Basic Material Characteristics Research Articles

4-D GEOMETRICAL MODELING OF MATERIAL AGING

The 4-dim intrinsic (material) Riemannian metric G of the material 4-D space-time continuum P is utilized as the characteristic of the aging processes developing in the material. Manifested through variation of basic material characteristics such as density, moduli of elasticity, yield stress, strength, and toughness., the aging process is modeled as the evolution of the metric G (most importantly of its time component G00) of the material space-time P embedded into 4-D Newtonian space-time with a Euclidean metric. The evolutional equation for the metric G is derived by the classical variational approach. Construction of the Lagrangian for an aging elastic medium and the derivation of a system of coupled elastostatic and aging equations constitute the central part of the work. The external and internal balance laws associated with symmetries of material and physical space-time geometries are briefly reviewed from a new viewpoint.

Synthesis and Characterization of ZnS Nanosized Semiconductor Particles within Mesoporous Solids

ZnS semiconductor quantum dots have been synthesized using a method involving melt exchange reaction inside the pores of MCM-41 and subsequent reaction with H(2)S. The ZnS quantum dots-MCM-41 composite, which has been studied with XRD, EDS, and BET techniques, is shown to have retained within the pores the formed quantum dots, with a size distribution exhibiting a maximum nanoparticle diameter of ca. 1.8 nm. The structure and the sorption properties of the ZnS/MCM-41 composite have been studied by means of X-ray diffraction, Fourier transform infrared spectroscopy, and surface area measurements. All experimental data reveal that all the final composite products, containing up to 9.3 wt % ZnS as verified by EDS analysis, keep the basic structural characteristics of MCM-41 materials, without significant reduction of their active surface areas. The quantum dot optical properties have been studied with UV-vis, photoluminescence, and photoluminescence excitation spectroscopies providing evidence for the low-dimensional character of the ZnS semiconductor particles.

Gauge length effect on the tensile properties of leather

AbstractTensile properties are important basic characteristics of materials and influence their end‐use and performance. More importantly, in the case of leather due to end‐use applications such as shoe uppers, automotive and furniture upholstery, mechanical properties such as tenacity are of extreme importance. Therefore, fundamental studies on the tensile properties of leather are needed. In this study, an attempt has been made to examine the effect of gauge length (GL) on the tensile properties of shoe upper leather. Two different specimens in the form of rectangular and dumbbell shapes have been cut from parallel and perpendicular directions to the body axis of the leather and have been tested. Results showed that the maximum breaking load and the percentage extension at break decreased with the increase in GL. Rectangular specimens showed a 30% decrease in maximum breaking load and a 13% decrease in percentage extension at break, while dumbbell specimens showed reductions in the order of 28 and 6%, respectively, as the GL increased from 9.53 cm to 23.5 cm. Highly varying supramolecular architecture of the collagen matrix and the frictional slippage caused by the free ends present in the collagen fibrils, which induce a weak‐link effect similar to the one found in cotton fibers and yarns, are considered to be the probable reasons for this behavior. A limited scanning electron microscopic study has been undertaken to pictorially represent the breakage of leather at different GLs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1202–1209, 2006

Temperature and dynamics problems of ultracapacitors in stationary and mobile applications

Ultracapacitors as a powerful energy storage systems are used in various areas of power electronics. Depending on the application, temperature and dynamics properties of these components have to be considered. These properties strongly depend on the characteristics of basic materials of the capacitors. The frequency and temperature dependence of the capacitance as well as of the internal resistance, ESR, is manly affected by the electrodes of activated carbon and the electrolyte. Under operating conditions differences of 15% and more of the capacitance due to a different structure of the electrodes are observed. Due to the reduced solubility of the conducting salt and the increased viscosity of the solvents for temperatures below freezing point the conductivity of the electrolyte drops drastically with decreasing temperatures. Thus, increases of the ESR between 200 and 700% between room temperature and −30 °C depending on the electrolyte are registered. Due to the slightly different selfdischarge of the single capacitors equivalent to a voltage drop of 4–12% within 3 days, the individual cell inside a module has to be protected by a cell voltage balancing unit. By an active cell voltage balancing unit connected in parallel to the capacitors a voltage drop will be leveled out after 1 h. In addition to the electrical characteristics of the ultracaps also the thermal properties of the single cell as well as of the modules have to be considered for the design in of these storage devices. By cooling elements integrated in the surface of the module casing and forced cooling the effective current load can be nearly doubled. Based on this know how ultracap modules were designed, which fulfill all the requirements of the applications in automotive and industrial electronics.

Crosslinked polyethylene compared to conventional polyethylene in total hip replacement: Pre-clinical evaluation, in-vitro testing and prospective clinical follow-up study

Background Polyethylene wear-induced osteolysis is a major cause of implant loosening in total hip arthroplasty. New crosslinked polyethylenes are presumed to give lower wear rates, but no long-term clinical results are available yet.Patients and methods We compared basic material characteristics and MTS hip joint simulator wear rates of a crosslinked polyethylene (Duration) to those of conventional polyethylene. In a randomized double-blind 5-year clinical follow-up study, 133 hips (67 conventional, 66 Duration) in 127 patients were followed-up for an average of 5 (3–6) years. Wear rates were measured using a computer-based edge detection method. The radiographic appearances of wear-related phenomena were recorded.Results The Duration polyethylene showed a significantly lower in-vitro wear rate in the simulator study (mean 22 (SD 2.3) vs. 40 (SD 1.5) mm3/106 cycles). Also, the in-vivo wear was lower for Duration (mean 0.083 (SD 0.056) mm/year) than for conventional polyethylene (mean 0.123 (SD 0.082) mm/year). All radiographic signs of osteolysis were less frequent in the Duration group.Interpretation Our study has given a substantial body of evidence—from lower wear rates, less frequent signs of osteolysis, and higher survival rates after a mean follow-up of 5 years—that Duration provides better clinical outcomes than conventional polyethylene.

Stimuli responsive materials: new avenues toward smart organic devices

“Smart” patternable polymer-based materials that can be designed from various molecular building blocks show great potential, as they may be used in many fields, including nanotechnology, biochemistry, organic and physical chemistry, and materials science. The focus of this highlight will be on the basic design characteristics of practical Stimuli Responsive Materials (SRMs), the wide range of potential applications and the challenges to be accomplished in this rapidly expanding area. In particular, recent developments are described which are related to two of the many fundamental aspects of stimuli triggered responses: those that are photo-triggered and those that are solvent triggered. These selected state-of-the-art examples demonstrate the large scope and diversity in terms of activation mechanism, response time and property control.

Methods for preventing magnetic deviation saturation of high power amorphous transformer

This paper summarizes the basic characteristics of amorphous materials, and thoroughly analyses the reason why magnetic deviation saturation occurs in high-power amorphous transformers. And also, the incremental amplitude method, the incremental pulse width method, the current integral pulse width adjustment method and some other methods are proposed to prevent magnetic deviation saturation.

Characterization of Starch Based Edible Coatings

While market globalization and increasing use of minimally processed foods require increased product shelf life, environmental care constraints induce us to search for natural materials to be used in effective packaging systems. Both these issues can be addressed by using edible coatings based on naturally occurring polymers. The characteristics of basic materials need to be modified in formulated coatings to obtain satisfactory results. As edible coatings must act as a barrier, the correct measurement of transport properties is extremely important in product development and in assessing effectiveness. In the present work, different starch samples were tested to obtain edible films or coatings. After optimizing concentration, composition, dispersion and gelatinization time and temperature, a high amylose starch was selected for preparation of the films. Films obtained by casting were characterized for water and oxygen permeability developing suitable and simple testing methods, finding a water vapour transfer rate of about 32 gm2 h−1 and an oxygen transfer rate of 5.6 cm3O2 m2 h−1. They were also tested for protection from UV radiation by adding foodapproved iron oxides.

Ensaio uniaxial de tração dos tendões dos músculos grácil e semitendinoso humanos

O uso de tendões humanos, de forma isolada ou associada, em reconstruções ligamentares do joelho é uma prática usual. A utilização desses enxertos (tendão patelar, duplo semitendinoso associado ao duplo grácil) apresenta evolução pós-operatória diferente, quando analisados os parâmetros : perda mínima da extensão, deslocamento ântero-posterior (artrômetro KT-2000), retorno as atividades esportivas. A presente pesquisa tem por objetivo analisar o comportamento mecânico de tendões humanos (grácil e semitendinoso), quando submetidos a ensaios uniaxiais de tração, até a ruptura. Como parâmetros mecânicos para análise e confronto foram considerados: tensão de ruptura (MPa), deformação relativa, módulo de elasticidade (MPa), energia de ruptura (N.mm) e velocidade de carregamento (mm/s). Os resultados permitiram concluir que: - o tendão do músculo semitendinoso é mais resistente que o tendão do músculo grácil; apresenta menores deformações relativas; acumula maior energia de ruptura; - a utilização destes tendões como enxerto único, impõe uma análise mecânica mais detalhada, pois apresentam comportamento mecânico distinto e são materiais história e tempo - dependentes (viscoelásticos).

ＡＺ３１マグネシウム合金板の深絞り成形性

Recently, magnesium alloys are often applied in the auto industries and electric appliances. Most of them are manufactured by using some casting methods. But, from the viewpoints of productivity and quality of product, it is easily expected that the development of press forming technology is strongly required along with other metals and alloys. It is therefore important to grasp the plasticity of magnesium alloys. The purpose of this work is to investigate the possibility of press forming on AZ31 magnesium alloy plate. So, the tensile tests were performed to understand its basic material characteristics, and press forming tests were strived to improve its deep-drawability. The results of this study are summarized as follows. From the tensile test, the elongation of AZ31 was about 10% at room temperature, but the elongation increases in increasing temperature and amounts to 80∼90% at 473 K. It was also found that the limit of drawing ratio of AZ31 plate resulted in 3.2 by heating the die at 473 K or above and by cooling the punch at room temperature or below.

Determination of the Mechanical Properties of Laminated Coatings at Various Temperatures

The basic physicomechanical characteristics of elastomer and polymer materials used in triboengineering as parts of laminated coatings are determined experimentally. The investigations are carried out under various mechanical and temperature loads. Results for some elastomer and polymer materials are presented as an example

Synthesis and characterization of copper containing mesoporous silicas

A series of copper containing mesoporous silicas has been prepared at room temperature using tetramethylorthosilicate as the source of silicon, a quaternary ammonium chloride salt as organic template surfactant and copper complexes obtained from organofunctional silicon molecules as ligands. Using this synthetic route, it was possible to prepare mesoporous materials containing up to 4.7 wt% copper. The structure and the sorption properties of the obtained materials have been studied by X-ray diffraction, Fourier-transform reflectance IR spectroscopy, transmission electron microscopy and surface area measurements. All experimental data reveal that calcined products containing up to 2.4 wt% copper retain the basic structural characteristics of MCM-41 materials, while higher copper loading leads to progressive destruction of hexagonal structure. Electron paramagnetic resonance was used to study the symmetry and environment of Cu(II) species in the silicate framework of the as synthesized and calcined materials, as well as the accessibility of these centers to polar adsorbed molecules, such as pyridine. The spectra of calcined materials indicate a distorted octahedral geometry for the Cu(II) centers which were easily accessible by pyridine molecules. Cyclic voltammetry showed that calcined copper containing mesoporous samples exhibit a marked electroactivity indicating that most of the copper centers are distributed on the mesoporous surfaces.

Geomagnetic Field Variations as Determined from Bulgarian Archaeomagnetic Data. Part II: The Last 8000 Years

The knowledge about past secular variations of the geomagnetic field is achieved on the basis of archaeomagnetic researches of which the Bulgarian studies form an extended data set. In Part I (Kovacheva and Toshkov, 1994), the methodology used in the Sofia palaeomagnetic laboratory was described and the secular variation curves for the last 2000 years were shown. In Part II (this paper), the basic characteristics of the prehistoric materials used in the archaeomagnetic studies are emphasised, particularly in the context of the rock magnetic studies used in connection with palaeointensity determinations. The results of magnetic anisotropy studies of the prehistoric ovens and other fired structures are summarised, including the anisotropy correction of the palaeointensity results for prehistoric materials, different from bricks and pottery. Curves of the direction and intensity of the geomagnetic field during the last 8000 years in Bulgaria are given. The available directional and intensity values have been used to calculate the variation curve of the virtual dipole moment (VDM) for the last 8000 years based on different time interval averages. The path of virtual geomagnetic pole (VGP) positions is discussed.

Electroluminescent Displays

AbstractThis paper will review the electrical and optical properties of both monochrome and color electroluminescent (EL) displays. A simple electrical model for thin film electroluminescent (TFEL) device operation will be presented and used to describe the luminance and power consumption of TFEL devices. The basic material characteristics desirable for EL phosphors will be described. Progress in the development of monochrome and color EL displays will be presented including TFEL and Active Matrix EL devices and phosphors.

Life–prediction for constant–stress fatigue in carbon–fibre composites

A detailed analysis has been carried out of the strength and fatigue behaviour under constant–stress cycling of four modern aerospace CFRP laminates, all having the common lay–up [(±45,0 2 ) 2 ] s . Despite some important differences in their basic material characteristics, the fatigue responses of the four materials were similar. This pattern of behaviour has resulted in the development of a descriptive model of constant–life fatigue which has then been used as the basis for a life–prediction procedure. Preliminary attempts at validation of the method have met with a reasonable degree of success and suggest that it could provide designers with a means of selecting newly developed composites for fatigue applications on the basis of far less experimental data than are currently needed for confidence in design.

Electroluminescent displays

This article will review the electrical and optical properties of thin film electroluminescent (EL) displays. A simple electrical model for thin film electroluminescent (TFEL) device operation will be presented and used to describe the luminance and power consumption of TFEL devices. The basic material characteristics that are desirable for EL phosphors will be described. Progress in the development of multicolor and full color EL displays will be presented including device structures and phosphor advancements. Recent work on devices that combine EL technology with high resolution active matrix circuitry to achieve high resolution displays for head-mounted applications will be described.

Electroluminescent displays

Abstract— This paper will review the electrical and optical properties of both monochrome and color electroluminescent (EL) displays. A simple electrical model for thin‐film‐electroluminescent (TFEL) device operation will be presented and used to describe the luminance and power consumption of TFEL devices. The basic material characteristics that are desirable for EL phosphors will be described. Progress in the development of multicolor and full‐color EL displays will be presented including device structures and phosphor advancements.

The compression mechanism of powders

Compaction of solid powders is an operation which is extensively carried out for the size enlargement of solid particles. Despite its crucial role in many fields, compaction is still more of an art than a science since many physical and chemical characteristics of the particles exert an influence during compression. In this study, basic characteristics of some pharmaceutical materials (microcrystalline cellulose and lactose) such as particle size and size distribution, particle shape, moisture content, surface area and apparent specific volume were measured. Their level of influence on compression and on the properties of the compact formed were assessed by measuring the strength of the compacts. A relationship was established between the apparent specific volume and compact properties. This paper discusses this relationship and applies it to ceramic powders.

Density matrix model for highly nondegenerate four-wave mixing in semiconductor laser devices

A model for highly nondegenerate fourwave mixing in semiconductor lasers has been implemented, with possible application to amplifiers operating under multifrequency optical fields and to oscillators used for frequency conversion. Fast phenomena, such as spectral hole burning and hot carrier effects, are accounted for in a unified approach through the density matrix formalism. Hence, the model is suitable for evaluating frequency mixing effects over a very wide range of beat frequency, starting from zero up to thousands of gigahertz. Interest in these phenomena has increased in recent years, both for the analysis of basic material characteristics and for application to devices for multichannel coherent optical communication systems. As an example, the model has been used to compute intermodulation effects in a travelling-wave amplifier, under multicarrier operation. The numerical simulation results are in satisfactory agreement with experimental measurements recently reported in the literature.

Impact of early surgery on outcome after aneurysmal subarachnoid hemorrhage. A population-based study.

Population-based patient materials have not been used earlier in assessing the effects of neurosurgical treatment on survival and functional outcome of subarachnoid hemorrhage. Moreover, the proportion of all subarachnoid hemorrhage patients who might be candidates for neurosurgical treatment has not been estimated. We compared the survival and functional outcome of two population-based patient materials from Central Finland in 1976 through 1978 (n = 146) and 1980 through 1987 (n = 351). The most important basic characteristics of both materials were similar. In the 1970s, only patients aged < 60 years with carotid territory aneurysms were operated on after an interval of 2 weeks from the bleeding. In the 1980s, early surgery was attempted, and the other exclusion criteria were abandoned. Allocation to medical or surgical treatment was not randomized. During the 1970s, only 14% of the patients had surgical treatment, with a median delay of 15 days after the bleeding; in the 1980s, the corresponding figures were 46% and 4 days. Despite these fundamental changes in the treatment policy, the survival up to 3 years in the 1980s was only marginally improved compared with the 1970s. Conversely, the functional outcome at 4 years after the bleeding was significantly better in the 1980s than the 1970s, with 82% and 64% of the survivors, respectively, being independent in the activities of daily living (P = .002). We estimated that 60% of all patients with subarachnoid hemorrhage might be candidates for neurosurgical treatment, provided that there are no delays in admission or evaluation. An active treatment policy of subarachnoid hemorrhage including early surgery only marginally improves survival, but the quality of life of the survivors is significantly better. Only 60% of all patients in the population with subarachnoid hemorrhage can, at least theoretically, benefit from surgical treatment.