Spatial inversion of gyrotropy parameter in conductivity tensor and charge transport peculiarities

Charge transfer is discussed for the case when gyrotropy parameter (Hall coefficient) varies along transport л-direction and inverses its sign. This situation takes place in contacts of the serially joined materials having electron and hole types of conductivity. Spatial inhomogeneity of conductivity and inversion of Hall coefficient sign are analyzed in terms of electric potential and current density distribution. It is shown that under inhomogeneous magnetic field the steady current skinning takes place in plate sample

Thermodynamic properties of Holstein polarons and the effects of disorder

The ground state and finite temperature properties of polarons are studied considering a two-site and a four-site Holstein model by exact diagonalization of the Hamiltonian. The kinetic energy, Drude weight, correlation functions involving charge and lattice deformations, and the specific heat have been evaluated as a function of electron-phonon (e-ph) coupling strength and temperature. The effects of site diagonal disorder on the above properties have been investigated. The disorder is found to suppress the kinetic energy and the Drude weight, reduces the spatial extension of the polaron, and makes the large-to-small polaron crossover smoother. Increasing temperature also plays similar role. For strong coupling the kinetic energy arises mainly from the incoherent hopping processes owing to the motion of electrons within the polaron and is almost independent of the disorder strength. From the coherent and incoherent contributions to the kinetic energy, the temperature above which the incoherent part dominates is determined as a function of e-ph coupling strength.Comment: 17 pages. 17 figure

Nitrile ligands activation in dinuclear aminocarbyne complexes

The diiron complexes [Fe(Cp)(CO){μ-η2:η2-C[N(Me)(R)]NC(C6H3R′)CCH(Tol)}Fe(Cp)(CO)] (R = Xyl, R′ = H, 3a; R = Xyl, R′ = Br, 3b; R = Xyl, R′ = OMe, 3c; R = Xyl, R′ = CO2Me, 3d; R = Xyl, R′ = CF3, 3e; R = Me, R′ = H, 3f; R = Me, R′ = CF3, 3g) are obtained in good yields from the reaction of [Fe2{μ-CN(Me)(R)}(μ-CO)(CO)(p-NCC6H4R′)(Cp)2]+ (R = Xyl, R′ = H, 2a; R = Xyl, R′ = Br, 2b; R = Xyl, R′ = OMe, 2c; R = Xyl, R′ = CO2Me, 2d; R = Xyl, R′ = CF3, 2e; R = Me, R′ = H, 2f; R = Me, R′ = CF3, 2g) with TolCCLi. The formation of 3 involves addition of the acetylide at the coordinated nitrile and C–N coupling with the bridging aminocarbyne together with orthometallation of the p-substituted aromatic ring and breaking of the Fe–Fe bond. Complexes3a–e which contain the N(Me)(Xyl) group exist in solution as mixtures of the E-trans and Z-trans isomers, whereas the compounds 3f,g, which posses an exocyclic NMe2 group, exist only in the Z-cis form. The crystal structures of Z-trans-3b, E-trans-3c, Z-trans-3e and Z-cis-3g have been determined by X-ray diffraction experiments

Diiron-aminocarbyne complexes with amine or imine ligands: C-N coupling between imine and aminocarbyne ligands promoted by tolylacetilyde addition to [Fe2{m-CN(Me)R}(m-CO)(CO)(NH=CPh2)(Cp)2][SO3CF3]

A terminally coordinated CO ligand in the complexes [Fe2{m-CN(Me)R}(m-CO)(CO)2(Cp)2][SO3CF3] (R = Me, 1a; R = Xyl, 1b; Xyl = 2,6-Me2C6H3), is readily displaced by primary and secondary amines (L), in the presence of Me3NO, affording the complexes [Fe2{m-CN(Me)R}(m-CO)(CO)(L)(Cp)2][SO3CF3] (R = Me, L = NH2Et, 4a; R = Xyl, L = NH2Et, 4b; R = Me, L = NH2Pri, 5a; R = Xyl, L = NH2Pri, 5b; R = Xyl, L = NH2C6H11, 6; R = Xyl, L = NH2Ph, 7; R = Xyl, L = NH3, 8; R = Me, L = NHMe2, 9a; R = Xyl, L = NHMe2, 9b; R = Xyl, L= NH(CH2)5, 10). In the absence of Me3NO, NH2Et gives addition at the CO ligand of 1b, yielding [Fe2{CN(Me)(Xyl)}(m-CO)(CO)C(O)NHEt(Cp)2] (11). Carbonyl replacement is also observed in the reaction of 1a-b with pyridine and benzophenone imine, affording [Fe2{m-CN(Me)R}(m-CO)(CO)(L)(Cp)2][SO3CF3] (R= Me, L= Py, 12a; R = Xyl, L= Py, 12b; R= Me, L= HN=CPh2, 13a; R = Xyl, L= HN=CPh2, 13b). The imino complex 13b reacts with p-tolylacetylide leading to the formation of the m-vinylidene-diaminocarbene compound [Fe2-C=C(Tol)C(Ph)2N(H)CN(Me)(Xyl)(m-CO)(CO)(Cp2)] (15) which has been studied by X-ray diffraction

Characteristic features of anharmonic effects in the lattice dynamics of fcc metals

The dispersion in the entire Brillouin zone and the temperature dependence (right up to the melting temperature) of the anharmonic frequency shift and phonon damping in a number of fcc metals is investigated on the basis of microscopic calculations. It is found that the anharmonic effects depend sharply on the wave vector in the directions $\Gamma$-X, X-W, and $\Gamma$-L and, in contrast to bcc metals, the magnitude of the effects is not due to the softness of the initial phonon spectrum. It is shown that the relative frequency shifts and the phonon damping near melting do not exceed 10-20%. The relative role of various anharmonic processes is examined, and the relation between the results obtained and existing experimental data is discussed.Comment: 4 pages, 5 figures, LaTe

Preliminary assessment of bovine trypanosomiasis and its vectors in Santa, Bali and Bafut Sub-Divisions of the, North West Region, Cameroon

A cross-sectional study involving a questionnaire, parasitological examination of cattle and entomological prospection were conducted in the Mezam Division of Cameroon from December 2013 to May 2014 in two seasons for the first time. The objectives were to determine the prevalence of bovine trypanosomiais and its vectors. Peasant farmers ﴾n=95﴿ were interviewed. Standard protocols for parasitological, hematocrit analysis as well as trypanosome identification were used. Acetone baited blue biconical traps ﴾n=5﴿ were used for entomological survey. Questionnaire survey revealed that trypanosomiasis was one of the major health problems affecting animals and a hindrance to agricultural activities. The overall prevalence was 10.3% ﴾31/301﴿. Trypanosome species identified consisted of: T. vivax (58.1%), T. brucei (25.8%), T. congolense (9.6%) and a mix infection (Trypanosoma congolense + Trypanosoma vivax) (6.5%). Vector survey revealed highest fly catch in Bafut subdivision as compared to others with a significant difference ﴾P<0.05﴿. Fly types recorded included: Tabanus 125 (71.4%), Stomoxys 31 (17.7%) and Glossina morsitans submorsitans 19 (10.9%). The overall Apparent Density (AD) was 1.53 fly per trap per day (f/t/d). Therefore, vector transmission and impact of the disease on production is alarming and should not be neglected. Control strategies have to be designed and implemented in Mezam Division in order to eradicate trypanosomiasis and its vectors.© 2016 International Formulae Group. All rights reserved.Keywords: Cattle, trypanosomiasis, Glossina, prevalence, Bafu

Path integrals approach to resisitivity anomalies in anharmonic systems

Different classes of physical systems with sizeable electron-phonon coupling and lattice distortions present anomalous resistivity behaviors versus temperature. We study a molecular lattice Hamiltonian in which polaronic charge carriers interact with non linear potentials provided by local atomic fluctuations between two equilibrium sites. We study a molecular lattice Hamiltonian in which polaronic charge carriers interact with non linear potentials provided by local atomic fluctuations between two equilibrium sites. A path integral model is developed to select the class of atomic oscillations which mainly contributes to the partition function and the electrical resistivity is computed in a number of representative cases. We argue that the common origin of the observed resistivity anomalies lies in the time retarded nature of the polaronic interactions in the local structural instabilities.Comment: 4 figures, to appear in Phys.Rev.B, May 1st (2001

Particle Path Correlations in a Phonon Bath

The path integral formalism is applied to derive the full partition function of a generalized Su-Schrieffer-Heeger Hamiltonian describing a particle motion in a bath of oscillators. The electronic correlations are computed versus temperature for some choices of oscillators energies. We study the perturbing effect of a time averaged particle path on the phonon subsystem deriving the relevant temperature dependent cumulant corrections to the harmonic partition function and free energy. The method has been applied to compute the total heat capacity up to room temeperature: a low temperature upturn in the heat capacity over temperature ratio points to a glassy like behavior ascribable to a time dependent electronic hopping with variable range in the linear chain.Comment: To be published in J.Phys.:Condensed Matte

Multi-level analysis of on-chip optical wireless links

Networks-on-chip are being regarded as a promising solution to meet the on-going requirement for higher and higher computation capacity. In view of future kilo-cores architectures, electrical wired connections are likely to become inefficient and alternative technologies are being widely investigated. Wireless communications on chip may be therefore leveraged to overcome the bottleneck of physical interconnections. This work deals with wireless networks-on-chip at optical frequencies, which can simplify the network layout and reduce the communication latency, easing the antenna on-chip integration process at the same time. On the other end, optical wireless communication on-chip can be limited by the heavy propagation losses and the possible cross-link interference. Assessment of the optical wireless network in terms of bit error probability and maximum communication range is here investigated through a multi-level approach. Manifold aspects, concurring to the final system performance, are simultaneously taken into account, like the antenna radiation properties, the data-rate of the core-to core communication, the geometrical and electromagnetic layout of the chip and the noise and interference level. Simulations results suggest that communication up to some hundreds of μm can be pursued provided that the antenna design and/or the target data-rate are carefully tailored to the actual layout of the chip