Decrease Of Switching Time Research Articles

Structure and electronic properties of thin Ge2Sb2Te5 films produced by DC ion-plasma spattering

The optical properties of Ge2Sb2Te5 thin films were studied as a function of thickness. An increase in optical band gap with decreasing film thickness has been observed. The current– voltage characteristics measured in Ge2Sb2Te5 thin films in the current mode are studied. A decrease in switching time and threshold voltage with decreasing film thickness is established.

Mixed convection heat transfer enhanced by PCD electrical field in a rectangular channel

For the cooling of transformer in the grid, the heat transfer efficiency of mixed convection is relatively low due to the low thermal conductivity and large viscosity of transformer oil. Therefore, this paper aims to study the PCD (periodically changed direction) electrical field to enhance the mixed convective heat transfer of transformer oil. Then, a semi empirical correlation is developed to calculate the Nusselt number affected by electrical field. Specially, the influences of heat flux, electrical field intensity and switching period on the heat transfer characteristics are discussed experimentally. As a result, the result reveals that the mixed convective heat transfer is enhanced increasingly with the decrease of switching time and improvement of voltage. Thus, the PCD electric field can effectively enhance the mixed convection heat transfer. In addition, the mechanism analysis shows that the PCD electrical field leads to the continuous change of fluid mode, and the polarized molecules continuously vibrate and move within a certain range, which leads to the violent disturbance of internal fluid. Meanwhile, the secondary flow induced by the electric field results in the disruption of thermal boundary layer, which strengths the heat transfer. Finally, the predicted results of the semi-empirical correlation are in good agreement with the experimental results, and the effect of electrical field intensity and switching periods are comprehensively considered in the correlation. The present study is of great importance for the transformer cooling.

Effect of γ-irradiation on various important physical properties of a room temperature ferroelectric liquid crystal mixture and its silver nanocomposite

A room temperature ferroelectric liquid crystal (FLC) mixture and its silver nanocomposite have been irradiated by various doses of γ-radiation from 60Co. Phase transition temperatures, dielectric permittivity, optical tilt angle, spontaneous polarization, rotational viscosity, switching time, and conductivity of the systems have been determined as a function of the irradiation dose and temperature. Phase transition temperatures and optical tilt angles of both the systems decrease significantly, more in the pristine mixture, meaning a decrease of the order parameter with irradiation. Remarkable changes are exhibited in the dielectric permittivity as well as in their molecular dynamics as confirmed by the change in Goldstone and soft mode relaxation frequencies. The conductivity of the irradiated mixture increases considerably compared to its nanocomposite probably due to the production of more ions by the radiolysis process. Spontaneous polarization, rotational viscosity, and switching time are also found to decrease linearly with irradiation dose. At the maximum absorbed dose, switching time decreases by 140 μs in the pristine mixture and 110 μs in the nanocomposite suggesting their more suitability in display applications. The concentration of the chiral dopant also influences the impact of irradiation.

Polarization switching behavior of (Pb,Nb)(Zr,Sn,Ti)O3 ferroelectric ceramics under high-power pulse condition in microsecond scale

In the present work, the polarization switching of polycrystalline (Pb,Nb)(Zr,Sn,Ti)O3 (PNZST) ferroelectric (FE) ceramics in microsecond scale was investigated by pulse switching experiment. Typical switching current similar to that of FE single crystal and thin films was observed in PNZST ceramics, directly proving the completion of the switching process in microsecond scale. The increase of switching current and decrease of switching time with increasing electric field and temperature were confirmed and explained by the acceleration of the nucleation and growth rate of domains. However, the distortion of the pulse voltage also results in difficulty to analyze the switching current via Merz’s equation, which was usually neglected in previous works. In addition, the pulse switching dynamic is also found to be a current-limiting process and strongly depends on the circuit parameters. By increasing the resistance of the in-series resistor, the switching process will be hindered, leading to the decrease of switching current and longer switching period. More importantly, the curve of polarization versus electric field (P–E) was obtained by the switching current and a distinct difference was observed compared with the 0.1 Hz P–E curve. The above results prove the possibility of using PNZST ceramics in high-power pulse technology and will give some important guidance for the designation of FE devices.

Impact of silica nanoparticles dispersion on the dielectric and electro-optical properties and absorption spectra of host ferroelectric liquid crystal

ABSTRACTThe present work concerns with the investigation of the effect of dispersion of Silica (SiO2) nanoparticles (NPs) in host ferroelectric liquid crystal (FLC) KCFLC10S on the dielectric and electro-optical properties and ultraviolet-visible (UV-VIS) absorption spectra of the pristine and dispersed systems. We have found that the dispersion of SiO2 NPs in the host FLC strongly influences the various properties of dispersed systems. No evidence of aggregates and clumps in the dispersed system has been observed. Due to SiO2 NPs dispersion, a rapid decrease in dielectric permittivity ε’, increase in conductivity σ with frequency, increase in spontaneous polarisation Ps and decrease in switching time with bias voltage have been observed. Based on the absorption spectra, we have also made an attempt to link the electro-optical and dielectric response with the mechanism of FLC–NPs interactions.

COGNITIVE AND AFFECTIVE DISORDERS AT EARLY STAGES OF PARKINSON’S DISEASE

Background: Non-motor signs, including affective and cognitive ones, are important initial manifestations of Parkinsons disease, along with motor dysfunction. Some of them manifest even before motor disorders and affect patients’ quality of life. Aim: To evaluate prevalence and severity of affective and cognitive disorders at early stages of Parkinson’s disease, as well as efficacy of their correction with a dopamine receptor agonist treatment. Materials and methods: We assessed 33 treatment-naive patients with Parkinsons disease Hoehn & Yahr stage I and II. Degree of motor dysfunction (UPDRS, Unified Parkinson's Disease Rating Scale), depressive (MADRS, Montgomery Asberg Depression Rating Scale), anxiety (HARS, Hamilton Anxiety Rating Scale) and cognitive (Montreal Cognitive Assessment – MoCA, symbols and figures test, Schulte tables, Gorbovs black and red tables) was assessed at baseline and after 1, 3 and 6 months of treatment with pramipexole. Results: Patients with early signs of Parkinson’s disease had subdepressive disorders, moderate anxiety disorders, mild cognitive disorders of a neurodynamic type and represented mainly be delayed recall of information and attention disorders. Treatment with pramipexole decreased the degree of depressive symptoms by 82% and of anxiety symptoms by 74%. There was an improvement in cognitive functions, indicated by an increase in a delayed recall (+34%), better efficacy (+31%), a decrease in switching time (-38%) and attention distribution (-33%); however, age-related normal values were not achieved. Conclusion: Already early stages of Parkinsons disease are characterized not only by motor abnormalities, but also by affective and neurodynamic cognitive dysfunction. Medical treatment with pramipexole was effective in correction of motor and neuropsychiatric disorders in patients with Parkinsons disease Hoehn & Yahr stage I–II.

Spin phenomena in asymmetrical [0 0 1] GaAs/Alx Ga1−x As quantum wells

Averkiev et al (2006 Phys. Rev. B 74 033305) studied carrier-spin phenomena in asymmetrical [0 0 1] GaAs/Alx Ga1−x As quantum wells by means of Hanle effect, i.e. with a magnetic field applied perpendicular to the growth direction. They interpreted their photoluminescence results with the help of a model that takes into account neither the full symmetry of carrier eigenstates nor the effect of the applied magnetic field and derived spin-relaxation times for the full photogenerated carrier population. Using the exact symmetry of carrier states, it is shown here that the magnetic field, even with a low strength, switches spin polarization of photocreated carriers along itself, whereas initial polarization is oriented along the growth direction. Switching time decreases with increasing magnetic field strength. The relevant parameter to describe spin phenomena under the field is therefore spin-switching time (whose ratio to radiative recombination time is provided versus magnetic field strength) and not spin-relaxation time. In addition, time-inversion invariance of the full carrier population under the field shows that its spin value vanishes at any time, making doubtful the concept of spin-relaxation time for the full carrier population. When no field is applied, the only meaningful spin-relaxation time is related to the growth axis. Its ratio value to radiative recombination time is 0.39. The above results demonstrate the importance of dealing with carrier wavefunctions having exact symmetry.

Microwave binstability in a planar ferrite-piezoelectric resonator

Bistability in a planar resonator containing an iron-yttrium garnet ferrite film and a lead zirconate titanate (PZT) plate is studied. The characteristics of the bistable resonator are measured in a frequency band of 0.8–16 GHz at an excitation power level ranging from 1 to 20 mW. Magnetic and electric tuning of the resonator frequency and switching of the resonator between stable states with the use of weak magnetic (∼0.5 Oe) and electric (0.75 kV/cm) fields are demonstrated. It is shown that, as the excitation power increases, the resonator’s switching time decreases from ∼1.7 to ∼0.3 μs.

Operation Strategies for Simulated Moving Bed in the Presence of Adsorbent Ageing

The effect of adsorbent ageing on the operation of Simulated Moving Bed (SMB) units is addressed, for two different systems (linear and non‐linear isotherms). Two different consequences of adsorbent deactivation are considered, one involving the loss of adsorption equilibrium capacity and the other related to the increase of mass transfer resistance. For each of these cases one direct and straightforward compensation measure is presented: the increase of the solid velocity (decrease of switching time) to compensate the adsorbent capacity decline and the decrease of solid and internal flow rates to compensate the mass transfer resistances increase. It is possible to compensate the adsorbent capacity decline, maintaining all SMB performance parameters, limited to the reduced contact time when high solid velocities are used. In the second case, when mass transfer resistance increases, it has been shown that the direct compensation strategy would lead to a decrease of productivity, to keep the same purity and recovery as with fresh adsorbent. Another possible corrective method to the ageing problem is the use of variable switching times in the non‐conventional “modus operandi”‐Varicol, a sort of re‐arrangement of the SMB columns distribution by sections, here tested for the case of adsorbent capacity decline case as a consequence of adsorbent ageing mechanisms.

Analysis of fast switching in tilted media

A uniform mode theory is used to find the parameter range for realizing fast switching below the Stoner–Wohlfarth limit in weakly coupled granular tilted media. The theory is used to estimate the field amplitudes and directions for simultaneous switching of a family of uniformly magnetized and noninteracting grains with dispersion in the easy axis and initial magnetization directions. The effect of interactions is then studied numerically by using a 3D finite element micromagnetic simulations. The numerical results shows that the theory provides rather accurate estimate. In addition, it is verified that in an appropriate range of applied field amplitudes the switching time decreases by decreasing the external field.

Fast switching of small magnetic particles

The numerical solution of the Landau–Lifshitz Gilbert equation shows that fast switching is possible at fields well below the anisotropy filed H a. In this regime the switching time decreases with decreasing external field. Non-uniform demagnetizing fields of irregularly shaped grains or finite temperature do not significantly change the field dependence of the switching time. At finite temperature the switching time decreases.

The Effect of Neutrons on the Characteristics of the Insulated Gate Bipolar Transistor (IGBT)

The effects of neutrons on the operating characteristics of Insulated Gate Bipolar Transistors (IGBT) are described. Experimental results are presented for devices that have been irradiated up to a fluence of 1013 neutrons/cm2, and an analytical model is presented which explains the observed effects. It is found that the on-state voltage increases, the switching time decreases, and the saturation current decreases with increasing neutron fluence. For the range of fluences studied, the observed effects result from a reduction in minority carrier lifetime in the IGBT and not from changes in the effective dopant density. The effects of neutrons on the IGBT are compared with the known effects on power MOSFETs, and it is shown that the IGBT characteristics begin to degrade at a fluence that is an order of magnitude less than the fluence at which the power MOSFET begins to degrade.

Polarization mode conversion in YIG rib waveguide

This paper describes the experimental results on the orthogonally polarized mode conversion in a YIG rib channel waveguide, in which a small magnetic field induced around the electrode deposited on the waveguide was used. The dependence of mode conversion efficiency on the coupling length and the effect of a d.c. bias field applied to the waveguide were investigated. The Faraday rotation angle of the fabricated YIG rib channel waveguide was found to be 160° cm−1, which was a reasonable value compared with that in the YIG planar waveguide reported previously. Furthermore, an increase in conversion efficiency and a decrease in switching time were found in the presence of a d.c. magnetic bias field.