Lowest Experimental Temperature Research Articles

Accelerated methane storage in clathrate hydrates using mesoporous (Organo-) silica materials

Methane (CH4) clathrate hydrates have gained much attention in the ever-growing search for novel energy storage methods; however, they are currently limited due to their poor water-to-hydrate conversions and slow formation kinetics. To surmount these bottlenecks, significant research has been centered on the design of novel methods (porous media). In this vein, the present work explores two hydrophobic mesoporous solids, an alkyl-grafted mesoporous silica (SBA-15 C8) and a periodic mesoporous organosilica (Ring-PMO), in their ability to promote CH4 clathrates. Both materials have shown to facilitate CH4 clathrate formation at mild operating conditions (6 MPa and 269–276 K). The study revealed that the maximal CH4 storage capacities are strongly linked to the critical/optimal quantity of water in the system which was determined to be at 130% and 200% of the pore volume for SBA-15 C8 and Ring-PMO, respectively. Up to 90% and 95% of the maximum water-to-hydrate conversions were achieved in 90 min at the lowest experimental temperature and critical water content for SBA-15 C8 and Ring-PMO, respectively. At these conditions, SBA-15 C8 and Ring-PMO showed a maximum gas uptake of 98.2 and 101.2 mmol CH4/mol H2O, respectively. Both the materials exhibited no chemical or morphological changes post-clathrate formations (characterized using FT-IR, N2 sorption, XRD, and TEM), inferring their viability as clathrate promoters for multiple cycles. An integrated multistep model was considered adequate for representing the hydrate crystallization kinetics and fits well with the experimental kinetic data with a low average absolute deviation in water-to-hydrate conversions among the three distinct kinetic models analyzed. Overall, the results from this study demonstrate hydrophobic porous materials as effective promoters of CH4 clathrates, which could make clathrate-based CH4 storage and transport technology industrially viable.

Temperature driven variations in VOC emissions from plastic products and their fate indoors: A chamber experiment and modelling study

Plastic products are ubiquitous in our homes, but we know very little about emissions from these products and their subsequent impact on indoor air quality. This is the first study to systematically determine temperature-dependent emissions of volatile organic compounds from commonly used plastic consumer products found in the home. The plastic types included high-density polyethylene (HDPE), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS) and polyester rubber. Plastic samples were exposed to increasing temperatures (between 18 and 28 °C) in controlled environmental chambers, connected to a proton-transfer-reaction time-of-flight mass-spectrometer (PTR-ToF-MS), where real-time emissions were detected. Average emission rates were determined and used to initialise an indoor air chemistry model (INCHEM-Py) at the highest and lowest experimental temperatures, to explore the impact these product emissions have on the indoor air chemistry. The PS tubing plastic proved to be the highest emitting polymer per surface area. Almost all selected VOC emissions were found to have a linear relationship with temperature. Upon observing the impacts of primary VOC emissions from plastics in modelled simulations, the hydroxyl radical concentration decreased by an average of 1.6 and 10 % relative to the baseline (with no plastics included) at 18 °C and 28 °C respectively. On the other hand, formaldehyde concentrations increased by 29 and 31.6 % relative to the baseline conditions at 18 °C and 28 °C respectively. The presence of plastic products indoors, therefore, has the potential to impact the indoor air quality.

Exploring the desiccation tolerance of the invasive bivalve Corbicula fluminea (M\xfcller 1774) at different temperatures

Corbicula fluminea (Müller, 1774) (Mollusca, Corbiculidae) is among the most successful and widespread invaders of aquatic ecosystems worldwide. Given its wide geographical distribution and documented effects on aquatic ecosystems, there is considerable interest in quantifying its behaviour, propagation and control. We conducted a series of laboratory experiments to assess the effects of complete desiccation (aerial exposure at high relative humidity) on a UK population of C. fluminea for: (1) different environmental temperatures (6 scenarios: from cool winter droughts to summer heatwave thermal conditions); and (2) two size classes (> 1 cm and ≤ 1 cm). A mortality rate of 100% was obtained for all experiments, except the lowest temperature scenario of 4 °C. For both high-temperature scenarios (25 and 30 °C) 100% mortality was recorded after 48 h, and an elevated mortality rate recorded after 24 h. An extended period of desiccation of 5–6 days would be necessary to reach a mortality rate of 90% at 15 °C and 3.5 days at 20 °C. Statistical analysis demonstrated a significant effect of temperature on mortality, but both size classes displayed similar responses to desiccation. The greatest difference in mortality was recorded between the highest and lowest experimental temperatures. C. fluminea was particularly tolerant to desiccation when low temperature and high humidity conditions coincided, suggesting it could potentially spread to regions beyond its current eco-geographical range. The results will be of direct interest for regulatory authorities considering desiccation (and water level management) as a means of managing and preventing the further spread of this species.

Withering syndrome susceptibility of northeastern Pacific abalones: A complex relationship with phylogeny and thermal experience.

Population declines in wild and cultured abalones (Haliotis spp.) due to a bacterial disease called withering syndrome (WS) have been documented along the northeastern Pacific Ocean. However, observed differences in species susceptibility to the disease are not well understood. Here, we examined the susceptibility of three temperate abalone species, the cool water (4-14 °C) pinto or northern abalone (Haliotis kamtschatkana), the intermediate water (8-18 °C) red abalone (H. rufescens), and the warm water (12-23 °C) pink abalone (H. corrugata), to experimental WS infection at temperatures facilitating disease proliferation. Mortality data paired with histological and molecular detection of the WS pathogen confirmed that these abalone species exhibit different levels of susceptibility to infection and resistance to WS development ranging from high susceptibility and low resistance in pinto abalone to moderate/low susceptibility and resistance in red and pink abalones. The temperature associated with WS induced mortalities also varied among species: pinto abalone died at the lowest experimental temperature (17.32 ± 0.09 °C), while red abalone died at an intermediate temperature (17.96 ± 0.16 °C), and pink abalone required the highest temperature (18.84 ± 0.16 °C). When data from the current and previous studies were examined, susceptibility to WS was inversely related to phylogenetic distance from white abalone (H. sorenseni), which had the highest susceptibility and lowest resistance of all abalone species tested prior to the current study. These results provide further evidence that an abalone's thermal optima and phylogenetic relationship can determine its susceptibility to WS; species with cool water evolutionary histories are most susceptible to WS and the most susceptible species appear to be closely related. Differences among the thermal ranges of abalone species have broad implications for WS disease dynamics and highlight the importance of understanding the mechanisms governing the abalone-WS relationship in order to properly manage declining abalone populations.

Hydrogen Adsorption on Zn-BDC, Cr-BDC, Ni-DABCO, and Mg-DOBDC Metal–Organic Frameworks

This work reports hydrogen adsorption properties of four different metal–organic frameworks (MOFs) namely Zn-BDC, Cr-BDC, Ni-DABCO, and Mg-DOBDC. Gravimetric hydrogen adsorption measurements are performed over a wide range of temperature (90 K to 298 K) and pressure (0 bar to 100 bar). At the lowest experimental temperature (90 K to 100 K) all the isotherms are saturated and the adsorption capacity is governed by pore volume. On the other hand, at room temperature the isotherms closely follow Henry’s law. Modeling of the excess isotherms is also done. Net adsorption isotherms, which can directly indicate the efficiency of porous adsorbent for storage, are also presented. In terms of volumetric efficiency, Mg-DOBDC MOF exhibits best storage capacity out of all the MOFs considered in this study.

Photosynthetic characteristics and physiological plasticity of an Aphanizomenon flos-aquae (Cyanobacteria, Nostocaceae) winter bloom in a deep oligo-mesotrophic lake (Lake Stechlin, Germany)

In winter of 2009/2010, Aphanizomenonflos-aquae bloomed in the ice and snow covered oligo-mesotrophic Lake Stechlin, Germany. The photosynthesis of the natural population was measured at eight temperatures in the range of 2–35°C, at nine different irradiance levels in the range of 0–1,320 μmol m−2 s−1 PAR at each applied temperature. The photoadaptation parameter (Ik) and the maximum photosynthetic rate (Pmax) correlated positively with the temperature between 2 and 30°C, and there was a remarkable drop in both parameters at 35°C. The low Ik at low temperatures enabled the active photosynthesis of overwintering populations at low irradiance levels under ice and snow cover. The optimum of the photosynthesis was above 20°C at irradiances above 150 μmol m−2 s−1. At lower irradiance levels (7.5–30 μmol m−2 s−1), the photosynthesis was the most intensive in the temperature range of 2–5°C. The interaction between light and temperature allowed the proliferation of A. flos-aquae in Lake Stechlin resulting in winter water bloom in this oligo-mesotrophic lake. The applied 2°C is the lowest experimental temperature ever in the photosynthesis/growth studies of A. flos-aquae, and the results of the P–I and P–T measurements provide novel information about the tolerance and physiological plasticity of this species.

Isobaric relaxation phenomenon of mixed PMMA/PS‐b‐PEO monolayers at different temperatures

AbstractThe objective of this research was to find out the effect of molecular weight of poly(methyl methacrylate) (PMMA) and temperature on the isobaric relaxation behaviors of mixed PMMA/poly(styrene)‐block‐poly(ethylene oxide) (PS‐b‐PEO) monolayers. Isobaric relaxation experiments of mixed monolayers of PMMA with different molecular weights and PS‐b‐PEO at the air/water interface were investigated at three different temperatures (10, 25, and 40°C). The PS‐b‐PEO monolayer was found to exhibit a fast relaxation curve (i.e., the surface area decreased significantly with increasing time). Addition of PMMA into PS‐b‐PEO slowed the relaxation behavior especially at the lowest experimental temperature (10°C). It was shown that the area relaxation process of mixed PMMA/PS‐b‐PEO monolayers could be well represented by a model considering the nucleation and growth mechanisms. The characteristic exponent x values were found to be almost temperature independent. The kx values were detected to decrease mostly as a result of temperature elevation regardless of pure or mixed monolayers. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Overwintering Tadpoles and Loss of Fitness Correlates In Polypedates braueri Tadpoles That Use Artificial Pools In A Lowland Agroecosystem

We studied growth, development, and metamorphic traits of Polypedates braueri tadpoles in Taiwan to elucidate the cause of tadpole overwintering in man-made water containers in lowland orchards on the Bagua Terrace. Polypedates braueri bred from March to August, but tadpoles were present year round. Laboratory experiments demonstrated that tadpole overwintering was facultative; low temperatures and limited food retarded both growth and development, resulting in overwintering in the tadpole stage. Tadpoles at the lowest experimental temperature (15°C) never reached metamorphosis. A field experiment demonstrated that 78, 28, and 4% of tadpoles raised in high, medium, and low food regimes, respectively, metamorphosed before the onset of winter. Tadpoles that did not metamorphose by fall continued to grow slowly and either metamorphosed during the winter or the following spring. These findings indicate that food availability plays a key role in inducing overwintering in tadpoles. Jumping performance of metamorphs was positively correlated with food regimes, but body lipid content was significantly higher in metamorphs raised with either low or high food regimes than in those with medium levels of food. Overwintering by P. braueri tadpoles has not been previously reported; however, agricultural activities have created new breeding habitats (i.e., man-made bodies of water), some of which are sufficiently food-limited that tadpoles overwinter to complete development and metamorphosis. An understanding of the survivorship, life history traits, and physiology of these frogs is needed to shed light on how man-made breeding sites affect the population dynamics of native frog populations.

Normal-superfluid interface for polarized fermion gases

Recent experiments on imbalanced fermion gases have proved the existence of a sharp interface between a superfluid and a normal phase. We show that, at the lowest experimental temperatures, a temperature difference between normal (N) and superfluid (SF) phases can appear as a consequence of the blocking of energy transfer across the interface. Such blocking is a consequence of the existence of a SF gap, which causes low-energy normal particles to be reflected from the N-SF interface. Our quantitative analysis is based on the Hartree-Fock--Bogoliubov--de Gennes formalism, which allows us to give analytical expressions for the thermodynamic properties and characterize the possible interface scattering regimes, including the case of unequal masses. Our central result is that the thermal conductivity is exponentially small at the lowest experimental temperatures.

On the degradation evolution equations of cellulose

Cellulose degradation is usually characterized in terms of either the chain scission number or the scission fraction of cellulose unit as a function of degree of polymerisation (DP) and cellulose degradation evolution equation is most commonly described by the well known Ekenstam equations. In this paper we show that cellulose degradation can be best characterized either in terms of the percentage DP loss or in terms of the percentage tensile strength (TS) loss. We present a new cellulose degradation evolution equation expressed in terms of the percentage DP loss and apply it for having a quantitative comparison with six sets of experimental data. We develop a new kinetic equation for the percentage TS loss of cellulose and test it with four sets of experimental data. It turns out that the proposed cellulose degradation evolution equations are able to explain the real experimental data of different cellulose materials carried out under a variety of experimental conditions, particularly the prolonged autocatalytic degradation in sealed vessels. We also develop a new method for predicting the degree of degradation of cellulose at ambient conditions by combining the master equation representing the kinetics of either percentage DP loss or percentage TS loss at the lowest experimental temperature with Arrhenius shift factor function.

Cooling kinetics experiments on different Stromboli lavas: Effects on crystal morphologies and phases composition

Controlled cooling experiments at atmospheric pressure and fO 2 of the NNO buffer were performed on three Stromboli lavas of calcalkaline (CA), high-K calcalkaline (HKCA) and shoshonitic (SHO) affinities. The experiments were conducted at cooling rates of 900 °C/h (fast cooling rate—FCR) and 1 °C/h (slow cooling rate—SCR), respectively, to investigate the kinetic factors governing textural and compositional features such as phase growth morphology, phase relations and phase compositions. The experiments produced different types of textures as both the cooling rate and the quenching temperatures were varied. In general, FCR experiments show a decrease of crystal size as well as a change in crystal shape from euhedral, to granular, to skeletal up to dendritic morphology with decreasing temperatures. SCR experiments produce less variable crystal size and crystal morphology. Measurements of plagioclases indicate that the crystal size and calculated crystal growth are functions of cooling rate; crystal growth rates are about two orders of magnitude higher in FCR experiments than SCR ones. Such textural responses are in agreement with the empirical calibration based on the plagioclase size dependence on cooling rate developed by Cashman (1993). Experimental phase relations display three main features of the crystallization process: (1) the delay in the crystallization of the liquidus phase in the FCR experiments with respect to the SCR ones; (2) crystallization, controlled by the multiphase cotectic relations (plagioclase + pyroxenes ± olivine), is more enhanced for FCR experiments compared to that of SCR ones at the lowest experimental temperature (1100 °C); (3) crystallization of augite and pigeonite is sensitive to cooling rate and system compositions; pigeonite, not found in the natural rocks, crystallizes in the CA sample across SCR and FCR runs, and in the HKCA sample just in the SCR experiments. FCR and SCR experiments produce similar liquid lines of descent for both CA and HKCA starting materials suggesting that the processes of nucleation and growth play reciprocal roles through mass balance as cooling rate varies. This is not true for the SHO composition where the trends of melt composition appear to be especially influenced by the different amounts of olivine crystallization at the different cooling rates. Data on mineral compositions show that plagioclase and clinopyroxene are the phases more strongly affected by the cooling gradients; crystals from SCR experiments and, to a lesser extent, from FCR experiments, show zoning patterns mainly at the lowest experimental temperature.

Respiratory electron transport system (ETS) activity and respiration rate in cold-stenothermal and eurythermal chironomid larvae from highmountain lakes

Respiratory electron transport system (ETS) activity and respiration rate were measured in four genera (Paratanytarsus, Procladius, Macropelopia, Zavrelimyia) of chironomid larvae from high-mountain lakes. Thermal responses were measured in the laboratory as differences in ETS activity and respiration rate of field animals at experimental temperatures of 5, 10, 15 and 20 °C. ETS activity and respiration rate of all genera increased with increasing experimental temperature up to maximal values. However, genera differed in their actual and potential respiratory response to increasing temperature. Cold-stenothermal genera (Macropelopia, Zavrelimyia) had significantly lower Arrhenius activation energy (E a ) for ETS activity and respiration rate than eurythermal genera (Paratanytarsus, Procladius). Therefore, cold-stenothermal genera had a relatively more efficient respiratory system at the lowest experimental temperature than at the highest one when compared with genera less limited by temperature. This indicates that cold-stenothermal genera have respiratory enzyme systems well adapted to function at low environmental temperature, but less so at higher temperatures. Lower ETS/R ratios of Macropelopia than of Procladius, and of Zavrelimyia than of Paratanytarsus, are also consistent with their narrower ecological tolerance.

Evidence of non-Arrhenius behaviour from laboratory aging and 24-year field aging of polychloroprene rubber materials

High-temperature oven aging exposures from 110 °C to 80 °C have been conducted on a commercial chloroprene rubber cable jacketing material where the time-dependent degradation at each temperature is monitored by following the ultimate tensile elongation. By time–temperature superposing the results at the lowest experimental temperature (80 °C), empirical shift factors are first derived and then analysed using the conventional Arrhenius approach and finally extrapolated using the derived activation energy E a of 96 kJ/mol in order to make predictions at 25 °C. To test the constant E a assumption underlying the Arrhenius extrapolation, we conducted oxygen consumption measurements at six temperatures ranging from 25 °C to 95 °C and found evidence for a slow drop in E a from ∼96 kJ/mol above 80 °C to an average value of ∼82 kJ/mol below 80 °C. This curvature predicts a 50% reduction in room temperature lifetime and suggests that certain higher E a degradation processes become less important as room temperature is approached. Analyses of the production rates for CO 2 show that CO 2 becomes less important relative to the oxygen consumed as the temperature is lowered, evidence in accord with the above suggestion. Further evidence for a similar drop in E a (from 89 kJ/mol above 70 °C to 71 kJ/mol below 70 °C) comes from comparisons of accelerated aging elongation data taken ∼25 years ago on another chloroprene rubber cable jacketing material with recent elongation results taken on samples that have aged for ∼24 years at ∼24 °C.

One‐Dimensional Magnetism in New, Layered Structures: Piperazine‐Linked Copper and Nickel Oxalate Chains

AbstractTwo new coordination network materials with the composition M(pip)(ox) ( pip = piperazine; ox = oxalate; M = Ni, Cu) have been synthesised under ambient and hydrothermal conditions. These compounds adopt related structures, both consisting of intersecting [M(pip)]∞ and [M(ox)]∞ chains, which result in layered structures. The nickel compound crystallises in P$\bar 1$ . The metal ions are octahedrally coordinated and are linked by symmetric chelating bridging oxalate ions. In contrast, the copper compound crystallises in the chiral space group P212121. Here the copper atom displays square pyramidal coordination geometry and the oxalate ions bridge metals in an unsymmetric fashion resulting in a polar metal‐oxalate chain structure. The magnetic behaviour is determined by the nature of the exchange‐coupled network. Only the antiferromagnetic interaction mediated by the bridging oxalate group is significant and the compounds are well modelled as 1‐D antiferromagnetically coupled chains. For the copper compound (S = 1/2) we determined J/kB to be −25.9 K, while the nickel compound (S = 1) shows a larger exchange coupling (J/kB = −42.2 K). In the nickel compound we see a significant deviation between the observed and calculated magnetic susceptibilities at the lowest experimental temperatures. This may be due either to the formation of a Haldane quantum antiferromagnetic ground state or to single‐ion zero‐field splitting effects. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Interactive effect of temperature and food concentration on growth rate: A test case using the small freshwater ciliate Urotricha farcta

The combined effect of temperature and food concentration on the growth rate, cell volume, and production of the freshwater ciliate Urotricha farcta was investigated in laboratory batch cultures. Experimental temperatures ranged from 9 to 25°C and food levels ranged from 0.1 to 4.4 µg C ml-1. The ciliates were fed the small cryptophyte Cryptomonas sp. The combined effect of temperature and food on growth and cell volume resulted in negative production rates at high temperatures and low to moderate food supply. Three main changes were observed in the shape of the numerical response (growth vs. food concentration) of U. farcta with temperature: change in the threshold level, where population net growth rates are zero; change in the initial slope of the numerical response curve; and change in maximum growth rate ( mmax). The threshold food concentration and mmax were shifted up at the highest temperatures. The threshold level was also higher at the lowest experimental temperature. The initial slope of the numerical response curve was several‐fold lower at both high and low temperatures. The analysis suggests that temperature altered the numerical response so that the species shifted from being adapted to low food concentrations at moderate temperatures to requiring, and potentially thriving at, high food concentrations at the temperature extremes. These findings support and extend conclusions previously obtained for metazooplankton and indicate that changes as small as 38C could alter the role of protozoa in planktonic food webs.

Effect of predator size and temperature on the predation of Deroceras reticulatum (Muller) (Mollusca) by carabid beetles

Twenty‐one carabid species were used in a laboratory study to determine the effect of beetle size and temperature on the predation of one day old Deroceras reticulatum (Muller) slugs. The beetles were caught in arable land at the study site. None of the five small‐sized beetle species killed slugs, whereas five of the seven medium‐sized beetle species and eight of the nine large‐sized beetle species killed slugs. Four of the most abundant beetle species at the study site were used to assess the effect of temperature on the predation of 1‐day‐old slugs. There were significant differences in the proportion of beetles predating slugs at the different temperatures. Regression analysis showed that there was a significant increase in the proportion of Pterostichus madidus (Fabricius) and Harpalus rufipes (Degeer) beetles predating slugs as temperature increased. Nebria brevicollis (Fabricius) inflicted its highest level of slug mortality at 8°C and its larvae were the only predators to significantly increase slug mortality at 4°C, the lowest experimental temperature. Harpalus aeneus (Fabricius) inflicted significant levels of slug mortality at 20°C, the highest experimental temperature. It appeared that the predatory activity of these beetle species at the five experimental temperatures reflected their annual activity periods in the field.

IQHE and FQHE in a wire with incompressible and compressible strips

We report the study of the longitudinal (RL) and Hall (RH) resistances in a wide ballistic wire (LH⪡W⪡l, l is mean free path, W is the width of wire, LH is the magnetic length in QHE regime) in the IQHE and FQHE regimes. It was observed a partial suppression of the RL minima in the IQHE and their practically total disappearance in the FQHE while the Hall resistance plateaus corresponding to these minima remained well pronounced in both the IQHE and FQHE regimes. At lower filling factors (ν<1/3) we have observed a quantum Hall liquid–quantized Hall insulator transition that takes place at a certain critical magnetic field Bc and a critical resistance value close to h/e2. Finally, at ν<1/2 and at the lowest experimental temperatures T<0.3K there have been observed correlated fluctuations in the longitudinal and in the Hall resistance both as a function of magnetic field and gate voltage. It is supposed that the observed features are due to interplay between wide compressible and narrow incompressible strips in the wire.

Fluidity of Neuronal Membranes of Crayfish ( Astacus astacus L.) Acclimated to 5°C and 20°C

The fluidity of microsomal membranes from nerve cords of eurythermal freshwater crayfish Astacus astacus acclimated to 5°C or to 20°C was measured by steady-state fluorescence polarization. Membrane fluidity was measured at 4–24°C during a cyclic temperature change (0.2°C/min) using 1,6-diphenyl-1,3,5-hexatriene (DPH) or 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) molecule as probes. The fluidity of neuronal membranes depended on temperature but not on the direction of temperature change. Thermal dependence of fluidity was higher with DPH than with TMA-DPH. Neuronal microsomal membranes of cold-acclimated crayfish were more fluid than those of warm-acclimated animals. Except at the lowest experimental temperatures, in both microsomal and plasma membranes, the TMA-DPH polarization values were higher than the DPH polarization values, indicating the anchorage of TMA-DPH to the more rigid hydrophilic surface of the bilayer at these temperatures in both membranes. Neuronal plasma membranes were more rigid than microsomal membranes measured with DPH. With TMA-DPH plasma membranes were more fluid than microsomal membranes.

Effect of Season and Temperature Acclimation on the Function of Crucian Carp (Carassius Carassius) Heart

ABSTRACT The temperature dependence of heart rate and isometric contractile properties of cardiac tissue was determined in thermally acclimated crucian carp (Carassius carassius L.). Fish were adapted for more than 3 weeks to 5 and 15°C during both summer and winter. At all but the lowest experimental temperatures, heart rate (FH), maximal isometric force (Fmax) and pumping capacity were higher in summer fish acclimated to 15°C than in winter fish acclimated to 5°C. Except for fH, similar acclimation effects were observed when comparing cold- and warm-acclimated crucian carp in both seasons. In contrast, the kinetics of isometric contraction was not modified either by seasonal acclimatization or by thermal acclimation within a given season: the temperature dependence of time to peak force (TPT) and time to half-relaxation (T1/2R) was independent of the previous thermal history of the fish. The hearts of winter fish were about 10% smaller than those of summer fish. These results show that acclimation to cold does not induce positive compensatory changes in function or size of crucian carp heart, as happens in many other teleost fishes. Instead, an inverse or noncompensatory acclimation was found. Owing to the inverse thermal acclimation, in winter (at 4°C) the contractile performance of the crucian carp heart is less than one-third of that in summer (at 20°C). The low cardiac activity in cold-acclimated crucian carp seems to be associated with its inactive life style, which is necessary during the winter months to minimize energy consumption in a severely hypoxic environment.

An Analysis of the Accuracy of the Calculation of the Second Virial Coefficient of Helium from Interatomic Potential Functions

In considering the second virial coefficient corrections for low temperature helium gas thermometry, the ITS-90 has incorporated data fits for the 4He and 3He second virial coefficients. An alternative is to use second virial coefficients calculated from recent interatomic potential functions for helium. We compare several functions using different computer codes to assess the accuracy of the calculations. The most recent function is the HFD-B2 of Aziz and Slaman. In the literature it is found that the potentials developed by different authors using their respective codes indicate a spread of only 0,4 cm3/mol at the lowest experimental temperature (2,6 K) for 4He. When calculations based on these same potentials are performed with the same code, the spread is nearly twice as large. However, calculations based on the two codes which have undergone recent improvements produce a spread of less than 0,01 cm3/mol when based on the same potential. For 3He, there is a relative difference between potential functions of 0,4 cm3/mol down to the lowest temperature of 1,5 K. There is a larger systematic difference between the calculations and the data fit which indicates that there is a contribution from the third virial in the latest 3He second virial coefficient data.