861 research outputs found
A Generalization of the Goldberg-Sachs Theorem and its Consequences
The Goldberg-Sachs theorem is generalized for all four-dimensional manifolds
endowed with torsion-free connection compatible with the metric, the treatment
includes all signatures as well as complex manifolds. It is shown that when the
Weyl tensor is algebraically special severe geometric restrictions are imposed.
In particular it is demonstrated that the simple self-dual eigenbivectors of
the Weyl tensor generate integrable isotropic planes. Another result obtained
here is that if the self-dual part of the Weyl tensor vanishes in a Ricci-flat
manifold of (2,2) signature the manifold must be Calabi-Yau or symplectic and
admits a solution for the source-free Einstein-Maxwell equations.Comment: 14 pages. This version matches the published on
Measuring co-authorship and networking-adjusted scientific impact
Appraisal of the scientific impact of researchers, teams and institutions
with productivity and citation metrics has major repercussions. Funding and
promotion of individuals and survival of teams and institutions depend on
publications and citations. In this competitive environment, the number of
authors per paper is increasing and apparently some co-authors don't satisfy
authorship criteria. Listing of individual contributions is still sporadic and
also open to manipulation. Metrics are needed to measure the networking
intensity for a single scientist or group of scientists accounting for patterns
of co-authorship. Here, I define I1 for a single scientist as the number of
authors who appear in at least I1 papers of the specific scientist. For a group
of scientists or institution, In is defined as the number of authors who appear
in at least In papers that bear the affiliation of the group or institution. I1
depends on the number of papers authored Np. The power exponent R of the
relationship between I1 and Np categorizes scientists as solitary (R>2.5),
nuclear (R=2.25-2.5), networked (R=2-2.25), extensively networked (R=1.75-2) or
collaborators (R<1.75). R may be used to adjust for co-authorship networking
the citation impact of a scientist. In similarly provides a simple measure of
the effective networking size to adjust the citation impact of groups or
institutions. Empirical data are provided for single scientists and
institutions for the proposed metrics. Cautious adoption of adjustments for
co-authorship and networking in scientific appraisals may offer incentives for
more accountable co-authorship behaviour in published articles.Comment: 25 pages, 5 figure
Recurrence of Diabetic Pedal Ulcerations Following Tendo-Achilles Lengthening
Foot and ankle surgeons are frequently challenged by the devastating systemic consequences of diabetes mellitus manifested through neuropathy, integumentary and joint breakdown, delayed healing, decreased ability to fight infection, and fragile tendon/ligaments. Diabetic neuropathic pedal ulcerations lead to amputations at an alarming rate and also carry a high mortality rate. This article will discuss causes of diabetic pedal ulcerations that persist or recur after tendo-Achilles lengthening and will highlight areas that need to be addressed by the practitioner such as infection, vascular and nutritional status, glucose control, off-loading, biomechanics, and patient compliance
Effects of bromopride on the healing of left colon anastomoses of rats
Objetivo: Avaliar os efeitos da bromoprida sobre a formação de aderências e a cicatrização de anastomoses de cólon esquerdo de
ratos. Métodos: Foram incluídos 40 ratos, divididos em dois grupos contendo 20 animais, para administração de bromoprida (grupo
de estudo- E) ou solução fisiológica (grupo controle- C). Cada grupo foi dividido em subgrupos contendo 10 animais cada, para
eutanásia no terceiro (E3 e C3) ou no sétimo dia (E7 e C7) de pós-operatório. Os ratos foram submetidos à secção do cólon esquerdo
e anastomose término-terminal. No dia da relaparotomia, foi avaliada a quantidade total de aderências e removido um segmento
colônico contendo a anastomose para análise histopatológica, da força de ruptura e da concentração de hidroxiprolina. Resultados:
Não houve diferença entre os grupos em relação à evolução clínica. Dois animais do grupo de estudo apresentaram deiscência
de anastomose bloqueada. Os animais que receberam bromoprida apresentaram número de aderências intracavitárias e aderências
à anastomose semelhantes ao grupo controle. As anastomoses dos animais do grupo E3 apresentaram menor resistência de ruptura
do que as do grupo C3 (p=0,04). Este efeito não ocorreu no sétimo dia de pós-operatório (p=0,37). Não houve diferença significativa
entre os grupos em relação à histopatologia ou concentração de hidroxiprolina das anastomoses. Conclusão: O uso da bromoprida
está associado à diminuição da resistência tênsil de anastomoses do cólon esquerdo de ratos no terceiro dia de pós-operatório.Objective: To evaluate the effects of bromopride on the formation of adhesions and anastomotic healing in the left colon of rats.
Methods: We divided 40 rats into two groups of 20 animals, administration of bromopride (study group-E) or saline (control group-
C). Each group was divided into subgroups containing 10 animals each for euthanasia in the third (C3 and E3) or the seventh (E7 and
C7) postoperative days. The rats were submitted to section of the left colon and end-to-end anastomosis. On the day of reoperation,
we evaluated the total amount of adhesions and removed a colonic segment containing the anastomosis for histopathological
analysis, assessment of rupture strength and hydroxyproline concentration. Results: There was no difference between groups in
relation to clinical outcome. Two animals in the study group had blocked anastomotic leakage. The animals that received bromopride
had the number of intracavitary adhesions and adhesions to the anastomosis similar to the control group. The anastomoses from the
group E3 animals showed lower resistance to rupture the one from the C3 group (p = 0.04). This effect did not occur on the seventh
postoperative day (p = 0.37). There was no significant difference between groups in relation to histopathology and hydroxyproline
concentration in the anastomoses. Conclusion: The use of bromopride was associated with decreased tensile strength of left colon
anastomosis in rats in the third postoperative day
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