16 research outputs found
Evaluation of Neurovascular Coupling by Functional Transcranial Doppler and Technetium-99M-HMPAO Single Photon Emission Computed Tomography
The viscosity cross-section for elastic electron-xenon collisions including electron spin polarization
The results of the evaluation of the viscosity cross-section for elastic electron-xenon
collisions, taking into account the spin-orbit interaction of the continuum electron, in the energy
interval from 0.1 eV to 50 eV are presented and discussed. The calculations are performed on the
basis of three theoretically derived sets of phase shift data obtained by different authors and on
the deduced relativistic expression for the viscosity cross-section in terms of phase shifts
discerning the spin-up and spin-down states of the scattered electrons. Comparison with viscosity
cross-sections, as evaluated from non-relativistic phase shifts extracted from experiments, strongly
favours the relativistic results. The assumption of isotropic scattering is critically examined and
the error induced by its use is shown to persist to the same extent as in non-relativistic
calculations, at least in the energy region considered
The viscosity cross-section for elastic electron-xenon collisions including electron spin polarization
Influence of solar X-ray flares on the earth-ionosphere waveguide
A simultaneous analysis of solar are X-ray irradiance and VLF signal amplitude on the GQD/22.1 kHz trace was carried out. Solar are data were taken from GOES 12 satellite listings. The VLF amplitude data were recorded by means of the AbsPAL (Absolute Phase and Amplitude Logger) at the Institute of Physics, Belgrade, Serbia. It was found that solar are events from class C to class X affect the VLF signal amplitude in various ways and can be classified according to the type of effect produced in the Earth-ionosphere waveguide on the VLF propagation
Advanced fit technique for astrophysical spectra
Aims.The purpose of this paper is to introduce a robust method of
data fitting convenient for dealing with astrophysical spectra contaminated by a large
fraction of outliers.
Methods.We base our approach on the suitable defined measure:
the density of the least squares (DLS) that characterizes subsets
of the whole data set. The best-fit parameters are obtained by the
least-square method on a subset having the maximum value of DLS
or, less formally, on the largest subset free of outliers.
Results.We give
the FORTRAN90 source code
of the
subroutine that implements the DLS method. The efficiency of the
DLS method is demonstrated on a few examples: estimation of
continuum in the presence of spectral lines, estimation of spectral line parameters in the presence of outliers, and
estimation of the thermodynamic temperature from the spectrum that is rich in spectral lines.
Conclusions.Comparison
of the present results with the ones obtained with the widely
used comprehensive multi-component fit yields agreement within error margins. Due to simplicity and robustness, the proposed
approach could be the method of choice whenever outliers are present, or whenever unwelcome features of the spectrum are to be
considered as formal outliers (e.g. spectral lines while estimating continuum)
Slowly propagating instabilities in plasmas with Margenau-Davydov electron distribution function
Classification of X-ray solar flares regarding their effects on the lower ionosphere electron density profile
The classification of X-ray solar flares is performed
regarding their effects on the Very Low Frequency (VLF) wave propagation
along the Earth-ionosphere waveguide. The changes in propagation are
detected from an observed VLF signal phase and amplitude perturbations, taking
place during X-ray solar flares. All flare effects chosen for the analysis
are recorded by the Absolute Phase and Amplitude Logger (AbsPal), during
the summer months of 2004–2007, on the single trace, Skelton (54.72 N,
2.88 W) to Belgrade (44.85 N, 20.38 E) with a distance along the Great Circle Path
(GCP) D≈2000 km in length.
The observed VLF amplitude and phase perturbations are simulated by the
computer program Long-Wavelength Propagation Capability (LWPC), using Wait's
model of the lower ionosphere, as determined by two parameters: the
sharpness (β in 1/km) and reflection height (H' in km). By varying the
values of β and H' so as to match the observed amplitude and phase
perturbations, the variation of the D-region electron density height profile
Ne(z) was reconstructed, throughout flare duration. The procedure is
illustrated as applied to a series of flares, from class C to M5
(5×10−5 W/m2 at 0.1–0.8 nm), each giving rise to a different time
development of signal perturbation.
The corresponding change in electron density from the unperturbed value at
the unperturbed reflection height, i.e. Ne(74 km)=2.16×108 m−3
to the value induced by an M5 class flare, up to Ne(74
km)=4×1010 m−3 is obtained. The β parameter is
found to range from 0.30–0.49 1/km and the reflection height H' to vary
from 74–63 km. The changes in Ne(z) during the flares, within height
range z=60 to 90 km are determined, as well
Stability of person-specific blood-based infrared molecular fingerprints opens up prospects for health monitoring
Health state transitions are reflected in characteristic changes in the molecular composition of biofluids. Detecting these changes in parallel, across a broad spectrum of molecular species, could contribute to the detection of abnormal physiologies. Fingerprinting of biofluids by infrared vibrational spectroscopy offers that capacity. Whether its potential for health monitoring can indeed be exploited critically depends on how stable infrared molecular fingerprints (IMFs) of individuals prove to be over time. Here we report a proof-of-concept study that addresses this question. Using Fourier-transform infrared spectroscopy, we have fingerprinted blood serum and plasma samples from 31 healthy, non-symptomatic individuals, who were sampled up to 13 times over a period of 7 weeks and again after 6 months. The measurements were performed directly on liquid serum and plasma samples, yielding a time- and cost-effective workflow and a high degree of reproducibility. The resulting IMFs were found to be highly stable over clinically relevant time scales. Single measurements yielded a multiplicity of person-specific spectral markers, allowing individual molecular phenotypes to be detected and followed over time. This previously unknown temporal stability of individual biochemical fingerprints forms the basis for future applications of blood-based infrared spectral fingerprinting as a multiomics-based mode of health monitoring