Using a microcalorimeter to measure the Lamb shift in hydrogenic gold and uranium on cooled, decelerated ion beams

A precise determination of the Lamb shift from photons emitted by highly charged, one electron ions represents one of the most sensitive tests of QED in strong electromagnetic fields. Recent progress in the production and cooling of intense beams of fully stripped Au and U in the SIS/ESR synchrotron storage ring at GSI, Darmstadt has made it possible to obtain precision spectroscopy of these ions. A fully stripped beam of either Au⁷⁹⁺ or U⁹²⁺ ions is injected, stored and cooled in the ESR and interacts with an internal gas target. The capture of an electron and the subsequent population of a 2p or 3p state will lead to a decay by either Lyman or Balmer X-ray emission. Although measurements of the 1 s Lamb shift in U with Ge ionization detectors accurate to 3% have provided a test of QED for the high Z domain, the experimental errors (±13 eV) are about one order of magnitude larger than the accuracy theoreticians presently claim (±1 eV). We present the results from initial broad band experiments using NTD Ge microcalorimeters to measure the 2 s Lamb Shift in Au and U at the ESR. The broad band coverage of the microcalorimeter makes it possible to reduce the systematic uncertainties in the Doppler corrections while the high-energy resolution reduces the statistical error in the absolute energy calibration.     

Macro- and micro-modelling of hot rolling of steel coupled by a micro-constitutive relationship

A macro- and micro-combined model has been developed to simulate the static and dynamic recrystallizations of austenite during hot rolling of steel. In addition to the coupled thermal and mechanical phenomena, a micro-constitutive relationship is used to link the macro and micro models. The macro model provides the thermal and deformation information for the micro model. A finishing line with seven stands is studied to verify the model's reliability. The results indicate that static recrystallization plays a more important role than the dynamic part in austenite refinement.     

Total equivalent warming impact: a measure of the global warming impact of CFC alternatives in refrigerating equipment

Chlorofluorocarbons (CFCs) are important components of refrigeration equipment, plastic for insulation for buildings and appliances, and solvent cleaning processes. The Montreal Protocol to Protect Stratospheric Ozone Layer and recent revisions to the protocol require a rapid phase-out of the production and use of CFCs and a transition to alternative materials and technologies. It is important that the alternative technologies selected do not exacerbate the global warming problem while attempting to preserve stratospheric ozone. A study was conducted to evaluate the total global warming impact of proposed alternatives to SFCs and this paper focuses on the aspects of that study relevant to refrigeration and air-conditiong. The concept of total equivalent warming impact (TEWI) is developed as a measure of the combined global warming impacts of the refrigirant losses to the atmosphere and the CO₂ emissions from fossil fuels to generate power to run the refrigeration and air-conditioning systems. Equipment using alternatives to CFCs has lower TEWIs than current systems in almost all cases, with dramatic reductions possible in some applications.     

Effects of aging on the phase transformation and sintering properties of TiO2 gels

Several research results suggest the binding energy of carbon–vacancy (C–V) complexes is of the order 35–55 kJ/mole in face-centered cubic (fcc) iron-base alloys. In addition to point-defect anelasticity, we examine data on self-diffusion of Fe in fcc Fe, which are quantitatively consistent with our results on point-defect structure modeling. Quenching, cold work, and electron irradiation increase the height of damping peaks associated with C motion, consistent with a contribution of C–V complexes to the relaxation strength of these peaks. The effect of increasing C content on self-diffusion of Fe in fcc Fe is to decrease the activation energy for self-diffusion, hence increase the diffusivity, and implies a C–V binding energy of 40 kJ/mol. We have used first-principles gradient-corrected density functional calculations to determine directly the binding energy of nearest-neighbor C–V pairs in fcc iron. A value of 35 kJ/mol is obtained.     

Application of a genetic algorithm: near optimal estimation of the rate and equilibrium constants of complex reaction mechanisms

In iterative non-linear least-squares fitting, the reliable estimation of initial parameters that lead to convergence to the global optimum can be difficult. Irrespective of the algorithm used, poor parameter estimates can lead to abortive divergence if initial guesses are far from the true values or in rare cases convergence to a local optimum. For determination of the parameters of complex reaction mechanisms, where often little is known about what value these parameters should take, the task of determining good initial estimates can be time consuming and unreliable. In this contribution, the methodology of applying a genetic algorithm (GA) to the task of determining initial parameter estimates that lie near the global optimum is explained. A generalised genetic algorithm was implemented according to the methodology and the results of its application are also given. The parameter estimates obtained were then used as the starting parameters for a gradient search method, which quickly converged to the global optimum. The genetic algorithm was successfully applied to both simulated kinetic measurements where the reaction mechanism contained one equilibrium constant and two rate constants to be fitted, and to kinetic measurements of the complexation of Cu²⁺ by 1,4,8,11-tetraazacyclotetradecane where two equilibrium and two rate constants were fitted. The implementation of the algorithm is such that it can be generally applied to any reaction mechanism that can be expressed by standard chemistry notation. The control parameters of the algorithm can be varied through a simple user interface to account for parameter range and the number of parameters involved.     

Measurements and modeling of the thermal properties of a calorimeter having a sapphire absorber

The response of a magnetic calorimeter with a sapphire crystal serving as an X-ray absorber has been studied as a function of temperature. Several different Au films were used to connect thermally the magnetic sensor to the absorber. The amplitude and time dependence of the signal resulting from the absorption of an X-ray were fit using an idealized model for the calorimeter. The values of the various parameters resulting from a fit of the data are internally consistent and provide a physical understanding of the processes determining the performance of the calorimeter. The fraction of the energy of the X-ray that is captured by the film without having first been down-converted to thermal phonons in the sapphire is found to depend on both the area and the thickness of the film. The rate at which the energy is transferred between thermal phonons in the sapphire and the electrons in the film is determined by the electron/phonon interaction in the gold. Also, an additional heat capacity was observed to be present in the sapphire, which, for want of a better means of characterization, is ascribed to the tunneling systems. The magnitude of this additional heat capacity and its thermal coupling to the lattice has been studied.     

Effects of spray parameters on the microstructure and property of Al2O3 coatings sprayed by a low power plasma torch with a novel hollow cathode

Al₂O₃ coating is deposited using a low power plasma torch with a novel hollow cathode through axial powder injection under a plasma power up to several kilowatts. The effects of the main processing parameters including plasma arc power, operating gas flow and spray distance on particle velocity during spraying, and the microstructure and property of the coating are investigated. The microstructure of the Al₂O₃ coating is examined using optical microscopy and X-ray diffraction analysis. The property of the coating is characterized by dry rubber wheel abrasive wear test. The velocity of in-flight particle is measured using a velocity/temperature measurement system for spray particle based on thermal radiation from the particle. The dependency of the microstructure and property of the coating on spray particle conditions are examined by comparing the particle velocity, and microstructure and abrasive wear weight loss of subsequent coating deposited by low power plasma spray with those of the coating by conventional plasma spray at a power one order higher. X-ray diffraction analysis of the coating revealed that Al₂O₃ particles during low power plasma spraying reach to sufficiently melting state prior to impact on the substrate with a velocity comparable to that in conventional plasma spraying. The experiment results have shown that processing parameters have significant influence on the particle conditions and performance of deposited Al₂O₃ coating. The coating of comparable microstructure and properties to that deposited by conventional plasma spray can be produced under a power one order lower. From the present study, it can be suggested that a comparable coating can be produced despite plasma power level if the comparable particle velocity and molten state are achieved.     

Analytical solutions using a higher-order refined theory for the static analysis of antisymmetric angle-ply composite and sandwich plates

Analytical formulations and solutions to the static analysis of simply supported anti-symmetric angle-ply composite and sandwich plates hitherto not reported in the literature based on a higher-order refined theory already reported in the literature are presented. The theoretical model presented herein incorporates laminate deformations, which account for the effect of transverse shear deformation and a non-linear variation of in-plane displacements with respect to the thickness coordinate. The transverse displacement is assumed to be constant throughout the thickness. The equations of equilibrium are obtained using principle of minimum potential energy. Solutions are obtained in closed form using Navier's technique by solving the boundary value problem. Accuracy of the theoretical formulations and the solution method is first ascertained by comparing the results with that already reported in the literature. After establishing the accuracy of the solutions, numerical results with real properties are presented for the multilayer antisymmetric angle-ply composite and sandwich plates, which will serve as a benchmark for future investigations.     

Effects of Mg and RE additions on the semi-solid microstructure of a zinc alloy ZA27

The effects of 2 mass% Mg and 0.8 mass% RE additions on the microstructural evolution of a Zr modified zinc alloy ZA27 during isothermal holding at semi-solid temperature of 460 °C have been studied by optical microscope and scanning electron microscope. Results show that these two elements all decrease the coarsening rate of solid primary particles, and improve the uniformity of particle size. The addition of Mg greatly decreases the solid fraction, and then increases the distance between particles. However, the element of RE mainly concentrates at the liquid regions between particles, and hinders both the atom diffusion and the welding of contact particles. In addition, the behaviors of particle coarsening of these two alloys, together with that of the Zr modified ZA27 alloy without the other elements, obey the LSW law after the three semi-solid systems reach at their solid–liquid equilibrium states. The additions of these two elements have no visible effect on the shape factor of particles.     

Comparison of the refrigerants HFC 134a and CFC 12

A comparison of the refrigerants HFC 134a and CFC 12 has been carried out and the results from a theoretical analysis and from tests with an open piston compressor are reported in this paper. The results indicate that the tested compressor will give a greater refrigerating capacity with HFC 134a than with CFC 12 for certain operating conditions. However, the results also indicate an increased operating power for the compressor over the entire temperature range. As a result the coefficient of performance is decreased. Another noticeable result is dependency of the compressor's isentropic efficiency on temperature when using HFC 134a. This might be explained by the properties of the polyalkene glycol oil which is used with HFC 134a. The increased cost of using HFC 134a is justified if the environmental aspects are considered and the practical problems, such as the influence on the material in the refrigeration cycle, can be solved.     

Experimental study and modelling of the crystallization of a water droplet

Modelling the crystallisation of a water droplet into a cold humid airflow is the first step in modelling the behaviour of water droplets sprayed out of a snow gun. This modelling, which is based on an experimental study, deals with the behaviour of the droplet which is transformed successively from the supercooled liquid phase to the liquid–solid phase and then the solid phase. These three transformations are brought about by various exchanges: heat transfer with conduction and convection as well as mass transfer with evaporation and sublimation. The supercooling phenomenon is naturally observed during experiments and taken into account in the modelling.     

Freezing of a water droplet due to evaporation—heat transfer dominating the evaporation–freezing phenomena and the effect of boiling on freezing characteristics

One of the authors has proposed a novel transport/storage system for the waste cold from the gasification process of liquefied natural gas (LNG), which consists of an evaporator, a cold trap, and a pipeline. In order to estimate the performance of this system, one should know the pressure in the evaporator, in which evaporation–freezing of a PCM occurs, and in the cold trap, as well as the pressure drop of the pipeline due to the flow of low pressure vapor of the PCM. In this paper, the cooling/freezing phenomena of a water droplet due to evaporation in an evacuated chamber was experimentally examined, and the heat transfer dominating the evaporation-freezing phenomena was investigated in order to estimate the pressure in the evaporator. From the results, it was shown that the water droplet in the evacuated cell is effectively cooled by the evaporation of water itself, and is frozen within a few seconds through a remarkable supercooling state, and that the cooling rate of the water droplets were dominated by heat transfer within the droplet under the abrupt evacuation condition. The later result means that, in order to obtain an ice particle by evaporation–freezing, the surroundings of the water droplet should be evacuated at the pressure as low as the saturate pressure of water at the maximum supercooling temperature of the droplet.     

An experimental and numerical study of the dynamic behaviour of a counter-flow evaporator

The dynamic behaviour of a counter-flow, water-heated evaporator is studied experimentally and numerically. The frequency distribution of the random oscillations of the mixture-vapour transition point and the superheat temperature at the exit of the evaporator is obtained for steady operation of the system. These oscillations are well correlated. The transition point movement is found to cause fluctuations in the refrigerant temperature over 1 m downstream of its range of motion. Step changes in the refrigerant flow rate and the heating water flow rate demonstrate the non-linear characteristics of the evaporator where the time constants for step increases and step decreases of the same magnitude differ significantly. The distributed model predicts the variation of the superheat temperature and the evaporator pressure following step changes in the inputs with good accuracy.     

Simulation and measurement on the full-load performance of a refrigeration system in a shipping containerSimulation et mesures de la performance d'un système frigorifique d'un conteneur maritime entièrement chargé

A mathematical model of a refrigeration system in a shipping container has been developed to allow for full-load simulation of its thermal performance. Sub-models are created on the key components: compressor, evaporator, condenser, and thermostatic expansion valve. The sub-models are then coupled by appropriate mass and energy transfer relations to form the full model. Comparison with a series of cooling capacity tests conducted on a 2.2 m (40 ft) fullscale container housed in a temperature-controlled environmental test chamber indicates good agreement, with simulation results being within ±10% uncertainty of measurements.