Excessive Heat Dissipation Research Articles

Pulsed Dye Laser-Resistant Port-wine Stains

Port-wine stains (PWSs) are congenital lesions characterized by ectatic vessels in the superficial dermis. The cause of these lesions is unknown, but 1 theory is that they result from a diminished neural regulation of the blood flow, secondary to a reduced number of perivascular nerves,¹which, in turn, results in erythrostasis and progressive vessel ectasia. The use of pulsed dye lasers is currently the treatment of choice for PWSs. The 577-nm or 585-nm wavelength selectively targets oxyhemoglobin and the 450-microsecond pulse duration is sufficient to cause intravascular coagulation without excessive heat dissipation to the epidermis or adjacent dermal structures.

Helmeted Honeyeaters Build Bulkier Nests in Cold Weather

Birds with long breeding seasons may encounter markedly varied environmental conditions as the breeding season progresses. In the Temperate Zone, one of the most universal of these changes is an increase in temperature. At low temperatures, incubation imposes an additional energetic cost (Haftorn and Reinertsen 1985), and the insulatory capabilities of even cup nests provide demonstrable advantages (Smith et al. 1974, Walsberg and King 1978). However, at higher temperatures nest material may impede the dissipation of excess heat (Ricklefs and Hainsworth 1969). Although seasonal changes in nest orientation are well documented and have been related to prevailing temperatures and wind (Ricklefs and Hainsworth 1969, Austin 1976), structural changes are poorly documented. Nolan (1978) reported that first nests of the Prairie Warbler (Dendroica discolor) were 21% heavier than replacement nests. The nest of the Helmeted Honeyeater (Lichenostomus melanops cassidix; Meliphagidae) is a substantial cup, usually both suspended from and supported by shrub twigs (Barrett 1933, Cooper 1967, Franklin et al. 1995). It is a tightly woven structure of bark fibers or strips, fine twigs, grass stems, and dry leaf strips. The nest is lined with diverse materials, such as pithy wood fragments, fine bark fibers, and flower buds. Construction of the nest takes about a week and is undertaken almost entirely by the female. The breeding season extends from midwinter to late summer, and a pair may make up to nine nest attempts (typically about four) in a breeding season. A new nest is built for each attempt. Wilson and Chandler (1910) noted that early nests were bulkier than later nests, and Wykes (unpubl. manuscript) suggested that this was due to a thinner lining. I examine that phenomenon. During the 1991-1992 and 1992-1993 breeding seasons I opportunistically measured Helmeted Honeyeater nests at Yellingbo (37?50'S, 145?29'E) in southern Victoria, Australia. Measurements (to nearest millimeter) taken were: cup depth; cup diameter; exter-

Fluid flow and heat transfer in sedimentary basins

Abstract One of the major assumptions underlying the science of geothermics over the last 100 years has been that heat is transported through the Earth’s crust only by conduction, except in the immediate vicinity of active volcanoes. In old shields this assumption may be justifiable, but in sedimentary basins the ability of water to move through permeable aquifers provides a means of heat transport that may under certain conditions be as effective as conduction. The thermal history of a basin depends on its tectonic origin and the circumstances of its development. The dissipation of excess heat associated with basin formation and the transfer of the continuous heat supply from the basement depend on the thermal properties of the strata and their water content. In some basins widespread contrasts of heat flow are observed, both laterally and vertically, suggesting forced convection by water migration. In basins where part of the surface is above sea-level a hydrological drive may be inferred from the topographic surface. In sub-sea basins this drive is not available in the same form. Nevertheless, patterns of heat-flow variation have been observed for which some form of water flow seems to be the most probable explanation. A complete quantitative description of the present thermal state has not yet been developed for any basin. Some two-dimensional numerical models have been developed, but, since flow directions may vary between aquifers, three-dimensional models must be the ultimate objective. There is scope to extend such models to the geological past by using palaeotemperature indicators such as vitrinite reflectance and fission-track measurements. So far we have been able to establish only an understanding of the principles and processes that control the thermal state of basins, so that detailed description of small parts or two-dimensional models may be developed.

The electrical characteristics of porous Al 2O 3 produced by anodization

The electrical characteristics of films of Al 2O 3 prepared by anodizing aluminium substrates were investigated. The Al 2O 3 consisted of a thin barrier layer of approximate thickness 150–180 Å surmounted by a thick porous layer of thickness 5–10 μm. Cobalt ions were deposited in the lower sections of the porous layer by a method of metal pigmentation. A number of different conduction processes were observed, including Schottky-type behaviour, field ion diffusion, space-charge-limited currents, ohmic conductivity and also electroforming and electron emission. A typical barrier height ∅ for Schottky emission at the AlAl 2O 3 interface of 1.11 eV was calculated, and an activation energy E = 0.50−0.68 eV was estimated for the space-charge-limited process. The observation of electroforming in samples of such thickness was ascribed to the field-induced growth of conducting filaments in regions of the porous material which had previously been destroyed by excess heat dissipation.

Closure to “The Dissipation of Excess Heat from Water Systems”

Closure to “The Dissipation of Excess Heat from Water Systems”

Discussion of “The Dissipation of Excess Heat from Water Systems”

Discussion of “The Dissipation of Excess Heat from Water Systems”

The Dissipation of Excess Heat from Water Systems

A model for the prediction of excess temperature is shown to have the form of the classical diffusion equation. The excess temperature in this model is defined as the difference between the actual water temperature and the water temperature which would have occurred provided that a particular heat source, such as a power plant, had never existed. This definition of excess temperature is convenient because it directly represents the incremental effect that a heat source has on a water system and, provided that historical water temperature records are available, the excess temperature can be predicted without the use of solar or atmospheric radiation data. A prediction equation for the surface transfer coefficient for excess heat illustrates that this coefficient is primarily dependent upon the water temperature and wind speed, and that it is almost independent of the humidity and temperature of the air.

Thermal limitations of the thin film transistor

In the simple treatment of the thin film transistor (TFT) it has been shown that the gain-bandwidth of the device is proportional to the carrier mobility and inversely proportional to the square of the source-drain spacing. To obtain high frequency operation it would appear only necessary to reduce the source-drain spacing and to use a high mobility semiconductor. However, a limitation enters the picture when a high mobility material is employed, namely excessive heat dissipation. In this paper the maximum gain-bandwidth obtainable from a device having a given permitted power dissipation is derived. A simple experimental determination of the permitted power dissipation is also presented and the improvement in using a substrate with a high thermal conductivity is outlined.