In view of this lack of information, the present work was undertaken to provide experimental ial mixing data for both gas and liquid phases, using a dynamic response technique(tracer measurements), for second-generation random packings and for structured packings, using a large-scale column. Such experimental mixing data will provide the first insight into the mixing behaviour in modern packings as well as to asses the effect of axial mixing on interphase mass transfer in column filled with such packings (AIChE Joural, 79, Vol 46, No. 1, 2000) Ex&. Nowadays, design practices that address complex integrated plants are well established as far as the steady stae is concerned. However, analysis of plant dynamics during the conceptual design state leading to better flowsheet al tematives from the controllability point of view is a recognized, but unresolved problem. Also in process systems science attempts to incorporate flowsheet synthesis are arely available( Mohideen et al., 1996). Clearly, a systematic analysis of plantwide dynamics and controllability is difficult, partly because of the effect of recycles. As Luyben noted"Processes with ecycle streams are quite common but their dynamics poorly understood"(Luyben, 1993a). This is crucial in the context of zerp-discharge plants, where even more material has to be recycled. A complex plant may involve strong interactions between recycle loops that sometimes lead to asignifi influence on the performance of individual units Therefore, a real need exists to find a quantitative methodology to analyze the effects of interactions Flowsheeting the effects of interactions. Flowsheeting is a well-establ ished technique reflecting the complexity of systems of an accurate, steady-state plant model ( Dimian, 1994). The curent practice in the anaysis of large plants seems to be limited to the exploration of the operating window by such flowsheeting. However, more essential design and operating knowledge is obtained thorugh dynamic flowsheeting, since it accounts for control features. In addition, large dynamic plant models in principle give access to a whole class of controllabil ity tools that usually are applied to small problems. However, this requires an adequate reduction of these models, which is not atrivial problem as will be discussed a forthcoming publ ication. The goal of this article is to present a methodology to combine large dynamic models with controllabil ity tools and to demonstrate their use by means of practical problem: the namIc of the plant material balance, and particularly that of impurities The objective of our approach is to obtain a quantitative measure of the plant perfomance using reference tracking and disturbance rejection in an early design stage. A better understanding of dynamic interactions between recycles is desired, from which design modifications with improved operabil ity characteristics are more readily invented without using complex control strategies We therefore use simple proportional feedback-control and controllabil ity tools in addition to extensive steady-state and dynamic simulations. A complex multivariable control system may be implemented fterward, but this is beyond the scope of this article Controllers and controllabil ity tools are only to be sed to measure the performance of the design and tofind the effect of design modifications In a case study about the handl ing of impurities in a complex plant, it is demonstrated how connectivity
In view of this lack of information, the present work was undertaken to provide experimental axial mixing data for both gas and liquid phases, using a dynamic response technique (tracer measurements), for second-generation random packings and for structured packings,using a large-scale column. Such experimental mixing data will provide the first insight into the mixing behaviour in modern packings as well as to asses the effect of axial mixing on interphase mass transfer in column filled with such packings. (AIChE Journal, 79 ,Vol. 46, No. 1, 2000). Ex 8..Nowadays, design practices that address complex integrated plants are well established as far as the steady stae is concerned. However, analysis of plant dynamics during the conceptual design state leading to better flowsheet alternatives from the controllability point of view is a recognized, but unresolved problem. Also in process systems science attempts to incorporate flowsheet synthesis are barely available (Mohideen et al., 1996). Clearly, a systematic analysis of plantwide dynamics and controllability is difficult, partly because of the effect of recycles. As Luyben noted “Processes with recycle streams are quite common but their dynamics poorly understood” (Luyben, 1993a). This is crucial in the context of zero-discharge plants, where even more material has to be recycled. A complex plant may involve strong interactions between recycle loops that sometimes lead to a significant influence on the performance of individual units. Therefore, a real need exists to find a quantitative methodology to analyze the effects of interactions. Flowsheeting the effects of interactions. Flowsheeting is a well-established technique reflecting the complexity of systems of an accurate, steady-state plant model (Dimian, 1994). The current practice in the anaysis of large plants seems to be limited to the exploration of the operating window by such flowsheeting. However, more essential design and operating knowledge is obtained thorugh dynamic flowsheeting, since it accounts for control features. In addition, large dynamic plant models in principle give access to a whole class of controllability tools that usually are applied to small problems. However, this requires an adequate reduction of these models, which is not a trivial problem as will be discussed in a forthcoming publication. The goal of this article is to present a methodology to combine large dynamic models with controllability tools and to demonstrate their use by means of practical problem: the dynamics of the plant material balance, and particularly that of impurities. The objective of our approach is to obtain a quantitative measure of the plant performance using reference tracking and disturbance rejection in an early design stage. A better understanding of dynamic interactions between recycles is desired, from which design modifications with improved operability characteristics are more readily invented without using complex control strategies. We therefore use simple proportional feedback-control and controllability tools in addition to extensive steady-state and dynamic simulations. A complex multivariable control system may be implemented afterward, but this is beyond the scope of this article. Controllers and controllability tools are only to be used to measure the performance of the design and tofind the effect of design modifications. In a case study about the handling of impurities in a complex plant, it is demonstrated how connectivity
ns between recycles can be flowsheet altematives with plantwide control structure that would be infeasible on a stand-alone unit( Dimian et al., 1996). The control structures may imply variables belonging to different units. The controllabil ity properties are determined by the competition between positive feedback effects, typically recycles, and negative feedback effects, like exit streams and chemical reactors. In this example an extra reactor is introduced where impurities that are difficult to handle are transformed into other componenets. Since these componenets are easily removed from the recycle, the clased-loop performance of the system improved with respect to disturbance rejection In future work we will investigate altermative recycle structures and their controllability properties (AIChE Journal 134 Vol 46, No. 1 2000) Ex 9 Cells in weak AC fields for time lasting more than several minutes shows mechanical effects dielectrophoresis [1-4]. These cells slowly align themsel ves and approach closer to aggregate in a form of pearl chain. Here the gap between two adjacent cell is about 250 to 150 A(pronase-treated cells)[5] High voltage DC pulsing is required for further membrane approach to establish molecular contact(5-8 In electroincorporation[9), strong and long duration multiple pulsing produce simi lar elctric field induced mechanical effect, and move microspheres through a distance of several cell layers, to target epiderthemal cell under different situation. This study is designed to find a single strong field pulse, which can produce mechanical effects on freely suspending model cells, to favour membrane electrofusion. The model cells are not in tight membrane contact prior to application of pulse. Work in this direction can provide an alternative protocal that would merge key step of cell adherence with high voltage fusogenic pulsing Predicting outcome of such protocol is a challenge because the distance involves between the freely suspending cells is large[ 13, 14 compared to artificially[1-5, 10-12]or naturally[ 13, 14 of the previous theoretical works in this respect consider membrane as spherical particle[ 15-17]. But in pre-pulse condition, initial intercellular interaction area is expected to be in the range ofo. 0 lum2 [18] Thus, one needs a molecular cell surface model while dealing with intercellular interactions. On this basis, a cell surface can be assumed as locally planar and more appropriately modeled as three layered structure[18, 19]. First layer(Im)is phospholipid bilayer and other membrane components, and 70Ain thickness. Second layer(L)is a fuzzy coat of biopolymer(majority glycoproteins), negatively charge, extending 100 A from the cell sur face and beyond that layer is an aqueous medium in which cell is uspended. The model can be used for realistic estimation of non-specific van der Waals and elctrostatic (Journal of Electroanal. Chem. 423, Vol 48, No2. 1999) Ex 10. The advantages that the use of electrokinetically driven flow offers over pressure
between units and interactions between recycles can be exploited to create flowsheet alternatives with plantwide control structure that would be infeasible on a stand-alone unit(Dimian et al., 1996). The control structures may imply variables belonging to different units. The controllability properties are determined by the competition between positive feedback effects, typically recycles, and negative feedback effects, like exit streams and chemical reactors. In this example an extra reactor is introduced, where impurities that are difficult to handle are transformed into other componenets. Since these componenets are easily removed from the recycle, the closed-loop performance of the system is improved with respect to disturbance rejection. In future work we will investigate alternative recycle structures and their controllability properties. (AIChE Journal 134 Vol.46, No.1 2000). Ex 9. Cells in weak AC fields for time, lasting more than several minutes shows mechanical effects, dielectrophoresis [1-4]. These cells slowly align themselves and approach closer to aggregate in a form of pearl chain. Here the gap between two adjacent cell is about 250 to 150 A (pronase-treated cells)[5]. High voltage DC pulsing is required for further membrane approach to establish molecular contact[5-8]. In electroincorporation [9], strong and long duration multiple pulsing produce similar elctric field induced mechanical effect, and move microspheres through a distance of several cell layers, to target epiderthemal cell under different situation. This study is designed to find a single strong field pulse, which can produce mechanical effects on freely suspending model cells, to favour membrane electrofusion. The model cells are not in tight membrane contact prior to application of pulse. Work in this direction can provide an alternative protocal that would merge key step of cell adherence with high voltage fusogenic pulsing. Predicting outcome of such protocol is a challenge because the distance involves between the freely suspending cells is large [13,14] compared to artificially [1-5,10-12] or naturally[13,14]. Theoretical approach to describe cellular interactions required a quantitative cell surface model. Most of the previous theoretical works in this respect consider membrane as spherical particle [15-17]. But in pre-pulse condition, initial intercellular interaction area is expected to be in the range of 0.01um2 [18]. Thus, one needs a molecular cell surface model while dealing with intercellular interactions. On this basis, a cell surface can be assumed as locally planar and more appropriately modeled as three layered structure [18,19]. First layer (lm) is phospholipid bilayer and other membrane components, and 70A in thickness. Second layer (L) is a fuzzy coat of biopolymer (majority glycoproteins), negatively charge, extending 100 A from the cell surface and beyond that layer is an aqueous medium in which cell is uspended. The model can be used for realistic estimation of non-specific van der Waals and elctrostatic energy in pre-pulse condition. (Journal of Electroanal.Chem.;423, Vol 48, No2. 1999). Ex 10.The advantages that the use of electrokinetically driven flow offers over pressure
driven flow have been well enumerated in recent review articles Capillary (21-24). The absence of a significant pressure drop across the column in Electrochromatography(CEC) allow for the use of longer capillaries packed with smaller particles than is typically possible using pressure-driven flow. This can lead to higher resolution separations, higher column efficiency, and shorter chromatographic run times. Here we present the results of the first application of capillary electrochromatography to the separation ofEPA 8830 mixture. Under isocratic conditions and using capillaries packed with 20cm of 1.5 um nonporous octydecylsilica(ODS) particles and moderate electric fields( 1000V/cm ) baseline separations of all 14 of the components were achieved in under 7 min ( Anal. Chem.70,No.15,1998,3276) Ex 11. In recent advances on lipase-catalyzed kinetic resolutions of chiral alcohols(1-5) rious methods for the artificial modulating method have been devised to improved the enantioselectivity (4-7). However, the development of a generally applicable method for relatively unsuitable primary alcohols is still an urgent subject. As a readily available method for synthetic organic chemists, we recently proposed a low-temperature method(0 C to-40C)in the lipase-catalyzed resolution of 3-phenyl-2H-azirine-2-methanol (4).It was the first example of an enzymatic reaction carried out at such very low temperatures as ar as we know (Tetrahedron Letters 39(1998)7881) Ex 12 Immunoassays offer significant advantages over more traditional methods of metal ion detection Immunoassays are quick, inexpensive, simple to perfom, and reasonably portable, they can also be both highly sensitive and selective. Although most environmental immunoassays are directed towards halogenated aromatic compounds and pesticides, the technique is theoretically applicable to any pollutant for which a suitable antibody can be generated. An antibody highly specific for mercury complexed to glutathione has been reported; this antibody is the basis for the only commercially available metal ion immunoassay (3, 4). Our laboratory has demonstrated that metal-specific monoclonal antibodies can also be generated by immunization with metal-chelate complexes(6). These antibodies have subsequently been used to develop immunoassays for specific metal ions(7-9). In this paper, we describe our immunoassay procedure and briefly review the binding properties of three representat ive monoclonal antibodies isolated and characterized by our laboratory. Analytica Chimica Acta 376(1998)13-19) Ex 13. Technetium-99(h1/2=2.2 X 105 years )is a fission product of 235U with approximately a 6% yield. Tc only exists naturally in minute quantities at 0. 25-0.31 ng
-driven flow have been well enumerated in recent review articles Capillary (21-24). The absence of a significant pressure drop across the column in Electrochromatography (CEC) allow for the use of longer capillaries packed with smaller particles than is typically possible using pressure-driven flow. This can lead to higher resolution separations, higher column efficiency, and shorter chromatographic run times. Here we present the results of the first application of capillary electrochromatography to the separation of EPA 8830 mixture. Under isocratic conditions and using capillaries packed with 20cm of 1.5 m nonporous octydecylsilica (ODS) particles and moderate electric fields ( 1000V/cm ), baseline separations of all 14 of the components were achieved in under 7 min. (Anal. Chem. 70, No.15, 1998, 3276 ) Ex 11. In recent advances on lipase-catalyzed kinetic resolutions of chiral alcohols (1-5), various methods for the artificial modulating method have been devised to improved the enantioselectivity.(4-7).However, the development of a generally applicable method for relatively unsuitable primary alcohols is still an urgent subject. As a readily available method for synthetic organic chemists, we recently proposed a low-temperature method (0 C to - 40 C ) in the lipase -catalyzed resolution of 3-phenyl-2H-azirine-2-methanol (4).It was the first example of an enzymatic reaction carried out at such very low temperatures as far as we know. (Tetrahedron Letters 39 (1998 ) 7881) Ex 12. Immunoassays offer significant advantages over more traditional methods of metal ion detection. Immunoassays are quick, inexpensive, simple to perform, and reasonably portable; they can also be both highly sensitive and selective. Although most environmental immunoassays are directed towards halogenated aromatic compounds and pesticides, the technique is theoretically applicable to any pollutant for which a suitable antibody can be generated. An antibody highly specific for mercury complexed to glutathione has been reported; this antibody is the basis for the only commercially available metal ion immunoassay (3,4). Our laboratory has demonstrated that metal-specific monoclonal antibodies can also be generated by immunization with metal-chelate complexes (6). These antibodies have subsequently been used to develop immunoassays forspecific metal ions (7-9). In this paper, we describe our immunoassay procedure and briefly review the binding properties of three representative monoclonal antibodies isolated and characterized by our laboratory.( Analytica Chimica Acta 376 (1998) 13-19 ) Ex 13.. Technetium-99 (t1/2 =2.2 x 105 years ) is a fission product of 235U with approximately a 6 % yield. Tc only exists naturally in minute quantities at 0.25-0.31 ng
kgin pitchblende arising from spontaneous fission (1). Most 9Tc in the environment is derived from the discharge of fission waste products from nuclear fuel reprocessing plants and from weapons'fallout The total input of Tc to theenvironment from weapons fallout is estimated at 140TBq(2), while the discharges to the marine environment from the Sellafield reprocessing plant in the UK have been estimated at 1220TBq from 1954 to 1996(3, 4). There have been significant increases in input of 99Tc into the Irish sea since the commissioning of the enhanced actinide removal plant(EARP)in 1994(5)and the subsequent treatment of stockpiled medium active concentrate ( MaC)waste Discharges from EARP in 1995 were 180 TBq with a reduction to 150 TBq in 1996(3) The main aim of this study is to develop an effective and robust method for 9Tc determination particularly suited to measurement of the isotope in sediments and marine biota. The low concentrations in many environmental samples, the volatility of T, Tc speciation and spectral interferences from yield monitors all cause potential difficulties Ex 14. Antioxidants play a vital role in biology, polymer chemistry, and the food industry By intercepting oxidizing species, predominantly reactive radicals, they prevent cellular damage and polymer or food degradation. Timely challenges in ant ioxidant research entail the assessment of spatial distributions of antioxidants in heterogeneous biological environments and the quantitationof their absolute reaction kinetics, 2 With respect to the latter, the react iv ity of ter-butoxyl(t-BuO*)or 1, 1 dipheny hydrazyl DDPH*) radicals(Scheme 1)toward antioxidants,has been studied by transient absorption spectroscopy. Alternatively, the reactivity ofn, t* triplet-excited ketones, mostly benzophenone(Ph2 CO), has been analyzed by laser flash photolysis to obtain direct information on antioxidant reactivity, 5, since it has long been recognized that n,*-excited states behave in a radical-like way and in their reactivity resemble simple alkoxy Ica We have now employed the n, T* singlet-excited state of 2, 3-diazabicyclo( 2. 2. 2)oct-2-ene (DBO)as a model for a radical-like reactive species. This opens for the first time the opportunity to probe for antioxidant reactivity by means of fluorescence, both time-resolved and steady-state. The superior performance of fluorescence detection for sensing molecular events, for example, when compared to alternative transient absorption and EPR measurements, is well recognized. It comprises high sensitivity of detection down to a single molecule, high selectivity, for example, little interference from reaction products, subnanosecond temporal and submicrometer spat ial resolution, ease of application and access, a great variety of experimental techniques, the possibil ity of noninvasive measurements and more than a century of scientific experience Ex 15 Carbon fibre is one of the most useful materials for preparing microelectrodes for in-vi1o oltammetry (1-3). In order to increase the sensitivity and avoid the interferences of ascorbic acid (AA)
kg-1 in pitchblende arising from spontaneous fission (1). Most 99Tc in the environment is derived from the discharge of fission waste products from nuclear fuel reprocessing plants and from weapons’ fallout. The total input of 99 Tc to the environment from weapons’ fallout is estimated at 140TBq (2), while the discharges to the marine environment from the Sellafield reprocessing plant in the UK have been estimated at 1220TBq from 1954 to 1996 (3,4). There have been significant increases in input of 99Tc into the Irish sea since the commissioning of the enhanced actinide removal plant (EARP) in 1994 (5) and the subsequent treatment of stockpiled medium active concentrate (MAC) waste. Discharges from EARP in 1995 were 180 TBq with a reduction to 150 TBq in 1996(3). The main aim of this study is to develop an effective and robust method for 99Tc determination particularly suited to measurement of the isotope in sediments and marine biota. The low concentrations in many environmental samples, the volatility of Tc, Tc speciation and spectral interferences from yield monitors all cause potential difficulties. Ex 14. Antioxidants play a vital role in biology, polymer chemistry, and the food industry. By intercepting oxidizing species, predominantly reactive radicals, they prevent cellular damage and polymer or food degradation. Timely challenges in antioxidant research entail the assessment of spatial distributions of antioxidants in heterogeneous biological environments and the quantitation of their absolute reaction kinetics1, 2 .With respect to the latter, the reactivity of ter-butoxyl (t-BuO * ) or 1,1 -diphenyl-2-picrylhydrazyl (DDPH * ) radicals (Scheme 1) toward antioxidants3, 4 has been studied by transient absorption spectroscopy. Alternatively, the reactivity of n,* triplet -excited ketones, mostly benzophenone (Ph2 CO), has been analyzed by laser flash photolysis to obtain direct information on antioxidant reactivity3, 5 , since it has long been recognized that n,*-excited states behave in a radical-like way and in their reactivity resemble simple alkoxyl radicals6-9 . We have now employed the n,* singlet-excited state of 2,3-diazabicyclo( 2.2.2)oct-2-ene (DBO) as a model for a radical-like reactive species. This opens for the first time the opportunity to probe for antioxidant reactivity by means of fluorescence, both time-resolved and steady-state. The superior performance of fluorescence detection for sensing molecular events, for example, when compared to alternative transient absorption and EPR measurements, is well recognized. It comprises high sensitivity of detection down to a single molecule, high selectivity, for example, little interference from reaction products, subnanosecond temporal and submicrometer spatial resolution, ease of application and access, a great variety of experimental techniques, the possibility of noninvasive measurements and more than a century of scientific experience Ex 15 Carbon fibre is one of the most useful materials for preparing microelctrodes for in-vivo voltammetry (1-3). In order to increase the sensitivity and avoid the interferences of ascorbic acid (AA)
different kinds of electrochemical procedures have been used to pretreat theelectrodes, such as triangular potential(4 ), cyclic vol tammetry(5), and constant current(6). For further improvement of the selectivity the electodes were chemically modified with different compounds or materials(7, 8). One of these materials is Nafion, which is polycationic exchanger to be modified on the electrodes(9, 10). However, d previously. In this report electrodes modified with Nafion and cellulose acetate(CA)are described. The incorporation of ion exchanging polymer to the cellulose acetate domain allows the binding of counterionic reactants, while maintaining the size exclusion discriminative properties of cellulose acetate. The modified microelectrodes show high stability and inhibit the oxidation od some neurotransmitter metabol ites and electroactive compounds, such as 3, 4-dihydroxyphenyl acetic acid (dOPAC), 5-hydroxy indolacetic acid (5-HI-AA), homovanillic acid(HVA), uric acid (UA)and AA. These composite polymer carbon fibre dopamine(DA)in rat brain, where ischemia was induced to the brain by temporary occlusion of bilateral arotid arteries for 30 mil Chinese Joumal of Chemistry, 710, Vol 18, No5, 2000) 3. Experimental Section 3. 1 In some books on the structure of a research paper, an altemative heading Materials and Methods is used for the section which others called Experimental. The two names cover broadly the same areaof a research paper. For it is within the Experimental section of the paper that we describe the Material employed and the Methods used for resolving a research question We prefer to use the heading Experimentalrather than Materials and Methods So we would expect then that it is within the Experimental section of the paper that the writer will begin describing the actual research that was introduced at the beginning of the paper. The section then is largely descriptive. Its purpose is to describe accurately the mater ials, apparatus, and equipment used and the procedures followed. The methods or procedures used are central to scientific research and they must be carefully planned and executed for them to b For Chemistry and Chemical Engineering research, we would normally expect the Experimental section to include Reagents and Solutions where an accurate account of the chemicals their source and quality and the methods of preparation of the chemical solutions will be stated. The writer will also
different kinds of electrochemical procedures have been used to pretreat the electrodes, such as triangular potential(4), cyclic voltammetry(5), and constant current (6). For further improvement of the selectivity, the electodes were chemically modified with different compounds or materials(7,8). One of these materials is Nafion, which is apolycationic exchanger to be modified on the electrodes(9,10). However, bilayerarrangement has not been reported previously. In this report, composite polymer carbonfibre electrodes modified with Nafion and cellulose acetate (CA) are described. The incorporation of ion exchanging polymer to the cellulose acetate domain allows the binding of counterionic reactants, while maintaining the size exclusion discriminative properties of cellulose acetate. The modified microelectrodes show high stability and inhibit the oxidation od some neurotransmitter metabolites and electroactive compounds, such as 3,4-dihydroxyphenyl acetic acid(DOPAC), 5-hydroxyindolacetic acid (5-HI-AA), homovanillic acid (HVA), uric acid (UA) and AA. These composite polymer carbon fibre electrodes were used for in-vivo determination to detect the oxidation current of neurotransmitter dopamine (DA) in rat brain, where ischemia was induced to the brain by temporary occlusion of bilateral carotid arteries for 30 mins. (Chinese Journal of Chemistry, 710, Vol.18, No.5, 2000). 3. Experimental Section 3.1 In some books on the structure of a research paper, an alternative heading Materials and Methods is used for the section which others called Experimental. The two names cover broadly the same area of a research paper. For it is within the Experimental section of the paper that we describe the Materials employed and the Methods used for resolving a research question. We prefer to use the heading Experimentalrather than Materials and Methods So we would expect then that it is within the Experimental section of the paper that the writer will begin describing the actual research that was introduced at the beginning of the paper. The section then is largely descriptive. Its purpose is to describe accurately the materials, apparatus, and equipment used and the procedures followed..The methods or procedures used are central to scientific research and they must be carefully planned and executed for them to be reproduced by fellow peers. . For Chemistry and Chemical Engineering research, we would normally expect the Experimental section to include Reagents and Solutions where an accurate account of the chemicals, their source and quality and the methods of preparation of the chemical solutions will be stated. The writer will also