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Search Results: 1 - 10 of 1145 matches for " Hartmut Scheel "
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Prediction of a common structural scaffold for proteasome lid, COP9-signalosome and eIF3 complexes
Hartmut Scheel, Kay Hofmann
BMC Bioinformatics , 2005, DOI: 10.1186/1471-2105-6-71
Abstract: During an exhaustive bioinformatical analysis of proteasome components, we detected multiple instances of tetratrico-peptide repeats (TPR) in the N-terminal region of most PCI proteins, suggesting that their homology is not restricted to the PCI domain. We also detected a previously unrecognized PCI domain in the eIF3 component eIF3k, a protein whose 3D-structure has been determined recently. By using profile-guided alignment techniques, we show that the structural elements found in eIF3k are most likely conserved in all PCI proteins, resulting in a structural model for the canonical PCI domain.Our model predicts that the homology domain PCI is not a true domain in the structural sense but rather consists of two subdomains: a C-terminal 'winged helix' domain with a key role in PCI:PCI interaction, preceded by a helical repeat region. The TPR-like repeats detected in the N-terminal region of PCI proteins most likely form an uninterrupted extension of the repeats found within the PCI domain boundaries. This model allows an interpretation of several puzzling experimental results.In eukaryotic organisms, there exist at least three distinct multi-protein assemblies that are jointly referred to as 'PCI complexes' [1] and have a similar subunit architecture despite their fundamentally different function: i) the proteasome lid, a subcomplex of the 19S proteasome regulator and the 26S proteasome, ii) the COP9 signalosome or CSN complex, and iii) the eukaryotic translation initiation factor eIF3. As a common feature, these complexes are composed of multiple subunits harbouring the PCI domain, named after the three participating complexes [2], sometimes also referred to as the PINT domain [3]. Other subunits of these complexes are characterized by a second shared homology domain called MPN (Mpr1-Pad1 N-terminal) [2,3].Among these complexes, the proteasome lid and the CSN share a particular degree of analogy. Both complexes consist of eight core subunits, six of them of the PCI
Single photons on demand from 3D photonic band-gap structures
Marian Florescu,Stefan Scheel,Hartmut Haeffner,Hwang Lee,Dmitry V. Strekalov,Peter L. Knight,Jonathan P. Dowling
Physics , 2002, DOI: 10.1209/epl/i2004-10453-5
Abstract: We describe a practical implementation of a (semi-deterministic) photon gun based on stimulated Raman adiabatic passage pumping and the strong enhancement of the photonic density of states in a photonic band-gap material. We show that this device allows {\em deterministic} and {\em unidirectional} production of single photons with a high repetition rate of the order of 100kHz. We also discuss specific 3D photonic microstructure architectures in which our model can be realized and the feasibility of implementing such a device using ${Er}^{3+}$ ions that produce single photons at the telecommunication wavelength of $1.55 \mu$m.
Self-repairing material systems―a dream or a reality?  [PDF]
Hartmut Fischer
Natural Science (NS) , 2010, DOI: 10.4236/ns.2010.28110
Abstract: Currently, most industrial materials rely entirely on passive protection mechanisms; such me chanisms are readily applicable and universal for many different materials systems. However, they will always stay passive, and therefore their lifetime and functionality is limited and related to the amount of protective additives and the intensity of their consumption. Therefore, better, and preferentially active process for the protection/repair of damaged materials―selfrepairing processes―were developed and need to be developed further. Although it sounds futuristic or like a fiction in the modern, trendy times, which in many ways affects also directions of research; self healing of material systems exists already for a long time in all sorts of systems of materials or functionalities. The aim of this work is to go beyond the scope of a classical review the ones published recently in this field which almost entirely focused only onto polymeric systems. In this work, an analysis of the underlying functional and constructional principles of existing natural and synthetically selfhealing systems spanning over a range of classes of materials is given leading to general rules and principles for the design of new and application tailored selfhealing material systems.
Lower bounds on the absorption probability of beam splitters
Stefan Scheel
Physics , 2005, DOI: 10.1103/PhysRevA.73.013809
Abstract: We derive a lower limit to the amount of absorptive loss present in passive linear optical devices such as a beam splitter. We choose a particularly simple beam splitter geometry, a single planar slab surrounded by vacuum, which already reveals the important features of the theory. It is shown that, using general causality requirements and statistical arguments, the lower bound depends on the frequency of the incident light and the transverse resonance frequency of a suitably chosen single-resonance model only. For symmetric beam splitters and reasonable assumptions on the resonance frequency $\omega_T$, the lower absorption bound is $p_{\min}\approx 10^{-6}(\omega/\omega_T)^4$.
Permanents in linear optical networks
Stefan Scheel
Physics , 2004,
Abstract: We develop an abstract look at linear optical networks from the viewpoint of combinatorics and permanents. In particular we show that calculation of matrix elements of unitarily transformed photonic multi-mode states is intimately linked to the computation of permanents. An implication of this remarkable fact is that all calculations that are based on evaluating matrix elements are generically computationally hard. Moreover, quantum mechanics provides simpler derivations of certain matrix analysis results which we exemplify by showing that the permanent of any unitary matrix takes its values across the unit disk in the complex plane.
Spinodal decomposition and coarsening fronts in the Cahn-Hilliard equation
Arnd Scheel
Mathematics , 2012,
Abstract: We study spinodal decomposition and coarsening when initiated by localized disturbances in the Cahn-Hilliard equation. Spatio-temporal dynamics are governed by multi-stage invasion fronts. The first front invades a spinodal unstable equilibrium and creates a spatially periodic unstable pattern. Secondary fronts invade this unstable pattern and create a coarser pattern in the wake. We give linear predictions for speeds and wavenumbers in this process and show existence of corresponding nonlinear fronts. The existence proof is based on Conley index theory, a priori estimates, and Galerkin approximations. We also compare our results and predictions with direct numerical simulations and report on some interesting bifurcations.
Designing and Verifying Communication Protocols Using Model Driven Architecture and Spin Model Checker  [PDF]
Prabhu Kaliappan, Hartmut Koenig
Journal of Software Engineering and Applications (JSEA) , 2008, DOI: 10.4236/jsea.2008.11003
Abstract: The need of communication protocols in today’s environment increases as much as the network explores. Many new kinds of protocols, e.g. for information sharing, security, etc., are being developed day-to-day which often leads to rapid, premature developments. Many protocols have not scaled to satisfy important properties like deadlock and livelock freedom, since MDA focuses on the rapid development rather than on the quality of the developed models. In order to fix the above, we introduce a 2-Phase strategy based on the UML state machine and sequence diagram. The state machine is converted into PROMELA code as a protocol model and its properties are derived from the sequence diagram as Linear Temporal Logic (LTL) through automation. The PROMELA code is interpreted through the SPIN model checker, which helps to simulate the behavior of protocol. Later the automated LTL properties are supplemented to the SPIN for the verification of protocol properties. The results are compared with the developed UML model and SPIN simulated model. Our test results impress the designer to verify the expected results with the system design and to identify the errors which are unnoticed during the design phase.
A Methodology to Assess the Safety of Aircraft Operations When Aerodrome Obstacle Standards Cannot Be Met  [PDF]
Hartmut Fricke, Christoph Thiel
Open Journal of Applied Sciences (OJAppS) , 2015, DOI: 10.4236/ojapps.2015.52007
Abstract: When Aerodrome Obstacle Standards cannot be met as a result of urban or technical development, an aeronautical study can be carried out with the permission of EASA, in conjunction with ICAO, to prove how aircrafts can achieve an equivalent level of safety. However currently, no detailed guidance for this procedure exists. This paper proposes such a safety assessment methodology in order to value obstacle clearance violations around airports. This method has already been applied to a safety case at Frankfurt Airport where a tower elevating 4 km out of threshold 25R severely violates obstacle limitation surfaces. The model data refers to a take-off and landing performance model (TLPM) computing precisely aircraft trajectories for both standard and engine out conditions at ground proximity. The generated tracks are used to estimate collision risk incrementally considering EASA/FAA, EU-OPS & ICAO clearance criteria. Normal operations are assessed with a probabilistic analysis of empirical take-off/landing track data generating the local actual navigation performance (ANP) on site. The ANP shows integration to collision risk for an aircraft with any obstacle. The obstacle is tested for clearance within a “5-step-plan” against all performance requirements for landing climb and take-off climb. The methodology thereby delivers a comprehensive risk picture: The presented safety case for Frankfurt Airport showed an equivalent safety level despite the violation of standards. The collision risk during both normal and degraded performance operations was still found to be within ICAO Collision Risk Model (CRM) limits, requiring only limited risk mitigation measures. The presented work should complement ICAO Doc 9774 Appendix 3.
LOS DESAFíOS DE ESCENIFICAR EL "ALMA NACIONAL": CHILE EN LA EXPOSICIóN IBEROAMERICANA DE SEVILLA (1929)
Dümmer Scheel,Sylvia;
Historia Crítica , 2010,
Abstract: this article examines chilean national imaginaries during the 1920s and their graphic and material representation. it does so through a concrete case: the preparations and staging of chile's pavilion in the ibero-american exposition of 1929 in seville. the study begins by explaining the influence of culturalist nationalism on chilean imaginaries and the need to represent the "national soul" in the exposition. it then analyzes how these ideas were physically and graphically represented in the country's exhibit. special attention is paid to the representational challenges and the negotiations between different participants concerning the content of the exhibit.
Leveraging organisational cultural capital
R Scheel,F Crous
South African Journal of Industrial Psychology , 2007, DOI: 10.4102/sajip.v33i1.258
Abstract: Organisational culture discourse mandates a linear approach of diagnosis, measurement and gap analysis as standard practice in relation to most culture change initiatives. Therefore, a problem solving framework geared toward “fixing ? and/or realigning an organisation’s culture is usually prescribed. The traditional problem solving model seeks to identify gaps between current and desired organisational cultural states, inhibiting the discovery of an organisation’s unique values and strengths, namely its cultural capital. In pursuit of discovering and leveraging organisational cultural capital, a descriptive case study is used to show how an Appreciative Inquiry process can rejuvenate the spirit of an organisation as a system-wide inquiry mobilises a workforce toward a shared vision.
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