18,834 research outputs found
Pulsar scintillations from corrugated reconnection sheets in the ISM
We show that surface waves along interstellar current sheets closely aligned
with the line of sight lead to pulsar scintillation properties consistent with
those observed. This mechanism naturally produces the length and density scales
of the ISM scattering lenses that are required to explain the magnitude and
dynamical spectrum of the scintillations. In this picture, the parts of warm
ionized interstellar medium that are responsible for the scintillations are
relatively quiescent, with scintillation and scattering resulting from weak
waves propagating along magnetic domain boundary current sheets, which are both
expected from helicity conservation and have been observed in numerical
simulations. The model statistically predicts the spacing and amplitudes of
inverted parabolic arcs seen in Fourier-transformed dynamical spectra of
strongly scintillating pulsars with only 3 parameters. Multi-frequency,
multi-epoch low frequency VLBI observations can quantitatively test this
picture. If successful, in addition to mapping the ISM, this may open the door
to precise nanoarcsecond pulsar astrometry, distance measurements, and emission
studies using these 10AU interferometers in the sky.Comment: 9 pages, 10 figures, accepted in MNRA
Charge inversion in DNA-amphiphile complexes: Possible application to gene therapy
We study a complex formation between the DNA and cationic amphiphilic
molecules. As the amphiphile is added to the solution containing DNA, a
cooperative binding of surfactants to the DNA molecules is found. This binding
transition occurs at specific density of amphiphile, which is strongly
dependent on the concentration of the salt and on the hydrophobicity of the
surfactant molecules. We find that for amphiphiles which are sufficiently
hydrophobic, a charge neutralization, or even charge inversion of the complex
is possible. This is of particular importance in applications to gene therapy,
for which the functional delivery of specific base sequence into living cells
remains an outstanding problem. The charge inversion could, in principle, allow
the DNA-surfactant complexes to approach negatively charged cell membranes
permitting the transfection to take place.Comment: Latex, 5 figure
Stereo Computation for a Single Mixture Image
This paper proposes an original problem of \emph{stereo computation from a
single mixture image}-- a challenging problem that had not been researched
before. The goal is to separate (\ie, unmix) a single mixture image into two
constitute image layers, such that the two layers form a left-right stereo
image pair, from which a valid disparity map can be recovered. This is a
severely illposed problem, from one input image one effectively aims to recover
three (\ie, left image, right image and a disparity map). In this work we give
a novel deep-learning based solution, by jointly solving the two subtasks of
image layer separation as well as stereo matching. Training our deep net is a
simple task, as it does not need to have disparity maps. Extensive experiments
demonstrate the efficacy of our method.Comment: Accepted by European Conference on Computer Vision (ECCV) 201
Vitamin D and its analogues: Do they protect against cardiovascular disease in patients with kidney disease?
Vitamin D and its analogs: Do they protect against cardiovascular disease in patients with kidney disease?BackgroundPatients with chronic kidney disease (CKD) are at high risk for cardiovascular disease, and despite recent advances in hypertension control, anemia management, and dialysis adequacy, mortality remains high. Improved understanding of nontraditional risk factors, including those present at early phases in CKD, may lead to novel therapeutic strategies. CKD has been demonstrated to be an independent risk factor for cardiovascular disease in the general population, but data are lacking as to the associated potential abnormalities that occur in association with reduced glomerular filtration rate (GFR), which may contribute to this increased risk. Data are accumulating regarding the role of abnormalities of calcium, phosphorus, vitamin D, and parathyroid hormone (PTH) in cardiovascular disease. Vitamin D deficiency is present even in the early stages of CKD. Vitamin D plays a central role in calcium-phosphorus homeostasis, regulation of PTH, and formation and maintenance of bone. However, until recently, vitamin D has not been considered to have a biologic role in CKD beyond mineral regulation, or has been considered as a negative factor contributing to soft tissue and cardiovascular calcification. In light of recent observational studies showing an association of vitamin D therapy and survival benefit in hemodialysis patients, the effects of vitamin D on cardiovascular system have become a heavily debated issue.MethodsA Medline search was performed to identify relevant literature describing the role of vitamin D in the pathogenesis of cardiovascular disease. Both the experimental and clinical literatures in English were reviewed.ResultsThe accumulating published data demonstrate both associative relationships and mechanisms for biologic plausibility. The following three potential mechanisms may be important for the protective effects of vitamin D against cardiovascular disease mortality: vitamin D can inhibit various aspects of inflammation, which have been established as a key pathogenic mechanism in atherosclerosis; vitamin D exerts an antiproliferative effect on myocardial cell hypertrophy and proliferation, which underlies the pathogenesis of congestive heart failure; and vitamin D acts as a negative endocrine regulator for the renin-angiotensin system, which itself plays an important independent role in hypertension and cardiovascular health.ConclusionVitamin D deficiency might be an underestimated nonclassical risk factor for cardiovascular disease in CKD. Based on a review of the evidence, from both basic science and clinical studies, this article supports the possible protective role of vitamin D beyond its effect on mineral metabolism, and suggests the need for ongoing evaluation of the role of vitamin D in cardiovascular health in the CKD population
Stimulus intensity-dependent modulations of hippocampal long-term potentiation by basolateral amygdala priming
There is growing realization that the relationship between memory and stress/emotionality is complicated, and may include both memory enhancing and memory impairing aspects. It has been suggested that the underlying mechanisms involve amygdala modulation of hippocampal synaptic plasticity, such as long-term potentiation (LTP). We recently reported that while in CA1 basolateral amygdala (BLA) priming impaired theta stimulation induced LTP, it enhanced LTP in the dentate gyrus (DG). However, emotional and stressfull experiences were found to activate synaptic plasticity within the BLA, raising the possibility that BLA modulation of other brain regions may be altered as well, as it may depend on the way the BLA is activated or is responding. In previous studies BLA priming stimulation was relatively weak (1 V, 50 μs pulse duration). In the present study we assessed the effects of two stronger levels of BLA priming stimulation (1 V or 2 V, 100 μs pulse duration) on LTP induction in hippocampal DG and CA1, in anesthetized rats. Results show that 1V-BLA priming stimulation enhanced but 2V-BLA priming stimulation impaired DG LTP; however, both levels of BLA priming stimulation impaired CA1 LTP, suggesting that modulation of hippocampal synaptic plasticity by amygdala is dependent on the degree of amygdala activation. These findings suggest that plasticity-induced within the amygdala, by stressful experiences induces a form of metaplasticity that would alter the way the amygdala may modulate memory-related processes in other brain areas, such as the hippocampus
Solution for the BFKL Pomeron Calculus in zero transverse dimensions
In this paper the exact analytical solution is found for the BFKL Pomeron
calculus in zero transverse dimensions, in which all Pomeron loops have been
included. The comparison with the approximate methods of the solution is given,
and the kinematic regions are discussed where they describe the behaviour of
the scattering amplitude quite well. In particular, the semi-classical approach
is considered, which reproduces the main properties of the exact solution at
large values of rapidity (). It is shown that the mean field
approximation leads to a good description of the scattering amplitude only if
the amplitude at low energy is rather large. However, even in this case, it
does not lead to the correct asymptotic behaviour of the scattering amplitude
at high energies.Comment: 37 pages,19 figures and one table, the revised versio
High energy Scattering in 2+1 QCD: A Dipole Picture
A dipole picture of high energy scattering is developed in the 2+1
dimensional QCD, following Mueller. A generalized integral equation for the
dipole density with a given separation and center of mass position is derived,
and meson-meson non-forward scattering amplitude is therefore calculated. We
also calculate the amplitude due to two pomeron exchange, and the triple
pomeron coupling. We compare the result obtained by this method to our previous
result based on an effective action approach, and find the two results agree at
the one pomeron exchange level.Comment: minor typos corrected. Postscript files are available through
anonymous ftp quark.het.brown.edu, in the directory /pub/preprints, file name
is 9407299. Hard copy is available upon reques
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