Reversed pulse duration

This situation is similar to the one we found for crossed fields. We will note by x the critical reverse pulse duration for which the... 

VII.3 Computer Simulation of Field Inversion Electrophoresis Figure 19 shows a diagram of relative velocity V/Vq as a function of the reverse pulse duration t for constant field and time ratios Eg = 2.0 and E =1.0, with 0 = 1.O. The arrows indicate where the pulse duration is equal to the critical time Back i - three molecular sizes... 

This effect has been observed by Lalande et al. who measured an increase of velocity from = 5.1 cm/65 hrs to = 6.5 cm/65 hrs for yeast chromosomes when the reverse pulse duration t was increased from 1 sec to thousands of seconds, with Hg = 2.0 and With these biases,... 

The character of reflection of electrons from the evanescent wave strongly depends on the relationship between the duration r of the laser pulse and the time of flight of an electron through the laser wave, rtr. It may be shown that when the laser pulse duration is much longer than the characteristic transit time rtr, the character of reflection of the electrons is close to the mirror. Where the relationship between these times is reversed, the mirrorlike character of reflection is disturbed. Let us make some simple estimates of the laser field and electron beam parameters with which the reflection of electrons is possible. 

Fig. I8K Current—reversal chronopotentiometry, for the oxidation of 1 niM PAP to PQl in 0.1 M H SO, at a platinum electrode, followed by hydrolysis to PBQ. i = 0.10 niAlcm. x is the transition time on the reverse pulse, following a forward pulse of duration t. From Gileadi, Kirowa-Eisner and...

Pulse duration is related to the time required for the dislocations to reorganize in certain patterns. During the shock time rise, dislocations are generated leading to permanent plastic deformation. However, some of the dislocations can possibly retrace their path during wave release reversibly [38], Pulse duration may influence the amount dislocation reversibility and as a result the saturated dislocation density. Fig. 12 shows that the saturation density of... 

Chemically reversible systems. If any electrode process carried out during the pulses can be reversed effectively at renewal will be accomplished by electrolysis when the potential returns to the base potential after each pulse. Because the electrode is normally held at E for a long time compared to the pulse duration, the products of the pulse can be essentially fully recollected and returned to the initial state. It is not important that the electrode kinetics be fast enough to be called reversible, only that the chemistry can be efficiently reversed at the base potential. 

Almost the reverse evolution can be observed for the other field disturbance (right). The response of the electrons is controlled at the beginning by the short relaxation time of some 10 s, at around half the pulse duration by the long relaxation time of some 10 s, and close to the end of the pulse again by the short relaxation time. As a result, large deviations between gain and loss in the power balance slowly arise at the beginning, reach their maximum at about half the pulse duration, and vanish almost without any delay at the end of the field pulse. 

Fig. 61. Magnitude of DLTS electron emission peak versus bias pulse amplitude for sample JH139 from data similar to that in Fig. 60. The ambient reverse bias was 5 V. The data represented by O and a correspond to voltage pulse durations of i and of the DLTS emission time constant, respectively. The solid line was calculated assuming a spatially uniform density of states. Note the good agreement between theory and experiment for the longer pulse data. [From Lang et al. (1982a).]...

Nevertheless, the pulsed field run commonly takes longer than 10 hr. The pulsed field is also not easily implemented in CE, except for periodical reversion of field direction (the so called field-inversion CE, FICE). The technique uses alternating electric fields with a frequency >100 Hz. Equal pulse durations in FICE provide the best resolution, while dilute polymer solutions provide the fastest separation. DNA fragments of 200 kbp-1.6 Mbp are separated within 13 min in a dilute methylcellulose solution. 

In conventional Ramsey spectroscopy of a two-level system [50], two short n/2 pulses are applied in succession. If the second pulse comes immediately after the first, the transition is completed and all the population is excited. If instead there is a delay time T between the two pulses, which is long compared to the pulse duration x, the transition probability becomes sensitive to small differences between the radiofrequency frequency and the molecular transition frequency. The internal coherence evolving at the transition frequency accumulates a phase between pulses of whereas the rf field evolves a phase coT. When the difference between these two reaches it, the second pulse reverses the effect of the first, returning all the population to the initial state. More generally, the probability that a molecule will end up in the excited state is... 

In consequence of much shorter pulse duration than is the usual drop time of DME the electrode process reversible in DCP could be quasi-re-versible in NPP measurements. An inverse situation is also possible the pulse polarogram shows reversible behavior, if the electron transfer is fast, but the chemical inactivation of the electrode product is slow. For... 

Recently, a method for the analysis of the DPP curves arising from slow electrode reaction has been presented [68, 69]. The influence of the first polarization time, of the pulse duration and potential step amplitude on the recorded current was clearly manifested. The solution may be applied to the static as well as to the dropping mercury electrodes. It was verified for the quasi-reversible system Cd(Hg)/Cd(II) in the presence of 2-(a-hydroxybenzyltriamine), a substance of biological interest. Also the irreversible system Cr(VI)/Cr(III) in NaOH medium (characterized by k° 10" m s" ) was followed according to this concept. 

FIGURE 3 Probability for reversal of a lithographically patterned magnetic element, as a function of pulse duration. Different curves are for varying pulse amplitudes. Data are well fitted to exponentials, with a decreasing time constant for increasing pulse amph-tude. Source Rizzo et al., 2002. Reprinted with permission. 

Fig. 10 Electrothermal tensile actuation for two-end-tethered, homochiral, wax-filled coiled CNT yams, (a) Tensile actuation strain versus time after 1,400,000 reversible cycles for an 11.5 (rai diameter, coiled Fermat yam having -25,000 tums/m twist when driven by a 18.3 V/cm, 20 Hz symmetric square-wave voltage while lifting a load that provided a 14.3 MPa stress, (b) Tensile actuation for the yam of (a) with 109 MPa pUed tensile stress when driven at 3 % duty cycle by 15 ms, 32 V/cm square-wave voltage pulses having a period of 500 ms. (c) Tensile strain versus time for a 150 pm diameter, diial-Aichimedean yam with 3,990 tums/m of inserted twist per preciusor sheet stack length, when supporting a 5.5 MPa tensile stress and driven by a 15 V/cm square wave having 50 ms pulse duration and 2.5 s period (From Lima et aL (2012). Reprinted with permission from AAAS)...

The cathodic to anodic pulse duration ratio was changed within 30-60, the anodic pulse time was 0.5-1.5 s at a current density of 15-50 A/dm. This allowed us to increase the carbide coating thickness to 100pm. The optimal parameters of the reversal mode were Tj.=45s, Ta=1.5s, r c = 8-10A/dm, ... 

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