113 research outputs found
Electronic structure and magnetic properties of RMnX (R= Mg, Ca, Sr, Ba, Y; X= Si, Ge) studied by KKR method
Electronic structure calculations, using the charge and spin self-consistent
Korringa- Kohn-Rostoker (KKR) method, have been performed for several Mn
compounds ( = Mg, Ca, Sr, Ba, Y; = Si, Ge) of the CeFeSi-type structure.
The origin of their magnetic properties has been investigated emphasizing the
role of the Mn sublattice. The significant influence of the Mn-Mn and Mn-
interatomic distances on the Mn magnetic moment value is delineated from our
computations, supporting many neutron diffraction data. We show that the marked
change of with the Mn-Mn and Mn- distances resulted from a
redistribution between spin-up and spin-down -Mn DOS rather than from
different fillings of the Mn 3-shell. Bearing in mind that the neutron
diffraction data reported for the Mn compounds are rather scattered, the
KKR computations of are in fair agreement with the experimental
values. Comparing density of states near obtained in different magnetic
orderings, one can notice that the entitled Mn systems seem to 'adapt'
their magnetic structures to minimize the DOS in the vicinity of the Fermi
level. Noteworthy, the SrMnGe antiferromagnet exhibits a pseudo-gap behaviour
at , suggesting anomalous electron transport properties. In addition,
the F-AF transition occurring in the disordered LaYMnSi alloy for
the range is well supported by the DOS features of
LaYMnSi. In contrast to the investigated Mn compounds,
YFeSi was found to be non-magnetic, which is in excellent agreement with the
experimental data.Comment: 10 pages + 14 figures, to appear in Eur. Phys. Jour.
Correlation between Crystallographic Alignment of Self-induced GaN Nanowires and Features of Si(111) Nitridation
Formation and spatial ordering of self-induced GaN nanowires grown by molecular beam epitaxy on a spatially pre-nitridazed Si(111) substrate have been studied. It was found the close correlation between Si substrate nitridation parameters and crystallographic alignment of NWs. Conditions for NWs nucleation and in- plane orientation are predefined by a structural anisotropy of silicon nitride nanolayer. Mechanism of NWs orderly emergence suggested.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3540
The Role of Oxygen in Coal Gasification
Air Products supplies oxygen to a number of coal gasification and partial oxidation facilities worldwide. At the high operating pressures of these processes, economics favor the use of 90% and higher oxygen purities. The effect of inerts in the oxidant on gasifier and downstream production units also favor the use of oxygen in place of air. Factors that must be considered in selecting the optimum oxygen purity include: end use of the gasifier products, oxygen delivery pressure and the cost of capital and energy. This paper examines the major factors in oxygen purity selection for typical coal gasifiers. Examples demonstrating the effect of oxygen purity on several processes are presented: production of synthetic natural gas (SNG), integrated gasification combined-cycle (IGCC) power generation and methanol synthesis. The potential impact of a non-cryogenic air separation process currently under development is examined based on integration with a high temperature processes
Constructive role of noise: Fast fluctuation asymptotics of transport in stochastic ratchets
The constructive role of random fluctuations is studied in the context of transport in stochastic ratchets. We discuss the interplay of independent white (thermal) and discrete (external) noises and their generation of transport in anisotropic potentials. The constructive cooperation of such fluctuations is most apparent in the asymptotic limit of fast discrete-valued noise, a limit which presents some interesting mathematical features. We describe the asymptotic analysis of the current in the limit of fast external noise, pointing out the strong qualitative dependence of the current on the interplay of the independent noise sources and its surprising sensitivity to the regularity of the underlying anisotropic ratchet potential. © 1998 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/69412/2/CHAOEH-8-3-643-1.pd
- …