Critical Temperature Rise Research Articles

Persistence of superconductivity in niobium ultrathin films grown on R-plane sapphire

We report on a combined structural and electronic analysis of niobium ultrathin films (from 2 to 10 nm) deposited in ultrahigh vacuum on atomically flat R-plane sapphire wafers. A textured polycrystalline morphology is observed for the thinnest films, showing that heteroepitaxy is not achieved under a thickness of 3.3 nm, which almost coincides with the first measurement of a superconducting state. The superconducting critical temperature rise takes place on a very narrow thickness range, of the order of a single monolayer (ML). The thinnest superconducting sample (3 nm/9 ML) has an offset critical temperature above 4.2 K and can be processed by standard nanofabrication techniques to generate air- and time-stable superconducting nanostructures, useful for quantum devices.

Thermal stability analysis of circular functionally graded sandwich plates of variable thickness using pseudo-spectral method

In the present study, the thermal stability of laminated functionally graded (FGM) circular plates of variable thickness subjected to uniform temperature rise based on the first-order shear deformation plate theory is presented. Furthermore, two models for FGM plates with variable thickness, corresponding with two manufacturing methods, are proposed. The laminated FGM plate with variable thickness is considered as a sandwich plate constituted of a homogeneous core of variable thickness and two constant thickness FGM face sheets whose material properties are assumed to be graded in the thickness direction according to a simple power law. In order to determine the distribution of the prebuckling thermal load along the radius, the membrane equation is solved using the shooting method. Subsequently, employing the pseudo-spectral method that makes use of Chebyshev polynomials, the stability equations are solved numerically to evaluate the critical temperature rise. The results demonstrate that the thermal stability is significantly influenced by the thickness variation profile, aspect ratio, the volume fraction index, and the core-to-face sheet thickness ratio.

Onset of Material Alterations Due to Laser-Induced Plasma Exposure in Nanofilms Deposited on Photomasks

Damage-free removal of sub-100 nm particles from photomasks with deposited nanofilms is a challenge in lithography. Laser-induced plasma (LIP) is an emerging noncontact, chemical-free, dry, and selective nanoparticle removal technique. Investigation of the onset of material alterations on bonded nanofilms for optimizing LIP particle removal process is the objective of this paper. Shockwave thermomechanical excitation and radiation heating from the plasma core are major potential sources of damage. Computational analyses reported here indicate radiation heating as the chief damage source. Damage thresholds for the critical nanofilm surface temperature rise and radial stress component have been identified for a given nanosecond pulsed laser.

Three-dimensional thermal buckling analysis of piezoelectric composite plates using thefinite layer method

The finite layer method is the most efficient numerical method for three-dimensionalanalysis of simply supported rectangular plates. Using this method, the three-dimensionalanalysis is transformed into one-dimensional analysis by virtue of the orthogonal propertiesof trigonometric interpolation functions. In the present study, the finite layer method isextended to the thermal buckling analysis of symmetrical cross-ply piezoelectric compositeplates with full coupling between the thermal, electrical and mechanical fields. Thepre-buckling state of the plate is assumed to be steady. Thus, the initial temperaturedistribution in the plate is independently determined based on the equation of heatconduction, and the associated thermal stresses are computed accordingly. The geometricalstiffness matrix is then formed in the same manner as in the elastic three-dimensionalbuckling analysis, and the critical temperature rise and buckling modes are obtained bysolving the related matrix equations. Numerical examples are presented to verify theproposed method. The critical temperature rise is determined for both the adiabaticand isothermal buckling processes. The thermal buckling behaviours of somepiezoelectric laminates and the effects of the thermo-electro-mechanical coupling are alsoinvestigated.

Impurities in two band model of superconductor order parameter anisotropy

The impurity concentration dependence of the superconducting transition temperature T c is studied within the framework of a two-band model of order parameter anisotropy. Both intraband and interband electron scattering by nonmagnetic and magnetic impurities are taken into account. It is demonstrated that at various values of model parameters, both types of impurity concentration dependence of T c are possible: weak dependence, typical of the model with s-wave order parameter, and strong suppression of T c by impurities with critical impurity concentration at which T c=0. It is found that in some cases there is a possibility of a rise of critical temperature with increasing impurity concentration. The obtained results are consistent with existing experimental data for the high-temperature superconductors.

Scuffing Failure of Hydrodynamic Bearings Due to an Abrasive Contaminant Partially Penetrated in the Bearing Over-Layer

Scuffing Failure of Hydrodynamic Bearings Due to an Abrasive Contaminant Partially Penetrated in the Bearing Over-Layer

Chemical structure of plasticizers, compatibility of components and phase equilibrium in plasticized cellulose diacetate

AbstractThe phase equilibrium of plasticized polymer systems on the basis of cellulose diacetate and ethylene glycol esters of dibasic aliphatic acids (from oxalic acid to 1,10‐decanedicarboxylic acid) was studied and the solubility parameters and the thermodynamic interaction parameters of the components were calculated. It is shown that an increase in molecular weight of the plasticizers leads to a lower miscibility of the components, a fact which is reflected in a regular rise of the upper critical solution temperature (UCST), a tendency of the systems for gelation, a decrease of the solubility parameter of the plasticizer δ1, and a growth of the interaction parameters χH and χ12. The results are discussed in terms of the existing theories for polymer solutions.

THE ROLE OF QUASI-ONE-DIMENSIONAL STRUCTURES IN HIGH-Tc SUPERCONDUCTIVITY

The critical exponents describing the decrease of correlation functions on long distances for the one-dimensional Hubbard model is obtained. The behaviour of correlators shows that Cooper pairs of electrons are formed. The electron tunneling between the chains leads to the existence of the anomalous mean values and to the superconductive current. The anisotropy of the quasi-one-dimensional system leads to the rise of critical temperature T c .

Elastic Instability of a Heated Annular Plate Under Lateral Pressure

On the basis of the dynamic version of the nonlinear von Karman equations, a theoretical analysis is performed on the elastic instability of a uniformly heated, thin, annular plate which has suffered a finite axisymmetric deformation due to lateral pressure. The linear free vibration problems around the finite axisymmetric deformation of the plate are solved by a finite-difference method. By examining the frequency spectrum with various asymmetric modes, the critical temperature rise under which the axisymmetric deformation becomes unstable due to the bifurcation buckling is determined, which is found to jump up to 7.2 times within a range of very small lateral pressure.

Critical temperature rise in a coolant in an annular channel

Critical temperature rise in a coolant in an annular channel

STUDIES ON SCORING OF SPUR GEARS : 3RD REPORT, EFFECT OF THE COEFFICIENT OF ADDENDUM MODIFICATION ON SCORING RESISTANCE

The scoring resistance of the Vau-Null gear pair whose centre distance is not changed by the variation of the amount of addendum modification was examined from the point of view of the critical surface temperature rise on the meshing faces of the gears, and the following correlations between scoring resistance and the amount of the addendum modification of the gears were clarified : (1) The position of the maximum surface temperature on the meshing faces of the Vau-Null gears is remarkable affected by the number of teeth of pinion, gear ratio, the coefficient of addendum modification of gears and module. (2) The effect of the coefficient of addendum modification on the surface temperature on the meshing faces is complicated, and the optimum value of the coefficient of addendum modification against the scoring resistance of gears is decided by gear ratio.

Limiting Loads for Scoring and Coefficient of Friction on a Disk-Machine : Effects of Lubricating Oil, Specific Sliding and Sliding Velocity, in the Case of Steel/Steel

Limiting Load for scoring and coefficient of friction, in the case of carburized and hardened steel, under various contact conditions of simultaneous rolling and sliding, were studied. Their characteristics were tested, changing widely the lubricating oils, sliding velocity and specific sliding. We got an approximate formula about the limiting load for scoring as a function of sliding velocity and specific sliding. The critical temperature rise by Blok was also discussed with our experimental results. Moreover we have compared the limiting load for scoring by means of FZG spur gear test and 4 ball test with our experimental results by means of our disk-machine.

Superconductivity in Dilute Alloys of TaS2with Fe

Single crystals of iron-doped Ta${\mathrm{S}}_{2}$ grown from sintered powders of composition ${\mathrm{Fe}}_{0.05}$-Ta${\mathrm{S}}_{2}$ show a rise in critical temperature to above 3 K and an enhanced anisotropy of ${H}_{c2}$ which is comparable to that observed in $2H$-Ta${\mathrm{S}}_{2}$${(\mathrm{pyridine})}_{\mathrm{\textonehalf{}}}$. Single crystals grown from ${\mathrm{Fe}}_{0.05}$${\mathrm{T}}_{0.95}$${\mathrm{S}}_{2}$ powders are stabilized in the $1T$ phase and are semiconducting at all temperatures below room temperature with no resistive anomaly at 200 K.

The safety of ultrasound in fetal monitoring

Since ultrasonic (Doppler) fetal monitoring systems are technically feasible, it is most important to establish whether repeated prolonged irradiations are safe to both the mother and the fetus. The safety of ultrasonic exposures was investigated in this study with particular regard to structural changes, congenital malformation, and chromosomal aberration. Intensity levels of 164, 272, 490, 1,050 mW. per square centimeter have been used at a frequency of 2.28 megahertz (MHz), for 5 or 60 minutes, either singly or for 5 consecutive exposures. At an intensity of 1,050 mW. per square centimeter, tissue damage was recorded proportional to the duration of exposure. Macroscopic and microscopic examinations including chromosomal analysis showed these tissue effects to be identical with those found in overheating. It has been found that an intensity level of 490 mW. per square centimeter did not cause critical tissue temperature rise. There were no pathologic findings on the macroscopic and microscopic examinations in the mothers, fetuses, and neonates, and no congenital malformations were recorded. Moreover, there were no pathologic findings in neonates of the third generation produced by brother-sister cross-mating from the fetuses which had been irradiated. All of the exposed mothers were able to conceive again, producing healthy offspring. Chromosome squash preparations were done from irradiated fetuses, revealing an equal incidence of chromosome aberrations as compared with that of the control group.

Self-heating and spontaneous ignition in the oxidation of gaseous hydrazine

The spontaneous ignition of gaseous mixtures of oxygen and hydrazine has been investigated in a 1 l. spherical vessel over the temperature range 690–770 K. Emphasis is placed on direct detection of pre-explosive self-heating in the reacting gas. Very fine thermocouples (made from 0.025 mm Pt and Pt-Rh wires) are used to follow temperature changes, and to map temperature-position profiles during oxidation: N2H4+ O2→ N2+ 2H2O, ΔH=–138 kcal mol–1.Unusually among gas-phase oxidations, this spontaneous ignition is clearly thermal in character. Strong self-heating is always observed. In accordance with a conductive theory of heat losses, temperatures are not uniform throughout the reactant but depend on the distance from the vessel centre, being greatest at the centre and least at the walls. The (approximately) parabolic form and the absence of any significant temperature-step at the walls confirm the absence of convection at the pressures concerned.A critical centre temperature rise exists above which stable reaction is impossible and ignition inevitable. Thermal theory predicts a critical value of 1.61 RT2a/E, i.e., about 70 K, under circumstances where reactant consumption can be ignored, and a value of 116 K when it is taken into account: the value observed here is 120 K.The hydrazine + oxygen system is more difficult to handle than some systems previously investigated and catalysis at the thermocouple is harder to eliminate. These effects, and the consequences of employing thermocouples of finite heat capacity, are also discussed.

Thermal effects accompanying spontaneous ignition in gases. IV. The decomposition of diethyl peroxide in a cylindrical vessel and the effect of diluents on self-heating

The investigation (see parts I to III) of the spontaneous ignition of gaseous diethyl peroxide as a thermal explosion is concluded by a series of experiments mainly in a cylindrical vessel, and including diluted mixtures. A very fine thermocouple (25 µ m diameter) has been used to probe the temperature distributions between the axis and the wall both in systems reacting subcritically and in systems on the verge of ignition. A multijunction thermocouple has also been employed to obtain instantaneous readings of distributed temperature in a spherical vessel. It is found that self heating is always present. In accordance with a conductive theory of heat losses, temperatures are not uniform throughout the reactant, but depend on the fractional distance ( z = r / r 0 ) from the vessel axis, being greatest at the axis and least at the walls. For the cylinder, the form of the profiles expected in a stationary state is ( T - T a )/( RT a 2 / E ) = 2 ln (1 + G )/(1 + Gz 2 ) and good agreement is found between theory and experiment. (The significance of G is discussed in the text.) This agreement, the symmetry of the profiles, and the absence of any temperature step at the walls confirm the absence of convection at the pressures concerned. A critical centre temperature rise exists above which ignition is inevitable. The greatest value of this increment is 23.3 K ; for simple theory, the predicted value is 19 K (1.39 RT a 2 / E ). Any temperature dependence of this critical increment lies beyond the discrimination of the present apparatus. Similar agreement is found between ‘measured’ and theoretically expected values for Frank-Kamenetskii’s δ . At criticality, the measured values average 2.25 against a theoretical value (uncorrected for finite vessel size or finite reaction rate) of 2 exactly. ‘Measured’ values for δ in subcritical systems are also in satisfactory accord with expectation. Other ‘indirect’ tests of thermal theory are also satisfied. Thus the curvature of the critical pressure limit (boundary on the p — T diagram between explosive and slow reaction) exactly corresponds to the activation energy measured in isothermal decomposition. Similar temperature-position profiles are found in diluted mixtures below criticality, and although critical explosion pressures depend on the degree of dilution, the critical temperature rise for ignition does not. The average value found is 19.0 K. Nor does the critical temperature gradient at the vessel boundary vary from the value ( — 2 exactly) predicted for any dilution of vessel geometry. There are the same influences on criticality as in the spherical vessel: in accord with stationary state conductive theory, thermal conductivity is the principal factor but its influence is distorted to varying degrees, first by the occurrence of dynamic heating accompanying gas entry, secondly by the rate of dissipation of this heating, which is governed by the thermal diffusivity, and thirdly by the departures from stationary state behaviour largely governed by the specific heat of the diluent. These influences explain an otherwise erratic dependence of critical ignition pressures on thermal conductivity.

The seaweedGracilaria confervoides, an important object for autecologic and cultivation research in the northern Adriatic Sea

1. The seaweedGracilaria confervoides Grev. is the only source of agar extraction in Italy. Large populations are present in the coastal lagoons of the Northern Adriatic Sea. In these habitats (e. g. Bay of Goro near Ferrara) periodical recordings were made during 1968 and 1969 of temperature, salinity, micronutrients, light intensity and O2 concentration. 2. The lagoon bays offer the best condition for the development ofGracilaria confervoides populations, especially near places of fresh water inflow containing large amounts of nutrients. Fresh water inflow also limits critical temperature rise during summer. 3. The natural habitat is shallow (average depth: 1 m); since the bottom is muddy, the water is very turbid and the light intensity significantly reduced. 4.Gracilaria confervoides lies unanchored on the mud in the vegetative sterile form in long densely branched threads, while the spores settle on shells. 5. In view of the industrial importance of this alga, we have established an experimental cultivation field in a lagoon fishing resort in order to assess the influence of various ecological factors. This study was made from 1968 through 1969 together with productivity tests (photosynthesis rates and biomass measurements).

Cool flame phenomena in the oxidation of n-pentane

The temperature and pressure changes associated with the passage of a cool flame through mixtures of n-pentane and oxygen (mainly 1:1 and 1:2 mixtures) have been examined simultaneously in the temperature range 277–364°C. The maximum temperature rise can be up to ∼250°C: it reached a “ceiling” value at high initial pressures of reactants. As the initial pressure was reduced, however, the magnitude of the temperature pulse suddenly decreased sharply and at the lower pressures the maximum temperature rise was < 50°C. The passage of a cool flame gave a permanent increase in the pressure that was approximately half the magnitude of the pressure pulse, and this is consistent with analytical data, which show that a significant proportion of the n-pentane is consumed during the passage of the cool flame. The use of a fast-response recording system has shown that the pressure pulse associated with the cool flame possesses an abrupt, almost isothermal step that precedes the thermal component of the pressure pulse. Thus the present results do not indicate that a critical temperature rise is required for the appearance of a cool flame. It is suggested, therefore, that the chain-branching reactions are important in the mechanism leading to cool flame formation when n-pentane is the fuel and that the corresponding very fast reaction produces the thermal effects accompanying the passage of a cool flame.

Thermal Buckling of Shallow Bimetallic Two-Hinged Arches

The snap-through phenomenon of shallow bimetallic two-hinged arches due to temperature rise is analyzed. Two types of arch geometry are included. The effect of the position of supporting hinges on the critical temperature rise for snap-through is discussed. Comparisons are made between the present more accurate solution of the critical temperature rise and the approximate solution obtained by Timoshenko. Striking discrepancies are found between these two solutions.

Thermal explosion in the sphere and the hollow spherical shell heated at the inner face

The steady state heat conduction equation for reactants of spherical symmetry decomposing by a zero-order exothermic process has been converted by means of the fifth-power (quintic) approximation ▪ (where α and β are constants) into a form which is soluble analytically. The method of solution depends upon the physical model under examination: two models have been discussed, that of self ignition of a hollow spherical shell of reactant heated at the inner face and cooling to the surroundings from the outer face and the solid sphere immersed in a constant temperature bath. Approximate Frank-Kamenetsky criticality criteria for hollow spheres of varying thickness and hot face temperatures were derived analytically by a method involving the use of incomplete elliptic integrals of the first kind. The results were compared with numerical solutions of the equation wherein the exponential approxiamation had been made and found to be in good agreement. It has been shown how these results fit into the pattern established by those for the asymmetrically heated slab and the infinite hollow cylindrical shell heated at the inner face. For the first time an analytical criticality criterion (δ crit. = 3/4α 4β), critical centre temperature rise [θ mcrit. = (□2−1)(α/β)] and temperature distribution, given by ( α + β θ ) 2 = 1 ⋅ 5 α 2 [ ( 1 + z 2 ) − ( 1 − z 2 ) { 1 − ( 4 α 4 δ β / 3 ) } 1 2 ] [ δ β ( 1 − z 2 ) 2 α 4 + 3 z 2 ] have been determined for the sphere by a method in which the phenomenon of criticality emerges naturally from the analysis.