1,331 research outputs found

    Tensor product of motives via K\"unneth formula

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    Following Nori's original idea we here provide certain motivic categories with a canonical tensor structure. These motivic categories are associated to a cohomological functor on a suitable base category and the tensor structure is induced by the cartesian tensor structure on the base category via a cohomological K\"unneth formula.Comment: Revised version to appear on JPA

    Photoproduction of electron-positron pairs in bent single crystals

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    The process of photoproduction of electron-positron pairs in bent single crystals is considered in this paper. In particular, it is shown that the probability of the process for gamma-quanta with energies from 100 GeV on is significantly higher than the one in an amorphous medium. A possible scenario for the experimental validation of the process is discussed and the positive features of the photoproduction in bent crystals compared to straight ones are underlined from the point of view of possible applications.Comment: 13 pages, 6 figure

    A strained silicon cold electron bolometer using Schottky contacts

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    We describe optical characterisation of a strained silicon cold electron bolometer (CEB), operating on a 350 mK stage, designed for absorption of millimetre-wave radiation. The silicon cold electron bolometer utilises Schottky contacts between a superconductor and an n++ doped silicon island to detect changes in the temperature of the charge carriers in the silicon, due to variations in absorbed radiation. By using strained silicon as the absorber, we decrease the electron-phonon coupling in the device and increase the responsivity to incoming power. The strained silicon absorber is coupled to a planar aluminium twin-slot antenna designed to couple to 160‚ÄČGHz and that serves as the superconducting contacts. From the measured optical responsivity and spectral response, we calculate a maximum optical efficiency of 50% for radiation coupled into the device by the planar antenna and an overall noise equivalent power, referred to absorbed optical power, of 1.1√ó10‚ąí16‚ÄČW‚ÄČHz‚ąí1/2 when the detector is observing a 300‚ÄČK source through a 4‚ÄČK throughput limiting aperture. Even though this optical system is not optimized, we measure a system noise equivalent temperature difference of 6‚ÄČmK‚ÄČHz‚ąí1/2. We measure the noise of the device using a cross-correlation of time stream data, measured simultaneously with two junction field-effect transistor amplifiers, with a base correlated noise level of 300‚ÄČpV‚ÄČHz‚ąí1/2 and find that the total noise is consistent with a combination of photon noise, current shot noise, and electron-phonon thermal noise

    A compact light readout system for longitudinally segmented shashlik calorimeters

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    The longitudinal segmentation of shashlik calorimeters is challenged by dead zones and non-uniformities introduced by the light collection and readout system. This limitation can be overcome by direct fiber-photosensor coupling, avoiding routing and bundling of the wavelength shifter fibers and embedding ultra-compact photosensors (SiPMs) in the bulk of the calorimeter. We present the first experimental test of this readout scheme performed at the CERN PS-T9 beamline in 2015 with negative particles in the 1-5~GeV energy range. In this paper, we demonstrate that the scheme does not compromise the energy resolution and linearity compared with standard light collection and readout systems. In addition, we study the performance of the calorimeter for partially contained charged hadrons to assess the e/ŌÄe/\pi separation capability and the response of the photosensors to direct ionization.Comment: To appear in Nuclear Instruments and Methods in Physics Research,

    Torsion pairs and rigid objects in tubes

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    We classify the torsion pairs in a tube category and show that they are in bijection with maximal rigid objects in the extension of the tube category containing the Pruefer and adic modules. We show that the annulus geometric model for the tube category can be extended to the larger category and interpret torsion pairs, maximal rigid objects and the bijection between them geometrically. We also give a similar geometric description in the case of the linear orientation of a Dynkin quiver of type A.Comment: 25 pages, 13 figures. Paper shortened. Minor errors correcte
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