Eliptičke krivulje i Mordell-Weilov teorem

Mordell-Weilov teorem kaže da je za algebarsku mnogostrukost A nad poljem brojeva K, grupa K-racionalnih točaka A(K) konačno generirana Abelova grupa, koju zovemo Mordell-Weilova grupa. Poseban slučaj, kad je A eliptička krivulja E te K polje racionalnih brojeva Q je Mordellov teorem. On odgovara na pitanje koje je navodno postavio Poincaré oko 1908. Teorem je dokazao Louis Mordell 1922. U ovom radu dokazujemo Mordellov teorem za eliptičke krivulje nad algebarskim poljima brojeva K.The Mordell–Weil theorem states that for an abelian variety A over a number field K, the group A(K) of K-rational points of A is a finitely-generated abelian group, called the Mordell-Weil group. The case with A an elliptic curve E and K the rational number field Q is Mordell’s theorem, answering a question apparently posed by Poincaré around 1908; it was proved by Louis Mordell in 1922. In this paper we prove Mordell’s theorem for elliptic curves on number fields K

TiO2-carbon xerogel composites as supports in the preparation of Pt catalysts for selective hydrogenation

In the last decades, considerable efforts have been devoted to the development of heterogeneous catalysts able to perform efficient selective hydrogenation of the carbonyl function in α,β-unsaturated aldehydes, to yield the corresponding unsaturated alcohols, which are important intermediates in organic synthesis of fine chemicals for several industries, such as flavor, fragrance and pharmaceutical. Unfortunately, high selectivities towards these alcohols are difficult to achieve, since thermodynamics favors the hydrogenation of the C=C over the C=O bond and due to kinetic reasons, as the reactivity of the olefinic bond is higher than that of the carbonyl

Mogućnosti poboljšanja efekata rada ventilacionog sistema u odeljenjima prasilište i odgajalište na farmi svinja 'Farkaždin'

Analysis of ventilation systems efficiency in farrowing room and nursery is presented in this paper. Those rooms are selected because of the most sensitive categories in pig production cycle. From this reason, these farm confinements should be carefully analyzed and, if possible, additionally equipped and specially adopted. Based on the present conditions analysis, this paper should suggest improvements of microclimate conditions in the researched confinements. Existing microclimate conditions are monitored in the piglets breath zone, in 12 measuring points, and the zones that are in front and between the fans, as well. Results of the existing conditions analysis emphasized the inefficiency of the present ventilation systems. Especially low effect is achieved in removal of harmful gasses and airborn dust particles. Along with the defined problems, possible solutions are suggested. The solutions included installation of additional ventilation equipment. Combined effects of the existing and the additional equipment, along with its possibilities for fine regulation, should significantly improve the existing conditions.U radu je prikazana analiza rada ventilacionih sistema u odeljenjima prasilišta i odgajališta. Ova odeljenja karakteristična su po tome što se u njima drže najosetljivije kategorije u svinjarskoj proizvodnji. Upravo stoga, ovim odeljenjima treba posvetiti pažnju, i ukoliko postoje mogućnosti i opravdanost uvođenja dodatnih uređaja i adaptacije objekata, iste treba razmotriti i uvesti u praksu. Cilj rada je da se na osnovu analize postojećeg stanja, veličine odeljenja i rasporeda bokseva, kao i rasporeda i broja ventilatora, formira predlog poboljšanja mikroklimatskih parametara u odeljenjima. Postojeće stanje mikroklime snimano je u zoni disanja životinja, u 12 mernih tačaka, pri čemu se vodilo računa da se obuhvati zona uticaja ventilatora, kao i delovi odeljenja gde je njihov efekat manje izražen. Analiza postojećeg stanja mikroklime otkrila je da su efekti rada postojećih sistema ventilacije nedovoljni. Pogotovo je slab efekat iznošenja gasovitih produkata i čestica prašine. Uz analizu, na osnovu uočenih problema, dati su i predlozi za prevazilaženje postojećih problema. Predložena rešenja podrazumevaju ugradnju dodatne ventilacione opreme. Kombinovanjem efekata rada postojeće opreme, sa dodatnom opremom, a pogotovo širokim mogućnostima njene regulacije, može se očekivati značajno poboljšanje postojećeg stanja

Photodeposition of Pt nanoparticles on Ce-Ti-O

Hydrogenation reactions are the most common examples where transition and noble metal nanoparticles are applied in colloidal solution as quasihomogeneous catalysts [1]. The main drawback in the use of colloidal nanoparticles for catalysis concerns the recovery and reuse of these particles. This is especially important if environmental issues are considered. Therefore, attention has been drawn to the use of supported nanoparticles. In this work, Ce-Ti-O supports were synthesized by the solvothermal method using methanol and a cationic surfactant (CTAB). Pt nanoparticles were then supported by photochemical deposition using a low-pressure mercury lamp with an emission line at 254 nm (ca.3 W of radiant flux) during 4 h. The catalysts were calcined in N2 (4 h, 100 mL min-1), reduced in H2 (2 h, 20 mL min-1) and flushed again with N2 during 30 min at 773 K. Ultrafine platelet shaped CeO2 particles with sizes ~ 3-8 nm were also produced by the solvothermal method. When Ti was combined with Ce, a nanostructured network was obtained. It was proved that Pt spherical nanoparticles (diameter ~ 2-4 nm) can be efficiently photodeposited on these supports. Fig.1 shows a HRTEM micrograph of the Pt/Ce-Ti-O catalyst, where a Pt nanoparticle (marked by an arrow) can be identified. These catalysts were tested in the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol. Enhancement in the catalytic activity for cinnamaldehyde hydrogenation and higher selectivity for cinnamyl alcohol production was observed with the Pt nanoparticles supported on Ce-Ti-O when compared with the single-oxide supports (CeO2 and TiO2)

Rheological, Microstructural and Thermal Properties of Magnetic Poly(Ethylene Oxide)/Iron Oxide Nanocomposite Hydrogels Synthesized Using a One-Step Gamma-Irradiation Method

Magnetic polymer gels are a new promising class of nanocomposite gels. In this work, magnetic PEO/iron oxide nanocomposite hydrogels were synthesized using the one-step γ-irradiation method starting from poly(ethylene oxide) (PEO) and iron(III) precursor alkaline aqueous suspensions followed by simultaneous crosslinking of PEO chains and reduction of Fe(III) precursor. γ-irradiation dose and concentrations of Fe3+, 2-propanol and PEO in the initial suspensions were varied and optimized. With 2-propanol and at high doses magnetic gels with embedded magnetite nanoparticles were obtained, as confirmed by XRD, SEM and Mössbauer spectrometry. The quantitative determination of γ-irradiation generated Fe2+ was performed using the 1, 10-phenanthroline method. The maximal Fe2+ molar fraction of 0.55 was achieved at 300 kGy, pH = 12 and initial 5% of Fe3+. The DSC and rheological measurements confirmed the formation of a well-structured network. The thermal and rheological properties of gels depended on the dose, PEO concentration and initial Fe3+ content (amount of nanoparticles synthesized inside gels). More amorphous and stronger gels were formed at higher dose and higher nanoparticle content. The properties of synthesized gels were determined by the presence of magnetic iron oxide nanoparticles, which acted as reinforcing agents and additional crosslinkers of PEO chains thus facilitating the one-step gel formation

Grazing-incidence small-angle X-ray scattering: application to the study of quantum dot lattices

The modelling of grazing-incidence small-angle X-ray scattering (GISAXS) from three-dimensional quantum dot lattices is described

Identification of injury risk in building construction – education, experience and type of work

Rad prikazuje istraživanje učestalosti povreda na radu građevinskih radnika sa aspekta obrazovanja, iskustva i stručne obučenosti prilikom realizacije različitih vrsta građevinskih radova. Istraživanje je obuhvatilo 719 povreda bez smrtnih posljedica u oblasti građevinarstva u Republici Srbiji u okviru Autonomne pokrajine Vojvodina. Analiza strukture građevinskih radnika, realizirana na osnovu podataka Zavoda za statistiku Republike Srbije, pokazala je da je većina građevinskih radnika (preko 89 %) završila osnovnu ili srednju školu kao i da 17 % radnika u Vojvodini ima manje od pet godina iskustva u građevinarstvu. Na osnovu analize baze podataka o povredama zaključeno je da najveći broj povređenih radnika ima osnovno ili srednje obrazovanje kao i da radnici s većim iskustvom impliciraju manji broj povreda. Također, zaključeno je da je veći dio povreda nastao uslijed nemara radnika na radu, a manji dio uslijed nesigurnih uvjeta rada.This paper presents an overview of research in the frequency of injuries at work among construction workers, from the aspect of education, experience and professional training in the realization of different types of construction works. The research included 719 injuries without fatal outcome in the field of building construction in the Republic of Serbia, within the Autonomous Province of Vojvodina. The analysis of construction workers structure, realized according to the data provided by Statistical Office of the Republic of Serbia, showed that the great majority of construction workers (over 89 %) have elementary or high school education levels, as well as that 17 % of workers in Vojvodina have less than five years of experience in construction. By analyzing the injury base, a conclusion was drawn that the highest number of injured workers has elementary or high school education level, as well as that longer working experience of workers imply smaller number of injuries. In addition, a conclusion was drawn that the injuries were caused to the largest extent owing to workers’ unsafe act, and less owing to unsafe conditions of work

Insights into electrochemical dealloying of Cu out of Au-doped Pt-alloy nanoparticles at the sub-nano-scale

Pt alloy nanoparticles present the most probable candidate to be used as the cathode cathodic oxygen reduction reaction electrocatalyst for achieving commercialization targets of the low-temperature fuel cells. It is therefore very important to understand its activation and degradation processes. Besides the ones known from the pure Pt electrocatalysts, the dealloying phenomena possess a great threat since the leached less-noble metal can interact with the polymer membrane or even poison the electrocatalyst. In this study, we present a solution, supported by in-depth advance electrochemical characterization, on how to suppress the removal of Cu from the Pt alloy nanoparticles

Development of stimuli-responsive graphene-based yolk-shell magnetic nanoparticles for controlled release of anticancer drugs

Magnetic drug delivery systems have attracted much attention in the last decades due to the possibility to improve the therapeutic efficacy of anticancer drugs, by enabling instable and poorly soluble drug agents to reach tumour cells after being guided by low magnetic fields and monitored by magnetic resonance imaging (MRI) [1]. Hence, a lower amount of anticancer drug is needed and the typical side effects of chemotherapy are minimized [2]. Commonly, these nanoparticles are designed with a magnetic core coated with a metal or a non-metal structure, such as gold or silica. However, these approaches present some drawbacks, such as low drug loading capacity and lack of stimuli-responsive release. Alternatively, carbon-coated magnetic nanoparticles offer higher chemical and thermal stability, larger surface area, biocompatibility and easier functionalization due to the high capacity of adsorption. Moreover, these materials have shown great ability to be used as pH stimuli-responsive controlled release platforms, due to the disruption of supramolecular interaction at acidic pH [3]. In this context, graphene-coated yolk-shell magnetic nanoparticles – hybrid materials comprising a superparamagnetic core coated by a graphene-based shell that covers a hollow region (i.e., Fe3O4@void@C), – were developed as super-drug nanocarriers systems, exhibiting high loading contents of the anticancer drug Doxorubicin due to the large cavity volume between the shell and the magnetic core, and a stimuliresponsive controlled release in response to acidic environments (pH 5), such as those found in tumour tissues. These results shed light on the development of new hybrid nanomaterials with high potential to be applied in biomedical applications.info:eu-repo/semantics/publishedVersio