High efficiency pump for space helium transfer

A centrifugal pump was developed for the efficient and reliable transfer of liquid helium in space. The pump can be used to refill cryostats on orbiting satellites which use liquid helium for refrigeration at extremely low temperatures. The pump meets the head and flow requirements of on-orbit helium transfer: a flow rate of 800 L/hr at a head of 128 J/kg. The overall pump efficiency at the design point is 0.45. The design head and flow requirements are met with zero net positive suction head, which is the condition in an orbiting helium supply Dewar. The mass transfer efficiency calculated for a space transfer operation is 0.99. Steel ball bearings are used with gas fiber-reinforced teflon retainers to provide solid lubrication. These bearings have demonstrated the longest life in liquid helium endurance tests under simulated pumping conditions. Technology developed in the project also has application for liquid helium circulation in terrestrial facilities and for transfer of cryogenic rocket propellants in space

Relay-Assisted User Scheduling in Wireless Networks with Hybrid-ARQ

This paper studies the problem of relay-assisted user scheduling for downlink wireless transmission. The base station or access point employs hybrid automatic-repeat-request (HARQ) with the assistance of a set of fixed relays to serve a set of mobile users. By minimizing a cost function of the queue lengths at the base station and the number of retransmissions of the head-of-line packet for each user, the base station can schedule an appropriate user in each time slot and an appropriate transmitter to serve it. It is shown that a priority-index policy is optimal for a linear cost function with packets arriving according to a Poisson process and for an increasing convex cost function where packets must be drained from the queues at the base station.Comment: 14 pages, 5 figures, submitted to the IEEE Transactions on Vehicular Technology in October 2008, revised in March 2009 and May 200

E-Coaching: Conceptual and Empirical Findings of a Virtual Coaching Programme

This article presents current empirical findings on a virtual coaching programme combining telephone coaching with an internet-based coaching programme. Within this study, 14 clients received three coaching sessions with a professional coach. Data was collected through interviews and by questionnaire. Findings indicate that this particular coaching format delivers positive results. Furthermore, some of the participants describe decisive advantages in both technological modalities (phone and internet-based coaching) in comparison to face-to-face coaching. Nevertheless, findings also indicate that a blended approach, combining this technology-mediated coaching approach with one or more face-to-face coaching sessions, appears as most promising

Coaching als individuelle Antwort auf gesellschaftliche Entwicklungen

In diesem Buch thematisieren die Beitragenden Gesellschaft als zentrale Referenz aktueller Coaching-Entwicklungen und präsentieren Coaching-Praxisfelder als individuelle Antworten auf gesellschaftliche Herausforderungen. Professionelles Coaching als Format der Förderung von Selbststeuerung wird damit in den Kontext gesamtgesellschaftlicher Ansprüche (steigende Flexibilitäts-, Produktivitäts- und Leistungsansprüche) gestellt. Insgesamt über 40 wissenschaftliche und praxisnahe Beiträge renommierter deutsch- und englischsprachiger AutorInnen bilden die Grundlage dieses Sammelbands

High-Resolution Structure of the Histidine-Containing Phosphocarrier Protein (HPr) from Staphylococcus aureus and Characterization of Its Interaction with the Bifunctional HPr Kinase/Phosphorylase

A high-resolution structure of the histidine-containing phosphocarrier protein (HPr) from Staphylococcus aureus was obtained by heteronuclear multidimensional nuclear magnetic resonance (NMR) spectroscopy on the basis of 1,766 structural restraints. Twenty-three hydrogen bonds in HPr could be directly detected by polarization transfer from the amide nitrogen to the carbonyl carbon involved in the hydrogen bond. Differential line broadening was used to characterize the interaction of HPr with the HPr kinase/phosphorylase (HPrK/P) of Staphylococcus xylosus, which is responsible for phosphorylation-dephosphorylation of the hydroxyl group of the regulatory serine residue at position 46. The dissociation constant K(d) was determined to be 0.10 ± 0.02 mM at 303 K from the NMR data, assuming independent binding. The data are consistent with a stoichiometry of 1 HPr molecule per HPrK/P monomer in solution. Using transversal relaxation optimized spectroscopy-heteronuclear single quantum correlation, we mapped the interaction site of the two proteins in the 330-kDa complex. As expected, it covers the region around Ser46 and the small helix b following this residue. In addition, HPrK/P also binds to the second phosphorylation site of HPr at position 15. This interaction may be essential for the recognition of the phosphorylation state of His15 and the phosphorylation-dependent regulation of the kinase/phosphorylase activity. In accordance with this observation, the recently published X-ray structure of the HPr/HPrK core protein complex from Lactobacillus casei shows interactions with the two phosphorylation sites. However, the NMR data also suggest differences for the full-length protein from S. xylosus: there are no indications for an interaction with the residues preceding the regulatory Ser46 residue (Thr41 to Lys45) in the protein of S. xylosus. In contrast, it seems to interact with the C-terminal helix of HPr in solution, an interaction which is not observed for the complex of HPr with the core of HPrK/P of L. casei in crystals

Regulation of the σE stress response by DegS: how the PDZ domain keeps the protease inactive in the resting state and allows integration of different OMP-derived stress signals upon folding stress

The unfolded protein response of Escherichia coli is triggered by the accumulation of unassembled outer membrane proteins (OMPs) in the cellular envelope. The PDZ-protease DegS recognizes these mislocalized OMPs and initiates a proteolytic cascade that ultimately leads to the σE-driven expression of a variety of factors dealing with folding stress in the periplasm and OMP assembly. The general features of how OMPs activate the protease function of DegS have not yet been systematically addressed. Furthermore, it is unknown how the PDZ domain keeps the protease inactive in the resting state, which is of crucial importance for the functioning of the entire σE stress response. Here we show in atomic detail how DegS is able to integrate the information of distinct stress signals that originate from different OMPs containing a ϕ-x-Phe C-terminal motif. A dedicated loop of the protease domain, loop L3, serves as a versatile sensor for allosteric ligands. L3 is capable of interacting differently with ligands but reorients in a conserved manner to activate DegS. Our data also indicate that the PDZ domain directly inhibits protease function in the absence of stress signals by wedging loop L3 in a conformation that ultimately disrupts the proteolytic site. Thus, the PDZ domain and loop L3 of DegS define a novel molecular switch allowing strict regulation of the σE stress response system