Measurement of representative landfill gas migration samples at landfill perimeters: a case study

This paper describes the development of a fully integrated autonomous system based on existing infrared sensing technology capable of monitoring landfill gas migration (specifically carbon dioxide and methane) at landfill sites. Sampling using the described system was validated against the industry standard, GA2000 Plus hand held device, manufactured by Geotechnical Instruments Inc. As a consequence of repeated sampling during validation experiments, fluctuations in the gas mixtures became apparent. This initiated a parallel study into what constitutes a representative sample of landfill gas migration as reported to the Environmental Protection Agency. The work described in this paper shows that gas mixture concentrations change with depth of extraction from the borehole well, but with evidence of a steady state after a time

Monitoring of gas emissions at landfill sites using autonomous gas sensors

Executive Summary This report details the work carried out during the Smart Plant project (2005-AIC-MS-43-M4). As part of this research, an autonomous platform for monitoring greenhouse gases (methane (CH4), carbon dioxide (CO2)) has been developed, prototyped and field validated. The modular design employed means that the platform can be readily adapted for a variety of applications involving these and other target gases such as hydrogen sulfide (H2S), ammonia (NH3) and carbon monoxide (CO) and the authors are in the process of completing several short demonstrator projects to illustrate the potential of the platform for some of these applications. The field validation for the greenhouse gas monitoring platform was carried out at two landfill sites in Ireland. The unit was used to monitor the concentration of CO2 and CH4 gas at perimeter borehole wells. The final prototype was deployed for over 4 months and successfully extracted samples from the assigned perimeter borehole well headspace, measured them and sent the data to a database via a global system for mobile (GSM) communications. The data were represented via an updating graph in a web interface. Sampling was carried out twice per day, giving a 60-fold increase on current monitoring procedures which provide one gas concentration measurement per month. From additional work described in this report, a number of conclusions were drawn regarding lateral landfill gas migration on a landfill site and the management of this migration to the site’s perimeter. To provide frequent, reliable monitoring of landfill gas migration to perimeter borehole wells, the unit needs to: • Be fully autonomous; • Be capable of extracting a gas sample from a borehole well independently of personnel; • Be able to relay the data in near real time to a base station; and • Have sensors with a range capable of adequately monitoring gas events accurately at all times. The authors believe that a unit capable of such monitoring has been developed and validated. This unit provides a powerful tool for effective management of landfill site gases. The effectiveness of this unit has been recognised by the site management team at the long-term deployment trial site, and the data gathered have been used to improve the day-to-day operations and gas management system on-site. The authors make the following recommendations: 1. The dynamics of the landfill gas management system cannot be captured by taking measurements once per month; thus, a minimum sampling rate of once per day is advised. 2. The sampling protocol should be changed: (i) Borehole well samples should not be taken from the top of the well but should be extracted at a depth within the headspace (0.5–1.0 m). The measurement depth will be dependent on the water table and headspace depth within the borehole well. (ii) The sampling time should be increased to 3 min to obtain a steady-state measurement from the headspace and to take a representative sample; and (iii) For continuous monitoring on-site, the extracted sample should be recycled back into the borehole well. However, for compliance monitoring, the sample should not be returned to the borehole well. 3. Devices should be placed at all borehole wells so the balance on the site can be maintained through the gas management system and extraction issues can be quickly recognised and addressed before there are events of high gas migration to the perimeter. 4. A pilot study should be carried out by the EPA using 10 of these autonomous devices over three to five sites to show the need and value for this type of sampling on Irish landfill sites

Memorie di guerra. Verso la riapertura del Bunker della Prefettura e della Torre delle Sirene di Milano

L’articolo tratta del percorso avviato da Città Metropolitana di Milano, in sinergia con il Politecnico di Milano, per restituire alla cittadinanza la Torre delle Sirene – sede della centrale di comando dell’allarme antiaereo della città di Milano – e il Bunker della Prefettura. Si tratta di due manufatti, comunicanti tra loro, particolarmente significativi per il ricordo della seconda guerra mondiale e, soprattutto, della vita quotidiana dei civili sotto assedio, condizione che ancora oggi accomuna numerose popolazioni nel mondo. Entrambi gli edifici sono in stato di abbandono e degrado da diversi anni, ma permangono ancora diverse tracce del passato utilizzo. Il percorso di riapertura appare oggi complesso, sia per i caratteri tecno-tipologici e localizzativi, che per la mancanza di risorse dedicate. L’obiettivo è la trasformazione dell’ex-centro nevralgico del sistema milanese di allerta antiaerea, in epicentro di un nuovo sistema di allerta collettivo sul tema della guerra, che operi proprio attraverso la memoria degli eventi passati. Inoltre, questo potrebbe divenire il polo del più ampio e diffuso sistema del patrimonio dei rifugi cittadini: un network di beni tangibili e intangibili, organizzati secondo una logica comune di valorizzazione della memoria, per far crescere la cultura della pace e realizzare un itinerario culturale nella città fondato sui valori della Storia.The paper concerns the project, promoted by Metropolitan city and Polytechnic university of Milan, of returning to public use Torre delle Sirene – seat of the Milan air-raid alert control unit – and Bunker della Prefettura. Two buildings connected to each other and very significant as memories of the Second World War and, most of all, of the ordinary life of civilian people under siege, a condition still regarding so many people around the world at present. Both the buildings have been neglected and deteriorated since a few years, but they still preserve traces of the past use. The reopening project is difficult due both to the typological and location characters of the buildings and to the lack of available financial resources. The objective of the project is to transform the former central point of the air-raid defence system into the epicentre of a new collective alert system on the topic of war, operating through memories of the past. Moreover, this could become the centre of a wider and widespread heritage system of local air-raid shelters: a network of material and immaterial goods organized by the common logic of enhancing memory, in order to strengthen the culture of peace and realize in the city a cultural itinerary based on historical values

Effects of multiscale geometry on the large-scale coherent structures of an axisymmetric turbulent jet

In this study, the effect of multiscale geometry on the near-field structure of an axisymmetric turbulent jet is examined at a global Reynolds number of ReG=10,000. With the aid of tomographic particle image velocimetry, the suppression of the coherent structures due to this fractal geometry is analysed and the changes to the near-field vorticity are evaluated. This particular geometry leads to the breakup of the azimuthal vortex rings present for round jets and to the formation of radial and streamwise opposite-signed patches of vorticity. The latter are found to be responsible for the axis switching of the jet, a phenomenon observed for some noncircular jets where the major axis shrinks and the minor one expands in the near field, effectively switching the two axes of the jet. This was the first time, to the knowledge of the authors, that axis switching has been observed for a jet where the coherent structures have been suppressed. Following the significant differences found in the near field, the far field is examined. There, the integral lengthscale of the large scale eddies Lur and the size of the jet evaluated in terms of the jet half-width r1/2 are found to evolve in a similar fashion, whilst the ratio Lur/r1/2 is found to be higher for the fractal jet than for the round jet, for which the near-field structures have not been suppressed

Autonomous greenhouse gas measurement system for analysis of gas migration on landfill sites

This paper describes the design, development and validation of an autonomous gas sensing platform prototype for monitoring of the greenhouse gases, methane (CH4) and carbon dioxide (CO2). The deployment undertaken for validation of the developed prototype monitored landfill gas migration to perimeter borehole wells on a landfill site. Target gas concentrations were captured via infrared gas sensors tuned for each target gas and data reported to an offsite data collection point at 12 hour intervals. This bespoke platform and the accompanying data recording and interface software provide a flexible alternative to the presently employed labor intensive, manual monitoring routines. This successful trial brought about a change in the management of the trial sites gas extraction system

Stability of Linear Continuous-Time Systems with Stochastically Switching Delays

Necessary and sufficient conditions for the stability of linear continuous-time systems with stochastically switching delays are presented in this paper. It is assumed that the delay random paths are piece-wise constant functions of time where a finite number of values may be taken by the delay. The stability is assessed in terms of the second moment of the state vector of the system. The solution operators of individual linear systems with constant de- lays, chosen from the set of all possible delay values, are extended to form new augmented operators. Then for proper formulation of the second moment in continuous time, tensor products of the augmented solution operators are used. Finally the finite-dimensional versions of the stability conditions, that can be obtained using various time discretization techniques, are presented. Some examples are provided that demonstrate how the stability conditions can be used to assess the stability of linear systems with stochastic delay

Invariants of the velocity gradient tensor in a spatially developing inhomogeneous turbulent flow

Tomographic PIV experiments were performed in the near-fiel d of the turbulent flow past a square cylinder. A classical Reynolds decomposition was p erformed on the resulting velocity fields into a time invariant mean flow and a fluctuatin g velocity field. This fluc- tuating velocity field was then further decomposed into cohe rent and residual/stochastic fluctuations. The statistical distributions of the second a nd third invariants of the ve- locity gradient tensor were then computed at various stream wise locations, along the centre line of the flow and within the shear layers. These inva riants were calculated from both the Reynolds-decomposed fluctuating velocity fields an d the coherent and stochas- tic fluctuating velocity fields. The range of spatial locatio ns probed incorporates regions of contrasting flow physics, including a mean recirculation region and separated shear layers, both upstream and downstream of the location of peak turbulence intensity along the centre line. These different flow physics are also reflecte d in the velocity gradients themselves with different topologies, as characterised by t he statistical distributions of the constituent enstrophy and strain-rate invariants, for the three different fluctuating velocity fields. Despite these differing flow physics the ubiq uitous self-similar “tear drop”- shaped joint probability density function between the seco nd and third invariants of the velocity gradient tensor is observed along the centre line a nd shear layer when calcu- lated from both the Reynolds decomposed and the stochastic v elocity fluctuations. These “tear drop”-shaped joint probability density functions ar e not, however, observed when calculated from the coherent velocity fluctuations. This “t ear drop” shape is classically associated to the statistical distribution of the velocity gradient tensor invariants in fully developed turbulent flows in which there are no coherent dyna mics present, and hence spectral peaks at low wavenumbers. The results presented in this manuscript, however, show that such “tear drops” also exist in spatially developi ng inhomogeneous turbulent flows. This suggests that the “tear drop” shape may not just be a universal feature of fully developed turbulence but of turbulent flows in general

Packing of R3 by crosses

The existence of tilings of R^n by crosses, a cluster of unit cubes comprising a central one and 2n arms, has been studied by several authors. We have completely solved the problem for R^2, characterizing the crosses which lattice tile R^2, as well as determining the maximum packing density for the crosses which do not lattice tile the plane. In this paper we motivate a similar approach to study lattice packings of R^3 by crosses.The existence of tilings of Rn by crosses, a cluster of unit cubes comprising a central one and 2n arms, has been studied by several authors. We have completely solved the problem for R2 characterizing the crosses which lattice tile R2 as well as determining the maximum packing density for the crosses which do not lattice tile the plane. In this paper we motivate a similar approach to study lattice packings of R3 by crosses.publishe