This paper demonstrates that if a linear dependence of arc dissipated power on power supplied is introduced at an initial stage of analysis, then, with some simplifying assumptions, the classical Mayr model is obtained. Similarly, if this dependence is taken into account in a model with residual conductance, the modified Mayr model is obtained. The study takes into consideration the local phenomenon of sudden voltage drop accompanying linear current decrease occurring in the circuit breaker. To account for this phenomenon, the Dirac delta function and its approximation by a Gaussian function, representing power or enthalpy disturbances, are introduced to the power balance equation. It is demonstrated that both variants yield the same effect, leading to identical differential equations. Macromodels of the circuit-breaker arc are created and connected with the power source circuit with lin- early decreasing current. The results obtained were found to be consistent with experimental data available in the literature. The models presented are based on a fairly uncomplicated 1st order differential equation and offer a straightforward physical interpretation of the phenomena in question.
The author of the dissertation described two unpublished so far hand written musical Oktoihs (Znamenny chant) of the Old Believers from his private collection. Based on those manuscripts the author indicates the important codicological and paleographical features of musical writing of the Theodosian and Pomorian Old Believers. Furthermore, the author presents the structure of the Oktoih book used by the Old Believers and makes overview of the polish literature concerning the discussed issues. The aim of the dissertation is to encourage other collectors of ancient manuscripts to share their collections and elaborations with researchers.
The paper presents an estimation of liquefaction susceptibility of some soils from the coast of the Marmara Sea, which was heavily striken by the Kocaeli earthquake in 1999. Firstly, the results of field investigations are summarized. Then, the results of laboratory investigations of physical and mechanical properties of the soils collated from the sites investigated are presented. The mechanical properties relate to the compaction/liquefaction model of saturated soils. This model is briefly outlined, then respective experimental procedures dealing with its calibration described, and values of material parameters listed. Liquefaction potential of investigated soils is analysed using standard procedures, based on the grain size distribution curves and SPTs. Finally, the simulation of pore-pressure generation and onset of liquefaction of Turkish soils is carried out, using the compaction/liquefaction model. Discussion of some standard empirical procedures of estimation of liquefaction potential of saturated soils, conducted from the analytical point of view, is also presented.
This paper presents numerical simulationsof the behavior of a sandy layer subjected to a cyclic horizontal acceleration in shaking table tests, with a particular attention focused on the settlements of a dry sand layer, and on the liquefaction of saturated sand. A compaction/liquefaction model (C/L) is applied to these simulations. The infl uence of specifi c parameters of the model on the compaction and liquefaction of a sandy layer is shown and discussed. The results of simulations are compared with selected experimental data.
This paper presents the findings of a study of gas emissivity and the volumetric gas flow rate from a patented modified cellulose mix used in production of disposable sand casting moulds. The modified cellulose mix with such additives as expanded perlite, expanded vermiculite and microspheres was used as the study material. The results for gas emissivity and the gas flow rate for the modified cellulose mix were compared with the gas emissivity of the commercial material used in gating systems in disposable sand casting moulds. The results have shown that the modified cellulose mix is characterized by a lower gas emissivity by as much as 50% and lower gas flow rate per unit mass during the process of thermal degradation at the temperature of 900°C, compared to the commercial mix. It was also noted that the amount of microspheres considerably affected the amount of gas produced.
The paper includes the TG-DTG thermogravimetric air-testing of a cellulose mixture modified with the additives of expanded vermiculite or expanded perlite. A thermal degradation test was carried out at 1000°C with a simultaneous qualitative analysis of the emitted gases. During the thermal degradation process, the thermal effects were also measured. The research results indicate that expanded vermiculite or expanded perlite do not emit toxic gases during thermal degradation. The cellulose mixture modification, with the additives of expanded vermiculite or perlite, does not result in the creation of new gaseous compounds in the process of thermal degradation. A s investigated below, the mixtures tested in this article find application in gating systems for supplying liquid metal in no-bake moulds. Such cellulose-based material solutions shall allow the foundry industry to introduce less gas vaporising technologies within the entire casting production process.
The paper discusses problems arising in attempts to accurately represent dynamic processes of an electric arc by means of simple mathematical models. It describes the properties of the universal Pentegov model, employing any shape of static voltagecurrent characteristics of an arc. Next, it presents spectral and integral measuring methods for determining arc parameters in the Mayr, Cassie and Pentegov models of the electric arc with a forced sinusoid current circuit, with the raising static characteristics of hyperbolic-flat and hyperbolic-linear shape. The influence is discussed of the random power supply disturbances on errors of determining the mathematical model parameters.
Thermo-chemical treatments are known to increase the fatigue life of industrial parts. Due to the imprecise consideration of residual stresses in predicting the durability of components subjected to cyclic loading and their effect on the fatigue life, the authors developed a numerical model combining the influence of residual stresses with stresses caused by bending. The authors performed the numerical simulation with the use of Finite Element Method to analyse material behaviour during cyclic loading. The residual stress state developed during nitriding was introduced onto cross-section of the numerical specimen. The goal of this work was better understanding of the real conditions of the nitride steel fatigue processes and improving the knowledge about numerical predicting of the fatigue life for parts with residual stresses. The results of simulation were compared with plane bending fatigue tests. The presented method indicates the possibility of increasing the accuracy of the fatigue analysis of elements after surface treatment, increasing its certainty and the ability to perform better optimization of service life.
This paper is both a review and a study. It discusses the taxonomic status of Yellow Archangel (Galeobdolon luteum Huds.) from historical and contemporary perspectives, and gives a comprehensive list of synonyms for the discussed genera, species and lower taxonomic units, including their publication details. In the study it is postulated that G. luteum should be included in the genus Lamium. The hypothesis is verified by a comparative analysis between the representatives of the genera Galeobdolon and Lamium in four DNA regions: ITS, accD, rpoC1 and trnH-psbA. The analysis supported the determination of phylogenetic relationships among the studied taxa: G. luteum is not genetically distant enough from Lamium to be considered a separate genus, and integration of Galeobdolon and Lamium is legitimate.
A new time interval/frequency generator with a jitter below 5 ps is described. The time interval generation mechanism is based on a phase shifting method with the use of a precise DDS synthesizer. The output pulses are produced in a Spartan-6 FPGA device, manufactured by Xilinx in 45 nm CMOS technology. Thorough tests of the phase shifting in a selected synthesizer are performed. The time interval resolution as low as 0.3 ps is achieved. However, the final resolution is limited to 500 ps to maximize precision. The designed device can be used as a source of high precision reference time intervals or a highly stable square wave signal of frequency up to 50 MHz.
Twist extrusion is a processing method involving the extrusion of a sample with a prismatic cross-section using a tool composed of four prismatic parts bisected by a screw component. A beneficial change in mechanical durability is one of the main factors enabling the use of highly durable Al-Mg-Mn-Sc-Zr alloys to construct functional components of non-stationary robots. As part of the present research, ANSYS® software was used to simulate a twist extrusion process. An analysis of a sample entering and passing through the entire twisting area was performed, up to the point of full twisting of the base of the sample. The stress conditions in the sample were analysed as it passed through the twisting area. The highest stress values (reaching up to 600 MPa) were detected at the tips of the sample face as the sample exited the twisting area. The lowest stress values, at around 170 MPa, were detected at the side edges of the sample.
This paper presents the findings of fatigue strength tests of 15CrNi6 steel following low-pressure carburizing and oil quenching, subjected to cycles of one-sided three-point bending. The fatigue fractures were compared with the results of fatigue strength studies of 16MnCr5 steel following low-pressure carburizing and nitrogen quenching. The fatigue tests for 16MnCr5 steel were conducted as part of a high-cycle resonance test, with a pendular bending load. The study also involved an analysis of the effects on non-metallic inclusions in the structure on the mechanism of fatigue destruction. The inclusions were found to initiate fatigue cracks. In both cases, a similar method of a fatigue fissure initiation was observed, independent of the study method or specimen material.
The herein paper contains the results of investigations on a new type of cellulose blend used for the manufacture of profiles applied in the process of making gating systems in the foundry industry. A standard cellulose profile was subjected to an experiment. During the experiment the profile was filled with a liquid cast iron and at the same time the temperatures of the liquid metal crystallizing inside the profile were measured as well as the temperature of the outer layer of the profile was controlled. Further, the microstructure of the cast iron, which crystallized out inside the cellulose profile, was analysed and the cellulose, thermally degraded after the experiment, was verified with the use of the chemical analysis method. Moreover, a quality analysis of the original as well as the degraded cellulose profile was run with the use of the FTIR infrared spectroscopy. The presented results revealed that the cellulose blend is aluminium silicate enriched and contains organic binder additives. The cast iron, which crystallized out, tended to have an equilibrium pearlitic structure with the release of graphite and carbides. The generation of disequilibrium ausferrite phases was also observed in the structure.