23,488 research outputs found
Transmission Expansion Planning Considering Energy Storage
In electricity transmission networks, energy storage systems (ESS) provide a
means of upgrade deferral by smoothing supply and matching demand. We develop a
mixed integer programming (MIP) extension to the transmission network expansion
planning (TEP) problem that considers the installation and operation of ESS as
well as additional circuits. The model is demonstrated on the well known
Garver's 6-bus and IEEE 25-bus test circuits for two 24 hour operating
scenarios; a short peak, and a long peak. We show optimal location and capacity
of storage is sensitive not only to cost, but also variability of demand in the
network
Room temperature spin relaxation in GaAs/AlGaAs multiple quantum wells
We have explored the dependence of electron spin relaxation in undoped GaAs/AlGaAs quantum wells on well width (confinement energy) at 300 K. For wide wells, the relaxation rate tends to the intrinsic bulk value due to the D'yakonov-Perel (DP) mechanism with momentum scattering by phonons. In narrower wells, there is a strong dependence of relaxation rate on well width, as expected for the DP mechanism, but also considerable variation between samples from different sources, which we attribute to differences in sample interface morphology. (C) 1998 American Institute of Physics. [S0003-6951(98)02541-8].</p
The Finite Field Kakeya Problem
A Besicovitch set in AG(n,q) is a set of points containing a line in every
direction. The Kakeya problem is to determine the minimal size of such a set.
We solve the Kakeya problem in the plane, and substantially improve the known
bounds for n greater than 4.Comment: 13 page
High magnetic field studies of the Vortex Lattice structure in YBa2Cu3O7
We report on small angle neutron scattering measurements of the vortex
lattice in twin-free YBa2Cu3O7, extending the previously investigated maximum
field of 11~T up to 16.7~T with the field applied parallel to the c axis. This
is the first microscopic study of vortex matter in this region of the
superconducting phase. We find the high field VL displays a rhombic structure,
with a field-dependent coordination that passes through a square configuration,
and which does not lock-in to a field-independent structure. The VL pinning
reduces with increasing temperature, but is seen to affect the VL correlation
length even above the irreversibility temperature of the lattice structure. At
high field and temperature we observe a melting transition, which appears to be
first order, with no detectable signal from a vortex liquid above the
transition
Full pf shell study of A = 47 and A = 49 nuclei
Complete diagonalizations in the pf major shell, lead to very good agreement
with the experimental data (level schemes, transitions rates, and static
moments) for the A=47 and A=49 isotopes of Ca, Sc, Ti, V, Cr, and Mn.
Gamow-Teller and M1 strength functions are calculated. The necessary monopole
modifications to the realistic interactions are shown to be critically tested
by the spectroscopic factors for one particle transfer from 48Ca, reproduced in
detail by the calculations. The collective behaviour of 47Ti, and of the mirror
pairs 47V-47Cr and 49Cr-49Mn is found to follow at low spins the particle plus
rotor model. It is then analysed in terms of the approximate quasi-SU(3)
symmetry, for which some new results are given.Comment: 30 Pages, RevTeX and epsf.sty, 23 figures included. Postscript
version available at http://www.ft.uam.es/~gabriel/a47-49.ps.g
The Ultraviolet Detection of Diffuse Gas in Galaxy Groups
A small survey of the UV-absorbing gas in 12 low- galaxy groups has been
conducted using the Cosmic Origins Spectrograph (COS) on-board the Hubble Space
Telescope (HST). Targets were selected from a large, homogeneously-selected
sample of groups found in the Sloan Digital Sky Survey (SDSS). A critical
selection criterion excluded sight lines that pass close ( virial radii)
to a group galaxy, to ensure absorber association with the group as a whole.
Deeper galaxy redshift observations are used both to search for closer galaxies
and also to characterize these to groups, the
most massive of which are highly-virialized with numerous early-type galaxies
(ETGs). This sample also includes two spiral-rich groups, not yet
fully-virialized. At group-centric impact parameters of 0.3-2 Mpc, these
-30 spectra detected HI absorption in 7 of 12 groups; high
(OVI) and low (SiIII) ion metal lines are present in 2/3 of the absorption
components. None of the three most highly-virialized, ETG-dominated groups are
detected in absorption. Covering fractions % are seen at all impact
parameters probed, but do not require large filling factors despite an enormous
extent. Unlike halo clouds in individual galaxies, group absorbers have radial
velocities which are too low to escape the group potential well without doubt.
This suggests that these groups are "closed boxes" for galactic evolution in
the current epoch. Evidence is presented that the cool and warm group absorbers
are not a pervasive intra-group medium (IGrM), requiring a hotter (
to K) IGrM to be present to close the baryon accounting.Comment: Resubmitted to ApJS after first review; 82 pages (27 for main text,
rest are Appendices and supplemental figures and tables), 47 figures, 21
table
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