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Structural Neuroimaging of Anorexia Nervosa: Future Directions in the Quest for Mechanisms Underlying Dynamic Alterations.
Anorexia nervosa (AN) is a serious eating disorder characterized by self-starvation and extreme weight loss. Pseudoatrophic brain changes are often readily visible in individual brain scans, and AN may be a valuable model disorder to study structural neuroplasticity. Structural magnetic resonance imaging studies have found reduced gray matter volume and cortical thinning in acutely underweight patients to normalize following successful treatment. However, some well-controlled studies have found regionally greater gray matter and persistence of structural alterations following long-term recovery. Findings from diffusion tensor imaging studies of white matter integrity and connectivity are also inconsistent. Furthermore, despite the severity of AN, the number of existing structural neuroimaging studies is still relatively low, and our knowledge of the underlying cellular and molecular mechanisms for macrostructural brain changes is rudimentary. We critically review the current state of structural neuroimaging in AN and discuss the potential neurobiological basis of structural brain alterations in the disorder, highlighting impediments to progress, recent developments, and promising future directions. In particular, we argue for the utility of more standardized data collection, adopting a connectomics approach to understanding brain network architecture, employing advanced magnetic resonance imaging methods that quantify biomarkers of brain tissue microstructure, integrating data from multiple imaging modalities, strategic longitudinal observation during weight restoration, and large-scale data pooling. Our overarching objective is to motivate carefully controlled research of brain structure in eating disorders, which will ultimately help predict therapeutic response and improve treatment
Absorption-Fluctuation Theorem for Nuclear Reactions: Brink-Axel, Incomplete Fusion and All That
We discuss the connection between absorption, averages and fluctuations in
nuclear reactions. The fluctuations in the entrance channel result in the
compound nucleus, Hauser-Feshbach, cross section, the fluctuations in the
intermediate channels, result in modifications of multistep reaction cross
sections, while the fluctuations in the final channel result in hybrid cross
sections that can be used to describe incomplete fusion reactions. We discuss
the latter in details and comment on the validity of the assumptions used in
the develpoment of the Surrogate method. We also discuss the theory of
multistep reactions with regards to intermediate state fluctuations and the
energy dependence and non-locality of the intermediate channels optical
potentials.Comment: 9 pages. Contribution to the International Workshop on
Compound-Nuclear Reactions and Related Topics (CNR*2007), October 22-26,
2007, Fish Camp, California. To be published in AIP Proceedings (Editor Jutta
Escher
Sensitivity Analysis of the Ultrasonic Response from a Non-Normal Surface-Breaking Crack
The use of computer simulations is becoming an increasing popular strategy for designing ultrasonic inspections. There are many benefits of accurate simulations, the most important one being their cost effectiveness. In many cases, before inspection procedures are finalized, it is possible to simulate the competing inspection plans, and to use the outputs of simulation trials to choose the best plan. This strategy is particularly useful when there is limited accessibility to the components that need to be inspected, as in the extreme case when the inspection procedure requires that operating equipment be removed from service. In such cases, it is best to be fully prepared before taking the inspection equipment to the test site and computer simulations can play an important role in such preparation, often at a significantly reduced cost with respect to traditional methods
Impaired Spatial Reorientation in the 3xTg-AD Mouse Model of Alzheimer's Disease.
In early Alzheimer's disease (AD) spatial navigation is impaired; however, the precise cause of this impairment is unclear. Recent evidence suggests that getting lost is one of the first impairments to emerge in AD. It is possible that getting lost represents a failure to use distal cues to get oriented in space. Therefore, we set out to look for impaired use of distal cues for spatial orientation in a mouse model of amyloidosis (3xTg-AD). To do this, we trained mice to shuttle to the end of a track and back to an enclosed start box to receive a water reward. Then, mice were trained to stop in an unmarked reward zone to receive a brain stimulation reward. The time required to remain in the zone for a reward was increased across training, and the track was positioned in a random start location for each trial. We found that 6-month female, but not 3-month female, 6-month male, or 12-month male, 3xTg-AD mice were impaired. 6-month male and female mice had only intracellular pathology and male mice had less pathology, particularly in the dorsal hippocampus. Thus, AD may cause spatial disorientation as a result of impaired use of landmarks
On the evolution of anomalous X-ray pulsars and soft gamma ray repeaters with fallback disks
We show that the period clustering of anomalous X-ray pulsars (AXPs) and soft
gamma-ray repeaters (SGRs), their X-ray luminosities, ages and statistics can
be explained with fallback disks with large initial specific angular momentum.
The disk evolution models are developed by comparison to self-similar
analytical models. The initial disk mass and angular momentum set the viscous
timescale. An efficient torque, with (1 - w^2) dependence on the fastness
parameter w leads to period clustering in the observed AXP-SGR period range
under a wide range of initial conditions. The timescale t_0 for the early
evolution of the fallback disk, and the final stages of fallback disk
evolution, when the disk becomes passive, are the crucial determinants of the
evolution. The disk becomes passive at temperatures around 100 K, which
provides a natural cutoff for the X-ray luminosity and defines the end of
evolution in the observable AXP and SGR phase. This low value for the minimum
temperature for active disk turbulence indicates that the fallback disks are
active up to a large radius greater than ~10^{12} cm. We find that transient
AXPs and SGRs are likely to be older than their persistent cousins. A fallback
disk with mass transfer rates corresponding to the low quiescent X-ray
luminosities of the transient sources in early evolutionary phases would have a
relatively lower initial mass, such that the mass-flow rate in the disk is not
sufficient for the inner disk to penetrate into the light cylinder of the young
neutron star, making mass accretion onto the neutron star impossible. The
transient AXP phase therefore must start later. The model results imply that
the transient AXP/SGRs, although older, are likely to be similar in number to
persistent sources (abridged).Comment: 42 pages, 22 figures. Accepted for publication in the Astrophysical
Journa
Bandit Models of Human Behavior: Reward Processing in Mental Disorders
Drawing an inspiration from behavioral studies of human decision making, we
propose here a general parametric framework for multi-armed bandit problem,
which extends the standard Thompson Sampling approach to incorporate reward
processing biases associated with several neurological and psychiatric
conditions, including Parkinson's and Alzheimer's diseases,
attention-deficit/hyperactivity disorder (ADHD), addiction, and chronic pain.
We demonstrate empirically that the proposed parametric approach can often
outperform the baseline Thompson Sampling on a variety of datasets. Moreover,
from the behavioral modeling perspective, our parametric framework can be
viewed as a first step towards a unifying computational model capturing reward
processing abnormalities across multiple mental conditions.Comment: Conference on Artificial General Intelligence, AGI-1
Under-ascertainment of Aboriginality in records of cardiovascular disease in hospital morbidity and mortality data in Western Australia: a record linkage study
<p>Abstract</p> <p>Background</p> <p>Measuring the real burden of cardiovascular disease in Australian Aboriginals is complicated by under-identification of Aboriginality in administrative health data collections. Accurate data is essential to measure Australia's progress in its efforts to intervene to improve health outcomes of Australian Aboriginals. We estimated the under-ascertainment of Aboriginal status in linked morbidity and mortality databases in patients hospitalised with cardiovascular disease.</p> <p>Methods</p> <p>Persons with public hospital admissions for cardiovascular disease in Western Australia during 2000-2005 (and their 20-year admission history) or who subsequently died were identified from linkage data. The Aboriginal status flag in all records for a given individual was variously used to determine their ethnicity (index positive, and in all records both majority positive or ever positive) and stratified by region, age and gender. The index admission was the baseline comparator.</p> <p>Results</p> <p>Index cases comprised 62,692 individuals who shared a total of 778,714 hospital admissions over 20 years, of which 19,809 subsequently died. There were 3,060 (4.9%) persons identified as Aboriginal on index admission. An additional 83 (2.7%) Aboriginal cases were identified through death records, increasing to 3.7% when cases with a positive Aboriginal identifier in the majority (≥50%) of previous hospital admissions over twenty years were added and by 20.8% when those with a positive flag in any record over 20 years were incorporated. These results equated to underestimating Aboriginal status in unlinked index admission by 2.6%, 3.5% and 17.2%, respectively. Deaths classified as Aboriginal in official records would underestimate total Aboriginal deaths by 26.8% (95% Confidence Interval 24.1 to 29.6%).</p> <p>Conclusions</p> <p>Combining Aboriginal determinations in morbidity and official death records increases ascertainment of unlinked cardiovascular morbidity in Western Australian Aboriginals. Under-identification of Aboriginal status is high in death records.</p
Long-range coupling and scalable architecture for superconducting flux qubits
Constructing a fault-tolerant quantum computer is a daunting task. Given any
design, it is possible to determine the maximum error rate of each type of
component that can be tolerated while still permitting arbitrarily large-scale
quantum computation. It is an underappreciated fact that including an
appropriately designed mechanism enabling long-range qubit coupling or
transport substantially increases the maximum tolerable error rates of all
components. With this thought in mind, we take the superconducting flux qubit
coupling mechanism described in PRB 70, 140501 (2004) and extend it to allow
approximately 500 MHz coupling of square flux qubits, 50 um a side, at a
distance of up to several mm. This mechanism is then used as the basis of two
scalable architectures for flux qubits taking into account crosstalk and
fault-tolerant considerations such as permitting a universal set of logical
gates, parallelism, measurement and initialization, and data mobility.Comment: 8 pages, 11 figure
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