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Notes: Abstract We constructed average histograms from responses evoked by flashing stimuli and noted previously described variations in the shape of the response profile, particularly with respect to sharpness of the peak. To express this variable, we measured the half-rise latency, which is the latency from stimulus onset required to reach half the maximum response. A short half-rise latency, which is characteristic of nonlagged cells, is associated with a brisk response and sharp peak; a long half-rise latency, characteristic of lagged cells, is associated with a sluggish response and broad peak. Nonlagged cells were readily seen; we attempted to identify cells with long latencies as lagged, but we were unable to do so unambiguously due to failure to observe lagged properties other than latency. We thus refer to these latter cells as having “lagged-like” responses to indicate that we are not certain whether these are indeed lagged cells. In addition to the histograms, we analyzed the individual response trials that were summed to create each histogram, and we used spike density analysis to estimate the initial response latency to the flashing spot for each trial. We found that lagged-like responses were associated with more variability in initial response latency than were nonlagged responses. We then employed an alignment procedure to eliminate latency variation from individual trials; that is, responses during individual trials were shifted in time as needed so that each had a latency equal to the average latency of all trials. We used these “aligned” trials to create a second, “aligned” response histogram for each cell. The alignment procedure had little effect on nonlagged responses, because these were already well aligned due to consistent response latencies amongst trials. For lagged-like responses, however, the alignment made a dramatic difference. The aligned histograms looked very much like those for nonlagged responses: the responses appeared brisk, with a sharply rising peak that was fairly high in amplitude. We thus conclude that the slow build up to a relatively low peak of firing of the lagged-like response histogram is not an accurate reflection of responses on single trials. Instead, the sluggishness of lagged-like responses inferred from average response histograms results from temporal smearing due to latency variability amongst trials. We thus conclude that there is relatively little difference in briskness between nonlagged and lagged-like responses to single stimuli.

Notes: Summary Prior studies of thalamic neurons have demonstrated that they exhibit at least two response modes: a relay mode and a burst mode. During the relay mode, sensory information is faithfully relayed to cortex; during the burst mode, which is caused by a voltagedependent Ca2+ conductance, this relay of sensory information is interrupted. We began in vivo studies of these response modes in neurons from the lateral geniculate nucleus of anesthetized, paralyzed cats. Each of the 9 X and 10 Y cells we recorded intracellularly displayed voltage-dependent, low threshold spikes that were presumably the Ca2+ spikes described from in vitro recording. These spikes were triangular in waveform and typically had 2–7 fast action potentials (interspike intervals of 1.2–4 ms) riding its crest. Furthermore, the cell's membrane had to be hyperpolarized to de-inactivate the low threshold spike before a depolarization could then activate it. We could activate these low threshold spikes in Y cells from EPSPs, whether spontaneous or evoked from activation of the optic chiasm. However, in only one of the X cells could we activate low threshold spikes from chiasm shock; in the remainder, we could activate low threshold spikes only via depolarizing current pulses, possibly because the EPSPs of these X cells were too small to activate these spikes. We also used extracellular recording to study spontaneous activity and responses to chiasm shock from 114 geniculate neurons and, as a control, 57 optic tract axons. We concentrated on periods of bursty responsiveness signifying the burst mode. We define a burst as 2–7 action potentials with interspike intervals 〈= 4 ms, and the bursts are separated by 〉 100 ms; from our intracellular recording, we know that such bursts signify low threshold spikes. We found that, during extracellular recording, 20 of the 39 X cells and each of the 75 Y cells displayed evidence of the burst response mode, although burst periods were rare in X cells. Electrical activation of the optic chiasm greatly enhanced the burstiness of Y cells for periods of 500 ms or more. We also electrically stimulated the parabrachial region of the midbrain, which provides a mostly cholinergic innervation to the lateral geniculate nucleus. Although parabrachial activation by itself had no detectable effect on Y cell response modes, prior parabrachial activation prevented the enhanced burstiness caused by chiasm stimulation. This parabrachial effect lasted for roughly 500 ms after stimulation. Neither chiasm nor parabrachial stimulation, singly or in combination, had a noticeable effect on the bursting activity of X cells. Finally, none of the extracellularly recorded retinogeniculate axons (23 X and 34 Y) showed any evidence of burst responses. This supports the conclusion that the burst responses we found for geniculate neurons represent an emergent property of the lateral geniculate nucleus, and this burstiness reflects an interruption of retinogeniculate transmission. We conclude that geniculate X and Y cells do indeed show evidence during extracellular recording of maintaining two very different response modes and that, under our recording conditions, Y cells are much more prone to burst activity than are X cells.

Notes: Boiling heat transfer from a porous layer sintered on a horizontal heater surface and heated from the base was analyzed for laminar to turbulent regions. The effects of the thickness of the porous layer, particle diameter, porosity, pore size distribution, and the properties of fluids on boiling heat transfer were analyzed. Reynolds number, parameter ψ, and a dimensionless heat flux were related to each other. Most experimental data used in this work fall in the region where the vapor Reynolds number is less than 100; very few data exceeded far beyond 1,000.For thick porous beds, the thickness no longer affects the heat transfer. For thin porous beds, heat transfer is affected by the thickness of the porous layer. The prediction equations of various investigators for dryout heat flux were put into dimensionless forms and the differences that exist among the equations are explained.

Notes: Two-mode boiling on a horizontal heated wire immersed in a pool of liquid under atmospheric pressure has been investigated. Methanol, acetone, isopropanol, and isobutanol were boiled using wires made of tungsten (0.15, 0.50, 0.82, 1.01, and 1.55 mm dia.), tantalum (0.30 and 0.82 mm dia.), molybdenum (0.125 and 1.01 mm dia.) and titanium (1.01 and 1.55 mm dia.). Two-mode boiling may be steady or unsteady. In steady two-mode boiling, both modes of boiling are stationary on the wire. The applied current in this case is referred to as the equilibrium current. In this article a method devised to calculate this current is discussed. The calculated results agreed well with the experimental results. In unsteady two-mode boiling, one of the two modes automatically takes over the other and boiling changes into a one-mode boiling. A method to calculate this transition velocity is presented. The calculated results correlated well with the experimental work.