Temperature Hysteresis Effects Research Articles

Temperature hysteresis and relaxation effects in amorphous Fe-Ni-Zr alloys (abstract)

Amorphous Fe-Ni-Zr alloys in the ‘‘as quenched’’ and irradiated state have been studied with 57Fe Mössbauer spectroscopy and ac and dc susceptibility. Samples were irradiated by 14-MeV neutrons at room temperature to fluences of ≊1017 ns/cm2 corresponding to a dpa of 3×10−4 at the Lawrence Livermore National Laboratory RTNS-II facility. Two samples (Fe89.7Ni0.3Zr10 and Fe70Ni20Zr10) ‘‘as quenched’’ and irradiated, have been studied between room temperature and ≊4 K. ac susceptibility shows reentrant magnetic behavior for both alloys. Temperature hysteresis (no applied fields) is observed initially in the Mössbauer spectra for both alloys, ‘‘as quenched’’ and irradiated. It decreases and virtually disappears after a few thermal cycles between 20 K and room temperature. Relaxation effects are present in the magnetic hyperfine spectra of both alloys, ‘‘as quenched’’ and irradiated. The usually assumed proportionality between the magnetic hyperfine splitting and the magnetization is probably not valid for these alloys.

Temperature hysteresis and time-dependent effect in the initial susceptibility of rapidly solidified Monel (abstract)

The temperature dependence of the ac susceptibility for a Cu-Ni alloy near the Monel composition (28 at. % Cu) was previously reported.1 A careful recording of this temperature dependence revealed the existence of temperature hysteresis for both the as-spun condition and after various isothermal anneals. The hysteresis is exhibited by higher susceptibility values during the cooling-down period compared to the warming up. The difference exists over the entire temperature range, though it is most pronounced around the peak. The peak for the as-spun sample is broader and therefore the effect is more clearly observed there. The time dependence decrease of the ac susceptibility was followed at room temperature for both the as-spun and the annealed samples and was found to have a long time constant. The decrease could be abruptly generated by ‘‘shaking’’ the sample with an external disturbing magnetic field. The hysteresis is attributed to the fact that above the peak and just below the Curie temperature, the sample is magnetically soft and is magnetized parallel or antiparallel to the alternating small magnetic field. Due to relaxation effects below the ac susceptibility peak (and the corresponding increase of the anisotropy), the direction of the magnetization tends to rotate to the local easy direction, but since the relaxation time constant is long compared to the measuring period, it partially retains its previous direction and thus the susceptibility remains higher during the cooling duration. The anisotropy keeps it at the lower value when the temperature is increased again.2

Investigation of human erythrocyte ghost membranes with intramolecular excimer probes

Human erythrocyte ghost membranes have been investigated using two intramolecular excimer probes, di(1-pyrenyl)propane and di(1-pyrenylmethyl) ether. Values for the viscosity of the direct probe environment in the ghost membranes range from 76 cP at 37°C to 570 cP at 5°C, as reported for di(1-pyrenyl)propane, with liquid paraffin as the reference solvent. For the activation energy of the excimer formation process, determined here mainly by the viscosity of the medium, a value of 37 kJ/mol is obtained. The other probe molecule reports a higher local viscosity, 133 cP at 37°C, as well as a higher activation energy of excimer formation, 54 kJ/mol. Neither thermotropic phase transitions nor temperature hysteresis effects are observed within the temperature range (0 to 40°C) studied. From the vibrational structure of the fluorescence spectrum of di(1-pyrenylmethyl) ether, a polarity of the probe environment close to that of hexanol ( ϵ = 13.3) results for the erythrocyte ghost membranes. The polarity measured in egg phosphatidylcholine membranes and in multibilayers of dimyristoylphosphatidylcholine is slightly larger, comparable to that of butanol ( ϵ = 17.5), whereas a polarity comparable to that of methanol ( ϵ = 32.7) is observed for aqueous micellar solutions of sodium dodecyl sulphate. Further, from the wavelength shifts in the absorption spectrum of di(1-pyrenyl)propane and di(1-pyrenylmethyl) ether, the polarizability of the probe surroundings can be determined, leading to a surprisingly high value for the apparent refractive index. This is attributed to a high local density of the direct environment of the probe, for which a location between the membrane/water interface and the unpolar bilayer mid-plane is deduced.

Temperature hysteresis effects in the dissipation of flow and superfluid density in 3He-A

Large scale temperature hysteresis effects have been observed in flowing superfluid 3He-A. On cooling 3He-A the flow acts as if it were “more superfluid” than on warming. This is observed in both the superfluid density and the dissipation present in the flow, and does not depend on whether the B transition occurs.

Hydrogen Annealed Nitride/Oxide Dielectric Structures for Radiation Hardness

In this paper we present a study of the influence of processing on low temperature (77°K) radiation effects in nitride/oxide dielectric structures used as an active gate insulator of an MIS device. We have shown that flatband shifts of less than -1.5 volts are obtained following 106 Rad: Si Co60 exposure performed at 77°K on 750Å nitride structures (as long as the oxide were less than 100Å). We have also detected a low temperature hysteresis effect caused by trapping. This hysteresis is removed by hydrogen anneals of the nitride after the last high temperature processing step seen by the uncovered insulator.

Nuclear magnetic resonance and light scattering studies of the aggregation of dipalmitoyl-phosphatidylcholine-Benzene systems

Magnetic resonance, light scattering measurements and visual observations have been performed on lecithin-benzene systems as a function of temperature from 80 to −60°C and concentration from n = n benzene /n DPPC = 3−200 . From these measurements the transition curves from micellar solution to the crystalline state were deduced. More than 5 benzene molecules per lecithin molecule are necessary to get a micellar solution. Both the size of crystallites and the distribution of pores in the crystalline state depend on the rate of cooling and history. For the crystal structure a biporous model is suggested. At about 0°C the bulk of the benzene freezes, but a small amount of about 3 benzene molecules per lecithin molecule remains unfrozen to about −50°C. The systems studied show considerable temperature hysteresis and ageing effects. Small amounts of water of one to two water molecules per lecithin molecule drastically change the properties of the lecithin systems.

Development of a minature pCO2 electrode for biomedical applications.

A miniaturepCO2 electrode for possible CO2 measurement in a biological system was constructed and evaluated. ThepCO2 electrode employed a miniature pH glass electrode and the Severinghaus configuration. The electrode was evaluated in both gas and liquid phases. A good linear relation existed between the measured electrode potential of thepCO2 electrode and the logarithm of the CO2 concentration at 20°C in both gas and liquid phases. The temperature dependence of the electrode over the temperature range of 20–60°C was evaluated. From 20 to 40°C, a change of CO2 of 0·15%/°C at a CO2 level of 9·6 mole% was observed. The response time,pCO2 and temperature-hysteresis effects, and long-term stability of thepCO2 electrode were also investigated and discussed.

Development of a miniature pH glass electrode with field-effect-transistor amplifier for biomedical applications.

A miniaturepH glass electrode for possible clinical and biomedical applications was constructed and evaluated in referencepH buffer solutions at 36°C. A field-effect-transistor (f.e.t.) amplifier was integrated into the system, and its effectiveness was investigated. The average e.m.f. efficiency of the developed electrode was 0·87±0·11V, and a minimum length of 7 mm was required for a goodpH response. Temperature dependence of the electrode was −1·51 mV/oK at apH of 7. Evaluation of the stability of the electrode showed a 1% drift over a 7 h operational time. ThepH and temperature hysteresis effects showed 0·5% and 1·0% deviations, respectively. The response time was within 4 s for 99% response. These electrode characteristics were also investigated in blood plasma and discussed.

Sorption and diffusion in crystalline elastomers. Part I. Solubility of isomeric hydrocarbons in stretched rubber

AbstractThe solubility coefficients of n‐ and isobutane for stretched crosslinked natural rubber have been measured for simple elongations of 0–400% in the temperature range 30–50°C. To minimize the effect of penetrant on the degree of crystallinity, regions of low concentration were chosen. The sorptive capacity of the rubber was not significantly altered by elongation until the extension was sufficient to permit crystallization to take place. For both stretched and unstretched samples temperature—hysteresis effects were absent and Henry's law was obeyed. The data indicate that the difference in solubility between stretched and unstretched rubber can be taken as a measure of the degree of crystallinity. A slight decrease in the solubility over extended periods of time was attributed to a corresponding slow increase in the degree of crystallinity. The dependence of the degree of crystallinity on temperature and elongation was well represented by that deduced from Flory's theory of strain‐induced crystallization.

A Superconducting Alloy with Resistance Temperature Hysteresis

IN some experiments made in collaboration with J. F. Allen and J. O. Wilhelm, we found that the resistance of a ternary alloy of bismuth, lead, and tin dropped slowly with temperature in the usual manner down to 9° K., where it suddenly fell to zero. On raising the temperature, the alloy remains superconducting up to a temperature of 13.2° K., at which point the resistance reappeared and rose quickly to a steady value at 13.8° K. This would appear to be the first time that a resistance temperature hysteresis effect has been observed and measured.