2,963 research outputs found
Superfluidity versus localization in bulk 4He at zero temperature
We present a zero-temperature quantum Monte Carlo calculation of liquid
He immersed in an array of confining potentials. These external potentials
are centered in the lattice sites of a fcc solid geometry and, by modifying
their well depth and range, the system evolves from a liquid phase towards a
progressively localized system which mimics a solid phase. The superfluid
density decreases with increasing order, reaching a value when the Lindemann's ratio of the model equals the experimental
value for solid He.Comment: 5 pages,5 figure
Identification of themes in communication related critical incidents in newly formed stepfamilies
Dissertation (Ph.D.)--University of Kansas, Communication Studies, 1989
Mechanism for nonequilibrium symmetry breaking and pattern formation in magnetic films
Magnetic thin films exhibit a strong variation in properties depending on
their degree of disorder. Recent coherent x-ray speckle experiments on magnetic
films have measured the loss of correlation between configurations at opposite
fields and at the same field, upon repeated field cycling. We perform finite
temperature numerical simulations on these systems that provide a comprehensive
explanation for the experimental results. The simulations demonstrate, in
accordance with experiments, that the memory of configurations increases with
film disorder. We find that non-trivial microscopic differences exist between
the zero field spin configuration obtained by starting from a large positive
field and the zero field configuration starting at a large negative field. This
seemingly paradoxical beahvior is due to the nature of the vector spin dynamics
and is also seen in the experiments. For low disorder, there is an instability
which causes the spontaneous growth of line-like domains at a critical field,
also in accord with experiments. It is this unstable growth, which is highly
sensitive to thermal noise, that is responsible for the small correlation
between patterns under repeated cycling. The domain patterns, hysteresis loops,
and memory properties of our simulated systems match remarkably well with the
real experimental systems.Comment: 12 pages, 10 figures Added comparison of results with
cond-mat/0412461 and some more discussio
Dependence of X-Ray Burst Models on Nuclear Reaction Rates
X-ray bursts are thermonuclear flashes on the surface of accreting neutron
stars and reliable burst models are needed to interpret observations in terms
of properties of the neutron star and the binary system. We investigate the
dependence of X-ray burst models on uncertainties in (p,),
(,), and (,p) nuclear reaction rates using fully
self-consistent burst models that account for the feedbacks between changes in
nuclear energy generation and changes in astrophysical conditions. A two-step
approach first identified sensitive nuclear reaction rates in a single-zone
model with ignition conditions chosen to match calculations with a
state-of-the-art 1D multi-zone model based on the {\Kepler} stellar evolution
code. All relevant reaction rates on neutron deficient isotopes up to mass 106
were individually varied by a factor of 100 up and down. Calculations of the 84
highest impact reaction rate changes were then repeated in the 1D multi-zone
model. We find a number of uncertain reaction rates that affect predictions of
light curves and burst ashes significantly. The results provide insights into
the nuclear processes that shape X-ray burst observables and guidance for
future nuclear physics work to reduce nuclear uncertainties in X-ray burst
models.Comment: 24 pages, 13 figures, 4 tables, submitte
Adjusting the frequency of mammography screening on the basis of genetic risk: Attitudes among women in the UK.
Purpose
To explore public attitudes towards modifying frequency of mammography screening based on genetic risk.
Methods
Home-based interviews were carried out with a population-based sample of 942 women aged 18–74 years in the UK. Demographic characteristics and perceived breast cancer (BC) risk were examined as predictors of support for risk-stratified BC screening and of the acceptability of raised or lowered screening frequency based on genetic risk, using multivariate logistic regression.
Results
Over two-thirds of respondents (65.8%) supported the idea of varying screening frequency on the basis of genetic risk. The majority (85.4%) were willing to have more frequent breast screening if they were found to be at higher risk, but fewer (58.8%) were willing to have less frequent screening if at lower risk (t (956) = 15.6, p < 0.001). Ethnic minority status was associated with less acceptability of more frequent screening (OR = 0.40, 95% CI = 0.21–0.74), but there were no other significant demographic correlates. Higher perceived risk of BC was associated with greater acceptability of more frequent screening (OR = 1.71, 95%CI = 1.27–2.30).
Conclusion
Women were positive about adjusting the frequency of mammography screening in line with personal genetic risk, but it will be important to develop effective communication materials to minimise resistance to reducing screening frequency for those at lower genetic risk
DiOlistic Labeling of Neurons in Tissue Slices: A Qualitative and Quantitative Analysis of Methodological Variations
Fine neuronal morphology, such as dendritic spines, classically has been studied using the Golgi technique; however, Golgi staining is difficult to combine with other histological techniques. With the increasing popularity of fluorescent imaging, a number of fluorescent dyes have been developed that enable the coupling of multiple fluorescent labels in a single preparation. These fluorescent dyes include the lipophilic dialkylcarbocyanine, DiI; traditionally used for anterograde and retrograde neuronal tracing. More recently, DiI labeling has been used in combination with the Gene Gun for “DiOlistic” labeling of neurons in slice preparations. DiI sequesters itself within and diffuses laterally along the neuronal membrane, however once the cell is permeabilized, the DiI begins to leak from the cell membrane. A DiI derivative, Cell Tracker™ CM-DiI, increases dye stability and labeling half-life in permeabilized tissue, however at much greater expense. Here, the DiI and CM-DiI DiOlistic labeling techniques were tested in side-by-side experiments evaluating dye stability within dendritic architecture in medium spiny neurons of the dorsal stratum in both non-permeabilized and permeabilized tissue sections. In tissue sections that were not permeabilized, spine density in DiI labeled sections was higher than in CM-DiI labeling. In contrast, tissue sections that were permeabilized had higher spine densities in CM-DiI labeled neurons. These results suggest that for experiments involving non-permeabilized tissue, traditional DiI will suffice, however for experiments involving permeabilized tissue CM-DiI provides more consistent data. These experiments provide the first quantitative analyses of the impact of methodological permutations on neuronal labeling with DiI
Smoothing the Rough Edges: Evaluating Automatically Generated Multi-Lattice Transitions
Additive manufacturing is advantageous for producing lightweight components
while addressing complex design requirements. This capability has been
bolstered by the introduction of unit lattice cells and the gradation of those
cells. In cases where loading varies throughout a part, it may be beneficial to
use multiple, distinct lattice cell types, resulting in multi-lattice
structures. In such structures, abrupt transitions between unit cell topologies
may cause stress concentrations, making the boundary between unit cell types a
primary failure point. Thus, these regions require careful design in order to
ensure the overall functionality of the part. Although computational design
approaches have been proposed, smooth transition regions are still difficult to
achieve, especially between lattices of drastically different topologies. This
work demonstrates and assesses a method for using variational autoencoders to
automate the creation of transitional lattice cells, examining the factors that
contribute to smooth transitions. Through computational experimentation, it was
found that the smoothness of transition regions was strongly predicted by how
closely the endpoints were in the latent space, whereas the number of
transition intervals was not a sole predictor.Comment: 23 Pages, 8 Figure
ESR Study of (C_5H_{12}N)_2CuBr_4
ESR studies at 9.27, 95.4, and 289.7 GHz have been performed on
(CHN)CuBr down to 3.7 K. The 9.27 GHz data were acquired
with a single crystal and do not indicate the presence of any structural
transitions. The high frequency data were collected with a polycrystalline
sample and resolved two absorbances, consistent with two crystallographic
orientations of the magnetic sites and with earlier ESR studies performed at
300 K. Below T, our data confirm the presence of a spin singlet
ground state.Comment: 2 pages, 4 figs., submitted 23rd International Conference on Low
Temperature Physics (LT-23), Aug. 200
A variable neurodegenerative phenotype with polymerase gamma mutation
mtDNA replication and repair, causes mitochondrial diseases including autosomal dominant
progressive external ophthalmoplegia (PEO),1 childhood hepato-encephalopathy (Alpers–
Huttenlocher syndrome), adult-onset spinocerebellar ataxia, and sensory nerve degeneration with
dysarthria and ophthalmoparesis (SANDO)
La estatura de los colombianos: un ensayo de antropometría histórica, 1910-2002
El presente documento estudia la evolución de la estatura promedio de los colombianos de 1910 al 2002. La evidencia antropométrica revela un sostenido mejoramiento en los estándares de vida biológicos durante ese período. Se trabaja con una base de datos de más de ocho millones de observaciones, proveniente de la cédula de ciudadanía de hombres y mujeres, para todo el país y por lugar de nacimiento. El análisis muestra un incremento significativo en la estatura de los colombianos nacidos entre 1910 y 1984. El promedio de la estatura de mujeres y hombres aumentó en 9 y 8 centímetros, respectivamente. La dispersión de la estatura, medida a través del coeficiente de variación cayó para el período, mostrando un proceso de convergencia en los estándares de calidad de vida biológica. Las diferencias inter-departamentales en la estatura promedio se explican en un 43% por el nivel del PIB per cápita y la composición racial.Antropometría,
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