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- 저자 : Britz, Alexander (검색결과 14 건)
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Britz, Alexander,Gawelda, Wojciech,Assefa, Tadesse A.,Jamula, Lindsey L.,Yarranton, Jonathan T.,Galler, Andreas,Khakhulin, Dmitry,Diez, Michael,Harder, Manuel,Doumy, Gilles,March, Anne Marie,Bajno American Chemical Society 2019 Inorganic chemistry Vol.58 No.14
<P>We have employed a range of ultrafast X-ray spectroscopies in an effort to characterize the lowest energy excited state of [Fe(dcpp)<SUB>2</SUB>]<SUP>2+</SUP> (where dcpp is 2,6-(dicarboxypyridyl)pyridine). This compound exhibits an unusually short excited-state lifetime for a low-spin Fe(II) polypyridyl complex of 270 ps in a room-temperature fluid solution, raising questions as to whether the ligand-field strength of dcpp had pushed this system beyond the <SUP>5</SUP>T<SUB>2</SUB>/<SUP>3</SUP>T<SUB>1</SUB> crossing point and stabilizing the latter as the lowest energy excited state. Kα and Kβ X-ray emission spectroscopies have been used to unambiguously determine the quintet spin multiplicity of the long-lived excited state, thereby establishing the <SUP>5</SUP>T<SUB>2</SUB> state as the lowest energy excited state of this compound. Geometric changes associated with the photoinduced ligand-field state conversion have also been monitored with extended X-ray absorption fine structure. The data show the typical average Fe-ligand bond length elongation of ∼0.18 Å for a <SUP>5</SUP>T<SUB>2</SUB> state and suggest a high anisotropy of the primary coordination sphere around the metal center in the excited <SUP>5</SUP>T<SUB>2</SUB> state, in stark contrast to the nearly perfect octahedral symmetry that characterizes the low-spin <SUP>1</SUP>A<SUB>1</SUB> ground state structure. This study illustrates how the application of time-resolved X-ray techniques can provide insights into the electronic structures of molecules-in particular, transition metal complexes-that are difficult if not impossible to obtain by other means.</P><P>Time-resolved X-ray emission and absorption spectroscopies have been used to probe the excited-state electronic and geometric structure of an Fe(II) polypyridyl complex. Analysis of the data revealed that the lowest energy excited state is high-spin (<I>S</I> = 2) in character. This determination had not been possible using other experimental techniques (e.g., time-resolved optical spectroscopy), demonstrating the potential for ultrafast X-ray methods to address scientific questions that are difficult to resolve by other means.</P> [FIG OMISSION]</BR>
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Rapid Design of Secondary Flow Geometry Using a Flow Network Modelling Approach
Vincent Britz,Bennie Du Toit,전형택 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.12
Accurate prediction of turbo machinery flow is essential during the design process of gas turbines. Substantial progress has been made in this area with three-dimensional calculation techniques of increasing complexity helped by computer hardware developments. Encouraging results are obtained from this work, however three-dimensional analysis is still very time consuming, both to describe the machine geometry and to obtain the results. These methods consequently are appropriate for use in the design context only when a finalized design is approached. In preliminary design a need exists for a less sophisticated but none the less reliable prediction technique suitable for use in iterative type calculations. In this study a commercial flow network tool, Flownex®, was used to model a portion of the secondary flow path in a gas turbine. The integrated mass, momentum and energy balance is solved using the continuity, momentum and energy equations applied to nodes and elements. These nodes and elements are the modular building blocks, typically semi-empirical and allow users to either select appropriate built-in correlations, or to define using specific equations through scripting. The method is tested using an optimization exercise. The results prove that this method of flow network modeling is an efficient way to optimize secondary flow geometry in the preliminary design stages of turbo machinery.
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Rapid Preliminary Combustor Design Using a Flow Network Approach
Vincent Britz,Bennie Du Toit,전형택 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.12
Preliminary combustor design usually requires that an extensive number of geometrical and operational conditions be evaluated and compared. During this phase important parameters the designer sought after are typically the mass flow rate distribution through air admission holes, associated pressure losses as well as liner wall temperatures. The process is therefore iterative in nature and can become expensive in terms of engineering analysis cost considering the time required to build and execute 3D CFD models. Network codes have the potential to fill the gap during this stage of the design since they can be setup and solved in timeframes that are orders of magnitude less than comprehensive CFD models, essentially leading to cost savings since overall less time is spent on 3D simulations and rig tests. An additional advantage using this approach is that results from the network solution can be applied as boundary conditions to subsequent more detailed 3D models. In this study a commercial flow network tool, Flownex®, was used to model a complete combustor including flow distribution, combustion and heat transfer. The integrated mass, momentum and energy balance is solved using the continuity, momentum and energy equations applied to nodes and elements. These nodes and elements are the modular building blocks, typically semi-empirical and allow users to either select appropriate built-in correlations, or to define using specific equations through scripting. Flow equations are fully compressible and applied to the gas mixture. The chemical composition of the reactants forming during combustion as well as the adiabatic flame temperature is determined from the NASA CEA package incorporated into the solution. Heat transfer mechanisms included in the model are gas-surface radiation, film convection, forced convection in ducts, surface-surface radiation, and 2D axially-symmetric conduction through solid walls. Results produced from the network were compared with test data obtained from the NASA E3 development combustor. Overall good agreement resulted, showcasing the success of the approach followed.
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Flow Network Modeling of the Priming of Spacecraft Propulsion System
Vincent Britz,Bennie Du Toit,전형택 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.12
The evacuated pipeline of the propulsion system of a spacecraft has to be filled during the start-up at high altitude. This process is known as priming and can generate severe pressure peaks due to propellant slamming against a closed thruster valve. Previous studies [1] investigated these large pressure surges (peaks as high as 200 bar) as they can potentially damage flow components in the fuel system if not correctly accounted for. In this study a commercial flow network tool, Flownex®, was used to model an experimental setup of this priming procedure. The integrated mass, momentum and energy balance is solved using the continuity, momentum and energy equations applied to nodes and elements. These nodes and elements are the modular building blocks, typically semi-empirical and allow users to either select appropriate built-in correlations, or to define using specific equations through scripting. An appropriate model to capture the pressure pulse was created using the components in Flownex®. Results produced from the network were compared with test data obtained from the DLR Lampoldshausen test-bench. Overall good agreement resulted, showcasing the success of the approach followed.
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Flow Network Modelling of a Nuclear Reactor Rocket
Vincent Britz,Bennie Du Toit,전형택 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.12
Nuclear thermal propulsion (NTP) has been identified as the preferred propulsion technology for manned missions to Mars in NASA"s Design Reference Architecture (DRA) [1]. The ability to predict the system performance of a nuclear reactor rocket under a variety of operating conditions is a critical part in the development of NTP. The development of system models has the potential to reduce the design, testing, time and cost required to reach flight-ready status. In this study a commercial flow network tool, Flownex®, was used in the development of a system model to model a nuclear reactor rocket. The integrated mass, momentum and energy balance is solved using the continuity, momentum and energy equations applied to nodes and elements. These nodes and elements are the modular building blocks, typically semi-empirical and allow users to either select appropriate built-in correlations, or to define using specific equations through scripting. By using Flownex®, a nuclear reactor rocket could be modeled and various operating conditions could be investigated during steady-state and transient simulations.
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Jang Ki-Hyo,Britz Margaret L. The Korean Society for Biotechnology and Bioengine 2005 Biotechnology and Bioprocess Engineering Vol.10 No.3
To investigate impediments to plasmid transformation in Brevibacterium flavum BF4 and B. lactofermentum BL1, cell surface barriers were determined by measuring growth inhibition whilst enzymatic barriers were determined by comparing DNA methylation properties. B. lactofermentum was more sensitive to growth inhibition by glycine than B. flavum. Release of cellular proteins during sonication was more rapid for B. lactofermentum than for B. flavum. Plasmid DNA (pCSL 17) isolated from B. flavum transformed recipient $McrBC^+$ strains of Escherichia coli with lower efficiency than $McrBC^-$. McrBC digestion of this DNA confirmed that B. flavum contain methylated cytidines in the target sequence of McrBc sequences but B. lactofermentum contained a different methylation pattern. DNA derived from the B. lactofermentum transformed recipient $EcoKR^+$ strains of E. coli with lower efficiency than $EcoKR^-$, indicating the presence of methylated adenosines in the target sequence of EcoK sequences. The present data describe the differences in the physical and enzymatic barriers between two species of corynebacteria and also provide some insight into the successful foreign gene expression in corynebacteria.
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Ki-Hyo Jang,Margaret L. Britz 한국생물공학회 2005 Biotechnology and Bioprocess Engineering Vol.10 No.3
To investigate impediments to plasmid transformation in Brevibacterium flavum BF4 and B. lactofermentum BL1, cell surface barriers were determined by measuring growth inhibition whilst enzymatic barriers were determined by comparing DNA methylation properties. B. lactofermentum was more sensitive to growth inhibition by glycine than B. flavum. Release of cellular proteins during sonication was more rapid for B. lactofermentum than for B. flavum. Plasmid DNA (pCSL17) isolated from B. flavum transformed recipient McrBC+ strains of Escherichia coli with lower efficiency than McrBC. McrBC digestion of this DNA confirmed that B. flavum contain methylated cytidines in the target sequence of McrBC sequences but B. lactofermentum contained a different methylation pattern. DNA derived from the B. lactofermentum transformed recipient EcoKR+ strains of E. coli with lower efficiency than EcoKR, indicating the presence of methylated adenosines in the target sequence of EcoK sequences. The present data describe the differences in the physical and enzymatic barriers between two species of corynebacteria and also provide some insight into the successful foreign gene expression in corynebacteria.
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Marzieh Hosseini Nezhad,Matthew Knight,Margaret Lorraine Britz 한국식품과학회 2012 Food Science and Biotechnology Vol.21 No.1
In this research, changes were observed in cell surface proteins of a typical strain of the Lactobacillus casei was investigated in response to acidic growth conditions. Two dimensional electrophoresis and Western blot analyses were carried out to detect changes in relative abundance of proteins at the cell surface. The identity of the differentially expressed proteins extracted by LiCl, a chemical routinely used to extract surface proteins of lactic acid bacteria, was determined by MALDI-TOF/TOF MS. Many enzymes involved in glycolysis were up-regulated in the cell surface fraction following growth at low pH, including enolase,lactate dehydrogenase, and glyceraldehyde-3-phosphate dehydrogenase. Several of these proteins were also related to adhesion and generalized stress responses. It is demonstrated that growth of L. casei under acidic conditions caused molecular changes at the cell surface to develop an adaptive strategy corresponding to slower growth at low pH.
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