Numerical Integration of Nonlinear Wave Equations for General Relativity

A second-order numerical implementation is given for recently derived nonlinear wave equations for general relativity. The Gowdy T$^3$ cosmology is used as a test bed for studying the accuracy and convergence of simulations of one-dimensional nonlinear waves. The complete freedom in space-time slicing in the present formulation is exploited to compute in the Gowdy line-element. Second-order convergence is found by direct comparison of the results with either analytical solutions for polarized waves, or solutions obtained from Gowdy's reduced wave equations for the more general unpolarized waves. Some directions for extensions are discussed.Comment: 19 pages (LaTex), 3 figures (ps

Actin-binding rho activating protein (Abra) is essential for fluid shear stress-induced arteriogenesis

OBJECTIVE: Arteriogenesis, the development of a collateral circulation, is important for tissue survival but remains functionally defective because of early normalization of fluid shear stress (FSS). Using a surgical model of chronically elevated FSS we showed that rabbits exhibited normal blood flow reserve after femoral artery ligature (FAL). Inhibition of the Rho pathway by Fasudil completely blocked the beneficial effect of FSS. In a genome-wide gene profiling we identified actin-binding Rho activating protein (Abra), which was highly upregulated in growing collaterals. METHODS AND RESULTS: qRT-PCR and Western blot confirmed highly increased FSS-dependent expression of Abra in growing collaterals. NO blockage by L-NAME abolished FSS-generated Abra expression as well as the whole arteriogenic process. Cell culture studies demonstrated an Abra-triggered proliferation of smooth muscle cells through a mechanism that requires Rho signaling. Local intracollateral adenoviral overexpression of Abra improved collateral conductance by 60% in rabbits compared to the natural response after FAL. In contrast, targeted deletion of Abra in CL57BL/6 mice led to impaired arteriogenesis. CONCLUSIONS: FSS-induced Abra expression during arteriogenesis is triggered by NO and leads to stimulation of collateral growth by smooth muscle cell proliferation

Financial Integration in Emerging Europe: An Enviable Development Opportunity with Tail Risks

This paper draws on the experience of emerging Europe and argues that foreign capital is an enviable development opportunity with tail risks. Financial integration and foreign savings supported growth in the EU12 and EU candidate countries. We argue that this was possible because of EU membership (actual or potential) and its role as an anchor for expectations. In contrast, the eastern partnership states did not benefit from the foreign savings-growth link. But financial integration also led to a buildup of vulnerabilities and now exposes emerging Europe to prolonged uncertainty and financial deleveraging due to eurozone developments. Nonetheless, we believe that external imbalances should not be eradicated-nor should emerging Europe pursue a policy of self-insurance. Instead, what we refer to as an acyclical fiscal policy stance could serve to counterbalance private sector behavior. Going forward, a more proactive macroprudential policy will also be needed to limit financial system vulnerabilities when external imbalances are large

Runway Scheduling Using Generalized Dynamic Programming

A generalized dynamic programming method for finding a set of pareto optimal solutions for a runway scheduling problem is introduced. The algorithm generates a set of runway flight sequences that are optimal for both runway throughput and delay. Realistic time-based operational constraints are considered, including miles-in-trail separation, runway crossings, and wake vortex separation. The authors also model divergent runway takeoff operations to allow for reduced wake vortex separation. A modeled Dallas/Fort Worth International airport and three baseline heuristics are used to illustrate preliminary benefits of using the generalized dynamic programming method. Simulated traffic levels ranged from 10 aircraft to 30 aircraft with each test case spanning 15 minutes. The optimal solution shows a 40-70 percent decrease in the expected delay per aircraft over the baseline schedulers. Computational results suggest that the algorithm is promising for real-time application with an average computation time of 4.5 seconds. For even faster computation times, two heuristics are developed. As compared to the optimal, the heuristics are within 5 % of the expected delay per aircraft and 1 % of the expected number of runway operations per hour and can be 1000x faster

Exercise linked to transient increase in expression and activity of cation channels in newly formed hind-limb collaterals

OBJECTIVE: This study aimed to compare arteriogenesis after femoral artery occlusion as influenced by exercise or arteriovenous shunt and follow changes in collateral transient receptor potential cation channel, subfamily V, member 4 (Trpv4). DESIGN: A prospective, controlled study wherein rats were subjected to femoral artery ligation (FAL), or FAL+arteriovenous shunt. Collateral Trpv4 was determined 0.5 and 6h post exercise. METHODS: Rats were subjected to exercise for 15 min, twice daily. The number and diameter of collaterals were assessed after 7 days. Collateral Trpv4 expression was quantified by reverse transcription-polymerase chain reaction. RESULTS: Collateral number and diameter per limb were significantly higher in the shunt group (number: 16.0+/-2.4 and diameter: 216.0+/-34 microm) compared to the ligature (number: 9.4+/-2 and diameter: 144+/-21 microm) and exercise groups (number: 9.9+/-2.5 and diameter: 151+/-15 microm). Trpv4 expression in collaterals harvested 0.5h post exercise was not significantly different from expression in shunted rats. It was significantly lower in collaterals harvested 6h post exercise (comparable to that in ligated rats). CONCLUSION: Collateral formation was greater in the shunt group than in the exercise group. Exercise-induced Trpv4 up-regulation, not significantly different from that achieved with shunt, returned to control values when evaluated 6h post exercise. More frequent exercise to chronically increase fluid shear stress, as with a shunt model, may be required for sufficient arteriogenesis to compensate for peripheral occlusion