Investigation of a passive control system for limiting cavitation inside turbomachinery under different operating conditions

Abstract Herein, a new passive control system for limiting cavitation inside turbomachinery has been applied to a NACA0009 hydrofoil. The basic idea is to introduce slots nearby its leading edge, connecting pressure and suction sides of the hydrofoil, in order to increase locally the pressure on its suction side and to prevent cavitation from developing. The cavitating flow developed around a two-dimensional hydrofoil is here considered since it is an archetype of cavitation nearby the leading edges of the impeller vanes. Thus, the flow field developed at the leading edge of both the original and modified hydrofoil has been studied at different angles of attack in order to reproduce a wide range of operating conditions that occur inside turbomachinery. Eventually, a comparison of their performance in terms of polars (C L and C D ) and vapour volume fractions (α v ) is performed

Controlled assembly of SNAP-PNA-fluorophore systems on DNA templates to produce fluorescence resonance energy transfer

The SNAP protein is a widely used self-labeling tag that can be used for tracking protein localization and trafficking in living systems. A model system providing controlled alignment of SNAP-tag units can provide a new way to study clustering of fusion proteins. In this work, fluorescent SNAP-PNA conjugates were controllably assembled on DNA frameworks forming dimers, trimers, and tetramers. Modification of peptide nucleic acid (PNA) with the O6-benzyl guanine (BG) group allowed the generation of site-selective covalent links between PNA and the SNAP protein. The modified BG-PNAs were labeled with fluorescent Atto dyes and subsequently chemo-selectively conjugated to SNAP protein. Efficient assembly into dimer and oligomer forms was verified via size exclusion chromatography (SEC), electrophoresis (SDS-PAGE), and fluorescence spectroscopy. DNA directed assembly of homo- and hetero-dimers of SNAP-PNA constructs induced homo- and hetero-FRET, respectively. Longer DNA scaffolds controllably aligned similar fluorescent SNAP-PNA constructs into higher oligomers exhibiting homo-FRET. The combined SEC and homo-FRET studies indicated the 1:1 and saturated assemblies of SNAP-PNA-fluorophore:DNA formed preferentially in this system. This suggested a kinetic/stoichiometric model of assembly rather than binomially distributed products. These BG-PNA-fluorophore building blocks allow facile introduction of fluorophores and/or assembly directing moieties onto any protein containing SNAP. Template directed assembly of PNA modified SNAP proteins may be used to investigate clustering behavior both with and without fluorescent labels which may find use in the study of assembly processes in cells

How Thioredoxin Dissociates Its Mixed Disulfide

The dissociation mechanism of the thioredoxin (Trx) mixed disulfide complexes is unknown and has been debated for more than twenty years. Specifically, opposing arguments for the activation of the nucleophilic cysteine as a thiolate during the dissociation of the complex have been put forward. As a key model, the complex between Trx and its endogenous substrate, arsenate reductase (ArsC), was used. In this structure, a Cys29Trx-Cys89ArsC intermediate disulfide is formed by the nucleophilic attack of Cys29Trx on the exposed Cys82ArsC-Cys89ArsC in oxidized ArsC. With theoretical reactivity analysis, molecular dynamics simulations, and biochemical complex formation experiments with Cys-mutants, Trx mixed disulfide dissociation was studied. We observed that the conformational changes around the intermediate disulfide bring Cys32Trx in contact with Cys29Trx. Cys32Trx is activated for its nucleophilic attack by hydrogen bonds, and Cys32Trx is found to be more reactive than Cys82ArsC. Additionally, Cys32Trx directs its nucleophilic attack on the more susceptible Cys29Trx and not on Cys89ArsC. This multidisciplinary approach provides fresh insights into a universal thiol/disulfide exchange reaction mechanism that results in reduced substrate and oxidized Trx

A Pre-Planned Local Repair Restoration Strategy for Failure Handling in Optical Transport Networks

Automatic provisioning and recovery of lightpaths with selectable traffic engineering policies are considered basic features of near future optical transport networks (OTN). Worldwide researchers recognize generalized multi-protocol label switching (GMPLS) architecture as the viable control plane solution to achieve these issues in OTN. Growing effort is ongoing to find new recovery models for handling failure conditions in the networks, trying to set up alternative strategies to classical heavy-cost SDH/SONET protection techniques. In this paper, a pre-planned local repair recovery strategy is described. Allocation of primary paths is provided using the interference concept, in order to set a threshold between resources dedicated to working paths and those allocable for local backups in case of failure. Tests of the strategy are shown for a sample national optical transport network, aimed at valuing local-repair recovery times at different failure location and seriousness