7,439 research outputs found
Compressed Air Energy Storage-Part I: An Accurate Bi-linear Cavern Model
Compressed air energy storage (CAES) is suitable for large-scale energy
storage and can help to increase the penetration of wind power in power
systems. A CAES plant consists of compressors, expanders, caverns, and a
motor/generator set. Currently used cavern models for CAES are either accurate
but highly non-linear or linear but inaccurate. Highly non-linear cavern models
cannot be directly utilized in power system optimization problems. In this
regard, an accurate bi-linear cavern model for CAES is proposed in this first
paper of a two-part series. The charging and discharging processes in a cavern
are divided into several virtual states and then the first law of
thermodynamics and ideal gas law are used to derive a cavern model, i.e., model
for the variation of temperature and pressure in these processes. Thereafter,
the heat transfer between the air in the cavern and the cavern wall is
considered and integrated into the cavern model. By subsequently eliminating
several negligible terms, the cavern model reduces to a bi-linear (linear)
model for CAES with multiple (single) time steps. The accuracy of the proposed
cavern model is verified via comparison with an accurate non-linear model.Comment: 8 page
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
A New Channel for the Detection of Planetary Systems Through Microlensing: II. Repeating Events
In the companion paper we began the task of systematically studying the
detection of planets in wide orbits () via microlensing surveys.
In this paper we continue, focusing on repeating events. We find that, if all
planetary systems are similar to our own Solar System, reasonable extensions of
the present observing strategies would allow us to detect 3-6 repeating events
per year along the direction to the Bulge. Indeed, if planetary systems with
multiple planets are common, then future monitoring programs which lead to the
discovery of thousands of stellar-lens events will likely discover events in
which several different planets within a single system serve as lenses, with
light curves exhibiting multiple repetitions. In this paper we discuss
observing strategies to maximize the discovery of all wide-orbit planet-lens
events. We also compare the likely detection rates of planets in wide orbits to
those of planets located in the zone for resonant lensing. We find that,
depending on the values of the planet masses and stellar radii of the lensed
sources (which determine whether or not finite source size is important), and
also on the sensitivity of the photometry used by observers, the detection of
planets in wide orbits may be the primary route to the discovery of planets via
microlensing. We also discuss how the combination of resonant and wide-orbit
events can help us to learn about the distribution of planetary system
properties (S 6.1). In addition, by determining the fraction of short-duration
events due to planets, we indirectly derive information about the fraction of
all short-duration events that may be due to low-mass MACHOs (S 6.2).Comment: 51 pages, 7 figures. To be published in the Astrophysical Journal, 20
February 1999. This completes the introduction to the discovery of planets in
wide orbits begun in astro-ph/9808075, also to appear in ApJ on 20 February
199
MHAV: multitier heterogeneous adaptive vehicular network with LTE and DSRC
Enabling cooperation between vehicles form vehicular networks, which provide safety, traffic efficiency and infotainment. The most vital of these applications require reliability and low latency. Considering these requirements, this paper presents a multitier heterogeneous adaptive vehicular (MHAV) network. Comprising of transport operator or authority owned vehicles in high tier and all the other privately owned vehicles in low tier, integrating cellular network with dedicated short range communications. The proposed framework is implemented and evaluated in Glasgow city center model. Simulation results demonstrate that the proposed architecture outperforms previous multitier architectures in terms of latency while offloading traffic from cellular networks
Compressed Air Energy Storage-Part II: Application to Power System Unit Commitment
Unit commitment (UC) is one of the most important power system operation
problems. To integrate higher penetration of wind power into power systems,
more compressed air energy storage (CAES) plants are being built. Existing
cavern models for the CAES used in power system optimization problems are not
accurate, which may lead to infeasible solutions, e.g., the air pressure in the
cavern is outside its operating range. In this regard, an accurate CAES model
is proposed for the UC problem based on the accurate bi-linear cavern model
proposed in the first paper of this two-part series. The minimum switch time
between the charging and discharging processes of CAES is considered. The whole
model, i.e., the UC model with an accurate CAES model, is a large-scale mixed
integer bi-linear programming problem. To reduce the complexity of the whole
model, three strategies are proposed to reduce the number of bi-linear terms
without sacrificing accuracy. McCormick relaxation and piecewise linearization
are then used to linearize the whole model. To decrease the solution time, a
method to obtain an initial solution of the linearized model is proposed. A
modified RTS-79 system is used to verify the effectiveness of the whole model
and the solution methodology.Comment: 8 page
A New Channel for the Detection of Planetary Systems Through Microlensing: I. Isolated Events Due to Planet Lenses
We propose and evaluate the feasibility of a new strategy to search for
planets via microlensing. This new strategy is designed to detect planets in
"wide" orbits, i.e., with orbital separation, greater than .
Planets in wide orbits may provide the dominant channel for the microlensing
discovery of planets, particularly low-mass (e.g., Earth-mass) planets. This
paper concentrates on events in which a single planet serves as a lens, leading
to an isolated event of short duration. We point out that a distribution of
events due to lensing by stars with wide-orbit planets is necessarily
accompanied by a distribution of shorter- duration events. The fraction of
events in the latter distribution is proportional to the average value of
, where is the ratio between \pl and stellar masses. The position
of the peak or peaks also provides a measure of the mass ratios typical of
planetary systems. We study detection strategies that can optimize our ability
to discover isolated short-duration events due to lensing by planets, and find
that monitoring employing sensitive photometry is particularly useful. If
planetary systems similar to our own are common, even modest changes in
detection strategy should lead to the discovery of a few isolated events of
short duration every year. We therefore also address the issue of the
contamination due to stellar populations of any microlensing signal due to
low-mass MACHOs. We describe how, even for isolated events of short duration,
it will be possible to test the hypothesis that the lens was a planet instead
of a low-mass MACHO, if the central star of the planetary system contributes a
measurable fraction of the baseline flux.Comment: 37 pages, 6 figure. To be published in the Astrophysical Journal.
This is part one of a series of papers on microlensing by planetary systems
containing wide-orbit planets; the series represents a reorganization and
extension of astro-ph/971101
Einstein Radii from Binary Lensing Events
We show that the Einstein ring radius and transverse speed of a lens
projected on the source plane, and , can be
determined from the light curve of a binary-source event, followed by the
spectroscopic determination of the orbital elements of the source stars. The
determination makes use of the same principle that allows one to measure the
Einstein ring radii from finite-source effects. For the case when the orbital
period of the source stars is much longer than the Einstein time scale, , there exists a single two-fold degeneracy in determining
. However, when the degeneracy can
often be broken by making use of the binary-source system's orbital motion.
%Once , and thus are determined, one can
%distinguish self-lensing events in the Large Magellanic Cloud %from Galactic
halo events. For an identifiable 8\% of all lensing events seen toward the
Large Magellanic Cloud (LMC), one can unambiguously determine whether the
lenses are Galactic, or whether they lie in the LMC itself. The required
observations can be made after the event is over and could be carried out for
the events seen by Alcock et al.\ and Aubourg et al.. In addition, we
propose to include eclipsing binaries as sources for gravitational lensing
experiments.Comment: 18 pages, revised version, submitted to Ap
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
Modification of Aluminium Surface Using Picosecond Laser for Printing Applications
Ultrafast picosecond laser pulses of wavelength of 1064nm have allowed the surface modification of anodised aluminium plate for potential industrial application. The interaction of the laser with the substrate created a hydrophilic surface, giving a contact angle of less than 10 degrees. On examination under a Scanning Electron Microscope (SEM), it was observed that these surfaces have an interesting ‘lotus-leaf’ like structure. It has been found that these laser processed hydrophilic surfaces revert with time. The potential for application in the printing industry is strong due to the reusability and sustainability of the process materials; initial trials confirm this. This technology would offer extra advantages as a non-chemical process without the need for developer, thereby reducing the overall cost and time of printin
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