221 research outputs found
Modelling colloids with Baxter's adhesive hard sphere model
The structure of the Baxter adhesive hard sphere fluid is examined using
computer simulation. The radial distribution function (which exhibits unusual
discontinuities due to the particle adhesion) and static structure factor are
calculated with high accuracy over a range of conditions and compared with the
predictions of Percus--Yevick theory. We comment on rigidity in percolating
clusters and discuss the role of the model in the context of experiments on
colloidal systems with short-range attractive forces.Comment: 14 pages, 7 figures. (For proceedings of "Structural arrest in
colloidal systems with short-range attractive forces", Messina, December
2003
A global assessment of the impact of climate change on water scarcity
This paper presents a global scale assessment of the impact of climate change on water scarcity. Patterns of climate change from 21 Global Climate Models (GCMs) under four SRES scenarios are applied to a global hydrological model to estimate water resources across 1339 watersheds. The Water Crowding Index (WCI) and the Water Stress Index (WSI) are used to calculate exposure to increases and decreases in global water scarcity due to climate change. 1.6 (WCI) and 2.4 (WSI) billion people are estimated to be currently living within watersheds exposed to water scarcity. Using the WCI, by 2050 under the A1B scenario, 0.5 to 3.1 billion people are exposed to an increase in water scarcity due to climate change (range across 21 GCMs). This represents a higher upper-estimate than previous assessments because scenarios are constructed from a wider range of GCMs. A substantial proportion of the uncertainty in the global-scale effect of climate change on water scarcity is due to uncertainty in the estimates for South Asia and East Asia. Sensitivity to the WCI and WSI thresholds that define water scarcity can be comparable to the sensitivity to climate change pattern. More of the world will see an increase in exposure to water scarcity than a decrease due to climate change but this is not consistent across all climate change patterns. Additionally, investigation of the effects of a set of prescribed global mean temperature change scenarios show rapid increases in water scarcity due to climate change across many regions of the globe, up to 2°C, followed by stabilisation to 4°C
Road Triangle Detection for Non-Road Area Elimination Using Lane Detection and Image Multiplication
The background has become the key issue in maintaining the accuracy of final analysis for object detection in the development of an image processing algorithm. Therefore, this paper focuses on intelligent transport system (ITS), in which some of the background characteristics such as trees, road divider, and buildings interfere in the detection system algorithm. Therefore, this paper presents an algorithm that can remove the unwanted background, outside the road area boundaries for dynamic video footage. Using the onboard camera to capture the road traffic, the background is always moving in motion together with the foreground; therefore, a region of interest that focuses only on the road region needs to be established. The algorithm consists of three main components: lane detection, vanishing point and image multiplication. From the three components, other methods are applied, namely Hough transform, line intersection, image masking and image multiplication, which are combined together to create the background subtraction system. In the final analysis, the test results under various road conditions show a good detection rate and background removal
Estimating ecosystem maximum light use efficiency based on the water use efficiency principle
Light use efficiency (LUE) defines the vegetation efficiency of converting radiative energy into biochemical energy through photosynthesis. Estimating the maximum LUE (Ï” max) is critical yet challenging for quantifying gross primary production (GPP) using LUE-based models. This study describes an analytical method for estimating Ï” max based on water use efficiency (WUE) as determined by plant water use and carbon gain. Unlike other complex parameterization schemes, this WUE-based method is simple and requires four variables relatively easy to acquire. The WUE-based Ï” max estimates compare favorably well with values based on traditional curve fitting method and that reported in the literature, and clearly distinguished Ï” max between C3 (1.48 0.33 {g C M}}{J}}{ - 1}) and C4 (2.63 0.21 {g C M}}{J}}{-1}}) dominated ecosystems. The range in Ï” max estimates was narrow across different years and sites within a biome. The WUE-based Ï” max estimate is theoretically constrained by vegetation water use and can be directly incorporated into LUE models for GPP estimation across ecosystems
Theory of continuum percolation III. Low density expansion
We use a previously introduced mapping between the continuum percolation
model and the Potts fluid (a system of interacting s-states spins which are
free to move in the continuum) to derive the low density expansion of the pair
connectedness and the mean cluster size. We prove that given an adequate
identification of functions, the result is equivalent to the density expansion
derived from a completely different point of view by Coniglio et al. [J. Phys A
10, 1123 (1977)] to describe physical clustering in a gas. We then apply our
expansion to a system of hypercubes with a hard core interaction. The
calculated critical density is within approximately 5% of the results of
simulations, and is thus much more precise than previous theoretical results
which were based on integral equations. We suggest that this is because
integral equations smooth out overly the partition function (i.e., they
describe predominantly its analytical part), while our method targets instead
the part which describes the phase transition (i.e., the singular part).Comment: 42 pages, Revtex, includes 5 EncapsulatedPostscript figures,
submitted to Phys Rev
A robust Gauss-Newton algorithm for the optimization of hydrological models: benchmarking against industry-standard algorithms
Optimization of model parameters is a ubiquitous task in hydrological and environmental modeling. Currently, the environmental modeling community tends to favor evolutionary techniques over classical Newtonâtype methods, in the light of the geometrically problematic features of objective functions, such as multiple optima and general nonsmoothness. The companion paper (Qin et al., 2018, https://doi.org/10.1029/2017WR022488) introduced the robust GaussâNewton (RGN) algorithm, an enhanced version of the standard GaussâNewton algorithm that employs several heuristics to enhance its explorative abilities and perform robustly even for problematic objective functions. This paper focuses on benchmarking the RGN algorithm against three optimization algorithms generally accepted as âbest practiceâ in the hydrological community, namely, the LevenbergâMarquardt algorithm, the shuffled complex evolution (SCE) search (with 2 and 10 complexes), and the dynamically dimensioned search (DDS). The empirical case studies include four conceptual hydrological models and three catchments. Empirical results indicate that, on average, RGN is 2â3 times more efficient than SCE (2 complexes) by achieving comparable robustness at a lower cost, 7â9 times more efficient than SCE (10 complexes) by trading off some speed to more than compensate for a somewhat lower robustness, 5â7 times more efficient than LevenbergâMarquardt by achieving higher robustness at a moderate additional cost, and 12â26 times more efficient than DDS in terms of robustnessâperâfixedâcost. A detailed analysis of performance in terms of reliability and cost is provided. Overall, the RGN algorithm is an attractive option for the calibration of hydrological models, and we recommend further investigation of its benefits for broader types of optimization problems.Youwei Qin, Dmitri Kavetski, George Kuczer
Test of the Kolmogorov-Johnson-Mehl-Avrami picture of metastable decay in a model with microscopic dynamics
The Kolmogorov-Johnson-Mehl-Avrami (KJMA) theory for the time evolution of
the order parameter in systems undergoing first-order phase transformations has
been extended by Sekimoto to the level of two-point correlation functions.
Here, this extended KJMA theory is applied to a kinetic Ising lattice-gas
model, in which the elementary kinetic processes act on microscopic length and
time scales. The theoretical framework is used to analyze data from extensive
Monte Carlo simulations. The theory is inherently a mesoscopic continuum
picture, and in principle it requires a large separation between the
microscopic scales and the mesoscopic scales characteristic of the evolving
two-phase structure. Nevertheless, we find excellent quantitative agreement
with the simulations in a large parameter regime, extending remarkably far
towards strong fields (large supersaturations) and correspondingly small
nucleation barriers. The original KJMA theory permits direct measurement of the
order parameter in the metastable phase, and using the extension to correlation
functions one can also perform separate measurements of the nucleation rate and
the average velocity of the convoluted interface between the metastable and
stable phase regions. The values obtained for all three quantities are verified
by other theoretical and computational methods. As these quantities are often
difficult to measure directly during a process of phase transformation, data
analysis using the extended KJMA theory may provide a useful experimental
alternative.Comment: RevTex, 21 pages including 14 ps figures. Submitted to Phys. Rev. B.
One misprint corrected in Eq.(C1
Bioengineering of the plant culture of Capsicum frutescens with vanillin synthase gene for the production of vanillin
Production of vanillin by bioengineering has gained popularity due to consumer demand towards vanillin produced by biological systems. Natural vanillin from vanilla beans is very expensive to produce compared to its synthetic counterpart. Current bioengineering works mainly involve microbial biotechnology. Therefore, alternative means to the current approaches are constantly being explored. This work describes the use of vanillin synthase (VpVAN), to bioconvert ferulic acid to vanillin in a plant system. The VpVAN enzyme had been shown to directly convert ferulic acid and its glucoside into vanillin and its glucoside, respectively. As the ferulic acid precursor and vanillin were found to be the intermediates in the phenylpropanoid biosynthetic pathway of Capsicum species, this work serves as a proof-of-concept for vanillin production using Capsicum frutescens (C. frutescens or hot chili pepper). The cells of C. frutescens were genetically transformed with a codon optimized VpVAN gene via biolistics. Transformed explants were selected and regenerated into callus. Successful integration of the gene cassette into the plant genome was confirmed by polymerase chain reaction. High performance liquid chromatography was used to quantify the phenolic compounds detected in the callus tissues. The vanillin content of transformed calli was 0.057% compared to 0.0003% in untransformed calli
Structure-property correlations in model composite materials
We investigate the effective properties (conductivity, diffusivity and elastic moduli) of model random composite media derived from Gaussian random fields and overlapping hollow spheres. The morphologies generated in the models exhibit low percolation thresholds and give a realistic representation of the complex microstructure observed in many classes of composites. The statistical correlation functions of the models are derived and used to evaluate rigorous bounds on each property. Simulation of the effective conductivity is used to demonstrate the applicability of the bounds. The key morphological features which effect composite properties are discussed
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