Dynamics of liquid penetration into capillary tubes

The dynamics of penetration is considered in the case where inertia effects are small. The effect of the contact line speed on the dynamic contact angle is taken into consideration. Analytical solutions are obtained for short and large times, and are found to cover together most of the time domain. The results obtained numerically show good agreement with the asymptotic solutions. The large-time solutions are valid in the case of penetration into horizontal capillaries. The large-time asymptotic solution shows a correction term compared to the Lucas-Washburn equation, which is found to be a limiting case valid for very large times (horizontal capillaries case). The analysis shows how to include gravity effects in the case of penetration into vertical tubes. Excellent agreement is found with available published experimental data.     

Electrophoretic mobility of a cylindrical colloidal particle in a salt-free medium

Approximate expressions are derived for the electrophoretic mobility of dilute cylindrical colloidal particles in a salt-free medium containing only counterions. The cylinder is assumed to be infinitely long. It is shown that as in the case of a spherical particle, there is a certain critical value of the particle surface charge separating two cases. When the particle surface charge is lower than the critical value (case 1), the electrophoretic mobility increases with increasing particle surface charge per unit length. When the particle surface charge is higher than the critical value (case 2), the mobility becomes constant (for a cylinder in a transverse field) or the increase in the electrophoretic mobility with the particle surface charge becomes suppressed (for a cylinder in a tangential field). These phenomena are caused by the effect of counterion condensation in the vicinity of the particle surface. The critical value of the particle charge is essentially independent of the particle volume fraction phi for the dilute case, unlike the case of a sphere, in which case the critical charge value is proportional to ln(1/phi).     

Reparametrization of models of non-stationary chemical kinetics as a method of investigation of the inverse problem

A new approach to solve the inverse problem of the non-stationary chemical kinetics by a reparametrization of the initial model is suggested. This approach permits to obtain all solutions of IP in the case of a finite number or some parametric functions in the case of the infinite number of solutions.     

Electrophoretic mobility of a soft particle in a salt-free medium

A theory is presented for the electrophoretic mobility mu of dilute spherical soft particles (i.e., polyelectrolyte-coated particles) in salt-free media containing only counterions. As in the case of other types of particles (rigid particles and liquid drops) in salt-free media, there is a certain critical value of the particle charge separating two cases, the low-surface-charge case and the high-surface-charge case. For the low-charge case, the mobility is proportional to the particle charge and coincides with that of a soft particle in an electrolyte solution in the limit of very low electrolyte concentrations kappa-->0 (Hückel's limit), where kappa is the Debye-Hückel parameter. For the high-charge case, however, mu becomes essentially constant, independent of the particle charge, due to the counterion condensation effect.     

One-dimensional trapped atoms: critical coupling parameter and critical number of particles

In this paper we consider the case of a Bose gas in low dimension in order to illustrate the applicability of a method that allows us to construct analytical relations, valid for a broad range of coupling parameters, for a function which asymptotic expansions are known. The method is well suitable to investigate the problem of stability of a collection of Bose particles trapped in one- dimensional configuration for the case where the scattering length presents a negative value. The eigenvalues for this interacting quantum one-dimensional many particle system become negative when the interactions overcome the trapping energy and, in this case, the system becomes unstable. Here we calculate the critical coupling parameter and apply for the case of Lithium atoms obtaining the critical number of particles for the limit of stability.     

Derivation of the Clebsch–Gordan coefficients by means of projection operators

The Clebsch–Gordan coefficients for the coupling of two angular momenta are derived by using the projection operator technique, developed by Löwdin. The derivation is done in two steps; first for the so-called principal case, i.e. k = m, then for the general case with an arbitrary m. Two different derivations are given for the principal case, a direct one and one based on a recursion procedure. The general case is obtained from the principal case with a step-down operator.     

Prediction of the effects of constitutive viscoelasticity on stress-diffusion coupling in gels

Modeling of stress/diffusion coupling in gels, originally developed by Doi for the case where the solid component of the gel is a linear elastic network, is here extended to the case of a linear viscoelastic solid component, thereby allowing for a mechanism of intrinsic relaxation. The extended model is solved for a cylindrical gel subjected to unconfined uniaxial compression. Depending on the respective values of the two characteristic times, i.e., diffusive and viscoelastic, measurable quantities like axial force and external radius of the cylindrical gel are calculated to display different qualitative behaviors. Calculated results for the case of uniaxial traction are also reported, which compare favorably with some available experimental results.     

Estimating the fire behavior of wood flooring using a cone calorimeter

This article analyzes the flammability characteristics in order to investigate the adequacy of a newly proposed sampling method for wood and PVC materials that are commonly used for residential flooring. Experiments on commercial products were performed using a cone calorimeter according to ISO 5660-1 specifications. Samples for the test procedure were prepared in two methods: either using a cone calorimeter sample preparation method (case 1), or the proposed sample preparation method, which a simplified form for the actual constructed shape (case 2). The thermal characteristics of the common wood products differed depending on the sampling method, where the peak heat release rate (PHRR) had either two peaks for case 1 or a single peak for case 2, and the total heat rate (THR) and smoke production rate (SPR) also differed according to the case. Especially, the wood flooring differed significantly between the two cases in terms of the number of PHRR peaks and the trend of the SPR curves. Due to these differences, we presented another HRR evaluation method depending on the raw material and the size of HRR to reduce the fire hazards in flooring.     

Simulation of the mechanical unfolding of ubiquitin: probing different unfolding reaction coordinates by changing the pulling geometry

Motivated by the recent experimental atomic force microscopy (AFM) measurements of the mechanical unfolding of proteins pulled in different directions [D. J. Brockwell et al., Nat. Struct. Biol. 10, 731 (2003); M. Carrion-Vazquez et al., ibid 10, 738 (2003)] we have computed the unfolding free energy profiles for the ubiquitin domain when it is stretched between its (A) N and C termini, (B) Lys48 and C terminus, (C) Lys11 and C terminus, and (D) N terminus and Lys63. Our results for cases (A) and (B) are in good agreement with the experimental unfolding forces measured for the N-C and Lys48-C linked polyubiquitin, in particular, indicating a considerably lower unfolding force in the latter case. Mechanical unfolding in case (A) involves longitudinal shearing of the terminal parallel strands while in case (C) the same strands are "unzipped" by the force. The computed unfolding forces in case (C) are found to be very low, less than 50 pN for pulling rates typical of AFM experiments. The unfolding free energy barrier found in case (C) is approximately 13 kcal/mol, which corresponds to a zero-force unfolding rate constant that is comparable to the rate of chemical unfolding extrapolated to zero denaturant concentration. The unfolding barrier calculated in case (A) in the limit of zero force is much higher, suggesting that mechanical unfolding in this case follows a pathway that is different from that of thermal/chemical denaturation.     

Effect of solvent composition on the association behavior of pectin in methanol-water mixtures

Turbidity, small-angle neutron scattering (SANS), and dynamic light scattering measurements have been carried out on semidilute systems of pectin in methanol-water media of various composition ratios. Structural and dynamical properties of pectin dissolved in water-methanol mixtures (case I) are compared with the corresponding conditions when pectin was dissolved in water before the prescribed amounts of methanol were added (case II). The turbidity rises as the percentage of methanol in the mixture increases and this trend is much stronger when the first procedure is used to dissolve pectin. The wavelength dependence of the turbidity indicates that larger association complexes are formed for the samples prepared according to case I. These findings indicate that at a given methanol-water composition, the preparation procedure in case I gives rise to poorer thermodynamic conditions of the system. Local structures probed by SANS experiments do not reveal any significant differences between the systems prepared by the two different procedures. The dynamic light scattering (DLS) results show that increasing methanol concentration in the mixture promotes the formation of association complexes and the disengagement relaxation time of individual chains or clusters is longer at higher percentage of methanol for case II. This can be attributed to stronger entanglement effects in case II. The features from DLS can be rationalized in the framework of the coupling model for constrained and interconnecting systems.     

An age-related model derived from ICRP 67 for plutonium dose calculation: Application to an updated case of contamination

The main innovative features of a new model developed for plutonium dose assessments are presented. The physiological assumptions and the improvement of model predictions for plutonium activity in biological samples are discussed. Preliminary results relating to dose calculations and sensitivity analysis are also presented. The model has been applied to a well documented case of contamination. This was the first opportunity to test the new features of the model in a practical case and to show how to apply sensitivity techniques to a complex data set of a contamination case.     

Evaluation of measurement uncertainty in analytical assays by means of Monte-Carlo simulation

The main limitations of the Guide to the expression of Uncertainty Measurement (GUM) approach for evaluating the measurement uncertainty of analytical assays are presented and explained. The advantages of using Monte-Carlo simulation against the GUM approach are outlined and discussed and the principle of propagation of distributions is explained. The procedure of Monte-Carlo analysis is illustrated by two case studies. A first simple example quoted from the EURACHEM Guide and dealing with the preparation of a calibration standard is used to present the technique with detail in a step-by-step way. In this case the results obtained by both approaches are very similar. A second example deals with the calibration of mass according to a strong non-linear model. In this case, the Monte-Carlo analysis leads to better results.     

Regularities of formation and luminescence of zinc sulfide nanoparticles modified with amino acids

The regularities of formation and luminescence of zinc sulfide nanoparticles modified with various amino acids were studied. The luminescence intensity of ZnS sols depends strongly on the nature of the modifier and from 30 to 40 times increases in the case of methionine and glycine or nearly completely disappears in the case of cysteine. Two main stages of formation of unmodified and surface-modified ZnS were revealed: a very rapid formation of ZnS nanoparticles and a relatively slow process of ordering of the internal particle structure with the formation of luminescence centers. In the case of modified objects, the role of such centers could be played by surface zinc ions bound to amino acids.     

Diffusiophoresis of concentrated suspensions of spherical particles with distinct ionic diffusion velocities

The diffusiophoresis of a concentrated spherical dispersion of colloidal particles subject to a small electrolyte gradient is analyzed theoretically for an arbitrary zeta potential and double layer thickness. In particular, the influence of the difference in the diffusivities of cations and anions is discussed. A unit cell model is used to simulate a spherical dispersion, and a pseudospectral method is adopted to solve the equations governing the phenomenon under consideration. We show that, as in the case of an infinitely dilute dispersion, when the diffusivities of cations and anions are different, the diffusiophoretic mobility is no longer an even function of the zeta potential or double layer thickness. In contrast to the case of identical diffusivity of cations and anions, a local electric field is induced in the present case due to an unbalanced charge distribution between higher and lower concentration regions. Depending upon the direction of this induced electric field, the diffusiophoretic mobility can be larger or smaller than that for the case of identical diffusivity. The diffusiophoretic mobility is influenced mainly by the induced electric field arising from the difference in the ionic diffusivities, the concentration gradient, and the effect of double layer polarization.     

On the validity of the Arrhenius equation for electron attachment rate coefficients

The validity of the Arrhenius equation for dissociative electron attachment rate coefficients is investigated. A general analysis allows us to obtain estimates of the upper temperature bound for the range of validity of the Arrhenius equation in the endothermic case and both lower and upper bounds in the exothermic case with a reaction barrier. The results of the general discussion are illustrated by numerical examples whereby the rate coefficient, as a function of temperature for dissociative electron attachment, is calculated using the resonance R-matrix theory. In the endothermic case, the activation energy in the Arrhenius equation is close to the threshold energy, whereas in the case of exothermic reactions with an intermediate barrier, the activation energy is found to be substantially lower than the barrier height.     

Electro-chromatography in the study of ions

Summary The migration distance in the case of a fast moving ion increases with time, as is to be expected, while in the case of a slow moving ion, it is nearly independent of time. Names of fast moving and slow moving ions and carrier electrolytes are shown in a table.     

Performance of a Gyratory Square-Shaped Capacitive Radio Frequency Discharge Plasma Sputtering Source for Materials Processing

We proposed a gyratory square-shaped capacitive radio-frequency discharge plasma sputtering source for materials processing and functional film preparation, composed of magnet arrangements consisting of eight neodymium bar magnets of dimensions 30 mm × 5 mm × 3 mm. In order to evaluate its performance, two square-shaped magnetic arrangements were investigated: case (a) without iron shielding and case (b) with iron shielding of dimensions 5 mm × 3 mm × 1 mm. The magnetic field simulation is analyzed, while the plasma discharge characteristics and the film properties are measured. The film thickness and the resistivity profiles of case (b) are more uniform than their corresponding profiles in case (a). The lowest electrical resistivity of the film is 4.33 × 10^?8 Ω m at r = 30 mm for case (b), which is of the same order as the bulk resistivity of the copper. The roughnesses of the film thickness profile for cases (a) and (b) are ±24.4 and ±7.2%, respectively. Using atomic force microscopy analysis, the film surface for case (b) was observed to show an improved smooth surface with reduced needle-shaped grain size and a lower surface roughness than that of case (a). The surface roughness of the films is approximately 3.73 and 2.49 nm for case (a) and case (b), respectively. From the X-ray diffraction patterns, the film texture, the relative intensity ratios of the (111) peak to the (200) [I₍₁₁₁₎/ I₍₂₀₀₎] were found to be 13.76 and 4.08 for the cases (a) and (b), respectively.     

A theory of field-induced birefringence applicable to systems of large molecules

We consider a molecule in an external constant field interacting with a linearly polarized photon. When the field is chosen to be magnetic and directed along the wave vector of the photon (longitudinal), we find that the time dependence of the state function implies a rotation of the plane of polarization of the photon characteristic of the Faraday effect. Similarly when the field is transverse, the time evolution of the state corresponds to the Kerr effect in the case of an electric, and the Cotton—Mouton effect in the case of a magnetic field. The theory is applicable to a dilute system of freely oriented molecules of any size: the long-wavelength approximation is not invoked. The general procedure for averaging over all molecular orientations is carried out explicitly in the case of the Faraday effect.     

Thermal performance evaluation of a solar air heater with and without thermal energy storage

This communication presents the experimental study and performance analysis of a solar air heater with and without phase change material (PCM) viz. paraffin wax and hytherm oil. There are three different arrangements viz. without PCM, with PCM and with hytherm oil to study the comparative performance of this experimental system. Inlet, outlet temperatures and radiation with respect to time have been recorded and found that the output temperature in case with thermal energy storage (TES) is higher than that of without TES, besides, the outlet temperature with paraffin wax is slightly greater than that of with hytherm oil. Also there is no energy gain in the evening in case of without TES but in case of with TES there is a heat gain for around 4 h in the evening which gives the backup for hot air for around four more hours which is the main advantage of this systems with TES. Based on the data, the efficiency of the system has been calculated and it is noted that the efficiency in the case of heat storage is higher than that of without TES, besides the efficiency in the case of the paraffin wax is slightly higher than that of the hytherm oil case.