Spin dynamics simulations of the magnetic dynamics of RbMnF3_3 and direct comparison with experiment

Spin-dynamics techniques have been used to perform large-scale simulations of the dynamic behavior of the classical Heisenberg antiferromagnet in simple cubic lattices with linear sizes $L\leq 60$. This system is widely recognized as an appropriate model for the magnetic properties of RbMnF$_3$. Time-evolutions of spin configurations were determined numerically from coupled equations of motion for individual spins using a new algorithm implemented by Krech {\it etal}, which is based on fourth-order Suzuki-Trotter decompositions of exponential operators. The dynamic structure factor was calculated from the space- and time-displaced spin-spin correlation function. The crossover from hydrodynamic to critical behavior of the dispersion curve and spin-wave half-width was studied as the temperature was increased towards the critical temperature. The dynamic critical exponent was estimated to be $z=(1.43\pm 0.03)$, which is slightly lower than the dynamic scaling prediction, but in good agreement with a recent experimental value. Direct, quantitative comparisons of both the dispersion curve and the lineshapes obtained from our simulations with very recent experimental results for RbMnF$_3$ are presented.Comment: 30 pages, RevTex, 9 figures, to appear in PR

Theoretical analysis of neutron scattering results for quasi-two dimensional ferromagnets

A theoretical study has been carried out to analyse the available results from the inelastic neutron scattering experiment performed on a quasi-two dimensional spin-1/2 ferromagnetic material $K_2CuF_4$. Our formalism is based on a conventional semi-classical like treatment involving a model of an ideal gas of vortices/anti-vortices corresponding to an anisotropic XY Heisenberg ferromagnet on a square lattice. The results for dynamical structure functions for our model corresponding to spin-1/2, show occurrence of negative values in a large range of energy transfer even encompassing the experimental range, when convoluted with a realistic spectral window function. This result indicates failure of the conventional theoretical framework to be applicable to the experimental situation corresponding to low spin systems. A full quantum formalism seems essential for treating such systems.Comment: 16 pages, 6 figures, 1 Table Submitted for publicatio

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Quasi-elastic neutron scattering from liquid gallium over the temperature range 163 to 333 K

Using a triple axis spectrometer we have measured the quasi-elastic scattering from liquid gallium droplets down to near the lowest temperature T L = 150 K at which the liquid remains in the supercooled state. Special reference was given to values of the wave-vector Q0 = 2.50 Å-1 and Q00 = 3.12 Å-1 corresponding respectively to the mean peak and the shoulder in the structure factor S(Q). At Q0 the full width at half height of the Lorentzian profile fitting the quasi-elastic peak is found to vary linearly with temperature below 333 K, with a rate equal to 0.001 6 ± 0.000 2 THz. K-1 approaching a zero value at T = 157 ± 10 K which we associate with the metastability limit of the liquid state.A l'aide d'un spectromètre à trois axes, nous avons étudié la diffusion quasi élastique de gouttelettes de gallium liquide jusqu'à des températures proches de la température minimale TL = 150 K à laquelle le liquide peut être maintenu en surfusion. Les mesures ont été essentiellement effectuées au voisinage des valeurs du vecteur d'onde Q0 = 2,50 Å-1 et Q00 = 3,12 Å-1 où le facteur de structure S(Q) présente respectivement un maximum principal et un épaulement. A Q0, la largeur à mi-hauteur du pic quasi élastique, bien représenté par une Lorentzienne, décroît linéairement en fonction de la température avec une pente égale à 0,001 6 ± 0,000 2 THz .K-1 et tend vers zéro à la température T = 157 ± 10 K. Cette température peut être considérée comme étant la limite en dessous de laquelle le liquide devient instable