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EN
The safety of mining operations in hard coal mines must be constantly developed and improved. There is ongoing multi-directional research focused at best recognition of the phenomenon associated with the properties of the coal-gas system and its connections with mining and geological conditions. This article presents the results of sorption experiments on coals from the Upper Silesian Coal Basin, which are characterized by varying degrees of coalification. One of the parameters that describes the kinetics of methane sorption, determining and providing valuable information about gas hazard and in particular the risk of gas and rock outbursts, is the effective diffusion coefficient De. It is derived from the solution of Fick’s second law using many simplifying assumptions. Among them is the assumption that the carbon matrix consists of only one type of pore-micropores. In fact, there are quite often at least two different mechanisms, which are connected to each other, related to the diffusion of methane from the microporous matrix and flows occurring in voids and macropores. This article presents both the unipore and bidisperse models and a set of comparisons which fit them to experimental curves for selected coals. For some samples the more complex bidisperse model gave much better results than the classic unipore one. The supremacy of the bidisperse model could be associated with the differences in the coal structure related to the coalification degree. Initial results justify further analyses on a wider set of coals using the methodology developed in this paper.
2
Content available remote Modelling of mass transport in watercourses at unsteady states
EN
In terms of quality particularly difficult to describe are processes of mass exchange between different phases (e.g., atmospheric air-water, water-river sediment, water-algae, etc.). Whitman's model is most often used to describe the mass transport processes through the phase boundary. Theoretical analysis of the mass transfer process through the phase boundary showed that in unsteady states, the calculation results obtained from Whitman's model differ from the results obtained using the accurate diffusion model. These differences are due to the fact that concentration profiles in the direction of diffusion process change in time. Assumptions for Whitman's model do not include changes in the concentration distribution over time. Therefore, the correction factor was introduced to Whitman's model. The correction factor is defined as a parameter that multiplies a concentration derivative over time in the mass transport model. The correction factor can be used to estimate the effective diffusion coefficient of the substance that permeates from the aqueous phase to the sediment. The correction factor improves the degree of fit of the mass transport model to the measurement data. It can be used to estimate the effective turbulent diffusion coefficient from water phase to the sediment phase.
EN
A model most often used for the description of the processes of mass transport through phase boundaries is the model of Whitman. Results of calculations obtained using this model may occasionally considerably differ from the results obtained using diffusion models. Thus an attempt has been made to correct the model proposed by Whitman. The dynamics of the processes of mass transport from a liquid phase (river water) to a solid phase (layer of material in the river bottom) has been analysed. Several equations have been derived describing the rate of absorption with a chemical reaction and periodical changes of the concentration of the analysed substance. An attempt has been made to determine the relation between the concentration gradient and concentration at the phase boundary. In dynamic conditions, the concentration gradient at the phase boundary can be approximated by means of time dependence of a linear combination of concentration, delayed concentration, and concentration derivative at the phase boundary. Analysis of the dynamics of the absorption process with the chemical reaction enabled one to derive an equation describing the stream of the substance penetrating to the inside of the solid phase. Such equations may be used to determine the error generated by the film model of Whitman for the process of mass penetration.
PL
W artykule podjęto temat wyboru techniki fotoporządkowania ciekłego kryształu. Technologia ta jest alternatywą dla najczęściej stosowanego rubbingu, czyli jednostronnego polerowania warstw poliimidowych i poliamidowych. Zarówno w przypadku rubbingu (buffingu), który ma naturę kontaktową, jak i bezkontaktowego fotoporządkowania efektem pracy jest wytworzenie anizotropii warstwy, która następnie ma za zadanie porządkować leżącą bezpośrednio na niej warstwę ciekłego kryształu (LC). Rubbing jest metodą stosunkowo prostą i tanią i jest zwyczajowo używany przy produkcji wyświetlaczy ciekłokrystalicznych. W trakcie polerowania mogą jednak powstawać uszkodzenia struktury matrycy aktywnej oraz tworzyć się pyły, które są szkodliwe zwłaszcza dla bardzo cienkich warstw ciekłego kryształu. W związku z tym poszukuje się metod alternatywnych porządkowania. Z fotoporządkowaniem mamy do czynienia wtedy, gdy anizotropia warstwy porządkującej wywołana jest przez ekspozycję materiału fotoczułego na działanie światła ultrafioletowego spolaryzowanego liniowo. Jest to proces bezkontaktowy, więc eliminuje on większość wymienionych wcześniej wad rubbingu. Ponadto umożliwia pracę na plastycznych oraz zakrzywionych podłożach. Istnieją cztery różne drogi realizacji procesu fotoporządkowania warstwy światłoczułych materiałów organicznych: 1) fotodegradacja w materiałach poliimidowych, 2) izomeryzacja cis-trans azozwiązków, 3) czysta reorientacja związków azowych w polu potencjału światła UV oraz 4) sieciowanie w strukturze polimerowej. W pracy przedstawiono krytyczny przegląd wyżej wymienionych metod. Zastosowanie fotoporządkowania badane jest pod kątem przydatności w komórkach działających w oparciu między innymi o efekty: FLC (ang. ferroelectric liquid crystal, ciekły kryształ ferroelektryczny), TN (ang. twisted nematic, skręcony nematyk), BTN (ang. bistable twisted nematic, bistabilny skręcony nematyk), VAN (ang. vertical alignment nematic, pionowa deformacja fazy nematycznej), IPS (ang. in plane switching, przełączanie w płaszczyźnie) i inne. Celem poniższej pracy jest porównanie i określenie przydatności różnych metod fotoporządkowania dla technologii przetworników ciekłokrystalicznych o dużej jasności zobrazowania.
EN
In this study we consider the topic of the photoalignment of liquid crystal material. It is an alternative method to the rubbing of polyimide and polyamide layers. Both techniques provide the anisotropy in organic layers. This anisotropy aligns overlaying liquid crystal. The rubbing is a well known and cheap technique and it's ordinarily used in liquid crystal displays manufacturing. However, it has several disadvantages, for example it produces dust particles and charges the layer. Furthermore it may damage the surface electronic. These drawbacks can be critical factors in working with thin liquid crystal layers (about 2-5 µm) for example ferroelectric and antiferroelectric Lcs. Heterogeneity at the microscopic level can be noxious especially in the area of some types of liquid crystals and in manufacturing high-resolution liquid crystal displays (over 40”) and state-of-art projector display systems. In order to omit these problems, very important for the future work is to develop a new, universal and high-performance, technique for liquid crystal aligning. One of alternatives is photoalignment. It eliminates many of drawbacks mentioned above. This technique uses light (generally linearly polarized ultraviolet light, LPUV) to produce anisotropy in photodephiniable materials. In addition this technique allows us to obtain layers on plastic or curve surfaces. We can distinguish four main photoalignment mechanisms (including photo-chemical reactions and photo-physical changes): (1) cis-trans isomerization in azo-structures: pure dyes films, polymers containing azo-groups and monolayers of azodyes, (2) pure reorientation of photo-chemically stable azo-dyes molecules, (3) photodegradation in polyimide materials and (4) crosslinking in cinnamoyl and coumarin side-chain polymers. There are some modifications among these procedures, such as polymerizable azo-dyes or Langmuir-Blodgett films. Photoalignment is investigated in diverse liquid crystal modes, such as: twisted nematic (TN), vertical alignment (VAN), in plane switching (IPS) and many others. In this paper we describe all of the photoalignment mechanisms mentioned above and compare their ability to align the liquid crystal material in the field of application in various modes of LC cells.
5
Content available remote Modeling of articular cartilage replacement materials
EN
The development of replacement material for human articular cartilage exhibiting similar mechanical properties as the native tissue is a problem of high actuality in biomeclicine. In the present work a new condensed collagen material is investigated. The study aims at developing a mechanical model especially adapted to this particular collagen material. For this purpose, a viscoelastic-diffusion (VED) model is proposed, accounting for two different diffusion evolutions assumed. Moreover, the need for a gradient material description is discussed in order to cover fabrication influences leading to a variable Young's modulus for the material. On this background, a phe-nornenological law is presented to predict deformation-dependent diffusion behavior and internal reaction forces. Furthermore, the present approach allows a practible identification of diffusion parameters. The theoretical model is implemented into a finite element code and parameters are identified by tension tests. The simulation results are validated experimentally.
6
Content available remote Model transportu i dyfuzji w aspekcie zarządzania środowiskiem naturalnym
PL
W artykule podjęto próbę zastosowania tez modelu transportu i dyfuzji do sterowania jakością powietrza atmosferycznego. Proponowany model umożliwia identyfikację sprawców zanieczyszczeń powietrza, a tym samym przypisanie im ekologicznych negatywnych skutków ich działalności. Zagadnienie sterowania jakością powietrza atmosferycznego sprowadzono do zagadnienia programowania liniowego.
EN
The paper presents the attemption to seploy so-named transportation and diffusion model to control of quality of the atmospheric air. The proposed model offers the possibility to identify pollution originators and to attribute them their activity results. The atmospheric air control problems comes to linear programming issues.
EN
The paper presents the modeling of transmittance measurement in a finite layer of whole blood. To describe light propagation in whole blood medium, a Monte Carlo simulation was used. The propagation of light in whole blood medium in the model required the assumption of photon transport approximation in highly scattering media. We have analyzed collimated-diffuse transmittance, which depended on the technique of free path length simulation. The Monte Carlo simulation was compared with the diffusion model designed for a finite incident light beam and available measurement data of whole blood optical density. The research revealed that discrepancy between the models discussed may be attributed to inaccuracy of the diffusion model due to an increase of anisotropic radiance under the thin sample conditions. Moreover, comparison of the Monte Carlo simulation versus measurement data showed that adding off-sets enabled agreement between them for hematocrit up to 60-70%, which is sufficient for many applications in oximetry. In fact, discrepancy in the Monte Carlo simulation, requiring off-sets to fit measurement data, most likely originates from measurement problem, such as divergence of light source or perturbation of light beam.
EN
The thermohaline characteristics of the Gulf of Aqaba, Red Sea, depict a well-defined seasonal pattern of winter mixing from December to April and summer stratification from May to November. This thermohaline structure is a major controlling factor of the nutrient, chlorophyll a and primary productivity seasonal cycles. The nitrate and chlorophyll a concentration records generated down to 200 m at a vertical resolution of 25 m - weekly during 1994, 1995 and every two weeks from April 1997 through to December 2000 - are employed to assess the nitrogen flux across the summer thermocline of the Gulf of Aqaba. The flux calculations are based on a simple diffusion model that incorporates the physical stress eddy diffusivity factor Kz and a biological stress factor k. Both Kz and k are calculated using the Michaelis-Menten equation and the nitrate concentration gradient. The total nitrate flux of the Gulf of Aqaba during the seven summer months (May-November) is estimated at 0.52 mole N m-2. In relation to established primary productivity values (75.5 g C m-2 (May November)-1) and the generated chlorophyll a records, this yields an f fraction of new to total primary production of 0.50. This relatively high f value is discussed with respect to the geophysical characteristics of the Gulf of Aqaba and similar oceanic basins. The remaining 50% is accounted for by cross-sectional flow from the relatively nutrient-rich coral reef coastal habitat and rapid recycling, triggered by high irradiance and water temperature.
9
Content available remote Double diffusivity from the distributed source on surface of a layer
EN
The solution has been obtained for the space problem of admixture diffusion by two ways allowing for mass transitions between the states under action of a constant circular source on a layer surface. This case has been compared with the solutions of the particular diffusion problems in a body with traps and diffusion in a medium with effective characteristics.
EN
The paper contains a macroscopic continuum model for adsorption in porous materials (B. Albers [1, 2]) which is an extension of the model for porous bodies by K. Wilmański [7] on mass exchange processes. We consider the flow of a fluid/adsorbate mixture through channels of a solid component. The fluid serves as carrier for an adsorbate whose mass balance equation contains a source term. Due to low adsorbate concentration we deal with a physical adsorption process which means that particles of the adsorbate stick to the skeleton due to weak van der Waals forces. The model contains two different permeability parameters whose nature is completely different: The first one, the usual bulk permeability coefficient, describes the resistance of the skeleton to the flow of the fluid/adsorbate mixture. The second one describes the surface resistance to the outflow of the mixture from the solid. This work shows within a simple example the range of these parameters and the dependence of adsorption/diffusion on them.
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