On the improvement of a scalable sparse direct solver for unsymmetrical linear equations

This paper focuses on the application level improvements in a sparse direct solver specifically used for large-scale unsymmetrical linear equations resulting from unstructured mesh discretization of coupled elliptic/hyperbolic PDEs. Existing sparse direct solvers are designed for distributed server systems taking advantage of both distributed memory and processing units. We conducted extensive numerical experiments with three state-of-the-art direct linear solvers that can work on distributed-memory parallel architectures; namely, MUMPS (MUMPS solver website, http://graal.ens-lyon.fr/MUMPS), WSMP (Technical Report TR RC-21886, IBM, Watson Research Center, Yorktown Heights, 2000), and SUPERLU_DIST (ACM Trans Math Softw 29(2):110–140, 2003). The performance of these solvers was analyzed in detail, using advanced analysis tools such as Tuning and Analysis Utilities (TAU) and Performance Application Programming Interface (PAPI). The performance is evaluated with respect to robustness, speed, scalability, and efficiency in CPU and memory usage. We have determined application level issues that we believe they can improve the performance of a distributed-shared memory hybrid variant of this solver, which is proposed as an alternative solver [SuperLU_MCDT (Many-Core Distributed)] in this paper. The new solver utilizing the MPI/OpenMP hybrid programming is specifically tuned to handle large unsymmetrical systems arising in reservoir simulations so that higher performance and better scalability can be achieved for a large distributed computing system with many nodes of multicore processors. Two main tasks are accomplished during this study: (i) comparisons of public domain solver algorithms; existing state-of-the-art direct sparse linear system solvers are investigated and their performance and weaknesses based on test cases are analyzed, (ii) improvement of direct sparse solver algorithm (SuperLU_MCDT) for many-core distributed systems is achieved. We provided results of numerical tests that were run on up to 16,384 cores, and used many sets of test matrices for reservoir simulations with unstructured meshes. The numerical results showed that SuperLU_MCDT can outperform SuperLU_DIST 3.3 in terms of both speed and robustness.     

Synthesis of opaque and colored hollow polymer pigments

A parametric study was carried out to investigate the effects of process parameters on the properties of opaque and/or colored polymer pigment. The core was synthesized using methyl methacrylate (MMA), methacrylic acid (MAA), and ethylene glycol dimethacrylate, and the shell from styrene. The surfactant/water (S/W) ratio was changed between 0.56 and 1.46, and the best ratio was determined to be 0.97. The increase in the amount of MAA and the pH of the medium increases the diameter of the swollen particles. The hollows could form only when the fraction of MAA in the monomer mixture was above 10%, and pH ≥ 10. The opaque pigment with the largest diameter could be obtained at the S/W ratio of 0.97 and the MAA content of 20%, as 350 nm. It gave an opacity value of 93.8% when mixed with an acrylic resin at 50% by volume. The colored opaque polymer pigments were synthesized by adding copper phthalocyanine into the monomer mixture. The addition of 2% copper phthalocyanine yielded a green‐blue color but 3% yielded blue color. The latter yielded a change in the lightness by a value of ?31.49, and a total color difference of 30.05 compared with that of white opaque polymer pigment. POLYM. ENG. SCI., 57:913–920, 2017. © 2016 Society of Plastics Engineers     

The Effects of Thermal Cycles on the Impact Fatigue Properties of Thermoplastic Matrix Composites

The effects of thermal cycles on the impact fatigue properties of unidirectional carbon fibre reinforced polyetherimide (PEI) matrix composites were investigated. During the thermal cycles, samples were immersed into boiling water (100 °C) and subsequently to ice water (0 °C), 50, 200 and 500 times. The changes in viscoelastic properties of the composites were investigated by means of dynamic mechanical thermal analyzer (DMTA). At the second step, thermal cycled composites were subjected to repeated impact loadings, with different impact energies. Instrumented impact test results were presented as a function of force, energy, deformation during the experiments. The scanning electron microscope (SEM) studies were done in order to understand the morphology of fractured samples after impact fatigue loading. The number of thermal cycles and applied impact energy of the hammer are found to have a great importance on the fracture morphology of repeatedly impacted material, as expected.     

Combinatorial detection of volatile organic compounds using metal-phthalocyanine field effect transistors

We apply percolation theory to explain the operation of multiple-use gas sensors based on organic field effect transistors (OFETs). For reversible operation, we predict that energetic disorder in the channel can obscure interactions with the analyte, because chemically induced traps are overwhelmed by the natural disorder. Consequently, the sensitivity of an energetically disordered OFET-based chemical sensor is significantly inferior to the ideal disorder-free case. Current modulation in disordered OFETs is predicted to rely on morphological alteration of percolation paths. The theory is compared to results from an array of metal phthalocyanine (MPC) transistors exposed to low concentrations of solvents. Despite the presence of very large adsorption fractions of solvent on the channel, the current modulation is small, consistent with theory. Chemical selectivity is possible, however, because the central metal atom of the MPC determines the strength of the solvent-MPC interaction, which in turn determines the amount of solvent adsorbed on the OFET channel. This work suggests that OFET-based sensors may be better suited to applications where the analyte binding energy exceeds the intrinsic energetic disorder of the organic semiconductor.     

Nonporous monosize polymeric sorbents: Dye and metal chelate affinity separation of lysozyme

Lysozyme adsorption onto dye‐attached nonporous monosize poly(2‐hydroxyethyl‐methacrylate‐methylmethacrylate) [poly(HEMA‐MMA)] microspheres was investigated. Poly(HEMA‐MMA) microspheres were prepared by dispersion polymerization. The monochloro‐triazine dye, Cibacron Blue F3GA, was immobilized covalently as dye–ligand. These dye‐affinity microspheres were used in the lysozyme adsorption–desorption studies. The effect of initial concentration of lysozyme and medium pH on the adsorption efficiency of dye‐attached and metal‐chelated microspheres were studied in a batch reactor. Effect of Cu(II) chelation on lysozyme adsorption was also studied. The nonspecific adsorption of lysozyme on the poly(HEMA‐MMA) microspheres was 3.6 mg/g. Cibacron Blue F3GA attachment significantly increased the lysozyme adsorption up to 247.8 mg/g. Lysozyme adsorption capacity of the Cu(II) incorporated microspheres (318.9 mg/g) was greater than that of the Cibacron Blue F3GA‐attached microspheres. Significant amount of the adsorbed lysozyme (up to 97%) was desorbed in 1 h in the desorption medium containing 1.0M NaSCN at pH 8.0 and 25 mM EDTA at pH 4.9. In order to examine the effects of separation conditions on possible conformational changes of lysozyme structure, fluorescence spectrophotometry was employed. We conclude that dye‐ and metal‐chelate affinity chromatography with poly(HEMA‐MMA) microspheres can be applied for lysozyme separation without causing any significant changes and denaturation. Repeated adsorption/desorption processes showed that these novel dye‐attached monosize microspheres are suitable for lysozyme adsorption. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 115–124, 2000     

Effect of fiber orientation on viscoelastic properties of polymer matrix composites subjected to thermal cycles

Fibers in polymer composites can be designed in various orientations for their usage in service life. Various fiber orientated polymer composites, which are used in aeroplane and aerospace applications, are frequently subjected to thermal cycles because of the changes in body temperatures at a range of −60 to 150°C during flights. It is an important subject to investigate the visco‐elastic properties of the thermal cycled polymer composite materials which have various fiber orientations during service life. Continuous fiber reinforced composites with a various fiber orientations are subjected to 1,000 thermal cycles between the temperatures of 0 and 100°C. Dynamic mechanic thermal analysis (DMTA) experiments are carried out by TA Q800 type equipment. The changes in glass transition temperature (T_g), storage modulus (E′), loss modulus (E′′) and loss factor (tan δ) are inspected as a function of thermal cycles for different fiber orientations. It was observed that thermal and dynamic mechanical properties of the polymer composites were remarkably changed by thermal cycles. It was also determined that the composites with [45°/−45°]_s fiber orientation presented the lowest dynamic mechanical properties. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Performance of diesel engine using biodiesel obtained from mixed feedstocks

Availability of identified tree species bearing non-edible oil has a region specific production characteristics and availability of sufficient amount at a given place is always uncertain. Moreover, the any prospective biodiesel production and utilization programe would need to consider more and one feedstock to meet the target. There could be another reason to investigate feasibility of mixed feedstocks considering strength and weakness of biodiesel fuel properties specific to feedstocks. Considering the above the present investigation is carried out to study the fuel characteristics of biodiesel obtain from mixed feedstocks of three species of oil feedstocks namely polonga, koroch and jatropha. An attempt has been made in this paper to give an overview of the application of mixed biodiesel in CI Engine. Properties of biodiesel obtained from mixed feedstocks (BOMF) satisfy different biodiesel standards. Performance of BOMF fueled engine gives better result than the individual biodiesels.     

Hygrothermal Fracture Analysis of Orthotropic Materials Using J k -Integral

A new computational method based on the J _k -integral is put forward for the purpose of conducting fracture analysis of orthotropic materials subjected to hygrothermal stresses. By utilizing the constitutive relations of plane orthotropic hygrothermoelasticity, an alternative expression for the J _k -integral is derived to replace the general limit definition. A numerical procedure is developed and integrated into a finite element analysis software to implement the proposed form of the J _k -integral. Temperature and specific moisture concentration fields, which are required in fracture calculations, are also computed through finite element analysis. Numerical results are generated by considering an embedded crack in a polymer matrix fibrous composite laminate, that is subjected to steady-state hygrothermal loading. Comparisons of the mixed-mode stress intensity factors computed by the J _k -integral based method to those evaluated via the displacement correlation technique demonstrate that, the proposed form of the J _k -integral is domain independent and leads to numerical results of high accuracy. Presented parametric analyses illustrate the influences of the fiber volume fraction and the crack location on the modes I and II stress intensity factors, the energy release rate, and the T-stress.     

Parametric Investigation of Viscous Dissipation Effects on Optimized Air Cooling Microchanneled Heat Sinks

The effects of viscous dissipation of working fluid on the optimum heat sink parameters are investigated for the case of air cooling with a micro-/narrow-channeled compact heat sink. For this purpose, an optimization method is introduced first on the basis of dimensionless groups while employing several assumptions. This method yields minimum pumping work or pressure drop with a set of optimized geometric/hydrodynamic parameters when outer dimension of a heat sink and imposed thermal load are specified. Especially for the case of laminar flow, the procedure presents an explicit existence of cooling limit by the viscous heat generation, giving an analytical expression of the maximum removable heat Q max . The relationships between thermal load and each parameter are calculated for both laminar and turbulent regimes under the conditions of compact heat sink dimension (20 mm 2 20 mm 2 2 mm) and circular cross-sectional shape of channels. The results show that the cooling capability under such conditions is largely limited by the salient manifestation of viscous dissipation, when compared with our previous investigation on water cooling presented in [1]. From the discussion, it was concluded that when a micro-/narrow-channeled heat sink is to be designed with air, the effect of viscous dissipation should be taken into account in order to avoid falling on wrong optimum solutions.