Thermal conductivity: A review of some important developments

Some recent developments are presented which relate to the thermal conductivity of metals and its measurement. These include the influence of sample size on the electronic thermal conductivity of very pure metals, the thermal conductivity minimum of aluminium and a few other metals at sub-normal temperatures, the high-temperature thermal conductivity and increasing Lorenz function of platinum, with particular reference to the experiments of Flynn and O'Hagan (1967), the thermal conductivity of molten metals and the recently reported Lorenz functions decreasing with increase in temperature to well below the theoretical value, and the encouraging results of an investigation in progress at the Thermophysical Properties Research Center (TPRC) on direct electrical heating methods for the measurement of metallic thermal conductivities to high temperatures. Modern computer techniques avoid the restrictions and approximations introduced in the many existing methods and allow thermal conductivity to be accurately evaluated from the observed temperature profile. This method has the additional advantage that many other properties can be obtained to high temperatures for the same sample and experimental conditions. The account shows that despite the amount of effort already devoted to thermal conductivity determinations, this still remains a most rewarding field requiring further accurate measurements.     

Chemical processing with lasers: Recent developments

Chemical processing of materials with lasers is a new and interdisciplinary field with many already realized and potential applications in different areas of technology. This overview summarizes some recent developments in this rapidly expanding field.     

Muonium in semiconductors: Recent experimental developments

Recent experiments covering a range of problems including the nuclear hyperfine structure of bond-centered muonium in diamond and GaP, charge-cycling reactions of muonium in Si at high temperatures, muonium state dynamics in Si probed by RF-SR, and endohedral muonium in semiconducting C₆₀ compounds, are discussed. These examples show that as traditionalSR techniques are continually being refined and new methods are being developed,SR is becoming an increasingly powerful tool to investigate the behavior of muonium and the in many respects analogous, and technologically relevant, hydrogen centers in semiconductors.     

Uncooled microbolometer detector: Recent developments at Ulis

Uncooled infrared focal plane arrays are being developed for a wide range of thermal imaging applications. Therefore, to answer these markets, a 35 μm pixel-pitch uncooled IR detector technology has been developed enabling high performance 160 × 120 and 384 × 288 arrays production. Besides a wide-band version from uncooled 320 × 240/45 μm array has been also developed in order to address process control and more precisely industrial furnaces control. The ULIS amorphous silicon technology is well adapted to manufacture low cost detector in mass production. After some brief microbolometer technological background, we present the characterization of 35 μm pixel-pitch detector as well as the wide-band 320 × 240 infrared focal plane arrays with a pixel pitch of 45 μm. Information on the new 640 × 480 array with a pixel pitch of 25 μm is also presented.     

Nuclear pears: Recent developments and future prospects

We report studies of examples of reflection-asymmetric nuclei which are difficult to access using compound nucleus reactions. The octupole radium isotopes withN>132 and radon isotopes are not accessible by reactions employing stable targets and beams; we have shown that multinucleon transfer reactions can populate these nuclei with sufficient yield for their structure to be determined. We report high-spin studies in^{218, 220, 222}Rn and^{222, 224, 226, 228, 230}Ra: these show that the Ra isotopes withA<228 have the characteristics of octupole deformed nuclei whereas the Rn isotopes behave like octupole vibrators. Measurements of theB(E1)/B(E2) ratios indicate that the electric dipole moment in these nuclei is constant with spin. The most octupole deformed nuclei are predicted to be uranium isotopes withN≈132; measurements of the very fissile nucleus²²⁶U suggest that it is octupole deformed and has a large intrinsic electric dipole moment. Finally, we speculate that the best examples of pear shapes are the hyperdeformed minima predicted to lie low in uranium isotopes withN≈140; their signature of high-multiplicity low-energyE1 photon cascades should be detectable using present-day high-efficiency germanium arrays.     

Longitudinally detected electron spin resonance: Recent developments

Multiple-quantum spectroscopies are reviewed in the frame of electron paramagnetic resonance. Some properties of different nonlinear techniques are discussed for both transverse and longitudinal detection. The connections of effects recently presented with the procedure of longitudinal detection of electron paramagnetic resonance (LODESR) in presence of double transverse irradiation are stressed. Peculiarities of LODESR spectroscopy and its capabilities in facing problems related to relaxations in presence of very slow dynamic processes are evidentiated. Recent results show the vitality of the LODESR technique, that in the future could be applied to new fields, owing to experimental updating.     

High-temperature/high-pressure X-ray diffraction: Recent developments

Abstract

We have developed two Merrill-Bassett diamond-anvil cells for specialized high-temperature uses. The first is constructed largely of rhenium to provide uniform, constant P and T on the order of 20 GPa at 1200 K for extended periods. The second is for single-crystal x-ray diffraction, but can be heated to 630 K at 20 GPa to grow single-crystal samples which cannot be produced at room temperature. With this cell, the crystal structure of ?-O₂ was shown to be monoclinic with a = 3.649 A, b = 5.493 A, c = 7.701 A, and β = 116.11° at 19.7 GPa.     

Two-dimensional gas of disks: Thermal conductivity

The phenomenon of heat conduction in a two-dimensional gas ofN hard disks is studied in the hydrostatic regime by means of nonequilibrium molecular dynamics (N ranging from 100 to 8000). For systems withN1500 the temperature and density profiles observed are in excellent agreement with the continuous theory, but the conductivityk differs from the one derived from Enskog's theory in a systematic way. This difference seems to slowly decrease with increasing density.     

Recent developments in chaotic dynamics

A brief review of chaotic dynamics is presented. Topics discussed include basic concepts, recent developments, and applications     

Recent developments in sonochemical polymerisation

High intensity ultrasound has been applied to two classes of step-growth polymerisation. The ring-opening polymerisation of cyclic lactones to polyesters was accelerated under 20 kHz ultrasound but, in the case of delta-valerolactone, sonication also promoted a depolymerisation reaction so that the molecular weight fell during later stages of the reaction. Sonication was also applied to the preparation of polyurethanes from a number of diisocyanates and diols. In all cases, the sonochemical reactions proceeded faster in the early stages and led to higher molecular weight polymers. The effect of changing the ultrasound intensity is discussed and some speculation as to the mechanisms of the reaction enhancements is given.