878 research outputs found
Optical spectroscopy of (La,Ca)14Cu24O41 spin ladders: comparison of experiment and theory
Transmission and reflectivity of La_x Ca_14-x Cu_24 O_41 two-leg spin-1/2
ladders were measured in the mid-infrared regime between 500 and 12000 1/cm.
This allows us to determine the optical conductivity sigma_1 directly and with
high sensitivity. Here we show data for x=4 and 5 with the electrical field
polarized parallel to the rungs (E||a) and to the legs (E||c). Three
characteristic peaks are identified as magnetic excitations by comparison with
two different theoretical calculations.Comment: 4 pages, 2 figures, submitted to SCES 200
Visualization of lateral water transport pathways in soybean by a time of flight-secondary ion mass spectrometry cryo-system
Water movement between cells in a plant body is the basic phenomenon of plant solute transport; however, it has not been well documented due to limitations in observational techniques. This paper reports a visualization technique to observe water movement among plant cells in different tissues using a time of flight-secondary ion mass spectrometry (Tof-SIMS) cryo-system. The specific purpose of this study is to examine the route of water supply from xylem to stem tissues. The maximum resolution of Tof-SIMS imaging was 1.8 μm (defined as the three pixel step length), which allowed detection of water movement at the cellular level. Deuterium-labelled water was found in xylem vessels in the stem 2.5 min after the uptake of labelled water by soybean plants. The water moved from the xylem to the phloem, cambium, and cortex tissues within 30–60 min after water absorption. Deuterium ion counts in the phloem complex were slightly higher than those in the cortex and cambium tissue seen in enlarged images of stem cell tissue during high transpiration. However, deuterium ion counts in the phloem were lower than those in the cambium at night with no evaporative demand. These results indicate that the stem tissues do not receive water directly from the xylem, but rather from the phloem, during high evaporative demand. In contrast, xylem water would be directly supplied to the growing sink during the night without evaporative demand
Magnetic excitations in two-leg spin 1/2 ladders: experiment and theory
Magnetic excitations in two-leg S=1/2 ladders are studied both experimentally
and theoretically. Experimentally, we report on the reflectivity, the
transmission and the optical conductivity sigma(omega) of undoped La_x Ca_14-x
Cu_24 O_41 for x=4, 5, and 5.2. Using two different theoretical approaches
(Jordan-Wigner fermions and perturbation theory), we calculate the dispersion
of the elementary triplets, the optical conductivity and the momentum-resolved
spectral density of two-triplet excitations for 0.2 <=
J_parallel/J_perpendicular <= 1.2. We discuss phonon-assisted two-triplet
absorption, the existence of two-triplet bound states, the two-triplet
continuum, and the size of the exchange parameters.Comment: 6 pages, 7 eps figures, submitted to SNS 200
Lumen - Gaia - Atlas : architectuur, kunst en tuinen van de gebouwen van de Environmental Sciences Group
The Environmental Sciences Group (ESG) is a collaboration between the Wageningen University Department of Environmental Sciences and the research institute Alterra. ESG contributes to realising a relatively high-quality and sustainable green living environment through expert and independent research in the fields of water and climate, soils, landscape, geo-information and ecosystems. This publication describes the architecture of the three buildings and mentions the art products and gardens in and around them
Boundaries, Cusps and Caustics in the Multimagnon Continua of 1D Quantum Spin Systems
The multimagnon continua of 1D quantum spin systems possess several
interesting singular features that may soon be accessible experimentally
through inelastic neutron scattering. These include cusps and composition
discontinuities in the boundary envelopes of two-magnon continuum states and
discontinuities in the density of states, "caustics", on and within the
continuum, which will appear as discontinuities in scattering intensity. In
this note we discuss the general origins of these continuum features, and
illustrate our results using the alternating Heisenberg antiferromagnetic chain
and two-leg ladder as examples.Comment: 18 pages, 10 figure
Electric field dependence of pairing temperature and tunneling
Using the Bethe-Salpeter equation including high electric fields, the
dependence of the critical temperature of onsetting superconductivity on the
applied field is calculated analytically. The critical temperature of pairing
is shown to increase with the applied field strength. This is a new field
effect and could contribute to the explanation of recent experiments on field
induced superconductivity. From the field dependence of the Bethe-Salpeter
equation, the two--particle bound state solution is obtained as a resonance
with a tunneling probability analogous to the WKB solution of a single particle
confined in a potential and coupled to the electrical field.Comment: 4 pages 1 figure, revised version from 29.10.02, Rev. B in pres
МЕТОДИКА ПРОВЕДЕННЯ ІСТОРИКО-КРАЄЗНАВЧИХ ЕКСПЕДИЦІЙ НА ПІВДНІ УКРАЇНИ ІНСТИТУТОМ ЕТНОГРАФІЇ АН СРСР у 50-60-ті рр. ХХ ст.
Український народ у своїй історії має великий досвід духовного життя, бо з покоління в покоління передає набуті навички, що стали невід’ємною части-ною нашої національності. Але з кожним роком наше покоління, на жаль, втра-чає зв’язок з попередніми поколіннями. Тому, щоб зберегти традиції, націона-льні особливості, в різні часи різноманітні інститути, товариства, окремі дослі-дники намагались створити найоптимальнішу методику організації та прове-дення історико-краєзнавчих експедицій
Costs of shoulder pain in primary care consulters: a prospective cohort study in The Netherlands
BACKGROUND: Shoulder pain is common in primary care, and has an unfavourable outcome in many patients. Information on the costs associated with health care use and loss of productivity in patients with shoulder pain is very scarce. The objective of this study was to determine shoulder pain related costs during the 6 months after first consultation in general practice METHODS: A prospective cohort study consisting of 587 patients with a new episode of shoulder pain was conducted with a follow-up period of 6 months. Data on costs were collected by means of a cost diary during 6 months. RESULTS: 84% of the patients completed all cost diaries. The mean consumption of direct health care and non-health related care was low. During 6 months after first consultation for shoulder pain, the mean total costs a patient generated were €689. Almost 50% of this total concerned indirect costs, caused by sick leave from paid work. A small proportion (12%) of the population generated 74% of the total costs. CONCLUSION: The total costs in the 6 months after first consultation for shoulder pain in primary care, mostly generated by a small part of the population, are not alarmingly high
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