483 research outputs found

    Obstructions to embeddability into hyperquadrics and explicit examples

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    We give series of explicit examples of Levi-nondegenerate real-analytic hypersurfaces in complex spaces that are not transversally holomorphically embeddable into hyperquadrics of any dimension. For this, we construct invariants attached to a given hypersurface that serve as obstructions to embeddability. We further study the embeddability problem for real-analytic submanifolds of higher codimension and answer a question by Forstneri\v{c}.Comment: Revised version, appendix and references adde

    Surface Modification of Polyethylene with Multi-End-Functional Polyethylene Additives

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    We have prepared and characterized a series of multifluorocarbon end-functional polyethylene additives, which when blended with polyethylene matrices increase surface hydrophobicity and lipophobicity. Water contact angles of >112° were observed on spin-cast blended film surfaces containing less than 1% fluorocarbon in the bulk, compared to 98° in the absence of any additive. Crystallinity in these films gives rise to surface roughness that is an order of magnitude greater than is typical for amorphous spin-cast films but is too little to give rise to superhydrophobicity. X-ray photoelectron spectroscopy (XPS) confirms the enrichment of the multifluorocarbon additives at the air surface by up to 80 times the bulk concentration. Ion beam analysis was used to quantify the surface excess of the additives as a function of composition, functionality, and molecular weight of either blend component. In some cases, an excess of the additives was also found at the substrate interface, indicating phase separation into self-stratified layers. The combination of neutron reflectometry and ion beam analysis allowed the surface excess to be quantified above and below the melting point of the blended films. In these films, where the melting temperatures of the additive and matrix components are relatively similar (within 15 °C), the surface excess is almost independent of whether the blended film is semicrystalline or molten, suggesting that the additive undergoes cocrystallization with the matrix when the blended films are allowed to cool below the melting point

    A high stability semiconductor laser system for a 88^{88}Sr-based optical lattice clock

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    We describe a frequency stabilized diode laser at 698 nm used for high resolution spectroscopy of the 1S0-3P0 strontium clock transition. For the laser stabilization we use state-of-the-art symmetrically suspended optical cavities optimized for very low thermal noise at room temperature. Two-stage frequency stabilization to high finesse optical cavities results in measured laser frequency noise about a factor of three above the cavity thermal noise between 2 Hz and 11 Hz. With this system, we demonstrate high resolution remote spectroscopy on the 88Sr clock transition by transferring the laser output over a phase-noise-compensated 200 m-long fiber link between two separated laboratories. Our dedicated fiber link ensures a transfer of the optical carrier with frequency stability of 7 \cdot 10^{-18} after 100 s integration time, which could enable the observation of the strontium clock transition with an atomic Q of 10^{14}. Furthermore, with an eye towards the development of transportable optical clocks, we investigate how the complete laser system (laser+optics+cavity) can be influenced by environmental disturbances in terms of both short- and long-term frequency stability.Comment: 9 pages, 9 figures, submitted to Appl. Phys.

    Lagrangian Klein bottles in R^{2n}

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    It is shown that the n-dimensional Klein bottle admits a Lagrangian embedding into R^{2n} if and only if n is odd.Comment: V.2 - explicit formula for the Luttinger-type surgery; V.3 - section 3 corrected, section 6 expanded; 6 page

    Women, men and coronary heart disease: a review of the qualitative literature

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    Aim. This paper presents a review of the qualitative literature which examines the experiences of patients with coronary heart disease. The paper also assesses whether the experiences of both female and male patients are reflected in the literature and summarizes key themes. Background. Understanding patients' experiences of their illness is important for coronary heart disease prevention and education. Qualitative methods are particularly suited to eliciting patients' detailed understandings and perceptions of illness. As much previous research has been 'gender neutral', this review pays particular attention to gender. Methods. Published papers from 60 qualitative studies were identified for the review through searches in MEDLINE, EMBASE, CINAHL, PREMEDLINE, PsychINFO, Social Sciences Citation Index and Web of Science using keywords related to coronary heart disease. Findings. Early qualitative studies of patients with coronary heart disease were conducted almost exclusively with men, and tended to generalize from 'male' experience to 'human' experience. By the late 1990s this pattern had changed, with the majority of studies including women and many being conducted with solely female samples. However, many studies that include both male and female coronary heart disease patients still do not have a specific gender focus. Key themes in the literature include interpreting symptoms and seeking help, belief about coronary 'candidates' and relationships with health professionals. The influence of social roles is important: many female patients have difficulties reconciling family responsibilities and medical advice, while male patients worry about being absent from work. Conclusions. There is a need for studies that compare the experiences of men and women. There is also an urgent need for work that takes masculinity and gender roles into account when exploring the experiences of men with coronary heart disease

    An Outcome Evaluation of the Implementation of the Triple P – Positive Parenting Program in Hong Kong

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    The present study evaluated the effectiveness of the Positive Parenting Program (Triple P) with a sample of Chinese parents of children with early onset conduct related problems in Hong Kong. The participants consisted of 91 parents whose children attended maternal and child health centers and child assessment centers for service, and were between three to seven years old. Participants were randomly assigned to the intervention (TP) and a waitlist control group (WL. There was no significant difference in pre-intervention measures between the two groups. However, at post intervention, participants in the TP group reported significantly lower levels of child behavior problems, lower dysfunctional parenting styles, and higher parent sense of competence, compared to the WL group. Implications of these findings for the use of Triple P with families of Chinese descent are discussed

    On the Kobayashi-Royden metric for ellipsoids

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    Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46237/1/208_2005_Article_BF01446557.pd

    Ethnographic understandings of ethnically diverse neighbourhoods to inform urban design practice

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    The aim of this paper is to inform urban design practice through deeper understanding and analysis of the social dynamics of public outdoor space in ethnically diverse neighbourhoods. We hypothesise that findings from ethnographic research can provide a resource that improves cultural literacy and supports social justice in professional practice. The primary method is a meta-synthesis literature review of 24 ethnographic research papers, all of which explore some dimensions of public open space use and values in UK urban contexts characterised by ethnic and racial diversity. We summarise thematic understandings and significance of neighbourhood places of shared activity, parks, spaces of passing-by and of retreat. We evaluate the implications for intercultural social dynamics, exploring the spatial and temporal dimensions of conviviality and racism in public open space. We then argue that it is possible to develop principles for urban design practice informed by this work, and propose four for discussion: maximising straightforward participation, legitimising diversity of activity, designing in micro-retreats of nearby quietness and addressing structural inequalities of open space provision. We conclude that ethnographic research can provide detailed insights into the use of the public realm and also inform a more nuanced understanding of outdoor sociality relevant for an increasingly diverse society. The challenge is two-fold: for ethnographers to become less cautious in engaging with decisions and priorities regarding how cities change, and for urban designers to explicitly embed informed understandings of difference into their broad desire for inclusive public space
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