Reduction Of Transients Research Articles

Switching Modes for Reduction of Peak Voltage Transients in GaN-Based Three Level ANPC Inverter

Switching Modes for Reduction of Peak Voltage Transients in GaN-Based Three Level ANPC Inverter

About ghost transients in spatial continuous media

The impact of space on ecosystem dynamics has been a matter of debate since the dawn of theoretical ecology. Several studies have revealed that space usually involves an increase in transients’ times, promoting the so-called supertransients. However, the effect of space and diffusion in transients close to bifurcations has not been thoroughly investigated. In non-spatial deterministic models such as those given by ordinary differential equations transients become extremely long in the vicinity of bifurcations. Specifically, for the saddle–node (s–n) bifurcation the time delay, τ, follows τ∼|μ−μc|−1/2; μ and μc being the bifurcation parameter and the bifurcation value, respectively. Such long transients are labeled delayed transitions and are governed by the so-called ghosts. Here, we explore a simple model with intra-specific cooperation (autocatalysis) and habitat loss undergoing a s–n bifurcation using a partial differential equations (PDE) approach. We focus on the effects of diffusion in the ghost extinction transients right after the tipping point found at a critical habitat loss threshold. Our results show that the bifurcation value does not depend on diffusion. Despite transients’ length typically increase close to the bifurcation, we have observed that at extreme values of diffusion, both small and large, extinction times remain long and close to the well-mixed results. However, ghosts lose influence at intermediate diffusion rates, leading to a dramatic reduction of transients’ length. These results, which strongly depend on the initial size of the population, are shown to remain robust for different initial spatial distributions of cooperators. A simple two-patch metapopulation model gathering the main results obtained from the PDEs approach is also introduced and discussed. Finally, we provide analytical results of the passage times and the scaling for the model under study transformed into a normal form. Our findings are discussed within the framework of ecological transients.

The influence of reduced cross-section on pressure transients from high-speed trains intersecting in a tunnel

Alleviation of the pressure transients caused by high-speed trains intersecting in a tunnel with partially reduced cross-section is investigated by numerical simulation. The RNG k-ε turbulence model and hybrid grid are adopted for the numerical simulation, which is validated by the moving model test. Two factors, the length of reduced section (L) and the train marshalling number, are considered to analyse the alleviation effect. The results show that, for reduction of the pressure transients induced by the intersection of three-car marshalling trains, the location of the change in cross-section is supposed to be near the location of the maximum value of the initial expansion wave (L → 240 ​m). In addition, for four-car marshalling trains intersecting in a tunnel of L ​= ​240 ​m, the excavation volume of the tunnel (tunnel volume) decreases by 14.4%, and the average pressure amplitude on the train surface decreases by 7.9%. Especially the pressure amplitude at the measurement point in the streamlined area of the tail car decreased by 28.6%. The reduced section tunnel has a good effect on decreasing the pressure transients around train body and the tunnel excavation volume (construction cost), which helps the tunnel design process.

Reduction of transients in switches using embedded machine learning

<p>Non-linear loads can cause transients in electronic switches. They also result in a fluctuating output when the device is switched ON or OFF. These transients can harm not only the switches but also the devices that they are connected to, by passing excess currents or voltages to the devices. By applying machine learning, we can improve the gate drive voltages of the switches and thereby reduce switch transients. A feedback system is built that measures the output transients and then feeds it to a neural network algorithm that then gives a proper gate drive to the device. This will reduce transients and also improve performances of switch based devices like inverters and converters.</p>

Thrust stand based on a single point load cell for impulse measurements from plasma thrusters.

We introduce a simple thrust stand for the direct measurement of the millinewton impulses or thrusts delivered by small thrusters intended for in-space electric propulsion. The thruster under test, with a weight below 1.5 kg, is disposed on a horizontal platform and its impulse is measured as an overweight by using a strain gauge cell physically protected from the ambient plasma and vacuum conditions. This system provides ten thrust readings per second with noise peak to peak amplitudes of 0.10-0.18 mN. The calibration procedures to verify its dynamic response to time dependent thrusts in the range of 0-15 mN using control weights as well as its minimum thrust sensitivity δTs = 0.3 mN are discussed. Additionally, its simple conception permits a plain data reduction and analysis of steady state and low frequency thrust transients. This thrust stand was employed under low pressure and plasma ambient conditions to measure the steady impulses delivered by the Alternative Low Power Hybrid Ion Engine (ALPHIE) of 0.4-4.0 mN with absolute errors ΔT = ±0.3 mN. Finally, the experimental results show that a control electric voltage governs the ALPHIE thruster throttle.

Reduction of pressure transients of high-speed train passing through a tunnel by cross-section increase

This study investigates the alleviation effect of partially enlarged cross-section on tunnel aerodynamics. By comparing the numerical results to moving model tests data, the SST k-ω turbulence model and hybrid grid are used for the numerical simulations of high-speed train passing through tunnel. The reduction effects of three parameters for the enlarged section are analyzed, i.e., length, cross-sectional area, and slope. Systematic numerical simulations show that the terminal location of the enlarged section should be close to the location of the initial compression wave amplitude along tunnel length direction. The reduction rates of the pressure transient amplitude and the average pressure variation follow a second order polynomial equation with the increase of the enlarged section area, and increase with the increase of enlarged section slope. Positive enlarged section slope is applied for reducing pressure transients in the tunnel. Furthermore, an engineering application equation is proposed, with which the reduction rates of enlarged sections on the pressure transient amplitude and the average pressure variation can be estimated effectively. The equation generalized in this study could well guide the tunnel design process.

Reduction of transients during lifting based spatial switching of two-channel filter banks

Time/space varying filter banks (FBs) are useful for non-stationary images. Lifting factorization of FBs results in structural perfect reconstruction even during the transition from one FB to other. This allows spatial switching between arbitrary FBs, avoiding the need to design border FBs. However, we show that lifting based switching between arbitrarily designed FBs induces spurious transients in the subbands during the transition. In this paper, we study the transients in lifting based switching of two-channel FBs. We propose two solutions to overcome the transients. One solution consists of a boundary handling mechanism to switch between any arbitrarily designed FBs, while the other solution proposes to design the FBs with a set of conditions applied on lifting steps. Both solutions maintain good frequency response during the transition and eliminate the transients. Using the proposed methods, we develop a spatial adaptive transform by switching between the long length FBs (either the JPEG2000 9/7 FB or the newly designed 13/11 FB) and the short length FBs (JPEG2000 5/3 FB) for lossy image compression. This adaptive transform shows PSNR improvement for images over JPEG2000 9/7 FB in low bit rate region (up to 0.2bpp) and subjective improvements with reduced ringing up to medium bit rates (up to 0.6bpp).

Mechanically Stable Lipid Bilayers in Teflon-Coated Silicon Chips for Single-Channel Recordings

We demonstrate the microfabrication of a low-noise silicon (Si) chip as a platform for suspending mechanically stable bilayer lipid membranes (BLMs). Microapertures with smoothly tapered edges were formed by isotropic etching in a silicon nitride layer deposited on a Si substrate. The surface of the Si chip was coated with insulator layers of Teflon and SiO2. The insulator coating worked to reduce the total capacitance, leading to noise reduction (1-2 pA in peak-to-peak after low-pass filtering at 1 kHz) and elimination of current transients ( < 0.5 ms). Since the tapered edges were necessary to maintain mechanically stable BLMs, the entire chip except for the aperture was coated with the insulators. Owing to this process, the BLMs formed in the Si chips still showed high mechanical stability after coating with the insulator layers. The membranes withstood high applied voltage (±1 V) and mechanical shocks during solution exchanges. The mechanically stable BLMs having electric properties suitable for recording activities of biological channels will open up a variety of applications including high-throughput analysis of ion-channel proteins. Keywords: Planar bilayer lipid membranes, single-channel recording, microfabrication, Teflon fabrication., low-noise silicon, BLMs, Fabrication, Insulator Coatings

Mechanically Stable Free-Standing Bilayer Lipid Membranes in Microfabricated Silicon Chips

ABSTRACTIn this paper, we will discuss our recent approaches for improving the mechanical stability of free-standing bilayer lipid membranes (BLMs) by combining with BLM formation and microfabrication techniques. BLMs were prepared across a microaperture fabricated in a silicon (Si) chip and their mechanical stability and electric properties were investigated. BLMs suspended in a thin Si3N4 septum showed a dramatic improvement of BLM stability. The BLMs were resistant to voltage of ±1 V and the membrane lifetime was 15- ~40 h with and without incorporated channels. The membrane containing gramicidin channel exhibited tolerance to repetitive solution exchanges. At first, electric properties of the BLMs, such as noise level and current transient, were necessary to be improved. However, after coating the chip with insulator layers of Teflon and SiO2, total chip capacitance was reduced, leading to noise reduction (1-2 pA in peak-to-peak after low-pass filtering at 1 kHz) and elimination of current transients (&lt; 0.5 ms). Since the vicinity of the aperture edge was remained uncoated, the BLMs formed in the Si chips still showed high mechanical stability after the insulator coatings. The mechanically stable BLMs having electric properties suitable for recording activities of biological channels will open up a variety of applications including high-throughput analysis of ion-channel proteins.

Investigating the Performance of Shunt FACTS for the Operation of Induction Motors under Different Voltage Sag Conditions

Shunt FACTS devices are prevalent in industrial application of induction motors. These equipments are effective to compensate disturbances and increase motor speeding up. In this study an assessment study between two different shunt FACTS (SVC and STATCOM) installed on terminals of motor is done. A conventional PI controller is used to control the thyristor firing angle of SVC or phase angle of STATCOM. A pole placement method is applied to specify the perfect gain settings of the controllers. The results of simulations display that STATCOM has better response over SVC for improving dynamic behavior of induction motor under ideal supply conditions. Power quality problem that influence the dynamic behavior of induction motor, include non ideal conditions such as harmonics, interruptions, voltage unbalance and voltage sags. Whereas voltage sags is one of the main cause of disturbances in distribution systems, the performances of the induction motor under symmetrical and unsymmetrical voltage sags are investigated in this study. The results prove that STATCOM is more effectual than SVC for reduction of transients and refinement the voltage profile.

PWM Dead Time Optimization Method for Automotive Multiphase DC/DC-Converters

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper introduces a PWM dead time optimization method for multiphase DC/DC-converters with synchronous rectifiers. The aim of the method is to reduce power losses. After a perturbation of the dead times in one converter phase, the phase-currents starts to deviate, whereby the most efficient phase has the higher current. A current balancing controller compensates for this deviation by adjusting duty cycles. Consequently, optimal dead times can be detected by duty cycle differences of the phases. The proposed optimization approach was implemented in a two-phase boost-/buck converter prototype for automotive dual-voltage power-nets. No additional components or circuit modifications were necessary. The detection of optimal dead times, increasing efficiency and reduction of voltage transients are discussed and investigated experimentally. </para>

North Pacific cyclonic and anticyclonic transients in a global warming context: possible consequences for Western North American daily precipitation and temperature extremes

Trajectories of surface cyclones and anticyclones were constructed using an automated scheme by tracking local minima and maxima of mean daily sea level pressure data in the NCEP-NCAR reanalysis and the Centre National de Recherches Meteorologiques coupled global climate Model (CNRM-CM3) SRES A2 integration. Mid-latitude lows and highs traveling in the North Pacific were tracked and daily frequencies were gridded. Transient activity in the CNRM-CM3 historical simulation (1950–1999) was validated against reanalysis. The GCM correctly reproduces winter trajectories as well as mean geographical distributions of cyclones and anticyclones over the North Pacific in spite of a general under-estimation of cyclones’ frequency. On inter-annual time scales, frequencies of cyclones and anticyclones vary in accordance with the Aleutian Low (AL) strength. When the AL is stronger (weaker), cyclones are more (less) numerous over the central and eastern North Pacific, while anticyclones are significantly less (more) numerous over this region. The action of transient cyclones and anticyclones over the central and eastern North Pacific determines seasonal climate over the West Coast of North America, and specifically, winter weather over California. Relationships between winter cyclone/anticyclone behavior and daily precipitation/cold temperature extremes over Western North America (the West) were examined and yielded two simple indices summarizing North Pacific transient activity relevant to regional climates. These indices are strongly related to the observed inter-annual variability of daily precipitation and cold temperature extremes over the West as well as to large scale seasonally averaged near surface climate conditions (e.g., air temperature at 2 m and wind at 10 m). In fact, they represent the synoptic links that accomplish the teleconnections. Comparison of patterns derived from NCEP-NCAR and CNRM-CM3 revealed that the model reproduces links between cyclone/anticyclone frequencies over the Northeastern Pacific and extra-tropical climate conditions but is deficient in relation to tropical climate variability. The connections between these synoptic indices and Western weather are well reproduced by the model. Under advanced global warming conditions, that is, the last half of the century, the model predicts a significant reduction of cyclonic transients throughout the mid-latitude North Pacific with the exception of the far northern and northeastern domains. Anticyclonic transients respond somewhat more regionally but consistently to strong greenhouse forcing, with notably fewer anticyclones over the Okhotsk/Kamchatka sector and generally more anticyclones in the Northeastern Pacific. These modifications of synoptic weather result in regional feedbacks, that is, regional synoptic alterations of the anthropogenic warming signal around the North Pacific. In the eastern Pacific, for example, synoptic feedbacks, having to do especially with the northward shift of the eastern Pacific storm-track (responding, in turn, to a weaker equator-to-pole temperature gradient), are favorable to more anticyclonic conditions off the American mid-latitude west coast and more cyclonic conditions at higher latitudes. These circulation feedbacks further reduce the equator-to-pole temperature gradient by favoring high-latitude mean winter warming especially over a broad wedge of the Arctic north of the Bering Sea and moderating the warming along the mid-latitude west coast of north America while also reducing precipitation frequencies from California to Northern Mexico.

Fluid Shear Stress Induces Less Calcium Response in a Single Primary Osteocyte Than in a Single Osteoblast: Implication of Different Focal Adhesion Formation

The immediate calcium response to fluid shear stress was compared between osteocytes and osteoblasts on glass using real-time calcium imaging. The osteoblasts were responsive to fluid shear stress of up to 2.4 Pa, whereas the osteocytes were not. The difference in flow-induced calcium may be related to differences in focal adhesion formation. To explore the immediate response to mechanical stress in a bone cell population, we examined flow-induced calcium transients. In addition, the involvement of focal adhesion-related calcium transients in response to fluid flow in the cells was studied. Bone cells were isolated from 16-day-old embryonic chicken calvaria by serial treatment with EDTA and collagenase. Single cells on glass without intercellular connections were subjected to fluid flow, and intracellular calcium concentration was measured using imaging with fluo-3. The identification of cell populations in the same field was performed with a chick osteocyte-specific antibody, OB7.3, and an alkaline phosphatase substrate, ELF-97, for osteoblast identification afterward. Immunofluorescence staining of vinculin was performed to visualize focal adhesions. The percentage of cells responding to fluid shear stress at 1.2 Pa was 5.5% in osteocytes, 32.4% in osteoblasts, and 45.6% in OB7.3/ELF-97-negative cells. Furthermore, osteoblasts and OB7.3/ELF-97-negative cells were more responsive to 2.4 Pa than 1.2 Pa, whereas osteocytes were less responsive. The elevation of calcium transients over baseline did not show any significant differences in the populations. To elucidate the mechanism accounting for the fact that single osteocytes are less sensitive to fluid shear stress of up to 2.4 Pa than osteoblasts, we studied focal adhesion-related calcium transients. First, we compared focal adhesion formation between osteocytes and osteoblasts and found a larger number of focal adhesions in osteoblasts than in osteocytes. Next, when the cells were pretreated with GRGDS (0.5 mM) before flow treatment, a significant reduction of calcium transients in osteoblasts (18%) was observed, whereas calcium transients in osteocytes were not changed by GRGDS. Control peptide GRGES did not reduce the calcium transients in either cell type. Furthermore, we confirmed that osteoblasts in calvaria showed a marked formation of vinculin plaques in the periphery of the cells. However, osteocytes in calvaria showed faint vinculin plaques only at the base of the processes. On glass, single osteocytes are less sensitive to fluid shear stress up to 2.4 Pa than osteoblasts. The difference in calcium transients might be related to differences in focal adhesion formation. Shear stress of a higher magnitude or direct deformation may be responsible for the mechanical response of osteocytes in bone.

Reduction of Transients between Steady States in the Continuous Production of High-Impact Polystyrene

This work theoretically investigates the reduction of transients during changes of grade in a continuous plant for the production of high-impact polystyrene (HIPS). A mathematical model was developed that predicts the global molecular structure and the melt flow index (MFI). The switching times of the off-specs accumulation period were selected on the basis of the admissible MFI ranges. Smoother transitions and reduced off-specs can be produced through a simple readjustment (with respect to the original plant policy) of the two intermediate chain transfer agent (CTA) loads into the batch dissolver. For the transitions that involve a large difference in their MFIs, the off-specs can be reduced by 60%, with respect to the original plant policy, by including a transient feed of CTA into an intermediate stirred reactor.

Reduction of amplitude transients and BER of direct Modulation laser using birefringent fiber loop

A birefringent fiber loop (BFL) is proposed to improve the signal from a directly modulated distributed feedback laser. The BFL is a simple and passive fiber device. The BFL reduces amplitude transients, frequency chirp, and pattern dependence. It also improves the extinction ratio of the directly modulated optical signal. We show that the BFL effectively extends the 10-Gb/s transmission range to 25 km at 1550-nm wavelength over conventional single-mode fiber.

Modelling and identification for reduction of overvoltage transients

The main problems that appear when using a long cable connection between a variable frequency drive (VFD) and the AC motor are overvoltages and bearing currents. The latter concerns especially EMC, while the overvoltage transients can be fatal to the motor. The ‘converter–cable–motor’ system behaviour concerning overvoltages is investigated and then an on-line identification of the cable parameters is proposed. This result could be used to reduce overvoltages. An algorithm is introduced that decreases the amplitude of the adverse overvoltage effect. The algorithm is based on the modification of the applied PWM pattern.

Evaluation of polyencapsulation, oxygen leak, and low energy ion bombardment in the reduction of secondary ion mass spectrometry surface ion yield transients

The accurate determination of dopant concentrations in the near-surface region of secondary ion mass spectrometry (SIMS) depth profiles is often complicated by surface ion yield transients. These ion yield transients, which result mainly from the implantation of the ion yield enhancing primary ion beam, can lead to errors in the quantification of impurity species as well as distortions in the dopant profile shape. Polyencapsulation, oxygen flooding, and matrix normalization have each proven to be useful in the reduction and elimination of these surface ion yield transients. The use of low primary beam energies has been shown to have the additional benefit of reducing profile broadening due to cascade mixing. In this study, three methods of transient reduction were evaluated in the SIMS characterization of ultra-shallow p+ junctions in Si (&amp;lt;1000 Å) using oxygen bombardment and positive secondary ion detection.

Video signals and switching transients in capacitor-photodiode and capacitor-phototransistor image sensors

A new configuration of the capacitor-photodiode type of image sensor is described which results in appreciable reduction of switching transients at the sensor's output. The modification consists of replacing the photodiode by a phototransistor operating in the common base configuration. A 32 × 32 element array capable of operating in either the photodiode or phototransistor mode was fabricated. The dynamic range, transfer characteristic, and switching transient voltage were calculated for both modes and compared with experiment. For the experimental array an order-of-magnitude improvement in signal-to-noise ratio has been realized in the transistor mode of operation.