The study examined the conditions under which lay people and health professionals living in Chile... more The study examined the conditions under which lay people and health professionals living in Chile find it acceptable for a physician to break confidentiality to protect the wife of a patient with a sexually transmitted disease (STD). One hundred sixty-nine lay persons, 10 physicians, 17 psychologists, and 11 paramedical professionals indicated the acceptability of breaking confidentiality in 48 scenarios. The scenarios were all possible combinations of five factors: disease severity (severe, lethal); time taken to discuss this with the patient (little time, much time); patient’s intent to inform his spouse about the disease (none, one of these days, immediately); patient’s intent to adopt protective behaviors (no intent, intent); and physician’s decision to consult an STD expert (yes, no), 2 x 2 x 3 x 2 x 2. The study also compared Chilean and French views, using data gathered previously in France. A cluster analysis conducted on the overall set of raw data revealed groups of partic...
AIS Transactions on Human-Computer Interaction, 2017
In this paper, we argue that one can understand the adoption and routine use of enterprise system... more In this paper, we argue that one can understand the adoption and routine use of enterprise systems by examining the fit between the system and the social structures of the organization. We develop a model of the adoption and longterm use of enterprise systems based on sociological concepts (Lord Anthony Giddens' structuration theory) rather than the usual cognitive psychology concepts. We focus on the adoption and use of three versions of an enterprise KMS to support sales representatives at a multinational pharmaceutical firm. Our first study (a five-year case study of the KMS that went through one failed deployment and two successful ones) shows that the structures of signification, legitimation, and domination all influence loyal use, although domination may be less important. Our second study (a survey of 893 users at the firm) shows that the structures of signification, legitimation, and domination explain about 50 percent of the variance in ongoing loyal use but that their relative importance depends on the job experience of the users: signification and legitimation influence novices more, and signification and domination influence experts more. We believe that this parsimonious three-factor model offers a useful approach for future research and practice.
Journal of the Association for Information Systems, 2007
This paper reports an empirical study intended to provide detailed comparisons amongst and betwee... more This paper reports an empirical study intended to provide detailed comparisons amongst and between the varieties of available measures of computer self-efficacy (CSE). Our purpose is to ascertain their relative abilities to isolate the CSE construct from other related constructs and to capture variance in performance attributed to changes in CSE level. In addition, we investigate the importance of ensuring the measure being used is sufficiently aligned with the task domain of interest. Finally, we explore the stability of CSE measures as they relate to the current state of evolution within the computing domain. Marakas, Yi, and Johnson (1998) proposed a framework for the construction of instruments intended to measure the CSE construct that we have adopted as a basis for this series of investigations. To that end, we advance and test a set of hypotheses derived from the Marakas et al. (1998) framework. Results of the analyses support the need for adherence to the tenets of the proposed framework as well as provide evidence that CSE measures suffer from degradation of their explanatory power over time. Further, this study brings forth the importance of appropriately validating measures of CSE using approaches intended for a formative rather than a reflective construct. These results suggest that the common practices of instrument validation and reuse of long-standing instruments to measure CSE may not be the most effective approach to the study of the construct. Implications for future research are discussed.
Journal of Modern Applied Statistical Methods, 2015
The ability to validate formative measurement has increased in importance as it is used to develo... more The ability to validate formative measurement has increased in importance as it is used to develop and test theoretical models. A method is proposed to gather convergent and discriminant validity evidence of formative measurement. Survey data is used to test the proposed method.
Proceedings of the 38th Annual Hawaii International Conference on System Sciences
This paper investigates the factors affecting the Loyal Use of a Knowledge Management System (KMS... more This paper investigates the factors affecting the Loyal Use of a Knowledge Management System (KMS). Unlike most other types of information systems, the value from using a KMS is temporally disassociated from the instance of use. We developed a model of the factors affecting the Loyal Use of a KMS and used data gathered from 1013 users of a well-established codification-based KMS in a multinational pharmaceutical firm to test the model using LISREL. Perceived Usefulness was found to be the strongest factor influencing Loyal Use. Extrinsic Motivation and perceived Voluntariness were also important but perceived ease of use played only a minor role. The quality of the system and quality of the knowledge were found to be key drivers of Perceived Usefulness.
This work in progress examines the roles that Trust in Technology (TRIT) and Computer Self-effica... more This work in progress examines the roles that Trust in Technology (TRIT) and Computer Self-efficacy (CSE) play in predicting post-adoptive usage behavior. Under the umbrella of social cognitive theory, it uses attribution theory and the trust literature to develop an integrative model of trust and self-efficacy. Specifically, we posit that TRIT impacts users' CSE and that these beliefs lead to post-adoptive information technology (IT) usage. To examine our model, we propose a study that brings CSE, TRIT, Deep System Usage, and Trying to Innovate with IT into a single articulated model. Using data from 372 students, we use PLS to examine the hypothesized relationships. We conclude with a discussion of findings.
New experimental data and theory are reported for obtaining three types of rate parameters contro... more New experimental data and theory are reported for obtaining three types of rate parameters controlling kinetics and molecular weight distributions in free-radical polymerizations. (1) (a) Propagation rate coefficients (kp) for butyl aery late are found using pulsed-laser polymerization, with the novel variant of carrying out the procedure at very low temperatures (−10 to −40 °C); this obviates some problems hitherto found with the technique, (b) A means of calculating kp from first principles from transition state theory is given, using accurate quantum mechanical computation of the transition state properties. These calculations give quantitative accord with experiment for ethylene, and reveal that the magnitude of the frequency factor for propagation is dominated by three hindered rotors in the transition state. Since these rotations are influenced by the penultimate unit, this suggests that significant penultimate unit effects are likely in copolymerizations. The effect of these rotations also explains the observed effect of deuteration on kp. (2) A new technique for measuring the transfer rate coefficient (k tr) is presented: initiation by pulsed laser, whence k tr can be obtained from the high molecular weight slope of a plot of ln(number molecular weight distribution) against molecular weight. The method, which can be employed even when extensive termination is taking place, is tested with transfer from MMA to triethylamine. (3) The rate coefficient for termination can be successfully modelled from a knowledge of the diffusion coefficients for oligomeric species as functions of the degree of polymerization and the polymer fraction. New PFG NMR diffusion data for a series of model compounds in polystyrene/benzene give results for this dependence which are in accord with a semiempirical scaling law suggested previously [Piton MC, Gilbert RG, Chapman BE, Kuchel PW (1993) Macromolecules 26: 4472], suggesting that this scaling should be a useful basis for predicting termination rate coefficients.
Page 1. Chapter 7 Termination Rate Coefficients from Molecular Weight Distributions Paul A. Clay,... more Page 1. Chapter 7 Termination Rate Coefficients from Molecular Weight Distributions Paul A. Clay, David I. Christie, and Robert G. Gilbert Chemistry School, Sydney University, New South Wales 2006, Australia An extended ...
ACM Transactions on Management Information Systems, 2011
Trust plays an important role in many Information Systems (IS)-enabled situations. Most IS resear... more Trust plays an important role in many Information Systems (IS)-enabled situations. Most IS research employs trust as a measure of interpersonal or person-to-firm relations, such as trust in a Web vendor or a virtual team member. Although trust in other people is important, this article suggests that trust in the Information Technology (IT) itself also plays a role in shaping IT-related beliefs and behavior. To advance trust and technology research, this article presents a set of trust in technology construct definitions and measures. We also empirically examine these construct measures using tests of convergent, discriminant, and nomological validity. This study contributes to the literature by providing: (a) a framework that differentiates trust in technology from trust in people, (b) a theory-based set of definitions necessary for investigating different kinds of trust in technology, and (c) validated trust in technology measures useful to research and practice.
Each year the University of Arizona conducts on-farm variety trials across the state to evaluate ... more Each year the University of Arizona conducts on-farm variety trials across the state to evaluate the performance of upland cotton varieties. These tests provide many segments of the industry with unbiased, independent data on the performance of varieties from several seed companies when tested side-by-side under typical production practices. Ten trials were planted in the cotton producing areas of the state, ranging from Wellton in Yuma county to Kansas Settlement in Cochise county. Seed companies entered a maximum of two varieties per location resulting in eight to thirteen commercially available varieties per test. The results show that many varieties performed well at several locations, indicating good adaptation to Arizona conditions.
Transactions of the American Mathematical Society, 1963
Introduction. Let iX,T) be a transformation group whose phase space X is a uniform space. Most of... more Introduction. Let iX,T) be a transformation group whose phase space X is a uniform space. Most of the results are stated for compact X. In this paper, four proximity relations, L, M, P, and Q, in X are defined and some of their properties studied. The relations P and Q were first defined and studied by Ellis and Gottschalk [5]. As a general reference for the notions occurring here, consult [8]. In Theorem 1, Lis shown to be an invariant equivalence relation in X, and in Theorem 3, L is characterized as the union of all orbit closures under (X x X, T) which are contained in P. Theorem 3 also shows that if P is closed, then P = L and P is a closed invariant equivalence relation in X. Theorem 4 establishes the productivity of the relations Land M, and in Theorem 7, it is shown that {X,T) is coterminous, i.e., P = Q = L= M, iff P = Q. Theorems 9 through 13 describe L, M, P, and Q under various hypotheses such as (X,T) distal; iX,T) minimal and Tabelian; (X,T) regionally mixing; and the like. Theorem 14 is an application of the general theory to obtain a characterization of iX,T) being uniformly equicontinuous, and as such represents a strengthening of a theorem by John D. Baum [2]. The author is indebted to Professor W. H. Gottschalk for his invaluable suggestions, mathematical stimulation, and sustained interest. Standing notation. Let(Z,T)be a transformation group where X is always a uniform space. Let sé be the class of all syndetic subsets of T, let J>f be the class or all compact subsets of T, let ^ be the uniformity of X, and for each x e X let jVx be the neighborhood filter of x. Definition 1. (1) The isimply) proximal relation ofiX,T) denoted PiX,T) of PiX) or Px or P, is defined to be the set of all (x,y) e X x X such that if <x e <?/, then there exists t e T such that (xi, yt) e oc. (2) The regionally isimply) proximal relation of iX,T), denoted QiX,T) or Q{X) or Qx or Q, is defined to be the set of all (x,y) e X x X such that if
... A. Lyons, Jelica Hutovic, Mark C. Piton, † David I. Christie, Paul A. Clay, Bart G. Manders, ... more ... A. Lyons, Jelica Hutovic, Mark C. Piton, † David I. Christie, Paul A. Clay, Bart G. Manders, ‡ Scott H. Kable, and Robert G. Gilbert*. School of Chemistry, Sydney University, Sydney, NSW 2006, Australia. Macromolecules , 1996, 29 (6), pp 1918–1927. DOI: 10.1021/ma950747n. ...
Many properties (e.g., film formation) of a polymer depend on the full molecular weight distribut... more Many properties (e.g., film formation) of a polymer depend on the full molecular weight distribution (MWD) as well as on the averages of this distribution. Moreover, the MWD contains the complete kinetic history of a polymerization system, and hence an experimental MWD can yield considerable mechanistic information. Complete equations are developed which enable the MWD to be calculated for a wide range of straight-chain free-radical polymerizations. These equations also give insight into the qualitative form of the MWD, thus providing a method for extracting kinetic and mechanistic information from experimental MWDs. Methods are also described which enable numerical solutions to be obtained for the resulting nonlinear integrodifferential equations. The scheme takes into account initiation, transfer, propagation, and termination, allowing all of these to be dependent upon the degrees of polymerization of the chains involved. The model is applicable to bulk and solution polymerizations and to compartmentalized systems (conventional and micro-and miniemulsion polymerizations); in the latter case, phase-transfer events (radical entry into and exit from latex particles, and the aqueous phase kinetics of the various radical species) are specifically included. The dependence of the termination rate coefficient upon the lengths of both participating chains is especially important in systems where termination is kinetically significant. Approximate analytical solutions are also developed for a number of cases of interest. These show that the instantaneous number MWD at high molecular weights is a single exponential-even when termination occurs to a significant extent-which is a direct consequence of the chain-length dependence of termination rate coefficients, Le., most termination events involve at least one very short chain. When the concentration of radicals in the system is low, the "decay constant" of the exponential part of the MWD is given by the ratio of transfer to propagation rate coefficients. In addition, the cumulative MWD frequently has the same behavior as the instantaneous MWD. This has the important implication that considerable mechanistic information can be obtained from size exclusion chromatography data by plotting ln(number MWD) against molecular weight. Such plots can reveal, for example, the termination mechanism that controls the MWD, values of transfer constants, and nucleation mechanisms in emulsion polymerization. Illustrative calculations are carried out for a number of systems. These verify the conclusions from the approximate analytic solutions and show also that the MWD in bulk or solution polymerizations at low conversions and high initiator concentrations is sensitive to the mode of termination (combination or disproportionation).
GPC trace = weight distribution (a) GPC n ... I I:, ,:&amp;#x27;It MALDI signal = number dist... more GPC trace = weight distribution (a) GPC n ... I I:, ,:&amp;#x27;It MALDI signal = number distribution) ... It is particularly applicable to low molecular weights (ca. lo4), is an absolute method requiring no polymer molec-ular-weight calibration, and uses tiny quantities of sample (as low as ...
Journal of Organizational Computing and Electronic Commerce, 2012
As online communities are becoming more and more relevant to business, it is critical to understa... more As online communities are becoming more and more relevant to business, it is critical to understand why individuals are motivated to contribute content longitudinally. In this paper, we draw on existing literature on motivation and technology characteristics to conceptualize a model of longitudinal content contribution. We view longitudinal content contribution phenomenon as a recursive process of interaction between contributors, other participants and IT artifact of online communities. We conclude with the implications of our conceptual model for future research.
An experimental investigation focusing on the effect of dissipation on the evolution of the Benja... more An experimental investigation focusing on the effect of dissipation on the evolution of the Benjamin–Feir instability is reported. A series of wave trains with added sidebands, and varying initial steepness, perturbed amplitudes and frequencies, are physically generated in a long wave flume. The experimental results directly confirm the stabilization theory of Segur et al. (J. Fluid Mech., vol. 539, 2005, pp. 229–271), i.e. dissipation can stabilize the Benjamin–Feir instability. Furthermore, the experiments reveal that the effect of dissipation on modulational instability depends strongly on the perturbation frequency. It is found that the effect of dissipation on the growth rates of the sidebands for the waves with higher perturbation frequencies is more evident than on those of waves with lower perturbation frequencies. In addition, numerical simulations based on Dysthe’s equation with a linear damping term included, which is estimated from the experimental data, can predict the ...
The study examined the conditions under which lay people and health professionals living in Chile... more The study examined the conditions under which lay people and health professionals living in Chile find it acceptable for a physician to break confidentiality to protect the wife of a patient with a sexually transmitted disease (STD). One hundred sixty-nine lay persons, 10 physicians, 17 psychologists, and 11 paramedical professionals indicated the acceptability of breaking confidentiality in 48 scenarios. The scenarios were all possible combinations of five factors: disease severity (severe, lethal); time taken to discuss this with the patient (little time, much time); patient’s intent to inform his spouse about the disease (none, one of these days, immediately); patient’s intent to adopt protective behaviors (no intent, intent); and physician’s decision to consult an STD expert (yes, no), 2 x 2 x 3 x 2 x 2. The study also compared Chilean and French views, using data gathered previously in France. A cluster analysis conducted on the overall set of raw data revealed groups of partic...
AIS Transactions on Human-Computer Interaction, 2017
In this paper, we argue that one can understand the adoption and routine use of enterprise system... more In this paper, we argue that one can understand the adoption and routine use of enterprise systems by examining the fit between the system and the social structures of the organization. We develop a model of the adoption and longterm use of enterprise systems based on sociological concepts (Lord Anthony Giddens' structuration theory) rather than the usual cognitive psychology concepts. We focus on the adoption and use of three versions of an enterprise KMS to support sales representatives at a multinational pharmaceutical firm. Our first study (a five-year case study of the KMS that went through one failed deployment and two successful ones) shows that the structures of signification, legitimation, and domination all influence loyal use, although domination may be less important. Our second study (a survey of 893 users at the firm) shows that the structures of signification, legitimation, and domination explain about 50 percent of the variance in ongoing loyal use but that their relative importance depends on the job experience of the users: signification and legitimation influence novices more, and signification and domination influence experts more. We believe that this parsimonious three-factor model offers a useful approach for future research and practice.
Journal of the Association for Information Systems, 2007
This paper reports an empirical study intended to provide detailed comparisons amongst and betwee... more This paper reports an empirical study intended to provide detailed comparisons amongst and between the varieties of available measures of computer self-efficacy (CSE). Our purpose is to ascertain their relative abilities to isolate the CSE construct from other related constructs and to capture variance in performance attributed to changes in CSE level. In addition, we investigate the importance of ensuring the measure being used is sufficiently aligned with the task domain of interest. Finally, we explore the stability of CSE measures as they relate to the current state of evolution within the computing domain. Marakas, Yi, and Johnson (1998) proposed a framework for the construction of instruments intended to measure the CSE construct that we have adopted as a basis for this series of investigations. To that end, we advance and test a set of hypotheses derived from the Marakas et al. (1998) framework. Results of the analyses support the need for adherence to the tenets of the proposed framework as well as provide evidence that CSE measures suffer from degradation of their explanatory power over time. Further, this study brings forth the importance of appropriately validating measures of CSE using approaches intended for a formative rather than a reflective construct. These results suggest that the common practices of instrument validation and reuse of long-standing instruments to measure CSE may not be the most effective approach to the study of the construct. Implications for future research are discussed.
Journal of Modern Applied Statistical Methods, 2015
The ability to validate formative measurement has increased in importance as it is used to develo... more The ability to validate formative measurement has increased in importance as it is used to develop and test theoretical models. A method is proposed to gather convergent and discriminant validity evidence of formative measurement. Survey data is used to test the proposed method.
Proceedings of the 38th Annual Hawaii International Conference on System Sciences
This paper investigates the factors affecting the Loyal Use of a Knowledge Management System (KMS... more This paper investigates the factors affecting the Loyal Use of a Knowledge Management System (KMS). Unlike most other types of information systems, the value from using a KMS is temporally disassociated from the instance of use. We developed a model of the factors affecting the Loyal Use of a KMS and used data gathered from 1013 users of a well-established codification-based KMS in a multinational pharmaceutical firm to test the model using LISREL. Perceived Usefulness was found to be the strongest factor influencing Loyal Use. Extrinsic Motivation and perceived Voluntariness were also important but perceived ease of use played only a minor role. The quality of the system and quality of the knowledge were found to be key drivers of Perceived Usefulness.
This work in progress examines the roles that Trust in Technology (TRIT) and Computer Self-effica... more This work in progress examines the roles that Trust in Technology (TRIT) and Computer Self-efficacy (CSE) play in predicting post-adoptive usage behavior. Under the umbrella of social cognitive theory, it uses attribution theory and the trust literature to develop an integrative model of trust and self-efficacy. Specifically, we posit that TRIT impacts users' CSE and that these beliefs lead to post-adoptive information technology (IT) usage. To examine our model, we propose a study that brings CSE, TRIT, Deep System Usage, and Trying to Innovate with IT into a single articulated model. Using data from 372 students, we use PLS to examine the hypothesized relationships. We conclude with a discussion of findings.
New experimental data and theory are reported for obtaining three types of rate parameters contro... more New experimental data and theory are reported for obtaining three types of rate parameters controlling kinetics and molecular weight distributions in free-radical polymerizations. (1) (a) Propagation rate coefficients (kp) for butyl aery late are found using pulsed-laser polymerization, with the novel variant of carrying out the procedure at very low temperatures (−10 to −40 °C); this obviates some problems hitherto found with the technique, (b) A means of calculating kp from first principles from transition state theory is given, using accurate quantum mechanical computation of the transition state properties. These calculations give quantitative accord with experiment for ethylene, and reveal that the magnitude of the frequency factor for propagation is dominated by three hindered rotors in the transition state. Since these rotations are influenced by the penultimate unit, this suggests that significant penultimate unit effects are likely in copolymerizations. The effect of these rotations also explains the observed effect of deuteration on kp. (2) A new technique for measuring the transfer rate coefficient (k tr) is presented: initiation by pulsed laser, whence k tr can be obtained from the high molecular weight slope of a plot of ln(number molecular weight distribution) against molecular weight. The method, which can be employed even when extensive termination is taking place, is tested with transfer from MMA to triethylamine. (3) The rate coefficient for termination can be successfully modelled from a knowledge of the diffusion coefficients for oligomeric species as functions of the degree of polymerization and the polymer fraction. New PFG NMR diffusion data for a series of model compounds in polystyrene/benzene give results for this dependence which are in accord with a semiempirical scaling law suggested previously [Piton MC, Gilbert RG, Chapman BE, Kuchel PW (1993) Macromolecules 26: 4472], suggesting that this scaling should be a useful basis for predicting termination rate coefficients.
Page 1. Chapter 7 Termination Rate Coefficients from Molecular Weight Distributions Paul A. Clay,... more Page 1. Chapter 7 Termination Rate Coefficients from Molecular Weight Distributions Paul A. Clay, David I. Christie, and Robert G. Gilbert Chemistry School, Sydney University, New South Wales 2006, Australia An extended ...
ACM Transactions on Management Information Systems, 2011
Trust plays an important role in many Information Systems (IS)-enabled situations. Most IS resear... more Trust plays an important role in many Information Systems (IS)-enabled situations. Most IS research employs trust as a measure of interpersonal or person-to-firm relations, such as trust in a Web vendor or a virtual team member. Although trust in other people is important, this article suggests that trust in the Information Technology (IT) itself also plays a role in shaping IT-related beliefs and behavior. To advance trust and technology research, this article presents a set of trust in technology construct definitions and measures. We also empirically examine these construct measures using tests of convergent, discriminant, and nomological validity. This study contributes to the literature by providing: (a) a framework that differentiates trust in technology from trust in people, (b) a theory-based set of definitions necessary for investigating different kinds of trust in technology, and (c) validated trust in technology measures useful to research and practice.
Each year the University of Arizona conducts on-farm variety trials across the state to evaluate ... more Each year the University of Arizona conducts on-farm variety trials across the state to evaluate the performance of upland cotton varieties. These tests provide many segments of the industry with unbiased, independent data on the performance of varieties from several seed companies when tested side-by-side under typical production practices. Ten trials were planted in the cotton producing areas of the state, ranging from Wellton in Yuma county to Kansas Settlement in Cochise county. Seed companies entered a maximum of two varieties per location resulting in eight to thirteen commercially available varieties per test. The results show that many varieties performed well at several locations, indicating good adaptation to Arizona conditions.
Transactions of the American Mathematical Society, 1963
Introduction. Let iX,T) be a transformation group whose phase space X is a uniform space. Most of... more Introduction. Let iX,T) be a transformation group whose phase space X is a uniform space. Most of the results are stated for compact X. In this paper, four proximity relations, L, M, P, and Q, in X are defined and some of their properties studied. The relations P and Q were first defined and studied by Ellis and Gottschalk [5]. As a general reference for the notions occurring here, consult [8]. In Theorem 1, Lis shown to be an invariant equivalence relation in X, and in Theorem 3, L is characterized as the union of all orbit closures under (X x X, T) which are contained in P. Theorem 3 also shows that if P is closed, then P = L and P is a closed invariant equivalence relation in X. Theorem 4 establishes the productivity of the relations Land M, and in Theorem 7, it is shown that {X,T) is coterminous, i.e., P = Q = L= M, iff P = Q. Theorems 9 through 13 describe L, M, P, and Q under various hypotheses such as (X,T) distal; iX,T) minimal and Tabelian; (X,T) regionally mixing; and the like. Theorem 14 is an application of the general theory to obtain a characterization of iX,T) being uniformly equicontinuous, and as such represents a strengthening of a theorem by John D. Baum [2]. The author is indebted to Professor W. H. Gottschalk for his invaluable suggestions, mathematical stimulation, and sustained interest. Standing notation. Let(Z,T)be a transformation group where X is always a uniform space. Let sé be the class of all syndetic subsets of T, let J>f be the class or all compact subsets of T, let ^ be the uniformity of X, and for each x e X let jVx be the neighborhood filter of x. Definition 1. (1) The isimply) proximal relation ofiX,T) denoted PiX,T) of PiX) or Px or P, is defined to be the set of all (x,y) e X x X such that if <x e <?/, then there exists t e T such that (xi, yt) e oc. (2) The regionally isimply) proximal relation of iX,T), denoted QiX,T) or Q{X) or Qx or Q, is defined to be the set of all (x,y) e X x X such that if
... A. Lyons, Jelica Hutovic, Mark C. Piton, † David I. Christie, Paul A. Clay, Bart G. Manders, ... more ... A. Lyons, Jelica Hutovic, Mark C. Piton, † David I. Christie, Paul A. Clay, Bart G. Manders, ‡ Scott H. Kable, and Robert G. Gilbert*. School of Chemistry, Sydney University, Sydney, NSW 2006, Australia. Macromolecules , 1996, 29 (6), pp 1918–1927. DOI: 10.1021/ma950747n. ...
Many properties (e.g., film formation) of a polymer depend on the full molecular weight distribut... more Many properties (e.g., film formation) of a polymer depend on the full molecular weight distribution (MWD) as well as on the averages of this distribution. Moreover, the MWD contains the complete kinetic history of a polymerization system, and hence an experimental MWD can yield considerable mechanistic information. Complete equations are developed which enable the MWD to be calculated for a wide range of straight-chain free-radical polymerizations. These equations also give insight into the qualitative form of the MWD, thus providing a method for extracting kinetic and mechanistic information from experimental MWDs. Methods are also described which enable numerical solutions to be obtained for the resulting nonlinear integrodifferential equations. The scheme takes into account initiation, transfer, propagation, and termination, allowing all of these to be dependent upon the degrees of polymerization of the chains involved. The model is applicable to bulk and solution polymerizations and to compartmentalized systems (conventional and micro-and miniemulsion polymerizations); in the latter case, phase-transfer events (radical entry into and exit from latex particles, and the aqueous phase kinetics of the various radical species) are specifically included. The dependence of the termination rate coefficient upon the lengths of both participating chains is especially important in systems where termination is kinetically significant. Approximate analytical solutions are also developed for a number of cases of interest. These show that the instantaneous number MWD at high molecular weights is a single exponential-even when termination occurs to a significant extent-which is a direct consequence of the chain-length dependence of termination rate coefficients, Le., most termination events involve at least one very short chain. When the concentration of radicals in the system is low, the "decay constant" of the exponential part of the MWD is given by the ratio of transfer to propagation rate coefficients. In addition, the cumulative MWD frequently has the same behavior as the instantaneous MWD. This has the important implication that considerable mechanistic information can be obtained from size exclusion chromatography data by plotting ln(number MWD) against molecular weight. Such plots can reveal, for example, the termination mechanism that controls the MWD, values of transfer constants, and nucleation mechanisms in emulsion polymerization. Illustrative calculations are carried out for a number of systems. These verify the conclusions from the approximate analytic solutions and show also that the MWD in bulk or solution polymerizations at low conversions and high initiator concentrations is sensitive to the mode of termination (combination or disproportionation).
GPC trace = weight distribution (a) GPC n ... I I:, ,:&amp;#x27;It MALDI signal = number dist... more GPC trace = weight distribution (a) GPC n ... I I:, ,:&amp;#x27;It MALDI signal = number distribution) ... It is particularly applicable to low molecular weights (ca. lo4), is an absolute method requiring no polymer molec-ular-weight calibration, and uses tiny quantities of sample (as low as ...
Journal of Organizational Computing and Electronic Commerce, 2012
As online communities are becoming more and more relevant to business, it is critical to understa... more As online communities are becoming more and more relevant to business, it is critical to understand why individuals are motivated to contribute content longitudinally. In this paper, we draw on existing literature on motivation and technology characteristics to conceptualize a model of longitudinal content contribution. We view longitudinal content contribution phenomenon as a recursive process of interaction between contributors, other participants and IT artifact of online communities. We conclude with the implications of our conceptual model for future research.
An experimental investigation focusing on the effect of dissipation on the evolution of the Benja... more An experimental investigation focusing on the effect of dissipation on the evolution of the Benjamin–Feir instability is reported. A series of wave trains with added sidebands, and varying initial steepness, perturbed amplitudes and frequencies, are physically generated in a long wave flume. The experimental results directly confirm the stabilization theory of Segur et al. (J. Fluid Mech., vol. 539, 2005, pp. 229–271), i.e. dissipation can stabilize the Benjamin–Feir instability. Furthermore, the experiments reveal that the effect of dissipation on modulational instability depends strongly on the perturbation frequency. It is found that the effect of dissipation on the growth rates of the sidebands for the waves with higher perturbation frequencies is more evident than on those of waves with lower perturbation frequencies. In addition, numerical simulations based on Dysthe’s equation with a linear damping term included, which is estimated from the experimental data, can predict the ...
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Papers by paul clay