376 research outputs found
Excitations from a Bose-Einstein condensate of magnons in coupled spin ladders
The weakly coupled quasi-one-dimensional spin ladder compound
(CH)CHNHCuCl is studied by neutron scattering in magnetic
fields exceeding the critical field of Bose-Einstein condensation of magnons.
Commensurate long-range order and the associated Goldstone mode are detected
and found to be similar to those in a reference 3D quantum magnet. However, for
the upper two massive magnon branches the observed behavior is totally
different, culminating in a drastic collapse of excitation bandwidth beyond the
transition point.Comment: 4 pages, 4 figure
Excitations in a four leg antiferromagnetic Heisenberg spin tube
Inelastic neutron scattering is used to investigate magnetic excitations in the quasi one dimensional quantum spin liquid system Cu2Cl4 D8C4SO2. Contrary to previously conjectured models that relied on bond alternating nearest neighbor interactions in the spin chains, the dominant interactions are actually next nearest neighbor in chain antiferromagnetic couplings. The appropriate Heisenberg Hamiltonian is equivalent to that of a S 1 2 4 leg spin tube with almost perfect one dimensionality and no bond alternation. A partial geometric frustration of rung interactions induces a small incommensurability of short range spin correlations
Jahn-Teller versus quantum effects in the spin-orbital material LuVO3
We report on combined neutron and resonant x-ray scattering results,
identifying the nature of the spin-orbital ground state and magnetic
excitations in LuVO3 as driven by the orbital parameter. In particular, we
distinguish between models based on orbital Peierls dimerization, taken as a
signature of quantum effects in orbitals, and Jahn-Teller distortions, in favor
of the latter. In order to solve this long-standing puzzle, polarized neutron
beams were employed as a prerequisite in order to solve details of the magnetic
structure, which allowed quantitative intensity-analysis of extended magnetic
excitation data sets. The results of this detailed study enabled us to draw
definite conclusions about classical vs quantum behavior of orbitals in this
system and to discard the previous claims about quantum effects dominating the
orbital physics of LuVO3 and similar systems.Comment: Phys. Rev. B 91, 161104(R) (2015
On the weak confinement of kinks in the one-dimensional quantum ferromagnet CoNb2O6
In a recent paper Coldea et al (2010 Science {\bf 327} 177) report
observation of the weak confinement of kinks in the Ising spin chain
ferromagnet CoNb2O6 at low temperatures. To interpret the entire spectra of
magnetic excitations measured via neutron scattering, they introduce a
phenomenological model, which takes into account only the two-kink
configurations of the spin chain. We present the exact solution of this model.
The explicit expressions for the two-kink bound-state energy spectra and for
the relative intensities of neutron scattering on these magnetic modes are
obtained in terms of the Bessel function.Comment: 18 pages, 9 figures; v2: figures 1,3,4 replaced, few misprints
correcte
Sulfate-reducing bacteria and their activities in cyanobacterial mats of Solar Lake (Sinai, Egypt)
The sulfate-reducing bacteria within the surface layer of the hypersaline cyanobacterial mat of Solar Lake (Sinai, Egypt) were investigated with combined microbiological, molecular, and biogeochemical approaches. The diurnally oxic surface layer contained between 106 and 107 cultivable sulfate-reducing bacteria ml-1 and showed sulfate reduction rates between 1,000 and 2,200 nmol ml-1 day-1, both in the same range as and sometimes higher than those in anaerobic deeper mat layers. In the oxic surface layer and in the mat layers below, filamentous sulfate-reducing Desulfonema bacteria were found in variable densities of 104 to 106 cells ml-1. A Desulfonema-related, diurnally migrating bacterium was detected with PCR and denaturing gradient gel electrophoresis within and below the oxic surface layer. Facultative aerobic respiration, filamentous morphology, motility, diurnal migration, and aggregate formation were the most conspicuous adaptations of Solar Lake sulfate-reducing bacteria to the mat matrix and to diurnal oxygen stress. A comparison of sulfate reduction rates within the mat and previously published photosynthesiS rates showed that CO2 from sulfate reduction in the upper 5 mm accounted for 7 to 8% of the total photosynthetic CO2 demand of the mat
Flexible CO<sub>2</sub> sensor architecture with selective nitrogen functionalities by one-step laser-induced conversion of versatile organic ink
Nitrogen-doped carbons (NC) are a class of sustainable materials for selective CO2 adsorption. We introduce a versatile concept to fabricate flexible NC-based sensor architectures for room-temperature sensing of CO2 in a one-step laser conversion of primary coatings cast from abundant precursors. By the unidirectional energy impact in conjunction with depth-dependent attenuation of the laser beam, a layered sensor heterostructure with porous transducer and active sensor layer is formed. Comprehensive microscopic and spectroscopic cross-sectional analyses confirm the preservation of a high content of imidazolic nitrogen in the sensor. The performance was optimized in terms of material morphology, chemical composition, and surface chemistry to achieve a linear relative resistive response of up to ∆R/R0 = -14.3% (10% of CO2). Thermodynamic analysis yields ΔadsH values of -35.6 kJ·mol-1 and 34.1 kJ·mol-1 for H2O and CO2, respectively. The sensor is operable even in humid environments (e.g., ∆R/R0,RH=80% = 0.53%) and shows good performance upon strong mechanical deformation
The Ministry of Works and the Development of Souvenir Guides from 1955
The first formal guidebooks for historic sites placed in state guardianship in the United Kingdom appeared in 1917. There was an expansion of the series in the 1930s and 1950s. However, from the late 1950s the Ministry of Works, and later the Ministry of Public Buildings and Works, started to produce an additional series of illustrated souvenir guides. One distinct group covered Royal Palaces: the Tower of London, Hampton Court Palace, Queen Victoria's residence of Osborne House on the Isle of Wight, and Holyroodhouse in Edin-burgh. This was followed by guides for archaeological sites such as Stone-henge and Avebury, the Neolithic flint mines at Grime's Graves, the Roman villa at Lullingstone, and Hadrian's Wall. In 1961, a series of guides, with covers designed by Kyffin Williams, was produced for the English castles constructed in North Wales. These illustrated guides, some with colour, prepared the way for the fully designed guides now produced by English Heritage, Cadw, and Historic Environment Scotland
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