2,918 research outputs found
Coherent oscillations and incoherent tunnelling in one - dimensional asymmetric double - well potential
For a model 1d asymmetric double-well potential we calculated so-called
survival probability (i.e. the probability for a particle initially localised
in one well to remain there). We use a semiclassical (WKB) solution of
Schroedinger equation. It is shown that behaviour essentially depends on
transition probability, and on dimensionless parameter which is a ratio of
characteristic frequencies for low energy non-linear in-well oscillations and
inter wells tunnelling. For the potential describing a finite motion
(double-well) one has always a regular behaviour. For the small value of the
parameter there is well defined resonance pairs of levels and the survival
probability has coherent oscillations related to resonance splitting. However
for the large value of the parameter no oscillations at all for the survival
probability, and there is almost an exponential decay with the characteristic
time determined by Fermi golden rule. In this case one may not restrict oneself
to only resonance pair levels. The number of perturbed by tunnelling levels
grows proportionally to the value of this parameter (by other words instead of
isolated pairs there appear the resonance regions containing the sets of
strongly coupled levels). In the region of intermediate values of the parameter
one has a crossover between both limiting cases, namely the exponential decay
with subsequent long period recurrent behaviour.Comment: 19 pages, 7 figures, Revtex, revised version. Accepted to Phys. Rev.
Absolute Reticulocyte Count Acts as a Surrogate for Fetal Hemoglobin in Infants and Children with Sickle Cell Anemia.
Hemoglobin switching is largely complete in humans by six months of age. Among infants with sickle cell anemia (HbSS, SCA), reticulocytosis begins early in life as fetal hemoglobin (HbF) is replaced by sickle hemoglobin (HbS). The objective of this study was to determine if absolute reticulocyte count (ARC) is related to HbF levels in a cohort of pediatric SCA patients. A convenience sample of 106 children with SCA between the ages of 1 month and 20 years who were not receiving hydroxyurea or monthly blood transfusions were enrolled in this observational study. Hematologic data, including ARC and HbF levels, were measured at steady state. F-cells were enumerated by flow cytometry. Initial studies compared infants with ARC greater than or equal to 200 K/μL (ARC ≥ 200) based upon the previously reported utility of this threshold as a predictive marker for SCA severity. Mean HbF and F-cell levels were significantly lower in the ARC ≥ 200 group when compared to the ARC \u3c 200 group. Both HbF and F-cell percentages were negatively correlated to ARC in infants and in children between the ages of 1 and 9 years. However, the inverse relationship was lost after the age of 10 years. Overall, decreased expression and distribution of HbF during childhood SCA is well-correlated with increased reticulocyte production and release into the peripheral blood. As such, these data further support the clinical use of reticulocyte enumeration as a disease severity biomarker for childhood sickle cell anemia
Shot noise suppression at room temperature in atomic-scale Au junctions
Shot noise encodes additional information not directly inferable from simple
electronic transport measurements. Previous measurements in atomic-scale metal
junctions at cryogenic temperatures have shown suppression of the shot noise at
particular conductance values. This suppression demonstrates that transport in
these structures proceeds via discrete quantum channels. Using a high frequency
technique, we simultaneously acquire noise data and conductance histograms in
Au junctions at room temperature and ambient conditions. We observe noise
suppression at up to three conductance quanta, with possible indications of
current-induced local heating and noise in the contact region at high
biases. These measurements demonstrate the quantum character of transport at
room temperature at the atomic scale. This technique provides an additional
tool for studying dissipation and correlations in nanodevices.Comment: 15 pages, 4 figures + supporting information (6 pages, 6 figures
Chirality driven anomalous Hall effect in weak coupling regime
Anomalous Hall effect arising from non-trivial spin configuration (chirality)
is studied based on the - model. Considering a weak coupling case, the
interaction is treated perturbatively. Scattering by normal impurities is
included. Chirality is shown to drive locally Hall current and leads to overall
Hall effect if there is a finite uniform chirality. This contribution is
independent of the conventional spin-orbit contribution and shows distinct low
temperature behavior. In mesoscopic spin glasses, chirality-induced anomalous
Hall effect is expected below the spin-glass transition temperature.
Measurement of Hall coefficient would be useful in experimentally confirming
the chirality ordering
Ma-Xu quantization rule and exact WKB condition for translationally shape invariant potentials
For translationally shape invariant potentials, the exact quantization rule
proposed by Ma and Xu is a direct consequence of exactness of the modified WKB
quantization condition proved by Barclay. We propose here a very direct
alternative way to calculate the appropriate correction for the whole class of
translationally shape invariant potentials
A New Precision Measurement of the 7Be(p,gamma)8B Cross section with an Implanted 7Be Target
The 7Be(p,gamma)8B reaction plays a central role in the evaluation of solar
neutrino fluxes. We report on a new precision measurement of the cross section
of this reaction, following our previous experiment with an implanted 7Be
target, a raster scanned beam and the elimination of the backscattering loss.
The new measurement incorporates a more abundant 7Be target and a number of
improvements in design and procedure. The point at Elab=991 keV was measured
several times under varying conditions, yielding a value of S17(Ec.m. =850 keV)
= 24.0(5) eV b. Measurements were carried out at lower energies as well. Due to
the precise knowledge of the implanted 7Be density profile it was possible to
reconstitute both the off- and on resonance parts of the cross section and to
obtain from the entire set of measurements an extrapolated value of
S17(0)=21.2(7) eV b.Comment: 4 Pages, 3 Figure
Light drinking in pregnancy, a risk for behavioural problems and cognitive deficits at 3 years of age?
Background
The objective of this study was to determine whether there was an association between mothers’ light drinking during pregnancy and risk of behavioural problems, and cognitive deficits in their children at age 3 years.
Methods
Data from the first two sweeps of the nationally representative prospective UK Millennium Cohort study were used. Drinking patterns during pregnancy and behavioural and cognitive outcomes were assessed during interviews and home visits. Behavioural problems were indicated by scores falling above defined clinically 15 relevant cut-offs on the parent-report version of the Strengths and
Difficulties Questionnaire (SDQ). Cognitive ability was assessed using the naming vocabulary subscale from the British Ability Scale (BAS) and the Bracken School Readiness Assessment (BSRA).
Results
There was a J-shaped relationship between mothers drinking
20 during pregnancy and the likelihood of high scores (above the cut-off) on the total difficulties scale of the SDQ and the conduct problems, hyperactivity and emotional symptom SDQ subscales. Children born to light drinkers were less likely to score above the cut-offs compared with children of abstinent mothers. Children 25 born to heavy drinkers were more likely to score above the cut-offs
compared with children of abstinent mothers. Boys born to mothers who had up to 1–2 drinks per week or per occasion were less likely to have conduct problems (OR 0.59, 95% CI 0.45–0.77) and hyperactivity (OR 0.71, 95% CI 0.54–0.94). These effects remained 30 in fully adjusted models. Girls were less likely to have emotional symptoms (OR 0.72, 95% CI 0.51–1.01) and peer problems (OR 0.68, 95% CI 0.52–0.92) compared with those born to abstainers. These effects were attenuated in fully adjusted models. Boys born to light drinkers had higher cognitive ability test scores [standard
35 deviations, (95% CI)] BAS 0.15 (0.08–0.23) BSRA 0.24 (0.16–0.32) compared with boys born to abstainers. The difference for BAS was attenuated on adjustment for socio-economic factors, whilst the difference for BSRA remained statistically significant.
Conclusions
Children born to mothers who drank up to 1–2 drinks per week or per occasion during pregnancy were not at increased risk of clinically relevant behavioural difficulties or cognitive deficits compared with children of abstinent mothers. Heavy drinking 5 during pregnancy appears to be associated with behavioural problems and cognitive deficits in offspring at age 3 years whereas light drinking does not
Semiclassical dynamics of a spin-1/2 in an arbitrary magnetic field
The spin coherent state path integral describing the dynamics of a
spin-1/2-system in a magnetic field of arbitrary time-dependence is considered.
Defining the path integral as the limit of a Wiener regularized expression, the
semiclassical approximation leads to a continuous minimal action path with
jumps at the endpoints. The resulting semiclassical propagator is shown to
coincide with the exact quantum mechanical propagator. A non-linear
transformation of the angle variables allows for a determination of the
semiclassical path and the jumps without solving a boundary-value problem. The
semiclassical spin dynamics is thus readily amenable to numerical methods.Comment: 16 pages, submitted to Journal of Physics
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