The production of custom variable neutral density filters using film and a computer controlled imaging device

A system for generating custom variable neutral density filters has been built, characterized, and demonstrated. The desired densities for a neutral density filter are entered into the controlling computer as a function of distance. The program which generates the filter density profile is designed to vary the exposure time by controlling the velocity of the film as it moves under a slit aperture. A custom illumination system was designed and built to provide constant lamp output. The technique can provide the film with the exposure necessary to produce a given density profile

Heritable Epigenetic Variation among Maize Inbreds

Epigenetic variation describes heritable differences that are not attributable to changes in DNA sequence. There is the potential for pure epigenetic variation that occurs in the absence of any genetic change or for more complex situations that involve both genetic and epigenetic differences. Methylation of cytosine residues provides one mechanism for the inheritance of epigenetic information. A genome-wide profiling of DNA methylation in two different genotypes of Zea mays (ssp. mays), an organism with a complex genome of interspersed genes and repetitive elements, allowed the identification and characterization of examples of natural epigenetic variation. The distribution of DNA methylation was profiled using immunoprecipitation of methylated DNA followed by hybridization to a high-density tiling microarray. The comparison of the DNA methylation levels in the two genotypes, B73 and Mo17, allowed for the identification of approximately 700 differentially methylated regions (DMRs). Several of these DMRs occur in genomic regions that are apparently identical by descent in B73 and Mo17 suggesting that they may be examples of pure epigenetic variation. The methylation levels of the DMRs were further studied in a panel of near-isogenic lines to evaluate the stable inheritance of the methylation levels and to assess the contribution of cis- and trans- acting information to natural epigenetic variation. The majority of DMRs that occur in genomic regions without genetic variation are controlled by cis-acting differences and exhibit relatively stable inheritance. This study provides evidence for naturally occurring epigenetic variation in maize, including examples of pure epigenetic variation that is not conditioned by genetic differences. The epigenetic differences are variable within maize populations and exhibit relatively stable trans-generational inheritance. The detected examples of epigenetic variation, including some without tightly linked genetic variation, may contribute to complex trait variation

Computations of Flow Field and Heat Transfer in a Stator Vane Passage Using the V2F Turbulence Model

In this study three-dimensional simulations of a stator vane passage flow have been performed using the v 2̄ -f turbulence model. Both an in-house code (CALC-BFC) and the commercial software FLUENT are used. The main objective is to investigate the v 2̄ -f model\u27s ability to predict the secondary fluid motion in the passage and its influence on the heat transfer to the end walls between two stator vanes. Results of two versions of the v 2̄ -f model are presented and compared to detailed mean flow field, turbulence, and heat transfer measurements. The performance of the v 2̄ -f model is also compared with other eddy-viscosity-based turbulence models, including a version of the v 2̄ -f model, available in FLUENT. The importance of preventing unphysical growth of turbulence kinetic energy in stator vane flows, here by use of the realizability constraint, is illustrated. It is also shown that the v 2̄ -f model predictions of the vane passage flow agree well with experiments and that, among the eddy-viscosity closures investigated, the v 2̄ -f model, in general, performs the best. Good agreement between the two different implementations of the v 2̄ -f model (CALC-BFC and FLUENT) was obtained. Copyright \ua9 2005 by ASME

Protein modification, bioconjugation, and disulfide bridging using Bromomaleimides

The maleimide motif is widely used for the selective chemical modification of cysteine residues in proteins. Despite widespread utilization, there are some potential limitations, including the irreversible nature of the reaction and, hence, the modification and the number of attachment positions. We conceived of a new class of maleimide which would address some of these limitations and provide new opportunities for protein modification. We report herein the use of mono- and dibromomaleimides for reversible cysteine modification and illustrate this on the SH2 domain of the Grb2 adaptor protein (L111C). After initial modification of a protein with a bromo- or dibromomaleimide, it is possible to add an equivalent of a second thiol to give further bioconjugation, demonstrating that bromomaleimides offer opportunities for up to three points of attachment. The resultant protein−maleimide products can be cleaved to regenerate the unmodified protein by addition of a phosphine or a large excess of a thiol. Furthermore, dibromomaleimide can insert into a disulfide bond, forming a maleimide bridge, and this is illustrated on the peptide hormone somatostatin. Fluorescein-labeled dibromomaleimide is synthesized and inserted into the disulfide to construct a fluorescent somatostatin analogue. These results highlight the significant potential for this new class of reagents in protein modification

In Cultured Oligodendrocytes the A/B-type hnRNP CBF-A Accompanies MBP mRNA Bound to mRNA Trafficking Sequences

Heterogeneous ribonucleoproteins (hnRNPs) have key roles in RNA biogenesis, including pre-mRNP assembly, transport and cytoplasmic localization. Here we show by biochemical fractionation of nuclear extracts and protein–protein interaction assays that the A/B-type hnRNP CBF-A is in a multiprotein complex with hnRNP A2 and A3 and hnRNP U. Using RNA affinity chromatography and gel retardation assays, CBF-A was found to bind directly to RNA trafficking sequences in the 3′-UTR of the myelin basic protein (MBP) mRNA. In primary oligodendrocytes, astrocytes, neurons, and mouse forebrain sections, CBF-A revealed a characteristic granular cytoplasmic distribution. In mouse forebrain CBF-A–positive granules were preferentially found in regions with loosely bundled myelin fibers. In cultured oligodendrocytes, CBF-A was found to be specifically associated with endogenous MBP mRNA and CBF-A gene silencing resulted in the retention of MBP granules in the cell body. Finally, immunoelectron microscopy in differentiating oligodendrocytes showed that CBF-A is located in cytoplasmic granules that are often associated with the cytoskeleton. The results suggest that CBF-A is a novel transacting factor required for cytoplasmic mRNA transport and localization