3,060 research outputs found
Vortex Interactions and Thermally Induced Crossover from Type-I to Type-II Superconductivity
We have computed the effective interaction between vortices in the
Ginzburg-Landau model from large-scale Monte-Carlo simulations, taking thermal
fluctuations of matter fields and gauge fields fully into account close to the
critical temperature. We find a change, in the form of a crossover, from
attractive to repulsive effective vortex interactions in an intermediate range
of Ginzburg-Landau parameters upon increasing
the temperature in the superconducting state. This corresponds to a thermally
induced crossover from \typeI to \typeII superconductivity around a temperature
, which we map out in the vicinity of the
metal-to-superconductor transition. In order to see this crossover, it is
essential to include amplitude fluctuations of the matter field, in addition to
phase-fluctuations and gauge-field fluctuations. We present a simple physical
picture of the crossover, and relate it to observations in \metal{Ta} and
\metal{Nb} elemental superconductors which have low-temperature values of
in the relevant range.Comment: 9 pages, 6 figures. Accepted for publication in Physical Review
Electron wavepacket propagation and entanglement in a chain of coupled quantum dots
We study the coherent dynamics of one- and two-electron transport in a linear
array of tunnel-coupled quantum dots. We find that this system exhibits a rich
variety of coherent phenomena, ranging from electron wavepacket propagation and
interference to two-particle bonding and entanglement. Our studies, apart from
their relevance to the exploration of quantum dynamics and transport in
periodic structures, are also aimed at possible applications in future quantum
computation schemes.Comment: 10 pages, 8 figure
Assessment of xenoestrogenic exposure by a biomarker approach: application of the E-Screen bioassay to determine estrogenic response of serum extracts
BACKGROUND: Epidemiological documentation of endocrine disruption is complicated by imprecise exposure assessment, especially when exposures are mixed. Even if the estrogenic activity of all compounds were known, the combined effect of possible additive and/or inhibiting interaction of xenoestrogens in a biological sample may be difficult to predict from chemical analysis of single compounds alone. Thus, analysis of mixtures allows evaluation of combined effects of chemicals each present at low concentrations. METHODS: We have developed an optimized in vitro E-Screen test to assess the combined functional estrogenic response of human serum. The xenoestrogens in serum were separated from endogenous steroids and pharmaceuticals by solid-phase extraction followed by fractionation by high-performance liquid chromatography. After dissolution of the isolated fraction in ethanol-DMSO, the reconstituted extract was added with estrogen-depleted fetal calf serum to MCF-7 cells, the growth of which is stimulated by estrogen. After a 6-day incubation on a microwell plate, cell proliferation was assessed and compared with the effect of a 17-beta-estradiol standard. RESULTS AND CONCLUSIONS: To determine the applicability of this approach, we assessed the estrogenicity of serum samples from 30 pregnant and 60 non-pregnant Danish women thought to be exposed only to low levels of endocrine disruptors. We also studied 211 serum samples from pregnant Faroese women, whose marine diet included whale blubber that contain a high concentration of persistent halogenated pollutants. The estrogenicity of the serum from Danish controls exceeded the background in 22.7 % of the cases, while the same was true for 68.1 % of the Faroese samples. The increased estrogenicity response did not correlate with the lipid-based concentrations of individual suspected endocrine disruptors in the Faroese samples. When added along with the estradiol standard, an indication of an enhanced estrogenic response was found in most cases. Thus, the in vitro estrogenicity response offers a promising and feasible approach for an aggregated exposure assessment for xenoestrogens in serum
Geometrodynamics of Variable-Speed-of-Light Cosmologies
This paper is dedicated to the memory of Dennis Sciama.
Variable-Speed-of-Light (VSL) cosmologies are currently attracting interest
as an alternative to inflation. We investigate the fundamental geometrodynamic
aspects of VSL cosmologies and provide several implementations which do not
explicitly break Lorentz invariance (no "hard" breaking). These "soft"
implementations of Lorentz symmetry breaking provide particularly clean answers
to the question "VSL with respect to what?". The class of VSL cosmologies we
consider are compatible with both classical Einstein gravity and low-energy
particle physics. These models solve the "kinematic" puzzles of cosmology as
well as inflation does, but cannot by themselves solve the flatness problem,
since in their purest form no violation of the strong energy condition occurs.
We also consider a heterotic model (VSL plus inflation) which provides a number
of observational implications for the low-redshift universe if chi contributes
to the "dark energy" either as CDM or quintessence. These implications include
modified gravitational lensing, birefringence, variation of fundamental
constants and rotation of the plane of polarization of light from distant
sources.Comment: 19 pages, latex 209, revtex 3.1; To appear in Physical Review D;
Numerous small changes of presentation and emphasis; new section on the
entropy problem; references updated; central results unaffecte
Four Generations: SUSY and SUSY Breaking
We revisit four generations within the context of supersymmetry. We compute
the perturbativity limits for the fourth generation Yukawa couplings and show
that if the masses of the fourth generation lie within reasonable limits of
their present experimental lower bounds, it is possible to have perturbativity
only up to scales around 1000 TeV. Such low scales are ideally suited to
incorporate gauge mediated supersymmetry breaking, where the mediation scale
can be as low as 10-20 TeV. The minimal messenger model, however, is highly
constrained. While lack of electroweak symmetry breaking rules out a large part
of the parameter space, a small region exists, where the fourth generation stau
is tachyonic. General gauge mediation with its broader set of boundary
conditions is better suited to accommodate the fourth generation.Comment: 27 pages, 5 figure
Emotion dysregulation mediates the relationship between nightmares and psychotic experiences: Results from a student population
Sleep-disruption is commonly associated with psychotic experiences. Whilst sparse, the literature to date highlights nightmares and related distress as prominent risk factors for psychosis in students. We aimed to further explore the relationship between specific nightmare symptoms and psychotic experiences in university students whilst examining the mediating role of emotion dysregulation. A sample (N=1273) of student respondents from UK universities completed measures of psychotic experiences, nightmare disorder symptomology, and emotion dysregulation. Psychotic experiences were significantly more prevalent in students reporting nightmares (n=757) relative to those who did not (n=516). Hierarchical linear regression analysis showed that psychotic experiences were significantly associated (Adjusted R2 = 32.4%) with perceived nightmare intensity, consequences and resulting awakenings, and with emotion regulation difficulties. Furthermore, multiple mediation analysis showed that the association between psychotic experiences and nightmare factors was mediated by emotion regulation difficulties. Adaptive regulation of dream content during rapid eye-movement sleep has previously been demonstrated to attenuate surges in affective arousal by controlling the intensity and variability of emotional content. Difficulties in emotion regulation may partially explain the experience of more intense and disruptive nightmares amongst individuals with psychotic experiences. Emotion regulation may represent an important control mechanism that safeguards dream content and sleep quality
The LOFAR Tied-Array All-Sky Survey: Timing of 35 radio pulsars and an overview of the properties of the LOFAR pulsar discoveries
The LOFAR Tied-Array All-Sky Survey (LOTAAS) is the most sensitive untargeted radio pulsar survey performed at low radio frequencies (119-151 MHz) to date and has discovered 76 new radio pulsars, including the 23.5-s pulsar J0250+5854, which up until recently was the slowest spinning radio pulsar known. In this paper, we report on the timing solutions of 35 pulsars discovered by LOTAAS, which include a nulling pulsar and a mildly recycled pulsar, and thereby complete the full timing analysis of the LOTAAS pulsar discoveries. We give an overview of the findings from the full LOTAAS sample of 76 pulsars, discussing their pulse profiles, radio spectra, and timing parameters. We found that the pulse profiles of some of the pulsars show profile variations in time or frequency, and while some pulsars show signs of scattering, a large majority display no pulse broadening. The LOTAAS discoveries have on average steeper radio spectra and longer spin periods (1.4
7), as well as lower spin-down rates (3.1
7) compared to the known pulsar population. We discuss the cause of these differences and attribute them to a combination of selection effects of the LOTAAS survey as well as previous pulsar surveys, though we cannot rule out that older pulsars tend to have steeper radio spectra
SOUND PRODUCTION IN THE REPRODUCTIVE BEHAVIOUR OF THE WEAKLY ELECTRIC FISH POLLIMYR US MARIANNE
- …