4,939 research outputs found
Modafinil-Induced changes in functional connectivity in the cortex and cerebellum of healthy elderly subjects
In the past few years, cognitive enhancing drugs (CEDs) have gained growing interest and the focus of investigations aimed at exploring their use to potentiate the cognitive performances of healthy individuals. Most of this exploratory CED-related research has been performed on young adults. However, CEDs may also help to maintain optimal brain functioning or compensate for subtle and or subclinical deficits associated with brain aging or early-stage dementia. In this study, we assessed effects on resting state brain activity in a group of healthy elderly subjects undergoing acute administration of modafinil, a wakefulness-promoting agent. To that aim, participants (n = 24) were investigated with resting state functional Magnetic Resonance Imaging (rs-fMRI) before and after the administration of a single dose (100 mg) of modafinil. Effects were compared to age and size-matched placebo group. Rs-fMRI effects were assessed, employing a graph-based approach and Eigenvector Centrality (EC) analysis, by taking in account topological changes occurring in functional brain networks. The main finding of the study is that modafinil promotes enhanced centrality, a measure of the importance of nodes within functional networks, of the bilateral primary visual (V1) cortex. EC analysis also revealed that modafinil-treated subjects show increased functional connectivity between the V1 and specific cerebellar (Crus I, Crus II, VIIIa lobule) and frontal (right inferior frontal sulcus and left middle frontal gyrus) regions. Present findings provide functional data supporting the hypothesis that modafinil can modulate the cortico-cerebellar connectivity of the aging brai
A Statistical Prescription to Estimate Properly Normalized Distributions of Different Particle Species
We describe a statistical method to avoid biased estimation of the content of
different particle species. We consider the case when the particle
identification information strongly depends on some kinematical variables,
whose distributions are unknown and different for each particles species. We
show that the proposed procedure provides properly normalized and completely
data-driven estimation of the unknown distributions without any a priori
assumption on their functional form. Moreover, we demonstrate that the method
can be generalized to any kinematical distribution of the particles
An Unbiased 1.3 mm Emission Line Survey of the Protoplanetary Disk Orbiting LkCa 15
The outer (>30 AU) regions of the dusty circumstellar disk orbiting the ~2-5
Myr-old, actively accreting solar analog LkCa 15 are known to be chemically
rich, and the inner disk may host a young protoplanet within its central
cavity. To obtain a complete census of the brightest molecular line emission
emanating from the LkCa 15 disk over the 210-270 GHz (1.4 - 1.1 mm) range, we
have conducted an unbiased radio spectroscopic survey with the Institute de
Radioastronomie Millimetrique (IRAM) 30 meter telescope. The survey
demonstrates that, in this spectral region, the most readily detectable lines
are those of CO and its isotopologues 13CO and C18O, as well as HCO+, HCN, CN,
C2H, CS, and H2CO. All of these species had been previously detected in the
LkCa 15 disk; however, the present survey includes the first complete coverage
of the CN (2-1) and C2H (3-2) hyperfine complexes. Modeling of these emission
complexes indicates that the CN and C2H either reside in the coldest regions of
the disk or are subthermally excited, and that their abundances are enhanced
relative to molecular clouds and young stellar object environments. These
results highlight the value of unbiased single-dish line surveys in guiding
future high resolution interferometric imaging of disks.Comment: 35 pages, 9 figures, accepted for publication in The Astrophysical
Journa
First ADS analysis of B- -> D0K- decays in hadron collisions
Proceedings of DISCRETE 2010, Symposium on Prospects in the Physics of
Discrete Symmetries, Rome (IT), 6-11 December 2010Comment: 7 pages, 5 figure
Radiation-dominated area metric cosmology
We provide further crucial support for a refined, area metric structure of
spacetime. Based on the solution of conceptual issues, such as the consistent
coupling of fermions and the covariant identification of radiation fields on
area metric backgrounds, we show that the radiation-dominated epoch of area
metric cosmology is equivalent to that epoch in standard Einstein cosmology.
This ensures, in particular, successful nucleosynthesis. This surprising result
complements the previously derived prediction of a small late-time acceleration
of an area metric universe.Comment: 23 pages, no figures; references adde
Chromatic Information and Feature Detection in Fast Visual Analysis
The visual system is able to recognize a scene based on a sketch made of very simple features. This ability is likely crucial for survival, when fast image recognition is necessary, and it is believed that a primal sketch is extracted very early in the visual processing. Such highly simplified representations can be sufficient for accurate object discrimination, but an open question is the role played by color in this process. Rich color information is available in natural scenes, yet artist's sketches are usually monochromatic; and, black-and-white movies provide compelling representations of real world scenes. Also, the contrast sensitivity of color is low at fine spatial scales. We approach the question from the perspective of optimal information processing by a system endowed with limited computational resources. We show that when such limitations are taken into account, the intrinsic statistical properties of natural scenes imply that the most effective strategy is to ignore fine-scale color features and devote most of the bandwidth to gray-scale information. We find confirmation of these information-based predictions from psychophysics measurements of fast-viewing discrimination of natural scenes. We conclude that the lack of colored features in our visual representation, and our overall low sensitivity to high-frequency color components, are a consequence of an adaptation process, optimizing the size and power consumption of our brain for the visual world we live in
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Chromatic Information and Feature Detection in Fast Visual Analysis
The visual system is able to recognize a scene based on a sketch made of very simple features. This ability is likely crucial for survival, when fast image recognition is necessary, and it is believed that a primal sketch is extracted very early in the visual processing. Such highly simplified representations can be sufficient for accurate object discrimination, but an open question is the role played by color in this process. Rich color information is available in natural scenes, yet artist's sketches are usually monochromatic; and, black-and-white movies provide compelling representations of real world scenes. Also, the contrast sensitivity of color is low at fine spatial scales. We approach the question from the perspective of optimal information processing by a system endowed with limited computational resources. We show that when such limitations are taken into account, the intrinsic statistical properties of natural scenes imply that the most effective strategy is to ignore fine-scale color features and devote most of the bandwidth to gray-scale information. We find confirmation of these information-based predictions from psychophysics measurements of fast-viewing discrimination of natural scenes. We conclude that the lack of colored features in our visual representation, and our overall low sensitivity to high-frequency color components, are a consequence of an adaptation process, optimizing the size and power consumption of our brain for the visual world we live in
Area metric gravity and accelerating cosmology
Area metric manifolds emerge as effective classical backgrounds in quantum
string theory and quantum gauge theory, and present a true generalization of
metric geometry. Here, we consider area metric manifolds in their own right,
and develop in detail the foundations of area metric differential geometry.
Based on the construction of an area metric curvature scalar, which reduces in
the metric-induced case to the Ricci scalar, we re-interpret the
Einstein-Hilbert action as dynamics for an area metric spacetime. In contrast
to modifications of general relativity based on metric geometry, no continuous
deformation scale needs to be introduced; the extension to area geometry is
purely structural and thus rigid. We present an intriguing prediction of area
metric gravity: without dark energy or fine-tuning, the late universe exhibits
a small acceleration.Comment: 52 pages, 1 figure, companion paper to hep-th/061213
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