Density of States and Conductivity of Granular Metal or Array of Quantum Dots

The conductivity of a granular metal or an array of quantum dots usually has the temperature dependence associated with variable range hopping within the soft Coulomb gap of density of states. This is difficult to explain because neutral dots have a hard charging gap at the Fermi level. We show that uncontrolled or intentional doping of the insulator around dots by donors leads to random charging of dots and finite bare density of states at the Fermi level. Then Coulomb interactions between electrons of distant dots results in the a soft Coulomb gap. We show that in a sparse array of dots the bare density of states oscillates as a function of concentration of donors and causes periodic changes in the temperature dependence of conductivity. In a dense array of dots the bare density of states is totally smeared if there are several donors per dot in the insulator.Comment: 13 pages, 15 figures. Some misprints are fixed. Some figures are dropped. Some small changes are given to improve the organizatio

Ge quantum dot arrays grown by ultrahigh vacuum molecular beam epitaxy on the Si(001) surface: nucleation, morphology and CMOS compatibility

Issues of morphology, nucleation and growth of Ge cluster arrays deposited by ultrahigh vacuum molecular beam epitaxy on the Si(001) surface are considered. Difference in nucleation of quantum dots during Ge deposition at low (<600 deg C) and high (>600 deg. C) temperatures is studied by high resolution scanning tunneling microscopy. The atomic models of growth of both species of Ge huts---pyramids and wedges---are proposed. The growth cycle of Ge QD arrays at low temperatures is explored. A problem of lowering of the array formation temperature is discussed with the focus on CMOS compatibility of the entire process; a special attention is paid upon approaches to reduction of treatment temperature during the Si(001) surface pre-growth cleaning, which is at once a key and the highest-temperature phase of the Ge/Si(001) quantum dot dense array formation process. The temperature of the Si clean surface preparation, the final high-temperature step of which is, as a rule, carried out directly in the MBE chamber just before the structure deposition, determines the compatibility of formation process of Ge-QD-array based devices with the CMOS manufacturing cycle. Silicon surface hydrogenation at the final stage of its wet chemical etching during the preliminary cleaning is proposed as a possible way of efficient reduction of the Si wafer pre-growth annealing temperature.Comment: 30 pages, 11 figure

Floristic Phenomena of the Samara Bend: The Fractal Organization of Taxonomic Diversity

Considering the problem of taxonomic diversity as a fractal object is the aim of this article. The prerequisites for such an approach were articles with varying degrees of detail and argumentation that substantiate taxonomic diversity from the standpoint of fractal geometry. Common to these papers is that the authors in their theoretical constructs start from the Willis rule (law) describing the rank distribution of the relationship between the number of taxa and their volume. The flora of the Samara Bend (the bend of the Volga River in its middle reaches) has become an object of the research. The authors distinguish seven basic floristic areas on the Samara Bend, the boundaries of which coincide with the respective landscapes. The authors discuss the efficiency of the Willis rule (law), which approximates the relationship between the number of taxa and their volume by rank distribution. The multifractal spectrum (a generalized geometric image of generic structure) of the taxonomic diversity of vascular plants of the Samara Bend is presented. Keywords: taxonomic diversity, fractal organization, Samara Ben

Organization of Repair of Locomotives on the Data of Moni-toring Their Technical Condition

The article discusses the structure of the organization of current repairs of modern locomotives equipped with microprocessor control and diagnostic systems. Based on these sys-tems, remote monitoring of the technical condition of locomotive units has been implemented. The block diagram of the recommendatory nature of the organization of current repairs using diagnostic information is presented. The above algorithm allows predicting the residual life by any of the studied parameters, thereby determining the mileage at the moment of which a fail-ure occurs on some parameter. This gives a huge advantage in preventing incidents, as well as in the long-term planning of repair work on wheel turning and rolling, based on the remaining life. Thus, the well-coordinated organization of current repairs using diagnostic information, allows operational methods to eliminate the faults of the nodes. A recommender structure in the form of a single integrated system for organizing repair cycles will allow establishing links between the involved repair personnel in the form of electronic terminals for notification of the actual technical condition of the locomotive. A program has been developed for calculating the residual mileage of wheel sets for the corresponding types of defects, which also allows long-term planning for turning and rolling of wheel-motor blocks wheelsets, as well as to regulate the overhaul runs of a locomotive. © Published under licence by IOP Publishing Ltd

Production of microfluidic chips from polydimethylsiloxane with a milled channeled surface for modeling oil recovery during porous rock waterflooding

Microfluidic chips with porous structures are used to study the flow of oil-containing emulsion in the rock. Such chips can be made from polydimethylsiloxane by casting into a master mold. At the initial stages of research, fast and cheap prototyping of a large number of different master molds is often required. It is proposed to use milling to make a channeled surface on a polymethyl methacrylate plate, from which a negative image should be taken, which is the master mold for casting positive polydimethylsiloxane chips in it. Several epoxy compositions have been tested to make this master mold. The main requirement in the search for the material was the exact replication of the geometry and sufficiently low adhesion to polymethyl methacrylate and polydimethylsiloxane for removing the product with minimal damage to the mold. It was possible to make master molds from all the materials used, but with defects and various degrees of damage. One of the epoxy compositions was found suitable for making a master mold with many elements simulating the grains of a porous medium (height to width ratio 2:3). The developed method makes it possible to use polydimethylsiloxane for prototyping chips simulating the porous structure of an oil rock

Behaviour of rare earth elements in molten salts in relation to pyrochemical reprocessing of spent nuclear fuels

The kinetics of chlorination of lanthanide oxides (by Cl2 and HCl) and precipitation of lanthanide phosphates was studied by in situ electronic absorption spectroscopy in 3LiC1-2KC1 and NaCl-KCl melts at 400-750°C Products of the chlorination are the corresponding hexachlorospecies, LnCl63-, and the rate of chlorination increases with increasing temperature. Composition of the precipitated phosphates depends on the melt composition and 1.5-5 fold excess of phosphate, depending on the nature of lanthanide, is needed for the complete removal of the lanthanides from the melt. Over three hours are required for completing the reaction of phosphate precipitation. copyright The Electrochemical Society.Electrochemical Society, Phys. Anal. Electrochem. Div.;Electrochemical Society, Electrodeposition Division;Electrochemical Society, High Temperature Materials Division;Electrochemical Society, Battery Division;Electrochemical Society, Energy Technology Divisio

Magnetic Gaps related to Spin Glass Order in Fermionic Systems

We provide evidence for spin glass related magnetic gaps in the fermionic density of states below the freezing temperature. Model calculations are presented and proposed to be relevant for explaining resistivity measurements which observe a crossover from variable-range- to activated behavior. The magnetic field dependence of a hardgap and the low temperature decay of the density of states are given. In models with fermion transport a new metal-insulator transition is predicted to occur due to the spin-glass gap, anteceding the spin glass to quantum paramagnet transition at smaller spin density. Important fluctuation effects due to finite range frustrated interactions are estimated and discussed.Comment: 4 pages, 1 Postscript figure, revised version accepted for publication in Physical Review Letter

Correlated electron states and transport in triangular arrays

We study correlated electron states in frustrated geometry of a triangular lattice. The interplay of long range interactions and finite residual entropy of a classical system gives rise to unusual effects in equilibrium ordering as well as in transport. A novel correlated fluid phase is identified in a wide range of densities and temperatures above freezing into commensurate solid phases. The charge dynamics in the correlated phase is described in terms of a height field, its fluctuations, and topological defects. We demonstrate that the height field fluctuations give rise to a ``free'' charge flow and finite dc conductivity. We show that freezing into the solid phase, controlled by the long range interactions, manifests itself in singularities of transport properties.Comment: 19 pages, 10 figure

Effects of gama irradiation on nucellar callus production of lhe 'Valência' sweet orange (Citrus sinsensis) Osb. in vitro.

Os métodos convencionais pouco têm contribuído para o melhoramento das espécies cítricas. A utilização das técnicas de cultura in vitro associadas à indução de mutações deverão trazer inestimável contribuição. Nucelos extraídos de frutos em desenvolvimento, doze semanas após a polinização, foram cultivados in vitro em meio "MS" adicionado (em mg/ 1) de: tiamina HCQ - 0,2; piridoxina HCQ - 1,0; ácido nicotínico - 1,0; mesoinositol - 100; extrato de malte - 500; sacarose - 50.000; ágar - 8.000, com pH ajustado para 5,7. Procedeu-se à irradiação, apenas do meio ou do nucelo, ou de ambos, nas doses de 0,0, 0,5, 1,0, 2,0, 4,0, 8.0 e 12,0 kR. A irradiação apenas do nucelo mostrou um efeito similar ao obtido pela irradiação tanto do nucelo como do meio. Doses baixas de radiação (até 2 kR) reduzem o número de embrióides diferenciados. A irradiação do meio de cultura aumenta a proliferação de calos, principalmente em doses mais elevadas.The conventional methods of plant breeding have not given a significative contribution for the citrus breeding. A precious iniprovement by the techniques of tissues culture in vitro, associated with induced mutations, is expected. Nucelli extracted from developping fruits with twelve weeks after pollination were cultured in vitro, on medium supplemented (in mg/ 1) by: thiamine HCQ 0.2; piridoxine HCL 1.0;  icotinic acid 1.0; mesoinositol 100; malt extract; sucrose 50.000; and agar 8.000 with pi-! = 5.7. The irradiation at 0.0; 0.5; 1.0; 2.0; 4.0; 8.0 and 12.0 kR doses was applied on, only medium, only nucellus, and medium and nucellus together. Irradiation of only nucellus and both nucellus and medium, at the same time, showed similar effects. Low doses of irradiation (until 2 kR) decrease the number of differential embryoids. The irradiation of culture medium, mainly at high doses, increases callus proliferatio

Optical study of strained double Ge/Si quantum dot layers

status: publishe