1,451 research outputs found
S.R. Lewis letter to Z. Eastman, March 5, 1874
No full textBrief letter from S.R. Lewis to Z. Eastman, marking the announcement of an abolitionists' reunion to be held in Chicago in June of 1875. Lewis requests that Eastman, given his close acquaintance with Benjamin Lundy, prepare a public statement of remembrance on Lundy and his contributions to the anti-slavery movement. Benjamin Lundy (1789-1839) was a prominent Quaker abolitionist best known for his development of abolitionist periodicals. His Genius of Universal Emancipation was first published in 1821 from his home in Mt. Pleasant, Ohio, and enjoyed a wide circulation across the antebellum United States. In the 1820s, the young William Lloyd Garrison came to work for The Genius. Benjamin Lundy traveled widely seeking subscriptions to The Genius, giving talks about the anti-slavery movement, and observing and documenting the conditions of enslaved people across the Americas. He was also involved in the establishment of freed slave colonies in Mexico
Modelling and optimization of a permanent-magnet machine in a flywheel
No full textThis thesis describes the derivation of an analytical model for the design and optimization of a permanent-magnet machine for use in an energy storage flywheel. A prototype of this flywheel is to be used as the peak-power unit in a hybrid electric city bus. The thesis starts by showing the feasibility of using a flywheel energy storage system for this application, as opposed to other energy storage technologies. It then continues by describing a prototype flywheel system and the required electrical machine: a radial-flux external-rotor permanent-magnet synchronous machine without slots in the stator iron and with a shielding cylinder. An analytical model for the machine is derived, based on 2D electromagnetic field calculations, including the reaction field of the eddy currents in the shielding cylinder. Torque and losses are calculated by means of the Theorem of Poynting and the Lorentz force. Such a machine was built and the analytical model has been validated by experimental measurements. Lastly, the thesis suggests and implements a machine optimization algorithm.Information Technology and System
Design metrics for evaluating the propulsive efficiency of future ships
No full textThere is an increasing need for the ship design process to take account of environmental issues such as the emission of greenhouse gases and the likely extension of a carbon dioxide charging mechanism to international shipping. These issues, together with the need for economic viability, provide further incentives to improve the efficiency of propulsion of ships. The main components of powering are firstly reviewed. Individual components and other power saving devices are identified which should contribute to improvements in the overall efficiency of propulsion. Suitable design metrics and procedures, taking into account economic and environmental factors, are recommended for the design of future ships
Description of S.R. Krom's system and machinery for dry crushing and concentrating ores.
No full textCover title.Mode of access: Internet.MAIN; TN500.K7 1876: Introduction signed by author, S.R. Krom
Refinement of solutions to the linear complimentarity problem
No full textNash equilibrium;game theaory;matrices
Toward more efficient heuristic construction of Boolean functions
No full textBoolean functions have numerous applications in domains as diverse as coding theory, cryptography,and telecommunications. Heuristics play an important role in the construction of Boolean functions with the desired properties for a specific purpose. However, there are only sparse results trying to understand the problem’s difficulty. With this work, we aim to address this issue. We conduct a fitness landscape analysis based on Local Optima Networks (LONs) and investigate the influence of different optimization criteria and variation operators. We observe that the naive fitness formulation results in the largest networks of local optima with disconnected components. Also, the combination of variation operators can both increase or decrease the network size. Most importantly, we observe correlations of local optima’s fitness, their degrees of interconnection, and the sizes of the respective basins of attraction. This can be exploited to restart algorithms dynamically and influence the degree of perturbation of the current best solution when restarting.Domagoj Jakobovic, Stjepan Picek, Marcella S.R. Martins, Markus Wagne
Correction to: Clinical Trials in High-Risk Medulloblastoma: Evolution of the SIOP-Europe HR-MB Trial (Cancers, (2022), 14, 2, (374), 10.3390/cancers14020374)
No full text\ua9 2024 by the authors.In the original publication [1], the funder Cancer Research UK, A2524 was not included. Keith Wheatley, Simon Gates, and Victoria Homer were not included as authors in the original publication. The reason we would like to add the authors is that the statistical element of the trial and the trial design were in a large part done by the statistical authors and the team were necessary for the running of the trial. The corrected Author Contributions Statement appears here. Author Contributions: Conceptualization, S.B., N.A., L.G., M.M., K.W., S.R. and S.C.C.; methodology, K.W., S.G. and V.H.; project administration, S.G. and V.H.; resources, S.B., N.A., L.G., M.M., S.R. and S.C.C.; writing—original draft preparation, S.B., N.A., L.G., M.M., S.R. and S.C.C.; writing—review and editing, S.B., N.A., L.G., M.M., S.R. and S.C.C. All authors have read and agreed to the published version of the manuscript. Author Contributions: Conceptualization, S.B., N.A., L.G., M.M., K.W., S.R. and S.C.C.; methodology, K.W., S.G. and V.H.; project administration, S.G. and V.H.; resources, S.B., N.A., L.G., M.M., S.R. and S.C.C.; writing—original draft preparation, S.B., N.A., L.G., M.M., S.R. and S.C.C.; writing—review and editing, S.B., N.A., L.G., M.M., S.R. and S.C.C. All authors have read and agreed to the published version of the manuscript. Cancer Research UK Clinical Trials Unit, University of Birimingham, Birmingham B15 2TT, UK; [email protected](K.W.); [email protected] (S.G.); [email protected] (V.H.) The authors apologize for any inconvenience caused and state that the scientific conclusions are unaffected. This correction was approved by the Academic Editor. The original publication has also been updated
Isogeometric Shape Optimization for Quasi-static and Transient Problems
No full textThe recently developed isogeometric analysis (IGA) was aimed, from the start, at integrating computer aided design (CAD) and analysis. This synthesis of geometry and analysis has naturally led to renewed interest in developing structural shape optimization. The advantages of using isogeometric analysis in shape optimization are embodied in its ability to preserve exact CAD geometrical descriptions and its enhanced potential to perform shape sensitivity analysis. Recent contributions in shape optimization within IGA have been limited to static or steady-state loading conditions. The purpose of this work was to extend the isogeometric shape optimization and identification to quasi-static and transient problems. The normalization approaches for the search directions in isogeometric shape optimization scheme and the mean value property of B-spline basis were also studied. Shape sensitivity analysis plays a critical role in structural shape optimization. In this dissertation, an adjoint sensitivity analysis was performed for arbitrary objective functionals defined for quasi-static and transient problems at the continuous level. The sensitivity for quasi-static and transient problems are essentially different with each other since the transient case has a time-derivative term involved in the time interval. The transport relations considering discontinuities were studied and used to derive the continuous adjoint shape sensitivity. Consideration of the discontinuities enabled the shape sensitivity analysis to be applicable for the problems where discontinuities were involved in the objective functional and state equations. Then within the context of IGA, the continuous sensitivity was discretized to obtain the discrete design sensitivity with respect to the design discretization, which was used to find the search directions used to update the shape numerically. A interesting phenomenon in shape optimization is that the use of the search direction directly predicted from the discrete shape gradient makes the optimization history strongly dependent on the discretization. This discretization dependency can affect convergence and may lead the optimization process into a sub-optimal solution. The source of this discretization dependency was traced to the lack of consistency with the local steepest descent search direction in the continuous formulation. This inconsistency was analyzed using the shape variation equations and subsequently illustrated with a volume minimization problem. It was found that the inconsistency originates from the NURBS discretization which induces a discrete quadratic norm to represent the continuous Euclidean norm. To fix this inconsistency, a standard normalization approach, which is used to find the steepest descent direction for quadratic norm problems, was proposed to obtain a consistent discretization independent search direction. The standard approach requires solving a linear system of equations. Using the diagonally lumped mapping matrix (DLMM) and the partition of unity property of NURBS, two simpler normalization approaches, which do not require solving a linear system of equations, were proposed. The discretization-independence of the proposed approaches was verified with a benchmark problem. The superiority of the proposed search direction and its suitability for numerical implementation is illustrated with examples of shape optimization for mechanical and thermal problems. In the derivation of the simplified normalization approaches, the mean value property of B-spline basis function is proposed and proved using mathematical induction method. Using the normalization approaches, two frameworks to solve shape optimization and identification problems for quasi-static and transient process, respectively, were developed and implemented numerically within the context of isogeometric analysis. Generalized objective functionals were used to accommodate both structural shape optimization and identification problems in arbitrary forms. The methodology and its numerical implementation were tested using benchmark problems or passive control approaches with priori known solutions. For the quasi-static case, application problems were considered where an external load was allowed to move along the surface of a structure. The shape of the structure was modified to control the time-dependent displacement of the point where the load was applied according to a pre-specified target. For the transient case, the shape optimization and identification was performed for a plunger design under a transient heating process and a thermal protection layer design for a ballistic re-entry vehicle.Aerospace Structures and MaterialsAerospace Engineerin
Radiative-Convective Equilibrium: Atmospheric Simulations in DALES
No full textUsing the Dutch Atmospheric Large-Eddy Simulation model (DALES) the atmosphere in both a pure radiative and a radiative-convective equilibrium is investigated. These simulations are performed on a domain which top is located at 30 kilometres. This high altitude requires some modifications of the radiative transfer code used in DALES. The effects of the imposed surface temperature on the resulting surface heat flux and evaporation, temperature profiles and cloud fields are investigated. The results of this thesis show that DALES can be well used to study equilibrium states of deep convective clouds, paving the way for future research.Applied PhysicsGeoscience and Remote SensingCivil Engineering and Geoscience
Multiscale Fracture Simulations for Composite Materials
No full textFor failure in composite materials the fracture mechanisms at the microscopic scale, such as matrix cracking, fiber cracking, fiber-matrix debonding or combinations thereof determine the growth of crack at the macroscopic scale. The goal is to develop a simple failure criterion in terms of a bilinear Traction-Separation Law (TSL) for unidirectional Carbon-Fiber Reinforced Plastic (CFRP) that represents the crack nucleation and evolution at the macroscopic scale. The microscopic fracture mechanisms are incorporated by calibrating this bilinear TSL for arbitrary loading conditions and material properties. The calibration is performed by an extensive parametric study on 2D a Representative Volume Element (RVE) in ABAQUS. For the parametric study five load cases are studied: uni-axial extension (pure mode I), simple shear (pure mode II) and three mixed loading cases. Fracture is simulated inserting cohesive elements along the boundaries of all bulk elements. The effect of five variables was studied: interface cohesive strength, fiber cohesive strength, interface fracture energy, fiber fracture energy and fiber volume fraction. An average of four realizations, i.e. fiber distributions, resulted in an effective TSL that represents the fracture behavior of the RVE. The resulting effective TSL is approximated by a bilinear TSL that has three parameters: initial slope, cohesive strength (peak) and fracture energy (area). Using the results of the parametric study a correlation is performed for these three parameters. First, the mode I and II parameters are correlated using the results of the uni-axial extension and simple shear load case. Secondly, the three bilinear TSL parameters dependence on the mode mixity is correlated using one of the mixed loading cases. As a result of this procedure simple closed-form expressions are established that can determine the macroscopic fracture mechanism, in terms of a bilinear TSL, as a function of the microscopic properties.Aerospace Structures and Computational MechanicsAerospace Engineerin
- …
