8,447 research outputs found
GW approximation with self-screening correction
The \emph{GW} approximation takes into account electrostatic self-interaction
contained in the Hartree potential through the exchange potential. However, it
has been known for a long time that the approximation contains self-screening
error as evident in the case of the hydrogen atom. When applied to the hydrogen
atom, the \emph{GW} approximation does not yield the exact result for the
electron removal spectra because of the presence of self-screening: the hole
left behind is erroneously screened by the only electron in the system which is
no longer present. We present a scheme to take into account self-screening and
show that the removal of self-screening is equivalent to including exchange
diagrams, as far as self-screening is concerned. The scheme is tested on a
model hydrogen dimer and it is shown that the scheme yields the exact result to
second order in where and are respectively
the onsite and offsite Hubbard interaction parameters and the hopping
parameter.Comment: 9 pages, 2 figures; Submitted to Phys. Rev.
ELVIS - ELectromagnetic Vector Information Sensor
The ELVIS instrument was recently proposed by the authors for the Indian
Chandrayaan-1 mission to the Moon and is presently under consideration by the
Indian Space Research Organisation (ISRO). The scientific objective of ELVIS is
to explore the electromagnetic environment of the moon. ELVIS samples the full
three-dimensional (3D) electric field vector, E(x,t), up to 18 MHz, with
selective Nyqvist frequency bandwidths down to 5 kHz, and one component of the
magnetic field vector, B(x,t), from a few Hz up to 100 kHz.As a transient
detector, ELVIS is capable of detecting pulses with a minimum pulse width of 5
ns. The instrument comprises three orthogonal electric dipole antennas, one
magnetic search coil antenna and a four-channel digital sampling system,
utilising flexible digital down conversion and filtering together with
state-of-the-art onboard digital signal processing.Comment: 8 pages, 3 figures. Submitted to the DGLR Int. Symposium "To Moon and
Beyond", Bremen, Germany, 2005. Companion paper to arXiv:astro-ph/050921
Statistical properties of ionospheric stimulated electromagnetic emissions
We have analysed the statistical properties of the stimulated electromagnetic emissions (SEE) spectral features in the steady state, reached after a long period of continuous HF pumping of the ionosphere in experiments performed at the Sura ionospheric radio research facility in Russia. Using a digital filter bank method, we have been able to analyse complex valued signals within narrow frequency bands. Each of the SEE spectral features are thereby separated into a number of narrow spectral components. Statistical tests were performed for all these spectral components and the distributions of the spectral amplitudes and phases were evaluated. Also, a test for sinusoidal components was performed. These tests showed that all observed SEE features were indistinguishable from coloured Gaussian noise. The test results exclude that the SEE features can be the result of a single isolated coherent process, but does not rule out that there could be many statistically independent parametric wave-wave processes taking place simultaneously at various parts of the HF-pumped ionosphere, as long as the superposition from all these is incoherent. Furthermore, from the test results, we cannot exclude the possibility that the waveforms of some, or all, of the SEE features may be chaotic
Early pathways of maternal mentalization: Associations with child development in the FinnBrain birth cohort study
Parental mentalization refers to a parentsâ capacity and interest to consider the individual experience and mental state underlying the behaviors of the child. Higher mentalization is considered a key aspect for parental sensitivity in interaction, fostering childâs socioemotional and self-regulatory development. Yet, previous studies have not examined the dynamic pathways through which the maternal mentalization may develop, nor their effects on child development. Thus, in the current person-oriented studies, first, we identify distinct profiles and longitudinal trajectories of maternal mentalization from pregnancy to childâs 2 years of age. Second, we test how the profiles and trajectories associate with childrenâs internalizing and externalizing problems, socialâemotional competence and effortful control at the age of 2 years. Third, we examine how the profiles and trajectories associate with contextual demographic and child related. The substudy was part of the FinnBrain Birth Cohort and included families from general population (nâ=â2,687). Mothers reported their parental reflective functioning (PRF) at late pregnancy, 6 months and 2 years of childâs age. Both mothers (nâ=â1,437) and fathers (nâ=â715) reported the developmental child outcomes at the childâs age of 2 years. Latent Profile Analysis and Latent Transition Analysis were used to identify PRF profiles and trajectories. The results showed decreasing heterogeneity in PRF from pregnancy to childâs age of 6 months and 2 years (i.e., four, three and two latent classes, respectively). Most mothers progressed towards high PRF over time. Second, the profiles and trajectories depicting high PRF associated with child high socialâemotional competence at the age of 2 years, yet no clear positive effects were found on childâs problems and effortful control. The group of mixed PRF trajectories showed strongest association with childâs internalizing and externalizing problems. Finally, there were theoretically meaningful associations between the PRF trajectories and both the contextual (e.g., parity) and child related (e.g., infant temperament) factors. This was the first study to explore the early unfolding of maternal mentalization. The results are discussed in relation with the potential mechanisms accounting for child development and with the nature and limitations of self-reported parental mentalization
Activation of NF- B protein prevents the transition from juvenile ovary to testis and promotes ovarian development in Zebrafish
Testis differentiation in zebrafish involves juvenile ovary to testis transformation initiated by an apoptotic wave. The molecular regulation of this transformation process is not fully understood. NF-ÎșB is activated at an early stage of development and has been shown to interact with steroidogenic factor-1 in mammals, leading to the suppression of anti-MĂŒllerian hormone (Amh) gene expression. Because steroidogenic factor-1 and Amh are important for proper testis development, NF-ÎșB-mediated induction of anti-apoptotic genes could, therefore, also play a role in zebrafish gonad differentiation. The aim of this study was to examine the potential role of NF-ÎșB in zebrafish gonad differentiation. Exposure of juvenile zebrafish to heat-killed Escherichia coli activated the NF-ÎșB pathways and resulted in an increased ratio of females from 30 to 85%. Microarray and quantitative real-time-PCR analysis of gonads showed elevated expression of NF-ÎșB-regulated genes. To confirm the involvement of NF-ÎșB-induced anti-apoptotic effects, zebrafish were treated with sodium deoxycholate, a known inducer of NF-ÎșB or NF-ÎșB activation inhibitor (NAI). Sodium deoxycholate treatment mimicked the effect of heat-killed bacteria and resulted in an increased proportion of females from 25 to 45%, whereas the inhibition of NF-ÎșB using NAI resulted in a decrease in females from 45 to 20%. This study provides proof for an essential role of NF-ÎșB in gonadal differentiation of zebrafish and represents an important step toward the complete understanding of the complicated process of sex differentiation in this species and possibly other cyprinid teleosts as well
The Distribution of Redshifts in New Samples of Quasi-stellar Objects
Two new samples of QSOs have been constructed from recent surveys to test the
hypothesis that the redshift distribution of bright QSOs is periodic in
. The first of these comprises 57 different redshifts among all
known close pairs or multiple QSOs, with image separations 10\arcsec,
and the second consists of 39 QSOs selected through their X-ray emission and
their proximity to bright comparatively nearby active galaxies. The redshift
distributions of the samples are found to exhibit distinct peaks with a
periodic separation of in identical to that claimed
in earlier samples but now extended out to higher redshift peaks and 4.47, predicted by the formula but never seen before. The periodicity
is also seen in a third sample, the 78 QSOs of the 3C and 3CR catalogues. It is
present in these three datasets at an overall significance level -
, and appears not to be explicable by spectroscopic or similar
selection effects. Possible interpretations are briefly discussed.Comment: submitted for publication in the Astronomical Journal, 15 figure
Interaction-free measurement and forward scattering
Interaction-free measurement is shown to arise from the forward-scattered
wave accompanying absorption: a "quantum silhouette" of the absorber.
Accordingly, the process is not free of interaction. For a perfect absorber the
forward-scattered wave is locked both in amplitude and in phase. For an
imperfect one it has a nontrivial phase of dynamical origin (``colored
silhouette"), measurable by interferometry. Other examples of quantum
silhouettes, all controlled by unitarity, are briefly discussed.Comment: 4 pages in RevTex + 1 figure in eps; submitted to Phys. Rev. A since
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Paying for Care Costs in Later Life Using the Value in Peopleâs Homes
With the number of U.K. citizens aged 75+ doubling to 10 million by 2040, and with 1.3 million people already receiving social care services in England alone, social care funding is a key public policy challenge. The government has launched a set of reforms designed to get social care funding onto a sustainable footing by establishing a new level for what individuals and the state will pay. The reforms are designed to encourage individuals to explore how best to use their available wealth and assets to meet care costs through a mixed system of local authority and private sector care-funding options. One option is to use the value in the home to bridge the cost between out-of-pocket costs and care home fees. In this article, we consider two new financial arrangements designed to meet the needs of people in different financial circumstances based on releasing equity from the home. These are an equity-backed insurance product and an âequity bankâ that lets a person draw down an income from their hom
Pre-galactic metal enrichment - The chemical signatures of the first stars
The emergence of the first sources of light at redshifts of z ~ 10-30
signaled the transition from the simple initial state of the Universe to one of
increasing complexity. We review recent progress in our understanding of the
formation of the first stars and galaxies, starting with cosmological initial
conditions, primordial gas cooling, and subsequent collapse and fragmentation.
We emphasize the important open question of how the pristine gas was enriched
with heavy chemical elements in the wake of the first supernovae. We conclude
by discussing how the chemical abundance patterns conceivably allow us to probe
the properties of the first stars and subsequent stellar generations, and allow
us to test models of early metal enrichment.Comment: 52 pages, 20 figures, clarifications, references added, accepted for
publication in the Reviews of Modern Physic
A Quantum solution to the Byzantine agreement problem
We present a solution to an old and timely problem in distributed computing.
Like Quantum Key Distribution (QKD), quantum channels make it possible to
achieve taks classically impossible. However, unlike QKD, here the goal is not
secrecy but agreement, and the adversary is not outside but inside the game,
and the resources require qutrits.Comment: 4 pages, 1 figur
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