A pure geometric approach to stellar structure

The present work represents a step in dealing with stellar structure using a pure geometric approach. Geometric field theory is used to construct a model for a spherically symmetric configuration. In this case, two solutions have been obtained for the field equations. The first represents an interior solution which may be considered as a pure geometric one in the sense that the tensor describing the material distributions is not a phenomenological object, but a part of the geometric structure used. A general equation of state for a perfect fluid, is obtained from, and not imposed on, the model. The second solution gives rise to Schwarzschild exterior field in its isotropic form. The two solutions are matched, at a certain boundary, to evaluate the constants of integration. The interior solution obtained shows that there are different zones characterizing the configuration: a central radiation dominant zone, a probable convection zone as a physical interpretation of the singularity of the model, and a corona like zone. The model may represent a type of main sequence stars. The present work shows that Einstein’s geometerization scheme can be extended to gain more physical information within material distribution, with some advantages.     

Effect of electroelastic anisotropy of DNA-like molecules on their tertiary structure

Under certain conditions, mechanical forces can cause an anisotropic molecule like DNA to assume a toroidal spatial structure. A simple model describing such a behavior is suggested. The model incorporates anisotropic elastic energy and external electrical forces. The steady-state structures formed by a macromolecule have been studied numerically using this model. There exist ranges of model parameters, namely, the anisotropy of the elastic tensor, magnitude and orientation of forces, and modulation periods, where molecules have toroidal, spherical, or extended structures. Estimates of parameters characteristic of these structures are consistent with experimental data. In particular, the toroidal structure dimension corresponds to experimental dimensions of toroidal globules produced as a result of so-called PSI condensation of DNA molecules. Zh. éksp. Teor. Fiz. 112, 2156–2168 (December 1997)     

The theory of pure operations

This paper continues the study started in [13] where classes of operations were investigated in the partially ordered vector space approach to the theory of statistical physical systems. In this approach the set of states is represented by a norm closed generating coneK in a complete base norm space (V, K, B) and the set of operations is represented by the setP of positive norm non-increasing linear operators onV. In actual physical experiments it is usually the case that only certain subsets ofK are available and it is supposed that the set (K) of such subsets is the set of split faces ofK. The properties of two important classes of operation are examined. The first classP of strong operations has the property that each member leaves every element of (K) invariant and therefore can be measured in every restricted situation. The second classP _P of pure operations has the property above and also sends pure states into pure states. A study is made, in terms of the structure of (K), of when such operations are physically relevant. The paper ends with an examination of (K),P, P _P in the Von Neumann algebra model.     

Preparation and electronic structure of phase pure K3C60

Phase pure K₃C₆₀ films have been grown using vacuum distillation. The structure of such films could be shown to be face centered cubic consistent with X-ray diffraction studies. The electronic structure of the films has been studied using electron energy-loss spectroscopy in transmission. From C1s core excitation measurements the unoccupied density of states has been determined. Performing the dielectric function has been derived in a wide energy range (0–45 eV). It is shown that the low energy part of the optical conductivity cannot be understood within a simple free electron model but that interband transitions between the three conduction bands have to be taken into account. The spectral weight of interband transitions between valence and conduction bands shows strong momentum dependence due to optical selection rules demonstrating the molecular-like nature of the electronic states.     

Networks of interactions in the secondary and tertiary structure of ribosomal RNA

We construct four different structural networks for both the secondary and tertiary structures of the 16S and 23S ribosomal RNAs (rRNAs) in the high-resolution crystal structures of the Thermus thermophilus 30S and Haloarcula marismortui 50S ribosomal subunits, and investigate topological characteristics of the rRNA structures by determining relevant measures, such as the characteristic path length, the clustering coefficient, and the helix betweenness. This study reveals that the 23S rRNA network is more compact than the 16S rRNA networks, reflecting the more globular overall structure of the 23S rRNA relative to the 16S rRNA. In particular, the large number of tertiary interactions in the 23S rRNA tends to cluster, accounting for its small-world network properties. In addition, although the rRNA networks are not the scale-free network, their helix betweenness has a power-law distribution and is correlated with the phylogenetic conservation of helices. The higher the helix betweenness, the more conserved the helix. These results suggest a potential role of the rRNA network as a new quantitative approach in rRNA research.     

Electronic structure of pure and doped orthorhombic La2CuO4

The electronic structure of orthorhombic La₂CuO₄ has been investigated by first principles pseudofunction band calculations and group theoretical analysis. We find that pure as well as doped compounds remain metallic at all finite temperatures as a conseqence of the Cmca (D¹⁸_2h) space group symmetry. The experimentally observed rapid rise in resistivity below 30°K suggests a structural transition to a lower symmetry space group that could be driven electronically or magnetically. One possible candidate is monoclinic C2/m (C³_2h) which is a subgroup of Cmca and can be obtained by distorting the CuO bonds or rotating the CuO₆ octahedra. Implications for superconductivity are discussed.     

RNAGCN: RNA tertiary structure assessment with a graph convolutional network

RNAs play crucial and versatile roles in cellular biochemical reactions. Since experimental approaches of determining their three-dimensional (3D) structures are costly and less efficient, it is greatly advantageous to develop computational methods to predict RNA 3D structures. For these methods, designing a model or scoring function for structure quality assessment is an essential step but this step poses challenges. In this study, we designed and trained a deep learning model to tackle this problem. The model was based on a graph convolutional network (GCN) and named RNAGCN. The model provided a natural way of representing RNA structures, avoided complex algorithms to preserve atomic rotational equivalence, and was capable of extracting features automatically out of structural patterns. Testing results on two datasets convincingly demonstrated that RNAGCN performs similarly to or better than four leading scoring functions. Our approach provides an alternative way of RNA tertiary structure assessment and may facilitate RNA structure predictions. RNAGCN can be downloaded from https://gitee.com/dcw-RNAGCN/rnagcn.     

Study of nanocomposite thick-film butanol vapor sensors

Gas sensing characteristics of multi-walled carbon nanotubes coated with tin dioxide nanoparticles nanocomposite thick-film structures (MWCNTs/SnO₂) prepared using hydrothermal synthesis, sol–gel technique and their combined process were investigated. Gas response test measurements of all studied nanocomposite structures carried out in air/target gas mixture showed that the most and at one time selective response to butanol vapor exposure in comparison to other mainly toxic and harmful gases such as acetone, toluene, formaldehyde, dimethylformamide, and others is observed for samples obtained by hydrothermal synthesis with 1:4 and 1:200 weight ratios of the nanocomposite components, respectively. These sensors are characterized by relatively short response and recovery times about 12 and 100 s, respectively, as well as low operating temperatures in the range of 150–200°C.     

The Raman spectra and structure of pure vitreous P2O5

We report the polarized Raman spectra of pure anhydrous vitreous P₂O₅ and conclude that this glass is a 3-connected network in which each P atom is surrounded almost tetrahedrally by three bridging O atoms and one double-bonded O terminator. Vibrational calculations on an anchored fragment are used to determine atomic motions in the higher frequency modes; these calculations confirm that the dominant Raman modes involve in-phase compression of neighboring PO bonds.     

The plasticity of pure single crystals

The theory of the work-hardening curve of a pure single crystal is discussed. An outline is given of the experimental methods available for the study of the mechanism of plastic deformation and work hardening. An attempt is made to correlate existing theories of work hardening. The theory is illustrated by discussions of copper, of other face-centred cubic metals, of the diamond and sphalerite structures, of hexagonal close-packed metals, of ionic face-centred cubic crystals and of body-centred cubic metals.     

Towards a canonical fermi mass matrix for a pure generation structure

Vertical constraints on the horizontal generation structure are discussed. The minimal electro/nuclear scheme for which the generation structure must be pure is identified to be the partially unified Pati-Salam SU(4)_C×SU(2)_L×SU(2)_R. SO(10) type unification furthermore requires the horizontal group factor to be axial. This in turn crucially affects the Yukawa couplings in such a way that a minimal Higgs system with only two conventional scalars is capable of uniquely giving rise to the ‘canonical’ Fritzsch-type mass matrix, for any arbitrary number of fermionic families. The anomaly-free equations then provide the desired one-to-one correspondence between the mass matrices in the two charged quark sectors. The derived horizontal quantum numbers suggest that the maximal horizontal group factor be SU(2), with the generations furnishing two neighbor $\text{j}\text{and}\text{j +}\text{1}\text{2}$ representations. Finally, a careful phase analysis shows that the tree-level soft and superwork CP-violation solely reflects the non-abelian character of the horizontal group, representing an induced internal rotation which is triggered by the phase elimination performed in the vertical sector.     

分子动力学模拟纯镁熔体凝固过程中结构演化

采用分子动力学模拟方法模拟了在周期性边界条件下由500个原子构成的液态Mg模型系统的凝固过程,分别考察了在5×10^14 K/s、5×10^13 K/s、1×10^13 K/s 、1×10^12 K/s的冷却速率下液态Mg熔体的凝固行为。模拟结果很好地重现了实验值。模拟中原子间作用势采用FS势,结构分析采用径向分布函数、均方位移、系统总能量分析、H-A键对分析技术等方法。结果表明,当冷却速率为5×10^14 K/s时,系统形成以1541键对为主的非晶态结构;当冷却速率分别为5×10^13 K/s、1×10^13 K/s、1×10^12 K/s时,系统形成以1421、1422键对为主的hcp晶态结构;另外,在快速冷却形成非晶的过程中,大部分bcc结构被保留下来,而在慢冷形成晶态的过程中,大部分bcc结构最终演化形成了hcp结构。     

纯铝熔体的微观动力学行为

利用反映原子多体相互作用的紧束缚模型及分子动力学计算机模拟技术,研究了液态金属Al的熔体结构与微观动力学行为。计算了纯金属熔体Al在不同温度下的双体分布函数,平均平方位移及速度自相关函数。模拟结果与实验结果吻合得很好,表明紧束缚模型能够描述纯铝熔体中原子间的相互作用     

The pure rotational atmospheric lines of hydroxyl

Pure rotational line positions of the hydroxyl radical (OH) have been calculated for all vibrational levels expected in the earth's atmosphere (v = 0–9) and for lower rotational quantum numbers J″=0.5–12.5. These positions have been tabulated and compared with those derived from energy levels obtained from precise near-i.r. vibration-rotation bands and show good agreement for low J″ values. A tentative identification has been made of three v = 0 lambda-type doublets in a high-resolution far-i.r. (30–120 cm^-1) emission spectrum of the atmosphere obtained at 30 km from a balloon-borne platform. Line strength (S_J′J″) and integrated intensity (S_q cm^-2atm^-1) values have been derived for these pure rotational transitions as an aid to further work and instrument design.     

The photonical, pure grid method

The paper presents an introduction on the pure grid method for deformation measurements in experimental mechanics. The pure grid method involves that the grid images are processed separately, and subsequently the results of these separate processings are substrated from each other in order to obtain a quantified deformation indication.The recording and processing of the grid images are currently performed photonically by means of digital image measurement systems. The basic data processing relations and set-ups of four different applicabilities of the photonical, pure grid method are presented in this paper. The applicabilities are discussed. Strains can be measured with errors smaller than 200 micro strain and displacements with errors smaller than of the diameter of the object as visible in the grid image. These figures can be improved substantially by future application of high resolving-power CCD cameras. Two examples are shown. The paper also contains an extensive bibliography for further explorations.     

Scattering of nonequilibrium acoustic phonons in coarse-grained pure ZnSe with random microtwin structure

Propagation of nonequilibrium acoustic phonons in a coarse-grained ZnSe produced through chemical synthesis from a vapor phase was studied for phonons generated optically or by a metallic heater. The material is characterized by a microtwin structure in randomly oriented grains. Phonon transport studies, in combination with low-temperature photoluminescence, optical and electron microscopy, and x-ray diffraction analysis, made it possible to establish the decisive role played by extended defects in scattering of high-frequency acoustic phonons in this matterial.     

The pure gauge sector of compactified superstrings

We study the classical field equations of the pure gauge sector of superstrings compactified to four dimensions. Instantons no longer turn out to be solutions of the field equations. We also determine the dynamical behavior of the gauge coupling g in the background of a monopole field, with the result that g and the strong CP-violating angle θ tend to a constant far from the monopole. The energy of such a field configuration is finite.