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

Sliding blocks with random friction and absorbing random walks

With the purpose of explaining recent experimental findings, we study the distribution $A(\lambda)$ of distances $\lambda$ traversed by a block that slides on an inclined plane and stops due to friction. A simple model in which the friction coefficient $\mu$ is a random function of position is considered. The problem of finding $A(\lambda)$ is equivalent to a First-Passage-Time problem for a one-dimensional random walk with nonzero drift, whose exact solution is well-known. From the exact solution of this problem we conclude that: a) for inclination angles $\theta$ less than \theta_c=\tan(\av{\mu}) the average traversed distance \av{\lambda} is finite, and diverges when $\theta \to \theta_c^{-}$ as \av{\lambda} \sim (\theta_c-\theta)^{-1}; b) at the critical angle a power-law distribution of slidings is obtained: $A(\lambda) \sim \lambda^{-3/2}$. Our analytical results are confirmed by numerical simulation, and are in partial agreement with the reported experimental results. We discuss the possible reasons for the remaining discrepancies.Comment: 8 pages, 8 figures, submitted to Phys. Rev.

Differential Cross Section for Higgs Boson Production Including All-Orders Soft Gluon Resummation

The transverse momentum $Q_T$ distribution is computed for inclusive Higgs boson production at the energy of the CERN Large Hadron Collider. We focus on the dominant gluon-gluon subprocess in perturbative quantum chromodynamics and incorporate contributions from the quark-gluon and quark-antiquark channels. Using an impact-parameter $b$-space formalism, we include all-orders resummation of large logarithms associated with emission of soft gluons. Our resummed results merge smoothly at large $Q_T$ with the fixed-order expectations in perturbative quantum chromodynamics, as they should, with no need for a matching procedure. They show a high degree of stability with respect to variation of parameters associated with the non-perturbative input at low $Q_T$. We provide distributions $d\sigma/dy dQ_T$ for Higgs boson masses from $M_Z$ to 200 GeV. The average transverse momentum at zero rapidity $y$ grows approximately linearly with mass of the Higgs boson over the range $M_Z < m_h \simeq 0.18 m_h + 18$~GeV. We provide analogous results for $Z$ boson production, for which we compute $\simeq 25$ GeV. The harder transverse momentum distribution for the Higgs boson arises because there is more soft gluon radiation in Higgs boson production than in $Z$ production.Comment: 42 pages, latex, 26 figures. All figures replaced. Some changes in wording. Published in Phys. Rev. D67, 034026 (2003

Thinking about growth : a cognitive mapping approach to understanding small business development

School of Managemen

Comparison of three wet-alkaline methods of digestion of biogenic silica in water

Methods for determination of low levels of biogenic silica (0.2–0.4 mg SiO 2 ) in aqueous samples after digestion with three wetalkaline extraction procedures compared favourably in both precision of replicates and recovery of silica utilized by diatoms in budgeted cultures. Leaching samples with 0.2 M NaOH for 10–15 min at 100°C was the least time consuming procedure. Also interference from silicate minerals was lower for this method than leaching with either 0.5 or 5% Na 2 CO 3 for 2 h at 85°C. The use of filters to concentrate samples enables detection of low levels of biogenic silica with colorimetric procedures. Polycarbonate filters are recommended in preference to cellulose acetate or polyvinyl chloride filters for sample collection. Time-course experiments are recommended for establishing digestion times and determining the presence of mineral silicate interference. Wet-alkaline digestion methods are recommended for routine analysis of biogenic silica in suspended matter in preference to infra-red analysis, alkaline fusion and hydrofluoric acid/nitric acid methods.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74725/1/j.1365-2427.1983.tb00658.x.pd

Surface finishing of intricate metal mould structures by large-area electron beam irradiation

The advancement of polymer moulding tools is increasingly focused on imparting not only form but also surface texture for functionality to the surfaces of parts that are created. Furthermore, the increasing demand for inexpensive and higher quality micro-components means that tools for replication processes must take advantage of advanced manufacturing techniques. Tools created by processes such as micro-investment casting, as in this case, may often suffer from excessive surface roughness, malformed edges and general deformation. This results in higher de-moulding forces and a reduction in fidelity of moulded parts to design intent. In this study, large-area electron beam irradiation (EB) is shown to be an effective technique for improving these metrics. For the first time, large population, high aspect ratio micro-features are subject to this process and the mechanisms of smoothing and key enhancement phenomena are demonstrated. The possibility of including EB irradiation in an integrated process chain for arriving at net shape is also discussed. Surfaces of protruding features are shown to have surface roughness reduced significantly from 126 to 22 nm Ra value, with bottom substrate also similarly improving from 150 to 27 nm Ra. Bottoms of recessed features are also observed to have much improved surface finishes. ‘Doming’ of tops of column features is also demonstrated, further enhancing form. These features would be far too fragile to be polished by any other mechanical method