198 research outputs found
Determination of Effective Spectrum of Medical Linear Electron Accelerators from Depth Dose Distributions
Development of the spectrum reconstruction method for bremsstrahlung beams with different field sizes, created medical electron linear accelerators (LAE), on the base of the deep dose distributions in a water phantom and determination of photon spectra for Varian Trilogy accelerator 6 MV. The proposed methodology is based on the use of dose kernels algorithm of point monoenergetic monodirectional source (pencil beam (PB)) for the depth dose distribution calculation, created different cross-section beams of in a water phantom, and experimental measurements of these distributions. For solving the inverse problem is applied Toolbox routines ’Optimtool’ knowing mathematical package MATLAB to solve. Bremsstrahlung energy spectrum generated medical accelerator Varian Triology with different sizes of square fields from 3 x 3 up to 40 x 40 cm2 and average energy photons, depending on the size of the fields were received. Dose kernels for a set of defined energies PB were calculated. Depth dose distribution in a water phantom, calculated using the obtained spectra and dose kernels agree well with measurement dose distributions. The proposed technique reconstruction of bremsstrahlung spectrum of medical accelerator is good adequate. Average energy spectra of photons for Varian Trilogy Accelerator in regime 6 MV varies from 1.71 to 1.43 MeV depending on the field size.
Keywords: radiation therapy, medical accelerators, bremsstrahlung, reconstruction of the photon spectrum
Determination of Small Beam Axial Dose Distribution in Water Based on the Mathematical Model of Pencil Beam Kernels
An analytical model of the dose kernel of pencil beam for photon with the Bremsstrahlung spectrum with maximum energy 6 MV was created in this work, which makes it possible to determine the primary and scattered components of the absorbed dose in water phantom with an acceptable error for practice. Using this model a simply method of dosimetry of small circular cross section 6 MV photon beam was proposed. It combines the absolute measurement of the absorbed dose in the water at the reference point for reference geometry with the calculation of the deep dose distribution by simple analytical formulas for circular beams with an arbitrary radius of the cross section.
Keywords: dose kernels, pencil beam, dosimetry, small photon beam, radiotherapy
The structure and evolution of M51-type galaxies
We discuss the integrated kinematic parameters of 20 M51-type binary
galaxies. A comparison of the orbital masses of the galaxies with the sum of
the individual masses suggests that moderately massive dark halos surround
bright spiral galaxies. The relative velocities of the galaxies in binary
systems were found to decrease with increasing relative luminosity of the
satellite. We obtained evidence that the Tully-Fisher relation for binary
members could be flatter than that for local field galaxies. An enhanced star
formation rate in the binary members may be responsible for this effect. In
most binary systems, the direction of orbital motion of the satellite coincides
with the direction of rotation of the main galaxy. Seven candidates for distant
M51-type objects were found in the Northern and Southern Hubble Deep Fields. A
comparison of this number with the statistics of nearby galaxies provides
evidence for the rapid evolution of the space density of M51-type galaxies with
redshift Z. We assume that M51-type binary systems could be formed through the
capture of a satellite by a massive spiral galaxy. It is also possible that the
main galaxy and its satellite in some of the systems have a common cosmological
origin.Comment: 8 pages, 4 figures, to be published in Astronomy Letter
Separation of signals from neutrons and gamma quanta by the method of normalized signals
The solution of the problem how to register fast neutrons in the presence of intense gamma radiation is required when solving such fundamental and applied problems as registration of the neutron and gamma background in underground low-background experiments (the low background detectors of the neutrino and dark matter); beam diagnostic at particle accelerators; radiation monitoring at nuclear facilities, nuclear medicine; environmental monitoring. To separate signals from neutrons and gamma quanta, scintillation detectors with organic scintillators are used. The best scintillators are organic crystals of stilbene and p-terpheny
First measurements of oblique ECE with a real-time moveable line-of-sight on TCV
Electron cyclotron (EC) emission (ECE) radiometers viewing perpendicular to the magnetic field are common on nearly all tokamaks for measuring the electron temperature with good spatio-temporal resolution. Two such radiometers are installed on TCV, one looking from the low field side (LFS) and the other from the high field side (HFS). The HFS radiometer is especially sensitive to non-Maxwellian emission in the presence of the strong EC current drive (ECCD) provided by the 3-MW second-harmonic (X2) EC system as the nonthermal radiation is not reabsorbed by the bulk when passing to the receiver. Simultaneous HFS and LFS measurements allow higher-order modeling of the electron distribution function as more constraints are provided by the dual measurements; however, the asymmetric nature of the electron distribution function required for ECCD to occur is not directly put in evidence by these lines of sight. Oblique ECE measurements of an asymmetric nonthermal electron distribution, on the other hand, are expected to also be asymmetric and can provide important information on the current-carrying features of the nonthermal population. A dedicated receiving antenna has been installed allowing real-time swept oblique ECE on TCV in both the co- and counter-looking directions. Proof-of-principle experiments are described in which Doppler-shifted emission is measured
BLR kinematics and Black Hole Mass in Markarian 6
We present results of the optical spectral and photometric observations of
the nucleus of Markarian 6 made with the 2.6-m Shajn telescope at the Crimean
Astrophysical Observatory. The continuum and emission Balmer line intensities
varied more than by a factor of two during 1992-2008. The lag between the
continuum and Hbeta emission line flux variations is 21.1+-1.9 days. For the
Halpha line the lag is about 27 days but its uncertainty is much larger. We use
Monte-Carlo simulation of the random time series to check the effect of our
data sampling on the lag uncertainties and we compare our simulation results
with those obtained by random subset selection (RSS) method of Peterson et al.
(1998). The lag in the high-velocity wings are shorter than in the line core in
accordance with the virial motions. However, the lag is slightly larger in the
blue wing than in the red wing. This is a signature of the infall gas motion.
Probably the BLR kinematic in the Mrk 6 nucleus is a combination of the
Keplerian and infall motions. The velocity-delay dependence is similar for
individual observational seasons. The measurements of the Hbeta line width in
combination with the reverberation lag permits us to determine the black hole
mass, M_BH=(1.8+-0.2)x10^8 M_sun. This result is consistent with the AGN
scaling relationships between the BLR radius and the optical continuum
luminosity (R_BLR is proportional to L^0.5) as well as with the black-hole
mass-luminosity relationship (M_BH-L) under the Eddington luminosity ratio for
Mrk 6 to be L_bol/L_Edd ~ 0.01.Comment: 17 pages, 10 figures, accepted for publication in MNRA
The 2015-2016 outburst of the classical EXor V1118 Ori
After a quiescence period of about 10 years, the classical EXor source V1118
Ori has undergone an accretion outburst in 2015 September. The maximum
brightness (DV > 4 mag) was reached in 2015 December and was maintained for
several months. Since 2016 September, the source is in a declining phase.
Photometry and low/ high-resolution spectroscopy were obtained with MODS and
LUCI2 at the {\it Large Binocular Telescope}, with the facilities at the Asiago
1.22 and 1.82 m telescopes, and with GIANO at the {\it Telescopio Nazionale
Galileo}. The spectra are dominated by emission lines of \hi\ and neutral
metallic species. From line and continuum analysis we derive the mass accretion
rate and its evolution during the outburst. Considering that extinction may
vary between 1.5 and 2.9 mag, we obtain m_acc= 0.32.0 10 m_sun/yr, in
quiescence and m_acc= 0.21.9 10 m_sun/yr, at the outburst peak. The
Balmer decrement shape has been interpreted by means of line excitation models,
finding that from quiescence to outburst peak, the electron density has
increased from 2 10 cm to 4 10 cm. The
profiles of the metallic lines are symmetric and narrower than 100 km s,
while \hi\, and \hei\,\,lines show prominent wings extending up to 500 km
s. The metallic lines likely originate at the base of the accretion
columns, where neutrals are efficiently shielded against the ionizing photons,
while faster ionized gas is closer to the star. Outflowing activity is
testified by the detection of a variable P Cyg-like profile of the H
and \hei\, 1.08\,m lines.Comment: Accepted by Ap
Relationship of the Content of Systemic and Endobronchial Soluble Molecules of CD25, CD38, CD8, and HLA-I-CD8 and Lung Function Parameters in COPD Patients
© 2017 Nailya Kubysheva et al. The definition of new markers of local and systemic inflammation of chronic obstructive pulmonary disease (COPD) is one of the priority directions in the study of pathogenesis and diagnostic methods improvement for this disease. We investigated 91 patients with COPD and 21 healthy nonsmokers. The levels of soluble CD25, CD38, CD8, and HLA-I-CD8 molecules in the blood serum and exhaled breath condensate (EBC) in moderate-to-severe COPD patients during exacerbation and stable phase were studied. An unidirectional change in the content of sCD25, sCD38, and sCD8 molecules with increasing severity of COPD was detected. The correlations between the parameters of lung function and sCD8, sCD25, and sHLA-I-CD8 levels in the blood serum and EBC were discovered in patients with severe COPD. The findings suggest a pathogenetic role of the investigated soluble molecules of the COPD development and allow considering the content of sCD8, sCD25, and sHLA-I-CD8 molecules as additional novel systemic and endobronchial markers of the progression of chronic inflammation of this disease
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