1,659 research outputs found
Thirteen category recognition map of Yellowstone National Park produced from ERTS-1 MSS data
There are no author-identified significant results in this report
Antigenic Complementarity in the Origins of Autoimmunity: A General Theory Illustrated With a Case Study of Idiopathic Thrombocytopenia Purpura
We describe a novel, testable theory of autoimmunity, outline novel predictions made by the theory, and illustrate its application to unravelling the possible causes of idiopathic thrombocytopenia purpura (ITP). Pairs of stereochemically complementary antigens induce complementary immune responses (antibody or T-cell) that create loss of regulation and civil war within the immune system itself. Antibodies attack antibodies creating circulating immune complexes; T-cells attack T-cells creating perivascular cuffing. This immunological civil war abrogates the self-nonself distinction. If at least one of the complementary antigens mimics a self antigen, then this unregulated immune response will target host tissues as well. Data demonstrating that complementary antigens are found in some animal models of autoimmunity and may be present in various human diseases, especially ITP, are reviewed. Specific mechanisms for preventing autoimmunity or suppressing existing autoimmunity are derived from the theory, and critical tests proposed. Finally, we argue that Koch's postulates are inadequate for establishing disease causation for multiple-antigen diseases and discuss the possibility that current research has failed to elucidate the causes of human autoimmune diseases because we are using the wrong criteria
Exact and approximate dynamics of the quantum mechanical O(N) model
We study a quantum dynamical system of N, O(N) symmetric, nonlinear
oscillators as a toy model to investigate the systematics of a 1/N expansion.
The closed time path (CTP) formalism melded with an expansion in 1/N is used to
derive time evolution equations valid to order 1/N (next-to-leading order). The
effective potential is also obtained to this order and its properties
areelucidated. In order to compare theoretical predictions against numerical
solutions of the time-dependent Schrodinger equation, we consider two initial
conditions consistent with O(N) symmetry, one of them a quantum roll, the other
a wave packet initially to one side of the potential minimum, whose center has
all coordinates equal. For the case of the quantum roll we map out the domain
of validity of the large-N expansion. We discuss unitarity violation in the 1/N
expansion; a well-known problem faced by moment truncation techniques. The 1/N
results, both static and dynamic, are also compared to those given by the
Hartree variational ansatz at given values of N. We conclude that late-time
behavior, where nonlinear effects are significant, is not well-described by
either approximation.Comment: 16 pages, 12 figrures, revte
Infrared Behaviour of Systems With Goldstone Bosons
We develop various complementary concepts and techniques for handling quantum
fluctuations of Goldstone bosons.We emphasise that one of the consequences of
the masslessness of Goldstone bosons is that the longitudinal fluctuations also
have a diverging susceptibility characterised by an anomalous dimension
in space-time dimensions .In these fluctuations diverge
logarithmically in the infrared region.We show the generality of this
phenomenon by providing three arguments based on i). Renormalization group
flows, ii). Ward identities, and iii). Schwinger-Dyson equations.We obtain an
explicit form for the generating functional of one-particle irreducible
vertices of the O(N) (non)--linear --models in the leading 1/N
approximation.We show that this incorporates all infrared behaviour correctly
both in linear and non-linear -- models. Our techniques provide an
alternative to chiral perturbation theory.Some consequences are discussed
briefly.Comment: 28 pages,2 Figs, a new section on some universal features of
multipion processes has been adde
Systematic corrections for bosonic and fermionic vector models without auxiliary fields
In this paper, colorless bilocal fields are employed to study the large
limit of both fermionic and bosonic vector models. The Jacobian associated with
the change of variables from the original fields to the bilocals is computed
exactly, thereby providing an exact effective action. This effective action is
shown to reproduce the familiar perturbative expansion for the two and four
point functions. In particular, in the case of fermionic vector models, the
effective action correctly accounts for the Fermi statistics. The theory is
also studied non-perturbatively. The stationary points of the effective action
are shown to provide the usual large gap equations. The homogeneous
equation associated with the quadratic (in the bilocals) action is simply the
two particle Bethe Salpeter equation. Finally, the leading correction in
is shown to be in agreement with the exact matrix of the model.Comment: 24 pages, uses REVTEX macros. Replaced with final version to appear
in Phys. Rev.
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MOLYBDENUM AND MOLYBDENUM-BASE ALLOYS. PART 1. HIGH-TEMPERATURE PROPERTIES OF A MOLYBDENUM-3 PER CENT THROIUM ALLOY. PART 2. EVALUATION OF A COLUMBIUM-ZIRCONIUM-TITANIUM CLADDING ALLOY
In the first section of this report, a study was made of the high- temperature properties of a Mo-3% Th alloy to determine whether this alloy should be rejected as valueless or a full research program should be proposed. Results of this investigation show that thorium should be studied more intensively as an alloying addition for molybdenum. In the second section, an evaluation is presented of the oxidation behavior, mechanical properties, and cladding properties of Nb - 55 at.% Zr - 5 at.% Ti alloy. (W.L.H.
The next to leading order effective potential in the 2+1 dimensional Nambu-Jona-Lasinio model at finite temperature
The finite temperature effective potential in the 2+1 dimensional
Nambu-Jona-Lasinio model is constructed up to the next to leading order in the
large expansion, where is the number of flavors in the model. The
distinctive feature of the analysis is an inclusion of an additional scalar
field, which allows us to circumvent the well known, and otherwise unavoidable
problem with the imaginary contribution to the effective potential. In
accordance with the Mermin-Wagner-Coleman theorem, applied to the dimensionally
reduced subsystem of the zero Matsubara modes of the composite boson fields,
the finite temperature effective potential reveals a global minimum at the zero
of the composite order parameter. This allows us to conclude that the
continuous global symmetry of the NJL model is not broken for any arbitrarily
small, finite temperature.Comment: 12 pages, 4 figures, REVTe
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