2,173 research outputs found
A note on Duffin-Kemmer-Petiau equation in (1+1) space-time dimensions
In the last years several papers addressed the supposed spin-1 sector of the
massive Duffin-Kemmer-Petiau (DKP) equation restricted to (1+1) space-time
dimensions. In this note we show explicitly that this is a misleading approach,
since the DKP algebra in (1+1) dimensions admits only a spin-0 representation.
Our result also is useful to understand why several recent papers found
coincident results for both spin-0 and spin-1 sectors of the DKP theory in
(3+1) dimensions when the dynamics is restricted to one space dimension.Comment: 3 pages, no figure
Interacting spin 0 fields with torsion via Duffin-Kemmer-Petiau theory
Here we study the behaviour of spin 0 sector of the DKP field in spaces with
torsion. First we show that in a Riemann-Cartan manifold the DKP field presents
an interaction with torsion when minimal coupling is performed, contrary to the
behaviour of the KG field, a result that breaks the usual equivalence between
the DKP and the KG fields.
Next we analyse the case of Teleparallel Equivalent of General Relativity
Weitzenbock manifold, showing that in this case there is a perfect agreement
between KG and DKP fields. The origins of both results are also discussed.Comment: 10 pages, no figures, uses REVTEX. Changes in the presentation, minor
misprints and one equation corrected. References updated. To appear in
General Relativity and Gravitatio
Conformal invariance of massless Duffin-Kemmer-Petiau theory in Riemannian space-times
We investigate the conformal invariance of massless Duffin-Kemmer-Petiau
theory coupled to riemannian space-times. We show that, as usual, in the
minimal coupling procedure only the spin 1 sector of the theory -which
corresponds to the electromagnetic field- is conformally invariant. We show
also that the conformal invariance of the spin 0 sector can be naturally
achieved by introducing a compensating term in the lagrangian. Such a procedure
-besides not modifying the spin 1 sector- leads to the well-known conformal
coupling between the scalar curvature and the massless Klein-Gordon-Fock field.
Going beyond the riemannian spacetimes, we briefly discuss the effects of a
nonvanishing torsion in the scalar case.Comment: 8 pages, no figures. Major changes in contend and results. To appear
in Class.Quant.Gra
Spin 1 fields in Riemann-Cartan space-times "via" Duffin-Kemmer-Petiau theory
We consider massive spin 1 fields, in Riemann-Cartan space-times, described
by Duffin-Kemmer-Petiau theory. We show that this approach induces a coupling
between the spin 1 field and the space-time torsion which breaks the usual
equivalence with the Proca theory, but that such equivalence is preserved in
the context of the Teleparallel Equivalent of General Relativity.Comment: 8 pages, no figures, revtex. Dedicated to Professor Gerhard Wilhelm
Bund on the occasion of his 70th birthday. To appear in Gen. Rel. Grav.
Equations numbering corrected. References update
Compactness and asymptotic behavior in nonautonomous linear parabolic equations with unbounded coefficients in
We consider a class of second order linear nonautonomous parabolic equations
in R^d with time periodic unbounded coefficients. We give sufficient conditions
for the evolution operator G(t,s) be compact in C_b(R^d) for t>s, and describe
the asymptotic behavior of G(t,s)f as t-s goes to infinity in terms of a family
of measures mu_s, s in R, solution of the associated Fokker-Planck equation
transsphenoidal surgery for secreting pituitary microadenomas: results with intraoperative application of absolute alcohol
ABSTRACT
Background: Pituitary adenomas represent a quite frequent neurosurgical disease. Secreting pituitary adenomas are represented by PRL, GH, ACTH and TSH tumours; the rate of postoperative hormonal recurrence is not ineligible. Methods: We present 106 patients affected by secreting pituitary microadenomas operated through transsphenoidal approach from 1998 through to 2008; in 54 (group 1) patients, intraoperative absolute alcohol was applied, while in the other 52 (group 2) it was not employed. The indications and the intraoperative technique of absolute alcohol application are presented. Hormonal recurrence was treated by hypofractionated stereotactic radiotherapy and/or medical therapy. Results: Postoperative hormonal and clinical remission was achieved in 50 and 47 patients respectively of group one and group two. At the first follow-up control, after 3 months from surgery, no patient of both groups presented hormonal/clinical recurrence. Six months after surgery, no patient of group one presented hormonal recurrence, while two patients of group 2 presented hormonal recurrence. After 2 years from surgery, two patients of group 1 and 4 patients of group 2 presented hormonal recurrence. Three years after operation, hormonal hypersecretion recurred in three patients of group one and in six patients of group 2. At 5 years follow-up, six patients of group one and 8 of group two presented hormonal recurrence. Conclusions: Intraoperative application of absolute alcohol, in selected cases, resulted useful to achieve better results in secreting pituitary microadenomas concerning both postoperative hormonal recurrence and hormonal persistence
Dynamic Transitions for Quasilinear Systems and Cahn-Hilliard equation with Onsager mobility
The main objectives of this article are two-fold. First, we study the effect
of the nonlinear Onsager mobility on the phase transition and on the
well-posedness of the Cahn-Hilliard equation modeling a binary system. It is
shown in particular that the dynamic transition is essentially independent of
the nonlinearity of the Onsager mobility. However, the nonlinearity of the
mobility does cause substantial technical difficulty for the well-posedness and
for carrying out the dynamic transition analysis. For this reason, as a second
objective, we introduce a systematic approach to deal with phase transition
problems modeled by quasilinear partial differential equation, following the
ideas of the dynamic transition theory developed recently by Ma and Wang
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