Delta Tc Research Articles

Evaluation of physical hardening and oxidative aging effects on Delta Tc of asphalt binders

The Delta T c ( Δ T c ) is a rheological parameter for asphalt binders, which has been adopted in the past years by many highway agencies in North America for asphalt binder selection. In this study, the effects of the low-temperature physical hardening and oxidative aging on Δ T c are experimentally investigated and analysed. The experimental study is performed on both plain and polymer-modified binders. The results show that both physical hardening and oxidative aging have strong effects on decreasing Δ T c . An approximate linear relationship is identified between Δ T c and rheological parameters, such as the creep stiffness (S) and the m-value. The linear relationship is theoretically explained by analytical derivation. Based on the linear relationship, a graphical method is proposed for interpreting Δ T c using the log(S)-m diagram. By this method, it is found that polymer modification increases the susceptibility of Δ T c to oxidative aging, while it does not significantly affect the susceptibility of Δ T c to physical hardening.

Individual variability in achievement of short-term heat acclimation during a fixed intensity protocol

IntroductionHeat acclimation (HA) occurs with ∼8-10d of repeated heat exposure; however, adaptations can occur earlier (<7d; termed short-term heat acclimation; STHA). PurposeTo test the hypothesis that some, but not all, young healthy men would achieve STHA after 5d of a standard HA protocol. MethodsWe conducted a novel, post-hoc analysis of data from 13 healthy men (21 ± 3 yrs; 173 ± 8 cm; 75.1 ± 12.2 kg) who participated in an 8d HA protocol (120 min treadmill walking: 5 km h−1, 2% grade; 40 °C, 40% relative humidity). Core temperature (Tc), heart rate (HR), and whole body sweating rate (SR) were compared across 1d, 5d, and 8d of HA. Criteria for HA were delta (Δ)Tc ≤ 0.9 °C and ΔHR≤33 beats·min−1. ResultsGroup averages on 1d, 5d, and 8d of HA for end exercise Tc (38.1 ± 0.34; 37.9 ± 0.3; 37.8 ± 0.3 °C) and HR (134 ± 17; 122 ± 13; 121 ± 13 beats·min−1) were decreased by 5d (p < 0.05) and did not decrease further by 8d. ΔTc (1.1 ± 0.36; 0.95 ± 0.45; 0.95 ± 0.33 °C) and ΔHR (36 ± 18; 33 ± 17; 33 ± 15 beats·min−1) showed similar patterns (p > 0.05). At 5d, 31% (4/13) of the volunteers achieved HA; the remaining 9 volunteers had further adaptations between 5d and 8d. SR was not different across 1d, 5d, and 8d (860 ± 148; 908 ± 210; 873 ± 203 mL h−1 respectively; p > 0.05). ConclusionOur results suggest that during a fixed-intensity HA protocol in young men, using criteria of changes in Tc and HR, ∼1/3 achieve STHA. Future research should evaluate potential mechanisms, and whether similar inter-individual variability occurs in women.

The Influence of a New Food Waste Bio-Oil (FWBO) Rejuvenating Agent on Cracking Susceptibility of Aged Binder and RAP

This research aims to deliver a new promising asphalt binder rejuvenator developed from food waste to mitigate the effects of aging on the asphalt. The research relied on three different binders: two unmodified PG 64–22 binders and a Polymer Modified (PMA) PG 76–22 binder. Moreover, a field-extracted RAP binder is utilized in evaluating the rejuvenator’s efficiency. For this study, the proposed food waste bio-oil (FWBO) is compared against two market-available rejuvenators. The experimental program relied on aging control binder samples for each asphalt type with no rejuvenation using the Rolling Thin Film Oven (RTFO) test, followed by the Pressure Aging Vessel (PAV) test for 20 hours to create an Artificial RAP (ARAP) binder. Then, ARAP and RAP binders were blended with 5% by their weight with one of the two on-market rejuvenators (#1, #2) or the proposed FWBO rejuvenator. Testing results reveal that low-temperature relaxation was significantly improved for all the investigated samples after an additional PAV aging cycle, as Delta Tc values increased compared to the control binders. Further, samples’ master curves were used to calculate the Glover–Rowe (G-R) parameter, crossover frequency, and modulus (ωc, Gc*). The results clearly showed the ability of the FWBO to reduce the aging rate and improve the rheological properties of RAP binders. Further, the Fourier Transform Infrared Spectroscopy (FTIR) test showed that the new FWBO rejuvenator reduces the oxidation levels of the aged RAP binders, as suggested by the carbonyl index.

Superconducting spin-valve effect in heterostructures with ferromagnetic Heusler alloy layers

The transport properties of two types of spin valves are analyzed, in which the Heusler alloy Co2Cr1-xFexAly was used as one of the two ferromagnetic layers in the F1/F2/S structures. The Heusler alloy layer was used: 1) as a weak ferromagnet, in the case of the F2 layer; 2) as a halfmetal, in the case of the F1 layer. In the first case, a large classical effect of the superconducting spin valve Delta Tc was obtained, which was facilitated by a significant triplet contribution to the effect of the superconducting spin valve Delta Tctrip. In the second case, a gigantic effect value Delta Tctrip was found reaching 0.5 K. Keywords: superconductivity, ferromagnetism, thin films, superconducting spin valve.

Examining Different Alternatives to Delta Tc (ΔTc) as a Parameter to Screen Asphalt Binders

Abstract The Superpave performance grading (or PG) framework or a variation of this framework is often used as a purchase specification in the United States and as a tool to evaluate the expected performance of modified and unmodified asphalt binders in many countries around the world. During the last decade and in response to changes in the use of modified binders and extenders, several modifications and improvements have been proposed and implemented to improve this framework. One such modification is the use of the ΔTc parameter, which is based on the stiffness and m-value of an asphalt binder measured at low temperatures, as a metric to screen asphalt binders that contain higher concentrations of potentially deleterious refining products or as an indicator for susceptibility to premature cracking. The estimation of this parameter requires the determination of the true low temperature grade of the asphalt binder based on measurements carried out using a bending beam rheometer at multiple temperatures. This study explores the expected variability associated with the determination of this parameter as well as alternative metrics that can be more easily used on a routine basis as a quality control tool to screen binders with a low ΔTc value. Based on the evaluation of nearly 200 binders from several different suppliers in and around the state of Texas, this study shows that a combined use of stiffness and m-value measured at the low grade test temperature of the asphalt binder can be used as an effective specification/screening tool to detect binders that result in a very low value of ΔTc.

Evaluating the Physical and Rheological Properties of Rejuvenated Styrene‐Butadiene‐Styrene‐Modified Asphalt Binders

To evaluate the physical and rheological properties of rejuvenated styrene‐butadiene‐styrene‐modified asphalt (SBSMA) binders designed for rapid in‐place pavement recycling, an aged SBSMA binder was rejuvenated with three rejuvenators (i.e., Types I, II, and III) in different dosages. The physical properties of rejuvenated SBSMA were obtained to determine the optimal type and dosage of rejuvenators for the first and second rejuvenation. Performance grade (PG) tests, multiple stress creep recovery (MSCR) tests, and linear amplitude sweep (LAS) tests were conducted to measure the rheological properties using the dynamic shear rheometer (DSR) and bending beam rheometer (BBR). The results exhibited that the rejuvenators could soften the multiple aged binder and enhance its high‐ and low‐temperature performance. The rejuvenation effect of rejuvenator Type I with the optimal dosage of 6∼8% was the most appropriate for the first rejuvenation. The optimal dosage of the second rejuvenation was 10∼12%. The addition of rejuvenators decreased the rutting factor (G∗/sin δ), creep stiffness (S), delta Tc (ΔTc) parameter, recovery response (R), and yield stress of rejuvenated SBSMA. On the other hand, an increase in the rate of relaxation (m-value), nonrecoverable creep compliance (Jnr), and yield strain of rejuvenated SBSMA was recorded. Overall, the study findings indicated an improvement in the elastic properties of rejuvenated SBSMA, which contributes to improving the rutting, thermal, and fatigue cracking resistance of asphalt binder and ultimately the response of asphalt pavements.

A solvent free method to characterize the effect of recycled asphalt shingles on virgin asphalt binder

Abstract: The current design guideline of asphalt mixtures containing recycled asphalt shingles requires accurate characterization of shingle binder and its effect on virgin binder. This characterization employs hazardous solvents to extract and recover the shingle binder prior to testing. The objective of this study was to determine whether an enhanced mortar characterization method, which eliminates the need for chemical solvents by testing mortars composed of virgin binder and fine shingle fraction, can be used to predict the rheological properties of shingle binder blends with virgin binder. Superpave binder tests (dynamic shear rheometer and bending beam rheometer) were performed on six mortars combinations of two shingle sources and three virgin binders. The change in true grade of virgin binders caused by shingle binder was quantified by using a parameter named grade change rate (°C/%shingle binder). True grades of shingle binder blends predicted by grade change rate were compared to values measured on manually-prepared binder blends at multiple binder replacement rates of 15%, 30% and 100%. High and low temperature grades measured on blended binders were successfully predicted by the enhanced mortar approach. Moreover, the critical low-temperature parameter (delta Tc), which has been used to describe the embrittlement introduced by shingle binder, was also accurately predicted by using the stiffness-based and relaxation-based grade change rate. In conclusion, the enhanced mortar approach not only provides accurate estimates of the rheological properties of binder blends, but also eliminates the exposure to hazardous solvents currently employed during the extraction and recovery of the recycled binder.

The Effect of Time of Day on Cold Water Ingestion by High-Level Swimmers in a Tropical Climate

The authors tested the effect of cold water ingestion during high-intensity training in the morning vs the evening on both core temperature (TC) and thermal perceptions of internationally ranked long-distance swimmers during a training period in a tropical climate. Nine internationally ranked long-distance swimmers (5 men and 4 women) performed 4 randomized training sessions (2 in the evening and 2 in the morning) with 2 randomized beverages with different temperatures for 3 consecutive days. After a standardized warm-up of 1000 m, the subjects performed a standardized training session that consisted of 10 x 100 m (start every 1'20″) at a fixed velocity. The swimmers were then followed for the next 3000 m of the training schedule. Heart rate (HR) was continuously monitored during the 10 x 100 m, whereas TC, thermal comfort, and thermal sensation (TS) were measured before and after each 1000-m session. Before and after each 1000 m, the swimmers were asked to drink 190 mL of neutral (26.5 ± 2.5°C) or cold (1.3 ± 0.3°C) water packaged in standardized bottles. Results demonstrated that cold water ingestion induced a significant effect on TC, with a pronounced decrease in the evening, resulting in significantly lower mean TC and lower mean delta TC in evening cold (EC) than in evening neutral (EN), concomitant with significantly lower TS in EC than in EN and a significant effect on exercise HR. Moreover, although TC increased significantly with time in MN, MC, and EN, TC was stabilized during exercise in EC. To conclude, we demonstrate that a cold beverage had a significant effect on TC, TS, and HR during training in high-level swimmers in a tropical climate, especially during evening training.

Template engineering of Co-doped BaFe2As2 single-crystal thin films

Understanding new superconductors requires high-quality epitaxial thin films to explore intrinsic electromagnetic properties and evaluate device applications. So far, superconducting properties of ferropnictide thin films seem compromised by imperfect epitaxial growth and poor connectivity of the superconducting phase. Here we report new template engineering using single-crystal intermediate layers of (001) SrTiO(3) and BaTiO(3) grown on various perovskite substrates that enables genuine epitaxial films of Co-doped BaFe(2)As(2) with a high transition temperature (T(c,rho=0) of 21.5 K, where rho=resistivity), a small transition width (DeltaT(c)=1.3 K), a superior critical current density J(c) of 4.5 MA cm(-2) (4.2 K) and strong c-axis flux pinning. Implementing SrTiO(3) or BaTiO(3) templates to match the alkaline-earth layer in the Ba-122 with the alkaline-earth/oxygen layer in the templates opens new avenues for epitaxial growth of ferropnictides on multifunctional single-crystal substrates. Beyond superconductors, it provides a framework for growing heteroepitaxial intermetallic compounds on various substrates by matching interfacial layers between templates and thin-film overlayers.

Diet‐induced Changes in Intra‐abdominal Adipose Tissue and CVD Risk in American Women

The aim of the study was to determine what effect weight loss had on intra-abdominal adipose tissue (IAAT) and cardiovascular disease (CVD) risk in 135 premenopausal overweight African-American (AA) and European-American (EA) women matched for BMI. Blood lipids, systolic blood pressure (SBP), diastolic BP (DBP), and IAAT (computed tomography determined) were examined prior to and after an 800 kcal/day diet producing 12 kg-weight loss. Significant decreases in IAAT (approximately 38%), total cholesterol (TC; 3%), low-density lipoproteins (LDLs: 6%), triglycerides (TGs: 27%), cholesterol/high-density lipoprotein ratio (C/HDL ratio: 18%), SBP (3%), and DBP (3%) occurred while HDL increased (16%), following weight loss and 1 month energy balance. Significant interactions between time and race showed that AA women decreased TG and increased HDL proportionately less than EA women. After adjusting for Delta IAAT, none of the CVD variables significantly changed after weight loss with the exception of HDL and C/HDL ratio. After adjusting for Delta LF (leg fat), Delta TC, Delta TG, Delta LDL, and Delta C/HDL ratio were significantly different. Multiple regression showed that independent of each other, Delta IAAT was significantly and positively related to Delta TC (adjusted beta = 0.24) and Delta TG (adjusted beta = 0.47), and Delta LF was negatively related to Delta TC (adjusted beta = -0.19) and Delta TG (adjusted beta = -0.18). Overweight and premenopausal AA and EA women benefitted from weight loss by decreasing IAAT and improving CVD risk. The changes in IAAT were significantly related to blood lipids, but loss of LF seems to be related to reduced improvement in TC and TG. Based on these results, interventions should focus on changes on IAAT.

Ambient-pressure synthesis of single-crystalMgB2and their superconducting anisotropy

We synthesized single crystalline and policrystalline MgB_2 under ambient pressures. The single crystals of MgB_2 were of good quality, where the crystal structure refinements were successfully converged with R = 0.020. The specific heat of policrystalline MgB_2 samples has been measured in a temperature range between 2 and 60 K in magnetic field up to 6 T. The measurement gave the coefficient of the linear term in the electronic specific heat, gamma = 3.51 mJ/K^2 mol, and the jump of the specific heat, 2.8 mJ/K^2 mol at 38.5 K. It is shown from the analysis of the specific heat that the electronic specific heat in the superconducting state differs largely from the conventional BCS weak coupling theory. From the results of measurements of the magnetic properties on single crystal samples, we found a sharp superconducting transition at 38 K with transition width Delta Tc = 0.8 K and the superconducting anisotropy ratio gamma increasing from about 1 near Tc to 4.0 at 25 K.

Exact local exchange potential from Fock equations at vanishing coupling constant, and delta Tc/ delta n from wave-function calculations at full coupling constant.

Consider H${\mathrm{^}}_{\ensuremath{\lambda}}$=T^+\ensuremath{\lambda}V${\mathrm{^}}_{\mathit{ee}}$+${\ensuremath{\sum}}_{\mathit{i}=1}^{\mathit{N}}$${\mathit{v}}_{\ensuremath{\lambda}}$(r${\ensuremath{\rightarrow}}_{\mathit{i}}$), where, in atomic units, T^=${\ensuremath{\sum}}_{\mathit{i}=1}^{{\mathit{N}}^{\mathrm{\ensuremath{-}}}}$1/2${\mathrm{\ensuremath{\nabla}}}_{\mathit{i}}^{2}$ and V${\mathrm{^}}_{\mathit{ee}}$=${\ensuremath{\sum}}_{\mathit{i}}$${\ensuremath{\sum}}_{\mathit{j}\mathrm{\ensuremath{\gtrsim}}\mathit{i}}$\ensuremath{\Vert}r${\ensuremath{\rightarrow}}_{\mathit{i}}$-r${\ensuremath{\rightarrow}}_{\mathit{j}}$${\mathrm{\ensuremath{\Vert}}}^{\mathrm{\ensuremath{-}}1}$ and the local-multiplicative potential ${\mathit{v}}_{\ensuremath{\lambda}}$ is constructed to keep n, the Hartree-Fock density of H${\mathrm{^}}_{\ensuremath{\lambda}}$, independent of the coupling constant \ensuremath{\lambda}. Moreover, n is simultaneously the exact physical ground-state density of interest and ${\mathit{v}}_{\ensuremath{\lambda}=0}$ is its Kohn-Sham potential. For the purpose of extracting the exact Kohn-Sham exchange potential ${\mathit{v}}_{\mathit{x}}$([n];r\ensuremath{\rightarrow}), it is shown that ${\mathit{v}}_{\mathit{x}}$([n];r\ensuremath{\rightarrow})=-\ensuremath{\partial}${\mathit{v}}_{\ensuremath{\lambda}}$([n];r\ensuremath{\rightarrow})/\ensuremath{\partial}\ensuremath{\lambda}${\mathrm{\ensuremath{\Vert}}}_{\ensuremath{\lambda}=0}$-\ensuremath{\int}[ n(r\ensuremath{\rightarrow}\ensuremath{'})/\ensuremath{\Vert}r\ensuremath{\rightarrow}-r${\ensuremath{\rightarrow}}^{\ensuremath{'}}$\ensuremath{\Vert}]${\mathit{d}}^{3}$${\mathit{r}}^{\ensuremath{'}}$. The correlation potential for n(r\ensuremath{\rightarrow}) is then obtained by subtracting the above ${\mathit{v}}_{\mathit{x}}$ from the exact exchange-correlation potential for n(r\ensuremath{\rightarrow}). Furthermore, it is shown that the potential ${\mathit{w}}_{\ensuremath{\lambda}}$(r\ensuremath{\rightarrow}), which keeps the exact ground-state density of T^+\ensuremath{\lambda}V${\mathrm{^}}_{\mathit{ee}}$+${\ensuremath{\sum}}_{\mathit{i}=1}^{\mathit{N}}$${\mathit{w}}_{\ensuremath{\lambda}}$(r${\ensuremath{\rightarrow}}_{\mathit{i}}$) independent of the value of \ensuremath{\lambda}, determines the functional derivative of ${\mathit{T}}_{\mathit{c}}$[n] with respect to the density, i.e., the kinetic contribution to the correlation potential ${\mathit{v}}_{\mathit{c}}$, \ensuremath{\delta}${\mathit{T}}_{\mathit{c}}$[\ensuremath{\rho}]/\ensuremath{\delta}\ensuremath{\rho}(r\ensuremath{\rightarrow})${\mathrm{\ensuremath{\Vert}}}_{\mathrm{\ensuremath{\rho}}=\mathit{n}}$=${\mathit{v}}_{\mathrm{xc}}$([n];r\ensuremath{\rightarrow})+\ensuremath{\int}n(r\ensuremath{\rightarrow}\ensuremath{'})${\mathit{d}}^{3}$${\mathit{r}}^{\ensuremath{'}}$/\ensuremath{\Vert}r\ensuremath{\rightarrow}-r${\ensuremath{\rightarrow}}^{\ensuremath{'}}$\ensuremath{\Vert}-\ensuremath{\partial}${\mathit{w}}_{\ensuremath{\lambda}}$([n];r\ensuremath{\rightarrow})/\ensuremath{\partial}\ensuremath{\lambda}${\mathrm{\ensuremath{\Vert}}}_{\ensuremath{\lambda}=1}$. \textcopyright{} 1996 The American Physical Society.

Suppression of phase separation in quenched turbulent binary liquids

Giving importance to the active participation of concentration fluctuations in the dynamics, a phenomenological model is proposed to describe the experimentally observed suppression of phase separation when a turbulent binary fluid mixture is quenched below its consolute point Tc. It is assumed that an inverse cascade of concentration fluctuations is acted upon by the turbulence-generated viscous shear together with a loss due to the presence of Alfven-like waves, which cuts off the inverse cascade at some scale. As a consequence, The apparent depression of critical temperature follows the power law Delta Tc approximately Rlambda with lambda =1.44 and 2.4 in two extreme theoretical limits (R=Reynolds number). This result is comparable to the experimental values of 1.4 and 2.1 in two different measurements.

Morphometric influences on intraoperative core temperature changes.

Intraoperative core hypothermia develops in three characteristic phases: 1) core-to-peripheral redistribution of body heat that is most prominent during the first hour after induction of anesthesia; 2) subsequent slow linear decrease in core temperature resulting largely from heat loss exceeding metabolic heat production; and 3) core temperature plateau resulting when thermoregulatory vasoconstriction decreases cutaneous heat loss and constrains metabolic heat to the core thermal compartment. Accordingly, we tested the hypotheses that: 1) core cooling does not depend on body fat (BF) or the ratio of weight-to-surface area (Wt/SA) during the initial redistribution phase; 2) the core cooling phase; 2) the core cooling rate is a function of the Wt/SA ratio during the second phase; and 3) the rate of core cooling during the plateau phase (after vasoconstriction) will be determined by the percentage of BF. In 40 patients undergoing elective colon surgery, the amount of redistribution hypothermia was inversely proportional to the percentage of BF (delta TC = 0.034.BF-2.2, r2 = 0.63) and the Wt/SA ratio (delta TC = 0.052.Wt/SA-3.35, r2 = 0.66). The core cooled linearly during the second phase, and the cooling rate was inversely proportional to the Wt/SA ratio (rate = 0.035.(Wt/SA)-2.2, r2 = 0.29). Thermoregulatory vasoconstriction was effective in virtually all patients independent of their morphology, and produced a four-fold reduction in the core cooling rate. These results indicate that patient morphometric characteristics substantially influence intraoperative core temperature changes, and that the effect depends on the hypothermia phase.

Mechanism of superconductivity in K3C60.

Using electronic states and phonon states from the first-principles calculations and including both conventional electron-phonon charge coupling and Jahn-Teller coupling, we predict Tc and other superconducting properties. The only adjustable parameter in the theory is the screening length, Rsc. Using Rsc = 0.8-1.0 A, we find excellent agreement with experiment for Tc (16-18 K), pressure dependence of Tc (Delta Tc = -6 to -10 K for 1 GPa), and 12 C to 13 C isotope shift (alphaC = 0.2); experimental values: 19 K, -7 K, and 0.3, respectively.

YBa2Cu3Ox epitaxial films prepared by RF magnetron sputtering: deposition mechanisms, structure and superconducting properties

YBa2Cu3Ox epitaxial films on (100) MgO crystal splits have been prepared by off-axis RF magnetron sputtering. Two deposition mechanisms of epitaxial film growth, atomic and molecular, have been observed at different deposition pressures. YBa2Cu3Ox films have Tco=81-85 K, Delta Tc=3-5 K and c-axis lattice parameter c=11.70-11.82 AA, depending on deposition conditions. Possible reasons for c-axis expansion have been considered. Expansion of the c-axis lattice parameter at low deposition pressure is explained by crystal defects due to inhomogeneous oxygen distribution in the YBa2Cu3Ox crystal structure. Epitaxial films with perfect structure and the best superconducting properties grow under molecular mechanism conditions and the absence of significant high energy particle bombardment.

Anomalies in elastic and thermal properties associated with the superconducting transition of single crystal Bi2Sr2CaCu2Oy

The authors have measured the in-plane Young's modulus sound velocity ve(T) at kHz frequencies and the specific heat Cp(T) of Bi2Sr2Ca1Cu2Oy single crystals with Tc=93.2 K. In the region of Tc a softening is observed in ve, corresponding to a discontinuity in dlnve/dT of 6.2 ppm/K and an indication of a change of Delta ve/ve of the order of 10 ppm. From Delta Cp/Tc approximately=16 mJ/(molK2) they find mod delta Tc/ delta sigma i mod approximately=0.1 K/kbar and - delta 2Tc/ delta sigma 12 approximately=10-3-10-2 K/kbar2 (i=1,2).

Processing and microstructure of highly dense Ba2LnCu3O7 prepared from co-precipitated oxalate powder

Sub-micrometre-size powders with good homogeneity and reactivity were synthesised by an ethanol-aided co-precipitation method with an oxalic acid precipitant for the superconducting system (Ba2LnCu3O7- delta ; Ln=Y, La, Ho, Dy). Sintering of these powders was carried out in flowing oxygen at temperatures between 900 and 1050 degrees C. A sintered density as high as 98.5% of the theoretical value has been achieved at 1020 degrees C for the Y system and 98% for the La, Dy and Ho systems. A prolonged annealing, as long as three weeks in flowing oxygen, was needed to attain the zero-resistivity critical temperature Tczero=92 K for the highly dense Y system. A sharp superconducting transition, Delta Tc=0.5 K, was then obtained as defined by a 10-90% resistive transition. An exaggerated grain growth was observed at 1000 degrees C and above.

The effect of isotopic substitution on the α-α' phase transition in metal-hydrogen systems

The observed decrease of the optic mode frequency of H with H/Pd measured by inelastic neutron scattering is employed to derive expressions for Delta Tc=TcH-TcD and for the isotope effect in the two-phase coexistence region of miscibility-gap metal-hydrogen systems. The results are expected to be of general validity for miscibility-gap metal-H systems, i.e. Delta Tc=Tcx-Tcy>0 where x and y are the light and heavy isotopes, respectively, and RTln(Py2/Px2)plat-RTln(py2/px2)r to o>0.

Iron impurity in Chevrel phases: determination methods and influence on superconductivity

The dependence of critical temperature Tc on pressure P and iron concentration x was measured for FexSnMo6S8. The iron concentration was determined by activation analysis. The variation of Tc(x) is similar to that predicted by Abrikosov and Gorkov (1960). The critical concentration is xcr=0.061 (0.42. at.%). For x=0.04, delta Tc/ delta P is three times higher in absolute value than for x=0 and reaches -3.2*10-4 kbar-1. The variation of Tc(P) is not linear and may be explained by the pressure-enhanced exchange interaction of electrons with the magnetic moment of the impurity atoms.