Equation of State Based Slip Spring Model for Entangled Polymer Dynamics

A mesoscopic, mixed particle- and field-based Brownian dynamics methodology for the simulation of entangled polymer melts has been developed. Polymeric beads consist of several Kuhn segments, and their motion is dictated by the Helmholtz energy of the sample, which is a sum of the entropic elasticity of chain strands between beads, slip springs, and nonbonded interactions. The entanglement effect is introduced by the slip springs, which are springs connecting either nonsuccessive beads on the same chain or beads on different polymer chains. The terminal positions of slip springs are altered during the simulation through a kinetic Monte Carlo hopping scheme, with rate-controlled creation/destruction processes for the slip springs at chain ends. The rate constants are consistent with the free energy function employed and satisfy microscopic reversibility at equilibrium. The free energy of nonbonded interactions is derived from an appropriate equation of state, and it is computed as a functional of the local density by passing an orthogonal grid through the simulation box; accounting for it is necessary for reproducing the correct compressibility of the polymeric material. Parameters invoked by the mesoscopic model are derived from experimental volumetric and viscosity data or from atomistic molecular dynamics simulations, establishing a "bottom-up" predictive framework for conducting slip spring simulations of polymeric systems of specific chemistry. The mesoscopic simulation methodology is implemented for the case of cis-1,4-polyisoprene, whose structure, dynamics, thermodynamics, and linear rheology in the melt state are quantitatively predicted and validated without a posteriori fitting the results to experimental measurements.Comment: 80 pages, 17 figure

Self-Consistent-Field Study of Adsorption and Desorption Kinetics of Polyethylene Melts on Graphite and Comparison with Atomistic Simulations

A method is formulated, based on combining self-consistent field theory with dynamically corrected transition state theory, for estimating the rates of adsorption and desorption of end-constrained chains (e.g. by crosslinks or entanglements) from a polymer melt onto a solid substrate. This approach is tested on a polyethylene/graphite system, where the whole methodology is parametrized by atomistically detailed molecular simulations. For short-chain melts, which can still be addressed by molecular dynamics simulations with reasonable computational resources, the self-consistent field approach gives predictions of the adsorption and desorption rate constants which are gratifyingly close to molecular dynamics estimates.Comment: 18 pages, 10 figure

Evaluation of the therapeutic potential of ant-TLR4-antibody MTS510 in experimental stroke and significa of different routes of application

Toll-like receptors (TLRs) are central sensors for the inflammatory response in ischemia-reperfusion injury. We therefore investigated whether TLR4 inhibition could be used to treat stroke in a standard model of focal cerebral ischemia. Anti-TLR4/MD2-antibody (mAb clone MTS510) blocked TLR4-induced cell activation in vitro, as reported previously. Here, different routes of MTS510 application in vivo were used to study the effects on stroke outcome up to 2d after occlusion of the middle cerebral artery (MCAO) for 45 min in adult male C57Bl/6 wild-type mice. Improved neurological performance, reduced infarct volumes, and reduced brain swelling showed that intravascular application of MTS510 had a protective effect in the model of 45 min MCAO. Evaluation of potential long-term adverse effects of anti-TLR4-mAb-treament revealed no significant deleterious effect on infarct volumes nor neurological deficit after 14d of reperfusion in a mild model of stroke (15 min MCAO). Interestingly, inhibition of TLR4 resulted in an altered adaptive immune response at 48 hours after reperfusion. We conclude that blocking TLR4 by the use of specific mAb is a promising strategy for stroke therapy. However, long-term studies with increased functional sensitivity, larger sampling sizes and use of other species are required before a clinical use could be envisaged

Random Exchange Disorder in the Spin-1/2 XXZ Chain

The one-dimensional XXZ model is studied in the presence of disorder in the Heisenberg Exchange Integral. Recent predictions obtained from renormalization group calculations are investigated numerically using a Lanczos algorithm on chains of up to 18 sites. It is found that in the presence of strong X-Y-symmetric random exchange couplings, a ``random singlet'' phase with quasi-long-range order in the spin-spin correlations persists. As the planar anisotropy is varied, the full zero-temperature phase diagram is obtained and compared with predictions of Doty and Fisher [Phys. Rev. B {\bf 45 }, 2167 (1992)].Comment: 9 pages + 8 plots appended, RevTex, FSU-SCRI-93-98 and ORNL/CCIP/93/1

Taphonomical observations on the pygmy hippopotamus site in Aghia Napa, Cyprus.

Στην εργασία αυτή παρουσιάζονται τα αποτελέσματα ταφονομικής ανάλυσης της Άνω πλειστοκαινικής θέσης της Αγίας Νάπας στην Κύπρο. Η πανίδα της απολιθωματοφόρου θέσης κυριαρχείται από σκελετικό υλικό νάνων ιπποπόταμων του είδους Phanourios minor, και εντοπίζεται κάτω από ένα φυσικό στέγαστρο εντός των ασβεστολιθικών σχηματισμών της περιοχής. Η εμφάνιση εκτείνεται σε μια περιοχή περίπου 72 τ.μ. από την οποία έχει συλλεχθεί ιδιαίτερα μεγάλος αριθμός ευρημάτων που υποδεικνύει την ύπαρξη περισσότερων από 160 ιπποπόταμων στη θέση. Στόχο της μελέτης αποτελεί και η απόδοση της αυξημένης συσσώρευσης του οστεολογικού υλικού σε συγκεκριμένους μηχανισμούς, εστιάζοντας στους παλαιοπεριβαλλοντικούς παράγοντες που πιθανά έχουν επηρεάσει και την επιβίωση του. Η ανάλυση στηρίζεται και σε παραμέτρους που μας πληροφορούν σχετικά με την αντιπροσώπευση και άρα την επιβίωση των διαφόρων σκελετικών στοιχείων. Η μελέτη του υλικού ανέδειξε την ύπαρξη λείανσης, κατακερματισμού και σημαντικής θραύσης, φαινόμενα που σχετίζονται με τον τύπο, το μέγεθος και το σχήμα των σκελετικών στοιχείων. Η συσσώρευση του υπό μελέτη υλικού ερμηνεύεται ως αποτέλεσμα φυσικής μεταφοράς τους στη θέση από την γύρω περιοχή, ενώ ο ρόλος του ανθρώπου σε αυτήν είναι ακόμη υπό διερεύνηση. In this paper data concerning the taphonomy of the Upper Pleistocene site Aghia Napa in Cyprus is presented. The site is dominated by skeletal material belonging to the pygmy Hippopotamus species Phanourios minor, and consists a littoral rockshelter. The fossiliferous assemblage is spread in a total area of about 72 m2 and a significantly large number of specimens were collected, indicating the presence of more than 160 individuals at the site. In this paper, we attempt to identify the causes or mechanisms that led to the accumulation of the endemic hippopotamus remains, focusing also on the palaeo-environmental parameters that might had affected the survivorship of the fossils. The taphonomical analysis is also based on parameters, which provide information concerning skeletal element representation and thus survivorship. The study of the skeletal material shows signs of abrasion, cracking and significant fragmentation which are related to the type, size and shape of the skeletal elements. The bone assemblage is interpreted as a result of transportation of the skeletal material from longer or shorter distances in the surrounding area while the impact of man concerning their accumulation is still under discussion

Nature reappraisers, benefits for the environment: A model linking cognitive reappraisal, the “being away” dimension of restorativeness and eco-friendly behavior

In the last decades, an increasingly prominent role has been given to the motivational factors that can promote pro-environmental behavior. In this contribution, we focus on the role of the individual’s ability to shape the emotions originating from nature in engaging in pro-environmental behavior. In particular, we expect that an emotion regulation strategy as cognitive reappraisal should positively predict pro-environmental behavior, through enhanced perceived restorativeness attributed to the natural environment in terms of the experience of “being away.” One-hundred and fifteen visitors to an urban park (Parco Nord Milano) filled out a questionnaire including measures of cognitive reappraisal, the experience of “being away,” and pro-environmental behaviour while in the park. Results confirmed that cognitive reappraisal was positively and significantly related to pro-environmental behavior. Importantly, the indirect effect of cognitive reappraisal on pro-environmental behavior through the experience of “being away” was significant. Findings suggest the importance of implementing interventions aimed at promoting the habitual use of cognitive reappraisal to enhance the experience of “being away” and, thus, sustain pro-environmental behavior

Numerical renormalization-group study of spin correlations in one-dimensional random spin chains

We calculate the ground-state two-spin correlation functions of spin-1/2 quantum Heisenberg chains with random exchange couplings using the real-space renormalization group scheme. We extend the conventional scheme to take account of the contribution of local higher multiplet excitations in each decimation step. This extended scheme can provide highly accurate numerical data for large systems. The random average of staggered spin correlations of the chains with random antiferromagnetic (AF) couplings shows algebraic decay like $1/r^2$, which verifies the Fisher's analytic results. For chains with random ferromagnetic (FM) and AF couplings, the random average of generalized staggered correlations is found to decay more slowly than a power-law, in the form close to $1/\ln(r)$. The difference between the distribution functions of the spin correlations of the random AF chains and of the random FM-AF chains is also discussed.Comment: 14 pages including 8 figures, REVTeX, submitted to Physical Review