Hydrological processes research remains a field that is severely measurement limited. While conventional tracers (geochemicals, isotopes) have brought extremely valuable insights into water source and flowpaths, they nonetheless have limitations that clearly constrain their range of application. Integrating hydrology and ecology in catchment science has been repeatedly advocated as offering potential for interdisciplinary studies that are eventually to provide a holistic view of catchment functioning. In this context, aerial diatoms have been shown to have the potential for detecting of the onset/cessation of rapid water flowpaths within the hillslope-riparian zone-stream continuum. However, many open questions prevail as to aerial diatom reservoir size, depletion and recovery, as well as to their mobilisation and transport processes. Moreover, aerial diatoms remain poorly known compared to freshwater species and new species are still being discovered. Here, we ask whether aerial diatom flushing can be observed in three catchments with contrasting physiographic characteristics in Luxembourg, Oregon (USA) and Slovakia. This is a prerequisite for qualifying aerial diatoms as a robust indicator of the onset/cessation of rapid water flowpaths across a wider range of physiographical contexts. One species in particular, (Hantzschia amphioxys (Ehr.) Grunow), was found to be common to the three investigated catchments. Aerial diatom species were flushed, in different relative proportions, to the river network during rainfall-runoff events in all three catchments. Our take-away message from this preliminary examination is that aerial diatoms appear to have a potential for tracing episodic hydrological connectivity through a wider range of physiographic contexts and therefore serve as a complementary tool to conventional hydrological tracers.
In his book Physics of the Impossible, Michio Kaku thinks that psycho-kinesis-i.e., a direct causal influence on physical processes by mental powers-will become a real possibility in a near future. From the point of view of metaphysical realism, this means that mental entities and mental causality are real phenomena. Contemporary scientific methodology regards the use of scientific instruments that amplify our sensibilities as a cognitive technology that deepens our knowledge of, and power over, real processes. It appears that the strongest and most productive methods are connected with scientific theories-they are theories ''in action''. Thus, scientific theories can regarded as mental cognitive technology by means of which humans get to know, and at the same time shape, reality. and Břetislav Fajkus
The text is divided into two parts. In the first part, the author describes the eternalists’ and presentists’ positions as the two basic possible statements of the ontology of time (there exists only what is present - presentism - and there also actually exists both what is past and what is future). The eternalist position and the emphasis it puts on the actual existence of past and future events (expressed usually by the use of present tense or of some tenseless form of the verb) are thoroughlly analysed in order to show that in fact, they end up making strings of symbols that are not correct statements. It is therefore necessary to step beyond these clumsy statements and try to understand more exactly the eternalist intuitions on a deeper, metaphysical level. That is the main concern of the second part of the text, in which the metaphysical implications of both positions are compared. At the end of the linguistical analysis in the first part, we got to a point where it may seem that presentism and eternalism are only different attempts at expressing what is in fact the same understanding of the nature of time, but in the metaphysical analysis that follows, it will turn out that they are not. Presentism and eternalism are shown to be two different ontological approaches of time in relation to space (time as a basically homogenous fourth dimension and time as something essentially different from space). The author then focuses on the consequences these two positions have especially on the concept of the present and of its flow through time. In the end, presentism and eternalism turn out to be completely different positions that - in parallel with the famous McTaggart’s argument - claim a very strong reality of time on the one hand (presentism) or, on the other hand, its utter unreality (eternalism)., Text je rozdělen do dvou částí. V první části autor popisuje postoje eternalistů a presentistů jako dvě základní možná prohlášení ontologie času (existuje pouze to, co je přítomno - presentismus - a tam také skutečně existuje to, co je minulost a co je budoucnost) . Postavení eternalistů a důraz, který kladou na skutečnou existenci minulých a budoucích událostí (vyjádřených obvykle pomocí přítomného času nebo nějaké napjaté podoby slovesa), jsou důkladně analyzovány, aby se ukázalo, že ve skutečnosti končí řetězců symbolů, které nejsou správné. Je proto nutné překonat tyto neohrabané výroky a snažit se přesněji pochopit eternalistické intuice na hlubší, metafyzické úrovni. To je hlavním zájmem druhé části textu, ve kterých jsou porovnány metafyzické důsledky obou pozic. Na konci lingvistické analýzy v první části jsme se dostali do bodu, kdy se může zdát, že presentismus a eternalismus jsou pouze různými pokusy o vyjádření toho, co je vlastně stejné chápání podstaty času, ale v metafyzické analýze, že následuje, ukáže se, že nejsou. Současnost a věčnost jsou ukázány jako dva rozdílné ontologické přístupy času ve vztahu k prostoru (čas jako v podstatě homogenní čtvrtá dimenze a čas jako něco, co je v podstatě odlišné od prostoru). Autor se pak zaměřuje na důsledky, které tyto dvě pozice mají zejména na koncepci přítomnosti a jejího toku v čase.Současnost a eternismus se nakonec ukázaly jako zcela odlišné pozice, které - paralelně s proslulým argumentem McTaggarta - tvrdí na jedné straně velmi silnou realitu času (presentismus) nebo na druhé straně její naprostou neskutečnost (eternalismus)., and Jacques Joseph
The paper describes results of experiments with rotating spherical particles moving in water. Rubber spherical balls with the density close to that of water were speeded up in a special inclined chute that ensured the required particle rotational and translational velocity in the given plane. A standard video system was used to capture particle trajectory and the evaluation was focused on the effects of two dimensionless parameters of the particle motion, Reynolds number and rotational Reynolds number. The values of the drag force and drag torque coefficients were determined from the experimental data and compared with the results of the numerical simulation of the particle motion. Relationships describing the above mentioned quantities, taking into account the mutual influence of the translational and the rotational particle movements and convenient for numerical models were found. and V příspěvku jsou prezentovány výsledky experimentálního výzkumu pohybu rotující kulovité částice ve vodě. Kulovitá částice vyrobená z gumy o hustotě blízké hustotě vody byla uvedena do pohybu v šikmé štěrbině, kde získala rotační i translační rychlost v osové rovině štěrbiny. Trajektorie částic ve vodě byly snímány standardní video kamerou a byl vyhodnocen vliv dvou bezrozměrných parametrů (Reynoldsova čísla a rotačního Reynoldsova čísla) na pohyb částice. Z experimentálních údajů byly určeny hodnoty odporového koeficientu a odporového momentu částice a tyto hodnoty byly porovnány s výsledky numerické simulace pohybu částice. Byly vyhodnoceny vztahy vhodné pro využití při numerickém modelování a popisující vzájemné závislosti výše uvedených veličin a vzájemný vliv translačního a rotačního pohybu částice.
The effect of solid concentration and mixture velocity on the flow behaviour, pressure drops, and concentration distribution of coarse particle-water mixtures in horizontal, vertical, and inclined smooth stainless steel pipes of inner diameter D = 100 mm was experimentally investigated. Graded basalt pebbles were used as solid particles. The study revealed that the coarse-grained particle-water mixtures in the horizontal and inclined pipes were significantly stratified. The solid particles moved principally in a layer close to the pipe invert; however for higher and moderate flow velocities, particle saltation became the dominant mode of particle conveyance. Frictional pressure drops in the horizontal pipe were found to be markedly higher than in the vertical pipe, while the frictional pressure drops in the ascending pipe increased with inclination angle up to about 30°.
For the safe and economical design and operation of freight pipelines it is necessary to know slurry flow behaviour in inclined pipe sections, which often form significant part of pipelines transporting solids. Fine-grained settling slurry was investigated on an experimental pipe loop of inner diameter D = 100 mm with the horizontal and inclined pipe sections for pipe slopes ranging from –45° to +45°. The slurry consisted of water and glass beads with a narrow particle size distribution and mean diameter d50 = 180 μm. The effect of pipe inclination, mean transport volumetric concentration, and slurry velocity on flow behaviour, pressure drops, deposition limit velocity, and concentration distribution was studied. The study revealed a stratified flow pattern of the studied slurry in inclined pipe sections. Frictional pressure drops in the ascending pipe were higher than that in the descending pipe, the difference decreased with increasing velocity and inclination. For inclination less than about 25° the effect of pipe inclinations on deposition limit velocity and local concentration distribution was not significant. For descending pipe section with inclinations over –25° no bed deposit
was observed.
In recent years, due to the occurrence of water shortage and drought problems, particularly in arid and semiarid regions of the world, new methods to reduce evaporation from the surface of dam reservoirs, lakes, and other waterfree surfaces are investigated. This study aimed to use hydrophobic bentonite to reduce water evaporation from water surfaces, on a laboratory scale, and field conditions for the first time. Bentonite initially became hydrophobic by stearic acid (SA). Under such conditions, hydrophobic bentonite floats on the surface of water and forms a thin coating layer. The produced hydrophobic bentonite had a contact angle of 150°, indicating its superhydrophobicity. Evaporation reduction was measured under laboratory and field conditions and it was compared to hexadecanol as the reference material. The results demonstrated that the hydrophobic bentonite efficiency under laboratory conditions was similar to that of hexadecanol and prevented water evaporation by 36%. However, under field conditions, hydrophobic bentonite and hexadecanol efficiencies were 40% and 23% to reduce evaporation for 30 days, respectively. In terms of stability, hexadecanol needed to be re-injected after three days, while hydrophobic bentonite was stable and remained on the surface for more than 100 days under laboratory conditions and for more than 15 days under field conditions without needing reinjection. This coverage with method can be used to reduce evaporation from lakes, tanks, and reservoirs of small dams.
Gravity-driven open-channel flows carrying coarse sediment over an erodible granular deposit are studied. Results of laboratory experiments with artificial sediments in a rectangular tilting flume are described and analyzed. Besides integral quantities such as flow rate of mixture, transport concentration of sediment and hydraulic gradient, the experiments include measurements of the one-dimensional velocity distribution across the flow. A vertical profile of the longitudinal component of local velocity is measured across the vertical axis of symmetry of a flume cross section using three independent measuring methods. Due to strong flow stratification, the velocity profile covers regions of very different local concentrations of sediment from virtually zero concentration to the maximum concentration of bed packing. The layered character of the flow results in a velocity distribution which tends to be different in the transport layer above the bed and in the sediment-free region between the top of the transport layer and the water surface. Velocity profiles and integral flow quantities are analyzed with the aim of evaluating the layered structure of the flow and identifying interfaces in the flow with a developed transport layer above the upper plane bed.