1,559 research outputs found
U.S. stock market interaction network as learned by the Boltzmann Machine
We study historical dynamics of joint equilibrium distribution of stock
returns in the U.S. stock market using the Boltzmann distribution model being
parametrized by external fields and pairwise couplings. Within Boltzmann
learning framework for statistical inference, we analyze historical behavior of
the parameters inferred using exact and approximate learning algorithms. Since
the model and inference methods require use of binary variables, effect of this
mapping of continuous returns to the discrete domain is studied. The presented
analysis shows that binarization preserves market correlation structure.
Properties of distributions of external fields and couplings as well as
industry sector clustering structure are studied for different historical dates
and moving window sizes. We found that a heavy positive tail in the
distribution of couplings is responsible for the sparse market clustering
structure. We also show that discrepancies between the model parameters might
be used as a precursor of financial instabilities.Comment: 15 pages, 17 figures, 1 tabl
CN and HCN in Dense Interstellar Clouds
We present a theoretical investigation of CN and HCN molecule formation in
dense interstellar clouds. We study the gas-phase CN and HCN production
efficiencies from the outer photon-dominated regions (PDRs) into the opaque
cosmic-ray dominated cores. We calculate the equilibrium densities of CN and
HCN, and of the associated species C+, C, and CO, as functions of the
far-ultraviolet (FUV) optical depth. We consider isothermal gas at 50 K, with
hydrogen particle densities from 10^2 to 10^6 cm^-3. We study clouds that are
exposed to FUV fields with intensities 20 to 2*10^5 times the mean interstellar
FUV intensity. We assume cosmic-ray H2 ionization rates ranging from 5*10^-17
s^-1, to an enhanced value of 5*10^-16 s^-1. We also examine the sensitivity of
the density profiles to the gas-phase sulfur abundance.Comment: Accepted for publication in ApJ, 33 pages, 8 figure
Modeling Eridani and asteroseismic tests of element diffusion
Taking into account the helium and metal diffusion, we explore the possible
evolutionary status and perform seismic analysis of MOST target: the star
Eridani. We adopt the different input parameters to construct the
models by fitting the available observational constraints: e.g., ,
, , . From computation, we obtain the average large spacings of
Eridani about Hz. The age of the diffused models has
been found to be about 1 Gyr, which is younger than one determined previously
by models without diffusion. We found that the effect of pure helium diffusion
on the internal structure of the young low-mass star is slight, but the metal
diffusion influence is obvious. The metal diffusion leads the models to have
much higher temperature in the radiation interior, correspondingly the higher
sound speed in the interior of the model, thereby the larger frequency and
spacings.Comment: 16 pages, 4 figures, accepted for publication in ChjA
Observations of Microwave Continuum Emission from Air Shower Plasmas
We investigate a possible new technique for microwave measurements of
ultra-high energy cosmic ray (UHECR) extensive air showers which relies on
detection of expected continuum radiation in the microwave range, caused by
free-electron collisions with neutrals in the tenuous plasma left after the
passage of the shower. We performed an initial experiment at the AWA (Argonne
Wakefield Accelerator) laboratory in 2003 and measured broadband microwave
emission from air ionized via high energy electrons and photons. A follow-up
experiment at SLAC (Stanford Linear Accelerator Center) in summer of 2004
confirmed the major features of the previous AWA observations with better
precision and made additional measurements relevant to the calorimetric
capabilities of the method. Prompted by these results we built a prototype
detector using satellite television technology, and have made measurements
indicating possible detection of cosmic ray extensive air showers. The method,
if confirmed by experiments now in progress, could provide a high-duty cycle
complement to current nitrogen fluorescence observations of UHECR, which are
limited to dark, clear nights. By contrast, decimeter microwave observations
can be made both night and day, in clear or cloudy weather, or even in the
presence of moderate precipitation.Comment: 15 pages, 13 figure
Uptake and mitochondrial dysfunction of alpha-synuclein in human astrocytes, cortical neurons and fibroblasts
© 2013 Braidy et al.; licensee BioMed Central Ltd.
This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.The accumulation and aggregation of alpha-synuclein (α-syn) in several tissue including the brain is a major
pathological hallmark in Parkinson’s disease (PD). In this study, we show that α-syn can be taken up by primary
human cortical neurons, astrocytes and skin-derived fibroblasts in vitro. Our findings that brain and peripheral cells
exposed to α-syn can lead to impaired mitochondrial function, leading to cellular degeneration and cell death,
provides additional evidence for the involvement of mitochondrial dysfunction as a mechanism of toxicity of α-syn
in human cells
Radio-Frequency Measurements of Coherent Transition and Cherenkov Radiation: Implications for High-Energy Neutrino Detection
We report on measurements of 11-18 cm wavelength radio emission from
interactions of 15.2 MeV pulsed electron bunches at the Argonne Wakefield
Accelerator. The electrons were observed both in a configuration where they
produced primarily transition radiation from an aluminum foil, and in a
configuration designed for the electrons to produce Cherenkov radiation in a
silica sand target. Our aim was to emulate the large electron excess expected
to develop during an electromagnetic cascade initiated by an ultra high-energy
particle. Such charge asymmetries are predicted to produce strong coherent
radio pulses, which are the basis for several experiments to detect high-energy
neutrinos from the showers they induce in Antarctic ice and in the lunar
regolith. We detected coherent emission which we attribute both to transition
and possibly Cherenkov radiation at different levels depending on the
experimental conditions. We discuss implications for experiments relying on
radio emission for detection of electromagnetic cascades produced by ultra
high-energy neutrinos.Comment: updated figure 10; fixed typo in equation 2.2; accepted by PR
Chemically induced Jahn–Teller ordering on manganite surfaces
Physical and electrochemical phenomena at the surfaces of transition metal oxides and their coupling to local functionality remains one of the enigmas of condensed matter physics. Understanding the emergent physical phenomena at surfaces requires the capability to probe the local composition, map order parameter fields and establish their coupling to electronic properties. Here we demonstrate that measuring the sub-30-pm displacements of atoms from high-symmetry positions in the atomically resolved scanning tunnelling microscopy allows the physical order parameter fields to be visualized in real space on the single-atom level. Here, this local crystallographic analysis is applied to the in-situ-grown manganite surfaces. In particular, using direct bond-angle mapping we report direct observation of structural domains on manganite surfaces, and trace their origin to surface-chemistryinduced stabilization of ordered Jahn–Teller displacements. Density functional calculations provide insight into the intriguing interplay between the various degrees of freedom now resolved on the atomic level
Migraine and sleep disorders: a systematic review
Migraine and sleep disorders are common and often burdensome chronic conditions with a high prevalence in the general population, and with considerable socio-economic impact and costs. The existence of a relationship between migraine and sleep disorders has been recognized from centuries by clinicians and epidemiological studies. Nevertheless, the exact nature of this association, the underlying mechanisms and interactions are complex and not completely understood. Recent biochemical and functional imaging studies identified central nervous system structures and neurotransmitters involved in the pathophysiology of migraine and also important for the regulation of normal sleep architecture, suggesting a possible causative role, in the pathogenesis of both disorders, of a dysregulation in these common nervous system pathways. This systematic review summarizes the existing data on migraine and sleep disorders with the aim to evaluate the existence of a causal relationship and to assess the presence of influencing factors. The identification of specific sleep disorders associated with migraine should induce clinicians to systematically assess their presence in migraine patients and to adopt combined treatment strategies
BN domains included into carbon nanotubes: role of interface
We present a density functional theory study on the shape and arrangement of
small BN domains embedded into single-walled carbon nanotubes. We show a strong
tendency for the BN hexagons formation at the simultaneous inclusion of B and N
atoms within the walls of carbon nanotubes. The work emphasizes the importance
of a correct description of the BN-C frontier. We suggest that BN-C interface
will be formed preferentially with the participation of N-C bonds. Thus, we
propose a new way of stabilizing the small BN inclusions through the formation
of nitrogen terminated borders. The comparison between the obtained results and
the available experimental data on formation of BN plackets within the single
walled carbon nanotubes is presented. The mirror situation of inclusion of
carbon plackets within single walled BN nanotubes is considered within the
proposed formalism. Finally, we show that the inclusion of small BN plackets
inside the CNTs strongly affects the electronic character of the initial
systems, opening a band gap. The nitrogen excess in the BN plackets introduces
donor states in the band gap and it might thus result in a promising way for
n-doping single walled carbon nanotubes
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