Faktor snage nanostrukturiranog bizmut telurida određen oblicima

Bismuth telluride is a thermoelectric material with high figure of merit, used for cooling applications at room temperature. To investigate the effect of morphology and grain size on transport parameters, nanostructured bismuth telluride has been synthesized under different reaction conditions and characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. From the measurement of electrical conductivity and thermoelectric power, power factor for different samples has been obtained. The results show that the transport parameters are critically influenced by the morphology and dimension of the samples that in turn depend on the condition of synthesis. The experimentally observed variation of electrical conductivity with the change of dimensionality of the samples from 2D to 0D, which is in line with the theoretical prediction made by other workers, is discussed. There is a variation of the power factor of the samples prepared under different conditions of synthesis.Bizmut telurid je termoelektrična tvar s visokom učinkovitošću koja se rabi za hlađenje na sobnim temperaturama. Radi istraživanja učinka oblika i veličine zrna na transportne parametre, sintetizirali smo nanostrukturirani bizmut telurid u različitim uvjetima i ispitivali rentgenskom difrakcijom, te propusnom i pretražnom elektronskom mikroskopijom. Mjerenjem električne vodljivosti i termoelektrične snage niza uzoraka odredili smo faktore snage. Ishodi analize pokazuju da transportni parametri jako ovise o obliku i veličini uzoraka, koji pak ovise o uvjetima njihove sinteze. Raspravljamo o opaženim promjenama električne vodljivosti ovisnim o dimenzionalnosti uzoraka od 2D do 0D i nalazimo sklad s teorijskim predviđanjima drugih autora. Nalazimo promjene faktora snage uzoraka pripremljenih uz različite uvjete sinteze

Using Local Public Goods to Attract and Retain the Creative Class: A Tale of Two Cities

We study the impact that the provision of a local public good (LPG) by two cities has on their ability to attract and retain members of the creative class. This creative class consists of two types of members known as engineers and artists. Engineers are wealthier than artists and they also value the LPG more. We first focus on each city in isolation. We compute the marginal value and the marginal cost of the LPG and then determine the provision of this LPG when the provision is determined by uniform contributions and majority voting. Next, we allow the creative class members to migrate between the two cities and analyze whether engineers or artists migrate, the equilibrium distribution of the creative class, and the efficiency of the LPG provision. Finally, we consider the situation in each city just before migration and study how much of the LPG is provided when proportional contributions and majority voting determine this provision. A related question we address is whether engineers or artists now have an incentive to migrate and, if yes, we identify who would like to migrate and to which city

Synthesis and Thermoelectric Properties of Bi2Se3 Nanostructures

Bismuth selenide (Bi2Se3) nanostructures were synthesized via solvothermal method. The crystallinity of the as-synthesized sample has been analyzed by X-ray diffraction, which shows the formation of rhombohedral Bi2Se3. Electron microscopy examination indicates that the Bi2Se3 nanoparticles have hexagonal flake-like shape. The effect of the synthesis temperature on the morphology of the Bi2Se3 nanostructures has also been investigated. It is found that the particle size increases with the synthesis temperature. Thermoelectric properties of the Bi2Se3 nanostructures were also measured, and the maximum value of dimensionless figure of merit (ZT) of 0.096 was obtained at 523 K

The Mechanism of Substrate Inhibition in Human Indoleamine 2,3-Dioxygenase

Indoleamine 2,3-dioxygenase catalyzes the O(2)-dependent oxidation of L-tryptophan (L-Trp) to N-formylkynurenine (NFK) as part of the kynurenine pathway. Inhibition of enzyme activity at high L-Trp concentrations was first noted more than 30 years ago, but the mechanism of inhibition has not been established. Using a combination of kinetic and reduction potential measurements, we present evidence showing that inhibition of enzyme activity in human indoleamine 2,3-dioxygenase (hIDO) and a number of site-directed variants during turnover with L-tryptophan (L-Trp) can be accounted for by the sequential, ordered binding of O(2) and L-Trp. Analysis of the data shows that at low concentrations of L-Trp, O(2) binds first followed by the binding of L-Trp; at higher concentrations of L-Trp, the order of binding is reversed. In addition, we show that the heme reduction potential (E(m)(0)) has a regulatory role in controlling the overall rate of catalysis (and hence the extent of inhibition) because there is a quantifiable correlation between E(m)(0) (that increases in the presence of L-Trp) and the rate constant for O(2) binding. This means that the initial formation of ferric superoxide (Fe(3+)-O(2)(•-)) from Fe(2+)-O(2) becomes thermodynamically less favorable as substrate binds, and we propose that it is the slowing down of this oxidation step at higher concentrations of substrate that is the origin of the inhibition. In contrast, we show that regeneration of the ferrous enzyme (and formation of NFK) in the final step of the mechanism, which formally requires reduction of the heme, is facilitated by the higher reduction potential in the substrate-bound enzyme and the two constants (k(cat) and E(m)(0)) are shown also to be correlated. Thus, the overall catalytic activity is balanced between the equal and opposite dependencies of the initial and final steps of the mechanism on the heme reduction potential. This tuning of the reduction potential provides a simple mechanism for regulation of the reactivity, which may be used more widely across this family of enzymes