Dependence Of Transit Time Research Articles

Analytical theory for a droplet squeezing through a circular pore in creeping flows under constant pressures

We derived equations and closed-form solutions of transit time for a viscous droplet squeezing through a small circular pore with a finite length at microscale under constant pressures. Our analyses were motivated by the vital processes of biological cells squeezing through small pores in blood vessels and sinusoids and droplets squeezing through pores in microfluidics. First, we derived ordinary differential equations (ODEs) of a droplet squeezing through a circular pore by combining Sampson flow, Poiseuille flow, and Young–Laplace equations and took into account the lubrication layer between the droplet and the pore wall. Second, for droplets wetting the wall with small surface tension, we derived the closed-form solutions of transit time. For droplets with finite surface tension, we solved the original ODEs numerically to predict the transit time. After validations against experiments and finite element simulations, we studied the effects of pressure, viscosity, pore/droplet dimensions, and surface tension on the transit time. We found that the transit time is inversely linearly proportional to pressure when the surface tension is low compared to the critical surface tension for preventing the droplet to pass and becomes nonlinear when it approaches the critical tension. Remarkably, we showed that when a fixed percentage of surface tension to critical tension is applied, the transit time is always inversely linearly proportional to pressure, and the dependence of transit time on surface tension is nonmonotonic. Our results provided a quick way of quantitative calculations of transit time for designing droplet microfluidics and understanding cells passing through constrictions.

An empirical model for calculating uniaxial compressive strength of oil well cements from ultrasonic pulse transit time measurements

Thirty-five cement samples were tested in an Ultrasonic Cement Analyzer (UCA) at varying curing conditions and for varying curing times, and then uniaxially compressed to failure in a hydraulic press. An attempt was made, using the ultrasonic transit time data measured with a UCA and the uniaxial compressive strength data measured using a hydraulic press, to derive an empirical model capable of accurately predicting uniaxial compressive strength from the ultrasonic transit time. Using the Levenberg-Marquardt algorithm, the experimental data was fit to two models. In addition to the transit time dependence, the first model presented incorporates a term that accounts for the curing time while the second model contains terms that account for both the curing time and cement composition. The results obtained illustrate the complexity of deriving a correlation with general applicability to all well cements. The best performing model based on both curve fit error and prediction performance for the samples tested was the model that accounted only for the curing time dependency of the cement strength development rate in addition to the measured transit time, indicating that the transit time measurement history is sufficient as a tool for characterizing well cement strength development.

A model for charge transport in semicrystalline polymer thin films

ABSTRACTA model for simulating the charge transport properties of semicrystalline polymer (SCrP) using Monte Carlo simulation is reinvented. The model is validated by reproducing the experimentally observed field and temperature dependence of mobility in Poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) thin films. This study also provides a new physical insight to the origin of much debated negative field dependence of mobility (NFDM) observed at low electric field strengths in P3HT thin films. The observed NFDM, which is not explainable with the mechanisms proposed earlier, is attributed to the weak dependence of transit time on the applied electric field strengths. In the semicrystalline films, the charge transport takes place mostly through the crystalline regions, in which the charge transport is weakly dependent on the strength of the applied electric field. In addition, a possible explanation for the origin of Arrhenius temperature dependence of mobility (lnμ ∝ 1/T) commonly observed in SCrP thin films is also proposed. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 137–141

Performance of a new accelerating-electrode-equipped fast-time-response PMT coupled with fast LGSO

In this study, we measured the performance of a newly developed Hamamatsu Photonics R13478 photomultiplier tube (PMT) and compared the results with those of an existing R9800 PMT. In R13478, an accelerating electrode is placed between the focusing electrode and first dynode for time resolution improvement through reduced transit time jitter. We investigated the time resolution dependence on the supply voltage and time pickoff method for R13478 and R9800 PMTs, each coupled with a 2.9 × 2.9 × 20 mm3 fast LGSO:Ce (0.025 mol%) crystal. In addition, we measured the PMT time resolutions coupled with the crystals in edge and laid positions to determine the effects of the reduced position dependence of transit time in R13478. R13478 exhibited a better time performance than R9800 in various ways. The rise time of R13478 for our experimental setup was 1.54 ns, 100 ps shorter than that of R9800 because of the reduced transit time. Further, R13478 achieved a 169 ps single time resolution at the recommended supply voltage, while this value was 187 ps for R9800. The time resolution of R13478 was also significantly better for a low time pickoff threshold level and a high supplied voltage, which are conditions vulnerable to transit time jitter and noise, respectively. A considerable difference in time resolution was observed for the laid position (R13478: 144 ps; R9800: 167 ps), indicating that the accelerating electrode reduced spatial transit time difference. Overall, we showed the effects of the differentiated characteristics of R13478 PMT compared with R9800 and confirmed its excellent time performance. We suggest use of this device as a photodetector effective for fast timing applications such as time-of-flight positron emission tomography.

Dynamic and Power Performance of Multiple State Electrostatically Formed Nanowire Transistors

Electrostatically formed nanowire (EFN)-based transistors have recently been proposed as a single device with multiplexer functionality. In these transistors, the conduction path between source and one of the drains is determined by the bias applied to the two junction-side gates. By applying a nonsymmetric bias on the side gates, the lateral position of the EFN is controlled. We present a detailed analysis of the different states of the multiple state electrostatically formed nanowire transistor device, the transient time between them and the power exerted during each transition. The dependence of transition time between states and leakage currents in cutoff states on different geometry parameters is also presented.

Predicting coronal mass ejections transit times to Earth with neural network

Predicting transit times of Coronal Mass Ejections (CMEs) from their initial parameters is a very important subject, not only from the scientific perspective, but also because CMEs represent a hazard for human technology. We used a neural network to analyse transit times for 153 events with only two input parameters: initial velocity of the CME, $v$, and Central Meridian Distance, CMD, of its associated flare. We found that transit time dependence on $v$ is showing a typical drag-like pattern in the solar wind. The results show that the speed at which acceleration by drag changes to deceleration is $v\approx$500 km s$^{-1}$. Transit times are also found to be shorter for CMEs associated with flares on the western hemisphere than those originating on the eastern side of the Sun. We attribute this difference to the eastward deflection of CMEs on their path to 1 AU. The average error of the NN prediction in comparison to observations is $\approx$12 hours which is comparable to other studies on the same subject.

Wavelength-dependent transition time of gain saturation in an erbium-doped fiber amplifier

We report a study of the wavelength dependence of the gain saturation transition time in an erbium-doped fiber amplifier. A self-probe method that enables us to probe the change of population in an amplifier by using a pulse to induce that change was used to evaluate the transition time over a wavelength range from 1528 to 1559 nm. It was found that the transition time changed from 400 ns to 1.65 μs with increasing wavelength. The wavelength dependence of the transition time was then analyzed using a model to describe the temporal evolution of the erbium population at the input end of a fiber based on McCumber theory.

Arrival time of solar eruptive CMEs associated with ICMEs of magnetic cloud and ejecta

The Coronal Mass Ejection (CME) is an eruptive event in which magnetic plasma is ejected from the Sun into space through the solar corona. We considered a set of 51 Interplanetary Coronal Mass Ejections (ICMEs) listed by Kim et al. (Solar Phys. 184:77, 2013) from Coordinated Data Analysis Workshop (CDAW, Gopalswamy et al. in Astrophys. J. 710:1111, 2010). Among the 51 events, 22 events are classified as Magnetic Clouds (MC) and 29 events are classified as Ejecta (EJ) where the MC and EJ are subsets of ICMEs. We have analyzed the physical properties of CMEs and ICMEs associated with MC and EJ, and correlated them with the CME’s transit time/arrival time from the Sun to the Earth. Main aims of the present study are to examine (a) dependence of transit time on the properties of CMEs and ICMEs, and (b) differences between MC and EJ. It is found that CME’s initial speed decides the transit time which is in support of the known results in literature. Apart from this, some important results from the present study are: (i) transit time predicted using an empirical relation obtained in the present work is found comparable with the observations (correlation coefficient=0.70). (ii) The transit time of MC and EJ-associated CMEs ranges from 20 to 120 hours and IP acceleration lies between −10 m/s2 to 5 m/s2. (iii) There are certain differences between MC and EJ such as: (a) Ejecta takes slightly more time to travel and only 30 % of them are accelerated in the interplanetary medium. Whereas, MC takes less time to travel and nearly 50 % of them are accelerated, (b) The correlations of IP acceleration and speed with transit time are higher for MC than that of EJ, (c) A weak relationship between the deflection and transit time is found for MC, but it is absent in the case of EJ and (d) Only EJ-type CMEs have wider range of direction parameter and acceleration. Further, we checked the solar wind speed as another parameter has any influence on CME acceleration and it shows that there is no clear dependence between the two parameters. While it is observed that the average acceleration of MC-associated CME is larger for lower direction parameter values ( 0.6).

Numerical Simulation of Passage of a Neutrophil through a Rectangular Channel with a Moderate Constriction

The authors have previously presented a mathematical model to predict transit time of a neutrophil through an alveolar capillary segment which was modeled as an axisymmetric arc-shaped constriction settled in a cylindrical straight pipe to investigate the influence of entrance curvature of a capillary on passage of the cell. The axially asymmetric cross section of a capillary also influences the transit time because it requires three-dimensional deformation of a cell when it passes through the capillary and could lead to plasma leakage between the cell surface and the capillary wall. In this study, a rectangular channel was introduced, the side walls of which were moderately constricted, as a representative of axially asymmetric capillaries. Dependence of transit time of a neutrophil passing through the constriction on the constriction geometry, i.e., channel height, throat width and curvature radius of the constriction, was numerically investigated, the transit time being compared with that through the axisymmetric model. It was found that the transit time is dominated by the throat hydraulic diameter and curvature radius of the constriction and that the throat aspect ratio little affects the transit time with a certain limitation, indicating that if an appropriate curvature radius is chosen, such a rectangular channel model can be substituted for an axisymmetric capillary model having the same throat hydraulic diameter in terms of the transit time by choosing an appropriate curvature radius. Thus, microchannels fabricated by the photolithography technique, whose cross section is generally rectangular, are expected to be applicable to in vitro model experiments of neutrophil retention and passage in the alveolar capillaries.

Impedance spectroscopy study on transport properties of N, N′-diphenyl- N, N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine

The transport properties of N, N′-diphenyl- N, N′-bis(1-naphthyl)-1,1′-biphenhyl-4,4′-diamine (NPB) have been investigated by using impedance spectroscopy (IS) and J– V measurements based on a single-layer structure of ITO/NPB/Al. The J– V characteristic of the device obeys Ohmic law below 0.6 V, and is in the space-charge limited current (SCLC) regime above 0.6 V. The density of the thermally generated charge carrier is determined to be about 3.1×10 16 cm −3. Impedance spectroscopy measurements showed that the device can be simulated by an equivalent parallel RC network with a contact resistance R S in series, in which the bulk capacitance C of NPB remains unchanged while the resistance R decreases along with bias voltage. The variation of the whole conductance and capacitance of the device with frequency and bias can be understood by the carrier response and the transit time dependence on the bias in the NPB film.

Induced base transit time of an epitaxial n +pn −n + bipolar transistor in saturation

Minority carrier recombination, drift and diffusion currents are considered in determining induced base transit time of an epitaxial n +pn −n + bipolar transistor operated in quasi-saturation and hard-saturation. The dependence of transit time upon the characteristics of the epitaxial–substrate interface is also studied for the transistor driven into hard saturation. The study shows that transit time in the induced base is significant when the transistor is driven into hard saturation and the interface is highly reflecting. The induced base transit time calculated analytically is compared with numerically obtained results in order to demonstrate the validity of the assumptions made in deriving analytical expressions. The closed form expressions for collector current density and transit time offer a physical insight into device operations at various bias conditions and are a useful tool in device design and optimization.

Power Law Behavior in Amorphous Si:H and Si:D Due to Hopping-Randomwalk of Electrons in Localized Band Tail States in Random Fractal Fluctuation

Electric field dependence of transit time in time-of-flight experiment has been investigated in four different a-Si:H films and three different a-Si:D films prepared in different conditions in order to identify the transport process of electrons and holes in a-Si:H and a-Si:D. It has been concluded that the dispersive transport of electrons and holes is due to hopping-randomwalk in localized band tail states in random fluctuation with fractal dimensions of 3.9. The hopping distance is in the range of 30 to 45 A while the thermal activation energy is in the range of 0.12 to 0.19 eV for an electron and in 0.33 to 0.39 eV for a hole. Furthermore, we have found that the dispersion parameter is related to the exponent in the power law decay of photoluminescence. This shows that the power law decay of the photoluminescence is understood from the geminate recombination coupled with the hopping randomwalk in the random fractal fluctuation as shown by Ando et al. [phys. stat. sol. (b) 230, 15 (2002)].

Analytical base transit time of integrated bipolar transistors in quasi-saturation and hard saturation

Based on the assumption of negligible recombination within the thin epitaxial collector layer of an integrated bipolar transistor switch in quasi-saturation, solutions to the collector minority carrier profile and transit time in the induced base are derived. In contrast to Dai and Yuan's analysis (1997), the present analysis takes both the drift and diffusion currents into account and is valid for all levels of injection. Dependence of transit time on characteristics of the epitaxial-substrate interface and recombination at the interface is studied for the transistor driven into hard saturation. At high effective surface recombination velocity, recombination at the interface cannot be neglected. The study shows that transit time increases more rapidly with collector current when the transistor operates in hard saturation and the interface is highly reflecting.

Carrier transport and intersubband population inversion in coupled quantum wells

We theoretically study the possibility of achieving intersubband population inversion in coupled GaAs quantum wells, taking into account the relevant physical mechanisms of resonant tunneling and intersubband emission-absorption processes. Two coupled quantum well structures having intersubband resonant wavelengths of 10 and 60 μm are considered. We find that, in the case of an operating wavelength of 60 μm, intersubband population inversion is achievable at acceptable injection current densities even for room-temperature operation. However, achievement of intersubband population inversion is significantly more difficult at the shorter wavelength. The temperature and carrier transit time dependence of intersubband population inversion are also calculated.

Chronopotentiometry at a tubular graphite electrode. Part 2. Experimental verification of theoretical results

The dependence of transition time on various electrode parameters such as the velocity of the solution flowing through the electrode, the initial concentration of the depolariser and the ratio of the limiting diffusion current and the applied current has been studied by oxidising potassium hexacyanoferrate(II), o-dianisidine and potassium iodide. Close agreement between the theory and the experimental results obtained was observed.

Space-charge effect on hole transport in resistive hydrogenated amorphous silicon

Hole transport properties of resistive hydrogenated amorphous silicon (1012 Ω cm) are studied by a pulsed photoconductivity technique. Transit time is analyzed by the Scher–Montroll plotting method. Estimation of mobility is done with photocurrent measurement under a space-charge-limited condition, and it is confirmed that the mobility value measured under this condition agrees with the calculated value found from space-charge-limited current. With no space-charge effect, temperature dependence and electric field dependence of transit time is represented by τ=τ0 E−1/α′ exp(Δ/kT).

An investigation of the laser optogalvanic effect for atoms and molecules in recombination-limited plasmas

In this paper the nature, the characteristics, and the potential applications of the optogalvanic effect are explored in a broad set of experiments. The optogalvanic effect was investigated, for the Ar, Ne, He, Ar +, He +, Cu and Na atoms and N2, H~, CO, CN, NH2, He2, and CuO molecules in recombination-limited hollow cathode plasmas, with the use of dye lasers. Comparative studies of the time dependence of transitions from metastable and non-metastable states of neutrals and non-metastable states of ions were made. Autoionizing transitions in Cu(I) were found to yield very strong OGE signals. An examination of the various processes known to be important in such plasmas indicates that associative ionization is a very effective means for coupling light energy into the plasma. Measurement of Rydberg transitions in the helium dimer suggests that optogalvanic spectroscopy in recombination plasmas may be useful as a way to study such molecules with repulsive ground states by generating them 'from the top down ' by recombination.

Infrared divergence and Scher-Montroll model for transient electrical transport in amorphous semiconductors

The Scher-Montroll model of transport in amorphous semiconductors is treated in the presence of very low energy excitations of infrared divergent nature. The discrepancy between temperature dependence of transit time given by time-of-flight experiments and other methods can be resolved in this way. It is shown that infrared divergent scattering without a wide distribution of transition rates results in a temperature dependence which is different from the experimentally observed one.

Indium phosphide microwave oscillators

A detailed examination has been carried out on the characteristics of transferred electron microwave oscillators constructed from epitaxial indium phosphide. Seven slices have been used, for which the layer thicknesses varied between 5.4 and 28 µm. It is shown that the mechanism of oscillation has a transit-time dependence and that the transit velocity which emerges (1.5-2 × 107cm/s) is approximately the same as the peak electron drift velocity. It is therefore concluded that propagating space-charge layers are responsible for the oscillations. However, in view of the high transit velocities involved, it is unlikely that the space-charge layers are well-formed dipolar domains. Despite the transit-time dependence, individual devices have been made to oscillate over very wide frequency ranges (8-28 GHz). Operation of devices at frequencies up to 40 GHz has established the high-frequency capability of the oscillators. The best pulsed results obtained have included 0.5 W, 6.3 percent at 13.8 GHz; 1.05 W, 4.2 percent at 18.0 GHz and 0.65 W, 2.6 percent at 25.0 GHz. Continuous operation of these diodes has not yet been possible due to material and thermal technology limitations.

A Packed Graphite Cell for Thin-Layer Electrochemistry

Abstract A thin-layer electrochemical cell, which consists of a bed of graphite granules, is described and evaluated for chronopotentiometric experiments. The dependence of transition time on concentration is linear (within 3%) for a single component and the transition time of a component is independent of the concentrations of other electroactive materials in the solution.