182 research outputs found
Optical spectra obtained from amorphous films of rubrene: Evidence for predominance of twisted isomer
In order to investigate the optical properties of rubrene we study the
vibronic progression of the first absorption band (lowest \pi -> \pi^*
transition). We analyze the dielectric function of rubrene in solution and thin
films using the displaced harmonic oscillator model and derive all relevant
parameters of the vibronic progression. The findings are supplemented by
density functional calculations using B3LYP hybrid functionals. Our theoretical
results for the molecule in two different conformations, i.e. with a twisted or
planar tetracene backbone, are in very good agreement with the experimental
data obtained for rubrene in solution and thin films. Moreover, a simulation
based on the monomer spectrum and the calculated transition energies of the two
conformations indicates that the thin film spectrum of rubrene is dominated by
the twisted isomer.Comment: 7 pages, 6 figure
Superplastična deformacija Al-Al4C3 kompozita
Deformation of the Al-Al4C3 composites with different volume fraction of Al-Al4C3 phase was investigated at different temperatures (293 - 723 K) and different strain rates (2,5 * 10-5 s-1 do 1,0 * 10-1 s-1). At temperatures 673 - 723 K and at the highest strain rate of 1,0 * 10-1 s-1, a significant ductility increase was observed. TEM analysis suggests the onset of superplasticity may be the result of dynamic grain polygonization, grain slip and rotation, partial recrystallization and dislocation creep in the tested system, which is known as strain induced dynamic recovery. Increase of the volume fraction of secondary phase in the studied composite resulted in a shift from slip on grain boundaries controlled mechanism to the grain rotation controlled deformation mechanism.Istraživana je deformacija Al-Al4C3 kompozita različitog volumnog udjela Al-Al4C3 faze kod različitih temperatura (od 293 do 723 K) i brzina deformacije (od 2,5 * 10-5 s-1 do 1,0 * 10-1 s-1). Kod temperatura od 673 do 723 K i najviše brzine deformacije od 1,0 * 10-1 s-1 zapaženo je značajno povećanje kovkosti. TEM analiza ukazuje da početak superplastičnosti može biti rezultat dinamičke poligonizacije zrna, klizanja i rotacije zrna, djelomične rekristalizacije i puzanja dislokacija u istraživanom sustavu, što je poznato kao deformacijom inducirano dinamičko oporavljanje. Porast volumnog udjela sekundarne faze u istraživanom kompozitu rezultirao je promjenom kontrolnog mehanizma deformacije od klizanja po granicama zrna do rotacije zrna
Evolution of the fishtail-effect in pure and Ag-doped MG-YBCO
We report on magnetic measurements carried out in a textured
YBaCuO and YBa(CuAg)O (at
0.02) crystals. The so-called fishtail-effect (FE) or second
magnetization peak has been observed in a wide temperature range
0.4~~0.8 for . The origin of the FE arises for
the competition between surface barrier and bulk pinning. This is confirmed in
a non-monotonically behavior of the relaxation rate . The value
for Ag-doped crystals is larger than for the pure one due to the presence of
additional pinning centers, above all on silver atoms.Comment: 6 pages, 6 figure
Estimation of the thermal diffusivity in a large electroceramic body by an invere method
Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.We investigate the temperature dependence of the thermal diffusivity for a large ceramic body of a cylindrical shape during firing up to 900 °C. The body was made of a ceramic material used in the production of electroporcelain insulators. We describe the corresponding heat transfer by the standard heat equation and solve the inverse problem by the Levenberg-Marquardt method. The results show that the method allows one to detect the physical-chemical processes occurring in the material during firing, namely, the liberation of physically bound water in the range up to 250 °C, the phase transformation of kaolinite into metakaolinite (dehydroxyla-tion) in the range ~ 450 °C – 650 °C, and solid-state sintering starting at ~ 700 °C.cf201
Magneto-caloric effect in the pseudo-binary intermetallic YPrFe17 compound
We have synthesized the intermetallic YPrFe17 compound by arc-melting. X-ray
and neutron powder diffraction show that the crystal structure is rhombohedral
with View the MathML source space group (Th2Zn17-type). The investigated
compound exhibits a broad isothermal magnetic entropy change {\Delta}SM(T)
associated with the ferro-to-paramagnetic phase transition (TC \approx 290 K).
The |{\Delta}SM| (\approx 2.3 J kg-1 K-1) and the relative cooling power
(\approx 100 J kg-1) have been calculated for applied magnetic field changes up
to 1.5 T. A single master curve for {\Delta}SM under different values of the
magnetic field change can be obtained by a rescaling of the temperature axis.
The results are compared and discussed in terms of the magneto-caloric effect
in the isostructural R2Fe17 (R = Y, Pr and Nd) binary intermetallic alloys.Comment: Preprint, 5 pages (postprint), 4 figures, regular pape
The First Phylogenetic Analysis of Palpigradi (Arachnida)—The Most Enigmatic Arthropod Order
Palpigradi are a poorly understood group of delicate arachnids, often found in caves or other subterranean habitats. Concomitantly, they have been neglected from a phylogenetic point of view. Here we present the first molecular phylogeny of palpigrades based on specimens collected in different subterranean habitats, both endogean (soil) and hypogean (caves), from Australia, Africa, Europe, South America and North America. Analyses of two nuclear ribosomal genes and COI under an array of methods and homology schemes found monophyly of Palpigradi, Eukoeneniidae, and a division of Eukoeneniidae into four main clades, three of which include samples from multiple continents. This supports either ancient vicariance or long-range dispersal, two alternatives we cannot distinguish with the data at hand. In addition, we show that our results are robust to homology scheme and analytical method, encouraging further use of the markers employed in this study to continue drawing a broader picture of palpigrade relationships.Organismic and Evolutionary Biolog
Nanostructure and magnetic anomaly of mechanosynthesized CeYO (x ≤ 0.3) solid solutions
Electromagnetic properties of complex oxide solid solutions containing Ce and Y attract increasing interests due to their high application potential. Their properties are known to be dependent on many factors including grain size and crystal defects. Here we focus on unique features of nanocrystalline CeYO (x ≤ 0.3) solid solutions prepared via a mechanosynthesis. Mechanically activated CeO and mechanosynthesized CeYO exhibit room-temperature ferromagnetism. The saturation magnetization reaches maximum for the CeYO solid solution. XPS and Raman spectra show that Ce4+s are partially reduced to Ce, with simultaneous introduction of oxygen vacancies accumulated on surface of the solid solutions. An analysis of the experimental magnetization data and the determination of both the spin state and the concentration of magnetic carriers revealed that a small part of the Ce spins (<1%) is responsible for the magnetic state of the CeYO system. Existence of clusters with a short-range antiferromagnetic order is also suspected
Molecular recognition in the P2Y14 receptor: Probing the structurally permissive terminal sugar moiety of uridine-5′-diphosphoglucose
The P2Y14 receptor, a nucleotide signaling protein, is activated by uridine-5′-diphosphoglucose 1 and other uracil nucleotides. We have determined that the glucose moiety of 1 is the most structurally permissive region for designing analogues of this P2Y14 agonist. For example, the carboxylate group of uridine-5′-diphosphoglucuronic acid proved to be suitable for flexible substitution by chain extension through an amide linkage. Functionalized congeners containing terminal 2-acylaminoethylamides prepared by this stratgegy retained P2Y14 activity, and molecular modeling predicted close proximity of this chain to the 2nd extracellular loop of the receptor. In addition, replacement of glucose with other sugars did not diminish P2Y14 potency. For example, the [5″]ribose derivative had an EC50 of 0.24 μM. Selective monofluorination of the glucose moiety indicated a role for the 2″- and 6″-hydroxyl groups of 1 in receptor recognition. The β-glucoside was 2-fold less potent than the native α-isomer, but methylene replacement of the 1″-oxygen abolished activity. Replacement of the ribose ring system with cyclopentyl or rigid bicyclo[3.1.0]hexane groups abolished activity. Uridine-5′-diphosphoglucose also activates the P2Y2 receptor, but the 2-thio analogue and several of the potent modified-glucose analogues were P2Y14-selective
AC loss in ReBCO pancake coils and stacks of them: modelling and measurement
Many applications of ReBCO coated conductors contain stacks of pancake coils.
In order to reduce their high AC loss, it is necessary to understand the loss
mechanisms. In this article, we measure and simulate the AC loss and the
critical current, I_c, in stacks of pancake coils ("pancakes"). We construct
stacks of up to 4 pancakes and we measure them by electrical means. We also
obtain the anisotropic field dependence of J_c from I_c measurements of the
tape. This J_c is the only input to the simulations, together with the coil
dimensions. After validating our computations with the measurements, we
simulate stacks of many pancakes, up to 32. We found that the AC loss in a
stack of (four) pancakes is very high, two orders of magnitude larger than for
a single tape. A double pancake behaves as a single one with double width but a
stack of more pancakes is very different. Finally, we found that a 2-strand
Roebel cable reduces the AC loss in a stack of pancakes but not in a single
pancake. In conclusion, the AC loss in stacks of pancakes is too high. However,
our simulations are useful to predict the AC loss and optimise the coil design,
reducing the AC loss.Comment: 34 pages, 18 figures. All figures are modified; figures 3, 7 and 10
are new. Text thoroughly revised and extende
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