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ITERATIVE SOLUTION OF SPATIAL NETWORK MODELS BY SUBSPACE DECOMPOSITION
No full text. We present and analyze a preconditioned conjugate gradient method (PCG) for solving spatial network problems. Primarily, we consider diffusion and structural mechanics simulations for fiber based materials, but the methodology can be applied to a wide range of models, fulfilling a set of abstract assumptions. The proposed method builds on a classical subspace decomposition into a coarse subspace, realized as the restriction of a finite element space to the nodes of the spatial network, and localized subspaces with support on mesh stars. The main contribution of this work is the convergence analysis of the proposed method. The analysis translates results from finite element theory, including interpolation bounds, to the spatial network setting. A convergence rate of the PCG algorithm, only depending on global bounds of the operator and homogeneity, connectivity and locality constants of the network, is established. The theoretical results are confirmed by several numerical experiments
Policies for scaling up technology-based firms
No full textThis study focuses on the scale up issue, which is crucial for numerous countries. The reason for policies in firms that want and have the opportunity to scale up their business is that these firms have a large potential to create job opportunities and economic development compared to investment in startups without any growth ambitions. The overall objective is therefore to study policies to facilitate technology-based firms\u27 scaling up. As a consequence of earlier research on high-growth firms, little attention has been paid to surviving and stable firms that may want to scale up. This study design comprises three main empirical areas: financial support, framwork conditions and innovation systems. The first contribution of this study is that it is an empirical description of policies at the country level to support technology-based firms. According to the literature, focusing on a specific industry is unnecessary because high-growth firms are in all industries. Another result is that scaling up firms can be identified by internal drivers, which is difficult for policymakers to identify. However, it is expedient to target specific technology-industry sectors and analyse and evaluate them. Innovation and entrepreneurial ecosystems, which are important for technology-based firms’ sustainability and growth, is often cut across different industries and there may be support for different types of firms (high-growth and surviving/stable firms and different industrial sectors). Researchers have reached a consensus that high growers contribute to the society; however, few empirical examples express the significant effects of high-growth firms on a macroeconomic level. Taxation, labour laws, and other regulations are essential; however, researchers do not agree how this should be implemented. \ua0Although policies aim to increase the proportion of high-growth firms, research literature indicates uncertainty about whether these firms contribute to overall industrial and economic growth. The difficulties primarily stem from the challenge of predicting the firms that will grow, the ambiguity surrounding what constitutes high growth, and the complex relationships between firm capabilities, growth, and macroeconomic benefits. One issue is that some high-growth innovative firms are "one-hit wonders," making it challenging for decision-makers to formulate appropriate policies for sustainable and long-term economic development. Some researchers argue that because of the significant role that high-growth innovative firms play, entrepreneurial policies should focus on firms with the highest growth potential. Others contend that it might be economically advantageous to support groups of firms that grow slowly or not at all. Several main conclusions can be drawn from this study and several opportunities for future improvements are identified. The study develops a conceptual model for evaluation of policies to promote technology-based firms. The model consists of three dimensions: perspectives/actors, analysis, and evaluation. The results in this study provide insights into (i) how policymakers can better examine crucial links between the scaleup populations and demand side policies and (ii) how policymakers can better comprehend the linkages between the three dimensions to evaluate policies
High-Temperature corrosion of P91/T91, 304L, Sanicro 28 and Inconel 625 exposed at 600 \ub0C under continuous KCl deposition
Full text linkThis study investigates the corrosion attack after breakaway oxidation on four commercial alloys (T91/P91, 304L, Sanicro 28 and Inconel 625) in the presence of KCl(g)/KCl(s) at 600 \ub0C. The study suggests that an increase in corrosion resistant alloying elements (mainly nickel and chromium) results in the decrease of the thickness of the general oxide scale and not equally deep alloy grain boundary attack for the austenitic alloys. The corrosion attack in the presence of KCl is suggested to proceed by chromate formation and chlorine-induced acceleration of the diffusion of ions through the scale
On some double Nahm sums of Zagier
No full textZagier provided eleven conjectural rank two examples for Nahm\u27s problem. All of them have been proved in the literature except for the fifth example, and there is no q-series proof for the tenth example. We prove that the fifth and the tenth examples are in fact equivalent. Then we give a q-series proof for the fifth example, which confirms a recent conjecture of Wang. This also serves as the first q-series proof for the tenth example, whose explicit form was conjectured by Vlasenko and Zwegers in 2011 and whose modularity was proved by Cherednik and Feigin in 2013 via nilpotent double affine Hecke algebras
Enablers toward 6G positioning and sensing
No full textThis chapter provides the reader with an overview of three major trends toward 6G, namely integrated sensing and communication, the ability to control radio wave propagation in the environment thanks to reconfigurable intelligent surfaces, and advances in model-based and model-free signal processing. This list of trends is by no means exhaustive, but only aims to highlight the tremendous potential for research and innovation toward 6G positioning
The Traffic Reaction Model: A kinetic compartmental approach to road traffic modeling
No full textIn this work, a family of finite volume discretization schemes for LWR-type first order traffic flow models (with possible on- and off-ramps) is proposed: the Traffic Reaction Model (TRM). These schemes yield systems of ODEs that are formally equivalent to the kinetic systems used to model chemical reaction networks. An in-depth numerical analysis of the TRM is performed. On the one hand, the analytical properties of the scheme (nonnegative, conservative, capacitypreserving, monotone) and its relation to more traditional schemes for traffic flow models (Godunov, CTM) are presented. Finally, the link between the TRM and kinetic systems is exploited to offer a novel compartmental interpretation of traffic models. In particular, kinetic theory is used to derive dynamical properties (namely persistence and Lyapunov stability) of the TRM for a specific road configuration. Two extensions of the proposed model, to networks and changing driving conditions, are also described
Effects of predeformation on torsional fatigue in R260 rail steel
Full text linkRolling contact loading induces severe plastic deformations and initiates cracks near the rail surface. Prevention of such rolling contact fatigue cracks requires a better understanding about the mechanical behavior of the deformed material in this region. Even so, current rail standards do not consider the plasticity-induced changes to mechanical behavior. They only evaluate the mechanical performance of virgin rail steels under uniaxial loading conditions, which is not representative for the material\u27s performance after years of service. This study proposes a new method for fatigue life evaluation of deformed material under loading conditions similar to rolling contact loading. Both virgin and predeformed test bars with a circumferential notch were subjected to strain-controlled torsional fatigue loading to evaluate the influence of axial loading, predeformation, and torsional loading direction. Superimposed compressive axial loads increase the fatigue life without affecting the torque response. The predeformed test bars exhibited longer lives, an effect we attribute to the combination of different torque responses, hardening, and anisotropy
Impact of powder properties on deoxidation and densification of carbon steels during powder bed fusion – Laser beam
Full text linkThis work examined the influence of powder properties on deoxidation and densification of carbon steels during powder bed fusion-laser beam (PBF-LB) at compositions between 0.06 and 1.1 wt% C. Analysis revealed that deoxidation was greatest in alloys with high carbon content, reaching losses of up to 440–600 ppm at compositions of 0.75 and 1.1 wt% C. This behavior was not due to enhanced oxygen removal by spatter, as spatter in high carbon alloys had less oxygen pickup (∼4% vs. ∼27%) and formed smaller oxide layers (∼42 nm vs. ∼82 nm). Instead, it was due to the high oxygen affinity of carbon at elevated temperature, which resulted in formation of gaseous carbon oxides that were subsequently removed by the process atmosphere. Regarding densification, powders with high avalanche energy (>7.75 mJ/kg), break energy (>4.75 mJ/kg), and particle size distribution (D10 > 25 μm) were more likely to form lack of fusion porosity at low energy input
Fluorescence Microscopy of Nanochannel-Confined DNA
Full text linkStretching of DNA in nanoscale confinement allows for several important studies. The genetic contents of the DNA can be visualized on the single DNA molecule level, and the polymer physics of confined DNA and also DNA/protein and other DNA/DNA-binding molecule interactions can be explored. This chapter describes the basic steps to fabricate the nanostructures, perform the experiments, and analyze the data
Transition from turbulence-dominated to instability-dominated combustion regime in lean hydrogen-air flames
No full textTo explore the importance of thermodiffusive and hydrodynamic instabilities of laminar flames in turbulent flows, previously generated direct numerical simulations of statistically one-dimensional complex-chemistry lean hydrogen-air flames in forced turbulence were continued by switching-off turbulence forcing. Three sets of flames characterized by different ratios of initial root-mean-square velocity to laminar flame speed, i.e., (A) u′/SL=2.2, (B) u′/SL=4.0, and (C) u′/SL=8.3, were addressed. Moreover, new complementary simulations of unstable laminar flames were performed. Analyses from the obtained numerical results indicate (but do not prove) that laminar flame instabilities play a minor role at sufficiently high Karlovitz numbers Ka. This supposition is supported, first, in cases B and C, where the initial value of turbulent burning velocity UT is significantly higher than burning velocity evaluated during non-linear stage of laminar flame instability development in the same computational domain. Second, regular large-scale perturbations of instantaneous flame surface are prominent in the unstable laminar flame but are not observed at high Ka. Third, Karlovitz numbers associated with appearance of such perturbations as the turbulence decays are scattered between 4 and 10 and are consistent within an order of magnitude to a recently proposed criterion (Chomiak and Lipatnikov, Phys. Rev. E 107: 015102, 2023) of importance for laminar flame instabilities in turbulent flows. Fourth, at such transition instants, a ratio of potential and solenoidal turbulent kinetic energies, averaged over the flame-brush leading edge, is close to 2.0 in 11 studied cases and a ratio of UT/SL varies between 3.0 and 3.5. Fifth, the maximum fuel consumption rate (over the computational domain) decreases as the turbulence decays. Thus, the initial maximum rates are significantly higher than the counterpart rate in the unstable laminar flame. Together these results show that the hypothesis that laminar flame instabilities play only a minor role at high Ka deserves further study