1,703 research outputs found
Reliability assessment of microgrid with renewable generation and prioritized loads
With the increase in awareness about the climate change, there has been a
tremendous shift towards utilizing renewable energy sources (RES). In this
regard, smart grid technologies have been presented to facilitate higher
penetration of RES. Microgrids are the key components of the smart grids.
Microgrids allow integration of various distributed energy resources (DER) such
as the distributed generation (DGs) and energy storage systems (ESSs) into the
distribution system and hence remove or delay the need for distribution
expansion. One of the crucial requirements for utilities is to ensure that the
system reliability is maintained with the inclusion of microgrid topology.
Therefore, this paper evaluates the reliability of a microgrid containing
prioritized loads and distributed RES through a hybrid analytical-simulation
method. The stochasticity of RES introduces complexity to the reliability
evaluation. The method takes into account the variability of RES through Monte-
Carlo state sampling simulation. The results indicate the reliability
enhancement of the overall system in the presence of the microgrid topology. In
particular, the highest priority load has the largest improvement in the
reliability indices. Furthermore, sensitivity analysis is performed to
understand the effects of the failure of microgrid islanding in the case of a
fault in the upstream network
Theory of a Continuous H Normal-to-Superconducting Transition
I study the transition within the Ginzburg-Landau model, with
-component order parameter . I find a renormalized fixed point free
energy, exact in limit, suggestive of a nd-order
transition in contrast to a general belief of a st-order transition. The
thermal fluctuations for force one to consider an infinite set of
marginally relevant operators for . I find , predicting
that the ODLRO does not survive thermal fluctuations in . The result is
a solution to a critical fixed point that was found to be inaccessible within
-expansion, previously considered in E.Brezin, D.R.Nelson,
A.Thiaville, Phys.Rev.B {\bf 31}, 7124 (1985), and was interpreted as a
st-order transition.Comment: 4 pages, self-unpacking uuencoded compressed postscript file with a
figure already inside text; to appear in Phys. Rev. Lett
Design of Beam Steering Electronic Circuits for Medical Applications
This thesis deals with the theory and design of a hemispherical antenna array circuit that is capable to operate in the intermediate zones. By doing that, this array can be used in Hyperthermia Treatment for Brain Cancer in which the aim is to noninvasively focus the fields at microwave frequencies to the location of the tumor cells in the brain. Another possible application of the array is to offer an alternative means of sustaining Deep Brain Stimulation other than using the traditional (surgical) approach.
The new noninvasive technique is accomplished by the use of a hemispherical antenna array placed on the human's head. The array uses a new beamforming technique that achieves 3 dimensional beamforming or focusing of the magnetic field of antennas to desired points in the brain to achieve either cell death by temperature rise (Hyperthermia Application) or to cause brain stimulation and hopefully alleviate the affects of Parkinson's Disease (Deep Brain Stimulation).
The main obstacle in this design was that the far field approximation that is usually used when designing antenna arrays does not apply in this case since the hemispherical array is in close proximity to where the magnetic field is desired to be focused. The antenna array problem is approached as a boundary-valued problem with the human head being modeled as a three layered hemisphere. The exact expressions for electromagnetic fields are derived. Health issues such as electric field exposure and specific absorption rate (SAR) are considered.
After developing the main antenna and beamforming theory, a neural network is designed to accomplish the beamforming technique used. The radio-frequency (RF) transmitter was designed to transmit the fields at a frequency of 1.8 GHz.
The antenna array can also be used as a receiver. The antenna and beamforming theory is presented. A new reception technique is shown which enables the array to receive multiple magnetic field sources from within the hemispherical surface. The receiver is designed to operate at 500 kHz with the RF receiver circuit designed to receive any signal from within the hemispherical surface at a frequency of 500 kHz
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Virtual Simulation for Multi-material LM Process
In an ONR funded MURI program, to improve quality of multi-material parts,
we've been developing an advanced computer simulation for the multi-material layered
manufacturing (LM) process. The CAD models and their .stLfiles are created using. the
commercially available software such as I-DEAS and ProE. Using this information, one
tool path file per material is generated. Our file preparation algorithm, systematically,
layer by layer, integrates all tool path files into one multi-material tool path file. The
results of the multi-material tool path are graphically visualized using the simulation
algorithm (written in c++ & SGI OpenGL). From a virtual simulation, we can check the
LM process, and make the best selection of tool path parameters afterwards. After several
trials from design to simulation, if the simulation result is acceptable, the real
manufacturing can be started. And the part's quality should be better than a part
manufactured without running simulation in advance. This paper will represent .•. new
studies on using real toadshapes to get more realistic simulation results. Many parts have
been successfully simulated using our method.Mechanical Engineerin
Comment on `Strong Vortex Liquid Correlation' from Multiterminal Measurements on Untwinned YBaCuO Single Crystals'
A.Rydh and \"O.Rapp [Phys. Rev. Lett. {\bf 86}, 1873 (2001).] claim that the
vortex liquid in untwinned YBaCuO crystals is correlated
above the melting transition, in striking contrast to previous work [D.L\'opez
{\it et al.}, Phys. Rev. Lett. {\bf 76}, 4034 (1996).]. In this Comment we
present new measurements using the same experimental technique on twinned and
untwinned YBaCuO crystals with similar overall
characteristics as those reported by Rydh and Rapp . The comparison of the
vortex correlation response in both cases indicates that the central conclusion
of their work is not correct. Our results reconfirm the work by L\'opez {\it et
al.} and points on the origin of the misinterpretation in the work of Rydh and
Rapp.Comment: comment on A.Rydh and \"O.Rapp, Phys. Rev. Lett. {\bf 86}, 1873
(2001). accepted in Phys. Rev. Let
First-Order Melting of a Moving Vortex Lattice: Effects of Disorder
We study the melting of a moving vortex lattice through numerical simulations
with the current driven 3D XY model with disorder. We find that there is a
first-order phase transition even for large disorder when the corresponding
equilibrium transition is continuous. The low temperature phase is an
anisotropic moving glass.Comment: Important changes from original version. Finite size analysis of
results has been added. Figure 2 has been changed. There is a new additional
Figure. To be published in Physical Review Letter
Ultra-performance liquid chromatography–tandem mass spectrometric determination of ramipril in human plasma
Purpose: To develop a sensitive and accurate ultra-performance liquid chromatography–tandem mass spectrometric (UPLC-MS) method for quantification of ramipril in human plasma.Methods: Ramipril was extracted from biological fluid using equal volumes of n-hexane and propanol (1:1, v/v), and then chromatographed in a suitable C18 column with methanol: 0.1 % HCOOH (4: 1, v/v) as mobile phase. Atorvastatin was used as an internal standard for the chromatographic separation and quantification. The method was validated according to the United States Food and Drug Administration guidelines for standard indices.Results: Ramipril was determined in the concentration range 0.05 and 1000 ng/mL the validation procedure exhibited a correlation coefficient of 0.9979 + 0.002 (p = 0.05). The studied drug was quantified with lower ceiling of 0.05 ng/mL, and showed an accuracy of 105.00 %.Conclusion: A sensitive UPLC-MS analytical method has been successfully developed for the quantification of ramipril in human plasma. This method can be applied efficiently for the quantification of ramipril in bioavailability and pharmacokinetic studies.
Keywords: Liquid chromatography–tandem mass, Ramipril, Stability, Biological fluids, Plasm
Energy cost associated with vortex crossing in superconductors
Starting from the Ginzburg-Landau free energy of a type II superconductor in
a magnetic field we estimate the energy associated with two vortices crossing.
The calculations are performed by assuming that we are in a part of the phase
diagram where the lowest Landau level approximation is valid. We consider only
two vortices but with two markedly different sets of boundary conditions: on a
sphere and on a plane with quasi-periodic boundary conditions. We find that the
answers are very similar suggesting that the energy is localised to the
crossing point. The crossing energy is found to be field and temperature
dependent -- with a value at the experimentally measured melting line of
, where is the Lindemann
melting criterion parameter. The crossing energy is then used with an extension
of the Marchetti, Nelson and Cates hydrodynamic theory to suggest an
explanation of the recent transport experiments of Safar {{\em et al.}\ }.Comment: 15 pages, RevTex v3.0, followed by 5 postscript figure
Nonlocal Conductivity in the Vortex-Liquid Regime of a Two-Dimensional Superconductor
We have simulated the time-dependent Ginzburg-Landau equation with thermal
fluctuations, to study the nonlocal dc conductivity of a superconducting film.
Having examined points in the phase diagram at a wide range of temperatures and
fields below the mean-field upper critical field, we find a portion of the
vortex-liquid regime in which the nonlocal ohmic conductivity in real space is
negative over a distance several times the spacing between vortices. The effect
is suppressed when driven beyond linear response. Earlier work had predicted
the existence of such a regime, due to the high viscosity of a
strongly-correlated vortex liquid. This behavior is clearly distinguishable
from the monotonic spatial fall-off of the conductivity in the higher
temperature or field regimes approaching the normal state. The possibilities
for experimental study of the nonlocal transport properties are discussed.Comment: 18 pages, revtex, 6 postscript figure
First order phase transition of the vortex lattice in twinned YBa2Cu3O7 single crystals in tilted magnetic fields
We present an exhaustive analysis of transport measurements performed in
twinned YBa2Cu3O7 single crystals which stablishes that the vortex solid-liquid
transition is first order when the magnetic field H is applied at an angle
theta away from the direction of the twin planes. We show that the resistive
transitions are hysteretic and the V-I curves are non-linear, displaying a
characteristic s-shape at the melting line Hm(T), which scales as
epsilon(theta)Hm(T,theta). These features are gradually lost when the critical
point H*(theta) is approached. Above H*(theta) the V-I characteristics show a
linear response in the experimentally accessible V-I window, and the transition
becomes reversible. Finally we show that the first order phase transition takes
place between a highly correlated vortex liquid in the field direction and a
solid state of unknown symmetry. As a consequence, the available data support
the scenario for a vortex-line melting rather than a vortex sublimation as
recently suggested [T.Sasagawa et al. PRL 80, 4297 (1998)].Comment: 10 pages, 8 figures, submitted to PR
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