Generate‐map‐reduce: An extension to map‐reduce to support shared data and recursive computations

It is difficult to express the parallelism present in complex computations by using existing higher level abstractions such as MapReduce and Dryad. These computations include applications from wide variety of domains, like Artificial Intelligence, Decision Tree Algorithms, Association Rule Mining, Recommender Systems, Graph Algorithms, Clustering Algorithms, Compute Intensive Scientific Workflows, Optimization Algorithms, and so forth. Their execution graphs introduce new challenges in terms of programmer expressibility and runtime performance such as iterative and recursive computations, shared communication model, and so forth. We propose an extension to MapReduce, called Generate‐Map‐Reduce (GMR), targeted towards modeling these applications. GMR introduces a new Generate abstraction into the MapReduce framework that captures recursive computations. The runtime also supports iterative jobs and a distributed communication model by using shared data structures. We illustrate recursive computations with GMR by modeling complex applications such as simulated annealing, A* search, and adaptive quadrature computation that require recursive spawning of new tasks to handle variable degree of parallelism. GMR runtime supports caching of common data across iterations in memory and local disks. We illustrate how this caching helps in achieving significant speedup for iterative computations by modeling k‐means clustering. Copyright © 2013 John Wiley & Sons, Ltd.     

Thermal and mechanical properties of blended polyimide and amine‐functionalized poly(orthosiloxane) composites

Nanocomposite films were prepared through the blending of polyimide (PI) with octaphenyl silsesquioxane (OPS) and an amino‐functionalized analogue, octaaminophenyl silsesquioxane (OAPS), with a solution‐casting method. Although the PI–OPS composites showed visible phase separation at 5 wt %, the PI–OAPS composites were transparent with visible phase separation occurring only at 50 wt % OAPS. The interfacial interactions and homogeneity of the composites were characterized with scanning electron microscopy (SEM) and dynamic mechanical analysis. SEM analysis showed a uniform fracture surface for OAPS composites at concentrations up to 20 wt %. Interestingly, OAPS‐rich particles with sizes of less than 1 μm were formed within the PI matrix for the 50 wt % composite. The PI–OAPS composites showed higher glass‐transition temperatures (T_g's) than the pure PI. The PI–OPS composites showed a T_g lower than that of the pure PI, and this suggested poor interfacial interactions. The slightly enhanced thermal stability of PI–OAPS composites (up to 20 wt %) was attributed to the inherent thermal stability of OAPS at higher temperatures. There were small increases in the modulus and strength for the composites with respect to the base polymer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Capacitance–voltage characteristics of P3HT:PCBM bulk heterojunction solar cells with ohmic contacts and the impact of single walled carbon nanotubes on them

Capacitance–voltage (C–V) characteristics of P3HT:PCBM devices of two different thicknesses are correlated with current density–voltage (J–V) characteristics. The rising portion of the C–V characteristics coincides with the exponential current density below the built-in voltage. The negative capacitance (NC) of these devices is a low frequency phenomenon and it occurs in trap-free space charge limited current (SCLC) regime. The onset frequencies of NC for devices with and without SWNTs also do not follow direct relation with effective mobility. The NC in thin devices has non-monotonic change with voltage for thin devices showing that interface state kinetics can be the reason for its occurrence. The NC of thick devices, on the other hand, increases monotonically with voltage showing that bulk properties dominate in these. Addition of SWNTs to these devices for efficiency improvement does not modify their built-in voltage. Also, the SWNTs do not affect the forward NC behaviour. However, the devices containing SWNTs show NC in reverse bias also which has different frequency dependence with voltage. The reverse bias NC is attributed to the large non-linear reverse current by charge injection into the additional energy levels introduced by SWNTs.     

Seaweeds for the remediation of wastewaters contaminated with zinc(II) ions

Eleven different species of marine macroalgae were screened at different pH conditions on the basis of zinc(II) biosorption potential. Among the seaweeds, a green alga, Ulva reticulata, exhibited a highest uptake of 36.1 mg/g at pH 5.5 and 100 mg/l initial zinc(II) concentration. Further experiments were conducted to evaluate the zinc(II) biosorption potential of U. reticulata. Sorption isotherm data obtained at different pH (5-6) and temperature (25-35 degrees C) conditions were fitted well with Sips model followed by Freundlich, Redlich-Peterson and Langmuir models. A maximum zinc(II) biosorption capacity of 135.5 mg/g was observed at optimum conditions of 5.5 (pH) and 30 degrees C (temperature), according to the Langmuir model. It was observed from the kinetic data that the zinc(II) biosorption process using U. reticulata follows pseudo-second-order kinetics. Various thermodynamic parameters, such as DeltaG degrees , DeltaH degrees and DeltaS degrees were calculated and they indicated that the present system was a spontaneous and an endothermic process. The influence of the co-ions (Na(+), K(+), Ca(2+) and Mg(2+)) along with zinc(II) present in the wastewater was also studied. Desorption of zinc(II) ions from the zinc(II)-loaded biomass were examined using 0.1 M CaCl(2) at different pH conditions in three sorption-desorption cycles. A fixed-bed column (2 cm i.d. and 35 cm height) was employed to evaluate the continuous biosorption performance of U. reticulata. The column experiments at different bed heights and flow rates revealed that the maximum zinc(II) uptake was obtained at the highest bed height (25 cm) and the lowest flow rate (5 ml/min). Column data were fitted well with Thomas, Yoon-Nelson and modified dose-response models. The column regeneration studies were carried out for three sorption-desorption cycles. A loss of sorption performance was observed during regeneration cycles indicated by a shortened breakthrough time and a decreased zinc(II) uptake.     

Cover Feature: Molecular Highway Patrol for Ribosome Collisions (ChemBioChem 20/2023)

During translation, messenger RNAs (mRNAs) are decoded by ribosomes which can stall for various reasons. These include chemical damage, codon composition, starvation, or translation inhibition. Trailing ribosomes can collide with stalled ribosomes, potentially leading to dysfunctional or toxic proteins. Such aberrant proteins can form aggregates and favor diseases, especially neurodegeneration. To prevent this, both eukaryotes and bacteria have evolved different pathways to remove faulty nascent peptides, mRNAs and defective ribosomes from the collided complex. In eukaryotes, ubiquitin ligases play central roles in triggering downstream responses and several complexes have been characterized that split affected ribosomes and facilitate degradation of the various components. As collided ribosomes signal translation stress to affected cells, in eukaryotes additional stress response pathways are triggered when collisions are sensed. These pathways inhibit translation and modulate cell survival and immune responses. Here, we summarize the current state of knowledge about rescue and stress response pathways triggered by ribosome collisions.     

Novel,synergistic composites of polypropylene and rice husk ash: Sustainable resource hybrids prepared by solid‐state shear pulverization

Rice husk ash (RHA) is an agrowaste byproduct resulting from the incineration of rice husks for power production; white RHA is ∼90 wt% or more silica, which makes it a potentially sustainable and inexpensive substitute for commercial (less “green”) silica filler. Past research on polypropylene (PP)‐RHA hybrids made by melt processing has yielded modest increments in Young's modulus, reduced yield strength, and drastic reductions in elongation at break relative to neat PP. Using the industrially scalable solid‐state shear pulverization (SSSP) process, PP‐RHA hybrids are made with 4–38 wt% RHA. As determined by microscopy and other methods, composites made by SSSP have much better RHA dispersion than composites reported in the literature made by twin‐screw extrusion. The superior dispersion leads to major enhancements in tensile modulus (up to 100% increases relative to neat PP) while maintaining the yield strength of neat PP and remarkably high values of elongation at break (e.g., 520% at 19 wt% RHA), far higher than composites made by melt processing. The properties of hybrids made by SSSP are competitive with and in some cases superior to those of PP hybrids made with commercial silica. The PP‐RHA hybrids also exhibit major increases in hardness, approaching that of polycarbonate in the case of a 38 wt% RHA hybrid. The 38 wt% RHA hybrid exhibits solid‐like rheology at low frequency. Nevertheless, all PP‐RHA hybrids made by SSSP exhibit viscosities at moderate to high shear rates that are little changed from that of neat PP. POLYM. COMPOS., 34:1211–1221, 2013. © 2013 Society of Plastics Engineers