Bulk and Interfacial Shear Thinning of Immiscible Polymers

Nonequilibrium molecular dynamics simulations are used to study the shear thinning behavior of immiscible symmetric polymer blends. The phase separated polymers are subjected to a simple shear flow imposed by moving a wall parallel to the fluid-fluid interface. The viscosity begins to shear thin at much lower rates in the bulk than at the interface. The entire shear rate dependence of the interfacial viscosity is consistent with a shorter effective chain length $s^*$ that also describes the width of the interface. This $s^*$ is independent of chain length $N$ and is a function only of the degree of immiscibility of the two polymers. Changes in polymer conformation are studied as a function of position and shear rate.Shear thinning correlates more closely with a decrease in the component of the radius of gyration along the velocity gradient than with elongation along the flow. At the interface, this contraction of chains is independent of $N$ and consistent with the bulk behavior for chains of length $s^*$. The distribution of conformational changes along chains is also studied. Central regions begin to stretch at a shear rate that decreases with increasing $N$, while shear induced changes at the ends of chains are independent of $N$.Comment: 8 pages, 8 figure

Mapping the Road from Childhood Trauma to Adult Somatization: The Role of Attachment

Objective: This study tested whether insecure attachment mediates the link between childhood trauma and adult somatization. Methods: A community sample of 101 couples completed self-report measures including the Relationship Scales Questionnaire, the Childhood Trauma Questionnaire, the Somatic Symptom Inventory, the Beck Depression Inventory, and the Conflict Tactics Scale. Results: Childhood trauma was associated with higher levels of somatization and insecure attachment. Insecure attachment style was also associated with higher levels of somatization. Controlling for age, income, and recent intimate partner violence, analyses showed that fearful attachment fully mediated the link between childhood trauma and somatization for women. For men there was no such mediation, but both childhood trauma and insecure attachment styles made independent contributions to predicting levels of somatization. Conclusions: Findings are consistent with the hypothesis that, for women, childhood trauma influences adult levels of somatization by fostering insecure adult attachment. For men, findings suggest that trauma and attachment are both important independent predictors of adult somatization. Study results support the idea that childhood trauma shapes patients’ styles of relating to others in times of need and these styles in turn influence the somatization process and how patients respond to providers. Screening for attachment style may provide information that could allow health care providers to tailor treatment more effectively. Key words: Attachment style, somatization, childhood trauma, interpersonal models. Abbreviations: CTQ = Childhood Trauma Questionnaire; CTS2 = Conflict Tactics Scale version 2; SSI = Somatic Symptom Inventory; RSQ = Relationship Scales Questionnaire; BDI = Beck Depression Inventory

Mapping the Road from Childhood Trauma to Adult Somatization: The Role of Attachment

Objective: This study tested whether insecure attachment mediates the link between childhood trauma and adult somatization. Methods: A community sample of 101 couples completed self-report measures including the Relationship Scales Questionnaire, the Childhood Trauma Questionnaire, the Somatic Symptom Inventory, the Beck Depression Inventory, and the Conflict Tactics Scale. Results: Childhood trauma was associated with higher levels of somatization and insecure attachment. Insecure attachment style was also associated with higher levels of somatization. Controlling for age, income, and recent intimate partner violence, analyses showed that fearful attachment fully mediated the link between childhood trauma and somatization for women. For men there was no such mediation, but both childhood trauma and insecure attachment styles made independent contributions to predicting levels of somatization. Conclusions: Findings are consistent with the hypothesis that, for women, childhood trauma influences adult levels of somatization by fostering insecure adult attachment. For men, findings suggest that trauma and attachment are both important independent predictors of adult somatization. Study results support the idea that childhood trauma shapes patients’ styles of relating to others in times of need and these styles in turn influence the somatization process and how patients respond to providers. Screening for attachment style may provide information that could allow health care providers to tailor treatment more effectively. Key words: Attachment style, somatization, childhood trauma, interpersonal models. Abbreviations: CTQ = Childhood Trauma Questionnaire; CTS2 = Conflict Tactics Scale version 2; SSI = Somatic Symptom Inventory; RSQ = Relationship Scales Questionnaire; BDI = Beck Depression Inventory

Random solids and random solidification: What can be learned by exploring systems obeying permanent random constraints?

In many interesting physical settings, such as the vulcanization of rubber, the introduction of permanent random constraints between the constituents of a homogeneous fluid can cause a phase transition to a random solid state. In this random solid state, particles are permanently but randomly localized in space, and a rigidity to shear deformations emerges. Owing to the permanence of the random constraints, this phase transition is an equilibrium transition, which confers on it a simplicity (at least relative to the conventional glass transition) in the sense that it is amenable to established techniques of equilibrium statistical mechanics. In this Paper I shall review recent developments in the theory of random solidification for systems obeying permanent random constraints, with the aim of bringing to the fore the similarities and differences between such systems and those exhibiting the conventional glass transition. I shall also report new results, obtained in collaboration with Weiqun Peng, on equilibrium correlations and susceptibilities that signal the approach of the random solidification transition, discussing the physical interpretation and values of these quantities both at the Gaussian level of approximation and, via a renormalization-group approach, beyond.Comment: Paper presented at the "Unifying Concepts in Glass Physics" workshop, International Centre for Theoretical Physics, Trieste, Italy (September 15-18, 1999

0.1 µm InP HEMT devices and MMICs for cryogenic low noise amplifiers from X-band to W-band

We present the TRW 0.1 µm InP HEMT MMIC production technology that has been developed and used for state-of-the-art cryogenic LNA applications. The 0.1 µm InP HEMT devices typically show cutoff frequency above 200 GHz and transconductance above 1000 mS/mm. Aspects of device design and fabrication are presented which impact important parameters including the InP HEMT device gain, gate leakage current, and parasitic capacitance. One example of state-of-the-art cryogenic MMIC performance is a W-band cryogenic MMIC LNA operated at 20 degrees Kelvin that shows above 23 dB gain and a noise temperature of 30 to 40 K (0.45 to 0.6 dB noise figure) over the band of 80-105 GHz

The scaling limit of the incipient infinite cluster in high-dimensional percolation. II. Integrated super-Brownian excursion

For independent nearest-neighbour bond percolation on Z^d with d >> 6, we prove that the incipient infinite cluster's two-point function and three-point function converge to those of integrated super-Brownian excursion (ISE) in the scaling limit. The proof is based on an extension of the new expansion for percolation derived in a previous paper, and involves treating the magnetic field as a complex variable. A special case of our result for the two-point function implies that the probability that the cluster of the origin consists of n sites, at the critical point, is given by a multiple of n^{-3/2}, plus an error term of order n^{-3/2-\epsilon} with \epsilon >0. This is a strong statement that the critical exponent delta is given by delta =2.Comment: 56 pages, 3 Postscript figures, in AMS-LaTeX, with graphicx, epic, and xr package

Disasters and Communities: Understanding Social ...

Abstract Social resilience is the capacity of social groups and communities to recover from, or respond positively to, crises. In this paper, we review the multifaceted nature of social resilience, and how this capacity is thought to have various properties, notably resistance, recovery and creativity. We also discuss the idea that social groups within a community differ insofar as their levels of resilience and the threats to which they are resilient. While research in the social sciences suggests that social resilience is a 'naturally emergent' response to disaster, we argue that emergency management plans must recognise and build on this capacity, and that improved indicators of social resilience are a priority area for future research

A NON-CLEAVABLE UmuD VARIANT THAT ACTS AS A UmuD' MIMIC

UmuD{sub 2} cleaves and removes its N-terminal 24 amino acids to form UmuD'{sub 2}, which activates UmuC for its role in UV-induced mutagenesis in E. coli. Cells with a non-cleavable UmuD exhibit essentially no UV-induced mutagenesis and are hypersensitive to killing by UV light. UmuD has been shown to bind to the beta processivity clamp (''beta'') of the replicative DNA polymerase, pol III. A possible beta-binding motif has been predicted in the same region of UmuD shown to be important for its interaction with beta. We performed alanine-scanning mutagenesis of this motif (14-TFPLF-18) in UmuD and showed that it has a moderate influence on UV-induced mutagenesis but is required for the cold sensitive phenotype caused by elevated levels of wild-type UmuD and UmuC. Surprisingly, the wild-type and the beta-binding motif variant bind to beta with similar K{sub d} values as determined by changes in tryptophan fluorescence. However, this data also implies that the single tryptophan in beta is in strikingly different environments in the presence of the wild-type versus the variant UmuD proteins, suggesting a distinct change in some aspect of the interaction with little change in its strength. Despite the fact that this novel UmuD variant is noncleavable, we find that cells harboring it exhibit phenotypes more consistent with the cleaved form UmuD', such as resistance to killing by UV light and failure to exhibit the cold sensitive phenotype. Cross-linking and chemical modification experiments indicate that the N-terminal arms of the UmuD variant are less likely to be bound to the globular domain than those of the wild-type, which may be the mechanism by which this UmuD variant acts as a UmuD' mimic

Universality and its Origins at the Amorphous Solidification Transition

Systems undergoing an equilibrium phase transition from a liquid state to an amorphous solid state exhibit certain universal characteristics. Chief among these are the fraction of particles that are randomly localized and the scaling functions that describe the order parameter and (equivalently) the statistical distribution of localization lengths for these localized particles. The purpose of this Paper is to discuss the origins and consequences of this universality, and in doing so, three themes are explored. First, a replica-Landau-type approach is formulated for the universality class of systems that are composed of extended objects connected by permanent random constraints and undergo amorphous solidification at a critical density of constraints. This formulation generalizes the cases of randomly cross-linked and end-linked macromolecular systems, discussed previously. The universal replica free energy is constructed, in terms of the replica order parameter appropriate to amorphous solidification, the value of the order parameter is obtained in the liquid and amorphous solid states, and the chief universal characteristics are determined. Second, the theory is reformulated in terms of the distribution of local static density fluctuations rather than the replica order parameter. It is shown that a suitable free energy can be constructed, depending on the distribution of static density fluctuations, and that this formulation yields precisely the same conclusions as the replica approach. Third, the universal predictions of the theory are compared with the results of extensive numerical simulations of randomly cross-linked macromolecular systems, due to Barsky and Plischke, and excellent agreement is found.Comment: 10 pages, including 3 figures (REVTEX

Randomly Crosslinked Macromolecular Systems: Vulcanisation Transition to and Properties of the Amorphous Solid State

As Charles Goodyear discovered in 1839, when he first vulcanised rubber, a macromolecular liquid is transformed into a solid when a sufficient density of permanent crosslinks is introduced at random. At this continuous equi- librium phase transition, the liquid state, in which all macromolecules are delocalised, is transformed into a solid state, in which a nonzero fraction of macromolecules have spontaneously become localised. This solid state is a most unusual one: localisation occurs about mean positions that are distributed homogeneously and randomly, and to an extent that varies randomly from monomer to monomer. Thus, the solid state emerging at the vulcanisation transition is an equilibrium amorphous solid state: it is properly viewed as a solid state that bears the same relationship to the liquid and crystalline states as the spin glass state of certain magnetic systems bears to the paramagnetic and ferromagnetic states, in the sense that, like the spin glass state, it is diagnosed by a subtle order parameter. In this review we give a detailed exposition of a theoretical approach to the physical properties of systems of randomly, permanently crosslinked macromolecules. Our primary focus is on the equilibrium properties of such systems, especially in the regime of Goodyear's vulcanisation transition.Comment: Review Article, REVTEX, 58 pages, 3 PostScript figure