3,699 research outputs found
New Measurements and Quantitative Analysis of Electron Backscattering in the Energy Range of Neutron Beta-Decay
We report on the first detailed measurements of electron backscattering from
plastic scintillator targets, extending our previous work on beryllium and
silicon targets. The scintillator experiment posed several additional
experimental challenges associated with charging of the scintillator target,
and those challenges are addressed in detail. In addition, we quantitatively
compare the energy and angular distributions of this data, and our previous
data, with electron transport simulations based on the Geant4 and Penelope
Monte Carlo simulation codes. The Penelope simulation is found globally to give
a superior description of the data. Such information is crucial for a broad
array of weak-interaction physics experiments, where electron backscattering
can give rise to the dominant detector-related systematic uncertainty.Comment: 7 pages, 3 figure
Interband electron Raman scattering in a quantum wire in a transverse magnetic field
Electron Raman scattering (ERS) is investigated in a parabolic semiconductor
quantum wire in a transverse magnetic field neglecting by phonon-assisted
transitions. The ERS cross-section is calculated as a function of a frequency
shift and magnetic field. The process involves an interband electronic
transition and an intraband transition between quantized subbands. We analyze
the differential cross-section for different scattering configurations. We
study selection rules for the processes. Some singularities in the Raman
spectra are found and interpreted. The scattering spectrum shows
density-of-states peaks and interband matrix elements maximums and a strong
resonance when scattered frequency equals to the "hybrid" frequency or
confinement frequency depending on the light polarization. Numerical results
are presented for a GaAs/AlGaAs quantum wire.Comment: 8 pages, 5 figure
Deriving amino acid contact potentials from their frequencies of occurence in proteins: a lattice model study
The possibility of deriving the contact potentials between amino acids from
their frequencies of occurence in proteins is discussed in evolutionary terms.
This approach allows the use of traditional thermodynamics to describe such
frequencies and, consequently, to develop a strategy to include in the
calculations correlations due to the spatial proximity of the amino acids and
to their overall tendency of being conserved in proteins. Making use of a
lattice model to describe protein chains and defining a "true" potential, we
test these strategies by selecting a database of folding model sequences,
deriving the contact potentials from such sequences and comparing them with the
"true" potential. Taking into account correlations allows for a markedly better
prediction of the interaction potentials
Thermodynamics of protein folding: a random matrix formulation
The process of protein folding from an unfolded state to a biologically
active, folded conformation is governed by many parameters e.g the sequence of
amino acids, intermolecular interactions, the solvent, temperature and chaperon
molecules. Our study, based on random matrix modeling of the interactions,
shows however that the evolution of the statistical measures e.g Gibbs free
energy, heat capacity, entropy is single parametric. The information can
explain the selection of specific folding pathways from an infinite number of
possible ways as well as other folding characteristics observed in computer
simulation studies.Comment: 21 Pages, no figure
Relation of Childhood Home Environment to Cortical Thickness in Late Adolescence: Specificity of Experience and Timing
What are the long-term effects of childhood experience on brain development? Research with animals shows that the quality of environmental stimulation and parental nurturance both play important roles in shaping lifelong brain structure and function. Human research has so far been limited to the effects of abnormal experience and pathological development. Using a unique longitudinal dataset of in-home measures of childhood experience at ages 4 and 8 and MRI acquired in late adolescence, we were able to relate normal variation in childhood experience to later life cortical thickness. Environmental stimulation at age 4 predicted cortical thickness in a set of automatically derived regions in temporal and prefrontal cortex. In contrast, age 8 experience was not predictive. Parental nurturance was not predictive at either age. This work reveals an association between childhood experience and later brain structure that is specific relative to aspects of experience, regions of brain, and timing
Effect of Socioeconomic Status (SES) Disparity on Neural Development in Female African-American Infants at 1 Month
There is increasing interest in both the cumulative and long term impact of early life adversity on brain structure and function, especially as the brain is both highly vulnerable and highly adaptive during childhood. Relationships between SES and neural development have been shown in children older than age two years. Less is known regarding the impact of SES on neural development in children before age two. This paper examines the effect of SES, indexed by income-to-needs (ITN) and maternal education, on cortical, deep gray, and white matter volumes in term, healthy, appropriate for gestational age, African American, female infants. At 44-46 post-conception weeks, unsedated infants underwent MRI (3.0T Siemens Verio scanner, 32-channel head coil). Images were segmented based on a locally-constructed template. Utilizing hierarchical linear regression, overall and component (maternal education and ITN) SES effects on MRI volumes were examined. In this cohort of healthy African American infants of varying SES, lower SES was associated with smaller cortical gray and deep gray matter volumes. These SES effects on neural outcome at such a young age build on similar studies of older children, suggesting that the biological embedding of adversity may occur very early in development
Snowmass Neutrino Frontier: Neutrino Interaction Cross Sections (NF06) Topical Group Report
A thorough understanding of neutrino cross sections in a wide range of
energies is crucial for the successful execution of the entire neutrino physics
program. In order to extract neutrino properties, long-baseline experiments
need an accurate determination of neutrino cross sections within their
detector(s). Since very few of the needed neutrino cross sections across the
energy spectrum are directly measured, we emphasize the need for theoretical
input and indirect measurements such as electron scattering, which would
complement direct measurements. In this report we briefly summarize the current
status of our knowledge of the neutrino cross sections and articulate needs of
the experiments, ongoing and planned, at energies ranging from CEvNS and
supernova neutrino energies to the DUNE and atmospheric neutrino energies.Comment: 38 pages, 1 figur
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