Linear Temperature Term Research Articles

Anisotropic spin-glass and magnetic behavior in single-crystalline U2PtSi3

The results of ac and dc susceptibilities, magnetization, magnetic relaxation, electrical resistivity, and specific heat measurements performed on a hexagonal AlB2-type single-crystalline U2PtSi3 are reported. The previously reported spin-glass transition in polycrystalline U2PtSi3 was confirmed to also occur in the single-crystalline sample with spin freezing temperature Tf=12.4 K. It is newly found that the spin-glass effect and magnetic behavior of U2PtSi3 measured along and perpendicular to the hexagonal c-axis show different magnetic field responses. Along the hard magnetization axis (c-axis), both the rate of change of Tf with the magnetic field and the detected magnetic viscosity coefficient are much smaller than those obtained in the c-plane. On the other hand, the low-temperature specific heat measurement yields an enhanced coefficient of the linear temperature term, and the temperature dependence of electrical resistivity illustrates a shallow minimum at the temperature much larger than Tf. The possible mechanisms for these phenomena are discussed by comparing with the corresponding properties observed in other ternary 2:1:3 uranium intermetallic compounds.

A Discrepancy in Thermal Conductivity Measurement Data of Quantum Spin Liquid β′-EtMe3Sb[Pd(dmit)2]2 (dmit = 1,3-Dithiol-2-thione-4,5-dithiolate)

A molecular Mott insulator β′-EtMe3Sb[Pd(dmit)2]2 is a quantum spin liquid candidate. In 2010, it was reported that thermal conductivity of β′-EtMe3Sb[Pd(dmit)2]2 is characterized by its large value and gapless behavior (a finite temperature-linear term). In 2019, however, two other research groups reported opposite data (much smaller value and a vanishingly small temperature-linear term) and the discrepancy in the thermal conductivity measurement data emerges as a serious problem concerning the ground state of the quantum spin liquid. Recently, the cooling rate was proposed to be an origin of the discrepancy. We examined effects of the cooling rate on electrical resistivity, low-temperature crystal structure, and 13C-NMR measurements and could not find any significant cooling rate dependence.

Models for sensing by nanowire networks: application to organic vapour detection by multiwall carbon nanotube—DNA films

Electronic sensors for volatile organic compounds have been prepared by drop-casting dispersions of multi-wall carbon nanotubes (MWCNTs) in aqueous solutions of λ-DNA onto Pt microband electrodes. The MWCNTs themselves show a metal-like temperature dependence of the conductance, but the conductance of DNA/MWCNT composites has an activated component that corresponds to inter-tube tunneling. The resistance of the composite was modelled by a series combination of a term linear in temperature for the nanotubes and a stretched exponential form for the inter-tube junctions. The resistance may increase or decrease with temperature according to the composition and may be tuned to be almost temperature-independent at 67% by mass of DNA. Upon exposure to organic vapours, the resistance of the composites increases and the time-dependence of this signal is consistent with diffusion of the vapour into the composite. The fractional change in resistance at steady-state provides an analytical signal with a linear calibration and the presence of DNA enhances the signal and adjusts the selectivity in favour of polar analytes. The temperature dependence of the signal is determined by the enthalpy of adsorption of the analyte in the inter-tube junctions and may be satisfactorily modelled using the Langmuir isotherm. Temperature and pressure-dependent studies indicate that neither charge injection by oxidation/reduction of the analyte nor condensation of analyte on the device is responsible for the signal. We suggest that the origin of the sensing response is an adsorption of the analyte in the inter-tube regions that modulates the tunneling barriers. This suggests a general route to tuning the selectivity of MWCNT gas sensors using non-conductive polymers of varying chemical functionality.

A modified Steinberg–Cochran–Guinan model applicable to solid–liquid mixed zone along the principle Hugoniot

A constitutive model is vital for describing the deviatoric stresses of metallic materials under intense impact loading. Although the classical Steinberg–Cochran–Guinan (SCG) model has been widely regarded as an acceptable scheme, it does not clearly describe the coupling effect of the strain hardening and temperature softening at high temperatures and pressures, especially for the solid–liquid mixed phase. In this work, a modified SCG (MSCG) model is proposed based on an idealized assumption that the shear modulus and yield strength are equal to zero at the complete melting temperature and pressure. The temperature-dependent shear modulus model is then introduced in the MSCG model. The proposed model avoids the over-temperature softening effect by discarding the linear temperature term. More importantly, the pressure–temperature coupling factor (k) is employed in the pressure term, and the k adjusts the coupling effect of the strain hardening and temperature softening. In addition, the asymmetric relation in the MSCG model indicates that the temperature softening effect is more dominant than the strain hardening effect during the whole shock loading process. Moreover, the MSCG model is compared with the SCG model, Li and Chen's SCG model, and available data; the comparison verified the ability of the model to reproduce the shear moduli and yield strengths of Al, Be, Cu, and W in the solid–liquid mixed phase.

Thermodynamic properties of glassy phonon states induced by strong electron correlations in 𝜃-type organic charge transfer salts

The appearance of electron correlations–induced glassy state of low-energy phonons in the non-dimeric organic charge transfer salt in [Formula: see text]-(BEDT-TTF)2CsZn(SCN)4 is considered as a strong evidence of charge lattice coupling in molecular charge transfer salts. We discuss the temperature and the magnetic field dependences of the heat capacity of this salt in terms of the soft potential model to describe the thermodynamic properties of enhanced phonons that occur in molecular glasses. The evaluated [Formula: see text] term of [Formula: see text]-(BEDT-TTF)2CsZn(SCN)4 is about 30 mJ K[Formula: see text] mol[Formula: see text], which is much larger than other charge transfer salts described by the low-temperature approximation of the Debye model. The magnetic fields dependence of the boson peak is almost negligible, but the low-energy term, for example, in the temperature-linear term of heat capacity shows a slight change, probably due to the small amount of localized spin moments. The comparison with other systems is also performed.

Unusual Magnetic State with Dual Magnetic Excitations in the Single Crystal of S = 1/2 Kagome Lattice Antiferromagnet CaCu3(OH)6Cl2 ∙ 0.6H2O

We have succeeded in preparing single crystals of CaCu3(OH)6Cl2 ∙ 0.6H2O, a candidate for the S = 1/2 Kagome lattice antiferromagnet. Magnetic properties of the compound are dominated by the nearest neighbor antiferromagnetic interaction J1, and the next nearest neighbor ferromagnetic J2 and an antiferromagnetic Jd across a hexagon, which is different from related compounds Kapellasite and Haydeeite with ferromagnetic J1. Magnetic susceptibility exhibits a sudden increase below 13 K and a cusp anomaly at T* = 7.2 K in the ab-plane, whereas only a moderate enhancement is observed below T* along the c-axis. A tiny peak detected in heat capacity at T* indicates the occurrence of a magnetic phase transition. The low temperature magnetic heat capacity was reproduced by assuming a two-dimensional spin-wave component and a temperature-linear term. The spin-wave contribution suggests a magnon excitation in a short-range ordered region, whereas the relatively large T-linear term 5.9 mJ/(Cu-mol·K2) at H = 0 T of th...

Thermal Hall conductivity of spin-triplet superconductor with time reversal symmetry breaking

The thermal Hall conductivity is investigated for the superconductor Sr2RuO4 assuming a time reversal symmetry breaking order parameter. The γ band of Sr2RuO4 has its Fermi level near the van Hove points, close to the Lifshitz transition. Within a Bogoliubov-de Gennes approach we calculate the thermal Hall conductivity for pairing symmetries including two exemplary cases, the usual chiral p-wave phase and a fx2−y2-wave phase of the structure . In the chiral p-wave phase the thermal Hall conductivity consists of a universal temperature-linear term and an exponential correction due to quasiparticle activation with a full excitation gap. Due to line-nodes in the gap we find a correction which is quadratic in temperature for fx2−y2-wave state. This difference in the corrections allows to analyze the gap structure of the superconducting phase.

Thermal Hall conductivity in the spin-triplet superconductor with broken time-reversal symmetry

Motivated by the spin-triplet superconductor Sr2RuO4, the thermal Hall conductivity is investigated for several pairing symmetries with broken time-reversal symmetry. In the chiral p-wave phase with a fully opened quasiparticle excitation gap, the temperature dependence of the thermal Hall conductivity has a temperature linear term associated with the topological property directly, and an exponential term, which shows a drastic change around the Lifshitz transition. Examining f-wave states as alternative candidates with $\bm d=\Delta_0\hat{z}(k_x^2-k_y^2)(k_x\pm ik_y)$ and $\bm d=\Delta_0\hat{z}k_xk_y(k_x\pm ik_y)$ with gapless quasiparticle excitations, we study the temperature dependence of the thermal Hall conductivity, where for the former state the thermal Hall conductivity has a quadratic dependence on temperature, originating from the linear dispersions, in addition to linear and exponential behavior. The obtained result may enable us to distinguish between the chiral p-wave and f-wave states in Sr2RuO4.

Superfluid density in the slave-boson theory

Despite of the success of the slave-boson theory in capturing qualitative physics of high-temperature superconductors like cuprates, it fails to reproduce the correct temperature-dependent behavior of superfluid density, let alone the independence of the linear temperature term on doping in the underdoped regimes of hole-doped cuprate, a common experimental observation in different cuprates. It remains puzzling up to now in spite of intensive theoretical efforts. For electron-doped case, even qualitative treatment is not reported at present time. Here we revisit these problems and provide an alternative superfluid density formulation by using the London relation instead of employing the paramagnetic current-current correlation function. The obtained formula, on the one hand, provides the correct temperature-dependent behavior of the superfluid density in the whole temperature regime, on the other hand, makes the doping dependence of the linear temperature term substantially weaken and a possible interpretation for its independence on doping is proposed. As an application, electron-doped cuprate is studied, whose result qualitatively agrees with existing experiments and successfully explains the origin of $d$- to anisotropic $s$-wave transition across the optimal doping. Our result remedies some failures of the slave-boson theory as employed to calculate superfluid density in cuprates and may be useful in the understanding of the related physics in other strongly correlated systems, e.g. Na$_{x}$CoO$_{2}$$\cdot$yH$_{2}$O and certain iron-based superconductors with dominating local magnetic exchange interaction.

Thermal Hall conductivity and topological transition in a chiralp-wave superconductor forSr2RuO4

The interplay between the thermal transport property and the topological aspect is investigated in a spin-triplet chiral p-wave superconductor Sr2RuO4 with the strong two-dimensionality. We show the thermal Hall conductivity is well described by the temperature linear term and the exponential term in the low temperature region. While the former term is proportional to the so-called Chern number directly, the latter is associated with the superconducting gap amplitude of the gamma band. We also demonstrate that the coefficient of the exponential term changes the sign around Lifshitz transition. Our obtained result may enable us access easily the physical quantities and the topological property of Sr2RuO4 in detail.

Electronic properties of a distorted kagome lattice antiferromagnetDy3Ru4Al12

Electronic properties of ${\mathrm{Dy}}_{3}{\mathrm{Ru}}_{4}{\mathrm{Al}}_{12}$ (hexagonal crystal structure, Dy atoms form distorted kagome nets) are studied on a single crystal by means of magnetization, neutron diffraction, specific heat, and resistivity measurements. The onset of a long-range magnetic order of Dy moments occurs at 7 K through a first-order phase transition. The compound has a noncollinear antiferromagnetic structure with a propagation vector (1/2 0 1/2). The configuration of the Dy moments is consistent with the monoclinic Shubnikov group ${C}_{c}2/c$. The \ensuremath{\gamma} coefficient in the temperature linear term of the specific heat is strongly enhanced to 500 mJ ${\mathrm{mol}}^{\ensuremath{-}1}$ ${\mathrm{K}}^{\ensuremath{-}2}$ taking into account the localized nature of Dy magnetism. An additional contribution originates from spin fluctuations induced in the $4d$ subsystem of Ru by the exchange field acting from the Dy $4f$ moments. In an applied magnetic field ${\mathrm{Dy}}_{3}{\mathrm{Ru}}_{4}{\mathrm{Al}}_{12}$ displays magnetization jumps along all crystallographic directions. All the metamagnetic transitions are accompanied by large positive magnetoresistance. The maximum effect (125%--140%) is attained for current along the [100] axis and field along the [120] or [001] axes. The large positive effect is explained by changes in the conduction electron spectra through the jumps as the conduction electrons interact with localized magnetic moments.

Optimization of catalytic glycerol steam reforming to light olefins using Cu/ZSM-5 catalyst

Response surface methodology (RSM) and multi-objective genetic algorithm was employed to optimize the process parameters for catalytic conversion of glycerol, a byproduct from biodiesel production, to light olefins using Cu/ZSM-5 catalyst. The effects of operating temperature, weight hourly space velocity (WHSV) and glycerol concentration on light olefins selectivity and yield were observed. Experimental results revealed the data adequately fitted into a second-order polynomial model. The linear temperature and quadratic WHSV terms gave significant effect on both responses. Optimization of both the responses indicated that temperature favouring high light olefin formation lied beyond the experimental design range. The trend in the temperature profile concurred commensurately with the thermodynamic analysis. Multi-objective genetic algorithm was performed to attain a single set of processing parameters that could produce both the highest light olefin selectivity and yield. The turn-over-frequency (TOF) of the optimized responses demonstrated a slightly higher value than the one which was not optimized. Combination of RSM, multi-objective response and thermodynamic is useful to determine the process optimal operating conditions for industrial applications.

Synergy in the effects of temperature and air pollution on mortality in 8 European cities. Results from the PHASE project.

Background: Numerous studies have associated excess heat or cold with increased mortality. Air pollution, especially particulate matter and ozone also deteriorate human health. Their joint effects, though, are less well studied and understood. Aim: Within the PHASE project, we used data from 8 European cities (Athens, Barcelona, Budapest, Helsinki, Paris, Rome, Stockholm and Valencia) to investigate possible synergistic effects of temperature and air pollution on mortality. Methods: City-specific Poisson regression models controlling for seasonality and other confounders were used separately for summer (April-September) and winter (October-March). Maximum apparent temperature was the exposure variable in summer, while minimum was used in winter. Based on previous results, threshold terms for summer and linear temperature terms for winter were used. Interaction terms between temperature and pollution variables were included in the models to investigate synergy on all cause, cardiovascular and respiratory mortality, in all ages and by age group. Results: Initial results provide evidence for synergy in several participating cities. For example, significant positive interaction between high temperature and PM10 was found in Athens and Paris, concerning both total and cardiovascular mortality in all ages. In Athens, significant synergy was also detected between high temperature and ozone on cardiovascular mortality in all ages. In Paris and Stockholm, a significant positive interaction between high temperature and ozone was found on total mortality in all ages. Conclusions: There is evidence for higher impact on mortality on days with both high temperature and high ozone or PM10 concentration, although this was not consistent across all cities. These findings should have implications on policy-making in Europe.

A Resistorless CMOS Voltage Reference Based on Mutual Compensation of $V_{T}$ and $V_{\rm TH}$

A novel temperature-stable nonbandgap voltage reference without resistors is presented in this brief, which is compatible with standard digital CMOS technology. Two linear-temperature terms, i.e., thermal voltage VT and threshold voltage VTH, are utilized to realize a low-temperature-dependent voltage reference with a significant reduction of nonlinear temperature terms. A self-biased threshold-voltage extractor circuit without any resistor is used to obtain the VTH and bias currents of the whole circuit. Based on ratioed transistors biased in a strong inversion region and the inverse-function technique, a temperature-insensitive gain can be applied to the proportional-to-absolute temperature term in the reference, and a weighted sum of VT and VTH is achieved. Experimental results of the proposed voltage reference implemented with a 0.35- μm CMOS process demonstrate that the output of voltage reference is 905.5 mV, a temperature coefficient of 14.8 ppm/°C with a temperature range of 0°C-100 °C is obtained at a 3.3-V power supply, and a power-supply noise attenuation of 61 dB is achieved without any filtering capacitor while dissipating a maximum supply current of 65 μA. The active area is 100 μm ×100 μm.

Temporal shifts in recruitment dynamics of North Atlantic fish stocks: effects of spawning stock and temperature

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 480:205-225 (2013) - DOI: https://doi.org/10.3354/meps10249 Temporal shifts in recruitment dynamics of North Atlantic fish stocks: effects of spawning stock and temperature Geir Ottersen1,2,*, Leif Christian Stige2, Joël M. Durant2, Kung-Sik Chan3, Tristan A. Rouyer2,6, Kenneth F. Drinkwater4, Nils Chr. Stenseth2,5 1Institute of Marine Research, Gaustadalléen 21, 0349 Oslo, Norway 2Centre for Ecological and Evolutionary Synthesis (CEES), Department of Biology, University of Oslo, PO Box 1066 Blindern, 0316 Oslo, Norway 3Department of Statistics and Actuarial Science, University of Iowa, Iowa City, Iowa 52242, USA 4Institute of Marine Research, PB 1870 Nordnes, 5817 Bergen, Norway 5Institute of Marine Research, Flødevigen Marine Research Station, 4817 His, Norway 6Present address: IFREMER, UMR EME 212, Sète, France *Email: geir.ottersen@imr.no ABSTRACT: Effects of variation in spawning stock and sea temperature on long-term temporal patterns in recruitment dynamics of 38 commercially harvested fish stocks in the northern North Atlantic were studied. Different statistical models were explored within a Ricker stock-recruitment framework. This includes, in order of complexity, adding a linear temperature term, a nonlinear (smooth) temperature effect, and non-stationarities (trends in intercept or in temperature effect) and finally allowing for a stepwise change (a threshold). The different models were compared in a uniform approach using Akaike’s information criterion corrected for small sample size as the model selection criterion. The relationship between recruitment, spawning stock biomass and temperature varied over time. The most frequent alteration in the non-stationary linear models was, for 14 stocks, in the intercept in recruitment success, suggesting a change in pre-recruit mortality over time. Threshold models performed better than the best linear or nonlinear stationary models for 27 of the stocks, suggesting that abrupt changes (maybe even regime shifts) are common. For half of the stocks studied, the temperature effect was statistically significant when added to the model of the relationship between recruitment success and spawning stock biomass. This includes all 6 of the herring stocks studied, with a positive effect for cold-water stocks and negative effect for stocks in the more temperate southern areas. For the 4 plaice stocks analysed, all located towards the centre of the overall distribution range of plaice, a tendency toward recruitment being favoured by lower temperatures was found. KEY WORDS: Recruitment · Spawning stock biomass · Temperature · North Atlantic · Statistical modelling · Non-stationarity · Climate Full text in pdf format PreviousNextCite this article as: Ottersen G, Stige LC, Durant JM, Chan KS, Rouyer TA, Drinkwater KF, Stenseth NC (2013) Temporal shifts in recruitment dynamics of North Atlantic fish stocks: effects of spawning stock and temperature. Mar Ecol Prog Ser 480:205-225. https://doi.org/10.3354/meps10249 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 480. Online publication date: April 22, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Thermal issues in Casimir forces between conductors and semiconductors

The Casimir effect between metal surfaces has now been well-verified at the few per cent level experimentally. However, the temperature dependence has never been observed in the laboratory, since all experiments are conducted at room temperature. The temperature dependence for the related Casimir–Polder force between an atom and a bulk material has, in contrast, been observed between a Bose–Einstein condensate and a silica substrate, with the environment and the silica held at different temperatures. There is a controversy about the temperature dependence for the force between metals, having to do with the magnitude of the linear temperature term for both low and high temperature, the latter being most prominent at large distances. There are also related anomalies pertaining to semiconductors. The status of this controversy, and of the relevant experiments, is reviewed in this report.

Effect of the Variables Time and Temperature on Volatile Compounds Extraction of Salami by Solid Phase Microextraction

The aim of this study was to determine the experimental conditions for extracting volatile compounds present in the headspace of a salami sample by solid phase microextraction (Carboxen/PDMS fiber), monitoring the individual aromas of the extracts directly in order to maintain the original aroma of the product. Additionally, extracts were analyzed in gas chromatograph equipped with flame ionization detector and mass spectrometer (GC-FID and GC/MS). Volatile compounds were separated in polar phase capillary column (DB-Wax). Response Surface Methodology was used to explain the effects of both time and temperature on the salami aroma and on the instrumental measurements. Trained judges analyzed the intensity of a characteristic aroma from 12 salami extracts directly in olfactometer coupled with a gas chromatograph. The sensory results generated a multivariate statistical model (R 2 = 0.72, p < 0.05) that included linear time and temperature terms. The optimal conditions were determined to be an extraction period of 45 min at 50 °C, as the resulting extract received a mean sensory score of 7.15. This method allowed us to obtain a highly representative aroma of the product in an adequate time.

Thermoelectromotive force in Bi2Sr2Ca2Cu4O11 bismuth-based high-temperature superconductor

The temperature dependence of the thermoemf in Bi2Sr2Ca2Cu4O11 bismuth-based high-temperature superconductors is studied. The thermoemf is positive at high temperatures (T > 300 K) and negative at low temperatures. As the temperature decreases, the thermoemf reaches a maximum slightly above Tc and then sharply drops to zero. The results can be explained in the framework of the two-band theory with a linear temperature term.

Determination of the parameters of the normal state in doped yttrium high-temperature superconductors from thermopower coefficients in terms of different models of electron transport

The temperature dependences of the thermopower coefficient for two systems of doped yttrium high-temperature superconductors Y1 − x Pr x Ba2Cu3O y (x = 0.1−0.6) and Y1 − x Ca x Ba1.5La0.5Cu3O y (x = 0.05–0.30) have been analyzed using three models of electron transport, i.e., the Xin two-band model, the two-band model with an additional term linear in temperature, and the narrow-band model. For parameters of different models with a similar physical meaning, identical tendencies have been revealed in their variation with an increase in the dopant content. The mechanisms of influence of the dopants under investigation on the parameters of the band spectrum and the systems of charge carriers have been examined. It has been demonstrated that the revealed features of the dynamics of the Fermi level in the Y1 − x Ca x Ba1.5La0.5Cu3O y system are explained by the formation of an additional peak in the density of states upon doping with calcium, and the energy position of this peak is estimated.

Pressure Collapse of the Magnetic Ordering in MnSi via Thermal Expansion

The itinerant quasi-ferromagnetic metal MnSi has been studied by detailed thermal expansion measurements under pressures and magnetic fields. A sudden decrease of the volume at the critical pressure P c ∼1.6 GPa has been observed and is in good agreement with the pressure variation of the volume fraction of the spiral magnetic ordering. This confirms that the magnetic order disappears by a first order phase transition. The energy change estimated by the volume discontinuity on crossing P c is of similar order as the Zeeman energy of the transition from the spiral ground state to a polarized paramagnetic one under magnetic field. In contrast to the strong pressure dependence of the transition temperature, the characteristic fields are weakly pressure dependent, indicating that the strength of the ferromagnetic and the Dzyaloshinskii–Moriya interactions do not change drastically around P c . The evaluated results of the thermal expansion coefficient and the magnetostriction are analyzed thermodynamically. The Sommerfeld coefficient of the linear temperature term of the specific heat is enhanced just below P c . The magnetic field-temperature phase diagrams in the ordered and paramagnetic phases are also compared. Comparison is made with other heavy fermion compounds with first order phase transition at 0 K.