Algorithms for the boundary selection problem

User-oriented clustering schemes enable the classification of documents based upon the user's perception of the similarity between documents, rather than on some similarity function presumed by the designer to represent the user's criteria. In an earlier paper it was shown that such a classification scheme can be developed in two stages. The first stage involves the accumulation of relevance judgements provided by users,vis-à-vis past query instances, into a suitable structure. The second stage consists of cluster identification. When the structure chosen, in the first stage, for the accumulation of corelevance characteristics of documents is a straight line, the second stage can be formulated as a function optimization problem termed the Boundary Selection Problem (BSP). A branch-and-bound algorithm with a good bounding function is developed for the BSP. Although significant pruning is achieved due to the bounding function, the complexity is still high for a problem of a large size. For such a problem a heuristic that divides it into a number of subproblems, each being solved by a branch-and-bound approach, is developed. Then the overall problem is mapped to an integer knapsack problem and solved by the use of dynamic programming. The tradeoff between accuracy and complexity can be controlled, giving the user a preference of one over the other. Assuming that the heuristic which divides the overall problem introduces no errors and is given sufficient time, the branch and bound with dynamic programming (BBDP) approach will converge to the optimal solution. Two other heuristic approaches, one with the application of a polynomial dynamic programming algorithm and the other which works in a greedy way, are also proposed for the BSP and an experimental comparison of all these approaches is provided. Experimental results indicate that all proposed algorithms show better performance compared with the existing algorithm.     

Hydrokinetic energy conversion systems and assessment of horizontal and vertical axis turbines for river and tidal applications: A technology status review

The energy in flowing river streams, tidal currents or other artificial water channels is being considered as viable source of renewable power. Hydrokinetic conversion systems, albeit mostly at its early stage of development, may appear suitable in harnessing energy from such renewable resources. A number of resource quantization and demonstrations have been conducted throughout the world and it is believed that both in-land water resources and offshore ocean energy sector will benefit from this technology. In this paper, starting with a set of basic definitions pertaining to this technology, a review of the existing and upcoming conversion schemes, and their fields of applications are outlined. Based on a comprehensive survey of various hydrokinetic systems reported to date, general trends in system design, duct augmentation, and placement methods are deduced. A detailed assessment of various turbine systems (horizontal and vertical axis), along with their classification and qualitative comparison, is presented. In addition, the progression of technological advancements tracing several decades of R&D efforts are highlighted.     

Development of a potential based code for MHD analysis of LLCB TBM

A two dimensional solver is developed for MHD flows with low magnetic Reynolds’ number based on the electrostatic potential formulation for the Lorentz forces and current densities which will be used to calculate the MHD pressure drop inside the channels of liquid breeder based Test Blanket Modules (TBMs). The flow geometry is assumed to be rectangular and perpendicular to the flow direction, with flow and electrostatic potential variations along the flow direction neglected. A structured, non-uniform, collocated grid is used in the calculation, where the velocity (u), pressure (p) and electrostatic potential (?) are calculated at the cell centers, whereas the current densities are calculated at the cell faces. Special relaxation techniques are employed in calculating the electrostatic potential for ensuring the divergence-free condition for current density. The code is benchmarked over a square channel for various Hartmann numbers up to 25,000 with and without insulation coatings by (i) comparing the pressure drop with the approximate analytical results found in literature and (ii) comparing the pressure drop with the ones obtained in our previous calculations based on the induction formulation for the electromagnetic part. Finally the code is used to determine the MHD pressure drop in case of LLCB TBM. The code gives similar results as obtained by us in our previous calculations based on the induction formulation. However, the convergence is much faster in case of potential based code.     

Effect of filler composition and crosslinker concentration on the tribological behavior of spent germ particle-based polymeric composites

Thermosetting composites have been prepared by the use of a biobased resin and spent germ filler, which is a byproduct from a wet ethanol production plant. Microscale tribological measurements were performed on samples with different concentrations of the filler as well as the crosslinker using a ball-on-flat reciprocating microtribometer. Microscale friction and wear behavior during dry sliding were evaluated using a spherical silicon nitride probe (radius 1.2 mm) and a conical diamond (radius 100 μm, cone angle 90°) probe to impose different contact conditions. Finally, a pin-on-disc tribometer was used to study the macroscale wear properties at high loads against an alumina pin. Scanning electron microscopy (SEM) images of wear tracks on the samples were obtained to elucidate deformation mechanisms. All samples showed evidence of abrasive wear in both micro- and macro-scales. It was found that an increase in the concentration of the filler resulted in higher friction coefficients against Si₃N₄, while an increase in the concentration of the crosslinker lowered the abrasive wear depth. These results provide some insight into the effectiveness of using biobased spent germ–tung oil polymer composites as potential tribomaterials.     

Tulip: A New Hash Based Cooperative Web Caching Architecture

With the exponential growth of WWW traffic, web proxy caching becomes a critical technique for Internet web services. Well-organized proxy caching systems with multiple servers can greatly reduce the user perceived latency and decrease the network bandwidth consumption. Thus, many research papers focused on improving web caching performance with the efficient coordination algorithms among multiple servers. Hash based algorithm is the most widely used server coordination mechanism, however, there's still a lot of technical issues need to be addressed. In this paper, we propose a new hash based web caching architecture, Tulip. Tulip aggregates web objects that are likely to be accessed together into object clusters and uses object clusters as the primary access units. Tulip extends the locality-based algorithm in UCFS to hash based web proxy systems and proposes a simple algorithm to reduce the data grouping overhead. It takes into consideration the access speed dispatch between memory and disk and replaces expensive small disk I/O with less large ones. In case a client request cannot be fulfilled by the server in the memory, the system fetches the whole cluster which contains the required object into memory, the future requests for other objects in the same cluster can be satisfied directly from memory and slow disk I/Os are avoided. It also introduces a simple and efficient data dupllication algorithm, few maintenance work need to be done in case of server join/leave or server failure. Along with the local caching strategy, Tulip achieves better fault tolerance and load balance capability with the minimal cost. Our simulation results show Tulip has better performance than previous approaches.     

Changes in DNA distributions and ploidy of CHO cells as a function of time in culture

Chinese hamster ovary (CHO) cells maintained in continuous culture for 3 to 5 months may undergo subtle changes in drug sensitivity response, growth kinetics, plating efficiencies, et cetera. Our studies done independently in two different laboratories, using flow cytometry, indicate that the DNA histogram patterns change at about 11 wk, from populations with an approximate diploid DNA content to populations also composed of triploid and tetraploid cells. Chromosome counts also change from distributions of 21 to 22 to populations of cells having 21 to 22, 34 to 35 and 44 to 46 chromosomes. These alterations occur earlier (at 8 to 9 wk) in cell populations previously treated with anticancer drugs.     

Performance characterization of multi-thread and multi-core processors based XML application oriented networking systems

There is a growing trend to insert application intelligence into network devices. Processors in this type of Application Oriented Networking (AON) devices are required to handle both packet-level network I/O intensive operations as well as XML message-level CPU intensive operations. In this paper, we investigate the performance effect of symmetric multi-processing (SMP) via (1) hardware multi-threading, (2) uni-processor to dual-processor architectures, and (3) single to dual and quad core processing, on both packet-level and XML message-level traffic. We use AON systems based on Intel Xeon processors with hyperthreading, Pentium M based dual-core processors, and Intel’s dual quad-core Xeon E5335 processors. We analyze and cross-examine the SMP effect from both highlevel performance as well as processor microarchitectural perspectives. The evaluation results will not only provide insight to microprocessor designers, but also help system architects of AON types of device to select the right processors.     

Multiwalled carbon nanotube/montmorillonite hybrid filled ethylene‐co‐vinyl acetate nanocomposites with enhanced mechanical properties,thermal stability,and dielectric response

Homogeneous multiwalled carbon nanotube/montmorillonite hybrid filler (HMM) dispersion was prepared by co‐ultrasonication and was subsequently used to prepare ethylene‐co‐vinyl acetate (EVA) nanocomposites by solution blending method. XRD and TEM analysis of HMM confirm significant interaction between the montmorillonite (MMT) layers and multiwalled carbon nanotubes (MWCNT) in line with previous reports. Analysis of the nanocomposites shows the constituent fillers to be homogeneously dispersed in EVA matrix. Mechanical properties of neat EVA are remarkably improved with HMM content up to 3 wt% followed by reversion. Maximum improvement observed in tensile strength, elongation at break, and toughness are 424%, 109%, and 1122%, respectively. Results show maximum thermal stability at 4 wt% and best dielectric response at 1 wt% HMM content. Exceptional mechanical and dielectric properties of EVA nanocomposites attained may be attributed to homogeneous dispersion of fillers and improved polymer–filler interaction. Comparison shows excellent synergy between MWCNT and MMT towards mechanical reinforcement of EVA. POLYM. ENG. SCI., 58:1155–1165, 2018. © 2017 Society of Plastics Engineers     

Absorbing and scattering properties of boundary layer aerosols over Dibrugarh,Northeast India

The absorbing aerosols, primarily black carbon (BC), play a unique and important role in the Earth’s climate system primarily by warming the atmosphere. This warming effect contrasts with the cooling effect of aerosols such as sulphates that are mostly of the scattering type. With a view to studying the characteristics of both absorbing and scattering aerosols within the boundary layer, collocated measurements using an aethalometer and a nephelometer were carried out over Dibrugarh (27.3° N, 94.6° E, 111 m amsl), Northeast India. The diurnal variation of BC mass concentration (M_BC) shows a primary peak during late evening (2000–2200 local time (LT)) while a weak secondary peak is observed in the morning (0600–0800 LT). A seasonal shift in diurnal peak M_BC was also observed. Both diurnal and seasonal variations in the scattering coefficient (β_sca) resemble that of M_BC. It may, therefore, be inferred that the majority of both absorbing and scattering types of aerosol prevalent over the study location have common production sources. The seasonal spectral variation in absorption coefficient (β_abs) shows monotonic decrease from shorter to longer wavelength in all seasons. The wavelength dependence of absorption by aerosols, as obtained from the absorption Ångström exponent (α_abs), indicates a stronger presence of absorbing aerosols originating from biomass burning than those originating from fossil fuel burning over Dibrugarh. The high values of single-scattering albedo (SSA) obtained over Dibrugarh reveal that the scattering type of aerosol is predominant in the ambient air. SSA, together with M_BCm, is a useful parameter for estimation of radiative forcing and hence the climatic impact of aerosols.