Top-down kinetic modeling from power law to elementary steps using KASTER: A methane steam reforming case study

A top-down methodology for kinetic model construction including regression against experimental data is proposed using “KASTER.” As a case study, it is applied in the assessment of methane steam reforming (MSR) including water–gas shift (WGS) on a Ni catalyst at 923 K. The degree of detail in the reaction mechanism and the corresponding model is gradually enhanced, typically ranging from a simple power law to a microkinetic model. The reactor equations are solved transiently, preventing the numerical challenges encountered in the steady-state solution, particularly for microkinetic models. The microkinetic variant indicated that CH₄ dissociative adsorption and CO formation are kinetically relevant steps in MSR, while COOH formation is rate-determining in WGS. However, the model providing the best balance between detail accounted for and parameter significance corresponded to a Langmuir–Hinshelwood–Hougen–Watson (LHHW) mechanism accounting for dissociative adsorption, with CO formation and COOH formation as rate-determining steps for MSR and WGS, respectively.     

A coupling algorithm for partitioned solvers applied to bubble and droplet dynamics

Bubbles and droplets both consist of a liquid in contact with a gas. In this paper, we consider the interface between the incompressible liquid and the gas as a zero thickness structure. The position of the interface is determined by the equilibrium between surface tension effects and the fluid pressure difference across the interface. So, the structure interacts with the fluids on either side. The behaviour of a limited number of bubbles and droplets can therefore be simulated as a Fluid-Structure Interaction (FSI) problem.Most existing techniques frequently used for studying bubble and droplet dynamics, such as Level Set or Volume Of Fluid, use monolithic schemes. The flow on both sides of the interface and the position of the interface are calculated in a single code. In this contribution, a partitioned approach is presented. The position of the interface is calculated with a structural solver. Given a displacement of the interface, a separate flow solver calculates the flow on the liquid side of the interface with the Arbitrary Lagrangian-Eulerian (ALE) technique. The structural solver uses a reduced order model of the flow solver to obtain implicit coupling between both solvers. This reduced order model is built up during the coupling iterations of a time step. Grid and time converged solutions of two axisymmetric problems are calculated: an oscillating water droplet in air and the growth and detachment of an air bubble from the outlet of a vertical needle, submerged in quiescent water.     

Visualization of a lost painting by Vincent van Gogh using synchrotron radiation based X-ray fluorescence elemental mapping

Vincent van Gogh (1853-1890), one of the founding fathers of modern painting, is best known for his vivid colors, his vibrant painting style, and his short but highly productive career. His productivity is even higher than generally realized, as many of his known paintings cover a previous composition. This is thought to be the case in one-third of his early period paintings. Van Gogh would often reuse the canvas of an abandoned painting and paint a new or modified composition on top. These hidden paintings offer a unique and intimate insight into the genesis of his works. Yet, current museum-based imaging tools are unable to properly visualize many of these hidden images. We present the first-time use of synchrotron radiation based X-ray fluorescence mapping, applied to visualize a woman's head hidden under the work Patch of Grass by Van Gogh. We recorded decimeter-scale, X-ray fluorescence intensity maps, reflecting the distribution of specific elements in the paint layers. In doing so we succeeded in visualizing the hidden face with unprecedented detail. In particular, the distribution of Hg and Sb in the red and light tones, respectively, enabled an approximate color reconstruction of the flesh tones. This reconstruction proved to be the missing link for the comparison of the hidden face with Van Gogh's known paintings. Our approach literally opens up new vistas in the nondestructive study of hidden paint layers, which applies to the oeuvre of Van Gogh in particular and to old master paintings in general.     

Contact-State Segmentation Using Particle Filters for Programming by Human Demonstration in Compliant-Motion Tasks

This paper presents a contribution to programming by human demonstration, in the context of compliant-motion task specification for sensor-controlled robot systems that physically interact with the environment. One wants to learn about the geometric parameters of the task and segment the total motion executed by the human into subtasks for the robot, that can each be executed with simple compliant-motion task specifications. The motion of the human demonstration tool is sensed with a 3-D camera, and the interaction with the environment is sensed with a force sensor in the human demonstration tool. Both measurements are uncertain, and do not give direct information about the geometric parameters of the contacting surfaces, or about the contact formations (CFs) encountered during the human demonstration. The paper uses a Bayesian sequential Monte Carlo method (also known as a particle filter) to do the simultaneous estimation of the CF (discrete information) and the geometric parameters (continuous information). The simultaneous CF segmentation and the geometric parameter estimation are helped by the availability of a contact state graph of all possible CFs. The presented approach applies to all compliant-motion tasks involving polyhedral objects with a known geometry, where the uncertain geometric parameters are the poses of the objects. This work improves the state of the art by scaling the contact estimation to all possible contacts, by presenting a prediction step based on the topological information of a contact state graph, and by presenting efficient algorithms that allow the estimation to operate in real time. In real-world experiments, it is shown that the approach is able to discriminate in real time between some 250 different CFs in the graph     

Alkylcarbenium Ion Concentrations in Zeolite Pores During Octane Hydrocracking on Pt/H-USY Zeolite

Hydroconversion of octane over platinum loaded acid zeolites was simulated using a single-event microkinetic model. Significantly different values for the alkene standard protonation enthalpies, i.e., ?59.2 and –94 kJ mol^?1 for the charging of secondary and tertiary carbon atoms respectively, were obtained. This difference is in favor of a carbocationic nature of the reactive intermediates on the acid sites rather than surface alkoxides. The concentration of alkylcarbenium ions on a Pt/H-USY catalyst resulting from protonation of alkenes in n-octane hydrocracking was calculated. It was strongly dependent on pressure and temperature. At a reaction temperature of 506 K, a total pressure of 0.45 MPa and H₂/HC molar ratio of 13.13, the concentration of alkylcarbenium ions corresponds to 15% of the total acid site concentration. At higher total pressures this percentage is lower and can be assumed to be negligible. The presence of a finite alkylcarbenium ion concentration in the zeolite pores results in a reduction of the free space available for physisorption of alkanes. Refined kinetic models are obtained when including this effect. Depending on the nature of the zeolite, alkylcarbenium ion concentrations can be significantly different owing to differences in alkane physisorption and alkene protonation. Literature data were rationalized using the refined kinetic model.     

Integrated instrumental chain for magnetic pulse measurement in strong static field environment

This paper describes an integrated analogue instrumental chain dedicated to measuring magnetic pulses with an amplitude of a few tens or hundreds of microteslas, superimposed to a strong static magnetic field, i.e. 1.5 T. The system features a silicon Hall sensor with nested-chopping-like biasing circuitry, DC Hall voltage compensation, amplifying and multistage filtering. Low-noise performances are achieved by applying 100 kHz spinning current to the Hall device and chopping at 200 kHz to the signal conditioning blocs downstream. The microsystem achieves 20 μT resolution over a 1.6 kHz bandwidth extending from 5 Hz to 1.6 kHz under 1.5 T static field.     

Detection and Localization of Delaminations in Thin Carbon Fiber Reinforced Composites with the Ultrasonic Polar Scan

In this paper, the hybrid compliance-stiffness matrix method for simulating wave propagation in (delaminated) multilayered media with viscoelastic anisotropy has been confronted with high-quality amplitude and phase experiments on delaminated composites, obtained using the ultrasonic polar scan setup (UPS) in transmission by considering harmonic as well as pulsed ultrasound. Results are presented for multiple thin carbon/epoxy laminates with an artificial edge delamination induced by a foil insert, showing a good agreement between experimental recording and numerical modeling. The obtained results further reveal the feasibility of the harmonic UPS to detect and even locate the depth-position of multiple delaminations in fiber reinforced composites. Considering that the harmonic UPS method does not rely on the detection of different echoes like the classical C-scan, but rather expounds the conditions for efficient stimulation of guided waves in the solid, the method is found to be highly suited for inspecting thin composite materials for the presence of delaminations.     

Sources of Inter-Firm Heterogeneity in Accessing Knowledge-Creation Benefits Within Technology Clusters

We build on recent literature to highlight the distinction between knowledge-diffusion and knowledge-creation benefits of technology clustering and argue that firms located in technology clusters will have differential access to the latter. To explain the antecedents of such differential access, we first argue that clustering gives rise to three knowledge-creation benefits: easier identification of potential knowledge partners with complementary knowledge, easier initiation of knowledge partnerships and increased effectiveness of knowledge partnerships. Subsequently, we develop a conceptual model and propositions that focus on a cluster firm's awareness of knowledge assets inside the cluster, attractiveness as a knowledge partner and ability to benefit from knowledge partnerships to explain differential access by firms to these three knowledge-creation benefits that clustering provides. This study highlights the theoretical significance of distinguishing externality-type benefits of technology clustering from benefits that firms need to actively pursue, and discusses implications for firms' location decisions.     

Ultrastrong Anchoring Yet Barrier‐Free Adsorption of Composite Microgels at Liquid Interfaces

Microgel particles display an interesting duality with properties attributed typically both to polymeric and colloidal systems. When adsorbed at a liquid‐liquid interface, this duality becomes particularly apparent as the various phenomena at play are governed by different aspects of these soft and responsive particles. The introduction of a solid, fluorescently labeled, polystyrene core into the microgels allows direct and accurate visualization without the necessity of potential perturbing sample preparation techniques. By combining in‐situ imaging and tensiometry, we determine that composite microgels at a wide variety of oil‐water interfaces anchor strongly, with adsorption energies of approximately 10⁶ k_BT, typical for particle adsorption, yet accumulate at the interface spontaneously without any energy barrier, which is more typical for polymers. The high adsorption energies allow the particle to spontaneously form very dense crystalline packings at the liquid interface in which the microgels are significantly compressed with respect to their swollen state in bulk solutions. Finally, we demonstrate the unique nature of these particles by producing highly stable and monodisperse microgel‐stabilized droplets using microfluidics.     

Physical Metallurgy of Multi‐Phase Steel for Improved Passenger Car Crash‐Worthiness

The dynamic testing of high strength automotive steel grades is of great practical importance if their crash‐worthiness is to be evaluated. During forming operations, steels are processed in a controlled dynamic manner. In collisions, the deformation is different in the sense that the deformation is not controlled, i.e. both strain and strain rate are not pre‐determined. No clear standard testing procedures are currently available to test high strength steels dynamically, in order to evaluate their performance during car crashes. High tensile strength TRIP‐aided steels have been developed by the steel industry because of their promising high strain rate performance. The present contribution focuses on the effect of the strain rate and temperature on the mechanical behaviour of the low alloy high strength TRIP steel. The tests were carried out on the separated phases in order to determine their specific high strain rate deformation response. The temperature‐dependence of the transformation rate of the retained austenite is presented. It is argued that the adiabatic conditions present during high strain rate deformations have a beneficial effect on the behaviour of TRIP steel.