358 research outputs found

    Ice-lens formation and geometrical supercooling in soils and other colloidal materials

    Full text link
    We present a new, physically-intuitive model of ice-lens formation and growth during the freezing of soils and other dense, particulate suspensions. Motivated by experimental evidence, we consider the growth of an ice-filled crack in a freezing soil. At low temperatures, ice in the crack exerts large pressures on the crack walls that will eventually cause the crack to split open. We show that the crack will then propagate across the soil to form a new lens. The process is controlled by two factors: the cohesion of the soil, and the geometrical supercooling of the water in the soil; a new concept introduced to measure the energy available to form a new ice lens. When the supercooling exceeds a critical amount (proportional to the cohesive strength of the soil) a new ice lens forms. This condition for ice-lens formation and growth does not appeal to any ad hoc, empirical assumptions, and explains how periodic ice lenses can form with or without the presence of a frozen fringe. The proposed mechanism is in good agreement with experiments, in particular explaining ice-lens pattern formation, and surges in heave rate associated with the growth of new lenses. Importantly for systems with no frozen fringe, ice-lens formation and frost heave can be predicted given only the unfrozen properties of the soil. We use our theory to estimate ice-lens growth temperatures obtaining quantitative agreement with the limited experimental data that is currently available. Finally we suggest experiments that might be performed in order to verify this theory in more detail. The theory is generalizable to complex natural-soil scenarios, and should therefore be useful in the prediction of macroscopic frost heave rates.Comment: Submitted to PR

    Ecology good, aut-ecology better; Improving the sustainability of designed plantings

    Get PDF
    © 2015 European Council of Landscape Architecture Schools (ECLAS). This paper explores how contemporary ecological science, and aut-ecology in particular, can improve the sustainability of designed vegetation. It is proposed that ecological understanding can be applied to design at three levels: 1) as representation, 2) as process, and 3) as aut-ecology, representing a gradient from the least to the most profound. Key ecological interactions that determine the success of designed plantings are explored via a review of relevant ecological research, challenging some widely held but unhelpful constructs about how both semi-natural and designed vegetation actually function. The paper concludes that there are real benefits to integrating aut-ecological understanding in the design of vegetation at all scales but that this will require ecological theory to be taught as a design toolkit rather than largely as descriptive knowledge

    Unsettling sustainability: the poetics of discomfort

    Get PDF
    peerreview_statement: The publishing and review policy for this title is described in its Aims & Scope. aims_and_scope_url: http://www.tandfonline.com/action/journalInformation?show=aimsScope&journalCode=rgrl2

    Follow-up of breast cancer in primary care vs specialist care: results of an economic evaluation

    Get PDF
    A randomized controlled trial (RCT) comparing primary-care-centred follow-up of breast cancer patients with the current standard practice of specialist-centred follow-up showed no increase in delay in diagnosing recurrence, and no increase in anxiety or deterioration in health-related quality of life. An economic evaluation of the two schemes of follow-up was conducted concurrent with the RCT. Because the RCT found no difference in the primary clinical outcomes, a cost minimization analysis was conducted. Process measures of the quality of care such as frequency and length of visits were superior in primary care. Costs to patients and to the health service were lower in primary care. There was no difference in total costs of diagnostic tests, with particular tests being performed more frequently in primary care than in specialist care. Data are provided on the average frequency and length of visits, and frequency of diagnostic testing for breast cancer patients during the follow-up period. © 1999 Cancer Research Campaig

    Evolutionary and socio-cultural influences on feelings and attitudes towards nature: a cross-cultural study

    Get PDF
    Mounting environmental issues have prompted reconsideration of the human–nature relationship. Accordingly, attitudes to nature, as an important dimension of human–nature interactions, have become a research focus. How feelings and attitudes towards nature are influenced by evolutionary and social-cultural constructions, and whether there is variation between different cultural groups, demands more attention. Using a survey of visitors to two very different National Parks, the New Forest National Park, England and Jiuzhaigou Scenic Area, China, this paper shows that of nationality and living environment, differences between the two nationalities were significant in respect of both attitudes and feelings. Specifically, it demonstrates that the biophilia thesis, which purports that people have an innate and a genetically inherited need for affiliation with nature, is influenced by their socio-cultural environment, in particular their national culture, but also by their current living place. The study contributes to our understanding of sustainable tourism in natural areas

    Family physicians' perspectives on practice guidelines related to cancer control

    Get PDF
    BACKGROUND: Family physicians (FPs) play an important role in cancer control. While FPs' attitudes towards, and use of guidelines in general have been explored, no study has looked at the needs of FPs with respect to guidelines for the continuum of cancer control. The objective of this study was to understand which guideline topics FPs consider important. METHODS: Five group interviews were conducted by telephone with FPs from across Ontario, Canada. Transcripts were analyzed inductively. Content analysis identified emergent themes. Themes are illustrated by representative quotes taken from the transcripts. RESULTS: The main areas where FPs felt guidelines were needed most included screening – a traditional area of responsibility for FPs – and treatment and follow-up – areas where they felt they lacked the knowledge to best support patients. Confusion over best practice when faced with conflicting guidelines varied according to disease site. FPs defined good guideline formats; the most often cited forms of presentation were tear-off sheets to use interactively with patients, or a binder. Computer-based dissemination was acknowledged as the best way of widely distributing material that needs frequent updates. However, until computer use is a common aspect of practice, mail was considered the most viable method of dissemination. Guidelines designed for use by patients were supported by FPs. CONCLUSIONS: Preferred guideline topics, format, dissemination methods and role of patient guidelines identified by FPs in this study reflect the nature of their practice situations. Guideline developers and those supporting use of evidence-based guidelines (e.g., Canadian Strategy for Cancer Control) have a responsibility to ensure that FPs are provided with the resources they identify as important, and to provide them in a format that will best support their use

    Laboratories, laws, and the career of a commodity

    Get PDF
    Unlike most foods, milk is produced fresh at least twice every day, thus recreating, over 700 times a year, a commodity ‘designed’ by the combination of nature, commerce, and law. The paper is a study of the ontogenesis of this commodity in Britain since 1800, stressing the emergence of two new objectivities: dairy science and the law on adulteration. In the words of Christopher Hamlin, what mattered was the “manufacture of certainty, however flimsy that certainty might later be shown to be.'' This was achieved by the collection of samples, the generation of facts by the deployment of the laboratory technologies of physics and chemistry, and a semimonopoly over the truth-power of dairy science that was gradually built up by the large commercial companies. A foundation of state-sponsored regulation provided an official legitimation of compositional standards that suited the interests of capital but ignored ‘natural’ variations in quality and often pilloried innocent producers. The public eventually became accustomed to the regulated quality of the milk in its ‘pinta’ and assumed it to be natural. Even the standardization of composition since 1993 has caused very little disquiet among the consuming public, although milk is now a fully constructed commodity like any other dairy product. Mechanical modernity has at last triumphed over a century of ‘milk as it came from the cow’

    Quantitative Measurements of Cell−Cell Signaling Peptides with Single-Cell MALDI MS

    Get PDF
    Cell-to-cell signaling peptides play important roles in neurotransmission, neuromodulation, and hormonal signaling. Significant progress has been achieved in qualitative investigations of signaling peptides in the nervous system using single cell matrix-assisted laser desorption/ionization mass spectrometry. However, quantitative information about signaling peptides is difficult to obtain with this approach because only small amounts of analytes are available for analysis. Here we describe several methods for quantitative microanalysis of peptides in individual Aplysia californica neurons and small pieces of tissue. Stable isotope labeling with d0- and d4-succinic anhydride and iTRAQ reagents has been successfully adopted for relative quantitation of nanoliter volume samples containing the Aplysia insulin Cβ peptide. Comparative analysis of the Cβ peptide release site, the upper labial nerve, and its synthesis location, the F- and C-clusters, shows that the release site possesses almost three times more of this compound. The method of standard addition permits absolute quantitation of the physiologically active neuropeptide cerebrin from small structures, including nerves and neuronal clusters, in the femtomole range with a limit of detection of 19 fmol. The simplicity of these methods and the commercial availability of the reagents allow quantitative measurements from a variety of small-volume biological samples
    corecore