Periods Of Low Speed Research Articles

Accuracy Improvement of Braking Force via Deceleration Feedback Functions Applied to Braking Systems.

Currently, braking control systems used in regional railways are open-loop systems, such as metro and tramways. Given that the performance of braking can be influenced by issues such as wheel sliding or the properties of the friction components present in brake systems, our study puts forward a novel closed-loop mechanism to autonomously stabilize braking performance. It is able to keep train deceleration close to the target values required by the braking control unit (BCU), especially in terms of the electrical-pneumatic braking transform process. This method fully considers the friction efficiency characteristics of brake pads and encompasses running tests using rolling stock. The test results show that the technique is able to stabilize the actual deceleration at a closer rate to the target deceleration than before and avoid wheel sliding protection (WSP) action, especially during low-speed periods.

Wheel wear prediction for high speed railway vehicles during acceleration

Wheel wear prediction for high-speed railway vehicles during the acceleration process is of great importance for the improvement of operating characteristics and the development of friction management strategy near the railway station, especially in complex climatic environments. This work analyzes and predicts the wheel wear evolution of high-speed motor cars during acceleration. Firstly, detailed dynamic models of the high-speed motor car are developed, in which a comprehensive gear transmission system is also adopted to capture the accurate dynamic responses of the motor car. Secondly, the length of the simulated track interval with different friction coefficients is set according to the Gaussian distribution function to consider the influence of the friction coefficient. Moreover, a Proportional-Integral(PI) creep controller is also introduced to meet the challenge due to varying wheel-rail contact conditions, and a wheel wear prediction model based on the aforementioned submodels is established to obtain the wheel wear evolution. Finally, simulation results of dynamic responses from the vehicle dynamic model and wheel wear prediction procedure are compared with the measured field data. The results show that the time-varying meshing stiffness from the gear transmission system will aggravate the interaction between wheel and rail and deteriorate the wheel wear. When the high-speed motor car passes through a poor adhesion zone in the acceleration, it is easier to trigger the creep controller at the low-speed period while it will not occur at the high-speed period.

Research on Constant Frequency Electrical Angle Start Method of LCI

Load-commutated inverters (LCIs) are the key starting device of wound-field synchronous motor. By detecting the rotor position and inputting a variable frequent current to the stator windings, the LCI can drive the motor from standstill to a given speed. Thus, rotor position detecting method comes to be the key techniques, but at the ultra-low speed period, the motor’s terminal voltage is too low to accurately sampling and is vulnerable to the interference, which brings risks to the variable frequency driving. In this paper, through analyzing the principles of LCIs and synchronous machine, a constant frequency electrical angle control methods is introduced to solve the difficulty of detecting the rotor position in the low speed period. A 98MW synchronous machine driven with an 18MW LCI are experimented in MATLAB and RTDS systems, the results show that the proposed control strategy can realize soft-start of the wound-field synchronous motor without detecting rotor’s position.

A New Method of Improving Low-Speed Performance of Variable Speed Hydraulic Systems: By Leaking Parallel Valve Control

Aiming at improving low-speed performance of variable speed hydraulic systems, the leaking parallel valve control is applied to the system during low-speed period. This method increases system damping ratios by increasing leakage controlled by the valve. In addition, the increase of damping ratios just compensates the reduction of damping ratios due to the friction negative slop, which helps to improve low-speed stability and achieve lower critical speed. In the whole process of closed loop control, the system in leaking parallel valve control has good speed performance with more stable and suitable damping ratios and basically avoids pressure impact at start and stop stages and still keeps comparatively high efficiency because the pump provides total flow and the valve only leaks out few flows.

CHLORINATION REACTION KINETICS OF THE LOW-CONCENTRATION NATURAL RUBBER LATEX

ABSTRACT The kinetics of the chlorination of low-concentration natural rubber latex was investigated. The kinetic data were derived from chlorine concentrations in chlorinated natural rubber (CNR) for different reaction times and temperatures. The chlorination reaction process can be divided into two stages—a high-speed period (stage 1) and a low-speed period (stage 2)—using the graphed curves of the change in chlorine content with change in reaction time. The relationship of the chlorination conversion ratio x to reaction time t and temperature T can be expressed as x = 1.15 − 0.916e−kt, where the kinetic constant k = 0.00907 + 6.39 × 10−6e0.0211T. The overall apparent reaction order n for the first stage is 4.8, whereas for the second stage it is 1.0, using kinetic fitting. The apparent activation energy Ea was calculated, using the Arrhenius equation, to be 5.32 kJ/mol for stage 2. The lower value of Ea suggests that the chlorination rate is less sensitive to reaction temperature in this stage. The chlorination reaction rate increases with the increase in reaction temperature during stage 2, but the effects are not visible. However, a temperature that is too high may result in energy being wasted. We conclude that the proper reaction temperature in stage 2, taking the kinetic effects into account, is between 323.15 and 353.15 K.

Outcomes of midterm circulatory support by left ventricular assist device implantation with descending aortic anastomosis

For some patients undergoing left ventricular assist device (LVAD) implantation, the perfusion tube is anastomosed to the descending aorta instead of the currently more prevalently used ascending aorta. Purpose of this study was to assess retrospectively the outcomes of LVAD patients with descending aortic anastomosis. Between March 2007 and March 2010, six patients underwent LVAD implantation with descending aortic anastomosis with Toyobo or Jarvik 2000 LVAD at our institute. Their average circulatory support time was 434(range 82-751)days. Both types of LVAD afforded adequate circulatory support, and inotrope treatment and mechanical ventilation were discontinued relatively early. Echocardiograms of the three patients with Jarvik 2000 LVAD revealed antegrade flow in the ascending aorta during the intermittent low-speed period. Among them, one patient developed infarction in the right brain hemisphere because of thromboembolism, whereas another patient developed pneumonia in the left lung followed by a lethal systemic infection. One patient on Toyobo LVAD support reached heart transplantation without morbidity. Another patient implanted with Toyobo LVAD, whose left ventricular function was too poor to generate forward flow through aortic valve, developed thrombus in the ascending aorta. No embolic events were observed in the organs below the diaphragm. In conclusion, descending aortic anastomosis of the perfusion tube can be used for LVAD implantation for some patients, but considerable risks of morbidities, including thromboembolic events and/or infection, should be recognized.

Automated Analysis of Cumulative Flow and Speed Curves

An automated procedure for analyzing cumulative flow and speed curves is described. The essential features of this method are a routine that uses a piecewise linear approximation to identify times that speed or flow changes and a set of rules to identify periods of queue discharge flow (QDF) and prequeue flow (PQF). These rules are based on speed thresholds, the duration of periods of low speed, the times congested flow is observed at different locations relative to the bottleneck, and (in the case of PQF) the regression slope of flow versus time. Results of the automated analysis are compared with those of a previous manual analysis of data from 21 bottlenecks. The automated analysis identified more, but shorter, periods of QDF than did the manual analysis, primarily because it was more likely to identify very short periods of QDF or recovery from congestion, but fewer and longer periods of PQF. Average flow for automatically identified periods of QDF was similar to that of manually identified periods, but average flow for automatically identified periods of PQF was almost always lower than that for those identified manually.

The M / G /1 queue with two service speeds

We consider an M/G/1 queue with the special feature that the speed of the server alternates between two constant values SL and SH > SL. The high-speed periods are exponentially distributed, and the low-speed periods have a general distribution. Our main results are: (i) For the case that the distribution of the low-speed periods has a rational Laplace-Stieltjes transform, we obtain the joint distribution of the buffer content and the state of the server speed. (ii) For the case that the distribution of the low-speed periods and/or the service request distribution is regularly varying at infinity, we obtain explicit asymptotics for the tail of the buffer content distribution. The two cases in which the offered traffic load is smaller respectively larger than the low service speed are shown to result in completely different asymptotics.

The M/G/1 queue with two service speeds

We consider an M/G/1 queue with the special feature that the speed of the server alternates between two constant values sL and sH > sL. The high-speed periods are exponentially distributed, and the low-speed periods have a general distribution. Our main results are: (i) for the case that the distribution of the low-speed periods has a rational Laplace–Stieltjes transform, we obtain the joint distribution of the buffer content and the state of the server speed; (ii) for the case that the distribution of the low-speed periods and/or the service request distribution is regularly varying at infinity, we obtain explicit asymptotics for the tail of the buffer content distribution. The two cases in which the offered traffic load is smaller or larger than the low service speed are shown to result in completely different asymptotics.

A dynamic voltage scaled microprocessor system

A microprocessor system is presented in which the supply voltage and clock frequency can be dynamically varied so that the system can deliver high throughput when required while significantly extending battery life during the low speed periods. The system consists of a dc-dc switching regulator, an ARM V4 microprocessor with a 16-kB cache, a bank of 64-kB SRAM ICs, and an I/O interface IC. The four custom chips were fabricated in a standard 0.6-/spl mu/m 3-metal CMOS process. The system can dynamically vary the supply voltage from 1.2 to 3.8 V in less than 70 /spl mu/s. This provides a throughput range of 6-85 MIPS with an energy consumption of 0.54-5.6 mW/MIP yielding an effective energy efficiency as high as 26200 MIPS/W.

Intracellular calcium levels correlate with speed and persistent forward motion in migrating neutrophils

The relationship between cytosolic free calcium concentration ([Ca2+]i) and human neutrophil motility was studied by video microscopy. Neutrophils stimulated by a uniform concentration of an N-formylated peptide chemoattractant (f-Met-Leu-Phe) were tracked during chemokinetic migration on albumin, fibronectin, and vitronectin. [Ca2+]i buffering with quin2 resulted in significant decreases in mean speed on albumin. To further characterize the relationship between [Ca2+]i changes and motility we carried out a cross-correlation analysis of [Ca2+]i with several motility parameters. Cross-correlations between [Ca2+]i and each cell's speed, angle changes, turn strength, and persistent forward motion revealed (i) a positive correlation between [Ca2+]i and cell speed (p < 0.05), (ii) no significant correlation between turns and calcium spikes, and (iii) the occurrence of turns during periods of low speed. Significant negative correlations between [Ca2+]i and angle change were noted on the high adhesion substrates vitronectin and fibronectin but not on the low adhesion substrate albumin. These data imply that there is a general temporal relationship between [Ca2+]i, speed, and persistent motion. However, the correlations are not sufficiently strong to imply that changes in [Ca2+]i are required proximal signals for velocity changes.