High Heat Production Research Articles

Body weight and range usage affect net energy utilisation in commercial free-range laying hens when evaluated in net energy chambers.

Within a given free-range flock, some hens prefer to spend the majority of their time in the shed (stayers), while others frequently access the range (rangers). Laying performance has been associated not only with the development of these sub-populations but also with different body weights (BW). The purpose of this study was to determine if range usage, BW or a combination of both is associated with energy metabolism and as such contribute to improved hen performance. Forty-eight Lohmann Brown hens at 74 wk of age were selected from a commercial free-range farm based on their BW and range usage over a 56-week period. Using a 2 × 2 factorial arrangement, hens were either classified as heavy (mean ± SEM; 2.01 ± 0.02 kg, n = 24) or light (1.68 ± 0.01 kg, n = 24), and also classified as rangers (accessed the range for 84.1% of available days, 242 ± 3.75 d; n = 24) or stayers (accessed the range for 7.17% of available days; 23.4 ± 6.08 d, n = 24). Stayers had significantly higher metabolizable energy (ME) intake per metabolic BW per d (0.852 vs. 0.798 MJ/kg BW0.75 per d; P = 0.025), higher heat production (0.637 vs. 0.607 MJ/kg BW0.75 per d; P = 0.005), higher heat increment (0.267 vs. 0.237 MJ/kg BW0.75 per d; P = 0.005) and retained more nitrogen (1.59 vs. 1.46 g/hen per d; P = 0.023) compared to the rangers. Light hens had significantly higher metabolic energy intake per metabolic BW (0.854 vs. 0.796 MJ/kg BW0.75 per d; P = 0.018), net energy (NE) intake (0.595 vs. 0.551 MJ/kg BW0.75 per d; P = 0.032), and retained energy (0.225 vs. 0.181 MJ/kg BW0.75 per d; P = 0.032), as well as lower heat production (0.936 vs. 1.003 MJ/hen per d; P = 0.002) compared to heavier hens. An interaction was observed across levels of analysis i.e. between light stayers and light rangers. The light rangers had significantly higher NE intake compared to the light stayers (9.77 vs. 9.27 MJ/kg BW0.75 per d; P = 0.024). In conclusion, light hens were more energy efficient compared to heavy hens. Moreover, light rangers had a more efficient feed utilisation compared to the light stayers.

A Comprehensive Review and Technical Guideline for Optimal Design and Operations of Fuel Cell-Based Cogeneration Systems

The need for energy is increasing from year to year and has to be fulfilled by developing innovations in energy generation systems. Cogeneration is one of the matured technologies in energy generation, which has been implemented since the last decade. Cogeneration is defined as energy generation unit that simultaneously produced electricity and heat from a single primary fuel source. Currently, the implementation of this system has been spread over the world for stationary and mobile power generation in residential, industrial and transportation uses. On the other hand, fuel cells as an emerging energy conversion device are potential prime movers for this cogeneration system due to its high heat production and flexibility in its fuel usage. Even though the fuel cell-based cogeneration system has been popularly implemented in research and commercialization sectors, the review regarding this technology is still limited. Focusing on the optimal design of the fuel cell-based cogeneration system, this study attempts to provide a comprehensive review, guideline and future prospects of this technology. With an up-to-date literature list, this review study becomes an important source for researchers who are interested in developing this system for future implementation.

Hydronic configurations of hybrid heat production systems in buildings: General design methodology and case studies

Hybrid heat production systems, in which sustainable technologies such as Combined Heat and Power (CHP) or heat pumps are combined with auxiliary heaters, have the potential to increase energy efficiency in buildings. In order to exploit this potential, a proper hydronic configuration of the production system is of uttermost importance. Unfortunately, both scientific literature and design guides have focussed little on this aspect.Therefore, this paper proposes a general simulation-based design methodology for selecting the hydronic configuration of a hybrid production system. To illustrate the methodology, it is applied on different case studies in which either a CHP or an Electrical ground-coupled Heat Pump (EHP) is assisted by an auxiliary boiler. The considered apartment building is equipped with a collective heating system for both space heating and domestic hot water (DHW) production, and four different combinations of the temperature levels are considered.Results show that if a CHP is considered, the auxiliary boiler should be implemented in parallel and be assisted by a modulating valve: this increases the Relative Primary Energy Savings (RPES) with up to 6.2 percentage points. EHPs require a separate circuit in the production system for space heating and DHW, preferably with preheating of the domestic cold water (an increase in RPES of up to 16.1 percentage points was reported).The use of a new type of Load Duration Curve to analyse the simulation results proved to be a comprehensible measure for decision making at the level of every stakeholder in the design process. In conclusion, the proposed methodology can assist these stakeholders in their pursuit of high performance hybrid heat production systems.

Economic evaluation of improvements in a waste-to-energy combined heat and power plant

Improving the efficiency of waste-to-energy combined heat and power plants increases their production of both electricity and heat. Economic evaluation of such improvements enables adequate decisions to be made between the various alternatives with respect to economic viability of the plant. In this study, the cost and profitability of different modifications to improve efficiency in a waste-to-energy plant are considered: these include the re-arrangement of air heaters, the introduction of a reheater, flue gas condensation (FGC) and an integrated gasification-combustion process. The base case and the modifications are evaluated and compared when operating either as a combined heat and power plant or as a power plant. Modelling, simulation and cost estimations were performed with the Aspen Plus software. Although the integrated gasification-combustion technology with FGC has the highest exergy efficiency, its higher capital cost is greater than all of the other alternatives. Modification 6, which involves both re-arrangement and changing the air heating medium has the lowest capital cost with respect to enhancing exergy efficiency. Modifications 1 and 7, involving FGC, are the best alternatives for the capital cost per total unit of revenue generated. These modifications not only provides the highest heat production but also the highest net present value (NPV). The base case and the modifications investigated all have positive NPV, indicating that a waste-to-energy combined heat and power plant is an attractive investment. However, an increase of about 122% in the gate fees would be required for a system with only electricity production to be profitable.

Interaction between Indoor Occupational Heat Stress and Environmental Temperature Elevations during Heat Waves

Abstract Occupational heat strain is a public health threat, and for outdoor industries there is a direct influence from elevated environmental temperatures during heat waves. However, the impact in indoor settings is more complex as industrial heat production and building architecture become factors of importance. Therefore, this study evaluated effects of heat waves on manufacturing productivity. Production halls in a manufacturing company were instrumented with 33 dataloggers to track air temperature and humidity. In addition, outdoor thermal conditions collected from a weather station next to the factory and daily productivity evaluated as overall equipment efficiency (OEE) were obtained, with interaction between productivity and thermal conditions analyzed before, during, and after four documented heat waves (average daily air temperature above 24°C on at least three consecutive days). Outdoor (before: 21.3° ± 4.6°C, during: 25.5° ± 4.3°C, and after: 19.8° ± 3.8°C) and indoor air temperatures (before: 30.4° ± 1.3°C, during: 32.8° ± 1.4°C, and after: 30.1° ± 1.4°C) were significantly elevated during the heat waves (p < 0.05). OEE was not different during the heat waves when compared with control, pre-heat-wave, and post-heat-wave OEE. Reduced OEE was observed in 3-day periods following the second and fourth heat wave (p < 0.05). Indoor workers in settings with high industrial heat production are exposed to a significant thermal stress that may increase during heat waves, but the impact on productivity cannot be directly derived from outdoor factors. The significant decline in productivity immediately following two of the documented heat waves could relate to a cumulative effect of the thermal strain experienced during work combined with high heat stress in the recovery time between work shifts.

A 4 Ga record of granitic heat production: Implications for geodynamic evolution and crustal composition of the early Earth

The radiogenic heat produced by granites has a significant influence on the thermal state of the crust due to both their relatively high heat production with respect to most rock types and high abundance. However, the variations in present day heat production with age are generally based on relatively few measurements that are poorly distributed geographically. In this study, we construct a global model for the heat production of granitic rocks for the past 4 Ga using 13,400 geochemical analyses. We observe a nearly monotonic increase in radiogenic heat production from 4.0 to 2.0 Ga, which mirrors a shift from more TTG-like calcic to more alkalic compositions. This shift towards high-heat-producing granites post-2.0 Ga is often attributed to enrichment related to reworking and/or erosion. However, there is a strong correlation between granitic heat production with that of similarly-aged basalts and gabbros, which suggests a dominant mantle-level component to granite generation rather than crustal reworking. Secular cooling and mantle depletion may affect heat production, but the signal is complex and cannot easily explain the heat production with age profile. The most likely mechanism to describe the observed heat production–age pattern is one of selective preservation as a consequence of thermal stability. High heat producing terranes that were not stable during the Archean become increasingly stable towards the present. This selective preservation model has significant implications for the growth and composition of the continental crust. Ferroan, alkalic and felsic compositions were less thermally stable in the Archean due to their generally higher heat production and thus may have been more common in the early Earth than assumed by most compositional models. The temporal heat production model determined in this study can be used to improve geotherm models, particularly within ancient terranes.

Petrology and Geochemistry of Acid Volcano-Plutonic Rocks from Riwasa and Nigana Areas of Neoproterozoic Malani Igneous Suite, Northwestern Peninsular India: An Understanding Approach to Magmatic Evolution

This paper discusses the geochemical and petrological characteristics of acid volcano-plutonic suite of rocks exposed in Riwasa and Nigana areas of Malani Igneous Suite (MIS), Northwestern India. Geochemically, these acidic rocks having peraluminous and alkalic to alkali-calcic nature and classified as volcanic phase (Riwasa rhyolites), plutonic phase (Nigana granites) and dyke phase (micro-granites). Petrographically, rhyolites show porphyritic, granophyric, glomeroporphyritic, aphyritic, spherulitic and perlitic textures whereas granites show hypidomorphic, granophyric and microgranophyric textures. They are high in silica, A/CNK, total alkalis, Fe/Mg, Ga/Al, Zr, Rb, U, Th, Cu, REEs (except Eu) and low in CaO, MgO, Sc, Cr, Ni, Sr and Eu abundances, which have affinity with A-type granitoids. Their chemistry also support that they are high heat production (HHP) granitoids and their crustal origin. The enrichment of trace elements indicates a genetic link between fractional crystallization of silicate minerals and post magmatic fluid alterations in magmatic chamber. Negative anomalies of Ti, P, Sr and Eu in the multi-element spider diagrams indicate that the emplacement of these granites and associated acid volcanics were controlled by fractionation of feldspar (alkali and plagioclase) and crustal contamination in the magmatic melt arise upward. Normative values of silicate oxides further suggests that these rocks are formed between 2–7 kb pressure ranges and may be emplaced from shallow to greater depth ranges (15–30 km and 450–900°C). Furthermore, geochemical features in acidic rocks such as strong linear positive correlation between LREE, Zr, Nb, Ga, Y and Rb emphasize that the behavior and enrichment of these elements are largely controlled by post-magmatic processes in plume related associations. Hence, the geochemical data presented here, are therefore consistent with an intraplate, co-magmatic and A2-subtype granite field emplaced in extensional tectonic regime of MIS.

U–Pb Geochronology of Hydrothermal Monazite from Uraniferous Greisen Veins Associated with the High Heat Production Mount Douglas Granite, New Brunswick, Canada

A combination of in situ laser ablation inductively coupled plasma–mass spectrometry (LA ICP–MS) analyses guided by Scanning Electron Microscope–Back-Scattered Electron imaging (SEM–BSE) was applied to hydrothermal monazite from greisen veins of the Late Devonian, highly evolved, uraniferous Mount Douglas Granite, New Brunswick, Canada. Understanding the uraniferous nature of the suite and characterizing the hydrothermal system that produced the associated mineralized greisen veins were the main goals of this study. The uraniferous nature of the Mount Douglas Granite is evident from previous airborne radiometric surveys, whole-rock geochemical data indicating high U and Th (2–22 ppm U; 19–71 ppm Th), the presence of monazite, zircon, xenotime, thorite, bastnaesite, and uraninite within the pluton and the associated hydrothermal greisen veins, as well as anomalous levels of U and Th in wolframite, hematite, and martite within greisen veins. New U–Pb geochronology of hydrothermal monazite coexisting with sulfide and oxide minerals yielded mineralization ages ranging from 344 to 368 Ma, with most of them (90%) younger than the crystallization age of the pluton (368 ± 3 Ma). The younger mineralization age indicates post-magmatic hydrothermal activities within the Mount Douglas system that was responsible for the mineralization. The production of uraniferous greisen veins by this process is probably associated with the High Heat Production (HHP) nature of this pluton, resulting from the radioactive decay of U, Th, and K. This heat prolongs post-crystallization hydrothermal fluid circulation and promotes the generation of hydrothermal ore deposits that are younger than the pluton. Assuming a density of 2.61 g/cm3, the average weighted mean radiogenic heat production of the Mount Douglas granites is 5.9 µW/m3 (14.1 HGU; Heat Generation Unit), in which it ranges from 2.2 µW/m3 in the least evolved unit, Dmd1, up to 10.1 µW/m3 in the most fractionated unit, Dmd3. They are all significantly higher than the average upper continental crust (1.65 µW/m3). The high radiogenic heat production of the Mount Douglas Granite, accompanied by a high estimated heat flow of 70 mW/m2, supports the assignment of the granite to a ‘hot crust’ (>7 HGU) HHP granite and highlights its potential for geothermal energy exploration.

Individual Acclimatization of Apis mellifera L. to the Thermal Homeostasis of the Colony

Bees play an important role in maintaining biodiversity by promoting the pollination of numerous plant species. Recent global climate changes are affecting the average air temperature, thereby altering the biological processes of many species. The objective of this study was to evaluate the adaptation of Apis mellifera L. bees to temperature increases and their responses to thermal homeostasis in the colony. Research was performed at the Federal University of Paraíba Laboratory of Bees using three treatments: Control, 33 °C and 40 °C. For the latter two treatments, colonies were kept in a 24 m² climate chamber with an opening at the hive entrance, giving the bees access to the outside environment. The following parameters were evaluated: difference between internal and external hive temperature, thorax surface temperature and total protein concentration in the hemolymph. Internal colony temperature varied according to the external hive temperature. Nurse bees that care for larvae exhibited higher heat production, expressed as thorax surface temperature. Total protein content in the hemolymph was highest in the 40 °C treatment and decreased with ambient temperature. External hive temperature influences internal hive temperature, and nurse bees have higher capacities for thermogenesis.

Radioactive heat production of Syrian territory

Gamma-ray spectrometry is applied to estimate equivalent uranium (eU), equivalent thorium (eTh), and K% of 748 rock samples collected from Syrian territory. The spectrometry results are used to evaluate and map the radioactive heat production (HP) of Syria. A new approach involving the multifractal technique with the concentration-number model (CN) and log-log plots was originally proposed and hence applied in this paper to map the distribution of uranium concentration and HP of Syria. This approach helps us to differentiate different eU and HP ranges related to different litho-types. The advantages of proposing and applying the fractal technique are that the boundaries of the distinguished radioactive ranges of eU and HP coincide well with the lithological boundaries, which gives this technique superiority over other traditional statistical methods. The fractal CN model with the use of log–log plots proves its efficacy in differentiating between several eU and HP populations that are related directly to the geology of Syrian territory. The fractal model shows four threshold break points corresponding to uranium concentrations of 3.1, 7.38, 16.6, and 28.8 ppm and an HP of 0.715, 1.86, 3.63, and 6.26 μW/m3, respectively. The highest HP ranges are mainly related to the phosphatic deposits, characterized by the highest uranium content.

Metamorphism and exhumation of basement gneiss domes in the Quadrilátero Ferrífero: Two stage dome-and-keel evolution?

The presence of dome-and-keel provinces in Archean cratons has been connected with the initiation of plate tectonics on Earth as these features are most commonly observed in Archean rocks. The Quadrilátero Ferrífero in Brazil has been identified as a Paleoproterozoic dome-and-keel province for more than three decades. The prevailing model suggests that it formed during the Rhyacian Transamazonian orogeny, making it unique among dome-and-keel provinces. However, a lack of appropriate lithologies, datable minerals and the metamorphic overprint of later orogenesis has resulted in a cryptic metamorphic record for the formation of this dome-and-keel province. A clinopyroxene-bearing migmatite from the core of the Bação dome has peak P–T conditions of 5–7 kbar and 700–750 °C and a published age of ca. 2730 Ma based on U–Pb ages of zircon from leucosomes, suggesting that this age represents the migmatisation event. A fine-grained epidote-albite-titanite assemblage overprints the coarse-grained clinopyroxene and amphibole, giving P–T conditions of 8–9 kbar and 550 °C with an associated titanite age of ca. 2050 Ma. A garnet-bearing amphibolite sample also from the core of the dome has peak P–T conditions of 7–8 kbar and 650–700 °C, and texturally late titanite from this sample produces an age of ca. 2060 Ma. Three additional samples were collected from the edges of the dome. A garnet-gedrite bearing felsic schist produces peak P–T conditions of 8–9 kbar and 650–700 °C on a clockwise P–T evolution. This sample has a U–Pb zircon age of ca. 2775 Ma, which could date metamorphism or be the age of its volcaniclastic protolith. Texturally unconstrained titanite from the sample gives an age of ca. 2040 Ma. A garnet-bearing amphibolite that occurs as a boudin within the felsic schist gives both zircon and titanite ages of ca. 2050 Ma and has peak P–T conditions of 5–6 kbar and 650–700 °C on a near isobaric P–T path. An amphibolite dike, observed to cross-cut the felsic schist produces a zircon U–Pb age of ca. 2760 Ma. Altogether this data suggests that the samples were metamorphosed in the Archean (ca. 2775–2730 Ma) and again during the Transamazonian event. The most plausible explanation for this data is that dome-and-keel formation occurred in the Archean with migmatisation and high-temperature metamorphism occurring at this time. The Paleoproterozoic event is interpreted as a reactivation of the dome-and-keel formation structures, with Paleoproterozoic keels crosscutting Archean keels and producing metamorphic aureoles. The high radiogenic heat production and the presence of dense sedimentary successions in Archean terranes make dome-and-keel provinces a uniquely Archean feature, but they are susceptible to reworking, resulting in an enigmatic record of formation.

Mechanistic Pathways of ATP Sensitive Potassium Channels Referring to Cardio-Protective Effects and Cellular Functions.

A study of potassium channels correlates the fundamentals of mechanistic pathways and various physiological functions. The knowledge of these pathways provides the background, how to determine unit cell functions and to affect cardio protection. ATP sensitive potassium channels adjust excitability of membrane and functions as per metabolic status of cell. A lot of energy consumption primarily occurred in skeletal muscles which also express high number of potassium channels. The increase in calcium release and high heat production is occurred due to loss of potassium channels. Such type of mediations determines metabolic changes and energy required in the dissipation. IPC reduces infarct size in anesthetized mice. In ischemic-reperfusion, pressure in left ventricle was watched while contractile power recovery did not happen. It was seen that elements of intact potassium channel are fundamental for Ischemic preconditioning (IPC). If more prominent is enactment of potassium channels and their cardiologic effects create high heart rate. All the more as of late, it has been suggested that mitochondrial ATP sensitive potassium channels are critical as closing stage effectors which trigger IPC as opposed to sarcolemmal potassium channels. Nevertheless, the importance of the potassium channels reconsidered in cardio-protection in present findings. These discoveries recommend that potassium channels in the adjusting ischemic-reperfusion damage in mice. The heart rate of the mouse occurred during ischemia; enhance watchful extrapolation applied to larger warm blooded animals.

Heat production estimation by using natural gamma-ray well-logging technique in phosphatic khneifis deposit in Syria

Natural gamma-ray (GR) well-logging technique is used to estimate the radioactive heat production (HP) parameter as a function of depth, in the phosphatic Khneifis deposit in Palmyrides region in Syria. Seven available drilled wells with their natural GR records are used to characterize and estimate the HP magnitude in the study region. The analysis of 2660 measured points in those wells shows that HP varies between a minimum of 0 and a maximum of 7.97 μw/m3, with an average of 1.33 μw/m3 and a standard deviation of 1.68 μw/m3.Multi-fractal approach with the use of concentration-number (C-N) model and log–log plots is originally proposed and used as a new approach for characterizing the HP variations and isolating different HP populations in the study region. The high HP ranges are mainly related to the phosphatic layers, relatively enriched by uranium concentrations, comparing with their surroundings.

Distribution of Radioactive Heat Sources and Thermal History of the Moon

AbstractThe initial distribution of heat sources in crustal and mantle reservoirs plays a major role in the thermal evolution of the Moon. We use new constraints on the thickness of the crust, the size of a nearside low in crustal magnetization, surface composition data from orbit, Apollo samples, and mass balance considerations to generate a set of plausible post magma ocean initial conditions. We then test those initial conditions using the 3‐D thermochemical mantle convection code Gaia and compare with observables. Models that use Lunar Prospector gamma‐ray spectrometer values of thorium throughout the highland crust cannot sustain long lasting volcanic activity, as low abundances of heat‐producing elements are left in the mantle to keep an Earth‐like bulk silicate composition. The low magnetic field intensities of the innermost Procellarum KREEP Terrane are consistent with a higher heat production than in the outermost portion and delayed cooling below the Curie temperature of iron metal until after 3.56 Ga when the dynamo field strength is known to have decreased by an order of magnitude. The distribution of crustal heat sources also influences the depth evolution of isotopic closure isotherms for a range of isotopic systems relevant to radiometric dating, which may be important for sample age estimation. Core crystallization can sustain a continuous dynamo for about 1 billion years, after which dynamo activity is potentially more episodic.

Effect of temperature on the thermal conductivity of a granite with high heat production from Central Portugal

We present new measurements on the thermal properties of granitic rocks collected from a nearly 1000-m deep well in Central Portugal, using a transient plane source technique with a hot disk sensor. At room-temperature, the granite has, on average, a thermal conductivity of 3.1 W m−1 K−1, a thermal diffusivity of 1.6 × 10−6 m2 s−1, a heat capacity of 1.9 × 106 J m−3 K−1 and a specific heat of 720.7 J kg−1 K−1. A nearly uniform distribution of thermal conductivity values was obtained across the well. We found that as temperature increases from 20 to 120 °C, the thermal conductivity decreases from 9 to 16%. Linear, exponential, power and logarithmic functions were used to fit the dataset and their validity studied by error analyses. This made it possible to obtain empirical relationships to extrapolate thermal conductivity from room temperature to higher temperatures. The application of these relationships to our dataset leads to a decrease in thermal conductivity of 17 to 19% within the temperature range of 20 to 200 °C. These temperature corrections for thermal conductivity will be used in future studies to calculate geotherms and to assess the deep geothermal potential in central Portugal.

Estimation and mapping of radioactive heat production by aerial spectrometric gamma and fractal modeling techniques in the Syrian desert (Area-1), Syria

Radioactive heat production (HP) in the Syrian desert (Area-1) is estimated by using the available data of aerial spectrometric gamma technique. The HP is separately well characterized for 10 geological units, which are identified on the already established Area-1 scored map. Fractal technique combined with concentration-number (C-N) model and log-log graphs is used to map total radioactivity, equivalent uranium, and HP in Area-1. The HP in Area-1 varies between a minimum of 0 and a maximum of 7.23 μw/m3, with an average of 0.584 μw/m3 and a standard deviation of 0.341 μw/m3. The lithological phosphatic units A, B, C, and D are characterized by a higher HP than their surrounding units, because of their richness in uranium concentrations.

Evaluation of the return temperature reduction potential of optimized substation control

Network temperatures play a major role in the overall efficiency of district heating networks. Low network temperatures are desirable, because they allow high heat production efficiency and low network heat losses. Furthermore, low network temperatures benefit the injection of low-temperature renewable and excess heat sources. At the same time, a high temperature difference between supply and return pipes is desired to limit the network flow rate. This reduces pumping power and increases the network capacity. Whereas the network supply temperature is governed by the heat supply, the network return temperature is determined by the connected customers. This paper focuses on an approach for reducing the network return temperature by considering the control of district heating substations for space heating. Optimal heating control curves exist for the secondary-side supply temperature and flow rate that minimize the network return temperature of indirect substations. The goal is to investigate the impact of optimized control curves on the network return temperature, under various circumstances.Using a steady-state model of an indirect substation connected to a radiator system, the optimal control strategy is calculated. Its performance is compared to that of traditional control using a pre-set heating curve. The results show that the biggest impact occurs in partial-load conditions, with a potential for reducing the network return temperature by up to 9.9 °C (average 6.0 °C) and primary flow rate reduction up to 14.7 % (average 7.6 %). A parametric analysis to evaluate the impact of the network supply temperature, heat demand and heating system design sizing is presented. It is concluded that the use of optimized substation control for space heating could significantly reduce the network return temperature and primary flow rate. This would benefit the overall energetic system performance of district heating grids.

Carbon Cycling and Habitability of Earth-Sized Stagnant Lid Planets

Models of thermal evolution, crustal production, and CO2 cycling are used to constrain the prospects for habitability of rocky planets, with Earth-like size and composition, in the stagnant lid regime. Specifically, we determine the conditions under which such planets can maintain rates of CO2 degassing large enough to prevent global surface glaciation but small enough so as not to exceed the upper limit on weathering rates provided by the supply of fresh rock, a situation which would lead to runaway atmospheric CO2 accumulation and an inhospitably hot climate. The models show that stagnant lid planets with initial radiogenic heating rates of 100-250 TW, and with total CO2 budgets ranging from ∼10-2 to 1 times Earth's estimated CO2 budget, can maintain volcanic outgassing rates suitable for habitability for ≈1-5 Gyr; larger CO2 budgets result in uninhabitably hot climates, while smaller budgets result in global glaciation. High radiogenic heat production rates favor habitability by sustaining volcanism and CO2 outgassing longer. Thus, the results suggest that plate tectonics may not be required for establishing a long-term carbon cycle and maintaining a stable, habitable climate. The model is necessarily highly simplified, as the uncertainties with exoplanet thermal evolution and outgassing are large. Nevertheless, the results provide some first-order guidance for future exoplanet missions, by predicting the age at which habitability becomes unlikely for a stagnant lid planet as a function of initial radiogenic heat budget. This prediction is powerful because both planet heat budget and age can potentially be constrained from stellar observations. Key Words: Exoplanets-Habitability-Stagnant lid tectonics-Carbon cycle-Volcanism. Astrobiology 18, 873-896.

Hypoxia, but not an electrolyte-imbalanced diet, reduces feed intake, growth and oxygen consumption in rainbow trout (Oncorhynchus mykiss)

Oxygen limitation and dietary imbalances are key aspects influencing feed intake (FI) and growth performance in cultured fish. This study investigated the combined effects of hypoxia and dietary electrolyte balance on the growth performance, body composition and nutrient utilization in a rainbow trout (Oncorhynchus mykiss) isogenic line. Fish were fed ad libitum two experimental diets: electrolyte-balanced or -imbalanced diets (DEB 200 or 700 mEq kg−1, respectively) and exposed to normoxia or hypoxia (7.9 or 4.5 mg O2 l−1, respectively) for 42 days. DEB did not affect FI, growth performance or body composition. Nevertheless, hypoxia had a negative impact, reducing FI (6%), growth rate (8%), oxygen consumption (19%), energy (5%) and lipid (42%) contents. Digestible energy intake and heat production were higher in normoxic fish (40% and 23%, respectively), retaining 64% more energy in lipid or protein. Hypoxia reduced the apparent digestibility of dry matter, ash, protein, lipid, carbohydrates and energy. Trout fed DEB 700 diet were energetically less efficient, reflected in higher heat production and energy requirements for maintenance. FI was inhibited by low dissolved oxygen levels, but not by electrolyte-imbalanced diet, in spite of the higher energy requirements for maintenance. This study highlights the importance that dietary-electrolyte content and DO levels have on energy balance and growth performance when fish are fed to satiation.

Jurassic high heat production granites associated with the Weddell Sea rift system, Antarctica

The distribution of heat flow in Antarctic continental crust is critical to understanding continental tectonics, ice sheet growth and subglacial hydrology. We identify a group of High Heat Production granites, intruded into upper crustal Palaeozoic metasedimentary sequences, which may contribute to locally high heat flow beneath the West Antarctic Ice Sheet. Four of the granite plutons are exposed above ice sheet level at Pagano Nunatak, Pirrit Hills, Nash Hills and Whitmore Mountains. A new UPb zircon age from Pirrit Hills of 178.0±3.5Ma confirms earlier RbSr and UPb dating and that the granites were emplaced approximately coincident with the first stage of Gondwana break-up and the developing Weddell rift, and ~5m.y. after eruption of the Karoo-Ferrar large igneous province. Aerogeophysical data indicate that the plutons are distributed unevenly over 40,000km2 with one intruded into the transtensional Pagano Shear Zone, while the others were emplaced within the more stable Ellsworth-Whitmore mountains continental block. The granites are weakly peraluminous A-types and have Th and U abundances up to 60.7 and 28.6ppm respectively. Measured heat production of the granite samples is 2.96–9.06μW/m3 (mean 5.35W/m3), significantly higher than average upper continental crust and contemporaneous silicic rocks in the Antarctic Peninsula. Heat flow associated with the granite intrusions is predicted to be in the range 70–95mW/m2 depending on the thickness of the high heat production granite layer and the regional heat flow value. Analysis of detrital zircon compositions and ages indicates that the high Th and U abundances are related to enrichment of the lower-mid crust that dates back to 200–299Ma at the time of the formation of the Gondwanide fold belt and its post-orogenic collapse and extension.