The entrainment rate for a row of turbulent jets

Entrainment rates for a row of isothermal circular air jets issuing into a quiescent environment are found by integrating velocity distributions measured by a linearized hot-wire anemometer. Jet spacing to jet diameter ratios of 2.5, 5, 10, and 20 are studied at jet Reynold's numbers ranging from 5110 to 12070. Velocity distributions are determined at regular downstream intervals at axial distances equal to 16.4 to 164 jet diameters from the jet source. The entrainment rates for the four spacing configurations vary monotonically with increasing spacing/diameter between the limiting case of the slot jet entrainment rate (where the jet spacing to diameter ratio is zero) and the circular jet entrainment rate (in which the spacing to diameter ratio is infinity)

Similarity solution of a jet flowing over a curved surface

Similarity solution of laminar two-dimensional incompressible jet flowing over curved surfac

Fibroblast growth factor 2 modulates transforming growth factor ß signaling in mouse embryonic fibroblasts and human ESCs (hESCs) to support hESC self-renewal

Fibroblast growth factor 2 (FGF2) is known to promote self-renewal of human embryonic stem cells (hESCs). In addition, it has been shown that transforming growth factor ß (TGFß) signaling is crucial in that the TGFß/Activin/Nodal branch of the pathway needs to be activated and the bone morphogenic protein (BMP)/GDF branch repressed to prevent differentiation. This holds particularly true for Serum Replacement-based medium containing BMP-like activity. We have reinvestigated a widely used protocol for conditioning hESC medium with mouse embryonic fibroblasts (MEFs). We show that FGF2 acts on MEFs to release supportive factors and reduce differentiation-inducing activity. FGF2 stimulation experiments with supportive and nonsupportive MEFs followed by genome-wide expression profiling revealed that FGF2 regulates the expression of key members of the TGFß pathway, with Inhba, Tgfb1, Grem1, and Bmp4 being the most likely candidates orchestrating the above activities. In addition, restimulation experiments in hESCs combined with global expression analysis revealed downstream targets of FGF2 signaling in these cells. Among these were the same factors previously identified in MEFs, thus suggesting that FGF2, at least in part, promotes self-renewal of hESCs by modulating the expression of TGFß ligands, which, in turn, act on hESCs in a concerted and autocrine manner

New half-range differential approximation for spherically-symmetric radiative transfer

Half range differential approximation for spherically symmetric radiative transfe

Hum Mutat

Reverse genetic approaches to generate mutants of model species are useful tools to assess functions of unknown genes. Recent work has demonstrated the feasibility of such strategies in several organisms, exploiting the power of chemical mutagenesis to disrupt genes randomly throughout the genome. To increase the throughput of gene-driven mutant identification, efficient mutation screening protocols are needed. Given the availability of sequence information for large numbers of unknown genes in many species, mutation detection protocols are preferably based on PCR. Using a set of defined mutations in the Hprt1 gene of mouse embryonic stem (ES) cells, we have systematically compared several PCR-based point mutation and deletion detection methods available for their ability to identify lesions in pooled samples, which is a major criterion for an efficient large-scale mutation screening assay. Results indicate that point mutations are most effectively identified by heteroduplex cleavage using CEL I endonuclease. Small deletions can most effectively be detected employing the recently described poison primer PCR technique. Further, we employed the CEL I assay followed by conventional agarose gel electrophoresis analysis for screening a library of chemically mutagenized ES cell clones. This resulted in the isolation of several clones harboring mutations in the mouse Sult1a1 locus, demonstrating the high-throughput compatibility of this approach using simple and inexpensive laboratory equipment. Hum Mutat 25:483-490, 2005. © 2005 Wiley-Liss, Inc

Analysis of Oct4-dependent transcriptional networks regulating self-renewal and pluripotency in human embryonic stem cells

The POU domain transcription factor OCT4 is a key regulator of pluripotency in the early mammalian embryo and is highly expressed in the inner cell mass of the blastocyst. Consistent with its essential role in maintaining pluripotency, Oct4 expression is rapidly downregulated during formation of the trophoblast lineage. To enhance our understanding of the molecular basis of this differentiation event in humans, we used a functional genomics approach involving RNA interference-mediated suppression of OCT4 function in a human ESC line and analysis of the resulting transcriptional profiles to identify OCT4-dependent genes in human cells. We detected altered expression of >1,000 genes, including targets regulated directly by OCT4 either positively (NANOG, SOX2, REX1, LEFTB, LEFTA/EBAF DPPA4, THY1, and TDGF1) or negatively (CDX2, EOMES, BMP4, TBX18, Brachyury [T], DKK1, HLX1, GATA6, ID2, and DLX5), as well as targets for the OCT4-associated stem cell regulators SOX2 and NANOG. Our data set includes regulators of ACTIVIN, BMP, fibroblast growth factor, and WNT signaling. These pathways are implicated in regulating human ESC differentiation and therefore further validate the results of our analysis. In addition, we identified a number of differentially expressed genes that are involved in epigenetics, chromatin remodeling, apoptosis, and metabolism that may point to underlying molecular mechanisms that regulate pluripotency and trophoblast differentiation in humans. Significant concordance between this data set and previous comparisons between inner cell mass and trophectoderm in human embryos indicates that the study of human ESC differentiation in vitro represents a useful model of early embryonic differentiation in humans

Systematic Analysis of Gene Expression Differences between Left and Right Atria in Different Mouse Strains and in Human Atrial Tissue

Background: Normal development of the atria requires left-right differentiation during embryonic development. Reduced expression of Pitx2c (paired-like homeodomain transcription factor 2, isoform c), a key regulator of left-right asymmetry, has recently been linked to atrial fibrillation. We therefore systematically studied the molecular composition of left and right atrial tissue in adult murine and human atria. Methods: We compared left and right atrial gene expression in healthy, adult mice of different strains and ages by employing whole genome array analyses on freshly frozen atrial tissue. Selected genes with enriched expression in either atrium were validated by RT-qPCR and Western blot in further animals and in shock-frozen left and right atrial appendages of patients undergoing open heart surgery. Results: We identified 77 genes with preferential expression in one atrium that were common in all strains and age groups analysed. Independent of strain and age, Pitx2c was the gene with the highest enrichment in left atrium, while Bmp10, a member of the TGFb family, showed highest enrichment in right atrium. These differences were validated by RT-qPCR in murine and human tissue. Western blot showed a 2-fold left-right concentration gradient in PITX2 protein in adult human atria. Several of the genes and gene groups enriched in left atria have a known biological role for maintenance of healthy physiology, specifically the prevention of atrial pathologies involved in atrial fibrillation, including membrane electrophysiology, metabolic cellular function, and regulation of inflammatory processes. Comparison of the array datasets with published array analyses in heterozygous Pitx2c+/2 atria suggested that approximately half of the genes with left-sided enrichment are regulated by Pitx2c. Conclusions: Our study reveals systematic differences between left and right atrial gene expression and supports the hypothesis that Pitx2c has a functional role in maintaining ‘‘leftness’’ in the atrium in adult murine and human hearts

ZeroMarking in French Impersonal Verbs: A Counter Trend to Clitic Morphologization?

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Optical Control of Field-Emission Sites by Femtosecond Laser Pulses

We have investigated field emission patterns from a clean tungsten tip apex induced by femtosecond laser pulses. Strongly asymmetric modulations of the field emission intensity distributions are observed depending on the polarization of the light and the laser incidence direction relative to the azimuthal orientation of tip apex. In effect, we have realized an ultrafast pulsed field-emission source with site selectivity on the 10 nm scale. Simulations of local fields on the tip apex and of electron emission patterns based on photo-excited nonequilibrium electron distributions explain our observations quantitatively.Comment: 4 pages, submitted to Physical Review Letter

Unit cell of graphene on Ru(0001): a 25 x 25 supercell with 1250 carbon atoms

The structure of a single layer of graphene on Ru(0001) has been studied using surface x-ray diffraction. A surprising superstructure has been determined, whereby 25 x 25 graphene unit cells lie on 23 x 23 unit cells of Ru. Each supercell contains 2 x 2 crystallographically inequivalent subcells caused by corrugation. Strong intensity oscillations in the superstructure rods demonstrate that the Ru substrate is also significantly corrugated down to several monolayers, and that the bonding between graphene and Ru is strong and cannot be caused by van der Waals bonds. Charge transfer from the Ru substrate to the graphene expands and weakens the C-C bonds, which helps accommodate the in-plane tensile stress. The elucidation of this superstructure provides important information in the potential application of graphene as a template for nanocluster arrays.Comment: 9 pages, 3 figures, paper submitted to peer reviewed journa