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Journal articles on the topic 'Structure density'

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Published: 4 June 2025
Last updated: 23 June 2025

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1

Phillips, Michael C. "High density lipoprotein structure." Frontiers in Bioscience 8, no. 4 (2003): d1044–1054. http://dx.doi.org/10.2741/1077.

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2

DiCarlo, D., R. E. Thorne, E. Sweetland, M. Sutton, and J. D. Brock. "Charge-density-wave structure inNbSe3." Physical Review B 50, no. 12 (1994): 8288–96. http://dx.doi.org/10.1103/physrevb.50.8288.

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3

Henderson, Thomas M., Carlos A. Jiménez-Hoyos, and Gustavo E. Scuseria. "Magnetic Structure of Density Matrices." Journal of Chemical Theory and Computation 14, no. 2 (2017): 649–59. http://dx.doi.org/10.1021/acs.jctc.7b01016.

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4

Percus, J. K. "The structure of density functionals." Journal of Physics: Condensed Matter 6, no. 23A (1994): A125—A130. http://dx.doi.org/10.1088/0953-8984/6/23a/015.

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5

Gonzalez Carmona, Juan Manuel, Alexander Ruden Muñoz, Christian Barbosa, Carolina Ortega Portilla, and Federico Sequeda Osorio. "Computational Study of Allotropic Structures of Carbon by Density Functional Theory (DTF)." Ingeniería y Ciencia 10, no. 19 (2014): 145–62. http://dx.doi.org/10.17230/ingciencia.10.19.7.

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In this paper using Density Functional Theory (DFT), the principal carbonallo tropic crystalline structures (Diamond, graphite, nanotube y fullerene-C60) were simulated. The results shows diamond sp3 bonds formation between carbon atomsand low reactivity, indicating low probability of lateral compound formation and high mechanical properties. Interplanar weakness was evidentin graphite structure, which is related to solid lubrication process. Carbon-Carbon metallic bonds and polarizations at the edges of the structure were observed in Armchair Carbon Nanotube, stabilizing the system which allows the nanotube continuous growth. In fullerene C60structureaFaraday nano-gauge behavior was confirmed, together withlowprobability of interatomic polarization, indicating high structural stability. Besides Total Energy (TE) and Nuclear Repulsion Energy (NRE) values were used to perform energetic comparisons between different structures, allowing the study of electronic stability and their relationship to mechanical properties.
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6

Sun, Yan, and René Fournier. "Density Functional Study of Beryllium Clusters." Computing Letters 1, no. 4 (2005): 210–19. http://dx.doi.org/10.1163/157404005776611448.

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Beryllium clusters Ben (n=2-20) were studied by Kohn-Sham theory with the local spin density approximation. We used a Tabu Search algorithm for structure optimization. The lowest energy structures fall into three distinct categories: compact structures typical of pairwise potentials for n=3–7; cage structures where all atoms have nearly equal coordinations for n=8–14; compact fragments of the hcp crystal at n =15–20. The electronic structure gradually evolves from van der Waals interactions (n =2,3) to metallic(n≥ 13). All clusters have singlet ground-states except n = 6 and n = 9 which are triplets. We also found low-lying excited triplet states at n=8 and 19 and a low-lying quintet state at n =7. In agreement with the jellium model, we find that clusters with n =4, 10, 17, and 20 atoms are especially stable and that the structures for n =4, 10, and 20 are quasi-spherical.
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Śledź, Paweł, Radosław Kamiński, Maksymilian Chruszcz, Matthew D. Zimmerman, Wladek Minor, and Krzysztof Woźniak. "An experimental charge density of HEPES." Acta Crystallographica Section B Structural Science 66, no. 4 (2010): 482–92. http://dx.doi.org/10.1107/s0108768110023025.

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We report the experimental charge density of HEPES [4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid], which is a common buffering agent. The structure was refined using the Hansen–Coppens formalism. The ability of the HEPES molecule to form stable intermolecular interactions and intermolecular hydrogen bonds in the crystal structure is discussed in terms of its buffering properties. The protonation mode observed in the crystal structure is different from that expected in solution, suggesting that additional factors must be taken into consideration in order to explain the solution properties of the compound. As ordered HEPES molecules are found in the active sites of proteins in several protein crystal structures, our results will allow for quantitative analysis of the electrostatic potential of the interacting surfaces of those proteins.
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8

Yao, Changhong, Meijiao Wang, and Lianzhen Cao. "Hydrogenated Planar Aluminum Clusters: A Density Functional Theory Study." Molecules 30, no. 6 (2025): 1389. https://doi.org/10.3390/molecules30061389.

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The low-lying energy structures of small planar aluminum clusters Aln (n = 3–6, 8–10), hydrogenated small planar aluminum clusters AlnHm (n = 3–8, m = 1–2) and the lowest-energy structure of AlnHm (n = 6–10, m = 0–2) are determined by density functional theory (DFT) calculations. Many stable planar structures have been found; some are consistent with the reported ones, and some are new configurations. The preservation of planar cluster structures has been observed during the dissociative adsorption of H2.Hydrogen is adsorbed at different positions on planar aluminum clusters. Dissociative adsorption configurations of the planar structure and lowest-energy structure experienced a decrease in hydrogen adsorption energy with an increase in cluster size. Among the clusters we calculated, Al4H1 and Al4H2 have the highest HOMO-LUMO gap, indicating that they may be more abundant than other clusters. The geometric structure and electronic properties of these clusters are also discussed.
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9

Lin, Yuxiang, Wentian Shi, Xiaohong Sun, et al. "Influence of Density Gradient on the Compression of Functionally Graded BCC Lattice Structure." Materials 16, no. 2 (2023): 520. http://dx.doi.org/10.3390/ma16020520.

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In this paper, five grading functional gradient lattice structures with a different density perpendicular to the loading direction were proposed, and the surface morphology, deformation behavior, and compression properties of the functional gradient lattice structures prepared by selective laser melting (SLM) with Ti-6Al-4V as the building material were investigated. The results show that the characteristics of the laser energy distribution of the SLM molding process make the spherical metal powder adhere to the surface of the lattice structure struts, resulting in the actual relative density of the lattice structure being higher than the designed theoretical relative density, but the maximum error does not exceed 3.33%. With the same relative density, all lattice structures with density gradients perpendicular to the loading direction have better mechanical properties than the uniform lattice structure, in particular, the elastic modulus of LF, the yield strength of LINEAR, and the first maximum compression strength of INDEX are 28.99%, 16.77%, and 14.46% higher than that of the UNIFORM. In addition, the energy absorption per unit volume of the INDEX and LINEAR is 38.38% and 48.29% higher, respectively, than that of the UNIFORM. Fracture morphology analysis shows that the fracture morphology of these lattice structures shows dimples and smooth planes, indicating that the lattice structure exhibits a mixed brittle and ductile failure mechanism under compressive loading. Finite element analysis results show that when the loading direction is perpendicular to the density gradient-forming direction, the higher density part of the lattice structure is the main bearing part, and the greater the density difference between the two ends of the lattice structure, the greater the elastic modulus.
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10

Yu Dong, Yu Dong, Guanglong Wang Guanglong Wang, Haiqiao Ni Haiqiao Ni, et al. "Short-wave infrared detector with double barrier structure and low dark current density." Chinese Optics Letters 14, no. 2 (2016): 022501–22505. http://dx.doi.org/10.3788/col201614.022501.

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11

Nefedov, V. G., and V. V. Matveev. "Structure, density and viscosity of water." Voprosy Khimii i Khimicheskoi Tekhnologii, no. 4 (July 2021): 96–105. http://dx.doi.org/10.32434/0321-4095-2021-137-4-96-105.

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We analyzed the possibilities of the use of the cluster model of water to assess its viscosity. The Nemethy-Scheraga model was used in our study. In a simplified version, this model implies the presence of water cluster that are linked by hydrogen bonds as well as individual molecules (monomolecules) interacting only by van der Waals forces. The paper gives an estimation of average cluster size. Based on the experimental temperature dependences of viscosity and density, the content of monomolecules in water was approximately determined. In the first case, the ratio of the viscosity of water to monomolecules was estimated from the inverse Arrhenius temperature dependence of viscosity by considering experimental activation energy ~18.6 kJ mol–1 (0÷300C) and energy of dispersion interactions ~7.4 kJ mol–1. Then, the volumetric content of monomolecules was estimated by using the inverse Betchelor's formula, which relates the viscosity of the suspension (clusters) and dispersion medium (monomolecules) to their ratio. On the other hand, a similar estimation was performed based on the density of water, clusters that were considered similar to ice floes, and the estimated density of monomolecules. Both estimates showed that the volumetric content of water not bound into clusters does not exceed 9%. It was concluded that the structure of water most likely corresponds to the clathrate model, according to which some of the H2O molecules move into the middle of ice-like clusters, and vacancies are stabilized by H3O+–OH– pairs.
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12

Schmidt, Matthias. "Fluid structure from density-functional theory." Physical Review E 62, no. 4 (2000): 4976–81. http://dx.doi.org/10.1103/physreve.62.4976.

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13

Hoffman, Y., and J. Shaham. "Local density maxima - Progenitors of structure." Astrophysical Journal 297 (October 1985): 16. http://dx.doi.org/10.1086/163498.

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14

Kohn, W., A. D. Becke, and R. G. Parr. "Density Functional Theory of Electronic Structure." Journal of Physical Chemistry 100, no. 31 (1996): 12974–80. http://dx.doi.org/10.1021/jp960669l.

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15

Merabia, Samy, and Ignacio Pagonabarraga. "Density dependent potentials: Structure and thermodynamics." Journal of Chemical Physics 127, no. 5 (2007): 054903. http://dx.doi.org/10.1063/1.2751496.

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16

Doweidar, H. "Density-structure correlations in silicate glasses." Journal of Non-Crystalline Solids 249, no. 2-3 (1999): 194–200. http://dx.doi.org/10.1016/s0022-3093(99)00310-5.

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17

Mestechkin, M. M., G. T. Klimko, and G. E. Vaiman. "Density matrix, superconductivity and molecular structure." Theoretical and Experimental Chemistry 27, no. 4 (1991): 341–56. http://dx.doi.org/10.1007/bf01372506.

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18

WEISSMAN, Paul R., and Stephen C. LOWRY. "Structure and density of cometary nuclei." Meteoritics & Planetary Science 43, no. 6 (2008): 1033–47. http://dx.doi.org/10.1111/j.1945-5100.2008.tb00691.x.

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19

Gineitite, V. L., and D. B. Shatkovskaya. "Density matrix structure for saturated molecules." Journal of Structural Chemistry 29, no. 5 (1989): 659–64. http://dx.doi.org/10.1007/bf00748136.

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20

Edmunds, Peter J., Hannah R. Nelson, and Lorenzo Bramanti. "Density-Dependence Mediates Coral Assemblage Structure." Bulletin of the Ecological Society of America 100, no. 1 (2019): e01472. http://dx.doi.org/10.1002/bes2.1472.

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21

Edmunds, Peter J., Hannah R. Nelson, and Lorenzo Bramanti. "Density‐dependence mediates coral assemblage structure." Ecology 99, no. 11 (2018): 2605–13. http://dx.doi.org/10.1002/ecy.2511.

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22

Tenzer, Robert. "Mathematical models of the Earth’s density structure and their applications in gravimetric forward modeling." Contributions to Geophysics and Geodesy 45, no. 2 (2015): 67–92. http://dx.doi.org/10.1515/congeo-2015-0014.

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Abstract A generalized mathematical model of the Earth’s density structure is presented in this study. This model is defined based on applying the spectral expressions for a 3-D density distribution within the arbitrary volumetric mass layers. The 3-D density model is then converted into a form which describes the Earth’s density structure by means of the density-contrast interfaces between the volumetric mass layers while additional correction terms are applied to account for radial density changes. The applied numerical schemes utilize methods for a spherical harmonic analysis and synthesis of the global density structure models. The developed the Earth’s density models are then defined in terms of the spherical density and density-contrast functions. We also demonstrate how these Earth’s density models can be applied in the gravimetric forward modeling and discuss some practical aspects of representing mathematically density structures within particular components of the Earth’s interior.
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23

Calaminici, Patrizia, José M. Vásquez-Pérez, and Diego A. Espíndola Velasco. "A density functional study of Rh13." Canadian Journal of Chemistry 91, no. 7 (2013): 591–97. http://dx.doi.org/10.1139/cjc-2012-0493.

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A density functional study was performed for the Rh13 cluster using the linear combination of Gaussian-type orbitals density functional theory (LCGTO-DFT) approach. The calculations employed both the local density approximation (LDA) as well as the generalized gradient approximation (GGA) in combination with a quasi-relativistic effective core potential (QECP). Initial structures for the geometry optimization were taken along Born–Oppenheimer molecular dynamics (BOMD) trajectories. The BOMD trajectories were performed at different temperatures and considered different potential energy surfaces (PES). As a result, several hundred isomers of the Rh13 cluster in different spin multiplicities were optimized with the aim to determine the lowest energy structures. All geometry optimizations were performed without any symmetry restriction. A vibrational analysis was performed to characterize these isomers. Structural parameters, relative stability energy, harmonic frequencies, binding energy, and most relevant Kohn–Sham (KS) molecular orbitals are reported. The obtained results are compared with available data from the literature. This study predicts a low symmetry biplanarlike structure as the ground-state structure of Rh13 with 11 unpaired electrons. This isomer was first noticed by inspection of first-principle Born–Oppenheimer molecular dynamics (BOMD) simulations between 300 and 600 K. This represents the most extensive theoretical study on the ground-state structure of the Rh13 cluster and underlines the importance of BOMD simulations to fully explore the PES landscapes of complicated systems.
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24

Sturm, K. "Dynamic Structure Factor: An Introduction." Zeitschrift für Naturforschung A 48, no. 1-2 (1993): 233–42. http://dx.doi.org/10.1515/zna-1993-1-244.

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Abstract The doubly differential cross-section for weak inelastic scattering of waves or particles by manybody systems is derived in Born approximation and expressed in terms of the dynamic structure factor according to van Hove. The application of this very general scheme to scattering of neutrons, x-rays and high-energy electrons is discussed briefly. The dynamic structure factor, which is the space and time Fourier transform of the density-density correlation function, is a property of the many-body system independent of the external probe and carries information on the excitation spectrum of the system. The relation of the electronic structure factor to the density-density response function defined in linear-response theory is shown using the fluctuation-dissipation theorem. This is important for calculations, since the response function can be calculated approximately from the independent-particle response function in self-consistent field approximations, such as the random-phase approximation or the local-density approximation of the density functional theory. Since the density-density response function also determines the dielectric function, the dynamic structure can be expressed by the dielectric function.
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25

Huo, Jin-Rong, Lu Li, Hai-Xia Cheng, Xiao-Xu Wang, Guo-Hua Zhang, and Ping Qian. "The structural, electronic and optical properties of Au–ZnO interface structure from the first-principles calculation." Modern Physics Letters B 32, no. 07 (2018): 1850107. http://dx.doi.org/10.1142/s0217984918501075.

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The interface structure, electronic and optical properties of Au–ZnO are studied using the first-principles calculation based on density functional theory (DFT). Given the interfacial distance, bonding configurations and terminated surface, we built the optimal interface structure and calculated the electronic and optical properties of the interface. The total density of states, partial electronic density of states, electric charge density and atomic populations (Mulliken) are also displayed. The results show that the electrons converge at O atoms at the interface, leading to a stronger binding of interfaces and thereby affecting the optical properties of interface structures. In addition, we present the binding energies of different interface structures. When the interface structure of Au–ZnO gets changed, furthermore, varying optical properties are exhibited.
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26

Xie, Miaoxia, Peng Zhang, Minghui Zhu, et al. "Energy Flow Analysis of High-Frequency Flexural Vibration of Wedge Beam Structures." Shock and Vibration 2022 (March 31, 2022): 1–10. http://dx.doi.org/10.1155/2022/2935655.

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Wedge members with variable thickness are widely used in ship structures, aerospace structures, and building structures. Considering their application scenarios, their high-frequency vibration characteristics have important research value. Energy finite element analysis (EFEA) is a powerful tool to predict high-frequency vibration response. EFEA is essentially applying finite element analysis to solve the energy density governing equation. However, the equation for wedge beam is missing. Energy flow analysis aims to obtain energy density governing equation. The energy flow model of wedge beam with variable thickness is established in this paper. Firstly, according to the geometric acoustic approximation method, the general displacement solution of the bending deformation equation for a wedge beam is deduced. Furthermore, the wave dispersion relation of bending deformation of wedge beam is derived. Then, the relationship between the time-averaged vibration energy density and energy flow of the wedge beam is also derived. Also, the governing equation taking energy density as a variable of the wedge beam structure is derived through the energy balance relationship in the microelement body. The governing equation is numerically solved, and the energy density distribution on the wedge beam structure is calculated. Finally, the energy density distribution of uniform beam and wedge beam under the same excitation is analyzed and summarized; the influence of different excitation frequencies and power exponent of thickness change on the performance of wedge beam structure is also summarized. Geometrically, the wedge beam satisfies the one-dimensional acoustic black hole structure. The calculation results show that the energy density on the beam structure increases with the decrease of thickness and reaches its maximum near the tip. The wedge acoustic black hole beam structure has a good energy absorption effect with a frequency between 250 Hz and 2000 Hz. With the further increase of excitation frequency, the energy absorption effect of the wedge beam structure has dropped significantly.
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27

Mostafa, Khaled G., Guilherme A. Momesso, Xiuhui Li, David S. Nobes, and Ahmed J. Qureshi. "Dual Graded Lattice Structures: Generation Framework and Mechanical Properties Characterization." Polymers 13, no. 9 (2021): 1528. http://dx.doi.org/10.3390/polym13091528.

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Additive manufacturing (AM) enables the production of complex structured parts with tailored properties. Instead of manufacturing parts as fully solid, they can be infilled with lattice structures to optimize mechanical, thermal, and other functional properties. A lattice structure is formed by the repetition of a particular unit cell based on a defined pattern. The unit cell’s geometry, relative density, and size dictate the lattice structure’s properties. Where certain domains of the part require denser infill compared to other domains, the functionally graded lattice structure allows for further part optimization. This manuscript consists of two main sections. In the first section, we discussed the dual graded lattice structure (DGLS) generation framework. This framework can grade both the size and the relative density or porosity of standard and custom unit cells simultaneously as a function of the structure spatial coordinates. Popular benchmark parts from different fields were used to test the framework’s efficiency against different unit cell types and grading equations. In the second part, we investigated the effect of lattice structure dual grading on mechanical properties. It was found that combining both relative density and size grading fine-tunes the compressive strength, modulus of elasticity, absorbed energy, and fracture behavior of the lattice structure.
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28

Toshihiro, Handa, Yoda Takahiro, and Kuno Nario. "Gas density histograms of galaxies: the observational density probability function of the interstellar gas density." Proceedings of the International Astronomical Union 10, H16 (2012): 619. http://dx.doi.org/10.1017/s1743921314012484.

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AbstractIn the steady state, the probability density function (PDF) of the gaseous interstellar matter (ISM) can be observed as a gas density histogram (GDH) of all cells in the system. We made GDHs of the Milky Way Galaxy (MWG) using Galactic plane surveys in CO lines. We found that the GDH in the MWG is log-normal which suggests that the density structure of the molecular gas is a result of many stochastic processes. Using the Nobeyama CO atlas, we made GDHs of nearby galaxies but in column density. Although some galaxies show log-normal, the others show completely different shapes, suggesting that the density structure of galaxies may be different from galaxy to galaxy.
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29

Xia, Ye, Chengqing Wu, and Terry Bennett. "An analytical model of linear density foam–protected structure under blast loading." International Journal of Protective Structures 8, no. 3 (2017): 454–72. http://dx.doi.org/10.1177/2041419617721543.

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Aluminium foam is widely known as an energy absorptive material which can be used as a protective cladding on structures to enhance blast resistance of the protected structures. Previous studies show that higher density provides larger energy absorption capacity of aluminium foam, but results in a larger transmitted pressure to the protected structure. To lower the transmitted pressure without sacrificing the maximum energy absorption, graded density foam has been examined in this study. An analytical model is developed in this article to investigate the protective effect of linear density foam on response of a structure under blast loading. The model is able to simulate structural deformation with reasonable accuracy compared with experimental data. The sensitivity of density gradient of foam cladding on reinforced concrete structure is tested in the article.
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30

Seharing, Asliah, Abdul Hadi Azman, and Shahrum Abdullah. "Finite element analysis of gradient lattice structure patterns for bone implant design." International Journal of Structural Integrity 11, no. 4 (2020): 535–45. http://dx.doi.org/10.1108/ijsi-03-2020-0028.

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PurposeThe objective of this paper is to identify suitable lattice structure patterns for the design of porous bone implants manufactured using additive manufacturing.Design/methodology/approachThe study serves to compare and analyse the mechanical behaviours between cubic and octet-truss gradient lattice structures. The method used was uniaxial compression simulations using finite element analysis to identify the translational displacements.FindingsFrom the simulation results, in comparison to the cubic lattice structure, the octet-truss lattice structure showed a significant difference in mechanical behaviour. In the same design space, the translational displacement for both lattice structures increased as the relative density decreased. Apart from the relative density, the microarchitecture of the lattice structure also influenced the mechanical behaviour of the gradient lattice structure.Research limitations/implicationsGradient lattice structures are suitable for bone implant applications because of the variation of pore sizes that mimic the natural bone structures. The complex geometry that gradient lattice structures possess can be manufactured using additive manufacturing technology.Originality/valueThe results demonstrated that the cubic gradient lattice structure has the best mechanical behaviour for bone implants with appropriate relative density and pore size.
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31

WU, HAIYING, HONG ZHANG, XINLU CHENG, and LINGCANG CAI. "AB INITIO CALCULATIONS OF STRUCTURAL AND ELECTRONIC PROPERTIES OF THE COMPOUND Li3AlB2O6." Modern Physics Letters B 22, no. 05 (2008): 343–52. http://dx.doi.org/10.1142/s0217984908014882.

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The two equilibrium structures of the compound Li 3 AlB 2 O 6 have been investigated via the minimization of the total energy within Local Spin Density Approximation (LSDA) based on the Density Functional Theory (DFT) in our work. The calculated lattice parameters are all in good agreement with their corresponding experimental values. The relative stability of the two structures are determined. We find that the structure suggested by He et al. is more stable than that proposed by Abdullaev et al. at zero pressure conditions. The reasons for which the structure suggested by He et al. is more stable are also described. Then the electronic properties of the compound Li 3 AlB 2 O 6 including the density of states and energy band structure are successfully obtained and compared for the two structures. We find that the properties of insulator decreases from the structure suggested by He et al. to the structure proposed by Abdullaev et al.
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32

Kowiel, Marcin. "Normalized structure factor analysis with theCentroMKprogram." Journal of Applied Crystallography 46, no. 1 (2013): 88–92. http://dx.doi.org/10.1107/s0021889812050145.

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Statistical analysis of the normalized structure factorEis important during space-group determination. Several approaches to solve this problem have been described in the literature. In this paper, the most popular approach, the ideal asymptotic probability density function developed by Wilson, is compared with the more accurate exact probability density functions described by Shmueli and co-workers. Furthermore, a new computer program,CentroMK, for normalized structure factor analysis, is presented. The program is capable of plotting histograms of the normalized structure factors and exact probability density functions. Moreover, the program calculates five estimators helpful during the space-group determination: 〈|E|〉, 〈|E2 − 1|〉, %E> 2, %E< 0.25 and the discrepancyRfunction. The two approaches and the error rates of the five listed estimators are compared for nearly 30 600 crystal structures obtained fromActa Crystallographica Section E.It is shown that within a space group the means 〈|E|〉 and 〈|E2 − 1|〉 of real crystal structures show high variability. The comparison shows that decisions based on the exact probability density function are more accurate, the computing time is reasonable, and estimators 〈|E|〉, %E< 0.25 andRare the most accurate and should be preferred during space-group determination.
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33

Cheng, Shangcong. "The Origin of Anomalous Density Behavior of Silica Glass." Materials 16, no. 18 (2023): 6218. http://dx.doi.org/10.3390/ma16186218.

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The anomalous density–temperature relationship of vitreous silica with low hydroxyl content is explained by the formation of medium-range ordering structure in the glass transition process. The ordered medium-range structure has the shape of a “nanoflake” and consists of two layers of SiO4 tetrahedra, bonded by O atoms located in the middle of the structure. The nanoflakes interact with their surrounding structures through both covalent chemical bonds and van der Waals bonds. In the formation of the van der Waals bonds, the orientation of SiO4 tetrahedra can change, which results in an increase in distance between the nanoflakes and their surrounding structures. Thus, there is a slight volume enlargement associated with the formation of nanoflakes. Since the nanoflakes’ formation starts at a temperature near 1480 °C, and the population of the nanoflakes grows continuously as temperature decreases until about 950 °C, the bulk volume of silica glass increases in the temperature range from about 1480 °C to 950 °C. Therefore, the density anomaly of silica glass can be explained as a byproduct of forming of medium-range ordering structure in the silica glass transition.
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34

Gleiter, Herbert. "Nanoglasses: A Way to Solid Materials with Tunable Atomic Structures and Properties." Materials Science Forum 584-586 (June 2008): 41–48. http://dx.doi.org/10.4028/www.scientific.net/msf.584-586.41.

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Recently, a new class of materials - called nanoglasses - with a glassy structure was synthesized. The novel feature of these materials is that the atomic structure in the entire volume of the material as well as the density of the material can be tuned. Nanoglasses are generated by introducing interfaces into metallic glasses on a nanometer scale. Interfaces in these nanoglasses delocalize upon annealing, so that the free volume associated with these interfaces spreads throughout the volume of the glass. This delocalization changes the atomic structure and the density of the glass throughout the volume. In fact, by controlling the spacing between the interfaces introduced into the glass as well as the degree of the delocalization (by modifying the annealing time and/or annealing temperature), the atomic structures as well as the density (and hence all structure/density dependent properties) of nanoglasses may be controlled. A comparable tuning of the atomic structure/density of crystalline materials is not conceivable, because defects in crystals do not delocalize upon annealing.
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35

Xu, Min. "Electronic Structure and Optical Properties of Cu-Doped SnO2." Applied Mechanics and Materials 716-717 (December 2014): 20–23. http://dx.doi.org/10.4028/www.scientific.net/amm.716-717.20.

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based on Density Functional Theory, we investigated the optical structures and the electronic properties of Cu doped SnO2with density of 12.5%, including band structure, the density of state (dos), Dielectric function and optical absorption spectrum. The results show that Fermi level access conduction band gradually with the doped density. It has enhanced the electrical and metal property of material. The peaks of reflectivity spectrum and absorption spectrum correspond density of state.
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36

Hasnip, Philip J., Keith Refson, Matt I. J. Probert, Jonathan R. Yates, Stewart J. Clark, and Chris J. Pickard. "Density functional theory in the solid state." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 372, no. 2011 (2014): 20130270. http://dx.doi.org/10.1098/rsta.2013.0270.

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Density functional theory (DFT) has been used in many fields of the physical sciences, but none so successfully as in the solid state. From its origins in condensed matter physics, it has expanded into materials science, high-pressure physics and mineralogy, solid-state chemistry and more, powering entire computational subdisciplines. Modern DFT simulation codes can calculate a vast range of structural, chemical, optical, spectroscopic, elastic, vibrational and thermodynamic phenomena. The ability to predict structure–property relationships has revolutionized experimental fields, such as vibrational and solid-state NMR spectroscopy, where it is the primary method to analyse and interpret experimental spectra. In semiconductor physics, great progress has been made in the electronic structure of bulk and defect states despite the severe challenges presented by the description of excited states. Studies are no longer restricted to known crystallographic structures. DFT is increasingly used as an exploratory tool for materials discovery and computational experiments, culminating in ex nihilo crystal structure prediction, which addresses the long-standing difficult problem of how to predict crystal structure polymorphs from nothing but a specified chemical composition. We present an overview of the capabilities of solid-state DFT simulations in all of these topics, illustrated with recent examples using the CASTEP computer program.
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37

Carrozzini, Benedetta, Giovanni Luca Cascarano, and Carmelo Giacovazzo. "Phase improvementviathePhantom Derivativetechnique: ancils that are related to the target structure." Acta Crystallographica Section D Structural Biology 72, no. 4 (2016): 551–57. http://dx.doi.org/10.1107/s2059798316002023.

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Density modification is a general standard technique which may be used to improve electron density derived from experimental phasing and also to refine densities obtained byab initioapproaches. Here, a novel method to expand density modification is presented, termed thePhantom derivativetechnique, which is based on non-existent structure factors and is of particular interest in molecular replacement. ThePhantom derivativeapproach uses randomly generated ancil structures with the same unit cell as the target structure to create non-existent derivatives of the target structure, called phantom derivatives, which may be used forab initiophasing or for refining the available target structure model. In this paper, it is supposed that a model electron density is available: it is shown that ancil structures related to the target obtained by shifting the target by origin-permissible translations may be employed to refine model phases. The method enlarges the concept of the ancil, is as efficient as the canonical approach using random ancils and significantly reduces the CPU refinement time. The results from many real test cases show that the proposed methods can substantially improve the quality of electron-density maps from molecular-replacement-based phases.
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38

Jiang, Cho-Pei, Alvian Toto Wibisono, and Tim Pasang. "Selective Laser Melting of Stainless Steel 316L with Face-Centered-Cubic-Based Lattice Structures to Produce Rib Implants." Materials 14, no. 20 (2021): 5962. http://dx.doi.org/10.3390/ma14205962.

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Selective laser melting has a great potential to manufacture biocompatible metal alloy scaffolds or implants with a regulated porosity structure. This study uses five face-centered cubic (FCC) lattice structures, including FCC, FCC-Z, S-FCC, S-FCC-Z, and FCC-XYZ. Specimens with different lattice structures are fabricated using two laser energy densities, 71 J/mm3 and 125 J/mm3. Density, tensile, compressive and flexural test results exhibit the effect of laser parameters and lattice structure geometries on mechanical properties. The higher laser energy density of 125 J/mm3 results in higher properties such as density, strength, and Young’s modulus than the laser energy density of 71 J/mm3. The S-FCC lattice has the lowest density among all lattices. The mechanical tests result show specimen with FCC-XYZ lattice structures fabricated using a laser energy density of 125 J/mm3 meet the tensile properties requirement for human ribs. This structure also meets the requirement in flexural strength performance, but its stiffness is over that of human ribs. The compression test results of lattices are still incomparable due to unavailable compression data of the human ribs. In short, The FCC-XYZ lattice design fabricated by the 125 J/mm3 laser energy density parameter can be used to manufacture customized rib implants.
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39

Hübner, Sven, and Martin Trömel. "Atomvolumen und Packungsdichte der Atome in metallischen Elementen Atomic Volume and Packing Density of Atoms in Metallic Elements." Zeitschrift für Naturforschung B 55, no. 12 (2000): 1137–40. http://dx.doi.org/10.1515/znb-2000-1206.

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In the body-centered cubic structure and in closest sphere-packings the atoms are arranged to give structures with equal densities. A measure of the packing density of atoms is derived. Several crystal structures of elements, including the bcc structure and the closest sphere packings, represent a state of maximum density in which the atomic volume is characteristic of each element. From any crystal structure of an element its atomic volume in this state can be calculated to a good approximation.
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40

Shen, Han Xin, Wen Zhang Zhu, and Ai Yu Li. "Structure of Chromium Atomic Chains." Advanced Materials Research 415-417 (December 2011): 553–56. http://dx.doi.org/10.4028/www.scientific.net/amr.415-417.553.

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The geometric and electronic structures of Cr chains are studied by the first-principles of density-functional method. The present calculation results show that chromium can form planar chains in linear, zigzag, dimer, and ladder form one-dimensional structures. The most stable geometry chain among the studied structures is the ladder-form chain with five nearest neighbors. The dimer structure is found to be more stable than the zigzag one. Further more, the relative structural stability, the electronic energy bands, the density of states is discussed based on the ab initio calculations.
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41

Kang, Hyun Goo, Toshiko Osada, and Hideshi Miura. "Density Gradient Materials by Direct Metal Laser Sintering." Advanced Materials Research 89-91 (January 2010): 281–84. http://dx.doi.org/10.4028/www.scientific.net/amr.89-91.281.

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The direct metal laser sintering process was applied to produce density gradient materials of stainless steel 316L. In order to understand the mechanism of forming porous structure, the influence of laser power, scan rate and scan pitch on the porosity were investigated by measuring density of produced samples and observing cross-sectional microstructures. Laser power greatly affected to the porosity by forming clusters of melted metal powders. It was found that the size change of clusters plays a role in forming porous structure. Eventually, three dimensional sample owing density gradient structures was manufactured.
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42

Lobos, Juan, Miguel A. Rodríguez-Pérez, Miguel del Carpio, and Jose A. de Saja. "Mechanical Behaviour of High Density Polyethylene Based Foams." Materials Science Forum 620-622 (April 2009): 781–84. http://dx.doi.org/10.4028/www.scientific.net/msf.620-622.781.

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This paper presents the mechanical properties of a collection of high density Polyethylene based foams. The produced materials are characterised by a reduction in density up to 60%, an excellent surface quality, cell sizes in the microcellular range (around 50 microns) and a multi-structured cellular structure (cranial structure) with dense skin and foamed core. The mechanical properties of these materials showed linear relationships between Young’s modulus and density for densities above 0.7 g/cm3. In addition, variations in the cell size did not influence the elastic properties.
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43

Alshammari, Maytha, and Jing He. "Combining Cryo-EM Density Map and Residue Contact for Protein Secondary Structure Topologies." Molecules 26, no. 22 (2021): 7049. http://dx.doi.org/10.3390/molecules26227049.

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Although atomic structures have been determined directly from cryo-EM density maps with high resolutions, current structure determination methods for medium resolution (5 to 10 Å) cryo-EM maps are limited by the availability of structure templates. Secondary structure traces are lines detected from a cryo-EM density map for α-helices and β-strands of a protein. A topology of secondary structures defines the mapping between a set of sequence segments and a set of traces of secondary structures in three-dimensional space. In order to enhance accuracy in ranking secondary structure topologies, we explored a method that combines three sources of information: a set of sequence segments in 1D, a set of amino acid contact pairs in 2D, and a set of traces in 3D at the secondary structure level. A test of fourteen cases shows that the accuracy of predicted secondary structures is critical for deriving topologies. The use of significant long-range contact pairs is most effective at enriching the rank of the maximum-match topology for proteins with a large number of secondary structures, if the secondary structure prediction is fairly accurate. It was observed that the enrichment depends on the quality of initial topology candidates in this approach. We provide detailed analysis in various cases to show the potential and challenge when combining three sources of information.
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44

Liu, Qiu Xiang, De Ping Lu, Rui Jun Zhang, Lei Lu, and Shi Fang Xie. "Structural Phase Transition and Electronic Properties of MgCe under High Pressure from First-Principles Calculations." Applied Mechanics and Materials 577 (July 2014): 102–7. http://dx.doi.org/10.4028/www.scientific.net/amm.577.102.

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The structural stability of MgCe under high pressures has been investigated by using the first-principles plane-wave pseudopotential density functional theory within the local density approximation (LDA). The obtained results predict that MgCe in the Ba structure is predicted to be the most stable structure corresponding to the ground state, because of lowest total energy. MgCe undergoes a pressure-induced phase transition from the Ba structure to B32 structure at 36 GPa. And no further transition is found up to 120 GPa. In addition, the electronic structures of four structures of MgCe are also calculated and discussed.
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45

MISHRA, KRISHNA KUMAR. "Study on structural, mechanical, electronic, vibrational, optical and thermo-dynamical behaviour of ZB Structured BeZ (Z=S, Se and Te) using ATK-DFT." Metallurgical and Materials Engineering 26, no. 3 (2020): 253–78. http://dx.doi.org/10.30544/475.

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The present research is a systematic computational study focused on structural, mechanical, electronic, vibrational, optical and thermo-dynamical properties of zinc-blende (B3) structured beryllium chalcogenides BeZ (Z=S, Se, Te) compounds using ATK-DFT method using PZ and PBEsol exchange and correlation potentials within the local density approximation (LDA) and the generalized gradient approximation (GGA) respectively and their comparison. The k-point and energy cut-off values were tested and provided convergence in self-consistent calculations. The structural parameters such as lattice constant, bulk modulus, second order elastic constants (C11, C12, C44) and material properties (B, G, Y and σ) for these crystals are computed and discussed. To explain the electronic properties, electronic energy band structure, complex band structures, phonon band structure, phonon density of state and electron density distribution are plotted. The effect of pressure on elastic constant, material properties and phase transitions are also studied, including phase transition from ZB structure to NiAs appearing at 53 GPa, 49 GPa and 33 GPa for BeS, BeSe, and BeTe respectively.
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46

Shan, Gui Hua, Jun Liu, and Xue Bin Chi. "Local Maximum Absorption Method for Structure Fitting in CryoEM." Key Engineering Materials 460-461 (January 2011): 77–82. http://dx.doi.org/10.4028/www.scientific.net/kem.460-461.77.

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Cryo-electron microscopy (CryoEM) is a very important method for studying the structures of macromolecules. Structure fitting is one of the key problems in CryoEM technique. We propose a novel structure fitting method for automatic alignment of the atomic model and CryoEM density map. Based on the domain knowledge, 3D density map is presented by local maximum points. And the atomic model is presented by atoms with high density value. According to characteristic of CryoEM density map, these atoms must correspond to one of the local maximum, then employ absolute orientation algorithm to calculate the rotation matrix and transfer vector. To show the efficiency of our method, we apply the algorithm on two pairs of test data.
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47

Tao, Chenglin, Xin Zhou, Zeliang Liu, Xi Liang, Wentao Zhou, and Huijian Li. "Crashworthiness Study of 3D Printed Lattice Reinforced Thin-Walled Tube Hybrid Structures." Materials 16, no. 5 (2023): 1871. http://dx.doi.org/10.3390/ma16051871.

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Based on the advantages of thin-walled tubes and lattice structures in energy absorption and improved crashworthiness, a hybrid structure of lattice-reinforced thin-walled tubes with different cross-sectional cell numbers and gradient densities was constructed, and a high crashworthiness absorber with adjustable energy absorption was proposed. The experimental and finite element characterization of the impact resistance of uniform density and gradient density hybrid tubes with different lattice arrangements to withstand axial compression was carried out to investigate the interaction mechanism between the lattice packing and the metal shell, and the energy absorption of the hybrid structure was increased by 43.40% relative to the sum of its individual components. The effect of transverse cell number configuration and gradient configuration on the impact resistance of the hybrid structure was investigated, and the results showed that the hybrid structure showed higher energy absorption than the empty tube, and the best specific energy absorption was increased by 83.02%; the transverse cell number configuration had a greater effect on the specific energy absorption of the hybrid structure with uniform density, and the maximum specific energy absorption of the hybrid structure with different configurations was increased by 48.21%. The gradient density configuration had a significant effect on the peak crushing force of the gradient structure. In addition, the effects of wall thickness, density and gradient configuration on energy absorption were quantitatively analyzed. This study provides a new idea to optimize the impact resistance of lattice-structure-filled thin-walled square tube hybrid structures under compressive loading through a combination of experiments and numerical simulations.
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48

ZHAO, Fanglei. "Variable Density Cellular Structure Design Method Base on Local Relative Density Mapping." Journal of Mechanical Engineering 54, no. 19 (2018): 121. http://dx.doi.org/10.3901/jme.2018.19.121.

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49

Beck, Thomas L. "A real-space stochastic density matrix approach for density functional electronic structure." Physical Chemistry Chemical Physics 17, no. 47 (2015): 31472–79. http://dx.doi.org/10.1039/c5cp01222h.

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50

Stern, Jonathan, Joseph F. Hennawi, J. Xavier Prochaska, and Jessica K. Werk. "A UNIVERSAL DENSITY STRUCTURE FOR CIRCUMGALACTIC GAS." Astrophysical Journal 830, no. 2 (2016): 87. http://dx.doi.org/10.3847/0004-637x/830/2/87.

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