Threshold Values Of Density Research Articles

Interaction of a fluxon with a local inhomogeneity in a long Josephson junction

The interaction of a fluxon with a local defect in a damped dc driven long Josephson junction (LJJ) is analyzed by means of perturbation theory. The defect is a combination of a micro-short or micro-resistor with a dissipative micro-inhomogeneity. Threshold (maximum) values of the bias current density admitting capture of a fluxon by a combined defect are calculated for various practically important cases. The dynamics of a fluxon moving through a lattice of dissipative defects is studied. The energy emitted by a fluxon moving past a local defect is calculated. It is demonstrated that the latter effect can be employed to design a Josephson micro-wave generator based upon a LJJ with an installed lattice of dissipative defects. That generator must be more effective than the one proposed earlier by McLaughlin and Scott.

Effect of time-varying magnetic fields on the action potential in lobster giant axon.

The possible influence of time-varying magnetic fields on action potential in the lobster giant axon was studied. The axon membrane was excited by galvanic stimulation and the action potential was recorded intracellularly with microelectrodes. During the propagation of the action potential along the axon, alternating or pulsed magnetic fields were applied across the middle part of the axon to study whether or not magnetic fields have any effect on parameters such as conduction velocity and refractory period of the nerve fibre and amplitude, duration and shape of the action potentials. No effect on these parameters was observed under different flux densities and frequencies of the magnetic fields. When simulating the conductive properties of tissue surrounding the nerve with the aid of an external conducting loop with a load resistance, action potentials were generated which made it possible to study the threshold value of the induced eddy current for nerve excitation. Based on the results of the experiment, the influence of magnetic flux density, frequency, conductivity, induced EMF and induced eddy current density is discussed, and a method is proposed for estimating the threshold values of magnetic flux density for nerve excitation.

Effects of injury to mice by microwave (2400 mHz) irradiation and subsequent recovery

Threshold values of power density (PD) and exposure at which the mortality did not exceed 0.1% were determined in experiments on 2200 mice. The rate of formation of the pathological changes and of repair reactions was found to be close to an exponential function of PD. The functional relations established describe the adaptive powers of mice to microwave irradiation quantitatively.

Optical radiation damage of SBN materials and pyroelectric detectors at 10.6 μm

Thermal damage of Sr1−xBaxNb2O6 (SBN) crystals and infrared pyroelectric detectors due to 10.6−μm CO2 laser radiation was investigated. Permanent damage in the form of cracking or charring was observed depending on the irradiation conditions. Threshold values of energy density for cracking and charring were determined for SBN crystals of typical detector dimensions as a function of irradiation time. These damage thresholds of SBN are about an order of magnitude larger than the corresponding thresholds previously measured in triglycine sulfate. The energy density thresholds for cracking are independent of irradiation time τ for short times and increase as τ for long times. The time dependence of the cracking thresholds under the particular experimental conditions investigated is described by the empirical equation E0=[3+2400τ/tan−1(82τ)1/2] J/cm2. The charring thresholds are given by the empirical equation E0= (8+470τ1/2) J/cm2. The theoretical models presented for thermally induced damage are in satisfactory agreement with the experimental data. The damage thresholds of commerical SBN pyroelectric detectors were measured and found to correspond to those for SBN crystals.

Thermoelastic destruction of transparent media by laser radiation

It is shown that thermoelastic stresses may be the mechanism for the laser destruction of homogeneous transparent media having high thermal and elastical strength, at least during the initial stage of this destruction. Threshold values of the radiation density required for thermoelastic destruction are calculated.