719,295 research outputs found
Probing the small distance structure of canonical quantum gravity using the conformal group
In canonical quantum gravity, the formal functional integral includes an
integration over the local conformal factor, and we propose to perform the
functional integral over this factor before doing any of the other functional
integrals. By construction, the resulting effective theory would be expected to
be conformally invariant and therefore finite. However, also the conformal
integral itself diverges, and the effects of a renormalization counter term are
considered. It generates problems such as unitarity violation, due to a
Landau-like ghost, and conformal anomalies. Adding (massive or massless) matter
fields does not change the picture. Various alternative ideas are offered,
including a more daring speculation, which is that no counter term should be
allowed for at all. This has far-reaching and important consequences, which we
discuss. A surprising picture emerges of quantized elementary particles
interacting with a gravitational field, in particular gravitons, which are
"partly classical". This approach was inspired by a search towards the
reconciliation of Hawking radiation with unitarity and locality, and it offers
basic new insights there.Comment: 22 pages (incl. title page), 1 figure. Substantial changes in the
discussion sections, minor errors corrected, and references adde
Search for Outbursts in the Narrow 511-keV Line from Compact Sources Based on INTEGRAL Data
We present the results of a systematic search for outbursts in the narrow
positron annihilation line on various time scales (5x10^4 - 10^6 s) based on
the SPI/INTEGRAL data obtained from 2003 to 2008. We show that no outbursts
were detected with a statistical significance higher than ~6 sigma for any of
the time scales considered over the entire period of observations. We also show
that, given the large number of independent trials, all of the observed spikes
could be associated with purely statistical flux fluctuations and, in part,
with a small systematic prediction error of the telescope's instrumental
background. Based on the exposure achieved in ~6 yr of INTEGRAL operation, we
provide conservative upper limits on the rate of outbursts with a given
duration and flux in different parts of the sky.Comment: 16 pages, 8 figures. To be published in Astronomy Letters, 2010, Vol.
36, No 4, p. 23
Localization of Control Synthesis Problem for Large-Scale Interconnected System Using IQC and Dissipativity Theories
The synthesis problem for the compositional performance certification of
interconnected systems is considered. A fairly unified description of control
synthesis problem is given using integral quadratic constraints (IQC) and
dissipativity. Starting with a given large-scale interconnected system and a
global performance objective, an optimization problem is formulated to search
for admissible dissipativity properties of each subsystems. Local control laws
are then synthesized to certify the relevant dissipativity properties.
Moreover, the term localization is introduced to describe a finite collection
of syntheses problems, for the local subsystems, which are a feasibility
certificate for the global synthesis problem. Consequently, the problem of
localizing the global problem to a smaller collection of disjointed sets of
subsystems, called groups, is considered. This works looks promising as another
way of looking at decentralized control and also as a way of doing performance
specifications for components in a large-scale system
Modern Approaches to Exact Diagonalization and Selected Configuration Interaction with the Adaptive Sampling CI Method.
Recent advances in selected configuration interaction methods have made them competitive with the most accurate techniques available and, hence, creating an increasingly powerful tool for solving quantum Hamiltonians. In this work, we build on recent advances from the adaptive sampling configuration interaction (ASCI) algorithm. We show that a useful paradigm for generating efficient selected CI/exact diagonalization algorithms is driven by fast sorting algorithms, much in the same way iterative diagonalization is based on the paradigm of matrix vector multiplication. We present several new algorithms for all parts of performing a selected CI, which includes new ASCI search, dynamic bit masking, fast orbital rotations, fast diagonal matrix elements, and residue arrays. The ASCI search algorithm can be used in several different modes, which includes an integral driven search and a coefficient driven search. The algorithms presented here are fast and scalable, and we find that because they are built on fast sorting algorithms they are more efficient than all other approaches we considered. After introducing these techniques, we present ASCI results applied to a large range of systems and basis sets to demonstrate the types of simulations that can be practically treated at the full-CI level with modern methods and hardware, presenting double- and triple-ζ benchmark data for the G1 data set. The largest of these calculations is Si2H6 which is a simulation of 34 electrons in 152 orbitals. We also present some preliminary results for fast deterministic perturbation theory simulations that use hash functions to maintain high efficiency for treating large basis sets
Hybrid optimization techniques based automatic artificial respiration system for corona patient
Artificial ventilation is widely used for various respiratory problems of human beings. The oxygen level of the corona patients has to be maintained for smooth breathing which is very difficult. For achieving this state, the air pressure should be controlled in the respiration system that has a piston mechanism driven by a motor. An Automatic respiration system model is designed and controller parameters are tuned using hybrid Optimization techniques. Hybrid Controllers like genetic algorithm based Fractional Order Proportional Integral Derivative controller (FOPID), Fmincon-Pattern search Algorithm based Proportional Integral Derivative (PID) controller, and Hybrid Model predictive control (MPC) â Proportional Integral Derivative (PID) controllers were designed and verified. Integral Square Error is considered as the objective function of the optimization technique to find the controller parameters. The output responses of all three hybrid controllers are compared based on the error indices, time domain specifications, set-point tracking and Convergence speed graph. The genetic algorithm-based FOPID controller gives better results when compared with the Fmincon-Pattern search Algorithm based Proportional Integral Derivative (PID) controller and Hybrid Model predictive control (MPC) â Proportional Integral Derivative (PID) for the proposed artificial ventilation system
Hard X-ray emission and Ti line features of Tycho Supernova Remnant
A deep hard X-ray survey of the INTEGRAL satellite first detected the
non-thermal emission up to 90 keV in the Tycho supernova (SN) remnant. Its 3 --
100 keV spectrum is fitted with a thermal bremsstrahlung of keV plus a power-law model of . Based on the
diffusive shock acceleration theory, this non-thermal emission, together with
radio measurements, implies that Tycho remnant may not accelerate protons up to
PeV but hundreds TeV. Only heavier nuclei may be accelerated to the cosmic
ray spectral "knee". In addition, we search for soft gamma-ray lines at 67.9
and 78.4 keV coming from the decay of radioactive Ti in Tycho remnant by
INTEGRAL. A bump feature in the 60-90 keV energy band, potentially associated
with the Ti line emission, is found with a marginal significance level
of 2.6 . The corresponding 3 upper limit on the
Ti line flux amounts to 1.5 10 ph cm s.
Implications on the progenitor of Tycho SN, considered to be the prototype of
type Ia SN, are discussed.Comment: 15 pages, 4 figures, accepted for publication in Ap
Tuning of AGC of interconnected reheat thermal systems with geneticalgorithms
This paper deals with the application of genetic algorithms for optimizing the automatic generation control (AGC) systems. An integral controller and a proportional-plus-integral controller are considered. A two-area reheat thermal system is considered to exemplify the optimum parameter search. A digital simulation is used in conjunction with the genetic algorithm optimization process. The integral of the square of the error and the integral of time-multiplied absolute value of the error performance indices are considered in the search for the optimal AGC parameters. The results reported in this paper demonstrate the effectiveness of the genetic algorithms in the tuning of the AGC parameter
Tuning of AGC of interconnected reheat thermal systems with geneticalgorithms
This paper deals with the application of genetic algorithms for optimizing the automatic generation control (AGC) systems. An integral controller and a proportional-plus-integral controller are considered. A two-area reheat thermal system is considered to exemplify the optimum parameter search. A digital simulation is used in conjunction with the genetic algorithm optimization process. The integral of the square of the error and the integral of time-multiplied absolute value of the error performance indices are considered in the search for the optimal AGC parameters. The results reported in this paper demonstrate the effectiveness of the genetic algorithms in the tuning of the AGC parameter
Semiclassical collision theory. Application of multidimensional uniform approximations to the atom-rigid-rotor system
The multidimensional Bessel and Airy uniform approximations developed earlier in this series for the semiclassical S matrix are applied to the atom rigidârotor system. The need is shown for (a) using a geoemetrical criterion for determining whether a stationary phase point (s.p.pt) is a maximum, minimum, or saddle point; (b) choosing a proper quadrilateral configuration of the s.p.pts. with the phases as nearly equal as possible; and (c) choosing a unit cell to favor nearâseparation of variables. (a) and (b) apply both to the Airy and to the Bessel uniform approximations, and (c) to the Bessel. The use of a contour plot both to understand and to facilitate the search in new cases is noted. The case of real and complexâvalued stationary phase points is also considered, and the Bessel uniformâinâpairs approximation is applied. Comparison is made with exact quantum results. As in the oneâdimensional case, the Bessel is an improvement over the Airy for ââk = 0ââ transitions, while for other transitions they give similar results. Comparison in accuracy with the results of the integral method is also given. As a whole, the agreement can be considered to be reasonable. The improvement of the present over various more approximate results is shown
First survey of Wolf-Rayet star populations over the full extension of nearby galaxies observed with CALIFA
The search of extragalactic regions with conspicuous presence of Wolf-Rayet
(WR) stars outside the Local Group is challenging task due to the difficulties
in detecting their faint spectral features. In this exploratory work, we
develop a methodology to perform an automated search of WR signatures through a
pixel-by-pixel analysis of integral field spectroscopy (IFS) data belonging to
the Calar Alto Legacy Integral Field Area survey, CALIFA. This technique
allowed us to build the first catalogue of Wolf-Rayet rich regions with
spatially-resolved information, allowing to study the properties of these
complexes in a 2D context. The detection technique is based on the
identification of the blue WR bump (around He II 4686 {\AA}, mainly associated
to nitrogen-rich WR stars, WN) and the red WR bump (around C IV 5808 {\AA} and
associated to carbon-rich WR stars, WC) using a pixel-by-pixel analysis. We
identified 44 WR-rich regions with blue bumps distributed in 25 galaxies of a
total of 558. The red WR bump was identified only in 5 of those regions. We
found that the majority of the galaxies hosting WR populations in our sample
are involved in some kind of interaction process. Half of the host galaxies
share some properties with gamma-ray burst (GRB) hosts where WR stars, as
potential candidates to being the progenitors of GRBs, are found. We also
compared the WR properties derived from the CALIFA data with stellar population
synthesis models, and confirm that simple star models are generally not able to
reproduce the observations. We conclude that other effects, such as the binary
star channel (which could extend the WR phase up to 10 Myr), fast rotation or
other physical processes that causes the loss of observed Lyman continuum
photons, are very likely affecting the derived WR properties, and hence should
be considered when modelling the evolution of massive stars.Comment: 33 pages, accepted for publication in A&
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