Premelting transition in uranium dioxide

Thermal analysis of the cooling curves of small samples of uranium dioxide, laser heated in a high-pressure autoclave on a subsecond time scale to a temperature just below the melting point, reveals, in the case of nominally stoichiometric UO_2.00, a significant -like heat capacity peak, indicating a premelting transition in this material. The results are discussed and a simple model is presented in terms of which the observed behavior can be described.Summary of a paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria. Because of its length, the full paper was published in a regular issue of this journal (Vol. 14, No. 2, 1993).     

Towards automated development of specialized algorithms for design synthesis: Knowledge compilation as an approach to computer-aided design

We describe the emerging area of artificial intelligence research on knowledge compilation, the transformation of explicitly represented knowledge about a domain into an efficient algorithm for performing some task in that domain. In particular, we are interested in the case where the task is design synthesis. We survey several research projects based on this approach, and we use an example of geartrain design from the DIOGENES project to illustrate it in detail. We assess the potential of this approach for improving computer-aided design and identify some of the obstacles that knowledge compilation will have to overcome first.Earlier versions of this paper were presented at the Workshop on Research Directions in AI and Design, at Stanford University, Stanford, CA, USA, in April 1989, and at the NSF Engineering Design Research Conference, at the University of Massachusetts, Amherst, MA, USA, in June 1989 [Mostow 89a].The opinions expressed in this paper are those of the author and do not reflect any policies, either expressed or implied, of any granting agency.     

The physical properties of alloys in the liquid and “mushy” states

Data on the physical properties of alloys at high temperatures are urgently needed for the mathematical modeling of high-temperature processes such as casting, welding, secondary refining, dip melting, spray forming, and metal powder production. Data are required for those properties which are involved in heat and fluid flow in high-temperature processes. Levitated drop methods have been adopted to measure the surface tensions, densities, and enthalpies of commercial alloys, and rapid, transient methods have been developed to measure thermal conductivities to avoid the problem of convection. The results obtained for the properties of commercial alloys for the liquid and mushy states are discussed.Paper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1995, Köln, Germany.     

The hierarchical Tobit model: A case study in Bayesian computing

In this paper we discuss the potentials of a new Bayesian inference tool, called the Gibbs sampler, for the analysis of the censored regression or Tobit model. Tobit models have a wide range of applications in empirical sciences, like econometrics and biometrics. The estimation results of the simple Tobit model will be compared to a hierarchical Tobit model, and the Gibbs sampling approach to the related classical algorithm of expectation-maximisation (EM). The underlying botanical example of this paper is concerned with the censoring mechanism in plant reproduction and proposes the Bayesian Tobit model for the growth relationship between the reproductive part and the rest of the plant.     

Subsecond measurements of the optical properties in the spectral range 0.4–1.1 μm near high-temperature transformations of samarium oxide

A new dynamic method is described for measuring the spectral directional-hemispherical reflectivity in the spectral range 0.4–1.1 m near high-temperature phase transformations of refractory materials. The use of diffuse sample irradiation enables one to exclude the influence of an abrupt variation of the angular reflection distribution of sample surface at the phase transitions. The experimental results on samarium oxide showed that light pulses are emitted by the sample during the high-temperature transformations.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

Influence of spherical indentor radius on the indentation-induced transformation behaviour of silicon

The force-displacement records of the indentation of silicon single crystals have been monitored with an ultra-micro indentation system using spherical-tipped diamond indentors. The observations with indentors of different radii varying from nominally 5–20 m all exhibited similar behaviour. At low loads, the behaviour was entirely elastic and exhibited complete reversibility. At slightly heavier loads the onset of non-linear behaviour occurred, which, in many cases, appeared to be completely reversible. In all the other cases at this and higher load levels, a pop-out event occurred during the unloading in what otherwise appeared to be an elastic unloading. The results are interpreted in terms of the indentation pressure-induced phase transformation from silicon-I to silicon-II on loading and to silicon-III upon unloading.     

On values for generalized characteristic functions

In this work we study a new generalization for the Shapley value. We consider games in coalitional form in which the characteristic function is defined on all possible orders. These games are useful to model some economic situations. Different axiomatic characterizations are found for the new value using marginality, balanced contributions, the potential and the consistency property.The authors are grateful to I. Garia-Jurado for helpful comments and the Spanish Ministry of Education and XUNTA of Galicia for financial support through grants PB94-0648-C01-02 and XUGA20704B95     

Codes over <Emphasis Type="Bold">Σ</Emphasis><Subscript>2</Subscript><Subscript><Emphasis Type="Italic">m</Emphasis></Subscript> and Jacobi forms over the Quaternions

We introduce codes over the ring We relate self-dual codes over this ring to quaternionic unimodular lattices and to self-dual codes over via a gray map. We study a connection between the complete weight enumerators of codes over the quaternionic ring _2m and Jacobi forms over the half-space of quaternions. This motivates us to construct an algebra homomorphism from a certain invariant polynomial ring, where the complete weight enumerators belong, to the ring of Jacobi forms over the quaternions. Higher genus modular forms over the quaternions are also constructed using joint weight enumerators of codes.This research was partially supported by KOSEF R01-2003-00011596-0Some of the results of this paper were presented at the IEEE Information Theory Workshop, April, 2003     

Measurement of the radiance temperature (at 655 nm) of melting graphite near its triple point by a pulse-heating technique

Measurements of the radiance temperature of graphite at 655 nm have been performed in the vicinity of its triple point by means of a rapid pulse-heating technique. The method is based on resistively heating the specimen in a pressurized gas environment from room temperature to its melting point in less than 20 ms by passing an electrical current pulse through it and simultaneously measuring the radiance temperature of the specimen surface every 120 s by means of a high-speed pyrometer. Results of experiments performed on two different grades of POCO graphite (AXM-5Q1 and DFP-1) at gas pressures of 14 and 20 MPa are in good agreement and yield a value of 4330±50 K for the radiance (or brightness) temperature (at 655 nm) of melting graphite near its triple point (triple-point pressure, 10 MPa). An estimate of the true (blackbody) temperature at the triple point is made on the basis of this result and literature data on the normal spectral emittance of graphite.Paper presented at the First Workshop on Subsecond Thermophysics, June 20–21, 1988, Gaithersburg, Maryland, U.S.A.Formerly National Bureau of Standards     

Picosecond laser heating and melting of graphite

Ultrashort laser pulses impinging onto solid, strongly absorbing surface deposit their energy within an absorption depth from the surface. This localized energy deposition may result in rapid and very efficient heating of the surface to temperatures far exceeding the melting or boiling point. Temperature evolution at the surface of samples and their electronic structure may be studied with nonperturbing, time-resolved optical diagnostic techniques. Picosecond laser pulses provide the fastest means for heating matter at high temperature, since the characteristic energy transfer times from photoexcited electrons to the lattice occur in this time scale. Surface evaporation is not affecting the observations in this time scale, simply because there is no time for the surface atoms to escape. As an illustration, measurements on graphite are presented here. The complex index of refraction of highly oriented pyrolytic graphite (HOPG) during picosecond laser irradiation has been measured at 1.06 m via time-resolved ellipsometry at angles of incidence up to 80. In particular, a value of the complex index of refraction for the liquid phase has been derived.Paper presented at the First Workshop on Subsecond Thermophysics, June 20–21, 1988, Gaithersburg, Maryland, U.S.A.     

The Exact Interface Model for Wetting in the Two-Dimensional Ising Model

We use exact methods to derive an interface model from an underlying microscopic model, i.e., the Ising model on a square lattice. At the wetting transition in the two-dimensional Ising model, the long Peierls contour (or interface) gets depinned from the substrate. Using exact transfer-matrix methods, we find that on sufficiently large length scales (i.e., length scales sufficiently larger than the bulk correlation length) the distribution of the long contour is given by a unique probability measure corresponding to a continuous interface model. The interface binding potential is a Dirac delta function with support on the substrate and, therefore, a distribution rather than a function. More precisely, critical wetting in the two-dimensional Ising model, viewed on length scales sufficiently larger than the bulk correlation length, is described by a reflected Brownian motion with a Dirac perturbation on the substrate so that exactly at the wetting transition the substrate is a perfectly reflecting surface; otherwise there exists a perturbation. A lattice solid-on-solid model was found to give identical results (albeit with modified parameters) on length scales sufficiently larger than the lattice spacing, thus demonstrating the universality of the continuous interface model.     

The transient regime of a multiwavelength pyrometer

The transient operation of a new multiwavelength pyrometer based on a dispersing prism and a Si photodiode array is presented. After calibration, transient tests were performed using a tungsten strip lamp, supplied by a current pulse of 0.3-s duration. Measurements were carried out with a data acquisition system consisting of a FET multiplexer, a DVM (14 bit, 100 kHz), and a buffer memory (64 kbytes). Pyrometer signals are processed off-line, and temperature vs time is displayed. With the present arrangement, temperature measurements at 20 wavelengths may be performed with 200s resolution. Faster measurements are possible with a reduced number of channels.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.Deceased     

Thermophysical properties of solid and liquid thorium

Experimental investigations of the thermophysical properties of both solid and liquid thorium have been made using our isobaric expansion facility. We have performed measurements under 0.06 GPa argon pressure up to the vicinity of the thorium boiling state ( 5000 K). Enthalpy, volume expansion, and electrical resistivity data are reported and discussed. The electrical resistivity data display the different phase transformations in the solid and liquid states, before showing a sharp rise indicating crossing of the spinodal line. The enthalpies of transformations are measured and are in very good agreement with the available data in literature. Volume measurements show a strong expansion of liquid thorium up to the boiling state (V/V ₀ 2 at 0.68 MJ · kg^–1).Paper presented at the Fourth International Workshop on Subsecond Thermophysics, June 27–29, 1995, Köln, Germany.     

Development of phospholipid vesicle-based permeation assay models capable of evaluating percutaneous penetration enhancing effect

Objectives: The phospholipid vesicle-based permeation assay (PVPA) model has recently been introduced as an in vitro model which can mimic stratum corneum (SC) barriers to estimate the skin permeability of drugs. The aim of this study was to evaluate whether the PVPA model was suitable for the evaluation of penetration enhancing effect of skin penetration enhancers (PE).

Methods: The PVPA model was optimized by changing the lipid composition of both small liposomes (SL), and large liposomes (LL). The barrier properties of the PVPA model were monitored by electrical resistance and permeability measurement of the fluorescent marker Rhodamine B (RB). Then the permeation studies of the five active compounds with different physicochemical properties, namely, ferulic acid, paeoniflorin, albiflorin, tetrahydrocolumbamine, and tetrahydropalmatine, were performed directly on PVPA model to evaluate the penetration enhancing effect of menthol.

Results and discussions: The enhancement ratio (ER) ranking of the five active compounds observed using the optimized PVPA model was in accordance with what observed with Franz diffusion cell device using porcine ear skin. Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) analysis of PVPA model and porcine ear skin after treatment with menthol has shown similar mechanism of menthol which perturbs the SC lipid arrangement and extracts the SC lipids.

Conclusions: In summary, the optimized PVPA model was used for the first time for the evaluation of the permeation enhancing effect. The optimized PVPA model has shown potential to be applied in a more standardized, cheaper, and ethical way for the screening of PE.     

Measurements of thermophysical properties of nickel with a new highly sensitive pyrometer

A new, sensitive, and fast (response time, 100 ns) pyrometer used for the measurement of temperature in pulse heating experiments is described. The monochromatic instrument may use two detectors, namely, a Si diode and an InGaAs diode. Since monochromatic pyrometers usually are self-calibrated with the plateau of the melting transition of the investigated metal, a high sensitivity is desirable. The pyrometer is sensitive down to 1000 K and may be used at the melting plateau of copper, a reference point on the International Temperature Scale of 1990. A wide temperature range in a single measurement is possible with the use of a fast operational amplifier with linear and logarithmic outputs. Electrical resistivity, heat capacity, and enthalpy of nickel were measured in the temperature range 1500 to 2200 K using a fast pulse heating technique.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

Mixing Rules for van der Waals-Type Equations of State Based on Activity-Coefficient Models

A new approach for incorporation of the excess free energy from an activity coefficient model (ACM) into an equation of state (EOS) has been proposed. The approach is based on a concept that any ACM is valid at a low but finite value of compressibility factor. This condition allows us to analyze the infinite pressure approximation in a general way. It is shown that the infinite pressure approach neglects the contribution of the repulsive term of the EOS to the excess free energy of a mixture. This, in turn, introduces inconsistency which results in the difference in the calculated excess free energy of the EOS and the base ACM. The new approach defines parameter a of the EOS as an implicit function of compositions and temperature, thus requiring an iterative procedure using the infinite pressure limit as a starting point. The new approach can be modified to provide the correct composition dependence of a mixture second virial coefficient. Applicability of the new method has been tested for binary systems under vapor–liquid and liquid–liquid equilibrium conditions.     

Applications of Composites, Optical Fibre Sensors and Smart Composites for Concrete Rehabilitation: An Overview

Many researches and developments in the field of concrete rehabilitation and repair by using fibre reinforced plastic (FRP) materials have been successfully carried out in the last decade. There is no doubt that these materials have been promisingly used to replace conventional steel reinforcements for concrete structure with providing excellent structural durability and margin of safety. Until the last few years, researchers from diverse disciplines have drawn into vigorous efforts to develop a structure, which is able to measure its own structural condition by using embedded optical fibre sensors. This structure was appreciated as Smart structure. However, the smart structures have not yet been adopted by the civil engineering applications. In this paper, a brief review on the applications of the FRP and optical fibre sensor in concrete repair and structural health monitoring, respectively, is given. Further discussions on the potential use of smart composites for civil engineering applications are also addressed.     

Bioresorbability and biocompatibility of aliphatic polyesters

The field of biodegradable polymers is a fast growing area of polymer science because of the interest of such compounds for temporary surgical and pharmacological applications. Aliphatic polyesters constitute the most attractive family among which poly(-hydroxy acids) have been extensively studied. In the past two decades, several excellent reviews have been published to present the general properties of aliphatic polyesters. The aim of this paper is to complete the information collected so far with a special attention to the complex phenomena of biodegradability and biocompatibility. Indeed, the degradation of a polymer leads to the delivery of low molecular weight degradation by-products whose effects on the host body have to be considered. The consequences of the absence of standard terminology are first discussed with respect to words such as biodegradable and bioresorbable. Poly(-hydroxy acids) derived from lactic and glycolic acids are then introduced in order to make easier the critical discussions of the following problems from literature data: biocompatibility, biodegradability, bioresorbability, mechanism of hydrolysis (enzymaticvs simple chemistry), polymodality of molecular weight distributions during degradation and the effects of the presence of oligomers. Finally, some specific comments are made on other aliphatic polyesters such as poly(hydroxy butyrate) and poly(-malic acid).     

Evaluation of gradients on the boundary using fully regularized hypersingular boundary integral equations

Summary The evaluation of the gradient of the primary variable on the boundary for the Laplace problem, and the stress for the elasticity problem, involves hypersingular boundary integrals (HBIEs). To obtain any meaningful results from these integrals, an appropriate regularization scheme needs to be developed. We present an elegant way of calculation of gradients on the boundary of a body, starting from HBIEs regularized by using simple solutions or modes. Our method is currently limited to the calculation of gradients at regular points on the boundary at which the gradients of the primary variables are continous. Theiterative scheme developed in this paper is shown to be extremely robust for the calculations of the gradients. The method is tested on two Laplace problems and two problems in linear elasticity. This method does not involve any limiting process and can be easily extended to 3-dimensions. The approach developed in this paper can also be extended to other problems like acoustics and elastodynamics.     

Random Surfaces from Hierarchical Deposition of Debris with Alternating Rescaling Factors

An analytical study of surface profiles that result from hierarchical random impact of debris on the line is performed in terms of logarithmic fractals theory. The hierarchical random deposition model is extended for the case of time-dependent probabilities P (for positioning a hill on the surface) and Q (for digging a hole) and spatial rescaling factor . The periodic deposition model is solved exactly, and the logarithmic fractal roughness of the surface profile is found to be robust with respect to time-dependent perturbations. The fractal amplitudes associated with the proliferation of the surface length are compared with those calculated in the static regime and are shown to have a nontrivial interaction. It is verified that amplitude repulsion, attraction, neutrality, and auto-repulsion take place. The transient regime is also studied and is shown to have exponential decay towards the asymptotic regime. Special attention is devoted to the case of alternating rescaling factors, for which new results are derived.