Delay Time Tau Research Articles

Analysis on RF Parameters of Nanoscale Tunneling Field-Effect Transistor Based on InAs/InGaAs/InP Heterojunctions

Tunneling field-effect transistors (TFETs) based on the quantum mechanical band-to-band tunneling (BTBT) have advantages such as low off-current and subthreshold swing (S) below 60 mV/dec at room temperature. For these reasons, TFETs are considered as promising devices for low standby power (LSTP) applications. On the other hand, silicon (Si)-based TFETs have a drawback in low on-state current (lon) drivability. In this work, we suggest a gate-all-around (GAA) TFET based on compound semiconductors to improve device performances. The proposed device materials consist of InAs (source), InGaAs (channel), and InP (drain). According to the composition (x) of Ga in In1-xGa(x)As layer of the channel region, simulated devices have been investigated in terms of both direct-current (DC) and RF parameters including tunneling rate, transconductance (g(m)), gate capacitance (Cg), intrinsic delay time (tau), cut-off frequency (fT) and maximum oscillation frequency (f(max)). In this study, the obtained maximum values of tau, fT, and f(max) for GAA InAs/In0.9Ga0.1As/InP heterojunction TFET were 21.2 fs, 7 THz, and 18 THz, respectively.

Linear stochastic system with delay: Energy balance and entropy production

We study the energy balance in a linear stochastic dynamics with delay under the impact of an external periodic force. The linearity of the model, in combination with a response function method, enables us to perform detailed analytic calculations of each term in the energy balance equation. From this, we discuss thermodynamics and entropy production rate sigma . With use of the delay time tau and strength of the external force A0 , sigma is simply expressed as sigma=sigma_{D,1}(tau)+A_{0};{2}eta(tau) , with both sigma_{D,1}(tau) and eta(tau) positive definite. We thus conclude that even when there is no external force (A_{0}=0) , the entropy production rate sigma=sigma_{D,1}(tau) is positive, meaning that the delay force produces work, which is dissipated into a reservoir. Numerical experiments are performed to confirm theoretical results.

Robust entrainment phenomena of oscillations by delay time in the photosensitive Oregonator model

The influences of delayed feedback on the oscillating behaviors are numerically investigated by using the photosensitive Oregonator model with a Hopf point. We find that the time delay in the robust entrainment phenomena determines the time scale of the system, that is, T_{m}=(tau+delta)N (N=1,2,cdots, three dots, centered) , where T_{m} is the mean period of the oscillation and delta is a small constant compared with the delay time tau . Further, our numerical simulation shows that, when the system has a characteristic period T0 under the feedback with time delay, there exists an asymptotical line delta=delta_{0}T_{0} ( delta_{0} independent of any parameters) in the entrainment region with increasing strength of the feedback control c ; when the system has no characteristic period, the above linear relation is also kept, and delta decreases with increasing c .

Resonant control of stochastic spatiotemporal dynamics in a tunnel diode by multiple time-delayed feedback

We study the control of noise-induced spatiotemporal current density patterns in a semiconductor nanostructure (double-barrier resonant tunneling diode) by multiple time-delayed feedback. We find much more pronounced resonant features of noise-induced oscillations compared to single time feedback, rendering the system more sensitive to variations in the delay time tau . The coherence of noise-induced oscillations measured by the correlation time exhibits sharp resonances as a function of tau , and can be strongly increased by optimal choices of tau . Similarly, the peaks in the power spectral density are sharpened. We provide analytical insight into the control mechanism by relating the correlation times and mean frequencies of noise-induced breathing oscillations to the stability properties of the deterministic stationary current density filaments under the influence of the control loop. Moreover, we demonstrate that the use of multiple time delays enlarges the regime in which the deterministic dynamical properties of the system are not changed by delay-induced bifurcations.

Inotropic effect of digoxin in humans: mechanistic pharmacokinetic/pharmacodynamic model based on slow receptor binding.

The purpose of this study was to construct a mechanistic pharmacokinetic/pharmacodynamic (PK/PD) model for digoxin that describes the relationship between plasma concentration and inotropic response. On the basis of results obtained in the isolated perfused rat heart, a PK/PD model for digoxin in humans was developed. In fitting the model to previously published bolus dose and concentration clamp data (shortening of electromechanical systole), the plasma concentration-time curves were used as forcing functions in the computer program ADAPT II. The mechanistic approach allowed a modeling of digoxin pharmacodynamics which is consistent with available inotropic response data. The estimates of the receptor binding parameters were in the same order of magnitude as those measured in vitro for ouabain. The mechanistic model explained the parameters of the empirical link model (EC50, Emax and delay time tau) in terms of the underlying processes, suggesting that the long equilibration half-time of 13 h is due to slow receptor binding. The empirical link model, in contrast, is not compatible with a noninstantaneous receptor binding process and led to estimates of the delay time tau that were dependent on the digoxin administration schedule. The new, mechanistic model may provide a rationale for better understanding of digoxin pharmacodynamics and could become a tool to bridge the gap between in vitro and in vivo studies.

The redshift distribution of type Ia supernovae: constraints on progenitors and cosmic star formation history

We use the redshift distribution of type-Ia supernovae (SNe) discovered by the Supernova Cosmology Project to constrain the star formation history (SFH) of the Universe and SN Ia progenitor models. Given some of the recent determinations of the SFH, the observed SN Ia redshift distribution indicates a long (>~1 h^-1 Gyr) mean delay time between the formation of a stellar population and the explosion of some of its members as SNe Ia. For example, if the Madau et al. (1998) SFH is assumed, the delay time tau is constrained to be tau > 1.7 (tau > 0.7) h^-1 Gyr at the 95%(99%) confidence level (CL). SFHs that rise at high redshift, similar to those advocated by Lanzetta et al. (2002), are inconsistent with the data at the 95% CL unless tau > 2.5 h^-1 Gyr. Long time delays disfavor progenitor models such as edge-lit detonation of a white dwarf accreting from a giant donor, and the carbon core ignition of a white dwarf passing the Chandrasekhar mass due to accretion from a subgiant. The SN Ia delay may be shorter, thereby relaxing some of these constraints, if the field star formation rate falls, between z=1 and the present, less sharply than implied, e.g., by the original Madau plot. We show that the discovery of larger samples of high-z SNe Ia by forthcoming observational projects should yield strong constraints on the progenitor models and the SFH. In a companion paper (astro-ph/0309797), we demonstrate that if SNe Ia produce most of the iron in galaxy clusters, and the stars in clusters formed at z~2, the SN Ia delay time must be lower than 2 Gyr. If so, then the Lanzetta et al. (2002) SFH will be ruled out by the data presented here.

Dynamical robustness of Lévy search strategies.

We study the role of dynamical constraints in the general problem of finding the best statistical strategy for random searching when the targets can be detected only in the limited vicinity of the searcher. We find that the optimal search strategy depends strongly on the delay time tau during which a previously visited site becomes unavailable. We also find that the optimal search strategy is always described for large step lengths l by a power-law distribution P(l) approximately l(-mu), with 1<mu(tau)</=2. Our findings appear to remain valid even if arbitrary energy costs of locomotion are considered.

Transmission delay times of localized waves.

We investigate the effects of wave localization on the delay time tau (frequency sensitivity of the scattering phase shift) of a wave transmitted through a disordered waveguide. Localization results in a separation tau=chi+chi(') of the delay time into two independent but equivalent contributions, associated to the left and right end of the waveguide. For N=1 propagating modes, chi and chi(') are identical to half the reflection delay time of each end of the waveguide. In this case the distribution function P(tau) in an ensemble of random disorder can be obtained analytically. For N>1 propagating modes the distribution function can be approximated by a simple heuristic modification of the single-channel problem. We find a strong correlation between channels with long reflection delay times and the dominant transmission channel.

Simple suppression of spurious peaks in TROSY experiments.

In (1)H-(15)N TROSY experiments of proteins and nucleic acids, where the second coherence transfer delay time tau' has been fixed as 5.6 ms, 1/(2(1)J(NH)), in order to achieve complete spin-state selection, spurious negative peaks are observed along the (15)N axes. These peaks are often annoyingly large, especially for nucleic acids. A simple product operator calculation, however, indicated that the shortening of the second delay time tau', which is next to the t1 period, would efficiently suppress these spurious peaks, without sacrificing the sensitivities of the TROSY peaks too much. We have shown for three systems, two 11- and 17-kDa proteins and one 8-kDa DNA duplex, that these spurious peaks can be effectively suppressed with delay times of 3.3 ms for the two proteins and 2.3 ms for the DNA. These delay times, optimized by trial and error, for the spurious peak suppression did not depend on the magnetic field strength and the temperature very much. Although the shortened tau' delay times attenuate the TROSY peak intensities by about 10 and 20% for the two proteins and the DNA, respectively, this simple modification will be useful for the quantitative uses of TROSY peaks and will result in cleaner spectra for various TROSY-based multiple resonance experiments.

Relation between the delay time and the tipping angle for superradiance

In optical superradiance studies, data were reported supporting a relation between the delay time (tau(D)) and the tipping angle (delta(0)), tau(D)=(tau(R/)4)[ln(delta(0)/2 pi)](2), where tau(R) is the radiation damping time constant. We found that the same data also satisfy another relation, tau(D) = tau(R) ln[cot(delta(0)/2)]. The derivation of the two relations is reexamined. It is found that the former relation does not have sound theoretical background, and could lead to considerable errors when it is used to interpret experimental results.

Probability distribitions of wigner delay times

We present results for the probability distribution of Wigner delay times of a two-dimensional disordered solid, described by a tight-binding Anderson model with diagonal disorder W. Using a numerical transfer matrix approach to yield the scattering matrix s of a finite width lattice, the delay time tau(ij) associated with scattering between two channels i,j is proportional to the energy-derivative of the phase of the s -matrix element s(ij). Positive delay times signify that the particle travels through the system more slowly than for, a perfectly clean system. For large positive tau, the probability distribution P(tau) varies as tau(-alpha), whereas for large negative tau it varies as \tau\(-beta) For ballistic systems where disorder W is small, we find beta approximate to 2 while alpha approximate to 4. With increasing W, the values of beta remain approximately constant, whereas alpha decreases, until for the largest values of W, where the system becomes Anderson localised, alpha approximate to beta approximate to 2.

Fractal character of the auditory neural spike train.

Long-counting-time pulse-number distributions (PND's) were measured from a broad variety of cat primary auditory fibers using different tone and noise stimuli, counting times T, and number of samples NT. Whereas short-counting-time PND's (T approximately 50 ms) manifest the presence of spike pairs (an enhancement of even over odd-count probabilities), the irregular shapes of the long-counting-time PND's (T approximately greater than 0.1 s) reveal that the underlying sequence of action potentials consists of spike clusters when viewed on a longer time scale. For all units measured, the count variance-to-mean ratio (Fano factor) F(T) varied little over some 90 dB change in the stimulus level. On the other hand, F(T) increased substantially as T and/or NT were increased, corresponding to the capture of larger and larger spike clusters in the counting time. A relationship is developed between the Fano-time function F(T) and the normalized coincidence rate function, g(tau) versus delay time tau. A plausible form for g(tau) leads to a Fano-time function in good accord with the data. The observed power-law growth of the Fano factor for large counting times [F(T) approximately T alpha where 0 less than alpha less than 1] is accompanied by a power-law decay of the coincidence rate for large delay times [g(tau) approximately tau alpha -1] and a power-law form for the power spectral density at low frequencies [S(f) approximately f -alpha]. The behavior of the PND's and the scale invariance implicit in these fractional-power-law relationships suggest that the neural events on all primary auditory fibers exhibit fractal behavior for sufficiently large times (sufficiently low frequencies). The spike pairs and spike clusters in the PND's are natural consequences of this behavior. The fractal dimension D identical to alpha is estimated to be in the range of 0.3 approximately less than D approximately less than 0.9 for counting times in the range 0.1-10 s. The fractal dimension provides a measure of the degree of event clustering, or irregularity of a sequence of events, that is preserved over different time scales. PND's from low-skew vestibular units, in contrast, do not exhibit fractal behavior. It is suggested that auditory neural-firing patterns may serve to efficiently sample natural fractal noises.

Fully self-aligned AlGaAs/GaAs heterojunction bipolar transistors for high-speed integrated-circuits application

Structure optimization, uniformity consideration, and high-speed circuit performance for an AlGaAs/GaAs heterojunction bipolar transistor (HBT) are described. The HBT is fabricated in a fully self-alignment manner using only a single photoresist mask for achieving submicrometer-dimension devices, and, thus reducing parasitic elements. The fabricated HBT's exhibit excellent threshold voltage deviation sigma V/sub BE/=2 mV on a 2-in wafer, a CML gate propagation delay time tau /sub pd/=9.5 ps, and a toggle frequency f/sub tog/=13.3 GHz for a CML divide-by-two frequency divider. >

Spectral and temporal features of the pumping of rhodamine 6G by radiation from a copper vapor laser

An experimental investigation was made of the influence of the relative delay time tau and of the intensity ratio R/sub 21/ of the spectral components emitted by a copper vapor laser on the energy and spectral characteristics of lasing in rhodamine 6G. For certain values of tau and P/sub 21/, lasing in the dye was disrupted. A clamping effect was discovered between the rhodamine 6G laser emission spectrum and the yellow line of the copper vapor laser. The results obtained were used to determine the parameters of an interference filter for suppressing the yellow line from the copper vapor laser, and this made it possible to raise the efficiency of conversion of the pump radiation into lasing in the dye.

Intensity fluctuation spectroscopy of charged Brownian particles: the coherent scattering function

Measurements are presented, which span wide ranges of scattering vector K and delay time tau , of the coherent intermediate scattering function F(K, tau ) for a dispersion of strongly-interacting charged Brownian particles (radius approximately 250 AA). Emphasis is on the long-time decay of F(K, tau ), i.e. for tau >> tau 1, where tau 1( approximately 10-4 s) is the particle's 'collision time'. DL, the diffusion coefficient describing this long-time decay, was found to be several times smaller than D0, the free-particle diffusion coefficient, and to be only weakly dependent on K. For K>Kmax, the position of the main peak in the particle structure factor S(K), F(K, tau ) approximately=FS(K, tau ), the self-scattering function which describes single-particle motions.