Narrow Spikes Research Articles

High-frequency properties of layered conductors in strong magnetic field

Dependence of the impedance of a layered conductor with quasi-two-dimensional electron energy spectrum on the incident wave polarization is studied theoretically. At certain orientations of the strong magnetic field H the penetration depth of the ac electric field along the normal n to the layers reveals narrow spikes as a function of the angle between the H and n vectors. Their experimental investigation will enable detailed analysis of the properties of electric-charge carrying elementary excitations in layered conductors.

The Pressure Relaxation of Liquid Jets After Isochoric Heating

During isochoric heating by fast neutron irradiation, a high pressure is almost instantaneously built up inside the falling liquid jets in a HYLIFE (ICF) reactor. It has been suggested that the jets will breakup as a consequence of negative pressure occurring during the relaxation. This is important to both the subsequent condensation process and the chamber wall design. In this paper the mechanism of the relaxation of liquid jets after isochoric heating has been studied with both incompressible and compressible models. The transient pressure field predicted is qualitatively similar for both models and reveals a strongly peaked tension in the wake of a rarefaction wave. The pressure then rises monotonically in radius to zero pressure on the boundary. The incompressible approximation greatly over predicts the peak tension, which increases with time as the rarefaction wave moves toward the center of the jet. Since the tension distribution is as a narrow spike rather than uniform, a cylindrical fracture is the most likely mode of failure. The paper also discusses the available methods for estimating liquid tensile strength.

Elemental boron and antimony doping of MBE Si and SiGe structures grown at temperatures below 600°C

This paper considers the low temperature doping of (100) Si and SiGe structures with elemental B and Sb sources particularly with regard to obtaining very narrow delta doping spikes. B is found to be an excellent dopant at SiGe growth temperatures incorporating in an active state at concentrations up to 10%. B delta layers of 1 nm or less have also been grown. Sb is also shown to be capable of providing delta doped layers less than 2 nm wide. The B deltalayers have been incorporated into modulation doped structures yielding an order of magnitude increase in mobility at 77 K.

Narrow gain spikes and frequency pulling in the midinfrared ammonia laser

The gain of a 12- mu m NH/sub 3/ laser transition, optically pumped by CO/sub 2/ laser radiation, has been measured under well-characterized conditions. Good agreement is found between the measured gain and theoretical calculations based on a three-level density matrix formalism. The theory was also employed to explain the stable frequency behavior of the NH/sub 3/ laser.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The precipitation of relativistic electrons near the trapping boundary

Highly relativistic electrons are known to be present at synchronous satellite altitude in time‐varying and sometimes large intensities; it is therefore important to consider the fluxes and locations of relativistic electrons precipitating into the atmosphere. Here we present measurements from the low‐altitude three‐axis‐stabilized satellite S81‐1 of trapped and precipitating electrons from 6 keV to above 1 MeV. Significant fluxes of precipitating relativistic electrons above 1 MeV within the bounce loss cone are much more often observed near midnight than noon and generally in narrow spikes &lt;100 km in width typically at L values between 4 and 6 near the radiation belt boundary. The tendency for many of the relativistic spikes to be near the trapping boundary is consistent with the general pattern at lower energies confirmed by the measurements presented here of intensity and threshold energy for isotropy versus L shell. A trend was observed for the higher‐energy precipitating electron fluxes to peak at somewhat lower L values. The precipitation of &gt;1‐MeV electrons has been measured to occur at intensities and in locations that are widely variable within a few minutes superposed on longer‐term variations. On one of the days of strongest precipitation the total nighttime input to the atmosphere during 12 hours from &gt;1‐MeV electrons within the bounce loss cone near the trapping boundary was ∼1019 ergs, which was an order of magnitude less than the loss rates estimated by Baker et al. from high‐altitude measurements, suggesting that precipitation in the drift loss cone may be significant.

Relativistic electron enhancements; Simultaneous measurements from synchronous and low altitude satellites

We present here for the first time simultaneous measurements of trapped relativistic electron enhancements at synchronous altitude and precipitating electrons in the bounce loss cone at low altitudes. The measurements show that the daily variations in the precipitation flux for L &gt; 5 correlated well with the daily variations in the total flux at high altitude, both with respect to sudden enhancements as well as flux depletions. The daily averaged precipitating flux (E &gt; 1 MeV) at L=6.1 to 7.1 was about 0.3 percent of the daily averaged directional flux (E ≥ 1.5 MeV) observed at synchronous altitude, whereas within narrow spikes the precipitating directional fluxes were often within a factor of 10 of the daily averaged trapped fluxes. Strong depletions in the synchronous altitude ≥1.5 MeV electron intensities are shown to be associated with low altitude measurements of the equatorward movement of precipitating spikes to lower L shells.

Characteristics of picosecond coherent anti-Stokes Raman spectroscopy with mode-locked dye lasers in comparison with stimulated Raman gain

Time-resolved coherent anti-Stokes Raman scattering (CARS) has been performed with a double synchronously pumped mode-locked dye-laser system that is the same as had been used earlier for stimulated Raman gain (SRG) experiments; the CARS signal is also spectrally resolved. We present an extensive experimental and theoretical study of the CARS technique and compare the results with the characteristics of SRG. Experimental tests have been performed on the 656- and 991-cm−1 modes in liquid CS2 and C6H6, respectively. In particular, the influence of the pulse chirps on the time resolutions in CARS and SRG has been examined. SRG profits from oppositely chirped dye-layer pulses. In these circumstances, the observed time resolution in SRG is typically a factor of 3 better than in CARS. Also, when measured under off-resonance conditions, CARS decay curves exhibit a narrow and pronounced coherence spike that is symmetrical near zero delay: its appearance is discussed in detail. In addition, we establish the conditions for which the phenomena, of critical frequency mistuning and spectral narrowing in time-delayed CARS are observable.

A subpopulation of cerebral B cluster neurones ofAplysia californicais involved in defensive head withdrawal but not appetitive head movements

ABSTRACTThe cerebral B cluster neurones of Aplysia californica were studied under experimental conditions designed to evoke head movements in a selective fashion: either to approach an appetitive stimulus, or to withdraw from an aversive one. Intracellular recordings indicated the presence of two types of B cluster neurones: Bn cells that had fast (narrow) spikes, and Bb cells that had slow (broad) spikes. Tactile stimulation of the tentacles, rhinophores and lips excited Bn neurones, but inhibited Bb neurones. Intracellular stimulation of Bn cells evoked contractions of body wall muscles. No contractions were observed when Bb cells were fired, indicating that it is unlikely that the Bb neurones are motor neurones. Several lines of evidence indicated that the Bn type neurones are involved in withdrawal responses but not in appetitive head turning. (1) Elimination of the descending axons of the Bn cells by lesioning the cerebropleural connectives (C-Pl connectives) did not affect the head-turning response. This lesion significantly altered the head-withdrawal response by selectively eliminating an initial fast component of the withdrawal movement. (2) In chronic recordings from the C-Pl connective, unit activity was obtained which was correlated with the presentation of an appetitive stimulus rather than with evoked or spontaneous turning movements. A substantial increase in activity also occurred during head withdrawal of the animal. On the basis of these data, we postulate that separate populations of motor neurones are responsible for the aversive withdrawal of the head, and for the directed turning response towards a stimulus.

Broad minded on narrow spikes

Broad minded on narrow spikes

Measurement of narrow Si dopant distributions in GaAs by SIMS

AbstractThere is a developing interest in the use of atomic plane or δ‐doping to produce narrow dopant spikes in molecular beam epitaxy GaAs. It is of importance to measure the dopant profile and to determine the growth conditions that minimize dopant spreading. We have used SIMS with low‐energy oxygen bombardment to study the incorporation of silicon in such layers. To aid the optimization of the SIMS depth resolution, a special δ‐doped layered structure has been produced by growth at 400°C. A critical evaluation of the SIMS data for these spikes shows that the profiles are broadened entirely by sputter‐induced relocation effects rather than by thermal diffusion processes. The form of these δ‐spike profiles therefore represents the SIMS resolution function with our specific experimental conditions. The absolute depth resolution (ΔZ) is found to be essentially constant for eroded depths up to ∼500 nm. With the lowest probe energy (0.7 keV per atom), giving a ΔZ of 2.7 nm, at least 68% of the Si is contained within nine atomic planes. Using appropriate sample handling, a detection limit of 1 × 1016 cm−3 Si is obtained after the erosion of only ∼ 15 nm. Analysis of structures grown at normal molecular beam epitaxy temperatures indicates that significant dopant spreading takes place during growth. It is shown that a knowledge of the resolution function enables the inherent SIMS broadening errors to be removed from these measurements. Thus, when the layer growth time is deliberately increased, the Si migrational process is dominated by Fickian diffusion, with the diffusion coefficient being equal to 3.8 × 10−17 cm2 s−1 at 553°C.

Solar narrowband decimetric spike bursts and associated phenomena

Based on the observational data of solar narrowband decimetric spike bursts on 1981 Nov 12–14 (Enome et al. 1985) and, associated phenomena, we propose a model of two acceleration regions during the impulsive phase of solar flare. One (region A) is formed in the current sheet by magnetic reconnection process, the other (region B), at the top of the flaring loop by turbulence acceleration. Region B is able to generate mildly relativistic electrons and to emit gyrosynchrotron radiation or decimeter waveband microwave bursts. Two accelerated electron streams escape from region A simultaneously. One travels through the outer corona and excites type III bursts, the other, injected into the emerging flaring-loop at a certain pitch angle, will stimulate electron-cyclotron maser with a “hollow beam” distribution and emit narrowband decimetric spike bursts. Utilizing the formulae of “hollon beam” electron cyclotron maser, we have evaluated the maximum growth rate of the 2nd harmonic wave of FX mode and reached the following conclusions. As the energy of the downward electron stream increases, the maximum growth rate, probability of spike emissions, relative bandwidth and brightlness temperature all increase, the linear size of the spike source decreases, and the peak flux remains fixed. In addition, we have clarified the close association between narrow band spike bursts and type III bursts, and hard X-ray bursts.

A 2.2 second period in the 1984 August 5 gamma-ray burst

view Abstract Citations (18) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A 2.2 Second Period in the 1984 August 3 Gamma-Ray Burst Kouveliotou, C. ; Desai, U. D. ; Cline, T. L. ; Dennis, B. R. ; Fenimore, E. E. ; Klebesadel, R. W. ; Laros, J. G. Abstract A time history and Fourier power spectrum are presented for the August 5, 1984 gamma-ray burst (GRB) observed with the SMM Hard X-ray Burst Spectrometer and the Pioneer Venus Orbiter spacecraft. A significant complex feature of the event is identifiable in both data sets: a gradual ripple with a well-defined 2.2-sec period lasting for seven cycles, with a series of narrow spikes, which appear always on the ascending phase of the sinusoidal ripple. This event is unusual in both its temporal and spectral attributes: it exhibits coexistence of periodic and nonperiodic features, and it was also reported as the most intense GRB event observed with the SMM Gamma-Ray Spectrometer, extending up to 100 MeV. Publication: The Astrophysical Journal Pub Date: July 1988 DOI: 10.1086/185214 Bibcode: 1988ApJ...330L.101K Keywords: Fourier Analysis; Gamma Ray Bursts; Periodic Variations; Power Spectra; Pioneer Venus Spacecraft; Ripples; Solar Maximum Mission; Time Measurement; X Ray Spectroscopy; Space Radiation; GAMMA RAYS: BURSTS full text sources ADS | data products SIMBAD (1)

A Sensitive Line Search in Circumstellar Envelopes

AbstractA molecular line search in the range between 85 and 89 GHz has been performed in the circumstellar envelopes of 11 evolved stars. Emissions of 29SiO J=2−1,28SiO J=2−1, HCN J=1−0, H13CN J=1−0, HC5 N J=33−32, HCO+ J=1−0 transitions and other transitions of C2 H, C4 H, and C3 N have been observed in 11 stars. We have detected the ground state 29SiO J=2−1 maser in several stars. We have also detected HCN emission in VY CMa. A narrow H13CN spike feature near the central velocity has been found in the spectrum of CRL 2688.

The Roller Pump Does Produce Pulsatile Flow

(J. Extra-Corpor. Technol. 19[3] p. 376-383 Fall 1987, 15 ref.) This study was undertaken to investigate, under experimental conditions, the nature of the roller pump output. Pressure and flow studies were done on 200° roller pumps using PVC and silastic formulations in the raceway. Polyvinyl chloride (PVC) tubing in all sizes produced comparatively higher pressure levels with narrow pressure spikes. Small bore tubing with high revolutions per minute (RPMs) delivered characteristic pulseless flow due to telescoping of flow and pressure pulses. Large bore PVC tubing produced pulsatile flow curves with spikes, ripples and artifacts. Silastic and fluorocarbon tubing achieves pulsatile flow curves without ripples or artifacts at a comparatively lower pressure range. A wide pulse width and a single roller ripple chararacterize it. Ideal combinations used clinically in over 1,500 cases result in appreciable pulse flow measurable in significant changes in renal output both in normothermic and hypothermic conditions. These results show that a regular roller pump, with the use of tubing with specific viscoelastic properties and the proper choice of stroke volume, will produce a significant level of pulsatile flow. There is no need for an add-on system. Preliminary work utilizing a single roller pump, as a means of enhancing the pulse wave, is presented. Techniques to remove the 200° single roller induced ripple is also discussed.

Effect of acoustic tone perception on brain‐generated electromagnetic waves: Preliminary evidence

Brain‐generated microwaves were detected and measured for each of four subjects in the frequency range of the lowest electromagnetic standing wave (mode) of the adult human brain/skull cavity (200–400 MHz) in the presence and absence of a loud acoustic tone. In each case, the center frequency of the mode was found at, or within, a megahertz of that measured for each subject 1 yr earlier, and is different for each subject. In all cases, mode center frequency is within 10% of that theoretically predicted based on a subject's skull dimensions [P. L. Stocklin and B. F. Stocklin, T.I.T.J. Life Sci. 9, 29–51 (1979)]. In the absence of the acoustic tone, mode structure consists of a cluster of frequency spikes, each 2 to 3 kHz wide extending over 30 to 50 kHz. In the presence of a loud 1500‐Hz continuous acoustic tone, the cluster of narrow spikes coalesces to one or two narrow spikes, 3 to 10 dB above the cluster average. [Work supported by Mentec Inc.]

Neutron-proton charge exchange scattering in a one-pion-exchange model with quark exchange

The neutron-proton charge exchange scattering cross section is calculated in the Born approximation with a modified one-pion-exchange potential which includes the effects of quark exchange between nucleons. The inclusion of these exchange effects leads to a natural interpretation of the narrow spike observed on the experimental cross section near the forward direction.

EVANESCENT EFFECTS IN ACOUSTICAL WAVE PROPAGATION*

ABSTRACTThe propagation of transient acoustic pressure waves in a layer enclosed between two, not necessarily identical, half‐spaces is considered. The source and the receivers are always located in the same half‐space and at the same depth. The source excitation function is a narrow causal spike. Several thicknesses of the layer are examined including the case in which the embedded layer vanishes.The phenomena of ‘constricted’ head waves and wide‐angle reflections in the layer are examined in detail using a ‘numerical experimentation’ approach. First, a closed‐form solution is numerically evaluated. Then this solution is developed in series and each term is evaluated separately using the same numerical techniques. When the contribution of an individual high‐order term becomes unimportant, all higher order terms are discarded, and the response is constructed by superposition of the previously computed low‐order terms only.Propagation by wide‐angle reflections from inside the layer is of interest. When the thickness of the layer is reduced to a fraction of the wavelength, these events consist typically of a low amplitude, high frequency, geometrical acoustics arrival, followed by higher amplitude, low frequency, non‐geometrical coda. When all important low‐order terms are added, the non‐geometrical events tend to interfere destructively, leaving a waveform nearly identical to that obtained by integration of the closed‐form solution.When the thickness of the embedded layer is measured in fractions of the dominant wavelength, none of the individual terms of the series development can be duplicated by asymptotic ray tracing. However, because the codas of the various terms interfere destructively, the total response may be well‐represented by the addition of a few low‐order rays, using asymptotic approximation. This discovery extends the usefulness of Huygens‐Kirchhoff ray tracing to modeling of wave propagation in thin layers.

Expanding shells in the filamentary edge of the young supernova remnant RCW 103

Long-slit, echelle spectrograms have been obtained of the Hα and [N II] lines over the young supernova remnant RCW 103. One notable velocity feature is a narrow velocity spike (⁠|$\simeq 20\text {km s}^{-1}$| wide) with |$V_{\text {HEL}}\simeq 2-44\text {km s}^{-1}$| which is near the mean for the whole nebula. The overall velocity curves fail to match those expected from a remnant expanding radially at |$1100-3000\text {km s}^{-1}$| as suggested by previous observations. Along the filamentary edge of the SNR several regions of ≲0.4 pc diameter are found which are expanding with velocities of up to |$300\text {km s}^{-1}$|⁠; these are explained in terms of a model involving bow shocks formed when the supernova blast-wave overruns pre-existing condensations. Other mechanisms are also suggested.

Monitoring observations of selected SiO maser sources at 7 MM wavelength - 1977-1979

High-spectral-resolution SiO maser observations at 7 mm wavelength were made for 13 circumstellar objects and Ori A over a 34 month interval from January 1977 to November 1979. These data precede and adjoin the SiO monitoring data taken at 3 and 7 mm wavelengths by Lane (1982) and at 3 mm wavelengths by Nyman and Olofsson (1985) and thus provide an important link in the record of the temporal behavior of SiO masers over a period of several years. The time-averaged center of the weak SiO maser emission pedestal gives the stellar radial velocity. This reinforces the idea that the SiO maser emission pedestal is representative of the true structure of a stellar SiO maser, while the more visible and stronger, narrow SiO emission spikes represent chance coherences along the velocity range of the pedestal. Similarities between the SiO maser velocity patterns of VY CMa and Ori A may suggest similarities in their evolutionary stages.

Relativistic electron and energetic ion precipitation spikes near the plasmapause

An investigation has been made of electron and associated ion precipitation spikes near the plasmapause that are narrow in L shell and in which relativistic electrons are favored. The electron energy spectra during the spikes sometimes had equivalent e fold energies in excess of 500 keV. In approximately 31% of these spike events observed from the low‐altitude polar orbiting satellites P72‐1, P78‐1, and S81‐1, nearly simultaneous precipitation was measured in energetic ions above ∼30 keV at about the same L value. Several of the precipitation spikes occurred primarily in the drift loss cone, but in some cases, significant precipitation (∼10−2 ergs/cm² s) was also observed in the bounce loss cone. The electron spikes occurred preferentially in the evening sector, and all of the associated narrow ion spikes were in that local time interval. Narrow relativistic electron spikes were observed on less than 1% of the crossings of the plasmapause. From the set of S81‐1 events a search was made for those also observed on the NOAA 6 spacecraft. On rare occasions, nearly simultaneous (&lt;2000 s) narrow spikes with hard electron spectra were found at approximately the same L value from both spacecraft and at longitudes differing by 8°–47°. These findings suggest a patchy profile, sometimes with an arc structure which may extend over longitude intervals as great as 25° and time intervals as long as 2000 s. From consideration of the AE index for 17 events, 12 were found to occur close to the times of substorms. The spike precipitation is interpreted in terms of cyclotron resonance wave‐particle interactions involving radiation belt particles, the narrow widths being associated with fine structure in the cold plasma density profiles near the plasmapause and the energy selectivity associated with an upper frequency cutoff in the waves.