Experimental test of the shadowing effect in Smith-Purcell radiation

The observation of a shadowing effect of a relativistic electron Coulomb field for the Smith-Purcell radiation generation is presented in this paper. For this purpose the surface current from the closest surface of grating element to the electron beam was measured for a downstream one shadowed by upstream element. The experimental results showed that shadowing effect for Smith-Purcell radiation depends on grating geometry

Electromagnetic field features at interaction of relativistic electron with matter

The features of electromagnetic field of relativistic electrons passing through a hole in an absorbing screen as a function of the distance from the screen in the range of radiation formation length were investigated for the transversal and longitudinal field components. The analysis of the obtained results allows approving the existence of a semi-bare electron with a particularly deprived Coulomb field, which turns into the stable state of the usual electron at the distance of radiation formation length

“Shadowing” of the electromagnetic field of relativistic charged particles

VIII International Symposium Radiation from Relativistic Electrons in Periodic Structures (RREPS-09), Zvenigorod, Russia, Sept. 7-11, 2009International audienceIn radiation processes such as a transition radiation, diffraction radiation, etc. based on relativistic electrons passing through or near an opaque screen, the electron self-field is partly shadowed after the screen over a distance of the order of the formation length γ2λ. This effect has been investigated on coherent diffraction radiation (DR) by electron bunches. Absorbing and conductive half-plane screens were placed at various distances L before a standard DR source (inclined half-plane mirror). The radiation intensity was reduced when the screen was at small L and on the same side as the mirror. No reduction was observed when the screen was on the opposite side. It is worth noting that absorbing and conductive half-plane screens produce the same shadowing effect. The shadowing effect is responsible for a bound on the intensity of Smith-Purcell radiation

The coherent Vavilov-Cherenkov radiation for a bunch length diagnostic

Coherent Vavilov-Cherenkov radiation generated by a 6.1MeV bunched electron beam traveling in the vicinity of a solid dielectric target (PTFE and Paraffin) has been investigated experimentally. In addition, we have also demonstrated the simple scheme of the Cerenkov interferometer for non-invasive longitudinal electron bunch length diagnostics

Experimental Research of the Diffraction and Vavilov-Cherenkov Radiation Generation in a Teflon Target

Geometry of Vavilov-Cherekov (VChR) radiation when an electron moves close to a dielectric target is in analogy to diffraction radiation (DR) geometry. In this case we may expect DR generation from the upstream face of the target besides that VChR. The joint observation of these booth types of radiation is very interesting from the pseudo-photon viewpoint, which is applicable for relativistic electrons. Unexpected results obtained in our experiment insist on reflection about nature both DR and VChR. The experiment was performed on the relativistic electron beam of the microtron of Tomsk Polytechnic University.Comment: This article will be published in Journal of Physic

Evolution of the Velocity Ellipsoids in the Thin Disk of the Galaxy and the Radial Migration of Stars

Data from the revised Geneva--Copenhagen catalog are used to study the influence of radial migration of stars on the age dependences of parameters of the velocity ellipsoids for nearby stars in the thin disk of the Galaxy, assuming that the mean radii of the stellar orbits remain constant. It is demonstrated that precisely the radial migration of stars, together with the negative metallicity gradient in the thin disk,are responsible for the observed negative correlation between the metallicities and angular momenta of nearby stars, while the angular momenta of stars that were born at the same Galactocentric distances do not depend on either age or metallicity. (abridged)Comment: Astronomy Reports, Vol. 86 No. 9, P.1117-1126 (2009

TiViPE Simulation of a Cortical Crossing Cell Model

Abstract. Many cells in cat and monkey visual cortex (area V1 and area 17) respond to gratings and bar patterns of different orientation between center and surround [18]. It has been shown that these cells respond on average 3.3 times stronger to a crossing pattern than to a single bar [16]. In this paper a computational model for a group of neurons that respond solely to crossing patterns is proposed, and has been implemented in visual programming environment TiViPE [10]. Simulations show that the operator responds very accurately to crossing patterns that have an angular difference between 2 bars of 40 degrees or more, the operator responds appropriately to bar widths that are bound by 50 to 200 percent of the preferred bar width and is insensitive to non-uniform illumination conditions, which appear to be consistent with the experimental results.

Selective Brain Hypothermia in the Comprehensive Rehabilitation of Patients with Chronic Consciousness Disorders

Aim: to evaluate clinical effectiveness of selective hypothermia of cerebral cortex for the recovery of awareness in patients with chronic disorders of consciousness (CDC).   Material and methods. 111 patients with CDC 30 and more days after a cerebral event (ischemic or hemorrhagic stroke, brain injury) were included in the study. Exclusion criteria were anoxic brain injury (sequelae of a prolonged asystole or asphyxia), active sepsis, arrhythmia, baseline hypothermia (body temperature lower than 35.5 °С). Experimental group included 60 patients, of them 39 patients were in a vegetative state (VS), 21 patients exhibited patterns of minimally conscious state (MCS). Control group incluted 51 patients, of them 32 patients were in VS and 19 patients were in MCS. Patients in the experimental group received 10 sessions (120 minutes each) of selective brain hypothermia (SBH) during the 14-days follow-up period. Patients of both groups received standard identical neurological treatment and rehabilitation procedures. Patients in the control group did not undergo brain hypothermia. The induction of SBH involved cooling of the whole surface of the craniocerebral area of scalp using special helmets. The temperature of the internal surface of the helmet was 3–7 °С. Temperature of the frontal lobes of the cortex was monitored with non-invasive microwave radiothermometry, axillary temperature was also registered. The level of consciousness was evaluated using «Coma Recovery Scale-Revised» (CRS-R) scale.   Results. 120-minutes long SBH session reduced the temperature of the frontal lobes of the cerebral cortex by 2.4–3.1 °С with no impact on the axillary temperature. Evaluation using CRS-R revealed improvement in all studied functions (auditory, visual, motor, oromotor, communication, arousal) in patients in the experimental group after 10 SBH sessions. Level of consciousness in patients from the experimental group in VS increased from 4.5 ± 0.33 to 8.7 ± 0.91 points (P < 0.001), for patients in MCS from 11.3 ± 1.0 to 18.2 ± 0.70 (P < 0.001) points. In the control group, scores of patients in VS rose from 4.3 ± 0.37 to 6.8 ± 0.49 (P < 0.001) points with the most significant changes in auditory and visual functions (P<0.001). In the control group of patients in MCS the oromotor function improved (P < 0.05), overall CRS-R scores changed insignificantly from 9.1 ± 0.57 to 10.1 ± 0.86 (P < 0.1). The best outcome (CRS-R > 19 points) was seen in patients from the experimental group [6 in VS (15.4 %) and 8 in MCS (31.8 %)]. In the control group, the best results did not exceed 10 points for the patents in VS, while 4 patients in MCS (21 %) reached 12–16 scores. During 30-day follow-up period of hospitalization after the SBH sessions mortality rate was 10 % (6 patients) in the experimental group and 21.6% (11 patients) in the control group.   Conclusion. Patients with CDC could benefit from serial SBH sessions performed as a part of comprehensive treatment and rehabilitation strategy. We suggest that selective reduction of frontal lobe temperature improves neurogenesis, neuronal regeneration, and neuroplasticity

Prevention of traumatic brain injury complications in sports

The aim of the review is to inform doctors and trainers of sports teams about technologies that prevent complications of sport brain injuries (SBI). Low levels of visibility of clinical manifestations, specific characteristics of individual reactions to injury, anti-aggravation behavior among sportsmen, absence of unbiased methods of diagnostics of SBI are the main reasons behind underestimation of the severity of trauma. Treatment and rehabilitation procedures of mild SBI do not currently consider specific characteristics of trauma, associated with the increase in body and brain temperature and reduced cerebral perfusion during the traumatizing intervention. Injury of the brain causes an increase in cerebral temperature, which, in turn, can aggravate the consequences of traumatization. The control of the temperature of the brain can be achieved with non-invasive method of microwave radiometry, while the technology of craniocerebral hypothermia (CCH), which has evident neuroprotective properties, can aid in the prevention of complications of SBI