Parallel Grain Research Articles

Grain boundary recombination in semiconductors: the grain boundary interaction case

AbstractThe recombination velocity and the barrier height at a grain boundary are investigated with respect to the interaction between two parallel grain boundaries. A self‐consistent calculation has been performed within the Read‐Hall‐Shockley framework. The procedure takes into account of the space‐charge region and the quasi‐neutral region assuming a rigid displacement of the bands. The grain‐boundary energy states are considered in the half‐filled‐level model. The dependence of the recombination parameters are reported versus the excitation and the semiconductor and grain‐boundary characteristics. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Simple reaction time to the onset of time-varying sounds.

Although auditory simple reaction time (RT) is usually defined as the time elapsing between the onset of a stimulus and a recorded reaction, a sound cannot be specified by a single point in time. Therefore, the present work investigates how the period of time immediately after onset affects RT. By varying the stimulus duration between 10 and 500 msec, this critical duration was determined to fall between 32 and 40 milliseconds for a 1-kHz pure tone at 70 dB SPL. In a second experiment, the role of the buildup was further investigated by varying the rise time and its shape. The increment in RT for extending the rise time by a factor of ten was about 7 to 8 msec. There was no statistically significant difference in RT between a Gaussian and linear rise shape. A third experiment varied the modulation frequency and point of onset of amplitude-modulated tones, producing onsets at different initial levels with differently rapid increase or decrease immediately afterwards. The results of all three experiments results were explained very well by a straightforward extension of the parallel grains model (Miller and Ulrich Cogn. Psychol. 46, 101-151, 2003), a probabilistic race model employing many parallel channels. The extension of the model to time-varying sounds made the activation of such a grain depend on intensity as a function of time rather than a constant level. A second approach by mechanisms known from loudness produced less accurate predictions.

NUMERICAL SIMULATION OF DIRECTIONAL SOLIDIFIED MICROSTRUCTURE OF WIDE-CHORD AERO BLADE BY BRIDGEMAN PROCESS

The aero turbine is spun by high-temperature and high-pressure burning gases. The practice has proven that the directional solidification(DS) turbine blade with perfect column grains has still excellent high-temperature performance in this kind of working environment. This means that the size and orientation of column grains have great influence on the high-temperature property and performance of turbine blades. On the other hand,the high-quality blade is not easy to be produced in DS process due to the difficulty of obtaining the desired temperature field needed to produce the grains with ideal morphology. In addition, the growth of columnar grains in the wide- chord hollow guide blade is obstructed by the complex camber and the platform. How to produce turbine blades with desired microstructures is the key problem in the DS process. Numerical simulation of the DS process is an effective way to investigate the growth and the morphology of the grains and hence to optimize the process.In this work, a mathematical- physical model for simulating the DS process of wide- chord blade is established in which nucleation and grain growth in the blade in the DS process are modeled by the cellular automation(CA)method with multi-scale dynamic bidirectional coupling technology. Some general analytic indicators are proposed to assess the morphology of mushy zone and grains in a blade quantitatively. Based on the simulated results by using the usual starter blocks 1, 2 and 3, a new starter block is designed considering numerically controlled cutting.Temperature fields and grains in DS processes and corresponding indicators at different withdrawal rates for above4 starter blocks are numerically predicted to investigate the influences of varying these technological parameters,and hence to determine the influence mechanism to the DS process. For comparison, the DS validation experiments by using starter blocks 1, 2 and 3 have been carried out. The numerical and experimental results agree well, their morphologies including those faulty grains are similar. It is found that higher withdrawal rate leads to larger concavation of mushy zone, but the effect of chill is stronger than that of withdrawal rate if the contact area between casting and chill plate is large enough. Better grain structure in a blade is achieved by starter block 3 than by starter blocks 1 and 2. By starter block 4, the amount of column grains is larger and the amount of lateral grain boundaries is smaller, compared with that of starter blocks 1, 2 and 3. Therefore higher withdrawal rate could be adoptable without excessive concavation of mushy zone, resulting in parallel column grains, finer dendrites in the blade, and much higher blade productivity. Optimum withdrawal rates are also determined for starter blocks 3 and 4.

Growth and electro-optical properties of Ga-doped ZnO films prepared by aerosol assisted chemical vapour deposition

Abstract Transparent conductive Ga-doped ZnO thin films were deposited onto glass substrates by a low-cost aerosol assisted chemical vapour deposition technique and the effect of gallium content on the ZnO film growth behaviour and opto-electronic properties was systematically investigated. It is found that, upon increasing Ga addition, the ZnO film crystallinity exhibits a continuous reduction in quality associated with the preferential orientation transformed from (002) to (102). The (002) oriented samples had a microstructure of parallel columnar grains while the (102) oriented coating was thickened by overlapping particles. The ZnO:Ga coatings exhibit high carrier concentration (up to 4.1 × 1020 cm− 3) but low carrier mobility (up to 0.8 cm2 V− 1 s− 1), resulting in a minimum resistivity value of 2.3 × 10− 2 Ω cm. The inferior carrier mobility performance could result from a profound ionized and neutral impurity scattering effect. Good visible transmittance (≈ 70–80%) is observed in these ZnO:Ga films and samples with higher carrier density present better infrared reflection performance (up to 37.2% at 2500 nm).

Synthesis of MgAl2O4spinel nanoparticles via polymer-gel and isolation-medium-assisted calcination

Abstract

The thermal crack characteristics of rolled tungsten in different orientations

Thermal shock resistance of rolled tungsten with elongated grains aligned parallel and perpendicular to the loading direction was examined. Parallel (type A) or perpendicular (type B) grain orientations influences crack characteristics including threshold, profile, pattern and parameter. Type B samples show a cracking threshold of 0.44–0.66GW/m2, which is much higher than type A samples (<0.22GW/m2). For type A samples, primary cracks appear with linear profiles and dense secondary cracks along grain boundaries. Type B samples exhibit circular primary crack profiles as the homogeneous bending strength on the loaded surface and no secondary cracks are observed. Type A samples exhibit deeper cracking (550–850μm) than type B samples (350–550μm). The maximum crack widths were 2–8μm for type A, again larger than those of type B (0–8μm). Thermal fatigue tests were performed on type B samples, and cracks were detected after 1000cycles.

Thermal Conductivity of Akar Bamboo (&lt;i&gt;Dendracalamus pendulus&lt;/i&gt;) and Semantan Bamboo (&lt;i&gt;Gigantochloa scortechinii&lt;/i&gt;)

Bamboo is known as economically and environmental friendly plant. The most common application of bamboos is furniture and traditional handcrafts. Many studies on mechanical and physical properties of bamboo have been conducted. However the thermal insulation property of these abundance species has never been recognized and commercially utilized which results in the reason why thermal properties of bamboo have never been studied. In this experiment, two species of bamboo which are Akar bamboo (Dendracalamus pendulus) and Semantan bamboo (Gigantochloa scortechinii) has been tested to determine their thermal conductivity. The test samples were prepared to conduct this experiment in parallel and perpendicular grain direction towards the heat source. Wood adhesive was used as the binder for cylindrical laminated bamboo. The result shows that thermal conductivity of bamboo is low in perpendicular direction towards the heat source compared to the parallel direction. Different species of bamboo also give significant result on thermal conductivity hence improved the insulation properties of the bamboo.

An Impulse-C Hardware Accelerator for Packet Classification Based on Fine/Coarse Grain Optimization

Current software-based packet classification algorithms exhibit relatively poor performance, prompting many researchers to concentrate on novel frameworks and architectures that employ both hardware and software components. The Packet Classification with Incremental Update (PCIU) algorithm, Ahmed et al. (2010), is a novel and efficient packet classification algorithm with a unique incremental update capability that demonstrated excellent results and was shown to be scalable for many different tasks and clients. While a pure software implementation can generate powerful results on a server machine, an embedded solution may be more desirable for some applications and clients. Embedded, specialized hardware accelerator based solutions are typically much more efficient in speed, cost, and size than solutions that are implemented on general-purpose processor systems. This paper seeks to explore the design space of translating the PCIU algorithm into hardware by utilizing several optimization techniques, ranging from fine grain to coarse grain and parallel coarse grain approaches. The paper presents a detailed implementation of a hardware accelerator of the PCIU based on an Electronic System Level (ESL) approach. Results obtained indicate that the hardware accelerator achieves on average 27x speedup over a state-of-the-art Xeon processor.

Proton conductivity of columnar ceria thin-films grown by chemical vapor deposition

Columnar thin films of undoped ceria were grown by metal-organic chemical vapor deposition. The films, deposited on Pt-coated MgO(100) substrates, display a columnar microstructure with nanometer scale grain size and ~30% overall porosity. Through-plane (thickness mode) electrical conductivity was measured by AC impedance spectroscopy. Proton conduction is observed below 350-400 °C, with a magnitude that depends on gas-phase water vapor pressure. The overall behavior suggests proton transport that occurs along exposed grain surfaces and parallel grain boundaries. No impedance due to grain boundaries normal to the direction of transport is observed. The proton conductivity in the temperature range of 200-400 °C is approximately four times greater than that of nanograined bulk ceria, consistent with enhanced transport along aligned grain surfaces in the CVD films.

The Harrison diffusion kinetics regimes in solute grain boundary diffusion

Knowledge of the limits of the principal Harrison kinetics regimes (Types A, B and C) for grain boundary diffusion is very important for the correct analysis of depth profiles in a tracer diffusion experiment. These regimes for self‐diffusion have been extensively studied in the past by making use of the phenomenological lattice Monte Carlo (LMC) method with the result that the limits are now well established. However, the relationship of these self‐diffusion limits to the corresponding ones for solute diffusion in the presence of solute segregation to the grain boundaries remains unclear. In the present study, the influence of solute segregation on the limits was investigated with the LMC method for the well‐known parallel grain boundary slab model by showing the equivalence of two diffusion models. It is shown which diffusion parameters are useful for identifying the limits of the Harrison kinetics regimes for solute grain boundary diffusion. It is also shown how the measured segregation factor from the diffusion experiment in the Harrison Type‐B kinetics regime may differ from the global segregation factor.

Rockfill shear strength evaluation: a rational method based on size effects

The shear strength of coarse granular materials, widely used in civil works such as rockfill in dam construction, is seldom measured because of severe practical experimental limitations. This paper presents an original method for evaluating the shear strength of such materials, based on size effects in granular materials affected by grain breakage according to fracture mechanics. Through a general size effect relation operating on shear strength envelopes, this method makes it possible to determine the shear strength of a coarse-grained granular material from the measured properties of a finer-grained granular material made of the same mineral. In the paper, the method is explicitly proved, taking into account the statistical distribution of breakage resistances of particles with different sizes, within materials that can be considered as physically similar, particularly having parallel grain size distributions and the same compactness. A wide set of independent experimental results is shown to validate the method consistently.

TEM and stress relaxation analysis of 99.1% aluminum processed by Equal Channel Angular Extrusion

Relaxation experiments were performed on 99.1% aluminum in addition to transmission electron microscopy and mechanical tests to follow the evolution of the microstructure and the mechanical properties changes after equal channel angular extrusion (ECAE). After deformation, weak beam investigations were conducted on selected specimens. The microstructure of deformed material shows the presence of almost parallel and elongated grains. Moreover, newly created subgrains separated by dislocation walls are observed. The tensile and Vickers hardness experiments for deformed samples showed an improvement of mechanical properties compared with the unextruded one. The activation volume, obtained from relaxation tests decreases with increasing the number of passes. This is due to change in mechanism from dislocation-dislocation interaction in coarse grains material (N = 0) to dislocation-grain boundary or grain deformation in ultra fine grains material (N≥1).

Time-course analysis of temporal preparation on central processes

Participants usually respond faster to a response signal (RS) when this signal is preceded by a warning stimulus than when it is not. A question of theoretical importance is the locus of this facilitating effect within the information processing stream. Recently, Los and Schut (Cogn Psychol 57:20-55, 2008) suggested that temporal preparation acts on central processes while perception of the RS is under way. The present study provides a stochastic model (central preparation model, CPM) based on this hypothesis and presents three experiments testing this model. To track the complete time-course of temporal preparation, the warning signal could either precede or follow the RS. The data show some systematic deviation from the model's predictions, questioning CPM's assumption that temporal preparation acts only on central processes. An alternative mechanism of temporal preparation based on the parallel grains model [Miller and Ulrich (Cogn Psychol 46:101-151, 2003)] is discussed.

Effect of Sample Size on the Behavior of Granular Materials

Abstract Natural soils or coarse granular materials containing large particles such as rockfill or ballast are often an issue for geotechnical projects. However, since it is usually complicated or impossible to set up a big enough experimental apparatus to test these materials, their mechanical behavior remains poorly known. To circumvent this difficulty, we have developed a set of triaxial cells of various sizes to study the experimental behavior of granular soils containing particle sizes of up to 160 mm. This paper presents the first results of a two-part experimental study. The first part consists of triaxial tests on sand samples of different sizes in order to examine specimen scale effects. Pre-peak behavior is not affected by the specimen size, whereas post-peak behavior depends on the test conditions that control the development of strain localizations. In the second part, we present drained triaxial compression tests on large samples of calcareous rockfill materials that have parallel grain size distributions. The results show a nonstandard evolution of the friction angle in relationship to grain size if compared to similar studies on coarse granular materials. Although grain crushing occurs during compression, the strain-stress curves of the different materials with different grain sizes do remain close. We explain this phenomenon by the strength evolution of the individual grains with respect to their sizes.

Strain softening along the MCT zone from the Sikkim Himalaya: Relative roles of Quartz and Micas

In the Darjeeling – Sikkim Himalaya, two distinct faults form the Main Central thrust (MCT), the structurally higher MCT1 and the lower MCT2; each has accommodated translation greater than 100 km. The lower MCT2 places Greater Himalayan amphibolite grade Paro-Lingtse gneiss over Lesser Himalayan greenschist grade Daling metapelites. The MCT2 is folded by the underlying Lesser Himalayan duplex and is exposed at different structural positions of the fold. At Pelling, the MCT2 zone is exposed as a ∼373 m thick NW dipping fault zone that exposes ∼19 m of hanging wall mylonitized Lingtse gneiss. The Lingtse protolith shows evidence of amphibolite grade plastic deformation features in quartz and feldspar. Within the hanging wall mylonite zone (HWMZ), quartz and feldspar have undergone grain-size reduction by different deformation mechanisms and feldspars are sericitized suggesting the presence of fluids during deformation. We estimate a temperature of ∼300 °C within the fault zone during fluid-assisted retrogression and deformation. Reaction softening of feldspars produced a large proportion of intrinsically weak matrix. This, in combination with development of a strong foliation defined by parallel mica grains, resulted in strain softening along the MCT2 zone, and concentrated the deformation along a thin zone or zones.

WAPM: A parallel programming model in large scale Internet distributed computing environments

Programming models like MPI or OpenMP are not suitable for large-scale Internet environments because of scalability or parallel grain issues. In this paper,a novel parallel programming model in large-scale Internet environments called Wide Area Programming Model (WAPM),which provided a feasible way for parallel programming,was designed and implemented. WAPM includes three modules: communication library,communication protocol and application programming interface. WAPM is a good programming model,and is strongly supported by its general programming,adaptive parallelism and fault tolerance. An example application was also demonstrated with WAPM on a specific distributed computing platform. In order to testify the efficiency of WAPM,a serial of simulation experiments were done. The results obtained from performance analysis show that WAPM is a general and feasible approach for parallel programming.

Multi-Grain Parallel H.264 Encoder for Homogeneous Multi-Core Architectures

As a new generation video coding standards,H.264 requires more intensive computation than before to achieve high coding performance. With the continuous development of multi-core processors,the development of the multi-grain parallel H.264 encoder has great significance to meet the requirements of video real-time transmission and large-scale sharing. Based on the open-source H.264 encoder project X264,an adaptive B-frame frame parallel algorithm is proposed through analysis of the dependency among the referent frames. According to the reference of related macroblocks,a macroblock-level parallel approach is designed in assembly-line fashion. A multi-grain parallel H.264 encoder is implemented on the homogeneous multi-core platform. This encoder efficiently combines four parallel grains,including frame,slice,macroblock and data level. Experimental results demonstrate that the encoding speedup is improved to a large extent,without obviously increasing bitrates. The high-quality video is kept in the encoding process.

The auditory redundant signals effect: An influence of number of stimuli or number of percepts?

In two experiments, we examined simple reaction times (RTs) for detection of the onsets and offsets of auditory stimuli. Both experiments assessed the redundant signals effect (RSE), which is traditionally defined as the reduction in RT associated with the presentation of two redundant stimuli, rather than a single stimulus. In Experiment 1, with two identical tones presented via headphones to the left ear, right ear, or both, no RSE was found in responding to tone onsets, but a large RSE was found in responding to their offsets. In Experiment 2, with a pure tone and white noise as the two stimulus alternatives, RSEs were found for responding to both onsets and offsets. The results support the notion that the occurrence of an RSE depends on the number of percepts, rather than the number of stimuli, and on the requirement to respond to stimulus onsets versus offsets. The parallel grains model (Miller & Ulrich, 2003) provides one possible account of this pattern of results.

Penetration of urea formaldehyde adhesives in wood tissue, Part II: Radial penetration of UF adhesives into silver fir

Penetration is the ability of the adhesive to move into the voids on the substrate surface or into the substrate itself. Wood's cellular nature allows significant penetration of the adhesive into the substrate. Objective of this work was the evaluation of the penetration and hence the distribution of urea-formaldehyde (UF) resins by means of microscopic detection of the penetration of such UF adhesives into the wood tissue. Tangentially cut 5 mm thick silver fir (Abies alba Mill.) plies, 100 mm long (parallel to the grain) and 30 mm width, were prepared for this study. Four types of UF resins with different degree of condensation were investigated in this research. Safranin was added to the resins and epi-fluorescence microscope was used for measuring the adhesive penetration. The UF adhesive mixes, consisting of the various resins, extender and hardener were applied to the surface of one ply. Two plies, one with applied adhesive mix and one without adhesive mix, were assembled with parallel grain direction. Samples were pressed in a hydraulic press at 120?C and 1.0 MPa for 15 minutes. Test-specimens of 20 ?m thickness were cut of each sample using a sliding microtome apparatus, exposing a bondline on a cross-sectional surface. The results show a significant correlation between the penetration behaviour and the degree of condensation (molecular sizes, viscosity) of the resins. The higher the degree of condensation, the lower the possibility for penetration, expresses as average penetration (AP) and as portion of filled tracheids on the whole cross section of interphase (filled interphase region FIR).

Near-surface and internal lamellar structure and orientation in thin films of rod–coil block copolymers

Controlling the three-dimensional structure of rod–coil block copolymer thin films is critical for the optimization of the carrier transport properties and exciton dissociation or carrier recombination efficiencies at interfaces in optoelectronic polymers. Using a model rod–coil block copolymer based on poly(alkoxyphenylenevinylene-b-isoprene) (PPV-b-PI), the structure and orientation of thermally self-assembled rod–coil block copolymer thin films is investigated with grazing-incidence small-angle X-ray scattering (GISAXS), dynamic secondary ion mass spectrometry (DSIMS), scanning force microscopy (SFM), and cross-sectional transmission electron microscopy. Grains of lamellae are grown in films with one supported and one free interface by thermal annealing below the order–disorder transition from an initially structureless solution-cast state. In films only a few lamellar layers thick, parallel lamellar grains that span the entire film thickness are formed due to surface templating of lamellar orientation. As film thickness is increased, the lamellar block copolymers take on a bimodal orientation, with parallel and perpendicularly oriented microphases distributed uniformly throughout the center of the film. The vacuum interface is coated in a ∼10 nm thick layer of perpendicular lamellae, while the supported interface is covered with a single parallel oriented layer of block copolymer due to surface segregation of the polyisoprene block. Further increasing the thickness results in partial loss of orientational order as the bulk structure is approached. Strong suppression of the primary scattering peak is observed near a coil fraction of 0.7 for parallel lamellae, indicating changes in form factor from the bulk or perpendicularly oriented structures. Large dilations in the average perpendicular lamellar domain spacing are also observed in thin films as defects between perpendicular lamellar grains. As the film thickness increases, the lamellar period asymptotically decreases to the bulk value. The lamellae dilate rather than bending due to the high modulus of the PPV liquid crystalline nanodomains. Parallel lamellae show no dilation because of the free interface.