372 research outputs found
Decoherence of a quantum gyroscope
We study the behavior of a quantum gyroscope, that is, a quantum system which
singles out a direction in space in order to measure certain properties of
incoming particles such as the orientation of their spins. We show that
repeated Heisenberg interactions of the gyroscope with several incoming
spin-1/2 particles provides a simple model of decoherence which exhibits both
relaxation and dephasing. Focusing on the semiclassical limit, we derive
equations of motion for the evolution of a coherent state and investigate the
evolution of a superposition of such states. While a coherent state evolves on
a timescale given by the classical ratio of the angular momentum of the
gyroscope to that of the incoming particles, dephasing acts on a much shorter
timescale that depends only on the angular difference of the states in the
superposition.Comment: 7 pages, 5 figure
Challenges in Reconciling Different Views of Neuroanatomy in a Reference Ontology of Anatomy
A fundamental requirement for integrating neuroscience data is a well-structured ontology that can incorporate, accommodate and reconcile different neuroanatomical views. Here we describe the challenges in creating such ontology, and, because of its principled design, illustrate the potential of the Foundational Model of Anatomy to be that ontology
Decoherence suppression via environment preparation
To protect a quantum system from decoherence due to interaction with its
environment, we investigate the existence of initial states of the environment
allowing for decoherence-free evolution of the system. For models in which a
two-state system interacts with a dynamical environment, we prove that such
states exist if and only if the interaction and self-evolution Hamiltonians
share an eigenstate. If decoherence by state preparation is not possible, we
show that initial states minimizing decoherence result from a delicate
compromise between the environment and interaction dynamics.Comment: 4 pages, 2 figure
Phased Array Feed Calibration, Beamforming and Imaging
Phased array feeds (PAFs) for reflector antennas offer the potential for
increased reflector field of view and faster survey speeds. To address some of
the development challenges that remain for scientifically useful PAFs,
including calibration and beamforming algorithms, sensitivity optimization, and
demonstration of wide field of view imaging, we report experimental results
from a 19 element room temperature L-band PAF mounted on the Green Bank
20-Meter Telescope. Formed beams achieved an aperture efficiency of 69% and
system noise temperature of 66 K. Radio camera images of several sky regions
are presented. We investigate the noise performance and sensitivity of the
system as a function of elevation angle with statistically optimal beamforming
and demonstrate cancelation of radio frequency interference sources with
adaptive spatial filtering.Comment: 19 pages, 13 figure
The genealogy of ‘∨’
The use of the symbol ∨ for disjunction in formal logic is ubiquitous. Where did it come from? The paper details the evolution of the symbol ∨ in its historical and logical context. Some sources say that disjunction in its use as connecting propositions or formulas was introduced by Peano; others suggest that it originated as an abbreviation of the Latin word for “or”, vel. We show that the origin of the symbol ∨ for disjunction can be traced to Whitehead and Russell’s pre-Principia work in formal logic. Because of Principia’s influence, its notation was widely adopted by philosophers working in logic (the logical empiricists in the 1920s and 1930s, especially Carnap and early Quine). Hilbert’s adoption of ∨ in his Grundzüge der theoretischen Logik guaranteed its widespread use by mathematical logicians. The origins of other logical symbols are also discussed
Gender differences in survival among adult patients starting antiretroviral therapy in South Africa: a multicentre cohort study.
Increased mortality among men on antiretroviral therapy (ART) has been documented but remains poorly understood. We examined the magnitude of and risk factors for gender differences in mortality on ART
Computer-aided whole-cell design:taking a holistic approach by integrating synthetic with systems biology
Computer-aided design for synthetic biology promises to accelerate the
rational and robust engineering of biological systems; it requires both
detailed and quantitative mathematical and experimental models of the processes
to (re)design, and software and tools for genetic engineering and DNA assembly.
Ultimately, the increased precision in the design phase will have a dramatic
impact on the production of designer cells and organisms with bespoke functions
and increased modularity. Computer-aided design strategies require quantitative
representations of cells, able to capture multiscale processes and link
genotypes to phenotypes. Here, we present a perspective on how whole-cell,
multiscale models could transform design-build-test-learn cycles in synthetic
biology. We show how these models could significantly aid in the design and
learn phases while reducing experimental testing by presenting case studies
spanning from genome minimization to cell-free systems, and we discuss several
challenges for the realization of our vision. The possibility to describe and
build in silico whole-cells offers an opportunity to develop increasingly
automatized, precise and accessible computer-aided design tools and strategies
throughout novel interdisciplinary collaborations
Water-Use Data in the United States: Challenges and Future Directions
In the United States, greater attention has been given to developing water supplies and quantifying available waters than determining who uses water, how much they withdraw and consume, and how and where water use occurs. As water supplies are stressed due to an increasingly variable climate, changing land-use, and growing water needs, greater consideration of the demand side of the water balance equation is essential. Data about the spatial and temporal aspects of water use for different purposes are now critical to long-term water supply planning and resource management. We detail the current state of water-use data, the major stakeholders involved in their collection and applications, and the challenges in obtaining high-quality nationally consistent data applicable to a range of scales and purposes. Opportunities to improve access, use, and sharing of water-use data are outlined. We cast a vision for a world-class national water-use data product that is accessible, timely, and spatially detailed. Our vision will leverage the strengths of existing local, state, and federal agencies to facilitate rapid and informed decision-making, modeling, and science for water resources. To inform future decision-making regarding water supplies and uses, we must coordinate efforts to substantially improve our capacity to collect, model, and disseminate water-use data
1972: Abilene Christian College Bible Lectures - Full Text
THE CHURCH AND THE FUTURE
Being the Abilene Christian College Annual Bible Lectures 1972
Published by
ABILENE CHRISTIAN COLLEGE BOOK STORE
ACC Station Abilene, Texas 7960
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