Time-Parallel Iterative Solvers for Parabolic Evolution Equations

We present original time-parallel algorithms for the solution of the implicit Euler discretization of general linear parabolic evolution equations with time-dependent self-adjoint spatial operators. Motivated by the inf-sup theory of parabolic problems, we show that the standard nonsymmetric time-global system can be equivalently reformulated as an original symmetric saddlepoint system that remains inf-sup stable with respect to the same natural parabolic norms. We then propose and analyse an efficient and readily implementable parallel-in-time preconditioner to be used with an inexact Uzawa method. The proposed preconditioner is non-intrusive and easy to implement in practice, and also features the key theoretical advantages of robust spectral bounds, leading to convergence rates that are independent of the number of time-steps, final time, or spatial mesh sizes, and also a theoretical parallel complexity that grows only logarithmically with respect to the number of time-steps. Numerical experiments with large-scale parallel computations show the effectiveness of the method, along with its good weak and strong scaling properties

Hochstromanwendungen mit Hochtemperatursupraleitern - technische Leiterentwicklung und Bau von Funktionsmodellen. YBCO Plattenleiterfertigung und Bau von Strombegrenzermodellen bis zu 1 MVA Abschlussbericht

In terms of materials, the main focus of the work was on the manufacture of large-area YBCO plate-type conductors with homogeneous properties and maximum current densities of j_c>1 MA/cm"2. j_c values of better than 3 MA/cm"2 were achieved reproducibly on sapphire substrates of 100 mm diameter and 10 x 20 cm"2 in size with a homogeneity of 10%; on polycrystalline substrates of 10 x 20 cm"2 in size, homogeneous j_c values of up to 2 MA/cm"2 were also successfully demonstrated. Of the total of four methods of coating available at the start of the project, thermal co-evaporation (TCE) proved best for YBCO thin films and the IBAD method best for quasi single-crystal buffer films. The latter are necessary to achieve high j_c on polycrystalline substrates such as ZrO_2(Y), glass and Al_2O_3. Polycrystalline substrates are essential in order to make the HTS current limiter as a future product commercially feasible. The favoured solutions ZrO_2(Y) and glass have not come up to expectations, because present investigations into quench propagation are showing that, with this approach, the high values of power density required for the switching process (1600 VA/cm"2) cannot be achieved. Towards the end of the project, polycrystalline Al_2O_3 began to be seen as a successful alternative; the work is being pursued further within the context of a follow-on project. The coating processes were stabilized successfully and, when combined with strict quality control, allowed the yield of tested, ready-to-use plate-type conductors to be improved to 85%. This success was an essential prerequisite for the building of a 3-phase, 1.2 MVA model (7.2 kV) comprising a total of sixty-three 100 mm plate-type conductors. At the Berlin factory the model has been successfully tested up to a prospective short-circuit current of 5 kV. This has demonstrated the basic suitability of HTS thin-film technology for use in current limiters. So far the model has been switched a total of 43 times without any problems at all. At present the model is the first resistive 3-phase HTS current limiter in the world. It has been installed in a factory-assembled container together with all the necessary supply and protection equipment for further long-term tests. However, it has taken several fresh starts to actually arrive at this milestone of development. The causes for this were initially the inadequate reproducibility of the coating process and subsequently new insights on the stresses that the plate-type conductors are exposed to during quenching, which only became apparent from the three-phase model tests. These unforeseen delays were also the reason why the 10 MVA model (that was planned at the beginning of the project) was not brought to fruition. (orig.)Available from TIB Hannover: F02B1638 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman

Intravenous NPA for the treatment of infarcting myocardium early: InTIME-II, a double-blind comparison on of single-bolus lanoteplase vs accelerated alteplase for the treatment of patients with acute myocardial infarction

Aims to compare the efficacy and safety of lanoteplase, a single-bolus thrombolytic drug derived from alteplase tissue plasminogen activator, with the established accelerated alteplase regimen in patients presenting within 6 h of onset of ST elevation acute myocardial infarction. Methods and Results 15 078 patients were recruited from 855 hospitals worldwide and randomized in a 2:1 ratio to receive either lanoteplase 120 KU. kg-1 as a single intravenous bolus, or up to 100 mg accelerated alteplase given over 90 min. The primary end-point was all-cause mortality at 30 days and the hypothesis was that the two treatments would be equivalent. By 30 days, 6.61% of alteplase-treated patients and 6.75% lanoteplase-treated patients had died (relative risk 1.02). Total stroke occurred in 1.53% alteplase- and 1.87% lanoteplase-treated patients (ns); haemorrhagic stroke rates were 0.64% alteplase and 1.12% lanoteplase (P=0.004). The net clinical deficit of 30-day death or non-fatal disabling stroke was 7.0% and 7.2%, respectively. By 6 months, 8.8% of alteplase-treated patients and 8.7% of lanoteplase-treated patients had died. Conclusion Single-bolus weight-adjusted lanoteplase is an effective thrombolytic agent, equivalent to alteplase in terms of its impact on survival and with a comparable risk-benefit profile. The single-bolus regimen should shorten symptoms to treatment times and be especially convenient for emergency department or out-of-hospital administration. (C) 2000 The European Society of Cardiology