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Scalable Graph Processing Frameworks: A Taxonomy and Open Challenges
No full textThe world is becoming a more conjunct place and the number of data sources such as social networks, online transactions, web search engines, and mobile devices is increasing even more than had been predicted. A large percentage of this growing dataset exists in the form of linked data, more generally, graphs, and of unprecedented sizes. While today's data from social networks contain hundreds of millions of nodes connected by billions of edges, inter-connected data from globally distributed sensors that forms the Internet of Things can cause this to grow exponentially larger. Although analyzing these large graphs is critical for the companies and governments that own them, big data tools designed for text and tuple analysis such as MapReduce cannot process them efficiently. So, graph distributed processing abstractions and systems are developed to design iterative graph algorithms and process large graphs with better performance and scalability. These graph frameworks propose novel methods or extend previous methods for processing graph data. In this article, we propose a taxonomy of graph processing systems and map existing systems to this classification. This captures the diversity in programming and computation models, runtime aspects of partitioning and communication, both for in-memory and distributed frameworks. Our effort helps to highlight key distinctions in architectural approaches, and identifies gaps for future research in scalable graph systems
Virtual Target based Obstacle Avoiding
No full textThe problem of Unmanned Aerial Vehicle(UAV) obstacle avoidance is considered. The UAV follows a virtual target of varying velocity with pure pursuit guidance such that the separation between them remains constant. The analysis of the guidance law is carried out and closed form expressions for virtual target's deviation angle is obtained. The analytic results are interpreted geometrically. Simulation studies demonstrate the effectiveness of the guidance law for different obstacle sizes. (C) 2018, IFAC (International Federation of Automatic Control) Hosting by Elsevier Ltd. All rights reserved
Wear and mechanical properties of novel (CuCrFeTiZn)(100-x)Pb-x high entropy alloy composite via mechanical alloying and spark plasma sintering
No full textThe present investigation reports a systematic study of the effect of Pb addition on microstructural evolution and tribological behavior of equiatomic CuCrFeTiZn high entropy alloy (HEAs). Versatile and interesting properties such as high hardness, reasonable ductility and fracture toughness make HEAs suitable candidates for wear resistance applications. Pb being immiscible with the other alloying elements of the HEA in the solid state is expected to form soft dispersoid in harder HEA matrix, which can act as a lubricant during wear. Different amount of Pb (5, 10 and 20 at%) were incorporated in the HEA by mechanical alloying (MA) followed by consolidation of MA powder using spark plasma sintering. The X-ray diffraction, SEM and TEM investigations reveal uniform dispersion of Pb in the dual phase HEA matrix. The mechanical and tribological properties of the composites show a good combination of hardness (3.5-6 GPa), compressive strength, plasticity (15-20%) and wear resistance. Efforts are made to relate mechanical properties and wear resistance with microstructure of these novel composites designed by CALPHAD modeling. Computational modeling of surface temperature rise during wear was performed to study the effect of temperature on wear mechanism. Surface and subsurface wear mechanism have been elucidated to explain excellent wear resistance. The excellent tribological properties of the present alloy render it as a potential candidate for bearing applications
Exploring the Corundum Structure as a Host for Colored Compounds - Synthesis, Structures, and Optical Studies of (MM)(3)TeO6 (M = Mg, Mn, Co, Ni, Zn; M = Mg, Mn, Co, Ni, Cu)
No full textWe describe the syntheses, crystal structures, and optical absorption studies of the transition-metal-substituted corundum-related oxides (MM)(3)TeO6 (M = Mg, Mn, Co, Ni, Zn; M = Mg, Mn, Co, Ni, Cu). The oxides are readily synthesized by the solid-state reactions of stoichiometric mixtures of the constituent binaries at 750-860 degrees C. The Rietveld refinements of the crystal structures from the powder X-ray diffraction (XRD) data show that the Mg/Mn/Ni/Co/ZnO6 octahedra are distorted. We have interpreted the unique colors and the optical absorption spectra of these materials in terms of the distorted coordination geometries of the Mg/Mn/Ni/Co/ZnO6 chromophores. We have also identified the role that metal-to-metal charge transfer (MMCT) from the partially filled transition-metal 3d orbitals to the empty Mo 4d orbitals plays in the color changes. We believe that the study of these transition-metal substituted corundum oxides suggests directions for the development of colored inorganic materials featuring distorted octahedra around the 3d transition-metal ions, as they may be useful as pigments
Paradoxical consequences of multipath coherence: Perfect interaction-free measurements
No full textQuantum coherence can be used to infer the presence of a detector without triggering it. Here we point out that, according to quantum mechanics, such interaction-free measurements cannot be perfect, i.e., in a single-shot experiment one has strictly positive probability to activate the detector. We formalize the extent to which such measurements are forbidden by deriving a trade-off relation between the probability of activation and the probability of an inconclusive interaction-free measurement. Our description of interaction-free measurements is theory independent and allows derivations of similar relations in models generalizing quantum mechanics. We provide the trade-off for the density cube formalism, which extends the quantum model by permitting coherence between more than two paths. The trade-off obtained hints at the possibility of perfect interaction-free measurements and indeed we construct their explicit examples. Such measurements open up a paradoxical possibility where we can learn by means of interference about the presence of an object in a given location without ever detecting a probing particle in that location. We therefore propose that absence of perfect interaction-free measurement is a natural postulate expected to hold in all physical theories. As shown, it holds in quantum mechanics and excludes the models with multipath coherence
Elastic flexibility tuning via interaction factor modulation in molecular crystals
No full textWe report the design of a series of nonhalogenated and halogenated molecular crystals with specific structural features, which are essential for pronounced elasticity. These features involve (a) isotropic weak and dispersive interactions, and (b) corrugated molecular packing with interlocked structures. The effects of intermolecular interactions on the elastic properties of the crystals are ascertained using nano-scale mechanical characterization methods
Diffusion processes in a poly-crystalline zeolitic material: A molecular dynamics study
No full textExtensive molecular dynamics simulations of xenon in two classes of zeolite crystal systems, one consisting of purely intra-crystalline space and the other with both intra-and inter-crystalline space are reported. The latter mimics a typical poly-crystalline sample of zeolite. Comparison of results from these two systems provides insights into the structure and dynamics in the presence of inter-crystalline space. The temperature, as well as the distance between the crystallites, has been varied. The density distribution and diffusivities calculated inside the poly-crystalline system show that the interfacial region between the crystal and the inter-crystalline region acts as a bottleneck for diffusion through the system. At lower temperatures, the particles are trapped at the interface due to the pronounced energy minima present in that region. With the increase in temperature, the particles are able to overcome this barrier frequently, and the transport across the inter-crystalline region is increased. A ballistic or superdiffusive motion is seen in the inter-crystalline region along all the axes except along the axis which has the inter-crystalline space. The transition time for ballistic to diffusive motion increases with the increase in the length of the inter-crystalline space. Velocity auto-and cross correlation functions exhibit strong oscillations and exchange of kinetic energy along directions perpendicular to the direction of the inter-crystalline space. These results explain why uptake and PFG-NMR measurements exhibit lower values for diffusivity for the same system when compared to Quasi-Elastic Neutron Scattering. Thus, using molecular dynamics simulations, we were able to correlate the difference of diffusivity values measured using various experimental methods where these intercrystalline regions are common. Published by AIP Publishing
Distinct frequency bands in the local field potential are differently tuned to stimulus drift rate
No full textLocal field potential (LFP) recorded with a microelectrode reflects the activity of several neural processes, including afferent synaptic inputs, microcircuit-level computations, and spiking activity. Objectively probing their contribution requires a design that allows dissociation between these potential contributors. Earlier reports have shown that the primate lateral geniculate nucleus (LGN) has a higher temporal frequency (drift rate) cutoff than the primary visual cortex (VI), such that at higher drift rates inputs into VI from the LGN continue to persist, whereas output ceases, permitting partial dissociation. Using chronic microclcctrode arrays, wc recorded spikes and LFP from VI of passively fixating macaques while presenting sinusoidal gratings drifting over a wide range. We further optimized the gratings to produce strong gamma oscillations, since recent studies in rodent VI have reported LGN-dependent narrow-band gaimna oscillations. Consistent with earlier reports, power in higher LFP frequencies (above similar to J40 Hz.) tracked the population firing rate and were tuned to preferred drift rates similar to those for spikes. Significantly, power in the lower (up to similar to 40 Hz) frequencies increased transiently in the early epoch after stimulus onset, even at high drift rates, and had preferred drift rates higher than for spikes/high gamma. Narrow-band gamma (50-80 Hz) power was not strongly correlated with power in high or low frequencies and had much lower preferred temporal frequencies. Our results demonstrate that distinct frequency bands of the VI LFP show diverse tuning profiles, which may potentially convey different attributes of the underlying neural activity. NEW & NOTEWORTHY In recent years the local field potential (LFP) has been increasingly studied, but interpreting its rich frequency content has been difficult. We use a stimulus manipulation that generates different tuning profiles for low, gamma, and high frequencies of the LFP, suggesting contributions from potentially different sources. Our results have possible implications for design of better neural prosthesis systems and brain-machine interfacing applications
Thermal stability and crystallization kinetics of Bi doped Si15Te85-xBix (0 <= x <= 2) chalcogenide glassy alloys
No full textBulk Si15Te85-xBix (0 <= x <= 2) chalcogenide glassy alloys were prepared by well-established melt quenching technique. Thermal stability and crystallization kinetics of these alloys were investigated by employing differential scanning calorimetry (DSC) technique at different heating rates, namely, 10, 15, 20 and 25 K/min under nonisothermal condition. Thermal parameters such as glass transition (T-g), onset crystallization (T-c) and peak crystallization (T-p) temperatures were observed. Double crystallization peaks observed in the DSC thermogram refer to the instability and phase separated network in the glasses. Various kinetic parameters such as thermal stability (Delta T), enthalpy (Delta H-c), entropy (Delta(s)), specific heat (Delta C-p) and fragility index are deduced. The calculated kinetic parameters suggest that the stability of glassy samples decreases with the increase in Bi addition. The activation energies of glass transition (E-g), and crystallization (E-c) were calculated using relevant kinetic formulae. We further discuss on the kinetics of the synthesized materials relevant for their applications in phase change memory (PCM) material (C) 2017 Elsevier Ltd. All rights reserved
Experimental Evaluation of Compressive Strength of PMMA-Seashell based Biocomposites for Orthopedic Applications
No full textBiocomposites are used to replace a part of body in a reliable and physiologically acceptable manner. Mechanical properties, especially compressive strength is a critical factor in deciding the suitability of bio composites when used as dentures. PMMA is widely used for fabricating dentures because of their good appearance, biocompatibility and low water absorption. The present work examines the compressive strength of PMMA based bio composites containing bio compatible sea shells grounded to micron and nano sizes. Effect of filler percentage and particle size on the compressive strength of the bio composite has been examined. The thermal characteristics of the newly processed biocomposites were also studied. The sea shell based bio composites were found to have maximum compressive strength when the fillers used were in nano size range. The thermal stability of the bio composite was also found to have enhanced with the addition of nano size filler. (C) 2017 Elsevier Ltd. All rights reserved