1,721,027 research outputs found
Arm retraction dynamics and bistability of a three-arm star polymer in a nanopore
No full textUsing molecular dynamics and Monte Carlo simulations as well as analytical considerations, we study the arm-retraction dynamics of a three-arm star polymer in a narrow nanotube as a function of arm length, N, and tube diameter, D. The system dynamics is analyzed and compared to the bistable collective behavior of a pair of polymer chains tethered in a nanopore. The bistability arises from alternate flipping of one arm of the star into the pore section occupied to that moment by a single arm only. We derive analytical expressions for the free-energy landscape of an arm flip and determine the barrier height as a function of N and D. In the related case of two chains in a narrow tube, we demonstrate that correlations lead to a bimodal distribution of the chain-end positions whereas in a polymer brush, made of equivalent chains at the same grafting density, one observes a single peak only. The residence time distribution between consecutive arm flips is shown to follow a power-exponential relationship, demonstrating good agreement between theory and simulation. © 2014 American Chemical Society.ALEXANDER S, 1977, J PHYS-PARIS, V38, P983, DOI 10.1051-jphys:01977003808098300; Arnold A, 2007, PHYS REV E, V76, DOI 10.1103-PhysRevE.76.031901; Arnold A, 2007, J CHEM PHYS, V127, DOI 10.1063-1.2799513; BARTELS CR, 1986, MACROMOLECULES, V19, P785, DOI 10.1021-ma00157a050; Binder K., 1996, MACROMOLECULES, V29, P341; Binder K, 1997, REP PROG PHYS, V60, P487, DOI 10.1088-0034-4885-60-5-001; Brown S, 2000, MACROMOL THEOR SIMUL, V9, P14; Camargo M, 2012, SOFT MATTER, V8, P4177, DOI 10.1039-c2sm06849d; Colley FR, 2003, J MATER CHEM, V13, P2765, DOI 10.1039-b303578f; de Gennes P. 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M., 2005, PHYS REV LETT, V95, P16602; Wiltshire JT, 2007, AUST J CHEM, V60, P699, DOI 10.1071-CH07128; Zhang Y, 2009, SOFT MATTER, V5, P3694, DOI 10.1039-b909147e1
Efficient separation of long polymer chains by contour length and architecture
No full textOn the basis of theoretical considerations and computer experiment, we suggest a new technique for separation of polymer molecules. The method is based on filling an array of nanochannels with macromolecules whereby the subsequent ejection time depends strongly on small differences in the end-to-end distances of elongated configurations inside the nanotubes. In contrast to conventional methods for chromatographic separation, the efficiency of the proposed method increases with growing molecular length of the chains. The method appears promising also for the separation of ring from linear polymer chains. © 2013 American Chemical Society.Balducci AG, 2008, MACROMOLECULES, V41, P9914, DOI 10.1021-ma8015344; Baumgaertel A, 2012, J CHROMATOGR A, V1240, P1, DOI 10.1016-j.chroma.2012.03.038; Chou CF, 2000, ELECTROPHORESIS, V21, P81, DOI 10.1002-(SICI)1522-2683(20000101)21:181::AID-ELPS813.0.CO;2-#; Julicher F, 1997, REV MOD PHYS, V69, P1269, DOI 10.1103-RevModPhys.69.1269; Macko T., 2003, ADV POLYM SCI, V163; Milchev A, 2010, MACROMOLECULES, V43, P6877, DOI 10.1021-ma1003826; NORDEN B, 1991, Q REV BIOPHYS, V24, P103; Pasch H, 2000, ADV POLYM SCI, V150, P1; Pasch H., 1997, HPLC POLYM; Schimpf M., 2000, FIELD FLOW FRACTIONA; Sheng JF, 2012, SOFT MATTER, V8, P367, DOI 10.1039-c1sm06562a; Skoog D., 2006, PRINCIPLES INSTRUMEN; Stephen L., 2010, CHEM SOC REV, V39, P1133; Sunada Wade M., 1997, Electrophoresis, V18, P2243, DOI 10.1002-elps.1150181215; Terranova GR, 2012, PHYS REV E, V85, DOI 10.1103-PhysRevE.85.061801; Trathnigg B, 2010, J SEP SCI, V33, P2052, DOI 10.1002-jssc.201000181; TRATHNIGG B, 1994, J CHROMATOGR A, V665, P47, DOI 10.1016-0021-9673(94)87030-6; Turner SWP, 2002, PHYS REV LETT, V88, DOI 10.1103-PhysRevLett.12810311
Universal properties of a single polymer chain in slit: Scaling versus molecular dynamics simulations
No full textWe revisit the classical problem of a polymer confined in a slit in both of its static and dynamic aspects. We confirm a number of well known scaling predictions and analyze their range of validity by means of comprehensive molecular dynamics simulations using a coarse-grained bead-spring model of a flexible polymer chain. The normal and parallel components of the average end-to-end distance, mean radius of gyration and their distributions, the density profile, the force exerted on the slit walls, and the local bond orientation characteristics are obtained in slits of width D=410 (in units of the bead diameter) and for chain lengths N=50300. We demonstrate that a wide range of static chain properties in normal direction can be described quantitatively by analytic model-independent expressions in perfect agreement with computer experiment. In particular, the observed profile of confinement-induced bond orientation is shown to closely match theory predictions. The anisotropy of confinement is found to be manifested most dramatically in the dynamic behavior of the polymer chain. We examine the relation between characteristic times for translational diffusion and lateral relaxation. It is demonstrated that the scaling predictions for lateral and normal relaxation times are in good agreement with our observations. A novel feature is the observed coupling of normal and lateral modes with two vastly different relaxation times. We show that the impact of grafting on lateral relaxation is equivalent to doubling the chain length. © 2008 American Institute of Physics.Allen M. P., 1987, COMPUTER SIMULATIONS; BISHOP M, 1991, J CHEM PHYS, V94, P6920, DOI 10.1063-1.460725; BLEHA T, 1990, POLYMER, V31, P1321, DOI 10.1016-0032-3861(90)90224-M; BROCHARD F, 1979, J PHYS LETT-PARIS, V40, pL399; Burkhardt TW, 1999, PHYS REV E, V59, P5833, DOI 10.1103-PhysRevE.59.5833; CARACCIOLO S, 1998, J PHYS A, V32, P1215; CIFRA P, 1988, MAKROMOL CHEM-RAPID, V9, P355; Cifra P, 2000, J CHEM PHYS, V113, P8313, DOI 10.1063-1.1314340; Cifra P, 2001, MACROMOLECULES, V34, P605, DOI 10.1021-ma000964a; Cifra P, 2002, POLYMER, V43, P2409, DOI 10.1016-S0032-3861(02)00040-X; Clausen-Schaumann H, 2000, CURR OPIN CHEM BIOL, V4, P524, DOI 10.1016-S1367-5931(00)00126-5; DAOUD M, 1977, J PHYS-PARIS, V38, P85, DOI 10.1051-jphys:0197700380108500; DEGENNES PG, 1983, J PHYS LETT-PARIS, V44, pL241; DEGENNES PG, 1972, PHYS LETT A, VA 38, P339, DOI 10.1016-0375-9601(72)90149-1; De Gennes PG, 1979, SCALING CONCEPTS POL; DEGENNES PG, 1981, MACROMOLECULES, V14, P1637, DOI 10.1021-ma50007a007; de Joannis J, 2000, EUROPHYS LETT, V51, P41, DOI 10.1209-epl-i2000-00335-x; des Cloizeaux J., 1990, POLYM SOLUTIONS THEI; Descas R, 2005, J CHEM PHYS, V122, DOI 10.1063-1.1868556; DUENWEG B, 1995, MONTE CARLO MOL DYNA; EISENRIEGLER E, 1982, J CHEM PHYS, V77, P6296, DOI 10.1063-1.443835; Eisenriegler E, 1993, POLYM NEAR SURFACES; FISHER ME, 1966, J CHEM PHYS, V44, P616, DOI 10.1063-1.1726734; Flory PJ, 1953, PRINCIPLES POLYM CHE; Freed K. F., 1987, RENORMALIZATION GROU; Grassberger P, 1997, PHYS REV E, V56, P3682, DOI 10.1103-PhysRevE.56.3682; GREST GS, 1986, PHYS REV A, V33, P3628, DOI 10.1103-PhysRevA.33.3628; Hagita K, 1999, J PHYS SOC JPN, V68, P401, DOI 10.1143-JPSJ.68.401; Hsu HP, 2004, J CHEM PHYS, V120, P2034, DOI 10.1063-1.1636454; Hsu HP, 2003, EUR PHYS J B, V36, P209, DOI 10.1140-epjb-e2003-00337-6; KOTELYANSKII M, 2004, COMPUTER SIMULATION; KREMER K, 1984, J CHEM PHYS, V81, P6381, DOI 10.1063-1.447549; Milchev A, 1998, EUR PHYS J B, V3, P477, DOI 10.1007-s100510050338; Milchev A, 1996, MACROMOLECULES, V29, P343, DOI 10.1021-ma950668b; MILCHEV A, 1994, MACROMOL THEOR SIMUL, V3, P305, DOI 10.1002-mats.1994.040030203; Milchev A, 1996, J PHYS II, V6, P21, DOI 10.1051-jp2:1996165; SCHFER L, 1999, EXCLUDED VOLUME EFFE; Sheng YJ, 2001, J CHEM PHYS, V114, P4724, DOI 10.1063-1.1345879; Sotta P, 2000, J CHEM PHYS, V112, P1565, DOI 10.1063-1.480704; Teraoka I, 2004, POLYMER, V45, P3835, DOI 10.1016-j.polymer.2004.03.070; Teraoka I, 2002, COLLOID SURFACE A, V206, P299, DOI 10.1016-S0927-7757(02)00046-8; Teraoka I, 2002, POLYMER, V43, P3025, DOI 10.1016-S0032-3861(02)00098-8; Thompson AP, 1996, MACROMOLECULES, V29, P4314, DOI 10.1021-ma9503219; VICTOR JM, 1990, J CHEM PHYS, V92, P1362, DOI 10.1063-1.458147; Wang YM, 1997, MACROMOLECULES, V30, P8473, DOI 10.1021-ma970741t; WEBMAN I, 1980, J PHYS-PARIS, V41, P579, DOI 10.1051-jphys:01980004106057900; Williams MC, 2002, CURR OPIN STRUC BIOL, V12, P330, DOI 10.1016-S0959-440X(02)00340-8; Wittmer JP, 2004, PHYS REV LETT, V93, DOI 10.1103-PhysRevLett.93.14780119222
The escape transition of a polymer: A unique case of non-equivalence between statistical ensembles
No full textA flexible polymer chain under good solvent conditions, end-grafted on a flat repulsive substrate surface and compressed by a piston of circular cross-section with radius L may undergo the so-called escape transition when the height of the piston D above the substrate and the chain length N are in a suitable range. In this transition, the chain conformation changes from a quasi-two-dimensional self-avoiding walk of blobs of diameter D to an inhomogeneous flower state, consisting of a stem (stretched string of blobs extending from the grafting site to the piston border) and a crown outside of the confining piston. The theory of this transition is developed using a Landau free-energy approach, based on a suitably defined (global) order parameter and taking also effects due to the finite chain length N into account. The parameters of the theory are determined in terms of known properties of limiting cases (unconfined mushroom, chain confined between infinite parallel walls). Due to the non-existence of a local order parameter density, the transition has very unconventional properties (negative compressibility in equilibrium, non-equivalence between statistical ensembles in the thermodynamic limit, etc.). The reasons for this very unusual behavior are discussed in detail. Using Molecular Dynamics (MD) simulation for a simple bead-spring model, with N in the range 50 \leq N \leq 300 , a comprehensive study of both static and dynamic properties of the polymer chain was performed. Even though for the considered rather short chains the escape transition is still strongly rounded, the order parameter distribution does reveal the emerging transition clearly. Time autocorrelation functions of the order parameter and first passage times and their distribution indicate clearly the strong slowing down associated with the chain escape. 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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Capillary Filling in Microchannels with Wall Corrugations: A Comparative Study of the Concus-Finn Criterion by Continuum, Kinetic, and Atomistic Approaches
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Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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