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Opis: Properties of mixed-metal MOFs depend on the distribution of different metals within their frameworks. Determination of this distribution is often very challenging. Using an example of aluminum- and iron-containing MIL-100, we demonstrate that 27Al NMR spectroscopy, when combined with first-principles calculations and magnetic, X-band electron paramagnetic resonance, Fe K-edge extended X-ray absorption fine structure, and Mössbauer measurements, enables one to accurately determine the arrangement of Al and Fe within the metal trimers, which are the basic building units of MIL-100. In this particular material, the incorporation of Fe and Al on the framework metal sites is random. Crucial for deciphering the arrangement is detecting NMR signals, shifted because of the strong hyperfine interaction between the 27Al nuclei and the unpaired electronic spins of Fe3+ ions, assigning the shifted signals aided by first-principles calculations of hyperfine couplings, and quantitatively evaluating the NMR intensities and the measured effective magnetic moment.
Ključne besede: Fe EXAFS, XANES, MIL100, MOF, magnetizem
Objavljeno v RUNG: 26.03.2019; Ogledov: 3236; Prenosov: 0
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Opis: Magistrsko delo Otroci v slovenskem celovečernem filmu obravnava razvoj otroškega in mladinskega slovenskega filma. Pri tem se sprašuje predvsem, v kakšni vlogi nastopajo otroci, katere ideološke misli podajajo in na kakšen način je njihova umestitev v zgodbo indikator političnega, socialnega in družbeno-kulturnega stanja v našem prostoru. V magistrsko delo je vključen tudi kronološki pregled otroških in mladinskih filmov, ki veljajo za najpomembnejše v slovenski kinematografiji. Ugotavljam, da se je idejna sporočilnost slovenskih celovečernih filmov z otroki spreminjala glede na ustaljen politični sistem. Če so obravnavani filmi vse od 50. let dalje pogosto podajali misel o partizanskem junaštvu in pomembnosti protiokupatorskega boja (nekateri obravnavani filmi pa izražajo idejo kvarnega vpliva tujcev in drugačnih, do česar v magistrski nalogi zavzemam kritičen odnos) so v 70. in 80. letih že izražali kritično misel o tedanjem sistemu. S prihodom 80. in 90. let (in »nove dobe«) je očiten vse pogostejši vpliv ameriške pop kulture in hollywoodskega filma. Seveda ne v vseh primerih, a vendar je očitno, da se mnogi filmi tovrstnega žanra še vedno držijo manj in bolj opaznih kompleksov, ki se jih slovenski otroški in mladinski film očitno še ni uspel popolnoma znebiti.
Ključne besede: Otroci, otroški film, mladinski film, konstrukt otroške čistosti, individualizem, kolektivizem, družbene vrednote, humanizem, kapitalizem, socializem, izobrazba, medgeneracijski nagovor, futurizem, eskapizem v ameriško kulturo, otroci – odrasli, moški – ženska, pristno slovensko
Objavljeno v RUNG: 29.11.2018; Ogledov: 4677; Prenosov: 170
Celotno besedilo (1,99 MB)
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Opis: Sulfur based batteries are considered as very attractive energy storage devices. Sulfur is one of the most abundant elements in the earth, it is electrochemically active material which can accept up to two electrons per atom. In combination with alkali metals, sulfur forms electrochemical couples with much higher theoretical energy density compared to Li-ion batteries commonly available today. At the moment, the electrochemical couple with Li is most extensively studied. While the main principle of operation is known the relevant operation mechanism(s) is not completely clear. Even more promising is the electrochemical couple with Mg providing almost twofold higher volumetric energy density due to its ability to provide two electrons during oxidation. However, Mg-S batteries are still in the very early stage of research and development and the complex mechanism of sulfur conversion has been less extensively studied. In order to improve the understanding of sulfur electrochemical conversion and its interactions within electrode, we need to apply new experimental approaches capable to provide precise information about local environment of S in the cathode during battery operation. In our work, resonant inelastic X-ray scattering (RIXS) and XAS measurements at the sulfur K-edge performed in operando mode were used to study the lithium-polysulfide formation during the discharge process. Measurements were performed at ID26 beamline of the ESRF synchrotron using tender X-ray emission spectrometer [1]. Resonant excitation condition enhanced the sensitivity for the lithium−polysulfide detection. On the other hand, the sulfate signal from the electrolyte was heavily suppressed and the self-absorption effects minimized due to fixed excitation energy. This experimental methodology was used to provide quantitative analysis of sulfur compounds in the cathode of a Li−S battery cell during the discharge process [2]. The high-voltage plateau in the discharge curve was characterized by a rapid conversion of solid sulfur into liquid phase Li polysulfides reaching its maximum at the end of this plateau. At this point the starting point for the precipitation of the Li2S from the liquid polysulfide phase was observed. The same approach has been used also for the Mg-S battery revealing similar mechanism as in case of Li-S battery [3]. The electrochemical conversion of sulfur with magnesium proceeds through two well-defined plateaus, which correspond to the equilibrium between sulfur and Mg polysulfides (high-voltage plateau) and polysulfides and MgS (low-voltage plateau).
Ključne besede: Mg-Sulphur batteries, XANES, RIXS
Objavljeno v RUNG: 13.09.2018; Ogledov: 4481; Prenosov: 0
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Opis: Magistrsko delo obravnava stanje na področju prašnih eksplozij v svetu. Na začetku so opisani prvi znanstveni pristopi k tej problematiki z navedbo statističnih podatkov, ki jim sledi opis znanstvenih teorij nastanka eksplozije. Zatem sledi predstavitev teoretičnih in zakonodajnih načinov za preprečitev eksplozije. Prikazana so doslej znana dejstva in različne teorije o vplivih aluminija na okolje in človeško telo. Pojasnjena je nevarnost eksplozije aluminijevih prahov ter podani napotki za varno in zdravo delo v eksplozijsko roženih prostorih. V eksperimentalnem delu smo določili osnovne karakteristike in lastnosti izbranih treh vzorcev Al prahu (dva prahova in zdrob), ki se proizvajajo. Vzorcem smo določili velikost in porazdelitev velikosti delcev, specifično površino delcev in termične lastnosti s termično analizo (TG/DTA). Obliko delcev vzorcev Al prahu smo določili z vrstično elektronsko mikroskopijo (SEM). Sledila je določitev minimalne vžigne energije MVE in maksimalnega eksplozijskega tlaka (pmax), maksimalne hitrosti rasti tlaka pri eksploziji (Δp/Δt)max ter izračun deflagracijskega indeksa prahu (Kst). Iz rezultatov analiz smo potrdili hipotezo, da so manjši delci eksplozijsko bolj občutljivi in popolneje izgorevajo ter kot taki pomenijo večje tveganje za nastanek prašne eksplozije. Ugotovili smo tudi, da so Al prahu z manjšimi delci dodani dodatki za zmanjšanje občutljivosti. Za konec smo dobljene rezultate primerjali z dostopnimi literaturnimi navedbami in ugotovili, da so odstopanja prevelika za varno uporabo. Zato je zaradi zagotavljanja zadostne varnosti pred načrtovanjem in delom priporočljivo določiti vsaj velikost in porazdelitev velikosti prašnih delcev. Ta podatek nam namreč omogoči, da v večini literature med kopico podatkov najdemo približno ustrezen vzorec. Seveda pa je potrebno za večjo verjetnost še bolje okarakterizirati vzorce in izvesti še več preizkusov, kar smo v našem primeru tudi izvedli. Vsaka eksplozija poleg takojšnjih vplivov na ljudeh in okolju pusti tudi dolgotrajne posledice, ki jih z današnjim stanjem tehnike in meritvami niti ne opazujemo in reguliramo. Zato velja, da je najboljši način preprečitve negativnih vplivov eksplozije onemogočanje pogojev za njen nastanek.
Ključne besede: aluminijev prah, prašna eksplozija, eksplozijski parametri, varnostni ukrepi pri proizvodnji aluminijevega prahu, vpliv aluminija na okolje in človeka
Objavljeno v RUNG: 04.09.2017; Ogledov: 5934; Prenosov: 357
Celotno besedilo (7,48 MB)
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Opis: In its upper course the Soča River is one of the best preserved Alpine rivers. Despite that, there have been few studies of its riverine forests, which are an integral part of the river. The research in this thesis encompasses part of the river basin between the towns of Kobarid and the confluence with the Tolminka River. It was found that the riverine forests in the study area are not a homogeneous habitat. Rather, they consist of numerous phytosociological communities with a syn-dynamic connection. The majority of riverine forests in the study area is younger than 50 years old and were established either by the overgrowing of agricultural land or from degraded forests. Accordingly, the forest structure is characterised mainly by uneven-aged stands or younger structural stages, which are frequently returned to their earlier stages due to human impacts. The majority of these forests have low quality prospects. Based on their vegetation and stand characteristics, the riverine forests under study were classified into six stand types. A comparison of the functions and characteristics of particular forest types revealed similarities between the stand types of initial willow, white willow and grey alder. Forests in this cluster are under the influence of soil water and high floodwaters. Their most pronounced function is ecological. In their growing stock, there is a large share of deciduous softwood. Forests in this cluster cover 62% of all riverine forests in the study area. Silvicultural measures are rare in these forests and are less important for the existence of the stands than environmental features like a high level of soil water and minimised human impact on their habitat and the river course. An important characteristic of the second cluster, which consists of pioneer forest on higher-lying river terraces and the riparian corridor stand type is a lack of contact with soil water. In the tree layer of the growing stock in this cluster, species appearing on drier riverine-forest sites prevail (European ash, small-leaved lime, European hornbeam, sessile oak). These forest stands have a greater timber industry potential; therefore, modest measures and limited human impact (especially that which leads to a change in land use like forest grazing and clearing) are recommended. The stands in this cluster cover 30% of the analysed riverine forest area. The third cluster of riverine forests consists of anthropogenic riverine forest stands where the human impact is so significant that they mainly perform a social function. The stand type of this cluster represents 8% of the riverine forests in the study area, and it is suggested that they should be managed as parkland and not as forest areas. Directing visitors to these areas would unburden other, more preserved stand types from the pressures created by human activities (tourism, recreation, construction work). Growth and increment analyses of the most common tree species in the riverine forests in the study area show that mainly olive and white willow, followed by grey alder, have substantial current height (both willow types up to 1.14 m/year), diametric (willow up to 1.4 cm/year) and volumetric increments. However, their rapid growth makes these subjects prone to rapid ageing. The region of northern Primorska was inhabited early in history. Accordingly, there was great pressure imposed on riverine forests already in the past. The analysis of old maps revealed that up to the beginning of the 20th century, the riverine forest area within the scope of analysis was under 50 ha. Within the process of the overgrowing of agricultural land in Slovenia, a process that is currently still underway, the aforementioned riverine forest area increased to 229.16 ha. This thesis shows that the study area is not an unspoiled wilderness. On contrary, just as in the past, it is a crossroads of numerous and frequently conflicting interests. The riverine forest situation on the Soča River in the area b
Ključne besede: the Soča river, riverine forests, successional stage, forest stand
Objavljeno v RUNG: 20.09.2016; Ogledov: 5771; Prenosov: 161
Celotno besedilo (8,00 MB)