Galactic porosity and a star formation threshold for the escape of ionising radiation from galaxies

The spatial distribution of star formation within galaxies strongly affects the resulting feedback processes. Previous work has considered the case of a single, concentrated nuclear starburst, and also that of distributed single supernovae (SNe). Here, we consider ISM structuring by SNe originating in spatially distributed clusters having a cluster membership spectrum given by the observed HII region luminosity function. We show that in this case, the volume of HI cleared per SN is considerably greater than in either of the two cases considered hitherto. We derive a simple relationship between the ``porosity'' of the ISM and the star formation rate (SFR), and deduce a critical SFR_crit, at which the ISM porosity is unity. This critical value describes the case in which the SN mechanical energy output over a timescale t_e is comparable with the ISM ``thermal'' energy contained in random motions; t_e is the duration of SN mechanical input per superbubble. This condition also defines a critical gas consumption timescale t_exh, which for a Salpeter IMF and random velocities of \simeq 10 km s-1 is roughly 10e10 years. We draw a link between porosity and the escape of ionising radiation from galaxies, arguing that high escape fractions are expected if SFR >~ SFR_crit. The Lyman Break Galaxies, which are presumably subject to infall on a timescale < t_exh, meet this criterion, as is consistent with the significant leakage of ionising photons inferred in these systems. We suggest the utility of this simple parameterisation of escape fraction in terms of SFR for semi-empirical models of galaxy formation and evolution and for modeling mechanical and chemical feedback effects.Comment: Accepted to MNRAS. 11 pages, 1 figure; uses mn2e.cls (included

The Superbubble Size Distribution in the Interstellar Medium of Galaxies

We use the standard, adiabatic shell evolution to predict the size distribution N(R) for populations of OB superbubbles in a uniform ISM. We derive N(R) for simple cases of superbubble creation rate and mechanical luminosity function (MLF). For R < the characteristic radius R_e, N(R) is dominated by stalled objects, while for R>R_e it is dominated by growing objects. We also briefly investigate N(R) resulting from momentum-conserving shell evolution. We predict a peak in N(R) corresponding to individual SNRs. To estimate the MLF, we also examine evolutionary effects on the HII region luminosity function (HII LF), finding that for nebular luminosity fading as a power law in time, there is a minimum observed slope for the HII LFs. Comparison with the largely complete HI hole catalog for the SMC shows surprising agreement in the predicted and observed slope of N(R), suggesting that no other fundamental process is needed to explain the size distribution of shells in the SMC. Further comparison with largely incomplete HI data for M31, M33, and Holmberg II is also encouraging. We present expressions for the ISM porosity parameters, and estimate that they are substantially <1 for all of the galaxies except Holmberg II. Most of these galaxies therefore may not be strongly dominated by a hot interstellar component. However, porosity results for the Galaxy remain inconclusive.Comment: 25 pages, MN latex, 4 figures. MNRAS accepted. Complete abstract and preprint also available at http://ast.cam.ac.uk/~oey/oeypubs.htm

3D printing and high tibial osteotomy

High tibial osteotomy (HTO) is a relatively conservative surgical option in the management of medial knee pain. Thus far, the outcomes have been variable, and apparently worse than the arthroplasty alternatives when judged using conventional metrics, owing in large part to uncer - tainty around the extent of the correction planned and achieved. This review paper introduces the concept of detailed 3D planning of the procedure, and describes the 3D printing technology that enables the plan to be performed. The different ways that the osteotomy can be undertaken, and the varying guide designs that enable accurate regis - tration are discussed and described. The system accuracy is reported. In keeping with other assistive technologies, 3D printing enables the surgeon to achieve a preoperative plan with a degree of accuracy that is not possible using conventional instruments. With the advent of low dose CT, it has been possible to confirm that the procedure has been under - taken accurately too. HTO is the ‘ultimate’ personal intervention: the amount of correction needed for optimal offloading is not yet com - pletely understood. For the athletic person with early medial joint line over - load who still runs and enjoys life, HTO using 3D printing is an attractive option. The clinical effectiveness remains unproven

IT solutions for parcel deliveries with electric vehicles in Central London - Technology-based solution to facilitate efficient allocation and cross-carrier routing. Data Report

This data report contains the results of the second set of Agile Urban Logistics trials that were funded by the Mayor of London and delivered 2015 to 2017 by Gnewt Cargo in partnership with the University of Westminster. The Agile Urban Logistics project was delivered under the Mayor’s Smart London Demonstrator programme. The aim was to trial innovative solutions for the light freight sector that allows it to adapt to changing regulatory and market conditions, mitigating congestion and emissions impacts. Agile 2: IT solutions for parcel deliveries trial The trial was designed to test a range of IT solutions for electric fleet management, improving efficient client communication management and routing and planning systems

Agile Gnewt Cargo: parcels deliveries with electric vehicles in Central London Multi-carrier central London micro-consolidation and final delivery via low carbon vehicles. Data Report

This dataset contains the results of the first Agile Urban Logistics trials that were funded by the Mayor of London and delivered by Gnewt Cargo in partnership with the University of Westminster. The Agile Urban Logistics project was delivered under the Mayor’s Smart London Demonstrator programme. The aim was to trial innovative solutions for the light freight sector that allows it to adapt to changing regulatory and market conditions, mitigating congestion and emissions impacts. The three trials were: Agile 1: Multi-carrier consolidation trial In the Agile Gnewt Cargo trial, the demonstrator carried parcels for final delivery in central London for several major parcels businesses (namely Hermes, TNT and DX, all of which are active in business-to-consumer (B2C), home deliveries, and business-to-business (B2B) operations in London and the UK). The area covered focuses around the London Congestion charge area with a keen focus on the west side of this highly polluted region

Parcel deliveries with electric vehicles in Central London - Category 3: Single carrier consolidation centre targeting poor air quality zones enabling manual delivery methods. Data Report

This Data Report contains the data of the third set of Agile Urban Logistics trials that were funded by the Mayor of London and delivered by Gnewt Cargo in partnership with the University of Westminster in 2015 to 2017. The Agile Urban Logistics project was delivered under the Mayor’s Smart London Demonstrator programme. The aim was to trial innovative solutions for the light freight sector that allows it to adapt to changing regulatory and market conditions, mitigating congestion and emissions impacts. Agile 3: Single-carrier consolidation trial The trial explored scenarios for consolidating deliveries of multiple retail and non- retail clients using a single carrier (Gnewt Cargo) in a single van. All deliveries were done using electric vans. The aim of the trial was to reduce the number of delivery trips, reduce congestion and improve air quality outputs compared to a diesel equivalent approach by utilizing zero emissions electric freight delivery vehicles