323,058 research outputs found
Vlassopoulos (Mrs), Eugenia, [No Service Number]
No full textThis record was harvested from a previous catalogue system and will be withdrawn in 2025. Information in this record may be superseded or incomplete. Visit this record in UMA's new catalogue at: https://archives.library.unimelb.edu.au/nodes/view/423156Surname: VLASSOPOULOS (MRS). Given Name(s) or Initials: EUGENIA. Military Service Number or Last Known Location: [No Registration Number]. Missing, Wounded and Prisoner of War Enquiry Card Index Number: 24461.249671
Item: [2016.0049.55417] "Vlassopoulos (Mrs), Eugenia, [No Service Number]
Peer pressure and productivity: The role of observing and being observed
No full textPeer effects arise in situations where workers observe each others' work activity. In this paper, we disentangle the effect of observing a peer from that of being observed by a peer, by setting up a real effort experiment in which we manipulate the observability of performance. In particular, we randomize subjects into three groups: in the first one subjects are observed by another subject, but do not observe anybody; in the second one subjects observe somebody else's performance, but are not observed by anybody; in the last group subjects work in isolation, neither observing, nor being observed. To assess the importance of payoff externalities in the emergence of peer effects, we consider both a piece rate compensation scheme, where pay depends solely on own performance, and a team compensation scheme, where pay also depends on the performance of other team members. Overall, we find some evidence that subjects who are observed increase productivity at least initially when compensation is team based, while we find that subjects observing react to what they see when compensation is based only on own performance. (C) 2015 Elsevier B.V. All rights reserved
Stress growth and relaxation of dendritically branched macromolecules in shear and uniaxial extension
No full textWe present unique nonlinear rheological data of well-defined symmetric Cayley-tree poly(methyl methacrylates) in shear and uniaxial extension. Earlier work has shown that their linear viscoelasticity is governed by the hierarchical relaxation of different generations, whereas the segments between branch points are responsible for their substantial strain hardening as compared to linear homopolymers of the same total molar mass at the same value of imposed stretch rate. Here, we extend that work in order to obtain further experimental evidence that will help understanding the molecular origin of the remarkable properties of these highly branched macromolecules. In particular, we address three questions pertinent to the specific molecular structure: (i) is steady state attainable during uniaxial extension? (ii) what is the respective transient response in simple shear? and (iii) how does stress relax upon cessation of extension or shear? To accomplish our goal we utilize state-of-the-art instrumentation, i.e., filament stretching rheometry (FSR) and cone-partitioned plate (CPP) shear rheometry for polymers with 3 and 4 generations, and complement it with state-of-the-art modeling predictions using the Branch-on-Branch (BoB) algorithm. The data indicates that the extensional viscosity reaches a steady state value, whose dependence on extension rate is identical to that of entangled linear and other branched polymer melts. Nonlinear shear is characterized by transient stress overshoots and the validity of the Cox-Merz rule. Remarkably, nonlinear stress relaxation is much broader and slower in extension compared to shear. It is also slower at higher generation, and rate-independent for rates below the Rouse rate of the outer segment. For extension, the relaxation time is longer than that of the linear stress relaxation, suggesting a strong ‘elastic memory’ of the material. These results are 2 described by BoB semi-quantitatively, both in linear and nonlinear shear and extensional regimes. Given the fact that the segments between branch points are less than 3 entanglements long, this is a very promising outcome that gives confidence in using BoB for understanding the key features. Moreover, the response of the segments between generations controls the rheology of the Cayley trees. Their substantial stretching in uniaxial extension appears responsible for strain hardening, whereas coupling of stretches of different parts of the polymer appears to be the origin of the slower subsequent relaxation of extensional stress. Concerning the latter effect, for which predictions are not available, it is hoped that the present experimental findings and proposed framework of analysis will motivate further developments in the direction of molecular constitutive models for branched and hyperbranched polymers
Viscoelastic behavior of semicrystalline thermoplastic polymers during the early stages of crystallization
No full textUsing rheological techniques, we investigate the evolution of the microstructure evolution during the early stages of crystallization of poly(1-Butene). In performing the measurements, use is made of an innovative experimental protocol, called “inverse quenching”, which allows stopping the crystallization process and producing a stable biphasic (crystalline/amorphous) system. In this way, very low frequency measurements at fixed degrees of crystallization are made possible. We find that crystallization, evidenced as a Liquid-to-Solid Transition (LST) under isothermal conditions, with characteristics of critical gel behavior, takes place at surprisingly low degrees of crystallinity (below 1.5%). The critical gel properties, which are found to depend on both crystallization temperature and molecular weight, can be reduced to a single master curve when the gel strength is plotted as a function of the relaxation exponent.. More importantly, the LST it is preceded by the development of a long, but finite relaxation process. This latter process, although not fully understood, brings analogies to the slow dynamics observed in hybrid colloid-polymer systems (block copolymer micelles or multiarm star polymers) as well as the recently suggested presence of dormant nuclei. It is clear, however, that the connectivity among crystallites, apparently via the amorphous segments, plays a key role in this new proces
Symbolic incentives and the recruitment of volunteers for citizen science projects
No full textThe provision of activities with external benefits that rely on voluntary contributions may often fall below societal needs. In this article, we focus on such contributions to a citizen science project (the World Community Grid) in which members of the general public are asked to offer unused computer power to advance cutting-edge scientific research. We investigate the role played by symbolic awards in stimulating existing contributors to recruit new contributors for this project. The recruitment campaign we study introduces badges for referrals (visible on each user’s public profile page) varying, across randomized treatment groups, the threshold of successful referrals needed to receive these badges. We find that these symbolic incentives are effective in boosting referrals, and more so when the minimum threshold for achieving symbolic awards is higher. However, the overall effect of the incentives is quite modest, highlighting the challenges of running referral campaigns for the recruitment of volunteers
A practical guide to mitigate edge fracture instability in sheared polymer melts
No full textThe measurement of nonlinear shear response of viscoelastic materials is often hindered by edge fracture instabilities. The phenomenon was first addressed theoretically by Tanner and Keentok and ever since has attracted the interest of experimentalists and theorists alike. Despite progress, accounting for or mitigating edge fracture remains a challenge, in particular when dealing with strongly viscoelastic materials such as entangled polymer melts. Here, we present and compare different experimental attempts to delay edge fracture in a cone-and-plate (CP) geometry, including the use of an immiscible fluid bath around the sample (that reduces the stress and interfacial gradients in comparison with the sample/air interface), a cone-partitioned plate (CPP) fixture, and an outer collar attached to the sample's edge (in a CP or CPP fixture). Focusing on the torque signal, we find that the combination of CPP and collar provides the best results. This may indeed help measuring highly elastic materials over an extended range of shear rates and, importantly, contribute to reliably measuring the normal stress coefficients in a cone-partitioned plate tool. It is, therefore, hoped that this simple idea will be further pursued in the direction of improving our current rheometric capabilities
Concern for relative standing and deception
No full textWe report results from a sender-receiver cheap talk game, which explores whether an individual's decision to deceive is influenced by a concern for relative standing in a reference group. We show theoretically that positively biased senders, who think they are higher in the deception distribution than they actually are, will correct their beliefs and increase their cheating, when presented with information on the actual deception distribution. Hence, a predominantly positively biased group of senders will increase its average deception. Moreover, within a group, being more positively biased implies cheating less. The experimental data confirm both of these hypothese
Viscoelasticity and crystallization of poly(ethylene oxide) star polymers of varying arm number and size
No full textWe investigated the linear melt viscoelasticity and the crystallization kinetics of a series of model poly(ethylene oxide) stars with different functionalities (f=4-32 arms) and moderately entangled arms (their molecular masses ranging from 5.5 kg/mol to 12 kg/mol). The limited data in the homogeneous state indicated that the zero-shear viscosity was adequately described by the Milner-McLeish model for functionalities f<32, where the core effect is insignificant; a similar behaviour was observed for the recoverable compliance which depended on both the molecular weight and the number of the arms. Below the melting point, the isothermal crystallization was measured with DSC and rheology, and analyzed in terms of the Avrami theory, expanding over a wide range of temperatures. The results were supported by additional polarizing optical microscopy data, and showed a strong dependence of the crystallization rate on the arm molecular weight, whereas the available experimental evidence is suggestive of some functionality dependence as well
Peer pressure and productivity: the role of observing and being observed
No full textPeer effects arise in situations where workers observe each others’ work activity. In this paper, we disentangle the effect of observing a peer from that of being observed by a peer, by setting up a real effort experiment in which we manipulate the observability of performance. In particular, we randomize subjects into three groups: in the first one subjects are observed by another subject, but do not observe anybody; in the second one subjects observe somebody else's performance, but are not observed by anybody; in the last group subjects work in isolation, neither observing, nor being observed. To assess the importance of payoff externalities in the emergence of peer effects, we consider both a piece rate compensation scheme, where pay depends solely on own performance, and a team compensation scheme, where pay also depends on the performance of other team members. Overall, we find some evidence that subjects who are observed increase productivity at least initially when compensation is team based, while we find that subjects observing react to what they see when compensation is based only on own performanc
Diffusive author(s), cohesive author: Analysis of S/N (1994)
No full textThis study indicates the ways in which various aspects of the author(s) are brought forth in Dumb type’s performance art, the S/N production. Previous research has suggested a non-hierarchical organization of Dumb type and the absence of a “privileged author” in Dumb type’s collaborative work, S/N. However, the results that I have investigated from member’s interviews on the creative process of S/N along with my analysis of the recorded images of S/N, indicate a different aspect of the author(s). First, S/N was created through, so to speak, the collective ideas of the members of Dumb type. Further, S/N has at least nine quotations from previous performances, installations, and printed writings, besides the work-in-progress technique. Explicating one of the “author functions” as given by Michel Foucault, each text has plural subjects of the author. However, it has been revealed from members’ interviews that Teiji Furuhashi had a decision-making role in selecting the members’ ideas within the performance. Since then, S/N has had plural subjects of creation; however, Furuhashi is one of the subjects of creation along with the “privileged author.” S/N has plural authors (diffusive authors) yet at the same time, it has a “privileged author,” Teiji Furuhashi (cohesive author)
- …
