1,721,038 research outputs found
The gadolinium effect on crystallization behavior and luminescence of β-NaYF4:Yb,Er phase
Get PDFSingle phase β-NaY0.8-xGdxYb0.18Er0.02F4 nanoparticles with different concentrations of gadolinium ions were prepared via PVP-assisted solvothermal treating at 200°C (PVP- polyvinylpyrrolidone). With the increase in Gd3+ concentration, size of the nanoparticles decreased. The up-converting spectra recorded upon 980 nm irradiation showed the green (510-560 nm) and red (640-690 nm) emissions, due to 2H11/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions, respectively. The strongest up-conversion luminescence was detected in 15 mol% Gd3+-doped nanoparticles obtained after 20 hours of solvothermal treating. With the rise of Gd3+ content up-conversion emission decreased due to increased defect concentration in the NaYF4 matrix. Fourier transform infrared spectroscopy proved in situ generation of hydrophilic nanoparticles as a result of PVP ligands retention at the particle surface.This is the peer-reviewed version of the article: Vuković Marina, Mančić Lidija, Dinić Ivana, Vulić Predrag, Nikolić Marko G., Tan Zhenquan, Milošević Olivera, "The gadolinium effect on crystallization behavior and luminescence of β-NaYF4:Yb,Er phase" International Journal of Applied Ceramic Technology, 17, no. 3 (2020):1445-1452,
[https://doi.org/10.1111/ijac.13363]Published version: [https://hdl.handle.net/21.15107/rcub_dais_8947
Meta-autunite from a Li-pegmatite of the Cer Mt., Serbia: Its mineralogical and XRD investigations
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
In situ dehydration behavior of veszelyite (Cu,Zn)2Zn(PO4)(OH)3·2H2O: A single-crystal X-ray study
No full textThe rare mixed copper-zinc phosphate mineral veszelyite (Cu,Zn)2Zn(PO4)(OH)3·2H2O space group P21/c, a = 7.5096(2), b = 10.2281(2), c = 9.8258(2) Å, β = 103.3040(10)°, V = 734.45(3) Å3 was investigated by in situ temperature-dependent single-crystal X-ray structure refinements. The atomic arrangement of veszelyite consists of an alternation of octahedral and tetrahedral sheets. The Jahn-Teller distorted CuO6 octahedra form sheets with eight-membered rings. The tetrahedral sheet composed of PO4 and ZnO3(OH) tetrahedra shows strong topological similarities to that of cavansite, gismondine, and kipushite.Diffraction data of a sample from Zdravo Vrelo, near Kreševo (Bosnia and Herzegovina) have been measured in steps of 25 up to 225 °C. Hydrogen positions and the hydrogen-bond system were determined experimentally from the structure refinements of data collected up to 125 °C. At 200 °C, the hydrogen-bonding scheme was inferred from bond-valence calculations and donor-acceptor distances. The hydrogen-bond system connects the tetrahedral sheet to the octahedral sheet and also braces the Cu sheet.At 150 °C, the H2O molecule at H2O2 was released and the Cu coordination (Cu1 and Cu2) decreased from originally six- to fivefold. Cu1 has a square planar coordination by four OH groups and an elongate distance to O3, whereas Cu2 has the Jahn-Teller characteristic elongate bond to H2O1. The unit-cell volume decreased 7% from originally 734.45(3) to 686.4(4) Å3 leading to a formula with 1 H2O pfu. The new phase observed above 150 °C is characterized by an increase of the c axis and a shortening of the b axis. The bending of T-O-T angles causes an increasing elliptical shape of the eight-membered rings in the tetrahedral and octahedral sheets. Moreover a rearrangement of the hydrogen-bond system was observed.At 225 °C, the structure degrades to an X-ray amorphous residual due to release of the last H2O molecule at H2O1. The stronger Jahn-Teller distortion of Cu1 relative to Cu2 suggests that Cu1 is fully occupied by Cu, whereas Cu2 bears significant Zn. H2O1 is the fifth ligand of Cu2. Zn at Cu2 is not favorable to adopt planar fourfold coordination. Thus, if the last water molecule is expelled the structure is destabilized.This study contributes to understanding the dehydration mechanism and thermal stability of supergene minerals characterized by Jahn-Teller distorted octahedra with mixed Cu, Zn occupancy
Kristalografsko proučavanje strukturne desimetrizacije granata grosularsko-andraditske izomorfne serije
Get PDFU ovoj Doktorskoj disertaciji proučavano je pet različitih zona makroskopski zonarnog grandita sa lokaliteta Meka Presedla (Kopaonik, Srbija). Pomoću hemijske i elektronske analize mikroprobe preračunati su relativno visoko homogeni sastavi zona, t.j.: Grs64±1Adr36±1Sps2 (A), Grs62±1Adr38±1Sps2 (B), Grs59±2Adr40±2Sps2 (C), Grs58±2Adr41±2Sps2 (D) i Grs58±1Adr41±1Sps2 (E). Glavne promene u sastavima izražene formulom: Ca2,93-2,97Mn0,05-0,06Mg0,00-0,01Al1,14-1,26Fe3+0,72-0,83Ti0,00-0,02Si2,97-3,02O12 ukazuju da je jedina značajnija varijacija ustanovljena samo kod Al-Fe3+ raspodela u oktaedarskom položaju. Ovakav hemijski sastav je potvrđen i sa matematičkim proračunima iz IC i Raman analiza. Urađena je takođe i karakterizacija zona Raman spektroskopskom metodom, ukazujući na dva tipa promena. Brojne strukture su određene Rietveld metodom. Ustanovljena je desimetrizacija u Fddd ili R‾3c prostornim grupama, pri čemu je prva prostorna grupa znatno verovatnija. Na taj način, ovi rezultati se mogu svrstati u samo nekoliko publikovanih radova u svetu u kojima je desimetrizacija grandita nesumnjivo dokazana, a prvi rad takve vrste sa podacima koji su dobijeni rendgenskom difrakcionom analizom praha. Pojedina značajna odstupanja u okviru među-jonskih rastojanja ukazuju da se rotacija tetraedra, poliedarske distorzije i najverovatnije valence poliedara razlikuju između zona. Uslovi postanka su procenjeni na: t=~650-690 (715) oC, p=2-3 kbara i XCO2 ≥ 0,6. Dobijeni rezultati argumentovano ukazuju da je desimetrizacija prouzrokovana pre svega termodinamikom i kinetikom postanka grandita, a ne njegovim sastavom.In this Doctoral Dissertation it was studied five different zones of the macroscopically zoned grandite from the Meka Presedla locality (Kopaonik Mt., Serbia). With the chemical and electron microprobe analyses it was recalculated relatively high homogeneity composition levels of the zones, i.e.: Grs64±1Adr36±1Sps2 (A), Grs62±1Adr38±1Sps2 (B), Grs59±2Adr40±2Sps2 (C), Grs58±2Adr41±2Sps2 (D) and Grs58±1Adr41±1Sps2 (E). Main compositional variations represented by formulae: Ca2,93-2,97Mn0,05-0,06Mg0,00-0,01Al1,14-1,26Fe3+0,72-0,83Ti0,00-0,02Si2,97-3,02O12 indicate that the only significant variation was established for Al-Fe3+ distribution within the octahedral position. Such chemical composition was also confirmed with mathematical calculations from IR and Raman analysis. Also, zones were characterized with Raman spectroscopical method, indicating two types of variation. Numerous structures were refined with Rietveld method. It was established dissymmetrization into Fddd or R‾3c space groups, whereby is the first one space group with quite more probability. In this way, these results may be seen in only a few published papers in the World in which the grandite dissymmetrization was undoubtedly proven, and the first work of its kind with the data obtained by X-ray powder diffraction analysis. Some major differences within the inter-ionic distances indicate that the tetrahedron rotations, polyhedral distortions and most probably valences of the polyhedrons differs accross the zones. Formation conditions were estimated to: t=~650-690 (715) oC, p=2-3 kbars and XCO2 ≥ 0.6. The obtained results reasonably indicate that dissymmetrization was caused primarily by thermodynamic and kinetic of the grandite formation, and not by composition
Synthesis and structural characterization of microporous arsenates and phosphates
No full textPredmet rada i istraživanja ove doktorske disertacije su sinteza i strukturne
karakteristike novih kristalnih arsenata i fosfata koji sadrže Mg, K, Ca, Mn, Fe, Co, Ni,
Cu, Zn, Sr, Ba i druge katjone. U strukturama arsenata i fosfata, AsO4- i PO4-tetraedri
najčešće se vezuju sa tetraedarski ili oktaedarski koordinisanim katjonima prelaznih
metala formirajući otvorene strukture (slojeve ili 3D mreže) sa širokim opsegom
različitih topologija. U šupljinama ili porama u obliku povezanih ili nepovezanih
kanala, tunela, kaveza i međuslojnog prostora mogu se ugraditi različiti vanmrežni joni
(obično alkalni i zemnoalkalni katjoni) ili molekuli (najčešće mali organski molekuli),
što čini ova jedinjenja veoma interesantnim zbog njihovih fizičkih i hemijskih osobina i
potencijalne primene.
U okviru ispitivanja sistema T1O–T2O–X2O5–(H2O)–Y, gde je T1 dvovalentni ili
jednovalentni (K+, Ca2+, Zn2+, Sr2+, Ba2+), T2 dvovalentni ili trovalentni (Mg2+, Mn2+,
Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Fe3+, Co3+), X petovalentni (P5+, As5+) katjon, a Y je
vanmrežni katjon H2(C2H8N2)2+ ili NH4
+ sintetisana su nova jedinjenja metodom
niskotemperaturne hidrotermalne sinteze i određene njihove kristalne strukture. Cilj je
bio da se u okviru ovog sistema sintetišu monokristali koji u mikroporama ili
međuslojnom prostoru sadrže različite jone i molekule kao što je etilendiamin,
C2H4(NH2)2, ili odgovarajuća protonovana forma.
Kvalitet dobijenih monokristala proveravan je pomoću optičkog mikroskopa ili
binokularne lupe i strukture kristala određene su metodom rendgenske difrakcije na
monokristalu. Za morfološku i hemijsku karakterizaciju korišćena je metoda skenirajuće
elektronske mikroskopije (SEM) dopunjena energetsko-disperzivnim sistemom (EDS).
Kod kristala koji su zahtevali preciznu kvantitativnu hemijsku analizu korišćena je
elektronska mikrosonda, a metoda ramanske spektroskopije korišćena je za određivanje
prisustva H2O, (OH)−, (NH4)+ i NH3.
Pokazano je da četiri sintetisana kristala imaju zeolitski DFT-tip strukture. To su
(H2en)[ZnAsO4]2 (ZnAs), (H2en)[Co0,1Zn0,9AsO4]2 (ZnCoAs),...The doctoral dissertation research subjects are the synthesis and structural
investigation of new arsenate and phosphate containing Mg, K, Ca, Mn, Fe, Co, Ni, Cu,
Zn, Sr, Ba and other cations. In the structures of arsenates and phosphates, AsO4- and
PO4-tetrahedra are usually linked with tetrahedrally and octahedrally coordinated
cations of transition metals forming open structures (layers or 3D frameworks) with a
wide range of different topologies. In the holes, or pores, which are in the form of a
connected or unconnected channels, tunnels, cages and the interlayered space, various
non-framework ions (usually alkaline and earth alkaline cations) or molecules (usually
small organic molecules) can be incorporated. Therefore these compounds are very
interesting due to their physical and chemical properties and potential applications.
In the course of the investigation of the T1O–T2O–X2O5–(H2O)–Y system,
where T1 is a divalent or monovalent (K+, Ca2+, Zn2+, Sr2+, Ba2+), T2 divalent or
trivalent (Mg2+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+, Fe3+, Co3+), X pentavalent (P5+,
As5+) cation, and Y is non-framework cation H2(C2H8N2)2+ or NH4
+, several novel
compounds have been synthesized using the low temperature hydrothermal synthesis
method, and their crystal structures have been determined. The aim was to synthesize
single crystals with micropores or interlayer space containing different ions and
molecules like the ethylenediamine, C2H4(NH2)2, or the corresponding protonated
forms.
The quality of the obtained single crystals was evaluated using an optical or
binocular microscope, and the crystal structure was solved using single-crystal X-ray
diffraction data. For the morphological and chemical characterization the scanning
electron microscopy (SEM), coupled with energy-dispersive system (EDS) was used.
The electron microprobe provide precise quantitative chemical analysis, and the Raman
spectroscopy method was used for the determination of the presence of H2O, (OH)−,
(NH4)+ and NH3..
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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