Papers by Keyword: Lifetime

Abstract: Thick 4H-SiC epilayers have be grown with n-type and p-type doping in the range 1x10¹⁴ cm^‑3 to mid 1x10¹⁸ cm^‑3, with the purpose of investigating the influence of doping on carrier lifetime. Growth conditions were identical for all grown epilayers, except for the dopant gas flow rates. A drastic decrease in carrier lifetime was observed with increasing doping level, in both n-type and p-type layers. The decrease in lifetime could not be related to the Z_1/2 center but are rather due to an enhanced effect of direct band-to-band and Auger recombination’s (AR) at higher doping levels. Calculations of Auger coefficients for the recombination’s are indicating Auger recombination’s as the main recombination mechanism at the highest doping levels. Indications are made stronger from the temperature dependence of Auger coefficients. An increased background intensity arises around 400 K during temperature dependent time-resolved photoluminescence measurements of n-type epilayers are observed and are thought to be related to boron impurities.

Abstract: An electricity board acquires several transformers from a manufacturer in a belief that their advertised lifetime of the transformer thus purchased is true. However, they don’t take in the case of negligence in maintenance of transformer, which is a strenuous job. The advertised thirty-year lifetime is reduced to a mere two-year lifetime, mainly because of the degradation of the insulation medium (Transformer oil), thus increasing losses in the transformer and decreasing its efficiency. The degradation of transformer oil leads to safety hazards like transformer bursting, consequently forcing the electricity board to replace the transformer, thus incurring huge amount of costs. This is the most relatable problem faced by the electricity board in every state. This research work aims at listing out various properties of transformer oil and ascertaining major impurities in a transformer oil by testing it using various techniques. The proposed work deals with long term observation and analysis of transformer oil to determine its degradation rate. Breakdown voltage, Moisture content, Resistivity, Acidity, Furan Analysis and Dissolved Gas Analysis were done using Mushroom electrodes, Karl Fischer Titration test, Tan delta test, Potassium Hydroxide Titration, High performance liquid chromatography, and dissolved gas analyzer respectively. The results reveal that, deviation of Breakdown Voltage, Moisture content, and 2-Furaldehyde (1197ppb) from the permissible limits can indicate the aging of the transformer.

Abstract: Outstanding durability of plastic pressure and non-pressure pipes can cause difficulties, when a reasonable lifetime estimation is needed. It is impossible to prove the lifetime by testing, but there is a method of calculation that can provide a certain idea about the expected lifetime. The lifetime estimation is based on the assumption that the failure occurs as a result of the slow crack growth mechanism and it is calculated using the linear elastic fracture mechanics approach. Numerical simulations of crack growth in the pipe are necessary for this calculation. These simulations must consider various effects that can play a role in the lifetime. This paper deals with the lifetime calculations of a pressure and a non-pressure corrugated pipe considering the soil loads acting on pipes when they are buried. In the simulation of the pressure pipe, a combination of loads is applied that consists of internal pressure, residual stress and the soil loads. The influence of the loads is discussed. The non-pressure corrugated pipe is loaded by the soil loads only.

Abstract: The development of polymers has not stopped growing and taking more and more emphasis in our lives. From high-performance industries to mass-market industries, polymers are ubiquitous in every aspect of our lives, from where comes the pressing need to know their properties, characteristics, and behaviors more rigorously. This work is based on a study of the mechanical characterizations of thermoplastic polymers under the effects of damage. To serve this purpose, an experimental study was carried out on thermoplastic ABS (Acrylonitrile Butadiene Styrene) specimens. At first, we worked on altered specimens to define the mechanical characteristics of our material such as the elastic limit, the stress maximum, the breaking stress and the Young's modulus. On the one hand, and on the other hand we have created geometrical defects (discontinuity) on specimens in (ABS), to have the effect of defects on the mechanical characteristics of the material, afterwards a study of damage carried out by two methods to determine the critical fraction of life. To determine the lifetime of the ABS.

Abstract: Charge transport is one of the most important phenomena, which directly influences the performance of the energy storage and conversation devices. In this work, the authors provide an overview of various rechargeable energy storage battery chemistries and designs, and discuss the charge transport processes related to power capability of the lithium-ion technology. The load distribution by parallel connection of high power batteries or supercapacitor and high-energy cells is discussed and general conclusions are provided. Thus, the reduced peak power load on the high-energy cells are approved by simulation and experiment in passive parallel circuitry of high power and a high energy lithium-ion cells. The definition and advantages of the earlier deduced electrical loss time are explained. It is shown, that at a constant C-rate, defined as the ratio of the applied current and the rated cell capacity in Ah, the electrical loss time has a direct linear correlation to efficiency, and that the electrical loss time allows a direct power capability comparison of various battery cell chemistries and systems. The power capability, specific energy, and energy density of the industry relevant Li-ion battery cells based on electrical loss time approach are summarized and the following conclusions made. Today prismatic cells reach the maximum specific energy of small cylindrical cells, at the same time showing a little bit better power capability, than the investigated high energy cylindrical cells.

Abstract: This paper deals with the problem of stresses in the surface layer of materials after machining. It analyzes residual stresses as one of the factors affecting the state of the surface layer after machining. It describes the methods for measuring residual stresses and evaluates them from the point of view of suitability for industrial practice. A new method of measuring residual stresses in the surface layer of a workpiece for laboratory use has been proposed and experimentally tested. At the end of the article the options for further solutions in this area are proposed.

Abstract: Efficient sustainability management requires the use of tools that enable the quantification, measurement or comparison of material, technological and construction variants. Tools of this kind which have been developed around the world in recent years include various indicators, indexes, etc. Generally, technical, economic, ecological and socio-cultural areas must all be included. Such a tool can be used as a powerful marketing aid and as support for the transition to the “circular economy”. Life Cycle Assessment (LCA) procedures are also used, alongside other approaches. LCA is a method that evaluates the life cycle of a structure from the point of view of its effect on the environment. Processes starting with the mining of mineral resources and including their transport, production and use up to their final processing as waste (recycling) are all taken into account. In addition, consideration is given to energy and raw material costs, and to environmental impact throughout the whole life cycle – e.g. through emissions. The presented contribution focuses on the quantification of sustainability connected with the use of various types of concrete with regard to their resistance against the effect of degrading influences. Sustainability factors are also determined using information regarding service life and “eco-costs”. The aim is to present a suitable methodology which can simplify decision-making concerning the design and choice of concrete mixes from a wider perspective, i.e. not only from the aspects of load-bearing capacity or durability.

Abstract: We performed deep level transient spectroscopy (DLTS), in capacitance, constant-capacitance and current mode, on 5 MeV proton irradiated 4H-SiC p⁺-i-n diodes. The study has revealed the presence of several majority and minority traps, ranging in the 0.4-1.6 eV below the conduction band edge and in the 0.4-1.5 eV above the valence band edge. We present a comparison of the results obtained with the three modes and discuss the nature of the detected traps, in the light of previous results found in the literature. At last, the impact of the irradiation on the minority carrier lifetime is evaluated by electrical measurements.

Abstract: The dynamics of n-heptane adsorption and desorption on two silicas (Si-A and SBA-15) with different porosity was studied using positron annihilation lifetime spectroscopy (PALS). Simplified method of spectra analysis consisting in the summation of counts in the long-lived part of PALS spectra was used. It allowed to observe changes occurring in the minute time scale. The dependence of the number of counts on time could be fairly well approximated by exponential functions. It was found that the time required for reaching equilibrium in long cylindrical pores is up to ten times longer than in bell-mouthed interconnected ones. The longest time constants (ca. 5 min in Si-A and ca. 60 min in SBA-15) were observed for desorption in both samples.

Abstract: Thermo-fluctuation model of failure of one-dimensional nanocrystals is offered for wide range of change in temperature, time and applied loading. Unlike the classic models, which are based on the theory of reaction rates, in present model the failure initiation is related to the instability of atomic interaction. It enables to account for the effect of both temperature and applied loading on the lifetime of crystal within a framework of the unified approach. The model proposed was employed to predict the temperature dependence of both strength and lifetime of carbyne nanoconductor (CNC). Obtained temperature dependences agree well with the MD-simulation findings. Within the framework of the above model, CNC lifetime was estimated. It is exhibited that for temperatures not higher than 600K, CNC have a long-lasting lifetime, so, they can be used in nanodevices.