Synthesis of bimodified carbon nanotubes—a nanocomposite material

A nanocomposite material consisting of nanotubes modified with nitrogen and metallic nickel is synthesized using membrane-based technology. It is shown that the Ni nanoparticles are encapsulated in the nanotubes, while nitrogen substitutes for carbon in graphitic shells and form pyridine-like groups.Translated from Neorganicheskie Materialy, Vol. 40, No. 12, 2004, pp. 1455–1458.Original Russian Text Copyright © 2004 by S. Brichka, Prikhodko, A. Brichka, Kislii.     

The interpretation and use of fracture-surface morphology — a special case for polystyrene

The surface morphology of a system of polystyrene incorporating multilayer impact-modifier particles revealed crescent-shaped traces that could be explained as the intersection of the propagating crack and the craze zones initiated by the impact-modifier particles. This view is supported by a computer simulation which showed the variation of the shape of the intersection loci with the craze velocity/crack velocity ratio. Hence, by shape comparison or direct dimensional measurement of the crack-craze intersection, the craze velocity/crack velocity ratio at any point of the fracture surface can be determined. Together with data obtained from an instrumented Charpy impact apparatus, the craze velocity and crack velocity can be calculated. These results revealed a 100-fold increase in the crack velocity over a very short distance ( 20 m) during ductile-brittle transition. This method of interpreting and using fracture-surface morphology could be a very useful tool in studying the impact-modification phenomenon of the current system or other systems showing similar fracture-surface morphology.     

Choice of a γ-emission source for phase analysis of a material by nuclear γ-resonance

Consideration is given to the influence of nonresonance attenuation of resonance -quanta by the lattice of a -emission source, on the shape of a monoline in the Mössbauer spectrum. It is shown that this effect leads to increased error in the phase analysis of a material in nuclear -resonance spectroscopy. Criteria are determined for the suitability of a -emission source for use in the phase analysis of materials by this method. The actuality of the problem is shown for the most widely used Mossbauer isotopes.Translated from Izmeritel'naya Tekhnika, No. 6, pp. 55–57, June, 1994.     

A porous material prepared from the layer-type complex consisting of montmorillonite and α-naphthylamine

Aqueous mixtures of montmorillonite and -naphthylamine with various mixing ratios were kept at 353 K for 3 days with stirring to convert them into the layer-type complex (MNC) consisting of both components, and then dried at 403 K. The resulting blocks, several centimetres in size, were heated below 1473 K under nitrogen. The addition of -naphthylamine (NA) in the equivalent amount to the cation exchange capacity of montmorillonite resulted in the most attractive porous material which includes homogeneous pores of 35nm radius and exhibits a maximum pore volume of 0.8 ml g^–1 at 873 K. The samples containing greater and lesser amounts of NA gave a very brittle block and a less porous block after heating to high temperature, respectively. The materials obtained were also characterized by the waved card-house structure. The amount of NA added and the heat-treatment temperature did not vary the pore size so widely.     

A prognosis of patent activity development — II. Verification of the statistical theory for estimating the rate of development of a technical field

This article is a continuation of a previous article in World Patent Information, Vol. 8 No. 2, pp. 122–142, which described the basis of a statistical theory of the development of a technical field. It presents a detailed verification of the possibility of failure of the theory through not describing the development of patent activity with sufficient accuracy. The analysis is based on the simplest model of the theory and discusses in detail:

• 1.1. Analysis of activity in the field of coil dialyzers.
• 2.2. Analysis of Edison's patents.
• 3.3. Application of the theory to several examples published in World Patent Information.
• 4.4. Analysis of citations.

The main conclusions are that the simple model of the theory is relatively accurate for fields of small extent but for large fields, or those comprising several sub- fields, the simple model is not satisfactory. For extensive files the simplest model can be used to provide a rough estimate of trend of development.     

Preparation and comparative characterization of keratin–chitosan and keratin–gelatin composite scaffolds for tissue engineering applications

We report fabrication of three dimensional scaffolds with well interconnected matrix of high porosity using keratin, chitosan and gelatin for tissue engineering and other biomedical applications. Scaffolds were fabricated using porous Keratin–Gelatin (KG), Keratin–Chitosan (KC) composites. The morphology of both KG and KC was investigated using SEM. The scaffolds showed high porosity with interconnected pores in the range of 20–100 μm. They were further tested by FTIR, DSC, CD, tensile strength measurement, water uptake and swelling behavior. In vitro cell adhesion and cell proliferation tests were carried out to study the biocompatibility behavior and their application as an artificial skin substitute. Both KG and KC composite scaffolds showed similar properties and patterns for cell proliferation. Due to rapid degradation of gelatin in KG, we found that it has limited application as compared to KC scaffold. We conclude that KC scaffold owing to its slow degradation and antibacterial properties would be a better substrate for tissue engineering and other biomedical application.     

Nuclear magnetic resonance imaging – a potential method for analysis of bone material

The basic usage of nuclear magnetic resonance (NMR) microimaging for materials characterization is introduced. An application of microimaging for three-dimensional structural study of trabecular bone is presented with elementary types of image presentation. Solid bone in itself does not produce any significant NMR intensity and natural lipids and/or added 70% ethanol has been used as a signal source. The applied pulse sequences were three-dimensional spin echo and three-dimensional chemical shift selective spin echo. © 1998 Chapman & Hall     

Sintering behaviour of MgAl2O4—a prospective anode material

Awareness in environmental hygiene and escalation in the energy cost in electrometallurgical industries have necessitated a reauditing of the production technologies, more so in the case of aluminium as it is a highly energy intensive process. Metal aluminates are of interest due to their technological applications in aggressive environments. The preparation of the metal aluminates usually involves the solid state reaction (SSR) of the corresponding metal oxides or sulphates at high temperatures. The present investigation is the preparation of MgAl₂O₄ using the metal oxides by solid state synthesis. The compacts were sintered at high temperatures and their properties such as particle size, density, porosity, hardness, ac electrical conductivity and dielectric behaviour were evaluated. The phase formation and structural properties have been ascertained by XRD, FTIR, TG/differential thermal analysis (DTA) and scanning electron micrograph (SEM) studies. The sinterability characteristics of the materials strongly dependent on the temperature of the processing. The XRD patterns confirm the phase formation of MgAl₂O₄. The FTIR spectra show the structural details of the synthesized compound. From the SEM micrographs, it is revealed that the agglomeration process progresses with the increasing temperature. The ac electrical conductivity and dielectric behaviour of aluminates strongly depend upon sintering time, temperature and spinel formation.     

Determination of the reduced matrix of the piezoelectric, dielectric, and elastic material constants for a piezoelectric material with C∞ symmetry

We present a procedure for determining the reduced piezoelectric, dielectric, and elastic coefficients for a C(∞) material, including losses, from a single disk sample. Measurements have been made on a Navy III lead zirconate titanate (PZT) ceramic sample and the reduced matrix of coefficients for this material is presented. In addition, we present the transform equations, in reduced matrix form, to other consistent material constant sets. We discuss the propagation of errors in going from one material data set to another and look at the limitations inherent in direct calculations of other useful coefficients from the data.     

Inelastic material behavior of polymers – Experimental characterization,formulation and implementation of a material model

In this contribution an experimental procedure based on displacement controlled tensile tests at different rates of loading, relaxation experiments and deformation controlled loading and unloading processes with intermediate relaxations to experimentally characterize and classify the nonlinear, inelastic mechanical behavior of polymers is presented. These experiments provide data for a structured approach to parameter identification. In line with the experiments, a small strain uniaxial viscoplastic material model is derived, subsequently generalized to multiaxial loadings and implemented into a finite element program. The combination of the experimental procedure and the proposed material model is then used to characterize and model the mechanical behavior of the thermoplastic polypropylene. After the identification of the necessary material parameters, stress–strain curves have been computed for different uni- and multiaxial loadings and are compared with experimental results.     

Wedge-plate shearing interferometers for collimation testing: use of a moiré technique

Various optical arrangements of a double-wedge-plate shearing interferometer are presented for checking laser beam collimation. The use of moiré fringes is found to be advantageous for setting the shear fringes parallel to the direction of shear in order to obtain a well-collimated laser beam. The experimental procedure and various details of the interferometer are discussed. A brief summary of a few methods for collimation testing that use a wedge plate is also given. The accuracies achievable with shearing interferometers that use a parallel plate, a wedge plate of small angle, a double wedge having a large wedge angle, a wedge plate of large angle along with two flat mirrors, and a wedge plate having a large angle are compared and summarized.     

Multi‐rate digital control for a cascaded system consisting of two subsystems with different input time delays

Abstract

This paper presents a multi‐rate state‐space control scheme for digital control of a cascaded continuous‐time system with fractional time delays. First, a discrete‐time state‐space representation of a continuous‐time system with a fractional input delay is established. Based on the time‐delay digital modelling, an ideal state reconstructor is also presented such that system states are exactly reconstructed via the measurement histories of inputs and outputs without a state observer. Next, a time‐delay subsystem (designated subsystem 1) with a fast sampling rate is designed to form the inner loop of the overall system, then the designed closed‐loop subsystem 1 is cascaded with a time‐delay open‐loop subsystem 2 with a slow sampling rate. A digital modelling of the time‐delay open‐loop subsystem 2, based on a fast‐rate sampling, is also formed for obtaining the digital modelling of the overall cascaded continuous‐time system by using the block‐pulse function approximation. Then, the fast‐rate overall system is converted into a slow‐rate model via the newly developed model conversion technique. Furthermore, subsystem 2 is separated from the slow‐rate overall system via a linear transformation for achieving a reduced‐order subsystem design. As a consequence, a digital control law is determined on some specific goals for the overall system. The proposed method is suitable for digital control of a multivariable, multi‐rate, time‐delay system in which state variables are not accessible.     

Crystal growth and structure of L-methionine L-methioninium hydrogen maleate—a new NLO material

Abstract

A new organic nonlinear optical (NLO) crystal from the amino acid family, viz., L-methionine L-methioninium hydrogen maleate (LMMM), has been grown by slow evaporation method from aqueous solution. Bulk crystals were grown using submerged seed solution method. The structure was elucidated using the single crystal x-ray diffraction data. The compound crystallized in the space group P2₁ and the unit cell contains a protonated L-methioninium cation and a zwitterionic methionine residue plus a maleate anion. The backbone conformation angles Ψ¹ and Ψ² are in cis and trans configurations for both the methionine and methioninium residues, respectively. Amino and carboxyl groups of the methioninium and methionine residues are connected through N–H…O hydrogen bonds leading to a ring R₂²(10) motif.     

Simulations of nonlinear fracture process zone in cementitious material—a boundary element approach

A boundary element method based numerical model is presented to simulate the nonlinear fracture process zone in cementitious materials. A cohesive type stress-separation constitutive relationship (-w curve) is incorporated in the model to represent the process zone. Numerical algorithms for both force-controlled (prescribed loading history) and crack-tip-control-led (prescribed crack tip position) are implemented to allow whole range simulations, including strain-softening and snap-back behavior. The numerical program includes special features to permit re-adjustment of nodal points such that accurate determination of the crack-tip position is achieved. A series of numerical simulations on both 3-point beams and double cantilever beams (DCB) are conducted to investigate the development of the inelastic process zone with respect to load level, loading configuration, specimen size, and the stress-separation relationship in the process zone. Size effect on fracture resistance is clearly demonstrated. Conclusions are drawn regarding the importance of determining the details of -w curve (i.e., the values of f _t and w _c )and the need for re-evaluating the R-curves approach in cementitious materials.     

Effect of an external electrostatic field on ultrasonic machining of a dielectric material—an experimental study

The paper deals with the experimental study of the effect of an applied electrostatic field on ultrasonic machining of glass. Cylindrical cavities are machined in glass specimens (? 1-3 mm thick), both without and in the presence of a field. It is found that the time required for a 0-38 mm deep cut is reduced by about 10-20% due to the presence of a field. Further, the tool penetration rate is found to increase with the penetration of the tool into the workpiece. Using the analysis of variance technique, the observed data are analysed to show that the change in the rate of machining in the two cases is not due to chance but due to the presence of the field.     

A surface ionization detector for gas chromatography: use of a supersonic free jet

A new design of a gas chromatographic surface ionization detector (SID) based on hyperthermal positive surface ionization is described. There are two requirements: use of a supersonic free jet nozzle and the high-work-function surface of rhenium oxide. This detector, which is sensitive in response to all the organics, can be operated as an universal detector with much higher sensitivity toward some species having low ionization energy but with selectivity to a lesser degree than that of a conventional SID. The minimum detectable amount (at S/N = 3) of pyrene is around 4.4 × 10(-)(13) g/s, with linearity greater than 10(6), while that of toluene is around 10(-)(12) g/s. Other unique properties are (1) the ability to control the degree of selectivity through molecular kinetic energy, the surface, and its temperature and (2) a very short response time.     

The SEĖ method for determination of behaviour laws for strain rate dependent material: Application to polymer material

The need to model fracture in crashworthiness by means of finite element codes is a real challenge for research. Before implementing fracture criteria, an excellent knowledge of the stress and strain states in the material just before the crack appearance is the first condition necessary to ensure the model development. At present, most of the material behaviour laws, for example for steel, are only defined until the maximum force when necking occurs. For polymers, the early occurrence of the diffuse necking leads to an experimental technique in which the speed loading is controlled in real time to maintain a constant strain rate during the test. This technique is not however used, due to technical limitations, for high strain rate behaviour laws. In this paper, the authors propose to use the heterogeneity of the displacement field on the surface of the tensile specimen as an initial condition to identify behaviour laws. The method developed uses the information in all the surface zone of the specimen by using digital image correlation. Stresses, strains and strain rates are then obtained to build a surface behaviour called the SE? surface. By cutting it, the experimental behaviour laws for a range of large strains and strain rates are then defined for model identification.