7,344 research outputs found
Multi-site, multi-year monitoring of the oscillating Algol-type eclipsing binary CT Her
We present the results of a multi-site photometric campaign carried out in
2004-2008 for the Algol-type eclipsing binary system CT Her, the primary
component of which shows Delta Scuti-type oscillations. Our data consist of
differential light curves collected in the filters B and V which have been
analysed using the method of Wilson-Devinney (PHOEBE). After identification of
an adequate binary model and removal of the best-matching light curve solution,
we performed a Fourier analysis of the residual B and V light curves to
investigate the pulsational behaviour. We confirm the presence of rapid
pulsations with a main period of 27.2 min. Up to eight significant frequencies
with semi-amplitudes in the range 3 to 1 mmag were detected, all of which
surprisingly lie in the frequency range 43.5-53.5 c\d. This result is
independent from the choice of the primary's effective temperature (8200 or
8700 K) since the light curve models for the binary are very similar in both
cases. This is yet another case of a complex frequency spectrum observed for an
accreting Delta Scuti-type star (after Y Cam). In addition, we demonstrate that
the amplitudes of several of these pulsation frequencies show evidence of
variability on time scales as short as 1-2 years, perhaps even less. Moreover,
our analysis takes into account some recently acquired spectra, from which we
obtained the corresponding radial velocities for the years 2007-2009.
Investigation of the O-C diagram shows that further monitoring of the epochs of
eclipse minima of CT Her will cast a new light on the evolution of its orbital
period.Comment: 13 pages, 13 encapsulated Postscript figures. Tables~3, 4, 9 and 12
will be available in electronic form only. Astronomy and Astrophysics, in
process (2011). Replaced the abstract with its final versio
Pyomo - Optimization Modeling in Python
INFORMS Journal of Computing, November 2012The article of record as published may be located at http://dx.doi.org/10.1287/ijoc.2012.4.brIf a simple, intuitive tool for a task exists, the task is done more often, by more people. This basic
principle is as true for gardening and gadgets, as it is for computation in operations research.
The book, Pyomo { Optimization Modeling in Python, documents a simple, yet versatile tool for
modeling and solving optimization problems
Peak positions and shapes in neutron pair correlation functions from powders of highly anisotropic crystals
The effect of the powder average on the peak shapes and positions in neutron
pair distribution functions of polycrystalline materials is examined. It is
shown that for highly anisotropic crystals, the powder average leads to shifts
in peak positions and to non-Gaussian peak shapes. The peak shifts can be as
large as several percent of the lattice spacing
Magnetocaloric Studies of the Peak Effect in Nb
We report a magnetocaloric study of the peak effect and Bragg glass
transition in a Nb single crystal. The thermomagnetic effects due to vortex
flow into and out of the sample are measured. The magnetocaloric signature of
the peak effect anomaly is identified. It is found that the peak effect
disappears in magnetocaloric measurements at fields significantly higher than
those reported in previous ac-susceptometry measurements. Investigation of the
superconducting to normal transition reveals that the disappearance of the bulk
peak effect is related to inhomogeneity broadening of the superconducting
transition. The emerging picture also explains the concurrent disappearance of
the peak effect and surface superconductivity, which was reported previously in
the sample under investigation. Based on our findings we discuss the
possibilities of multicriticality associated with the disappearance of the peak
effect.Comment: 30 pages, 10 figure
The stellar content of the young open cluster Trumpler 37
With an apparent cluster diameter of 1.5{\deg} and an age of ~4 Myr, Trumpler
37 is an ideal target for photometric monitoring of young stars as well as for
the search of planetary transits, eclipsing binaries and other sources of
variability. The YETI consortium has monitored Trumpler 37 throughout 2010 and
2011 to obtain a comprehensive view of variable phenomena in this region. In
this first paper we present the cluster properties and membership determination
as derived from an extensive investigation of the literature. We also compared
the coordinate list to some YETI images. For 1872 stars we found literature
data. Among them 774 have high probability of being member and 125 a medium
probability. Based on infrared data we re-calculate a cluster extinction of
0.9-1.2 mag. We can confirm the age and distance to be 3-5 Myr and ~870 pc.
Stellar masses are determined from theoretical models and the mass function is
fitted with a power-law index of alpha=1.90 (0.1-0.4 M_sun) and alpha=1.12
(1-10 M_sun).Comment: 9 pages, 10 figures, 2 long tables, accepte
Advances in surface EMG signal simulation with analytical and numerical descriptions of the volume conductor
Surface electromyographic (EMG) signal modeling is important for signal interpretation, testing of processing algorithms, detection system design, and didactic purposes. Various surface EMG signal models have been proposed in the literature. In this study we focus on 1) the proposal of a method for modeling surface EMG signals by either analytical or numerical descriptions of the volume conductor for space-invariant systems, and 2) the development of advanced models of the volume conductor by numerical approaches, accurately describing not only the volume conductor geometry, as mainly done in the past, but also the conductivity tensor of the muscle tissue. For volume conductors that are space-invariant in the direction of source propagation, the surface potentials generated by any source can be computed by one-dimensional convolutions, once the volume conductor transfer function is derived (analytically or numerically). Conversely, more complex volume conductors require a complete numerical approach. In a numerical approach, the conductivity tensor of the muscle tissue should be matched with the fiber orientation. In some cases (e.g., multi-pinnate muscles) accurate description of the conductivity tensor may be very complex. A method for relating the conductivity tensor of the muscle tissue, to be used in a numerical approach, to the curve describing the muscle fibers is presented and applied to representatively investigate a bi-pinnate muscle with rectilinear and curvilinear fibers. The study thus propose an approach for surface EMG signal simulation in space invariant systems as well as new models of the volume conductor using numerical methods
A systematic review of the international published literature relating to quality of institutional care for people with longer term mental health problems.
BACKGROUND: A proportion of people with mental health problems require longer term care in a psychiatric or social care institution. However, there are no internationally agreed quality standards for institutional care and no method to assess common care standards across countries. We aimed to identify the key components of institutional care for people with longer term mental health problems and the effectiveness of these components.
METHODS: We undertook a systematic review of the literature using comprehensive search terms in 11 electronic databases and identified 12,182 titles. We viewed 550 abstracts, reviewed 223 papers and included 110 of these. A "critical interpretative synthesis" of the evidence was used to identify domains of institutional care that are key to service users' recovery.
RESULTS: We identified eight domains of institutional care that were key to service users' recovery: living conditions; interventions for schizophrenia; physical health; restraint and seclusion; staff training and support; therapeutic relationship; autonomy and service user involvement; and clinical governance. Evidence was strongest for specific interventions for the treatment of schizophrenia (family psychoeducation, cognitive behavioural therapy (CBT) and vocational rehabilitation).
CONCLUSION: Institutions should, ideally, be community based, operate a flexible regime, maintain a low density of residents and maximise residents' privacy. For service users with a diagnosis of schizophrenia, specific interventions (CBT, family interventions involving psychoeducation, and supported employment) should be provided through integrated programmes. Restraint and seclusion should be avoided wherever possible and staff should have adequate training in de-escalation techniques. Regular staff supervision should be provided and this should support service user involvement in decision making and positive therapeutic relationships between staff and service users. There should be clear lines of clinical governance that ensure adherence to evidence-based guidelines and attention should be paid to service users' physical health through regular screening
Interplay between pulsations and mass loss in the blue supergiant 55 Cygnus = HD 198478
Blue supergiant stars are known to display photometric and spectroscopic
variability that is suggested to be linked to stellar pulsations. Pulsational
activity in massive stars strongly depends on the star's evolutionary stage and
is assumed to be connected with mass-loss episodes, the appearance of
macroturbulent line broadening, and the formation of clumps in the wind. To
investigate a possible interplay between pulsations and mass-loss, we carried
out an observational campaign of the supergiant 55 Cyg over a period of five
years to search for photospheric activity and cyclic mass-loss variability in
the stellar wind. We modeled the H, He I, Si II and Si III lines using the
nonlocal thermal equilibrium atmosphere code FASTWIND and derived the
photospheric and wind parameters. In addition, we searched for variability in
the intensity and radial velocity of photospheric lines and performed a moment
analysis of the line profiles to derive frequencies and amplitudes of the
variations. The Halpha line varies with time in both intensity and shape,
displaying various types of profiles: P Cygni, pure emission, almost complete
absence, and double or multiple peaked. The star undergoes episodes of variable
mass-loss rates that change by a factor of 1.7-2 on different timescales. We
also observe changes in the ionization rate of Si II and determine a
multiperiodic oscillation in the He I absorption lines, with periods ranging
from a few hours to 22.5 days. We interpret the photospheric line variations in
terms of oscillations in p-, g-, and strange modes. We suggest that these
pulsations can lead to phases of enhanced mass loss. Furthermore, they can
mislead the determination of the stellar rotation. We classify the star as a
post-red supergiant, belonging to the group of alpha Cyg variables.Comment: 20 pages, 18 figures, 3 tables, accepted to Astronomy & Astrophysic
Hysteretic properties of a magnetic particle with strong surface anisotropy
We study the influence of surface anisotropy on the zero-temperature
hysteretic properties of a small single-domain magnetic particle, and give an
estimation of the anisotropy constant for which deviations from the
Stoner-Wohlfarth model are observed due to non-uniform reversal of the
particle's magnetisation. For this purpose, we consider a spherical particle
with simple cubic crystalline structure, a uniaxial anisotropy for core spins
and radial anisotropy on the surface. The hysteresis loop is obtained by
solving the local (coupled) Landau-Lifschitz equations for classical spin
vectors. We find that when the surface anisotropy constant is at least of the
order of the exchange coupling, large deviations are observed with respect to
the Stoner-Wohlfarth model in the hysteresis loop and thereby the
limit-of-metastability curve, since in this case the magnetisation reverses its
direction in a non-uniform manner via a progressive switching of spin clusters.
In this case the critical field, as a function of the particle's size, behaves
as observed in experiments.Comment: 12 pages, 15 eps figure
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