1,115 research outputs found
Proton-neutron pairing in the deformed BCS approach
We examine isovector and isoscalar proton-neutron pairing correlations for
the ground state of even-even Ge isotopes with mass number A=64-76 within the
deformed BCS approach. For N=Z 64Ge the BCS solution with only T=0
proton-neutron pairs is found. For other nuclear systems (N>Z) a coexistence of
a T=0 and T=1 pairs in the BCS wave function is observed. A problem of fixing
of strengths of isoscalar and isovector pairing interactions is addressed. A
dependence of number of like and unlike pairs in the BCS ground state on the
difference between number of neutrons and protons is discussed. We found that
for nuclei with N much bigger than Z the effect of proton-neutron pairing is
small but not negligible.Comment: 24 pages, 6 figure
Do Lognormal Column-Density Distributions in Molecular Clouds Imply Supersonic Turbulence?
Recent observations of column densities in molecular clouds find lognormal
distributions with power-law high-density tails. These results are often
interpreted as indications that supersonic turbulence dominates the dynamics of
the observed clouds. We calculate and present the column-density distributions
of three clouds, modeled with very different techniques, none of which is
dominated by supersonic turbulence. The first star-forming cloud is simulated
using smoothed particle hydrodynamics (SPH); in this case gravity, opposed only
by thermal-pressure forces, drives the evolution. The second cloud is
magnetically subcritical with subsonic turbulence, simulated using nonideal
MHD; in this case the evolution is due to gravitationally-driven ambipolar
diffusion. The third cloud is isothermal, self-gravitating, and has a smooth
density distribution analytically approximated with a uniform inner region and
an r^-2 profile at larger radii. We show that in all three cases the
column-density distributions are lognormal. Power-law tails develop only at
late times (or, in the case of the smooth analytic profile, for strongly
centrally concentrated configurations), when gravity dominates all opposing
forces. It therefore follows that lognormal column-density distributions are
generic features of diverse model clouds, and should not be interpreted as
being a consequence of supersonic turbulence.Comment: 6 pages, 6 figures, accepted for publication in MNRA
The "Ram Effect": A "Non-Classical" Mechanism for Inducing LH Surges in Sheep
During spring sheep do not normally ovulate but exposure to a ram can induce ovulation. In some ewes an LH surge is induced immediately after exposure to a ram thus raising questions about the control of this precocious LH surge. Our first aim was to determine the plasma concentrations of oestradiol (E2) E2 in anoestrous ewes before and after the "ram effect" in ewes that had a "precocious" LH surge (starting within 6 hours), a "normal" surge (between 6 and 28h) and "late» surge (not detected by 56h). In another experiment we tested if a small increase in circulating E2 could induce an LH surge in anoestrus ewes. The concentration of E2 significantly was not different at the time of ram introduction among ewes with the three types of LH surge. "Precocious" LH surges were not preceded by a large increase in E2 unlike "normal" surges and small elevations of circulating E2 alone were unable to induce LH surges. These results show that the "precocious" LH surge was not the result of E2 positive feedback. Our second aim was to test if noradrenaline (NA) is involved in the LH response to the "ram effect". Using double labelling for Fos and tyrosine hydroxylase (TH) we showed that exposure of anoestrous ewes to a ram induced a higher density of cells positive for both in the A1 nucleus and the Locus Coeruleus complex compared to unstimulated controls. Finally, the administration by retrodialysis into the preoptic area, of NA increased the proportion of ewes with an LH response to ram odor whereas treatment with the α1 antagonist Prazosin decreased the LH pulse frequency and amplitude induced by a sexually active ram. Collectively these results suggest that in anoestrous ewes NA is involved in ram-induced LH secretion as observed in other induced ovulators
Progress in neutrino oscillation searches and their implications
Neutrino Oscillation, in which a given flavour of neutrino transforms into
another is a powerful tool for probing small neutrino masses. The intrinsic
neutrino properties involved are neutrino mass squared difference
and the mixing angle in vacuum . In this talk I will summarize the
progress that we have achieved in our search for neutrino oscillation with
special emphasis on the recent results from the Sudbury Neutrino Observatory
(SNO) on the measurement of solar neutrino fluxes. I will outline the current
bounds on the neutrino masses and mixing parameters and discuss the major
physics goals of future neutrino experiments in the context of the present
picture.Comment: Plenary Talk, WHEPP-7, January 2002, published in Pramana, Vol. 60,
261, 200
Constraints on Three-Neutrino Mixing from Atmospheric and Reactor Data
Observations of atmospheric neutrinos are usually analyzed using the
simplifying approximation that either or
two-flavor mixing is relevant. Here we
instead consider the data using the simplifying approximation that only one
neutrino mass scale is relevant. This approximation is the minimal three-flavor
notation that includes the two relevant two-flavor approximations. The
constraints in the parameter space orthogonal to the usual, two-flavor analyses
are studied.Comment: 15 pages, preprint IUHET-26
Comparing and contrasting the and solutions to the atmospheric neutrino problem with SuperKamiokande data
The and solutions to the
atmospheric neutrino problem are compared with SuperKamiokande data. The
differences between these solutions due to matter effects in the Earth are
calculated for the ratio of -like to -like events and for up-down flux
asymmetries. These quantities are chosen because they are relatively
insensitive to theoretical uncertainties in the overall neutrino flux
normalisation and detection cross-sections and efficiencies. A
analysis using these quantities is performed yielding ranges which
are approximately given by and for
for the and solutions, respectively. Values of smaller than about
eV are disfavoured for the
solution, suggesting that future long baseline experiments should see a
positive signal if this scenario is the correct one.Comment: revtex, 22 pages, 12 figure
Bare Quark Matter Surfaces of Strange Stars and Emission
We show that the Coulomb barrier at the quark surface of a hot strange star
may be a powerful source of pairs which are created in an extremely
strong electric field of the barrier and flow away from the star. The
luminosity in the outflowing pair plasma depends on the surface temperature
and may be very high, up to at
K. The effect of pair creation by the Coulomb barrier may
be a good observational signature of strange stars which can give an answer to
the question of whether a compact object is a neutron or strange star.Comment: 5 pages, 1 figure, LATEX, accepted for publication in the Physical
Review Letter
Impaired decisional impulsivity in pathological videogamers
Abstract
Background
Pathological gaming is an emerging and poorly understood problem. Impulsivity is commonly impaired in disorders of behavioural and substance addiction, hence we sought to systematically investigate the different subtypes of decisional and motor impulsivity in a well-defined pathological gaming cohort.
Methods
Fifty-two pathological gaming subjects and age-, gender- and IQ-matched healthy volunteers were tested on decisional impulsivity (Information Sampling Task testing reflection impulsivity and delay discounting questionnaire testing impulsive choice), and motor impulsivity (Stop Signal Task testing motor response inhibition, and the premature responding task). We used stringent diagnostic criteria highlighting functional impairment.
Results
In the Information Sampling Task, pathological gaming participants sampled less evidence prior to making a decision and scored fewer points compared with healthy volunteers. Gaming severity was also negatively correlated with evidence gathered and positively correlated with sampling error and points acquired. In the delay discounting task, pathological gamers made more impulsive choices, preferring smaller immediate over larger delayed rewards. Pathological gamers made more premature responses related to comorbid nicotine use. Greater number of hours played also correlated with a Motivational Index. Greater frequency of role playing games was associated with impaired motor response inhibition and strategy games with faster Go reaction time.
Conclusions
We show that pathological gaming is associated with impaired decisional impulsivity with negative consequences in task performance. Decisional impulsivity may be a potential target in therapeutic management
An accurate and efficient identification of children with psychosocial problems by means of computerized adaptive testing
Background: Questionnaires used by health services to identify children with psychosocial problems are often rather short. The psychometric properties of such short questionnaires are mostly less than needed for an accurate distinction between children with and without problems. We aimed to assess whether a short Computerized Adaptive Test (CAT) can overcome the weaknesses of short written questionnaires when identifying children with psychosocial problems. Method: We used a Dutch national data set obtained from parents of children invited for a routine health examination by Preventive Child Healthcare with 205 items on behavioral and emotional problems (n = 2,041, response 84%). In a random subsample we determined which items met the requirements of an Item Response Theory (IRT) model to a sufficient degree. Using those items, item parameters necessary for a CAT were calculated and a cut-off point was defined. In the remaining subsample we determined the validity and efficiency of a Computerized Adaptive Test using simulation techniques, with current treatment status and a clinical score on the Total Problem Scale (TPS) of the Child Behavior Checklist as criteria. Results: Out of 205 items available 190 sufficiently met the criteria of the underlying IRT model. For 90% of the children a score above or below cut-off point could be determined with 95% accuracy. The mean number of items needed to achieve this was 12. Sensitivity and specificity with the TPS as a criterion were 0.89 and 0.91, respectively. Conclusion: An IRT-based CAT is a very promising option for the identification of psychosocial problems in children, as it can lead to an efficient, yet high-quality identification. The results of our simulation study need to be replicated in a real-life administration of this CAT
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