Elektronsko mikroskopijsko proučavanje uređenja ravnina–“lanaca” kod visokotemperaturnih supravodiča tipa YBCO

Structures of a number of high-Tc superconducting cuprates related to the prototype YBCO compound, were studied by means of high resolution electron microscopy (HREM) and electron diffraction (ED). Commensurate superstructures or incommensurate modulated structures were induced by various metal atom substitutions for Cu in the \u27\u27chain\u27\u27-layer and its ordering. Metal (M) and oxygen (O) atom ordering is confined mainly in the MO1-x-"chain\u27\u27 layers, while the remaining part of the crystal structure, as well as the material\u27s superconducting features, are hardly affected.Strukture nekih supravodljivih kuprata, sličnih osnovnom spoju YBCO s visokim Tc, proučavane su tehnikom visoko-razlučujuće elektronske mikroskopije i elektronske difrakcije. Nađeno je da zamjena atoma bakra u ravninama “lanaca” raznim metalnim atomima uzrokuje njihovo uređenje i pojavu sumjerljivih nadstruktura ili nesumjerljivo moduliranih struktura. Odgovarajuće uređenje metalnih (M) i kisikovih (O) atoma ograničeno je na MO1−x ravnine “lanaca” bez većeg utjecaja kako na ostali dio strukture, tako i na osnovna supravodljiva svojstva

Uređenje (Ba/Sr)O-dvoslojeva u supravodljivom kupratu RE2(Ba/Sr)2GaCu2O9

Ordering in the (Ba/Sr/Nd)O bi-layers (of "Rock-Salt" type structure) of the RE2(Ba0.65Sr0.20Nd0.15)2GaCu2O9 high-Tc superconducting cuprate was investigated by electron microscopy and diffraction. Besides the average layered structure based on the tetragonal perovskite cell ap×ap×cp and the meandering chain superstructure based on the orthorhombic 4ap×2ap×cp cell in the GaO-layers, an additional ordering was found in the pairs of (Ba/Sr/Nd)O-...-(Ba/Sr/Nd)O layers. We propose a model for ordering of 3Ba and 1Sr cations on a two-dimensional 2ap×2ap lattice cell in each (Ba/Sr/Nd)O layer. This compositional intra-layer ordering is accompanied by the inter-layer plane stacking disorder. The 4-fold symmetry of the average tetragonal structure is preserved, while the translation parameters in the (a,b) plane are doubled. This local ordering in the RS-type bi-layers hardly affects the symmetry of the basic structure; however, it may act as a source of weak anisotropy in the CuO2-layers.Strukturno uređenje (Ba/Sr/Nd)O dvoslojeva u supravodljivom kupratu sastava RE2(Ba/Sr)2GaCu2O9 istraživano je pomoću elektronske mikroskopije i difrakcije. Osim prosječne tetragonske strukture na osnovi slojevite perovskitske tetragonske ćelije ap i ap i cp, i nadstrukture meandrirajućih lanaca u GaO-ravninama s ortorombskom ćelijom 4ap i 2ap i cp, nad–eno je dodatno uređenje u parovima (Ba/Sr/Nd)O-...-(Ba/Sr/Nd)O ravnina. Predložen je model uređenja 3Ba i 1Sr kationa unutar 2ap i 2ap dvodimenzijske ćelije u svakoj (Ba/Sr/Nd)O ravnini. Ovo unutar-ravninsko uređenje popraćeno je među-ravninskim neredom u nizu slaganja slojeva. Simetrija 4-reda, koja je svojstvena prosječnoj tetragonskoj strukturi ostaje sačuvana, uz podvostručenje parametara rešetke u j a k bl ravnini. Opaženo uređenje unutar (Ba/Sr/Nd)O dvoslojeva ovog supravodljivog kuprata nema jaki utjecaj na simetriju osnovne strukture, ali može biti izvor lokalne anizotropije u CuO2-ravninama

Bone Densitometric Study of Mandibular Density Using Dental Panoramic Radiographs

Svrha rada bila je ocijeniti preciznost mikrodenzitometrijske metode na ortopantomogramima. U tu je svrhu upotrebljen bakreni kalibracijski klin (BKK) sastavljen od 5 slojeva, debeo od 0,1 do 0,5 mm. Ortopantomogrami su digitalizirani, a na digitaliziranim su snimkama izmjerene razine sivila na bakrenom kalibracijskom klinu te u području istraživanja. Izmjerene vrijednosti svih razina sivila, uz pomoć polinomne funkcije trećeg stupnja izražene su u ekvivalentima debljine bakrenog kalibracijskog klina. Uspoređujući vrijednosti ekvivalenata u području istraživanja na prvoj i drugoj digitaliziranoj snimci istog pacijenta vidljivo je da se razlike među njima kreću unutar 10%. Deset pacijenata dobrovoljaca slikano je dva puta, u vremenskom razmaku od 5 minuta. Rezultati su pokazali da je mikrodenzitometrijskom metodom moguće otkriti promjene u mineralnom sastavu koπtanoga tkiva kada one dosegnu 10%.The precision of the method of microdensitometry on panoramic radiographs (PR), using a five step copper stepwedge, was examined. Two PRs, one after the other, were made for each of the six examined patients. All the PRs were digitised. Gray levels were measured on the stepwedge and on the region of the interest. Measured gray level values were expressed in equivalents of the stepwedge thickness using 3rd degree polynomial. Comparing the values of the equivalents in the region of interest on the first and the second digitised image of the same patient, the differences were within 10%. The results revealed that the method detects mineral bone changes, which surpass more than 10% of the density on PR

Magnetic anisotropy of spin tetramer system SeCuO3_3 studied by torque magnetometry and ESR spectroscopy

We present an experimental study of macroscopic and microscopic magnetic anisotropy of a spin tetramer system SeCuO$_3$ using torque magnetometry and ESR spectroscopy. Large rotation of macroscopic magnetic axes with temperature observed from torque magnetometry agrees reasonably well with the rotation of the $\textbf{g}$ tensor above $T \gtrsim 50$~K. Below 50~K, the $\textbf{g}$ tensor is temperature independent, while macroscopic magnetic axes continue to rotate. Additionally, the susceptibility anisotropy has a temperature dependence which cannot be reconciled with the isotropic Heisenberg model of interactions between spins. ESR linewidth analysis shows that anisotropic exchange interaction must be present in SeCuO$_3$. These findings strongly support the presence of anisotropic exchange interactions in the Hamiltonian of the studied system. Below $T_N=8$~K, the system enters a long - range antiferromagnetically ordered state with easy axis along the $^*$ direction. Small but significant rotation of magnetic axes is also observed in the antiferromagnetically ordered state suggesting strong spin-lattice coupling in this system.Comment: 14 pages, 13 figure

Unified Assessment of the Effects of Van der Waals Interactions on the Structural and Electronic Properties of Some Layered Organic Solids kappa-(BEDT-TTF)2X

Proper inclusion of van der Waals interactions (vdW) in ab initio calculations based on the density functional theory (DFT) is crucial to describe soft, organic, layered solids such as κ -(BEDT-TTF) 2X . Since no consensus has been reached on the reliability of available vdW DFT functionals, most of the first principles calculations have been based on experimental crystal structure data without any structural optimization. Here, we explore optimal DFT-based schemes that account for the effects of vdW interactions on the structural and electronic band properties of three paradigmatic charge transfer salts, κ -(BEDT-TTF) 2 Cu 2 (CN) 3 , κ -(BEDT-TTF) 2 Ag 2 (CN) 3 , and κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl, for which a unified optimization of the structure is possible. Detailed examination of the prototype test system κ -(BEDT-TTF) 2 Cu[N(CN) 2 ]Cl shows that the optB88-vdW functional performs slightly better than the PBE-vdW and that the choice of pseudopotentials is critical to obtaining realistic results

Study of the deamalgamation process in silver-tin-base amalgams

Deamalgamation of the common dentistry amalgam scrap, as well as of a model Ag_70Sn_17Cu_13 prealloy amalgam, was studied by metallography, microhardness, X-ray diffraction and differential thermal analysis techniques. The results are discussed from the view-point of the possible powder-metallurgical application of the process

Istraživanje deamalgamacijskog procesa u amalgamima slitina bogatih srebrom i kositrom

Proces deamalgamacije u amalgamima slitina bogatih srebrom i kositrom istraživan je metalografijom, mjerenjem mikrotvrdoće, rentgenskom difrakcijom i diferencijalnom termičkom analizom. Dobiveni rezultati raspravljeni su s gledišta regeneracije otpadnog amalgama (reciklaže, tj. obnavljanja strukture i svojstava polaznih komponenti), kao i moguće uporabe ovog procesa u metalurgiji praha

Solid/Liquid Equilibria in Aqueous Systems of Dodecyl Benzene Sulphonate and Alkaline Earth Ions

SolubUi.ty/ precipitability boundaries and the morphology of solid pha ses were investigated and equilibria cons t ants calculated for Mg, Ca, Sr, Ba - dodecyl benzene sulphonate salts. The experimental methods of tyndallometry, polari ~ing microscopy and X-ray diffraction gave consistent results. The measurements were performed at 293 K. The so,lubilLty of MCDBS)2 salts decreased in the order Mg > Ca > Sr >Ba; pK0sp were calcula ted to be: (10.80±0.07) for MgCDBSh, (10.48±0.07) for Mg(DBS)2 (for DBS dimer) , (11.23±0.03) for CaCDBSh, (12.00±0.08) for Sr(DBSh, (12.4 ± 0.2) for Ba(DBSh It is demonstrated that at least two prec:ipitated phases can be obtained : a partially ·ordered phase, probably belonging to the smectic A liquid crysta.1, while the other phase appears to be a solid crystal