6,197 research outputs found

    On The Orbital Evolution of Jupiter Mass Protoplanet Embedded in A Self-Gravity Disk

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    We performed a series of hydro-dynamic simulations to investigate the orbital migration of a Jovian planet embedded in a proto-stellar disk. In order to take into account of the effect of the disk's self gravity, we developed and adopted an \textbf{Antares} code which is based on a 2-D Godunov scheme to obtain the exact Reimann solution for isothermal or polytropic gas, with non-reflecting boundary conditions. Our simulations indicate that in the study of the runaway (type III) migration, it is important to carry out a fully self consistent treatment of the gravitational interaction between the disk and the embedded planet. Through a series of convergence tests, we show that adequate numerical resolution, especially within the planet's Roche lobe, critically determines the outcome of the simulations. We consider a variety of initial conditions and show that isolated, non eccentric protoplanet planets do not undergo type III migration. We attribute the difference between our and previous simulations to the contribution of a self consistent representation of the disk's self gravity. Nevertheless, type III migration cannot be completely suppressed and its onset requires finite amplitude perturbations such as that induced by planet-planet interaction. We determine the radial extent of type III migration as a function of the disk's self gravity.Comment: 19 pages, 13 figure

    Crystallization of Adenylylsulfate Reductase from Desulfovibrio gigas: A Strategy Based on Controlled Protein Oligomerization

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    Adenylylsulfate reductase (adenosine 5′-phosphosulfate reductase, APS reductase or APSR, E.C.1.8.99.2) catalyzes the conversion of APS to sulfite in dissimilatory sulfate reduction. APSR was isolated and purified directly from massive anaerobically grown Desulfovibrio gigas, a strict anaerobe, for structure and function investigation. Oligomerization of APSR to form dimers–α_2β_2, tetramers–α_4β_4, hexamers–α_6β_6, and larger oligomers was observed during purification of the protein. Dynamic light scattering and ultracentrifugation revealed that the addition of adenosine monophosphate (AMP) or adenosine 5′-phosphosulfate (APS) disrupts the oligomerization, indicating that AMP or APS binding to the APSR dissociates the inactive hexamers into functional dimers. Treatment of APSR with β-mercaptoethanol decreased the enzyme size from a hexamer to a dimer, probably by disrupting the disulfide Cys156—Cys162 toward the C-terminus of the β-subunit. Alignment of the APSR sequences from D. gigas and A. fulgidus revealed the largest differences in this region of the β-subunit, with the D. gigas APSR containing 16 additional amino acids with the Cys156—Cys162 disulfide. Studies in a pH gradient showed that the diameter of the APSR decreased progressively with acidic pH. To crystallize the APSR for structure determination, we optimized conditions to generate a homogeneous and stable form of APSR by combining dynamic light scattering, ultracentrifugation, and electron paramagnetic resonance methods to analyze the various oligomeric states of the enzyme in varied environments

    An ERP System Life Cycle-Wide Management and Support Framework for Small- and Medium-Sized Companies

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    Currently, the companies that have introduced the ERP system in Taiwan are mostly large enterprises. Due to the high cost of introduction and uncertain performance, however, ordinary small- and medium-sized enterprises can hardly afford the system. Thus, not only would a reference model for ERP life offer cycle-wide management support and assist large enterprises in evaluating and renewing the system, but it would also offer small- and medium-sized enterprises a set of procedures to successfully introduce the ERP system. The objective of this research is to explore the life cycle-wide management and support activities of an ERP system in order to establish a managerial model which can be used as a guideline for managers in dealing with their critical managerial activities. This study applied both the results from the literature review and Delphi study on the basis of Gowin\u27s Vee Approach. Through literature review, this research initially determined the life cycle-wide activities of the ERP system and then used the Grounded Theory to develop a prototype of the reference model for ERP life cycle-wide management and support. Subsequently, this study used the Delphi Method to collect the opinions of field experts. After analyzing and organizing the results, comparison and amendments were made to propose a final set of reference models for ERP life cycle-wide management and support. From the perspective of academic research, the authors believe that this study contributes to the development of a managerial model and provides prospective researchers with future directions in this subject area. As for the business sector, this managerial model can assist large enterprises through a better approach in management and support of the current ERP system, while small- and medium-sized enterprises are provided with a set of concrete steps to facilitate the successful introduction of the ERP system

    Critical Factors of Adopting Enterprise Application Integration Technology: An Empirical Study on Larger Hospitals

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    As hospitals extend their service scope, they adopt more information systems. These systems are implemented in different timelines and the interfaces of databases become varied. Frequently, the exchange of information between various systems requires additional coordination or even manual input for unifying data. To embrace automation, the solution is to adopt enterprise application integration (EAI) technology, the middleware, to convert data from among various information systems to enable an efficient flow of data in the hospital. In this paper, we discuss and verify the impact factors on the integration levels of EAI by surveying larger hospitals above the regional level in Taiwan and testing a proposed research model. The findings of this study show that information technology infrastructure, hospital size, external pressure, internal pressure, and external support significantly affect the EAI level

    Modular detergents tailor the purification and structural analysis of membrane proteins including G-protein coupled receptors

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    Detergents enable the purification of membrane proteins and are indispensable reagents instructural biology. Even though a large variety of detergents have been developed in the lastcentury, the challenge remains to identify guidelines that allowfine-tuning of detergents forindividual applications in membrane protein research. Addressing this challenge, here weintroduce the family of oligoglycerol detergents (OGDs). Native mass spectrometry (MS)reveals that the modular OGD architecture offers the ability to control protein purificationand to preserve interactions with native membrane lipids during purification. In addition to abroad range of bacterial membrane proteins, OGDs also enable the purification and analysisof a functional G-protein coupled receptor (GPCR). Moreover, given the modular design ofthese detergents, we anticipatefine-tuning of their properties for specific applications instructural biology. Seen from a broader perspective, this represents a significant advance forthe investigation of membrane proteins and their interactions with lipids

    Minimum Renyi and Wehrl entropies at the output of bosonic channels

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    The minimum Renyi and Wehrl output entropies are found for bosonic channels in which the signal photons are either randomly displaced by a Gaussian distribution (classical-noise channel), or in which they are coupled to a thermal environment through lossy propagation (thermal-noise channel). It is shown that the Renyi output entropies of integer orders z>1 and the output Wehrl entropy are minimized when the channel input is a coherent state.Comment: Minimal revision. Accepted for publication on Phys. Rev.

    Lifetimes of states in 19Ne above the 15 O + alpha breakup threshold

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    The 15O(alpha,gamma)19Ne reaction plays a role in the ignition of Type I x-ray bursts on accreting neutron stars. The lifetimes of states in 19Ne above the 15O + alpha threshold of 3.53 MeV are important inputs to calculations of the astrophysical reaction rate. These levels in 19Ne were populated in the 3He(20Ne,alpha)19Ne reaction at a 20Ne beam energy of 34 MeV. The lifetimes of six states above the threshold were measured with the Doppler shift attenuation method (DSAM). The present measurements agree with previous determinations of the lifetimes of these states and in some cases are considerably more precise
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