Simulations of the Evolution of the Heterophase Electrode of a Vacuum Transmission Line During the Passage of a High Current Pulse

Plasma Physics Reports - In electromagnetic generators of the terawatt range with current pulse of 1–30 MA, electric explosion of the surface of current-carrying electrodes takes place. One...     

Detailing Radio Frequency Heating Induced by Coronary Stents: A 7.0 Tesla Magnetic Resonance Study

The sensitivity gain of ultrahigh field Magnetic Resonance (UHF-MR) holds the promise to enhance spatial and temporal resolution. Such improvements could be beneficial for cardiovascular MR. However, intracoronary stents used for treatment of coronary artery disease are currently considered to be contra-indications for UHF-MR. The antenna effect induced by a stent together with RF wavelength shortening could increase local radiofrequency (RF) power deposition at 7.0 T and bears the potential to induce local heating, which might cause tissue damage. Realizing these constraints, this work examines RF heating effects of stents using electro-magnetic field (EMF) simulations and phantoms with properties that mimic myocardium. For this purpose, RF power deposition that exceeds the clinical limits was induced by a dedicated birdcage coil. Fiber optic probes and MR thermometry were applied for temperature monitoring using agarose phantoms containing copper tubes or coronary stents. The results demonstrate an agreement between RF heating induced temperature changes derived from EMF simulations versus MR thermometry. The birdcage coil tailored for RF heating was capable of irradiating power exceeding the specific-absorption rate (SAR) limits defined by the IEC guidelines by a factor of three. This setup afforded RF induced temperature changes up to +27 K in a reference phantom. The maximum extra temperature increase, induced by a copper tube or a coronary stent was less than 3 K. The coronary stents examined showed an RF heating behavior similar to a copper tube. Our results suggest that, if IEC guidelines for local/global SAR are followed, the extra RF heating induced in myocardial tissue by stents may not be significant versus the baseline heating induced by the energy deposited by a tailored cardiac transmit RF coil at 7.0 T, and may be smaller if not insignificant than the extra RF heating observed under the circumstances used in this study.     

The meaning of the auditory sensory systems asymmetry in highly coordinated manual movement

Analysis of the stable correlation of asymmetry of the acoustic stem evoked potentials intervals with parameters of bimanual coordination was performed. Different mechanisms of the auditory asymmetry at the stem level were found in men and women. Optimum bimanual performance in men is provided by adequate co-adjustment of sensor-motor system elements, and is connected with sensory input and the feature of its bilateral irradiation through the right input. The left channel input and its sensory asymmetry is much more important in women. Bilateral irradiation in this case does not lead to adequate integration of the systems elements in performance of the motor task, that indicates the lower level of bimanual coordination.     

Variations of chromatin, tubulin and actin structures in primate oocytes arrested during in vitro maturation and fertilization--what is this telling us about the relationships between cytoskeletal and chromatin meiotic defects?

A nonhuman primate model was applied to investigate the relationships between variations in the organization of microtubules, microfilaments, and chromatin in metaphase I and metaphase II oocytes. Marmoset oocytes were subjected to in vitro maturation and coincubation with sperm. Oocytes which failed to cleave were investigated for chromatin, tubulin, and actin using Hoechst 33258, fluorescein isothiocyanate (FITC)-labeled alpha-tubulin antibody and rhodamine-labeled phalloidin, respectively. Spindles were categorized according to size, shape and microtubule organization: normal, large, multipolar, disorganized, absent spindle, and spindles with broad poles. Actin caps were categorized as: normal, small, split, and disorganized. Chromosomal condensation and alignment were described as normal or abnormal. Improper chromosomal condensation was associated with both abnormal microfilament and microtubule arrangement. This was further associated with abnormal actin organization, disorientation and late stabilization of microtubules, but not related to abnormal organization of spindle poles. Chromosomal misalignment was associated with disorientation and late stabilization of tubulin, but not to broad spindle pole. Additionally, abnormal actin polarization appeared not to be related to abnormal spindle poles. The model system presented in this study could be used as an experimental platform for studying the contribution of different factors to the exactness of late meiotic events in primate oocytes. The present study provides basic information on spindle, chromosome, and actin normal and abnormal organization, which can be observed in in vitro matured, but failed to cleave primate oocytes.     

Effect of the high-voltage electrode polarity and wire preheating on the energy characteristics of electric explosion of fine tungsten wires in vacuum

Results are presented from experiments on the explosion of 30.5-μm tungsten wires at a current density of up to 140 MA/cm² and resistive-heating time of 40–100 ns. The experiments were performed both with and without preheating of wires and at different polarities of the high-voltage electrode. The effect of plasma production at the electrodes on the initiation of breakdown along the exploding wire was investigated by using a frame camera. It is shown that, when the polarity of the high-voltage electrode is positive, breakdown begins with the formation of a bright spot on the wire surface near the cathode, whereas at the negative polarity, breakdown begins with the formation of bright spots on the cathode surface. A comparative analysis of the main characteristics of wire explosions is performed. It is shown that preheating of the conductor increases the resistive-heating time and, accordingly, the energy deposited in the wire core. This effect takes place during explosions of both single wires and wire arrays. The evolution of the state of a metal during the explosion (including melting and evaporation) is studied by one-dimensional simulations by using a semiempirical equation of state describing the properties of tungsten over a wide range of parameters.     

Energetic parameters as a reflection of transition states in batch cultures of Escherichia coli with addition of substrate

The physiology of Escherichia coli feed batch cultures grown in a mineral medium with glucose was studied by analysing the intracellular content of adenylate nucleotides, the respiration rate, and the calculated economic coefficients of substrate and oxygen utilisation (Yx/s and YO2) which were compared with the growth parameters. The cultures were characterised by a rapid change of the transitional states associated with substrate exhaustion, limited oxygen supply, incomplete growth synchronisation and metabolite poisoning. The transitional states determined the oscillatory mode of the constructive and energetic parameters whose comparison allowed one to reveal the periods of incomplete coupling between reactions which generated and consumed the energy.     

Pharmacoprotective influences on different links of the mechanism underlying 6-hydroxydopamine-induced degeneration of nigro-striatal dopaminergic neurons

In this study we examined the possibility of preventing degeneration of dopaminergic nigro-striatal neurons caused in rats by a neurotoxin, 6-hydroxydopamine. We showed that an antioxidant, Trolox, an inhibitor of nitric oxide synthase, N_ω-nitro-L-arginine methyl ester, and an inhibitor of caspases, zinc chloride, are capable of preventing to a considerable extent the neurotoxin-induced apoptosis of dopaminergic neurons of the substantia nigra. Neirofiziologiya/Neurophysiology, Vol. 38, No. 2, pp. 150–156, March–April, 2006.     

Studies of plasma dynamics in megampere X-pinches

Results are presented from experimental studies of the dynamics and parameters of the plasma generated by megampere (up to 2.3 MA) currents flowing through X-pinches formed from crossed wires made of various materials. The experiments were performed with different numbers of wires and different wire diameters. The X-ray yield in neon-like molybdenum lines (in the 2.5- to 3-keV photon energy range) from a <20 μm hot spot was larger than 10 J, and the soft X-ray power emitted from this spot reached 120 GW. The hot-spot lifetime estimated by comparing the measured and calculated emission intensities and line profiles of helium-like Fe and Cr ions was ～10 ps. Hard X-ray emission in the photon energy range ≥800 keV was also detected.