Propane Dehydrogenation Using Transition Metal Cluster Catalysts

Our research seeks to determine the propane dehydrogenation (PDH) reaction pathways using various transition-metal cluster catalysts. We are studying the first step of the reaction, in which a C-H bond is broken. This has been previously shown to be the rate-limiting step of the PDH reaction. We are calculating the PDH activation energy (Ea) using the Vienna Ab-Initio Simulation Package (VASP) in conjunction with the nudged elastic band algorithm. Thus far, we have studied Pt, Ta, and Ni clusters ranging in size from 2-10 atoms. Our goal is to better understand the dependence of Ea on metal type and cluster size

Can Hyperfine Excitation explain the Observed Oscillation-Puzzle of Nuclear Orbital Electron Capture of Hydrogen-like Ions?

Modulated in time orbital electron capture (EC) decays have been observed recently in stored H-like $^{140}$Pr$^{58+}$ and $^{142}$Pm$^{60+}$ ions. Although, the experimental results are extensively discussed in literature, a firm interpretation has still to be established. Periodic transitions between the hyperfine states could possible lead to the observed effect. Both selected nuclides decay to stable daughter nuclei via allowed Gamow-Teller transitions. Due to the conservation of total angular momentum, the allowed EC decay can only proceed from the hyperfine ground state of parent ions. In this work we argue that periodic transitions to the excited hyperfine state (sterile) in respect to the allowed EC decay ground state cannot explain the observed decay pattern

Models of Social Groups in Blogosphere Based on Information about Comment Addressees and Sentiments

This work concerns the analysis of number, sizes and other characteristics of groups identified in the blogosphere using a set of models identifying social relations. These models differ regarding identification of social relations, influenced by methods of classifying the addressee of the comments (they are either the post author or the author of a comment on which this comment is directly addressing) and by a sentiment calculated for comments considering the statistics of words present and connotation. The state of a selected blog portal was analyzed in sequential, partly overlapping time intervals. Groups in each interval were identified using a version of the CPM algorithm, on the basis of them, stable groups, existing for at least a minimal assumed duration of time, were identified.Comment: Gliwa B., Ko\'zlak J., Zygmunt A., Models of Social Groups in Blogosphere Based on Information about Comment Addressees and Sentiments, in the K. Aberer et al. (Eds.): SocInfo 2012, LNCS 7710, pp. 475-488, Best Paper Awar

Band gap stability in Kondo insulators

We report on magnetic measurements and electronic structure investigations of CeNiSn and CeRhSb. Both belong to the group of Kondo insulators. The magnetic susceptibility shows the nonmagnetic ground state for these compounds and their alloys. The 3d X-ray photoemission spectroscopy spectra show evidence for the mixed valence state of Ce in CeRhSb alloys, as also seen for CeNiSn, whereas the spectra for the La substituted (Ce,La)NiSn compounds show only evidence for a pure Ce 3+ ground state. We suggest the presence of Kondo-hole states in (Ce,La)RhSb. The location of the pseudogap in CeRhSb varies with the number of free electron, the valence of Ce, and the f—d hybridization. We discuss the similar crystallographic properties and the closed electronic structures of ZrNiSn-type semi-Heusler alloys and CeNiSn-type Kondo insulators

Analysis of roles and groups in blogosphere

In the paper different roles of users in social media, taking into consideration their strength of influence and different degrees of cooperativeness, are introduced. Such identified roles are used for the analysis of characteristics of groups of strongly connected entities. The different classes of groups, considering the distribution of roles of users belonging to them, are presented and discussed.Comment: 8th International Conference on Computer Recognition Systems, CORES 201

Hybridization gap in some ternary f-electron and d-electron intermetallics

In this work we have discussed electronic structure, structural and magnetic properties of the CeMX-type compounds, where M is a transition metal and X is an sp element. The main goal of this presentation is to find the influence of metal M on the coherent gap formation at the Fermi level in the Ce-Kondo insulators. We also discuss a similar semiconductor-like resistance anomaly of Fe2TiSn and CeNiSn-type Kondo insulators

Electro-acoustic transducers on the basis of thin PZT-films

In the present work PZT-type thin films have been obtained by RF sputtering and electroacoustic transducers characterized by high sensitivity (t), wide range of measured relative deformations (q) and high working frequencies (w) were built. Polycrystalline ferroelectric thin films with the perovskite type structure and chemical composition Pb(Zro.33Tio.4sWo.oiCdo.oi)03 have been fabricated by RF sputtering. The films exhibited slightly lower values of dielectric constant, residual polarization and piezoelectric coefficient </33 = 80 x 10“12 C/N, as compared with the ceramics of the same chemical composition. The thin films keep such a value of du up to the Curie point. On the basis of the PZT-type thin films the isotropic and anisotropic piezoelectric sensors were built and investigated. The electrical signal of the isotropic sensors is proportional to the sum of the main components of the relative deformation tensor whereas the signal of the anisotropic sensors depends on the angle between the sensor axis and the main axis of the deformation tensor of the sample under investigation. The sensors are characterized by high stability of the generated signal

The β-polymorph of uranium phosphide selenide

β-UPSe was synthesized from the reaction of U2Se3, P and Se in a CsCl flux in a fused-silica tube. It crystallizes with four formula units in the tetra­gonal space group I4/mmm in the UGeTe structure type. The asymmetric unit comprises one U (site symmetry 4mm), one Se (4mm), and one P (mmm.) atom. The U atom is coordinated in a monocapped square-anti­prismatic arrangement, where the square face is formed by P atoms and the other five vertices are Se atoms. The P site is disordered about a mirror plane, showing half-ocupancy for each of the two resulting P atoms. The title structure is related to that of α-UPSe, which crystallizes with two formula units in the tetra­gonal space group P4/nmm in the PbFCl structure type

On Critical Velocities in Exciton Superfluidity

The presence of exciton phonon interactions is shown to play a key role in the exciton superfluidity. We apply the Landau criterion for an exciton-phonon condensate moving uniformly at zero temperature. It turns out that there are essentially two critical velocities in the theory. Within the range of these velocities the condensate can exist only as a bright soliton. The excitation spectrum and differential equations for the wave function of this condensate are derived.Comment: 7 pages, Latex; to be published in Phys.Rev.Lett (1997