Effect Of Pulse Length Research Articles

Numerical simulations of the effect of record field pulse length on medium coercivity at finite temperatures

Thin film media under consideration for high density recording in the range of 5 Gbit/in/sup 2/ and beyond will utilize extremely small grains in order to achieve acceptable signal-to-noise ratio limits. Numerical simulations of the reversal process including thermal fluctuations are utilized to determine medium coercivity versus field duration. Typically media with grain diameter 10 nm will have a 23% decrease in coercivity over a 1-100 nsec range.

Measurements of differential scattering cross section using a ring transducer.

A procedure for the measurement of intrinsic scattering object properties is presented and used to obtain illustrative results. The procedure is based on the measurement of the scattered acoustic field as a function of scattering angle and frequency. Measurements are normalized using analytically determined expressions for emitter and detector beams resulting from a combination of unfocused linear elements arranged in a circular configuration. The spatial effects of finite emitter pulse length and detector gate length are represented by a convolution formula valid for narrow-band transmitted signals and long receiver gates. The normalization includes correction for target absorption as well as measurement of the directly transmitted acoustic power in the free field and yields the average differential scattering cross section per unit volume. Under the Born approximation, this quantity is directly proportional to the spatial-frequency spectrum of the scattering medium inhomogeneities. Measured results are reported for two phantoms consisting of glass microspheres embedded in a weakly absorbing agar background medium. For the phantoms employed, scattering effects, rather than increased absorption, are shown to account for most of the difference in transmission loss between pure agar and agar with glass spheres. The measured differential scattering cross sections are compared with theoretical cross sections for distributions of glass spheres measured experimentally. The measured values show good relative agreement with theory for varying angle, frequency, and phantom properties. The results are interpreted in terms of wave space resolution and the potential for tissue characterization using similar fixed transducer configurations.

Simultaneous Removal of NOx and SO2 from Combustion Flue Gas by Pulsed Electron Beams

This paper presents the results of plasma chemistry calculations to study the effect of dose rate, pulse length and pulse repetition rate on pulsed electron beam processing of NOx and SO2 in combustion flue gases. The main objective is to determine if the proposed combinations of dose rate, pulse length and pulse repetition rate would have any deleterious effect on the utilization of radicals for pollutant removal. For a dose rate of 2 × 106 kGy per second and a pulse length of 30 nanoseconds, the average dose per pulse is sufficiently low to prevent any deleterious effect on process efficiency because of radical-radical recombination reactions. During each post-pulse period, the radicals are utilized in the oxidation of NOx and SO2 in a timescale of around 200 microseconds; thus, with pulse frequencies of around 5 kilohertz or less, the radical concentrations remain sufficiently low to prevent any significant competition between radical -pollutant and radical - radical reactions. The main conclusion is that a pulsed electron beam reactor, operating with a dose rate of 2 × 106kGy per second, pulse length of 30 ns and pulse repetition rate of up to around 5 kHz, will have the same plasma chemistry efficiency as an electron beam reactor operating with a very low dose rate in continuous mode

Transient thermal stability of the x-ray mask SiC-W under short pulse irradiation

The transient thermal stability of x-ray mask SiC-W has been numerically studied with special reference to the effect of silicon carbide (SiC) thermal conductivity. This paper presents the transient modeling of an x-ray lithography mask undergoing short x-ray pulses (from a laser plasma or similar source). The computations based on a finite element method are performed for a SiC-W mask under a helium gas environment using powerful analytical capabilities of NISA®. Heat generated in the mask membrane, a tungsten absorber, and helium during x-ray exposure is taken into consideration for the transient thermal stability simulation. Parametric studies are performed to identify the effects of the SiC's thermal conductivity, pulse length, x-ray wavelength and pulses repetition rate. Three thermal conductivity values of SiC were studied: 0.41, 1.9 and 3.5 W/cm °C. The temperature distributions obtained were used as input in order to study the mechanical deformations of the membrane and absorber. A three-dimensional finite element models are developed to analyze the heat transfer mechanisms in the mask and mapping the mask distortions resulting from the short pulse irradiation. Results show that pattern thermal distortion can be minimized if low thermal conductivity of the deposit SiC membrane was obtained.

Velocity measurements in a ceramic candle filter element undergoing pulse cleaning

Ceramic candle filters have been developed for cleaning high-temperature gas streams. They have demonstrated high collection efficiencies under normal operating conditions, but the brittle materials can fail suddenly with disastrous consequences. Reverse pulse cleaning has been shown to introduce severe thermal stressing of the material. Modelling of the flows to estimate the life of the element is difficult due to non-uniformities in the material. It is important to obtain experimental measurements of flows in the candle to provide input to stress models. In addition it is essential to ensure uniform cleaning of the filter and knowledge of the pulse cleaning flow processes are also important for this. This paper reports velocity measurements obtained using a hot-wire probe located at different positions along the length of a ceramic candle filter. The data have been analysed to estimate the outflow along the length of the candle filter to investigate the cleaning potential of different configurations and operating parameters. The effect of pulse length on cleaning performance was investigated for cases with and without a venturi educer. It was found that the maximum peak mean velocity was produced at a pulse duration of 0.2 s. Longer duration pulses did not have a significant influence on the maximum velocity levels inside the filter.

Effects of pulse length and strength on electroporation efficiency.

Electroporation is now a standard method of transfection and cell loading. There is a variety of commercial electroporation equipment, and many published and manufacturer-supplied protocols. Many of these protocols are results of trial and error. These empirical protocols are valuable guides for successful applications of electroporation. Because experimental conditions vary case by case, new and modified protocols are constantly needed to optimize the transfection yield. Developing new protocols for new cases by trial and error in each laboratory is wasteful in terms of time and energy. This chapter is intended to present a guide, based on known theories of electroporation, to help users modify existing protocols and develop new protocols for new applications. Succeeding in doing so would take some guess work out of experimental trials in tailoring protocols for individual case needs.

Effects of pulse length and strength on electroporation efficiency.

AbstractElectroporation is now a standard method of transfection and cell loading. There is a variety of commercial electroporation equipment, and many published and manufacturer-supplied protocols. Many of these protocols are results of trial and error. These empirical protocols are valuable guides for successful applications of electroporation.KeywordsTransfection EfficiencyPulse Electric FieldBreakdown PotentialMembrane PermeationPore EdgeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Measurements of peak power enhancement and power conservation in magnetically gain-modulated chemical oxygen-iodine laser

A periodically pulsed regime of the magnetically gain-switched chemical oxygen iodine laser was investigated. The effects of different magnetic field intensity and pulse length on the laser power pulse enhancement and the mean power conservation were studied experimentally.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Pulse length effects on the transmissivity of bubbly water

The passage of sound through bubbly water is strongly attenuated by scattering and absorption. Such attenuation is most severe around the frequency of resonance of individual bubbles. A bubble takes a finite time to ring up to steady-state conditions and continues to oscillate for a finite time after the driving pressure ceases. Low backscatter for short pulse lengths has been observed in near-surface seawater [Akulichev et al., Sov. Phys. Acoust. 32 (3), 177–180 (1986)]. An experiment is described that looked for a corresponding enhancement in transmission. Comparisons were made between the attenuations of brief waveform bursts and longer bursts. The center frequency of this experiment was 120 kHz. The bubbles were made by the electrolysis of fresh water in a small laboratory tank. For bursts from 6 to 20 cycles in duration, no difference in the attenuations was discerned in comparison with a 2.6-oscillation burst.

Further studies on beam breakup growth reduction by cavity cross-couplings in recirculating accelerators: effects of long pulse length and multiturn recirculation

Cavity cross-coupling was recently found to reduce beam breakup (BBU) growth in a recirculating accelerator known as the Spiral Line Induction Accelerator (SLIA). Here, we extend the analyses in two respects: long beam pulse lengths and a SLIA upgrade geometry which accelerates a 10 kA, 35 ns beam to 25 MeV via a 70 cavity, 7 turn recirculation. We found that when the beam pulse length τ exceeds the beam's transit time τ′ between cross-coupled cavities. BBU growth may be worsened as a result of the cross-couplings among cavities. This situation is not unlike other long pulse recirculating accelerators where beam recirculation leads to beam breakup of a regenative type. Thus, the advantage of BBU reduction by cavity cross-coupling is restricted primarily to beams with τ<τ′, a condition envisioned for all SLIA geometries. For the 70 gap, 7 turn SLIA upgrade, we found that cavity cross-coupling may reduce BBU growth up to factors of a thousand when the quality factor Q of the deflecting modes are relatively high (like 100). In these high Q cases, the amount of growth reduction depends on the arrangement and sequence of beam recirculation. For Q⪅20, BBU growth reduction by factors of hundreds is observed, but this reduction is insensitive to the sequence of beam recirculation. The above conclusions were based on simple models of cavity coupling that have been used in conventional microwave literature. Not addressed is the detail design consideration that leads to the desired degree of cavity coupling.

Pulse length effects on the transmissivity of bubbly water

The passage of sound through bubbly water is strongly attenuated by scattering and absorption. Such attenuation is most severe around the frequency of resonance of individual bubbles. A bubble takes a finite time to ring up to steady‐state conditions and continues to oscillate for a finite time after the driving pressure erases. Low backscatter for short pulse lengths has been observed in near‐surface seawater [Akulichev et al., Soc. Phys. Acoust. 32, no. 3]. An experiment is described that looked for a corresponding enhancement in transmission. Comparisons were made between the attenuations of brief waveform bursts and longer bursts. The frequency range of this experiment was 50–200 kHz. The bubbles were made by the electrolysis of fresh water in a small laboratory tank. For bursts of 6–20 wavelengths in duration, no difference in the attenuations was discerned in comparison with a 2.7 wavelength duration burst. [Work supported by ONR.]

Displaying the results from NMR pulse sequence simulations as stereo diagrams

In some situations, it is so easy to simulate a pulse sequence that the simulation is done even before one has developed an experimental “feel” for the imperfections of a given pulse sequence. Recalling the pedagogical nature of Bloch diagrams, it is beneficial to display calculated spin magnetizations in a similar manner. However, for spin systems with the potential for dipolar or quadrupolar order, the length and the, orientation of the spin magnetization vectors are variable. To indicate both the length and the orientation of a vector on a 2D display, be it on paper or a computer screen, requires some three-dimensional visual cuing. Herein, the possibilities of stereo diagrams are explored. Stereo diagrams are most commonly seen by chemists as ORTEP diagrams of crystal structures ( 1). As is known to many chemists, stereo diagrams may be viewed with the aid of a low-cost stereo viewer (2) or without any aid whatsoever, using the technique of naked-eye stereopsis (3). Naked-eye stereopsis is an easily learned technique for many people. As an introduction to stereo diagrams, the evolution of the deuterium spin magnetization for a solution-state spin-echo pulse sequence, 90,” -~~-180,0T~-ACQ, with e2qz,Q/ h = 0 kHz, is shown in Fig. 1. As the off-resonance condition increases, finite pulse length effects reduce the refocusing efficiency of the spin-echo pulse sequence. Since the quadrupole coupling constant is zero, there can be no quadrupolar order; thus the length of the spin magnetization vector will be constant, in the absence of relaxation effects, and equal to the equilibrium magnetization, MO. The radius of the sphere is set equal to MO. “X” marks the spot on the trace where signal acquisition is to begin. In viewing the stereo diagram with naked-eye stereopsis, the instructions of J. C. Speakman are helpful (3): “look at the diagram from your normal reading distance, with spectacles if these be worn ordinarily; be careful to keep the horizontal line relating the pair parallel to a line connecting your eyes. To foster the illusion, at first, it may help to hold a piece of card (say, 20 cm X 8 cm) as an extension of the nose, so that the right eye sees only the right-hand picture, and ‘vice versa’. Be sure the diagram is well illuminated and free from unilateral shadows cast by the card. When

Progress report on the Beijing FEL project

The progress of the Beijing IR-FEL project carried out at IHEP is reported. Some specific developments of software and hardware are described, rather than striving for general coverage. First, computational studies of the effects of emittance and pulse length on the small-signal gain are presented. Then some experimental results for the microwave electron gun injector are given. Modifications of the beam transport system and the optimization and measurements of the NdFeB undulator are described. Finally, some aspects of the beam diagnostics and a spontaneous-emission experiment are discussed.

Finite pulse length effects in quadrupolar CPMG sequences

Finite pulse length effects in quadrupolar CPMG sequences

Transient electric birefringence measurements of the rotational and internal motions of a 1010 base pair DNA fragment - field strength and pulse length effects

Transient electric birefringence measurements of the rotational and internal motions of a 1010 base pair DNA fragment - field strength and pulse length effects

Effect of pulse length on efficiency of CO2 laser interaction with a target in air

Effect of pulse length on efficiency of CO2 laser interaction with a target in air

Isoelectronic bound excitons in In- and T1-doped Si: A novel semiconductor defect

We present the results of detailed transient photoluminescence measurements on the isoelectronic bound excitons associated with the deep acceptors In and T1 in Si. The novel results are explained in terms of a model in which the binding centers can exist in more than one configuration, and in which the bound excitons can make transitions from one configuration to the other. Although the nature of the binding center and the exciton states is not yet known, the transient results are well described by rate equations based upon this model. Additional support is provided by a study of the effects of excitation pulse length on the Si:In transient results, as well as by comparing above-gap excitation versus resonant excitation of the bound excitons.

The practical design of ultrasonic test tanks

A systematic approach to the design of ultrasonic test tanks is outlined in which criteria are given first for the choice of tank length and subsequently for the choice of tank width and height. Calculations are presented for typical transducer beam measurements in the low megahertz frequency range, indicating the individual and combined effects of side lobe inclusion and excitation pulse length. The methods used may be easily extended to determine, for a given situation, either the minimum tank size that needs to be used, or the limits imposed by an existing tank on the experiments that can be performed in it.

The effect of pulse length on transient cavitation inception

Most ultrasonic systems used for diagnostic purposes employ short acoustic pulse rather than cw operation in order to accomplish imaging or Doppler scanning. It is also commonly thought that these short‐pulse systems, although driven at high acoustic pressure amplitudes, do not induce cavitation effects due to the low duty cycle of the ultrasound. Although stable cavitation typically requires cw operation for its effects to be present, transient cavitation can theoretically occur in pulse lengths as short as one cycle. We have developed a detection scheme utilizing sonoluminescence to observe the cavitation produced by pulses of varying length and repetition rate. Normal detection methods that examine noise emitted by the collapsing cavity can not be used in short‐pulse excitation due to the high spectral content of the pulse itself. We have observed transient cavitation effects (sonoluminescence) in pulse lengths as low as a few tens of cycles and are modifying our apparatus to go to even shorter pulses. [Work supported in part by the ONR and the NSF.]

Effect of gas pressure and pulse length on the isotopically selective multiphoton dissociation of CF3Cl under CO2 laser pulses

The multiphoton dissociation of CF3Cl induced by TEA-CO2 laser pulses has been studied in a focused beam geometry. TheR(10) [00°1–02°0] (\(\bar v = 1071.9cm^{ - 1} \)) laser line was used, so as to dissociate preferentially the minor isotopic component13CF3Cl. The isotopic selectivityS and the dissociation probability per pulse ω were measured in the pressure range between 0.25 and 8 Torr. With short laser pulses (90 ns FWHM),S is found to increase slightly with gas pressure up to 2 Torr, and ω, to increase almost linearly over the whole pressure range studied. A schematic model is proposed which satisfactorily explains these results if the transition rates across the energy level spectrum of the CF3Cl molecules are assumed to increase with gas pressure.