Canonical theory of spherically symmetric spacetimes with cross-streaming null dusts

The Hamiltonian dynamics of two-component spherically symmetric null dust is studied with regard to the quantum theory of gravitational collapse. The components--the ingoing and outgoing dusts--are assumed to interact only through gravitation. Different kinds of singularities, naked or "clothed", that can form during collapse processes are described. The general canonical formulation of the one-component null-dust dynamics by Bicak and Kuchar is restricted to the spherically symmetric case and used to construct an action for the two components. The transformation from a metric variable to the quasilocal mass is shown to simplify the mathematics. The action is reduced by a choice of gauge and the corresponding true Hamiltonian is written down. Asymptotic coordinates and energy densities of dust shells are shown to form a complete set of Dirac observables. The action of the asymptotic time translation on the observables is defined but it has been calculated explicitly only in the case of one-component dust (Vaidya metric).Comment: 15 pages, 3 figures, submitted to Phys. Rev.

Toward a Quantization of Null Dust Collapse

Spherically symmetric, null dust clouds, like their time-like counterparts, may collapse classically into black holes or naked singularities depending on their initial conditions. We consider the Hamiltonian dynamics of the collapse of an arbitrary distribution of null dust, expressed in terms of the physical radius, $R$, the null coordinates, $V$ for a collapsing cloud or $U$ for an expanding cloud, the mass function, $m$, of the null matter, and their conjugate momenta. This description is obtained from the ADM description by a Kucha\v{r}-type canonical transformation. The constraints are linear in the canonical momenta and Dirac's constraint quantization program is implemented. Explicit solutions the constraints are obtained for both expanding and contracting null dust clouds with arbitrary mass functions.Comment: 10 pages, 2 figures (eps), RevTeX4. The last two sections have been revised and corrected. To appear in Phys. Rev.

Juxtarenal aortic aneurysm repair

ObjectivesJuxtarenal aortic aneurysms (JAA) account for approximately 15% of abdominal aortic aneurysms. Despite advances in endovascular aneurysm repair, open repair requiring suprarenal aortic cross-clamping is still the treatment of choice for JAA. We performed a systematic review of the literature to determine perioperative mortality and postoperative renal dysfunction after open repair for non-ruptured JAA.MethodsThe Medline, Embase, and Cochrane databases were searched to identify all studies reporting non-ruptured JAA repair published between January 1966 and December 2008. Two independent observers selected studies for inclusion, assessed the methodologic quality of the included studies, and performed the data extraction. Study heterogeneity was assessed using forest plots and by calculating the between-study variance. Outcomes were perioperative mortality, postoperative renal dysfunction, and new onset of dialysis. Summary estimates with 95% confidence interval (95% CI) were calculated using a random effects model based on the binomial distribution.ResultsTwenty-one non-randomized cohort studies from 1986 to 2008, reporting on 1256 patients, were included. Heterogeneity between the studies was low. The mean perioperative mortality was 2.9% (95% CI, 1.8 to 4.6). The mean incidence of new onset of dialysis was 3.3% (95% CI, 2.4 to 4.5). Incidence of postoperative renal dysfunction could be derived from 13 studies and ranged from 0% to 39% (median, 18%). In seven studies, cold renal perfusion during suprarenal clamping was performed in order to preserve renal function; however, based upon the included data, definitive conclusions regarding its efficacy could not be drawn.ConclusionsOpen repair of non-ruptured JAA using suprarenal cross-clamping can be performed with acceptable perioperative mortality; however, postoperative deterioration of renal function is a common complication. Preservation of renal function after JAA repair requires further investigation