296 research outputs found
Superscaling in dilute Fermi gas and its relation to general properties of the nucleon momentum distribution in nuclei
The superscaling observed in inclusive electron scattering is described
within the dilute Fermi gas model with interaction between the particles. The
comparison with the relativistic Fermi gas (RFG) model without interaction
shows an improvement in the explanation of the scaling function in
the region , where the RFG result is . It is found
that the behavior of for depends on the particular
form of the general power-law asymptotics of the momentum distribution
at large . The best agreement with the empirical
scaling function is found for in agreement with the asymptotics
of in the coherent density fluctuation model where . Thus,
superscaling gives information about the asymptotics of and the NN
forces.Comment: 6 pages, 5 figures, accepted for publication in Physical Review
Direct evidence for a bystander effect of ionizing radiation in primary human fibroblasts
Bystander responses underlie some of the current efforts to develop gene therapy approaches for cancer treatment. Similarly, they may have a role in strategies to treat tumours with targeted radioisotopes. In this study we show direct evidence for the production of a radiation-induced bystander response in primary human fibroblasts. We utilize a novel approach of using a charged-particle microbeam, which allows individual cells within a population to be selected and targeted with counted charged particles. Individual primary human fibroblasts within a population of 600â800 cells were targeted with between 1 and 15 helium ions (effectively, α-particles). The charged particles were delivered through the centre of the nucleus with an accuracy of ± 2 ÎŒm and a detection and counting efficiency of greater than 99%. When scored 3 days later, even though only a single cell had been targeted, typically an additional 80â100 damaged cells were observed in the surviving population of about 5000 cells. The yield of damaged cells was independent of the number of charged particles delivered to the targeted cell. Similar results of a 2â3-fold increase in the background level of damage present in the population were observed whether 1 or 4 cells were targeted within the dish. Also, when 200 cells within one quadrant of the dish were exposed to radiation, there was a 2â3-fold increase in the damage level in an unexposed quadrant of the dish. This effect was independent of the presence of serum in the culture medium and was only observed when a cell was targeted, but not when only the medium was exposed, confirming that a cell-mediated response is involved. © 2001 Cancer Research Campaign http://www.bjcancer.co
Dark spot, spiral waves and the SW Sextantis behaviour: It is all about UX Ursae Majoris
We present an analysis of time-resolved, medium-resolution optical spectroscopic observations of UX Ursae Majoris (UX UMa) in the blue (3920-5250 Ă
) and red (6100-7200 Ă
) wavelength ranges that were obtained in 1999 April and 2008 March, respectively. The observed characteristics of our spectra indicate that UX UMa has been in different states during those observations. The blue spectra are very complex. They are dominated by strong and broad single-peaked emission lines of hydrogen. The high-excitation lines of He ii λ4686 and the Bowen blend are quite strong as well. All the lines consist of a mixture of absorption and emission components. Using Doppler tomography, we have identified four distinct components of the system: the accretion disc, the secondary star, the bright spot from the gas stream/disc impact region and the unique compact area of absorption in the accretion disc seen as a dark spot in the lower left-hand quadrant of the tomograms. In the red wavelength range, both the hydrogen (Hα) and neutral helium (He i λ6678 and He i λ7065) lines were observed in emission and both exhibited double-peaked profiles. Doppler tomography of these lines reveals spiral structure in the accretion disc, but in contrast to the blue wavelength range, there is no evidence for either the dark spot or the gas stream/disc impact region emission, while the emission from the secondary star is weak. During the observations in 1999, UX UMa showed many of the defining properties of the SW Sextantis stars. However, all these features almost completely disappeared in 2008. We have also estimated the radial velocity semi-amplitudes K 1 and K 2 and evaluated the system parameters of UX UMa. These estimates are inconsistent with previous values derived by means of analysis of white dwarf eclipse features in the light curve in different wavelength ranges. © 2010 The Authors. Journal compilation © 2010 RAS
Effect of pulsed magnetic field pre-treatment of AISI 52100 steel on the coefficient of sliding friction and wear in pin-on-disk tests
Disc specimens manufactured from commercial bearing rollers (AISI 52100 steel, 62â63 HRC) in initial state and after pre-treatment by pulsed magnetic field (PMF) with a magnetic field strength of 1â7 MA/m were tested with sunflower oil using pin-on-disk apparatus. According to the obtained results the treatment causes a reduction in the coefficient of friction and wear. To explain the results, nano- and microhardness tests as well as optical and atomic force microscopy were used. Reasons of the effect of PMF on the friction and wear were discussed.Peer reviewe
Nonmonotonical crossover of the effective susceptibility exponent
We have numerically determined the behavior of the magnetic susceptibility
upon approach of the critical point in two-dimensional spin systems with an
interaction range that was varied over nearly two orders of magnitude. The full
crossover from classical to Ising-like critical behavior, spanning several
decades in the reduced temperature, could be observed. Our results convincingly
show that the effective susceptibility exponent gamma_eff changes
nonmonotonically from its classical to its Ising value when approaching the
critical point in the ordered phase. In the disordered phase the behavior is
monotonic. Furthermore the hypothesis that the crossover function is universal
is supported.Comment: 4 pages RevTeX 3.0/3.1, 5 Encapsulated PostScript figures. Uses
epsf.sty. Accepted for publication in Physical Review Letters. Also available
as PostScript and PDF file at http://www.tn.tudelft.nl/tn/erikpubs.htm
Disk precession and quasi-periodic brightness oscillations of V603 Aql in 2001-2002
We present the photometric observations of the old nova V603 Aql with the RTT 150 Russian-Turkish telescope during eleven nights of 2001-2002. We show that the star at this time was in a state with positive superhumps and its photometric period of 0.d1440.d145 was longer than the orbital period. We found night-to-night variations in the mean brightness of the system that are consistent with disk precession periods of 3.d3 and 3.d0 in 2001 and 2002, respectively. Analysis of the results and their comparison with the results of other authors using current theoretical models for disk precession lead us to suggest that the change in the disk precession period was caused by a change in the accretion rate in the system. V603 Aql in a state with negative superhumps was found to be brighter than it is in a state with positive superhumps by 0.m2-0.m3. We hypothesize that the transition between these states could also be caused by a change in the accretion rate. Quasi-periodic oscillations (QPOs) of the brightness with typical time scales of 9-70 min were detected on each observing night. These time scales were found to change from night to night. The detection of QPOs with a period of about 0.05 of the orbital period and its multiples on certain nights provides evidence for the model of QPO generation through accretion-rate modulation by ionization-front oscillations on the surface of the donor star near the inner Lagrangian point. © 2004 MAIK "Nauka/Interperiodica"
Crossover scaling from classical to nonclassical critical behavior
We study the crossover between classical and nonclassical critical behaviors.
The critical crossover limit is driven by the Ginzburg number G. The
corresponding scaling functions are universal with respect to any possible
microscopic mechanism which can vary G, such as changing the range or the
strength of the interactions. The critical crossover describes the unique flow
from the unstable Gaussian to the stable nonclassical fixed point. The scaling
functions are related to the continuum renormalization-group functions. We show
these features explicitly in the large-N limit of the O(N) phi^4 model. We also
show that the effective susceptibility exponent is nonmonotonic in the
low-temperature phase of the three-dimensional Ising model.Comment: 5 pages, final version to appear in Phys. Rev.
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