19 research outputs found
Tests of Two-Body Dirac Equation Wave Functions in the Decays of Quarkonium and Positronium into Two Photons
Two-Body Dirac equations of constraint dynamics provide a covariant framework
to investigate the problem of highly relativistic quarks in meson bound states.
This formalism eliminates automatically the problems of relative time and
energy, leading to a covariant three dimensional formalism with the same number
of degrees of freedom as appears in the corresponding nonrelativistic problem.
It provides bound state wave equations with the simplicity of the
nonrelativistic Schroedinger equation. Here we begin important tests of the
relativistic sixteen component wave function solutions obtained in a recent
work on meson spectroscopy, extending a method developed previously for
positronium decay into two photons. Preliminary to this we examine the
positronium decay in the 3P_{0,2} states as well as the 1S_0. The two-gamma
quarkonium decays that we investigate are for the \eta_{c}, \eta_{c}^{\prime},
\chi_{c0}, \chi_{c2}, \pi^{0}, \pi_{2}, a_{2}, and f_{2}^{\prime} mesons. Our
results for the four charmonium states compare well with those from other quark
models and show the particular importance of including all components of the
wave function as well as strong and CM energy dependent potential effects on
the norm and amplitude. The results for the \pi^{0}, although off the
experimental rate by 15%, is much closer than the usual expectations from a
potential model. We conclude that the Two-Body Dirac equations lead to wave
functions which provide good descriptions of the two-gamma decay amplitude and
can be used with some confidence for other purposes.Comment: 79 pages, included new sections on covariant scalar product and added
pages on positronium decay for 3P0 and 3P_2 state
A Tale of Three Equations: Breit, Eddington-Guant, and Two-Body Dirac
G.Breit's original paper of 1929 postulates the Breit equation as a
correction to an earlier defective equation due to Eddington and Gaunt,
containing a form of interaction suggested by Heisenberg and Pauli. We observe
that manifestly covariant electromagnetic Two-Body Dirac equations previously
obtained by us in the framework of Relativistic Constraint Mechanics reproduce
the spectral results of the Breit equation but through an interaction structure
that contains that of Eddington and Gaunt. By repeating for our equation the
analysis that Breit used to demonstrate the superiority of his equation to that
of Eddington and Gaunt, we show that the historically unfamiliar interaction
structures of Two-Body Dirac equations (in Breit-like form) are just what is
needed to correct the covariant Eddington Gaunt equation without resorting to
Breit's version of retardation.Comment: 15 pages latex, published in Foundations of Physics, Vol 27, 67
(1997
Relativistic Calculation of the Meson Spectrum: a Fully Covariant Treatment Versus Standard Treatments
A large number of treatments of the meson spectrum have been tried that
consider mesons as quark - anti quark bound states. Recently, we used
relativistic quantum "constraint" mechanics to introduce a fully covariant
treatment defined by two coupled Dirac equations. For field-theoretic
interactions, this procedure functions as a "quantum mechanical transform of
Bethe-Salpeter equation". Here, we test its spectral fits against those
provided by an assortment of models: Wisconsin model, Iowa State model,
Brayshaw model, and the popular semi-relativistic treatment of Godfrey and
Isgur. We find that the fit provided by the two-body Dirac model for the entire
meson spectrum competes with the best fits to partial spectra provided by the
others and does so with the smallest number of interaction functions without
additional cutoff parameters necessary to make other approaches numerically
tractable. We discuss the distinguishing features of our model that may account
for the relative overall success of its fits. Note especially that in our
approach for QCD, the resulting pion mass and associated Goldstone behavior
depend sensitively on the preservation of relativistic couplings that are
crucial for its success when solved nonperturbatively for the analogous
two-body bound-states of QED.Comment: 75 pages, 6 figures, revised content
Transcatheter placement of a low-profile biodegradable pulmonary valve made of small intestinal submucosa: A long-term study in a swine model
ObjectiveWe sought to investigate a placement of a percutaneous low-profile prosthetic valve constructed of small intestinal submucosa in the pulmonary position in a swine model.MethodsTwelve female farm pigs were stented at the native pulmonary valve to induce pulmonary insufficiency. Once right ventricular dilation occurred, the small intestinal submucosa valve was implanted. The pigs were followed up with transthoracic echocardiographic Doppler scanning. One animal died of heart failure before valve replacement. Animals were euthanized at 1 day, 1 month, 3 months, 6 months, and 12 months after valve implantation.ResultsThe small intestinal submucosa pulmonary valve showed effective reversal of pulmonary regurgitation. There were no misplacements during deployment. There were no embolizations. One-year echocardiographic follow-up showed minimal regurgitation and no stenosis for a valve/vessel ratio of 0.78 or greater. Histologic examination demonstrated intensive remodeling of the small intestinal submucosal valve. Within 1 month, the surface was covered by endothelium, and fibroblasts invaded the interior. Over the following months, the small intestinal submucosal valve remodeled without apparent graft rejection.ConclusionThe small intestinal submucosa valve has the potential for graft longevity without the need for anticoagulation or immunosuppression. Histologic remodeling of the valve tissue provides a replacement capable of resembling a native valve that can be placed percutaneously with low-profile delivery systems
Stone Mills, Glenora, ca 1813
Photographie: Hartill Art Associates. ACa-0635; Date du début des travaux de réalisation : Ca 1813
The UN conference on sustainable development (Rio+20): A sign of the times or ‘ecology as spectacle’?
International Business Transactions: a Problem-Oriented Coursebook. 11th edition
The 11th edition of this popular problem-oriented coursebook introduces law students to the conduct of business in the world community. Problems on international contracting, financing, trade regulation, licensing and technology transfers, foreign investment, and international business dispute resolution are presented. The book provides a current, in-depth examination of issues that clients are likely to face, such as defending against import competition; expanding exports and overseas markets; and dealing with NAFTA, the WTO, and other trade agreements. The coursebook is designed to survey a wide range of laws involving trade, licensing, and investment, and explore how issues and problems are addressed by lawyers serving as problem solvers.https://digitalcommons.law.umaryland.edu/books/1042/thumbnail.jp
International Business Transactions: Trade and Economic Relations (Special Break-out edition)
This is a special break-out edition adapted from the authors\u27 widely used International Business Transactions: A Problem-Oriented Coursebook , 11th. The purpose of this volume is to facilitate a focused study of the law of international trade and economic relations. After a brief introduction to the conduct of business in the world community, the book uses hypothetical problems to present some of the most typical and important issues regarding imports, exports, technology transfers, and dispute settlement in conjunction with related readings and materials. The primary focus is on lawyers, public and private, as problem solvers