The Internal Validation of a National Model of Long Distance Traffic.

During 1980/81, the Department of Transport developed a model for describing the distribution of private vehicle trips between 642 districts in Great Britain, using data from household and roadside interviews conducted in 1976 for the Regional Highways Traffic Model, and a new formulation of the gravity model, called a composite approach, in which shorter length movements were described at a finer level of zonal detail than longer movements. This report describes the results of an independent validation exercise conducted for the Department, in which the theoretical basis of the model and its the quality of its fit to base year data were examined. The report discusses model specification; input data; calibration issues; and accuracy assessment. The main problems addressed included the treatment of intrazonal and terminal costs, which was thought to be deficient; the trip-end estimates to which the model was constrained, which were shown to have substantial variability and to be biassed (though the cause of the latter could be readily removed), with some evidence of geographical under-specification; and the differences between roadside and household interview estimates. The report includes a detailed examination of the composite model specification and contains suggestions for improving the way in which such models are fitted. The main technical developments, for both theory and practice, are the methods developed for assessing the accuracy of the fitted model and for examining the quality of its fit with respect to the observed data, taking account of the variances and covariances of modelled and data values. Overall, the broad conclusion was that, whilst there appeared to be broad compatibility between modelled and onserved data in observed cells, there was clear evidence of inadequacy in certain respects, such as for example underestimation of intradistr ict trips. This work was done in co-operation with Howard Humphreys and Partners and Transportation Planning Associates, who validated the model against independent external data; their work is reported separately

What are the errors we should be seeking to minimise in the estimation process?

Three methods of fitting a gravity model - a triproportional model - to an observed trip matrix are compared. The first is the familiar practical method of choosing row, column and cost factors so that the model has the same row, column and cost sums as the grossed-up data. The second method, a true maximum likelihood estimation, chooses the factors so that the sums of the observed counts (not grossed-up) are matched. This differs from the first method only when the sampling probabilities vary from cell to cell. The third method applies the more modern approach of selecting a loss function which represents the practical effect of differences between the model values and the true values, and then chooses the model factors so that the expected loss, as far as it can be determined fromthe sample data and any prior information, is minimised. Squared error in flow times travel time is proposed as the loss function. It is noted that there is a loss function whose use is equivalent to maximum likelihood. When the sample counts are large and the model fits well, each of the methods reduced to minimising the weighted squared, difference between the model and the saturated value. The variations in these weights show the differences between the three methods

Higher Education Exchange:2005

This annual publication serves as a forum for new ideas and dialogue between scholars and the larger public. Essays explore ways that students, administrators, and faculty can initiate and sustain an ongoing conversation about the public life they share.The Higher Education Exchange is founded on a thought articulated by Thomas Jefferson in 1820: "I know no safe depository of the ultimate powers of the society but the people themselves; and if we think them not enlightened enough to exercise their control with a wholesome discretion, the remedy is not to take it from them, but to inform their discretion by education."In the tradition of Jefferson, the Higher Education Exchange agrees that a central goal of higher education is to help make democracy possible by preparing citizens for public life. The Higher Education Exchange is part of a movement to strengthen higher education's democratic mission and foster a more democratic culture throughout American society.Working in this tradition, the Higher Education Exchange publishes interviews, case studies, analyses, news, and ideas about efforts within higher education to develop more democratic societies

Instability of CII is needed for efficient switching between lytic and lysogenic development in bacteriophage 186

The CII protein of temperate coliphage 186, like the unrelated CII protein of phage λ, is a transcriptional activator that primes expression of the CI immunity repressor and is critical for efficient establishment of lysogeny. 186-CII is also highly unstable, and we show that in vivo degradation is mediated by both FtsH and RseP. We investigated the role of CII instability by constructing a 186 phage encoding a protease resistant CII. The stabilised-CII phage was defective in the lysis-lysogeny decision: choosing lysogeny with close to 100% frequency after infection, and forming prophages that were defective in entering lytic development after UV treatment. While lysogenic CI concentration was unaffected by CII stabilisation, lysogenic transcription and CI expression was elevated after UV. A stochastic model of the 186 network after infection indicated that an unstable CII allowed a rapid increase in CI expression without a large overshoot of the lysogenic level, suggesting that instability enables a decisive commitment to lysogeny with a rapid attainment of sensitivity to prophage induction.Iain M Murchland, Alexandra Ahlgren-Berg, Julian M J Pietsch, Alejandra Isabel, Ian B Dodd, Keith E Shearwi

A discrete MMAP for analysing the behaviour of a multi-state complex dynamic system subject to multiple events.

A complex multi-state system subject to different types of failures, repairable and/or nonrepairable, external shocks and preventive maintenance is modelled by considering a discrete Markovian arrival process with marked arrivals (D-MMAP). The internal performance of the system is composed of several degradation states partitioned into minor and major damage states according to the risk of failure. Random external events can produce failures throughout the system. If an external shock occurs, there may be an aggravation of the internal degradation, cumulative external damage or extreme external failure. The internal performance and the cumulative external damage are observed by random inspection. If major degradation is observed, the unit goes to the repair facility for preventive maintenance. If a repairable failure occurs then the system goes to corrective repair with different time distributions depending on the failure state. Time distributions for corrective repair and preventive maintenance depend on the failure state. Rewards and costs depending on the state at which the device failed or was inspected are introduced. The system is modelled and several measures of interest are built into transient and stationary regimes. A preventive maintenance policy is shown to determine the effectiveness of preventive maintenance and the optimum state of internal and cumulative external damage at which preventive maintenance should be taken into account. A numerical example is presented, revealing the efficacy of the model. Correlations between the numbers of different events over time and in non-overlapping intervals are calculated. The results are expressed in algorithmic-matrix form and are implemented computationally with Matlab.Junta de Andalucía, Spain, under the grant FQM307Ministerio de Economía y Competitividad, España, MTM2017-88708-PEuropean Regional Development Fund (ERDF

The Arrow that Flies By Day: Existential Images of the Human Condition from Socrates to Hannah Arendt: A Philosophy for Dark Times

This study contends that existentialism is the perennial philosophy thus going against the assumption that it is a school of more recent provenance. Anthologies or introductory texts used begin with Kierkegaard (the so-called father of existentialism) and go on to emphasize Nietzsche, Sartre, and Heidegger. This book reflects a more catholic mapping, including three thinkers from the classical period (Socrates, Augustine, and the Stoics), who are argued to be just as existential as more modern thinkers (who are also treated) and indeed influence the latter in important ways. Also included are three Americans (Thoreau, James, and Hannah Arendt) who are rarely considered existentialists. Furthermore, the book has a pedagogical emphasis, reflecting students\u27 points-of-view: what they learn, how they react, questions they have, and how in general existentialism meets their education needs and expectations. It is, therefore, necessarily interdisciplinary in character, pointing out implications of existentialism for education, concerns like happiness, war and peace, democracy, sexuality, and terrorism.https://digitalcommons.owu.edu/phil_books/1001/thumbnail.jp