43 research outputs found
Finite-Size Studies on the SO(5) Symmetry of the Hubbard Model
We present numerical evidence for the approximate SO(5) symmetry of the
Hubbard model on a 10 site cluster. Various dynamic correlation functions
involving the operators, the generators of the SO(5) algebra, are studied
using exact diagonalisation, and are found to possess sharp collective peaks.
Our numerical results also lend support on the interpretation of the recent
resonant neutron scattering peaks in the YBCO superconductors in terms of the
Goldstone modes of the spontaneously broken SO(5) symmetry.Comment: 4 pages, Rev-Tex, includes 2 eps figure
Phase Space Analysis of Quintessence Cosmologies with a Double Exponential Potential
We use phase space methods to investigate closed, flat, and open
Friedmann-Robertson-Walker cosmologies with a scalar potential given by the sum
of two exponential terms. The form of the potential is motivated by the
dimensional reduction of M-theory with non-trivial four-form flux on a
maximally symmetric internal space. To describe the asymptotic features of
run-away solutions we introduce the concept of a `quasi fixed point.' We give
the complete classification of solutions according to their late-time behavior
(accelerating, decelerating, crunch) and the number of periods of accelerated
expansion.Comment: 46 pages, 5 figures; v2: minor changes, references added; v3: title
changed, refined classification of solutions, 3 references added, version
which appeared in JCA
Morphological abnormalities in the cladoceran Ilyocryptus spinifer (Apipucos Reservoir, Pernambuco State, Brazil)
In a sample taken from Apipucos Reservoir (Recife, PE, Brazil) for taxonomic study, a high percentage (40%) was found of cladoceran Ilyocryptus spinifer individuals with morphological abnormalities on their postabdomen. There was not a fixed pattern of the malformations, which varied in gravity, and could affect the postanal spines or terminal claws. The postabdominal abnormalities are described and compared to the ones described in the literature. The hypothesis of the morphological abnormalities being induced by an occasional environmental toxicant is discussed
Characterization of A Stable Intermediate Trapped during Reversible Refolding of Bacillus Subtilisalpha-Amylase
Investigation of Proliferative Activity in the Developing Human Tooth Using Ki-67 Immunostaining
Objective: The aim of this study was to investigate the proliferation of the developing human tooth germ and its surrounding tissues using Ki-67 immunostaining. Materials and Methods: Sections of mandibular dental arch tissues collected from 4 cadaveric human fetuses of 13, 16, 21 and 30 weeks of gestation were used. The immunoreactivity of Ki-67 in the tissue sections was assessed visually under a light microscope. Immunohistochemical controls were performed by replacing the primary antibody with phosphate-buffered saline or normal rabbit IgG. Results: The control sections did not display Ki-67 immunoactivity. Specimens of 13 weeks of gestation revealed intense Ki-67 immunostaining throughout the entire developing mandibular primary molars. At 16 weeks of gestation, immunostaining was observed in the inner enamel epithelium and dental papilla, in conjunction with the dental lamina showing decreased immunostaining. At 21 weeks, Ki-67 immunostaining was observed only in the inner enamel epithelium and dental papilla. The immunoreactivity of active ameloblasts and odontoblasts decreased, along with the proliferation capacity of the dental lamina. At 30 weeks, both enamel and dentin formation was observed along the cusped aspect of the tooth germ. Ameloblasts and odontoblasts were no longer immunoreactive in this region, while both types of cells were immunoreactive at the cervical regions of the crown. Dental lamina cells showed disintegration and were totally Ki-67-negative at 30 weeks of gestation. Conclusion: The Ki-67 immunoreactivity of the dental lamina decreased during intrauterine tooth development. Positive immunostaining was observed at specific sites in the enamel organ and dental papilla during the cap and bell stages. Copyright (C) 2007 S. Karger AG, Basel.WoSScopu