272 research outputs found
The Magnetic Field Gradiometer
This report has two principal goals. First, to present a general review of magnetic field gradiometers and, second, to provide new data concerning these gradiometers, including new information about their response to magnetic dipole fields. A system of nomenclature is introduced that is consistent with the mathematical concept of gradient and which provides a basis for discussions of the different functions of magnetic field gradiometers and differential magnetometers. The distinction between component gradiometers and total field gradiometers is also stressed.Office of Naval TechnologyNaval Postgraduate SchoolOffice of Naval ResearchAdditional support for this work was provided by the Office of Naval Research through Contracts No.N00014-75-C-1095 and N00014-77-C-0292.Approved for public release; distribution unlimited
The Magnetic Field Gradiometer
Final Technical Report No. E723-1This report has two principal goals: First, to present a general review of magnetic field
gradiometers and, second, to provide new data concerning these gradiometers, including new
information about their response to magnetic dipole fields. A system of nomenclature is introduced that is consistent with the mathematical concept of gradient and which provides a
basis for discussions of the different functions of magnetic field gradiometers and differential
magnetometers. The distinction between component gradiometers and total field gradiometers
is also stressed. An historical review provides an opportunity to describe the different characteristics of the many kinds of magnetic field gradiometers that have been developed since
the first report of such a gradiometer in 1925: rotating induction loop, fixed induction loop,
fluxgate, proton precession, optically pumped, and superconducting gradiometers are discussed.
It is pointed out how the great sensitivity of superconducting gradiometers, and possibly other
varieties of modern magnetic field gradiometers, may invalidate the popular 'source-free' asssumption under particular circumstances. Further, because these high sensitivities will make
the gradiometers more susceptible to the geomagnetic field gradient, expressions are derived
for the components of this gradient and some representative numerical values are calculated.
The response of both component and total field gradiometers to dipole sources is considered
for a number of different source-gradiometer configurations. On a more speculative note, two
varieties of rotating component gradiometers are discussed, with particular attention being
given to their possibly unique characteristics. The report ends by recapitulating the many
applications of magnetic field gradiometers, particularly in such important areas as medicine,
energy production, and defense, and by stressing the need for gradiometer-related basic research.Office of Naval TechnologyNaval Postgraduate SchoolOffice of Naval ResearchN00228-81-C-AB56Approved for public release; distribution is unlimited
A review of the relationship between eggshell colour and water vapour conductance
This review brings together the available literature that examines the effect of variations in pigmentation on the gas conductance of avian eggshells. Pheasant and Houbara bustard eggs provide some evidence that shell abnormalities can impact upon colour and conductance. By contrast, data from wild birds suggest that neither the degree of maculation or intensity of ground colour impact upon gas conductance. Those studies that purport to show variation in rates of water loss in eggs with different degrees of pigmentation may have been confounded by variation in nest humidity. This emerging field of research remains very much in its infancy
Anthropogenic Space Weather
Anthropogenic effects on the space environment started in the late 19th
century and reached their peak in the 1960s when high-altitude nuclear
explosions were carried out by the USA and the Soviet Union. These explosions
created artificial radiation belts near Earth that resulted in major damages to
several satellites. Another, unexpected impact of the high-altitude nuclear
tests was the electromagnetic pulse (EMP) that can have devastating effects
over a large geographic area (as large as the continental United States). Other
anthropogenic impacts on the space environment include chemical release ex-
periments, high-frequency wave heating of the ionosphere and the interaction of
VLF waves with the radiation belts. This paper reviews the fundamental physical
process behind these phenomena and discusses the observations of their impacts.Comment: 71 pages, 35 figure
Magnetic Coordinate Systems
Geospace phenomena such as the aurora, plasma motion, ionospheric currents
and associated magnetic field disturbances are highly organized by Earth's main
magnetic field. This is due to the fact that the charged particles that
comprise space plasma can move almost freely along magnetic field lines, but
not across them. For this reason it is sensible to present such phenomena
relative to Earth's magnetic field. A large variety of magnetic coordinate
systems exist, designed for different purposes and regions, ranging from the
magnetopause to the ionosphere. In this paper we review the most common
magnetic coordinate systems and describe how they are defined, where they are
used, and how to convert between them. The definitions are presented based on
the spherical harmonic expansion coefficients of the International Geomagnetic
Reference Field (IGRF) and, in some of the coordinate systems, the position of
the Sun which we show how to calculate from the time and date. The most
detailed coordinate systems take the full IGRF into account and define magnetic
latitude and longitude such that they are constant along field lines. These
coordinate systems, which are useful at ionospheric altitudes, are
non-orthogonal. We show how to handle vectors and vector calculus in such
coordinates, and discuss how systematic errors may appear if this is not done
correctly
Deriving Non-decoupling Effects of Heavy Fields from the Path Integral: a Heavy Higgs Field in an SU(2) Gauge Theory
We describe a method to remove non-decoupling heavy fields from a quantized
field theory and to construct a low-energy one-loop effective Lagrangian by
integrating out the heavy degrees of freedom in the path integral. We apply
this method to the Higgs boson in a spontaneously broken SU(2) gauge theory
(gauged linear sigma-model). In this context, the background-field method is
generalized to the non-linear representation of the Higgs sector by applying (a
generalization of) the Stueckelberg formalism. The (background) gauge-invariant
renormalization is discussed. At one loop the log M_H-terms of the heavy-Higgs
limit of this model coincide with the UV-divergent terms of the corresponding
gauged non-linear sigma-model, but vertex functions differ in addition by
finite (constant) terms in both models. These terms are also derived by our
method. Diagrammatic calculations of some vertex functions are presented as
consistency check.Comment: 33 Pages LaTeX, 6 figures uuencoded postscrip
A origem das parcerias público-privada na governança global da educação
Durante a última década, a globalização da governança educacional por meio de parcerias público-privadas (PPP) tem gerado considerável debate quanto ao seu significado, propósito, status e resultados. Este debate é particularmente aquecido no setor da educação por causa da ampla aceitação da educação como atividade complexa, social e política que deve permanecer, em grande parte, se não totalmente, no setor público, servindo a interesses públicos. O artigo analisa a rápida expansão das parcerias público-privadas em educação (PPPE) articulada à introdução de regras de mercado no setor. Neste estudo nos concentramos sobre o papel de uma rede de desenvolvimento global, fundamental na globalização de um tipo particular de PPPE, indicando que a ideia de PPP encaixa-se em um projeto mais amplo de reconstituição da educação pública no âmbito do setor de serviços, a ser governada como parte da construção de uma sociedade de mercado.Over the past decade, the globalization and governing of education through Public Private Partnerships (PPPs) have generated considerable debate as to their meaning, purpose, status and outcomes. This debate is particularly heated in the education sector because of the widely-held view that education is a complex social and political activity that should remain largely, if not wholly, in the public sector serving public interests. The article analyses the rapid expansion of Education Public Private Partnerships (EPPPs) and the associated introduction of market rules into the education sector. We focus on the role of a key global development network in globalizing a particular kind of ePPPs, and show that the EPPP idea fi ts into a wider project of reconstituting public education as an education services industry to be governed as part of the construction of a market society
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