Effect of Channel Geometry and Properties of a Vapor–Gas Mixture on Volume Condensation in a Flow through a Nozzle

A method of direct numerical solution of the kinetic equation for the droplet size distribution function was used for the numerical investigation of volume condensation in a supersonic vapor–gas flow. Distributions of temperature for the gas phase and droplets, degree of supersaturation, pressure, fraction of droplets by weight, the number of droplets per unit mass, and of the nucleation rate along the channel were determined. The influence of nozzle geometry, mixture composition, and temperature dependence of the mixture properties on the investigated process was evaluated. It has been found that the nozzle divergence angle determines the vapor–gas mixture expansion rate: an increase in the divergence angle enhances the temperature decrease rate and the supersaturation degree raise rate. With an increase or decrease in the partial pressure of incondensable gas, the droplet temperature approaches the gas phase temperature or the saturation temperature at the partial gas pressure, respectively. A considerable effect of the temperature dependence of the liquid surface tension and properties on gas phase parameters and the integral characteristics of condensation aerosol was revealed. However, the difference in results obtained with or without considering the temperature dependence of evaporation heat is negligible. The predictions are compared with experimental data of other investigations for two mixtures: a mixture of heavy water vapor with nitrogen (incondensable gas) or n-nonane vapor with nitrogen. The predictions agree quite well qualitatively and quantitatively with the experiment. The comparison of the predictions with numerical results from other publications obtained using the method of moments demonstrates the usefulness of the direct numerical solution method and the method of moments in a wide range of input data.     

Multiple-Input–Multiple-Output Linear-Quadratic Control of the Energy Production of a Synchronous Generator in a Nuclear Power Plant

—A multiple-input–multiple-output linear-quadratic servo controller is proposed for a synchronous generator operating in a nuclear power plant that keeps the active power at the desired level and performs reactive power reference tracking using the reactive power demand from a central dispatch center. The controller design was based on the locally linearized version of a previous non-linear dynamical model of the synchronous electrical generator [1 Anderson, P., and Fouad, A., Power-Systems-Control and Stability, Ames, IA: The IOWA State University Press, Chap. 4, 1977. [Google Scholar], 2 Fodor, A., Magyar, A., and Hangos, K.M., Control-oriented modeling of the energy-production of a synchronous generator in a nuclear power plant, Energy, . 39, pp. 135–145, 2012.[Crossref], [Web of Science ®] , [Google Scholar]], the parameters of which have been identified using measured data from Paks Nuclear Power Plant (Hungary). The method can easily be applied to any industrial power plant generator connected to the electrical grid after estimating its parameters. The proposed observer-based multiple-input–multiple-output state feedback controller is a linear-quadratic servo controller with very good reference tracking and disturbance rejection properties, which were confirmed by simulation experiments.     

PET–MR imaging using a tri-modality PET/CT–MR system with a dedicated shuttle in clinical routine

Tri-modality PET/CT–MRI includes the transfer of the patient on a dedicated shuttle from one system into the other. Advantages of this system include a true CT-based attenuation correction, reliable PET-quantification and higher flexibility in patient throughput on both systems. Comparative studies of PET/MRI versus PET/CT are readily accomplished without repeated PET with a different PET scanner at a different time point. Additionally, there is a higher imaging flexibility based on the availability of three imaging modalities, which can be combined for the characterization of the disease. The downside is a somewhat higher radiation dose of up to 3 mSv with a low dose CT based on the CT-component, longer acquisition times and potential misalignment between the imaging components. Overall, the tri-modality PET/CT–MR system offers comparative studies using the three different imaging modalities in the same patient virtually at the same time, and may help to develop reliable attenuation algorithms at the same time.     

A full 3D non-equilibrium Green functions study of a stray charge in a nanowire MOS transistor

The effect of the location of a negative stray charge associated with an acceptor type defect state in the channel of a nanowire transistor has been investigated using a Non Equilibrium Green’s Function Formalism in the effective mass approximation. Due to the fact that the nanowire cross-section is 2.2×2.2 nm², we have calculated the effective masses using Tight Binding (TB) calculations. A third neighbor sp ³ TB model has been used. We have found that the on current is two time smaller when the charge is located in the source end as compared to its location in the drain end. We have also studied the effect on the current of the spatial distribution of the acceptor charge. The calculations show that when the charge is more distributed (de-localized) the effect of the blocking of the current is less efficient, so the current is higher.     

Vessel wall characterization using quantitative MRI: what’s in a number?

The past decade has witnessed the rapid development of new MRI technology for vessel wall imaging. Today, with advances in MRI hardware and pulse sequences, quantitative MRI of the vessel wall represents a real alternative to conventional qualitative imaging, which is hindered by significant intra- and inter-observer variability. Quantitative MRI can measure several important morphological and functional characteristics of the vessel wall. This review provides a detailed introduction to novel quantitative MRI methods for measuring vessel wall dimensions, plaque composition and permeability, endothelial shear stress and wall stiffness. Together, these methods show the versatility of non-invasive quantitative MRI for probing vascular disease at several stages. These quantitative MRI biomarkers can play an important role in the context of both treatment response monitoring and risk prediction. Given the rapid developments in scan acceleration techniques and novel image reconstruction, we foresee the possibility of integrating the acquisition of multiple quantitative vessel wall parameters within a single scan session.     

＂3＋1＂-To Create a New Power Pattern in Northeast China

Northeast region was an old industrial base of Chinai, but after three economic flourishing areas newly arose in Zhujiang River Delta, Changjiang River Delta and Beijing-Tianjin-Tangshan Region, this old industrial base has been economically stagnated ,paced haltingly.     

Down-scaling limitations in CMOS devices: Is there a role for the ferroelectrics?

Abstract

This paper reviews down-scaling limitations in CMOS devices, with a special emphasis on the possible application of ferroelectric materials. Ultimate limit in reduction of the thickness of gate oxide is found as the most important limitation. The possibility of replacing or enhancing the gate oxide by a ferroelectric material is critically considered in view of the desired properties of the silicon - to - gate insulator interface.     

Ignition of an organic water–coal fuel droplet floating in a heated-air flow

Ignition of an organic water–coal fuel (CWSP) droplet floating in a heated-air flow has been studied experimentally. Rank B2 brown-coal particles with a size of 100 μm, used crankcase Total oil, water, and a plasticizer were used as the main CWSP components. A dedicated quartz-glass chamber has been designed with inlet and outlet elements made as truncated cones connected via a cylindrical ring. The cones were used to shape an oxidizer flow with a temperature of 500–830 K and a flow velocity of 0.5–5.0 m/s. A technique that uses a coordinate-positioning gear, a nichrome thread, and a cutter element has been developed for discharging CWSP droplets into the working zone of the chamber. Droplets with an initial size of 0.4 to 2.0 mm were used. Conditions have been determined for a droplet to float in the oxidizer flow long enough for the sustainable droplet burning to be initiated. Typical stages and integral ignition characteristics have been established. The integral parameters (ignition-delay times) of the examined processes have been compared to the results of experiments with CWSP droplets suspended on the junction of a quick-response thermocouple. It has been shown that floating fuel droplets ignite much quicker than the ones that sit still on the thermocouple due to rotation of an CWSP droplet in the oxidizer flow, more uniform heating of the droplet, and lack of heat drainage towards the droplet center. High-speed video recording of the peculiarities of floatation of a burning fuel droplet makes it possible to complement the existing models of water–coal fuel burning. The results can be used for a more substantiated modeling of furnace CWSP burning with the ANSYS, Fluent, and Sigma-Flow software packages.     

Piezoelectric effects on carrier capturing time in a hybrid p–n junction system: a numerical study using finite element method

The piezoelectric influence on carrier (electrons and holes) trapping time in a hybrid p–n junction system is investigated in this paper. The hybrid nature of the junction is the conceptual combination of p–n junction solar cell and piezoelectricity. The mechanism is that the piezoelectric field induced on the p–n interface can affect the transport of free carriers such as electrons and holes present inside the junction system. These free carriers included are dissociated from excitons which are generated by the light or by the piezoelectric field on the interface via Langevin recombination. The numerical analysis focuses on carrier density (n, p), carrier velocity \((v_{n},v_{p})\), carrier capture cross section \((\sigma _{n},\sigma _{p})\), and carrier capturing time \((\tau _{n},\tau _{p})\) using the finite element method. These parameters are affected by the piezoelectric potential induced by different vertical stresses \((T_{z})\) on the p–n interface. Based on these features, the simulation of the distribution of the carrier (electrons or holes) capturing time over the junction system can be used to analyze the piezophototronic devices where traps are present.     

Reliability of velocity pulsatility in small vessels on 3Tesla MRI in the basal ganglia: a test–retest study

Objective

Recent work showed the feasibility of measuring velocity pulsatility in the perforating arteries at the level of the BG using 3T MRI. However, test–retest measurements have not been performed, yet. This study assessed the test–retest reliability of 3T MRI blood flow velocity measurements in perforating arteries in the BG.

Materials and methods

Two-dimensional phase-contrast cardiac gated (2D-PC) images were acquired for 35 healthy controls and repeated with and without repositioning. 2D-PC images were processed and analyzed, to assess the number of detected perforating arteries (N_detected), mean blood flow velocity (V_mean), and velocity pulsatility index (vPI). Paired t-tests and Bland–Altman plots were used to compare variance in outcome parameters with and without repositioning, and limits of agreement (LoA) were calculated.

Results

The LoA was smallest for V_mean (35%) and highest for vPI (79%). Test–retest reliability was similar with and without repositioning of the subject.

Discussion

We found similar LoA with and without repositioning indicating that the measurement uncertainty is dominated by scanner and physiological noise, rather than by planning. This enables to study hemodynamic parameters in perforating arteries at clinically available scanners, provided sufficiently large sample sizes are used to mitigate the contribution of scanner- and physiological noise.

     

Forced Compressed Air Cooling System for a 300 MW Steam Turbine in Waigaoqiao Power Plant

The 300 MW steam turbine installed in Waigaoqiao Power Plant with combined HPIP cylinders of double casing structure is a product of the Shanghai Turbine Works utilizing licensed technology. It has a large heat storage capacity and good thermal insulation, so the metal temperature of first stage of HP cylinder (FSMTI) may reach 400-450℃ after shut down and it takes 7-8 days to cool to 150℃ by natural cooling, Now with a forced cooling system the cooling time may be reduced to 40 hours, so that the turbine may be opened for repair work in about 5-6 days. The cooling system for #2 unit and test procedure are briefly described below.     

Negative differential resistance in graphene-nanoribbon–carbon-nanotube crossbars: a first-principles multiterminal quantum transport study

We simulate quantum transport between a graphene nanoribbon (GNR) and a single-walled carbon nanotube (CNT) where electrons traverse vacuum gap between them. The GNR covers CNT over a nanoscale region while their relative rotation is 90^°, thereby forming a four-terminal crossbar where the bias voltage is applied between CNT and GNR terminals. The CNT and GNR are chosen as either semiconducting (s) or metallic (m) based on whether their two-terminal conductance exhibits a gap as a function of the Fermi energy or not, respectively. We find nonlinear current-voltage (I–V) characteristics in all three investigated devices—mGNR-sCNT, sGNR-sCNT and mGNR-mCNT crossbars—which are asymmetric with respect to changing the bias voltage from positive to negative. Furthermore, the I–V characteristics of mGNR-sCNT crossbar exhibits negative differential resistance (NDR) with low onset voltage V _NDR?0.25 V and peak-to-valley current ratio ?2.0. The overlap region of the crossbars contains only ?460 carbon and hydrogen atoms which paves the way for nanoelectronic devices ultrascaled well below the smallest horizontal length scale envisioned by the international technology roadmap for semiconductors. Our analysis is based on the nonequilibrium Green function formalism combined with density functional theory (NEGF-DFT), where we also provide an overview of recent extensions of NEGF-DFT framework (originally developed for two-terminal devices) to multiterminal devices.     

Reduced order H∞ TCSC controller & PSO optimized fuzzy PSS design in mitigating small signal oscillations in a wide range

This paper proposes hybrid control schemes for compensation of parametric and non-parametric uncertainties arising in modern power systems. The robust loop shaping design procedure considering non-parametric uncertainty term is used to design H_∞ TCSC. To further enhance steady state stability, and consider the effect of parametric uncertainties occurring due to variation in loading conditions, robust TCSC is supplemented with three types of PSS i.e. PSO-PID PSS, PSO Mamdani FPSS and PSO TS FPSS. PSO is used to optimize the parameters of PID based and Fuzzy type PSS. The proposed hybrid control schemes are found to compensate uncertainty well by stabilizing the power system over whole parametric uncertainty range. However, the proposed hybrid controller involving robust TCSC and PSO-Takagi–Sugeno FPSS shows best performance with enhanced steady state stability among all schemes. Also the T–S FPSS performs better as compared to Mamdani FPSS.     

Time–frequency multiresolution of fault-generated transient signals in transmission lines using a morphological filter

The ongoing transformation of electrical power systems highlights the weaknesses of the protection schemes of traditional devices because they are designed and configured according to traditional characteristics of the system. Therefore, this work proposes a new methodology to study the fault-generated high frequency transient signals in transmission lines through multiresolution analysis. The high frequency components are determined by a new digital filtering technique based on mathematical morphology theory and a spectral energy index. Consequently, wide spectra of signals in the time–frequency domain are obtained. The performance of this method is verified on an electrical power system modeled in ATP-Draw, where simulation and test signals are developed for different locations, fault resistances, inception angles, high frequency noises, sampling frequencies, types of faults, and shapes of the structuring element. The results show the characteristics of the fault such as the traveling wave frequency, location, and starting time.     

Mapping duality as a means to allow finite βF compensation in bipolar log filters

Log-domain filters are a promising design paradigm for analog signal processing. They achieve tunability and operation up to high frequencies, with voltage and power requirements typically better than those of conventional filtering architectures. Implementation can be based only on capacitors, current sources and an exponential, differential V/I converter referred to as the E-cell. Non-idealities in the E-cell, like the presence of non-negligible input currents due to finite β_F, can reduce system performance. The aim of this paper is to investigate E-cell-based design strategies and to introduce a duality principle whose exploitation can allow finite β_F compensation. As a validation, HSPICE simulation results are illustrated for a second-order bandpass filter. Copyright © 2000 John Wiley & Sons, Ltd.     

Improving the accuracy of multisided travelling wave determination of location of a fault in a power line by means of the difference–distance-measuring technique

The double-ended travelling wave method of determination of location of a fault in electrical networks has significant errors due to changes in the propagation velocity of electromagnetic waves. We have developed a travelling wave method of improving the accuracy of location of a fault determination in power transmission lines that is based on navigation algorithms. The method is applicable to lines with branches. The distance to fault determination for the developed method is up to twice as accurate as the double-ended travelling wave location of a fault method. The accuracy of the developed method is less influenced by external factors (change of sag, soil resistance, the instantaneous value of the current at the fault time) than is the accuracy of the double-ended travelling wave location of a fault method. The proposed method allows reducing the errors in determining distance to the location of a fault, and its accuracy is less affected by external factors. The developed method can be incorporated into existing and prospective devices based on travelling wave methods of location of a fault determination.     

Application of a system with distributed architecture for information acquisition and processing in tasks of active–adaptive voltage control in distribution electric grids

An active–adaptive control system for power grids with distributed architecture of data acquisition and processing is considered. The advantages of the proposed control principle are compared with commonly used methods. A domestic apparatus—a programmable recording bay controller (PRBC)—is described. This hardware was designed to measure the basic electrical parameters and create distributed systems for data acquisition and processing. The procedure is considered of supervisory control and data acquisition (SCADA) by the SONATA system based on a multicore distributed architecture having high reliability and supporting a rigid real-time mode. A full-function full-scale model of active–adaptive voltage control system (AAVC) was set up using proposed software and hardware. The AAVC makes it possible to use the results of calculating–measuring procedures to select a corresponding on-load tap-changer (OLTC) on the actual voltage levels in the nodes of distribution grid. This approach to centralized voltage control in distribution grids makes it possible to ensure the required level of voltage in the greatest possible number of power consumers owing to prediction of voltage change. The effect of emergencies (random failure of control equipment) during the operation of an active–adaptive voltage control system is analyzed. A qualitative evaluation of the effect of faults on regulation quality and choice of OLTC connection is carried out. It is shown that, for undisturbed operation of an active–adaptive voltage control system, additional diagnostic tools, backup, and data loss compensation are needed.     

Assessment of Supply-Voltage Quality in a Ship’s Electric-Power System by Means of Computer Simulation

A ship’s electric-power system (SEPS) provides reliable functioning of ship systems, as well as safety in navigation and the living conditions and work of the crew. SEPSs in large-displacement vessels can have a capacity of more than 100 MW and consist of thousands of interconnected components and subsystems. On ships with a propulsion system (PS), the SEPS powers both the PS, which consumes most of the power generated by a ship power plant, and numerous general consumers of power on the ship. The PS includes frequency converters with dc links; for a ship’s power plant, these converters are a high-power nonlinear load that causes significant voltage distortions in the ship’s network. When designing a vessel, at the stage of selecting the structure and components of the SEPS, electromagnetic compatibility between the PS and general vessel users needs to be provided. According to the requirements specified in the Russian Maritime Register of Shipping, the nonsinusoidal voltage in the ship’s electrical network must not exceed 10%. Computer simulation is the only effective tool for assessing the quality of ship-network voltage at the initial stages of design. In this paper, we present the results of estimating two alternative SEPS designs by means of the MATLAB Simulink package. It is shown that high-power transformers can be removed from the PS without significant deterioration of network-voltage quality, which makes it possible to reduce the cost, weight, and dimensions of electrical equipment.