Reversible Temperature Research Articles

Membrane Design Criteria and Practical Viability of Pressure-Driven Distillation.

Pressure-driven distillation (PD) is a novel desalination technology based on hydraulic pressure driving force and vapor transport across a hydrophobic porous membrane. In theory, PD offers near-perfect rejection for nonvolatile solutes, chlorine resistance, and the ability to decouple water and solute transport. Despite its advantages, pore wetting and the development of a reverse transmembrane temperature difference are potential critical concerns in PD, with the former compromising the salt rejection and the latter reducing or even eliminating the driving force for vapor transport. We herein present an analysis to evaluate the practical viability and membrane design principles of PD with a focus on the dependence of flux and salt rejection (SR) on membrane properties. By modeling the mass transfer in a PD process under different conditions, we arrive at two important conclusions. First, a practically detrimental reverse transmembrane temperature difference does not develop in PD under all relevant circumstances and is thus not a practical concern. Second, for a PD process to achieve an acceptable SR, the membrane pores should be at the nanometer scale with a highly uniform pore size distribution. This analysis demonstrates the practical viability of PD and provides the principles for designing robust and high-performance PD membranes.

Thermo-Programmed Synthetic DNA-Based Receptors

Herein, we present a generalizable and versatile strategy to engineer synthetic DNA ligand-binding devices that can be programmed to load and release a specific ligand at a defined temperature. We do so by re-engineering two model DNA-based receptors: a triplex-forming bivalent DNA-based receptor that recognizes a specific DNA sequence and an ATP-binding aptamer. The temperature at which these receptors load/release their ligands can be finely modulated by controlling the entropy associated with the linker connecting the two ligand-binding domains. The availability of a set of receptors with tunable and reversible temperature dependence allows achieving complex load/release behavior such as sustained ligand release over a wide temperature range. Similar programmable thermo-responsive synthetic ligand-binding devices can be of utility in applications such as drug delivery and production of smart materials.

Sign reversal of planar Hall effect with temperature in La-doped Sr2IrO4 films

Electron-doped Sr2IrO4 is the best candidate for unconventional superconductivity, but direct evidence of superconductivity has not been experimentally confirmed. Therefore, it is urgent to explore the complex and rich physical properties caused by doping. The planar Hall effect (PHE) is a sensitive technique for the characterization of intrinsic magnetic properties in magnetic thin films and is applied widely in spintronic devices. In this work, the PHE for La-doped Sr2IrO4 films as a function of the magnetic field direction and temperature exhibited unique properties caused by electron doping. The amplitude of PHE is proportional to the strength of the applied magnetic field. Remarkably, as the temperature increased, a sign reversal of angle-dependent PHE occurred at 90 K, which indicated the change of magnetic anisotropy. Subsequent variable-temperature traditional Hall measurements and time-resolved optical studies eliminated different types of carrier interactions. The anisotropic magnetoresistance measurements indicated that the sign reversal can be attributed to the changes of a spin structure after electron doping, and the reversal temperature is related to the strength of ferromagnetism. These results provide a platform to study the magnetic interactions and suggest the possibility of realizing thermal controllable magnetic sensor devices in electron-doped Sr2IrO4 films.

In situ formation of TiB2 and TiH2 catalyzed Li/Mg based dual-cation borohydride with a low onset dehydrogenation temperature below 100 °C

Chemical complex borohydride is a promising hydrogen storage material due to its large gravimetric and volumetric hydrogen capacities. However, the high dehydrogenation temperature and sluggish kinetics still place strong restrictions on its practical application in the hydrogen storage field. In this work, a synergetic approach of partial cation substitution and catalysis is developed to enhance the hydrogen storage properties of LiBH4. The Li/Mg based dual-cation borohydride (LiMg2(BH4)5, LMBH) was successfully synthesized by wet chemical ball milling of LiBH4 and MgCl2. The optimal (LMBH (4.5:1) sample, LiBH4 and MgCl2 in molar ratios of 4.5:1, possesses a maximum hydrogen desorption capacity (11.27 wt%) and the outstanding initial decomposition temperature (∼250 °C). Importantly, the LMBH (4.5:1) doped with TiF3 shows a remarkable onset dehydrogenation temperature as low as 97.2 °C, which is about 190 °C lower than that of pristine LiBH4. The LMBH (4.5:1) doped with TiF3 system releases 7.98 wt% H2 within 170 min below 350 °C. And the dehydrogenation product of doped composite can reversibly absorb ∼4.72 wt% H2 at a relatively moderate temperature of 280 °C, which is substantially lower than the reversible hydrogen absorption temperature of previous modified borohydride systems. Based on the structural characteristic analyses, the TiF3 reacts with LMBH (4.5:1) to in-situ form actual catalytic components of TiB2 and TiH2 as the actual catalysts for LMBH (4.5:1), resulting in the improved hydrogen re/dehydrogenation properties. The synergetic modification of Li/Mg dual-cation substitution and TiB2/TiH2 catalysis may lead to the development of light-metal borohydrides with outstanding hydrogen storage properties.

Aerodynamic performance of the reversible axial fan for high air temperatures

The paper presents the aerodynamic performance of an axial reversible fan for high air temperatures, obtained by applying the similarity theory and numerical flow simulations. This analysis was performed for the possibility of installing the existing structure of an impeller of a reversible fan in a jet fan for the longitudinal ventilation of a tunnel. The direction of forced flow in tunnels changes, and it is always towards low atmospheric pressure, i.e. in the direction of natural air-flow. These fans often work with high air temperatures in the event of a fire. The paper shows the performance of fans for high operating air temperatures, up to 400?C. The results were obtained through numerical simulations of the flow in an original design fan, whose performance was experimentally determined for normal atmospheric operating conditions (? = 1.2 kg/m3). Performances are given for two fan speeds. Unnecessary corrections of the existing impeller design for use in jet fans for tunnel ventilation were also considered.

A reversible room temperature phosphorescence/delayed fluorescence switch trigged by solvent exchange in a Ca-based coordination polymer

Presented here is a coordination polymer whose initial delayed fluorescence can be reversibly converted to room temperature phosphorescence through the reversible exchange of DMSO and H2O solvent molecules.

Unraveling the low-temperature activity of Rh-CeO2 catalysts in CO oxidation: probing the local structure and Red-Ox transformation of Rh3+ species.

The local structure of the active sites is one of the key aspects of establishing the nature of the catalytic activity of the systems. In this work, a detailed structural investigation of the Rh-CeO2 catalysts prepared by the co-precipitation method was carried out. The application of a variety of physicochemical methods such as XRD, Raman spectroscopy, XPS, TEM, TPR-H2, and XAS revealed the presence of highly dispersed Rh3+ species in the catalysts: Rh3+ single ions and RhOx clusters. The substitution of Ce4+ ions by Rh3+ species, which provided a strong distortion of the CeO2 lattice, is shown. XAS data ensured the refinement of the Rh local structure. It was shown that single Rh3+ sites located next to each other can merge the formation of RhOx clusters with Rh local environment close to the one in Rh2O3 and CeRh2O5 oxides. The distortion of the CeO2 lattice around single and cluster rhodium species had a beneficial effect on the catalytic activity of the samples in low-temperature CO oxidation (LTO-CO). TEM, XAS, and in situ XRD data allowed establishing the structural transformations of the catalysts under Red-Ox treatments. The reduction treatment led to Rhn metallic cluster formation localized on defects of the reduced CeO2-δ. The reduced sample demonstrated efficient CO conversion at 0 °C. However, this system was not stable: its contact with air led to ceria reoxidation and partial reoxidation of Rh to highly dispersed Rh3+ species at room temperature, while heating in an oxidizing atmosphere resulted in the complete reoxidation of metallic rhodium species. The results of the work shed light on the structural aspects of the reversibility of the Rh-CeO2 catalysts based on the highly dispersed Rh3+ species under treatment in the reaction conditions.

Control-oriented performance prediction of solid oxide electrolysis cell and durability improvement through retard oxygen electrode delamination with reverse operation

Oxygen electrode delamination is the key degradation mechanism of reversible solid oxide cells (rSOC) operating in the electrolysis mode. Previous experimental studies have shown that rSOC operating in fuel cell mode can mitigate this degradation and extend its lifetime. As a result, this paper proposes a multiscale degradation model that integrates microscale structures, mesoscale parameters, and macroscale performances to investigate the sensitivity of the alleviation of oxygen electrode delamination to reverse operating conditions. After that, the model is validated by available experimental data at the microscale and macroscale. Subsequently, the multiscale degradation behaviors regarding certain operating conditions are discussed. The analysis demonstrates that, on the one hand, the cell degradation is mainly attributed to lanthanum zirconate oxide (LZO) formation during long-term operation; on the other hand, the higher the temperature and current density, the faster the degradation. Consequently, a new parameter of LZO layer thickness related to oxygen electrode delamination is introduced to assess the sensitivities of durability improvement to reverse operating variables, namely starting switch moment, operating duration, and operating temperature. Meanwhile, voltage degradation rate and hydrogen production are also evaluated. The result indicates that a decrease in the starting switch moment and an increase in the operating duration can reduce the growth of LZO layer thickness and prolong the incubation time for oxygen electrode delamination. It can also decrease the degradation rate and hydrogen production. However, improving reverse operating temperature reduces the LZO layer thickness growth rate and degradation rate without affecting hydrogen production.

Thermally Induced Reversible Fluorescence Switching of Lead Chloride Hybrids for Anticounterfeiting and Encryption.

Metal halide hybrids with thermally induced fluorescence transition have the potential to be utilized as the next generation of smart materials in optoelectronic devices. However, the fabrication of thermochromic materials with simultaneously reversible and lower transition temperatures is still a challenge. Herein, we present a novel one-dimensional (1D) organic-inorganic lead chloride hybrid (TPA)PbCl3-Green (TPA = tetrapropylammonium) single crystal that exhibits green emission and up to 30% photoluminescence quantum yield (PLQY). It is worth noting that the (TPA)PbCl3-Green crystal changes emission from green to blue light when heated at 323 K. The emission spectra indicate that the blue light is attributed to the combination of two emission peaks located at 438 and 520 nm, respectively. Furthermore, the green luminescence is restored after natural cooling to room temperature. The dynamic transition process is demonstrated via steady-state photoluminescence, single-crystal X-ray diffraction (SCXRD), and powder X-ray diffraction (XRD). (TPA)PbCl3-Green crystals and (TPA)PbCl3-Green@PVP complexes have also been explored as fluorescent security inks for dynamic anticounterfeiting and message encryption as well as optical logic gate applications due to the excellent cycling stability and low transition temperature. This material offers a completely new option for thermochromic materials used for security information.

Super-high coercivity NdFeB magnet fabricated with double Tb-rich/lean shells by double alloy method and grain boundary diffusion

In this work, the high performance NdFeB magnet were fabricated by double alloy method and grain boundary diffusion Tb70Cu20Ga10 alloys. The maximum energy product (BH)max and coercivity Hcj of the magnet are 45.33 MGOe and 35.46 kOe, respectively. The reversible temperature coefficients of coercivity of the diffusion magnets improve from − 0.456%/°C to − 0.412%/°C at the range of 22 °C −180 °C. The magnetostatic loss of NdFeB magnet was analyzed in high temperature applications by general finite element method (FEM). The RE-(Fe,CuGaO) grain boundary phases and double Tb-rich/lean shells improve the utilization rate of heavy rare earths and coercivity of magnets after diffusion. The magnetization reversal mechanism of double core-shell microstructures had been discussed. This work may shed light on developing coercivity above 30 kOe of NdFeB magnet with low heavy rare earth through modified microstructure.

Maximizing adiabatic temperature change in elastocaloric polymers

Designing polymers exhibiting large and reversible temperature variations triggered by uniaxial stress is an expanding research field aimed at addressing the urgent need for new means of cooling. In <i>Cell Reports Physical Science</i>, Wang and co-workers propose the synthesis of elastomers at the plastic-rubber transition to maximize their elastocaloric activity.

Stimuli‐responsive polypeptoid block copolymers containing o‐nitrobenzyl groups with extremely sharp transition

AbstractBioinspired thermoresponsive polymers have received increasing attention for many applications. Here, we report a series of thermoresponsive polypeptoid block copolymers containing o‐nitrobenzyl groups, that is, poly(ethylene glycol)‐b‐poly[N‐[2‐[N‐(o‐nitrobenzyloxycarbonyl)‐amino]‐ethyl]‐glycine] (PEG‐b‐PN[oNB]G), prepared by ring‐opening polymerization. The polypeptoid block copolymers show reversible lower critical solution temperature (LCST)‐type behavior in water with tunable phase transition properties dependent on the pH values, chemical compositions, and concentrations of the copolymers. The dynamic light scattering results reveal the formation of spherical micelles and temperature‐induced aggregation of PEG‐b‐PN(oNB)G. Notably, the phase transition of the block copolymer solution upon heating appears extremely sharp (∆T &lt; 1°C), superior to bench mark poly(N‐isopropylacrylamide). In addition, we present the removal of photo‐responsive o‐nitrobenzyl groups can result in the increased clouding point and even the loss of phase transition properties, acting as an excellent regulator to tune the LCST behavior. We demonstrate that the hydrogen‐bonding interaction may play a critical part on the LCST behavior. The prepared diblock copolymers show great potential for many applications and its structure–property may shed light on highly designable stimuli‐responsive polymeric materials.

Thermoresponsive Block Copolymer Core-Shell Nanoparticles with Tunable Flow Behavior in Porous Media.

With the purpose of investigating new polymeric materials as potential flow modifiers for their future application in enhanced oil recovery (EOR), a series of amphiphilic poly(di(ethylene glycol) methyl ether methacrylate-co-oligo(ethylene glycol) methyl ether methacrylate) [P(DEGMA-co-OEGMA)]-based core-shell nanoparticles were prepared by aqueous reversible addition-fragmentation chain transfer-mediated polymerization-induced self-assembly. The developed nano-objects were shown to be thermoresponsive, demonstrating a reversible lower-critical solution temperature (LCST)-type phase transition with increasing solution temperature. Characterization of their thermoresponsive nature by variable-temperature UV-vis and dynamic light scattering analyses revealed that these particles reversibly aggregate when heated above their LCST and that the critical transition temperature could be accurately tuned by simply altering the molar ratio of core-forming monomers. Sandpack experiments were conducted to evaluate their pore-blocking performance at low flow rates in a porous medium heated at temperatures above their LCST. This analysis revealed that particles aggregated in the sandpack column and caused pore blockage with a significant reduction in the porous medium permeability. The developed aggregates and the increased pressure generated by the blockage were found to remain stable under the injection of brine and were observed to rapidly dissipate upon reducing the temperature below the LCST of each formulation. Further investigation by double-column sandpack analysis showed that the blockage was able to reform when re-heated and tracked the thermal front. Moreover, the rate of blockage formation was observed to be slower when the LCST of the injected particles was higher. Our investigation is expected to pave the way for the design of "smart" and versatile polymer technologies for EOR applications in future studies.

Structural and cryogenic magnetic properties of the RE2MoO6 (RE = Er and Ho) compounds

The rare earth (RE) based magnetic materials with large low temperature magnetocaloric effect (MCE) have attracted much research interest due to their potential application for the environment-friendly magnetic refrigeration (MR) technology. Herein, a systematic investigation on the crystal structure, micro morphology together with the low temperature magnetic properties and MCE performances have been conducted on the RE2MoO6 (RE = Er and Ho) compounds. Both compounds crystallize in monoclinic structure and exhibit large reversible low temperature MCE. The maximum magnetic entropy changes (−ΔSMmax) at magnetic field change (ΔH) of 0–5 T reach 15.3 and 15.8 J kg−1 K−1 for Er2MoO6 and Ho2MoO6, respectively. The corresponding relative cooling power/refrigeration capacity (RCP/RC) values are 197.4/149.7 and 286.0/222.3 J/kg. These obtained MCE parameters for present RE2MoO6 compounds are close to those of reported RE based MCE materials, which make them of potential for low temperature MR application.

Numerical simulations of the Hebb-Wagner polarization kinetics: (I) weakly acceptor-doped perovskite oxides

The Hebb-Wagner polarization method can be used to separate the partial electronic conductivity of mixed ionic and electronic conductors (MIEC) from the partial ionic conductivity by polarizing the material between an ion-blocking and a reversible electrode using an external electric voltage. The electronic conductivity is then calculated from the steady state I-V curve where the partial current of the blocked ionic species is zero. The kinetics of the relaxation process towards the steady state and the corresponding relaxation time were, however, not investigated until now, although they are crucial to the success of the Hebb-Wagner method. In this contribution, the kinetics of the relaxation process during the Hebb-Wagner polarization of a nominally undoped perovskite-type oxide ABO3 (mixed ionic and electronic conductor) is simulated by means of numerical methods and using SrTiO3 as a model system. The simulation results show an unexpected dependence of the relaxation time of the polarization process on the applied voltage. The relaxation time first decreases until a certain voltage is reached, where it remains constant for a few voltage steps, and afterwards it increases again for higher voltage values. We show that these three different relaxation time dependencies correspond to the transition from (i) a prevailing electron hole conduction at high oxygen partial pressures to (ii) a predominant oxygen ion conduction near the p − n transition at intermediate oxygen partial pressures followed by (iii) a predominant electron conduction at low partial pressures. Additionally, the dependence on other parameters and experimental variables, such as surface exchange coefficient at the reversible electrode, acceptor concentration, temperature, and sample length, is investigated, which reveals that a slight change of one of these parameters can change the relaxation time by several orders of magnitude. The obtained insight from the numerical simulation of the electrochemical polarization process is advantageous for the experimental realization of the Hebb-Wagner polarization method, and in particular for its application to nominally undoped perovskite-type oxides, like SrTiO3.

CO2 capture using in-situ polymerized amines into pore-expanded-SBA-15: Performance evaluation, kinetics, and adsorption isotherms

Over the last decades, carbon dioxide capture has attracted lots of attention and different solution have been proposed, yet the global CO2 concentration is still increasing along with its environmental impacts. Covalently tethered amines were in-situ polymerized into mesoporous silica support, namely PE-SBA-15, for the reversible temperature swing CO2 adsorption. The in-situ polymerization approach shows high loadings of amines in comparison to the grafting technique which was confirmed via thermal decomposition and CHN elemental analysis. The covalent tethering of amines, evidenced by the characteristic absorption peaks via FTIR, resulted in good thermal stability of the sorbent and constant CO2 uptake during multicycle operation. Porosimetry analysis, pore volume and BET surface area, showed a noticeable decrease upon the functionalization of support indicating that most of the pores of the support are occupied by the amines. CO2 capture of the sorbent at different concentrations and temperatures, from 400 ppm for the direct air CO2 capture to 15 % CO2 for coal-powered plants showed good performance. A reduction in CO2 uptake was noticed upon the decrease in adsorption temperature with an optimum temperature of 25 °C. Adsorption kinetics were found to be best represented by a pseudo-second order model with significant adsorption rates. Dry adsorption isotherms of CO2 and N2 were studied at different temperatures and the CO2 isotherms were found to follow Langmuir dual site (LDS) model with a very high selectivity towards CO2. This study shows that in-situ polymerization is a key route for mitigating the continuous increase in atmospheric CO2 concentration.

Migration and diffusion of unsteady-state flow of volatile organic compounds on activated carbon adsorption beds under reverse ventilation

Despite increasing attention to the influence of unsteady-state volatile organic compounds (VOCs) on the adsorption of activated carbon, studies in this regard are rare. Therefore, in this study, an investigation into the migration and diffusion of unsteady-state VOCs on activated carbon adsorption beds under reverse ventilation was conducted. Here, reverse clean air was introduced when the activated carbon bed reached the penetration point. The influence of reverse ventilation temperature, reverse superficial gas velocity, activated carbon filling height, and different ventilation modes on the adsorption of unsteady toluene by activated carbon were studied. Our experimental results show that when the reverse ventilation temperature increased from 20 °C to 60 °C, the quasi-first-order desorption rate constant increased from 0.00356 min−1 to 0.00807 min−1, an increase in the reverse superficial gas velocity led to a higher rate constant, and at greater reverse superficial gas velocities, the stripping capacity increased. It was observed that the maximum stripping capacity was achieved at a reverse superficial gas velocity of 0.3 m/s. For different activated carbon filling heights, following reverse ventilation, the stripping capacity of a 5 cm and 30 cm activated carbon bed accounted for 41.43% and 65.85% of the original adsorption capacity, respectively. The study concludes that concentration of toluene first increased and then decreased with time under forward ventilation, whereas the concentration gradually decreased under reverse ventilation.

A quantitative study on the thermomechanical coupling effect of elasticity and plasticity of polymethyl methacrylate

Quantitative study on the elastic and plastic thermomechanical coupling effect of solid materials has important theoretical significance for monitoring the deformation state and stability evaluation of engineering components. In this study, the sample is made of polymethyl methacrylate (PMMA), and uniaxial compression experiments are carried out. The sample experiences the elastic state and then the plastic state until the failure of the sample. The thermoelastic effect and thermoplastic effect in the deformation process of PMMA materials are monitored by infrared thermography and digital speckle system (DIC). That is, the relationship between the reversible elastic temperature change ΔTe and average stress change Δσm, and the relationship between the irreversible plastic temperature rise ΔTp and the dissipated energy ΔUp during the failure deformation process. The results show that when the sample is in the elastic regime, there is only elastic temperature change ΔTe inside the sample. When the sample enters the plastic deformation regime, the total temperature change ΔT includes elastic temperature change ΔTe and plastic temperature change ΔTp, and the temperature change has an obvious memory effect on the previous maximum load. When the previous maximum load exceeded, ΔTp increases rapidly. When the load P is removed, ΔTe disappears, and ΔTp remains. Combined with the theory of thermodynamics and solid mechanics, starting from the 3D stress state, the approximate linear incremental relationship between Te and σm, and the accurate exponential total quantity relationship are derived. The incremental relationship and the full relationship combined with thermodynamic theory and the energy conservation principle, the relationship between the overall plastic temperature rise ΔTp and local plastic temperature rise ΔTpmax of the sample and the energy dissipation value ΔUp experienced by the sample and the local dissipation specific energy Δup is obtained. The theoretical calculation results of ΔTe and ΔTp are in good agreement with the experimental results. The research results can provide a new method for monitoring and identifying the stress and deformation state of engineering components through the temperature field.

Deformation induced martensite stabilization of NiTi in constrained composite systems

This study investigated the effect of tensile deformation on the transformation behaviour of NiTi within the constrained environment of NiTi–Nb composites. Particular attention is given to the deformation-induced stabilisation of the stress-induced martensite manifested as the increase of the reverse transformation temperature. Two different forms of the NiTi–Nb composites were used, including nanowires and microparticles, in comparison with the single-component binary NiTi alloy. This stabilisation effect has been reported for NiTi in the literature. The effect is attributed to the changes in the internal elastic and plastic states of the martensite variant structure caused by the deformation. The NiTi–Nb nanocomposites present different internal mechanics environments. It was found that the presence of a second phase within the NiTi matrix hinders the lattice distortion martensitic transformation, enlarging its hysteresis in the order of the binary NiTi, the NiTi–Nb microparticle composite and the NiTi–Nb nanowire composite. After deformation, the NiTi–Nb microparticle composite exhibited the highest stabilisation effect, followed by the NiTi–Nb nanowire composite and then the binary NiTi alloy. These contrasting observations are attributed to dual effects of the Nb inclusions within the NiTi matrix, to obstruct the lattice distortions of the martensitic transformation, and to retain elastic strains and thus stresses that may assist and resist a transformation depending on their relative directions.

Temperature independence of haemoglobin-oxygen affinity in smalleye Pacific opah (Lampris incognitus) and swordfish (Xiphias gladius).

Smalleye Pacific opah and swordfish can conserve metabolic heat and maintain specific body regions warmer than ambient water temperature (i.e. regional heterothermy). Consequently, blood O2 uptake at the gills occurs at the environmental temperature at which the individual is found, but O2 offloading will occur at different temperatures in different tissues. While several regionally heterothermic fishes (e.g. billfishes, tunas and sharks) show a reduced temperature effect on haemoglobin (Hb)-O2 affinity, the temperature dependence of Hb-O2 affinity in opah and swordfish is unknown. We hypothesized that the Hb of opah and swordfish would also show a reduced temperature dependence. Opah whole-blood-O2 affinity exhibited a reverse temperature dependence above 50% Hb-O2 saturation (10-20°C, pH7.2-8.0), while the temperature dependence of swordfish blood-O2 affinity (10-25°C) was saturation and pH dependent, becoming temperature independent below 50% Hb-O2 saturation and pH7.4. Experiments on stripped haemolysates showed that adding ATP ([ATP]/[Hb]=30) decreased the temperature sensitivity of Hb-O2 affinity, changing the overall oxygenation enthalpy (ΔH') values of opah (10-20°C) and swordfish (10-25°C) Hbs at pH7.4 from -15 and -42 kJ mol-1 O2, respectively, to +84 and -9 kJ mol-1 O2. Swordfish blood-O2 affinity was high compared with that of other large, pelagic, marine teleosts, which may be the result of unusually low ATP/Hb levels, but might also enable swordfish to forage in the potentially low-oxygenated water of the upper reaches of the oxygen minimum layer. The existence of Hbs with reduced temperature sensitivity in regionally heterothermic fishes may prevent marked changes in Hb-O2 affinity between the cold and warm tissues.