Ferromagnetism and anomalous transport in GaAs doped by implantation of Mn and Mg ions

GaAs layers doped by implantation of Mn and Mg ions to increase the hole concentration were synthesized and studied. Measurements using a SQUID magnetometer showed that there is ferromagnetism at temperatures as high as 400 K, which is related to the formation of the MnAs and Mn _y Ga_{1 ? y} clusters as a result of high-temperature annealing, in addition to the formation of the Ga_{1 ? x} Mn _x As alloy. The anomalous Hall effect was observed at temperatures in the range from 4.2 to 200 K. As temperature was increased starting with 4.2 K, the negative magnetoresistance with extremely large magnitude transformed into a giant positive magnetoresistance at T ≈ 35 K.     

Low-temperature anti-icing reagents in the Ca(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>-Mg(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>-CO(NH<Subscript>2</Subscript>)<Subscript>2</Subscript>-H<Subscript>2</Subscript>O system and their properties

The polytherms of ice melting in sections of the Ca(NO₃)₂-Mg(NO₃)₂-CO(NH₂)₂-H₂O system with different component ratios were studied in the temperature interval from 0 to −40°C. A series of nitrate and nitrate-carbonate reagents that are promising for the creation of anti-acing reagents were found, which form eutectics with ice at temperatures from −25 to −39°C. Their properties, viz., melting properties with respect to ice and corrosiveness on metals and alloys, were determined. An effective corrosion inhibitor was selected.     

Modification of Polydimethylsiloxane Coatings by H2 RF Plasma,Xe2* Excimer VUV Radiation,and Low‐Energy Electron Beams

The crosslinking of thin liquid PDMS layers by three different technically relevant processes, H₂ radio‐frequency plasma treatment, Xe₂* excimer VUV irradiation, and low‐energy electron beam processing is investigated. The modifications to the layers due to the processing are monitored by means of RAIRS. Plasma processing of liquid PDMS leads to a direct conversion to a SiO_x‐like material of the topmost layers, whereas a gradual transition from PDMS to the same product is observed upon VUV irradiation. Electron exposure does not induce oxidation. The initiating steps of the conversion induced by the interaction with VUV photons, low‐energy electrons, or their combined effect with ions and H atoms in the plasma are discussed. The latter creates a high density of damage sites.

     

Identification and analysis of possible splits for azeotropic mixtures. 2. Method for simple columns

A new method for the design of distillation units based on the behaviour of the mode of infinitely sharp split is presented. The method is non-iterative, fail free and fast. It can lead to the creation of more optimised process flow sheets, and can automate the design process. The first step of the method consists of fast delimitation of the product regions in the concentration simplex and the identification of the ends of the pinch branches at each section. In this way a qualitative evaluation of the arrangement of the pinch branches and the bundles of trajectories can be obtained as the bundles of trajectories depend only on the relations between the values of the coefficients of the phase equilibrium of components at certain points in the concentration simplex. This first step of the method was described in a previous article. In the present article, the second step is described, namely the identification of the possible splits in simple two-sectional columns. If some split is possible, trajectories of both sections intersect each other. The simple, necessary and sufficient condition of the separability has been established: trajectories of both sections intersect each other if pinch branches of both sections have common terminals (ending points). The check-up of this simple condition does not request the calculation of pinch branches and trajectories. The identification of the possible splits is the basis for any algorithm in the synthesis of flowsheets. An algorithm for the identification of one interactive bundle at each section among many is presented here. The interactivity of bundles depends on the location of the point of products. This information about the interactive bundles will be used for subsequent steps of designing e.g. for the calculation of minimal reflux and necessary trays for given reflux.     

A Physical Model of Power Electronic Devices Based on Static Voltage Transducers

A physical model of a thyristor ac voltage regulator with microcontroller control operating under an active-inductive load is considered. To increase the level of energy efficiency of existing electric power systems, the arrangement of the control of voltage level of supplied centers both above and below the rated value is an important condition. In existing structures, the transformation ratio generally is a constant, which does not make it possible to take into account the real irregularities of electric energy consumption. Using a transformer in a thyristor voltage regulator makes it possible to solve this problem. It shows that it may be possible to enter a preliminary stage of physical modeling of the considered process by means of creation of a program–technical complex making it possible to simulate the process of transportation of electrical energy from supply centers to consumers.     

Electronic transport in single molecule junctions: control of the molecule-electrode coupling through intramolecular tunneling barriers

We report on single molecule electron transport measurements of two oligophenylenevinylene (OPV3) derivatives placed in a nanogap between gold (Au) or lead (Pb) electrodes in a field effect transistor device. Both derivatives contain thiol end groups that allow chemical binding to the electrodes. One derivative has additional methylene groups separating the thiols from the delocalized pi-electron system. The insertion of methylene groups changes the open state conductance by 3-4 orders of magnitude and changes the transport mechanism from a coherent regime with finite zero-bias conductance to sequential tunneling and Coulomb blockade behavior.     

Calculation of amplitudes of echo signals for a normal transceiver and reflectors in the form of flat-bottom holes of different shapes

The acoustic path for a noncircular reflector is calculated on the basis of the method for determining the echo-signal amplitude from a reflector in the form of a flat-bottom hole using the Kirchhoff approximation in the far-field zone of a normal transceiver. Examples of calculations of the directivity characteristics for reflectors in the form of an ellipse, triangle, and rhomb are presented. In limiting cases of circular and square reflectors, the results of numerical calculations of the directivity characteristics coincide with the data obtained from known analytic expressions.     

Thermal Polycondensation Process and Petroleum Pitch Production

Chemistry and Technology of Fuels and Oils - The article discusses the thermal polycondensation methods of petroleum pitch production. The main attention is paid to the characteristics of petroleum...