2,074 research outputs found
Improving Monolithic Perovskite Silicon Tandem Solar Cells From an Optical Viewpoint
Perovskite silicon tandem solar cells are the most promising concept for a future photovoltaic technology. We report on recent progress from an optical viewpoint and disucss how we achieved more than 25 device efficienc
Thermoelectric Processes and Materials
Contains reports on three research projects.United States Navy, Office of Naval Research (Contract Nonr-1841(51)
EXPLORING SIMILARITIES AND VARIATIONS OF HUMAN MOBILITY PATTERNS IN THE CITY OF LONDON
The availability of new spatial data represents an unprecedented opportunity to better understand and plan cities. In particular, extensive data sets of human mobility data supply new information that can empower urbanism research to unveil how people use and visit urban places over time, overcoming traditional limitations related to the lack of large, detailed data sets. In this work, we explore patterns of similarities and spatial differences in human mobility flows in London, analysing their temporal variations in relation to the liveliness measured in a number of places. Using data sourced from the Oyster smart card and Twitter, we perform a time-series cluster analysis, exploring the similarity of temporal trends amongst places assigned to each cluster. Results suggest that differences in patterns appear to be related to the central and peripheral location of places, which present two or more temporal trends over the week. The type of transport network connecting the places (Tube, Railways, etc.) also appears to be a factor in determining significant differences. This work contributes to current urbanism research investigating the daily rhythms in cities. It also explores how to use mobility data to classify places according to their temporal features, with the aim of enhancing conventional analysis tools and integrating them with new quantitative information and methods
Comparing Extraction Methods for Biomarker Steroid Characterisation from Soil and Slurry
Clean water is a precious resource, and
policies/programmes are implemented worldwide to protect and/or improve water quality. Faecal pollution can be
a key contributor to water quality decline causing eutrophication through nutrient enrichment and pathogenic
contamination. The robust sourcing of faecal pollutants
is important to be able to target the appropriate sector and
to engage managers. Biomarker technology has the potential for source confirmation, by using, for example the
biomarker suite of steroids. Steroids have been used in
the differentiation of human and animal faeces; however,
there is no unequivocal extraction technique. Some of the
methods used include (i) Soxhlet extraction, (ii) Bligh
and Dyer (BD) extraction, and (iii) accelerated solvent
extraction (ASE). The less costly and time intensive
technique of ASE is particularly attractive, but a current
research gap concerns further comparisons regarding
ASE lipid extraction from soils/slurries compared with
the more traditional Soxhlet and BD extractions. Accordingly, a randomised complete block experiment was
implemented to assess differences between the three
extraction methods, differences between the different
sample types, and the interactions between these two
factors. Following GC-MS, it was found that there was
no significant difference between the results of the steroid
extraction methods, regardless of the type of sample
used, for the quantity of each steroid extracted. It was
concluded that ASE could be used confidently instead of
the more established steroid extraction methods, thereby
delivering time and cost savings
Coupled steroid and phosphorus leaching from cattle slurry at lysimeter scale
Water quality degradation can be caused by excessive agricultural nutrient transfers from fertilised soils exposed to wet weather. Mitigation measures within the EU Nitrates Directive aim to reduce this pressure by including ‘closed’ fertiliser spreading periods during wet months. For organic fertilisers such as slurry and manure, this closed period requires sufficient on-farm winter storage and good weather conditions to relieve storage at the end of the period. Therefore, robust scientific evidence is needed to support the measure. Incidental nutrient transfers of recently applied organic fertilisers in wet weather can also be complicated by synchronous transfers from residual soil stores and tracing is required for risk assessments. The combination of nutrient monitoring and biomarker analyses may aid this and one such biomarker suite is faecal steroids. Accordingly, this study investigated the persistence of steroids and their association with phosphorus during leaching episodes. The focus was on the coupled behaviour of steroids and total phosphorus (TP) concentrations in sub-surface hydrological pathways. Cattle slurry was applied to monolith lysimeters either side of a closed period and concentrations of both steroids and TP were monitored in the leachate. The study showed no significant effect of the treatment (average p = 0.17), though tracer concentrations did significantly change over time (average p = 0.001). While the steroidal concentration ratio was validated for herbivorous faecal pollution in the leachate, there was a weak positive correlation between the steroids and TP. Further investigation at more natural scales (hillslope/catchment) is required to confirm tracer behaviours/correlations and to compliment this sub-surface pathway study
Length scale dependence of dynamical heterogeneity in a colloidal fractal gel
We use time-resolved dynamic light scattering to investigate the slow
dynamics of a colloidal gel. The final decay of the average intensity
autocorrelation function is well described by , with and
decreasing from 1.5 to 1 with increasing . We show that the dynamics is not
due to a continuous ballistic process, as proposed in previous works, but
rather to rare, intermittent rearrangements. We quantify the dynamical
fluctuations resulting from intermittency by means of the variance
of the instantaneous autocorrelation function, the analogous of
the dynamical susceptibility studied in glass formers. The amplitude
of is found to grow linearly with . We propose a simple --yet
general-- model of intermittent dynamics that accounts for the dependence
of both the average correlation functions and .Comment: Revised and improved, to appear in Europhys. Let
Mobility Data as a Proxy for Urban Vitality
In this paper, we propose an innovative approach to Jane Jacobs’s concept of diversity and vitality,
analysing spatial big data to obtain quantitative measurements of urban qualities frequently employed
to evaluate places. We use mobility data collected from public transport to calculate a diversity value
for each research unit. Diversity is composed by three dynamic attributes: intensity, variability and
consistency, each measuring different temporal variations of mobility flows. Using various datasets as
proxy for activity density to validate results, we then use a regression model to establish the relation
between diversity and vitality and unveil which are the most lively areas in London
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