Magnitudes Of Pulses Research Articles

Numerical modeling of ship wave generation using Green’s functions based on linear dispersive wave theory

ABSTRACT In this study, an efficient numerical model for predicting ship waves was developed using Green’s functions. Avoiding detailed description of the complex boundary conditions around a ship, this model simply used an inversion technique for estimating the wave source induced by a ship as a function of the navigation route and adjacent measured water level fluctuations. The Green’s functions were determined as linear summations of the water level fluctuations generated from discrete points along the navigation route. At each point, a time-varying wave source was determined as a linear summation of Gaussian pulses introduced at segments along the longitudinal direction of the ship. The linear inversion was then applied for estimating the optimum combinations of the magnitudes of these Gaussian pulses. Linear dispersive wave theory was applied to compute the water level fluctuations generated by a single Gaussian pulse so that the model can reproduce the dispersive characteristics of ship waves. The developed model was tested against experimental data and showed satisfactorily predictive skills of water level fluctuations for cases not used in the inversion. The present model was also found to be robust in that the estimated best-fitted wave source was not sensitive to changes in the conditions of the measured data used for the inversion.

Quantum Dot Gate (QDG) Quantum Dot Channel (QDC) Multistate Logic Non-Volatile Memory (NVM) with High-K Dielectric HfO2 Barriers

This paper presents the theory, fabrication and experimental testing results for a multiple state Non-Volatile Memory (NVM), comprised of hafnium oxide high-k dielectric tunnel and gate barriers as well as a Silicon Quantum Dot Superlattice (QDSL) implemented for the floating gate and inversion channel (QDG) and (QDC) respectively. With the conclusion of Moore’s Law for conventional transistor fabrication, regarding the minimum gate size, current efforts in memory cell research and development are focused on bridging the gap between the conventions of the past sixty years and the future of computing. One method of continuing the increasing chip density is to create multistate devices capable of storing and processing additional logic states beyond 1 and 0. Replacing the silicon nitride floating gate of a conventional Flash NVM with QDSL gives rise to minibands that result in greater control over charge levels stored in the QDG and additional intermediate states. Utilizing Hot Carrier Injection (HCI) programming, for the realized device, various magnitudes of gate voltage pulses demonstrated the ability to accurately control the charge levels stored in the QDG. This corresponds to multiple threshold voltage shifts allowing detection of multiple states during read operations.

A giant magnetoimpedance effect based nonvolatile Boolean logic gate

The biphase magnetic heterostructure (Ni/Fe20Ni45Co25Si2B8/micro-planarcoil/Fe20Ni45Co25Si2B8/micro-planar coil/Fe20Ni45Co25Si2B8/Ni) bonded with a pair of thin magnets shows an improved asymmetric and hysteretic giant magnetoimpedance (GMI) effect with respect to an external dc magnetic field. This is attributed to the modification of the soft amorphous magnetic alloy’s (Fe20Ni45Co25Si2B8) permeability by the hysteretic magnetostrictive stress from the neighboring magnetostrictive Ni layer besides the magnetostatic coupling. More importantly, nonvolatile logic gates, such as NOR and NAND, can be implemented with either a single GMI laminate or arrays. On one hand, after applying two sequential magnetic field pulses as the logic inputs to a single proposed laminate, the nonvolatile output voltages are positive high (logic 1) or positive low (logic 0) depending on the signs and magnitudes of pulses. On the other hand, after applying the magnetic field pulses parallel to the GMI laminates arrays, different logic functions can be programmed and realized at run-time. The integration of memory and logic functions enables the proposed GMI laminate to be a possible candidate for future computing systems beyond von Neumann architecture.

2D Metal–Organic Framework Nanosheets with Time‐Dependent and Multilevel Memristive Switching

AbstractMetal–organic framework (MOF) nanosheets have attracted significant interests for sensing, electrochemical, and catalytic applications. Most significantly, 2D MOF with highly accessible sites on the surface is expected to be applicable in data storage. Here, the memory device is first demonstrated by employing M‐TCPP (TCPP: tetrakis(4‐carboxyphenyl)porphyrin, M: metal) as resistive switching (RS) layer. The as‐fabricated resistive random access memory (RRAM) devices exhibit a typical electroforming free bipolar switching characteristic with on/off ratio of 103, superior retention, and reliability performance. Furthermore, the time‐dependent RS behaviors under constant voltage stress of 2D M‐TCPP–based RRAMs are systematically investigated. The properties of the percolated conducting paths are revealed by the Weibull distribution by collecting the measured turn‐on time. The multilevel information storage state can be gotten by setting a series of compliance current. The charge trapping assisted hopping is proposed as operation principle of the MOF‐based RRAMs which is further confirmed by atomic force microscopy at electrical modes. The research is highly relevant for practical operation of 2D MOF nanosheet–based RRAM, since the time widths, magnitudes of pulses, and multilevel‐data storage can be potentially set.

Geometrical modeling of the shape of a multilink rod structure in weightlessness under the influence of pulses on the end points of its links

We have examined a geometrical model of the new technique for unfolding a multilink rod structure under conditions of weightlessness. Displacement of elements of the links occurs due to the action of pulses from pyrotechnic jet engines to the end points of links in a structure. A description of the dynamics of the obtained inertial unfolding of a rod structure is performed using the Lagrange equation of second kind, built using the kinetic energy of an oscillatory system only. The relevance of the chosen subject is indicated by the need to choose and explore a possible engine of the process of unfolding a rod structure of the pendulum type. It is proposed to use pulse pyrotechnic jet engines installed at the end points of links in a rod structure. They are lighter and cheaper as compared, for example, with electric motors or spring devices. This is economically feasible when the process of unfolding a structure in orbit is scheduled to run only once. We have analyzed manifestations of possible errors in the magnitudes of pulses on the geometrical shape of the arrangement of links in a rod structure, acquired as a result of its unfolding. It is shown at the graphical level that the error may vary within one percent of the estimated value of the magnitude of a pulse. To determine the moment of fixing the elements of a multilink structure in the preset unfolded state, it is proposed to use a «stop-code». It is a series of numbers, which, by using functions of the generalized coordinates of the Lagrange equation of second kind, define the current values of angles between the elements of a rod structure. Results are intended for geometrical modeling of the unfolding of large-size structures under conditions of weightlessness, for example, power frames for solar mirrors, or cosmic antennae, as well as other large-scale orbital facilities.

Physical mechanisms of partial discharges at nitrogen filled delamination in epoxy cast resin power apparatus

For proper insulation design of epoxy cast resin power apparatus such as molded transformers, it is important to consider the criticality of defects that might exist into the dielectric material. One of the most important defects is the delamination defect at the interface between resin and conductor. Accordingly, this paper aims to investigate partial discharge (PD) characteristics and to clarify their mechanisms for micro gap delamination defect of epoxy cast resin power apparatus. An experimental model simulating delamination defect was built. Nitrogen gas at atmospheric pressure was used as a typical filled gas inside the delamination of epoxy cast resin power apparatus. Simultaneous measurements of PD light emission intensity, PD light emission image and PD current pulse were carried out. PD inception voltage was measured for different delamination depths. PD generation characteristics were recorded. It was found that multiple PD events were detected only by PD light emission images and could not be detected by their current pulses as a result of very small magnitudes of PD current pulses. Time transition of PD activity for 10 minutes were obtained and analyzed using the captured light emission images. Based on the obtained results and comparing with SF6 gas filled delamination, physical mechanisms behind PD activity could be discussed.

Verification of percolating nature of ferromagnetic-paramagnetic transition in bulk manganite La0.75Ca0.25MnO3 with current-pulse conductivity study

A study of nonlinear effects in conductivity of a bulk sample of La0.75Ca0.25MnO3 grown by the floating-zone technique is presented. It was found in previous studies that paramagnetic-ferromagnetic (PM-FM) transition in this compound is of first order and has been suggested to have a percolating character. The aim of this study has been to reveal such effects. For this purpose, the conductivity in the PM-FM transition region has been studied by applying single ramp millisecond pulses (“sawtooth” shape) of current that linearly increase with time. Driving current pulse J(t) and its response voltage U(t) were recorded for different temperatures and magnitudes of current pulses. It was found that U(t) behavior in the temperature range of the PM-FM transition has features that must be attributed to a mixed phase state of the manganite sample near the ferromagnetic-paramagnetic transition and percolation character of this transition.

Predicting the release of metals from ombrotrophic peat due to drought-induced acidification

Ombrotrophic peats in northern England and Scotland, close to industrial areas, have substantial contents of potentially toxic metals (Al, Ni, Cu, Zn, Cd and Pb) and of pollutant sulphur, all derived from atmospheric deposition. The peat sulphur, ordinarily in reduced form, may be converted to sulphuric acid under drought conditions, due to the entry of oxygen into the peats. The consequent lowering of soil solution pH is predicted to cause the release of metals held on ligand sites of the peat organic matter. The purpose of the present study was to explore, by simulation modelling, the extent of the metal response. Chemical variables (elemental composition, pH, metal contents) were measured for samples of ombrotrophic peats from three locations. Water extracts of the peats, and samples of local surface water, were also analysed, for pH, dissolved organic carbon (DOC) and metals. Metal release from peats due to acidification was demonstrated experimentally, and could be accounted for reasonably well using a speciation code (WHAM/Model VI). These data, together with information on metal and S deposition, and meteorology, were used to construct a simple description of peat hydrochemistry, based on WHAM/Model VI, that takes into account ion-binding by humic substances (assumed to be the “active” constituents of the peat with respect to ion-binding). The model was used to simulate steady state situations that approximated the observed soil pH, metal pools and dissolved metal concentrations. Then, drought conditions were imposed, to generate increased concentrations of H 2SO 4, in line with those observed during the drought of 1995. The model calculations suggest that the pH will decrease from the initial steady state value of 4.3 to 3.3–3.6 during rewetting periods following droughts, depending upon assumptions about the amount of potentially mobile soil S. The pH decreases will be accompanied by increases in concentrations of dissolved metals (Mg, Al, Ca, Ni, Cu, Zn, Cd, Pb) of an order of magnitude or more, depending upon assumptions about the replenishment of soil metal pools by deposition. In the most realistic scenario for present conditions, the severity of pH depressions will gradually decline due to the relatively slow depletion of the soil S pool by droughts. However, the magnitudes of heavy metal pulses will decline quite rapidly (over two or three droughts) because current and future metal deposition is unable to compensate for leaching losses from the soil pools.

Seasonal phytoplankton composition, productivity and biomass in the Neuse River estuary, North Carolina

Phytoplankton community composition, productivity and biomass characteristics of the mesohaline lower Neuse River estuary were assessed monthly from May 1988 to February 1990. An incubation method which considered water-column mixing and variable light exposure was used to determine phytoplankton primary productivity. The summer productivity peaks in this shallow estuary were stimulated by increases in irradiance and temperature. However, dissolved inorganic nitrogen loading was the major factor controlling ultimate yearly production. Dynamic, unpredictable rainfall events determined magnitudes of seasonal production pulses through nitrogen loading, and helped determine phytoplankton species composition. Dinoflagellates occasionally bloomed but were otherwise present in moderate numbers; rainfall events produced large pulses of cryptomonads, and dry seasons and subsequent higher salinity led to dominance by small centric diatoms. Daily production was strongly correlated ( r = 0·82) with nitrate concentration and inversely correlated ( r = −0·73) with salinity, while nitrate and salinity were inversely correlated ( r = −0·71), emphasizing the importance of freshwater input as a nutrient-loading source to the lower estuary. During 1989 mean daily areal phytoplankton production was 938 mgC m −2, mean chlorophyll a was 11·8 mg m −3, and mean phytoplankton density was 1·56 × 10 3 cells ml −1. Estimated 1989 annual areal phytoplankton production for the lower estuary was 343 gC m −2.

Nocturnal and early morning secretion of ACTH and cortisol in humans

It is well established that the adrenocorticotropic hormone (ACTH) stimulates the synthesis and release of cortisol from the adrenal cortex, but the role of ACTH in the physiological regulation of basal cortisol secretion has received surprisingly little study. The authors studied the nocturnal and early morning secretory pulses of cortisol and ACTH in normal subjects. A pulse detection algorithm was developed. The relationship between ACTH and cortisol pulses in terms of temporal and proportional relationship is described. Pulse concomitance for ACTH with cortisol was 47% and for cortisol with ACTH pulses it was 60%. The first description of the relationship between concomitant ACTH and cortisol pulse magnitudes in humans is presented. A highly significant linear relationship between the magnitudes of ACTH and cortisol pulses is shown. Putative reasons for dissociated pulses and the potential implication of these findings are discussed.

Measurement of IEMP Currents Using Magnetic Thin Film Sensors

Accurate measurement of currents induced in complex electronic circuits by nuclear radiation is difficult due to circuit perturbations by the measurement technique itself, as well as normal instrumentation difficulties. Passive thin ferromagnetic films can be used to record the magnitudes of internal current pulses in the nanosecond region without seriously affecting the circuit being measured. This paper presents a summary of experiments conducted to determine the feasibility of using thin film sensors in radiation environments and the accuracy to which current can be measured in such environments with the thin film sensors.

Analysis of Pressure Pulse Generation Due to Gas Release from Failed Fuel Pins in a Liquid-Metal Fast Breeder Reactor

A model for the analysis of pressure pulse generation due to sudden gas release from failed pins in a liquid-metal fast breeder reactor is presented. The predictions of the model are compared to experimental data on sudden gas release in the ducts of the Experimental Breeder Reactor II. The predicted magnitudes of pressure pulses are in good agreement with the experimental observations. The predicted pressure pulse, however, seems to decay at a faster rate than the experimentally observed rate. The effects of the pin internal pressure upon rupture, the rupture area, and the amount of compressed gas are studied parametrically. The pressure pulse magnitude is found to be more sensitive to the internal pin pressure upon rupture than to either the rupture area or the compressed gas volume.

Incipient Boiling Pressure Pulse of Sodium under Forced Convection by Direct Heating

An account is given of experiments on incipient boiling pressure pulses imparted by liquid sodium, performed in a forced convection loop. The sodium is heated by direct current applied to the liquid metal itself in a vertical tube of 14.9 mm inner diameter through which the medium pumped. The experiments were carried out with the following ranges: Input power: 6–12kW,Pressure at condenser: 0.6–1.0 kg/cm2, Inlet temperature: 780°–850°C, Flow rate: 1.0–3. 5 l/min Typical pressure pulses registered during incipient boiling presented the form of damped oscillation. The initial pressure pulses were dependent on the location of boiling inception along the test section, the incipient boiling pattern and the degree of superheat. The initial pressure pulses observed were in the range of 0–3. 5 kg/cm2. The pressure pulses increased with the degree of superheat, which ranged 0°–150°C. The magnitudes of pressure pulses exceeded the saturation vapor pressure corresponding to the temperature of superheated liquid. Cons...

The use of double-beam detection systems with pulsed sources of vacuum ultraviolet radiation

Pulsed sources of far ultraviolet radiation may show intensity variations of ±5% from flash to flash. The use of a double-beam optical system can reduce the effect of this variation on measured parameters of reactions produced by the ultraviolet radiation. This paper describes the principle of the double-beam method and considers a particular application to the measurement of reflectivity in the far ultraviolet where there are problems associated with collimation and the creation of the second beam. The alternative approaches of integrating and counting methods of detection are briefly described, and the adoption of the integrating method is justified for the case when there is a high photon flux in a short time interval: equations are derived for the signal produced by the photomultiplier dark current in this situation. Block diagrams and circuits are given for a detection system which can record on paper tape the relative magnitudes of the simultaneous charge pulses from the photomultipliers used to detect the two beams of radiation. The experimental results from single and double-beam systems are compared.

Recurrence Phenomena in Cosmic-Ray Intensity

The adaptation of Chree's method of analyzing geomagnetic data, as carried out by Monk and Compton for their Mexican cosmic-ray data, has been applied to cosmic-ray intensity measurements at Boulder, Colorado. Secondary pulses in the cosmic-ray intensity are apparent in the difference curves. These occur at approximately 28-day intervals both before and after the primary pulse, in good agreement with the findings of Monk and Compton, but the Boulder pulses are somewhat smaller and more irregular. Within the four (previous and subsequent) pulse intervals investigated, magnitudes of the secondary pulses do not appear to depend upon the interval from the primary pulse.