Switch-off Time Research Articles

Properties of a Thermotropic Nematic Liquid Crystal Doped with Graphene Oxide

Graphene oxide (GO) nanoparticles of two different sizes are dispersed in the nematic liquid crystal (LC) 5CB covering a wide concentration range. The dielectric properties, as well as the electrooptic behavior, including threshold voltage, elastic constant, and response times are investigated as a function of GO concentration. It is found that small graphene oxide flakes of mean size of 560 nm are better and easier dispersible than larger flakes of 2.8 μm mean size. The nematic–isotropic transition only increases slightly for the (GO+LC) hybrid systems. For increasing GO concentrations the threshold voltage and splay elastic constant dramatically increase, until saturation for a concentration of ≈1% by weight GO. The field driven switching‐on time is practically independent of concentration, while the switching‐off time, which is purely elastically driven, exhibits a strongly decreasing behavior. Dielectric spectroscopy reveals a noncollective relaxation which is absent in the neat liquid crystal. This may be attributed to a drastically slowed down molecular relaxation related to the rotation around the short axis of the liquid crystal molecules. When heating the thermotropic liquid crystal into its isotropic phase, the latter acts as a solvent for the GO particles, and a lyotropic nematic phase with largely reduced birefringence is formed.

Investigation of high-voltage integral pulse thyristors in single-pulse and pulse-train modes

The results of studying the switching capabilities of recently developed high-voltage integral pulse thyristors (HIPTs) with a working area of 0.45 cm2 and an operating voltage of 3 kV are presented. A silicon chip of a thyristor consists of a large number of microthyristor cells that are enabled strictly synchronously with a control-current pulse, thus providing low switching energy losses and allowing a current of up to 8 kA at a pulse duration of 1.5 μs to be switched within 500 ns in a single-pulse mode. The HIPT switching-off time is several microseconds when, after a power-current pulse terminates, a field-effect transistor with a low (tens of milliohms) channel resistance closes the emitter–base circuit. The low switching energy loss and the short switching-off time made it possible to use HIPTs in the mode of switching current pulses with an amplitude of 500 А at a frequency of 50 kHz.

Accompagnement de l’enfant malade en fin de vie et soutien de sa famille en réanimation pédiatrique en France

The author presents a panorama of the evolution of the reflections and practices at the heart of pediatric resuscitation units both with regards to limitations and stopping of treatment (LAT) and the role of parents in these decisions. Professional recommendations and legal requirements have very likely contributed, but one should not underestimate the importance of ethical reflection carried out by many caring pediatric and neonatal resuscitation teams who were able to benefit from the contribution of parents, child psychiatrists and palliative care professionals. Starting from the idea that this decision was too serious for the families alone, and the need to avoid having them be associated in order to protect them, currently one simply seeks information and collection of the consent or non-opposition of the parents of the sick child with regard to a LAT. This is an uncontested moral and legal requirement, although French legislation has ruled that an LAT decision ultimately rests with the doctor. The recommended attitude towards the parents departs from any systematic approach in order to permit a personalized one, leaving the parents free to choose their level of involvement with regard to the decision of the care team. This is also reflected in the possible presence of parents with their child, a period of reflection (on the order of 24 to 48hours) between the time when the care team makes a collegial decision and the agreement of the parents not to pursue treatment, and the effective switch-off time. This attitude implies a greater team cohesion where nurses and doctors are together with families and children, but it also requires that teams facing such difficult decisions can be assisted.

Deep Hyperthermia Applicators: Σ-60 or Σ-Eye?

Abstract Aim: The goal of this study was functional evaluation of two deep hyperthermia (DHT) applicators to know whether we can replace Σ-60 with Σ-Eye (or vice versa). Methods: Data of all 48 patients with locally advanced cervical cancer who were treated within both applicators were analyzed. No performance of the longitudinal SAR-steering (SAR: specific absorption rate) option of Σ-Eye was done; thus, Σ-Eye was used as an Σ-60 with a modified water-bolus and shape. Temperature and RF-power (RF: radio frequency) indices were analyzed. Additionally a subgroup-analysis was applied for subgroups, categorized for the reasons of switching between the two applicators. Results: Analysis demonstrated a significant difference for power indices as applied to the two applicators; however, no difference was seen for temperature indices. The subgroup analyses revealed that when we applied Σ-Eye the power indices were mildly higher than those for the Σ-60. Contrarily, in majority of the patients applying Σ-Eye, number of off-switches and total switch-off time were lower than those for Σ-60. For the largest subgroup patients treated within the Σ-Eye, all temperature indices were slightly lower (ΔT=0.2–0.5°C) than those for the Σ-60 (p<0.028). Conclusion: In case of severe patients discomfort for DHT applicator, or when we are not satisfactory for the achieved temperatures, one can freely switch between the Σ-60 and Σ-Eye or vice versa during a DHT treatment series without loss in quality of treatment.

Dynamics of Helfrich-Hurault deformations in smectic-A liquid crystals

A dynamics of the Helfrich-Hurault deformations in the SmA sample in the case of a rigid homeotropic anchoring has been theoretically investigated. It has been found that, unlike the Freedericksz transition, in the nematic liquid crystals, both the switching-on and switching-off characteristic times for this phenomenon are linearly proportional to the SmA sample thickness, and the switching-off process is much faster than the switching-on one.

Model for the overall phase-space acceptance in a Zeeman decelerator

We present a new formalism to calculate phase-space acceptance in a Zeeman decelerator. Using parameters closely mimicking previous Zeeman deceleration experiments, this approach reveals a hitherto unconsidered velocity dependence of the phase stability which we ascribe to the finite rise and fall times of the current pulses that generate the magnetic fields inside the deceleration coils. It is shown that changing the current switch-off times as the sequence progresses, so as to maintain a constant mean acceleration per pulse, can lead to a constant phase stability and hence a beam with well-defined characteristics. We also find that the time overlap between fields of adjacent coils has an influence on the phase-space acceptance. Previous theoretical and experimental results suggested unfilled regions in phase space that influence particle transmission through the decelerator. Our model provides, for the first time, a means to directly identify the origin of these effects due to coupling between longitudinal and transverse dynamics. Since optimum phase stability is restricted to a rather small parameter range in terms of the reduced position of the synchronous particle, only a limited range of final velocities can be attained using a given number of coils. We evaluate phase stability for different Zeeman deceleration sequences, and, by comparison with numerical three-dimensional particle trajectory simulations, we demonstrate that our model provides a valuable tool to find optimum parameter sets for improved Zeeman deceleration schemes. An acceleration-deceleration scheme is shown to be a useful approach to generating beams with well-defined properties for variable-energy collision experiments. More generally, the model provides significant physical insights applicable to other types of particle decelerators with finite rise and fall time fields.

Optofluidic microsystem with quasi-3 dimensional gold plasmonic nanostructure arrays for online sensitive and reproducible SERS detection

Practical applications of chemical and biological detections through surface-enhanced Raman scattering (SERS) require high reproducibility, sensitivity, and efficiency, along with low-cost, straightforward fabrication. In this work, we integrated a poly-(dimethylsiloxane) (PDMS) chip with quasi-3D gold plasmonic nanostructure arrays (Q3D-PNAs), which serve as SERS-active substrates, into an optofluidic microsystem for online sensitive and reproducible SERS detections. The Q3D-PNA PDMS chip was fabricated through soft lithography to ensure both precision and low-cost fabrication. The optimal dimension of the Q3D-PNA in PDMS was designed using finite-difference time-domain (FDTD) electromagnetic simulations with a simulated enhancement factor (EF) of 1.6×106. The real-time monitoring capability of the SERS-based optofluidic microsystem was investigated by kinetic on/off experiments through alternatively flowing Rhodamine 6G (R6G) and ethanol in the microfluidic channel. A switch-off time of ∼2min at a flow rate of 0.3mLmin−1 was demonstrated. When applied to the detection of low concentration malathion, the SERS-based optofluidic microsystem with Q3D-PNAs showed high reproducibility, significantly improved efficiency and higher detection sensitivity via increasing the flow rate. The optofluidic microsystem presented in this paper offers a simple and low-cost approach for online, label-free chemical and biological analysis and sensing with high sensitivity, reproducibility, efficiency, and molecular specificity.

Multiscale models of colloidal dispersion of particles in nematic liquid crystals.

We use homogenization theory to develop a multiscale model of colloidal dispersion of particles in nematic liquid crystals under weak-anchoring conditions. We validate the model by comparing it with simulations by using the Landau-de Gennes free energy and show that the agreement is excellent. We then use the multiscale model to study the effect that particle anisotropy has on the liquid crystal: spherically symmetric particles always reduce the effective elastic constant. Asymmetric particles introduce an effective alignment field that can increase the Fredericks threshold and decrease the switch-off time.

Investigation of main coolant pump trip problem in case of SB LOCA for Kozloduy Nuclear Power Plant, WWER-440/V230

This paper presents the results of thermal-hydraulic calculation of accident scenarios that involve the trip of main coolant pump (MCP) in case of Small break loss of coolant accident (SB LOCA) for WWER-440/V230 units at Kozloduy Nuclear Power Plant (KNPP), done in support of the development of Symptom Based Emergency Operating Procedures (SB EOPs) for this plant. The main purpose of these analyses is to show how the different time of MCP switching off results in primary inventory depletion in case of SB LOCA and it is reflect on peak cladding temperature. According to this, the SB LOCA scenario is regarded from the point of view of an inadequate core cooling. Therefore, the primary concern is Critical Safety Function (CSF) “Core cooling” and “Primary inventory”. High core residual heat, minimal safety injection flow and other initial conditions challenging the mentioned CSFs are the main particularities of the accepted scenarios.The RELAP5/MOD3.2 computer code has been used to perform the analyses in a WWER-440 Nuclear Power Plant (NPP) model. A model of WWER-440 based on Unit 4 of Kozloduy NPP has been developed for the system’s thermal-hydraulics code RELAP5/MOD3.2 at the Institute for Nuclear Research and Nuclear Energy – Bulgarian Academy of Sciences (INRNE-BAS), Sofia.

Development of the 3.7 GHz LHCD system on HL-2A

A 2 MW-3.7 GHz lower hybrid current drive (LHCD) system is under development for physics experiments on the HL-2A device. The RF Power is generated by four TH2103A klystron amplifiers and propagates in the TE10 mode through WR284 waveguides. The transmission lines with a length of 20 m to 30 m are pressurized with 2 bars of nitrogen to decrease the possibility of arcing. The launcher, based on the passive-active multi-junction (PAM) concept, has been developed and is currently being realized. It was designed for a power spectrum peaked at N|| = 2.75 with good coupling properties over a wide range of plasma parameters. The four klystrons are fed by a high-voltage power supply (HVPS) based on the pulse step modulation (PSM) concept with a fast switch-off time of less than ten μs. This system is expected to be in operation within 1 years and will explore many international thermonuclear experimental reactor (ITER) related LH experiments in the following years.

Active Clamping Circuit With Status Feedback for Series-Connected HV-IGBTs

Active clamping circuits can effectively suppress the voltage imbalance between series-connected insulated-gate bipolar transistors (IGBTs). However, while the active clamping circuit is conducting, extra current is injected into the gate of the IGBT, the gate voltage increases, and the IGBT operates in the active region. Therefore, long time conduction and frequent actions of the active clamping circuit will lead to extremely high switching loss of the IGBT with high collector-emitter voltage and serious switching loss imbalance between the series-connected IGBTs, which imperils the efficiency and safety of the system, particularly in the applications of high-voltage IGBT (HV-IGBT) series connection. In this paper, a novel active clamping circuit with status feedback is proposed for series-connected HV-IGBTs. A high-speed status feedback subcircuit is designed for transforming the operation status of an active clamping circuit into optical signal and feeding it back to the control system. According to the feedback signals, the microcontroller regulates the switching-on time and switching-off time of the series-connected HV-IGBTs' drive signals timely in order to implement voltage balancing and, thus, to restrain the actions of active clamping circuits. By applying this voltage balancing method to the HV-IGBT series connection circuit, the voltage balancing performance is expected to improve, and high switching loss and serious switching loss imbalance are expected to be suppressed. Experimental results verify the validity and superiorities of the proposed voltage balancing circuit and control strategy.

MZI-Semiconductor-Based All-Optical Switch With Switching Gain

In this paper, we propose and design a novel all-optical switch that exhibits switching gain, based on feasibly realizable symmetric passive Mach-Zehnder interferometer with direct bandgap active arms. The switching is based on the absorption modulation of active arms through carrier depletion by a weak data pulse to switch a stronger pump beam. The proposed switch does not require electrical driving, and because of switching gain, it may not require energy-consuming re-shaping and re-amplification stages. Hence, the power requirement is significantly low. We show that by suitably designing the length of the active arms, operating wavelength and operating intensity of the pump beam, a switching gain >2 can be achieved when input signal pulse is less than 1/8× the strength of pump beam. We also show that the slow switch-off time caused by carrier band-filling is circumvented by using an additional delayed signal pulse to deplete carriers in both arms at a faster switch-on rate. With an inherent switching gain, low power operation and a switching speed that can reach ~100 Gbps, it could be a scalable and feasible solution to large scale broadband switching and wavelength conversion for silicon photonics.

Energy-Aware Base Stations: The Effect of Planning, Management, and Femto Layers

We compare the performance of three base station management schemes on three different network topologies. In addition, we explore the effect of offloading traffic to heterogeneous femtocell layer upon energy savings taking into account the increase of base station switch-off time intervals. Fairness between mobile operator and femtocell owners is maintained since current femtocell technologies present flat power consumption curves with respect to served traffic. We model two different user-to-femtocell association rules in order to capture realistic and maximum gains from the heterogeneous network. To provide accurate findings and a holistic overview of the techniques, we explore a real urban district where channel estimations and power control are modeled using deterministic algorithms. Finally, we explore energy efficiency metrics that capture savings in the mobile network operator, the required watts per user and watts per bitrate. It is found that the newly established pseudo distributed management scheme is the most preferable solution for practical implementations and together with the femotcell layer the network can handle dynamic load control that is regarded as the basic element of future demand response programs.

A high performance charge plasma based lateral bipolar transistor on selective buried oxide

In this paper, we present a new structure of lateral bipolar transistor on selective buried oxide. The device does not use highly doped regions; however, it employs the concept of creating n and p type charge plasma in undoped silicon by using metal electrodes of different work functions. The proposed device is named as the selective buried oxide based bipolar charge plasma transistor (SELBOX-BCPT). An extensive 2D simulation study has revealed that the proposed SELBOX-BCPT device not only possesses all the advantages of the conventional BCPT device, but it also addresses various severe problems of the BCPT device. A significant improvement in major issues of poor cutoff frequency (fT), low breakdown voltage and thermal efficiency has been achieved. It has been observed that the fT has increased by ∼94.6%, the breakdown voltage by 23.47% and the device is much cooler than the conventional BCPT device. A large current gain is obtained in the proposed device and is on a par with the conventional BCPT device. Further, by using mixed-mode simulation feature of the Atlas simulator, inverting amplifiers based on SELBOX-BCPT and the conventional BCPT have been realized. A significant improvement of 15% in switching-on transient time and 25.8% in switching-off transient time has been achieved in the proposed device in comparison to the conventional BCPT device.

Study on Switch-On and Switch-Off Time of On-Line Monitoring for the Vacuum Circuit Breaker in Traction Substation

This paper studies the method of determining switch-on and switch-off time of on-line monitoring system for vacuum circuit breakers in traction substation based on engineering project. In switch-on and switch-off process, the on-line monitoring system gets displacement signal of moving contact through the guyed displacement sensor, and gets vibration signal through the piezoelectric acceleration sensor, then the signal monitored is sent to the industrial personal computer through the data acquisition unit taking DSP as the core and the communication network. After comprehensive analysis by the backstage management software in the computer, switch-on and switch-off time can be determined.

Pulse Power Nanosecond-Range DSRD-Based Generators for Electric Discharge Technologies

New design of power nanosecond-range generators for electric discharge in gases is described. These generators are based on semiconductor opening switches-Drift Step Recovery Diodes (DSRD). The main advantages of DSRD are very short switching-off time (<;3 ns), high commutated power (>500 kW for single DSRD with 2 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of semiconductor structure), and high reliability of high voltage stacks consisting of many connected in series DSRD. The experimental results of DSRDbased generator application for ozone production and waste gas cleaning are presented. The main parameters of the generators: output pulse voltage up to 36 kV, pulse rise time <;4 ns, pulse repetition rate up to 3.5 kHz, output pulse power >4.5 MW.

Experimental investigation of plasma recovery during the pulse-off time in plasma source ion implantation

Experimental results pertaining to the plasma recovery process during the pulse-off time in plasma source ion implantation are presented. A series of experiments conducted in low-pressure argon plasma with various pulse voltages and pulse-on times reveals that the plasma recovery time is almost linearly proportional to the sheath thickness at the switch-off time. However, for sheaths larger than several centimeters, the plasma recovery times are observed to be shorter than those predicted by a simple theoretical model, expressed as 5s/uB where uB and s are the Bohm speed and the sheath thickness at the switch-off time, respectively. The reduction of plasma recovery time is found to be the consequence of realistic plasma parameters such as non-uniform density and ion drift velocity distributions in front of a target, which were not considered in the theoretical model.

Decoupling of the Ericksen–Leslie equations

We examine the hydrodynamic behaviour of a nematic liquid crystal confined between two parallel electrodes and subject to a non-uniform electric field across the layer. By decoupling the Ericksen–Leslie equations for the nematic, we are able to derive a dynamic equation for the director orientation which is not explicitly dependent on the fluid velocity, rather a non-local term contains the effects of flow. The flow velocity and electric potential are determined subsequently from the calculated director profile. Our numerical scheme enables us to predict an effective rotational viscosity which takes account of fluid shear viscosities and allows us to establish the behaviour in special symmetry cases. Significantly, our calculations also demonstrate how kickback can be avoided, and the switch-off time optimised, by restricting the applied voltage to an appropriate range.

Study of third-order nonlinear optical and all-optical switching properties of palladium metal–organic complex

We report the results of studies on third-order nonlinear optical properties of a newly synthesized palladium metal–organic complex [PdLPPh3] (L=N-(2-pyridyl)-N′-(5-chlorosalicylidene)hydrazine) both in film and solution form using Z-scan and degenerate four wave mixing (DFWM) techniques. Experiments were performed using Q-switched Nd: YAG laser with nanosecond pulses at 532nm. Investigations revealed that the palladium metal–organic complex possesses nonlinear absorption coefficient βeff which is of the order of 10−9m/W due to reverse saturable absorption (RSA) and negative nonlinear refractive index (self-defocusing) n2 which is of the order of 10−9esu. The real and imaginary parts of the third-order nonlinear optical susceptibility (χ(3)) were found to be of the order of 10−11esu. The second-order hyperpolarizability (γh) was estimated to be of the order of 10−30esu. The results of pump–probe experiments show that the switch-on and switch-off times of the palladium metal–organic complex were in μs for different pump intensities and the energy dependent transmission studies reveal better limiting property of the compound at nanosecond regime. Thus the nonlinear response of the material suggests that it has a potential application for high sensitive photonic devices.

Lateral Contact Three-State RF MEMS Switch for Ground Wireless Communication by Actuating Rhombic Structures

A laterally actuated three-state RF microelectromechanical systems switch for ground wireless communication applications is proposed, fabricated, and tested. By electrostatically actuating a rhombic beam, the proposed switch can not only realize the off-state to on -state shifting but also provide an additional deep off state. The switch was fabricated by silicon on glass (SOG) bulk silicon micromachining. The 2- μm-thick gold electroplating layers were introduced in the SOG process to enhance the performance of lateral contacts. The off-state and deep- off-state isolations of the prototype switch were measured to be -67.6 dB and - 72.2 dB at 0.9 GHz and -48.3 dB and -53.0 dB at 6 GHz, respectively. The measured insertion loss is -0.13 dB at 0.9 GHz and -0.38 dB at 6 GHz, respectively. The measured actuation voltage is 78 V. The switching-on and switching-off response times are 72 and 64 μs, respectively.