Bicontinuous microemulsion in binary blends of complementary diblock copolymers.

The phase behavior of binary blends of AB diblock copolymers of compositions f and 1 - f is examined using field-theoretic simulations. Highly asymmetric compositions (i.e., f ≈ 0) behave like homopolymer blends macrophase separating into coexisting A- and B-rich phases as the segregation is increased, whereas more symmetric diblocks (i.e., f ≈ 0.5) microphase separate into an ordered lamellar phase. In self-consistent field theory, these behaviors are separated by a Lifshitz critical point at f = 0.2113. However, its lower critical dimension is believed to be four, which implies that the Lifshitz point should be destroyed by fluctuations. Consistent with this, it is found to transform into a tricritical point. Furthermore, the highly swollen lamellar phase near the mean-field Lifshitz point disorders into a bicontinuous microemulsion (BµE), consisting of large interpenetrating A- and B-rich microdomains. BµE has been previously reported in ternary blends of AB diblock copolymer with its parent A- and B-type homopolymers, but in that system the homopolymers have a tendency to macrophase separate. Our alternative system for creating BµE is free of this macrophase separation.

Accounting for the ultraviolet divergence in field-theoretic simulations of block copolymer melts.

This study examines the ultraviolet (UV) divergence in field-theoretic simulations (FTSs) of block copolymer melts, which causes an unphysical dependence on the grid resolution, Δ, used to represent the fields. Our FTSs use the discrete Gaussian-chain model and a partial saddle-point approximation to enforce incompressibility. Previous work has demonstrated that the UV divergence can be accounted for by defining an effective interaction parameter, χ=z∞χb+c2χb 2+c3χb 3+⋯, in terms of the bare interaction parameter, χb, used in the FTSs, where the coefficients of the expansion are determined by a Morse calibration. However, the need to use different grid resolutions for different ordered phases generally restricts the calibration to the linear approximation, χ ≈ z∞χb, and prevents the calculation of order-order transitions. Here, we resolve these two issues by showing how the nonlinear calibration can be translated between different grids and how the UV divergence can be removed from free energy calculations. By doing so, we confirm previous observations from particle-based simulations. In particular, we show that the free energy closely matches self-consistent field theory (SCFT) predictions, even in the region where fluctuations disorder the periodic morphologies, and similarly, the periods of the ordered phases match SCFT predictions, provided the SCFT is evaluated with the nonlinear χ.

Calibration of a lattice model for high-molecular-weight block copolymer melts.

The Morse calibration is applied to a lattice model designed for efficient simulations of two-component polymer melts of high molecular weight. The model allows multiple occupancy per site, which results in high invariant polymerization indices, and interactions are limited to monomers within the same site, which enhances the computational speed. The calibration maps the interaction parameter of the lattice model, α, onto the Flory-Huggins χ parameter of the standard Gaussian-chain model, by matching the disordered-state structure function, S(k), of symmetric diblock copolymers to renormalized one-loop predictions. The quantitative accuracy of the calibration is tested by comparing the order-disorder transition of symmetric diblock copolymer melts to the universal prediction obtained from previous simulations. The model is then used to confirm the universality of fluctuation corrections to the critical point of symmetric binary homopolymer blends.

A non-neurologist's guide to understanding the EMG/NCV report.

Podiatrists often refer patients to electromyographers to determine the cause of pain, tingling, numbness, and other paresthesias of unknown cause. Hence, some knowledge of the study and an understanding that it is an extension of the patient's history and physical examination is imperative. To enhance the podiatrist's understanding of electromyography, a review of basic neurophysiology, the neurologic examination, and electromyography/nerve conduction velocities (EMG/NCV) are discussed. Definitions are provided for the terms introduced in the article.

Molecular cloning and characterization of a novel mouse macrophage gene that encodes a nuclear protein comprising polyglutamine repeats and interspersing histidines.

Simple tandem repeats of the trinucleotide sequence CAG encode homopolymeric stretches of glutamine. Although polyglutamine has been identified in diverse proteins, it is present predominantly in transcription factors. We observed that oncogene-immortalized mouse macrophages express several genes that contain a CAG repeat motif. Therefore, we attempted to clone a novel gene that contains a CAG repeat and is associated with cytokine activation of macrophages. Screening of a mouse macrophage cDNA library with a probe comprising 12 consecutive CAG triplets identified at least one unique clone. The cDNA encodes a protein (named GRP-1 or glutamine repeat protein-1) with 171 amino acids, a calculated molecular mass of 21.6 kDa, and a predicted pI of 10.67. Greater than two-thirds of GRP-1 are only two amino acids, namely glutamine (50%) and histidine (18%). There are four polyglutamine motifs interspersed with histidine-rich regions. There is also a putative nuclear localization signal flanked by sites for possible serine phosphorylation. GRP-1 mRNA was expressed constitutively in some macrophage cell lines and B and T cell lines. Interferon-gamma or lipopolysaccharide augmented GRP-1 mRNA expression in the mouse macrophage cell line ANA-1. Western blot analyses using an antipeptide serum revealed that GRP-1 was localized in the nucleus of ANA-1 macrophages and transfected 3T3 fibroblasts. Overexpression of GRP-1 decreased Sp1-driven chloramphenicol acetyltransferase gene expression in transient cotransfection experiments. Because polyglutamine motifs can cause protein oligomerization and can function as transcriptional activation domains, we suggest that GRP-1 may be a transcription factor associated with interferon-gamma- or lipopolysaccharide-induced activation of macrophages.

An example of medical audit under political pressure.

Management of medical services necessitates decisions regarding the possibly ineffective treatment programmes, hospitals and (even) individual practitioners. Although rigorous evaluations of effectiveness can only be achieved by randomized trials there has been, in recent years, much increase in audit (or peer review) activity. Ideally medical audit is undertaken as a collaborative exercise, and follows preplanned methods of data collection and evaluation of outcome. However, real management situations frequently do not conform to the ideal, as when the medico-political finger of accusation points at one particular hospital and asks for an immediate enquiry. This audit analyses the mortality and morbidity after coronary artery bypass graft surgery in the 'suspect' hospital and in control hospitals. The paper describes the difficulties of obtaining comparable records post hoc and the interpretations of small differences, mostly non-significant statistically yet possibly 'real', both in the characteristics of patients operated on and in the outcomes of operations.