Water impact analysis of space shuttle solid rocket motor by the finite element method

Preliminary analysis showed that the doubly curved triangular shell elements were too stiff for these shell structures. The doubly curved quadrilateral shell elements were found to give much improved results. A total of six load cases were analyzed in this study. The load cases were either those resulting from a static test using reaction straps to simulate the drop conditions or under assumed hydrodynamic conditions resulting from a drop test. The latter hydrodynamic conditions were obtained through an emperical fit of available data. Results obtained from a linear analysis were found to be consistent with results obtained elsewhere with NASTRAN and BOSOR. The nonlinear analysis showed that the originally assumed loads would result in failure of the shell structures. The nonlinear analysis also showed that it was useful to apply internal pressure as a stabilizing influence on collapse. A final analysis with an updated estimate of load conditions resulted in linear behavior up to full load

Seminiferous tubule transfection in vitro to define post-meiotic gene regulation

The electronic version of this article is the complete one and can be found online at: http://www.rbej.com/content/7/1/67Background: Post-meiotically expressed genes in the testis are essential for the proper progression of spermatogenesis, and yet, aside from the construction of individual transgenic mice using specific promoters to drive reporter plasmids, there are only very limited possibilities for relevant and quantitative analysis of gene promoters. This is due to the special nature of post-meiotic haploid cells, which to date are not represented in any appropriate cell-lines. This article reports the development of novel methodology using isolated and cultured rat seminiferous tubules in a multiwell format, into which promoter-reporter constructs can be introduced by a combination of microinjection and electroporation. Methods: Culture conditions were developed which allowed the continued incubation of isolated rat seminiferous tubules for up to 48 h without obvious cell death and loss of post-meiotic cells. Transfection of intact seminiferous tubules by microinjection and electroporation was optimized to achieve high expression efficiencies of control plasmids, using either fluorescent protein or luciferase as reporters, thereby allowing both morphological as well as quantitative assessment. Results: Successful transfection was achieved into all cell types except for mature spermatozoa. However, there appeared to be only limited cell-type specificity for the promoters used, even though these had appeared to be specific when used in transgenic animals. Conclusion: We have devised a methodology which allows relatively high throughput analysis of post-meiotic gene promoters into primary cells of intact seminiferous tubules. An apparent lack of cell-type specificity suggests that the gene fragments used do not contain sufficient targeting information, or that the transient episomal expression of the constructs does not encourage appropriate expression specificity. The results also highlight the doubtful interpretation of many studies using heterologous transfection systems to analyse post-meiotically expressed genes.Sandra Danner, Christiane Kirchhoff and Richard Ivel

Local festivals, social capital and sustainable destination development: experiences in East London

This paper explores the nature of social capital arising from engagement in local festivals and the implications of this for the social sustainability of an emerging destination. Two case studies are developed from a longitudinal research project which investigates local festivals staged in the Hackney Wick and Fish Island area adjacent to Queen Elizabeth Olympic Park in East London, UK between 2008 and 2014. This area has been directly affected by extensive development and regeneration efforts associated with the staging of the London 2012 Olympic Games. The two festivals considered here respond to the challenges and opportunities arising for local people as the area changes. One festival aims to foster a sense of community by creating shared experiences and improving communication across diverse groups. The other draws together the cultural community, links them to the opportunities arising as the area emerges as a destination, and attracts visitors. These festivals increase social capital in the area, but its distribution is very uneven. The accrual of social capital exacerbates existing inequalities within the host community, favouring the “haves” at the expense of the “have nots”. There are tensions between the development of social capital and social sustainability in this emerging destination

Voluntary disclosure of corporate strategy: determinants and outcomes. An empirical study into the risks and payoffs of communicating corporate strategy.

Business leaders increasingly face pressure from stakeholders to be transparent. There appears however little consensus on the risks and payoffs of disclosing vital information such as corporate strategy. To fill this gap, this study analyzes firm-specific determinants and organisational outcomes of voluntary disclosure of corporate strategy. Stakeholder theory and agency theory help to understand whether companies serve their interest to engage with stakeholders and overcome information asymmetries. I connect these theories and propose a comprehensive approach to measure voluntary disclosure of corporate strategy. Hypotheses from the theoretical framework are empirically tested through panel regression of data on identified determinants and outcomes and of disclosed strategy through annual reports, corporate social responsibility reports, corporate websites and corporate press releases by the 70 largest publicly listed companies in the Netherlands from 2003 through 2008. I found that industry, profitability, dual-listing status, national ranking status and listing age have significant effects on voluntary disclosure of corporate strategy. No significant effects are found for size, leverage and ownership concentration. On outcomes, I found that liquidity of stock and corporate reputation are significantly influenced by voluntary disclosure of corporate strategy. No significant effect is found for volatility of stock. My contributions to theory, methodology and empirics offers a stepping-stone for further research into understanding how companies can use transparency to manage stakeholder relations

High capacity extrachromosomal gene expression vectors.

Extrachromosomal gene expression vectors that contain native genomic gene expression elements have numerous advantages over traditional integrating mini-gene vectors. In this protocol chapter we describe our work using episomal vectors where expression of a cDNA is controlled by a 10 kB piece of genomic DNA encompassing the promoter of the low density lipoprotein receptor. We explain methods to sub-clone large genomic inserts into gene expression vectors. We also illustrate various methods employed to ascertain whether expression from these vectors is robust and physiologically relevant by investigating their sensitivity to changes in cellular milieu. Delivery of gene expression vectors in vivo is also described using hydrodynamic tail vein injection, a high pressure, high volume tail vein injection used for liver-directed gene transfer

Gamete physiology, fertilization and egg activation in teleost fish

The fertilization and activation of fish oocytes are vital, but unfortunately overlooked, processes in fisheries research. This paper sets out to review our present understanding of these important events in teleost fish and, drawing comparisons with mammalian research, to highlight areas in which research effort is urgently required. Presently, the commercial culture of many important freshwater, but especially marine, teleosts is beset by problems associated with fertilization, hatching and early embryonic development. These problems have been particularly acute in certain species leading to the application of spawning induction technologies in an effort to optimize production. Increased knowledge of the processes of egg activation and fertilization in these groups of fish is likely to make significant contribution to commercial aquaculture. Studies of a wide variety of animal and plant species has demonstrated that development at fertilization is triggered by an increase in intracellular Ca2+ concentration within the egg that occurs as either a single transient or a series of distinctive oscillations depending upon the species under investigation. This increase in intracellular Ca2+ activates the egg and also appears to play an important role in later embryonic development. Teleost reproductive strategies and more importantly, teleost oocytes and spermatozoa, exhibit a remarkable variety of adaptations. Currently, studies of egg activation in teleosts are confined to laboratory species such as medaka Oryzias latipes and zebrafish Brachydanio rerio. Nevertheless, even between these two species, although an increase in intracellular Ca2+ appears to be the trigger in both cases, the mechanism of Ca2+ release may be quite different. Activation in medaka is initiated only through direct contact with conspecific sperm, suggesting the involvement of a sperm-specific factor, while zebrafish eggs appear to require only contact with the external spawning medium. In view of the highly variable fertility rates evident in many commercially cultured teleosts, it could be very rewarding to investigate the mechanism of egg activation in representative teleost groups using the findings and theories emerging from other animal groups as a starting point. In order to successfully conduct such an investigation, it will be necessary to employ a combination of physiological, molecular and recombinant approaches

In vivo gene transfer into the testis by electroporation and viral infection--a novel way to study testis and sperm function.

The study of gene function in testis and sperm has been greatly assisted by creation of transgenic mice by injection of a transgene into the fertilised egg. However this approach is costly and laborious and is not applicable to other species of importance for the study of sperm function, such as the hamster. We have investigated alternative ways of expressing transgenes in mouse and hamster testis and sperm by in vivo gene transfer. DNA expression constructs were introduced into the testis by injection of DNA followed by electroporation, or by injection of a lentiviral vector. Expression of fluorescent proteins was assessed by fluorescence microscopy. In vivo gene transfer by electroporation led to expression of a fluorescent reporter protein and a fluorescently tagged version of sperm protein phospholipase C zeta in hamster and mouse testis and epididymal sperm. In vivo gene transfer by lentiviral infection led to high level expression of a fluorescent reporter protein in male germ cells. In conclusion, in vivo gene transfer offers a novel way to study gene function in testis and sperm and may also have potential as a way of creating transgenic versions of important model organisms such as the hamster