Dynamic Polarization Effects in Ion Channeling Through Single-Well Carbon Nanotubs

Ion channeling through a single-wall carbon nanotube is simulated by solving Newton’s equations for ion motion at intermediate energies, under the action of both the surface-atom repulsive forces and the polarization forces due to the dynamic perturbation of the nanotube electrons. The atomic repulsion is described by a continuum potential based on the Thomas-Fermi-Moliere model, whereas the dynamic polarization of the nanotube electrons is described by a two-dimensional hydrodynamic model, giving rise to the transverse dynamic image force and the longitudinal stopping force. In the absence of centrifugal forces, a balance between the image force and the atomic repulsion is found to give rise to ion trajectories which oscillate over peripheral radial regions in the nanotube, provided the ion impact position is not too close to the nanotube wall, the impact angle is sufficiently small, and the incident speed is not too high. Otherwise, the ion is found to oscillate between the nanotube walls, passing over a local maximum of the potential in the center of the nanotube, which results from the image interaction. The full statistical analysis of 103 ion trajectories has been made to further demonstrate the actual effect of dynamic polarization on the ion channeling

Dynamics of the species diversity and composition of the ruderal vegetation of Slovak and Czech cities

This study reports the results of the evaluation of changes in the species diversity and composition of ruderal vegetation of three Slovak and one Czech city over the time. The dataset of 1489 relevés from five ruderal syntaxa from the cities Bratislava, Malacky, Trnava and Brno was used. Data were from two different time periods, the older dataset from the years 1960–1982, the more recent dataset from the years 2005–2016. The statistical analysis revealed the decrease of Shannon–Wiener diversity index of all (native + alien) species in the majority of classes of ruderal vegetation of cities. The analysis of the changes in the Pielou's measure of species evenness showed that in some of the classes and cities, the species evenness remained unchanged, in the other ones it decreased. The percentage of native species in the ruderal vegetation did not change over the time, but the percentage of invasive alien species in the majority of syntaxa and cities increased significantly. In total, 38 invasive taxa were recorded in the ruderal vegetation of cities. Most of them are neophytes, therophytes and belong to the family Asteraceae. The majority of invasive taxa were recorded in both time periods. Some of the invasive species, e.g. Fallopia japonica and Juncus tenuis were recorded only in the more recent time period. Our results contribute to the knowledge about biological invasions in the cities

Effects of invasive plant species on species diversity: implications on ruderal vegetation in Bratislava City, Slovakia, Central Europe

Invasive species pose one of the most serious global environmental threats. Our study aimed to examine the correlation between the proportion of invasive alien taxa and species diversity of ruderal vegetation in the urban ecosystem of Bratislava, located in Central Europe. Ruderal habitats serve as the means of spread of invasive species to seminatural and natural habitats. Twenty-six invasive taxa were recorded among the ruderal vegetation of Bratislava. The majority of the recorded invasive species were neophytes, which came from North America and represent the Asteraceae family. Half of them were introduced accidentally, whereas the remaining species were introduced deliberately. Correlation and regression analyses showed that the proportion of invasive taxa has a negative effect on the species diversity of all the analyzed syntaxa in the ruderal vegetation of Bratislava

Comparison of the differences in the composition of ruderal flora between conventional tram tracks and managed green tram tracks in the urban ecosystem of the city of Bratislava

Green infrastructure (GI) brings many benefits to urban ecosystems (e.g. better air and water quality) and it presents a helpful tool in the effort to reduce the consequences of climate change. Green tram tracks can be considered to be a part of GI. The presented study is focused on the comparison of the frequency of ruderal plant species, as well as species composition when comparing conventional tram tracks with green tram tracks (with planted succulents and ornamental plants) in Bratislava, Slovakia, Central Europe. This comparison also provides an insight into the changes of the flora of tram tracks over time, as we compare the results of the older research (from the years 2014–2019) with recent research on green tram tracks, which were built in Bratislava in 2020. The data were analysed by cluster analysis, Sign test and Wilcoxon two-sample test in the R 3.5.1. The results revealed significant differences in the composition of flora between conventional tram tracks and green tram tracks. In particular, the total number of species has decreased over time, as green tram tracks host fewer spontaneously growing taxa than conventional ones. The frequency of occurrence of archaeophytes and neophytes has decreased on the strict rail yard (covered by planted succulents) while on the tracksides (covered by non-succulent ornamental plants) it has increased. Green tram tracks deliver positive features to ecosystems, but may also have negative aspects because they present a pool of alien, potentially invasive plants. &nbsp

An oxygen isotope test for the origin of Archean mantle roots

The origin of the peridotites that form cratonic mantle roots is a central issue in understanding the history and survival of Earth’s oldest continents. A long-standing hypothesis holds that the unusual bulk compositions of some cratonic peridotites stem from their origin as subducted oceanic serpentinite, dehydrated during subduction to form rigid buoyant keels (Schulze, 1986; Canil and Lee, 2009). We present oxygen isotope data from 93 mantle peridotites from five different Archean cratons to evaluate their possible origin as serpentinites. Cratonic mantle peridotite shows remarkably uniform δ18O values, identical to modern MORB-source mantle, that do not vary with bulk rock Si-enrichment or Ca-depletion. These data clearly conflict with any model for cratonic lithosphere that invokes serpentinite as a protolith for cratonic peridotite, and place additional constraints on cratonic mantle origins. We posit that the uniform δ18O was produced by sub-arc and/or MOR depletion processes and that the Si-enriched nature of some samples is unlikely to be related to slab melt infiltration. Instead, we suggest a peridotitic source of Si-enrichment, derived from ascending mantle melts, or a water-fluxed depleted mantle. These variably Si-enriched, cratonic mantle protoliths were then collisionally compressed into the thick cratonic roots that have protected Earth’s oldest continental crust for over 2.5 Gyr

Matematičko modeliranje induktivnog mašinskog učenja / Mathematical modeling of inductive machine learning

U radu se razmatra modeliranje induktivnog mašinskog učenja (inductive machine learning). Izloženi su najznačajniji matematički modeli i njihov odnos prema praktično realizovanim algoritmima. Prikazane su osnovne karakteristike najpoznatijih svetskih i jednog sopstvenog sistema induktivnog učenja, kao i primeri upotrebe sistema u zadacima predviđanja. / This paper considers mathematical modeling of inductive machine learning Most important mathematical models and their relations to practical realizations of algorithms are reviewed. The basic characteristics of some best known systems and one author's system for inductive rules learning are described and some examples of using systems in prediction tasks are presented

Návrh na manažment biotopov vybraných taxónov z rodu Ophrys L. (Orchidaceae) na Devínskej Kobyle (Bratislava)

Many valuable and threatened taxons of the family Orchidaceae, including the representatives of genus Ophrys, are disappearing from semi-natural grasslands because of the advancing secondary succession. Conservation and restoration of calcareous grasslands rich in species at the Devínska Kobyla Mt. requires appropriate interventions after the traditional forms of management will be finished. Bromus erectus is the dominant species at the Devínska Kobyla Mt., hence it is necessary to choose adequate intervention aim of which would be the reduced dominance of this species. Restoration of extensive sheep grazing in this calcareous grassland is not realistic. This is the reason why it is proposed to mow every year or at least every two years (and remove the mown mass) the growths where the taxons of genus Ophrys occur. The best moment for mowing is after maturation of the Orchid Genus Ophrys seeds. With regard to the phenologic cycles of the species concerned, the following mowing terms are proposed: end of June for the locality with occurrence of Early Spider Orchid (Ophrys sphegodes), July for localities with occurrence of Late Spider Orchid (O. holosericea) and Fly Orchid (O. insectifera). The locality with Bee Orchid (Ophrys apifera) does not require mowing due to shallow soil (Lithosol) and vegetation that is close to Poo badensis-Festucetum pallentis association. If mowing cannot be used on the particular dates, it is proposed to mow the growths with the dominating species Bromus erectus in October. The study presents the example how the number of flowering Early Spider Orchid (Ophrys sphegodes) individuals increased after the locality was mown by the employees of the State Nature Conservation in autumn 2004. Their number more than quadrupled in 2005

Optimal position of solar collectors: A review

© 2018, Serbian Academic Center. All rights reserved. Solar energy is the most abundant, inexhaustible and clean of all the renewable energy resources till today. Solar energy has received much more attention in building energy systems in recent years. During the first years of the twenty-first century, extensive efforts have been undertaken to alleviate global warming of the earth caused by emission of CO2 in atmosphere. These emissions are generated by intensive burning of fossil fuels to satisfy the growing energy needs of humanity. The emissions may be mitigated when part of energy needs is satisfied by using non-polluting energy sources such as solar energy, instead of fossil fuels. In households, customary is to use electricity for heating of DHW. Most of electricity is produced by using coal with high greenhouse emission. Accordingly, worldwide, the most rewarding application of solar energy is when it replaces electrical energy for heating of DHW in households. The solar collector has to take the optimal position that will guarantee the highest generation of heat. Optimal positioning must be based on rigorous calculations and not on the basis of experience. Such calculations lead to the improvement of the operation of solar energy systems. This paper gives a review of research with the objective of presenting, classifying and analysing the different criteria by which the authors observed an optimal position of the solar collector. In addition, it is important to have a high efficiency of conversion of solar energy to heat. Then, the highest amount of avoided primary energy, avoided electrical energy, avoided exergy, and decrease in CO2 emissions may be expected

A Visual Servoing Scheme for Autonomous Aquaculture Net Pens Inspection Using ROV

Aquaculture net pens inspection and monitoring are important to ensure net stability and fish health in the fish farms. Remotely operated vehicles (ROVs) offer a low-cost and sophisticated solution for the regular inspection of the underwater fish net pens due to their ability of visual sensing and autonomy in a challenging and dynamic aquaculture environment. In this paper, we report the integration of an ROV with a visual servoing scheme for regular inspection and tracking of the net pens. We propose a vision-based positioning scheme that consists of an object detector, a pose generator, and a closed-loop controller. The system employs a modular approach that first utilizes two easily identifiable parallel ropes attached to the net for image processing through traditional computer vision methods. Second, the reference positions of the ROV relative to the net plane are extracted on the basis of a vision triangulation method. Third, a closed-loop control law is employed to instruct the vehicle to traverse from top to bottom along the net plane to inspect its status. The proposed vision-based scheme has been implemented and tested both through simulations and field experiments. The extensive experimental results have allowed the assessment of the performance of the scheme that resulted satisfactorily and can supplement the traditional aquaculture net pens inspection and tracking systems