Temperature Slope Research Articles

Vortex pinning properties in Fe-chalcogenides

Among the families of iron-based superconductors, the 11-family is one of the most attractive for high field applications at low temperatures. Optimization of the fabrication processes for bulk, crystalline and/or thin film samples is the first step in producing wires and/or tapes for practical high power conductors. Here we present the results of a comparative study of pinning properties in iron-chalcogenides, investigating the flux pinning mechanisms in optimized Fe(SeTex) and FeSe samples by current–voltage characterization, magneto-resistance and magnetization measurements. In particular, from Arrhenius plots in magnetic fields up to 9 T, the activation energy is derived as a function of the magnetic field, whereas the activation energy as a function of temperature, is derived from relaxation magnetization curves. The high pinning energies, high upper critical field versus temperature slopes near critical temperatures, and highly isotropic pinning properties make iron-chalcogenide superconductors a technological material which could be a real competitor to cuprate high temperature superconductors for high field applications.

Effects of the post-perovskite phase transition properties on the stability and structure of primordial reservoirs in the lower mantle of the Earth

Two key features of the lowermost Earth's mantle are the presence of Large Low Shear Velocity Provinces (LLSVPs), which may be reservoirs of primordial, chemically distinct material, and the phase change from perovskite (pv) to post-perovskite (pPv), which may occur at lowermost mantle conditions. However, the influence of this phase change on the shape, dynamics, and stability of chemically distinct reservoirs is not well constrained. Here, we performed numerical experiments of thermo-chemical convection in 2-D spherical annulus geometry to investigate the effects on thermo-chemical structure in the lower mantle of three parameters affecting the pPv phase change: the core–mantle boundary (CMB) temperature (TCMB), the viscosity ratio between pv and pPv (ΔηpPv), and the Clapeyron slope of the pPv phase transition (ΓpPv). Our results indicate that increasing CMB temperature increases the wavelength of the primordial reservoirs. Furthermore, a high CMB temperature promotes the development of plumes outside the reservoir of primordial material. High CMB temperature and large Clapeyron slope both favour the formation of pPv patches and of a double-crossing of the phase boundary, thus preventing the formation of continuous layer of pPv above the CMB. Combined with a low CMB temperature and/or a low Clapeyron slope of the pPv phase transition, a full layer of weak pPv above the CMB strongly enhances the mixing efficiency of primordial material with ambient regular mantle material, which may not allow the generation of large reservoirs. Based on our experiments, we conclude that the models of convection best describing the Earth's mantle dynamics include a large pPv Clapeyron slope (typically in the range of 13–16 MPa/K), and a moderate CMB temperature (around 3750 K). Our models do not provide further constraints on the value of the pPv viscosity, both regular and low values giving similar results on stability and structure of large primordial reservoirs for models with a moderate CMB temperature and large Clapeyron slope, but more plumes can be observed outside these large reservoirs in the cases with regular pPv than those in the cases with weak pPv.

Observation of π Berry phase in quantum oscillations of three‐dimensional Fermi surface in topological insulator Bi2Se3

We report the quantum transport studies on Bi2Se3 single crystal with bulk carrier concentration of ∼1019 cm–3. The Bi2Se3 crystal exhibits metallic character, and at low temperatures, the field dependence of resistivity shows clear Shubnikov–de Haas (SdH) oscillations above 6 T. The analysis of these oscillations through Lifshitz–Kosevich theory reveals a non‐trivial π Berry phase coming from three‐dimensional (3D) Fermi surface, which is a strong signature of Dirac fermions with three‐dimensional dispersion. The large Dingle temperature and non zero slope of Williamson–Hall plot suggest the presence of enhanced local strain field in our system which possibly transforms the regions of topological insulator to 3D Dirac fermion metal state. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Variation in plant thermal reaction norms along a latitudinal gradient – more than adaptation to season length

Little is known about the extent to which observed phenological responses to changes in climate are the result of phenotypic plasticity or genetic changes. We also know little about how plasticity, in terms of thermal reaction norms, vary spatially. We investigated if the thermal reaction norms for flower development of five crucifer species (Brassicaceae) differed among three regions along a south–north latitudinal gradient in replicated experiments. The mean response (elevation) of thermal reaction norms of flowering differed among regions in all study species, while sensitivity of flower development to temperature (slope) differed in only one of the species. Differences in mean responses corresponded to cogradient patterns in some species, but countergradient patterns in other. This suggests that differences among regions were not solely the result of adaptation to differences in the length of the growing season, but that other factors, such as herbivory, play an important role. Differences in development rate within species were mainly explained by variation in early phases of bud formation in some species but by variation in later phases of bud formation in other species. The differences in latitudinal patterns of thermal reaction norms among species observed in this study are important, both to identify agents of selection and to predict short‐ and long‐term responses to a warming climate.

Recent changes in north-west Greenland climate documented by NEEM shallow ice core data and simulations, and implications for past-temperature reconstructions

Abstract. Combined records of snow accumulation rate, δ18O and deuterium excess were produced from several shallow ice cores and snow pits at NEEM (North Greenland Eemian Ice Drilling), covering the period from 1724 to 2007. They are used to investigate recent climate variability and characterise the isotope–temperature relationship. We find that NEEM records are only weakly affected by inter-annual changes in the North Atlantic Oscillation. Decadal δ18O and accumulation variability is related to North Atlantic sea surface temperature and is enhanced at the beginning of the 19th century. No long-term trend is observed in the accumulation record. By contrast, NEEM δ18O shows multidecadal increasing trends in the late 19th century and since the 1980s. The strongest annual positive δ18O values are recorded at NEEM in 1928 and 2010, while maximum accumulation occurs in 1933. The last decade is the most enriched in δ18O (warmest), while the 11-year periods with the strongest depletion (coldest) are depicted at NEEM in 1815–1825 and 1836–1846, which are also the driest 11-year periods. The NEEM accumulation and δ18O records are strongly correlated with outputs from atmospheric models, nudged to atmospheric reanalyses. Best performance is observed for ERA reanalyses. Gridded temperature reconstructions, instrumental data and model outputs at NEEM are used to estimate the multidecadal accumulation–temperature and δ18O–temperature relationships for the strong warming period in 1979–2007. The accumulation sensitivity to temperature is estimated at 11 ± 2 % °C−1 and the δ18O–temperature slope at 1.1 ± 0.2 ‰ °C−1, about twice as large as previously used to estimate last interglacial temperature change from the bottom part of the NEEM deep ice core.

A computational approach for solution of boundary layer equations for the free convection along a vertical plate

In this letter, the shifted Legendre polynomials are employed for solving the natural heat convection heat transfer. The operational matrix of derivative for the shifted Legendre polynomial are derived. Then the shifted Legendre polynomials expansions along with this operational matrix are applied for solving the natural convection governing equations. The advantage of the proposed method is that the need for guessing and correcting the velocity and temperature slopes, f ′′(0), and θ′(0) during the solution procedure is eliminated. Moreover, by using the given boundary conditions in the problem, a stable solution can be derived. The proposed method is evaluated by obtaining the similarity solutions of free convection along a vertical isothermal flat plate. The results obtained through this direct innovative solution show higher efficiency and performance in comparison with the conventional shooting method.

Combined facial heating and inhalation of hot air do not alter thermoeffector responses in humans.

The influence of thermoreceptors in human facial skin on thermoeffector responses is equivocal; furthermore, the presence of thermoreceptors in the respiratory tract and their involvement in thermal homeostasis has not been elucidated. This study tested the hypothesis that hot air directed on the face and inhaled during whole body passive heat stress elicits an earlier onset and greater sensitivity of cutaneous vasodilation and sweating than that directed on an equal skin surface area away from the face. Six men and two women completed two trials separated by ∼1 wk. Participants were passively heated (water-perfused suit; core temperature increase ∼0.9°C) while hot air was directed on either the face or on the lower leg (counterbalanced). Skin blood flux (laser-Doppler flowmetry) and local sweat rate (capacitance hygrometry) were measured at the chest and one forearm. During hot-air heating, local temperatures of the cheek and leg were 38.4 ± 0.8°C and 38.8 ± 0.6°C, respectively (P = 0.18). Breathing hot air combined with facial heating did not affect mean body temperature onsets (P = 0.97 and 0.27 for arm and chest sites, respectively) or slopes of cutaneous vasodilation (P = 0.49 and 0.43 for arm and chest sites, respectively), or the onsets (P = 0.89 and 0.94 for arm and chest sites, respectively), or slopes of sweating (P = 0.48 and 0.65 for arm and chest sites, respectively). Based on these findings, respiratory tract thermoreceptors, if present in humans, and selective facial skin heating do not modulate thermoeffector responses during passive heat stress.

(Invited) Current Filamentation in Rram As Measured By High Speed Electrical Thermometry

In this paper, we review our method of measuring the local device temperature in oxide RRAM cells by taking high speed pulsed electrical measurements of the device I-V characteristics. These measurements are taken sufficiently fast (< 5 ns) as to avoid local joule heating of the device, revealing the device’s “true” room temperature I-V characteristics. Repeating these measurements as a function of stage temperature allows the construction of a unique I-V-T map, where T is the device temperature. This calibrated map can then be used under more general I-V interrogation where self-heating is present to extract the actual device temperature from I-V measurements. This method has been applied to a variety of RRAM-type oxide switches, including TiO2, Ta2O5 and HfO2 devices. Both pristine devices (prior to the initial filament forming breakdown step) as well as devices that have a filament present and can be repeatedly switched between high and low resistance states have been examined. The measurements show that internal device temperatures can range from 50ºC to 400ºC at the onset of the electroforming event, with temperatures above 600ºC when the event is completed. During switching, temperatures within the filaments peak at 300ºC-400ºC during each switching event. Temperature dependent resistivity measurements reveal that the filament has a metallic nature in materials like TiO2 (resistivity increases with increasing temperature) with a resistivity value of approximately 6000 nΩ-m. The surrounding matrix is semiconducting (resistivity decreases strongly with increasing temperature) and displays highly non-linear I-V curves. By combining the above thermometry technique with modeling of the thermal transport in the filament and its surrounding region, it is possible to get an estimate of the filament radius. Specifically, a unique filament radius is determined that self-consistently explains both the filament I-V behavior and slope of filament temperature vs dissipated power (the filament thermal resistance, Rth ). This analysis reveals that the filaments in oxide RRAM memory devices are typically 1 nm in diameter and have a hot zone around them that grows to several nm during the switching event. We are also able to apply this same analysis to the transient (i.e. non-permanent) current filaments that form prior to the permanent filament, during so-called threshold switching events. These measurements confirm for oxides the same picture reported in the literature for chalcogenide phase change materials many years ago - that a transient electrical current filament precedes the permanent structural one in these devices. Moreover, it is most likely that the heating within this transient filament that allows for the microstructural arrangement of the oxide atoms that results in a permanent conducting filament able to participate in the memory switching event.

Enhancing the thermoelectric performance of free solidified p-type Bi0.5Sb1.5Te3 alloy by manipulating its parent liquid state

In this work, an irreversible temperature induced liquid–liquid structural transition (TI-LLST) during the heating process was suggested by abnormal resistivity behaviors of Bi0.5Sb1.5Te3 melt. Based on this information, by manipulating the parent liquid state in free solidification, series of explorations were carried out on the solidified structures and TE properties of Bi0.5Sb1.5Te3 alloy. We found that, from the melt after TI-LLST, the solidified microstructures are evidently refined with more Te-rich eutectic strips precipitating on matrix boundaries. More significantly, hierarchical crystal defects are obviously increased, with tinier nanoprecipitates, more subgrains and boundaries, and much more densified lattice distortions. Consequently, the thermal conductivity, especially the lattice thermal conductivity, is decreased notably with the power factor increased moderately at high temperature. In addition, the ambipolar excitation temperature is shifted to higher value and the slope of thermal conductivity vs temperature is also declined. All these alterations contribute to a synergistic enhancement of the TE figure of merit (ZT) and the maximum figure shifts to higher temperature, with ZTmax = 0.78 at 442 K. The present work may provide a new hint for innovating preparation methods of bulk TE materials with simple free solidification.

The seasonal cycle of submesoscale flows

The seasonal cycle of submesoscale flows in the upper ocean is investigated in an idealised model domain analogous to mid-latitude open ocean regions. Submesoscale processes become much stronger as the resolution is increased, though with limited evidence for convergence of the solutions. Frontogenetical processes increase horizontal buoyancy gradients when the mixed layer is shallow in summer, while overturning instabilities weaken the horizontal buoyancy gradients as the mixed layer deepens in winter. The horizontal wavenumber spectral slopes of surface temperature and velocity are steep in summer and then shallow in winter. This is consistent with stronger mixed layer instabilities developing as the mixed layer deepens and energising the submesoscale. The degree of geostrophic balance falls as the resolution is made finer, with evidence for stronger non-linear and high-frequency processes becoming more important as the mixed layer deepens. Ekman buoyancy fluxes can be much stronger than surface cooling and are locally dominant in setting the stratification and the potential vorticity at fronts, particularly in the early winter. Up to 30% of the mixed layer volume in winter has negative potential vorticity and symmetric instability is predicted inside mesoscale eddies as well as in the frontal regions outside of the vortices.

The weakness of evidence supporting tropical niche conservatism as a main driver of current richness–temperature gradients

AbstractAimGeographical variations in species richness are highly correlated with current temperature. The tropical niche conservatism hypothesis proposes that this relationship is driven by the evolutionarily conserved ancestral tolerances of species to the warm environments in which most clades originated. The hypothesis predicts that the slope of the richness–temperature gradient is positively related to the temperature of the period during which the clade originated. Here, we test this prediction for bird and mammal families in the Americas and by revisiting a global analysis of 343 groups of organisms (Romdal et al., 2013, Global Ecology and Biogeography, 22, 344–350).LocationThe Americas and world‐wide.MethodsWe computed the slope of the species richness–current temperature relationship within each bird and mammal family in the Americas. We used palaeoclimate reconstructions to estimate temperature at the time of the family's origination, taken from the fossil record. We then tested how much of the among‐family variance in the richness–temperature slope could be explained by the temperature at the time of family origination. We repeated this test for the 343 groups of organisms world‐wide.ResultsContrary to the prediction of tropical niche conservatism, the temperature at which bird and mammal families originated does not explain variations in the richness–temperature relationships. Similarly, we show that, although the predicted relationship was statistically detected in a broad range of groups of organisms in a previous study, it in fact statistically explains only 1.2–2.9% of the variance among groups in the slope of richness gradients.Main conclusionsWe found evidence inconsistent with the hypothesis that tropical niche conservatism is the main mechanism underlying the ubiquitous richness–climate relationship.

Modulation of muscle metaboreceptor activation upon sweating and cutaneous vascular responses to rising core temperature in humans.

The present study investigated the role of muscle metaboreceptor activation on human thermoregulation by measuring core temperature thresholds and slopes for sweating and cutaneous vascular responses during passive heating associated with central and peripheral mechanisms. Six male and eight female subjects inserted their lower legs into hot water (43°C) while wearing a water perfusion suit on the upper body (34°C). One minute after immersion, an isometric handgrip exercise--40% of maximum voluntary contraction-was conducted for 1.5 min in both control and experimental conditions, while postexercise occlusion was performed in the experimental condition only for 9 min. The postexercise forearm occlusion during passive heating consistently stimulated muscle metaboreceptors, as implicated by significantly elevated mean arterial blood pressure throughout the experimental period (P <0.05). Stimulation of the forearm muscle metaboreceptors increased sweating and cutaneous vascular responses during passive heating, and was associated with significant reductions in esophageal temperature threshold of sweating and cutaneous vasodilation (Δ threshold, sweating: 0.33 ± 0.05 and 0.16 ± 0.04°C, cutaneous vascular conductance: 0.38 ± 0.08 and 0.16 ± 0.05°C for control and experimental groups, respectively, P < 0.05). The slopes of these responses were not different between the conditions. These results suggest that muscle metaboreceptor activation in the forearm accelerates sweating and cutaneous vasodilation during passive heating associated with a reduction in core temperature thresholds and may be related to central mechanisms controlling heat loss responses.

Influence of Carbon Nanotube Aspect Ratio on Glass Transition Temperature of Polymers: A Molecular Dynamics Simulation Study

Molecular dynamics (MD) simulations on three single walled carbon nanotube (SWCNT) reinforced epoxy resin composites were conducted to study the influence of SWCNT type on the glass transition temperature (Tg) of the composites. The composite matrix is cross-linked epoxy resin based on the epoxy monomers bisphenol A diglycidyl ether (DGEBA) cured by diaminodiphenylmethane (DDM). MD simulations of NPT (constant number of particles, constant pressure and constant temperature) dynamics were carried out to obtain density as a function of temperature for each composite system. The Tg was determined as the temperature corresponding to the discontinuity of plot slopes of the densityvsthe temperature. In order to understand the motion of polymer chain segments above and below the Tg, various energy components and the MSD at various temperatures of the composites were investigated and their roles played in the glass transition process were analyzed. The results show that the Tg of the composites increases with increasing aspect ratio of the embedded SWCNT

Does Whirling Disease Mediate Hybridization between a Native and Nonnative Trout?

AbstractThe spread of nonnative species over the last century has profoundly altered freshwater ecosystems, resulting in novel species assemblages. Interactions between nonnative species may alter their impacts on native species, yet few studies have addressed multispecies interactions. The spread of whirling disease, caused by the nonnative parasite Myxobolus cerebralis, has generated declines in wild trout populations across western North America. Westslope Cutthroat Trout Oncorhynchus clarkii lewisi in the northern Rocky Mountains are threatened by hybridization with introduced Rainbow Trout O. mykiss. Rainbow Trout are more susceptible to whirling disease than Cutthroat Trout and may be more vulnerable due to differences in spawning location. We hypothesized that the presence of whirling disease in a stream would (1) reduce levels of introgressive hybridization at the site scale and (2) limit the size of the hybrid zone at the whole‐stream scale. We measured levels of introgression and the spatial extent of hybridization between Rainbow Trout and Westslope Cutthroat Trout in four disease‐positive streams and six disease‐negative streams within the Blackfoot River basin of Montana. In addition to disease status, we considered habitat quality, stream slope, distance from the confluence, temperature, and elevation. Whirling disease presence was not associated with either the level of introgression at a site or the size of the hybrid zone. Temperature, elevation, and stream slope were all influential in determining levels of introgression at the site scale. Stream slope was the most influential factor determining the size of the hybrid zone, as longer, steeper streams contained smaller hybrid zones. Stream slope is a driver of many habitat characteristics that may provide refuge from invasive species in the coming decades. Although the multispecies interactions examined in this study did not alter the impacts of invasion on native species, community assemblages will continue to change with the spread of nonnative species, requiring continued assessment to determine their impacts on native species.Received May 15, 2014; accepted January 7, 2015

Phase behavior and characterization of the poly(methyl methacrylate-co-octafluoropentyl methacrylate) [P(MMA-co-OFPMA)] by supercritical dispersion polymerization

Various industries have been moving away from the use of organic solvents because of environmental regulations on safety hazards. To reduce the consumption of organic solvent to the minimum, a number of studies have been carried out using supercritical carbon dioxide (scCO2) as reaction medium to synthesize a variety of polymers in a heterogeneous reaction system. In this study, poly(methyl methacrylate-co-2,2,3,3,4,4,5,5-octafluoropentyl methacrylate) [P(MMA-co-OFPMA)] as a fluoric copolymer was prepared using supercritical dispersion polymerization in scCO2. The characterization for the prepared P(MMA-co-OFPMA) was investigated using the particle size and shape, the molecular weight (Mw), and thermal analysis. In addition, Pressure isotherms for phase behavior of binary and ternary systems between P(MMA-co-OFPMA) and association liquid fluid as well as the influence of quality of association solvents, weight average molecular weight (Mw), and cosolvents were measured.The experimental data of high pressure phase behavior for the P(MMA-co-OFPMA) in supercritical CHF3, CH2F2 and CHClF2 are presented for binary and ternary mixtures at temperatures ranging from 334K to 454K and pressures up to 194MPa. Changes of the pressure–temperature (p–T) slope of cloud–point curves for the P(MMA-co-OFPMA) [25:1]+CH2F2+methyl methacrylate (MMA) (or CHClF2) systems were measured and compared, along with cosolvents MMA (or CHClF2) mass fraction of 0.0∼30.0wt%. The phase behavior data for the P(MMA-co-OFPMA)+CH2F2+0.0∼95.0wt% CHClF2 systems are reported as a change in the p–T curve from upper critical solution temperature (UCST) region to lower critical solution temperature (LCST) region as the CHClF2 mass fraction increases. The cloud–point curves for the P(MMA-co-OFPMA)+CHF3 and +CHClF2 mixtures were measured for a LCST region accordingly as the AIBN (1.0, 2.0, 3.0 and 4.0wt%) and mole ratio (MMA:OFPMA=20:1, 22:1, 25:1 and 30:1) increases.

Development of martensite transformation kinetics of NiTi shape memory alloys under compression

Martensite transformation kinetics is the principal factor underlying the constitutive model of shape memory alloys (SMAs). Therefore, the transformation kinetics formulation is essential for predicting the thermo-mechanical behavior of SMAs. In this work, we show that previous models, including the Brinson model, which is the most widely used one-dimensional phenomenological model, cannot describe the compressive thermo-mechanical behavior of SMAs due to the tension–compression asymmetry. In addition, a new transformation kinetics is derived which precisely predicts the compressive behavior of SMAs based on the following experimental results: (1) drastic variation exists during transformation, and the plastic deformation is not ignored in compression; (2) the plastic deformation increases in proportion to the volume fraction of detwinned martensite; and (3) the critical stress–temperature slopes largely increase and the slopes of the start and finish temperatures of each phase are not identical to each other. Finally, numerical calculations using the suggested transformation equation are conducted to verify its capability through a comparison with the compressive experimental results. According to the results, the suggested transformation kinetics can predict the thermo-mechanical behavior of SMAs more precisely under compression.

Barotropic phenomena in binary mixtures

This contribution aims to theoretically describe the most common cases of mass and molar density inversions, as they can be observed in multi-component fluid mixtures in sub-critical phase equilibrium. These phenomena – also known as barotropy – affect the relative position of phases in a gravitational field for the case of mass barotropy, while the total population of species along the interfacial length is drastically affected for the case of molar barotropy. Rigorous and analytical relationships are developed here to detect both mass and molar density inversions ending at the critical points of mixtures. These conditions, which are useful to describe the existence and persistence of density inversions, are then applied to unequivocally demonstrate that mass and molar barotropy are physically independent phenomena. Qualitative evidence pointing to that conclusion is discussed at the light of the global phase diagram of van der Waals mixtures composed by molecules of different size. Particularly, it has been established that molar density inversions appearing in feasible temperature ranges are sensitive to differences between the molecular hard core volumes of the constituents, a conclusion that is well supported by experimental results. Mass density inversions, in contrast, depend not only on the molecular size but also in the molecular weights of the constituents, in such a way that mixtures may exhibit mass barotropy without exhibiting molar inversions, and vice versa.Analytical relationships for establishing the slope of density inversions on a P–T projection have also been obtained both for mass and molar barotropy. From the comparison with the temperature slope of the three-phase line, we conclude about the possibility of observing density inversions between immiscible liquid phases or between a liquid and a gas phase.

Evaluation of thermal resistance of carbon nanotube film fabricated using an improved slope control of temperature profile growth

We have successfully improved the weight density of a 40-µm-long carbon nanotube (CNT) to 0.27 g/cm3 by improving the slope control of temperature profile (STEP) growth. It was found that the CNT growth is reaction-limited in the early stage of STEP growth and supply-limited in the late stage. We succeeded in doubling the CNT density over the conventional method by optimizing the raw material supply and temperature slope during the reaction-limited and supply-limited periods. A CNT thermal interface material was fabricated using a CNT film prepared by this method. Thermal resistance was 11% below a conventional indium thermal interface material. Owing to the above reasons, CNTs show promise as heat dissipation materials.

Superelastic response of a single crystalline FeMnAlNi shape memory alloy under tension and compression

Polycrystalline FeMnAlNi shape memory alloys were recently shown to possess a small temperature dependence of the stress for the onset of martensitic transformation (σSIM). In this work, the superelastic behavior of single crystalline Fe43.5Mn34Al15Ni7.5 samples oriented along the [100] direction was investigated under tension and compression after a precipitation heat treatment at 200°C. In constant strain, multi-temperature experiments, the single crystals showed a σSIM vs. temperature slope of 0.54MPa°C−1 in tension and 0.41MPa°C−1 in compression, and superelasticity over a wide temperature range from −80°C to 160°C. The irrecoverable strains in both tension and compression samples detected during the superelastic experiments were found to be due to retained martensite in detailed transmission electron microscopy investigations. The volume fraction of the retained martensite in the samples tested under tension was considerably larger than those for the samples tested in compression showing that the transformation is less recoverable in tension. The differences in the volume fraction of retained martensite and reversibility in both tension and compression are attributed to high density of dislocations in the tension samples as compared to the compression samples. The differences between the shape of the stress–strain curves under tension and compression are attributed to the lower number of martensite variants activated under tension as compared to compression, which were clearly verified with the transmission electron microscopy examinations.

Metabolic dependence of phytoplankton species richness

AbstractAimTo analyse the dependence of phytoplankton species richness on temperature within the framework of the metabolic theory of ecology (MTE) with explicit consideration of its assumptions and predictions.LocationLakes from the Southern Hemisphere – South America (Argentinean Pampa to Tierra del Fuego) and Antarctica – and Northern Hemisphere – North America (USA) and Europe (Denmark to Spain).MethodsThe MTE proposes that natural logarithm of species richness and the inverse of temperature are linearly related, with a slope equal to the activation energy. The MTE assumes that the total community abundance, average body size and per species average community productivity are independent of the temperature. These predictions and assumptions are here evaluated using c. 660 phytoplankton lake communities and a literature review of 281 experimental measures of growth rate. Linear, curvilinear and segmented models were contrasted with empirical trends.ResultsTemperature–richness relationships showed a three‐phase segmented form in two of the three continents. Generally, at temperatures above 17 °C and below 11 °C there was a weak relationship or none. Intermediate temperatures showed the expected positive association with richness, but with steeper slopes (c. 1) than MTE expectations (c. 0.3). Statistical models including total community abundance and average body size explained up to 64% of the variance in richness.Main conclusionsIn its original formulation the MTE is not a satisfactory model for large‐scale richness patterns in phytoplankton. However, the MTE is able to better explain richness patterns when the temperature dependence of abundances and body size are explicitly accounted for in the model. These temperature dependences improve the performance of MTE predictions but question the interpretation of the richness–temperature slope as a measure of activation energy. The balance among activation energy, abundance and body size produced the observed segmented pattern in temperature–richness relationships for lake phytoplankton.