Cube Method Research Articles

Flammability of Some Ornamental Species in Wildland–Urban Interfaces in Southeastern France: Laboratory Assessment at Particle Level

Assessment of the flammability of ornamental vegetation (particularly hedges) planted around houses is necessary in light of the increasing urbanization of the wildland-urban interfaces (WUIs) and the high fire occurrence in such areas. The structure and flammability of seven of the species most frequently planted as hedges in Provence (southeastern France) were studied at particle level. Spatial repartition of the different types of fuel particles within plants was assessed by means of the cube method. The leaf flammability was assessed using an epiradiator as a burning device, and measurements of foliar physical characteristics and gross heat of combustion (GHC) helped to explain the results of burning experiments. Co-inertia analysis revealed that species with thin leaves were quick to ignite (Pyracantha coccinea, Phyllostachys sp.) and species with high leaf GHC burned the longest (Pittosporum tobira, Nerium oleander). Species presenting high ignitability (Photinia fraseri, Phyllostachys sp. and Pyracantha coccinea) were characterized by high foliar surface area-to-volume ratio, and species presenting lower ignitability were characterized by high GHC (Pittosporum tobira, Nerium oleander, Cupressus sempervirens). Hierarchical cluster analysis of the flammability variables (ignition frequency, time-to-ignition and flaming duration) categorized the relative flammability of the seven species (including dead Cupressus sempervirens) in five clusters of species from poorly flammable (Pittosporum tobira) to extremely flammable (dead Cupressus sempervirens).This study provides useful information for reducing fire risk in WUIs in the study area.

SU‐C‐WAB‐01: Computerized Production of Statistical Clinical Target Volume Models in Prostate Cancer Radiation Treatment Planning

Purpose: Inter‐and intra‐observer variability of clinical target volume (CTV) contours for prostate cancer is a critical issue in radiation treatment planning. Automated contouring based on statistical CTV models could be one of possible approaches for reducing the variability. Therefore, the purpose of our study is to develop a computerized method for producing the statistical CTV models to be used as CTV templates for automated contouring in prostate cancer radiation treatment planning. Methods: Eighteen, seventeen and sixteen radiation oncologists belonging to different facilities delineated CTV contours for low‐, intermediate‐and high‐risk prostate cancers, respectively. The low‐risk, intermediate‐risk, and high‐risk CTVs include only a prostate, a prostate plus a 1‐cm seminal vesicle base, and a prostate plus 2‐cm seminal vesicle, respectively. The statistical CTV models for the three risk types were derived based on a principal component analysis (PCA), which statistically took into account the inter‐observer variability. CTV regions were triangulated by using a marching cubes method. For matching the number of points on the surfaces of all CTV regions, the number of vertices on each CTV region was reduced to 1,000 with a quadric error metrics. All CTV regions were registered with a reference CTV by using an iterative closest point algorithm for calculation of a covariance matrix to be employed for the PCA‐based CTV modeling. Results: CTV models of three risk types were produced, which consisted of a mean CTV and PCA coefficients multiplied by eigenvectors, i.e., eigen‐CTV image. Average Euclidean distances between corresponding points of a mean CTV and the other CTVs for three risk types were 2.05 mm, 3.64 mm, 2.55 mm, respectively. Conclusion: The proposed method could provide probabilistic CTV models to be used as CTV templates in delineating CTV contours.

Further study of grain boundary fracture in the breakage of single multiphase particles using X-ray microtomography procedures

The present work aims to verify the 3D quantitative analysis of grain boundary fracture in the breakage of single multiphase particles using X-ray microtomography. The breakage of single multiphase copper ore particles (6mm cubic particles) by slow compression was examined. From XMT reconstructed images using the Marching Cube method, interfacial areas between copper mineral grains and host rock were determined for both parent particles and progeny particles. In this way, the specific interfacial area ratio was calculated as a metric for grain boundary fracture. Preferential grain boundary fracture only occurs at low energy dissipation rates and the current results confirm initial results for 3mm cubes published previously by Garcia et al. (2009).

Normalised LCS-based method for indexing multidimensional data cube

Query processors fail to retrieve information of interest in the presence of misspelled keywords given by users. The above problem persists because most of currently used indexing system does not have fault-tolerance ability to map the misspelled keywords to the correct records stored at physical level of databases. Therefore, the information retrieval systems need additional support of spell check mechanism with limitations for correction of misspelled keywords before submitting them to query processors. In this paper, a data indexing system is introduced for indexing multidimensional data cube, which maps the keywords to the records stored at physical level in multidimensional data structure and also has normalised longest common subsequence-based string approximation method to find correct keywords against misspelled keywords which comes directly to indexing processes through user queries. It provides more than 90% accurate results in mapping misspelled keywords to the physically stored records. These results are consistent even for large datasets.

Doubly balanced spatial sampling with spreading and restitution of auxiliary totals

A new spatial sampling method is proposed in order to achieve a double property of balancing. The sample is spatially balanced or well spread so as to avoid selecting neighbouring units. Moreover, the method also enables to satisfy balancing equations on auxiliary variables available on all the sampling units because the Horvitz–Thompson estimator is almost equal to the population totals for these variables. The method works with any definition of distance in a multidimensional space and supports the use of unequal inclusion probabilities. The algorithm is simple and fast. Examples show that the method succeeds in using more information than the local pivotal method, the cube method and the Generalized Random‐Tessellation Stratified sampling method, and thus performs better. An estimator of the variance for this sampling design is proposed in order to lead to an inference that takes the effect of the sampling design into account. Copyright © 2012 John Wiley & Sons, Ltd.

Measuring saturated hydraulic conductivity and anisotropy of peat by a modified split-container method

Long-term changes in the physical and hydraulic properties of peat result from the decomposition and consolidation processes. The saturated hydraulic conductivity (K s) of peat is depth-dependent and could increase or decrease with depth; therefore, K s determination on a large number of samples is required to more accurately assess field variability. The cube method is a popular laboratory procedure to determine K s because it allows use of smaller sample dimensions, while minimizing edge effects. This article describes the design and use of an alternate split container to enclose undisturbed peat cubes during measurement of K s and the application of this method to a field site in Northwest Territories, Canada. The method allows for simpler and more controlled K s measurements while also permitting anisotropy measurements. Matched tests on identical samples (K s range 21–314 m/d), using the split-container and wax methods, showed a good agreement for intermediate K s values; however, significant deviations occurred for low and high K s values. Hydraulic-conductivity measurements taken on field samples showed a decrease with depth and exhibited anisotropic hydraulic conductivity as expected based on previous studies.

On a characterization of ordered pivotal sampling

When auxiliary information is available at the design stage, samples may be selected by means of balanced sampling. Deville and Tillé proposed in 2004 a general algorithm to perform balanced sampling, named the cube method. In this paper, we are interested in a particular case of the cube method named pivotal sampling, and first described by Deville and Tillé in 1998. We show that this sampling algorithm, when applied to units ranked in a fixed order, is equivalent to Deville’s systematic sampling, in the sense that both algorithms lead to the same sampling design. This characterization enables the computation of the second-order inclusion probabilities for pivotal sampling. We show that the pivotal sampling enables to take account of an appropriate ordering of the units to achieve a variance reduction, while limiting the loss of efficiency if the ordering is not appropriate.

Exciton coupling in the photosystem I reaction center

The point dipole approximation, transition charge method and transition density cube method are used to investigate the influences of the packing structures such as face-to-face distance and shift distance on the exciton coupling between theChlorophyll-a model dimers. The results show that the coupling strength obtained from three methods are very similar when the distance between the dimer molecules is larger than the molecule size; while the point dipole approximation will overestimate the exciton coupling and transition density cube method will give more reasonable coupling values when the distance is smaller than the molecule size. Based on these three method, we also calculated the couplings between Chlorophyll a pigments in both the crystal structure (1jb0.pdb) and the QM-MM optimized structure of the photosystem I reaction center. The exciton coupling of the special pair (P700) from the transition density cube method is 23.8 cm^-1 for optimized structure, which is very similar with the one 20 cm^-1 from full INDO Hamiltonian decomposition including Förster and Dexter term contributions. This explained that the strongest coupling dimer in the PSI reaction center is not the P700, but the dimer pair of the ecA1-ecB2 (-153 cm^-1) and ecB1-ecA2 (-152 cm^-1).

Item Selection for the Development of Parallel Forms From an IRT-Based Seed Test Using a Sampling and Classification Approach

Two sampling-and-classification–based procedures were developed for automated test assembly: the Cell Only and the Cell and Cube methods. A simulation study based on a 540-item bank was conducted to compare the performance of the procedures with the performance of a mixed-integer programming (MIP) method for assembling multiple parallel test forms. The study investigated the statistical equivalence of the forms generated by the three test assembly methods (Cell Only, Cell and Cube, and MIP) in terms of test information functions, test characteristic curves, mean square deviations, and practical constraints, such as content balancing and nonoverlap among forms. The results indicated that the 13-point MIP method outperformed the other two methods in terms of the “closeness” test information functions between the reference form and the assembled parallel tests. Regarding test characteristic curves, the Cell Only and Cell and Cube methods yielded more similar test characteristic curves than the MIP method. Constraining test information functions apparently does not guarantee that the assembled forms will yield similar test characteristic curves. Overall, the Cell Only and Cell and Cube methods have the potential to provide results similar to the optimization approach.

Calculation of bulk madelung constants by direct summation without complications of conditional convergence

Calculation of bulk Madelung constants is not a straightforward process. In a direct summation, the infinite series is only conditionally convergent, and the value depends on the way the terms are grouped and truncated. For this reason, the traditional direct summation method taking an expanding sphere method cannot be generalized to an expanding cube method, and vice versa. We propose a straightforward method of calculating Madelung’s constants by direct summation of the screened Coulomb interaction that is applicable in both expanding modes. We demonstrate that the bulk Madelung constants of the sodium-chloride structure and the cesium-chloride crystal structure can be calculated regardless of the constraints on the unit cell shape or the expanding mode. Although the exponential factor in the screened potential generally slows down the convergence of the Madelung series, it is possible in many cases to accelerate the convergence with an appropriate choice of the unit cell. Since conditional convergence is eliminated by this simple method, we may choose any unit cell configuration to achieve a faster convergence of the Madelung constant.

Geometry determination of complexes in a molecular liquid mixture using electron–vibration–vibration two-dimensional infrared spectroscopy with a vibrational transition density cube method

We demonstrate the use of a new vibrational transition density cube (VTDC) method for determining the geometry of complexes in a molecular liquid mixture from electron-vibration-vibration two-dimensional infrared (EVV 2DIR) spectra. The VTDC method was used to calculate the electrically-mediated intermolecular vibrational coupling and thereby the EVV 2DIR spectra. Using the 1:1 benzonitrile-phenylacetylene (BN-PA) liquid mixture as a test case, the new method leads to a distance of 3.60 Å between the interacting BN-PA pair, a much more accurate value than the distance previously obtained using a dipolar approximation for the electrical coupling. We also show that molecular dynamics simulations of the liquid mixture predict a modal geometry of complexation which agrees well with the geometry determined from the 2DIR data via VTDC analysis. We therefore conclude the combination of VTDC and EVV 2DIR data is a useful approach for the determination of the geometry of molecular complexes in the condensed phase.

A Hybrid Scheme for the Near Wall Treatment of Building Cube Method

A Hybrid Scheme for the Near Wall Treatment of Building Cube Method

INVERSE SCATTERING SHAPE RECONSTRUCTION OF 3D BACTERIA USING THE LEVEL SET ALGORITHM

Bacteria exist in a variety of groups of shapes, sizes, and single or multiple cell formations. In this paper, the level set shape reconstruction technique, the method of moments, and the marching cubes methods are integrated in the high frequency band for imaging three dimensional bacteria. The time step and the resolution of the marching cubes method are investigated to smooth the error function of the level set and hence speed up the convergence at high frequencies. The numerical results demonstrate the robustness of the level set algorithm for the detection of bacteria based on their shapes. The three dimensional shape reconstructions of unknown bacteria can be utilized to classify biological warfare agents.

Level Set Algorithm for Shape Reconstruction of Non-Overlapping Three-Dimensional Penetrable Targets

This paper presents a 3-D shape reconstruction algorithm based on the level set method. Multiple dielectric and non-overlapping objects are considered. The level set algorithm is a gradient-type optimization approach that aims to minimize a cost function between measurements and computer-simulated data. The algorithm is capable of retrieving the shape and location of multiple targets made of two different and slightly lossy materials. An appropriate form of the deformation velocity based on the forward and adjoint fields is calculated. The method of moment surface integral equation is implemented to calculate the deformation velocity of the evolving objects. Two sets of Hamilton-Jacobi equations, associated with the two dielectric materials, are solved simultaneously to update the evolving objects. During the inversion scheme, the marching cubes method is employed to restore the surface meshes necessary for the forward solver. The algorithm is tested on corrupted synthetic data with signal-to-noise ratio of 10 dB.

Influences of domain extensions to a moderately stenosed patient‐specific carotid bifurcation

PurposeThe purpose of this paper is to numerically study blood flow through a subject‐specific carotid artery with a moderately severe stenosis, also to thoroughly analyse the wall shear stress (WSS), oscillatory shear index (OSI) and WSS angular deviation (WSSAD). One of the important aspects of this study is the investigation on the influence of the extensions attached to the domain outlets.Design/methodology/approachThe segmentation of the carotid artery is carried out using a deformable model based on a level set method. A geometric potential force (GPF) is employed to deform the level set to obtain the carotid artery geometry. The initial surface meshing is generated using an advanced marching cubes (MC) method, before improving the quality of the surface mesh via a number of mesh cosmetic steps. The volume mesh generation has two parts. In the first part, a quasi‐structured, boundary layer mesh is generated in the vicinity of the geometry walls. The second part of the meshing involves unstructured tetrahedral meshing of the inner part of the geometry. After the meshing stage, the flow boundary conditions are generated by numerically solving the Helmholtz equation in both space and time. Finally, the explicit characteristic‐based split (CBS) method is employed in a parallel environment to produce a detailed analysis of wall quantities.FindingsIn general, WSS is very high in the vicinity of the carotid artery apex and in the proximity of the stenosis. From the results obtained, it is clear that the influence of outlet domain extension is marginal. While the peak instantaneous WSS differs by a maximum of 5.7 per cent, the time‐averaged WSS difference due to extended domain is only 1.3 per cent. Two other derived parameters are also examined in the paper, the oscillating shear index and the WSSAD. Both these quantities also display minor or negligible differences due to domain extension.Originality/valueIt has been perceived that domain extension is essential to avoid wrong application of boundary conditions. The results obtained, however, conclusively show that the outlet domain extension has only a moderate influence on WSS. Thus, outlet extension to the domains may not be essential for arterial blood flows. It is also observed that the dramatic values of peak WSS obtained near the stenosis is the result of high resolution mesh along with boundary layers used in this study. Both the outcomes represent the originality of this paper.

Evaluation of Excitonic Coupling and Charge Transport Integrals in P3HT Nanocrystal

An attempt has been made to predict the crystallographic packing parameters of poly(3-hexylthiophene) (P3HT) nanocrystal with the help of both X-ray diffraction and computational methods. Excitonic coupling integrals were calculated using various methods such as point-dipole approximation (PDA), line-dipole approximation (LDA), ZINDO method, and transition density cube (TDC) method in crystallographic directions. ZINDO method leads to reasonably accurate integrals when compared to TDC results. PDA and LDA approaches fail badly in predicting the excitonic coupling integrals, though latter yields improved results. The calculations one more time show that PDA should be avoided in cases where interchromophoric distance is comparable to chromophore size. In general, the magnitude of both excitonic and charge transfer integrals are larger in stacking direction of chains than those in other crystallographic directions, suggesting preferential diffusion of both excitons and charge carriers between the chains. The...

Realistic, fast, and controllable simulation of solid combustion

AbstractWe present a realistic, fast, and controllable model to simulate fire propagation on solid objects with the object decomposition process involved. A hybrid structure of grids is employed to simulate the whole process efficiently. An improved burning surface update scheme based on level set and a novel method for visualizing the burning surface are proposed to produce convincing results. To achieve interactive simulation speed, a few acceleration techniques are employed, including a moving grid generated to dynamically track the fire propagation, a refined Marching Cubes method to reconstruct the burning surface, and a hardware‐implemented fluid solver. By controlling a few physical and geometric parameters, we are able to simulate various solid combustion phenomena. Copyright © 2011 John Wiley & Sons, Ltd.

Markerless Shape and Motion Capture From Multiview Video Sequences

We propose a new markerless shape and motion capture approach from multiview video sequences. The shape recovery method consists of two steps: separating and merging. In the separating step, the depth map represented with a point cloud for each view is generated by solving a proposed variational model, which is regularized by four constraints to ensure the accuracy and completeness of the reconstruction. Then, in the merging step, the point clouds of all the views are merged together and reconstructed into a 3-D mesh using a marching cubes method with silhouette constraints. Experiments show that the geometric details are faithfully preserved in each estimated depth map. The 3-D meshes reconstructed from the estimated depth maps are watertight and present rich geometric details, even for non-convex objects. Taking the reconstructed 3-D mesh as the underlying scene representation, a volumetric deformation method with a new positional-constraint computation scheme is proposed to automatically capture motions of the 3-D object. Our method can capture non-rigid motions even for loosely dressed humans without the aid of markers.

INVERSE SCATTERING OF THREE-DIMENSIONAL PEC OBJECTS USING THE LEVEL-SET METHOD

A 3D shape reconstruction algorithm for multiple PEC objects immersed in air is presented. The Hamilton-Jacobi PDE is solved in the entire computational domain with employing the marching cubes method to retrieve the unknown objects. The method of moment surface integral equation is used as the forward solver. An appropriate form of the deformation velocity, based on the forward and adjoint flelds, is implemented to minimize the mismatch between the measurements and simulated scattered flelds from the evolving objects. The inversion algorithm demonstrated good shape reconstruction results even when using limited view data or noisy corrupted data with SNR of 5dB.

Effects of Laboratory Procedures on the Integrity of a Sandy-Loam Soil Sample for Bi-Directional Measurement of Saturated Hydraulic Conductivity

Practical and validated methods to measure anisotropy of saturated, Ks, or field-saturated, Kfs, soil hydraulic conductivity on a single soil sample are still lacking. The objective of this investigation was to test factors affecting anisotropy measured in a sandy-loam soil by the constant-head laboratory permeameter and the modified cube method. The ratio, RK, between the conductivity results obtained with a long (6 h) and a short (0.5 h) duration run varied from a minimum of 0.29 to a maximum of 0.88 with the considered experimental procedure, differing by both the employed constant-head device (Mariotte bottle, siphon) and the initial soil water content (unsaturated, saturated). Maximum time stability was detected with a siphon and an initially saturated soil sample, suggesting that soil alteration at the surface may influence the measured conductivity, and more reliable anisotropy measurements have to be expected for Ks than Kfs. A short-duration run carried out with a siphon and a calcium solution was also suggested for laboratory determination of Ks anisotropy since more representative results were obtained for a single cube of soil (i.e., horizontal, Kh, to vertical, Kv, conductivity ratio varying from 1.78 to 1.82 with the measurement sequence) as compared with the ones associated with using tap water (ratio varying from 1.24 to 2.09). The Kh/Kv ratio varied between 1.80 and 2.81 on two dates (April and July 2009) differing by the soil water content at the time of sampling (close to field capacity; lower than the permanent wilting point, respectively), and a significant temporal variability was only detected for Kv. Therefore, temporal variability of Ks anisotropy cannot be predicted by measuring one-dimensional Ks.