3,844 research outputs found
Framework for the energetic assessment of South and South-East Asia fixed chimney bull’s trench kiln
One of the major sources of fuel consumption and greenhouse gas emission in South and South-East Asia is brick manufacturing. One of the most commonly implemented technologies for brick manufacturing in this region is the fixed chimney Bull’s trench kiln (FCBTK). This type of technology largely depends on manual labour and is very inefficient when compared to more modern technologies. Because the adoption of more advanced technologies is hindered by the socio-economical background, the much needed innovations in the brick sector are necessarily related to improving/modifying the FCBTK already operational. However, few scientific studies have been conducted on FCBTK probably due to the basic level of technological development. Such studies are however important to systematically and methodologically assess the challenges and solutions in FCBTK. In this study we develop a thermo-energetic model to evaluate the importance of the parameters pertained to FCBTK construction and operation. The prospective of this study is to build an initial thermo-energetic framework that will serve as a basis to investigate possible energetic improvements
Metallicity Evolution in the Early Universe
Observations of the damped Lya systems provide direct measurements on the
chemical enrichment history of neutral gas in the early universe. In this
Letter, we present new measurements for four damped Lya systems at high
redshift. Combining these data with [Fe/H] values culled from the literature,
we investigate the metallicity evolution of the universe from z~1.5-4.5.
Contrary to our expectations and the predictions of essentially every chemical
evolution model, the N(HI)-weighted mean [Fe/H] metallicity exhibits minimal
evolution over this epoch. For the individual systems, we report tentative
evidence for an evolution in the unweighted [Fe/H] mean and the scatter in
[Fe/H] with the higher redshift systems showing lower scatter and lower typical
[Fe/H] values. We also note that no damped Lya system has [Fe/H] < -2.7 dex.
Finally, we discuss the potential impact of small number statistics and dust on
our conclusions and consider the implications of these results on chemical
evolution in the early universe.Comment: 6 pages, 2 encapsulated figures, Latex2e, uses emulateapj.sty and
onecolfloat.sty. Accepted for publication in ApJ Letters: Feb 28, 200
Assessing the modelling approach and datasets required for fault detection in photovoltaic systems
Reliable monitoring for photovoltaic assets (PVs) is essential to ensuring uptake, long term performance, and maximum return on investment of renewable systems. To this end this paper investigates the input data and machine learning techniques required for day-behind predictions of PV generation, within the scope of conducting informed maintenance of these systems. Five years of PV generation data at hourly intervals were retrieved from four commercial building-mounted PV installations in the UK, as well as weather data retrieved from MIDAS. A support vector machine, random forest and artificial neural network were trained to predict PV power generation. Random forest performed best, achieving an average mean relative error of 2.7%. Irradiance, previous generation and solar position were found to be the most important variables. Overall, this work shows how low-cost data driven analysis of PV systems can be used to support the effective management of such assets
Tackling coolant freezing in generation-IV molten salt reactors
In this study we describe an experimental system designed to simulate the conditions of transient freezing which can occur in abnormal behaviour of molten salt reactors (MSRs). Freezing of coolant is indeed one of the main technical challenges preventing the deployment of MSR. First a novel experimental technique is presented by which it is possible to accurately track the growth of the solidified layer of fluid near a cold surface in an internal flow of liquid. This scenario simulates the possible solidification of a molten salt coolant over a cold wall inside the piping system of the MSR. Specifically, we conducted measurements using water as a simulant for the molten salt, and liquid nitrogen to achieve high heat removal rate at the wall. Particle image velocimetry and planar induced fluorescence were used as diagnostic techniques to track the growth of the solid layer. In addition this study describes a thermo-hydraulic model which has been used to characterise transient freezing in internal flow and compares the said model with the experiments. The numerical simulations were shown to be able to capture qualitatively and quantitatively all the essential processes involved in internal flow transient freezing. Accurate numerical predictive tools such the one presented in this work are essential in simulating the behaviour of MSR under accident conditions
The development of a carbon roadmap investment strategy for carbon intensive food retail industries
This work presents an approach to develop an innovative decarbonisation investment strategy framework for carbon intensive UK industries by using statistical analysis and optimisation modelling. The case study focuses on taking a representative sample of retail buildings and assesses the financial viability of installing low-carbon Combined Heat and Power units (CHPs) and Photovoltaic Solar Panels (PVs) across a portfolio of buildings. Simulation of each building are initially conducted, and the results generate a set of regression coefficients, via a multivariate adaptive regression splines (MARS), which are inputted into a Mixed Integer Linear Programming (MILP) problem. Solving the MILP yields the optimal decarbonisation investment strategy for the case study up to 2050, considering market trends such as electricity prices, gas prices and policy incentives. Results indicate the level of investment required per year, the operational and carbon savings associated, and a program for such investments. This method is reiterated for several scenarios where different parameters such as utility prices, capital costs and grid carbon factors are forecasted up to 2050 (following the Future Energy Scenarios from National Grid). This work shows how a clear mathematical framework can assist decision-makers in commercial organisations to reduce their carbon footprint cost-effectively and thus reach science-based targets
The Low Redshift Lyman Alpha Forest in Cold Dark Matter Cosmologies
We study the physical origin of the low-redshift Lyman alpha forest in
hydrodynamic simulations of four CDM cosmologies. Our main conclusions are
insensitive to the cosmological model but depend on our assumption that the UV
background declines at low redshift. We find that the expansion of the universe
drives rapid evolution of dN/dz (the number of absorbers per unit z) at z >
1.7, but that at lower redshift the fading of the UV background counters the
influence of expansion, leading to slow evolution. At every redshift, weaker
lines come primarily from moderate fluctuations of the diffuse, unshocked IGM,
and stronger lines originate in shocked or radiatively cooled gas of higher
overdensity. However, the neutral hydrogen column density associated with
structures of fixed overdensity drops as the universe expands, so an absorber
at z = 0 is dynamically analogous to an absorber with neutral hydrogen column
density 10 to 50 times higher at z = 2-3. We find no clear distinction between
lines arising in "galaxy halos" and lines arising in larger scale structures;
however, galaxies tend to lie near the dense regions of the IGM that produce
strong Lyman alpha lines. The simulations provide a unified physical picture
that accounts for the most distinctive observed properties of the low redshift
Lyman alpha forest: (1) a sharp transition in the evolution of dN/dz at z ~
1.7, (2) stronger evolution for absorbers of higher equivalent width, (3) a
correlation of increasing Lyman alpha equivalent width with decreasing galaxy
impact parameter, and (4) a tendency for stronger lines to arise in close
proximity to galaxies while weaker lines trace more diffuse large scale
structure. (Abridged)Comment: 57 pages, 18 figures, submitted to Ap
A new 21-cm absorber identified with an galaxy
We present Giant Metrewave Radio Telescope (GMRT) observations of redshifted
21-cm absorption from the metal line absorption system towards PKS
1243-072. HI absorption is clearly detected; the absorption profile has a
velocity spread of km/s. Detection of 21-cm absorption indicates that
the absorber has an HI column density large enough to be classified as a damped
Lyman- system. Follow up ground based optical imaging and spectroscopy
allow us to identify the absorber with an galaxy at an impact
parameter of kpc from the line of sight to the QSO. The absorbing
galaxy is unusual in that it has bright emission lines. On the basis of the
optical spectrum we are unable to uniquely classify the galaxy since its
emission line ratios lie in the transition region between starburst and Seyfert
II type spectra.Comment: 5 pages, 3 figures. Accepted for publication in Astronomy &
Astrophysic
HI 21cm imaging of a nearby Damped Lyman-alpha system
We present Giant Metrewave Radio Telescope (GMRT) HI 21cm emission images of
the z=0.009 damped Lyman-alpha (DLA) absorber towards the QSO HS 1543+5921. The
DLA has been earlier identified as a low surface brightness galaxy SBS 1543+593
at an impact parameter of ~ 400 pc to the QSO line of sight. The extremely low
redshift of the absorber allows us to make spatially resolved images of the
21cm emission; besides the HI mass, this also enables us to determine the
velocity field of the galaxy and, hence, to estimate its dynamical mass.
We obtain a total HI mass of ~ 1.4x10^9 Msun, considerably smaller than the
value of M*(HI) determined from blind 21cm emission surveys. This continues the
trend of low HI mass in all low redshift DLAs for which HI emission
observations have been attempted. We also find that the QSO lies behind a
region of low local HI column density in the foreground galaxy. This is
interesting in view of suggestions that DLA samples are biased against high HI
column density systems. The dynamical mass of the galaxy is found to be Mdyn ~
5x10^9 Msun.Comment: Accepted for publication in A&
Long-Term Survival in Adult Neuroblastoma with Multiple Recurrences
Neuroblastoma (NB) rarely occurs in adults, and less than 10% of the cases occur in patients older than 10 years. Currently, there are no standard treatment guidelines for adult NB patients. We report the case of a young man suffering from NB in adulthood with multiple recurrences. Treatment included multiple resections, chemotherapy, and radiotherapy. This patient remains free of clinical disease more than 7 years after diagnosis
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