The morphology of ordered block copolymer patterns as probed by high resolution imaging

The microphase separation of block copolymer (BCP) thin films can afford a simple and cost-effective means to studying nanopattern surfaces, and especially the fabrication of nanocircuitry. However, because of complex interface effects and other complications, their 3D morphology, which is often critical for application, can be more complex than first thought. Here, we describe how emerging microscopic methods may be used to study complex BCP patterns and reveal their rich detail. These methods include helium ion microscopy (HIM) and high resolution x-section transmission electron microscopy (XTEM), and complement conventional secondary electron and atomic force microscopies (SEM and TEM). These techniques reveal that these structures are quite different to what might be expected. We illustrate the advances in the understanding of BCP thin film morphology in several systems, which result from this characterization. The systems described include symmetric, lamellar forming polystyrene-b-polymethylmethacrylate (PS-b-PMMA), cylinder forming polystyrene-b-polydimethylsiloxane (PS-b-PDMS), as well as lamellar and cylinder forming patterns of polystyrene-b-polyethylene oxide (PS-b-PEO) and polystyrene-b-poly-4-vinylpyridine (PS-b-P4VP). Each of these systems exhibits more complex arrangements than might be first thought. Finding and developing techniques whereby complex morphologies, particularly at very small dimensions, can be determined is critical to the practical use of these materials in many applications. The importance of quantifying these complex morphologies has implications for their use in integrated circuit manufacture, where they are being explored as alternative pattern forming methods to conventional UV lithography.

Three-dimensional outcomes of twin-block appliance treatment and the influence of the postured wax bite

Aims 1 To identify the 3D soft tissue volumetric and linear landmark changes following treatment with the Twin-Block Appliance TBA. 2 To estimate the TBA treatment outcome on the soft tissue facial profile volumetric and linear landmark changes from the Postured Wax Bite (PWB). 3 To identify if there is any association between certain soft tissue landmark variables and successful treatment outcome of the TBA as measured by the reduction in overjet. 4 To assess the effects of TBA treatment on facial expressions. Materials and Methods Forty-seven Caucasian subjects with Class II division 1 were recruited. 3D images captured of each subject, pre-treatment (T1), with the PWB (T2) and at the end of treatment (T3). Soft tissue volumetric and linear changes as well as the correlation between facial parameters and successful treatment were calculated. Results The mean soft tissue volumetric change from T1 to T3 was 22.24 ± 16.73 cm³. Soft tissue profile linear changes from T1-T3 for lower facial landmarks were 4-5 mm. From T1-T3, the mean soft tissue volumetric change of the total sample was 60% of the change produced by the PWB (T1 to T2). Correlations were weak for all 3D facial parameters and successful overjet reduction. Facial expression changes were only significant for the lower landmarks. Conclusions 1 TBA treatment, in growing subjects, increased the lower facial soft tissue volume and caused forward movement of the lower soft tissue facial profile landmarks.2 The PWB can be used to estimate the treatment outcome of the TBA on soft tissue profile changes.3 No association was found between soft tissue landmark variables and successful overjet reduction.4 TBA treatment had no effect on the upper facial landmarks for each facial expression but it changed the lower facial expressions significantly except for maximal smile in males.

Reversibly Photo-Crosslinkable Polycarbonate-Based Polymersomes for Drug Encapsulation and Delivery

This thesis describes the preparation of polymersomes from poly(ethylene glycol)-block-polycarbonate (PEG-PC) copolymers functionalized with pendant coumarin groups. Coumarin groups undergo photo-reversible dimerization when irradiated with specific ultraviolet wavelengths, so they can be used to prepare polymers with photo-responsive properties. In this case, the pendant coumarin groups enable stabilization of the polymersome membrane through photo-crosslinking of the hydrophobic block. Initially, several novel cinnamoyl and coumarin functionalized cyclic carbonate monomers were synthesized using ester, ether, or amide linkages. While the homopolymerization of these functionalized monomers proved challenging due to their high melting points, both cinnamoyl and coumarin functionalized monomers were successfully copolymerized with trimethylene carbonate (TMC) at 100 ℃ using a catalyst-free melt polymerization process where the TMC doubled as a solvent for the higher melting point monomer. Using this system, polycarbonate copolymers with up to 33% incorporation of the functionalized monomers were prepared. In addition, an investigation of some anomalous polymerization results identified previously unreported triethylamine-based catalysts for the melt polymerization of carbonate monomers. These studies also demonstrated that the catalyst-free polymerization of TMC occurs faster and at lower temperatures than previously reported. Subsequently, the photo-crosslinking of cinnamoyl and coumarin functionalized polycarbonates was compared and coumarin was identified as the more effective crosslinking agent when using 300-400 nm UV. An investigation of the photo-reversibility of the coumarin dimerization revealed no discernible change in the properties of crosslinked networks, but rapid photo-reversion in dilute solutions. The photo-crosslinking and photo-reversion kinetics of the coumarin functionalized polycarbonates were determined to be second-order in both cases. Finally, the self-assembly of PEG-PC diblock copolymers functionalized with coumarin was examined and both reverse solvent evaporation and solvent displacement were found to induce self-assembly, with hydrophilic mass fractions (f-factors) of 12-28% resulting in the formation of solid microparticles and nanoparticles and f-factors of 33-43% resulting in the formation of polymersomes. The stabilization of these polymersome membranes through photo-initiator-free photo-crosslinking was demonstrated with the crosslinking allowing polymersomes to withstand centrifugation at 12,000 x g. In addition, the encapsulation of calcein, as a model small molecule drug, in the stabilized polymersomes was successfully demonstrated using confocal microscopy.

NleH effectors interact with Bax inhibitor-1 to block apoptosis during enteropathogenic Escherichia coli infection

The human pathogens enteropathogenic (EPEC) and enterohemorrhagic Escherichia coli and the related mouse pathogen Citrobacter rodentium subvert a variety of host cell signaling pathways via their plethora of type III secreted effectors, including triggering of an early apoptotic response. EPEC-infected cells do not develop late apoptotic symptoms, however. In this study we demonstrate that the NleH family effectors, homologs of the Shigella effector kinase OspG, blocks apoptosis. During EPEC infection, NleH effectors inhibit elevation of cytosolic Ca(2+) concentrations, nuclear condensation, caspase-3 activation, and membrane blebbing and promote cell survival. NleH1 alone is sufficient to prevent procaspase-3 cleavage induced by the proapoptotic compounds staurosporine, brefeldin A, and tunicamycin. Using C. rodentium, we found that NleH inhibits procaspase-3 cleavage at the bacterial attachment sites in vivo. A yeast two-hybrid screen identified the endoplasmic reticulum six-transmembrane protein Bax inhibitor-1 (BI-1) as an NleH-interacting partner. We mapped the NleH-binding site to the N-terminal 40 amino acids of BI-1. Knockdown of BI-1 resulted in the loss of NleH's antiapoptotic activity. These results indicate that NleH effectors are inhibitors of apoptosis that may act through BI-1 to carry out their cytoprotective function.

Towards structured, block-based PDF

The Portable Document Format (PDF), defined by Adobe Systems Inc. as the basis of its Acrobat product range, is discussed in some detail. Particular emphasis is given to its flexible object-oriented structure, which has yet to be fully exploited. It is currently used to represent not logical structure but simply a series of pages and associated resources. A definition of an Encapsulated PDF (EPDF) is presented, in which EPDF blocks carry with them their own resource requirements, together with geometrical and logical information. A block formatter called Juggler is described which can lay out EPDF blocks from various sources onto new pages. Future revisions of PDF supporting uniquely-named EPDF blocks tagged with semantic information would assist in composite-pagemakeup and could even lead to fully revisable PDF.

The cytokinesis-block micronucleus (CBMN) assay in human populations exposed to styrene: a systematic review and meta-analysis

Styrene is a building-block of several compounds used in a wide array of materials and products. The most important human exposure to this substance occurs in industrial settings, especially among reinforced-plastics industry workers. The effect of occupational exposure to styrene on cytogenetics biomarkers has been previously reviewed with positive association observed for chromosomal aberrations, and inconclusive data for the micronucleus assay. Some limitations were noted in those studies, including inadequate exposure assessment and poor epidemiological design. Furthermore, in earlier studies micronuclei frequency was measured with protocols not as reliable as cytokinesis-block micronucleus (CBMN) assay. Aim of the present systematic review and meta-analysis is to investigate genomic instability and DNA damage as measured by the CBMN assay in lymphocytes of subjects exposed to styrene. A total of 11 studies published between 2004 and 2012 were included in the meta-analysis encompassing 479 styrene-exposed workers and 510 controls. The quality of each study was estimated by a quality scoring system which ranked studies according to the consideration of major confounders, exposure characterization, and technical parameters. An overall increase of micronuclei frequencies was found in styrene-exposure workers when compared to referents (meta-MR 1.34; 95% CI 1.18–1.52), with significant increases achieved in six individual studies. The consistency of results in individual studies, the independence of this result from major confounding factors and from the quality of the study strengthens the reliability of risk estimates and supports the use of the CBMN assay in monitoring genetic risk in styrene workers.

Tau Functions and the Limit of Block Toeplitz Determinants

International audience

Programa de gestión de seguridad y salud ocupacional para la empresa Celo-Block, S.A. de C.V., ubicada en el municipio de Guazapa departamento de San Salvador.

La empresa Celo- Block S.A. de C.V. a lo largo de su historia como centro de trabajo, cuenta con numerosos casos de accidentes de trabajo, por la falta de un programa dirigido a la prevención de riesgos ocupacionales. Es por ello, que se ha considerado diseñar un Programa de Gestión de Seguridad y Salud Ocupacional, teniendo como base principal los lineamientos contenidos en los artículos 8 y 13 de la Ley General de Prevención de Riesgos en los Lugares de Trabajo. Todo ello con la intención de proteger a los trabajadores enfocando la investigación en el análisis de las condiciones físicas actuales, en materia de Seguridad y Salud Ocupacional. La Seguridad y Salud Ocupacional aplicada a los lugares de trabajo tiene como objetivo salvaguardar la vida de los trabajadores, a la vez proteger la salud y la integridad física de los mismos, por medio de la puesta en práctica de medidas encaminadas a proporcionar condiciones óptimas en el trabajo. Por lo que la Seguridad y Salud Ocupacional debería ser uno de los puntos clave de cualquier empresa. Dicha propuesta busca como objetivo principal, mejorar el ambiente de trabajo, y contribuir a la reducción de accidentes que pueden lesionar a los trabajadores. Por medio de la elaboración de una política que sirva de guía para la prevención de accidentes ocupacionales, según lo establece la Ley General de Prevención de Riesgos en los Lugares de Trabajo. La metodología utilizada en la investigación, consistió en la elaboración de un diagnóstico, que permitió conocer la situación actual en materia de Seguridad y Salud Ocupacional en la empresa, el método de investigación que se implementó fue el análisis, el tipo de investigación que se realizó fue el descriptivo, el diseño de la investigación fue la no experimental, y las fuentes de investigación fueron las primarias y secundarias y se logró a través de las técnicas de investigación como entrevista, encuestas, y observación directa, realizar un mapa de riesgos y localizar los puntos más críticos a los que se encuentran expuestos los trabajadores dentro de su jornada laboral. La sistemática anterior, permitió obtener los siguientes resultados: que la empresa no ha establecido formalmente un Comité de Seguridad y Salud Ocupacional y que por lo tanto no cuenta con la estructuración formal de un Programa de Gestión de Seguridad y Salud Ocupacional que contenga planes políticas y procedimientos preventivos que ayuden al bienestar de los trabajadores. El área donde ocurren más accidentes es en Descargado y Colocado debido a que es donde se encuentran la mayoría de factores de riesgo. De acuerdo a la encuesta y la inspección realizada, la empresa carece de señalización en las diferentes áreas, y por último la empresa no posee registro detallado de accidentes laborales, entre otros. Para poder superar las deficiencias encontradas, se realizan las siguientes recomendaciones contenidas dentro de la propuesta de esta investigación: la creación y funcionamiento de un Comité de Seguridad y Salud Ocupacional, la creación de políticas por parte de las autoridades de la empresa, el equipamiento de seguridad así como la compra de los insumos básicos de primeros auxilios para la atención de accidentes, la implementación de capacitaciones tanto para el Comité de Seguridad y Salud Ocupacional así como también para el resto de los trabajadores, y simulacros los cuales se recomienda que realicen por lo menos dos veces al año. Todo lo anterior, permitirá obtener grandes beneficios a la empresa como la disminución de riesgos de accidentes y enfermedades profesionales, fomentar una cultura de prevención, cumplir con la legislación actual en la materia y evitarse infracciones ocasionadas por incumplimiento de la misma.

3D Block Modeling and Reserve Estimation of a Garnet Deposit

The purpose of this project is to develop a three-dimensional block model for a garnet deposit in the Alder Gulch, Madison County, Montana. Garnets occur in pre-Cambrian metamorphic Red Wash gneiss and similar rocks in the vicinity. This project seeks to model the percentage of garnet in a deposit called the Section 25 deposit using the Surpac software. Data available for this work are drillhole, trench and grab sample data obtained from previous exploration of the deposit. The creation of the block model involves validating the data, creating composites of assayed garnet percentages and conducting basic statistics on composites using Surpac statistical tools. Variogram analysis will be conducted on composites to quantify the continuity of the garnet mineralization. A three-dimensional block model will be created and filled with estimates of garnet percentage using different methods of reserve estimation and the results compared.

Synthesis and Characterization of Photochromic Copolymers Containing 3-Indolylfulgides/Indolylfulgimides

Fulgides and fulgimides are important organic photochromic compounds and can switch between the open forms and the closed forms with light. The 3-indolylfulgides and 3-indolylfulgimides exhibit promising photochromic properties and have great potential in optical memory devices, optical switches and biosensors. Copolymers containing 3-indolylfulgides/indolylfulgimides synthesized via free radical polymerizations increase conformation changes and allow the photochromic compounds to be uniformly distributed in the polymer matrix. A trifluoromethyl 3-indolylfulgide and two trifluoromethyl 3-indolylfulgimides with one or two polymerizable N-stryryl group(s) were prepared. Copolymerization with methyl methacrylate provided two linear copolymers or a cross-linked copolymer. The properties of the monomeric fulgide/fulgimides and copolymers in toluene or as thin films were characterized. In general, the photochromic monomers and copolymers revealed similar photochromic properties and exhibited good thermal and photochemical stability. All compounds absorb visible light in both open forms and closed forms. The closed form copolymers were more stable than the open form copolymers and showed little or no degradation after 400 h. The photochemical degradation rate was less than 0.03% per cycle. In films, conformational restrictions were observed for the open forms suggesting that the preparation of films from the closed forms is advantageous. Two novel methyl 3-indolylfulgimides with one or two polymerizable N-stryryl group(s) were prepared. Copolymerization of acrylamide with the methyl indolylfulgimides or the trifluoromethyl indolylfulgimides yielded two aqueous soluble linear copolymers and two photochromic hydrogels. The closed form copolymers containing trifluoromethyl indolylfulgimides were hydrolyzed in aqueous solution by replacing the trifluoromethyl group with a carboxylic acid group. The resulting carboxylic copolymers were also photochromic. The copolymers containing methyl fulgimides were stable in aqueous solutions and did not hydrolyze. Both methyl and carboxylic copolymers exhibited good stability in aqueous solutions. In general, the open form copolymers were more stable than the closed form copolymers, and the copolymers revealed better stability in acidic solution than neutral solution. The linear copolymers displayed better photochemical stability in neutral solution and degraded up to 22% after 105 cycles. In contrast, the hydrogels showed enhanced fatigue resistance in acidic condition and underwent up to 60 cycles before degrading 24%.

The conjugate gradient partitioned block frequency-domain for multichannel adaptive filtering

The conjugate gradient is the most popular optimization method for solving large systems of linear equations. In a system identification problem, for example, where very large impulse response is involved, it is necessary to apply a particular strategy which diminishes the delay, while improving the convergence time. In this paper we propose a new scheme which combines frequency-domain adaptive filtering with a conjugate gradient technique in order to solve a high order multichannel adaptive filter, while being delayless and guaranteeing a very short convergence time.

Reply to the Editor—Prevalence of interatrial block during lifetime

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