Melting and Cavity Growth in the Vicinity of Crack Tips Subjected to Short-Duration Current Pulses

2008 ◽  
Author(s):  
F. Gallo ◽  
S. Satapathy ◽  
K. Ravi-Chandar
Keyword(s):  
Short Duration ◽  
Cavity Growth ◽  
Current Pulses ◽  
Crack Tips

Strain Evolution in Metal Conductors Subjected to Short-Duration Current Pulses

2007 ◽  
Vol 43 (1) ◽  
pp. 338-342 ◽  
Author(s):  
F. Gallo ◽  
R. Watkins ◽  
K. Ravi-Chandar ◽  
S. Satapathy
Keyword(s):  
Short Duration ◽  
Strain Evolution ◽  
Current Pulses

Effects of chronic spinalization on ankle extensor motoneurons. II. Motoneuron electrical properties

1994 ◽  
Vol 71 (4) ◽  
pp. 1468-1479 ◽  
Author(s):  
S. Hochman ◽  
D. A. McCrea
Keyword(s):  
Electrical Properties ◽  
Action Potential ◽  
Short Duration ◽  
Time Constant ◽  
Triceps Surae ◽  
Resting Membrane Potential ◽  
Primary Analysis ◽  
Membrane Hyperpolarization ◽  
Current Pulses ◽  
Voltage Transients

1. Intracellular recording and stimulation techniques were used in a comparison of electrical properties of triceps surae and plantaris motoneurons between unlesioned and 6-wk chronic spinal (L1-L2) cats. The primary analysis was restricted to 195 motoneurons with action potential heights > or = 80 mV. 2. Voltage transients resulting from short-duration current pulses (0.5 ms) were used to estimate membrane time constant (tau m) and equivalent cylinder electrotonic length (L). Although L was unchanged, tau m and the equalization phase time constant were significantly lower (17%) in motoneurons from chronic spinal preparations. Estimated total cell surface area was also reduced by 11%. The incidence of sag conductances, as judged from observations of the decay of voltage transients, increased from 3% to 29% after chronic spinalization. 3. Input resistance, as measured from either the amplitude of voltage responses to long-duration (50 ms) hyperpolarizing pulses (RinL) or from the area of the short-duration current pulse-induced voltage transients, was unchanged in the chronic spinal preparation. 4. Rheobase current was unchanged but threshold voltage (V Th) was increased in chronic spinal motoneurons. Increased V Th was not a result of membrane hyperpolarization because both mean action potential height (88 mV) and resting membrane potential (70 mV) were identical in both preparations. 5. The threshold current for action potential activation by short-duration (0.5 ms) current pulses increased 28% in chronic spinal preparations. This is consistent with the increase in V Th in the same motoneurons. 6. Measured V Th was identical to that calculated from the product of RinL and rheobase in the unlesioned preparation but was significantly larger than calculated V Th in chronic spinal preparations. This may indicate an increased incidence or magnitude of subthreshold rectification processes in motoneurons from chronic spinal preparations. These results in barbiturate-anesthetized preparations suggest that ankle extensor motoneurons are less excitable in the chronic spinal state. 7. Mean afterhyperpolarization duration was 10% shorter in motoneurons from chronic spinal preparations, whereas amplitude was unchanged. 8. Electrical properties were also compared in chronic spinal and unlesioned preparations using motoneurons with action potential heights of 60-79 mV. In these motoneurons with presumably poorer impalements there were no significant differences between unlesioned and chronic spinal preparations. 9. Ia monosynaptic excitatory postsynaptic potentials (EPSPs) recorded in the same motoneurons have decreased half-widths and rise times and increased amplitudes.(ABSTRACT TRUNCATED AT 400 WORDS)

A study of cometary eruptions through OH radio-lines

1999 ◽  
Vol 173 ◽  
pp. 249-254
Author(s):  
A.M. Silva ◽  
R.D. Miró
Keyword(s):  
Short Duration ◽  
Growth Curves ◽  
The Other ◽  
Initial Mass ◽  
Radio Lines ◽  
Other Hand ◽  
Sudden Rise

AbstractWe have developed a model for theH2OandOHevolution in a comet outburst, assuming that together with the gas, a distribution of icy grains is ejected. With an initial mass of icy grains of 108kg released, theH2OandOHproductions are increased up to a factor two, and the growth curves change drastically in the first two days. The model is applied to eruptions detected in theOHradio monitorings and fits well with the slow variations in the flux. On the other hand, several events of short duration appear, consisting of a sudden rise ofOHflux, followed by a sudden decay on the second day. These apparent short bursts are frequently found as precursors of a more durable eruption. We suggest that both of them are part of a unique eruption, and that the sudden decay is due to collisions that de-excite theOHmaser, when it reaches the Cometopause region located at 1.35 × 105kmfrom the nucleus.

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