Material Density Distribution Research Articles

Parenchymal density changes in acute pulmonary embolism: Can quantitative CT be a diagnostic tool? A preliminary study

PurposeDetermine the ability of quantitative CT (QCT) in defining parenchymal density changes in acute pulmonary embolism (PE). Material & methodsMean lung density (MLD) and percentage distribution values (PDV) were calculated in 34 patients suspected of PE using software application based on computerized volumetric anatomical segmentation. ResultsTotal, left, and right MLD differed significantly between emboli positive(n=23) and negative(n=11) groups(p<0.006, p<0.009, p<0.014). PDVs differed between groups (p<0.05) except for LUZ and RLZ. When PE was present in lobe &/segment branches, PDVs were significantly lower except RUZ. ConclusionQCT is a promising application for defining parenchymal density changes in PE revealing potential functional impact of emboli. This preliminary study suggests QCT could provide added value to CTPA in peripheral PE.

An Assessment of Appropriateness of the Choice of Parameters for Refractory Stampings Fabrication Process

Abstract The paper presents results of an analysis of material density distribution in stampings press-moulded in metal dies from raw refractory materials based on alumina-magnesia-carbon aggregate. The stampings, fabricated on LAEIS HPF 1250 pressing machine, are blanks from which refractory precast shapes are manufactured by means of drying and firing. Samples for material density evaluation were cut out from test stampings with the use of diamond-reinforced disc. Density of the material was determined in thirteen layers of stampings denoted with letters A through M.

Quantum Magnetic Oscillations of the Surface Tension at a Metal-Insulator Interface

Any metal–insulator transition (MI transition) in a crystalline material must be a transition from a situation in which electronic bands overlap to a situation when they do not (Mott, Metal–insulator, 2nd edn. Taylor@Francis, London, 1990). For this case the self-consistent equations for the two-band conductor are formulated (cf. Dubovskii, JETP Lett. 99(1):22–26, 2014). The description of the MI phase transition is based on two order parameters. The first one is the material density distribution at the MI boundary \(\rho ({\vec {r}})\). The second one is a four-component complex vector in spin space \(\Upsilon ({\vec {r}})\). The value \(\Upsilon ({\vec {r}})\) determines the electron density in the metallic or semimetallic phase in the presence of an external magnetic field. Two different components of the vector describe possible spin states of electrons and holes inserted in the external magnetic field. The solution gives a singular behavior of the surface tension at the MI interface in the vicinity of the MI phase transition. At low temperature quantum oscillations of the surface tension in the magnetic field take place.

Structural Design Optimization of Dynamic Crack Propagation Problems Using Peridynamics

Based on a bond-based peridynamics theory for dynamic crack propagation problems, this paper presents a design sensitivity analysis and optimization method. Peridynamics has a peculiar advantage over the existing continuum theory in the mathematical modelling of problems where discontinuities arise. For the design optimization of the crack propagation problems, a non-shape design sensitivity is derived using the adjoint variable method. The obtained adjoint sensitivity of displacement and strain energy turns out to be very accurate and efficient compared to the finite different sensitivity. The obtained design sensitivities are futher utilized to optimally control the position of bifurcation point in the design optimization of crack propagation in a plate under tension. A numerical experiment demonstrates that the optimal distribution of material density could delay the position of bifurcation.

Mapping the complete bonding network in KBH4 using the combined power of powder diffraction and maximum entropy method

The combined power of the maximum entropy method (MEM) and synchrotron powder X-ray diffraction (SPXRD) is exerted to accurately reconstruct the electron density distribution (EDD) of the hydrogen storage material, KBH4. Its crystal structure features thermally activated disorder among the BH4- moieties, and weak secondary bonding effects occupy a key role in determining the energetic barrier for this dynamical effect. The MEM reconstruction is meticulously optimised and inspected for errors, in what may be envisaged as a general manual for this kind of studies. The successful outcome constitutes an experimental EDD of cutting-edge quality, from which atomic charges and the complete bonding network are mapped by topological descriptors. Remarkably, the chemical insights even extend to the delicate interplay of closed-shell bonding in excellent correspondence with ab initio and two-channel MEM calculations. For the current class of functional materials, access to such subtle electronic features is essential for the fundamental understanding of hydrogen desorption pathways.

Proposal and use of a void model for inclusion cracking for simulating inner fracture defects in drawing of ferrite–pearlite steels

A void model for inclusion cracking is proposed and used for simulating inner fracture defects in the drawing of ferrite–pearlite steels. First, a void model for inclusion cracking is proposed based on the void model for inclusion-matrix separation previously proposed by the author. Next the simulation and experiment of the multipass drawing are performed using four types of ferrite–pearlite steels. The inner diameter of the die at which the material fractures, the material density distribution in the radial direction after drawing through the die preceding that at which the material fractures, and the material shape in the longitudinal section after drawing through the die at which the material fractures calculated from the simulation, are compared with those obtained experimentally. Finally, the validity of the proposed void model is confirmed by comparing the simulation and experimental results.

Modeling electron density distributions from X-ray diffraction to derive optical properties: Constrained wavefunction versus multipole refinement

The rational design of next-generation optical materials requires an understanding of the connection between molecular structure and the solid-state optical properties of a material. A fundamental challenge is to utilize the accurate structural information provided by X-ray diffraction to explain the properties of a crystal. For years, the multipole refinement has been the workhorse technique for transforming high-resolution X-ray diffraction datasets into the detailed electron density distribution of crystalline material. However, the electron density alone is not sufficient for a reliable calculation of the nonlinear optical properties of a material. Recently, the X-ray constrained wavefunction refinement has emerged as a viable alternative to the multipole refinement, offering several potential advantages, including the calculation of a wide range of physical properties and seeding the refinement process with a physically reasonable starting point. In this study, we apply both the multipole refinement and the X-ray constrained wavefunction technique to four molecules with promising nonlinear optical properties and diverse structural motifs. In general, both techniques obtain comparable figures of merit and generate largely similar electron densities, demonstrating the wide applicability of the X-ray constrained wavefunction method. However, there are some systematic differences between the electron densities generated by each technique. Importantly, we find that the electron density generated using the X-ray constrained wavefunction method is dependent on the exact location of the nuclei. The X-ray constrained wavefunction refinement makes smaller changes to the wavefunction when coordinates from the Hartree-Fock-based Hirshfeld atom refinement are employed rather than coordinates from the multipole refinement, suggesting that coordinates from the Hirshfeld atom refinement allow the X-ray constrained wavefunction method to produce more accurate wavefunctions. We then use the experimentally derived wavefunctions to calculate the molecular dipole moment, polarizability, hyperpolarizability, and refractive index and show that these are in good agreement with the values calculated using ab initio methods. Thus, this study shows that experimental wavefunctions can be reliably generated from X-ray diffraction datasets, and that optical properties can be reliably calculated from these wavefunctions. Such a concerted interplay of experiment and computation via the X-ray constrained wavefunction refinement stands to enable the molecular engineering of tailor-made next-generation optical materials.

Assessing the Nanoscale Structure and Mechanical Properties of Polymer Monoliths used for Chromatography

Concerning polymeric monolithic materials utilized in separation science, the structural and mechanical characteristics from the nanoscopic to the macroscopic scale remain of great interest. Suitable analytical tools are urgently required to understand the polymer monolith's constituent structure, particularly in the case of nanoscale polymer properties that tend to develop gel porosity in contact with a mobile phase ultimately affecting the chromatographic performance. Herein described are our first findings from a characterization of commercially available analytical polymer monoliths based on styrene/divinylbenzene and methacrylate chemistries utilizing confocal Raman spectroscopy imaging and atomic force microscopy (AFM). Confocal Raman spectroscopy can be used to generate a three-dimensional representation of monoliths in both dry state and in contact with solvent. AFM force-indentation measurements on individual cross-sectioned globular features permit detailed assessment of mechanical properties of the stationary phase. This approach allowed so far unprecedented insight and identification of a heterogeneous cross-link density distribution of polymer material within individual globular features on a submicrometer scale.

Sedimentary Features of Tsunami Deposits in Carbonate-Dominated Beach Environments: A Case Study from the 25 October 2010 Mentawai Tsunami

This study provides a case history of tsunami deposition in a carbonate-dominated environmental setting. We present the results of a sedimentological investigation conducted on deposits formed by the 25 October 2010 Mentawai Island Tsunami and report on deposits analyzed at three sites on North Pagai Island: Sabeu Gunggung, Macaroni Resort, and Tumalei. The deposits are mainly composed of medium to coarse sand-sized fragments of corals, shells and foraminifera, with thickness ranging from 3 to 26 cm. The deposits consist of two to five layers, with fining-upward trends dominating. Local topography noticeably affects the thickness, number of layers, and distribution of tsunami deposits. The foraminiferal assemblage and diversity vary at each sample point, along transect and between different transects. Based on the foraminiferal content, most of the deposit material likely came from shallower depths. In addition, density distribution of the tsunami deposit material exhibits some degree of variability in terms of the range of densities in each sample and the trend of the overall density along each transect. In contrast to heavy mineral-dominated deposits, the density of carbonate grains as a function of size may be an important consideration when carbonate-dominated deposits are used to interpret hydraulic conditions that created a particular tsunami deposit. Since there are relatively few studies of tsunami deposits in carbonate-dominated environmental settings such as the Mentawai Islands, our study provides a useful case history of tsunami deposition in such an environmental setting.

Three-Dimensional Layout Design of Steel-Concrete Composite Structures Using Topology Optimization

For generating a more reasonable initial layout configuration, a three-dimensional topology optimization methodology of the steel-concrete composite structure is presented. Following Solid Isotropic Material with Penalization (SIMP) approach, an artificial material model with penalization for elastic constants is assumed and elemental density variables are used for describing the structural layout. The considered problem is thus formulated as to find the optimal material density distribution that minimizes the material volume under specified displacement constraints. By using the adjoint variable method for the sensitivity analysis, the optimization problem is efficiently solved by the gradient-based optimization algorithm. Numerical result shows that the proposed topology approach presented a novel structural topology of the simply-supported steel-concrete composite beam.

Single-loop system reliability-based topology optimization considering statistical dependence between limit-states

This paper presents a single-loop algorithm for system reliability-based topology optimization (SRBTO) that can account for statistical dependence between multiple limit-states, and its applications to computationally demanding topology optimization (TO) problems. A single-loop reliability-based design optimization (RBDO) algorithm replaces the inner-loop iterations to evaluate probabilistic constraints by a non-iterative approximation. The proposed single-loop SRBTO algorithm accounts for the statistical dependence between the limit-states by using the matrix-based system reliability (MSR) method to compute the system failure probability and its parameter sensitivities. The SRBTO/MSR approach is applicable to general system events including series, parallel, cut-set and link-set systems and provides the gradients of the system failure probability to facilitate gradient-based optimization. In most RBTO applications, probabilistic constraints are evaluated by use of the first-order reliability method for efficiency. In order to improve the accuracy of the reliability calculations for RBDO or RBTO problems with high nonlinearity, we introduce a new single-loop RBDO scheme utilizing the second-order reliability method and implement it to the proposed SRBTO algorithm. Moreover, in order to overcome challenges in applying the proposed algorithm to computationally demanding topology optimization problems, we utilize the multiresolution topology optimization (MTOP) method, which achieves computational efficiency in topology optimization by assigning different levels of resolutions to three meshes representing finite element analysis, design variables and material density distribution respectively. The paper provides numerical examples of two- and three-dimensional topology optimization problems to demonstrate the proposed SRBTO algorithm and its applications. The optimal topologies from deterministic, component and system RBTOs are compared with one another to investigate the impact of optimization schemes on final topologies. Monte Carlo simulations are also performed to verify the accuracy of the failure probabilities computed by the proposed approach.

A study of the material density distribution of space debris

Material density is an important, yet often overlooked, property of orbital debris particles. Many models simply use a typical density to represent all breakup fragments. While adequate for modeling average characteristics in some applications, a single value material density may not be sufficient for reliable impact damage assessments. In an attempt to improve the next-generation NASA Orbital Debris Engineering Model, a study on the material density distribution of the breakup fragments has been conducted and summarized in this paper.The material density distribution of the on-orbit breakup debris population may be estimated by combining three sources of data: available pre-launch information on satellite materials, ground-based satellite breakup experiments, and chemical compositions of residuals collected from returned surfaces. Analysis of these data provides a basis to compile a simple mass density distribution. For example, about 75% of on-orbit breakup debris fragments come from upper stages, which are simpler and more standardized than payloads in construction and composition. Available material information from manufacturers can be used to develop a reasonable distribution function for this component. For spacecraft breakup debris, it has been found that the range of material densities may be simplified into three representative values: high (e.g. steel), medium (e.g. aluminum), and low (e.g. plastic). The current study develops preliminary distributions for breakup debris: rocket body debris is 90% medium-density and 10% high-density (by number); payload debris is 70% low-density, 27% medium, and 3% high-density. Although the three data sources mentioned above are not comprehensive, and some interpretation and extrapolation are needed, the resulting density distributions still represent a step forward in providing more reliable damage assessments for future debris models. Future work will refine the data and provide distributions as functions of particle size and orbital altitude.

Possible evidence for a common radial structure in nearby AGN tori

We present a quantitative and relatively model-independent way to assess the radial structure of nearby AGN tori. These putative tori have been studied with long-baseline infrared (IR) interferometry, but the spatial scales probed are different for different objects. They are at various distances and also have different physical sizes that apparently scale with the luminosity of the central engine. Here we look at interferometric size information, or visibilities, as a function of spatial scales normalized by the size of the inner torus radius Rin. This approximately eliminates luminosity and distance dependence and, thus, provides a way to uniformly view the visibilities observed for various objects and at different wavelengths. We can construct a composite visibility curve over a wide range of spatial scales if different tori share a common radial structure. The currently available observations do suggest, independent of models, a common radial surface brightness distribution in the mid-IR that is roughly of a power-law form r −2 as a function of radius r and extends to ∼100 times Rin. Taking into account the temperature decrease toward outer radii with a simple torus model, this corresponds to the radial surface density distribution of dusty material directly illuminated by the central engine roughly in the range between r 0 and r −1 . This should be tested with further data.

Design of cellular structures for optimum efficiency of heat dissipation

Metal cellular material is a new material attractive for its light weight and potential multifunctionality. In the present paper, we study cylindrical structures made of linear metal cellular material. The outer surface of the cylindrical structure is subjected to thermal boundary condition, and cooling fluid is forced through the cylinder to remove heat through the inner cell walls. Optimum design aims at maximization of heat dissipation efficiency under prescribed flow pressure. Two classes of design variables, relative density, and local aperture distribution of cellular material are to be determined by optimization under given total material volume constraints. Although similar to the structural topology optimization concept of material distribution, our formulation results in a structure with realistic cellular material of finite-sized aperture. Numerical results for different cross-sectional shapes and thermal boundary conditions are presented. Interestingly, our present formulation leads to optimum designs for cellular structures that mimic natural biomaterials. We discuss in general the guideline for cellular structure design to maximize heat dissipation efficiency based on insights from these optimization results.

Can a Trigonometric Function Serve Both as the Vibration and the Buckling Mode of an Axially Graded Structure?

It is well known that for homogeneous beams that have simply supported or guided ends a trigonometric function serves both as a vibration and a buckling mode. The research in this paper shows that, remarkably, the same result is valid for some axially graded beams. Specifically, three cases of harmonically varying vibration modes are postulated and the associated semi-inverse problems that result in the distributions of elastic modulus that together with a specific variation of material density and axial load distribution satisfy the governing eigenvalue problem for the inhomogeneous Bernoulli-Euler beam are solved. In all cases the closed-form solutions are obtained for the natural frequency. Those closed-form solutions are contrasted with approximate solutions based on appropriate polynomial functions, serving as trial functions in an energy method.

Measurement of density variations in tablets using X-ray computed tomography

In this paper the application of X-ray computed tomography (CT) to measure the material density distribution in pharmaceutical tablets is discussed. X-ray CT is a non-destructive inspection technique which provides cross-sectional images in different planes through a component. The CT image values provide information on the local X-ray attenuation coefficients. For a particular material and X-ray energy, X-ray attenuation is approximately proportional to material density. Determination of quantitative density distributions requires consideration of non-linear instrumental effects including scatter and “beam hardening”. Density maps in tablets manufactured under controlled conditions are presented. The results are discussed with reference to the local properties of the material within the tablet and the tablet design features.

Reconstruction of the surface layer density profile by the X-ray reflectometry method

The method for reconstructing the profile of the material density distribution arbitrarily varying over the depth of the subsurface layer of the specimen from X-ray reflectometry data is suggested. For the first time, the recurrent relationships for the derivatives of the specular reflection coefficient with respect to the parameters of the subsurface layer are obtained, which reduce the volume of the necessary computations by one to two orders of magnitude. The class of functions for which such density-profile reconstruction can be made within a 5% error is characterized. The method is tested on thin tungsten and carbon films on silicon substrates and thin films of porous silicon films with p+-type conductivity.

Analysis of Inner Fracture Defect in Drawing Using a Micromodel.

Using our proposed and modified micromodel which judges whether ductile fracture occurs or not and our proposed evolution equation which represents the change of void volume fraction, analysis of inner fracture defect in drawing is performed. The obtained results are summarized as follows. Firstly, the two types of void shape and those of void configuration in our previous papers are unified and one type of void shape and that of void configuration are defined. Secondly, the inner diameter of the die at which the material fractures, the material density distribution in the radial direction after drawing through the die which precedes the die at which the material fractures, and the shape of inner fracture defect after drawing through the die at which the material fractures, calculated from analysis agree with those obtained by experiment. Thirdly, the inner diameter of the die at which the material fractures calculated from analysis agrees with that calculated using the Oyane's equation of fracture criterion. The number of unknown constant in our proposed evolution equation is equal to that in the Oyane's equation. Hence, the validity of our proposed micromodel and evolution equation is confirmed.

Proposal and use of a void model for the simulation of ductile fracture behavior

A ductile fracture model derived from a microscopic point of view is proposed and is proved to be effective in the analysis of multipass drawing. First, a method of predicting ductile fracture is proposed using a model from a microscopic point of view. The relationship between the void volume fraction and the strain to fracture, calculated from the model, agrees well with the relationship obtained from the Thomason model. Next, the analysis and experiment of multipass drawing are performed using various reductions in area and die angles. The inner diameter of the die at which the material fractures and the material density distribution in the radial direction, calculated from the analysis, agree with those obtained from the experiment. Finally, a simulation of drawing at the die at which the material fractures is performed and inner fracture defects are observed to appear periodically in the drawing direction.

Results of geological and archaeological observations at Switchback Road Pit, Maidenhead, Berkshire

Gravel extraction at Switchback Road Pit, Maidenhead, which lay between Cannoncourt Farm, Furze Platt and Lower Mount Farm, Cookham - two of the most important locations for Palaeolithic handaxes in the middle Thames Valley - was monitored as an archaeological condition of planning consent. Extraction at Switchback Road has now ceased and the results have identified the probable northern extent of the Furze Platt implement scatter and an additional discrete cluster of Palaeolithic handaxes within an otherwise low density distribution of material. Most of these implements are in a slightly rolled condition, indicating that they have not moved far from their original point of deposition. Lithological analyses have confirmed the geological deposits as part of the Lynch Hill Gravel, which was probably deposited between Oxygen Isotope Stages 10 and 8 (350 000-250 000 bp ).