6,736 research outputs found
Commentary: Providing Versus Packaging Support for Bereaved Parents After Perinatal Loss
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73421/1/j.1523-536X.1992.tb00384.x.pd
Constructing networks of defects with scalar fields
We propose a new way to build networks of defects. The idea takes advantage
of the deformation procedure recently employed to describe defect structures,
which we use to construct networks, spread from small rudimentary networks that
appear in simple models of scalar fields.Comment: 5 pages, 4 figures, version with new title, motivations and
references, to appear in PL
A Note on the Generalized Friedmann Equations for a Thick Brane
Within our thick brane approach previously used to obtain the cosmological
evolution equations on a thick brane embedded in a five-dimensional
Schwarzschild Anti-de Sitter spacetime it is explicitly shown that the
consistency of these equations with the energy conservation equation requires
that, in general, the thickness of the brane evolves in time. This varying
brane thickness entails the possibility that both Newton's gravitational
constant and the effective cosmological constant are time
dependent.Comment: 6 pages,To appear in GR
Lifetime reproductive output over two generations in patients with psychosis and their unaffected siblings:the Uppsala 1915-1929 Birth Cohort Multigenerational Study
BACKGROUND: Schizophrenic patients have fewer offspring than the general population but it is unclear whether (i) this persists for more than one generation, (ii) the reduced fertility is compensated by increased fertility in unaffected relatives, (iii) sociodemographic factors confound or interact with the association, and (iv) patients with affective psychosis have a similar fertility disadvantage. This study measured biological fitness over two generations in patients with schizophrenia or affective psychosis, and their unaffected siblings. METHOD: We conducted a historical cohort study using a Swedish birth cohort of 12 168 individuals born 1915-1929 and followed up until 2002. We compared biological fitness over two generations in patients with schizophrenia (n=58) or affective psychosis (n=153), and their unaffected siblings, with the population, adjusting for a range of sociodemographic variables from throughout the lifespan. RESULTS: Patients with schizophrenia had fewer children [fertility ratio (FR) 0.42, 95% confidence interval (CI) 0.29-0.61] and grandchildren (FR 0.51, 95% CI 0.33-0.80) than the population. Some of this reduction was related to lower marriage rates in schizophrenic patients. The unaffected siblings of schizophrenic patients showed no evidence of any compensatory increase in fitness, but there was a trend towards enhanced fertility among the offspring of schizophrenia patients. Patients with affective psychosis and their relatives did not differ from the general population on any fertility measure. CONCLUSIONS: Schizophrenia, but not affective psychosis, is associated with reduced biological fertility; this disadvantage is partly explained by marital status and persists into the second generation
Wave-like Solutions for Bianchi type-I cosmologies in 5D
We derive exact solutions to the vacuum Einstein field equations in 5D, under
the assumption that (i) the line element in 5D possesses self-similar symmetry,
in the classical understanding of Sedov, Taub and Zeldovich, and that (ii) the
metric tensor is diagonal and independent of the coordinates for ordinary 3D
space. These assumptions lead to three different types of self-similarity in
5D: homothetic, conformal and "wave-like". In this work we present the most
general wave-like solutions to the 5D field equations. Using the standard
technique based on Campbell's theorem, they generate a large number of
anisotropic cosmological models of Bianchi type-I, which can be applied to our
universe after the big-bang, when anisotropies could have played an important
role. We present a complete review of all possible cases of self-similar
anisotropic cosmologies in 5D. Our analysis extends a number of previous
studies on wave-like solutions in 5D with spatial spherical symmetry
Gradient expansion approach to multiple-band Fermi liquids
Promoted by the recent progress of Berry phase physics in spin
galvanomagnetic communities, we develop a systematic derivation of the reduced
Keldysh equation (RKE) which captures the low-energy dynamics of
quasi-particles constrained within doubly degenerate bands forming a single
Fermi surface. Specifically, we project out the fully occupied/empty band
degrees of freedom perturbatively in the gradient expansion, whose coupling
constant measures how a system is disequilibrated. As for the electron-electron
interactions, however, we only employ the so-called adiabatic assumption of the
Fermi liquid theory, so that the effect of electron correlations onto the
adiabatic transport of quasi-particles, i.e. the hermitian (real) part of the
self-energy, is taken into account in an unbiased manner.Comment: 29 pages, 7 figure
Mass and Charge in Brane-World and Non-Compact Kaluza-Klein Theories in 5 Dim
In classical Kaluza-Klein theory, with compactified extra dimensions and
without scalar field, the rest mass as well as the electric charge of test
particles are constants of motion. We show that in the case of a large extra
dimension this is no longer so. We propose the Hamilton-Jacobi formalism,
instead of the geodesic equation, for the study of test particles moving in a
five-dimensional background metric. This formalism has a number of advantages:
(i) it provides a clear and invariant definition of rest mass, without the
ambiguities associated with the choice of the parameters used along the motion
in 5D and 4D, (ii) the electromagnetic field can be easily incorporated in the
discussion, and (iii) we avoid the difficulties associated with the "splitting"
of the geodesic equation. For particles moving in a general 5D metric, we show
how the effective rest mass, as measured by an observer in 4D, varies as a
consequence of the large extra dimension. Also, the fifth component of the
momentum changes along the motion. This component can be identified with the
electric charge of test particles. With this interpretation, both the rest mass
and the charge vary along the trajectory. The constant of motion is now a
combination of these quantities. We study the cosmological variations of charge
and rest mass in a five-dimensional bulk metric which is used to embed the
standard k = 0 FRW universes. The time variations in the fine structure
"constant" and the Thomson cross section are also discussed.Comment: V2: References added, discussion extended. V3 is identical to V2,
references updated. To appear in General Relativity and Gravitatio
Theory of Pump Depletion and Spike Formation in Stimulated Raman Scattering
By using the inverse spectral transform, the SRS equations are solved and the
explicit output data is given for arbitrary laser pump and Stokes seed profiles
injected on a vacuum of optical phonons. For long duration laser pulses, this
solution is modified such as to take into account the damping rate of the
optical phonon wave. This model is used to interprete the experiments of Druhl,
Wenzel and Carlsten (Phys. Rev. Lett., (1983) vol. 51, p. 1171), in particular
the creation of a spike of (anomalous) pump radiation. The related nonlinear
Fourier spectrum does not contain discrete eigenvalue, hence this Raman spike
is not a soliton.Comment: LaTex file, includes two figures in LaTex format, 9 page
Long-term variability of the optical spectra of NGC 4151: II. Evolution of the broad Ha and Hb emission-line profiles
Results of the long-term (11 years, from 1996 to 2006) H and H
line variations of the active galactic nucleus of NGC 4151 are presented. High
quality spectra (S/N>50 and R~8A) of H and H were investigated.
We analyzed line profile variations during monitoring period. Comparing the
line profiles of H and H, we studied different details (bumps,
absorption features) in the line profiles. The variations of the different
H and H line profile segments have been investigated. Also, we
analyzed the Balmer decrement for whole line and for line segments. We found
that the line profiles were strongly changing during the monitoring period,
showing blue and red asymmetries. This indicates a complex BLR geometry of NGC
4151 with, at least, three kinematically distinct regions: one that contributes
to the blue line wing, one to the line core and one to the red line wing. Such
variation can be caused by an accelerating outflow starting very close to the
black hole, where the red part may come from the region {closer to the black
hole than the blue part, which is coming} from the region having the highest
outflow velocities. Taking into account the fact that the BLR of NGC 4151 has a
complex geometry (probably affected by an outflow) and that a portion of the
broad line emission seems to have not a pure photoionization origin, one can
ask the question whether the study of the BLR by reverberation mapping may be
valid in the case of this galaxy.Comment: 24 pages, 18 figures, accepted for publications in A&
Effective spacetime from multi-dimensional gravity
We study the effective spacetimes in lower dimensions that can be extracted
from a multidimensional generalization of the Schwarzschild-Tangherlini
spacetimes derived by Fadeev, Ivashchuk and Melnikov ({\it Phys. Lett,} {\bf A
161} (1991) 98). The higher-dimensional spacetime has
dimensions, where and are the number of "internal" and "external" extra
dimensions, respectively. We analyze the effective spacetime obtained
after dimensional reduction of the external dimensions. We find that when
the extra dimensions are compact (i) the physics in lower dimensions is
independent of and the character of the singularities in higher dimensions,
and (ii) the total gravitational mass of the effective matter distribution
is less than the Schwarzshild mass. In contrast, when the extra dimensions
are large this is not so; the physics in does explicitly depend on
, as well as on the nature of the singularities in high dimensions, and the
mass of the effective matter distribution (with the exception of wormhole-like
distributions) is bigger than the Schwarzshild mass. These results may be
relevant to observations for an experimental/observational test of the theory.Comment: A typo in Eq. (24) is fixe
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