518 research outputs found
Catching NGC4051 in the low state with XMM-Newton
The Narrow Line Seyfert 1 galaxy NGC4051 shows unusual low flux states,
lasting several months, when the 2-10 keV X-ray spectrum becomes unusually hard
(photon index<1) while the spectrum at lower X-ray energies is dominated by a
large soft excess. A Chandra TOO of the low state has shown that the soft
excess and hard components are variable and well-correlated. The variability of
the hard component rules out an origin in a distant reflector. Here we present
results from a recent XMM-Newton TOO of NGC4051 in the low state, which allows
a much more detailed examination of the nature of the hard and soft spectral
components in the low state. We demonstrate that the spectral shape in the low
state is consistent with the extrapolation of the spectral pivoting observed at
higher fluxes. The XMM-Newton data also reveals the warm absorbing gas in
emission, as the drop in the primary continuum flux unmasks prominent emission
lines from a range of ion species.Comment: 4 pages, 4 figures. Proc. of the meeting: "The Restless High-Energy
Universe" (Amsterdam, The Netherlands), E.P.J. van den Heuvel, J.J.M. in 't
Zand, and R.A.M.J. Wijers Ed
Management practices for the amelioration of urban stormwater
AbstractUrban runoff has been identified as a non-point source (NPS) contributor. The most effective mechanism for controlling urban NPS pollution is to reduce the amount of runoff through infiltration and storage on the landscape. Traditional infiltration best management practices (BMPs) have lacked long-term effectiveness because of clogging. The addition of vegetation to the system enhances the longevity of infiltration BMPs by enhancing soil structure. In order to better understand the design and function of vegetated, infiltration-based BMPs, Kansas State University is monitoring several sites in Kansas. Results indicate that vegetation enhances the ability of stormwater systems to store water and reduce down channel erosion and flooding
Fluctuations of an evaporating black hole from back reaction of its Hawking radiation: Questioning a premise in earlier work
This paper delineates the first steps in a systematic quantitative study of
the spacetime fluctuations induced by quantum fields in an evaporating black
hole. We explain how the stochastic gravity formalism can be a useful tool for
that purpose within a low-energy effective field theory approach to quantum
gravity. As an explicit example we apply it to the study of the
spherically-symmetric sector of metric perturbations around an evaporating
black hole background geometry. For macroscopic black holes we find that those
fluctuations grow and eventually become important when considering sufficiently
long periods of time (of the order of the evaporation time), but well before
the Planckian regime is reached. In addition, the assumption of a simple
correlation between the fluctuations of the energy flux crossing the horizon
and far from it, which was made in earlier work on spherically-symmetric
induced fluctuations, is carefully analyzed and found to be invalid. Our
analysis suggests the existence of an infinite amplitude for the fluctuations
of the horizon as a three-dimensional hypersurface. We emphasize the need for
understanding and designing operational ways of probing quantum metric
fluctuations near the horizon and extracting physically meaningful information.Comment: 10 pages, REVTeX; minor changes, a few references added and a brief
discussion of their relevance included. To appear in the proceedings of the
10th Peyresq meeting. Dedicated to Rafael Sorkin on the occasion of his 60th
birthda
The Specific Heat of Normal, Degenerate Quark Matter: Non-Fermi Liquid Corrections
In normal degenerate quark matter, the exchange of dynamically screened
transverse gluons introduces infrared divergences in the quark self-energies
that lead to the breakdown of the Fermi liquid description. If the core of
neutron stars are composed of quark matter with a normal component, cooling by
direct quark Urca processes may be modified by non-Fermi liquid corrections. We
find that while the quasiparticle density of states is finite and non-zero at
the Fermi surface, its frequency derivative diverges and results in non-Fermi
liquid corrections to the specific heat of the normal, degenerate component of
quark matter. We study these non-perturbative non-Fermi liquid corrections to
the specific heat and the temperature dependence of the chemical potential and
show that these lead to a reduction of the specific heat.Comment: new discussion, updated references, accepted in PR
Geometric Configurations, Regular Subalgebras of E10 and M-Theory Cosmology
We re-examine previously found cosmological solutions to eleven-dimensional
supergravity in the light of the E_{10}-approach to M-theory. We focus on the
solutions with non zero electric field determined by geometric configurations
(n_m, g_3), n\leq 10. We show that these solutions are associated with rank
regular subalgebras of E_{10}, the Dynkin diagrams of which are the (line)
incidence diagrams of the geometric configurations. Our analysis provides as a
byproduct an interesting class of rank-10 Coxeter subgroups of the Weyl group
of E_{10}.Comment: 48 pages, 27 figures, 5 tables, references added, typos correcte
Ten Proofs of the Generalized Second Law
Ten attempts to prove the Generalized Second Law of Thermodyanmics (GSL) are
described and critiqued. Each proof provides valuable insights which should be
useful for constructing future, more complete proofs. Rather than merely
summarizing previous research, this review offers new perspectives, and
strategies for overcoming limitations of the existing proofs. A long
introductory section addresses some choices that must be made in any
formulation the GSL: Should one use the Gibbs or the Boltzmann entropy? Should
one use the global or the apparent horizon? Is it necessary to assume any
entropy bounds? If the area has quantum fluctuations, should the GSL apply to
the average area? The definition and implications of the classical,
hydrodynamic, semiclassical and full quantum gravity regimes are also
discussed. A lack of agreement regarding how to define the "quasi-stationary"
regime is addressed by distinguishing it from the "quasi-steady" regime.Comment: 60 pages, 2 figures, 1 table. v2: corrected typos and added a
footnote to match the published versio
Evolving collective structures in the transitional nuclei W-162 and W-164
Excited states in the neutron-deficient nuclides W8874162 and W9074164 were investigated by using the γ-ray spectrometer Jurogam. A change in structure is apparent from the first rotational alignments in W162 and W164, whose rotationally aligned bands are interpreted as ν(h9/2)2 and ν(i13/2)2 configurations, respectively. The level schemes have been extended using recoil (-decay) correlations with the observation of excited collective structures. Configuration assignments have been made on the basis of comparisons of the deduced aligned angular momentum, as a function of rotational frequency, with the predictions of the cranked shell model
Precision Measurement of PArity Violation in Polarized Cold Neutron Capture on the Proton: the NPDGamma Experiment
The NPDGamma experiment at the Los Alamos Neutron Science Center (LANSCE) is
dedicated to measure with high precision the parity violating asymmetry in the
emission after capture of spin polarized cold neutrons in
para-hydrogen. The measurement will determine unambiguously the weak
pion-nucleon-nucleon () coupling constant {\it f}Comment: Proceedings of the PANIC'05 Conference, Santa Fe, NM, USA, October
24-28, 2005, 3 pages, 2 figure
Role of dynamical particle-vibration coupling in reconciliation of the puzzle for spherical proton emitters
It has been observed that decay rate for proton emission from
single particle state is systematically quenched compared with the prediction
of a one dimensional potential model although the same model successfully
accounts for measured decay rates from and states. We
reconcile this discrepancy by solving coupled-channels equations, taking into
account couplings between the proton motion and vibrational excitations of a
daughter nucleus. We apply the formalism to proton emitting nuclei
Re to show that there is a certain range of parameter set of the
excitation energy and the dynamical deformation parameter for the quadrupole
phonon excitation which reproduces simultaneously the experimental decay rates
from the 2, 3 and 1 states in these nuclei.Comment: RevTex, 12 pages, 4 eps figure
Controller-observer design and dynamic parameter identification for model-based control of an electromechanical lower-limb rehabilitation system
[EN] Rehabilitation is a hazardous task for a mechanical system, since the device has to interact with the human extremities without the hands-on experience the physiotherapist acquires over time. A gap needs to be filled in terms of designing effective controllers for this type of devices. In this respect, the paper describes the design of a model-based control for an electromechanical lower-limb rehabilitation system based on a parallel kinematic mechanism. A controller-observer was designed for estimating joint velocities, which are then used in a hybrid position/force control scheme. The model parameters are identified by customising an approach based on identifying only the relevant system dynamics parameters. Findings obtained through simulations show evidence of improvement in tracking performance compared with those where the velocity was estimated by numerical differentiation. The controller is also implemented in an actual electromechanical system for lower-limb rehabilitation tasks. Findings based on rehabilitation tasks confirm the findings from simulations.This work was partially financed by the Plan Nacional de I+D, Comision Interministerial de Ciencia y Tecnologia (FEDERCICYT) under the project DPI2013-44227-R and by the Instituto U. de Automatica e Informatica Industrial (ai2) of the Universitat Politecnica de Valencia.Valera Fernández, Á.; Díaz-Rodríguez, M.; Vallés Miquel, M.; Oliver, E.; Mata Amela, V.; Page Del Pozo, AF. (2017). Controller-observer design and dynamic parameter identification for model-based control of an electromechanical lower-limb rehabilitation system. International Journal of Control. 90(4):702-714. https://doi.org/10.1080/00207179.2016.1215529S702714904Åström, K. J., & Murray, R. M. (2010). Feedback Systems. doi:10.2307/j.ctvcm4gdkAtkeson, C. G., An, C. H., & Hollerbach, J. M. (1986). 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