15,761 research outputs found
Reproductive and developmental effects of phthalate diesters in females.
Phthalate diesters, widely used in flexible plastics and consumer products, have become prevalent contaminants in the environment. Human exposure is ubiquitous and higher phthalate metabolite concentrations documented in patients using medications with phthalate-containing slow release capsules raises concerns for potential health effects. Furthermore, animal studies suggest that phthalate exposure can modulate circulating hormone concentrations and thus may be able to adversely affect reproductive physiology and the development of estrogen sensitive target tissues. Therefore, we conducted a systematic review of the epidemiological and experimental animal literature examining the relationship between phthalate exposure and adverse female reproductive health outcomes. The epidemiological literature is sparse for most outcomes studied and plagued by small sample size, methodological weaknesses, and thus fails to support a conclusion of an adverse effect of phthalate exposure. Despite a paucity of experimental animal studies for several phthalates, we conclude that there is sufficient evidence to suggest that phthalates are reproductive toxicants. However, we note that the concentrations needed to induce adverse health effects are high compared to the concentrations measured in contemporary human biomonitoring studies. We propose that the current patchwork of studies, potential for additive effects and evidence of adverse effects of phthalate exposure in subsequent generations and at lower concentrations than in the parental generation support the need for further study
The generic character table of a Sylow -subgroup of a finite Chevalley group of type
Let be a Sylow -subgroup of the finite Chevalley group of type
over the field of elements, where is a power of a prime . We
describe a construction of the generic character table of
Quantum state transfer in spin chains with q-deformed interaction terms
We study the time evolution of a single spin excitation state in certain
linear spin chains, as a model for quantum communication. Some years ago it was
discovered that when the spin chain data (the nearest neighbour interaction
strengths and the magnetic field strengths) are related to the Jacobi matrix
entries of Krawtchouk polynomials or dual Hahn polynomials, so-called perfect
state transfer takes place. The extension of these ideas to other types of
discrete orthogonal polynomials did not lead to new models with perfect state
transfer, but did allow more insight in the general computation of the
correlation function. In the present paper, we extend the study to discrete
orthogonal polynomials of q-hypergeometric type. A remarkable result is a new
analytic model where perfect state transfer is achieved: this is when the spin
chain data are related to the Jacobi matrix of q-Krawtchouk polynomials. The
other cases studied here (affine q-Krawtchouk polynomials, quantum q-Krawtchouk
polynomials, dual q-Krawtchouk polynomials, q-Hahn polynomials, dual q-Hahn
polynomials and q-Racah polynomials) do not give rise to models with perfect
state transfer. However, the computation of the correlation function itself is
quite interesting, leading to advanced q-series manipulations
Electron Wave Filters from Inverse Scattering Theory
Semiconductor heterostructures with prescribed energy dependence of the
transmittance can be designed by combining: {\em a)} Pad\'e approximant
reconstruction of the S-matrix; {\em b)} inverse scattering theory for
Schro\"dinger's equation; {\em c)} a unitary transformation which takes into
account the variable mass effects. The resultant continuous concentration
profile can be digitized into an easily realizable rectangular-wells structure.
For illustration, we give the specifications of a 2 narrow band-pass 12 layer
filter with the high energy peak more than {\em twice
narrower} than the other.Comment: 4 pages, Revtex with one eps figur
A Note on Hartle-Hawking Vacua
The purpose of this note is to establish the basic properties--- regularity
at the horizon, time independence, and thermality--- of the generalized
Hartle-Hawking vacua defined in static spacetimes with bifurcate Killing
horizon admitting a regular Euclidean section. These states, for free or
interacting fields, are defined by a path integral on half the Euclidean
section. The emphasis is on generality and the arguments are simple but formal.Comment: 5 pages, LaTe
'Heaven starts at your parents' feet' : adolescent bowing to parents and associated spiritual attitudes
In a quantitative survey of religious attitudes and practices in a multi-religious sample of
369 school pupils aged between 13 and 15 in London, the practice of bowing to parents was
found widespread in 22% of adolescents spanning several religious affiliations and
ethnicities – especially Buddhists, Hindus and those of Indian, African and ‘Other Asian’
ethnicity. Whether an adolescent bowed correlated significantly with spiritual attitudes such
as wanting to abstain from alcohol, hearing religious stories, being inspired by religious
festivals and liking the idea of seeing God in everything. Findings suggest bowing to
parents can have religious significance on all three levels of Jackson’s Interpretive
Approach and therefore cannot be regarded as a ‘cultural accretion’ of religion. Study of
bowing to parents could form a unifying exercise in shared values for study of religion in
the plural classroom and facilitate community cohesion in certain religious membership
groups
Quantum communication and state transfer in spin chains
We investigate the time evolution of a single spin excitation state in certain linear spin chains, as a model for quantum communication. We consider first the simplest possible spin chain, where the spin chain data (the nearest neighbour interaction strengths and the magnetic field strengths) are constant throughout the chain. The time evolution of a single spin state is determined, and this time evolution is illustrated by means of an animation. Some years ago it was discovered that when the spin chain data are of a special form so-called perfect state transfer takes place. These special spin chain data can be linked to the Jacobi matrix entries of Krawtchouk polynomials or dual Hahn polynomials. We discuss here the case related to Krawtchouk polynomials, and illustrate the possibility of perfect state transfer by an animation showing the time evolution of the spin chain from an initial single spin state. Very recently, these ideas were extended to discrete orthogonal polynomials of q-hypergeometric type. Here, a remarkable result is a new analytic model where perfect state transfer is achieved: this is when the spin chain data are related to the Jacobi matrix of q-Krawtchouk polynomials. This case is discussed here, and again illustrated by means of an animation
Semiclassical time--dependent propagation in three dimensions: How accurate is it for a Coulomb potential?
A unified semiclassical time propagator is used to calculate the
semiclassical time-correlation function in three cartesian dimensions for a
particle moving in an attractive Coulomb potential. It is demonstrated that
under these conditions the singularity of the potential does not cause any
difficulties and the Coulomb interaction can be treated as any other
non-singular potential. Moreover, by virtue of our three-dimensional
calculation, we can explain the discrepancies between previous semiclassical
and quantum results obtained for the one-dimensional radial Coulomb problem.Comment: 8 pages, 4 figures (EPS
Improved detection of small atom numbers through image processing
We demonstrate improved detection of small trapped atomic ensembles through
advanced post-processing and optimal analysis of absorption images. A fringe
removal algorithm reduces imaging noise to the fundamental photon-shot-noise
level and proves beneficial even in the absence of fringes. A
maximum-likelihood estimator is then derived for optimal atom-number estimation
and is applied to real experimental data to measure the population differences
and intrinsic atom shot-noise between spatially separated ensembles each
comprising between 10 and 2000 atoms. The combined techniques improve our
signal-to-noise by a factor of 3, to a minimum resolvable population difference
of 17 atoms, close to our ultimate detection limit.Comment: 4 pages, 3 figure
- …