724 research outputs found
The Hamiltonian Structures of the super KP hierarchy Associated with an Even Parity SuperLax Operator
We consider the even parity superLax operator for the supersymmetric KP
hierarchy of the form and obtain
the two Hamiltonian structures following the standard method of Gelfand and
Dikii. We observe that the first Hamiltonian structure is local and linear
whereas the second Hamiltonian structure is non-local and nonlinear among the
superfields appearing in the Lax operator. We discuss briefly on their
connections with the super algebra.Comment: 14 pages, Plain tex, IC/93/17
First record of Helichrysum foetidum (L.) Moench. (Asteraceae, Gnaphalieae) for South America.
We provide the first record of Helichrysum foetidum (Asteraceae, Gnaphalieae) for South America, based on new collections made in the state of Rio Grande do Sul, southern Brazil. This species is native from Africa and cultivated in Europe, where it is used as an ornamental or medicinal herb. Helichrysum foetidum is recognized by the discolorous leaves with adaxial surface dark green, tomentose and abaxial surface grey, lanose tomentose margins, large heads organized in a corymbiform capitulescence and bright yellow bracts and flowers. Description, a map of distribution in South America and images of the collected specimens are provided
Constrained Analysis of Topologically Massive Gravity
We quantize the Einstein gravity in the formalism of weak gravitational
fields by using the constrained Hamiltonian method. Special emphasis is given
to the 2+1 spacetime dimensional case where a (topological) Chern-Simons term
is added to the Lagrangian.Comment: 15 pages, IF-UFRJ-21/9
Canonical Transformations in a Higher-Derivative Field Theory
It has been suggested that the chiral symmetry can be implemented only in
classical Lagrangians containing higher covariant derivatives of odd order.
Contrary to this belief, it is shown that one can construct an exactly soluble
two-dimensional higher-derivative fermionic quantum field theory containing
only derivatives of even order whose classical Lagrangian exhibits chiral-gauge
invariance. The original field solution is expressed in terms of usual Dirac
spinors through a canonical transformation, whose generating function allows
the determination of the new Hamiltonian. It is emphasized that the original
and transformed Hamiltonians are different because the mapping from the old to
the new canonical variables depends explicitly on time. The violation of
cluster decomposition is discussed and the general Wightman functions
satisfying the positive-definiteness condition are obtained.Comment: 12 pages, LaTe
Total And Segmental Colonic Transit Time In Constipated Patients With Chagas' Disease Without Megaesophagus Or Megacolon.
Manometric and pharmacological tests have shown that motor abnormalities may occur in the non-dilated colons of chagasic patients. In order to investigate the presence of abnormalities of colonic function in constipated patients with Chagas' disease (ChC) without megaesophagus or megacolon, studies of total and segmental colonic transit time with radiopaque markers were performed on 15 ChC patients, 27 healthy volunteers and 17 patients with idiopathic constipation (IC). The values obtained for the control group were similar to those reported in the literature (total colonic time: 34. 1 +/- 15.6 h; right colon: 9.9 +/- 7.3 h; left colon: 10.8 +/- 10 h, and rectosigmoid: 12.6 +/- 9.9 h). Colonic transit time data permitted us to divide both IC and ChC patients into groups with normal transit and those with slow colonic transit. Colonic inertia was detected in 41% of IC patients and in 13% of ChC patients; left colon isolated stasis (hindgut dysfunction) was detected in 12% of IC patients and 7% of ChC patients, and outlet obstruction was detected in 6% of IC patients and 7% of ChC patients. There were no significant differences in total or segmental colonic transit times between slow transit IC and slow transit ChC patients. In conclusion, an impairment of colonic motility was detected in about 30% of constipated patients with Chagas' disease without megaesophagus or megacolon. This subgroup of patients presented no distinctive clinical feature or pattern of colonic dysmotility when compared to patients with slow transit idiopathic constipation.3343-
Vegetative compatibility and genetic analysis of Colletotrichum lindemuthianum isolates from Brazil.
Lagrangian approach to a symplectic formalism for singular systems
We develop a Lagrangian approach for constructing a symplectic structure for
singular systems. It gives a simple and unified framework for understanding the
origin of the pathologies that appear in the Dirac-Bergmann formalism, and
offers a more general approach for a symplectic formalism, even when there is
no Hamiltonian in a canonical sense. We can thus overcome the usual limitations
of the canonical quantization, and perform an algebraically consistent
quantization for a more general set of Lagrangian systems.Comment: 30 page
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