Impulse Transfer Research Articles

Specific features of sacricin action on the disturbances in phospholipid metabolism during seizures

1 is a brain disease characterized by strong hyperactivity of neuronal populations. The goal of our research was to study different aspects of lipid metabolism in different phases of convulsive body response, namely, before and after a sacricin injection. Sacricin, a derivative of polycyclic carboxylic acid, possesses rather large anticonvulsant effect. The phospholipid (PL) extraction was performed with the use of Folch method [1], using Karagezyan’s modification [2]. PLs were fractionated by one-dimensional ascending chromatography in a thin layer of silica gel (Merk, Germany) using the solvent system chloroform : methanol : ammonia (65 : 35 : 5). Convulsive activity is characterized by disturbances of membrane-bound enzyme functional activity, a decrease in the number of receptors, increase in “flip-flop” transfers of phospholipids, and probable hydrolysis of phosphatidylinositols, which are involved in nerve impulse transfer and affect transport of PLs and diglyceride, which are secondary messengers [3, 4] responsible for maintenance of the functional activity of a cell. Taking into consideration the role of lipids in the structure‐functional organization of biological membranes [5, 6], we studied PL‐PL conversions in the brain cortex and cerebellum of rats during pentylenetetrazol seizures in the presence and absence of sacricin. Based on the presented results, we assumed the following: the convulsions enhanced the activity of phospholipase A 2 , which catalyzes reactions of PL deacyla1 Corresponding author; address: Hasratyan St. 7, Yerevan 0014, Armenia; e-mail: art79@rambler.ru tion and the formation of nonesterified fatty acids, which are substrates for the formation of a large quantity of lipid peroxides. We observed qualitative and quantitative shifts in the PL-PL ratio. Especially strong shifts were observed in the contents of phosphatidylcholines, phosphatidylserines, and mainly in lysophosphatidylcholines, which are the products of lysis of phosphatidylcholines. Injection of sacrisin strongly normalized PL metabolism and lipid peroxidation. The molecular mechanisms of the normalizing effect of this drug are associated with systems that regulate the reactions of PL‐PL interactions and peroxidation of lipids.

Linking pulses of atmospheric deposition to DOC release in an upland peat‐covered catchment

Changes in atmospheric deposition have been proposed as one possible explanation of the widespread increase in DOC concentration observed in many Northern Hemisphere catchments. This study uses detailed, long‐term, monthly monitoring records of pH, conductivity SO4, and DOC in precipitation, soil water, and runoff chemistry from an upland peat‐covered catchment in northern England. By deriving impulse transfer functions this study explores whether changes in deposition lead to significant changes in the occurrence of each component in the soil and runoff water; especially significant changes in DOC. The study shows that (1) impulses in the deposition of acidity have no significant effect upon pH or DOC in soil water or runoff. (2) DOC in soil water and runoff is responsive to impulses in SO4 and conductivity, but only when those impulses are changes in soil water chemistry and not when they are in atmospheric deposition. (3) The effects of changes in SO4 and/or conductivity can easily be overemphasized if memory effects are not accounted for, and their effect is limited to only 1 or 2 months after a severe drought. This study can support the view that changes in ionic strength can result in changes in DOC concentration in soil water or runoff, but the system studied is unresponsive to changes in atmospheric deposition. Impulses in soil water SO4 do not lead to increases in DOC concentrations, and so this mechanism does not provide an explanation for DOC increases.

Bispectral analysis of the long‐term recording of surface pressure at Jakarta

The long‐term series of surface pressure at Jakarta (6 S, 107 E) from 1842 to 2000 are analyzed for nonlinear three‐wave interaction. In the tropics, the variations of surface pressure are mainly caused by variations of the water vapor pressure. Jakarta is located in the strongest zone of water vapor convection of the Earth, and the pressure variations at Jakarta essentially influence or drive the circulation of the Earth's atmosphere. The bispectrum evaluates the phase relationships and the magnitudes of oscillation triads having the frequencies f1, f2, and f3 = f1 + f2. Analysis of the bispectrum from intraseasonal to decadal timescales quantifies the degree of nonlinearity in the troposphere and reveals the dominant oscillation triads. The bispectrum also informs about the energy and impulse transfer from low to high frequencies and vice versa. We find following main results for the Jakarta series: (1) a strong annual oscillation and strong harmonics up to the fourth order and higher, (2) strong interactions between the annual oscillation (AO) and the biennial oscillation (BO) and several components of the quasi‐biennial oscillation (QBO with periods at 2.79, 2.39, 1.72, 1.56‐year), (3) mixing processes between the annual harmonics and the interannual and decadal oscillations (10 to 40‐year) are obvious in the bispectrum, FFT‐spectrum, and in the temporal evolution of the amplitudes (derived from the bandpass‐filtered time series), and (4) a close relationship is found between the amplitudes of the semi‐annual oscillation and the quasi 4‐year oscillation (nonlinear interaction 2 cycles/a + 0.25 cycles/a = 2.25 cycles/a). The bispectral analysis of the Jakarta series gives us a detailed insight into the self‐organization of the atmospheric oscillations by nonlinear three‐wave interaction and permits the development of a strategy for improved detection, modeling, and forecasting of atmospheric variability.

Measuring and Modeling Violin Sound Radiation for Sound Equalization

During a performance a violin is put into vibration and this vibration is radiated to the air. Depending on the distance and direction of the listener, he perceives a slightly different sound. Sound radiation at each point in the space is determined by the impulse response or transfer function between vibration of the violin and sound pressure at that point. There is variety of methodologies to obtain acoustic impulse responses of violins. They differ mainly in the way of exciting the violin, the point of excitation, the position where the acoustic response is measured and how excitation and response signals are deconvolved. In this work we measure violin vibration with a bridge pickup and we 1) propose a method to calculate the transfer function between signals from the bridge pickup and a microphone, 2) use a 3D motion tracker to get the position of the microphone respect to the violin so that we can calculate the response for different directions and distances and 3) we model sound radiation as a "reference" impulse response and a parametric filter whose response depends on distance and orientation with respect to the "reference" position.

Identification of Nonlinear Systems: Volterra Series Simplification

Traditional measurement of multimedia systems, e.g. linear impulse response and transfer function, are sufficient but not faultless. For these methods the pure linear system is considered and nonlinearities, which are usually included in real systems, are disregarded. One of the ways to describe and analyze a nonlinear system is by using Volterra Series representation. However, this representation uses an enormous number of coefficients. In this work a simplification of this method is proposed and an experiment with an audio amplifier is shown.

Orbital transfer: Some links between the low-thrust and the impulse cases

Here, we investigate an orbital transfer from a low Earth orbit to the geostationary one where the considered criterion to maximize is the final mass. We seek to observe numerically the connections between the impulse transfer and the low-thrust one after giving two computational methods in each cases. We see that the links are very strong and that the impulse transfer can be viewed as the limit of the low-thrust transfer when its number of revolutions increases.

Maximum length sequences versus random telegraph noise in measuring impulse responses and transfer functions

Maximum length sequences (MLS) are commonly used to measure impulse responses and transfer functions of linear systems. The remarkable utility of the MLS comes from the property that its autocorrelation is approximately a delta function, and this approximation becomes more valid for higher orders (lengths) of MLS. However, the autocorrelation of a random telegraph noise (RTN) sequence also approaches a delta function in the long-sequence limit. Advances in computer hardware make it possible to use long sequences of RTN. Consequently one wonders if the MLS still confers an advantage. This study presents a quantitative analysis of the accuracy of MLS and RTN for all lengths up to 2N−1=262,143. RTN sequences were generated by scrambling the elements of an MLS. A special case wherein the approximate length of the impulse response is prior knowledge allows the measured impulse response to be windowed. Even with this advantage applied to RTN (but not to MLS), MLS measurements are clearly more accurate. The numerical experiments conclude than any MLS sequence longer than the impulse response outperforms a RTN of any practical order by an order of magnitude. [Work supported by the NIDCD grant DC 00181.]

Particular solutions and Riemann problem for modified shallow water equations

In this article gas-dynamic analogy for shallow water equations is generalized in the case when initial conditions depend on vertical coordinate. Simple parameterization of advective term allowing full theoretical analysis of solutions of simple waves and Riemann problem for modified shallow water equations is suggested. The simple wave solutions obtained have permitted to find dimensionless parameter, which restricts limits of applicability of classical shallow water equations and neglecting advective impulse transfer. Solution of the initial discontinuity decay problem for modified shallow water equations is found.

Interaction Between Amygdala and Neocortical Inputs in the Perirhinal Cortex

The rhinal cortices play a critical role in high-order perceptual/mnemonic functions and constitute the main route for impulse traffic to and from the hippocampus. However, previous work has revealed that neocortical stimuli that activate a large proportion of perirhinal neurons are unable to discharge entorhinal cells. In search of mechanisms that might facilitate impulse transfer from the neocortex to the entorhinal cortex, we have examined changes in excitability produced by activation of the lateral amygdala (LA) in isoflurane-anesthetized animals. LA stimulation activated a large proportion of peri- and entorhinal neurons. However, conditioning LA stimuli did not increase the ability of neocortical inputs to activate entorhinal cells even though such pairing produced marked increases in neocortically evoked field potentials and orthodromic firing in the perirhinal cortex. Moreover, increased neocortically evoked perirhinal field potentials and unit responses persisted when the conditioning LA shock was replaced by another neocortical stimulus at the same or at a different site as the testing shock. This perirhinal paired-pulse facilitation (PPF) was maximal with interstimulus intervals of approximately 100 ms. Intracellular recordings of perirhinal neurons revealed that the PPF was generally associated with a rapid shift in the balance between inhibition and excitation, leading to an overall increase in perirhinal responsiveness. The significance of these findings for the role of the perirhinal cortex is discussed.

Low-probability transmission of neocortical and entorhinal impulses through the perirhinal cortex.

One model of episodic memory posits that during slow-wave sleep (SWS), the synchronized discharges of hippocampal neurons in relation to sharp waves "replay" activity patterns that occurred during the waking state, facilitating synaptic plasticity in the neocortex. Although evidence of replay was found in the hippocampus in relation to sharp waves, it was never shown that this activity reached the neocortex. Instead, it was assumed that the rhinal cortices faithfully transmit information from the hippocampus to the neocortex and reciprocally. Here, we tested this idea using 3 different approaches. 1) Stimulating electrodes were inserted in the entorhinal cortex and temporal neocortex and evoked unit responses were recorded in between them, in the intervening rhinal cortices. In these conditions, impulse transfer occurred with an extremely low probability, in both directions. 2) To rule out the possibility that this unreliable transmission resulted from the artificial nature of electrical stimuli, crosscorrelation analyses of spontaneous neocortical, perirhinal, and entorhinal firing were performed in unanesthetized animals during the states of waking and SWS. Again, little evidence of propagation could be obtained in either state. 3) To test the idea that propagation occurs only when large groups of neurons are activated within a narrow time window, we computed perievent histograms of neocortical, perirhinal, and entorhinal neuronal discharges around large-amplitude sharp waves. However, these synchronized entorhinal discharges also failed to propagate across the perirhinal cortex. These findings suggest that the rhinal cortices are more than a relay between the neocortex and hippocampus, but rather a gate whose properties remain to be identified.

CONTRIBUTION TO THE EXTENSION OF MODAL ANALYSIS TO NON-LINEAR STRUCTURE USING VOLTERRA FUNCTIONAL SERIES

Modal analysis is extensively used to study dynamic behaviour of linear mechanical structures. The extension of this tool to non-linear structures is examined here, using Volterra functional series which generalises the superposition principle and permits to obtain impulse responses and transfer functions of various orders. These functions will be presented in close-form expressions which allow going from one class of functions to another one.

Input–Output Identifiability of Continuous-Time Linear Systems

In time-domain identification of linear systems the aim is to estimate the impulse response or transfer function of a linear system to within a given tolerance using a finite number of noisy observations of the output. Whether this is possible depends on the model set, that is, a given set to which the system is assumed to belong a priori. We give necessary and sufficient conditions on the model set to ensure that such identification is possible in the continuous-time case.

Quantitative modelling of crude oil toxicity using the approach of cybernetics and structured mechanisms of microbial processes.

Cybernetics and structured approach to biochemical processes in microbial cells offer the status of using various cell components of Azotobacter as molecular markers in toxicity assay of environmental toxicants. The intra-linked dynamic physicochemical reactions of the basic macromolecules--DNA, protein and membrane lipids--with respect to the crude oil in the growth environment, results in an 'impulse transfer function'. The structured effects are reduction in both DNA and protein levels, and an elevated level of lipid peroxidation products. Toxicity index (Ti) of the crude oil, at a given concentration, is the percent ratio of the summation of the products of these effect parameters' and their respective weightings, relative to control. The EC50 is the effective percent (w/v) concentration of the crude oil at which a toxicity index of 50% was recorded, and this corresponded with about 44% loss in nitrogen fixation of the diazotrophic bacterium.

Close-range blast loading of aluminium foam panels

Full-scale field tests have been carried out in order to investigate the behaviour of aluminium foam panels subjected to blast loading. Charges were detonated at a given standoff distance in front of the foam panels, which were attached to the bob of a ballistic pendulum. Using this test set-up, the maximum swing of the pendulum after each test was used to calculate the energy and impulse transfer from the blast loading. Tests were carried out by varying the foam panel density and charge mass. Experiments were also done with an aluminium cover plate attached to the front of the foam panels. In general, it was observed that the energy and impulse transfer to the pendulum increased by adding a foam panel. In order to investigate this phenomenon, an analytical solution based on shock-wave theory was proposed in order to describe the deformation behaviour of a one-dimensional foam bar subjected to a linearly decaying blast loading. However, using this approach, it was found that the addition of a foam bar should not change the global response of the pendulum. On the other hand, similarities between the present case and recent investigations reported in the literature suggest that the observed increase in maximum swing of the pendulum when adding foam panels may be due to the continuous changing of the shape of the initially plane panel surface into a concave shape. In this way, surface effects could be controlling the energy and impulse transfer.

Recursive Halfband-Filters

The paper describes the properties and the design of recursive halfband-filters.The two possibilities of being complementary are introduced. The lowpass with the transfer function HLp(z)and the corresponding highpass, described by HHp(z) = HLp(-z)can either be strictly complementary or power complementary. According to the respective symmetry, the impulse responses, transfer functions and frequency responses possess certain characteristic properties, which are described in section 2. It turns out that these resulting symmetries of the frequency response reduce the number of the choosable design parameters. We can only prescribe the cutoff frequency and the tolerated deviation either for the passband or the stopband. In the third section we treat the design of halfband-filters with approximately linear phase. By coupling an appropriately designed allpass of even degree nA with a delay of order m=nA±1 we obtain the desired solution by solving a corresponding approximation problem for the phase of the allpass. The resulting lowpass and highpass are strictly as well as power complementary!The kind of approximation will be done in the sense of maximal flatness, where a closed form solution exists [8], or in the sense of Chebychev, where the solution is obtained iteratively [13]. The design of systems with minimum phase is presented in section 4. The resulting lowpass and highpass are power complementary. Closed form solutions yield Butterworthand Cauer filters, if a maximal flat or a Chebychev approximation is desired. In all cases a fixed relation exists between the passband frequency ΩP and the tolerated deviation δP in the passband when the degree n has been chosen.

Layered sacrificial claddings under blast loading Part I — analytical studies

In this paper, we present the behaviour of layered sacrificial claddings subjected to blast loading.The cladding layers are constructed out of thin mild steel sheets. The blast load was modelled as an equivalent triangular blast pulse. Both experimental and numerical analyses have been carried out. The analytical work is presented in this paper. Finite element analysis with step by step time marching under large deformation and large strain is carried out. Contact interface elements are used at the foldings of the sheet metal during the collapse of the layers. Isotropic strain hardening with dynamic yield properties according to Cowper–Symonds relation were employed for the material properties at the integration points at every time step. The layers undergo large plastic deformations and absorb energy before collapsing to a more stable configuration. The layers collapse successively, one after the other. The mode of collapse of the unit cell in any layer is always same. Substantial reduction in impulse transfer is observed at the base of the cladding structure as much of the energy is absorbed due to plastic deformations. A simple analytical model is also proposed for the sacrificial cladding structures.Under blast loading, layered sacrificial claddings are very effective in energy absorption and they have a predictable behaviour. Hence, they can be used in design of reliable blast resistant structures.

Introduction to fractional linear systems. Part 2: Discrete-time case

In the paper, the class of discrete linear systems is enlarged with the inclusion of discrete-time fractional linear systems. These are systems described by fractional difference equations and fractional frequency responses. It is shown how io compute the impulse response and transfer function. Fractal signals are introduced as output of special linear systems: fractional differaccumulators, systems that can be considered as having fractional poles or zeros. The concept of fractional differaccumulation is discussed, gencralising the notions of fractal and lif noise, and introducing two kinds of fractional differaccumulated stochastic proccss: hyperbolic, resulting from fractional accumulation (similar to the continuous-time casc), and parabolic noise, resulting from fractional differencing.

Linear systems analysis in a karst aquifer

A linear systems analysis applied to groundwater flow is presented as an alternative modeling technique to traditional discretized groundwater models (i.e. finite-difference and finite-element), which require elaborate parameters and boundary conditions. Linear systems analysis has been used extensively for surface-water modeling and to a lesser extent for groundwater applications. We present a method for the analysis of an aquifer's response in hydraulic head to recharge that comprises two major components. The first component is to predict the drop in hydraulic head over time if recharge is eliminated. By fitting logarithmic curves to selected short-term hydraulic head recession periods, a long-term recession or “base head” can be established. The estimation of base head is necessary for the second component of the method, which is the derivation of an impulse response function or transfer function. The transfer function was derived by deconvolution of two time series data sets—estimated recharge and the measured response in hydraulic head. An aquifer's response to recharge can be characterized and modeled by using the transfer function, which also establishes the time to peak response, the response time distribution, and the total memory length of the system. The method requires fitting smooth curves to the oscillatory transfer function derived by deconvolution in the Fourier transform domain. The smooth curve is considered to be the physically valid transfer function. In this analysis, curve fitting was more effective than other smoothing techniques commonly used. We applied the method to the karstic Madison aquifer and found that the time to peak response is less than one month, the system's total memory is about six years, and a logarithmic curve best fits the system response. This method has potential to be useful as a predictive tool in aquifer management.

Optimal flights to near-Earth asteroid

The spacecraft flights to the Near-Earth asteroid in order to give an impact influence on the asteroid, correct its orbit and prevent the asteroid’s collision with the Earth are analyzed. In the first part, the impulse flights are analyzed in the Lambert approach. There are determined the optimal trajectories maximizing the asteroid deviation from the Earth. In the second part, the flights with the chemical and electric-jet engines are analyzed. The high thrust is used to launch the spacecraft from the geocentric orbit, and the low thrust is applied for the heliocentric motion. On the base of optimal impulse transfer, the optimal low thrust trajectories are determined using Pontryagin maximum principle. The numerical results are given for the flight to the asteroid Toutatis. Parameters of the spacecraft impact on the asteroid are determined. The asteroid deviation from the Earth caused by the spacecraft influence is presented.

The intrinsic dynamics of retinal bipolar cells isolated from tiger salamander

We studied how intrinsic membrane properties affect the gain and temporal pattern of response in bipolar cells dissociated from retinae of tiger salamanders. Currents specified by a pseudorandom binary sequence, an m-sequence, superimposed on various means, were injected into the cells. From the resultant membrane voltage response for each mean current, impulse responses were estimated. From each impulse response, transfer function, gain, and time constant were calculated. The bipolar cells acted as quasilinear adaptive filters whose gain and response speed are determined by the mean input current. Near resting potential, gain. and time constant were maximum. Dynamics were slow and low-pass, characterized by an approximately exponential impulse response. With depolarization, gains were reduced sharply, responses were much faster, and dynamics became band-pass, as indicated by an undershoot in the impulse response. For any given mean current, the shape of the impulse response did not depend on the amplitude of the m-sequence currents. Thus, bipolar cells behaved in a quasilinear fashion. The adaptive behavior was eliminated by blocking a potassium current, which implicates the role of a voltage-gated potassium conductance. Computer simulations on a model neuron including a delayed-rectifier reconstructed the observed behavior, and provided insight into other, less readily observable, parameters. Thus, bipolar cells, even when isolated, possess mechanisms which regulate, with unsuspected elaborateness, the sensitivities and dynamics of their responsiveness. Implications for adaptation and neuronal processing are discussed.