The effect of a forepole umbrella system on the stability of a tunnel face in clay

A new series of three-dimensional centrifuge model tests using soft clay has been conducted using the geotechnical centrifuge facility at City University London. These tests aim to quantify the reinforcing proficiency of different arrangements of steel pipes in a Forepoling Umbrella System (FUS). The results highlight some interesting effects of the FUS on tunnel stability and the spread of ground movements in the vicinity of the tunnel heading

Design and development of a large shear box for testing working platform material

On large construction projects where deep foundations are to be installed, a working platform is placed across the entire site. This is comprised of a layer of aggregate (often crushed construction waste) usually with a particle size ranging from 120 mm downwards. Deep foundations are installed using heavy and tall drilling rigs and the working platform is thus safety critical to reduce the risk of machinery sinking and/or toppling which would lead to accidents and often serious injury to workers. Currently available design guidance is felt to result in conservative designs and there are many benefits to be gained from a greater understanding of the behaviour of working platform material. The design of these platforms is primarily governed by the angle of friction of the platform material. The measurement of friction angle for geomaterials that have large particle sizes is problematic (due to reasons of scale) and is often addressed by scaling down the material's grading curve prior to testing in small to medium size direct shear apparatus. The work presented here details the design of and the rationale for a large scale direct shear apparatus suitable for testing geomaterials with particle size distributions of the type that would be utilised in working platforms

Plans, Preferences or Going with the Flow: an Online Exploration of Women’s Views and Experiences of Birth Plans

Objective To explore women’s views of birth plans, and experiences of their completion and use. Design A qualitative, exploratory study, using Internet-mediated research methods. Setting The discussion boards of two well-known, UK-based, online parenting forums, where a series of questions relating to birth plans were posted. Participants Members of the selected parenting forums who had written and used, or who had chosen not to write or use, a birth plan. Findings Women responded with a range of views and experiences relating to the completion and use of birth plans. The benefits of birth plans were described in terms of communication with healthcare professionals, potentially enhancing awareness of available options, and maintaining a sense of control during labour and birth. However, many respondents believed the idea of ‘planning’ birth was problematic, and described a reluctance to write a formal plan. The support of healthcare professionals, particularly midwives, was considered essential to the success of both writing and using birth plans. Key conclusions Our findings show a continued debate among women on the benefits and challenges involved in writing and using birth plans, suggesting problems for a ‘one size fits all’ approach often seen in the use of birth plan templates. In the context of maternity policy supporting women’s choice and personalised care, and as a way of acknowledging perceived problems of ‘planning’ for birth, a flexible approach to birth plans is required, including the consideration of employing alternative nomenclature. Implications for practice Birth plans remain a point of contention in care contexts around the world. Midwives and other healthcare providers play a central role in supporting women to discuss available options, whether or not they decide to complete a formal birth plan

Enhanced He-alpha emission from "smoked" Ti targets irradiated with 400nm, 45 fs laser pulses

We present a study of He-like 1s(2)-1s2p line emission from solid and low-density Ti targets under similar or equal to 45 fs laser pulse irradiation with a frequency doubled Ti: Sapphire laser. By varying the beam spot, the intensity on target was varied from 10(15) W/cm(2) to 10(19) W/cm(2). At best focus, low density "smoked" Ti targets yield similar to 20 times more He-alpha than the foil targets when irradiated at an angle of 45 degrees with s-polarized pulses. The duration of He-alpha emission from smoked targets, measured with a fast streak camera, was similar to that from Ti foils

Pathways to ethnic inequalities in COVID-19 health outcomes in the United Kingdom: A systematic map

Background Marked ethnic inequalities in COVID-19 infection and its consequences have been documented. The aim of this paper is to identify the range and nature of evidence on potential pathways which lead to ethnic inequalities in COVID-19 related health outcomes in the United Kingdom (UK). Methods We searched six bibliographic and five grey literature databases from 1st December 2019 to 23rd February 2022 for research on pathways to ethnic inequalities in COVID-19 health outcomes in the UK. Meta-data were extracted and coded, using a framework informed by a logic model. Open Science Framework Registration: DOI 10.17605/OSF.IO/HZRB7. Results The search returned 10,728 records after excluding duplicates, with 123 included (83% peer-reviewed). Mortality was the most common outcome investigated (N = 79), followed by infection (N = 52). The majority of studies were quantitative (N = 93, 75%), with four qualitative studies (3%), seven academic narrative reviews (6%), nine third sector reports (7%) and five government reports (4%), and four systematic reviews or meta-analyses (3%). There were 78 studies which examined comorbidities as a pathway to mortality, infection, and severe disease. Socioeconomic inequalities (N = 67) were also commonly investigated, with considerable research into neighbourhood infrastructure (N = 38) and occupational risk (N = 28). Few studies examined barriers to healthcare (N = 6) and consequences of infection control measures (N = 10). Only 11% of eligible studies theorised racism to be a driver of inequalities and 10% (typically government/third sector reports and qualitative studies) explored this as a pathway. Conclusion This systematic map identified knowledge clusters that may be amenable to subsequent systematic reviews, and critical gaps in the evidence-base requiring additional primary research. Most studies do not incorporate or conceptualise racism as the fundamental cause of ethnic inequalities and therefore the contribution to literature and policy is limited

Atomic excitation during recollision-free ultrafast multi-electron tunnel ionization

Modern intense ultrafast pulsed lasers generate an electric field of sufficient strength to permit tunnel ionization of the valence electrons in atoms. This process is usually treated as a rapid succession of isolated events, in which the states of the remaining electrons are neglected. Such electronic interactions are predicted to be weak, the exception being recollision excitation and ionization caused by linearly-polarized radiation. In contrast, it has recently been suggested that intense field ionization may be accompanied by a two-stage `shake-up' reaction. Here we report a unique combination of experimental techniques that enables us to accurately measure the tunnel ionization probability for argon exposed to 50 femtosecond laser pulses. Most significantly for the current study, this measurement is independent of the optical focal geometry, equivalent to a homogenous electric field. Furthermore, circularly-polarized radiation negates recollision. The present measurements indicate that tunnel ionization results in simultaneous excitation of one or more remaining electrons through shake-up. From an atomic physics standpoint, it may be possible to induce ionization from specific states, and will influence the development of coherent attosecond XUV radiation sources. Such pulses have vital scientific and economic potential in areas such as high-resolution imaging of in-vivo cells and nanoscale XUV lithography.Comment: 17 pages, 4 figures, original format as accepted by Nature Physic

The PHIN photoinjector for the CTF3 Drive beam

A new photoinjector for the CTF3 drive beam has been designed and is now being constructed by a collaboration among LAL, CCLRC and CERN within PHIN, the second Joint Research Activity of CARE. The photoinjector will provide a train of 2332 pulses at 1.5 GHz with a complex timing structure (sub-trains of 212 pulses spaced from one another by 333 ps or 999 ps) to allow the frequency multiplication scheme, which is one of the features of CLIC, to be tested in CTF3. Each pulse of 2.33 nC will be emitted by a Cs2Te photocathode deposited by a co-evaporation process to allow high quantum efficiency in operation (>3% for a minimum of 40 h). The 3 GHz, 2 1/2 cell RF gun has a 2 port coupler to minimize emittance growth due to asymmetric fields, racetrack profile of the irises and two solenoids to keep the emittance at the output below 20 p.mm.mrad. The laser has to survive very high average powers both within the pulse train (15 kW) and overall (200 W before pulse slicing). Challenging targets are also for amplitude stability (<0.25% rms) and time jitter from pulse to pulse (<1ps rms). An offline test in a dedicated line is foreseen at CERN in 2007

First Results from Commissioning of the Phin Photo Injector for CTF3

Installation of the new photo-injector for the CTF3 drive beam (PHIN) has been completed on a stand-alone test bench. The photo-injector operates with a 2.5 cell RF gun at 3 GHz, using a Cs2Te photocathode illuminated by a UV laser beam. The test bench is equipped with transverse beam diagnostic as well as a 90-degree spectrometer. A grid of 100 micrometer wide slits can be inserted for emittance measurements. The laser used to trigger the photo-emission process is a Nd:YLF system consisting of an oscillator and a preamplifier operating at 1.5 GHz and two powerful amplifier stages. The infrared radiation produced is frequency quadrupled in two stages to obtain the UV. A Pockels cell allows adjusting the length of the pulse train between 50 nanoseconds and 50 microseconds. The nominal train length for CTF3 is 1.272 microseconds (1908 bunches). The first electron beam in PHIN was produced in November 2008. In this paper, results concerning the operation of the laser system and measurements performed to characterize the electron beam are presented

Relativistic plasma surfaces as an efficient second harmonic generator

We report on the characterization of the specular reflection of 50 fs laser pulses in the intensity range 10(17)-10(21)Wcm(-2) obliquely incident with p-polarization onto solid density plasmas. These measurements show that the absorbed energy fraction remains approximately constant and that second harmonic generation (SHG) achieves efficiencies of 22 +/- 8% for intensities approaching 10(21)Wcm(-2). A simple model based on the relativistic oscillating mirror concept reproduces the observed intensity scaling, indicating that this is the dominant process involved for these conditions. This method may prove to be superior to SHG by sum frequency mixing in crystals as it is free from dispersion and retains high spatial coherence at high intensity