4,671 research outputs found
Constructed wetlands: Treatment of concentrated storm water runoff (part A)
The aim of this research was to assess the treatment efficiencies for gully pot liquor of experimental vertical-
flow constructed wetland filters containing Phragmites australis (Cav.) Trin. ex Steud. (common
reed) and filter media of different adsorption capacities. Six out of 12 filters received inflow water spiked
with metals. For 2 years, hydrated nickel and copper nitrate were added to sieved gully pot liquor to simulate
contaminated primary treated storm runoff. For those six constructed wetland filters receiving heavy
metals, an obvious breakthrough of dissolved nickel was recorded after road salting during the first winter.
However, a breakthrough of nickel was not observed, since the inflow pH was raised to eight after
the first year of operation. High pH facilitated the formation of particulate metal compounds such as nickel
hydroxide. During the second year, reduction efficiencies of heavy metal, 5-days at 20°C N-Allylthiourea
biochemical oxygen demand (BOD) and suspended solids (SS) improved considerably. Concentrations of
BOD were frequently ïżœ20 mg/L. However, concentrations for SS were frequently ïżœ30 mg/L. These are
the two international thresholds for secondary wastewater treatment. The BOD removal increased over
time due to biomass maturation, and the increase of pH. An analysis of the findings with case-based reasoning
can be found in the corresponding follow-up paper (Part B)
Joint Access-Backhaul Perspective on Mobility Management in 5G Networks
The ongoing efforts in the research development and standardization of 5G, by
both industry and academia, have resulted in the identification of enablers
(Software Defined Networks, Network Function Virtualization, Distributed
Mobility Management, etc.) and critical areas (Mobility management,
Interference management, Joint access-backhaul mechanisms, etc.) that will help
achieve the 5G objectives. During these efforts, it has also been identified
that the 5G networks due to their high degree of heterogeneity, high QoS demand
and the inevitable density (both in terms of access points and users), will
need to have efficient joint backhaul and access mechanisms as well as enhanced
mobility management mechanisms in order to be effective, efficient and
ubiquitous. Therefore, in this paper we first provide a discussion on the
evolution of the backhaul scenario, and the necessity for joint access and
backhaul optimization. Subsequently, and since mobility management mechanisms
can entail the availability, reliability and heterogeneity of the future
backhaul/fronthaul networks as parameters in determining the most optimal
solution for a given context, a study with regards to the effect of future
backhaul/fronthaul scenarios on the design and implementation of mobility
management solutions in 5G networks has been performed.Comment: IEEE Conference on Standards for Communications & Networking,
September 2017, Helsinki, Finlan
Costs and benefits of superfast broadband in the UK
This paper was commissioned from LSE Enterprise by Convergys Smart Revenue Solutions to stimulate an open and constructive debate among the main stakeholders about the balance between the costs, the revenues, and the societal benefits of âsuperfastâ broadband. The intent has been to analyse the available facts and to propose wider perspectives on economic and social interactions. The paper has two parts: one concentrates on superfast broadband deployment and the associated economic and social implications (for the UK and its service providers), and the other considers alternative social science approaches to these implications. Both parts consider the potential contribution of smart solutions to superfast broadband provision and use. Whereas Part I takes the ânational perspectiveâ and the âservice provider perspectiveâ, which deal with the implications of superfast broadband for the UK and for service providers, Part II views matters in other ways, particularly by looking at how to realise values beyond the market economy, such as those inherent in neighbourliness, trust and democrac
Modeling and optimization of hybrid solar thermoelectric systems with thermosyphons
We present the modeling and optimization of a new hybrid solar thermoelectric (HSTE) system which uses a thermosyphon to passively transfer heat to a bottoming cycle for various applications. A parabolic trough mirror concentrates solar energy onto a selective surface coated thermoelectric to produce electrical power. Meanwhile, a thermosyphon adjacent to the back side of the thermoelectric maintains the temperature of the cold junction and carries the remaining thermal energy to a bottoming cycle. Bismuth telluride, lead telluride, and silicon germanium thermoelectrics were studied with copperâwater, stainless steelâmercury, and nickelâliquid potassium thermosyphon-working fluid combinations. An energy-based model of the HSTE system with a thermal resistance network was developed to determine overall performance. In addition, the HSTE system efficiency was investigated for temperatures of 300â1200 K, solar concentrations of 1â100 suns, and different thermosyphon and thermoelectric materials with a geometry resembling an evacuated tube solar collector. Optimizations of the HSTE show ideal system efficiencies as high as 52.6% can be achieved at solar concentrations of 100 suns and bottoming cycle temperatures of 776 K. For solar concentrations less than 4 suns, systems with thermosyphon wall thermal conductivities as low as 1.2 W/mK have comparable efficiencies to that of high conductivity material thermosyphons, i.e. copper, which suggests that lower cost materials including glass can be used. This work provides guidelines for the design, as well as the optimization and selection of thermoelectric and thermosyphon components for future high performance HSTE systems.United States. Dept. of Energy. Office of Basic Energy Sciences (MIT S3TEC Center, an Energy Frontier Research Center)Natural Sciences and Engineering Research Council of Canad
Abundance distributions over the surfaces of magnetic ApBp stars: theoretical predictions
Recently published empirical abundance maps, obtained through (Zeeman)
Doppler mapping (ZDM), do not currently agree with the abundance structures
predicted by means of numerical models of atomic diffusion in magnetic
atmospheres of ApBp stars. In a first step towards the resolution of these
discrepancies, we present a state of the art grid of equilibrium abundance
stratifications in the atmosphere of a magnetic Ap star with T_eff = 10000 K
and log g = 4.0. A description of the behaviour of 16 chemical elements
including predictions concerning the over- and/or under-abundances over the
stellar surface is followed by a discussion of the possible influence of
presently neglected physical processes.Comment: 8 pages. To be published in Monthly Notices of the Royal Astronomical
Society Main Journal. Accepted 2015 September 2
Physical Layer Techniques for High Frequency Wireline Broadband Systems
This thesis collects contributions to wireline and wireless communication systems with an emphasis on multiuser and multicarrier physical layer technology. To deliver increased capacity, modern wireline access systems such as G.fast extend the signal bandwidth up from tens to hundreds of MHz. This ambitious development revealed a number of unforeseen hurdles such as the impact of impedance changes in various forms. Impedance changes have a strong effect on the performance of multi-user crosstalk mitigation techniques such as vectoring. The first part of the thesis presents papers covering the identification of one of these problems, a model describing why it occurs and a method to mitigate its effects, improving line stability for G.fast systems.A second part of the thesis deals with the effects of temperature changes on wireline channels. When a vectored (MIMO) wireline system is initialized, channel estimates need to be obtained. This thesis presents contributions on the feasibility of re-using channel coefficients to speed up the vectoring startup procedures, even after the correct coefficients have changed, e.g., due to temperature changes. We also present extensive measurement results showing the effects of temperature changes on copper channels using a temperature chamber and British cables. The last part of the thesis presents three papers on the convergence of physical layer technologies, more specifically the deployment of OFDM-based radio systems using twisted pairs in different ways. In one proposed scenario, the idea of using the access copper lines to deploy small cells inside users' homes is explored. The feasibility of the concept, the design of radio-heads and a practical scheme for crosstalk mitigation are presented in three contributions
Diagnostics of seeded RF plasmas: An experimental study related to the gaseous core reactor
Measurements of the temperature profiles in an RF argon plasma were made over magnetic field intensities ranging from 20 amp turns/cm to 80 amp turns/cm. The results were compared with a one-dimensional numerical treatment of the governing equations and with an approximate closed form analytical solution that neglected radiation losses. The average measured temperatures in the plasma compared well with the numerical treatment, though the experimental profile showed less of an off center temperature peak than predicted by theory. This may be a result of the complex turbulent flow pattern present in the experimental torch and not modeled in the numerical treatment. The radiation term cannot be neglected for argon at the power levels investigated. The closed form analytical approximation that neglected radiation led to temperature predictions on the order of 1000 K to 2000 K higher than measured or predicted by the numerical treatment which considered radiation losses
- âŠ