Variations In Heat Production Research Articles

Heat flow map of northern and central parts of the Fennoscandian Shield based on geochemical surveys of heat producing elements

The heat flow-heat production ( Q- A) relationship is a useful tool in geothermal research, and it has been widely used for delineating geothermal provinces and determining characteristic parameters of heat production in the continental crust. In this study, a simple but rarely used technique of utilizing the heat flow-heat production relationship is discussed. In central and northern parts of the Fennoscandian Shield extensive geochemical surveys have produced 1483 samples taken from glacial till with a sampling density of 1 sample/300 km 2. Heat production values determined from U, Th and K concentrations in these samples were used to calculate a map of heat flow density. A previously determined Q- A relationship, Q = 15.8 + 10.8 · A, was applied. The compiled map covers all Finland, northern Sweden and northern Norway, about 35% of the exposed shield area in Fennoscandia. Heat flow density and heat production increase with decreasing geological age and correlate with granitoid types. The calculated heat flow density values on the map were controlled with 12 drill hole measurements not used in calculating the applied Q- A regression line. Nine of them are from previously unpublished data from the Finnish part of the Shield. The agreement with drill hole measurements and the geochemical estimate is reasonable, although not perfect in all cases. The differences can be attributed to anomalous vertical variation in heat production, reliability of the applied Q- A plot, reliability of till geochemistry in bedrock studies, convective groundwater disturbances or local structural effects. The calculated heat flow map can be used as a data set supplementing drill hole measurements to determine representative values of heat flow density in areas with low numbers of drill hole measurements.

Maintenance requirements in metabolizable energy of adult, nonpregnant, nonlactating Charolais cows.

The objective of this study was to determine the maintenance requirements in metabolizable energy (MEm) of adult, nonlactating, nonpregnant Charolais cows. A feeding trial was conducted using 12 cows fed at one of two feeding levels (75 [L] and 113 [H] kcal of ME.kg BW-.75.d-1) for 116 d. Body composition was estimated from subcutaneous adipocyte diameter. Body weight changes averaged -468 and +46 g/d, respectively. Diet DM digestibility averaged .496. The L cows spent less time eating and ruminating but had other behavioral characteristics similar to those of H cows. Estimates of MEm were calculated from BW or body composition changes and amounted to 109 and 124 kcal of ME.kg BW-.75.d-1, respectively. Heat production (HP) was then measured over 67 d in a second trial on two L and two H cows from the feeding trial and planes of feeding were switched after 14 d. Estimates of MEm varied from 112 to 105 kcal.kg BW-.75.d-1. Within animal, day-to-day variations in heat production were high (4.6% on average) and prevented the detection of any precise changes of HP with time on treatment. None of the trials showed any significant effect of level of feeding on MEm.

Heat‐flow constraints on the West African lithosphere structure

Heat production measurements from the West‐African shield have been compiled using various samples of crustal rocks. There is no clear indication for a systematic variation of heat production with age which could explain the regional heat flow density (HFD) variations by corresponding variations of the crustal component. HFD values are positively correlated with the P‐wave travel time residuals deduced from teleseismic observations and negatively correlated with gravity isostatic anomalies. We propose that regional HFD variations are significative of change in the upper mantle structure.

Diurnal variation in heat production related to some physical activities in laying hens

1. Heat production, standing and eating activities, and hourly food intake of 4 laying hens were observed simultaneously and the effects of activity and food intake on heat production were studied. 2. Average heat production during the dark period (20.00 to 06.00 h) was 18.9 kJ/kgW0.75 h which was 33% lower than that during the light period. About 76% of the light-dark difference in the rate of heat production was probably associated with activity and posture. 3. Standing time, which included a range of behavioural activities, occupied 90% of the light period and the increased rate of heat production associated with standing was estimated to be about 18% of daily heat production. 4. Eating time occupied 40% of the light period; the heat production associated with eating activity represented about 5% of daily heat production or 3% of ME intake. 5. Because the regression of heat production on time spent eating agreed with the regression of heat production on hourly food intake, it is suggested that the energy expenditure associated with ad libitum feeding can be estimated for hens from the regression of heat production on hourly food intake.

Heat-Producing Elements and the Thermal and Baric Patterns of Metamorphic Belts

The character of sedimentary basins, before they are deformed and metamorphosed, may strongly influence the thermal and baric patterns of metamorphic belts. Crustal thickening of anoxic sedimentary basins and subsequent thermal reequilibration may produce large areas of high-grade metamorphic rocks and granites because the concentrations of the heat-producing elements are high in such basins. In New England there is a spatial association among granites and high-grade metasedimentary rocks rich in U and Th that now form the Central Maine terrane. The high content of heat-producing elements in these rocks is attributed to fixing of U and Th in highly reduced sediments that were deposited in an anoxic basin that formed in the Silurian. When the basin was thickened during the Devonian Acadian orogeny, the thermal energy generated by the U- and Th-rich sediments produced the observed broad zone of high-grade rocks and anatectic granites. This hypothesis was tested with thermal calculations that reproduce most of the first-order thermal and baric patterns of the Acadian Appalachians, if pretectonic lateral variations in heat production are assumed.

Terrestrial heat flow and radiogenic heat production in Finland, the central Baltic Shield

Heat flow density and radiogenic heat production of the bedrock were studied in Finland in part of the central Baltic (Fennoscandian) Shield. Heat flow data were collected from 35 holes 270–1080 m deep. The heat production values at the sites were determined from the drill core samples by gamma ray spectrometry. The areal variation in heat production was studied with the aid of K, U and Th analyses of 1054 glacial till samples collected for the “Geochemical Atlas of Finland”. A heat production map constructed from this data set revealed a strong areal variation that can be attributed to the known lithological, geochemical and tectonic features of the bedrock. In general, heat production seems to increase with decreasing geological age. The presented data strongly suggest that the southern and western parts of Finland are geothermally anomalous (apparent heat flow density 38–68 mW/m2, surface heat production > 2.0 μW/m3) in contrast to the other parts of the country (< 42 mW/m2, < 2.0 μW/m3). The heat production-heat flow density plots were constructed from apparent and palaeoclimatically corrected heat flow densities; the heat production values were determined from both drill core samples and till samples. The plot constructed from the till data and apparent heat flow densities, which yielded a scale depth of 10.8 ± 2.6 km and a reduced heat flow density of 15.8 ± 4.9 mW/m2, was considered the most reliable. The results are discussed in terms of crustal fracturing and deep groundwater flow. If the crystalline bedrock is approached as a medium consisting of blocks internally conductive but bounded by fracture zones in which heat is transported by groundwater flow, an alternative hypothesis can be constructed for interpreting the linear heat production-heat flow density plots. According to this hypothesis, the scale depth and reduced heat flow densities refer only to the geothermal properties of the uppermost bedrock block. In the present study, this concept is supported by results from deep electromagnetic and seismic soundings.

Heat production in an Archean crustal profile and implications for heat flow and mobilization of heat-producing elements

We have measured concentrations of heat producing elements (Th, U, and K) in 58 samples representative of the main lithologies in a 100 km transect of the Superior Province of the Canadian Shield, from the Michipicoten (Wawa) greenstone belt, near Wawa, Ontario, through a domal gneiss terrane of amphibolite grade, to the granulite belt of the Kapuskasing Structural Zone, near Foleyet. This transect has been interpreted as an oblique cross section through some 25 km of crust, uplifted along a major thrust fault, and thus provides an opportunity to examine in detail a continuous profile into deep continental crust of Archean age. Mean heat production values for these terranes, based on aereal distribution of major rock types and calculated from their Th, U, and K concentrations are: Michipicoten greenstone belt = 0.72 μW m −3; Wawa domal gneiss terrane (amphibolite grade) = 1.37 μW m −3; Kapuskasing granulites = 0.44 μW m −3. Among the silicic plutonic rocks (tonalites, granites, and their derivative gneisses), the relatively large variation in heat production correlates with modal abundances of accessory minerals including allanite, sphene, zircon, and apatite. We interpret these variations as primary (pre-metamorphic). The relatively high weighted mean heat production of the domal gneiss terrane can be accounted for by the larger proportion there of late-stage Th-, U-, and K-rich granitoid plutons. These may have been derived from the underlying Kapuskasing granulite terrane, leaving it slightly depleted in heat producing elements. Transport of Th, U, and K, therefore, could have taken place in silicate melts rather than in aqueous or carbonic metamorphic fluids. This conclusion is supported by the lack of a statistically significant difference in heat production between tonalites, tonalite gneisses and mafic rocks of amphibolite versus granulite grade. The pre-metamorphic radioactivity profile for this crustal section is likely to have been uniformly low, with a mean heat production value less than 1 μW m −3. This result is distinctly different from measured profiles in more silicic terranes, which show decreasing heat production with depth. This implies fundamental differences in crustal radioactivity distributions between granitic and more mafic terranes, and may be an important factor in selective reactivation of lithologically different terranes, possibly resulting in preferential stabilization of basic terranes in the geological record. Our results indicate that a previously determined apparently linear heat flow-heat production relationship for the Kapuskasing area does not relate to the distribution of heat production with depth. Low, but significant heat production, 0.4–0.5 μW m −3, continues to lower crustal depths with no correlation to the depth parameter from the linear relationship. This low heat production may be a minimum average granulite heat production and suggests that, in general, heat flow through the Moho is 8–10 mW m −2 lower than the reduced heat flow calculated from the heat flow-heat production regression.

Heat production and thermal conductivity of rocks from the Pikwitonei–Sachigo continental cross section, central Manitoba: implications for the thermal structure of Archean crust

The Pikwitonei and Sachigo subprovinces of central Manitoba provide a cross-sectional view of the Superior Province crust. In cross section, the upper to mid-level crust is composed of synformal greenstone belts surrounded by tonalitic gneisses, both of which are intruded by granitoid plutons. This crustal structure persists downward into the granulite facies, where keels of the greenstone belts can be found. To constrain thermal models of the crust, we measured heat production and thermal conductivity in 60 rocks from this terrain using standard gamma-ray spectrometry and divided bar techniques. Large vertical and lateral heterogeneities in heat production in the upper crust are evident; heat production is high in granites and metasedimentary rocks, intermediate in tonalite gneisses, and low in the portions of greenstone belts dominated by mafic meta-igneous rocks. In the deeper granulite facies rocks, heat production decreases by a factor of two in the tonalitic gneisses and remains low in the high-grade mafic rocks. When applied to the Pikwitonei–Sachigo crust cross section, the laboratory data here do not support step function or exponential models of the variation of heat production with depth. However, estimates of surface heat flow and surface heat production for various sites in the crustal model yield the well-known linear relationship between surface heat production and surface heat flow observed for heat-flow provinces for both one- and two-dimensional models. This demonstrates that determinations of heat production with depth based on inversion of the linear heat-production–heat-flow relationship are nonunique.

Factors controlling the distribution of heat production in selected UK granites

The variation of heat production with respect to magma evolution is examined in four UK granites in which fractional crystallization accounts for the range of rock compositions present. Accessory minerals are the dominant hosts of U and Th in these granites and their role in controlling variations of these heat producing elements is assessed. Melt compositional parameters determine which accessory minerals precipitate (solubility control) and influence the partitioning of radioelements between early‐crystallizing (fractionating) minerals and residual liquid. As a result, parental magma compositions and the effect of critical properties, such as alkalinity, aluminosity and volatile contents (particularly F‐complexing) on magma evolution are considered important in controlling the primary distribution of radioelements in granites.

The effect of ambient temperature and activity on the daily variation in heat production of growing pigs kept in groups.

In two experiments, pigs with initial weights of 20 kg were kept in climate-controlled respiration chambers. After a 7-day adaptation period at 22-24 degrees C the temperature was reduced in 4 degrees C steps to 8 degrees C and then increased to 24 degrees C. Each temperature treatment lasted 3 days. Feed contained 12 kJ metabolizable energy per g and was given at 93 and 83 g/kg0.75 per day in experiments 1 and 2, respectively. Lower temperature increased 24 h heat production, but not 24 h activity. The mean activity periods moved from before and after feeding to after feeding, especially in the afternoon. During the afternoon, activity decreased at the lower ambient temperature, whereas metabolic rate remained constant. It is concluded that the effect of ambient temperature on metabolic rate depends on the time of day. (Abstract retrieved from CAB Abstracts by CABI’s permission)

A Field Study of Thermoregulation in the Carpenter Bee Xylocopa virginica virginica (Hymenoptera: Anthophoridae)

Thoracic, abdominal, and head temperatures were measured in individual fieldcollected Xylocopa virginica virginica performing a variety of behaviors over a wide range of ambient conditions. The bees were highly endothermic during activity, with thoracic temperatures ($T_{TH}$) that ranged from 31.4 to 48.5 C (at ambient temperatures, $T_{A}$, from 15 to 35 C) and a mean thoracic temperature excess ($T_{TH}-T_{A}$) of approximately 16 C under low insolation levels. Linear regressions of $T_{TH}$ on ambient temperature indicate a well-developed thermoregulatory ability (slopes of $T_{TH}$ vs. $T_{A}$: male = .25; female = .23). Air temperature, solar radiation, and, in some cases, humidity and wind speed significantly affected body temperatures. Behavior, too, significantly affected body temperatures, apparently in large part because of associated variations in heat production as well as environmental effects on body temperature. Head temperature ($T_{H}$) appears to be regulated, at least in males, by cont...

Geographical variations in heat production and dissipation within two populations of Rhabdomys pumilio (Muridae)

1. 1. A comparative study of heat production and dissipation was carried out on Rhabdomys pumilio from two extremely different climatic zones. 2. 2. Our results show higher oxygen consumption ( V O 2 ) values for the desert population at T a = 5°C when compared to the mesic population. The overall thermal conductance is also higher for the desert population. 3. 3. It seems as though penetration into mesic areas of R. pumilio, which originated in an arid zone, was accompanied by an increase in body mass.

Adaptive variations in heat production within Gerbils (genus Gerbillus) from different habitats

Species of the genus Gerbillus are very common among the rodent fauna inhabiting arid zones and dune habitats in the palaearctic region. In Israel G. nanus is distributed in extreme arid areas, while G. allenbyi is common in coastal plain dune habitats, of mesic and semi-arid areas. Therefore, their distribution pattern is considered allopatric.Heat production, estimated by the oxygen consumption (Vo2), and body temperature (T b) at various ambient temperatures were measured in both gerbils. The thermoneutral zone for G. allenbyi is between T a=28-35° C ([Formula: see text] T b=36.3-38.3° C) and for G. nanus is at T a=33±1° C ([Formula: see text], T b=38.8° C). The [Formula: see text] values at thermoneutrality are 75.7% and 50.6% respectively of the calculated values for rodents with a mean body weight of 35.3 g and 28.4 g.Nonshivering thermogenesis (NST) was measured in both species as the maximal response to an injection of noradrenaline (2.0 mg/Kg s.c.). NST magnitude was the same for both species.The results show that both gerbils are adapted to arid environments. The difference in the thermoneutral zones of the two species is discussed in terms of its adaptive nature.

The thermal structure and thermal evolution of the continental lithosphere

For thermal considerations, the lithosphere is defined as the outer layer of the Earth in which heat transfer is dominated by conduction. Low density continental crust caps the continental lithosphere preventing its subduction, and thus it has, in general, a long and complex thermal history. The thermal regime in the near surface zone of the continental lithosphere is commonly complex, and is responsible for much of the scatter in shallow heat flow data, the main data set used to examine the thermal structure and evolution of the continental lithosphere. A review of continental heat flow data shows that while heat flow is commonly high in areas of recent tectonic activity, there is no simple relationship between heat flow and age of tectogenesis. Low heat flow values are found in some areas of recent tectonic activity, and high heat flow values are found in some areas of older tectonism. An analysis of the parameters controlling the thermal structure of stable continental lithosphere shows that for the same heat flux into the base of the lithosphere, the main factors controlling temperatures within the lithosphere and surface heat flow are the quantity and distribution of heat producing elements within the lithosphere. In regions of recent tectonic and/or magmatic activity, perturbations in the thermal structure of the lithosphere are a function of the style and intensity of the tectonothermal disturbance. In hot spot and extensional settings, the lithosphere is thinned and its thermal gradient increased. The thermal effects at strike-slip boundaries are generally only of local importance, but can be significant when lithospheres with different thermal structures are juxtaposed. A variety of thermal phenomena are observed and predicted for zones of convergence, including low heat flow associated with subduction, high heat flow associated with magmatic activity, and thermal inversions associated with underthrusting. In seventeen continental areas, sufficient data are available to estimate the contribution of upper crustal heat production to the surface heat flow. This contribution is highly variable, and does not appear to correlate with crustal age for Proterozoic and Phanerozoic sites, but appears to be generally lower and less variable in Archean sites. In contrast, the component of heat flow from below the upper heat producing layer, the reduced heat flow, is relatively uniform, around 27 mW m −2 for sites which last experienced tectonism or magmatic activity in pre-Mesozoic times, but is highly variable for younger sites. From the uniform reduced heat flow for pre-Mesozoic sites, the stable thickness of the continental lithosphere is estimated to range from 90 to 220 km, thinner lithosphere being associated with higher heat production in the lithosphere. From this thickness, thermal perturbations in the lithosphere associated with tectonothermal activity are predicted to last no more than a few 100 m.y., a prediction consistent with available reduced heat flow data. Some prolongation of thermal relaxation is expected due to post-tectonic sedimentation and erosion, but these effects appear to be negligible at sites of Early Paleozoic age and older. The scatter in surface heat flow values at these sites is primarily the result of crustal heat production variations and near surface effects. Relatively low and uniform heat flow at Archean sites perhaps reflects relatively low and uniform crustal heat production at these sites.

Effect of confinement in a respiration chamber and changes in temperature and plane of nutrition on heat production of 25 kg pigs

SummaryA closed-circuit respiration chamber was used to study (a) the effect of confinement in a chamber on the heat production of pigs already accustomed to restraint in a metabolism cage; (b) changes in daily heat production of pigs following a reduction in the energy intake; and (c) the effect of increasing or decreasing the environmental temperature.An automatically recharged version of the oxygen burette used by Waring &amp; Brown (1965) is described. During tests of the chamber and burette system the mean recoveries of carbon dioxide and oxygen were, respectively, 0·994 and 0·995.It is concluded that measurements of heat production on the first day of confinement were within the normal range of variation and provided valid estimates of energy expenditure.The minimum value for the respiratory quotient (RQ) occurred on the third day following a reduction in energy intake, and it is concluded that the direct effect of previously ingested nutrients was eliminated by the third day. However, there appeared to be a further decline in heat production until 6–7 days following the reduction in energy intake.The heat production of singly caged pigs fed almost to appetite was similar at 22 and 29 °C. Heat production increased at 15 °C, indicating that this was below the lower critical temperature of fed 25 kg pigs. The response of heat production to the low temperature continued for at least 18 days. Variations in heat production between animals and litters were as high as 15% in three experiments.

Studies on diurnal variations of heat production and the effective lower critical temperature of early-weaned pigs under commercial conditions of feeding and management

1. The heat production of groups of pigs, weaned at 10 d of age, was determined in an open-circuit respiration chamber at various ages between 10 and 33 d at temperatures above and below the lower critical temperature (Tcl). 2. The heat production was lowest on the second or third day post weaning when pigs were given feed increasing by 25 g/pig per d from day 2. There was a marked diurnal pattern in heat production, the lowest values being recorded between 24.00 and 08.00 h. 3. The mean thermal conductance (H/delta T, kJ/h per m2 per degrees delta T, where H is total heat production, m2 is the surface area calculated as 0.097 W kg0.633 (Brody, 1945) and degrees delta T is the difference between rectal temperature, taken as 39 degrees, and air temperature) below Tcl was calculated as 18.0, 16.9, 18.5 and 21.2 respectively at 10, 17, 24 and 31 d of age. Maximum values of H/delta T obtained during feeding periods were, on average, 4.5 kJ/h per m2 per degrees delta T higher than the mean values. 4. The maximum value for Tcl during the immediate post-weaning period was 25.9 degrees. The mean Tcl at 17, 24 and 31 d were respectively 21.7, 18.4 and 18.6 degrees for pigs fed almost to appetite.

Activity and energy expenditure in laying hens

SummaryThe energy cost of nesting activity and oviposition of hens in different environments has been determined.The oxygen consumption of hens on a wire floor reached a peak during the last 15 min before oviposition. However, the oxygen uptake of hens accustomed to a litter floor had fallen to a minimum at this time.The energy cost of expelling the egg is minimal. There is a good correlation between the locomotor activity and the heat production.The variations in heat production and body temperature on different types of floors are explicable by the differences in nesting activity.

Analysis of Heat Flow Data–Vertical Variations of Heat Flow and Heat Producing Elements in Sediments

Gamma ray spectrometric techniques have been used for the determination of uranium, thorium and potassium contents from cores selected at 3 to 4 m intervals from a 600 m deep borehole in sedimentary formations and the results compared with a similarly detailed examination of heat flow, and some physical properties, from the same borehole.The results indicate a broad positive correlation between thermal resistivity and some of the radio-element parameters and between heat flow and heat production. The heat production variations down the borehole are not quantitatively sufficient to explain the observed heat flow variations. The uranium series appears to be in radioactive equilibrium even in those sections where the uranium content is low, the porosity relatively high and the heat flow low; it is therefore concluded that the depletion of uranium is due to an ancient rather than a recent leaching process and that it is unlikely that the heat flow variations along the borehole are due to existing or recent underground waterflows. Long term geochemical reactions are now thought to be the most likely explanation of the heat flow variations.

The heat production of hens and cockerels maintained for an extended period of time at a constant environmental temperature of 23 °C

SUMMARYHens and cockerels of a White Leghorn strain (‘H &amp; N’) were kept at a constant temperature of 23 °C from 1 year until 2¼ years of age. The mean fasting heat production, which was measured 6 times during this period, varied between 404 and 464 kJ/kg0·75/day for the hens and between 223 and 349 kJ/kg0·75/day for the cockerels. The sex difference in heat production is discussed and an attempt is made to explain the variation in heat production for each sex.

Terrestrial Heat Flow, the Neutrino Problem, and a Possible Energy Source in the Core

DETAILED measurements in a single borehole have revealed a real variation of heat flow with depth1. To determine the origin of these variations we determined a detailed profile of the U, Th and K concentrations in the rocks through which the borehole passed to estimate the heat production values. A similarity between the heat flow and heat production profiles was indeed found2 but, using the presently accepted values for the heat production constants of the common radio elements, the magnitude of the heat production variations was not sufficient to explain the magnitude of the heat flow variations.