1,940 research outputs found

    High Precision Laser and Microwave Spectroscopy of Antiprotonic Helium

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    This talk gives an overview of the recent results on the precision spectroscopy of antiprotonic helium which was performed by the ASACUSA collaboration at the Antiproton Decelerator of CERN. The laser spectroscopy of energy levels of the antiproton has reached a relative accuracy of 107\sim 10^{-7}, and by comparing the experimental value for the transition wavelengths with theoretical calculations, a CPT test on the equality of proton and antiproton charge and mass of <6×108<6\times10^{-8} has been obtained. In a recent experiment, the hyperfine structure of the (n,l)=(37,35)(n,l)=(37,35) state of antiprotonic helium has been measured for the first time with an accuracy of 3×1053 \times 10^{-5}.Comment: Invited talk at the XIVth Rencontres de Blois on Matter-Antimatter Asymmetry, Blois, June 200

    A Facility for Low-energy Antiproton and Ion Research

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    The future accelerator facility for beams of ions and antiprotons at Darmstadt will provide antiproton beams of intensities that are two orders of magnitude higher than currently available. Within the foreseen scheme, antiprotons can be decelerated to 30 MeV. The low-energy antiproton community has recently formed a users group to make use of this opportunity to create a next-generation low-energy antiproton facility called FLAIR, which will be able to provide cooled antiproton beams well below 100 keV kinetic energy. This talk gives an overview of the layout and physics program of the proposed facility.Comment: Proceedings of the XLII Interantional Winter Meeting on Nuclear Physics, Bormio (Italy), Janaury 25 - February 1, 200

    In-beam hyperfine spectroscopy of antihydrogen, hydrogen and deuterium

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    The ASACUSA collaboration is developing a polarized beam of antihydrogen atoms to precisely determine the ground-state hyperfine structure for studies of CPT and Lorentz invariance. Using a beam of ordinary hydrogen, measurements of both the σ\sigma and π\pi-transition have been performed, investigating orientation-dependent SME coefficients. Furthermore a first hyperfine experiment with a beam of deuterium is being prepared.Comment: 5 pages, 3 figures. Presented at the Ninth Meeting on CPT and Lorentz Symmetry, Bloomington, Indiana, May 17-26, 202

    Pull-out strength of axially loaded steel rods bonded in glulam perpendicular to the grain

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    A total of 86 pull-out strength tests on glued-in steel rods with metric threads M12, M16 and M20 are reported in this paper. The rods were bonded in glulam made of Norway spruce lamellas perpendicular to the grain by means of an epoxy-type adhesive using the GSA®-system. The slenderness ratios of the rods λ calculated from the anchoring lengths ℓ with respect to the diameter of the drill hole d h (λ=ℓ/d h) varied between 7.5 and 12.5. Registered failure loads were considerably higher than design values derived from different existing approaches. The pull-out strength was found to be almost directly proportional to the surface area of the bond line. Based on this an approach to estimate the pull-out strength is suggested. Dependence between pull-out strength and anchoring length ℓ as well as slenderness ratio λ exists, whereas such dependence for the diameter of the rod was not found. The pull-out strength is influenced by the wood density. Compared to rods bonded in parallel to the grain, pull-out strength of rods with same diameter and anchoring length set perpendicular to the grain are 20-50% highe

    Pull-out strength of axially loaded steel rods bonded in glulam parallel to the grain

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    Bonded-in steel rods are very efficient in withstanding high forces applied to timber members. Investigations of bonded-in rods started in the late eighties of the last century and several design models were published since. By comparing these approaches on base of an extensive literature review a certain degree of discrepancy and partly even contradiction can be found. The paper describes a test program which aimed to study the influence of timber density and of geometric parameters on the pull-out strength of single axially loaded steel rods. Following the GSA®-procedure, which is a well established glued-in rods joint in Switzerland, rods with metric thread were bonded in glulam made of Norway spruce lamellas using an epoxy-type adhesive. The tests showed that the influence of the timber density can be quantified by a power function of ρ with an exponent of 0.6. The parameters length of the glued zone ℓ and diameter of the hole d H can be summarized in the slenderness ratio λ = ℓ/d H, which itself is related to the mean shear strength in the anchoring zone by an exponent of approximately −1/3. In order to prevent the specimens from premature splitting, distances between the axis of the rod and the edge of the specimen of 2.3 times the diameter of the rod have been use

    Polar and magnetic order in GaV4Se8

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    In the present work, we provide results from specific heat, magnetic susceptibility, dielectric constant, ac conductivity, and electrical polarization measurements performed on the lacunar spinel GaV4Se8. With decreasing temperature, we observe a transition from the paraelectric and paramagnetic cubic state into a polar, probably ferroelectric state at 42 K followed by magnetic ordering at 18 K. The polar transition is likely driven by the Jahn-Teller effect due to the degeneracy of the V4 cluster orbitals. The excess polarization arising in the magnetic phase indicates considerable magnetoelectric coupling. Overall, the behavior of GaV4Se8 in many respects is similar to that of the skyrmion host GaV4S8, exhibiting a complex interplay of orbital, spin, lattice, and polar degrees of freedom. However, its dielectric behavior at the polar transition markedly differs from that of the Jahn-Teller driven ferroelectric GeV4S8, which can be ascribed to the dissimilar electronic structure of the Ge compound.Comment: 7 pages, 6 figures. Revised version according to suggestions of referee