12,371 research outputs found
An Advanced LMI-Based-LQR Design for Load Frequency Control of an Autonomous Hybrid Generation System
Part 13: Energy GenerationInternational audienceThis paper proposes a load frequency control scheme for an autonomous hybrid generation system consisting of wind turbine generator (WTG), diesel engine generator (DEG), fuel cell (FC), aquaelectrolyzer (AE) and battery energy storage system (BESS). In wind power generation systems, operating conditions are changing continually due to wind speed and load changes, having an effect on system frequency. Therefore, a robust controller is required for load frequency control. The control scheme is based on Linear Matrix Inequality (LMI)-Linear Quadratic Regulator (LQR). The control optimization problem is obtained in terms of a system of LMI constraints and matrix equations that are simultaneously solved. The proposed load frequency control scheme with the advanced LMI-based-LQR (ALQR) design is applied for the autonomous hybrid generation system. The effectiveness and robustness of the proposed controller is demonstrated for different load and wind power perturbations. The results suggest superior performance of the proposed ALQR controller against an optimal output state feedback controller. The integrated control could be realized though the web by applying Internet of Things technologies within the future smart grid
Tomographic approach to resolving the distribution of LISA Galactic binaries
The space based gravitational wave detector LISA is expected to observe a
large population of Galactic white dwarf binaries whose collective signal is
likely to dominate instrumental noise at observational frequencies in the range
10^{-4} to 10^{-3} Hz. The motion of LISA modulates the signal of each binary
in both frequency and amplitude, the exact modulation depending on the source
direction and frequency. Starting with the observed response of one LISA
interferometer and assuming only doppler modulation due to the orbital motion
of LISA, we show how the distribution of the entire binary population in
frequency and sky position can be reconstructed using a tomographic approach.
The method is linear and the reconstruction of a delta function distribution,
corresponding to an isolated binary, yields a point spread function (psf). An
arbitrary distribution and its reconstruction are related via smoothing with
this psf. Exploratory results are reported demonstrating the recovery of binary
sources, in the presence of white Gaussian noise.Comment: 13 Pages and 9 figures high resolution figures can be obtains from
http://www.phys.utb.edu/~rajesh/lisa_tomography.pd
The Planetary Mass Companion 2MASS1207-3932 B: Temperature, Mass and Evidence for an Edge-On Disk
We present J-band imaging and H+K-band low-resolution spectroscopy of
2MASS1207-3932 AB, obtained with VLT NACO. For the putative planetary mass
secondary, we find J = 20.0+/-0.2 mag. The HK spectra of both components imply
low gravity, and a dusty atmosphere for the secondary. Comparisons to synthetic
spectra yield Teff_A ~ 2550+/-150K, and Teff_B ~ 1600+/-100K, consistent with
their late-M and mid-to-late L types. For these Teff, and an age of 5-10 Myrs,
evolutionary models imply M_A ~ 24+/-6 M_Jup and M_B ~ 8+/-2 M_Jup. Independent
comparisons of these models to the observed colors, spanning ~I to L', also
yield the same masses and temperatures. Our primary mass agrees with other
recent analyses; however, our secondary mass, while still in the planetary
regime, is 2-3 times larger than claimed previously. This discrepancy can be
traced to the luminosities: while the absolute photometry and Mbol of the
primary agree with theoretical predictions, the secondary is ~ 2.5+/-0.5 mag
fainter than expected in all bands from I to L' and in Mbol. This accounts for
the much lower secondary mass (and temperature) derived earlier. We argue that
this effect is highly unlikely to result from a variety of model-related
problems, and is instead real. This conclusion is bolstered by the absence of
any luminosity problems in either the primary, or in AB Pic B which we also
analyse. We therefore suggest grey extinction in 2M1207B, due to occlusion by
an edge-on circum-secondary disk. This is consistent with the observed
properties of edge-on disks around T Tauri stars, and with the known presence
of a high-inclination evolved disk around the primary. Finally, the system's
implied mass ratio of ~0.3 suggests a binary-like formation scenario.
(abridged)Comment: Accepted by The Astrophysical Journal, 43 pages text + 16 figs + 1
tabl
An all-sky search algorithm for continuous gravitational waves from spinning neutron stars in binary systems
Rapidly spinning neutron stars with non-axisymmetric mass distributions are
expected to generate quasi-monochromatic continuous gravitational waves. While
many searches for unknown, isolated spinning neutron stars have been carried
out, there have been no previous searches for unknown sources in binary
systems. Since current search methods for unknown, isolated neutron stars are
already computationally limited, expanding the parameter space searched to
include binary systems is a formidable challenge. We present a new hierarchical
binary search method called TwoSpect, which exploits the periodic orbital
modulations of the continuous waves by searching for patterns in doubly
Fourier-transformed data. We will describe the TwoSpect search pipeline,
including its mitigation of detector noise variations and corrections for
Doppler frequency modulation caused by changing detector velocity. Tests on
Gaussian noise and on a set of simulated signals will be presented.Comment: 22 pages, 10 figures, 1 table, Submitted to Classical and Quantum
Gravit
Mesoscopic BCS pairing in the repulsive 1d-Hubbard model
We study mesoscopic pairing in the one dimensional repulsive Hubbard model
and its interplay with the BCS model in the canonical ensemble. The key tool is
comparing the Bethe ansatz equations of the two models in the limit of small
Coulomb repulsion. For the ordinary Hubbard interaction the BCS Bethe equations
with infinite pairing coupling are recovered; a finite pairing is obtained by
considering a further density-dependent phase-correlation in the hopping
amplitude of the Hubbard model. We find that spin degrees of freedom in the
Hubbard ground state are arranged in a state of the BCS type, where the
Cooper-pairs form an un-condensed liquid on a ``lattice'' of single particle
energies provided by the Hubbard charge degrees of freedom; the condensation in
the BCS ground state corresponds to Hubbard excitations constituted by a sea of
spin singlets.Comment: 15 pages, 6 figures. To be published on Physical Review
The pattern of distant metastasis and clinicopathological factors associated with de-novo metastatic cervical cancer: a retrospective analysis
Background: Metastatic cervical cancer carries poor prognosis. The factors associated with distant metastasis in newly diagnosed cervical cancer patients are not clear.Methods: A retrospective analytical study was performed to study the pattern of distant metastasis, and to evaluate the factors associated with de-novo metastatic cervical cancer. Univariate and multivariate analysis (by MANOVA) were used to evaluate the association. P≤0.05 was considered significant.Results: Out of 1321 newly diagnosed cervical cancer patients, 54 (4.1%) had de-novo metastatic disease and most of which (81%) were found at single site. Common sites of distant metastasis were non-regional nodes, followed by liver, lung, peritoneum and bone. Univariate analysis showed the factors associated with de-novo metastasis were non squamous subtype, high grade histology, bulky primary tumor (>4 cm), pelvic/para-aortic lymphadenopathy, and hydroureteronephrosis. Multivariate analysis revealed the factors associated with de-novo metastasis were bulky primary tumor (>4 cm), high grade histology, pelvic/para aortic lymphadenopathy, hydroureteronephrosis.Conclusions: Newly diagnosed cervical cancer patients with bulky primary tumor, high grade histology, pelvic or para aortic lymphadenopathy, hydroureteronephrosis are associated with higher risk of de-novo distant metastasis
Saturation of dephasing time in mesoscopic devices produced by a ferromagnetic state
We consider an exchange model of itinerant electrons in a Heisenberg
ferromagnet and we assume that the ferromagnet is in a fully polarized state.
Using the Holstein-Primakoff transformation we are able to obtain a
boson-fermion Hamiltonian that is well-known in the interaction between light
and matter. This model describes the spontaneous emission in two-level atoms
that is the proper decoherence mechanism when the number of modes of the
radiation field is taken increasingly large, the vacuum acting as a reservoir.
In the same way one can see that the interaction between the bosonic modes of
spin waves and an itinerant electron produces decoherence by spin flipping with
a rate proportional to the size of the system. In this way we are able to show
that the experiments on quantum dots, described in D. K. Ferry et al. [Phys.
Rev. Lett. {\bf 82}, 4687 (1999)], and nanowires, described in D. Natelson et
al. [Phys. Rev. Lett. {\bf 86}, 1821 (2001)], can be understood as the
interaction of itinerant electrons and an electron gas in a fully polarized
state.Comment: 10 pages, no figure. Changed title. Revised version accepted for
publication in Physical Review
Phase-coherence time saturation in mesoscopic systems: wave function collapse
A finite phase-coherence time emerges from iterative
measurement onto a quantum system. For a rapid sequence, the phase-coherence
time is found explicitly. For the stationary charge conduction problem, it is
bounded. At all order, in the time-interval of measurements, we propose a
general expression for .Comment: 8 pages, 0 figures, Late
Chern-simon type photon mass from fermion electric dipole moments at finite temperature in 3+1 dimensions
We study the low energy effective field theory of fermions with electric and
magnetic dipole moments at finite temperature. We find that at one loop there
is an interaction term of the Chern-Simon form . The four vector is interpreted as a Chern- Simon type mass of photons,
which is determined by the electric (magnetic) dipole moments ()
of the fermions in the vacuum polarisation loop diagram. The physical
consequence of such a photon mass is that, photons of opposite circular
polarisations, propagating through a hot medium, have different group
velocities. We estimate that the time lag between the arrival times of the left
and right circularly polarised light signals from pulsars. If the light
propagates through a hot plasma (where the temperature in some regions is ) then the time lag between the two circularly polarised signals
of frequency will be . It may
be possible to observe this effect in pulsar signals which propagate through
nebula at high temperatures.Comment: plain TeX, 9 page
Simultaneous Multi-Wavelength Observations of Magnetic Activity in Ultracool Dwarfs. III. X-ray, Radio, and H-alpha Activity Trends in M and L Dwarfs
[Abridged] As part of our on-going investigation into the magnetic field
properties of ultracool dwarfs, we present simultaneous radio, X-ray, and
H-alpha observations of three M9.5-L2.5 dwarfs (BRI0021-0214,
LSR060230.4+391059, and 2MASSJ052338.2-140302). We do not detect X-ray or radio
emission from any of the three sources, despite previous detections of radio
emission from BRI0021 and 2M0523-14. Steady and variable H-alpha emission are
detected from 2M0523-14 and BRI0021, respectively, while no H-alpha emission is
detected from LSR0602+39. Overall, our survey of nine M8-L5 dwarfs doubles the
number of ultracool dwarfs observed in X-rays, and triples the number of L
dwarfs, providing in addition the deepest limits to date, log(L_X/L_bol)<-5.
With this larger sample we find the first clear evidence for a substantial
reduction in X-ray activity, by about two orders of magnitude, from mid-M to
mid-L dwarfs. We find that the decline in both X-rays and H-alpha roughly
follows L_{X,Halpha}/L_bol ~ 10^[-0.4x(SP-M6)] for SP>M6. In the radio band,
however, the luminosity remains relatively unchanged from M0 to L4, leading to
a substantial increase in L_rad/L_bol. Our survey also provides the first
comprehensive set of simultaneous radio/X-ray/H-alpha observations of ultracool
dwarfs, and reveals a clear breakdown of the radio/X-ray correlation beyond
spectral type M7, evolving smoothly from L_{\nu,rad}/L_X ~ 10^-15.5 to
~10^-11.5 Hz^-1 over the narrow spectral type range M7-M9. This breakdown
reflects the substantial reduction in X-ray activity beyond M7, but its
physical origin remains unclear since, as evidenced by the uniform radio
emission, there is no drop in the field dissipation and particle acceleration
efficiency.Comment: Submitted to ApJ; 19 pages, 10 figures, 5 table
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