80,703 research outputs found
Analytical modeling of flash-back phenomena
To understand the flame flash-back phenomena more extensively, an analytical model was formed and a numerical program was written and tested to solve the set of differential equations describing the model. Results show that under a given set of conditions flame propagates in the boundary layer on a flat plate when the free stream is at or below 1.8 m/s
A study of the use of vibration and stress wave sensing for the detection of bearing failure
Results from an experimental study of vibrations and stress waves emitted from ball bearings are presented. Fatique tests were run with both high quality bearings and man faulted bearings, all of one size. Tests were instrumented with different sensors to detect the noises from 10 Hz to 1 MHz. Frequency spectrum plots are presented. The modulation characteristics of the ultrasonic noises were analyzed, and acoustic emission type measurements were conducted. Results are presented which show that there are usable acoustic signal levels even beyond 500 KHz. These signal levels are modulated by a low frequency carrier which is a function of the stress loading and acoustic transmissibility. The results were correlated to fault size in the bearings. The correlation shows that the sensor used for signals from 100 KHz to 1 MHz gave the best sensitivity and detected the generation of very small spalls or pits
Global behavior of cosmological dynamics with interacting Veneziano ghost
In this paper, we shall study the dynamical behavior of the universe
accelerated by the so called Veneziano ghost dark energy component locally and
globally by using the linearization and nullcline method developed in this
paper. The energy density is generalized to be proportional to the Hawking
temperature defined on the trapping horizon instead of Hubble horizon of the
Friedmann-Robertson-Walker (FRW) universe. We also give a prediction of the
fate of the universe and present the bifurcation phenomenon of the dynamical
system of the universe. It seems that the universe could be dominated by dark
energy at present in some region of the parameter space.Comment: 8 pages, 7 figures, accepted for publication in JHE
Wireless Broadcast with Physical-Layer Network Coding
This work investigates the maximum broadcast throughput and its achievability
in multi-hop wireless networks with half-duplex node constraint. We allow the
use of physical-layer network coding (PNC). Although the use of PNC for unicast
has been extensively studied, there has been little prior work on PNC for
broadcast. Our specific results are as follows: 1) For single-source broadcast,
the theoretical throughput upper bound is n/(n+1), where n is the "min
vertex-cut" size of the network. 2) In general, the throughput upper bound is
not always achievable. 3) For grid and many other networks, the throughput
upper bound n/(n+1) is achievable. Our work can be considered as an attempt to
understand the relationship between max-flow and min-cut in half-duplex
broadcast networks with cycles (there has been prior work on networks with
cycles, but not half-duplex broadcast networks).Comment: 23 pages, 18 figures, 6 table
Quantum Error Correction of Time-Correlated Errors
The complexity of the error correction circuitry forces us to design quantum
error correction codes capable of correcting a single error per error
correction cycle. Yet, time-correlated error are common for physical
implementations of quantum systems; an error corrected during the previous
cycle may reoccur later due to physical processes specific for each physical
implementation of the qubits. In this paper we study quantum error correction
for a restricted class of time-correlated errors in a spin-boson model. The
algorithm we propose allows the correction of two errors per error correction
cycle, provided that one of them is time-correlated. The algorithm can be
applied to any stabilizer code when the two logical qubits and
are entangled states of basis states in
.Comment: 14 pages, 3 figure
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