Using formal methods to develop WS-BPEL applications

In recent years, WS-BPEL has become a de facto standard language for orchestration of Web Services. However, there are still some well-known difficulties that make programming in WS-BPEL a tricky task. In this paper, we firstly point out major loose points of the WS-BPEL specification by means of many examples, some of which are also exploited to test and compare the behaviour of three of the most known freely available WS-BPEL engines. We show that, as a matter of fact, these engines implement different semantics, which undermines portability of WS-BPEL programs over different platforms. Then we introduce Blite, a prototypical orchestration language equipped with a formal operational semantics, which is closely inspired by, but simpler than, WS-BPEL. Indeed, Blite is designed around some of WS-BPEL distinctive features like partner links, process termination, message correlation, long-running business transactions and compensation handlers. Finally, we present BliteC, a software tool supporting a rapid and easy development of WS-BPEL applications via translation of service orchestrations written in Blite into executable WS-BPEL programs. We illustrate our approach by means of a running example borrowed from the official specification of WS-BPEL

Production of steviol glycosides in recombinant hosts

Properties of nitrogen cluster plasmas produced by an intense, ultrashort laser pulse have been investigated numerically and experimentally. The classical dynamics simulations show that on increasing the cluster size a plasma with residual electron energy above 1 keV can be created due to collisional heating, which is considerably higher than the value obtained with a conventional low-density gas target. Experimentally, nitrogen gas jets created by two types of nozzles were irradiated with a laser pulse of 55 fs, up to 1.2× 1017 / cm2. A seeded gas jet consisting of nitrogen and helium was also employed to promote the production of large clusters. The influences of the shape of nozzle, the seeded gas, and the gas jet stagnation pressure on the properties of plasmas were examined by spectroscopic observations. K -shell emissions showed that for the gas jet using the conical nozzle the electrons underwent intense collisional heating within the large clusters, resulting in the production of highly charged ions. In contrast, the emissions observed with the capillary nozzle exhibited the characteristics of a cold plasma without suffering substantial electron heating, indicating the absence of large clusters. That is, the differences between the two types of nozzles in the efficiency of electron heating and subsequent residual energies after the passage of the laser pulse, which are strongly dependent upon the cluster size, drastically changed the properties of the produced plasmas. The reason that for the capillary gas jet the plasma density deduced from the recombination spectra was significantly higher than the value obtained using the conical nozzle is also given by the difference in residual electron energy

Role of the Rad52 Amino-terminal DNA Binding Activity in DNA Strand Capture in Homologous Recombination*

Saccharomyces cerevisiae Rad52 protein promotes homologous recombination by nucleating the Rad51 recombinase onto replication protein A-coated single-stranded DNA strands and also by directly annealing such strands. We show that the purified rad52-R70A mutant protein, with a compromised amino-terminal DNA binding domain, is capable of Rad51 delivery to DNA but is deficient in DNA annealing. Results from chromatin immunoprecipitation experiments find that rad52-R70A associates with DNA double-strand breaks and promotes recruitment of Rad51 as efficiently as wild-type Rad52. Analysis of gene conversion intermediates reveals that rad52-R70A cells can mediate DNA strand invasion but are unable to complete the recombination event. These results provide evidence that DNA binding by the evolutionarily conserved amino terminus of Rad52 is needed for the capture of the second DNA end during homologous recombination