71 research outputs found
Quanta Without Quantization
The dimensional properties of fields in classical general relativity lead to
a tangent tower structure which gives rise directly to quantum mechanical and
quantum field theory structures without quantization. We derive all of the
fundamental elements of quantum mechanics from the tangent tower structure,
including fundamental commutation relations, a Hilbert space of pure and mixed
states, measurable expectation values, Schroedinger time evolution, collapse of
a state and the probability interpretation. The most central elements of string
theory also follow, including an operator valued mode expansion like that in
string theory as well as the Virasoro algebra with central charges.Comment: 8 pages, Latex, Honorable Mention 1997 GRG Essa
Maximal benefits and possible detrimental effects of binary decision aids
Binary decision aids, such as alerts, are a simple and widely used form of
automation. The formal analysis of a user's task performance with an aid sees
the process as the combination of information from two detectors who both
receive input about an event and evaluate it. The user's decisions are based on
the output of the aid and on the information, the user obtains independently.
We present a simple method for computing the maximal benefits a user can derive
from a binary aid as a function of the user's and the aid's sensitivities.
Combining the user and the aid often adds little to the performance the better
detector could achieve alone. Also, if users assign non-optimal weights to the
aid, performance may drop dramatically. Thus, the introduction of a valid aid
can actually lower detection performance, compared to a more sensitive user
working alone. Similarly, adding a user to a system with high sensitivity may
lower its performance. System designers need to consider the potential adverse
effects of introducing users or aids into systems
Hazard Avoidance Alerting With Markov Decision Processes
This thesis describes an approach to designing hazard avoidance alerting systems based on a
Markov decision process (MDP) model of the alerting process, and shows its benefits over
standard design methods. One benefit of the MDP method is that it accounts for future decision
opportunities when choosing whether or not to alert, or in determining resolution guidance.
Another benefit is that it provides a means of modeling uncertain state information, such as
knowledge about unmeasurable mode variables, so that decisions are more informed.
A mode variable is an index for distinct types of behavior that a system exhibits at different
times. For example, in many situations normal system behavior is safe, but rare deviations from
the normal increase the likelihood of a harmful incident. Accurate modeling of mode
information is needed to minimize alerting system errors such as unnecessary or late alerts.
The benefits of the method are illustrated with two alerting scenarios where a pair of aircraft
must avoid collisions when passing one another. The first scenario has a fully observable state
and the second includes an uncertain mode describing whether an intruder aircraft levels off
safely above the evader or is in a hazardous blunder mode.
In MDP theory, outcome preferences are described in terms of utilities of different state
trajectories. In keeping with this, alerting system requirements are stated in the form of a reward
function. This is then used with probabilistic dynamic and sensor models to compute an alerting
logic (policy) that maximizes expected utility. Performance comparisons are made between the
MDP-based logics and alternate logics generated with current methods. It is found that in terms
of traditional performance measures (incident rate and unnecessary alert rate), the MDP-based
logic can meet or exceed that of alternate logics
Generalized Philosophy of Alerting with Applications for Parallel Approach Collision Prevention
An alerting system is automation designed to reduce the likelihood of undesirable
outcomes that are due to rare failures in a human-controlled system. It accomplishes this
by monitoring the system, and issuing warning messages to the human operators when
thought necessary to head off a problem. On examination of existing and recently
proposed logics for alerting it appears that few commonly accepted principles guide the
design process. Different logics intended to address the same hazards may take disparate
forms and emphasize different aspects of performance, because each reflects the intuitive
priorities of a different designer. Because performance must be satisfactory to all users
of an alerting system (implying a universal meaning of acceptable performance) and not
just one designer, a proposed logic often undergoes significant piecemeal modification
before gaining general acceptance. This report is an initial attempt to clarify the common
performance goals by which an alerting system is ultimately judged. A better
understanding of these goals will hopefully allow designers to reach the final logic in a
quicker, more direct and repeatable manner. As a case study, this report compares three
alerting logics for collision prevention during independent approaches to parallel
runways, and outlines a fourth alternative incorporating elements of the first three, but
satisfying stated requirements.NASA grant NAG1-218
A Probability-Base Alerting Logic for Aircraft on Parallel Approach
This document discusses the development and evaluation of an airborne collision alerting logic for aircraft on closely-spaced approaches to parallel runways. A novel methodology is used when links alerts to collision probabilities: alerting thresholds are set such that when the probability of a collision exceeds an acceptable hazard level an alert is issued. The logic was designed to limit the hazard level to that estimated for the Precision Runway Monitoring system: one accident in every one thousand blunders which trigger alerts. When the aircraft were constrained to be coaltitude, evaluations of a two-dimensional version of the alerting logic show that the achieved hazard level is approximately one accident in every 250 blunders. Problematic scenarios have been identified and corrections to the logic can be made. The evaluations also show that over eighty percent of all unnecessary alerts were issued during scenarios in which the miss distance would have been less than 1000 ft, indicating that the alerts may have been justified. Also, no unnecessary alerts were generated during normal approaches
Investigation of Alert Zone and Display Concepts for Free Flight
To better understand the potential benefits and drawbacks of utilizing a probability-based method, a number of alternative approaches to the collision avoidance problem were examined and summarized in the paper "Survey of Conflict Detection and Resolution Modeling Methods" which was presented in August 1997 at the AIAA Guidance, Navigation, and Control Conference. The paper provides a summary and comparative evaluation of the many different approaches that have been used in the past to perform conflict analysis. Each method is categorized in its dynamic modeling approach and method of handling conflict detection and conflict resolution. For example, one category included the extrapolation method used to predict future trajectories of which 3 were defined: nominal, probabilistic, and worst-case. Another category listed the metrics and parameters used by each method to make conflict decisions (i.e. estimated time to closest point of approach, miss distance, current separation, expected maneuvering cost, probability of conflict). Other useful information such as the ability to handle multi-aircraft conflicts and cooperative and non-cooperative maneuvering is also included
Time and Time Functions in Parametrized Non-Relativistic Quantum Mechanics
The ``evolving constants'' method of defining the quantum dynamics of
time-reparametrization-invariant theories is investigated for a particular
implementation of parametrized non-relativistic quantum mechanics (PNRQM). The
wide range of time functions that are available to define evolving constants
raises issues of interpretation, consistency, and the degree to which the
resulting quantum theory coincides with, or generalizes, the usual
non-relativistic theory. The allowed time functions must be restricted for the
predictions of PNRQM to coincide with those of usual quantum theory. They must
be restricted to have a notion of quantum evolution in a time-parameter
connected to spacetime geometry. They must be restricted to prevent the theory
from making inconsistent predictions for the probabilities of histories.
Suitable restrictions can be introduced in PNRQM but these seem unlikely to
apply to a reparametrization invariant theory like general relativity.Comment: 18pages, 1postscript figure in separate file, uses REVTEX 3.
Supersymmetric Quantization of Anisotropic Scalar-Tensor Cosmologies
In this paper we show that the spatially homogeneous Bianchi type I and
Kantowski-Sachs cosmologies derived from the Brans-Dicke theory of gravity
admit a supersymmetric extension at the quantum level. Global symmetries in the
effective one-dimensional actions characterize both classical and quantum
solutions. A wide family of exact wavefunctions satisfying the supersymmetric
constraints are found. A connection with quantum wormholes is briefly
discussed.Comment: In Press, Class. Quantum Grav. 20 pages, Late
Existing and Required Modeling Capabilities for Evaluating ATM Systems and Concepts
ATM systems throughout the world are entering a period of major transition and change. The combination of important technological developments and of the globalization of the air transportation industry has necessitated a reexamination of some of the fundamental premises of existing Air Traffic Management (ATM) concepts. New ATM concepts have to be examined, concepts that may place more emphasis on: strategic traffic management; planning and control; partial decentralization of decision-making; and added reliance on the aircraft to carry out strategic ATM plans, with ground controllers confined primarily to a monitoring and supervisory role. 'Free Flight' is a case in point. In order to study, evaluate and validate such new concepts, the ATM community will have to rely heavily on models and computer-based tools/utilities, covering a wide range of issues and metrics related to safety, capacity and efficiency. The state of the art in such modeling support is adequate in some respects, but clearly deficient in others. It is the objective of this study to assist in: (1) assessing the strengths and weaknesses of existing fast-time models and tools for the study of ATM systems and concepts and (2) identifying and prioritizing the requirements for the development of additional modeling capabilities in the near future. A three-stage process has been followed to this purpose: 1. Through the analysis of two case studies involving future ATM system scenarios, as well as through expert assessment, modeling capabilities and supporting tools needed for testing and validating future ATM systems and concepts were identified and described. 2. Existing fast-time ATM models and support tools were reviewed and assessed with regard to the degree to which they offer the capabilities identified under Step 1. 3 . The findings of 1 and 2 were combined to draw conclusions about (1) the best capabilities currently existing, (2) the types of concept testing and validation that can be carried out reliably with such existing capabilities and (3) the currently unavailable modeling capabilities that should receive high priority for near-term research and development. It should be emphasized that the study is concerned only with the class of 'fast time' analytical and simulation models. 'Real time' models, that typically involve humans-in-the-loop, comprise another extensive class which is not addressed in this report. However, the relationship between some of the fast-time models reviewed and a few well-known real-time models is identified in several parts of this report and the potential benefits from the combined use of these two classes of models-a very important subject-are discussed in chapters 4 and 7
Influence of a montmorency cherry juice blend on indices of exercise-induced stress and upper respiratory tract symptoms following marathon running—a pilot investigation
Background: Prolonged exercise, such as marathon running, has been associated with an increase in respiratory mucosal inflammation. The aim of this pilot study was to examine the effects of Montmorency cherry juice on markers of stress, immunity and inflammation following a Marathon.
Methods: Twenty recreational Marathon runners consumed either cherry juice (CJ) or placebo (PL) before and after a Marathon race. Markers of mucosal immunity secretory immunoglobulin A (sIgA), immunoglobulin G (IgG), salivary cortisol, inflammation (CRP) and self-reported incidence and severity of upper respiratory tract symptoms (URTS) were measured before and following the race.
Results: All variables except secretory IgA and IgG concentrations in saliva showed a significant time effect (P < 0.01). Serum CRP showed a significant interaction and treatment effect (P < 0.01). The CRP increase at 24 and 48 h post-Marathon was lower (P < 0.01) in the CJ group compared to PL group. Mucosal immunity and salivary cortisol showed no interaction effect or treatment effect. The incidence and severity of URTS was significantly greater than baseline at 24 h and 48 h following the race in the PL group and was also greater than the CJ group (P < 0.05). No URTS were reported in the CJ group whereas 50 % of runners in the PL group reported URTS at 24 h and 48 h post-Marathon.
Conclusions: This is the first study that provides encouraging evidence of the potential role of Montmorency cherries in reducing the development of URTS post-Marathon possibly caused by exercise-induced hyperventilation trauma, and/or other infectious and non-infectious factors
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