471,135 research outputs found
On the Issue of the Thermal Emission Cathode Resource on the Oxide Films of Hafnium and Zirconium
The article shows the results of research on the destruction of the thermionic cathode of an arc plasma torch when inserting hafnium and zirconium along the trace of the spot of a gas-discharge arc by means of electronic metallography with spectral analysis in the control region. The depth of penetration of the spot into the metal of the cathode insert was determined due to the discrete mechanism of action on the metal at the time of attachment. The erosion rate of zirconium oxide films was experimentally established, the extension of the operating life substantiated while mechanisms for its increase were revealed, and two types of arc contact with a hafnium or zirconium insert - the "contracted" and "diffused" ones - were offered. The theoretical operating life of the cathode is calculated
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A discrete-time performance model for congestion control mechanism using queue thresholds with QOS constraints
This paper presents a new analytical framework for the congestion control of Internet traffic using a
queue threshold scheme. This framework includes two discrete-time analytical models for the performance
evaluation of a threshold based congestion control mechanism and compares performance measurements through
typical numerical results. To satisfy the low delay along with high throughput, model-I incorporates one
threshold to make the arrival process step reduce from arrival rate Âż1 directly to Âż2 once the number of packets in
the system has reached the threshold value L1. The source operates normally, otherwise. Model-II incorporates
two thresholds to make the arrival rate linearly reduce from Âż1 to Âż2 with system contents when the number of
packets in the system is between two thresholds L1 and L2. The source operates normally with arrival rate Âż1
before threshold L1, and with arrival rate Âż2 after the threshold L2. In both performance models, the mean packet
delay W, probability of packet loss PL and throughput S have been found as functions of the thresholds and
maximum drop probability. The performance comparison results for the two models have also been made
through typical numerical results. The results clearly demonstrate how different load settings can provide
different tradeoffs between throughput, loss probability and delay to suit different service requirements
Adaptive Discrete Second Order Sliding Mode Control with Application to Nonlinear Automotive Systems
Sliding mode control (SMC) is a robust and computationally efficient
model-based controller design technique for highly nonlinear systems, in the
presence of model and external uncertainties. However, the implementation of
the conventional continuous-time SMC on digital computers is limited, due to
the imprecisions caused by data sampling and quantization, and the chattering
phenomena, which results in high frequency oscillations. One effective solution
to minimize the effects of data sampling and quantization imprecisions is the
use of higher order sliding modes. To this end, in this paper, a new
formulation of an adaptive second order discrete sliding mode control (DSMC) is
presented for a general class of multi-input multi-output (MIMO) uncertain
nonlinear systems. Based on a Lyapunov stability argument and by invoking the
new Invariance Principle, not only the asymptotic stability of the controller
is guaranteed, but also the adaptation law is derived to remove the
uncertainties within the nonlinear plant dynamics. The proposed adaptive
tracking controller is designed and tested in real-time for a highly nonlinear
control problem in spark ignition combustion engine during transient operating
conditions. The simulation and real-time processor-in-the-loop (PIL) test
results show that the second order single-input single-output (SISO) DSMC can
improve the tracking performances up to 90%, compared to a first order SISO
DSMC under sampling and quantization imprecisions, in the presence of modeling
uncertainties. Moreover, it is observed that by converting the engine SISO
controllers to a MIMO structure, the overall controller performance can be
enhanced by 25%, compared to the SISO second order DSMC, because of the
dynamics coupling consideration within the MIMO DSMC formulation.Comment: 12 pages, 7 figures, 1 tabl
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