The Hopkinson pressure bar has been developed to calibrate and assess high g accelerometers’ capacity. The extreme caution is indispensable for performing calibration of severe characteristics, like the bearable super-high overload peak and wide duration of stress. In the paper, the Hopkinson bar calibrating system is being critically appraised. A limiting formula is deduced based on the stress wave theory. It indicates that the overload peak and duration of stress are limited by the elastic limit and wave speed of Hopkinson bar material. Both stress wave configurations in the form of linear ramp and cosine functions were designed theoretically to meet typical calibrating requirements. They were confirmed experimentally with the aid of the pulse shaping technique. Their corresponding calibration characteristics were analysed critically, and it was found that the cosine stress wave can achieve the values of acceleration peak or duration by π/2 times greater than those obtained with the linear stress wave. Finally, some suggestions are proposed for more extreme calibration requirements.
The paper presents the method of control of an induction squirrel-cage machine supplied by a voltage source converter. The presented idea is based on an innovative method of the voltage source converter control, consisting in direct joining of the motor control system with the voltage source rectifier control system. The combined control system gives good dc-bus voltage stabilization. In the applied control system the limits of the reference variables have been introduced. A correction of the estimated machine load torque is proposed. The new proposed solutions are confirmed by mathematical dependences, simulation and experimental results.
The article discusses the rules for judicial proceedings in cases for the establishment and distribution of a fund for limiting liability for maritime claims as they are set out in the Maritime Code and the Convention on Limitation of Liability for Maritime Claims (LLMC 1996). The author presented the basic convention principles regarding the constitution of the fund and related effects as well as the issue of their interpretation and application in national law of selected countries parties of the convention. The article discusses the regulation of the main stages of the fund proceeding in the Polish civil procedure.
The paper presents results of a study concerning an AlSi7Mg alloy and the effect of subjecting the liquid metal to four different processes: conventional refining with hexachloroethane; the same refining followed by modification with titanium, boron, and sodium; refining by purging with argon carried out in parallel with modification with titanium and boron salts and strontium; and parallel refining with argon and modification with titanium, boron, and sodium salts. The effect of these four processes on compactness of the material, parameters of microstructure, and fatigue strength of AlSi7Mg alloy after heat treatment. It has been found that the highest compactness (the lowest porosity ratio value) and the most favorable values of the examined parameters of microstructure were demonstrated by the alloy obtained with the use of the process including parallel purging with argon and modification with salts of titanium, boron, and sodium. It has been found that in the fatigue cracking process observed in all the four variants of the liquid metal treatment, the crucial role in initiation of fatigue cracks was played by porosity. Application of the process consisting in refining by purging with argon parallel to modification with Ti, B, and Na salts allowed to refine the microstructure and reduce significantly porosity of the alloy extending thus the time of initiation and propagation of fatigue cracks. The ultimate effect consisted in a distinct increase of the fatigue limit value.
The paper is dedicated to the discussion of elastic coefficients of wood. Parameters for wood presented in the literature are critically evaluated and discussed. The orthotropic mathematical model, with nine different elastic parameters, is one of the most often used models of wood. However, mathematical limitations on these parameters for the correct model are not well known. Based on these limitations, the verification of orthotropic elastic parameters for different species of wood is presented. The analysis shows that the published data are often unclear and sometimes wrong. The attempt to relate experimental results to the mean values specified in the standards is the second aspect considered in this paper. The designer, a user of these standards, should have clear information that the given parameters are specified for specific mathematical model and species of wood. This paper attempts to propose such a classification.
Financial management in a capital group is very important for its growth and operation. Liquidity risk management can be analyzed regarding their static and dynamic dimensions. The process can also be facilitated by cash management products offered by financial institutions. One of the mechanisms influencing the increase in cash management efficiency of a capital group examined in this article is cash pooling, notably multicurrency cash pooling. This type of product is based frequently on the virtual consolidation. Its essence is the consolidation of cash available on the accounts of individual system participants. Using this solution the capital group can manage surpluses and shortages achieving the “economies of scale” (cost reduction and maximization of interest income). Available one the banking services market solutions offer consolidation in USD, EUR, CHF, GBP. The article presents the definition of cash pooling and the essence of its operation. Based on the literature analysis, the article lists types of cash pooling and benefits associated with it. Following on from the solution described, the article presents a model of multicurrency cash pooling in a capital group, including steps necessary to implement it and proposed technical solutions. The solution is described, can be also successfully applied in capital groups of energy sector. Using multicurrency consolidation is very useful solution in deposits management for transactions concluded in international commodities exchanges.
This paper draws on an anthropological perspective on social security to explore the complex ways in which Czech- and Slovak-speaking migrants living in Glasgow negotiated their healthcare concerns and built security in the city and beyond. It is based on 12 months of ethnographic research conducted in 2012 with migrants who moved to Glasgow after 2004. Inquiring into healthcare issues and the re-sulting insecurities from the migrants’ perspective and in their everyday lives, the paper demonstrates how these issues were largely informed by migrants’ experiences of ‘uncaring care’ in Glasgow, rather than due to their lack of knowledge or understanding of the Scottish/UK health system. Furthermore, the findings reveal how these migrants drew on multiple resources and forms of support and care – both locally and transnationally – in order to mitigate and overcome their health problems. At the same time, the analysis also highlights constraints and limitations to the actors’ care negotiations, thus going be-yond a functional approach to social security, which tends to overlook instances of ‘unsuccessful’ or unrealised care arrangements. In conclusion, I propose that migrants’ care negotiations can be best understood as an ongoing process of exploring potentialities of care by actively and creatively opening up, probing, rearranging and trying out sources of support and care in their efforts to deal with per-ceived risks and insecurities in their everyday lives.
With the availability of UHV engineering technology, the scale of the power network is expanding, and the level of the short-circuit current is getting higher, which brings hidden trouble to the safe and stable operation of the power network. Further this article issued a method that optimized the configuration of a current limiter based on the reliability of the power network. According to the reliability analysis under the influence of a short circuit, the quantitative evaluation of reliability of the power network is realized by the calculation of the short-circuit current.Aquantitative model is established among reliability evaluation and the short-circuit current as well as load loss, the candidate installation site of a current limiter can be determined according to reliability quantification results. This method uses the particle swarm optimization algorithm to optimize the distribution of the limiter, aiming at the reliability level and the minimum number of current limiters in the short circuit of a power grid. Finally, taking the actual power grid of a province as an example, the result shows that this method can reduce the search space of the optimal solution, optimize the configuration of the current limiter, and effectively limit the short-circuit current and improve the reliability of the power network.
Increasing of the efficiency of convective cooling of the inner surface of a short duct by changing its geometry was studied by the use of electrochemical limiting current technique (ELDCT). The duct consisted of seven identical, cylindrical segments. The changes of the duct geometry were obtained by mutual displacement of neighbouring segments, towards the radial direction. Mean values of the mass transfer coefficient for each segment and friction losses for the whole channel were measured for Reynolds numbers spanning the range 7700–35300 at the five values of displacement parameter. The results were used for estimation of cooling efficiency. Recommended values of displacement were determined to point the favourable conditions of heat/mass transfer in the duct. The results may be used, e.g. in the design of heat exchangers and channels for cooling of turbine blades and electronic equipment.
The never before published paper is one of the last writings of Juliusz Żórawski (1898–1967), professor architect and theoretician of architecture. The notion of limited complexity introduced here relates to individual characteristics of the conceptual abilities of man. Tasks of architecture are based on prognoses, and this brings with it the risk of making errors. The author criticises J. Fourastié’s prognoses related to the Earth’s overpopulation in 3000 AD, which would force building new cities above the ground, contrary to human psychosomatic nature and habitude.
In this paper, flysch is presented as a representative material of a wide section of the Carpathian Mountains, with some areas in Poland highlighted. The geological structure of this area is complex due to the alternating layers of blocky rock masses and soil (Vessia et al., 2017). Such a complex pattern is seen in some Alpine flysch slopes, such as the Ingelsberg landslide area (Romeo et al., 2015). Many authors are monitored, predicted landslides (Allasia et al., 2013; Bertacchini et al., 2009; Casagli et al., 2010) by sophisticated sensors. The rock-soil flysch successions have become intensively fissured as a result of their geological history, weathering (precipitation and snowmelt), and long-term water retention, especially on the surface layers. These complex materials are characterised by heterogeneous lithologies, whose mechanical properties are largely uncertain. These geological structures have also been confirmed by monitoring and control studies performed on a large number of landslides (Bednarczyk, 2014). One of the most striking phenomena is the sudden decrease in the strength parameters in the studied rocks in the direction parallel to the layers due to watering. The process is made possible by heterogeneous fractured strong rock layers with high permeability coefficients for water. This study precisely describes the phenomena occurring at the contact area between the component layers of flysch under the wet conditions of a weak plane. An elastic-plastic analysis method that considers the developed strength model at the surfaces of the contact areas (Biernatowski & Pula, 1988; Pula, 1997) has been used to estimate the load capacity for piles working under a horizontal load. The piles are part of a reliability chain (Pula, 1997) in a given construction and are the first element of concern for monitoring (Muszynski & Rybak, 2017). A particular device intended to study the dependence of the shear stress on a fixed failure surface in a controlled consolidation condition was utilized. The study was conducted for a wide range of displacements and for different values of stabilized vertical stresses of consolidation. The complexity of the processes occurring in the shear zone, presented as a detailed study of the material crack mechanics, is highlighted. The laboratory results were used to construct the mechanical model of the slip surface between the soil and rock with the description supported by a neural network (NN) approximation. The artificial NN was created as a multi-layered, easy to use approach for interpreting results and for quick reconstruction of approximated values useful for the calculations presented in laterally loaded piles. For the calculations, long, sheared strips of material were considered in a semi-analytical procedure to solve a differential equation of stability. The calculations are intended to reveal the safety indexes for a wide range of boundary tasks as the most significant indicator for design decisions.
Due to rapid development of wireless systems and future implementation of the 5G system, it is necessary to increase number of the stations and/or number of radio emissions in current and new mobile service frequency bands. For each of the new or modified radio installation in Poland the Electromagnetic Field (EMF) strength levels has to be evaluated and measured/validated in accordance with allowable limits. In the paper the model of estimation of total EMF levels coming from mobile base stations radio emissions to be used for estimation of the whole country territory EMF levels is proposed. Results of preliminary analysis were also shown on practical examples. The model presented in the paper can be used for initial finding of possible places where exist the risk of exceedance of the maximum exposure limits and for analysis of potential radio network development taking into account current regulatory limits. The model will be used in computerized system SI2PEM which is developing in Poland for EMF levels controlling and validation purposes.