On the Brittleness of Bayesian Inference

With the advent of high-performance computing, Bayesian methods are increasingly popular tools for the quantification of uncertainty throughout science and industry. Since these methods impact the making of sometimes critical decisions in increasingly complicated contexts, the sensitivity of their posterior conclusions with respect to the underlying models and prior beliefs is a pressing question for which there currently exist positive and negative results. We report new results suggesting that, although Bayesian methods are robust when the number of possible outcomes is finite or when only a finite number of marginals of the data-generating distribution are unknown, they could be generically brittle when applied to continuous systems (and their discretizations) with finite information on the data-generating distribution. If closeness is defined in terms of the total variation metric or the matching of a finite system of generalized moments, then (1) two practitioners who use arbitrarily close models and observe the same (possibly arbitrarily large amount of) data may reach opposite conclusions; and (2) any given prior and model can be slightly perturbed to achieve any desired posterior conclusions. The mechanism causing brittlenss/robustness suggests that learning and robustness are antagonistic requirements and raises the question of a missing stability condition for using Bayesian Inference in a continuous world under finite information.Comment: 20 pages, 2 figures. To appear in SIAM Review (Research Spotlights). arXiv admin note: text overlap with arXiv:1304.677

Factors shaping the evolution of electronic documentation systems

The main goal is to prepare the space station technical and managerial structure for likely changes in the creation, capture, transfer, and utilization of knowledge. By anticipating advances, the design of Space Station Project (SSP) information systems can be tailored to facilitate a progression of increasingly sophisticated strategies as the space station evolves. Future generations of advanced information systems will use increases in power to deliver environmentally meaningful, contextually targeted, interconnected data (knowledge). The concept of a Knowledge Base Management System is emerging when the problem is focused on how information systems can perform such a conversion of raw data. Such a system would include traditional management functions for large space databases. Added artificial intelligence features might encompass co-existing knowledge representation schemes; effective control structures for deductive, plausible, and inductive reasoning; means for knowledge acquisition, refinement, and validation; explanation facilities; and dynamic human intervention. The major areas covered include: alternative knowledge representation approaches; advanced user interface capabilities; computer-supported cooperative work; the evolution of information system hardware; standardization, compatibility, and connectivity; and organizational impacts of information intensive environments

Should Cairo be Governed?

This work on urban research strategies in Egypt is the product of several factors. First of all is the challenge, excitement, diversity and stimulation of living in Egyptian cities, Cairo above all. Not only are Egyptian cities rooted in deep antiquity, but they have the richly stratified layers of a host of great civilizations. Modern urban Egypt is immeasurably complex in its own right, but its quite astounding past only adds to its wonderment. Thus, the chief inspiration for this publication is the wealthy cultural and historical context in which these scholars were assembled and where they sought to interpret a range of adjustments and reacdons to modern urban life. The second factor is found in the intellectual fecundity and the traditions of the Social Research Center (SRC) at the American University in Cairo which has, for three decades, been at the epicenter of social investigation and evaluation in Egyptian society. Its contribution is truly without adequate definition in terms of published works, academic interaction, research and development. The SRC represents the intellectual birthplace of a host of Egyptian, American and other foreign scholars who have come to study Egypt. The creation of the Urban Development Unit in 1982 as a section of the SRC has underscored the pioneering on another area of specialized research in Egypt. The workshop held on 6-7 June 1982 on Strategies for Urban Research in the 1980s\u27 was sponsored by this new unit of the SRC. The third factor which made the workshop possible was represented in the unpaid, voluntary contributions of time and effort of the assembled participants and contributors and especially of the Workshop Preparatory Committee, composed mainly but not exclusively of the following: Mark Kennedy, Ibrahim Omar, Madiha Al-Safty, Marina Ottaway, Barbara Ibrahim, Nick Hopkins, Saneya Saleh, Assad Nadim, Soha Abdel Kader, Tim Sullivan and myself. Finally, the pleasant atmosphere, ample luncheons and refreshments, secretarial support and other details. of the workshop\u27s inf ras true ture were sustained through the generosity of the Cairo office of the Ford Foundation and its Director, John Gerhart. Here, appreciation for all of the above is very gratefully recorded. Some of the participants were invited only to enjoy the academic interaction and to enrich the base of discussion with comments from their own pertinent experiences. Others were invited to prepare papers for the workshop. As far as possible, the papers were reproduced and circulated before and during the workshop to make a qualitative contribution to the depth and intensity of the discussion which followed each group of papers. For various reasons, all of the papers originally presented are not published here but certain among them were selected and edited for this special publication. Also, while the discussions followed each unit of grouped papers, the versions presented here are really a distillation of this stimulating dialogue. Special mention needs to be made to the Editorial Board of CAIRO PAPERS IN SOCIAL SCIENCE at the American University in Cairo which has been willing to publish these papers as Volume 6, Number 2 of this journal. Since the decision was made, I have been asked to join the Editorial Board and have benefitted from the collegial criticisms and general support of the Board. In this context, particular note is due for the contribution of Mahmoud Abdel-Fadil. His workshop paper was actually a condensed version of a larger work on the same topic which Md already been submitted to CAIRO PAPERS for publication. Since the study of the urban informal sector was so strongly featured in the workshop discussions, the Editorial Board concluded and Dr. Abdel-Fadil agreed that hie paper would be best published in its entirety in this publication. I believe that we all benefit from his flexibility and understanding. The other papers represent on-going research and/or were specially prepared for the workshop. Finally, acknowledgement of the critical secretarial support for this publication is very gratefully offered to Hekmat. Wasef, Yvonne Shunbo, Mona Tawfik, Brenda Carpenter and Joan Bickelhaupt who helped with some of the transcriptions of the taped discussion.https://fount.aucegypt.edu/faculty_book_chapters/1855/thumbnail.jp

Day 1: Wednesday, 17 August 2005: Biodiversity and Critical Habitat

6 pages (includes color illustration). Contains references

Brittleness of Bayesian inference under finite information in a continuous world

We derive, in the classical framework of Bayesian sensitivity analysis, optimal lower and upper bounds on posterior values obtained from Bayesian models that exactly capture an arbitrarily large number of finite-dimensional marginals of the data-generating distribution and/or that are as close as desired to the data-generating distribution in the Prokhorov or total variation metrics; these bounds show that such models may still make the largest possible prediction error after conditioning on an arbitrarily large number of sample data measured at finite precision. These results are obtained through the development of a reduction calculus for optimization problems over measures on spaces of measures. We use this calculus to investigate the mechanisms that generate brittleness/robustness and, in particular, we observe that learning and robustness are antagonistic properties. It is now well understood that the numerical resolution of PDEs requires the satisfaction of specific stability conditions. Is there a missing stability condition for using Bayesian inference in a continuous world under finite information

Small molecule tandem organic photovoltaic cells incorporating an α-NPD optical spacer layer

We report an improvement in power conversion efficiency in a small molecule tandem organic photovoltaic (OPV) device by the optimisation of current balancing of the sub-cells using an optical spacer layer. A co-deposited layer of N,N’-bis(1-naphthyl)-N,N′-diphenyl-1,1’-biphenyl-4,4’-diamine (α-NPD) and molybdenum oxide was used as the optical spacer layer and provided a highly transparent and conductive layer. Optical simulations showed the addition of the optical spacer in a boron subphthalocyanine (SubPc)/C60 based tandem OPV device increased the SubPc absorption in the front sub-cell and resulted in current balancing through the device. Fabricated tandem OPV devices showed similar trends, with the power conversion efficiency increasing from 2.3% to 4.2% with the addition of an optimised optical spacer thickness. External quantum efficiency and total absorption efficiency measurements back up the optical model data which attribute the increased performance to improved SubPc absorption in the front sub-cell, balancing the photocurrents of the two sub-cells