Deformation of an elastic cell in a uniform stream and in a circulatory flow

The deformation of a circular, inextensible elastic cell is examined when the cell is placed into two different background potential flows: a uniform stream and a circulatory flow induced by a point vortex located inside the cell. In a circulatory flow a cell may deform into a mode m shape with m-fold rotational symmetry. In a uniform stream, shapes with two-fold rotational symmetry tend to be selected. In a weak stream a cell deforms linearly into an ellipse with either its major or its minor axis aligned with the oncoming flow. This marks an interesting difference with a bubble with constant surface tension in a uniform stream, which can only deform into a mode 2 shape with its major axis perpendicular to the stream (Vanden-Broeck & Keller, 1980b). In general, as the strength of the uniform stream is increased from zero, solutions emerge continuously from the cell configurations in quiescent fluid found by Flaherty et al. (1972). A richly populated solution space is described with multiple solution branches which either terminate when a cell reaches a state with a point of self-contact or loop round to continuously connect cell states which exist under identical conditions in the absence of flow

Phase-field approach to heterogeneous nucleation

We consider the problem of heterogeneous nucleation and growth. The system is described by a phase field model in which the temperature is included through thermal noise. We show that this phase field approach is suitable to describe homogeneous as well as heterogeneous nucleation starting from several general hypotheses. Thus we can investigate the influence of grain boundaries, localized impurities, or any general kind of imperfections in a systematic way. We also put forward the applicability of our model to study other physical situations such as island formation, amorphous crystallization, or recrystallization.Comment: 8 pages including 7 figures. Accepted for publication in Physical Review

Solitary waves on a ferrofluid jet

The propagation of axisymmetric solitary waves on the surface of an otherwise cylindrical ferrofluid jet subjected to a magnetic field is investigated. An azimuthal magnetic field is generated by an electric current flowing along a stationary metal rod which is mounted along the axis of the moving jet. A numerical method is used to compute fully-nonlinear travelling solitary waves and predictions of elevation waves and depression waves by Rannacher & Engel (2006) using a weakly-nonlinear theory are confirmed in the appropriate ranges of the magnetic Bond number. New nonlinear branches of solitary wave solutions are identified. As the Bond number is varied, the solitary wave profiles may approach a limiting configuration with a trapped toroidal-shaped bubble, or they may approach a static wave (i.e. one with zero phase speed). For a sufficiently large axial rod, the limiting profile may exhibit a cusp

The changing profile of surrogacy in the UK – implications for national and international policy and practice

Since 2007, the numbers of UK Parental Orders granted following surrogacy have markedly increased. More recently, eligibility criteria have been extended to unmarried heterosexual couples and same-sex couples rather than only married couples. Numbers seeking fertility treatments, including through surrogates, outside their country of residence have also increased. This paper presents the limited data currently available – from UK General Register Offices, Child and Family Court Advisory and Support Service for England and the UK surrogacy agencies: COTS, Surrogacy UK, British Surrogacy Centre – to consider potential reasons for the increase and to consider policy and practice implications. It charts the apparent decline in involvement of surrogacy agencies and suggests the potential for exploitation where scrutiny of arrangements and follow up are limited. It recommends improvements to data collection and argues the need for a more integrated approach to review of surrogacy arrangements both nationally and internationally

Can soil moisture be mapped onto the terrain?

International audienceSoil moisture heterogeneity has an effect on the rainfall?runoff characteristics of a landscape. The aggregate effect on the mean water balance over an area can be quantified successfully using models such as the PDM (Moore, 1986) and TOPMODEL (Beven and Kirkby, 1979). These rainfall?runoff models have been embedded in the large-scale land surface schemes used in meteorological models. However, there is also a requirement (e.g. model validation) to identify the spatial structure of the fine-scale soil moisture heterogeneity that makes up these aggregate models. In some types of landscape, this will be dictated by topography, in others by soil characteristics, or by a combination of both. A method to distribute area-average soil moisture according to the likely effect of local topography is presented and tested. The heterogeneity of the soil moisture is described by the Xinanxiang distribution (Zhao et al., 1980), commonly used to describe the natural spatial heterogeneity of the landscape. This distribution is then mapped onto the terrain using a topographic index to locate the wettest and driest areas. Soil moisture data from the Wye catchment in Wales and from the Pang catchment in Berkshire, England, are used to test the method. It is found that soil moisture data from the Wye catchment follow the topographic index reasonably well, whereas data from the quick-draining, chalky Pang catchment do not. The conclusion that topographic index is a useful indicator only in some landscapes applies equally to using this mapping method and those models that use topographic index directly. Keywords: soil moisture, heterogeneity, topographic index, dat

Expectations and experiences of gamete donors and donor-conceived adults searching for genetics relatives using DNA linking through a voluntary register

STUDY QUESTION: What are the experiences of donor-conceived adults and donors who are searching for a genetic link through the use of a DNA-based voluntary register service? SUMMARY ANSWER: Donor-conceived adults and donors held positive beliefs about their search and although some concerns in relation to finding a genetically linked relative were reported, these were not a barrier to searching. WHAT IS KNOWN ALREADY: Research with donor-conceived people has consistently identified their interest in learning about-and in some cases making contact with-their donor and other genetic relatives. However, donor-conceived individuals or donors rarely have the opportunity to act on these desires. STUDY DESIGN, SIZE, AND DURATION: A questionnaire was administered for online completion using Bristol Online Surveys. The survey was live for 3 months and responses were collected anonymously. PARTICIPANTS/MATERIALS, SETTING, AND METHODS: The survey was completed by 65 donor-conceived adults, 21 sperm donors and 5 oocyte donors who had registered with a DNA-based voluntary contact register in the UK. The questionnaire included socio-demographic questions, questions specifically developed for the purposes of this study and the standardized Aspects of Identity Questionnaire (AIQ). MAIN RESULTS AND THE ROLE OF CHANCE: Motivations for searching for genetic relatives were varied, with the most common reasons being curiosity and passing on information. Overall, participants who were already linked and those awaiting a link were positive about being linked and valued access to a DNA-based register. Collective identity (reflecting self-defining feelings of continuity and uniqueness), as assessed by the AIQ, was significantly lower for donor-conceived adults when compared with the donor groups (P 0.05) for donor-conceived adults. LIMITATIONS, REASONS FOR CAUTION: Participants were members of a UK DNA-based registry which is unique. It was therefore not possible to determine how representative participants were of those who did not register for the service, those in other countries or of those who do not seek information exchange or contact. WIDER IMPLICATIONS OF THE FINDINGS: This is the first survey exploring the experiences of donor-conceived adults and donors using a DNA-based voluntary register to seek information about and contact with genetic relatives and the first to measure aspects of identity using standardized measures. Findings provide valuable information about patterns of expectations and experiences of searching through DNA linking, identity and of having contact in the context of donor conception that will inform future research, practice and policy development

Secrets and disclosure in donor conception

This paper considers the disclosure, sharing and exchange of information on being donor conceived within families, drawing on data from a study undertaken with donor-conceived adults registered with UK Donor Link (a voluntary DNA-linking register). It considers the narratives of how respondents found out they were donor-conceived and what events triggered disclosure of this information. It goes on to examine the role secrecy played in their family life and uses the concept of ‘display’ to explore how it affected their relationships with their immediate and extended family. Secrets are notoriously ‘leaky’ and we found complex patterns of knowing and uncertainty about whom in the family knew that the person was donor-conceived. We argue that what is kept secret and from whom provides insights into the multifaceted web of social relationships that can be created by donor-conception, and how knowledge can be managed and controlled in attempts to display and maintain family narratives of biogenetic connection

Searching for ‘relations’ using a DNA linking register by adults conceived following sperm donation

This paper considers how sperm donor-conceived adults registered with a voluntary DNA linking register, UK DonorLink, constructed identity and relatedness by examining two areas: how their identity was affected by becoming aware that they were donor-conceived; and the process of searching for their donor and donor-conceived siblings. The views and experiences of donor-conceived adults has, until recently, been a neglected area. This study is the first to consider the experiences of those searching through a DNA-based register, and contributes to the growing literature on searching. This paper presents qualitative data from a questionnaire-based study with 65 adults conceived following sperm donation. It examines emerging linkages by investigating how ideas of relatedness, kinship and identity were enacted and how narrative certainties were moved and removed by opening up new conceptions of what it means to be ‘related’. Their knowledge of being donor-conceived was both a powerful disrupter and a consolidator of family relationships. No single story of being donor-conceived emerged – with competing narratives about the effects and implications for respondents’ kinship relationships and sense of identity. This study sheds light on how kinship relationships are negotiated and managed in adulthood by those conceived following sperm donation and how this can change over the life-course

Gamete donors’ reasons for, and expectations and experiences of, registration with a voluntary donor linking register

This paper reports on a study of the views and experiences of 21 sperm donors and five egg donors registered with UK DonorLink (UKDL), a voluntary DNA-based contact register established to facilitate contact between adults who wish to identify and locate others to whom they are genetically related following donor conception. Specifically, the paper examines donors’ reasons for searching for, or making information about themselves available to donor-conceived offspring. Their expectations of registration with UKDL, experiences of being registered and finally, the experiences of those who had contacted donor-conceived offspring and other genetic relatives are investigated. While most respondents reported largely positive experiences of registration, the study found significant issues relating to concerns about donation, DNA testing, possible linking with offspring and expectations of any relationship that might be established with offspring that have implications for support, mediation and counselling. Research that puts the experiences, perceptions and interests of gamete donors as the central focus of study is a relatively recent phenomenon. This study contributes to this debate and highlights directions for future research in this area

Voluntary DNA-based information exchange and contact services following donor conception: an analysis of service users’ needs

Medical science has enabled the creation of families through the use of donor conception but some lifelong policy and practice implications are only recently being recognized. Research and practice have shown that donor conception can, for some, carry substantial long-term consequences. In this paper we present findings from a questionnaire-based study that sought to shed light on donor-conceived adults’ and gamete donors’ views on service and support needs when searching for genetic relatives with the aid of DNA testing. The findings demonstrate the complexity and sensitivity of providing services in this newly emerging area of need. Such provision requires collaboration between very different disciplines and agencies (scientific and psychosocial), introduces the potential for blurring of lines of accountability and responsibility, and highlights the challenges of identifying appropriate funding streams. In addition, the findings demonstrate the opportunities and limitations afforded by the use of DNA in identifying unknown genetic relatives