Network Revenue Management with Inventory-Sensitive Bid Prices and Customer Choice

We develop an approximate dynamic programming approach to network revenue management models with customer choice that approximates the value function of the Markov decision process with a non-linear function which is separable across resource inventory levels. This approximation can exhibit significantly improved accuracy compared to currently available methods. It further allows for arbitrary aggregation of inventory units and thereby reduction of computational workload, yields upper bounds on the optimal expected revenue that are provably at least as tight as those obtained from previous approaches, and is asymptotically optimal under fluid scaling. Computational experiments for the multinomial logit choice model with distinct consideration sets show that policies derived from our approach outperform available alternatives, and we demonstrate how aggregation can be used to balance solution quality and runtime

The Geoff Egan Memorial Lecture 2011. Artefacts, art and artifice: reconsidering iconographic sources for archaeological objects in early modern Europe

A first systematic analysis of historic domestic material culture depicted in contemporaneous Western painting and prints, c.1400-1800. Drawing on an extensive data set, the paper proposes to methodologies and hermeneutics for historical analysis and archaeological correspondence

A Generalized Diffusion Tensor for Fully Anisotropic Diffusion of Energetic Particles in the Heliospheric Magnetic Field

The spatial diffusion of cosmic rays in turbulent magnetic fields can, in the most general case, be fully anisotropic, i.e. one has to distinguish three diffusion axes in a local, field-aligned frame. We reexamine the transformation for the diffusion tensor from this local to a global frame, in which the Parker transport equation for energetic particles is usually formulated and solved. Particularly, we generalize the transformation formulas to allow for an explicit choice of two principal local perpendicular diffusion axes. This generalization includes the 'traditional' diffusion tensor in the special case of isotropic perpendicular diffusion. For the local frame, we motivate the choice of the Frenet-Serret trihedron which is related to the intrinsic magnetic field geometry. We directly compare the old and the new tensor elements for two heliospheric magnetic field configurations, namely the hybrid Fisk and the Parker field. Subsequently, we examine the significance of the different formulations for the diffusion tensor in a standard 3D model for the modulation of galactic protons. For this we utilize a numerical code to evaluate a system of stochastic differential equations equivalent to the Parker transport equation and present the resulting modulated spectra. The computed differential fluxes based on the new tensor formulation deviate from those obtained with the 'traditional' one (only valid for isotropic perpendicular diffusion) by up to 60% for energies below a few hundred MeV depending on heliocentric distance.Comment: 8 pages, 6 figures, accepted in Ap

Identification of depression in a rural general practice

Major depression is underdiagnosed by general practitioners, but the reasons for this are not clear. This study aimed to establish the prevalence of major depression and coexisting generalised anxiety disorder in a rural general practice in the Orange Free State. It also assessed the predictive value of a screening questionnaire for use by general practitioners. The two practitioners evaluated 858 patients over a 4-week period. Those who met the screening criteria, together with a random sample of 60 patients who did not, were re-evaluated by a registrar in psychiatry who was unaware of the findings of his colleagues. Of the patients studied, 134 (15,6%) had major depression; 59 of these (44,0%) also had coexisting generalised anxiety disorder. The general practitioners had . correctly diagnosed major depression in 32 patients (3,7%) before the study started. The screening questionnaire had a 42% chance of correctly identifying a patient with depression and a 97% chance of correctly identifying a patient who did not have major depression. Both practitioners were equally capable at identifying major depression. The study confirmed both the high prevalence of depression in a rural general practice and its low identification rate. It also showed the advantage of using a screening questionnaire to alert practitioners to the possibility of depression in their patients

The relationship between leisure activities and psychological resources that support a sustainable career: The role of leisure seriousness and work-leisure similarity

While leisure plays an increasingly important role in individuals' lives, little is known about its potential to influence career sustainability. Drawing on Conservation of Resources (COR) theory, we investigate whether investing extra time into leisure will have a positive or negative impact on career sustainability by either generating or depleting resources. Specifically, we examine the effects of time spent on leisure on the career-related resources of resilience and self-efficacy using data on within-person changes over the course of 7 monthly surveys. We propose that the effects of leisure on resources depend on the interplay between a) the approach individuals take to their leisure activity, in particular the level of “seriousness” of a leisure activity (i.e., the extent to which individuals identify with, and persevere in, their activity), and b) the similarity between work and leisure (i.e., the extent to which work and leisure involve similar demands and skills). We found that time spent on leisure over and above an individual's average was positively related to work-related self-efficacy, but only when the individual's leisure activities were high in seriousness and low in work-leisure similarity, or when they were low in seriousness and high in similarity. Investing time in leisure was negatively associated with self-efficacy when leisure activities were high in seriousness and similar to an individual's work. Our findings paint a complex picture of the potential influence of leisure on career sustainability and highlight the need to take a nuanced approach when studying the effects of leisure

Effects of Agricultural Commercialization on Food Crop Input Use and Productivity in Kenya

The objective of this report is to analyze the effects of smallholder commercialization on food crop input use and productivity in rural Kenya. The main research issues were: (1) To examine the determinants of smallholder fertilizer use on food crops, with a focus on the effects of household and regional agricultural commercialization; (2) To examine the determinants of food crop productivity, again with a focus on the effects of commercialization; and (3) To discuss the implications of the findings for policy and additional research necessary to improve the contribution of cash cropping to rural food productivity growth and food security. A main premise of the paper is that the effects of commercialization are not uniform and cannot be generalized. The effects are hypothesized to differ both according to differences in the institutional/contractual arrangements between firms and smallholders, management decisions, and the level of credit and extension support provided to smallholders by the various private and parastatal firms involved in promoting smallholder cash crops.food security, food policy, food crop productivity, food crop input, Crop Production/Industries, Productivity Analysis, Downloads May 2008 - July 2009: 78, Q18,

Effects of Agricultural Commercialization on Food Crop Input Use and Productivity in Kenya

Crop Production/Industries, Downloads July 2008 - July 2009: 23,

Microwave and hard X-ray observations of a solar flare with a time resolution of better than 100 MS

Simultaneous microwave and X-ray observations are presented for a solar flare detected on 1980 May 8 starting at 1937 UT. The X-ray observations were made with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission and covered the energy range from 28-490 keV with a time resolution of 10 ms. The microwave observations were made with the 5 and 45 foot antennas at the Itapetinga Radio Observatory at frequencies of 7 and 22 GHz, with time resolutions of 100 ms and 1 ms respectively. Detailed correlation analysis of the different time profiles of the event show that the major impulsive in the X-ray flux preceded the corresponding microwave peaks at 22 GHz by about 240ms. For this particular burst the 22 GHz peaks preceded the 7 GHz by about 1.5s. Observed delays of the microwave peaks are too large for a simple electron beam model but they can be reconciled with the speeds of shock waves in a thermal model