Dynamics of autodyne response formation in microwave generators

The paper presents results of studying the dynamics of autodyne response formation when switching on a radio-pulse microwave generator which is subject to the influence of its own reflection radiation. Basic relations for a step-wise calculation of autodyne response as a function of time delay, autodyne response time constant, distortion parameter and intrinsic parameters of the self-oscillating system are obtained. Calculation and analysis of peculiarities of autodyne signal generation by radio-pulse oscillator are conducted for the cases of motionless and moving reflecting object under relatively low, medium and high inertia properties of the oscillator if compared to the propagation time of the reflected radiation. Experimental research results that confirm conclusions of theoretical analysis are obtained for a common hybrid-integrated autodyne TIGEL-08 module of the 8-mm frequency-range implemented on a planar two-meza Gunn diodes and the same module stabilized by the external high-Q resonator. © 2013 Allerton Press, Inc

Particles at oil–air surfaces : powdered oil, liquid oil marbles, and oil foam

The type of material stabilized by four kinds of fluorinated particles (sericite and bentonite platelet clays and spherical zinc oxide) in air–oil mixtures has been investigated. It depends on the particle wettability and the degree of shear. Upon vigorous agitation, oil dispersions are formed in all the oils containing relatively large bentonite particles and in oils of relatively low surface tension (γla < 26 mN m⁻¹) like dodecane, 20 cS silicone, and cyclomethicone containing the other fluorinated particles. Particle-stabilized oil foams were obtained in oils having γla > 26 mN m⁻¹ where the advancing air–oil–solid contact angle θ lies between ca. 90° and 120°. Gentle shaking, however, gives oil-in-air liquid marbles with all the oil–particle systems except for cases where θ is <60°. For oils of tension >24 mN m⁻¹ with omniphobic zinc oxide and sericite particles for which advancing θ ≥ 90°, dry oil powders consisting of oil drops in air which do not leak oil could be made upon gentle agitation up to a critical oil:particle ratio (COPR). Above the COPR, catastrophic phase inversion of the dry oil powders to air-in-oil foams was observed. When sheared on a substrate, the dry oil powders containing at least 60 wt % of oil release the encapsulated oil, making these materials attractive formulations in the cosmetic and food industries

Stabilizing and maneuvering angle rigid multi-agent formations with double-integrator agent dynamics

This paper studies formation stabilization and maneuvering of mobile agents governed by double-integrator dynamics. The desired formation is described by a set of triple-agent angles. A carefully chosen such set of angle constraints guarantees that the desired formation is angle rigid. To achieve the desired angle rigid formation, a stabilization control law is proposed using only local velocity and direction measurements. We show that the closed-loop dynamics of the formation, when each agent is modeled by a double-integrator, are closely related to the corresponding one in single-integrator agent dynamics. Sufficient conditions are constructed to guarantee the closed-loop stability for identical and distinct velocity damping gains, respectively. To guide an angle rigid formation to move with the desired translational velocity, orientation and scale, formation maneuvering laws are then proposed. Simulation examples are also provided to validate the results

Development of Multivariate Powder X-ray Diffraction Techniques and Total Scattering Analyses to Enable Informatic Calibration of Solid Dispersion Potential

The objective of this work was to introduce a novel method for predicting solid dispersion potential enabled by the ability to differentiate phase-separated co-solidified products from amorphous molecular solid dispersions. The central hypothesis states that a combination of materials properties exists that defines the propensity of an active pharmaceutical ingredient to form a binary amorphous molecular solid dispersion with polyvinylpyrrolidone:vinyl acetate copolymer using a melt-quench procedure. Testing this hypothesis required execution of specific aims directed to address issues inherent to characterizing amorphous materials. The work herein is presented with respect to two separate subjects: (1) analytical development and (2) theoretical applications. In the first few chapters, advanced powder X-ray diffraction data processing techniques are explored and adapted to composite pharmaceutical systems. Specific emphasis will be placed ontotal scattering data manipulations and their benefits over traditional practices. The concluding part of this work is devoted to illustrating the use of materials informatics in modeling solid dispersion potential, ultimately afforded by implementing the materials characterization methodologies developed in the initial stages. Molecular descriptors, commonly employed in quantitative structure-property relationship assessment, were tested for correlation to dispersion potential across a library of small molecule organic compounds. The final model accurately predicted dispersion potential for all 12 calibration compounds and three test compounds

Second All-Union Seminar on Hydromechanics and Heat and Mass Exchange in Weightlessness, summaries of reports

Abstracts of reports are given which were presented at the Second All Union Seminar on Hydromechanics and Heat-Mass Transfer in Weightlessness. Topics include: (1) features of crystallization of semiconductor materials under conditions of microacceleration; (2) experimental results of crystallization of solid solutions of CDTE-HGTE under conditions of weightlessness; (3) impurities in crystals cultivated under conditions of weightlessness; and (4) a numerical investigation of the distribution of impurities during guided crystallization of a melt

Shear strength behaviour of sugarcane bagasse reinforced soils

Sugarcane is considered as the most abundant plant based crop grown in the tropics and part of the temperate climates. Its by-product, sugarcane bagasse, constitutes 30% of the total production. In the past, it was considered as waste material but contemporaries through innovative research projects over the years have found uses for it. Among these projects is soil reinforcement, which provides an alternative application to industrial by-products and natural fibres as a way of reducing their environmental footprints and contributing to sustainable geotechnics. Although bagasse morphological composition contains structural elements ideal for reinforcement and composite materials, it has received little research as a standalone reinforcement material. Because of this, a direct shear test was therefore initiated to establish the usefulness of using sugarcane bagasse as a soil reinforcement material by comparing the extent of shear strength and stiffness response due to its inclusion to unreinforced soil. Three different types of bagasse, fibre, millrun and pith, were added to unreinforced soil in percentage by weight content of 0.3 - 1.7. The bagasse was added to Klipheuwel sand, Cape Flats sand and Kaolin Clay at both dry and moist conditions. In addition, durability studies involving 12 cycles of wetting and drying, and soaking for a period of 14 days were constituted

Toward Reproducible Domain-Wall Conductance in Lithium Niobate Single Crystals

Conductive domain walls (DWs) in lithium niobate (LiNbO3, LNO) are promising constituents for potential applications in nanoelectronics, due to their high conductance, as compared to the surrounding bulk material, their high local confinement at the nanometer scale, and the ability to be created quasi-on-will through dedicated high-voltage poling. However, electrically contacting the DWs unavoidably leads to the formation of a potential barrier between the DW itself and the electrode material. Thus, the focus of this work is the investigation of the various factors influencing the electronic transport across that barrier, namely, the type of electrode material, the quality of the LNO surface (atomically-smooth versus mirror polished), the quality of the crystal lattice (i.e., the presence of higher concentrations of lithium and oxygen vacancies VLi and VO), and the magnitude of the applied voltages during the domain-wall conductivity (DWC) enhancement procedure. It is found that all the above-mentioned factors have a significant impact on the current-voltage characteristics of the DW-electrode system. For example, the metal electrodes deposited onto the surface of the LNO crystal, once, impede the DW motion, while, secondly, stabilizing the DWs inclination across the LNO crystal. Another important finding is the major role played by large negative voltages in the DWC-enhancement procedure that strongly influences the near-surface structure of the DW, and hence the qualitative characteristics of the formed potential barrier, such as characteristic voltage and saturation current. The application of moderate voltages from –50 V to –100 V is also found to influence the structure of the near-surface DW. The creation of a variety of vacancy defects inside the bulk LNO that accompanies the formation of an atomically-smooth surface, is found to have far more influence on the DW charge transport than the quality of the surface, due to the formation and repulsive interaction of a multitude of spike domains stemming from these defects. In summary, the results demonstrate the importance of providing known and reproducible sample surface conditions and identifying promising directions for implementing reproducible domain wall conductivity