A simple analytical method is developed to estimate frequencies of longitudinal modes in closed hard-walled ducts with discontinuities in a cross-sectional area. The approach adopted is based on a general expression for the acoustic impedance for a plane wave motion in a duct and conditions of impedance continuity at duct discontinuities. Formulae for mode frequencies in a form of transcendental equations were found for one, two and three discontinuities in a duct cross-section. An accuracy of the method was checked by a comparison of analytic predictions with calculation data obtained by use of numerical implementation based on the forced oscillator method with a finite difference algorithm.
Aramaic receipts and title-deeds on clay tablets are formally distinguished in the 7th century B.C., although they are closely related juridical documents. Only two receipts are known at present and both have a triangular shape like loan contracts. Instead, titledeeds, often called sale acts, have a rectangular shape and are narrowest along the lines of writing. They are sealed on the upper edge of the tablet or in the upper part of the obverse. So far, there is only one Aramaic title-deed concerning a field and a second one fixing the boundary between two properties. Instead, four or five deeds concern the acquisition of persons, not necessarily slaves. Considering the state of the clay tablets and their somewhat inadequate edition, a new transliteration and translation of the operative parts of the deeds are provided below, omitting the lists of witnesses. Short comments are proposed also for the fragment of a title-deed dated in the 34th year of Nebuchadnezzar II.
In this paper, flow systems which are commonly used in fittings elements such as contractions in ice slurry pipelines, are experimentally investigated. In the study reported in this paper, the consideration was given to the specific features of the ice slurry flow in which the flow behaviour depends mainly on the volume fraction of solid particles. The results of the experimental studies on the flow resistance, presented herein, enabled to determine the loss coefficient during the ice slurry flow through the sudden pipe contraction. The mass fraction of solid particles in the slurry ranged from 5 to 30%. The experimental studies were conducted on a few variants of the most common contractions of copper pipes: 28/22 mm, 28/18 mm, 28/15 mm, 22/18 mm, 22/15 mm and 18/15 mm. The recommended (with respect to minimal flow resistance) range of the Reynolds number (Re about 3000-4000) for the ice slurry flow through sudden contractions was presented in this paper.
Standard shipping documents such as bills of lading, charter parties, ship management contracts or cargo declarations are prepared to facilitate international maritime traffic. Their application improves the process of determining the content of various types of contracts, which is important in view of the increasing pace of economic turnover. The Baltic and International Maritime Council (BIMCO) plays a leading role in the development of such documents. The shipping documents it creates, as well as individual contractual clauses, are widely used in global shipping. BIMCO's activity, including its contribution to the creation of rules, general terms and standard contracts for international trade, is fundamental, and BIMCO itself can be considered the most important international maritime non-governmental organization in this respect.
Over the past two years, coking coal prices have been the most volatile among major bulk commodities. On the supply side, the most important factor determining the movement of coal prices were weather problems affecting the exports of coal from Australia (Queensland), where the production of the best quality coking coals is concentrated. On the demand side, an important factor is the growing role of China on the market, which, being the world’s largest producer and consumer of metallurgical coal, has also become its largest importer. The dominant, about 75% share of China in the global spot market has resulted in their level of activity influencing the periodic price decreases or increases in international trade and prices based on CFR China (along with Australian FOB prices) have become important indicators to monitor market trends and determine levels of negotiated benchmarks. The exceptional volatility on the market led to a change in the quarterly price fixing mechanism for hard-load hard coal contractors in mid–2017 to apply a formula that assumes the valuation of their quarterly volumes based on the average of the basket of spot price indices. This reflects the broader trend of the evolving market, with growing spot market activity. The article describes the current situation on the international coking coal market and presents short-term forecasts for hard coking hard coal prices (PHCC LV), which are a reference point for fixing prices of other types of metallurgical coal (hard standard, semi-soft, PCI).
Over the past decade, the growing demand for imported coal from consumers (mainly Asian) coincided with supply constraints on the part of major suppliers. The sequence of events is referred to as force majeure. There were many events in the exporting countries, mainly including the cyclone and floods in Australia (Queensland, the world’s largest hard coking coal mining region). Imbalance between supply and demand causes commodity prices to be subject to cyclical changes, but in recent years the frequency and dynamics of these changes in the international metallurgical market (hard coking coal, semi-soft coking coal, PCI coal) has been extremely high. China, the world’s largest producer and consumer of coking coal, played a leading role in these events. Political action by the Chinese authorities regarding their domestic mining and metallurgical industries and the coke-chemical industry has made the country dethrone Japan since 2013 and has become a global leader in metallurgical coal imports. The rise of China’s importance in coal trading has become an important benchmark for monitoring market trends and benchmarking benchmarks. The market has become more bipolar and CFR China’s prices (in addition to Australia’s FOB prices). The paper describes the path of pricing mechanism changes in international trade contracts for metallurgical coal, against the background of market conditions that generate these changes.
The article is an attempt to present circumstances that nowadays determine negotiating, conclusion and performance of a multimodal transport contract in Poland. Author focuses in particular on parties’ approach, their business and legal conscience in this respect, as well as their decisions’ practical consequences. Doctrinal aspects of a multimodal transport contract are taken into account only as long as it is essential in examining the most common practices of the parties to the contract. Due to particular character of this publication, the method of author’s views presentation is as brief as possible.
The paper deals with the issue of financial efficiency, measured by the arithmetic rate of return, of indirect financial investments in the area of strategic raw materials (hard coal, copper, crude oil). Two forms of indirect investments were analyzed: shares of natural resources companies listed on the Warsaw Stock Exchange and futures contracts for strategic commodities: hard coal, copper and crude oil.
The time of the analysis is the first 6 months of 2019 and 2020. The year 2019 was regarded as an analysis of the period of economic growth, and the year 2020 was the analysis of the period of economic crisis. The comparisons were made in two dimensions. Firstly, it whether indirect commodity investments show the characteristics of efficiency resilience to the time of the economic crisis was checked (by comparing the achieved rates of return in the two analyzed periods). Secondly, which of the analyzed forms of investment (stocks, contracts) gives better investment results during economic growth and economic crisis was compared.
As it was shown in the paper, indirect commodity investments do not show an above-average rate of return neither during economic growth nor economic crisis. The achieved rates of return on shares compared to changes in the WIG20 index in the analyzed first half of 2019 were negative. Only one company showed a positive and significantly higher than the market rate of return. Very similar results were achieved by the analyzed companies in 2020.
On the other hand, the analysis of prices and rates of return on commodity futures contracts showed that in the period of economic growth it is effective to take a long position on crude oil contracts and a short position on hard coal contracts. In a period of economic crisis, the opposite position is profitable due to the observed growth in hard coal prices and a significant drop in crude oil prices.
The answers to the research questions posed in the paper do not provide indications for recommending indirect forms of investment in commodities as an alternative to analogous forms of other sectors of the economy. The analysis shows that the impact of the economic situation on the efficiency of commodity investment is most noticeable for crude oil, and the least (among the analyzed commodities) for indirect copper-based investments.
Blockchain is a technology, which could revolutionize many industries in the future. A system like that is based on a chain of blocks that is used for storing and transferring various data, forming a decentralized ledger. Although various fundamental projects based on the blockchain system in the energy industry are in their early stage of development, as well as other solutions, applications of blockchain technology in the broadly understood power engineering sector are considered to have a very large potential. This paper presents a brief description of the blockchain technology, its general operating principle and the possibilities it brings. The next section of the article contains a characterization of two exemplary and possible blockchain technology applications, which in the perspective of time may have a significant impact on the power engineering sector. The first solution is related to carrying out energy transactions, which could be conducted in an easy way directly between energy producers and consumers. Thanks to blockchain technology, this could lead to a partial decentralization in that area. The second proposed example concerns energy resources origin tracking, which would allow fixed origin attributes and parameters affecting the environment to be assigned to the generated energy. By implementing that solution, it would be possible to construct a fuel footprint of individual generating units. The article also mentions examples of other potential applications of blockchain technology in the power engineering sector.
The “plain and intelligible language” requirement performs a dual function within the framework of Council Directive 93/13/EEC of 5 April 1993 on unfair terms in consumer contracts. First, it is listed as a requirement for application of the exemption included in Art. 4(2) as regards policing terms relating to the main subject matter of the contract or to the adequacy of the price and remuneration. Second, the “plain and intelligible language” requirement is a general requirement addressed at all consumer contracts executed in writing (Art. 5). This paper examines the boundaries of the precept, and places particular emphasis on the recent developments in both EU and Polish law, where the requirement has been used to imply a host of information duties aimed at enhancing consumers’ capacity to foresee the consequences of the terms that they are assenting to. This apparently novel approach, which has been developing in piecemeal fashion in the CJEU’s ever-expanding case law, may trigger significant consequences in the field of consumer contract law. In some ways, expansion of the substantive scope of the requirement may be said to be motivated by the fact that courts, under Art. 4(2) of Directive 93/13, are unable to subject the adequacy of the price and remuneration against the services or supply of goods received in exchange to the substantive fairness test under Art. 3(1) (examination of terms through the prism of the notions of good faith and significant imbalance in the parties’ rights and obligations to the detriment of the consumer).
Hybrid Power Sources/Systems (HPS) are generally treated as local prosumer supplies. The paper presents a new approach to the strategy of electricity contracting from HPS, considering hybrid systems as a new type of quasi-centrally dispatched power units operating in Polish market conditions. The possibilities of contracting electricity from HPS, consisting of three electricity generation technologies: biogas plant, wind power plant and solar power plant, are presented. The opportunity to obtain additional income from the electricity trading on the balancing market was used. Proposals for a new mathematical description of HPS topology were also presented, including a feasibility function, which can be used for technical and economic analyses. The obtained results can be used as a direction of development in the field of optimization of hybrid source operation in cooperation with the power grid. Based on the conducted analyses, it can be observed that electricity sales contracts concluded for each hour of the day may bring additional profit for the investor. However, the strong dependence of the proposed strategy on the situation on the balancing market or other local electricity markets similar in their operations should be emphasized.
The article examines two Aramaic contracts found on the island Elephantine and dating from the early fifth century B.C. The first one is a loan contract providing for payment of compound interest on silver lent: interest not paid timely is to be added to the capital and itself becomes interest-bearing at the same rate until actual repayment. If this is not done at an agreed date, the remaining debt is doubled. The second contract concerns delivery of barley and lentils from a ship to a royal store-house deserving a garrison. The parties are the ship-officer and functionaries acting on behalf of the store-house, where barley and lentils are supposed to be brought. It is a contract of delivery combining its acceptation on the ship and the foreseen completion of the contract in the store-house with expected financial results. Both contracts refer to silver “by the stone-weights of Ptah” and record its alloy.