemission spectroscopy and LDA+U density of states studies
Electronic states of PrCoO are studied using x-ray photoemission
spectroscopy. Pr 3d core level and valence band (VB) were recorded
using Mg K source. The core level spectrum shows that the 3d
level is split into two components of multiplicity 4 and 2, respectively due to
coupling of the spin states of the hole in 3d with Pr 4f holes spin
state. The observed splitting is 4.5 eV. The VB spectrum is interpreted using
density of states (DOS) calculations under LDA and LDA+U. It is noted that LDA
is not sufficient to explain the observed VB spectrum. Inclusion of on-site
Coulomb correlation for Co 3d electrons in LDA+U calculations gives DOS which
is useful in qualitative explanation of the ground state. However, it is
necessary to include interactions between Pr 4f electrons to get better
agreement with experimental VB spectrum. It is seen that the VB consists of Pr
4f, Co 3d and O 2p states. Pr 4f, Co 3d and O 2p bands are highly mixed
indicating strong hybridization of these three states. The band near the Fermi
level has about equal contributions from Pr 4f and O 2p states with somewhat
smaller contribution from Co 3d states. Thus in the Zaanen, Sawatzky, and Allen
scheme PrCoO can be considered as charge transfer insulator. The charge
transfer energy can be obtained using LDA DOS calculations and the
Coulomb-exchange energy U' from LDA+U. The explicit values for PrCoO are
= 3.9 eV and U' = 5.5 eV; the crystal field splitting and 3d bandwidth
of Co ions are also found to be 2.8 and 1.8 eV, respectively.Comment: 12 pages, 7 figures; to appear J. Phys.: Condens. Matte
Effects of exenatide and liraglutide on heart rate, blood pressure and body weight : systematic review and meta-analysis
Objectives: To synthesise current evidence for the effects of exenatide and liraglutide on heart rate, blood pressure and body weight.
Design: Meta-analysis of available data from randomised controlled trials comparing Glucagon-like peptide-1 (GLP-1) analogues with placebo, active antidiabetic drug therapy or lifestyle intervention.
Participants: Patients with type 2 diabetes.
Outcome measures: Weighted mean differences between trial arms for changes in heart rate, blood pressure and body weight, after a minimum of 12-week follow-up.
Results: 32 trials were included. Overall, GLP-1 agonists increased the heart rate by 1.86 beats/min (bpm) (95% CI 0.85 to 2.87) versus placebo and 1.90 bpm (1.30 to 2.50) versus active control. This effect was more evident for liraglutide and exenatide long-acting release than for exenatide twice daily. GLP-1 agonists decreased systolic blood pressure by −1.79 mm Hg (−2.94 to −0.64) and −2.39 mm Hg (−3.35 to −1.42) compared to placebo and active control, respectively. Reduction in diastolic blood pressure failed to reach statistical significance (−0.54 mm Hg (−1.15 to 0.07) vs placebo and −0.50 mm Hg (−1.24 to 0.24) vs active control). Body weight decreased by −3.31 kg (−4.05 to −2.57) compared to active control, but by only −1.22 kg (−1.51 to −0.93) compared to placebo.
Conclusions: GLP-1 analogues are associated with a small increase in heart rate and modest reductions in body weight and blood pressure. Mechanisms underlying the rise in heart rate require further investigation
A rapidly expanding Bose-Einstein condensate: an expanding universe in the lab
We study the dynamics of a supersonically expanding ring-shaped Bose-Einstein
condensate both experimentally and theoretically. The expansion redshifts
long-wavelength excitations, as in an expanding universe. After expansion,
energy in the radial mode leads to the production of bulk topological
excitations -- solitons and vortices -- driving the production of a large
number of azimuthal phonons and, at late times, causing stochastic persistent
currents. These complex nonlinear dynamics, fueled by the energy stored
coherently in one mode, are reminiscent of a type of "preheating" that may have
taken place at the end of inflation.Comment: 12 pages, 7 figure
Opto-mechanical micro-macro entanglement
We propose to create and detect opto-mechanical entanglement by storing one
component of an entangled state of light in a mechanical resonator and then
retrieving it. Using micro-macro entanglement of light as recently demonstrated
experimentally, one can then create opto-mechanical entangled states where the
components of the superposition are macroscopically different. We apply this
general approach to two-mode squeezed states where one mode has undergone a
large displacement. Based on an analysis of the relevant experimental
imperfections, the scheme appears feasible with current technology.Comment: 7 pages, 6 figures, to appear in PRL, submission coordinated with
Sekatski et al. who reported on similar result
COBE ground segment attitude determination
The Cosmic Background Explorer (COBE) spacecraft was launched in November 1989 by NASA to survey the sky for primordial radiation left from the Big Bang explosion. The success of the mission requires an accurate determination of the spacecraft attitude. While the accuracy of the attitude obtained from the attitude sensors is adequate for two of the experiments, the higher accuracy required by the Diffuse Infrared Background Experiment (DIRBE) is obtained by using the DIRBE instrument as a special type of star sensor. Presented here is an overview of the attitude processing algorithms used at the Cosmology Data Analysis Center (CDAC) and the results obtained from the flight data
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