Effective power-law dependence of Lyapunov exponents on the central mass in galaxies

Using both numerical and analytical approaches, we demonstrate the existence of an effective power-law relation $L\propto m^p$ between the mean Lyapunov exponent $L$ of stellar orbits chaotically scattered by a supermassive black hole in the center of a galaxy and the mass parameter $m$, i.e. ratio of the mass of the black hole over the mass of the galaxy. The exponent $p$ is found numerically to obtain values in the range $p \approx 0.3$--$0.5$. We propose a theoretical interpretation of these exponents, based on estimates of local `stretching numbers', i.e. local Lyapunov exponents at successive transits of the orbits through the black hole's sphere of influence. We thus predict $p=2/3-q$ with $q\approx 0.1$--$0.2$. Our basic model refers to elliptical galaxy models with a central core. However, we find numerically that an effective power law scaling of $L$ with $m$ holds also in models with central cusp, beyond a mass scale up to which chaos is dominated by the influence of the cusp itself. We finally show numerically that an analogous law exists also in disc galaxies with rotating bars. In the latter case, chaotic scattering by the black hole affects mainly populations of thick tube-like orbits surrounding some low-order branches of the $x_1$ family of periodic orbits, as well as its bifurcations at low-order resonances, mainly the Inner Lindbland resonance and the 4/1 resonance. Implications of the correlations between $L$ and $m$ to determining the rate of secular evolution of galaxies are discussed.Comment: 27 pages, 19 figure

Quantum vortices and trajectories in particle diffraction

We investigate the phenomenon of the diffraction of charged particles by thin material targets using the method of the de Broglie-Bohm quantum trajectories. The particle wave function can be modeled as a sum of two terms $\psi=\psi_{ingoing}+\psi_{outgoing}$. A thin separator exists between the domains of prevalence of the ingoing and outgoing wavefunction terms. The structure of the quantum-mechanical currents in the neighborhood of the separator implies the formation of an array of \emph{quantum vortices}. The flow structure around each vortex displays a characteristic pattern called `nodal point - X point complex'. The X point gives rise to stable and unstable manifolds. We find the scaling laws characterizing a nodal point-X point complex by a local perturbation theory around the nodal point. We then analyze the dynamical role of vortices in the emergence of the diffraction pattern. In particular, we demonstrate the abrupt deflections, along the direction of the unstable manifold, of the quantum trajectories approaching an X-point along its stable manifold. Theoretical results are compared to numerical simulations of quantum trajectories. We finally calculate the {\it times of flight} of particles following quantum trajectories from the source to detectors placed at various scattering angles $\theta$, and thereby propose an experimental test of the de Broglie - Bohm formalism.Comment: 17 pages, 7 figures, accepted by IJB

The impact of work placements on graduate earnings

This study investigates whether the completion of an optional ‘sandwich’ work placement enhances graduate starting salaries. We use a variety of multivariate regression techniques to investigate this issue and find that the graduate starting salaries of students who took professional work placements were significantly higher by £1686 ($2105) compared to non-placement students. We make a methodological contribution to the literature by controlling for self-selection bias. That is, our analysis takes into consideration that certain students self-select in to work placements and that they would have had higher starting salaries regardless of whether choosing to take a work placement. Additional insights showed that placements may be detrimental in terms of alleviating class and gender pay inequality but may have helped to reduce ethnic pay inequality. Our results have important implications for graduate employability and its impact on wider society

Molecular Detection of the 1BL.1RS Translocation in Hellenic Bread Wheat Cultivars

The main motive of the present work was to detect and confirm the presence of the 1BL.1RS wheat-rye translocation in elite Hellenic bread wheat germplasm. For this, a molecular method was employed and seven Hellenic bread wheat cultivars (Acheloos, Acheron, Chios, Elisavet, Myconos, Orpheus, and Vergina) were studied. A rye population originated from Florina, and cultivar Kavkaz/Cgn, one of the donors of the 1BL.1RS translocation to bread wheat, were used as positive checks. The polymerase chain reaction was applied and two promoters for bread wheat gene alleles located on short arm of chromosome 1B (GLU-B3, GLI-B3) and one promoter for a rye gene (SEC I) located on short arm of chromosome 1R, were involved. It was demonstrated that cultivars Acheron, Elisavet and Orpheus do carry the 1BL.1RS translocation, whereas the rest of the varieties studied, they do not it. It was concluded that cultivars Acheron, Elisavet and Orpheus that carry the translocation, could be crossed to other elite genotypes lucking the translocation and produce new varieties possessing the advantages of the 1BL.1RS translocation. A special attention should be given to cultivar Acheron since this cultivar, despite the presence of the translocation carries favourable alleles in other gene loci affecting positively the quality of the produced bread

Space-by-time manifold representation of dynamic facial expressions for emotion categorization

Visual categorization is the brain computation that reduces high-dimensional information in the visual environment into a smaller set of meaningful categories. An important problem in visual neuroscience is to identify the visual information that the brain must represent and then use to categorize visual inputs. Here we introduce a new mathematical formalism—termed space-by-time manifold decomposition—that describes this information as a low-dimensional manifold separable in space and time. We use this decomposition to characterize the representations used by observers to categorize the six classic facial expressions of emotion (happy, surprise, fear, disgust, anger, and sad). By means of a Generative Face Grammar, we presented random dynamic facial movements on each experimental trial and used subjective human perception to identify the facial movements that correlate with each emotion category. When the random movements projected onto the categorization manifold region corresponding to one of the emotion categories, observers categorized the stimulus accordingly; otherwise they selected “other.” Using this information, we determined both the Action Unit and temporal components whose linear combinations lead to reliable categorization of each emotion. In a validation experiment, we confirmed the psychological validity of the resulting space-by-time manifold representation. Finally, we demonstrated the importance of temporal sequencing for accurate emotion categorization and identified the temporal dynamics of Action Unit components that cause typical confusions between specific emotions (e.g., fear and surprise) as well as those resolving these confusions

Do neuropsychological tests detect preclinical Alzheimer's disease: Individual-test versus cognitive-discrepancy score analyses.

Attempts to identify cognitive markers of a preclinical phase of Alzheimer’s disease (AD) have yielded inconsistent findings. The problem may stem in part from methodologies that are insensitive to potential subgroups within the at-risk, preclinical AD population (PCAD). The present study investigated the utility of asymmetric cognitive profiles in identifying individ-uals at risk for AD. Twenty elderly adults who were later diagnosed with AD (PCAD) and 20 matched control participants were compared on measures of cognitive asymmetry derived from difference scores on tests of verbal and visuospatial ability. Although both groups performed similarly on the individual tests, comparisons using difference scores revealed significantly larger discrepancies between naming and visuoconstruction skills in the PCAD group. The PCAD group also had a higher frequency of asymmetric cognitive profiles relative to a normative group. Subtle cognitive changes can precede the onset of Alz-heimer’s disease (AD) by as many as 7 to 10 years (Elias et al., 2000; Linn, Wolf, Bachman, & Knoefel, 1995). Find-ings of a long prodromal period have fostered new researc

Validation of the Finnish version of the Brief International Cognitive Assessment for Multiple Sclerosis (BICAMS) and evaluation of the applicability of the Multiple Sclerosis Neuropsychological Questionnaire (MSNQ) and the Fatigue Scale for Motor and Cognitive Functions (FSMC)

Objectives Cognitive impairment is frequent in multiple sclerosis (MS) as approximately half of the patients manifest some degree of cognitive impairment. The Brief International Cognitive Assessment for Multiple Sclerosis (BICAMS) has been designed for brief cognitive evaluation. The purpose of the study was to validate the BICAMS along with the Finnish versions of one self-rating questionnaire each for cognition and fatigue. Methods A total of 65 MS patients and 45 healthy controls (HC) were assessed with the BICAMS, the Multiple Sclerosis Neuropsychological Questionnaire (MSNQ), and the Fatigue Scale for Motor and Cognitive Functions (FSMC) twice, approximately within nine days. Results MS patients scored markedly lower than the HCs on each of the three tests of the BICAMS. Of the patients, 60% scored at least 1.5 SD below the mean of the HCs on at least one test; 49% on the SDMT, 26% on the CVLT-II, and 28% on the BVMT-R. Correlation coefficients for the repeated measurement were between 0.75 and 0.89 for the three tests in the whole study sample. MS patients reported more cognitive symptoms and more fatigue than the HCs. Cronbach's alpha was 0.94 for the MSNQ and 0.98 for the FSMC. Correlation coefficient for the repeated measurement was 0.91 for the MSNQ and between 0.92 and 0.94 for the FSMC scores for the whole study sample. Conclusions The present study supports the validity of the Finnish version of the BICAMS. The SDMT was the most sensitive of the three BICAMS tests and showed cognitive impairment in half of the patients. The Finnish versions of the MSNQ and the FSMC proved useful tools in approaching concerns related to cognition and fatigue.Peer reviewe

Glucose enhancement of memory is modulated by trait anxiety in healthy adolescent males

Glucose administration is associated with memory enhancement in healthy young individuals under conditions of divided attention at encoding. While the specific neurocognitive mechanisms underlying this ‘glucose memory facilitation effect’ are currently uncertain, it is thought that individual differences in glucoregulatory efficiency may alter an individual’s sensitivity to the glucose memory facilitation effect. In the present study, we sought to investigate whether basal hypothalamic–pituitary–adrenal axis function (itself a modulator of glucoregulatory efficiency), baseline self-reported stress and trait anxiety influence the glucose memory facilitation effect. Adolescent males (age range = 14–17 years) were administered glucose and placebo prior to completing a verbal episodic memory task on two separate testing days in a counter-balanced, within-subjects design. Glucose ingestion improved verbal episodic memory performance when memory recall was tested (i) within an hour of glucose ingestion and encoding, and (ii) one week subsequent to glucose ingestion and encoding. Basal hypothalamic–pituitary–adrenal axis function did not appear to influence the glucose memory facilitation effect; however, glucose ingestion only improved memory in participants reporting relatively higher trait anxiety. These findings suggest that the glucose memory facilitation effect may be mediated by biological mechanisms associated with trait anxiety

Non-invasive management of peripheral arterial disease.

BACKGROUND: Peripheral arterial disease (PAD) is common and symptoms can be debilitating and lethal. Risk management, exercise, radiological and surgical intervention are all valuable therapies, but morbidity and mortality rates from this disease are increasing. Circulatory enhancement can be achieved using simple medical electronic devices, with claims of minimal adverse side effects. The evidence for these is variable, prompting a review of the available literature. METHODS: Embase and Medline were interrogated for full text articles in humans and written in English. Any external medical devices used in the management of peripheral arterial disease were included if they had objective outcome data. RESULTS: Thirty-one papers met inclusion criteria, but protocols were heterogenous. The medical devices reported were intermittent pneumatic compression (IPC), electronic nerve (NMES) or muscle stimulators (EMS), and galvanic electrical dressings. In patients with intermittent claudication, IPC devices increase popliteal artery velocity (49-70 %) and flow (49-84 %). Gastrocnemius EMS increased superficial femoral artery flow by 140 %. Over 4.5-6 months IPC increased intermittent claudication distance (ICD) (97-150 %) and absolute walking distance (AWD) (84-112 %), with an associated increase in quality of life. NMES of the calf increased ICD and AWD by 82 % and 61-150 % at 4 weeks, and 26 % and 34 % at 8 weeks. In patients with critical limb ischaemia IPC reduced rest pain in 40-100 % and was associated with ulcer healing rates of 26 %. IPC had an early limb salvage rate of 58-83 % at 1-3 months, and 58-94 % at 1.5-3.5 years. No studies have reported the use of EMS or NMES in the management of CLI. CONCLUSION: There is evidence to support the use of IPC in the management of claudication and CLI. There is a building body of literature to support the use of electrical stimulators in PAD, but this is low level to date. Devices may be of special benefit to those with limited exercise capacity, and in non-reconstructable critical limb ischaemia. Galvanic stimulation is not recommended