95,901 research outputs found
How to read probability distributions as statements about process
Probability distributions can be read as simple expressions of information.
Each continuous probability distribution describes how information changes with
magnitude. Once one learns to read a probability distribution as a measurement
scale of information, opportunities arise to understand the processes that
generate the commonly observed patterns. Probability expressions may be parsed
into four components: the dissipation of all information, except the
preservation of average values, taken over the measurement scale that relates
changes in observed values to changes in information, and the transformation
from the underlying scale on which information dissipates to alternative scales
on which probability pattern may be expressed. Information invariances set the
commonly observed measurement scales and the relations between them. In
particular, a measurement scale for information is defined by its invariance to
specific transformations of underlying values into measurable outputs.
Essentially all common distributions can be understood within this simple
framework of information invariance and measurement scale.Comment: v2: added table of contents, adjusted section numbers v3: minor
editing, updated referenc
An analysis of hurricane seasons in the pre-HURDAT era (1751-1850)
An extensive database of the tracks of tropical cyclones in the North Atlantic Ocean since 1851 is known as the North Atlantic Hurricane Database (HURDAT). While this database is valuable to public and private agencies, many of the deadliest hurricanes on record occurred prior to 1851. This study will address the research problem of the availability of historical information and the feasibility of collecting data and producing historical tropical cyclone tracks. This thesis describes a methodology for identifying tropical cyclones that existed during the one hundred year period from 1751-1850 referred to as the “pre-HURDAT era” in this study. Uncovering historical tropical cyclone tracks are important for researchers seeking long term patterns in the climate record. This study is a synthesis of all readily available historical data which can be used to identify the tracks of documented tropical cyclones that occurred during the pre-HURDAT era. To emphasize the applicability of historical hurricane tracks, a study comparing landfall patterns of landfalling east coast hurricanes was also done. These tracks were analyzed using historical chronologies, ship data, and other “regional literature”.Department of GeographyThesis (M.S.
Microbial metabolism: optimal control of uptake versus synthesis
Microbes require several complex organic molecules for growth. A species may
obtain a required factor by taking up molecules released by other species or by
synthesizing the molecule. The patterns of uptake and synthesis set a flow of
resources through the multiple species that create a microbial community. This
article analyzes a simple mathematical model of the tradeoff between uptake and
synthesis. Key factors include the influx rate from external sources relative
to the outflux rate, the rate of internal decay within cells, and the cost of
synthesis. Aspects of demography also matter, such as cellular birth and death
rates, the expected time course of a local resource flow, and the associated
lifespan of the local population. Spatial patterns of genetic variability and
differentiation between populations may also strongly influence the evolution
of metabolic regulatory controls of individual species and thus the structuring
of microbial communities. The widespread use of optimality approaches in recent
work on microbial metabolism has ignored demography and genetic structure
Receptor uptake arrays for vitamin B12, siderophores and glycans shape bacterial communities
Molecular variants of vitamin B12, siderophores and glycans occur. To take up
variant forms, bacteria may express an array of receptors. The gut microbe
Bacteroides thetaiotaomicron has three different receptors to take up variants
of vitamin B12 and 88 receptors to take up various glycans. The design of
receptor arrays reflects key processes that shape cellular evolution.
Competition may focus each species on a subset of the available nutrient
diversity. Some gut bacteria can take up only a narrow range of carbohydrates,
whereas species such as B.~thetaiotaomicron can digest many different complex
glycans. Comparison of different nutrients, habitats, and genomes provide
opportunity to test hypotheses about the breadth of receptor arrays. Another
important process concerns fluctuations in nutrient availability. Such
fluctuations enhance the value of cellular sensors, which gain information
about environmental availability and adjust receptor deployment. Bacteria often
adjust receptor expression in response to fluctuations of particular
carbohydrate food sources. Some species may adjust expression of uptake
receptors for specific siderophores. How do cells use sensor information to
control the response to fluctuations? That question about regulatory wiring
relates to problems that arise in control theory and artificial intelligence.
Control theory clarifies how to analyze environmental fluctuations in relation
to the design of sensors and response systems. Recent advances in deep learning
studies of artificial intelligence focus on the architecture of regulatory
wiring and the ways in which complex control networks represent and classify
environmental states. I emphasize the similar design problems that arise in
cellular evolution, control theory, and artificial intelligence. I connect
those broad concepts to testable hypotheses for bacterial uptake of B12,
siderophores and glycans.Comment: Added many new references, edited throughou
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