Doping, density of states and conductivity in polypyrrole and poly(p-phenylene vinylene)

The evolution of the density of states (DOS) and conductivity as function of well controlled doping levels in OC_1C_10-poly(p-phenylene vinylene) [OC_1C_10-PPV] doped by FeCl_3 and PF_6, and PF_6 doped polypyrrole (PPy-PF_6 have been investigated. At a doping level as high as 0.2 holes per monomer, the former one remains non-metallic, while the latter crosses the metal-insulator transition. In both systems a similar almost linear increase in DOS as function of charges per unit volume c* has been observed from the electrochemical gated transistor data. In PPy-PF_6, when compared to doped OC_1C_10-PPV, the energy states filled at low doping are closer to the vacuum level; by the higher c* at high doping more energy states are available, which apparently enables the conduction to change to metallic. Although both systems on the insulating side show log(sigma) proportional to T^-1/4 as in variable range hopping, for highly doped PPy-PF_6 the usual interpretation of the hopping parameters leads to seemingly too high values for the density of states.Comment: 4 pages (incl. 6 figures) in Phys. Rev.

Emergence of a non-scaling degree distribution in bipartite networks: a numerical and analytical study

We study the growth of bipartite networks in which the number of nodes in one of the partitions is kept fixed while the other partition is allowed to grow. We study random and preferential attachment as well as combination of both. We derive the exact analytical expression for the degree-distribution of all these different types of attachments while assuming that edges are incorporated sequentially, i.e., a single edge is added to the growing network in a time step. We also provide an approximate expression for the case when more than one edge are added in a time step. We show that depending on the relative weight between random and preferential attachment, the degree-distribution of this type of network falls into one of four possible regimes which range from a binomial distribution for pure random attachment to an u-shaped distribution for dominant preferential attachment

String dynamics near a Kaluza-Klein black hole

The dynamics of a string near a Kaluza-Klein black hole are studied. Solutions to the classical string equations of motion are obtained using the world sheet velocity of light as an expansion parameter. The electrically and magnetically charged cases are considered separately. Solutions for string coordinates are obtained in terms of the world-sheet coordinate $\tau$. It is shown that the Kaluza-Klein radius increases/decreases with $\tau$ for electrically/magnetically charged black hole.Comment: Latex2e file with six postscript figures. Minor changes, more accurate numerical results and updated reference

Changing trends in ferro-alloy consumption in an integrated steel plant

Ferro-alloy addition for the purpose of deoxidation or alloying, is an integral part of steelmaking. The grade of alloy used is influenced by technical, economic and avail-ability considerations.In addition to ferro-alloys, requir-ements can also be met partly from plant return scrap

A new approach to the analysis of a noncommutative Chern-Simons theory

A novel approach to the analysis of a noncommutative Chern--Simons gauge theory with matter coupled in the adjoint representation has been discussed. The analysis is based on a recently proposed closed form Seiberg--Witten map which is exact in the noncommutative parameter.Comment: 9 pages latex, some new results added. To be published in Modern Physics Letters

Shape and Size Controlled Deposition of ZnO Thin Films: Comparative Sensitivity towards Methane Gas

The effect of different solutes and solvents on the morphology of Galvanically deposited ZnO thin films is reported here. Hexagonal grains with c – axis orientation were obtained from aqueous Zn(NO3)2 bath (System A), whereas, the aqueous ZnSO4 bath (System B) yielded cages of ZnO flakes on the xy plane. Almost spherical grains with smaller sizes were obtained from the DMF bath of Zn(NO3)2 (System C). The highest average roughness (Ra) was shown by the flake like morphology (107.11 nm) and the lowest by the spherical one (16.82 nm). The value of Ra was 21.5 nm for System A. Surface roughness is responsible for adsorbing the test gas, one of the most important factors influencing the sensitivity. Same thing is reflected here by the deposited films for methane sensing. At 300 C, System B showed maximum efficiency (89 %) and the minimum was 69 %, as shown by System C. On the other hand, System A showed an inbetween value of efficiency of about 75 %. The response time at 300 C was also lowest for System B, whereas, System A & C showed similar values. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3499

Spectra of Quarkonia at Finite Temperature

Finite-temperature spectra of heavy quarkonia are calculated by combining potential model and thermofield dynamics formalisms. The mass spectra of the heavy quarkonia with various quark contents are calculated. It is found that binding mass of the quarkonium decreases as temperature increases.Comment: 12 pages, 1 figure. To appear Mod.Phys.Lett.

Discrete antiferromagnetic spin-wave excitations in the giant ferric wheel Fe18

The low-temperature elementary spin excitations in the AFM molecular wheel Fe18 were studied experimentally by inelastic neutron scattering and theoretically by modern numerical methods, such as dynamical density matrix renormalization group or quantum Monte Carlo techniques, and analytical spin-wave theory calculations. Fe18 involves eighteen spin-5/2 Fe(III) ions with a Hilbert space dimension of 10^14, constituting a physical system that is situated in a region between microscopic and macroscopic. The combined experimental and theoretical approach allowed us to characterize and discuss the magnetic properties of Fe18 in great detail. It is demonstrated that physical concepts such as the rotational-band or L&E-band concepts developed for smaller rings are still applicable. In particular, the higher-lying low-temperature elementary spin excitations in Fe18 or AFM wheels in general are of discrete antiferromagnetic spin-wave character.Comment: 16 pages, 10 figure