The choice of global geopotential model used in remove-restore technique for determination of regional quasi geoid from gravity data may affect the solution, in particular when the accuracy is supposed to reach a centimetre level. Global geopotential model plays also an important role in validating height anomalies at GPS/levelling sites that are used for the estimation of the external accuracy of quasigeoid models. Six different global geopotential models are described in the paper. Three kinds of numerical tests with use of terrestrial gravity data and GPS/levelling height anomalies were conducted. The first one concerned comparison of height anomalies at GPS/levelling sites ia Poland with corresponding ones computed from various global geopotential models. In the second one the terrestrial gravity anomalies in Poland and neighbouring countries were compared with corresponding gravity anomalies computed from global geopotential models. Finally the quasigeoid models obtained from gravity data with use of different global geopotential models were verified against corresponding height anomalies at GPS/levelliag sites in Poland. Data quality was discussed and best fitting global geopotential model in Poland was specified.

Energy management plays a crucial role in cabin comfort as well as enormously affects the driving range. In this paper energy balances contemplating the implementation of a heat pump and an expansion device in battery electric vehicles are elaborated, by comparing the performances of refrigerants R1234yf and R744, from –20°C to 20°C. This work calculates the coefficient of performance, energy requirements for ventilation (from 1 to 5 people in the cabin) and energy required with the implementation of a heat pump, with the employment of a code in Python with the aid of Cool- Prop library. The work ratio is also estimated if the work recovery device recuperates the work during the expansion. Comments on the feasibility of the implementation are as well explicated. The results of the analysis show that the implementation of an expansion device in an heat pump may cover the energy requirement of the compressor from 27% to more than 35% at 20°C in cycles operating with R744, and from 15% to more than 20% with refrigerant R1234yf, considering different compressor efficiencies. At –20°C, it would be possible to recuperate between around 30 and 24%. However, the risk of suction when operating with R1234yf at ambient temperatures below –10°C shows that the heat pump can only operate with R744. Thus, it is the only refrigerant that achieves the reduction of energy consumption at these temperatures.

2D position error in the Global Positioning System (GPS) depends on the Horizontal Dilution of Precision (HDOP) and User Equivalent Range Error UERE. The non-dimensional HDOP coefficient, determining the influence of satellite distribution on the positioning accuracy, can be calculated exactly for a given moment in time. However, the UERE value is a magnitude variable in time, especially due to errors in radio propagation (ionosphere and troposphere effects) and it cannot be precisely predicted. The variability of the UERE causes the actual measurements (despite an exact theoretical mathematical correlation between the HDOP value and the position error) to indicate that position errors differ for the same HDOP value.
The aim of this article is to determine the relation between the GPS position error and the HDOP value. It is possible only statistically, based on an analysis of an exceptionally large measurement sample. To this end, measurement results of a 10-day GPS measurement campaign (900,000 fixes) have been used. For HDOP values (in the range of 0.6–1.8), position errors were recorded and analysed to determine the statistical distribution of GPS position errors corresponding to various HDOP values.
The experimental study and statistical analyses showed that the most common HDOP values in the GPS system are magnitudes of: 0.7 (�� = 0•353) and 0.8 (�� = 0•432). Only 2.77% of fixes indicated an HDOP value larger than 1. Moreover, 95% of measurements featured a geometric coefficient of 0.973 – this is why it can be assumed that in optimal conditions (without local terrain obstacles), the GPS system is capable of providing values of HDOP ≤ 1, with a probability greater than 95% (2��). Obtaining a low HDOP value, which results in a low GPS position error value, calls for providing a high mean number of satellites (12 or more) and low variability in their number.

The research of development capabilities is a fundamental of strategic issues, which has to be taken into consideration by coal mines. This is particularly difficult in the current environment, which is determined by its crisis situation. In such conditions, it is necessary to take difficult decisions, and serious, strategic challenges into account, which allow for the crisis to be overcome, for the renewal and economic effectiveness of the operation of these coal mines, which have potential to grow, and closing the coal mines, which have not potential to grow. Due to the effects of such decisions, which concern not only coal mines but also the Silesian region, it is essential to prepare information to support them and promote rational choices. This is related to the issue of research for development possibilities. The article presents considerations related to the subject of research for development possibilities of coal mines in a crisis situation. Taking the results of literature study into account, the model of research process was developed, and identified the research issues concerning the following:

- the identification of external factors which determine the possibility of development of the Polish mines and drawing a schedule of their changes in the future,

- the identification of internal factors which determine the possibility of development of the Polish mines,

- developing a way for the assessment of the development potential of the coal mines, to show appropriate strategic options and action programmes for these options,

- determining possible strategic options and corresponding schedules, appropriate for the specific nature of the mines.

The proposition of their solutions, which were obtained in the process of using the specific methods and research tools, allowed the guidelines in terms of research of development capabilities of coal mines to be presented.

The economy of Slovakia experienced a turning point in the 1st half of 2008 and entered a phase of decline. The negative impacts of the global economic crisis became evident in the 2nd half of 2008 and led into a recession in the 1st quarter of 2009. The composite leading indicator was originally intended for forecasting of business cycle turning points between the decline and growth phases. The aim of this paper is to transform the qualitative information from composite leading indicator into quantitative forecast and verify whether the beginning of recession in Slovakia could have been identied in advance. The ARIMAX and error correction models are used for the composite reference series and GDP forecasts respectively. The nal result shows that the composite leading indicator is useful not only for identifying turning points, but also for the prediction of recession phase.

Structural biology is concerned with the three-dimensional atomic structure of the molecules of life, proteins and nucleic acids. It was born in mid-1950s with a visionary application of X-ray diffraction to structure determination of protein crystals, and for several decades “structural biology” and “protein crystallography” were synonymous. In the 1980s structural biology received new experimental support from NMR spectroscopy, but a true breakthrough occurred only recently, with the development of atomic-resolution cryo-electron microscopy (cryo- EM), enabling direct visualization of macromolecular objects without the need of growing crystals. The Protein Data Bank (PDB) was created in 1971 with merely seven protein structures known. In mid-1990s the PDB entered an explosive growth phase, ignited by advances of biotechnological methods of protein production and, even more importantly, by widespread use of synchrotrons as extremely powerful X-ray sources. The technological advances did not stop there, and today we have on offer ever more powerful X-ray Free Electron Lasers (XFELs), producing astronomically bright femtosecond X-ray pulses, which allow studying the structure of nanometer-sized crystals or even of single macromolecules. Thanks to all those methodological developments, the PDB holds today over 210,000 experimental macromolecular structures, many of which (such as those related to HIV or SARS-CoV-2) have fundamental importance for medicine as targets for rational drug design. In addition to innovative experimental methodology, structural biology has recently seen a huge progress of artificial intelligence (AI)-based methods of protein structure prediction, capable now of quite accurate divination of the three-dimensional structure for billions of protein sequences in very short time. However, those machine-learning algorithms, such as AlphaFold, recognize patterns that have been seen before, while for truly new sequences and for oligomeric proteins the prediction is still less than certain and needs experimental validation. It appears then that experimental structural biology is not quite dead yet and will remain the main source of reliable novel structural information for the foreseeable future.