3,328 research outputs found

    Bottom-Up and Top-Down Controls on Food Webs in Headwater Streams

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    Headwater streams account for 70% of stream channel length in the USA and are important as hotspots of nutrient uptake and native biodiversity. Biofilm, the mixed auto- and heterotrophic microbial community covering stream substrates, is where the majority of nutrient processing occurs, and forms the base of stream food webs, particularly in heavily shaded, oligotrophic streams. Both bottom-up (e.g., nutrients, light) and top-down (i.e., consumption) processes are known to affect periphyton, the autotrophic component of biofilm, but little is known about what controls the biofilm community as a whole. Top-down effects are common in streams, where fish are often the top predator and can cause cascading effects. However, salamanders – not fish – are the top predators in many small headwater streams, and the top-down effects of salamanders on stream food webs have received much less attention. I used experimental and observational approaches to investigate the role of top-down and bottom-up controls on headwater stream food webs. Specifically, I used stream mesocosms with two salamander species, Eurycea bislineata and Gyrinophilus porphyriticus, alone or in combination, to test the effects of salamander community composition on benthic and emergent macroinvertebrate density, biomass and community composition. To assess the relative importance of bottom-up and top-down determinants of biofilm biomass, I used a combination of stream surveys and pre-existing stream chemistry data from across the oligotrophic headwater streams of the Hubbard Brook Experimental Forest (HBEF). My experiment showed that stream salamanders alter benthic macroinvertebrate densities, but only when G. porphyriticus occurs alone, as it consumes E. bislineata, the smaller species, when it is present. This intraguild predation removes the top-down effects of G. porphyriticus on benthic macroinvertebrates. In my stream surveys, bottom-up variables (i.e., aspect, canopy cover, nutrients and pH) determined biofilm biomass, not salamander occupancy or benthic macroinvertebrate biomass. However, I did not encounter streams with the specific salamander community (i.e., G. porphyriticus present and E. bislineata absent) shown to produce top-down effects in my experimental study. My results demonstrate that salamanders can exert top-down control on benthic macroinvertebrate communities. This effect is, however, dependent on the salamander species present, and can be removed by intraguild interactions between salamander species. Furthermore, bottom-up factors, in particular light, appear to play the primary role in determining biofilm biomass. Despite prior evidence for the dominance of heterotrophic microbes in biofilms at the HBEF, the importance of light in controlling biofilm biomass suggests that the autotrophic component of these biofilms may be disproportionately important, and emphasizes the importance of understanding both the auto-and heterotrophic components of stream biofilms. My work links the rich history of research on stream salamander community ecology to broader studies of stream food webs, providing new avenues for future research

    Federal Regulation of Emerging Genetic Technologies

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    Over the past ten years scientists have perfected revolutionary techniques in the field of genetic engineering. Although this new technology promises to have enormous commercial and industrial value, some scientists fear that the risks accompanying genetic experimentation may outweigh its social benefits. In their Article Professor McGarity and Mr. Bayer examine the legal debate over how government should regulate this emerging technology. After describing various genetic engineering techniques and the risks underlying their use, Professor McGarity and Mr. Bayer discuss the elements of a regulatory framework adequate to handle the new technology and assess the existing regulatory structure in terms of a more appropriate framework. They conclude that the appropriate existing federal agencies immediately should undertake data collection and risk assessments to identify the dangers in the experimentation, manufacture, and practical use of genetically altered micro-organisms. Professor McGarity and Mr. Bayer recommend that Congress be prepared to enact new legislation if the existing regulatory framework fails to meet the challenge of this exciting new technology

    Division, adjoints, and dualities of bilinear maps

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    The distributive property can be studied through bilinear maps and various morphisms between these maps. The adjoint-morphisms between bilinear maps establish a complete abelian category with projectives and admits a duality. Thus the adjoint category is not a module category but nevertheless it is suitably familiar. The universal properties have geometric perspectives. For example, products are orthogonal sums. The bilinear division maps are the simple bimaps with respect to nondegenerate adjoint-morphisms. That formalizes the understanding that the atoms of linear geometries are algebraic objects with no zero-divisors. Adjoint-isomorphism coincides with principal isotopism; hence, nonassociative division rings can be studied within this framework. This also corrects an error in an earlier pre-print; see Remark 2.11

    АНАЛІЗ ФАКТОРІВ, ЩО ВИЗНАЧАЮТЬ ОСОБИСТІСНУ СТІЙКІСТЬ ЗА УМОВ СОЦІАЛЬНИХ РЕПРЕСІЙ

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    On the basis of the consideration of theoretical sources from the contiguous areas of psychological science some intrapersonal and external factors which could be regarded as auxiliary in the process of personality’s capture of destructive influences of the soviet management system are selected.На основе рассмотрения теоретических источников из смежных областей психологиче­ской науки выделены некоторые внутриличностные и внешние факторы, которые могли выступить как вспомогательные в овладении личностью разрушительных влияний совет­ской административной системы.На основі розгляду теоретичних джерел із суміжних областей психологічної науки ви­окремлено деякі внутрішньоособистісні та зовнішні фактори, що могли виступити як до­поміжні в опануванні особистістю руйнівних впливів радянської адміністративної системи

    ПРОБЛЕМА СУБ’ЄКТИВНОГО ОБРАЗУ СВІТУ В РОБОТАХ ВІТЧИЗНЯНИХ ТА ЗАРУБІЖНИХ АВТОРІВ

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    Наведено стислий огляд основних теорій та концепцій психологічної науки, що стосуються опису та структури феномену суб’єктивного образу світу. Матеріал може бути застосований із метою розширення курсу лекцій із дисципліни «Загальна психологія», розділ – психологія пізнання

    Dignity Therapy as a Method of Palliative Psychological Assistance

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    Methodological and theoretical grounding of a brief psychological intervention, new for Ukraine, are presented ‒ of so-called dignity therapy created by a Canadian researcher Harvey M. Chochinov the aim of which is fostering the feeling of the personhood of patients, actualization of their feeling of dignity and, as a result, decreasing of sufferings and increasing the quality of their lives. The scope of requests and conditions where dignity therapy could be helpful is defined, palliative care and psychological support of the elderly in particular. The factor contents of the model of dignity around which the intervention is constructed is revealed: feelings around the illness, behavioural repertoire related to the feeling of dignity, and the social model of dignity. The stages of dignity therapy implementation (preparatory, the stage of interview, and the stage of creating Generativity Document), its eight components  (setting, comprehension check, probing questions, exploration of one's life path, refocusing, encouraging for meaningful expressions, general processes of the therapy) as well as questions that a therapist asks a patient in order to start a foreseen process are listed and described. Approximate contents of Generativity Document  which is a key material product of dignity therapy on the example of summarized results of thematic analysis in the relevant research from different countries is presented (the developed themes include “Family”, “Pleasure”, “Caring”, “A Sense of Accomplishment” and others). The description of the procedure of estimation of efficacy of dignity therapy is provided, in particular through the use of self-reports and with the inclusion of groups of experts. A brief outline of the demands for therapists who implement the intervention is defined (namely, the  standardized training with standardized teaching materials, the work at standardized cases, providing supervisions and additional expert support). The importance of the attitude of a specialist towards realization of dignity therapy is stressed ‒ sensitive, self-aware as well as self-reflective

    Do effective properties for unsaturated weakly layered porous media exist? An experimental study

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    International audienceIn a multi-step outflow experiment we found that a weak heterogeneity within a sand column prevents the estimated effective hydraulic parameters from being unique. We compared vertical water content profiles calculated from these parameters with profiles measured by x-ray attenuation. A layered material model based on x-ray data was able to reproduce the outflow curve and also the water content distribution inside the column. We also calculated effective parameters for the layered model turned upside down and obtained large differences to the set of values of the original sample

    The orbifold cohomology of moduli of genus 3 curves

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    In this work we study the additive orbifold cohomology of the moduli stack of smooth genus g curves. We show that this problem reduces to investigating the rational cohomology of moduli spaces of cyclic covers of curves where the genus of the covering curve is g. Then we work out the case of genus g=3. Furthermore, we determine the part of the orbifold cohomology of the Deligne-Mumford compactification of the moduli space of genus 3 curves that comes from the Zariski closure of the inertia stack of M_3.Comment: 29 pages, 2 figures. Minor changes, to appear in Manuscripta Mat

    Control of interlayer exchange coupling in Fe/Cr/Fe trilayers by ion beam irradiation

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    The manipulation of the antiferromagnetic interlayer coupling in the epitaxial Fe/Cr/Fe(001) trilayer system by moderate 5 keV He ion beam irradiation has been investigated experimentally. It is shown that even for irradiation with very low fluences (10^14 ions/cm^2) a drastic change in strength of the coupling appears. For thin Cr-spacers (below 0.6 - 0.7 nm) the coupling strength decreases with fluence, becoming ferromagnetic for fluences above (2x10^14 ions/cm^2). The effect is connected with the creation of magnetic bridges in the layered system due to atomic exchange events caused by the bombardment. For thicker Cr spacers (0.8 - 1.2 nm) an enhancement of the antiferromagnetic coupling strength is found. A possible explanation of the enhancement effect is given.Comment: Submitted to PR
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