Simultaneous Pulses Research Articles

Simultaneous propagation of heat waves induced by sawteeth and electron cyclotron heating power modulation in the RTP tokamak.

The incremental electron heat diffusivity ${\mathrm{\ensuremath{\chi}}}^{\mathrm{inc}}$ is determined in Rijnhuizen Tokamak Project plasmas by measurements of simultaneous heat pulses due to (1) the sawtooth instability and (2) modulated electron cyclotron heating. No systematic difference is observed between the two measured ${\mathrm{\ensuremath{\chi}}}^{\mathrm{inc}}$ values, which are both significantly larger (${\mathrm{\ensuremath{\chi}}}^{\mathrm{inc}}$/${\mathrm{\ensuremath{\chi}}}_{\mathit{e}}^{\mathrm{PB}}$=2-4) than the diffusivity obtained from power balance analysis, ${\mathrm{\ensuremath{\chi}}}_{\mathit{e}}^{\mathrm{PB}}$.

Elementary quanta of open systems

It is argued that elementary quanta of an open system are determined by the spectral decomposition of a thermodynamic Hamiltonian, not an ordinary Hamiltonian. Recently observed spectral shifts in semiconductors irradiated with two simultaneous laser pulses may be manifestation of this fundamental role of the thermodynamic Hamiltonian.

Design and performance of new instrumentation to measure the shielding capabilities of materials against electrostatic discharges

The shielding required to maintain a ‘static safe’ environment inside packaging used to transport semiconductor devices and microelectronic assemblies through uncontrolled environments needs to provide 1000:1 attenuation of electric field transients over the frequency range from 10 Hz to 1 GHz. The paper describes the principles, practical design features and the performance of a new method for assessing the characteristics of shielding materials and practical packages. The method described uses simultaneous positive and negative high electric field pulses of balanced amplitude and form to apply an electric stress across a defined width of material. With symmetrical pulses no nett charge is transferred to the layer under test. This means that the layer can be isolated from earth so the test is equally applicable to materials with surface or volume conductivity or with buried conducting layers. It also means that the signals observed on the reverse side of the layer have no common mode component. Attenuation performance is analysed as frequency components for each decade of frequency from 10 Hz to GHz. The problems of shot to shot variation of high voltage pulses are overcome by observing all frequency components simultaneously as the ratio of signals observed through the test material with those observed directly. The approach is effectively a single shot ratiometric spectrum analyser.

An 85-kJ high performance capacitor bank with double-mode trigatrons

The present article describes the constructional aspects of an 85-kJ capacitor bank at 20 kV for the production of pulsed high magnetic fields. The discharge current magnitude is 56 kA at a ringing frequency of 1.1 kHz. The bank employs 8 double-mode trigatrons in parallel which are triggered into conduction by the application of 16 simultaneous low jitter high voltage pulses generated by a multiple trigger pulse generator. The performance of the bank with double-mode trigatrons is compared with that obtained by conventional single-mode trigatrons. The waveforms of discharge current in time domain and fast fourier frequency spectrum for single- and double-mode trigatrons are presented and analyzed for performance evaluation. The performance with double-mode trigatrons is characterized by distinctly superior synchronization in the closing of trigatron switches over a wide range of operating voltage resulting in high peak discharge current and low waveform distortion.

Demonstration of nuclear recoil discrimination for low temperature dark matter detectors, by measurement of simultaneous ionization and thermal pulses in silicon

We report experiments using a silicon target exposed to a neutron source, giving both nuclear recoil events from neutron scattering and electron recoil events from photon scattering. We show that simultaneous measurement of ionization and thermal energy for each event allows the neutron and photon events to be separated. The degree of separation of the nuclear recoil events, and their absolute event rate, are consistent with theoretical expectation.

Mechanisms of electrostimulated plasticity during wire-drawing of stainless steel Kh18N10T

To clarify the mechanisms by-which current pulses affect plastic deformation, an electron-microscope study has been made of the evolution of the fine structure of steel Kh18N10T subjected to electrostimulated (current density 1200 MA/m2, frequency 200 Hz) and conventional wire-drawing at a speed of 1.88 m/sec with total reduction up to 58%. The evolution of the microstructure of steel during conventional plastic deformation of drawing is similar to that produced by conventional drawing and simultaneous current pulses. Quantitative characteristics of microstructure such as scalar dislocation density, azimuthal disorientation, and distance between subboundaries have been measured and statistically evaluated. The effect of the current is connected with the reduction of the scalar dislocation density and partial recovery of the substructure. Proposed models are supported by the data on microplastic deformation.

Metastable operation in RS flip-flops

A new model for representing the different types of behaviour exhibited by an RS flip-flop under metastable operation is presented. Although it reflects flip-flop transient operation, the new model handles logical variables instead of continuous time ones. The model is applied to flip-flops for both simultaneous input changes and runt pulses.

Analysis of multiple-pulse-based heteronuclear J cross polarization in liquids

Classical heteronuclear J cross polarization in liquids utilizing two CW RF fields has largely been replaced by pulse-interrupted free-precession methods because of difficulties in obtaining a Hartmann-Hahn match of the two fields within the size ofthe heteronuclear J coupling. Here previously suggested contact schemes are investigated in which both nuclei are subjected to sequences of simultaneous RF pulses. It is shown both experimentally and computationally that efficient cross polarization in liquids over a wide range of RF field mismatches can be obtained with these methods, and nonideal behavior is analyzed. Experimental results show that multiple-pulse-based J-cross-polarization spectra compare favorably in sensitivity, phase, and enhancement distribution with those obtained from pulse-interrupted free-precession methods. It is also shown that concurrent homonuclear/heteronuclear Hartmann-Hahn transfer can be achieved over a very wide bandwidth with these sequences.

LUTEINIZING HORMONE AND FOLLICLE STIMULATING HORMONE SECRETION PATTERNS IN GIRLS THROUGHOUT PUBERTY MEASURED USING HIGHLY SENSITIVE IMMUNORADIOMETRIC ASSAYS

Pulsatile gonadotrophin secretion patterns were studied in 36 healthy girls by measuring every 10 min and applying immunoradiometric assays (IRMA). Different stages of puberty were associated with significant changes in the plasma LH and FSH levels, pulse numbers (Pno) and pulse amplitudes (pA). Plasma LH was not detectable by day or night in young prepubertal girls (B1), neither was plasma oestradiol (E2); however, plasma FSH was detectable in a pulsatile pattern. In the older prepubertal girls (B1-onset) a discrete pulsatile LH pattern became detectable only during the night; plasma FSH tended to rise, while E2 became just detectable. In the early pubertal girls (B2) most daytime LH values were above the detection limit, in some with low-amplitude pulses. At night, pulses with a wide range of pulse amplitudes were detected. Plasma FSH increased further, plasma E2 only slightly. With the progression of puberty the plasma LH and FSH levels, Pno and pA increased significantly from stage B2 to B3 during the day (P less than or equal to 0.05) and close to significance during the night (0.05 less than or equal to P less than or equal to 0.1). However, in stage B4 the secretory characteristics tended to decline, while from stage B3 onwards plasma E2 started to rise rapidly (P less than or equal to 0.05, during the night from stage B2 to B3, during the day from B3 to B4m-). Simultaneous LH and FSH pulses were observed throughout puberty, usually during the night. Using these IRMA methods nocturnal LH in older prepubertal girls and both diurnal and nocturnal FSH pulsatility could be demonstrated in young prepubertal girls. From this study we conclude that (1) puberty in girls, as in boys, may be brought about by an increasing GnRH secretion both in frequency and amplitude, first appearing during the night. This increased GnRH stimulation results in LH secretion only during the night; (2) a cyclical pulsatile LH pattern including an LH surge can be established before the menarche; the capacity for positive feedback activity is not the final maturation characteristic to achieve an ovulatory menstrual cycle.

Simultaneous multivolume spectroscopy (simuvosp) using local techniques

MR spectra simultaneously acquired from different locations in the human body may be obtained with the SIMUVOSP technique (Simultaneous Multivolume Spectroscopy). SIMUVOSP is based on multifrequency selective RF pulses which encode positional information of the spins into the phase of the MR signal. This paper describes SIMUVOSP strategies for 1H, 31P and 13C spectroscopy. For 1H SIMUVOSP the STEAM experiment may be modified by replacing the selective RF pulses with SIMUFREX pulses (Simultaneous Multifrequency Excitation pulses). This modification allows the simultaneous spectroscopic examination of different regions in the human brain. For 31P SIMUVOSP the ISIS method is combined with SIMUFRIN (Simultaneous Multifrequency Inversion) pulses, which generate the inversion of multiple regions during the RF pulse. An application of 31P SIMUVOSP is the study of the metabolic heterogeneity of the high energy phosphates within the human body. For 13C spectroscopy a localized polarization transfer experiment is combined with multivolume excitation. In this way SIMUVOSP on protons is extended to 13C multivolume spectroscopy.

Three-dimensional N.M.R. correlation spectroscopy with selective radiofrequency pulses

Three-dimensional N.M.R. correlation spectroscopy makes it possible to identify three chemical species, I, S and R that have resolved scalar couplings. This experiment can be implemented by applying two simultaneous selective radiofrequency pulses that are scanned independently through narrow frequency ranges (F 1 and F 2) encompassing the I and S-spin chemical shifts. Coherence transfer signals are detected in the form of a three-dimensional cross-peak at the R-spin frequency. This soft-pulse experiment avoids the problem of very large three-dimensional data matrices implicit in the three-dimensional Fourier transform method. A product operator treatment is presented which indicates that coherence is transferred by way of an intermediate stage of pure zero-quantum or pure double-quantum coherence. Consequently, relative signs of coupling constants may be obtained by inspection of the fine structure of the cross-peaks. The predictions of the theory are borne out by experiments carried out on proton three-...

Pulsatile patterns of gonadotropins and ovarian steroids during estrus and pseudopregnancy in the rabbit.

Consecutive daily plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), estradiol-17 beta (E2), progesterone (P4) and 20 alpha-hydroxypregn-4-en-3-one (20 alpha-OHP) were monitored in estrous rabbits and in these same doses during pseudopregnancy (PSP); these daily hormone levels, as well as the immediate post-coital changes in gonadotropin secretion, were similar to those in previous reports. To examine the pulsatile patterns of the gonadotropins and ovarian steroids, sequential, 10-min plasma samples were collected for 6 h from estrous does and on Days 3, 10, and 17 of PSP. All five hormones were measured in the serial samples from estrous and PSP Day 10 does; LH and FSH only were assayed in the remaining sequential samples. The amplitude and frequency of FSH pulses did not differ between any of these stages. In marked contrast, LH pulse amplitudes, and even pulse frequencies in Day 17 does, were profoundly increased during PSP above those in estrous does. Progestin secretions, both P4 and 20 alpha-OHP, also were sharply elevated in PSP Day 10 does as compared with those in estrous rabbits; the pulse amplitudes of both progestins were severalfold higher during PSP. P4 pulse frequencies were also increased at this time. Conversely, the parameters of E2 secretion did not differ between estrous and PSP Day 10 animals. In PSP Day 10 does, high amplitude pulses of both P4 and 20 alpha-OHP occurred simultaneously with high amplitude LH pulses. Simultaneous E2 and P4 pulses were evident in these same sequential plasma samples, and this E2-P4 pulse association was greater than that of 20 alpha-OHP pulses with E2 pulses. Our findings failed to identify conclusively the trophic stimulus for the progestin pulse patterns, but the mechanism may involve the coordinated action of LH and E2. The results do demonstrate that each gonadotropin and ovarian steroid is secreted in a pulsatile manner in both estrous and pseudopregnant rabbits. There are altered profiles in LH and progestin pulses, without major changes in FSH and E2 patterns, between the stages of estrus and PSP. The causes and consequences of these divergent endocrine shifts cannot be deduced from these data.

Iontophoretic study of the action of excitatory amino acids on rod horizontal cells of the dogfish retina

Much interest has been focused on the amino acids, L-glutamate and L-aspartate, as possible neurotransmitters of vertebrate photoreceptors. These amino acids and a number of their analogues were applied iontophoretically to rod horizontal cells on the surface of dark-adapted dogfish retinal slices under visual control. L-glutamate and kainate were found to be of approximately equal potency in depolarizing rod horizontal cells, while L-aspartate was about one tenth as potent. Simultaneous iontophoretic pulses applied to two barrels, each containing either L-glutamate or kainate, produced a larger depolarization than expected for linear summation. Potentiation was most prominent when synaptic transmitter release was reduced by light, demonstrating that these agonists interact with the same postsynaptic receptors as those acted upon by the rod neurotransmitter. Analysis of dose—response curves indicated that at least two molecules of agonist were required to open a cationic channel, presumably the basis for the depolarization. The cells did not become desensitized to long or repeated exposures of the agonists.

ARE THERE SEVERAL PHOTORECEPTORS INVOLVED IN PHOTOTROPISM OF Phycomyces blakesleeunus? KINETIC STUDIES OF DICHROMATIC IRRADIATION*

Abstract— Photogeotropic equilibrium angles were measured for Phycomyces blakesleeanus wild type firstly by means of dichromatic fluence rate response curves using simultaneous irradiation with near threshold 450 nm reference light (constant at 1.2 × 10−8 W m−2) and variable fluence rates of test light (498–630 nm) from the same side. These curves showed minima for test light fluence rates that were close to the photogeotropic threshold for these wavelengths. Secondly, the time course of this inhibitory effect was studied with both the inductive reference 450 nm light (2 × 10−‐7 W m−2) and the test light (606 or 450 nm) given as light pulses of 2 s duration (2 s light/48 s dark periods for 6 h). The dark period between the onset of the inductive reference light and test light pulses was varied between 0 and 48 s. No inhibitory effects were observed for simultaneous pulses; however, inhibitory effects were demonstrated for delay times of 2 s and 20 s for 606 nm as well as 450 nm test light. If the test light pulses were given immediately before the inductive reference light, only 606 nm test light was effective in producing a significant inhibitory effect.The results are discussed with regard to a multichromophoric photoreceptor system and to the wavelength dependence of the effects observed. The data and conclusions favor a photoreceptor system with at least two separate chromophoric absorptions of the blue light receptor type, one acting positively, the other acting inhibitorily, and at least one other photoreceptor of presumably minor influence.

Simultaneous pulses in light and electric field from stepped leaders near ground level

During the summer of 1982 we used a collimated narrow slit and photomultiplier tube in conjunction with a broadband electric‐field system to study light and electric‐field signals from cloud‐to‐ground lightning flashes in Gainesville, Florida. For three flashes at a range of about 2 km, we observed correlated sequences of light and electric‐field pulses from sections of channel about 12 m long and about 80 m above ground for 50–100 μs prior to the first return strokes. These time intervals included all the leader light pulses that were recorded in each case. In one case there were at least nine distinct light pulses. Sometimes there were measurable electric‐field pulses preceding the first light pulse. Early or intermediate light pulses were the largest in amplitude. Electric‐field pulses generally increased in amplitude with time up to the return stroke. We interpret these observations as the result of leader steps passing through the field of view of the slit. Both light and electric‐field pulses occurred at intervals of 5–20 μs, had 10 to 90% risetimes of 0.5–0.9 μs, and had full widths at half maximum of 0.8–1.5 μs. We estimate that stepped‐leader speeds within 100 m of ground were between 0.8×106 and 3.9×106 m s−1.

Exact solitary-wave solution of short different-wavelength optical pulses in many-level atomic absorbers

A new exact result is presented on the lossless propagation of simultaneous different-wavelength optical pulses through an atomic medium with general $N$ energy levels in an extended $\ensuremath{\Lambda}$ or $V$ configuration.

Pulsatile, synchronous basal insulin and glucagon secretion in man.

The basal plasma insulin, glucagon, and glucose concentrations of 28 normal subjects were measured at 1-min intervals for periods of 45-120 min. Regular plasma insulin and/or glucagon cycles were detected in 11 subjects by autocorrelation (mean periods 13.1 and 13.7 min, respectively). Individual plasma insulin cycles were defined in all subjects (mean period 10.7 min, amplitude 1.1 mU/L), and were associated, after averaging, with plasma glucagon (amplitude 5.5 pg/ml) and plasma glucose (0.02 mmol/L) cycles. There was a significant correlation between the amplitudes of simultaneous plasma insulin and glucagon cycles (r = 0.23, P = less than 0.05, N = 124). Cross-correlation demonstrated a delay of 2 min between the changes in plasma insulin and glucagon. No comparable oscillations in plasma pancreatic polypeptide were detected. The synchronous pulsatile secretion of glucagon and insulin may be a mechanism by which insulin's hepatic effects are limited, thereby maintaining hepatic glucose production but allowing sufficient peripheral insulin concentrations to inhibit excessive catabolism. The simultaneous pulses of insulin and glucagon may be stimulated by a pacemaker, with the A-B intercellular connections producing insulin and glucagon synchrony.

Dual-Gate MESFET Variable-Gain Constant-Output Power Amplifier

The use of a dual-gate GaAs FET as a broad-band variable gain and constant output power amplifier is described. A five-stage variable gain-constant output power amplifier has been realized which provides a constant output power of 3 dBm (/spl plusmn/2 dB) for a large dynamic range of input power of -45 dBm to 0 dBm over the 4-8-GHz band. The amplifier uses a feed-forward AGC circuit for preadjusting the gain of the amplifier stages depending upon the strength of the signal at the output of preceding stages. The amplifier has the capability of detecting two or more simultaneous RF pulses having different amplitudes and separated by more than 15-ns time intervals. Also it preserves any amplitude modulation of the individual pulse.

Theory of lossless propagation of simultaneous different-wavelength optical pulses

Propagation of short different-wavelength optical pulses in many-level absorbers is studied. New analytic solutions to the appropriate Maxwell-Bloch equations having the form of simultaneous different-wavelength optical solitons, so called simulton solutions, have been found. In order for simulton propagation to occur, both the pulses and the medium have to be initially prepared in a manner determined by the medium's physical parameters. The analytic findings are extended with the use of numerical modelling.

Two frequency laser produced plasma heating

Simulation results of single laser pulse plasma heating and that of two simultaneous pulses with different frequencies are compared for available frequencies and the frequency dependence of light absorption is examined.