179 research outputs found
Numerical Method for Shock Front Hugoniot States
We describe a Continuous Hugoniot Method for the efficient simulation of
shock wave fronts. This approach achieves significantly improved efficiency
when the generation of a tightly spaced collection of individual steady-state
shock front states is desired, and allows for the study of shocks as a function
of a continuous shock strength parameter, . This is, to our knowledge, the
first attempt to map the Hugoniot continuously. We apply the method to shock
waves in Lennard-Jonesium along the direction. We obtain very good
agreement with prior simulations, as well as our own benchmark comparison runs.Comment: 4 pages, 3 figures, from Shock Compression of Condensed Matter 200
Patterns in Illinois Educational School Data
We examine Illinois educational data from standardized exams and analyze
primary factors affecting the achievement of public school students. We focus
on the simplest possible models: representation of data through visualizations
and regressions on single variables. Exam scores are shown to depend on school
type, location, and poverty concentration. For most schools in Illinois,
student test scores decline linearly with poverty concentration. However
Chicago must be treated separately. Selective schools in Chicago, as well as
some traditional and charter schools, deviate from this pattern based on
poverty. For any poverty level, Chicago schools perform better than those in
the rest of Illinois. Selective programs for gifted students show high
performance at each grade level, most notably at the high school level, when
compared to other Illinois school types. The case of Chicago charter schools is
more complex. In the last six years, their students' scores overtook those of
students in traditional Chicago high schools.Comment: 9 pages, 6 figure
Weak localization in mesoscopic hole transport: Berry phases and classical correlations
We consider phase-coherent transport through ballistic and diffusive
two-dimensional hole systems based on the Kohn-Luttinger Hamiltonian. We show
that intrinsic heavy-hole light-hole coupling gives rise to clear-cut
signatures of an associated Berry phase in the weak localization which renders
the magneto-conductance profile distinctly different from electron transport.
Non-universal classical correlations determine the strength of these Berry
phase effects and the effective symmetry class, leading even to
antilocalization-type features for circular quantum dots and Aharonov-Bohm
rings in the absence of additional spin-orbit interaction. Our semiclassical
predictions are quantitatively confirmed by numerical transport calculations
Different Proctolin Neurons Elicit Distinct Motor Patterns From a Multifunctional Neuronal Network
Distinct motor patterns are selected from a multifunctional neuronal network by activation of different modulatory projection neurons. Subsets of these projection neurons can contain the same neuromodulator(s), yet little is known about the relative influence of such neurons on network activity. We have addressed this issue in the stomatogastric nervous system of the crab Cancer borealis. Within this system, there is a neuronal network in the stomatogastric ganglion (STG) that produces many versions of the pyloric and gastric mill rhythms. These different rhythms result from activation of different projection neurons that innervate the STG from neighboring ganglia and modulate STG network activity. Three pairs of these projection neurons contain the neuropeptide proctolin. These include the previously identified modulatory proctolin neuron and modulatory commissural neuron 1 (MCN1) and the newly identified modulatory commissural neuron 7 (MCN7). We document here that each of these neurons contains a unique complement of cotransmitters and that each of these neurons elicits a distinct version of the pyloric motor pattern. Moreover, only one of them (MCN1) also elicits a gastric mill rhythm. The MCN7-elicited pyloric rhythm includes a pivotal switch by one STG network neuron from playing a minor to a major role in motor pattern generation. Therefore, modulatory neurons that share a peptide transmitter can elicit distinct motor patterns from a common target network
Recommended from our members
A Preliminary Study of Apolipoprotein E Genotype and Psychiatric Manifestations of Alzheimer's Disease
We evaluated the frequency of depression and psychosis in 46 patients with AD and 135 control subjects with the apolipoprotein (APO) E3/3 or E3/4 genotype. Patients with AD and the APOE3/4 genotype had a more than threefold increase in the signs of depression and psychosis when compared with either patients with the APOE3/3 genotype or to control subjects. Our preliminary study suggests that the phenotype of AD associated with the epsilon 4 allele is more likely to include psychiatric manifestations
Recommended from our members
The characteristics of cognitive neuroscience tests in a schizophrenia cognition clinical trial: Psychometric properties and correlations with standard measures.
In comparison to batteries of standard neuropsychological tests, cognitive neuroscience tests may offer a more specific assessment of discrete neurobiological processes that may be aberrant in schizophrenia. However, more information regarding psychometric properties and correlations with standard neuropsychological tests and functional measures is warranted to establish their validity as treatment outcome measures. The N-back and AX-Continuous Performance Task (AX-CPT) are two promising cognitive neuroscience tests designed to measure specific components of working memory and contextual processing respectively. In the current study, we report the psychometric properties of multiple outcome measures from these two tests as well as their correlations with standard neuropsychological measures and functional capacity measures. The results suggest that while the AX-CPT and N-back display favorable psychometric properties, they do not exhibit greater sensitivity or specificity with functional measures than standard neurocognitive tests
Understanding the association between negative symptoms and performance on effort-based decision-making tasks: The importance of defeatist performance beliefs
Effort-based decision-making paradigms are increasingly utilized to gain insight into the nature of motivation deficits. Research has shown associations between effort-based decision making and experiential negative symptoms; however, the associations are not consistent. The current study had two primary goals. First, we aimed to replicate previous findings of a deficit in effort-based decision making among individuals with schizophrenia on a test of cognitive effort. Second, in a large sample combined from the current and a previous study, we sought to examine the association between negative symptoms and effort by including the related construct of defeatist beliefs. The results replicated previous findings of impaired cognitive effort-based decision making in schizophrenia. Defeatist beliefs significantly moderated the association between negative symptoms and effort-based decision making such that there was a strong association between high negative symptoms and deficits in effort-based decision making, but only among participants with high levels of defeatist beliefs. Thus, our findings suggest the relationship between negative symptoms and effort performance may be understood by taking into account the role of defeatist beliefs, and finding that might explain discrepancies in previous studies
Recommended from our members
Clinical Trials in Hiv-Associated Cognitive Impairment: Cognitive and Functional Outcomes
Cognitive and functional outcomes are of primary interest in the design of efficacy trials in HIV-associated cognitive impairment. In a longitudinal cohort study, weak associations were found between measures of cognitive performance and commonly used measures of daily functioning (mostly self-report measures) in HIV-infected individuals. Modifications of current functional scales or new functional instruments are needed to assess the clinical relevance of cognitive changes in clinical trials of HIV-associated cognitive impairment
Recommended from our members
Inter-Rater Reliability of a Clinical Staging of HIV-Associated Cognitive Impairment
Objective: To determine the inter-rater reliability of a modification of the Memorial Sloan-Kettering (MSK) Staging for HIV-associated cognitive impairment. Methods: Data were abstracted on neurologic, neuropsychological, and functional status on 100 individuals participating at four sites in the Northeast AIDS Dementia (NEAD) Consortium cohort study, a longitudinal study of predictors of cognitive impairment in HIV-infected individuals. Neuropsychological performance was defined 1) based on the neuropsychologist’s global impression and 2) solely based on neuropsychological test scores. Raters at each site used the abstracted data to assign an MSK stage to each subject blind to any identifying information. Inter-rater reliability was assessed using kappa statistics. Agreement between computer-generated ratings and site-generated ratings was also assessed. Results: Kappa statistics for pair-wise agreement among the sites regarding MSK stage ranged from 0.70–0.91, representing good to excellent agreement between sites. Agreement between computer-generated ratings and site-generated ratings was in the good to excellent range (0.62–0.79). Conclusions: The authors have modified the MSK rating scale and developed a reliable instrument that can be used in multicenter studies. This instrument will be useful in staging HIV-dementia in future longitudinal studies and will be valuable in increasing accuracy of clinicopathologic studies
Recommended from our members
HIV-Associated Cognitive Impairment before and after the Advent of Combination Therapy
The objective of this study was to describe the occurrence of HIV dementia and neuropsychological testing abnormalities in a new cohort of HIV-seropositive individuals at high risk for HIV dementia and to compare these results to a cohort before the advent of highly active antiretroviral therapy (HAART). HAART has been associated with improvements in cognitive performance in some HIV-infected patients. However, it is uncertain whether HAART has changed the frequency of specific neurocognitive abnormalities. Baseline data from 272 HIV-seropositive subjects in the Dana cohort recruited from January, 1994, to December, 1995, and 251 HIV-seropositive subjects in the Northeastern AIDS Dementia Consortium (NEAD) cohort recruited from April, 1998, to August, 1999, were compared. Participants in both cohorts received nearly identical assessments. After adjusting for differences in age, education, gender, race, and CD4 count between the two cohorts, there were no differences in the occurrence of HIV dementia or abnormalities either 1 SD or 2 SDs below established norms for any of the neuropsychological tests. Even though HAART has reduced the incidence of HIV dementia, HIV-associated cognitive impairment continues to be a major clinical problem among individuals with advanced infection
- …