25,363 research outputs found

    Theory of water and charged liquid bridges

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    The phenomena of liquid bridge formation due to an applied electric field is investigated. A new solution for the charged catenary is presented which allows to determine the static and dynamical stability conditions where charged liquid bridges are possible. The creeping height, the bridge radius and length as well as the shape of the bridge is calculated showing an asymmetric profile in agreement with observations. The flow profile is calculated from the Navier Stokes equation leading to a mean velocity which combines charge transport with neutral mass flow and which describes recent experiments on water bridges.Comment: 10 pages 12 figures, misprints corrected, assumptions more transparen

    A new proton fluence model for E greater than 10 MeV

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    Researchers describe a new engineering model for the fluence of protons with energies greater than 10 MeV. The data set used is a combination of observations made primarily from the Earth's surface between 1956 and 1963 and observations made from spacecraft in the vicinity of Earth between 1963 and 1985. With this data set we find that the distinction between ordinary proton events and anomalously large proton events made in earlier work disappears. The greater than 10 MeV fluences at 1 AU calculated with the new model are about twice those expected on the basis of models now in use. In contrast to earlier models, results do not depend critically on the fluence from any one event

    Empowering international and culturally diverse honours and project students through mentoring activities

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    This paper reports on an initiative to develop a successful school based student mentoring program in the context of a Computer Science based school which has a high proportion of international and culturally diverse student population. A review of literature was made of three areas of research related to mentoring and peer support. This provided evidence for the role of mentoring and peer support in empowering student learning, with particular emphasis on how mentoring can provide both social and academic support; on the role of mentoring in different contexts; within the Computer Science field and within an international and culturally diverse education perspective and finally on the role of and qualities required by the mentor in the mentoring process. The paper examines the findings from an email based survey of current and former members of student mentor group which has existed since 2003. The questionnaire was categorized into five sections including demographic information, factors influencing choice of the group, reflections on the mentoring experience (joining the group, project activities), on commitments and skills development (commitments, interpersonal/interaction, improving skills) and additional support services. The overarching finding from the research was that the mentoring experience was a positive one for both mentor and mentees. The mentor group provided a supportive respectful environment which could offer both academic and technical skills development and provide social support. Students also identified the most important qualities and obligations that the mentor group leader should provide to include, subject knowledge and technical expertise, and quality traits of trustworthiness, intercultural understanding and friendliness. From the research findings a framework was proposed to support the implementation of a school based mentor group program. This is seen as beneficial to project and research students especially in an international and culturally diverse student population

    A Solvable Model for Decoupling of Interacting Clusters

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    We consider M clusters of interacting particles, whose in-group interactions are arbitrary, and inter-group interactions are approximated by oscillator potentials. We show that there are masses and frequencies that decouple the in-group and inter-group degrees of freedom, which reduces the initial problem to M independent problems that describe each of the relative in-group systems. The dynamics of the M center-of-mass coordinates is described by the analytically solvable problem of M coupled harmonic oscillators. This paper derives and discusses these decoupling conditions. Furthermore, to illustrate our findings, we consider a charged impurity interacting with a ring of ions. We argue that the impurity can be used to probe the center-of-mass dynamics of the ions.Comment: Version accepted for publication in EP

    Infections with cytomegalovirus and other herpesviruses in 121 liver transplant recipients: Transmission by donated organ and the effect of OKT3 antibodies

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    One hundred twenty-one adult liver transplant recipients were studied for the incidence, risk factors, and morbidity associated with herpesviruses infections after transplantation. The overall incidence of infection was 59% for cytomegalovirus (CMV), 35% for herpes simplex virus (HSV), 25% for Epstein-Barr virus (EBV), and 7% for varicella-zoster virus (VZV). Primary CMV infection occurred in 46% and reactivation CMV infection in 67% of the susceptible recipients. Symptomatic and disseminated CMV diseases were more common when patients developed primary infection (P .10). Although most HSV infections were oral or genital reactivations, three cases of HSV hepatitis occurred - one was primary infection. Symptomatic reactivations of HSV were observed in 53% of HSV-seropositive recipients who received OKT3, versus 31% of seropositive recipients who did not receive OKT3 (P = .05)

    The activities of hospital nursing unit managers and quality of patient care in South African hospitals: a paradox?

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    PKBackground: Improving the quality of health care is central to the proposed health care reforms in South Africa. Nursing unit managers play a key role in coordinating patient care activities and in ensuring quality care in hospitals. Objective: This paper examines whether the activities of nursing unit managers facilitate the provision of quality patient care in South African hospitals. Methods: During 2011, a cross-sectional, descriptive study was conducted in nine randomly selected hospitals (six public, three private) in two South African provinces. In each hospital, one of each of the medical, surgical, paediatric, and maternity units was selected (n 36). Following informed consent, each unit manager was observed for a period of 2 hours on the survey day and the activities recorded on a minute-by-minute basis. The activities were entered into Microsoft Excel, coded into categories, and analysed according to the time spent on activities in each category. The observation data were complemented by semi-structured interviews with the unit managers who were asked to recall their activities on the day preceding the interview. The interviews were analysed using thematic content analysis. Results: The study found that nursing unit managers spent 25.8% of their time on direct patient care, 16% on hospital administration, 14% on patient administration, 3.6% on education, 13.4% on support and communication, 3.9% on managing stock and equipment, 11.5% on staff management, and 11.8% on miscellaneous activities. There were also numerous interruptions and distractions. The semi-structured interviews revealed concordance between unit managers’ recall of the time spent on patient care, but a marked inflation of their perceived time spent on hospital administration. Conclusion: The creation of an enabling practice environment, supportive executive management, and continuing professional development are needed to enable nursing managers to lead the provision of consistent and high-quality patient care

    Elimination of Clock Jitter Noise in Spaceborn Laser Interferometers

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    Space gravitational wave detectors employing laser interferometry between free-flying spacecraft differ in many ways from their laboratory counterparts. Among these differences is the fact that, in space, the end-masses will be moving relative to each other. This creates a problem by inducing a Doppler shift between the incoming and outgoing frequencies. The resulting beat frequency is so high that its phase cannot be read to sufficient accuracy when referenced to state-of-the-art space-qualified clocks. This is the problem that is addressed in this paper. We introduce a set of time-domain algorithms in which the effects of clock jitter are exactly canceled. The method employs the two-color laser approach that has been previously proposed, but avoids the singularities that arise in the previous frequency-domain algorithms. In addition, several practical aspects of the laser and clock noise cancellation schemes are addressed.Comment: 20 pages, 5 figure
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