Typical Delay Time Research Articles

Probing the Nature of the Weakest Intergalactic Magnetic Fields with the High‐Energy Emission of Gamma‐Ray Bursts

We investigate the delayed, secondary GeV-TeV emission of gamma-ray bursts and its potential to probe the nature of intergalactic magnetic fields. Geometrical effects are properly taken into account for the time delay between primary high energy photons and secondary inverse Compton photons from electron-positron pairs, which are produced in $\gamma$-$\gamma$ interactions with background radiation fields and deflected by intervening magnetic fields. The time-dependent spectra of the delayed emission are evaluated for a wide range of magnetic field strengths and redshifts. The typical flux and delay time of secondary photons from bursts at $z \sim 1$ are respectively $\sim 10^{-8}$ GeV cm$^{-2}$ s$^{-1}$ and $\sim 10^4$ s if the field strengths are $\sim 10^{-18}$ G, as might be the case in intergalactic void regions. We find crucial differences between the cases of coherent and tangled magnetic fields, as well as dependences on the field coherence length.

The effect of diluent gases on ignition delay times in the shock tube and in the rapid compression machine

The diluent gas used in the preparation of test fuel/oxygen mixtures is inert and does not take part in the chemical reaction. However, it does have an effect on the measured ignition delay time both in rapid compression machines and in shock tubes—argon decelerates ignition in the RCM, but accelerates it in the shock tube under some conditions. This opposite effect is due to the times scales involved in these experimental devices. Typical ignition delay times in the RCM are in the region of 1–200 ms, while those in the shock tube are much shorter (10–1000 μs). Comparative RCM experiments and simulations for helium, argon, xenon, and nitrogen have shown extreme heat loss in the postcompression period, particularly for helium. Autoignition measurements of 2,3-dimethylpentane have highlighted a direct dependency of ignition delay time on the type of diluent used, where longer ignition delay time were recorded with argon. This increased ignition delay time is due to the extreme cooling of argon in the postcompression period. This observation was strengthened by comparative experiments with helium and argon, where the diluent effect was even stronger for helium, caused by its higher thermal conductivity. In the shock tube, the diluent effect is opposite to that in the RCM. For dilute mixtures of isooctane, calculations have predicted that mixtures with argon will ignite faster than those with nitrogen, based on the relative heat capacities of the two diluent gases. Overall, we conclude that the choice of diluent gases in experimental devices must be made with care, as ignition delay times can depend strongly on the type of diluent gas used.

Direct Measurement of Light Speed Reduction in a RubidiumVapour Medium Coherently Prepared by Electromagnetically InducedTransparency

We have experimentally observed the reduction of light speed in arubidium vapour medium coherently prepared by electromagneticallyinduced transparency. The light speed reduction was deduced by directlymeasuring the time delay of a probe light when it passed through themedium. The time delay varies with the intensity of the coupling laser,and the typical time delay we recorded was 1.8 μs, corresponding to alight speed of 56000 m/s.

Quantum graphs: a simple model for chaotic scattering

We connect quantum graphs with infinite leads, and turn them to scattering systems. We show that they display all the features which characterize quantum scattering systems with an underlying classical chaotic dynamics: typical poles, delay time and conductance distributions, Ericson fluctuations, and when considered statistically, the ensemble of scattering matrices reproduce quite well the predictions of appropriately defined Random Matrix ensembles. The underlying classical dynamics can be defined, and it provides important parameters which are needed for the quantum theory. In particular, we derive exact expressions for the scattering matrix, and an exact trace formula for the density of resonances, in terms of classical orbits, analogous to the semiclassical theory of chaotic scattering. We use this in order to investigate the origin of the connection between Random Matrix Theory and the underlying classical chaotic dynamics. Being an exact theory, and due to its relative simplicity, it offers new insights into this problem which is at the fore-front of the research in chaotic scattering and related fields.

Steps toward Determination of the Size and Structure of the Broad‐Line Region in Active Galactic Nuclei. XVI. A 13 Year Study of Spectral Variability in NGC 5548

We present the final installment of an intensive 13 year study of variations of the optical continuum and broad H beta emission line in the Seyfert 1 galaxy NGC 5548. The database consists of 1530 optical continuum measurements and 1248 H beta measurements. The H beta variations follow the continuum variations closely, with a typical time delay of about 20 days. However, a year-by-year analysis shows that the magnitude of emission-line time delay is correlated with the mean continuum flux. We argue that the data are consistent with the simple model prediction between the size of the broad-line region and the ionizing luminosity, r is proportional to L(sup 1/2)(sub ion). Moreover, the apparently linear nature of the correlation between the H beta response time and the nonstellar optical continuum F(sub opt) arises as a consequence of the changing shape of the continuum as it varies, specifically F(sub opt) is proportional to F(sup 0.56)(sub UV).

The Decline of the Source Population of Gamma‐Ray Bursts and Their Luminosity Function

The source population of gamma-ray bursts (GRBs) declines toward the present epoch, being consistent with the measured decline of the star formation rate. We show this using the brightness distribution of 3255 long BATSE GRBs found in an off-line scan of the BATSE continuous 1.024 s count rate records. The significance of this conclusion is enhanced by the detection of three GRBs with known redshifts brighter than 1052 ergs s-1 during the last two years. This is an argument in favor of the generally believed idea that GRBs are strongly correlated with star production, at least on cosmological timescales, and favors the association of long GRBs with collapses of supermassive stars. However, we still cannot rule out neutron star mergers if the typical delay time for binary system evolution is relatively short. If we assume a steep decline of the GRB population at z > 1.5, then their luminosity function can be clearly outlined. The luminosity function is close to a power law, dN/dL ∝ L-1.4, for low luminosities over at least 1.7 orders of magnitude. Then, the luminosity function breaks to a steeper slope or to an exponential decline around L ~ 3 × 1051 ergs s-1 in the 50-300 keV range, assuming isotropic emission.

Dynamics of the substorm expansive phase

Meridian‐scanning photometer (MSP) and magnetometer data from the Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) ground‐based array have been used to study the dynamics of the substorm expansive phase. The relative latitudinal motions of the MSP 630.0, 557.7, and 486.1 nm emissions for eight isolated events have been studied. The data show the expansive phase to comprise three stages: an explosive (tens of seconds) onset; rapid poleward motion of 557.7 nm emissions of the order of a few minutes; and a period of slower (tens of minutes) poleward moving 630.0 nm emissions. We interpret the rapid poleward motion of the 557.7 nm data in terms of a region of instability, expanding rapidly down the magnetotail, possibly accelerating plasma sheet electrons as it proceeds. All events show that lobe flux reconnection occurs after near‐Earth onset, with typical time delays between 1 and 5 min. The extremely short time interval between near‐Earth onset and the beginning of lobe flux reconnection presents a severe observational constraint on any substorm model which attempts to explain the substorm expansive phase. Magnetometer data from the CANOPUS Churchill line have been used to study the dynamics of the substorm electrojets during the growth and early expansive phases of the substorm. The borders of these electrojets closely follow the motion of the MSP data during the growth and expansive phases. At the instant of expansive phase onset the growth phase electrojets (as observed along the Churchill meridian line) disappear, being replaced by the substorm westward electrojet associated with the current wedge. The equatorward border of the substorm westward electrojet is embedded within the proton aurora emissions and appears at expansive phase onset ∼2° equatorward of the growth phase electrojets, further showing the near‐Earth proximity of expansive phase onset. No indication of reconnection on closed field lines prior to expansive phase onset was observed in either the magnetometer or the photometer data.

Short‐time electrical effects during volcanic eruption: Experiments and field measurements

Laboratory experiments on the fragmentation and expansion of magmatic melt have been performed using remelted volcanic rock at magmatic temperatures as magma simulant. A specially designed dc amplifier in combination with high speed data recording was used to detect short‐time electrostatic field effects related to the fragmentation and expansion history of the experimental system, as documented by simultaneous force and pressure recording, as well as by high‐speed cinematography. It was found that (1) the voltage‐time ratio of electrostatic field gradients (100 to 104 V/s) reflects different physical mechanisms of fragmentation and expansion and (2) the maximum voltage measured in 1 m distance (−0.1 to −180 V) can be correlated with the intensity of the respective processes. Based on these experimental results, a field method was developed and tested at Stromboli volcano in Italy. A 0.8 m rod antenna was used to detect the dc voltage against local ground (i.e., the electrostatic field gradient), at a distance of 60 to 260 m from the respective vent. Upwind position of the detection site was chosen to prevent interference caused by contact of charged ash particles with the antenna. A standard 8 Hz geophone was used to detect the accompanying seismicity. Three types of volcanic activity occurred during the surveillance operation; two of these could be clearly related to specific electrical and seismical signals. A typical delay time was found between the electrical and the seismical signal, corresponding to the seismic velocity within the crater deposits. Using a simple first‐order electrostatic model, the field measurements were recalibrated to the laboratory scale. Comparison of field and laboratory data at first approximation revealed striking similarities, thus encouraging the further development of this technique for real‐time surveillance operation at active volcanoes.

MC68HC11 Microcontroller Control of a Greenhouse Environment as a Time Delay System

The paper presents a microcontroller design and control implementation for modern greenhouses. The nature of the greenhouse problems in conjunction with the microcontroller capabilities is given as a time delay control system and states decoupling problems are discussed. The greenhouse modelcontroller system operation is simulated and the results are discussed Different plants greenhouse environmental demands are taken into account by changing controller set points, control architectures and data base integration. Greenhouse control is considered a batch control system during start-up and run as continuous time discrete control algorithm later in the background. Greenhouse control is a typical time delay system.

Measurement of the distribution of anion exchange function in normal human red cells.

1. The aim of the present work was to investigate cell-to-cell variation in anion exchange turnover in normal human red cells. Red cells permeabilized to protons and K+ dehydrate extremely rapidly by processes that are rate-limited by the induced K+ permeability or by anion exchange turnover. Conditions were designed to render dehydration rate-limited by anion exchange turnover. Cell-to-cell variation in anion exchange function could then be measured from the distribution of delay times required for dehydrating cells to attain resistance to haemolysis in a selected hypotonic medium. 2. Red cells were suspended at 10% haematocrit in a low-K+ solution and, after a brief preincubation with 20 microM SITS at 4 degrees C, were warmed to 24 degrees C, and the protonophore CCCP was added (20 microM) followed 2 min later by valinomycin (60 microM). Delay times for cells to become resistant to lysis were measured from the instant of valinomycin addition by sampling suspension aliquots into thirty volumes of 35 mM NaCl. After centrifugation the per cent lysis was estimated by measuring the haemoglobin concentration in the supernatant. Typical median delay times with this standardized method were 4-5 min. 3. The statistical parameters of the delay time distributions report the population spread in the transport function that was limiting to dehydration. In the absence of SITS and CCCP, dehydration was limited by the diffusional Cl- permeability (PCl). Delay time distributions for PCl- and anion exchange-limited dehydration were measured in red cells from three normal donors. For both distributions, the coefficients of variation ranged between 13.0 and 15.2%, indicating a high degree of uniformity in PCl and anion exchange function among individual red cells.

Anisotropy and the splitting of PS waves

The PS wave is radially polarized in an isotropic spherically symmetric Earth owing to the P to SV conversion at the free surface. If we choose stations with weak SKS splitting to minimize the effect of the receiver, we can measure the anisotropy beneath the bounce point of the PS wave. We find that with a deep source and epicentral range of 90° < Δ < 125°, the PS phase can be distinguished from other phases. Owing to the limitation of recent large deep events with epicentral range between 90° and 125°, we analyze data from stations in North America and events beneath the Bonin Islands and the Fiji Islands. For events in these two regions, the bounce points of the PS wave are roughly located northwest of the Kuril Islands and near the Nova-Canton Trough in the central Pacific, respectively. Because the first Fresnel zone for the PS wave at this distance range is roughly 700 km across, each PS splitting observation must be interpreted as a local average of anisotropic properties. The average direction of the fast axis of anisotropy below the Nova-Canton Trough region is N104.2°E with a standard deviation 12.7° and a typical delay time of 1.8 s. Landward of the Kuril Islands, the average direction of the fast axis is N127.6°E clockwise from north, and the standard deviation is 11.3°, with a typical delay time of 1.2 s. We have compared the fast axis with the direction of fossil seafloor spreading and with the present-day absolute plate motion. The fast axis of anisotropy at the Nova-Canton Trough agrees well with the direction of absolute plate motion, and poorly with the complex fossil spreading pattern. This suggests that significant upper-mantle shear anisotropy exists in this part of the central Pacific, and is consistent with mineral alignment owing to strain associated with present-day plate motion. Similarly, the fast axis beneath the Kuril Islands parallels the convergent motion of the slab. Coupled-mode synthetics constructed with the ‘strong’ Born approximation can be used to model the interaction of the PS waves with anisotropic structure that has a horizontal axis of symmetry. We use all free oscillations up to 35 mHz in the calculation. The coupled-mode synthetics show shear-wave splitting with delay time and fast axis consistent with the ray theory prediction.

Pulsed X-ray emission and resonance absorption in a 1.053 μm laser produced plasma

Time-resolved X-ray emission recorded during high intensity (⩾10 15 W/cm 2) irradiation of a 1.053 μm laser produced aluminum plasma, shows time dependent structure. These bursts are separated by typical time delays, long compared with the inverse of the ion acoustic frequency, and can be correlated with time-resolved back-scattered second harmonic spectra, recorded at the same time, which also exhibit pulsation. These results can be explained by quasi-periodic collapsing of resonantly excited plasmons at the critical surface.

The influence of IMF BY on the high‐latitude thermospheric circulation during northward IMF

Thermospheric neutral wind data, obtained by the Fabry‐Perot Interferometer (FPI) and Wind and Temperature Spectrometer (WATS) on the Dynamics Explorer 2 satellite during periods of northward interplanetary magnetic field (IMF Bz positive), show a dependence of the circulation on the magnitude and sign of the east–west component (By) of the IMF. Averaged thermospheric neutral wind vector fields, for the northern hemisphere, and data from several sets of satellite orbits, that illustrate the variation in the neutral wind structure as a function of time and IMF orientation, are presented and discussed. The results show that near December solstice, at solar maximum: (1) sunward neutral winds develop inside the geomagnetic polar cap during periods of persistent positive Bz and relatively low By; (2) typical time delays in the establishment of sunward winds following a northward turning of the IMF are approximately 4 hours; (3) sunward winds are not observed when the magnitude of the Bz component of the IMF is less than +4 nT; (4) the maximum‐velocity antisunward winds, in the central geomagnetic polar cap region, are on the duskside (dawnside) in the northern hemisphere during periods of northward IMF and By negative (positive). A similar asymmetry exists in the sunward flow in the center of the polar cap; (5) if the absolute magnitude of the By component of the IMF exceeds that of Bz (i.e., if the By/Bz ratio is greater than 1.0) then sunward winds inside the geomagnetic polar cap are rarely observed; instead, one sees a pattern of neutral winds similar to that expected for the given sign of By under southward IMF conditions; (6) the summer hemisphere has neutral wind signatures that are similar to those seen in the winter hemisphere for Bz northward, i.e., sunward winds occur in the polar cap for persistently northward Bz, provided the magnitude of By does not exceed that of Bz.

Macromodeling CMOS circuits for timing simulation

A macromodeling and timing simulation technique is presented that allows fast and accurate delay calculations for CMOS circuits. This method is well suited for delay calculations of regular structure VLSI circuits, as well as circuits designed from standard cell libraries. Timing models for both logic gate and transmission gate circuit forms are developed. Typical delay times were within 5% for logic gate circuits and 10% for transmission gate circuits when compared with SPICE results. The execution time of experimental simulator was over two orders of magnitude faster than SPICE.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Amorphous silicon logic integrated circuits

Amorphous silicon thin-film integrated circuits, with between 4 and 18 transistor functions per chip, have been fabricated on glass substrates. The amorphous silicon and the dielectric layers are deposited by rf glow discharge. The circuits have been designed to realize basic logic functions such as inverters, NAND and NOR gates, and addressable memory cells. For the first time, an amorphous silicon flip flop requiring a supply voltage of only 4.5 V has been manufactured. The logic voltage levels of the flip flop are compatible with standard bipolar TTL circuits. Measurements on an inverter chain show a typical propagation delay time of 70 μs and a power-delay-time product of 65 pJ. All of the circuits use n-channel enhancement type load transistors instead of integrated ohmic load resistors. The channel length of the driver transistors is 15 μm with a gate source/drain overlap of 7.5 μm. Experimental geometry ratios range from β=2.25 to β=21. Generally, the driver transistors exhibit on/off ratios greater than 106 for supply voltages smaller than 5 V. At these voltages the measured on-currents per unit channel width are in the order of 5...10nA/μm. The influence of the geometry ratio on static inverter characteristic and switching speed is discussed by means of a simple model. Two different manufacturing schemes for the fabrication of the integrated circuits are outlined. Mask layouts and experimental transfer characteristics of several integrated circuits are presented.

A 256-channel C/SUP 2/MOS LSI time-switch using shift-register pipeline multiplexer

SOS technology has been used to retain the pipeline processing speed advantage by controlling the capacitance of on-chip lines that must be long to provide 256-channel operation. Clocked CMOS (C/SUP 2/MOS) circuits have been used to avoid clock-skew problems. A 1.5-/spl mu/m C/SUP 2/MOS/SOS technology has made it possible to integrate 900 transistors into a 4.0/spl times/2.4-mm/SUP 2/ area, and to realize a 256-channel time-switch LSI, with a 15-ns typical output delay time and a 300-mW power dissipation during 25-MHz operation.

A triple-level wired 24K-gate CMOS gate array

A 24K-gate CMOS gate array has been developed using triple-level wiring and a hierarchical layout method. A typical delay time is 1.6 ns with a fanout of 3 and a 3-mm metal interconnect length. The master chip was designed to be freely divided into blocks. A previously developed digital signal processor has been realized on the array. The design time was reduced to 25% of the normal design cycle although the chip size is 3.3 times larger than was realized by a handcrafted design.

A subnanosecond 8K-gate CMOS/SOS gate array

An 8370-gate CMOS/SOS gate array has been developed using a Si-gate CMOS/SOS process with two-level metallization. The gate lengths of the transistors are 1.8 and 1.9 /spl mu/m for the n-channel and p-channel, respectively. Subnanosecond typical gate delay times have been obtained. Typical delay times of inverter, two-input NAND, and two-input NOR gates are 0.67, 0.87, and 0.99 ns, respectively, under a typical loading condition (three fan outs and 2 mm first metal). It is shown that ECL speed with CMOS power can be achieved in a system by using the CMOS/SOS gate array. Advantages of the SOS device on speed performance are also discussed.

500 Gates GaAs Gate Array

High speed GaAs DCFL gate array consisting of 500 3-INPUT NOR gates, in which 2000 FETs are integrated, has been successfully fabricated by a Pt buried gate planar E/D process technology. Eleven different 15-stage ring oscillators were made on this gate array to investigate the dependence of gate performance on various loading conditions. Typical propagation delay times per gate were 0.16 ns and 0.69 ns under unloaded and loaded (fan-out=3, interconnection length=3 mm, cross-over=20) conditions at a power dissipation of 0.50 mW for 1.7 µm gate devices.

A new submicrometer channel/High-speed MOS-LSI technology

A new self-aligned submicrometer channel length (0.25 to 0.86 µm) MOS device (SMOS) and its application to integrated-circuit technology are proposed and demonstrated. The self-aligned SMOS structure has been developed by a double ion implantation of boron and arsenic through a specific bird's beak shape of continuous oxide thickness change created by LOCOS oxidation techniques. SMOS showed a gate threshold voltage of 0.6 to 1.0 V, breakdown voltages of 12-16 V, and a transconductance approximately three times larger than 2-µm channel MOS devices. A 21-stage ring oscillator with an enhancement/depletion (E/D) mode inverter showed typical delay times of 0.8 to 1.8 ns per gate and power dissipation per gate of 0.2 to 0.6 mW. It can be expected from a comparison of the device structures that the SMOS might have up to 15-50 percent higher packing density than in DMOS and VMOS in most kinds of recent logic and memory integrated circuits.