38,672 research outputs found
Cognitive performance in multiple system atrophy
The cognitive performance of a group of patients with multiple system atrophy (MSA) of striato-nigral predominance was compared with that of age and IQ matched control subjects, using three tests sensitive to frontal lobe dysfunction and a battery sensitive to memory and learning deficits in Parkinson's disease and dementia of the Alzheimer type. The MSA group showed significant deficits in all three of the tests previously shown to be sensitive to frontal lobe dysfunction. Thus, a significant proportion of patients from the MSA group failed an attentional set-shifting test, specifically at the stage when an extra-dimensional shift was required. They were also impaired in a subject-ordered test of spatial working memory. The MSA group showed deficits mostly confined to measures of speed of thinking, rather than accuracy, on the Tower of London task. These deficits were seen in the absence of consistent impairments in language or visual perception. Moreover, the MSA group showed no significant deficits in tests of spatial and pattern recognition previously shown to be sensitive to patients early in the course of probable Alzheimer's disease and only a few patients exhibited impairment on the Warrington Recognition Memory Test. There were impairments on other tests of visual memory and learning relative to matched controls, but these could not easily be related to fundamental deficits of memory or learning. Thus, on a matching-to-sample task the patients were impaired at simultaneous but not delayed matching to sample, whereas difficulties in a pattern-location learning task were more evident at its initial, easier stages. The MSA group showed no consistent evidence of intellectual deterioration as assessed from their performance on subtests of the Wechsler Adult Intelligence Scale (WAIS) and the National Adult Reading Test (NART). Consideration of individual cases showed that there was some heterogeneity in the pattern of deficits in the MSA group, with one patient showing no impairment, even in the face of considerable physical disability. The results show a distinctive pattern of cognitive deficits, unlike those previously seen using the same tests in patients with Parkinson's and Alzheimer's diseases, and suggesting a prominent frontal-lobe-like component. The implications for concepts of 'subcortical' dementia and 'fronto-striatal' cognitive dysfunction are considered
Implications of gauge-mediated supersymmetry breaking with vector-like quarks and a ~125 GeV Higgs boson
We investigate the implications of models that achieve a Standard Model-like
Higgs boson of mass near 125 GeV by introducing additional TeV-scale
supermultiplets in the vector-like 10+\bar{10} representation of SU(5), within
the context of gauge-mediated supersymmetry breaking. We study the resulting
mass spectrum of superpartners, comparing and contrasting to the usual
gauge-mediated and CMSSM scenarios, and discuss implications for LHC
supersymmetry searches. This approach implies that exotic vector-like fermions
t'_{1,2}, b',and \tau' should be within the reach of the LHC. We discuss the
masses, the couplings to electroweak bosons, and the decay branching ratios of
the exotic fermions, with and without various unification assumptions for the
mass and mixing parameters. We comment on LHC prospects for discovery of the
exotic fermion states, both for decays that are prompt and non-prompt on
detector-crossing time scales.Comment: 32 pages. v2: references added, figure caption 5.3 correcte
Escape path complexity and its context dependency in Pacific blue-eyes (Pseudomugil signifer)
The escape trajectories animals take following a predatory attack appear to
show high degrees of apparent 'randomness' - a property that has been described
as 'protean behaviour'. Here we present a method of quantifying the escape
trajectories of individual animals using a path complexity approach. When fish
(Pseudomugil signifer) were attacked either on their own or in groups, we find
that an individual's path rapidly increases in entropy (our measure of
complexity) following the attack. For individuals on their own, this entropy
remains elevated (indicating a more random path) for a sustained period (10
seconds) after the attack, whilst it falls more quickly for individuals in
groups. The entropy of the path is context dependent. When attacks towards
single fish come from greater distances, a fish's path shows less complexity
compared to attacks that come from short range. This context dependency effect
did not exist, however, when individuals were in groups. Nor did the path
complexity of individuals in groups depend on a fish's local density of
neighbours. We separate out the components of speed and direction changes to
determine which of these components contributes to the overall increase in path
complexity following an attack. We found that both speed and direction measures
contribute similarly to an individual's path's complexity in absolute terms.
Our work highlights the adaptive behavioural tactics that animals use to avoid
predators and also provides a novel method for quantifying the escape
trajectories of animals.Comment: 9 page
Fronto-striatal cognitive deficits at different stages of Parkinson's disease
Groups of patients with idiopathic Parkinson's disease, either medicated or unmedicated, were compared with matched groups of normal controls on a computerized battery previously shown to be sensitive to frontal lobe dysfunction, including tests of planning, spatial working memory and attentional set-shifting. In a series of problems based on the 'Tower of London' test, medicated patients with Parkinson's disease were shown to be impaired in the amount of time spent thinking about (planning) the solution to each problem. Additionally, an impairment in terms of the accuracy of the solution produced on this test was only evident in those patients with more severe clinical symptoms and was accompanied by deficits in an associated test of spatial short-term memory. Medicated patients with both mild and severe clinical symptoms were also impaired on a related test of spatial working memory. In contrast, a group of patients who were unmedicated and 'early in the course' of the disease were unimpaired in all three of these tests. However, all three Parkinson's disease groups were impaired in the test of attentional set-shifting ability, although unimpaired in a test of pattern recognition which is insensitive to frontal lobe damage. These data are compared with those previously published from a group of young neurosurgical patients with localized excisions of the frontal lobes and are discussed in terms of the specific nature of the cognitive deficit at different stages of Parkinson's disease
Detection of volatile organic compounds (VOCs) using an optical fibre long period grating with a calixarene anchored mesoporous thin film
A long period grating (LPG) modified with a mesoporous film infused with a functional compound, calix[4]arene, was employed for the detection of volatile organic compounds (VOCs). The mesoporous film consisted of an inorganic part, of SiO2 nanoparticles (NPs) along with an organic moiety of poly(allylamine hydrochloride) polycation PAH, which was finally infused with functional compound, p-sulphanatocalix[4]arene (CA[4]). The LPG sensor was designed to operate at the phase matching turning point to provide the highest sensitivity. The sensing mechanism is based on the measurement of the refractive index (RI) change induced by the complexion of the VOCs with calix[4]arene (CA). The LPG modified with 5 cycles of (SiO2 NPs/PAH)5PAA responded to exposure to chloroform and benzene vapours. The sensitivity to humidity as an interfering parameter was also investigated
Prediction and Generation of Binary Markov Processes: Can a Finite-State Fox Catch a Markov Mouse?
Understanding the generative mechanism of a natural system is a vital
component of the scientific method. Here, we investigate one of the fundamental
steps toward this goal by presenting the minimal generator of an arbitrary
binary Markov process. This is a class of processes whose predictive model is
well known. Surprisingly, the generative model requires three distinct
topologies for different regions of parameter space. We show that a previously
proposed generator for a particular set of binary Markov processes is, in fact,
not minimal. Our results shed the first quantitative light on the relative
(minimal) costs of prediction and generation. We find, for instance, that the
difference between prediction and generation is maximized when the process is
approximately independently, identically distributed.Comment: 12 pages, 12 figures;
http://csc.ucdavis.edu/~cmg/compmech/pubs/gmc.ht
The Radial Extent and Warp of the Ionized Galactic Disk. I. A VLBA Survey of Extragalactic Sources Toward the Anticenter
We report multifrequency Very Long Baseline Array observations of twelve
active galactic nuclei seen toward the Galactic anticenter. All of the sources
are at |b| < 10 degrees and seven have |b| < 0.5 degrees. Our VLBA observations
can detect an enhancement in the angular broadening of these sources due to an
extended H II disk, if the orientation of the H II disk in the outer Galaxy is
similar to that of the H I disk. Such an extended H II disk is suggested by the
C IV absorption in a quasar's spectrum, the appearance of H I disks of nearby
spiral galaxies, and models of Ly-alpha cloud absorbers and the Galactic
fountain. We detect eleven of the twelve sources at one or more frequencies;
nine of the sources are compact and suitable for an angular broadening
analysis. A preliminary analysis of the observed angular diameters suggests
that the H II disk does not display considerable warping or flaring and does
not extend to large Galactocentric distances (R >~ 100 kpc). A companion paper
(Lazio & Cordes 1997) combines these observations with those in the literature
and presents a more comprehensive analysis.Comment: 19 pages, LaTeX2e with AASTeX macro aaspp4, accepted for publication
in ApJS, Vol. 115, 1998 April; Figures 1, 3, and 4 included, for figures of
individual sources see
http://astrosun.tn.cornell.edu/students/lazio/Anticenter/anticenterI.htm
On the Significance of Absorption Features in HST/COS Data
We present empirical scaling relations for the significance of absorption
features detected in medium resolution, far-UV spectra obtained with the Cosmic
Origins Spectrograph (COS). These relations properly account for both the
extended wings of the COS line spread function and the non-Poissonian noise
properties of the data, which we characterize for the first time, and predict
limiting equivalent widths that deviate from the empirical behavior by \leq 5%
when the wavelength and Doppler parameter are in the ranges \lambda = 1150-1750
A and b > 10 km/s. We have tested a number of coaddition algorithms and find
the noise properties of individual exposures to be closer to the Poissonian
ideal than coadded data in all cases. For unresolved absorption lines, limiting
equivalent widths for coadded data are 6% larger than limiting equivalent
widths derived from individual exposures with the same signal-to-noise. This
ratio scales with b-value for resolved absorption lines, with coadded data
having a limiting equivalent width that is 25% larger than individual exposures
when b \approx 150 km/s.Comment: 25 pages, 3 tables, 7 figures, accepted for publication in PAS
Interstellar Carbon in Translucent Sightlines
We report interstellar C II column densities or upper limits determined from
weak absorption of the 2325.4029 A intersystem transition observed in six
translucent sightlines with STIS. The sightlines sample a wide range of
interstellar characteristics including total-to-selective extinction, R_{V} =
2.6 - 5.1; average hydrogen density along the sightline, = 3 - 14
cm^{-3}; and fraction of H in molecular form, 0 - 40%. Four of the sightlines,
those toward HD 37021, HD 37061, HD 147888 and HD 207198, have interstellar
gas-phase abundances that are consistent with the diffuse sightline ratio of
161 +/- 17 carbon atoms in the gas per million hydrogen nuclei. We note that
while it has a gas-phase carbon abundance that is consistent with the other
sightlines, a large fraction of the C II toward HD 37061 is in an excited
state. The sightline toward HD 152590 has a measured interstellar gas-phase
carbon abundance that is well above the diffuse sightline average; the column
density of C in this sightline may be overestimated due to noise structure in
the data. Toward HD 27778 we find a 3 sigma abundance upper limit of <108 C
atoms in the gas per million H, a substantially enhanced depletion of C as
compared to the diffuse sightline value. The interstellar characteristics
toward HD 27778 are otherwise not extreme among the sample except for an
unusually large abundance of CO molecules in the gas.Comment: Accepted for publication in the Astrophysical Journa
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