117,942 research outputs found

    Proposed acousto-optic filter

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    Narrow band optical filter is electronically tunable over a large wavelength region. The filter utilizes collinear acousto-optic diffraction in an optically anisotropic media

    Acousto-optic filter for electronic laser tuning

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    Electronically tunable lithium niobate filter utilizes acoustic-optic diffraction for tuning laser to desired frequencies. Filter placed inside laser cavity diffracts incident optical signal of one polarization into orthogonal polarization by collinearly propagating acoustic beam to desired wavelength

    Discrete Group Actions on Spacetimes: Causality Conditions and the Causal Boundary

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    Suppose a spacetime MM is a quotient of a spacetime VV by a discrete group of isometries. It is shown how causality conditions in the two spacetimes are related, and how can one learn about the future causal boundary on MM by studying structures in VV. The relations between the two are particularly simple (the boundary of the quotient is the quotient of the boundary) if both VV and MM have spacelike future boundaries and if it is known that the quotient of the future completion of VV is past-distinguishing. (That last assumption is automatic in the case of MM being multi-warped.)Comment: 32 page

    Flax fibre: innovation and change in the early Neolithic: a technological and material perspective

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    Flax (Linum sp.) was one of the first domestic plants in Neolithic Europe, providing a potential cultivable source of fibres for the first farmers. As the plant provides both oil and fibre, it is a matter of enquiry as to whether the plant was first domesticated for its seeds or stem. Through examining new data collected by the EUROEVOL Project, UCL it is possible to chart the earliest archaeobotanical evidence for flax species in Europe. This provides the basis on which to consider the origin of fibres from the flax plant (linen) as a basis for change and innovation in the fibre resources used for textiles. These are then explored from a technological and material perspective. From a technological perspective I compare the chaßne opératoire of linen with contemporary sources of fibre, namely tree bast fibres and other wild resources in central and northern Europe. From a material perspective I consider the properties of flax and lime bast. Through these approaches this paper suggests that flax had a special role as a fibre domesticate in Europe, providing a versatile, valuable resource for the production and use of textiles during the Neolithic period

    Counseling Customers: Emerging Roles for Genetic Counselors in the Direct-to-Consumer Genetic Testing Market

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    Individuals now have access to an increasing number of internet resources offering personal genomics services. As the direct-to-consumer genetic testing (DTC GT) industry expands, critics have called for pre- and post-test genetic counseling to be included with the product. Several genetic testing companies offer genetic counseling. There has been no examination to date of this service provision, whether it meets critics’ concerns and implications it may have for the genetic counseling profession. Considering the increasing relevance of genetics in healthcare, the complexity of genetic information provided by DTC GT, the mediating role of the internet in counseling, and potential conflicts of interest, this is a topic which deserves further attention. In this paper we offer a discourse analysis of ways in which genetic counseling is represented on DTC GT websites, blogs and other online material. This analysis identified four types of genetic counseling represented on the websites: the integrated counseling product; discretionary counseling; independent counseling; and product advice. Genetic counselors are represented as having the following roles: genetics educator; mediator; lifestyle advisor; risk interpreter; and entrepreneur. We conclude that genetic counseling as represented on DTC GT websites demonstrates shifting professional roles and forms of expertise in genetic counseling. Genetic counselors are also playing an important part in how the genetic testing market is taking shape. Our analysis offers important and timely insights into recent developments in the genetic counseling profession, which have relevance for practitioners, researchers and policy makers concerned with the evolving field of personal genomics. Keywords Genetic counseling Internet Direct-to-consumer genetic testing Discourse analysis

    Ultrahigh reflection from a medium with ultraslow group velocity

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    We show that an incident wavepacket at the boundary to a medium with extremely slow group velocity, experiences enhanced reflection and a substantial spatial and temporal distortion of the transmitted wave packet. In the limit of vanishing group velocity, light cannot be transferred into the medium due to its perfect reflectivity.Comment: 3 pages, 3 figure
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