Monotony analysis and sparse-grid integration for nonlinear chance constrained process optimization

The numerical solution of a nonlinear chance constrained optimization problem poses a major challenge. The idea of back-mapping as introduced by M. Wendt, P. Li and G. Wozny in 2002 is a viable approach for transforming chance constraints on output variables (of unknown distribution) into chance constraints on uncertain input variables (of known distribution) based on a monotony relation. Once transformation of chance constraints has been accomplished, the resulting optimization problem can be solved by using a gradient-based algorithm. However, the computation of values and gradients of chance constraints and the objective function involves the evaluation of multi-dimensional integrals, which is computationally very expensive. This study proposes an easy-to-use method for analysing monotonic relations between constrained outputs and uncertain inputs. In addition, sparse-grid integration techniques are used to reduce the computational time decisively. Two examples from process optimization under uncertainty demonstrate the performance of the proposed approach.     

The Influence of Potassium Clavulanate on the Rate of Amoxicillin Sodium Degradation in Phosphate and Acetate Buffers in the Liquid State

The stability of aqueous admixtures of amoxicillin sodium and potassium clavulanate was studied in the liquid state at selected pH values. Potassium clavulanate was found to catalyze the rate of degradation of amoxicillin sodium under the conditions of this study. In phosphate buffer (at pH 7.0) both amoxicillin sodium and potassium clavulanate showed first-order degradation when stored separately. However, when combined the rate of amoxicillin degradation increased and t₉₀ values for amoxicillin decreased from 69.6 min for amoxicillin alone to 10.8 min for amoxicillin in the combination at 55°C. A kinetic model was developed that explained the catalytic behavior of potassium clavulanate and phosphate buffer. In acetate buffer the rate of degradation of amoxicillin sodium followed first-order kinetics, but the catalytic effect of clavulanate caused curvature in the rate plots at higher temperatures and clavulanate concentrations. This catalytic effect was less than that occurred in phosphate buffer (where the t₉₀ value of amoxicillin decreased from 137.3 min for amoxicillin alone to 52.5 min for amoxicillin in combination at 55°C). First-order bi-exponential decay occurred with amoxicillin degradation, which explained this change in rate.     

Quantification of seismic performance factors for self‐centering controlled rocking special concentrically braced frame

Modern self‐centering controlled rocking special concentrically braced frame (SC‐CR SCBF) is capable of reducing structural damage compared with conventional buildings following an earthquake. This investigation quantifies three seismic performance factors, including over‐strength factor (Ω₀), period‐based ductility (μ_T) and response modification coefficient (R), for low‐ and mid‐rise SC‐CR SCBFs. Nonlinear static analysis is conducted to derive Ω₀ and μ_T factors for 12 SC‐CR archetypes. Validity of trial R coefficient is also evaluated using a collapse‐based assessment procedure by comparing adjusted collapse margin ratios with the established acceptance criteria. Results indicate that the Ω₀ and μ_T factors are in the range of 1.39 to 2.29 and 12.25 to 29.0, respectively, and R of 8 is proposed for design of SC‐CR archetypes. A reliability study is also performed to examine the effects of modeling and ground motion parameters on the safety margin of designed SC‐CR archetypes with the proposed R value. Results indicate that the design of mid‐rise space archetypes in high‐seismicity regions with the R coefficient of 8 is more reliable than that of the low‐rise perimeter ones in low‐seismicity regions. Copyright © 2016 John Wiley & Sons, Ltd.     

Crystallization of indium tin oxide nanoparticles: from cooperative behavior to individuality

The crystallization pathway of indium tin oxide nanoparticles during solvothermal synthesis in benzyl alcohol was investigated. The synthesis was stopped after different reaction times in the range of 1-24 h, and the structural and morphological characteristics of the products were analyzed by powder X-ray diffraction, electron microscopy, and UV/Vis spectroscopy. Interestingly, the crystallization mechanism does not proceed along a simple nucleation and growth pathway, but involves a two-step process. In the first 12 h an intermediate phase is formed, which consists of nanocrystallites 3-6 nm in size stabilized by an organic matrix. In this organic-inorganic network the nanoparticles are aligned into superstructures, but without any crystallographic orientation. After 12 h the intermediate phase is abruptly transformed into indium tin oxide nanoparticles with the bixbyite structure and with crystallite sizes of about 10-12 nm. This step is accompanied by the disappearance of the organic phase and the loss of the superstructure.     

Investigation of Proposed Concrete Filled Steel Tube Connections under Reversed Cyclic Loading

Concrete-filled steel tube (CFT) columns are used in the primary lateral resistance systems. The objective of this research is to analyse the behavior of the steel beam to CFT column connections. A three-dimensional numerical model for simulating the behavior of CFT connections was developed with the aid of the general purpose nonlinear finite element analysis package ABAQUS. In this paper, 90 CFT connection specimens include simple and moment connections that were tested under reversed cyclic loading. Shear capacity of joint, moment-drift response, energy absorption, and displacement ductility were studied in those models. The results have indicated that, the hysteresis curve of CFT columns was plump; no pinch phenomenon can be found; the damage and degradation degree of the strength and stiffness of specimens is lower; and high energy dissipation capacity can be achieved. Improvement in the behavior of CFT connection depends on the beam characteristics and column features.     

Colloidal-quantum-dot photovoltaics using atomic-ligand passivation

Colloidal-quantum-dot (CQD) optoelectronics offer a compelling combination of solution processing and spectral tunability through quantum size effects. So far, CQD solar cells have relied on the use of organic ligands to passivate the surface of the semiconductor nanoparticles. Although inorganic metal chalcogenide ligands have led to record electronic transport parameters in CQD films, no photovoltaic device has been reported based on such compounds. Here we establish an atomic ligand strategy that makes use of monovalent halide anions to enhance electronic transport and successfully passivate surface defects in PbS CQD films. Both time-resolved infrared spectroscopy and transient device characterization indicate that the scheme leads to a shallower trap state distribution than the best organic ligands. Solar cells fabricated following this strategy show up to 6% solar AM1.5G power-conversion efficiency. The CQD films are deposited at room temperature and under ambient atmosphere, rendering the process amenable to low-cost, roll-by-roll fabrication.     

Directed placement of gold nanorods using a removable template for guided assembly

We have used a temperature sensitive polymer film as a removable template to position, and align, gold nanorods onto an underlying target substrate. Shape-matching guiding structures for the assembly of nanorods of size 80 nm × 25 nm have been written by thermal scanning probe lithography. The nanorods were assembled into the guiding structures, which determine both the position and the orientation of single nanorods, by means of capillary interactions. Following particle assembly, the polymer was removed cleanly by thermal decomposition and the nanorods are transferred to the underlying substrate. We have thus demonstrated both the placement and orientation of nanorods with an overall positioning accuracy of ≈10 nm onto an unstructured target substrate.     

Patterned polymer carpets

For the development of polymer carpets as active devices for micro- and nanotechnology, a control of the polymer carpet morphology and especially control of the stimulus responsive polymer brush is needed. Here, we report on the first example for the fabrication of patterned polymer carpets. On a two-dimensional framework of fully crosslinked and chemically patterned nanosheets, polymer brushes of styrene and 4-vinyl pyridine were grafted by self-initiated surface photopolymerization and photografting (SIPGP). It was found that polymer grafting by SIPGP occurred over the entire nanosheets but with a preferred grafting on the amino functionalized nanosheet areas. This results in continuous polymer carpets with an intact nanosheet framework but with amplification of the chemical patterning into a three dimensional topography of the grafted polymer brush. In the case of negative patterned nanosheets, the patterned carpet could be prepared as freestanding ultrathin membranes. Furthermore, swelling experiments with poly(4-vinyl pyridine) carpets showed that the patterns induces a directional buckling of the flexible polymer carpet. This may open the possibility of the development of micro- or nanoactuator devices with anisotropic responds upon environmental changes.     

Small-angle X-ray scattering experiments and computer simulations to characterise anisotropy of activated carbons prepared from wood

Small-angle scattering was measured from activated carbon monoliths prepared from three different wood species (European beech, Pedunculate oak and Norwegian spruce). Substantial differences were found in the scattering images of axial and tangential slices, attributed to their characteristic phytogenic structures. The decrease in anisotropy in the nanostructured carbon matrix due to the activation process is also different among the three investigated types of wood. For quantitative characterization of the anisotropy and its decrease, the degree of alignment was calculated from the azimuthal scattering curves. A simple numeric model was constructed on the basis of direct information obtained by atomic force microscopy. Scattering patterns calculated from the model were compared with the experimental ones to explain the possible structural changes in the carbon skeleton.