Laminar Separation Bubble Dynamics on a Finite Wing

Laminar separation bubbles substantially influence the performance of finite wings at low chord Reynolds numbers. The objective of this study is to explore the influence of wingtip effects on three-dimensional laminar separation bubble topology and dynamics on a finite wing. An experimental investigation is conducted on a laminar separation bubble forming on the suction surface of a cantilevered rectangular NACA 0018 wing with a semi-aspect ratio of 2.5 at a chord Reynolds number of 125 000 and an angle of attack of 6 degrees. Surface pressure and particle image velocimetry measurements are employed to investigate the separation bubble flowfield. Using a two-dimensional airfoil of the same profile, the separation bubble on the wing is compared to a nominally two-dimensional separation bubble at similar effective angles of attack. On the portion of the wing where laminar boundary layer separation occurs, the separated shear layer rolls up into spanwise uniform vortices which develop similarly to the vortices observed on the two-dimensional airfoil, despite spanwise changes to the mean separation bubble structure along the wingspan. Whereas a decrease in the angle of attack of the two-dimensional airfoil causes a downstream shift in the locations of separation and reattachment and a reduction in the frequency of shear layer vortex shedding, spanwise variations of these parameters on the wing are much smaller than the variations expected due to the reduction in effective angle of attack near the wingtip. On the inboard portion of the wing, the location and vortex shedding frequency of the separation bubble are analogous to the separation bubble on the two-dimensional airfoil at the effective angle of attack of the wing root. Downwash from the wingtip vortex inhibits boundary layer separation in proximity to the wingtip, suppressing shear layer vortex shedding and causing a delay in transition near the wingtip. Unlike a canonical two-dimensional separation bubble, the separation bubble on the wing becomes an open separation near the wingtip, where the spanwise pressure gradient causes fluid to enter into the separation bubble, producing a substantial spanwise flow within recirculation region. A comparison with the results of previous studies suggests a similar bubble topology across different wing geometries and experimental conditions. The results of this investigation quantify the influence of wingtip effects on a laminar separation bubble, elucidating the three-dimensional changes to the bubble’s mean structure and dynamics along the wingspan

Insufficient maintenance DNA methylation is associated with abnormal embryonic development

<p>Abstract</p> <p>Background</p> <p>Early pregnancy loss (EPL) is a frustrating clinical problem, whose mechanisms are not completely understood. DNA methylation, which includes maintenance methylation and <it>de novo </it>methylation directed by DNA methyltransferases (DNMTs), is important for embryo development. Abnormal function of these DNMTs may have serious consequences for embryonic development.</p> <p>Methods</p> <p>To evaluate the possible involvement of DNA methylation in human EPL, the expression of DNMT proteins and global methylation of DNA were assessed in villous or decidua from EPL patients. The association of maintenance methylation with embryo implantation and development was also examined.</p> <p>Results</p> <p>We found that DNMT1 and DNMT3A were both expressed in normal human villous and decidua. DNMT1 expression and DNA global methylation levels were significantly down-regulated in villous of EPL. DNMT3A expression was not significantly changed in the EPL group compared to controls in either villous or decidua. We also found that disturbance of maintenance methylation with a DNMT1 inhibitor may result in a decreased global DNA methylation level and impaired embryonic development in the mouse model, and inhibit <it>in vitro </it>embryo attachment to endometrial cells.</p> <p>Conclusions</p> <p>Our results demonstrate that defects in DNA maintenance methylation in the embryo, not in the mother, are associated with abnormal embryonic implantation and development. The findings of the current study provide new insights into the etiology of EPL.</p

Loss of DNMT1o Disrupts Imprinted X Chromosome Inactivation and Accentuates Placental Defects in Females

The maintenance of key germline derived DNA methylation patterns during preimplantation development depends on stores of DNA cytosine methyltransferase-1o (DNMT1o) provided by the oocyte. Dnmt1omat-/- mouse embryos born to Dnmt1Δ1o/Δ1o female mice lack DNMT1o protein and have disrupted genomic imprinting and associated phenotypic abnormalities. Here, we describe additional female-specific morphological abnormalities and DNA hypomethylation defects outside imprinted loci, restricted to extraembryonic tissue. Compared to male offspring, the placentae of female offspring of Dnmt1Δ1o/Δ1o mothers displayed a higher incidence of genic and intergenic hypomethylation and more frequent and extreme placental dysmorphology. The majority of the affected loci were concentrated on the X chromosome and associated with aberrant biallelic expression, indicating that imprinted X-inactivation was perturbed. Hypomethylation of a key regulatory region of Xite within the X-inactivation center was present in female blastocysts shortly after the absence of methylation maintenance by DNMT1o at the 8-cell stage. The female preponderance of placental DNA hypomethylation associated with maternal DNMT1o deficiency provides evidence of additional roles beyond the maintenance of genomic imprints for DNA methylation events in the preimplantation embryo, including a role in imprinted X chromosome inactivation. © 2013 McGraw et al

Patterns of Hybrid Loss of Imprinting Reveal Tissue- and Cluster-Specific Regulation

Background: Crosses between natural populations of two species of deer mice, Peromyscus maniculatus (BW), and P. polionotus (PO), produce parent-of-origin effects on growth and development. BW females mated to PO males (bw6po) produce growth-retarded but otherwise healthy offspring. In contrast, PO females mated to BW males (PO6BW) produce overgrown and severely defective offspring. The hybrid phenotypes are pronounced in the placenta and include PO6BW conceptuses which lack embryonic structures. Evidence to date links variation in control of genomic imprinting with the hybrid defects, particularly in the PO6BW offspring. Establishment of genomic imprinting is typically mediated by gametic DNA methylation at sites known as gDMRs. However, imprinted gene clusters vary in their regulation by gDMR sequences. Methodology/Principal Findings: Here we further assess imprinted gene expression and DNA methylation at different cluster types in order to discern patterns. These data reveal PO6BW misexpression at the Kcnq1ot1 and Peg3 clusters, both of which lose ICR methylation in placental tissues. In contrast, some embryonic transcripts (Peg10, Kcnq1ot1) reactivated the silenced allele with little or no loss of DNA methylation. Hybrid brains also display different patterns of imprinting perturbations. Several cluster pairs thought to use analogous regulatory mechanisms are differentially affected in the hybrids. Conclusions/Significance: These data reinforce the hypothesis that placental and somatic gene regulation differs significantly, as does that between imprinted gene clusters and between species. That such epigenetic regulatory variatio

Assisted reproduction treatment and epigenetic inheritance

Background: The subject of epigenetic risk of assisted reproduction treatment (ART), initiated by reports on an increase of children with the Beckwith–Wiedemann imprinting disorder, is very topical. Hence, there is a growing literature, including mouse studies. Methods: In order to gain information on transgenerational epigenetic inheritance and epigenetic effects induced by ART, literature databases were searched for papers on this topic using relevant keywords. Results: At the level of genomic imprinting involving CpG methylation, ART-induced epigenetic defects are convincingly observed in mice, especially for placenta, and seem more frequent than in humans. Data generally provide a warning as to the use of ovulation induction and in vitro culture. In human sperm from compromised spermatogenesis, sequence-specific DNA hypomethylation is observed repeatedly. Transmittance of sperm and oocyte DNA methylation defects is possible but, as deduced from the limited data available, largely prevented by selection of gametes for ART and/or non-viability of the resulting embryos. Some evidence indicates that subfertility itself is a risk factor for imprinting diseases. As in mouse, physiological effects from ART are observed in humans. In the human, indications for a broader target for changes in CpG methylation than imprinted DNA sequences alone have been found. In the mouse, a broader range of CpG sequences has not yet been studied. Also, a multigeneration study of systematic ART on epigenetic parameters is lacking. Conclusions: The field of epigenetic inheritance within the lifespan of an individual and between generations (via mitosis and meiosis, respectively) is growing, driven by the expansion of chromatin research. ART can induce epigenetic variation that might be transmitted to the next generation

Effects of DNMT1o deficiency on embryos

DNA methylation constitutes an epigenetic modification of DNA that is initiated during gametogenesis and is essential for normal development. Methylation is postulated to be the molecular mark underlying genomic imprinting whereby genes are differentially expressed according to parental origin. The loss of the oocyte-derived DNMT1o maintenance methyltransferase affects the methylation imprints during preimplantation development, producing epigenetic mosaic embryos. Here we show that embryos that develop in the absence of DNMT1o demonstrate profound phenotypic variation in both fetal and extraembryonic tissues, as well as severe pregnancy loss by midgestation. Morphological assessment was complemented with methylation analysis of fetal and extraembryonic tissues at the differentially methylated domain (DMD) of the imprinted gene Snrpn. The general conclusion from this study is that extragenetic programming in the embryo greatly influences pregnancy outcome and phenotype in mouse embryos. The relevance of this work to human imprinting disorders and cloning technologies is discussed

“The Hyacinth Macaw”: America Through the Broken Looking Glass

Taking inspiration from fantasy novels and historic photography, I desired to create a reality that was a tilted version of our own. The imagery of a broken mirror followed me through the creative process and I was able to conceive costumes that were inspired by our own clothing but with a twist. My goal was to give the audience a sense that they were travelling to a peculiar world that was deceivingly familiar

Turbulence

Turbulence is related to both the ideology and practices of eight artists enrolled in the summer Visual Arts Program at the Banff Centre. Biographical notes. 1 bibl. ref

Armature

Survey of recent studio work created at the Banff Centre. Brief biographical notes on all six artists