5,081 research outputs found
N=2 Coset Compactifications with Non-Diagonal Invariants
We consider 4-dimensional string models obtained by tensoring N=2 coset
theories with non-diagonal modular invariants. We present results from a
systematic analysis including moddings by discrete symmetries.Comment: 29 page
Turbulence Time Series Data Hole Filling using Karhunen-Loeve and ARIMA methods
Measurements of optical turbulence time series data using unattended
instruments over long time intervals inevitably lead to data drop-outs or
degraded signals. We present a comparison of methods using both Principal
Component Analysis, which is also known as the Karhunen--Loeve decomposition,
and ARIMA that seek to correct for these event-induced and mechanically-induced
signal drop-outs and degradations. We report on the quality of the correction
by examining the Intrinsic Mode Functions generated by Empirical Mode
Decomposition. The data studied are optical turbulence parameter time series
from a commercial long path length optical anemometer/scintillometer, measured
over several hundred metres in outdoor environments.Comment: 8 pages, 9 figures, submitted to ICOLAD 2007, City University,
London, U
Jo Labanyi. Spanish Culture from Romanticism to the Present: Structures of Feeling. Legenda, 2019.
Review of Jo Labanyi. Spanish Culture from Romanticism to the Present: Structures of Feeling. Legenda, 2019. 349 pp
Orphans of the Motherland: Puerto Rican Images of Spain in Jacobo Morales\u27s Linda Sara
Puerto Rican identity has been confounded by Puerto Rico\u27s prolonged colonial relationship to Spain (nearly 80 years longer than that of most other Latin American colonies) and its abrupt change in status to that of United States protectorate in 1898 after the Spanish American War. Increasingly, Puerto Rican identity has been theorized in sole reference to the political relationship with the United States. The residual presence of Spain and Spaniards in the construction of the new Puerto Rican collective, and the denial or nostalgia that might still be elicited by the former empire, have gradually receded into the background. Perhaps surprisingly, the presence of Spain and reactions to it find their widest outlet in popular culture. This article analyzes the complex portrayal of the continuing substratum of the Spanish heritage in Puerto Rico in one example from Puerto Rican popular culture—Jacobo Morales\u27s 1994 film Linda Sara. The film\u27s characters either willingly or unknowingly falsify their Spanish past, recounting their (hi)story according to their present needs
Gravitational waves from the Papaloizou-Pringle instability in black hole-torus systems
Black hole (BH)--torus systems are promising candidates for the central
engine of gamma-ray bursts (GRBs), and also possible outcomes of the collapse
of supermassive stars to supermassive black holes (SMBHs). By three-dimensional
general relativistic numerical simulations, we show that an
nonaxisymmetric instability grows for a wide range of self-gravitating tori
orbiting BHs. The resulting nonaxisymmetric structure persists for a timescale
much longer than the dynamical one, becoming a strong emitter of large
amplitude, quasiperiodic gravitational waves. Our results indicate that both,
the central engine of GRBs and newly formed SMBHs, can be strong gravitational
wave sources observable by forthcoming ground-based and spacecraft detectors.Comment: 4 pages, 4 figure, to be published in PR
Nonlinear r-modes in Rapidly Rotating Relativistic Stars
The r-mode instability in rotating relativistic stars has been shown recently
to have important astrophysical implications (including the emission of
detectable gravitational radiation, the explanation of the initial spins of
young neutron stars and the spin-distribution of millisecond pulsars and the
explanation of one type of gamma-ray bursts), provided that r-modes are not
saturated at low amplitudes by nonlinear effects or by dissipative mechanisms.
Here, we present the first study of nonlinear r-modes in isentropic, rapidly
rotating relativistic stars, via 3-D general-relativistic hydrodynamical
evolutions. Our numerical simulations show that (1) on dynamical timescales,
there is no strong nonlinear coupling of r-modes to other modes at amplitudes
of order one -- unless nonlinear saturation occurs on longer timescales, the
maximum r-mode amplitude is of order unity (i.e., the velocity perturbation is
of the same order as the rotational velocity at the equator). An absolute upper
limit on the amplitude (relevant, perhaps, for the most rapidly rotating stars)
is set by causality. (2) r-modes and inertial modes in isentropic stars are
predominantly discrete modes and possible associated continuous parts were not
identified in our simulations. (3) In addition, the kinematical drift
associated with r-modes, recently found by Rezzolla, Lamb and Shapiro (2000),
appears to be present in our simulations, but an unambiguous confirmation
requires more precise initial data. We discuss the implications of our findings
for the detectability of gravitational waves from the r-mode instability.Comment: 4 pages, 4 eps figures, accepted in Physical Review Letter
Estimation of muscular forces from SSA smoothed sEMG signals calibrated by inverse dynamics-based physiological static optimization
The estimation of muscular forces is useful in several areas such as biomedical or rehabilitation engineering. As muscular forces cannot be measured in vivo non-invasively they must be estimated by using indirect measurements such as surface electromyography (sEMG) signals or by means of inverse dynamic (ID) analyses. This paper proposes an approach to estimate muscular forces based on both of them. The main idea is to tune a gain matrix so as to compute muscular forces from sEMG signals. To do so, a curve fitting process based on least-squares is carried out. The input is the sEMG signal filtered using singular spectrum analysis technique. The output corresponds to the muscular force estimated by the ID analysis of the recorded task, a dumbbell weightlifting. Once the model parameters are tuned, it is possible to obtain an estimation of muscular forces based on sEMG signal. This procedure might be used to predict muscular forces in vivo outside the space limitations of the gait analysis laboratory.Postprint (published version
A class of non-supersymmetric orientifolds
We study type IIB orientifolds on T^{2d}/Z_N with supersymmetry broken by the
compactification. We determine tadpole cancellation conditions including
anti-branes and considering different actions for the parity Omega. Using these
conditions we then obtain the spectrum of tachyons and massless states. Various
examples with N even correspond to type 0B orientifolds.Comment: 49 pages, Late
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