229 research outputs found

    Magnetism of a tetrahedral cluster spin-chain

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    We discuss the magnetic properties of a dimerized and completely frustrated tetrahedral spin-1/2 chain. Using a combination of exact diagonalization and bond-operator theory the quantum phase diagram is shown to incorporate a singlet-product, a dimer, and a Haldane phase. In addition we consider one-, and two-triplet excitations in the dimer phase and evaluate the magnetic Raman cross section which is found to be strongly renormalized by the presence of a two-triplet bound state. The link to a novel tellurate materials is clarified.Comment: 8 pages, 8 figure

    Dynamical structure factors of S=1/2S=1/2 two-leg spin ladder systems

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    We investigate dynamical properties of S=1/2S=1/2 two-leg spin ladder systems. In a strong coupling region, an isolated mode appears in the lowest excited states, while in a weak coupling region, an isolated mode is reduced and the lowest excited states become a lower bound of the excitation continuum. We find in the system with equal intrachain and interchain couplings that due to a cyclic four-spin interaction, the distribution of the weights for the dynamical structure factor and characteristics of the lowest excited states are strongly influenced. The dynamical properties of two systems proposed for SrCu2O3{\rm SrCu_2O_3} are also discussed.Comment: 5 pages, 6 figure

    Design and Performance of a Pilot Scale High-Gradient Magnetic Filter Using a Mandhala Magnet and Its Application for Soy-Whey Protein Purification

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    The scalability of economic high-gradient magnetic separation (HGMS) technology is essential in order to demonstrate the feasibility of the concept. One of the means is the application of a permanent magnet with a hollow cylindrical volume made from identical magnetic blocks (e.g., Mandhala), another is the development of a High-Gradient Magnetic Filter (HGMF) with a new backwashing concept. The Mandhala (Magnetic Arrangement for Novel Discrete Halbach Layout) magnet produces a dipolar transversal magnetic field in the center of the bore and its usable volume is easily adaptable to the separation device\u27s extensions. The chapter presents the pilot scale design of the Mandhala magnet and the HGMF as well as experimental performance tests using a water-magnetic beads model system. Subsequently, experiments using soy-whey as a real feedstock demonstrate the purification of the protein Bowman-Birk inhibitor (BBI), an agent against cancer and multiples sclerosis

    Dynamical structure factors of the magnetization-plateau state in the S=1/2S=1/2 bond-alternating spin chain with a next-nearest-neighbor interaction

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    We calculate the dynamical structure factors of the magnetization-plateau state in the S=1/2S=1/2 bond-alternating spin chain with a next-nearest-neighbor interaction. The results show characteristic behaviors depending on the next-nearest-neighbor interaction α\alpha and the bond-alternation δ\delta. We discuss the lower excited states in comparison with the exact excitation spectrums of an effective Hamiltonian. From the finite size effects, characteristics of the lowest excited states are investigated. The dispersionless mode of the lowest excitation appears in adequate sets of α\alpha and δ\delta, indicating that the lowest excitation is localized spatially and forms an isolated mode below the excitation continuum. We further calculate the static structure factors. The largest intensity is located at q=πq=\pi for small δ\delta in fixed α\alpha. With increasing δ\delta, the wavenumber of the largest intensity shifts towards q=π/2q=\pi/2, taking the incommensurate value.Comment: to appear in Phys. Rev. B (2001

    Infrared and optical properties of pure and cobalt-doped LuNi_2B_2C

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    We present optical conductivity data for Lu(Ni1x_{1-x}Cox_x)2_2B2_2C over a wide range of frequencies and temperatures for x=0 and x=0.09. Both materials show evidence of being good Drude metals with the infrared data in reasonable agreement with dc resistivity measurements at low frequencies. An absorption threshold is seen at approximately 700 cm-1. In the cobalt-doped material we see a superconducting gap in the conductivity spectrum with an absorption onset at 24 +/- 2 cm-1 = 3.9$ +/- 0.4 k_BT_c suggestive of weak to moderately strong coupling. The pure material is in the clean limit and no gap can be seen. We discuss the data in terms of the electron-phonon interaction and find that it can be fit below 600 cm-1 with a plasma frequency of 3.3 eV and an electron-phonon coupling constant lambda_{tr}=0.33 using an alpha^{2}F(omega) spectrum fit to the resistivity.Comment: 10 pages with 10 embedded figures, submitted to PR

    Observation of two-magnon bound states in the two-leg ladders of (Ca,La)14Cu24O41

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    Phonon-assisted 2-magnon absorption is studied at T=4 K in the spin-1/2 two-leg ladders of Ca_14-x La_x Cu_24 O_41 (x=5 and 4) for polarization of the electrical field parallel to the legs and the rungs, respectively. Two peaks at about 2140 and 2800 1/cm reflect van-Hove singularities in the density of states of the strongly dispersing 2-magnon singlet bound state, and a broad peak at about 4000 1/cm is identified with the 2-magnon continuum. Two different theoretical approaches (Jordan-Wigner fermions and perturbation theory) describe the data very well for J_parallel = 1050 - 1100 1/cm and J_parallel / J_perp = 1 - 1.1. A striking similarity of the high-energy continuum absorption of the ladders and of the undoped high T_c cuprates is observed.Comment: 4 pages, 3 figures, Revte

    A Systematic Review and Evidence Synthesis of Non-Medical Triage, Self-Referral and Direct Access Services for Patients with Musculoskeletal Pain.

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    Introduction The demand for musculoskeletal (MSK) care is rising, and is a growing challenge for general practice. Direct access to physiotherapy and other healthcare services may offer appropriate care for MSK pain patients but there is uncertainty regarding the effectiveness or efficiency of this approach in practice. This study aimed to review the evidence regarding characteristics, outcomes, barriers and facilitators of MSK triage and direct access services. Methods A comprehensive search of eight databases (including MEDLINE, EMBASE, and Cochrane library) up to February 2018 was conducted to identify studies (trials, cohorts and qualitative evidence) on direct access services for MSK in primary care settings. Using predefined inclusion and exclusion criteria, titles, abstracts, and subsequent full texts were independently screened by reviewers. Methodological quality of eligible studies was assessed using the mixed methods appraisal tool, and extracted data regarding study characteristics and results were independently reviewed. A narrative synthesis and grading of evidence was undertaken. Approaches to MSK triage and direct access were profiled along with their respective outcomes of care relating to patient-oriented and socioeconomic outcomes. Barriers and facilitators of each model of direct access services were also highlighted. Results 9010 unique citations were screened, of which 26 studies were eligible. Three approaches (open access, combination and service pathway models) to MSK triage and direct access shared similar goals but were heterogeneous in application. MSK patients using direct access showed largely similar characteristics (age, sex and duration of symptoms) compared to GP-led care, although they were often younger, slightly more educated and with better socio-economic status than patients seen through GP-led care. Although many studies showed limitations in design or methods, outcomes of care (patient oriented outcomes of pain, and disability) did not show large differences between direct access and GP-led care. In most studies direct access patients were reported to have lower healthcare utilisation (fewer physiotherapy or GP consultations, analgesics or muscle relaxants prescriptions, or imaging procedures) and less time off work compared to GP-led care. Discussion This study provides insight into the current state of evidence regarding MSK triage and direct access services and highlights potential implications for future research, healthcare services planning, resource utilisation and organising care for MSK patients in primary care. There is consistent, although limited, evidence to suggest that MSK triage and direct access services lead to comparable clinical outcomes with lower healthcare consumption, and can help to manage GP workload. However, due to the paucity of strong empirical data from methodologically robust studies, a scale up and widespread roll out of direct access services cannot as yet be assumed to result in long term health and socio-economic gains

    Soft X-Ray Projection Lithography Using a 1-1 Ring Field Optical-System

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    An iridium-coated Offner 1:1 ring field camera has been used to carry out projection lithography using 42 nm light from an undulator in the vacuum ultra violet storage ring at Brookhaven National Laboratory. Near-diffraction-limited resolution has been obtained showing features as small as 0.2-mu-m within a 2 mm x 0.25 mm image field. Images of both transmission and reflection masks have been obtained. The impact of source coherence on imagery has been investigated. Hydrocarbon contamination problems experienced in this photon energy range have been investigated and possible solutions are suggested

    Fractional and Integer Excitations in Quantum Antiferromagnetic Spin 1/2 Ladders

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    Spectral densities are computed in unprecedented detail for quantum antiferromagnetic spin 1/2 two-leg ladders. These results were obtained due to a major methodical advance achieved by optimally chosen unitary transformations. The approach is based on dressed integer excitations. Considerable weight is found at high energies in the two-particle sector. Precursors of fractional spinon physics occur implying that there is no necessity to resort to fractional excitations in order to describe features at higher energies.Comment: 6 pages, 4 figures included, minor text changes, improved figure

    Study protocol for the development and internal validation of Schizophrenia Prediction of Resistance to Treatment (SPIRIT): a clinical tool for predicting risk of treatment resistance to antipsychotics in first-episode schizophrenia.

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    INTRODUCTION: Treatment-resistant schizophrenia (TRS) is associated with significant impairment of functioning and high treatment costs. Identification of patients at high risk of TRS at the time of their initial diagnosis may significantly improve clinical outcomes and minimise social and functional disability. We aim to develop a prognostic model for predicting the risk of developing TRS in patients with first-episode schizophrenia and to examine its potential utility and acceptability as a clinical decision tool. METHODS AND ANALYSIS: We will use two well-characterised longitudinal UK-based first-episode psychosis cohorts: Aetiology and Ethnicity in Schizophrenia and Other Psychoses and Genetics and Psychosis for which data have been collected on sociodemographic and clinical characteristics. We will identify candidate predictors for the model based on current literature and stakeholder consultation. Model development will use all data, with the number of candidate predictors restricted according to available sample size and event rate. A model for predicting risk of TRS will be developed based on penalised regression, with missing data handled using multiple imputation. Internal validation will be undertaken via bootstrapping, obtaining optimism-adjusted estimates of the model's performance. The clinical utility of the model in terms of clinically relevant risk thresholds will be evaluated using net benefit and decision curves (comparative to competing strategies). Consultation with patients and clinical stakeholders will determine potential thresholds of risk for treatment decision-making. The acceptability of embedding the model as a clinical tool will be explored using qualitative focus groups with up to 20 clinicians in total from early intervention services. Clinicians will be recruited from services in Stafford and London with the focus groups being held via an online platform. ETHICS AND DISSEMINATION: The development of the prognostic model will be based on anonymised data from existing cohorts, for which ethical approval is in place. Ethical approval has been obtained from Keele University for the qualitative focus groups within early intervention in psychosis services (ref: MH-210174). Suitable processes are in place to obtain informed consent for National Health Service staff taking part in interviews or focus groups. A study information sheet with cover letter and consent form have been prepared and approved by the local Research Ethics Committee. Findings will be shared through peer-reviewed publications, conference presentations and social media. A lay summary will be published on collaborator websites
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