7,500 research outputs found
Overview of Final Exchange Regulations
Summarizes rules and regulations for establishing and operating state health insurance exchanges, as well as implications for eligibility determinations, verification rules, qualified health plans, and user fees and financial support for exchanges
Distributed Estimation of the Operating State of a Single-Bus DC MicroGrid without an External Communication Interface
We propose a decentralized Maximum Likelihood solution for estimating the
stochastic renewable power generation and demand in single bus Direct Current
(DC) MicroGrids (MGs), with high penetration of droop controlled power
electronic converters. The solution relies on the fact that the primary control
parameters are set in accordance with the local power generation status of the
generators. Therefore, the steady state voltage is inherently dependent on the
generation capacities and the load, through a non-linear parametric model,
which can be estimated. To have a well conditioned estimation problem, our
solution avoids the use of an external communication interface and utilizes
controlled voltage disturbances to perform distributed training. Using this
tool, we develop an efficient, decentralized Maximum Likelihood Estimator (MLE)
and formulate the sufficient condition for the existence of the globally
optimal solution. The numerical results illustrate the promising performance of
our MLE algorithm.Comment: Accepted to GlobalSIP 201
Phase field study of the tip operating state of a freely growing dendrite against convection using a novel parallel multigrid approach
Alloy dendrite growth during solidification with coupled thermal-solute-convection fields has been studied by phase field modeling and simulation. The coupled transport equations were solved using a novel parallel-multigrid numerical approach with high computational efficiency that has enabled the investigation of dendrite growth with realistic alloy values of Lewis number ∼104 and Prandtl number ∼10−2. The detailed dendrite tip shape and character were compared with widely recognized analytical approaches to show validity, and shown to be highly dependent on undercooling, solute concentration and Lewis number. In a relatively low flow velocity regime, variations in the ratio of growth selection parameter with and without convection agreed well with theory
On the role of confinement on solidification in pure materials and binary alloys
We use a phase-field model to study the effect of confinement on dendritic
growth, in a pure material solidifying in an undercooled melt, and in the
directional solidification of a dilute binary alloy. Specifically, we observe
the effect of varying the vertical domain extent () on tip selection,
by quantifying the dendrite tip velocity and curvature as a function of
, and other process parameters. As decreases, we find that the
operating state of the dendrite tips becomes significantly affected by the
presence of finite boundaries. For particular boundary conditions, we observe a
switching of the growth state from 3-D to 2-D at very small , in both
the pure material and alloy. We demonstrate that results from the alloy model
compare favorably with those from an experimental study investigating this
effect.Comment: 13 pages, 9 figures, 3 table
Experiments on the dynamic behavior of cavitating pumps
This paper describes experiments performed to measure the dynamic transfer matrices for cavitating (and noncavitating) pumps. These transfer matrices describe the relationship between small linear oscillatory perturbations in the pressures and mass flow rates at inlet and discharge from the hydraulic machine. The matrices were deduced from direct measurements of these fluctuating quantities for different modes of excitation of the machine. Results for a cavitating inducer are presented as functions of frequency and mean operating state. Though some of the trends in the data are consistent with existing theoretical models of inducer dynamics, others are not, indicating a need for further theoretical investigation of the dynamic characteristics of such flows. The results exhibit increasingly complex dynamics with increasing cavitation; it appears that the hydraulic machine deviates from an essentially passive response without cavitation to an increasingly active response as the cavitation number is reduced
Microwave Power Combiner/Switch Utilizing a Faraday Rotator
A proposed device for combining or switching electromagnetic beams would have three ports, would not contain any moving parts, and would be switchable among three operating states: Two of the ports would be for input; the remaining port would be for output. In one operating state, the signals at both input ports would be coupled through to the output port. In each of the other two operating states, the signal at only one input port would be coupled to the output port. The input port would be selected through choice of the operating state
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