528 research outputs found

    Spin Dynamics in the Magnetic Chains Arrays of Sr14Cu24O41: a Neutron Inelastic scattering Investigation

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    Below about 150 K, the spin arrangement in the chain arrays of Sr14Cu24O41 is shown to develop in two dimensions (2D). Both the correlations and the dispersion of the observed elementary excitations agree well with a model of interacting dimers. Along the chains, the intra- and inter-dimer distances are equal to 2 and about 3 times the distance (c) between neighboring Cu ions. While the intra-dimer coupling is J about 10 meV, the inter-dimer couplings along and between the chains are of comparable strenght, J// about -1.1 meV and Jperp about 1.7 meV, respectively. This remarkable 2D arrangement satisfies the formal Cu valence of the undoped compound. Our data suggest also that it is associated with a relative sliding of one chain with respect to the next one, which, as T decreases, develops in the chain direction. A qualitative analysis shows that nearest inter-dimer spin correlations are ferromagnetic, which, in such a 2D structure, could well result from frustration effects.Comment: 4 pages, 5 figures, submitted to Phys.Rev.B, date of receipt 29 June 199

    The ARIEL Space Mission

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    ARIEL, the Atmospheric Remote-Sensing Infrared Exoplanet Large-survey, has been selected to be the next ESA M4 space misson. From launch in 2028 and during its 4 years of operation, ARIEL will perform a spectroscopic survey of the atmospheres of about 1 000 transiting planets orbiting stars other than our Sun. ARIEL will provide the scientific community the first spectroscopic survey of a statistically significant sample of exoplanet atmospheres, covering the portion of the electromagnetic spectrum spanning from the visible to the mid-IR. ARIEL will allow us to answer questions about the true nature of these far away worlds, their atmospheric and physical conditions, and their formation and evolutionary histories

    Everyday pain, analgesic beliefs and analgesicbehaviours in Europe and Russia: An epidemiologicalsurvey and analysis

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    Беше проведено анкетно проучване в осем държави, в т.ч. Белгия, Германия, Великобритания, Италия, Полша, Русия и Испания. Оценена беше честотата на оплакване от болка при 8 506 души (52% жени), както и използването на аналгетици и нагласите спрямо тях. Предварителните анализи потвърждават високата честота на оплаквания от болка, като 70% от анкетираните посочват, че поне веднъж в месеца изпитват такава. Най-често се съобщава за главоболие и болки в гърба, a болшинството анкетирани лица - 77%, споделят, че използват аналгетични средства, когато страдат от болка. Предмет на по-нататъшните анализи бяха различията по пол, статус на заетост, държава по местоживеене и възраст. В сравнение с мъжете, жените по-често изпитват болка, употребата на аналгетици сред тях е по-голяма, както и притесненията им във връзка с тази употреба, като проявяват склонност да базират употребата върху своите познания относно лекарствените продукти. Безработните също съобщават за по-голямо използване на аналгетици и повече притеснения във връзка с това, сравнено със заетите лица. Като цяло при хората, живеещи в Русия и Полша, се отчита по-рядко болка и по-малко използване на обезболяващи средства в сравнение с останалата част на Европа. Те също така се тревожат повече във връзка с аналгетиците и по отношение на това, че използването на аналгетици от тяхна страна е слабо свързано с познания относно лекарствата. Отчитането на фактора „възраст` показва, че при по-младите епизодите на болка са по-малко, употребата на аналгетици - по-честа, a притесненията относно аналгетиците са по-слаби в сравнение с по-възрастните. Също така, по-младите са по-склонни да използват аналгетици въз основа на своите познания за продукта. Тези резултати повтарят съществуващи констатации във връзка с честотата на болката. Дават и нови сведения за различията при изпитването на болка, използването на аналгетици и нагласите към аналгетиците в Европа и Русия.

    Phases of two coupled Luttinger liquids

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    A model of two interacting one--dimensional fermion systems (``Luttinger liquids'') coupled by single--particle hopping is investigated. Bosonization allows a number of exact statements to be made. In particular, for forward scattering only, the model contains two massless boson sectors and an Ising type critical sector. For general interactions, there is a spin excitation gap and either s-- or d--type pairing fluctuations dominate. It is shown that the same behavior is also found for strong interactions. A possible scenario for the crossover to a Fermi liquid in a many chain system is discussed.Comment: revised version, some changes, 11 pages, no figures, RexTeX3.

    The Mid-Infrared Instrument for the James Webb Space Telescope, VIII: The MIRI Focal Plane System

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    We describe the layout and unique features of the focal plane system for MIRI. We begin with the detector array and its readout integrated circuit (combining the amplifier unit cells and the multiplexer), the electronics, and the steps by which the data collection is controlled and the output signals are digitized and delivered to the JWST spacecraft electronics system. We then discuss the operation of this MIRI data system, including detector readout patterns, operation of subarrays, and data formats. Finally, we summarize the performance of the system, including remaining anomalies that need to be corrected in the data pipeline

    Long term durability of protected silver coating for the mirrors of Ariel mission telescope

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    Ariel (Atmospheric Remote-sensing Infrared Exoplanet Large survey) is the fourth medium-size mission in ESA “Cosmic Vision” program. It is scheduled to launch in 2029. Ariel will conduct spectroscopic and photometric observations of a large sample of known exoplanets to survey their atmospheres with the transit method. Ariel is based on a 1 m class telescope designed for the visible and near infrared spectrum, but optimized specifically for spectroscopy in the waveband between 1.95 and 7.8 μm. Telescope and instruments will be operating in cryogenic conditions in the range 40-50 K. The telescope mirrors will be manufactured in aluminum 6061, with a protected silver coating deposited onto the optical surface to enhance reflectivity and prevent oxidation and corrosion. During the preliminary definition phase of the development work, leading to mission adoption, a silver coating with space heritage was selected and underwent a qualification process on disc-shaped samples of the mirrors substrate material. The samples were deposited through magnetron sputtering and then subjected to a battery of tests, including environmental durability tests, accelerated aging, cryogenic tests and mechanical resistance tests. Further to the qualification, the samples have been stored in cleanroom conditions and periodically re-examined and measured to detect any sign of coating degradation. The test program, still ongoing at the time of writing this article, consists of visual inspection with a high intensity lamp, spectral reflectance measurements and Atomic Force Microscopy (AFM) evaluation of nanometric surface features. The goal is to ensure stability of the optical performance, in terms of coating reflectance, during a time span comparable to the period that the actual mirrors of the telescope will spend in average cleanroom conditions. This study presents the interim results after three years of storage

    Two-magnon Raman scattering in spin-ladder geometries and the ratio of rung and leg exchange constants

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    We discuss ways in which the ratio of exchange constants along the rungs and legs of a spin-ladder material influences the two-magnon Raman scattering spectra and hence can be determined from it. We show that within the Fleury-Loudon-Elliott approach, the Raman line-shape does not change with polarization geometries. This lineshape is well known to be difficult to calculate accurately from theory. However, the Raman scattering intensities do vary with polarization geometries, which are easy to calculate. With some assumptions about the Raman scattering Hamiltonian, the latter can be used to estimate the ratio of exchange constants. We apply these results to Sugai's recent measurements of Raman scattering from spin-ladder materials such as La6_6Ca8_8Cu24_{24}O41_{41} and Sr14_{14}Cu24_{24}O41_{41}.Comment: 5 pages, revtex. Latest version focuses on ladder materials, with a detailed examination of the role of Heisenberg-like coupling constants which appear in the Fleury-Loudon-Elliott scattering operator but are rarely discussed in the literatur

    Yb-Yb correlations and crystal-field effects in the Kondo insulator YbB12 and its solid solutions

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    We have studied the effect of Lu substitution on the spin dynamics of the Kondo insulator YbB12 to clarify the origin of the spin-gap response previously observed at low temperature in this material. Inelastic neutron spectra have been measured in Yb1-xLuxB12 compounds for four Lu concentrations x = 0, 0.25, 0.90 and 1.0. The data indicate that the disruption of coherence on the Yb sublattice primarily affects the narrow peak structure occurring near 15-20 meV in pure YbB12, whereas the spin gap and the broad magnetic signal around 38 meV remain almost unaffected. It is inferred that the latter features reflect mainly local, single-site processes, and may be reminiscent of the inelastic magnetic response reported for mixed-valence intermetallic compounds. On the other hand, the lower component at 15 meV is most likely due to dynamic short-range magnetic correlations. The crystal-field splitting in YbB12 estimated from the Er3+ transitions measured in a Yb0.9Er0.1B12 sample, has the same order of magnitude as other relevant energy scales of the system and is thus likely to play a role in the form of the magnetic spectral response.Comment: 16 pages in pdf format, 9 figures. v. 2: coauthor list updated; extra details given in section 3.2 (pp. 6-7); one reference added; fig. 5 axis label change

    Excitation Spectrum and Superexchange Pathways in the Spin Dimer VODPO_4 . 1/2 D_2O

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    Magnetic excitations have been investigated in the spin dimer material VODPO_4 \cdot 1/2 D_2O using inelastic neutron scattering. A dispersionless magnetic mode was observed at an energy of 7.81(4) meV. The wavevector dependence of the scattering intensityfrom this mode is consistent with the excitation of isolated V^{4+} spin dimers with a V-V separation of 4.43(7) \AA. This result is unexpected since the V-V pair previously thought to constitute themagnetic dimer has a separation of 3.09 \AA. We identify an alternative V-V pair as the likely magnetic dimer, which involves superexchange pathways through a covalently bonded PO_4 group. This surprising result casts doubt on the interpretation of (VO)_2P_2O_7 as a spin ladder.Comment: 4 pages, 4 postscript figures - identical to previous paper but figure 2 and 3 hopefully more compatible .p
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