Mean Energy Density Research Articles

Consistency Restrictions on Maximal Electric-Field Strength in Quantum Field Theory

Quantum field theory with an external background can be considered as a consistent model only if backreaction is relatively small with respect to the background. To find the corresponding consistency restrictions on an external electric field and its duration in QED and QCD, we analyze the mean-energy density of quantized fields for an arbitrary constant electric field E, acting during a large but finite time T. Using the corresponding asymptotics with respect to the dimensionless parameter eET2, one can see that the leading contributions to the energy are due to the creation of particles by the electric field. Assuming that these contributions are small in comparison with the energy density of the electric background, we establish the above-mentioned restrictions, which determine, in fact, the time scales from above of depletion of an electric field due to the backreaction.

Distribution, abundance and ecological relevance of pelagic fishes in the Lazarev Sea, Southern Ocean

The distribution and abundance of larval and postlarval fishes was investigated in the Lazarev Sea, Southern Ocean, in March and April 2004. The upper 200 m of the water column were sampled with an 8 m 2 rectangular midwater trawl at 93 stations. The larval species community clus- tered in a diverse coastal community with high densities of Antarctic silverfish Pleuragramma antarcticum larvae and a less diverse offshore community dominated by Antarctic jonasfish Notolepis coatsi and the lanternfish Electrona antarctica. No postlarval fish were caught in coastal areas. The offshore community of postlarval fishes consisted of the deep-sea smelt Bathylagus antarcticus, and the lanternfishes Gymnoscopelus braueri, G. nicholsi and E. antarctica. The latter species clearly dominated, occurring at mean individual and wet mass densities of 0.17 individuals m -2 and 0.26 g m -2 , respectively. A generalized additive model significantly related the density of postlarval E. antarctica to the abundance of Antarctic krill Euphausia superba, ocean depth and sea surface tem- perature. The diet of E. antarctica was dominated by copepods and euphausiid larvae. Mean energy density of E. antarctica in the upper 200 m was 2.8 kJ m -2 , which is equivalent to 36% of the energy stored in Antarctic krill stocks and probably would be considerably higher if a greater depth range were considered. This suggests that E. antarctica is a major energy transmitter in the food web of the Lazarev Sea, challenging the classical krill-dominated food web paradigm of the Southern Ocean.

Viscous, Resistive Magnetorotational Modes

We carry out a comprehensive analysis of the behavior of the magnetorotational instability (MRI) in viscous, resistive plasmas. We find exact, nonlinear solutions of the nonideal magnetohydrodynamic (MHD) equations describing the local dynamics of an incompressible, differentially rotating background threaded by a vertical magnetic field when disturbances with wavenumbers perpendicular to the shear are considered. We provide a geometrical description of these viscous, resistive MRI modes and show how their physical structure is modified as a function of the Reynolds and magnetic Reynolds numbers. We demonstrate that when finite dissipative effects are considered, velocity and magnetic field disturbances are no longer orthogonal (as is the case in the ideal MHD limit) unless the magnetic Prandtl number is unity. We generalize previous results found in the ideal limit and show that a series of key properties of the mean Reynolds and Maxwell stresses also hold for the viscous, resistive MRI. In particular, we show that the Reynolds stress is always positive and the Maxwell stress is always negative. Therefore, even in the presence of viscosity and resistivity, the total mean angular momentum transport is always directed outward. We also find that, for any combination of the Reynolds and magnetic Reynolds numbers, magnetic disturbances dominate both the energetics and the transport of angular momentum and that the total mean energy density is an upper bound for the total mean stress responsible for angular momentum transport. The ratios between the Maxwell and Reynolds stresses and between magnetic and kinetic energy densities increase with decreasing Reynolds numbers for any magnetic Reynolds number; the lowest limit of both ratios is reached in the ideal MHD regime. The analytical results presented here provide new benchmarks for the various algorithms employed to solve the viscous, resistive MHD equations in the shearing box approximation.

Dietary energy density but not glycemic load is associated with gestational weight gain

BackgroundMost pregnant women gain more weight than the ranges recommended. Excessive weight gain is linked to pregnancy complications and to long-term maternal and child health outcomes. ObjectiveThe objective was to examine the impact of dietary glycemic load and energy density on total gestational weight gain and the weight gain ratio (observed weight gain/expected weight gain). DesignData are from 1231 women with singleton pregnancies who participated in the Pregnancy, Infection, and Nutrition Cohort Study. Dietary information was collected at 26–29 wk of gestation with the use of a semiquantified food-frequency questionnaire. Linear regression models were used to estimate the associations between quartiles of glycemic load and energy density with total gestational weight gain and weight gain ratio. ResultsDietary patterns of pregnant women significantly differed across many sociodemographic and behavioral characteristics, with the greatest contrasts seen for glycemic load. After adjustment for covariates, compared with women in the first quartile consuming a mean dietary energy density of 0.71 kcal/g (reference), women in the third quartile consuming a mean energy density of 0.98 kcal/g gained an excess of 1.13 kg (95% CI: 0.24, 2.01), and women in the fourth quartile consuming a mean energy density of 1.21 kcal/g gained an excess of 1.08 kg (95% CI: 0.20, 1.97) and had an increase of 0.13 (95% CI: 0.006, 0.24) units in the weight gain ratio. All other comparisons of energy intakes were not statistically significant. Glycemic load was not associated with total gestational weight gain or weight gain ratio. ConclusionDietary energy density is a modifiable factor that may assist pregnant women in managing gestational weight gains.

Mach’s principle and Yukawa-like corrections to the Newtonian potential as a bound for the mean energy density of the universe

The (Newton + Yukawa)-type gravitational potential V(r)=−(γM/r)[1+Aexp (−r/B)](γ= the gravitational constant as measured at infinity, M= the mass of the source, A, B are constants) is considered in the framework of the Sciama linear approach to Mach’s principle. The coupling constant A of the Yukawa component is found to be related to the mass density and size of the observable (causally connected) universe.

Could the Savory Taste of Snacks Be a Further Risk Factor for Overweight in Children?

The quantity, type and composition of snack foods may play a role in the development and maintenance of obesity in children. A high consumption of energy-dense snacks may promote fat gain. To assess the type and number of snacks consumed weekly by a large sample of 8- to 10-year-old children, as well as to assess its relationship with body size. The children consumed on average 4 snacks per day. There was no statistical difference in the number of servings per day between obese and nonobese children. However, the mean energy density of the foods consumed was significantly higher for obese and overweight children than for normal weight children [6.8 (0.3) kJ/g, 6.8 (0.16) kJ/g, and 6.3 (0.08) kJ/g, respectively; P < 0.05]. Logistic regression analysis showed that the energy density of the snacks (kJ/g), their savory taste (servings/week), television viewing (hours/day) and sports activity (hours/week) independently contributed to predict obesity in children. However, when the parents' body mass index was included among the independent variables of the regression, only salty foods and sports activity showed an independent association with childhood obesity. Parents' eating habits and lifestyle influence those of their children, as suggested by the association between parents' obesity and their children's energy-dense food intake at snacktime, the savory taste of snacks and sedentary behavior. However, regardless of parents' body mass index, the preference for savory snacks seems to be associated with overweight in prepubertal children.

Energy Density of Patagonian Aquatic Organisms and Empirical Predictions Based on Water Content

AbstractWe measured the energy density for key species in the freshwater and marine ecosystems of Patagonia, providing the first database of such information for poorly known fauna, including fish, cephalopods, crustaceans, gastropods, annelids, and insects. We then considered an empirical model linking energy density (which is costly to estimate) to water content (which is easy to estimate) and compared the fit of the model with data from different taxonomic groups. Finally, we evaluated the predictive power of models with different levels of taxonomic aggregation to estimate energy density from water content. Fish (7,148‐3,443 J/g of wet weight) had the highest energy density, followed by crustaceans (5,906‐2,507 J/g), insects (5,794‐1,334 J/g), mollusks (5,014‐1,661 J/g), and annelids (4,542‐1,954 J/g). The use of water content as a predictor of energy density provided greatly improved predictions as compared with use of the mean energy density value. As expected, the predictive power improved when more specific levels of taxonomic aggregation were employed. Nevertheless, we were able to identify levels of aggregation that provided high levels of predictive power. We regard the data generated as primary products for future research on energy fluxes in Patagonian aquatic ecosystems.

The energy density of jellyfish: Estimates from bomb-calorimetry and proximate-composition

Two techniques are described to calculate energy densities for the bell, gonad and oral arm tissues of three scyphozoan jellyfish ( Cyanea capillata, Rhizostoma octopus and Chrysaora hysoscella). First, bomb-calorimetry was used, a technique that is readily available and inexpensive. However, the reliability of this technique for gelatinous material is contentious. Second, further analysis involving the more labour intensive proximate-composition analysis (protein, fat and carbohydrate) was carried out on two species ( C. capillata and R. octopus). These proximate data were subsequently converted to energy densities. The two techniques (bomb-calorimetry and proximate-composition) gave very similar estimates of energy density. Differences in energy density were found both amongst different species and between different tissues of the same species. Mean (± S.D.) energy density estimates for whole animals from bomb-calorimetry were 0.18 ± 0.05, 0.11 ± 0.04, and 0.10 ± 0.03 kJ g wet mass − 1 for C. capillata, R. octopus, and C. hysoscella respectively. The implications of these low energy densities for species feeding on jellyfish are discussed.

Solar X-ray flare hazards on the surface of Mars

Putative organisms on the Martian surface would be exposed to potentially high doses of ionizing radiation during strong solar X-ray flares. We extrapolate the observed flare frequency-energy release scaling relation to total X-ray energies much larger than seen so far for the Sun, an assumption supported by observations of flares on other solar- and subsolar-mass main sequence stars. Flare spectra are taken as power laws, with the logarithmic slope a parameter based on the observed statistics of the most energetic hard X-ray flare spectra. We calculate surface spectra using a Monte Carlo code we developed for the transport of X-rays and gamma rays, including photoabsorption and detailed Compton scattering. Biological doses from indirect genome damage are calculated for each parameterized flare spectrum by integration over the X-ray opacity of water. The resulting doses depend sensitively on spectral slope, which varies greatly and unsystematically for solar flares. Using the roughly uniform observed distribution of spectral slopes, we estimate the mean waiting time for solar flares producing a given biological dose of ionizing radiation on Mars and compare with lethal dose data for a wide range of terrestrial organisms. These timescales range from decades for significant human health risk to 0.5 Myr for D. radiodurans lethality. Such doses require total flare energies of 10 33 – 10 38 erg, the lower range of which has been observed for other stars. Flares are intermittent bursts, so acute lethality will only occur on the sunward hemisphere during a sufficiently energetic flare, unlike low-dose-rate, extended damage by cosmic rays. We estimate the soil and CO 2 ice columns required to provide 1 / e shielding as 4 – 9 g cm - 2 , depending on flare mean energy and atmospheric column density. Topographic altitude variations give a factor of two variation in dose for a given flare. Life in ice layers that may exist ∼ 100 g cm - 2 below the surface would be well protected. Finally, we point out that designing spacesuits to sufficiently block this radiation on Mars missions may be difficult, given the conflict between solutions for lightweight protection from energetic particles and those from X-rays.

On ergodic properties for harmonic crystals

We consider the dynamics of a harmonic crystal in n dimensions with d com- ponents, where d and n are arbitrary, d;n > 1. The initial data are given by a random function with finite mean energy density which also satisfies a Rosenblatt- or Ibragimov-type mixing condition. The random function is close to diverse space-homogeneous processes as xn ! §1, with the distributions "§. We prove that the phase flow is mixing with respect to the limit measure of statistical solutions. equations and harmonic crystals. Here we study the properties of the equilibrium measures for harmonic crystals. Consider a discrete subgroup i of R n which is isomorphic to Z n . We may assume that i =Z n after a suitable change of coordinates. A lattice inR n is a set of the points of the form r‚(x) = x+»‚, where x 2 Z n , »‚ 2 R n , ‚ = 1;:::;⁄. The points of the lattice represent equilibrium positions of the atoms (molecules, ions, ::: ) of the crystal. Denote by r‚(x;t) the positions of the atoms in dynamics. Then the dynamics of the displacements r‚(x;t)ir‚(x) is governed by the equations of the form 8 > > ¨(x;t) = i X y2Zn V (x i y)u(y;t); x 2Z n ; t 2R;

Evaluation of Winter Severity on Growth of Young‐of‐the‐Year Atlantic Salmon

AbstractOverwinter growth of young‐of‐the‐year (age‐0) Atlantic salmon Salmo salar was studied during two winters in central New York streams. We hypothesized that longer and colder winters would negatively influence the growth of age‐0 Atlantic salmon. Further, we predicted that Atlantic salmon growth and survival would be positively correlated with their size before the winter period. Four cages were placed in streams at three sites in the winters of 2000 and 2001, with six individually marked Atlantic salmon per cage. One cage was retrieved monthly at each site and the weight, length, and energy density of each fish were measured to calculate growth rate and condition factor. All fish survived the winter experiment irrespective of starting size. Mean energy density of fish at the conclusion of each experiment was positively related to fish weight at the start. Winter conditions were different between years, stream temperatures being colder in 2000 than in 2001 (overall winter mean [SD], 0.71°C [2.487°C] versus 1.93°C [2.87°C]), accompanied by less variable temperatures, lower discharge, and more ice cover. Growth rates were negative during both winters, weight loss being significantly greater in the year with warmer, more variable temperatures. Growth rates were also significantly different between months, weight loss being greater in December and January and less (or replaced by positive growth) by the end of the winters (March). Mean energy density of salmon increased during the colder winter of 2000 but declined in 2001. Based on the observations in the current study, lower threshold temperatures for feeding activity may be even lower than previously reported, possibly near 0°C. We discuss the energetic implications of variable winter conditions on age‐0 Atlantic salmon.

Low Nutrient Intakes among Infants in Rural Bangladesh Are Attributable to Low Intake and Micronutrient Density of Complementary Foods

We assessed the adequacy of nutrient intakes of 135 rural Bangladeshi breast-fed infants 6-12 mo of age and examined nutritional trade-offs due to possible displacement of breast milk by complementary foods. Observers completed 12-h daytime measurements of breast milk and complementary food intakes; data for the previous 12 h were obtained from maternal recall, yielding estimates of total 24-h intakes. On average, infants were mildly wasted (mean +/- SD weight-for-length Z-score = -0.92 +/- 0.88) and moderately stunted (length-for-age Z-score = -1.49 +/- 0.96). Total energy intakes at 6-8 and 9-12 mo were 88 and 86% of absolute energy requirements (kJ/d), 106 and 105% of requirements per kg body weight, and 97 and 94% of requirements per kg median weight-for-length, respectively. Breast milk contributed 78% of energy intake at 6-8 mo and 75% at 9-12 mo. Mean meal frequency and energy density of complementary foods were generally consistent with recommendations, but only small amounts of food were offered. Nevertheless, only 72% of the food energy offered was consumed. Total energy intake was positively correlated with meal frequency, quantity consumed per meal, and energy intake from breast milk, but not with energy density of complementary foods. Energy intake from complementary foods was inversely related to energy intake from breast milk. The diets fell short of recommended intakes for numerous vitamins and minerals. We conclude that although greater intakes of complementary foods were associated with higher total energy intake, micronutrient intake remained low due to the low micronutrient density of the complementary foods consumed and the partial displacement of breast milk.

Climate change impacts on wind speeds and wind energy density in northern Europe: empirical downscaling of multiple AOGCMs

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 29:183-198 (2005) - doi:10.3354/cr029183 Climate change impacts on wind speeds and wind energy density in northern Europe: empirical downscaling of multiple AOGCMs S. C. Pryor1,*, J. T. Schoof1,3, R. J. Barthelmie2,1 1Atmospheric Science Program, Department of Geography, Indiana University, Bloomington, Indiana 47405, USA2Department of Wind Energy and Atmospheric Physics, Risø National Laboratory, 4000 Roskilde, Denmark3Present address: Center for Ocean-Atmospheric Prediction Studies, The Florida State University, Tallahassee, Florida 32310, USA *Email: spryor@indiana.edu ABSTRACT: We present empirical downscaling of 5 state-of-the-art AOGCMs (Atmosphere-Ocean General Circulation Models) to investigate potential changes in wind speeds and energy density in northern Europe. The approach is based on downscaling the Weibull parameters of wind speed probability distributions from AOGCM-derived 500 hPa relative vorticity and sea-level pressure gradients, and is demonstrated to generate accurate depictions of the wind climate during the transfer function conditioning period. Bootstrapping is used to develop 100 realizations for each downscaling period and these are used to assess the uncertainty in the results due to stochastic effects in the AOGCM-derived downscaling predictors. Projected changes in the wind speed probability distribution vary with the AOGCMs from which the predictors are derived, but generally it is shown that mean wind speeds, 90th percentile wind speeds and energy density are slightly lower in the 2081–2100 climate projection period than during 1961–1990 at the majority of the 46 stations studied. Conversely it is found that there is no significant difference between conditions during 2046–2065 and 1961–1990 based on the ensemble of downscaling results. Equally, the winter time of 2046–2065 is largely indistinguishable from 1961–1990 for the majority of stations, while the winters of 2081–2100 appear to be associated with lower mean and 90th percentile wind speeds and energy density. KEY WORDS: Wind speeds · AOGCM · Climate projections · Empirical downscaling Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 29, No. 3. Online publication date: October 17, 2005 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2005 Inter-Research.

Season variation in nutrient composition of Alaskan walleye pollock

A popular hypothesis for the noted steady decline in the population of Steller sea lions, Eumetopias jubatus (Schreber, 1776), in the regions from Prince William Sound through the Aleutian Islands relates to their nutritional status. Sea lion diets appear to have shifted from primarily small schooling fatty fishes to low-fat fish such as walleye pollock, Theragra chalcogramma (Pallas, 1814). We examined the seasonal changes in proximate nutrients of pollock collected in the Bering Sea. Mean energy density (dry mass) of pollock peaked in October then declined and remained low throughout winter. Energy recovery occurred in the summer months with strong recovery observed in female fish caught in July. Contrary to whole fish carcass energy contents, both total protein and moisture contents were at their highest levels in winter (January) when total crude lipid content was at its lowest (p &lt; 0.05). This trend gradually declined to its lowest levels in the fall when lipid content was high. The decline in total lipids during winter seasons appeared to parallel gonad development during the prespawning period. Sex differences in energy densities were not found. Proximate analysis data for moisture, protein, ash, and lipid content also did not show any significant variation between males and females. Protein digestibility of pollock was higher (p &lt; 0.05) in the summer than in the spring, but not different for winter or fall. We concluded that the nutrient content of walleye pollock may have some impact on the Steller sea lions that feed on them, particularly the energetic value that appears to be low during important feeding periods for this marine mammal.

Development of a friction energy capacity approach to predict the surface coating endurance under complex oscillating sliding conditions

In the case of surface coatings application it is crucial to establish when the substrate is reached to prevent catastrophic consequences. In this study, a model based on local dissipated energy is developed and related to the friction process. Indeed, the friction dissipated energy is a unique parameter that takes into account the major loading variables which are the pressure, sliding distance and the friction coefficient. To illustrate the approach a sphere/plane (Alumina/TiC) contact is studied under gross slip fretting regime. Considering the contact area extension, the wear depth evolution can be predicted from the cumulated dissipated energy density. Nevertheless, some difference is observed between the predicted and detected surface coating endurance. This has been explained by a coating spalling phenomenon observed below a critical residual coating thickness. Introducing an effective wear coating parameter, the coating endurance is better quantified and finally an effective energy density threshold, associated to a friction energy capacity approach, is introduced to rationalize the coating endurance prediction. The surface treatment lifetime is then simply deduced from an energy ratio between this specific energy capacity and a mean energy density dissipated per fretting cycle. The stability of this approach has been validated under constant and variable sliding conditions and illustrated through an Energy Density–Coating Endurance chart.

Pattern of long-term fat intake and BMI during childhood and adolescence--results of the DONALD Study.

Adverse dietary habits have been discussed as being conducive to the increased prevalence of obesity in children and adolescents. No single dietary factor has been clearly identified so far. We analyzed long-term fat intake patterns during childhood and adolescence and their influence on body fatness. Four clusters with different patterns of percent energy from fat were found in 228 individuals from the age of 2-18 y participating in the DONALD Study (Dortmund Nutritional Anthropometric Longitudinally Designed Study) with at least 10 yearly weighed dietary records between 1985 and 2002. Clusters were evaluated with regard to macronutrient and food group intakes and body mass index (BMI). The mean energy density and the ratio of energy intake to estimated basal metabolic rate per subject differed significantly between clusters. All calculated macronutrients (per energy intake) with the exception of dietary fiber differed significantly as well as intakes of Meat/Fish/Eggs, Fats/Oils and Fruit/Vegetables. Although these differences in dietary characteristics persisted during the study period, no differences of BMI (calculated as standard deviation score) were found either at the first or last examination per subject. The mean BMI during the study period differed significantly, with the highest BMI in the low fat intake cluster. BMI could not be explained by different dietary patterns during childhood and adolescence in this long-term evaluation of dietary records. Underreporting especially in obese subjects, the problem of detecting minor overconsumption of energy intake that favors the development of obesity over long periods, and the small study sample may explain these conflicting results.

Seasonal variations in internal wave energy in a Scottish sea loch

Near-continuous observations of an internal wave field were made over a period of 13 months at a location in Inchmarnock Water at the northern end of the Clyde Sea. This paper sets out to determine the seasonal form of the energy density of the internal wave field at this location based on the hypothesis that it varies smoothly throughout the year, being greater in summer than in winter. The mooring was maintained between June 1999 and July 2000 in 150-m water with seven deployments. Estimates of kinetic and potential energy density were derived from Acoustic Doppler Current Profiler (ADCP) and vertical temperature profiles respectively. Both were shown to vary on time scales less than 1 month with median values of mean kinetic energy (KE) density∼0.5 J m−3 and for mean potential energy (PE) density∼0.01 J m−3. The energy of the internal wave field was found to be continuous and without a clear seasonal form. Further, it was also always non-zero with intermittent peaks of much higher energy. In the late autumn the system experienced complete vertical overturning driven by local convective processes destroying the thermocline and causing a reduction in the overall KE density.

Optical diagnostics of the hollow needle to plate electrical discharge in air at atmospheric pressure

Vibrational and rotational excitation of the N2(C3Πu) state in a DC hollow needle to plate electrical discharge at atmospheric pressure was studied by means of multichannel emission spectrometry. Vibrational distributions and rotational temperatures of the N2(C3Πu) electronic state were obtained for a negative polarity of the needle as a function of mean energy density dissipated in the discharge reactor. Vibrational excitation of the N2(C3Πu) apparently decreases with increasing energy density and the shape of vibrational distributions reflects predominant processes responsible for the N2(C3Πu) state population, i.e. electron impact excitation of N2(X1Σg+,ν) ground state and energy pooling mechanism by N2(A3Σu+) metastables. Rotational temperatures evolve in the range 1000 ÷ 1800 K and show linear increase with energy density dissipated in the discharge reactor.

Cold, Northern Winters: The Importance of Temperature to Overwinter Mortality of Age-0 White Crappies

Survival during the first winter of life can influence the recruitment of many fishes. We used field sampling and laboratory experiments to explore the mechanisms underlying first winter growth and survival of white crappie Pomoxis annularis, which exhibits variable recruitment. We sampled age-0 white crappies from four Ohio reservoirs before winter to evaluate whether large individuals had a greater energy density (kJ/g) than small ones and whether mean energy density differed among reservoirs. Energy density increased with fish size in all reservoirs, suggesting that small fish could die earlier if energy stores become limiting during winter. Mean energy density varied among reservoirs as well, suggesting that prewinter energy reserves could influence recruitment variability across reservoirs through their effects on winter starvation. Our laboratory experiment evaluated how fish size (small or large), feeding level (starved or fed), and winter severity (mild or severe) interact to influence the growth and survival of age-0 white crappies. The two winter severity treatments represented two extremes for Ohio winters (i.e., mild and severe). We calculated daily individual growth rates for all fish, energy density for a subset of fish, and percent survival across treatments. Winter severity strongly influenced survival: only 47% of all white crappies survived the severe winter, whereas 97% survived the mild winter. In the severe winter, neither size nor feeding level influenced mortality. Bomb calorimetry revealed energy density to be similar among fish that died and those that survived the severe winter, suggesting that energy depletion did not cause mortality. Rather, osmoregulatory failure may have occurred during exposure to temperatures colder than 4°C for at least 1 week. Thus, the availability of warm (≥4°C), oxygenated water during winter may be critical to the survival of age-0 white crappies. In the northern portion of their range, winter temperatures may account for some of the recruitment variability common to white crappie populations.

Energy density and its seasonal variation in desert beetles

Energy densities of adult beetles from the Simpson Desert, central Australia, were measured to provide a basis for understanding seasonal energy allocation, prey switching and selection among insectivores, and variation among taxa. The mean energy density of adult beetles is 21.14±2.29 J mg −1 ash-free dry weight (AFDW), energy density varying significantly among families. The energy density of beetles exhibits significant seasonal variation, and is maximum in autumn (22.13±2.24 J mg −1 AFDW) and minimum in spring (19.84±2.03 J mg −1 AFDW). Also, energy density is higher in the abdomen (21.98±2.68 J mg −1 AFDW) than the thorax (20.56±2.81 J mg −1 AFDW), head (20.11±2.88 J mg −1 AFDW) and legs (19.62±2.91 J mg −1 AFDW); each body region changes seasonally, as it does for the whole beetle. Energy density is correlated negatively with body water content ( r=−0.559, P<0.001). Seasonal shifts in energy density among taxa and body components indicate different strategies for conservation and use of energy among desert beetles. Such shifts may also explain prey switching and selection among insectivores.