20,687 research outputs found
Peaks and Troughs in Helioseismology: The Power Spectrum of Solar Oscillations
I present a matched-wave asymptotic analysis of the driving of solar
oscillations by a general localised source. The analysis provides a simple
mathematical description of the asymmetric peaks in the power spectrum in terms
of the relative locations of eigenmodes and troughs in the spectral response.
It is suggested that the difference in measured phase function between the
modes and the troughs in the spectrum will provide a key diagnostic of the
source of the oscillations. I also suggest a form for the asymmetric line
profiles to be used in the fitting of solar power spectra.
Finally I present a comparison between the numerical and asymptotic
descriptions of the oscillations. The numerical results bear out the
qualitative features suggested by the asymptotic analysis but suggest that
numerical calculations of the locations of the troughs will be necessary for a
quantitative comparison with the observations.Comment: 18 pages + 8 separate figures. To appear in Ap
Improved bounds and new techniques for Davenport-Schinzel sequences and their generalizations
Let lambda_s(n) denote the maximum length of a Davenport-Schinzel sequence of
order s on n symbols. For s=3 it is known that lambda_3(n) = Theta(n alpha(n))
(Hart and Sharir, 1986). For general s>=4 there are almost-tight upper and
lower bounds, both of the form n * 2^poly(alpha(n)) (Agarwal, Sharir, and Shor,
1989). Our first result is an improvement of the upper-bound technique of
Agarwal et al. We obtain improved upper bounds for s>=6, which are tight for
even s up to lower-order terms in the exponent. More importantly, we also
present a new technique for deriving upper bounds for lambda_s(n). With this
new technique we: (1) re-derive the upper bound of lambda_3(n) <= 2n alpha(n) +
O(n sqrt alpha(n)) (first shown by Klazar, 1999); (2) re-derive our own new
upper bounds for general s; and (3) obtain improved upper bounds for the
generalized Davenport-Schinzel sequences considered by Adamec, Klazar, and
Valtr (1992). Regarding lower bounds, we show that lambda_3(n) >= 2n alpha(n) -
O(n), and therefore, the coefficient 2 is tight. We also present a simpler
version of the construction of Agarwal, Sharir, and Shor that achieves the
known lower bounds for even s>=4.Comment: To appear in Journal of the ACM. 48 pages, 3 figure
Macroscopic Observables Detecting Genuine Multipartite Entanglement and Partial Inseparability in Many-Body Systems
We show a general approach for detecting genuine multipartite entanglement
(GME) and partial inseparability in many-body-systems by means of macroscopic
observables (such as the energy) only. We show that the obtained criteria, the
"GME gap" and "the k-entanglement gap", detect large areas of genuine
multipartite entanglement and partial entanglement in typical many body states,
which are not detected by other criteria. As genuine multipartite entanglement
is a necessary property for several quantum information theoretic applications
such as e.g. secret sharing or certain kinds of quantum computation, our
methods can be used to select or design appropriate condensed matter systems.Comment: 4 pages, 3 figures, published version, title extende
Asteroseismology of Massive Stars : Some Words of Caution
Although playing a key role in the understanding of the supernova phenomenon,
the evolution of massive stars still suffers from uncertainties in their
structure, even during their "quiet" main sequence phase and later on during
their subgiant and helium burning phases. What is the extent of the mixed
central region? In the local mixing length theory (LMLT) frame, are there
structural differences using Schwarzschild or Ledoux convection criterion?
Where are located the convective zone boundaries? Are there intermediate
convection zones during MS and post-MS phase, and what is their extent and
location? We discuss these points and show how asteroseismology could bring
some light on these questions.Comment: 10 pages, 5 figures, IAU Symposium 307, New windows on massive stars:
asteroseismology, interferometry, and spectropolarimetry, G. Meynet, C.
Georgy, J.H. Groh & Ph. Stee, ed
Sensitivity to Timing and Order in Human Visual Cortex
Visual recognition takes a small fraction of a second and relies on the
cascade of signals along the ventral visual stream. Given the rapid path
through multiple processing steps between photoreceptors and higher visual
areas, information must progress from stage to stage very quickly. This rapid
progression of information suggests that fine temporal details of the neural
response may be important to the how the brain encodes visual signals. We
investigated how changes in the relative timing of incoming visual stimulation
affect the representation of object information by recording intracranial field
potentials along the human ventral visual stream while subjects recognized
objects whose parts were presented with varying asynchrony. Visual responses
along the ventral stream were sensitive to timing differences between parts as
small as 17 ms. In particular, there was a strong dependency on the temporal
order of stimulus presentation, even at short asynchronies. This sensitivity to
the order of stimulus presentation provides evidence that the brain may use
differences in relative timing as a means of representing information.Comment: 10 figures, 1 tabl
On the tensor convolution and the quantum separability problem
We consider the problem of separability: decide whether a Hermitian operator
on a finite dimensional Hilbert tensor product is separable or entangled. We
show that the tensor convolution defined for certain mappings on an almost
arbitrary locally compact abelian group, give rise to formulation of an
equivalent problem to the separability one.Comment: 13 pages, two sections adde
Cooperativity and Stability in a Langevin Model of Protein Folding
We present two simplified models of protein dynamics based on Langevin's
equation of motion in a viscous medium. We explore the effect of the potential
energy function's symmetry on the kinetics and thermodynamics of simulated
folding. We find that an isotropic potential energy function produces, at best,
a modest degree of cooperativity. In contrast, a suitable anisotropic potential
energy function delivers strong cooperativity.Comment: 45 pages, 16 figures, 2 tables. LaTeX. Submitted to the Journal of
Chemical Physic
The Coping Patterns among Primary Care Givers of the Persons with Schizophrenia - An Empirical Study
"Over the past half century, the model for mental health care has changed from the institutionalization of individuals suffering from mental disorders to a community care approach backed by the availability of beds in general hospitals for acute cases. This change is based both on respect for the human rights of individuals with mental disorders, and on the use of updated interventions and techniques" (WH0, 2001). Recovery from schizophrenia is a long-term goal and a journey that has to be made. There will be good and bad days in the journey, and it may be easy to get tired of fighting the illness and give up. Support and encouragement for the Person getting the family to take a constructive role in the journey are important. This is way it is so important to have someone who can help and guide the person and the families managing the illness and the social problems. The present empirical study on the Coping Patterns among primary care givers of the persons with schizophrenia by researchers would definitely through light to practitioners to intervene. By adopting systematic random sampling procedure the authors have drawn 60 samples, from every second name among the list of 120 universes. A self prepared questionnaire has been used to collect socio-demographic data and to measure the level of coping patterns the three point scale developed by Priya Daniyal (1997) has been used. The study reveals that the majority (72%) of the respondents expressed overall high level of coping mechanism. Keywords: Coping Patterns, Schizophrenia, Primary care-givers and community care approach
A New Test of the Einstein Equivalence Principle and the Isotropy of Space
Recent research has established that nonsymmetric gravitation theories like
Moffat's NGT predict that a gravitational field singles out an orthogonal pair
of polarization states of light that propagate with different phase velocities.
We show that a much wider class of nonmetric theories encompassed by the formalism predict such violations of the Einstein equivalence principle.
This gravity-induced birefringence of space implies that propagation through a
gravitational field can alter the polarization of light. We use data from
polarization measurements of extragalactic sources to constrain birefringence
induced by the field of the Galaxy. Our new constraint is times sharper
than previous ones.Comment: 21 pages, Latex, 3 Postscript figure
- …