951 research outputs found
Doubly Periodic Instanton Zero Modes
Fermionic zero modes associated with doubly periodic SU(2) instantons of unit
charge are considered. In cases where the action density exhibits two
`instanton cores' the zero mode peaks on one of four line-segments joining the
two constituents. Which of the four possibilities is realised depends on the
fermionic boundary conditions; doubly periodic, doubly anti-periodic or mixed.Comment: 12 pages, 4 figure
Microbiological influences on fracture surfaces of intact mudstone and the implications for geological disposal of radioactive waste
The significance of the potential impacts of microbial activity on the transport properties of host rocks for geological repositories is an area of active research. Most recent work has focused on granitic environments. This paper describes pilot studies investigating changes in transport properties that are produced by microbial activity in sedimentary rock environments in northern Japan. For the first time, these short experiments (39 days maximum) have shown that the denitrifying bacteria, Pseudomonas denitrificans, can survive and thrive when injected into flow-through column experiments containing fractured diatomaceous mudstone and synthetic groundwater under pressurized conditions. Although there were few significant changes in the fluid chemistry, changes in the permeability of the biotic column, which can be explained by the observed biofilm formation, were quantitatively monitored. These same methodologies could also be adapted to obtain information from cores originating from a variety of geological environments including oil reservoirs, aquifers and toxic waste disposal sites to provide an understanding of the impact of microbial activity on the transport of a range of solutes, such as groundwater contaminants and gases (e.g. injected carbon dioxide)
Yang-Mills Solutions on Euclidean Schwarzschild Space
We show that the apparently periodic Charap-Duff Yang-Mills `instantons' in
time-compactified Euclidean Schwarzschild space are actually time independent.
For these solutions, the Yang-Mills potential is constant along the time
direction (no barrier) and therefore, there is no tunneling. We also
demonstrate that the solutions found to date are three dimensional monopoles
and dyons. We conjecture that there are no time-dependent solutions in the
Euclidean Schwarzschild background.Comment: 12 pages, references added, version to appear in PR
Water-like anomalies for core-softened models of fluids: One dimension
We use a one-dimensional (1d) core-softened potential to develop a physical
picture for some of the anomalies present in liquid water. The core-softened
potential mimics the effect of hydrogen bonding. The interest in the 1d system
stems from the facts that closed-form results are possible and that the
qualitative behavior in 1d is reproduced in the liquid phase for higher
dimensions. We discuss the relation between the shape of the potential and the
density anomaly, and we study the entropy anomaly resulting from the density
anomaly. We find that certain forms of the two-step square well potential lead
to the existence at T=0 of a low-density phase favored at low pressures and of
a high-density phase favored at high pressures, and to the appearance of a
point at a positive pressure, which is the analog of the T=0 ``critical
point'' in the Ising model. The existence of point leads to anomalous
behavior of the isothermal compressibility and the isobaric specific heat
.Comment: 22 pages, 7 figure
How musical selection impacts the performance of the interaction with the computer
In this busy society of ours people push their limits to work
better and more in order to remain competitive with their peers. Nonetheless,
working longer hours does not necessarily improves productivity nor
performance. In order to prevent the negative consequences of this increasing
trend, the evolution of performance throughout the day of work
should be more closely monitored. This could avoid undesirable states or
even breakdowns, which have social and economical implications. In this
work we measure user performance through their interaction with the
computer. We monitor its evolution during a day of work and how di erent
types of music may increase or decrease its natural daily degradation.
We conclude that the relationship between types of music and its e ects
is not universal and depends, among other things, on the musical pro le
of the individual. A prototype for a distributed music recommendation
service is presented that suggests musics at an individual and group level,
based on user musical pro les and objectives.This work is part-funded by ERDF - European Regional Development Fund
through the COMPETE Programme (operational programme for competitiveness)
and by National Funds through the FCT - Fundação para a CiĂȘncia e a
Tecnologia (Portuguese Foundation for Science and Technology) within project
FCOMP-01-0124-FEDER-028980 (PTDC/EEI-SII/1386/2012)
A Simple Model of Liquid-liquid Phase Transitions
In recent years, a second fluid-fluid phase transition has been reported in
several materials at pressures far above the usual liquid-gas phase transition.
In this paper, we introduce a new model of this behavior based on the
Lennard-Jones interaction with a modification to mimic the different kinds of
short-range orientational order in complex materials. We have done Monte Carlo
studies of this model that clearly demonstrate the existence of a second
first-order fluid-fluid phase transition between high- and low-density liquid
phases
Quadrupole deformation of deuterons and final state interaction in scattering on tensor polarized deuterons at CEBAF energies
The strength of final state interaction (FSI) between struck proton and
spectator neutron in scattering depends on the alignment of
the deuteron. We study the resulting FSI effects in the tensor analyzing power
in detail and find substantial FSI effects starting at still low missing
momentum p_m \gsim 0.9 fm^{-1}. At larger p_m \gsim 1.5 fm^{-1}, FSI
completely dominates both missing momentum distribution and tensor analyzing
power. We find that to a large extent FSI masks the sensitivity of the tensor
analyzing power to models of the deuteron wave function. For the transversely
polarized deuterons the FSI induced forward-backward asymmetry of the missing
momentum distribution is shown to have a node at precisely the same value of
as the PWIA missing momentum distribution. The position of this node is
not affected by FSI and can be a tool to distinguish experimentally between
different models for the deuteron wave function.Comment: 24 pages, figures available from the authors on reques
Retinal nerve fiber layer thickness predicts CSF amyloid/tau before cognitive decline
Background: Alzheimer's disease (AD) pathology precedes symptoms and its detection can identify at-risk individuals who may benefit from early treatment. Since the retinal nerve fiber layer (RNFL) is depleted in established AD, we tested whether its thickness can predict whether cognitively healthy (CH) individuals have a normal or pathological cerebrospinal fluid (CSF) A
f42 (A) and tau (T) ratio.
Methods: As part of an ongoing longitudinal study, we enrolled CH individuals, excluding those with cognitive impairment and significant ocular pathology. We classified the CH group into two sub-groups, normal (CH-NAT, n = 16) or pathological (CH-PAT, n = 27), using a logistic regression model from the CSF AT ratio that identified >85% of patients with a clinically probable AD diagnosis. Spectral-domain optical coherence tomography (OCT) was acquired for RNFL, ganglion cell-inner plexiform layer (GC-IPL), and macular thickness. Group differences were tested using mixed model repeated measures and a classification model derived using multiple logistic regression.
Results: Mean age (\ub1 standard deviation) in the CH-PAT group (n = 27; 75.2 \ub1 8.4 years) was similar (p = 0.50) to the CH-NAT group (n = 16; 74.1 \ub1 7.9 years). Mean RNFL (standard error) was thinner in the CH-PAT group by 9.8 (2.7) \u3bcm; p < 0.001. RNFL thickness classified CH-NAT vs. CH-PAT with 87% sensitivity and 56.3% specificity.
Conclusions: Our retinal data predict which individuals have CSF biomarkers of AD pathology before cognitive deficits are detectable with 87% sensitivity. Such results from easy-to-acquire, objective and non-invasive measurements of the RNFL merit further study of OCT technology to monitor or screen for early AD pathology
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