Improving patient-specific assessments of regional aortic mechanics via quantitative magnetic resonance imaging with early applications in patients at elevated risk for thoracic aortopathy

Unstable aortic aneurysms and dissections are serious cardiovascular conditions associated with high mortality. The current gold standards for assessment of stability, however, rely on simple geometric measurements, like cross-sectional area or increased diameter between follow-up scans, and fail to incorporate information about underlying aortic mechanics. Displacement encoding with stimulated echoes (DENSE) magnetic resonance imaging (MRI) has been used previously to determine heterogeneous circumferential strain patterns in the aortas of healthy volunteers. Here, I introduce technical improvements to DENSE aortic analysis and early pilot application in patients at higher risk for the development of aortopathies. Modifications to the DENSE aortic postprocessing method involving the separate spatial smoothing of the inner and outer layers of the aortic wall allowed for the preservation of radial and shear strains without impacting circumferential strain calculations. The implementation of a semiautomatic segmentation approach utilizing the intrinsic kinematic information provided by DENSE MRI reduced lengthy post-processing times while generating circumferential strain distributions with good agreement to a manually generated benchmark. Finally, a new analysis pipeline for the combined use and spatial correlation of 4D phase-contrast MRI alongside DENSE MRI to quantify both regional fluid and solid mechanics in the descending aorta is explored in a limited pilot study

Using the PUMA System

This document describes the operation of the Lisp Machine interface to the Unimation Puma 600 Robot Arm. The interface is evolved from a system described in an earlier paper, and much is the same. However, the under-lying interface between the Lisp Machine and the Puma has changed and some enhancements have been made. VAL has been replaced with a PDP-11/23, communicating with the Lisp Machine over the Chaosnet. The purpose of this document is to provide instruction and information in the programming of the Puma arm from the Lisp Machine. The network protocol is not described here, nor are the internals of the implementation. These details are provided in separate documentation. The reader will find in this paper both a tutorial section and a reference section. The tutorial will lead the reader through a sample session using the Puma by directly calling the primitive operations, and will provide an introduction to programming using the primitives. The reference section provides an overview of the network protocol and describes all of the primitive operations provided. Please note that this document corresponds to the version of the Puma system in use on 11 March, 1985. The system is still undergoing development and enhancement, and there may be additional features, if you are running a newer system. The authors welcome reports of errors, inaccuracies, or suggestions for clarification or improvement in either the documentation or the code for the Puma system. Please send electronic mail to [email protected] Artificial Intelligence Laborator

Puma/Cougar Implementor's Guide

This document is intended to be a guide to assist a programmer in modifying or extending the Lisp Puma system, the Puma PDP-11 system, or the Cougar PDP-11 system. It consists mostly of short descriptions or hints, and is not intended to be a polished manual. The reader is expected to be familiar with the use of the Puma system, as described in "Using the PUMA System," and the Lisp flavor system, as described in the Lisp Machine Manual.MIT Artificial Intelligence Laborator

Geometric Quantum Computation

We describe in detail a general strategy for implementing a conditional geometric phase between two spins. Combined with single-spin operations, this simple operation is a universal gate for quantum computation, in that any unitary transformation can be implemented with arbitrary precision using only single-spin operations and conditional phase shifts. Thus quantum geometrical phases can form the basis of any quantum computation. Moreover, as the induced conditional phase depends only on the geometry of the paths executed by the spins it is resilient to certain types of errors and offers the potential of a naturally fault-tolerant way of performing quantum computation.Comment: 15 pages, LaTeX, uses cite, eepic, epsfig, graphicx and amsfonts. Accepted by J. Mod. Op

An X-Ray Study of the Supernova Remnant G290.1-0.8

G290.1-0.8 (MSH 11-61A) is a supernova remnant (SNR) whose X-ray morphology is centrally bright. However, unlike the class of X-ray composite SNRs whose centers are dominated by nonthermal emission, presumably driven by a central pulsar, we show that the X-ray emission from G290.1-0.8 is thermal in nature, placing the remnant in an emerging class which includes such remnants as W44, W28, 3C391, and others. The evolutionary sequence which leads to such X-ray properties is not well understood. Here we investigate two scenarios for such emission: evolution in a cloudy interstellar medium, and early-stage evolution of a remnant into the radiative phase, including the effects of thermal conduction. We construct models for these scenarios in an attempt to reproduce the observed center-filled X-ray properties of G290.1-0.8, and we derive the associated age, energy, and ambient density conditions implied by the models. We find that for reasonable values of the explosion energy, the remnant age is of order (1 - 2) x 10^{4} yr. This places a fairly strong constraint on any association between G290.1-0.8 and PSR J1105-610, which would require an anomalously large velocity for the pulsar.Comment: 7 pages, 7 figures, ApJ, accepte

Evaluating Participatory Modeling: Developing a Framework for Cross-case Analysis

Participatory modeling is increasingly recognised as an effective way to assist collective decision-making processes in the domain of natural resource management. This paper introduces a framework for evaluating projects that have adopted a participatory modeling approach. This framework – known as the ‘Protocol of Canberra’ – was developed through a collaboration between French and Australian researchers engaged in participatory modeling and evaluation research. The framework seeks to assess the extent to which different participatory modeling practices reinforce or divert from the theoretical assumptions they are built upon. The paper discusses the application of the framework in three case-studies, two from Australia and one from the Pacific island of the Republic of Kiribati. The paper concludes with some comments for future use of the framework in a range of participatory modeling contexts, including fostering consideration of why and how different methodological approaches are used to achieve project aims and to build a collective vision amongst diverse stakeholders.participation, modeling, evaluation, complex systems science

Particle Acceleration in Supernova Remnants and the Production of Thermal and Nonthermal Radiation

If highly efficient, cosmic ray production can have a significant effect on the X-ray emission from SNRs as well as their dynamical evolution. Using hydrodynamical simulations including diffusive shock acceleration, we produce spectra for both the thermal and nonthermal forward shock emission. For a given ambient density and explosion energy, we find that the position of the forward shock at a given age is a strong function of the acceleration efficiency, providing a signature of cosmic-ray production. Using an approximate treatment for the ionization state of the plasma, we investigate the effects of slow vs. rapid heating of the postshock electrons on the ratio of thermal to nonthermal X-ray emission at the forward shock. We also investigate the effects of magnetic field strength on the observed spectrum for efficient cosmic-ray acceleration. The primary effect of a large field is a considerable flattening of the nonthermal spectrum in the soft X-ray band. Spectral index measurements from X-ray observations may thus be indicators of the postshock magnetic field strength. The predicted gamma-ray flux from inverse-Compton (IC) scattering and neutral pion decay is strongly affected by the ambient conditions and, for the particular parameters used in our examples, the IC emission at E ~ 1 TeV exceeds that from pion decay, although at both lower and higher energies this trend is reversed for cases of high ambient density. More importantly, high magnetic fields produce a steepening of the electron spectrum over a wide energy range which may make it more difficult to differentiate between IC and pion-decay emission solely by spectral shape.Comment: 30 pages, 12 figures, submitted to ApJ January 200

Variations in Public Health Governance

Background: Studies of public health departments have found mixed results regarding the relevance of governance through local boards of health (LBOHs). Some studies find that LBOHs can be an important component in higher performance by local health departments. Other analyses, however, find no advantage for local health departments having or not having a LBOH. The hypothesis was that a typology of LBOHs nationwide can define different types of LBOHs based on their powers and responsibilities. Methods: Using national profile sample data from the National Association of Local Boards of Health, LBOHs were categorized using 34 variables based on four domains of responsibilities and duties: enforcement powers, regulatory powers, human resource powers, and budgetary powers. Correlations between types of LBOHs defined by this typology were then computed, and whether they shared significant characteristics in terms of the race, ethnicity, sex, and educational demographics of their board members was determined. ArcGIS was used to analyze the data spatially for regional and national patterns. Results: LBOHs vary considerably across the country - from LBOHs with no budgetary, enforcement, regulatory, or human resources authorities to those that have all four. Conclusions: Different types of LBOHs may have different influences on their associated local boards of health. This study provides a typology for future research to allow analysts to distinguish different types of LBOHs nationally

After the Conservation Reserve Program: Economic Decisions with Wildlife in Mind

6 pp, 2 photos, 4 tablesAs Conservation Reserve Program (CRP) contracts begin to expire, landowners must decide to re-enroll the land in the program, convert it back to crops or leave it in permanent cover for grazing and for wildlife. This publication is one of a series exploring those options