Optical study of flow and combustion in an HCCI engine with negative valve overlap

One of the most widely used methods to enable Homogeneous Charge Compression Ignition (HCCI) combustion is using negative valve overlapping to trap a sufficient quantity of hot residual gas. The characteristics of air motion with specially designed valve events having reduced valve lift and durations associated with HCCI engines and their effect on subsequent combustion are not yet fully understood. In addition, the ignition process and combustion development in such engines are very different from those in conventional spark-ignition or diesel compression ignition engines. Very little data has been reported concerning optical diagnostics of the flow and combustion in the engine using negative valve overlapping. This paper presents an experimental investigation into the in-cylinder flow characteristics and combustion development in an optical engine operating in HCCI combustion mode. PIV measurements have been taken under motored engine conditions to provide a quantitative flow characterisation of negative valve overlap in-cylinder flows. The ignition and combustion process was imaged using a high resolution charge coupled device (CCD) camera and the combustion imaging data was supplemented by simultaneously recorded in-cylinder pressure data which assisted the analysis of the images. It is found that the flow characteristics with negative valve overlapping are less stable and more valve event driven than typical spark ignition in-cylinder flows, while the combustion initiation locations are not uniformly distributed. © 2006 IOP Publishing Ltd

Millimetre and submillimetre molecular line observations of the reflection nebula NGC 2023

Observations in the CO J = 2 - 1, CO J = 3 - 2 and HCO+ J = 4 - 3 transitions of the molecular cloud associated with NGC 2023 are presented. The observations reveal the complex structure of the gas in the surrounding cloud, and show the presence of several hot-spots which may represent separate bodies of gas. A search has been made for the source of excitation of two nearby groups of Herbig-Haro objects recently discovered by Malin et al. (1987). No such objects can be clearly identified from the data. CO J = 3 - 2 spectra taken at positions lying on the CO J = 1 - 0 shell observed by Gatley et al. (1987) show marked enhancements in peak line strength relative to coincident CO J = 2 - 1 data. By contrast, no such enhancements are observed away from the shell. Observations of the submillimeter wavelength HCO+ J = 4 - 3 transition show that the line strength is greatest in the vicinity of the shell structure. Simple large velocity gradient modeling of the excitation conditions of the shell material suggests that the gas may be hot (Tkin ~ 140 K), dense, and optically thin

Green cities and health: a question of scale?

<p><b>Background:</b> Cities are expanding and accommodating an increasing proportion of the world's population. It is important to identify features of urban form that promote the health of city dwellers. Access to green space has been associated with health benefits at both individual and neighbourhood level. We investigated whether a relationship between green space coverage and selected mortality rates exists at the city level in the USA.</p> <p><b>Methods:</b> An ecological cross-sectional study. A detailed land use data set was used to quantify green space for the largest US cities (n=49, combined population of 43 million). Linear regression models were used to examine the association between city-level ‘greenness’ and city-level standardised rates of mortality from heart disease, diabetes, lung cancer, motor vehicle fatalities and all causes, after adjustment for confounders.</p> <p><b>Results:</b> There was no association between greenness and mortality from heart disease, diabetes, lung cancer or automobile accidents. Mortality from all causes was significantly higher in greener cities.</p> <p><b>Conclusions:</b> While considerable evidence suggests that access to green space yields health benefits, we found no such evidence at the scale of the American city. In the USA, greener cities tend also to be more sprawling and have higher levels of car dependency. Any benefits that the green space might offer seem easily eclipsed by these other conditions and the lifestyles that accompany them. The result merits further investigation as it has important implications for how we increase green space access in our cities.</p&gt

The contribution of stakeholder involvement to policy making for sustainable development in National Parks

It is widely accepted that new governance structures are needed to support sustainable development, because of both the nature of the challenges faced, and the incapacity of existing modes of government to address them in a context of eroded legitimacy. A burgeoning range of participatory practices rests on an established orthodoxy that sustainable development requires increased public involvement in policy making. Alongside this, governance is increasingly characterised by partnership working with a wide range of stakeholders. However evidence suggests that radical policy ideas may be weakened rather than strengthened by deliberation, and there is as yet limited understanding of the effectiveness of different deliberative practices. The aim of the research was to examine this problem by analysing and comparing the contribution of different forms of stakeholder representation and involvement to the capacity of planning authorities to make the difficult choices and trade-offs implicit in implementing sustainable development. This was achieved through analysis of transport policy making within the Peak District National Park which allowed comparison between the effectiveness of ‘old’ and ‘new’ deliberative processes

An all-fibre PM MOPA pumped high-power OPO at 3.82 microns based on large aperture PPMgLN

We report a large aperture PPMgLN based OPO generating 21W of average output power at a slope efficiency of 45%, pumped by the output from a polarization maintaining Ytterbium doped fiber MOPA operating at 1060nm producing 58W of average output power and 20ns pulses at a repetition rate of 100kHz. A maximum of 5.5W of optical power was recorded at the idler wavelength of 3.82µm without thermal roll-off. We have experimentally verified that the pulse rise/fall time plays a significant role in the OPO conversion efficiency and that further enhancement in the OPO conversion efficiency will be possible using sub-nanosecond rise and fall times

Fast nonadiabatic dynamics of many-body quantum systems

Modeling many-body quantum systems with strong interactions is one of the core challenges of modern physics. A range of methods has been developed to approach this task, each with its own idiosyncrasies, approximations, and realm of applicability. However, there remain many problems that are intractable for existing methods. In particular, many approaches face a huge computational barrier when modeling large numbers of coupled electrons and ions at finite temperature. Here, we address this shortfall with a new approach to modeling many-body quantum systems. On the basis of the Bohmian trajectory formalism, our new method treats the full particle dynamics with a considerable increase in computational speed. As a result, we are able to perform large-scale simulations of coupled electron-ion systems without using the adiabatic Born-Oppenheimer approximation

A submillimetre wavelength spectral line search of the Orion molecular cloud core

A submillimetre wavelength molecular line search of the Orion molecular cloud has been made covering a total of about 5 percent of the frequency range 342.8 - 358.6 GHz. This search, coupled with the authors' previous observations of submillimetre transitions in this cloud, has led to the detection of 22 transitions of 14 molecular species, of which 16 are reported here for the first time. No unidentified lines have been detected in the present search. Mapping observations have been obtained for several of the lines and, in the case of H2CO the authors have been able to compare the present data with that obtained from other telescopes, to estimate the density and abundance in the emitting region