Pareto navigator for interactive nonlinear multiobjective optimization

We describe a new interactive learning-oriented method called Pareto navigator for nonlinear multiobjective optimization. In the method, first a polyhedral approximation of the Pareto optimal set is formed in the objective function space using a relatively small set of Pareto optimal solutions representing the Pareto optimal set. Then the decision maker can navigate around the polyhedral approximation and direct the search for promising regions where the most preferred solution could be located. In this way, the decision maker can learn about the interdependencies between the conflicting objectives and possibly adjust one’s preferences. Once an interesting region has been identified, the polyhedral approximation can be made more accurate in that region or the decision maker can ask for the closest counterpart in the actual Pareto optimal set. If desired, (s)he can continue with another interactive method from the solution obtained. Pareto navigator can be seen as a nonlinear extension of the linear Pareto race method. After the representative set of Pareto optimal solutions has been generated, Pareto navigator is computationally efficient because the computations are performed in the polyhedral approximation and for that reason function evaluations of the actual objective functions are not needed. Thus, the method is well suited especially for problems with computationally costly functions. Furthermore, thanks to the visualization technique used, the method is applicable also for problems with three or more objective functions, and in fact it is best suited for such problems. After introducing the method in more detail, we illustrate it and the underlying ideas with an example.     

Influence of pulp bleaching and compatibilizer selection on performance of pulp fiber reinforced PLA biocomposites

This article focuses on the effect of pulp bleaching and emerging commercial compatibilizers on physical performance of pulp fiber reinforced poly(lactic acid) (PLA) biocomposites. Industrially bleached and unbleached hardwood kraft pulp fibers are treated with several additive types, and compounded with PLA to fiber content of 30 wt %. After injection molding, the produced biocomposites are evaluated by their mechanical performance and fiber–matrix adhesion. For selected materials, fiber surface and fiber properties are reflected to composite performance by analyzing the compositions, dimensions, and lignin coverage of original fibers, as well as fiber dispersion and dimensions after melt processing. As a conclusion, unbleached kraft pulp fibers provide significant improvement in physical properties of PLA/pulp fiber composites. Of the screened compatibilizers, epoxidated linseed oil has a clear positive effect on performance when bleached kraft pulp fibers are used. The improvements correspond to enhanced fiber–matrix adhesion and differences in remaining fiber length distributions. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47955.     

Comparing double-step and penalty-based semirecursive formulations for hydraulically actuated multibody systems in a monolithic approach

The simulation of mechanical systems often requires modeling of systems of other physical nature, such as hydraulics. In such systems, the numerical stiffness introduced by the hydraulics can become a significant aspect to consider in the modeling, as it can negatively effect to the computational efficiency. The hydraulic system can be described by using the lumped fluid theory. In this approach, a pressure can be integrated from a differential equation in which effective bulk modulus is divided by a volume size. This representation can lead to numerical stiffness as a consequence of which time integration of a hydraulically driven system becomes cumbersome. In this regard, the used multibody formulation plays an important role, as there are many different procedures for the constraint enforcement and different sets of coordinates to choose from. This paper introduces the double-step semirecursive approach and compares it with a penalty-based semirecursive approach in case of coupled multibody and hydraulic dynamics within the monolithic framework. To this end, hydraulically actuated four-bar and quick-return mechanisms are analyzed as case studies. The two approaches are compared in terms of the work cycle, energy balance, constraint violation, and numerical efficiency of the mechanisms. It is concluded that the penalty-based semirecursive approach has a number of advantages compared with the double-step semirecursive approach, which is in accordance with the literature.

     

Spatial and temporal variations in water temperature in a high-altitude deep dimictic mountain lake (Nam Co), central Tibetan Plateau

Water temperature and the related thermal structure and stratification of a lake are very important to lake ecosystems because of their significant effects on the vertical exchanges of dissolved and particulate matter. In this study, we present high resolution, seasonal variations in water temperature at different depths of a large deep lake on the central Tibetan Plateau. The results show that Nam Co is a typical dimictic lake whose thermal stratification begins and ends in early June and early November, respectively. Increases in the water temperature during spring and the establishment of thermal stratification in the eastern small sub-basin occur approximately one month prior to the main basin which is likely caused by the different morphometry, different water transparency during spring, and the possible presence of a spring thermal bar. The Schmidt stability of the water column is directly controlled by surface water temperature. During the ice-covered period, the homogeneous water temperature exhibits a continuous increasing trend from approximately 0.5 °C to 3.5 °C. The daily mean surface water temperature of the main open lake area is highly correlated to the air temperature but shows a hysteresis effect of approximately 38 days, which shows the significant heat storage in such a large deep lake. Nam Co is a typical lake in this area in terms of its altitude, water depth and climatic conditions, so our results have broader significance for limnological and paleolimnological studies of similar lakes on the Tibetan Plateau.     

Robust estimation of bioaffinity assay fluorescence signals.

In this paper, the challenging problem of robust mean-signal estimation of a single-step microparticle bioaffinity assay is investigated. For this purpose, a density estimation-based robust algorithm (DER) was developed. The DER algorithm was comparatively evaluated with four other parameter estimation methods (mean value, median filtering, least square estimation, Welsch robust m-estimator). Two important questions were raised and investigated: 1) Which of the five methods can robustly estimate the mean bioaffinity signal? and 2) How many microparticles need to be measured in order to obtain an accurate estimate of the mean signal value? To answer the questions, bootstrap and coefficient of variation (CV) analyses were performed. In the CV analysis, the DER algorithm gave the best results: The CV ranged from 0.8% to 4.9% when the number of microparticles used for the mean signal estimation varied from 800 to 30. In the bootstrap analysis of the standard error, the DER algorithm had the smallest variance. As a conclusion, it can be underlined that: 1) of all methods tested, the DER algorithm gave the most consistent and reproducible results according to the bootstrap and CV analysis; 2) using the DER algorithm accurate estimates could be calculated based on 80-100 particles, corresponding to a typical assay measurement time of 1 min; and 3) the investigated bioaffinity signals contained a large number of outliers (observations that severely deviate from the majority of data) and therefore robust techniques were necessary for the mean signal estimation tasks.     

The Helsinki Office Environment Study: Air Change in Mechanically Ventilated Buildings

Abstract The objective of this study was to assess the magnitude and balance of mechanical ventilation in the rooms of Helsinki metropolitan office buildings with different types of ventilation systems. A random sample of 50 office buildings was selected from the Building Registry. Of these buildings, the 33 that have a mechanical ventilation system were included in this study. Most office buildings in the Helsinki metropolitan area have a ducted supply and exhaust system and hot water radiator heating. Air recirculation is used in about half of the buildings which have a mechanical supply and exhaust system. The average exhaust airflow was 1.2 L/s, m² (SD 0.73) or 17.2 L/s per person (SD 11.6). The variation of the airflows was found to be very high among the buildings, and among the rooms within the buildings. Therefore, even though the ventilation rates on average comply with the Finnish building code, it was found that many people were working in offices with airflows which were either too low or unnecessarily high.     

REPLICA MBTAC: multithreaded dual-mode processor

Prevailing trend in design of chip multiprocessors (CMP) has been that single-core processors are replicated. Therefore, they typically define asynchronous computational model, require heavily locality-aware memory allocation, and present high overheads in intercommunication. This kind of properties make parallel programming very challenging and prone to errors. We introduce our new dual-mode MultiBunched/Threaded Architecture with Chaining (MBTAC) processor core, the main building block of the REPLICA CMP. It provides a modern, sophisticated way for writing general purpose parallel programs backed up by native execution capabilities/realization of key concepts. These include support for cost-efficient machine instruction-level synchronization and uniform shared global memory for enabling easy-to-program memory allocation of data structures and data movement. MBTAC makes use of low-overhead thread-context switching solution; it has parallel computing savvy functional unit organization to exploit inter-thread instruction-level parallelism and highly efficient multioperations. To evaluate the goodness of our proposal, we implemented three MBTAC constellations featuring up to 2048 parallel threads on FPGA, compared it with respect to DLX and Intel’s Core i7 processors. The results point toward high performance in communication-intensive problems, simplified parallel programmability, and regular, implementation-friendly structure.     

Performance and programmability comparison of the thick control flow architecture and current multicore processors

The Journal of Supercomputing - Commercial multicore central processing units (CPU) integrate a number of processor cores on a single chip to support parallel execution of computational tasks....