14,542 research outputs found
Holomorphic Bisectional Curvatures, Supersymmetry Breaking, and Affleck-Dine Baryogenesis
Working in supergravity, we utilize relations between holomorphic
sectional and bisectional curvatures of Kahler manifolds to constrain
Affleck-Dine baryogenesis. We show the following No-Go result: Affleck-Dine
baryogenesis cannot be performed if the holomorphic sectional curvature at the
origin is isotropic in tangent space; as a special case, this rules out spaces
of constant holomorphic sectional curvature (defined in the above sense) and in
particular maximally symmetric coset spaces. We also investigate scenarios
where inflationary supersymmetry breaking is identified with the supersymmetry
breaking responsible for mass splitting in the visible sector, using conditions
of sequestering to constrain manifolds where inflation can be performed.Comment: 9 page
Aspects of Horava-Lifshitz cosmology
We review some general aspects of Horava-Lifshitz cosmology. Formulating it
in its basic version, we extract the cosmological equations and we use
observational data in order to constrain the parameters of the theory. Through
a phase-space analysis we extract the late-time stable solutions, and we show
that eternal expansion, and bouncing and cyclic behavior can arise naturally.
Concerning the effective dark energy sector we show that it can describe the
phantom phase without the use of a phantom field. However, performing a
detailed perturbation analysis, we see that Horava-Lifshitz gravity in its
basic version suffers from instabilities. Therefore, suitable generalizations
are required in order for this novel theory to be a candidate for the
description of nature.Comment: 10 pages, 4 figures, invited talk given at the 2nd International
Workshop on Dark Matter, Dark Energy and Matter-Antimatter Assymetry,
National Tsing Hua University, Hsinchu, Taiwan, November 5-6, 201
Empirical modelling and simulation of transmission loss between wireless sensor nodes in gas turbine engines
Transmission loss measurements between a grid of hypothetical WSN node locations on the surface of a gas turbine engine are reported for eight frequencies at 1 GHz intervals in the frequency range 3.0 to 11.0 GHz. An empirical transmission loss model is derived from the measurements. The model is incorporated into an existing system channel model implemented using Simulink as part of a wider project concerning the development of WSNs for the testing and condition monitoring of gas turbine engines
Timely-Throughput Optimal Coded Computing over Cloud Networks
In modern distributed computing systems, unpredictable and unreliable
infrastructures result in high variability of computing resources. Meanwhile,
there is significantly increasing demand for timely and event-driven services
with deadline constraints. Motivated by measurements over Amazon EC2 clusters,
we consider a two-state Markov model for variability of computing speed in
cloud networks. In this model, each worker can be either in a good state or a
bad state in terms of the computation speed, and the transition between these
states is modeled as a Markov chain which is unknown to the scheduler. We then
consider a Coded Computing framework, in which the data is possibly encoded and
stored at the worker nodes in order to provide robustness against nodes that
may be in a bad state. With timely computation requests submitted to the system
with computation deadlines, our goal is to design the optimal computation-load
allocation scheme and the optimal data encoding scheme that maximize the timely
computation throughput (i.e, the average number of computation tasks that are
accomplished before their deadline). Our main result is the development of a
dynamic computation strategy called Lagrange Estimate-and Allocate (LEA)
strategy, which achieves the optimal timely computation throughput. It is shown
that compared to the static allocation strategy, LEA increases the timely
computation throughput by 1.4X - 17.5X in various scenarios via simulations and
by 1.27X - 6.5X in experiments over Amazon EC2 clustersComment: to appear in MobiHoc 201
Laser Surface Engineering of Metallic Components
The engineering solution to improve the surface dependent properties like wear, corrosion and oxidation resistance involves tailoring the surface composition and/or micro-structure of the near-surface region of a component without affecting the bulk. This may be achieved, using a
high power laser beam as a source of heat, by surface hardening, melting, alloying and cladding. Fast heat-ing /cooling rate (104-1011 K/s), very high thermal grad-ient(106-108 K/m)and ultra-rapid resolidification veloc-ity (1-30 m/s) are the characteristics of this process which often develop exotic microstructures and composit-ions having large extension of solid solubility and meta-stable or even amorphous phases in the surface. This paper gives a brief review of the present status and future
scope of laser assisted surface engineering with parti-cular reference to the authors' work
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