1,454 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
A protective estimator for linear regression with nonignorably missing Gaussian outcomes
No full textWe propose a method for estimating the regression parameters in a linear regression model for Gaussian data when the outcome variable is missing for some subjects and missingness is thought to be nonignorable. Throughout, we assume that missingness is restricted to the outcome variable and that the covariates are fully observed. Although maximum likelihood estimation of the regression parameters is possible once joint models for the outcome variable and the nonignorable missing data mechanism have been specified, these models are fundamentally nonidentifiable unless unverifiable modeling assumptions are imposed. In this paper, rather than explicitly modeling the nonignorable missingness mechanism, we consider the use of a ‘protective’ estimator of the regression parameters (Brown, 1990). To implement the proposed method, it is necessary to assume that the outcome variable and one of the covariates have an approximate bivariate normal distribution, conditional on the remaining covariates. In addition, it is assumed that the missing data mechanism is conditionally independent of this covariate, given the outcome variable and the remaining covariates; the latter is referred to as the ‘protective’ assumption. A method of moments approach is used to obtain the protective estimator of the regression parameters; the jackknife (Quenouille, 1956) is used to estimate the variance. The method is illustrated using data on the persistence of maternal smoking from the Six Cities Study of the health effects of air pollution (Ware et al., 1984). The results of a simulation study are presented that examine the magnitude of any finite sample bias. © 2004, Sage Publications. All rights reserved.status: Publishe
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
Bias in Estimating Association Parameters for Longitudinal Binary Responses with Drop‐Outs
No full textThis paper considers the impact of bias in the estimation of the association parameters for longitudinal binary responses when there are drop-outs. A number of different estimating equation approaches are considered for the case where drop-out cannot be assumed to be a completely random process. In particular, standard generalized estimating equations (GEE), GEE based on conditional residuals, GEE based on multivariate normal estimating equations for the covariance matrix, and second-order estimating equations (GEE2) are examined. These different GEE estimators are compared in terms of finite sample and asymptotic bias under a variety of drop-out processes. Finally, the relationship between bias in the estimation of the association parameters and bias in the estimation of the mean parameters is explored.sponsorship: NIEHS NIH HHS|ES07142, NIGMS NIH HHS|GM29745, NIMH NIH HHS|MH17119status: Publishe
Slope estimation of covariates that influence renal outcome following renal transplant adjusting for informative right censoring
No full textA new statistical model is proposed to estimate population and individual slopes that are adjusted for covariates and informative right censoring. Individual slopes are assumed to have a mean that depends on the population slope for the covariates. The number of observations for each individual is modeled as a truncated discrete distribution with mean dependent on the individual subjects' slopes. Our simulation study results indicated that the associated bias and mean squared errors for the proposed model were comparable to those associated with the model that only adjusts for informative right censoring. The proposed model was illustrated using renal transplant dataset to estimate population slopes for covariates that could impact the outcome of renal function following renal transplantation. © 2012 Copyright Taylor and Francis Group, LLC.Fletcher R., 1987, PRACTICAL METHODS OP; Jaffa MA, 2010, RENAL FAILURE, V32, P691, DOI 10.3109-0886022X.2010.486495; Jaffa MA, 2011, J R STAT SOC A STAT, V174, P387, DOI 10.1111-j.1467-985X.2010.00671.x; JENNRICH RI, 1986, BIOMETRICS, V42, P805, DOI 10.2307-2530695; Laird N.M., 1988, STAT MED, V44, P175; LAIRD NM, 1982, BIOMETRICS, V38, P963, DOI 10.2307-2529876; LAIRD NM, 1990, CONTROL CLIN TRIALS, V11, P405, DOI 10.1016-0197-2456(90)90018-W; Linsdstrom MJ, 1988, J AM STAT ASSOC, V83, P1014; MORI M, 1994, BIOMETRICS, V50, P39, DOI 10.2307-2533195; Pinheiro J. C., 1995, J COMPUTATIONAL GRAP, V4, P12, DOI [10.1080-10618600.1995.10474663, DOI 10.2307-1390625]; REED E, 1992, TRANSPLANT P, V24, P2670; RICHIE RE, 1983, ANN SURG, V197, P672, DOI 10.1097-00000658-198306000-00005; SAS (Statistical Analysis System) Institute, 2002, SAS STAT 9 2 US GUID; SCHLUCHTER MD, 1992, STAT MED, V11, P1861, DOI 10.1002-sim.4780111408; STEFANSKI LA, 1985, ANN STAT, V13, P1335, DOI 10.1214-aos-1176349741; VONESH EF, 1987, BIOMETRICS, V43, P617, DOI 10.2307-2531999; WU MC, 1988, BIOMETRICS, V44, P175, DOI 10.2307-2531905; WU MC, 1988, CONTROL CLIN TRIALS, V9, P32, DOI 10.1016-0197-2456(88)90007-4; WU MC, 1989, BIOMETRICS, V45, P939, DOI 10.2307-25316940
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
A bivariate pseudo-likelihood for incomplete longitudinal binary data with nonignorable non-monotone missingness
No full textFor analyzing longitudinal binary data with nonignorable and nonmonotone missing responses, a full likelihood method is complicated algebraically, and often requires intensive computation, especially when there are many follow-up times. As an alternative, a pseudolikelihood approach has been proposed in the literature under minimal parametric assumptions. This formulation only requires specification of the marginal distributions of the responses and missing data mechanism, and uses an independence working assumption. However, this estimator can be inefficient for estimating both time-varying and time-stationary effects under moderate to strong within-subject associations among repeated responses. In this article, we propose an alternative estimator, based on a bivariate pseudolikelihood, and demonstrate in simulations that the proposed method can be much more efficient than the previous pseudolikelihood obtained under the assumption of independence. We illustrate the method using longitudinal data on CD4 counts from two clinical trials of HIV-infected patients.sponsorship: We are grateful for the support provided by grants from the U.S. National Institutes of Health, and the Natural Sciences and Engineering Research Council of Canada. (U.S. National Institutes of Health, Natural Sciences and Engineering Research Council of Canada)status: Publishe
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