Change In Transmission Coefficient Research Articles

Device for detection of activity-dependent changes in neural spheroids at MHz and GHz frequencies

Intracellular processes triggered by neural activity include changes in ionic concentrations, protein release, and synaptic vesicle cycling. These processes play significant roles in neurological disorders. The beneficial effects of brain stimulation may also be mediated through intracellular changes. There is a lack of label-free techniques for monitoring activity-dependent intracellular changes. Electromagnetic (EM) waves at frequencies larger than 1x106 Hz (1 MHz) were previously used to probe intracellular contents of cells, as cell membrane becomes “invisible” at this frequency range. EM waves interact with membranes of intracellular organelles, proteins, and water in the MHz – GHz range. In this work, we developed a device for probing the interaction between active neurons’ intracellular contents and EM waves. The device used an array of grounded coplanar waveguides (GCPWs) to deliver EM waves to a three-dimensional (3D) spheroid of rat cortical neurons. Neural activity was evoked using optogenetics, with synchronous detection of propagation of EM waves. Broadband measurements were conducted in the MHz-GHz range to track changes in transmission coefficients. Neuronal activity was found to reversibly alter EM wave transmission. Pharmacological suppression of neuronal activity abolished changes in transmission. Time constants of changes in transmission were in the seconds – tens of seconds range, suggesting the presence of relatively slow, activity-dependent intracellular processes. This study provides the first evidence that EM transmission through neuronal tissue is activity-dependent in MHz – GHz range. Device developed in this work may find future applications in studies of the mechanisms of neurological disorders and the development of new therapies.

Optical Nonreciprocity in Double Optomechanical Systems with Quadratic Coupling

In this paper, the optical nonreciprocal phenomena in double optomechanical systems with quadratic coupling are studied. Our model belongs to an optomechanical system in which three coupling modes coexist, that is, the two cavity fields are coupled with the mechanical oscillator at the same time and the couplings are in the form of quadratic interactions. In addition, there is a linear coupling mode between the two cavity fields. In the entire system, each cavity field is effectively coupled by a control field and a probe field simultaneously. The expression of the transmission coefficient of the probe field is obtained by solving the dynamic evolution equation satisfied by the system. Using numerical analysis, we analyze the change in transmission coefficient of the probe field under the conditions of different physical parameters. The results show that we can realize optical nonreciprocal transmission in this system. Appropriate choices about physical parameters can achieve perfect nonreciprocity. Our theoretical scheme to realize optical nonreciprocal transmission in a double optomechanical system provides a theoretical basis for optical circulators, cyclic amplifiers and directional amplifiers.

Спиновые клапаны CoFe/Cu/CoFe/FeMn и трехслойные наноструктуры CoFe/Cu/CoFe на микроволновых частотах

The microwave magnetoresistance of CoFe/Cu/CoFe/FeMn spin valves and CoFe/Cu/CoFe three-layer nanostructures with high magnetoresistance has been studied. The transmission and reflection coefficients were measured at the frequency range from 26 to 38 GHz in magnetic fields up to 12 kOe. It is shown that the dependences of the transmission coefficient of spin valves are not symmetric with respect to the H = 0 axis, as well as the dependences of magnetoresistance. It is established that the relative changes in the microwave transmission coefficient are 1.5–2 times higher than the relative magnetoresistance measured at direct current. Changes in the reflection coefficient have a smaller value and the opposite sign with respect to changes in the transmission coefficient.

CoFe/Cu/CoFe/FeMn spin valves and CoFe/Cu/CoFe three-layer nanostructures at microwave frequencies

The microwave magnetoresistance of CoFe/Cu/CoFe/FeMn spin valves and CoFe/Cu/CoFe three-layer nanostructures with high magnetoresistance has been studied. The transmission and reflection coefficients were measured at the frequency range from 26 to 38 GHz in magnetic fields up to 12 kOe. It is shown that the dependences of the transmission coefficient of spin valves are not symmetric with respect to the H=0 axis, as well as the dependences of magnetoresistance. It is established that the relative changes in the microwave transmission coefficient are 1.5-2 times higher than the relative magnetoresistance measured at direct current. Changes in the reflection coefficient have a smaller value and the opposite sign with respect to changes in the transmission coefficient. Keywords: metal superlattices, spin valves, ferromagnetic resonance, ferromagnetic antiresonance, microwave giant magnetoresistance effect.

Detection of Neural Activity of Brain Functional Site Based on Microwave Scattering Principle

A method of detecting brain neural activity with the microwave transmission technology is presented in this paper. This method is based on the fact that the dielectric properties of brain functional site vary with the electrophysiological neural activity. The analysis of the uniform plane wave propagation of dynamic layered medium shows that the phase change of transmission coefficient (S-parameters) is consistent with the variation frequency of permittivity in the dynamic dielectric layer. A 3D head model was introduced to assign dynamic dielectric properties to the cerebral cortex by embedding a tissue piece in this head model. A six-element horn antenna array around the head model was designed, and two types of brain activity at various locations (visual cortex and auditory cortex) inside the head model has been discussed. The simulation results of microwave scattering in different directions show that forward scattering has better applicability. The frequency of the permittivity variation associated with the brain neuronal activity (10 Hz, 20 Hz) can be extracted from the phase variation on S-parameters. In addition, the specific absorption rate analysis ensures the safety of using the microwave in the design of human head detection systems.

Influence irradiation argon ion SnO2 on optical and electrical characteristics

Tin oxide in the form of films has been deposited by reactive magnetron sputtering on glass substrates a room temperature. Process was carried out in such mode when the deposited films were conductive. The deposited films were irradiated with argon ions. Have been studied happening at that the changes optical and electric properties of films. Have been investigated optical properties of films in the range of 300-1100 nanometers by means of photometry. For research structure of films was used the x-ray diffractometry. Diffractometric researches have shown that the films deposited on a substrate have crystal structure from shares of a quasicrystal phase and after influence of argon ions she completely became quasicrystal. It is established that change transmission of a film correlates with change her electric resistance. Average value transmission in the range of 380-1100 nanometers as well as the electric resistance of a film with growth of irradiation time increases to the values exceeding initial. At the same time at irradiation time ∼ 13,2 sec. are observed their slight decrease. To this value of irradiation time there corresponds the minimum value of electric resistance and transmission films. Change of transmission coefficient correlates with change of surface resistance.

Nonlinear change in refractive index and transmission coefficient of silicon at long-pulse, mJ-range, 1.54-μm excitation

An experimental study and theoretical modeling of the nonlinear changes in transmission coefficient and refractive index of mono-crystalline Silicon (Si) at long-pulse, mJ-range, single-beam Z-scan probing at 1.54 μm wavelength are reported. It is shown experimentally that at increasing pulse energy density the photo-induced darkening permanently increases in Si while its photo refraction properties demonstrate a more complicate character, being a product of various type nonlinearities. A theoretical analysis based on simple assumptions of a square-shape pulse in the time domain and Gaussian spatial distribution of the probe beam allows fitting of a whole of the experimentally measured open- and closed-aperture Z-scans through an account of the main contributions in the light-induced absorption and refractive index nonlinearities. These are revealed to originate from non-direct two-photon absorption and Kerr effect, induced absorption and dispersion of light-generated free carriers, and light-induced thermal lensing.

Measurement of nonlinear absorption coefficients in GaAs, InP and Si by an optical pump THz probe technique

An optical pump terahertz (THz) probe method for measuring carrier mobility and multiphoton absorption coefficients in semiconductors is demonstrated. A THz probe pulse is used to detect the transient photoconductivity generated by an optical pump pulse. The change in transmission coefficient at THz frequencies due to a pump pulse with photon energy greater than the band gap energy is used to determine the sum of electron and hole mobilities. The weak nonlinear absorption of a pump pulse with photon energy less than the band gap energy produces an approximately uniform free carrier distribution. The THz transmission coefficient vs. pump fluence, and the mobility, are used in a bulk photoconductivity model to determine the multiphoton absorption coefficients. For GaAs, InP and Si we find two photon absorption coefficients at 1305 nm of 42.5 ± 11, 70 ± 18 and 3.3 ± 0.9 cm/GW, respectively. For GaAs and InP we determine three photon absorption coefficients at 2144 nm of 0.19 ± 0.07 and 0.22 ± 0.08 cm 3/GW 2.

Change in transmission coefficient of screen glass melting in a flame tank furnace

Change in transmission coefficient of screen glass melting in a flame tank furnace

High-frequency magnetoimpedance in nanocomposites

The transmission of millimeter-range electromagnetic waves (30–50 GHz) through a magnetic nanocomposite thin film exhibiting tunnel magnetoresistance (TMR) is calculated. The relative change of transmission coefficient in an applied magnetic field due to the magnetorefractive effect is approximately linear with TMR and strongly depends on nanocomposite resistivity and film thickness. The obtained results are in a good agreement with experiment.

Change in transmission coefficient of screen glass melting in a flame tank furnace

The practical experience of modifying the transmission coefficient of glass for electron monitor screens in an operating tank furnace is considered. Calculation formulas are proposed that can be used to minimize the period of substandard product yield.

Compatibility of HTc superconductor technology with SAW technique

Abstract First experiments with YBaCuO ceramic thin films on the surface of piezoelectric substrates are performed in the aim to clarify the features of possible future superconductive-acoustic devices. The technological compatibility of LiNbO3 substrate to Y1Ba2Cu3O7−x granular and almost epitaxial films is observed without loosing high temperature superconductive (HTc) and piezoelectrical properties. Granular and epitaxial films influence on surface acoustic waves (SAW) behavior is investigated in simplest delay lines with HTc superconductive Interdigital transducers (ITD). Sharp changes in transmission coefficient are observed near the superconducting transition. Future possible switchable devices and elements are discussed.

Organization of phospholipids in biological membranes

AbstractPreferred conformations of phospholipids have been predicted through quantum‐chemical techniques and classical potential functions. An essential condition for a conformation to exist in a biomembrane is that it should be possible for it to organize in the form of a bilayer. Taking into consideration the conformational flexibility of the polar head group, organization at the lipid–water interface has been considered. The biological implications of such an organization in terms of formation of “hydrophobic channels” is discussed. Quantum‐mechanical investigations on the transport phenomenon have shown that the “selectivity” of biological membranes is connected with the “organization.” Calculations of the quantum‐mechanical transmission coefficients for different model potential profiles indicate that minor differences in the height of potential barriers in certain regions can lead to significant changes in transmission coefficients. The “directional selectivity” of substrates (differences in transmission coefficients for flow in and out of the cell) can be explained on the basis of differences in membrane organization. These results have some important consequences in the evolutionary process in biological membranes.

Diffraction characteristics of a slit formed by two staggered parallel planes

The diffraction of a plane electromagnetic wave by a slit formed by two staggered parallel planes is investigated using an asymptotic Wiener-Hopf technique. By following a standard procedure the problem is formulated in terms of two coupled Wiener-Hopf equations. For large edge-edge separation, the decoupling of the equations is accomplished by evaluating certain integrals by the saddle point method of integration. The results thus obtained can be conveniently identified as rays emanating from the two edges. It is shown that various changes in transmission coefficient and diffraction pattern of a slit can be obtained by changing the angle of stagger of the planes. Plots of transmission coefficients and diffraction patterns are presented for various slit widths and angles of stagger to show these characteristics.