Mode II Macrocrack Initiation in Orthotropic Composite Viscoelastic Plate

Safe loads and initiation time for a straight macrocrack in viscoelastic orthotropic material that is intended to model a fiber composite plate under shear loads is investigated. The composite material is modeled by viscoelastic orthotropic medium. Determination of expression for crack shear displacement as function of time is based on the corresponding elastic solution and the method of operator continued fractions. Initiation time is obtained as a solution of integral equation for the incubation period. Numerical calculations are given for mode II macrocrack initiation.     

Time-resolved x-ray imaging of aluminum alloy solidification processes

Time-resolved direct-beam X-ray imaging, with intense, coherent, and monochromatic third-generation synchrotron radiation, and a high-resolution fast-readout detector system have been used for in-situ studies of dendritic and eutectic growth processes in Al-Cu alloys. Temporal and spatial resolutions down to 0.25 seconds and 2.5 μm, respectively, were obtained with a field of view up to 1.4×1.4 mm². Solid-liquid interfaces and various phase-specific segregates could be observed, and their dynamics could be traced in a sequence of temporally resolved images formed by phase and amplitude contrast from the sample. This article does not present any detailed analysis of a specific solidification phenomenon; instead, it presents to the scientific community an innovative technique for in-situ monitoring of such a phenomenon in real metallic systems.     

Mixed Explosives and Determination of Their Detonation Parameters

A model of the effective characteristics of heterogeneous systems is given. The model is based on the methods of field theory of many bodies. The suitability of the given approach for a quantitative assessment of the characteristics of explosives and detonation is shown. In particular, two‐component mixtures of TNT/RDX and three‐component mixtures of aluminum with energetic materials are considered. The values of a few parameters (density, impact sensitivity, heat of explosion, detonation velocity) calculated by means of the proposed model agree satisfactorily with known experimental data.     

Preparation,structure, and properties of biocomposites based on low‐density polyethylene and lignocellulosic fillers

This article examines compositions based on low density polyethylene containing various lignocellulosic fillers–flax shive, sunflower husk, hay, birch leaves, lignosulfonate, and banana skin. The ethylene‐vinyl acetate copolymer is used as a compatibilizing component. The article is aimed at identifying the main factors determining biodegradation rate of the compositions. Thermal resistance and morphology of the fillers, mechanical and structural characteristics of the compositions, and their stability in aqueous media and ground soil were studied. The influence of the filler particle shape on the resistance of the compositions against various effects was shown. It was found that an increase in the length‐to‐diameter (L/D) ratio of the filler particles increases strength and water absorption, reduces melting viscosity, and accelerates biodegradation in soil. POLYM. COMPOS., 37:1461–1472, 2016. © 2014 Society of Plastics Engineers     

Chemical substitution of Cd ions by Hg in CdSe nanorods and nanodots: Spectroscopic and structural examination

The chemical substitution of cadmium by mercury in colloidal CdSe quantum dots (QDs) and nanorods has been examined by absorption, photoluminescence and Raman spectroscopy. The crystalline structure of original CdSe QDs used for Cd/Hg substitution (zinc blende versus wurtzite) shows a strong impact on the optical and structural properties of resultant Cd_xHg_1−xSe nanocrystals. Substitution of Cd by Hg in isostructural zinc blende CdSe QDs converts them to ternary Cd_xHg_1−xSe zinc blende nanocrystals with significant NIR emission. Whereas, the wurtzite CdSe QDs transformed first to ternary nanocrystals with almost no emission followed by slow structural reorganization to a NIR-emitting zinc blende Cd_xHg_1−xSe QDs. CdSe nanorods with intrinsic wurtzite structure show unexpectedly intense NIR emission even at early Cd/Hg substitution stage with PL active zinc blende Cd_xHg_1−xSe regions.     

Strength of frozen saline silt under triaxial compression with high strain rate

Frozen saline silt under triaxial compression with high strain rates and temperatures close to freezing of the pore solution is tested. The goal of this study is to examine the effects of high strain rates and hydrostatic pressures on the strength of frozen saline soil at temperatures close to the temperature of freezing. Results of shear strength tests are presented. The significant influence of strain rate, radial stresses, and temperature on shear strength is outlined.     

Optimal ensemble control of stochastic time-varying linear systems

We consider the optimal guidance of an ensemble of independent, structurally identical, finite-dimensional stochastic linear systems with variation in system parameters between initial and target states of interest by applying a common control function without the use of feedback. Our exploration of such ensemble control systems is motivated by practical control design problems in which variation in system parameters and stochastic effects must be compensated for when state feedback is unavailable, such as in pulse design for nuclear magnetic resonance spectroscopy and imaging. In this paper, we extend the notion of ensemble control to stochastic linear systems with additive noise and jumps, which we model using white Gaussian noise and Poisson counters, respectively, and investigate the optimal steering problem. In our main result, we prove that the minimum norm solution to a Fredholm integral equation of the first kind provides the optimal control that simultaneously minimizes the mean square error (MSE) and the error in the mean of the terminal state. The optimal controls are generated numerically for several example ensemble control problems, and Monte Carlo simulations are used to illustrate their performance. This work has immediate applications to the control of dynamical systems with parameter dispersion or uncertainty that are subject to additive noise, which are of interest in quantum control, neuroscience, and sensorless robotic manipulation.     

A multi-state Markov model for a short-term reliability analysis of a power generating unit

This paper presents a multi-state Markov model for a coal power generating unit. The paper proposes a technique for the estimation of transition intensities (rates) between the various generating capacity levels of the unit based on field observation. The technique can be applied to such units where output generating capacity is uniformly distributed. In order to estimate the transition intensities a special Markov chain embedded in the observed capacity process was defined. By using this technique, all transition intensities can be estimated from the observed realization of the unit generating capacity stochastic process. The proposed multi-state Markov model was used to calculate important reliability indices such as the Forced Outage Rate (FOR), the Expected Energy Not Supplied (EENS) to consumers, etc. These indices were found for short-time periods (about 100 h). It was shown that these indices are sensibly different from those calculated for a long-term range. Such Markov models could be very useful for power system security analysis and short-term operating decisions.