Adaptable beam profiles from a dual-cavity Nd:YAG laser

We report a technique to tailor a laser beam profile from a donut to quasi-top-hat intensity distribution, directly from the laser, simply achieved by simultaneous excitation and control of the relative contributions of the fundamental (TEM00) and first order Laguerre-Gaussian (LG01) transverse modes. Exploiting a dual-cavity configuration with a single Nd:YAG gain element, adaptable continuous-wave laser beam profiles from the primary cavity could be obtained by varying the diffraction loss of an acousto-optic modulator in the secondary cavity. We investigated the resultant beam profiles as a function of pump power and the AOM diffraction loss, and discuss the prospects for tunable laser beams profiles

Cryogenically-cooled two-micron solid-state lasers: recent results and future prospects

Efficient powerful laser sources in the two-micron regime are in demand for many applications in the areas of remote-sensing, defence, medicine, and materials interactions. Recently, dramatic progress has been shown in scaling cw output power from 2-micron fibre lasers

Children As Researchers: Exploring Issues And Barriers In English Primary Schools

This thesis identifies and explores the issues and barriers that appear to influence children's and adults' experiences of children's engagement in self-directed empirical research in five English primary schools associated with the Children's Research Centre at The Open University. As far as is known, this is the first in-depth study of children as independent researchers in the context of English primary schools. A flexible, multimethod research design was adopted. Predominantly qualitative data was generated through focus groups held with, and questionnaires distributed to, the young researchers and their peers and through individual unstructured interviews with adults. The qualitative data generated through these methods was analysed in the style of Grounded Theory (Glaser and Strauss, 1967; Strauss and Corbin, 1998). Quantitative data was subject to exploratory data analysis. This complemented and informed the qualitative analyses. The central categories which emerged from the data and, in particular, the identification of important issues by the children, have together informed the staged construction of a new model. This model illustrates the factors and processes that had an impact on both the children's experiences of research training and the research process and outcomes. The model demonstrates that these are inextricably interrelated. It is hoped that consideration of the issues and barriers identified will provide a basis for the further implementation and evaluation of young researcher initiatives in schools. The findings of the study have been drawn on to make recommendations for policy, practice and future research, particularly in those areas which are identified as significant by, and to, the children involved. It is also hoped that this study will address a gap in our knowledge and understanding of children as researchers and inform critical debate concerning children's voice and participation, adult-child power relationships and children's rights in English primary schools and more widely

A versatile experimental hypothermic-hyperbaric oxygen chamber for whole organ preservation

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Gaussian limits for multidimensional random sequential packing at saturation (extended version)

Consider the random sequential packing model with infinite input and in any dimension. When the input consists of non-zero volume convex solids we show that the total number of solids accepted over cubes of volume $\lambda$ is asymptotically normal as $\lambda \to \infty$. We provide a rate of approximation to the normal and show that the finite dimensional distributions of the packing measures converge to those of a mean zero generalized Gaussian field. The method of proof involves showing that the collection of accepted solids satisfies the weak spatial dependence condition known as stabilization.Comment: 31 page

Effects of hydrostatic pressure on the magnetic susceptibility of ruthenium oxide Sr3Ru2O7: Evidence for pressure-enhanced antiferromagnetic instability

Hydrostatic pressure effects on the temperature- and magnetic field dependencies of the in-plane and out-of-plane magnetization of the bi-layered perovskite Sr3Ru2O7 have been studied by SQUID magnetometer measurements under a hydrostatic helium-gas pressure. The anomalously enhanced low-temperature value of the paramagnetic susceptibility has been found to systematically decrease with increasing pressure. The effect is accompanied by an increase of the temperature Tmax of a pronounced peak of susceptibility. Thus, magnetization measurements under hydrostatic pressure reveal that the lattice contraction in the structure of Sr3Ru2O7 promotes antiferromagnetism and not ferromagnetism, contrary to the previous beliefs. The effects can be explained by the enhancement of the inter-bi-layer antiferromagnetic spin coupling, driven by the shortening of the superexchange path, and suppression, due to the band-broadening effect, of competing itinerant ferromagnetic correlations.Comment: 11 pages, 4 figure

Adsorption of Line Segments on a Square Lattice

We study the deposition of line segments on a two-dimensional square lattice. The estimates for the coverage at jamming obtained by Monte-Carlo simulations and by $7^{th}$-order time-series expansion are successfully compared. The non-trivial limit of adsorption of infinitely long segments is studied, and the lattice coverage is consistently obtained using these two approaches.Comment: 19 pages in Latex+5 postscript files sent upon request ; PTB93_

h/e oscillations in interlayer transport of delafossites

Funding: This project was funded by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (grant no. 715730, MiTopMat) and also was supported by the Max Planck Society. A.P.M. and R.M. acknowledge support from the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter (EXC 2147). M.D.B., P.M., and V.S. acknowledge studentship funding from the EPSRC under grant no. EP/L015110/1. A.S. was supported by the Israel Science Foundation, the European Research Council (Project LEGOTOP), and the DFG through projectno.CRC-183. M.K. acknowledges support from the SIRIUS irradiation facility through project no. EMIR 2019 18-7099.Microstructures can be carefully designed to reveal the quantum phase of the wave-like nature of electrons in a metal. Here, we report phase-coherent oscillations of out-of-plane magnetoresistance in the layered delafossites PdCoO2 and PtCoO2 The oscillation period is equivalent to that determined by the magnetic flux quantum, h/e, threading an area defined by the atomic interlayer separation and the sample width, where h is Planck's constant and e is the charge of an electron. The phase of the electron wave function appears robust over length scales exceeding 10 micrometers and persisting up to temperatures of T > 50 kelvin. We show that the experimental signal stems from a periodic field modulation of the out-of-plane hopping. These results demonstrate extraordinary single-particle quantum coherence lengths in delafossites.PostprintPeer reviewe

Investigation of the ferromagnetic transition in the correlated 4d perovskites SrRu1−x_{1-x}Rhx_xO3_3

The solid-solution SrRu$_{1-x}$Rh$_x$O$_3$ ($0\le x \le1$) is a variable-electron-configuration system forming in the nearly-cubic-perovskite basis, ranging from the ferromagnetic 4$d^4$ to the enhanced paramagnetic 4$d^5$. Polycrystalline single-phase samples were obtained over the whole composition range by a high-pressure-heating technique, followed by measurements of magnetic susceptibility, magnetization, specific heat, thermopower, and electrical resistivity. The ferromagnetic order in long range is gradually suppressed by the Rh substitution and vanishes at $x \sim 0.6$. The electronic term of specific-heat shows unusual behavior near the critical Rh concentration; the feature does not match even qualitatively with what was reported for the related perovskites (Sr,Ca)RuO$_3$. Furthermore, another anomaly in the specific heat was observed at $x \sim 0.9$.Comment: Accepted for publication in PR