5,376 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
Second Backbend in the Mass A ~ 180 Region
Within the framework of selfconsistent cranked Hartree-Fock- Bogoliubov
theory(one-dimensional) we predict second backbend in the yrast line of Os-182
at , which is even sharper than the first one observed
experimentally at .
Around such a high spin the structure becomes multi-quasiparticle type, but
the main source of this strong discontinuity is a sudden large alignment of
i_13/2 proton orbitals along the rotation axis followed soon by the alignment
of j_15/2 neutron orbitals. This leads to drastic structural changes at such
high spins. When experimentally confirmed, this will be observed for the first
time in this mass region, and will be at the highest spin so far.Comment: 13 pages, 4 ps figure
Experimental investigation of some aspects of insect-like flapping flight aerodynamics for application to micro air vehicles
Insect-like flapping flight offers a power-efficient and highly manoeuvrable basis for micro air vehicles for indoor applications. Some aspects of the aerodynamics associated with the sweeping phase of insect wing kinematics are examined by making particle image velocimetry measurements on a rotating wing immersed in a tank of seeded water. The work is motivated by the paucity of data with quantified error on insect-like flapping flight, and aims to fill this gap by providing a detailed description of the experimental setup, quantifying the uncertainties in the measurements and explaining the results. The experiments are carried out at two Reynolds numbers-500 and 15,000-accounting for scales pertaining to many insects and future flapping-wing micro air vehicles, respectively. The results from the experiments are used to describe prominent flow features, and Reynolds number-related differences are highlighted. In particular, the behaviour of the leading-edge vortex at these Reynolds numbers is studied and the presence of Kelvin-Helmholtz instability observed at the higher Reynolds number in computational fluid dynamics calculations is also verified
Optimal Microlensing Observations
One of the major limitations of microlensing observations toward the Large
Magellanic Cloud (LMC) is the low rate of event detection. What can be done to
improve this rate? Is it better to invest telescope time in more frequent
observations of the inner high surface-brightness fields, or in covering new,
less populated outer fields? How would a factor 2 improvement in CCD
sensitivity affect the detection efficiency? Would a series of major (factor
2--4) upgrades in telescope aperture, seeing, sky brightness, camera size, and
detector efficiency increase the event rate by a huge factor, or only
marginally? I develop a simplified framework to address these questions. With
observational resources fixed at the level of the MACHO and EROS experiments,
the biggest improvement (factor ~2) would come by reducing the time spent on
the inner ~25 deg^2 and applying it to the outer ~100 deg^2. By combining this
change with the characteristics of a good medium-size telescope (2.5 m mirror,
1" point spread function, thinned CCD chips, 1 deg^2 camera, and dark sky), it
should be possible to increase the detection of LMC events to more than 100 per
year (assuming current estimates of the optical depth apply to the entire LMC).Comment: Submitted to ApJ, 13 pages plus 3 figure
Microlens Parallaxes with SIRTF
The Space Infrared Telescope Facility (SIRTF) will drift away from the Earth
at about 0.1 AU/yr. Microlensing events will therefore have different
characteristics as seen from the satellite and the Earth. From the difference,
it is possible in principle to measure v-tilde, the transverse velocity of the
lens projected onto the observer plane. Since v-tilde has very different values
for different populations (disk, halo, Large Magellanic Cloud), such
measurements could help identify the location, and hence the nature, of the
lenses. I show that the method previously developed by Gould for measuring such
satellite parallaxes fails completely in the case of SIRTF: it is overwhelmed
by degeneracies which arise from fact that the Earth and satellite observations
are in different band passes. I develop a new method which allows for
observations in different band passes and yet removes all degeneracies. The
method combines a purely ground-based measurement of the "parallax asymmetry"
with a measurement of the delay between the time the event peaks at the Earth
and satellite. In effect, the parallax asymmetry determines the component of
v-tilde in the Earth-Sun direction, while the delay time measures the component
of v-tilde in the direction of the Earth's orbit.Comment: 21 pages plus 3 figure
Morphology of Tigris River within Baghdad City
In recent years, substantial changes have occurred in the morphology of the River Tigris within Baghdad City. Although huge volumes of sediment are being trapped in recently constructed headwater reservoirs, the number of islands in the Tigris at Baghdad is increasing. The debris of bridges destroyed in the wars of 1991 and 2003 and their subsequent reconstruction have enhanced the development of these islands. As a consequence the ability of the river to carry the peaks of flood waters has been reduced. This has led to potential increase of flooding in parts of the city. <br><br> The bed of the River Tigris has been surveyed on three occasions (1976, 1991, and 2008). The most recent survey was conducted by the Ministry of Water Resources, extended 49 km from the Al-Muthana Bridge north Baghdad to the confluence with the Diyala River south Baghdad. It yielded cross-section profiles at 250 m intervals. The data are used to predict the maximum flood capacity for the river using the one-dimensional hydraulic model for steady flow "HEC-RAS" modeling. Calibration of the model was carried out using field measurements for water levels along the last 15 km of the reach and the last 10 yr of observation at the Sarai Baghdad gauging station. <br><br> The model showed a significant predicted reduction in the current river capacity below that which the river had carried during the floods of 1971 and 1988. The three surveys conducted on the same reach of the Tigris indicated that the ability of the river to transport water has decreased
Nonclassical Light in Interferometric Measurements
It is shown that the even and odd coherent light and other nonclassical
states of light like superposition of coherent states with different phases may
replace the squeezed light in interferometric gravitational wave detector to
increase its sensitivity. (Contribution to the Second Workshop on Harmonic
Oscillator, Cocoyoc, Mexico, March 1994)Comment: 8 pages,LATEX,preprint of Naples University,
INFN-NA-IV-94/30,DSF-T-94/3
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