Temperature shock waves in magnetic hydrodynamics with account for the hyperbolic heat transfer (solution of the running–wave type)

By the method of running waves the solution of magnetic hydrodynamics equations for media with infinite electrical conduction and heat transfer at heat-flow relaxation has been investigated. The characteristics of the considered system of hyperbolic equations have been determined. By means of the theory of generalized solutions of first-order, quasi-linear equations the stability of strong discontinuities of magnetohydrodynamic and thermal values has been proved.     

Large-area,transferable sub-10 nm polymer membranes at the air–water interface

Nano Research - Large-area, pinhole-free, and ultrathin polymer membranes with thicknesses of only a few nanometers have attracted increasing attention for their applications in molecular...     

Zener–Stroh crack at the interface of multi-layered structures

A Zener–Stroh (Z–S) crack can be nucleated on the interface of a multi-layered structure when a dislocation pileup is stopped by the interface which works as an obstacle. During the entire fracture of a crack, Z–S crack mechanism controls the initial stage, or the first phase of crack initiation and propagation. In our current research, investigation on a Z–S crack at the interface of a multi-layered structure is carried out. The problem is formulated into a set of singular integral equations by applying the distributed dislocation based fracture mechanics. The obtained integral equations are then solved with numerical method after the singularities at crack tips are carefully checked. In the solution procedure, the contact zone model is adopted to cease the oscillation behavior. The contact zone length, the stress field near the crack tips and the stress intensity factors (SIFs) of the crack are discussed based on the numerical results of two typical structures. It was found that the contact zone length could be very large and was determined by the properties of all the three materials and loading conditions. Our analysis also shows that the thickness of the middle thin layer plays a critical role for the fracture behavior of the crack when it is comparable to the crack length.     

Cooperative effects at the interface of nanocrystalline metal–organic frameworks

Controlling the chemistry at the interface of nanocrystalline solids has been a challenge and an important goal to realize desired properties. Integrating two different types of materials has the potential to yield new functions resulting from cooperative effects between the two constituents. Metal–organic frameworks (MOFs) are unique in that they are constructed by linking inorganic units with organic linkers where the building units can be varied nearly at will. This flexibility has made MOFs ideal materials for the design of functional entities at interfaces and hence allowing control of properties. This review highlights the strategies employed to access synergistic functionality at the interface of nanocrystalline MOFs (nMOFs) and inorganic nanocrystals (NCs).

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Real-time measurement of in vitro enamel demineralization in the vicinity of the restoration–tooth interface

An X-ray attenuation method using photon counting (scanning microradiography) is presented for the real-time study of in vitro demineralization of dental tissues in the vicinity of the restoration–tooth interface. By repeated measurement of mineral content profiles during the course of demineralization, the pattern of lesion development and the rate of mineral loss can be studied. The method is illustrated by comparison of enamel demineralization near a polyacid-modified composite resin restoration, near a bis-GMA/TEGMA composite resin restoration, and in an unrestored control. The method has potential for study of the influence of restorative materials on susceptibility of tooth tissue to demineralization. ©©1999©Kluwer Academic Publishers     

A study of the heat-removal process at the semiconductor–ceramics interface in solar cells by the laser thermal-wave method

The influence of the solder layer between a semiconductor solar cell and heat-removing ceramics on the nonstationary heat-transfer processes has been investigated by the laser thermal-wave method. A theoretical model taking into account the presence of additional thermal resistance and thermal capacitance at the soldered junction is proposed. Different soldering modes are considered. It is shown that the laser thermal- wave methods within the developed model allow one to correctly estimate the thermophysical properties of multilayer structures.     

Micromechanics modeling of the electrical conductivity of carbon nanotube (CNT)–polymer nanocomposites

A mixed micromechanics model was developed to predict the overall electrical conductivity of carbon nanotube (CNT)–polymer nanocomposites. Two electrical conductivity mechanisms, electron hopping and conductive networks, were incorporated into the model by introducing an interphase layer and considering the effective aspect ratio of CNTs. It was found that the modeling results agree well with the experimental data for both single-wall carbon nanotube and multi-wall carbon nanotube based nanocomposites. Simulation results suggest that both electron hopping and conductive networks contribute to the electrical conductivity of the nanocomposites, while conductive networks become dominant as CNT volume fraction increases. It was also indicated that the sizes of CNTs have significant effects on the percolation threshold and the overall electrical conductivity of the nanocomposites. This developed model is expected to provide a more accurate prediction on the electrical conductivity of CNT–polymer nanocomposites and useful guidelines for the design and optimization of conductive polymer nanocomposites.     

On the essential work of fracture in polymer–metal multilayers

Polyethylene terephtalate (PET) metallized with aluminium by physical vapour deposition was investigated through classical physical chemistry techniques and mechanical characterization. The amount of aluminium altered the amount of crystallinity of the PET substrate, but appeared unrelated to the mechanical properties obtained with regular tensile test. In contrast, the essential work of fracture (EWF), as obtained with Cotterell tests, permitted to better discriminate the perforation resistance. It is shown that increasing the amount of crystallinity within the PET linearly reduced the EWF.     

Characteristic times of oxygen mass transfer at the liquid metal–vapour interface

The interactions of liquid metals and alloys with the environment mostly depends on the thermodynamic properties of the liquid surface. In fact, the surface tension is strongly influenced by the presence in the surrounding atmosphere of reactive gases through solution, adsorption mechanisms and/or surface reactions. In particular, oxygen, which shows a high surface activity towards a large number of metallic systems, is the most important contaminant of liquid metals and alloys.Theoretical approaches for estimating the oxygen mass transfer at the liquid–vapour interface under inert atmosphere and vacuum have been developed already in order to relate the observed physical properties to the real surface composition data.In the present work a model of the interfacial transport of a liquid metal–oxygen system under Knudsen conditions that foresees the temporal evolution of the interfacial composition is presented. The diffusion characteristic times for reaching steady-state conditions are evaluated in order to define two system sizes depending on the different oxygen transport mechanisms in the liquid phase.An experimental study of the interface evolution is at present under way and preliminary results show a satisfactory agreement with theoretical studies.     

Monolayer studies of sugar- and nucleoside-terminated dendrimers at the air–water interface

Sugar- and adenosine-terminated dendrimers, [1,2-o-Isopropylideneribosyl-(G₁-12acid), -(G₂-36acid)] and [Adenosyl-(G₁-12acid), -(G₂-36acid)], were synthesized using Newkome's dendrimer synthetic method. Langmuir and Langmuir–Blodgett (LB) monolayers of these dendrimers have been constructed and characterized at the air–water interface and on solid substrates by measuring surface pressure–molecular area (Π–A) isotherms, atomic force microscopy (AFM), ellipsometry and contact angle measurement. Π–A isotherms and AFM images showed that these dendrimers formed stable and homogeneous monolayers without aggregation on pure water surface. The first and second generation of sugar-terminated dendrimers show molecular areas of 647 and 1359 Ų, respectively. Ellipsometry measurement indicates that the thickness of both the first and the second generation of sugar-terminated dendrimers were about 10 Å. This reflects a flat orientation of both molecules at the air–water interface. On the other hand, the first generation of adenosine-terminated dendrimer shows an area of 105.6 Ų per molecule with a thickness of 16 Å, and for the second generation, the area was 738.4 Ų with a thickness of 27 Å. These results suggested that adenosine-terminated dendrimers maintain a spherical form at the air–water interface. It was found that small difference in the structure of thymine and uracil in the subphase critically affects the interaction of the molecules and conformation of the dendrimers at the interface.     

Numerical and experimental evaluation of the influence of the filler–bitumen interface in mastics

The successful use of additives in modified asphalt mixtures, such as warm mix asphalt, depends largely on the effect such modification has on the mastic. Previous research indicated that such modifiers do not simply change the bitumen properties, but can also change the interaction between the filler and the bitumen matrix. Understanding the effect of the properties of the fillers, the bitumen and their interaction is thus important for future asphalt mix design. In order to investigate this and to define the dominant relationships, this paper combines a numerical and experimental approach. In the experiments, the viscosities of modified and unmodified mastics with different filler concentrations and types were systematically investigated utilizing a novel testing protocol. In the numerical analyses, the Finite Element Method was utilized for a micro-mechanical analysis, in which the shape and size of the filler particles were varied in the bitumen matrix. Combining the experimental and numerical results allowed for a detailed investigation of the effect of the interface properties, with and without modifiers. The research further indicated that the effect of the shape and size of the fillers varied, depending on the interface properties. From the research relationships were established between the overall mastic viscosity and the influence of the filler–bitumen interface, considering shape and size. The conclusion of this paper can thus be useful for the effective development of modified asphalt mixtures and gives strong indications towards future research directions.     

Frictional stresses at the disc–jaw interface during the standardized execution of the Brazilian disc test

An attempt to more accurately describe the boundary conditions of the standardized Brazilian disc test is presented. Specifically addressed is the problem of quantitatively relating the radial pressure with the tangential (frictional) stresses generated at the disc–jaw interface according to a physically acceptable law. A novel approach is proposed based on the notion that friction is directly related to the mismatch between the tangential components of displacement of the disc and jaw along their common interface due to the different deformability of the two materials. The surface displacements in both jaw and disc are determined using the complex potentials method, and the difference between their tangential components along the common contact arc is calculated. This difference in combination with the radial contact pressure tends to generate relative lateral displacements between the disc and jaw that are counterbalanced by frictional forces. The distribution of friction stresses along the contact rim obtained from the present approach fulfils all physical and intuitive imposed conditions. In addition, it is strongly skewed, attaining its maximum value at two-thirds distance from the centre of the contact arc, in good agreement with the earlier results based on a completely different approach.     

Osseointegration behavior of novel Ti–Nb–Zr–Ta–Si alloy for dental implants: an in vivo study

This study aimed to evaluate the effects of Ti–Nb–Zr–Ta–Si alloy implants on mineral apposition rate and new BIC contact in rabbits. Twelve Ti–Nb–Zr–Ta–Si alloy implants were fabricated and placed into the right femur sites in six rabbits, and commercially pure titanium implants were used as controls in the left femur. Tetracycline and alizarin red were administered 3 weeks and 1 week before euthanization, respectively. At 4 weeks and 8 weeks after implantation, animals were euthanized, respectively. Surface characterization and implant-bone contact surface analysis were performed by using a scanning electron microscope and an energy dispersive X-ray detector. Mineral apposition rate was evaluated using a confocal laser scanning microscope. Toluidine blue staining was performed on undecalcified sections for histology and histomorphology evaluation. Scanning electron microscope and histomorphology observation revealed a direct contact between implants and bone of all groups. After a healing period of 4 weeks, Ti–Nb–Zr–Ta–Si alloy implants showed significantly higher mineral apposition rate compared to commercially pure titanium implants (P?<?0.05), whereas there was no significant difference between Ti–Nb–Zr–Ta–Si alloy implants and commercially pure titanium implants (P?>?0.05) at 8 weeks. No significant difference of bone-to-implant contact was observed between Ti–Nb–Zr–Ta–Si alloy implants and commercially pure titanium implants implants after a healing period of 4 weeks and 8 weeks. This study showed that Ti–Nb–Zr–Ta–Si alloy implants could establish a close direct contact comparedto commercially pure titanium implants implants, improved mineral matrix apposition rate, and may someday be an alternative as a material for dental implants.     

Investigation of the heat conductivity of niobium in the temperature range 0.05–23 K

We report thermal conductivity measurements on a single-crystal niobium specimen of resistivity ratio 33,000 over the temperature range 0.05–23 K in the superconducting state and above 9.1 K in the normal state. The axis of the niobium rod was [110] oriented. The surface roughness was varied by sandblasting of the sample. The values of the thermal conductivity in the range from the lowest temperatures up to the maximal value covered a range of six orders of magnitude (=2×10^–5 W cm^–1 K^–1 at 50 mK to =22 W cm^–1 K^–1 at 9 K). Above 2 K the results for the untreated and the sandblasted sample are in accord, whereas below 2 K the influence of the sample surface is discernible. The various conduction and scattering mechanisms are discussed.     

Modeling of the solid–liquid bubble interface in partial nucleate boiling

Several models of heat transfer in partial nucleate boiling are identified in order to determine the relationship between the dominant physical parameters. The correlations are different for different models, so the main goal of this analysis is to determine the validity of each model and to identify the most dominant physical phenomenon in the nucleate boiling heat transfer. This is done by comparing the results of different models with a vast range of reliable experimental data. The comparison shows that the Sakashita and Kumada model gives the best results in the nucleate boiling heat transfer. It is also shown that the most dominating phenomenon in isolated partial bubbles zones is the transient conduction taking place mainly under the bubbles. This is in contradiction with a majority of the models that consider convection as the most important mode in the nucleate boiling heat transfer. The selected model can also be extrapolated and used in the case of fully developed bubbles zones.     

A theoretical study of H absorption at a Fe(110)–Pd(100) interface and Fe–Pd alloys

The electronic structure and bonding at a Fe(110)–Pd(100) interface was theoretically analyzed in the framework of semi-empirical quantum chemical calculations. The Fe–Pd interface was modeled by a Fe₇₄Pd₇₄ cluster and a Fe–Pd six layer slab.The extended Hückel tight binding (EHTB) method and its modifications, including repulsive interactions, were used to calculate the interfacial adhesion and the H-absorption energy.The energetic minimum position for H is found at the Fe–Pd interface closer to the Pd layer.The interfacial Fe–Pd distance result to be 1.73 Å where Fe–Pd develops a strong bonding interaction. An important metal–metal adhesion was also found.The changes in the Density of States (DOS) and the Crystal Orbital Overlap Population (COOP) were compared in different structures: clusters, slab and two types of Fe–Pd alloys.The H as an impurity is responsible for a Fe–Fe and Pd–Pd bond weakening.However, the H effect is much less detrimental for the Fe–Pd bonds at the interface.When H is located at interstitial sites in bulk Fe–Pd alloys, the Pd–Pd overlap population shows a notorious decrease in the case of fcc structures while for fct structures the change is only 12%. The intermetallic bonding was also weakened as compared with the pure alloys. The objective of this work is to bring a plausible explanation to the null permeability to hydrogen in Pd-coated Fe films.     

In vitro and in vivo assessment of the biocompatibility of an Mg–6Zn alloy in the bile

There is a great clinical need for biodegradable bile duct stents. Biodegradable stents made of an Mg–6Zn alloy were investigated in both vivo animal experiment and in vitro cell experiments. During the in vivo experiments, blood biochemical tests were performed to determine serum magnesium, serum creatinine (CREA), blood urea nitro-gen (BUN), serum lipase (LPS), total bilirubin (TB) and glutamic-pyruvic transaminase (GPT) levels. Moreover, tissue samples of common bile duct (CBD), liver and kidney were taken for histological evaluation. In the in vitro experiments, primary mouse extrahepatic bile duct epithelial cells (MEBDECs) were isolated and cultured. Cytotoxicity testing was carried out using the MTT method. Flow cytometry analyses with propidium iodide staining were performed to evaluate the effect of Mg–6Zn alloy extracts on cell cycle. The in vivo experiments revealed no significant differences (P > 0.05) in serum magnesium, CREA, BUN, LPS, TB or GPT before and after the operation. Based on the HE results, hepatocytes, bile duct epithelial cells, renal glomerulus and renal tubule tissues did not present significant necrosis. In the in vitro experiments, the cell relative growth rate curve did not change significantly from 20 to 40 % extracts. In vitro experiments showed that 20–40 % Mg–6Zn extracts are bio-safe for MEBDECs. In vivo experiments showed that Mg–6Zn stents did not affect several important bio-chemical parameters or, harm the function or morphology of the CBD, kidney, pancreas and liver. Our data suggested that this Mg–6Zn alloy is a safe biocompatible material for CBD.     

Feasibility of poly (ε-caprolactone-co-DL-lactide) as a biodegradable material for in situ forming implants: evaluation of drug release and in vivo degradation

The purpose of this study was to evaluate the technical feasibility of poly (ε-caprolactone-co-DL-lactide), P (CL/DL-LA), for injectable in situ forming implants (ISFI). The ISFI was prepared by dissolving P (CL/DL-LA) in N-methyl-2-pyrrolidone (NMP), and Testosterone undecanoate (TU) was used as model drug. The effect of various polymer concentrations, molecular weights (Mws) and drug loads on the drug release from the TU-loaded ISFI systems was investigated in vitro. The release of TU-loaded ISFI was also evaluated in rats. In addition, a subcutaneous rabbit model was used to evaluate the degradation and foreign-body reaction of P (CL/DL-LA) ISFI. The use of higher concentration of P (CL/DL-LA) with higher molecule weight and larger CL:DL-LA monomer ratio for the TU-loaded ISFI gave a slower drug release. The ISFI of 80/20 P (CL/DL-LA) (Mw 61?753):NMP 20:80 with 16% TU formulation increased serum testosterone levels in rats over a period of three months. The in vivo degradation and biocompatibility study of ISFI shows that P (CL/DL-LA) degrades by a process of bulk degradation and that the foreign-body reaction of this biomaterial is relatively mild. In summary, our investigations demonstrate that in situ parenteral drug delivery systems can be obtained from P (CL/DL-LA) solutions.     

Effect of bovine serum albumin on the functionality and structure of catanionic surfactant at air–buffer interface

Interaction of bovine serum albumin (BSA) with the solvent spread monolayer of a catanionic surfactant, octadecyltrimethylammonium dodecylsulfate, (C₁₈TA⁺DS^?) at the air–buffer interface was investigated by measuring the surface pressure with time and change in surface area. Dipalmitoylphosphatidylcholine (DPPC) was used as reference. Kinetics of BSA desorption from the interface to the buffer subphase, that of C₁₈TA⁺DS^? and DPPC through their interaction with BSA, were also studied at different BSA concentrations (in the subphase) and surface pressures. Surface pressure (π)–area (A) isotherms (at pH = 5.4, μ = 0.01, T = 298 K) revealed that the coacervate/DPPC monolayer becomes expanded in the presence of BSA at low π while their protein bound species are released into the subphase at high π. Film morphology, studied by epifluorescence microscopy (EFM) and atomic force microscopy (AFM), reveals that the sizes of the domains of both DPPC and coacervate decrease in the presence of BSA. Presence of BSA in the coacervate and DPPC monolayer was supported from AFM data analysis.