Simple Exponential Decay Function Research Articles

Supercollisions of fast H-atom with ethylene on an accurate full-dimensional potential energy surface.

The collisions transferring large portions of energy are often called supercollisions. In the H + C2H2 reactive system, the rovibrationally cold C2H2 molecule can be activated with substantial internal excitations by its collision with a translationally hot H atom. It is interesting to investigate the mechanisms of collisional energy transfer in other important reactions of H with hydrocarbons. Here, an accurate, global, full-dimensional potential energy surface (PES) of H + C2H4 was constructed by the fundamental invariant neural network fitting based on roughly 100 000 UCCSD(T)-F12a/aug-cc-pVTZ data points. Extensive quasi-classical trajectory calculations were carried out on the full-dimensional PES to investigate the energy transfer process in collisions of the translationally hot H atoms with C2H4 in a wide range of collision energies. The computed function of the energy-transfer probability is not a simple exponential decay function but exhibits large magnitudes in the region of a large amount of energy transfer, indicating the signature of supercollisions. The supercollisions among non-complex-forming nonreactive (prompt) trajectories are frustrated complex-forming processes in which the incoming H atom penetrates into C2H4 with a small C-H distance but promptly and directly leaves C2H4. The complex-forming supercollisions, in which either the attacking H atom leaves (complex-forming nonreactive collisions) or one of the original H atoms of C2H4 leaves (complex-forming reactive trajectories), dominate large energy transfer from the translational energy to internal excitation of molecule. The current work sheds valuable light on the energy transfer of this important reaction in the combustion and may motivate related experimental investigations.

Carbon Sequestration Due to Commercial Forestry: An Equilibrium Analysis

Abstract Carbon sequestration is one of the tools being used to respond to climate change risks. It is known that carbon stored in wood products is a type of sequestration. However, time frames for evaluating wood use can affect conclusions about sequestration benefits; a long-term perspective and large spatial scale may help clarify these issues. Therefore, I undertook an equilibrium analysis of ongoing commercial forestry operations, relative to carbon sequestration, at the landscape scale. I found that for simple exponential decay functions for wood remaining in use over time, the total sequestered wood at equilibrium is simply the integral of the decay function multiplied by wood product produced. I show that this simple multiplier is a linear function of half-life. For a 50-year wood half-life, this equilibrium multiplier is 72.1. The half-life depends on the specific wood product (lumber, etc.). For waste wood used for energy at mills, typical values yielded a 100-year sequestration (avoided emissions) value of 12H where H is tons of carbon in logs delivered to the mill. This exercise demonstrates that commercial forestry is a significant provider of carbon sequestration through wood products, in addition to other sequestration benefits. The simple multipliers developed here are intuitive and can be easily used with operational wood product data at any scale.

Extending the range of time constants recorded by the SPECTREM AEM system

In order to get the correct amplitudes of the secondary field measurements, the correct value for the primary signal must be subtracted from the input signal where both secondary and primary are recorded together. This is due to the secondary signals being measured while the transmitter is on. The onboard data system approximates the transmitter signal by the total signal value in the last window, it being assumed that the secondary signal has decayed to a negligible value at that delay time.The result of subtracting too much from the secondary signal and adding this excess to the primary signal is that the secondary signals are no longer sums of simple exponential decay functions. A procedure is described to estimate the decay functions as well as the offset to be subtracted from the initial estimate of the primary.

Temperature dependence scaling behavior of the dynamic hysteresis in 0.715Bi0.5Na0.5TiO3-0.065BaTiO3-0.22SrTiO3 ferroelectric ceramics

Temperature dependent dynamic hysteresis of 0.715Bi0.5Na0.5TiO3-0.065BaTiO3-0.22SrTiO3 (BNT-BT-ST) bulk ferroelectric ceramic was systematically studied. The scaling relations were estimated for corrective electric field remnant polarization and hysteresis loop area as a function of temperature It was observed that and for a constant magnitude of electric field To understand the domain dynamics, back-switching polarization as a function of is also predicted. The relation between back-switching polarization and temperature is estimated by well described Arrhenius law to evaluate the average activation energy. It also depends on the applied electric field; the relation fits well to a simple exponential decay function. The saturation polarization as a function of was also evaluated to estimate the electrocaloric effect. It was found that electrocaloric effect and heat extract capacity in BNT-BT-ST ceramic is of a similar order to that observed in most other lead-free bulk ferroelectric ceramics. It can be said that BNT-BT-ST is also a promising material for solid state refrigeration. These results can be helpful to understand the temperature dependent hysteresis behavior and polarization switching in lead-free ferroelectric ceramics.

Efficient Algorithm for Generating Maxwell Random Variables

A fast, easily implemented and high efficiency algorithm is derived for sampling from the Maxwell distribution. The algorithm is derived from the rejection-acceptance sampling method using the simple exponential decay function as an envelope function for the Maxwell distribution. The derived algorithm requires less number of random numbers per iteration, consumes less number of random numbers per sample and requires less expensive computation functions than the direct and Johnk’s algorithms. The speed of the proposed algorithm is about 1.6 times that of the direct algorithm and is about 1.5 times that of Johnk’s algorithm. Since the proposed algorithm for sampling from Maxwell distribution verified high efficiency and speed, Watt random variables can be generated by transforming Maxwell random variables generated by the proposed algorithm. The speed of generating Watt random variables using the proposed algorithm is about 1.1 times that generated from Kalos’s algorithm.

Probabilistic Characterization of Spatially Correlated Response Spectra for Earthquakes in Japan

Seismic hazard and risk assessments of spatially distributed infrastructural systems require seismic demand models that capture random but correlated simultaneous seismic effects at multiple sites. This study characterizes spatially correlated ground-motion parameters probabilistically using comprehensive databases of the K-NET and KiK-net strong-motion networks in Japan by developing a ground-motion prediction equation and then investigating the correlation structure of regression residuals from the prediction equation. Analysis results indicate that (1) interevent residuals of ground-motion parameters at different vibration periods are more strongly correlated than intraevent and total residuals with zero separation distance; and (2) intraevent spatial correlation coefficients can be described as a simple exponential decay function that is independent of the way the event-based intraevent standard deviation is calculated, of the earthquake type, and of the vibration period. The developed overall correlation model of spatially correlated ground-motion parameters may be used for seismic hazard and risk assessments in a subduction environment.

Rotating disk apparatus for polymer-induced turbulent drag reduction

In order to investigate turbulent drag reduction (DR), a rotating disk apparatus (RDA) generating an “external flow” was designed and then polymer-induced DR efficiency of water-soluble polymers both poly (ethylene oxide) (PEO) and poly (acryl amide) (PAAM) were examined as a function of either polymer concentration or temperature. The need for a sensitive measuring system at high Reynolds numbers has stimulated the development of a high-precision computer-aided system, which is able to measure the difference between the torques for a Newtonian fluid and a dilute polymeric solution with drag reducers very accurately. Their mechanical degradation behavior in the RDA as a function of time in a turbulent flow was also analyzed using both a simple exponential decay function and a fractional exponential decay equation. The fractional exponential decay equation was found to fit the experimental data better than the simple first-order degradation exponential decay function in the case of PEO.

Fitting light saturation curves measured using modulated fluorometry

A blue diode PAM (Pulse Amplitude Modulation) fluorometer was used to measure rapid Photosynthesis (P) versus Irradiance (E) curves (P vs. E curves) in Synechococcus (classical cyanobacteria), Prochlorothrix (prochlorophyta), Chlorella (chlorophyta), Rhodomonas (cryptophyta), Phaeodactylum (bacillariophyta) Acaryochloris (Chl d/a cyanobacteria) and Subterranean Clover (Trifolium subterraneum, Papilionaceae, Angiospermae). Effective quantum yield (Phi(PSII)) versus irradiance curves could be described by a simple exponential decay function (Phi(PSII) = Phi(PSII, maxe(-kE)) although Log/Log transformation was sometimes found to be necessary to obtain the best fits. Photosynthesis was measured as relative Electron Transport Rate (rETR) standardised on a chlorophyll basis. P versus E curves were fitted to the waiting-in-line function (an equation of the form P = P(max) x k x E x e(-kE)) allowing half-saturating and optimal irradiances (E(optimum)) to be estimated. The second differential of the equation shows that at twice optimal light intensities, there is a point of inflection in the P versus E curve. Photosynthesis is inhibited 26.4% at this point of inflection. The waiting-in-line model was found to be a very good descriptor of photosynthetic light saturation curves and superior to hyperbolic functions with an asymptotic saturation point (Michaelis-Menten, exponential saturation and hyperbolic tangent). The exponential constants (k) of the Phi(PSII) versus E and P versus E curves should be equal because rETR is directly proportional to Phi(PSII) x E. The conventionally calculated Non-Photochemical Quenching (NPQ) in Synechococcus was not significantly different to zero but NPQ versus E curves for the other algae could be fitted to an exponential saturation model. The kinetics of NPQ does not appear to be related to the kinetics of Phi(PSII) or rETR.

Improved adaptive spatial distance-weighted median filter

This paper introduces a new class of weighted median filters. The proposed algorithm employs a spatial distance weighting function, which is based on the conclusion that the degree of similarity between two stimuli can be quantified as a simple exponential decay function of a normalized distance in a psychological space. Depending on two parameters of the weighting function, the proposed approach can provide filtering performance ranging from an identity operation to that of the standard median filter (SMF), and by adaptively adjusting one of the parameters, the best possible filtering effect may be achieved. The experimental results show the supriority of the proposed solution to the SMF and some other median filtering methods in terms of both the objective measures and the perceptual visual quality.

Interpretation of EIS data from accelerated exposure of coated metals based on modeling of coating physical properties

Electrochemical studies on the accelerated weathering of corrosion protective coatings systems in this laboratory have yielded time series data in the low frequency portion of the spectrum that can be fit by a simple exponential decay function in time. A description of how this can be empirically used for lifetime prediction for coatings has already been presented. Attempts have been made to use other parts of the EIS spectrum for analyzing coating performance in accelerated exposure, but these have not yet yielded a predictive model for the effects of exposure on the structure and performance of organic coatings. First, a simple model which considers only loss of coating thickness by UV-induced ablation is applied to the interpretation of EIS time series results from coatings systems undergoing accelerated weathering. Next, more complete models which include a diffusion front of electrolyte that moves with either Fickian or Type II diffusion kinetics are applied to the same problem. Incorporating these models for degradation as a simple RC equivalent circuit representation of a coating gives predictions of EIS performance that have reasonable agreement with experimental data. Further, using a two layer representation of coating changes due to water intrusion and known effective medium theories for dielectric and resistivity changes due to water intrusion allow prediction of the changes in EIS spectra seen in immersion or other accelerated testing of coating films. These results provide further evidence of the power of modeling physical processes in interpreting EIS data and predicting coating protective lifetimes.

Correlation between the crystalline environment and optical property of Mn2+ ions in ZnGa2O4: Mn2+ phosphor

Sol-gel-driven ZnGa2O4:Mn2+ phosphors are annealed at various temperatures. As an increase of the annealing temperature of as-grown ZnGa2O4:Mn2+ phosphors, their lattice constants and crystallinities are increased. The resonance signal intensity of Mn2+ ions on Td sites is drastically increased whereas that of Mn2+ ions on Oh sites is decreased as the annealing temperature is increased. The decay curves are well fitted with two simple exponential decay functions indicating the existence of two origins. Liquid nitrogen-temperature emission spectra show two emission peaks suggesting that they originate from Mn2+ ions on Td and on Oh sites. The emission intensity of Mn2+ ions on Td sites is drastically increased whereas that of Mn2+ ions on Oh sites is decreased. The variation of the optical characteristics agrees with the concentration of Mn2+ ions at Td site and its site environment.

Relative phase dynamics in perturbed interlimb coordination: stability and stochasticity.

Various stability features of bimanual rhythmic coordination, including phase transitions, have been modeled successfully by means of a one-dimensional equation of motion for relative phase obeying a gradient dynamics, the Haken-Kelso-Bunz model. The present study aimed at assessing pattern stability for stationary performance and estimating the model parameters (a, b, and Q) for the stochastic extension of this model. Estimates of a and b allowed for reconstruction of the potential defining the gradient dynamics. Two coordination patterns between the forearms (in-phase, antiphase) were performed at seven different frequencies. Model parameters were estimated on the basis of an exponential decay parameter describing the relaxation behavior of continuous relative phase following a mechanical perturbation. Variability of relative phase and relaxation time provided measures of pattern stability. Although the predicted inverse relation between pattern stability and movement frequency was observed for the lower tempo conditions, it was absent for the higher tempos, reflecting the influence of task constraints. No statistically significant differences in stability were observed between the two coordination modes, indicating the influence of intention. The reconstructed potential reflected the observed stability features, underscoring the adequacy of the parameter estimations. The relaxation process could not be captured adequately by means of a simple exponential decay function but required an additional oscillatory term. In accordance with previous assumptions, noise strength Q did not vary as a function of movement frequency. However, systematic differences in Q were observed between the two coordination modes. The advantages and (potential) pitfalls of using stationary performance of single patterns to examine the stability features of a bistable potential were discussed.

Flicker and the efficiency of cues for capturing attention

In this paper, we present new experimental results which speak of the topic of temporal properties of processes underlying the selection of spatial location. We used the double motion induction paradigm to assess the strength of the selective effects. Prior exposure of an area to flicker, decreased the effectiveness of a cueing spot presented later at that location. This effect lasted for at least 1.5 s. In further experiments, it was found that both static and flickering cues, with time, lose their effectiveness to facilitate processing. While the static cueing decays quickly to very low effectiveness, flicker cueing decays to a level of effectiveness which can be maintained for a long time. Thus with time two flickering cues presented with a temporal offset become equivalent to each other, but remain more effective than a static cue. We conclude that mechanisms coding temporal change determine cue effectiveness for capturing attention. Simple exponential decay functions with different temporal constants and different lower asymptotes can describe these effects.

Size of the Zinc Pools That Exchange Rapidly with Plasma Zinc in Humans: Alternative Techniques for Measuring and Relation to Dietary Zinc Intake

A relatively simple technique was used to estimate the size of the combined pools of zinc with which plasma zinc exchanges within 2 d (EZP). EZP size was determined from the amount of isotope introduced into the plasma and the coefficient of the simple exponential decay function fitting enrichment data between d 3 and 9 after isotope administration. Using data from 11 healthy adults, comparisons were made of EZP size estimations using oral and intravenous isotopes (r = 0.93 using urine) and urine and plasma enrichment (r = 0.85 for intravenous). EZP size estimations from urine and plasma enrichment following intravenous isotope administration were 2.35 +/- 0.84 and 2.83 +/- 0.86 mmol, respectively (mean +/- SD, P < 0.01). EZP size correlated with habitual dietary zinc intake (partial r = 0.74, P < 0.02). Cumulative declines in EZP size in two healthy adults after 3 wk of consuming a moderately zinc-restricted diet followed by 1 wk of severe zinc restriction were 26 and 32%. These results indicated that EZP size is dependent on dietary intake. We conclude that this technique is adequate to demonstrate EZP differences that are of nutritional and physiological interest. EZP size estimates can be obtained using orally or intravenously administered isotope and using plasma or urine enrichment data.

Internal motions in proteins and gating kinetics of ionic channels

Single-channel current recordings have revealed a complex kinetic behavior of ionic channels. Many channels exhibit closed-time distributions in which long waiting times occur with a much higher frequency than predicted by a simple exponential decay function. In this paper a model for opening-closing transitions that accounts for internal motions in the protein matrix is discussed. The model is based on the notion that the transition between a conductive and a nonconductive state of the channel represents a local process in the protein, such as the movement of a small segment of a peptide chain or the rotation of a single amino-acid residue. When the blocking group moves into the ion pathway, a structural defect is created consisting in a region of loose packing and/or poor hydrogen bonding. By rearrangements of neighboring groups, the defect may migrate within the protein matrix, carrying out a kind of random walk. Once the defect has moved away from the site where it was formed, a transition back to the open state of the channel is possible only when the defect has returned by chance to the original position. The kinetic properties of this model are analyzed by stochastic simulation of defect diffusion in a small domain of the protein. With a suitable choice of domain size and diffusion rate, the model is found to predict closed-time distributions that agree with experimental observations.

Time, interference, and rate of presentation in short-term recognition memory for items

A list of 9 or 15 letters was presented at a rate of 1, 2, or 4 letters per second, followed by a test letter, followed by the subject's decision as to whether the test letter appeared in the previous list. The decay of trace strength was a simple exponential decay function of delay. However, the rate of decay was not constant for different rates of presentation, whether delay was measured in time or intervening items. Rather, time decay rate increased approximately linearly with presentation rate, but with a positive intercept, not a zero intercept as required by the hypothesis that delay is measured in intervening items. Decay rate for previous items appears to be greater during the time (less than 0.25 sec.) for acquisition of an item than during the time between acquisition of adjacent items.

Energy transfer in organic systems V. Lifetime studies of anthracene-perylene transfer in benzene solutions

The fluorescence response functions of oxygen-free benzene solutions containing 3 × 10-3M anthracene and concentrations of up to 1·2 × 10-3M perylene were observed using the phase and modulation fluorometer. The response functions of the directly excited anthracene and perylene fluorescence are simple exponential decay functions, while that of the perylene fluorescence, indirectly excited by energy transfer from anthracene, is the difference of the two exponential decay functions. Stern-Volmer kinetics are applicable because of the statistical `mixing' of the molecules by diffusion, which increases the effective critical dipole-dipole transfer radius from 31 Angstrom to 43 Angstrom.

Application of a trace model to the retention of information in a recognition task

A stochastic model is proposed to account for the behavior of subjects in recognition tasks in which stimuli are presented, one at a time, in a protracted sequence. The basic assumption is that the memory trace resulting from the presentation of a particular stimulus not only fades away during the presentation of subsequent stimuli but also “diffuses” in such a way as to become decreasingly stimulus specific. An account is thereby provided for both (a) the increase in the probability of false recognition with the total number of stimulus presentations and (b) the departure of curves of forgetting from the previously proposed simple exponential decay functions. An expression for the amount of information carried along when the number of stimulus presentations becomes large is then derived for subjects who conform with the model.