1,721,458 research outputs found
Experimental observation of flow instability in a semi-closed two-phase natural circulation loop
No full textIn this experimental study, the flow instabilities within a semi-closed two-phase natural circulation loop were examined, with an emphasis placed on the role of the expansion-tank-line resistance. Six different modes of loopwise natural circulation were identified: the single-phase natural circulation, periodic two-phase natural circulation with a nonboiling period between the cycles, two-phase continuous circulation (stable circulation), and three other modes of the two-phase natural circulation characterized by different ranges of the cyclic period. The results were also shown in the instability map in the plane of the heat Aux and the heater-inlet subcooling. When the frictional resistance at the expansion-tank line becomes larger, the circulation becomes stable, especially at the high heat-flux and high inlet-subcooling conditions, and, as a whole, the stable operation region becomes larger in the instability map. Similarly, the longer expansion-tank line stabilizes the system. However, unlike the analytical prediction, the excursive instability was not identified with the semi-closed loop due to the flow restriction at the expansion-tank line. (C) 2000 Elsevier Science S.A. All rights reserved
Polydiacelylene (PDA)-based colorimetric detection of biotin-streptavidin interactions
No full textThe natural binding of streptavidin (STA) for a small molecule, biotin, has made it a useful tool in specific targeting application, due to their most specific noncovalent biological interactions in nature. Here, we describe a polydiacetylene (PDA)-based colorimetric biosensor to detect the STA-biotin interactions. We synthesized two kinds of biotin-labeled 10,12-pentacosadiynoic acid (PCDA) monomers having 2(ethylene oxide) or 3(ethylene oxide) spacer and prepared biotin-modified PDA liposomes using them. Upon the addition of STA, the modified PDA liposomes showed a color change from blue to red in about I h followed by their aggregation and precipitation. The aggregation was found to be due to the cross-linking between the PDA liposomes caused by the STA having four biotin binding sites, which was confirmed by their TEM analysis. Since the STA-biotin interactions are widely adopted for various biological detection systems; the biotin-modified PDA sensor developed in this study has enormous potentials for the development of various colorimetric biosensors. (c) 2005 Elsevier B.V. All rights reserved.We thankKorea Basic Science Institute for assistance with
TEM experiments. Also, this research was supported by the
Brain Korea 21 (BK 21) and Center for Ultramicrochemical
Process Systems (CUPS) projects
Analytical frequency-dependent infinite elements for soil-structure interaction analysis in two-dimensional medium
No full textAnalytical frequency-dependent dynamic infinite elements are developed to model the far field of a two-dimensional layered half-space soil medium for soil-structure interaction analysis. Using the proposed infinite elements, the element mass and stiffness matrices can be obtained in analytical forms of frequency and constant matrices representing the wave propagation characteristics in the far field soil medium. The compliances of rigid strip foundations on a homogeneous half-space, on a layered half-space, and on a layer strip with rigid bedrock are calculated using the present formulation, and the results are compared with those by other approaches. The comparison indicates that the proposed infinite elements give accurate solutions. The equation of motion including the present frequency-dependent dynamic stiffness matrix for the far field region can be analytically transformed into a time domain equation, and the soil-structure interaction analysis may be carried out in time domain. (C) 1999 Elsevier Science Ltd. All rights reserved
Electrical-properties of Sol-gel Processed PLZT Thin-films
No full textSol-gel processed lanthanum-modified lead zirconate titanate (PLZT) thin films consisting of two different perovskite phase contents were fabricated on indium tin oxide coated Corning 7059 glass substrates with two different heating schedules: direct insertion at 650-degrees-C for 30 min and at 500-degrees-C for 2 h. Optical transmittance spectra, polarization versus electric field curves, relative dielectric constant versus frequency and capacitance versus d.c. bias voltage curves of the samples were investigated. The samples showed a good transparency of over 70% and interference oscillation. A thin film consisting of mainly perovskite phase showed a slim loop hysteresis in the polarization versus electric field curve and in the capacitance versus d.c. bias voltage curve, indicating the presence of ferroelectric domains, but a film consisting of mainly pyrochlore phase did not. The dielectric constant and loss factor of the thin film consisting of mainly perovskite phase were about 90 and about 0.2, respectively, at relatively low frequency and showed dispersion of the dipolar polarization of permanent dipole moment in the ferroelectric perovskite phase in the frequency range between 10 kHz and 1 MHz
Cre/loxP- and large T antigen/SV40 ori-mediated in vivo excision and amplification of large genomic segments in human cell
No full textFluid-structure-soil interaction analysis of cylindrical liquid storage tanks subjected to horizontal earthquake loading
No full textThis paper presents a method of seismic analysis for a cylindrical liquid storage structure considering the effects of the interior fluid and exterior soil medium in the frequency domain. The horizontal and rocking motions of the structure are included in this study. The fluid motion is expressed in terms of analytical velocity potential functions, which can be obtained by solving the boundary value problem including the deformed configuration of the structure as well as the sloshing behavior of the fluid. The effect of the fluid is included in the equation of motion as the impulsive added mass and the frequency-dependent convective added mass along the nodes on the wetted boundary of the structure. The structure and the near-field soil medium are represented using the axisymmetric finite elements, while the far-field soil is modeled using dynamic infinite elements. The present method can be applied to the structure embedded in ground as well as on ground, since it models both the soil medium and the structure directly. For the purpose of verification, earthquake response analyses are performed on several cases of liquid tanks on a rigid ground and on a homogeneous elastic half-space. Comparison of the present results with those by other methods shows good agreement. Finally, an application example of a reinforced concrete tank on a horizontally layered soil with a rigid bedrock is presented to demonstrate the importance of the soil-structure interaction effects in the seismic analysis for large liquid storage tanks
Mesoporous molecular sieve with binary transition metal (Zr-Cr) oxide framework
No full textA mesoporous molecular sieve with binary transition metal (Zr-Cr) oxide framework has been synthesized for the first time, and the material exhibits good thermal stability with a high surface area
Development of a markerless gene knock-out system for Mannheimia succiniciproducens using a temperature-sensitive plasmid
No full textA temperature-sensitive derivative of the Mannheimia varigena plasmid pMVSCS1 was constructed by hydroxylamine treatment for use in the development of a markerless gene knock-out system for Mannheimia succiniciproducens. The temperature-sensitive plasmid pMVSCS1-ts was stably maintained at 30 degrees C, but failed to replicate at 42 degrees C. DNA sequencing of the replication origin revealed a single base substitution as being responsible for its temperature sensitivity. The region of replication origin was amplified by PCR to construct an Escherichia coli-M. succiniciproducens shuttle vector pME19-ts to further examine the thermosensitivity. To make markerless mutants of M. succiniciproducens, the Cre-lox system with the variant lox66 and lox71 sites was used to prevent the instability caused by multiple loxP sites in the genome. The transient cre expression was carried out using the temperature-sensitive plasmid pCRX5, which was consequently cured after the verification of the markerless mutant by growing cells at 42 degrees C. For the demonstration of the markerless deletion of multiple genes using this method, the ldhA gene and the oadGAB operon of M. succiniciproducens encoding lactate dehydrogenase and oxaloacetate decarboxylase, respectively, were successfully deleted sequentially. This markerless deletion method should be useful for further metabolic engineering of M. succiniciproducens, which is a promising industrial bacterium for succinic acid production from renewable resources.The authors thank Stefan Schwarz and Oh Suk Kwon for
providing the plasmids pMVSCS1 and pMS3, respectively.
The authors also thank Hyohak Song and Seh Hee Jang for
their helpful discussion. This work was supported by the
Genome-Based Integrated Bioprocess Development Project
of the Ministry of Science and Technology through the
Korea Science and Engineering Foundation (KOSEF).
Further support by the LG Chem Chair Professorship and
the Center for Ultramicrochemical Process Systems sponsored
by KOSEF is appreciated
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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