We discuss structure-preserving model order reduction for port-Hamiltonian systems based on a nonlinear approximation ansatz which is linear with respect to a part of the state variables of the ...reduced-order model. In recent years, such nonlinear approximation ansatzes have gained more and more attention especially due to their effectiveness in the context of model reduction for transport-dominated systems which are challenging for classical linear model reduction techniques. We demonstrate that port-Hamiltonian reduced-order models can often be obtained by a residual minimization approach where a suitable weighted norm is used for the residual. Moreover, we discuss sufficient conditions for the resulting reduced-order models to be stable. Finally, the methodology is illustrated by means of two transport-dominated numerical test cases, where the ansatz functions are determined based on snapshot data of the full-order state.
The effect of nanoparticle concentration on zeta-potential measurement results at dilute concentrations was evaluated. The values of the zeta-potential for four different types of nanoparticles, ...Ludox （silica）, multi-walled carbon nanotubes （bamboo-shaped and hollow nanotubes） and gold, at various concentrations, were obtained using a laser Doppler electrophoresis instrument. The size of the nanoparticles on dilution was measured using dynamic light scattering （DLS）. The results show that there is a concentration range within which the zeta-potential, and particle size, are not affected by nanoparticle concentration. The lower concentration limit for the system to produce consistent results was dependent on the nature of the sample under study and ranged between 10-2 and 10-4 wt%. Below this concentration, there was an apparent shift in zeta-potential values to less negative values, which was accompanied by an increase in the particle size. The shift in zeta-potential was attributed to an increase in contribution of the signal from extraneous particulate matter. The increase in particle size was attributed to the nature of the homodyne optical configuration of the instrument. The aim of this study was to elucidate the range in nanoparticle concentration that allows for accurate and reliable measurement of the zeta-potential and DLS data.
Waste not wasted: A mechanistic study of the autoxidative coupling of xanthene with cyclopentanone uncovered an autoinductive effect of the waste product hydrogen peroxide. It generates radicals in ...the presence of acid and ketones, which accelerate the reaction by providing an additional pathway to the reactive hydroperoxide intermediate. This discovery could be applied to achieve other Brønsted acid catalyzed oxidative coupling reactions.
N
α-2-thiophenoyl-
d
-phenylalanine-2-morpholinoanilide (MMV688845, IUPAC:
N
-(1-((2-morpholinophenyl)amino)-1-oxo-3-phenylpropan-2-yl)thiophene-2-carboxamide) from the Pathogen Box
®
library ...(Medicines for Malaria Ventures, MMV) is a promising lead compound for antimycobacterial drug development. Two straightforward synthetic routes to the title compound starting from phenylalanine or its Boc-protected derivative are reported. Employing Boc-phenylalanine as starting material and the T3P
®
and PyBOP
®
amide coupling reagents enables racemization-free synthesis, avoiding the need for subsequent separation of the enantiomers. The crystal structure of the racemic counterpart gives insight into the molecular structure and hydrogen bonding interactions in the solid state. The
R
-enantiomer of the title compound (derived from
d
-phenylalanine) exhibits activity against non-pathogenic and pathogenic mycobacterial strains, whereas the
S
-enantiomer is inactive. Neither of the enantiomers and the racemate of the title compound shows cytotoxicity against various mammalian cells.
We propose a new hyper-reduction method for a recently introduced nonlinear model reduction framework based on dynamically transformed basis functions and especially well-suited for ...transport-dominated systems. Furthermore, we discuss applying this new method to a wildland fire model whose dynamics feature traveling combustion waves and local ignition and is thus challenging for classical model reduction schemes based on linear subspaces. The new hyper-reduction framework allows us to construct parameter-dependent reduced-order models (ROMs) with efficient offline/online decomposition. The numerical experiments demonstrate that the ROMs obtained by the novel method outperform those obtained by a classical approach using the proper orthogonal decomposition and the discrete empirical interpolation method in terms of run time and accuracy.
•We survey the assembly line balancing research of the past 15 years.•Progress in all stages of the decision-making process is elaborated.•Important new problems, models, and algorithms are ...surveyed.•Future research needs are identified.
Ever since the times of Henry Ford up to today’s industry 4.0 era, flow-oriented assembly processes, where an assembly line conveys the workpieces from workstation to workstation, are very important for mass-producers in manifold branches of industry. Among the most elementary optimization problems in this context is the assembly line balancing problem, which decides on the division of labor among the stations of an assembly line. This paper surveys the scientific literature on assembly line balancing that has been published since the last major review papers have appeared in 2006 and 2007, respectively. We cover all essential stages of the decision making process: we address novel methods to efficiently gather the relevant (precedence graph) data, review especially new problem variants and models treated in the literature, and survey the most important algorithmic developments. Furthermore, we outline a possible research agenda for the next fifteen years.
The problem of finding a fair assignment of tasks to agents that minimizes the total sum of squared workloads was introduced by Karsu and Azizoglu (2019) as the Minimum Squared Load Assignment ...Problem (MSLAP). To solve this problem, the authors developed a tailored branch-and-bound algorithm. While this algorithm was shown to produce better results than CPLEX on a mixed binary linear programming formulation of the MSLAP, about 71% of the 1200 benchmark instances yet remained unsolved. In this note, we test two state-of-the-art solvers on different mathematical programming formulations of the MSLAP. Our computational results show that the performance of the solvers is heavily dependent on the type of mathematical optimization model. The best results are obtained when the MSLAP is expressed as a quadratically-constrained program. Such a formulation allows one of the solvers to find and verify an optimal solution for every problem in the existing benchmark data sets within just a few seconds per problem, on average. Additional experiments on large-sized instances demonstrate that the solvers’ performances remain at a high level.
•The minimum squared load assignment problem is analyzed.•(Mixed) binary linear and nonlinear mathematical programming formulations are presented.•Comprehensive computer experiments with different solvers are conducted.•Optimal solutions for all 1200 problems in the benchmark data sets of Karsu and Azizoglu are found.•New sets of large-sized test problems are generated.
Progress in microchip enantioseparations Nagl, Stefan; Schulze, Philipp; Ludwig, Martin ...
Electrophoresis,
August 2009, Letnik:
30, Številka:
16
Journal Article
Recenzirano
Advances in microfluidic chips for chiral separations from 2003 to early 2009 are discussed. Microchip-based separation techniques promise higher speed, throughput, portability, less sample and ...reagent consumption, better environmental compatibility, reduced cost and the prospect of system integration. Microchip electrophoresis is the most promising technique for miniaturized enantioseparations and has been performed with a variety of designs and analytes, however, other formats such as microchip electrochromatography are also gaining in popularity. Microchip fabrication, chemistry and detection issues are critically discussed and highlighted. Integration of enantioseparation techniques into multifunctional microchips are currently a rapidly advancing area of research and methods are discussed that may eventually enable enantioseparations to be the part of a holistic chemical microchip.
We present a data-driven realization for systems with delay, which generalizes the Loewner framework. The realization is obtained with low computational cost directly from measured data of the ...transfer function. The internal delay is estimated by solving a least-square optimization over some sample data. Our approach is validated by several examples, which indicate the need for preserving the delay structure in the reduced model.
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