Self-assembled MnN superstructure

Self-assembled MnN nanoislands have been prepared on Cu(001) substrate. The nanoislands show a square shape and a well-defined size. They are regularly arrayed with a periodicity of (3.5+/-0.1) nanometer and form a two-dimensional square superstructure. The MnN island superstructure is stabilized by a short-range mechanism. A structural model has been proposed to explain the self-assembly and the high quality of the superstructure.     

Fibonacci quasi-periodic superstructure fiber Bragg gratings

Superstructure fiber Bragg gratings constructed following the Fibonacci sequence are proposed and simulated by using the transfer matrix method. The reflection spectrum has a multi-fractal structure as a function of the wavelength and is symmetric to the center. The reflectivity has self-similarity and scaling with respect to the Fibonacci sequence order at the central wavelength. For the transmission spectrum, the interaction of the core-cladding mode is investigated and the particular wavelengths for which the resonance condition is satisfied are located by varying the grating parameters. The potential application of the quasi-periodic structure as fiber sensors is also proposed.     

Fermi gap stabilization of an incommensurate two-dimensional superstructure

The compressed, incommensurate approximately (9.5 x 9.5) moire superstructure of the Ag monolayer on Cu(111) displays a filled surface state band with a Fermi energy gap at the Brillouin zone boundary. By contrast, the surface band is gapless for the less compressed, commensurate (9 x 9) moire of two Ag layers. A simple estimate of the energy gain rendered by opening this gap gives a value similar to the elastic energy change required to modify the commensurate structure, thereby suggesting that the approximately (9.5 x 9.5) incommensurate phase is stabilized by such a gap opening. The possible presence of a charge density wave state is discussed.     

Iron-nickel superstructure in metal particles of Alfianello meteorite

We report on Mössbauer spectroscopy in metal particles of the Alfianello meteorite. The FeNi 50-50 ordered phase (tetrataenite) was detected in coexistence with a high proportion of the corresponding disordered phase. The order-disorder process is discussed in terms of shock events.     

Ordered surface phases

We give a simple proof of the coexistence of an ordered surface phase with a disordered bulk one.     

Partially Ordered Models

We provide a formal definition and study the basic properties of partially ordered random fields (PORF). These systems were proposed to model textures in image processing and to represent independence relations between random variables in statistics (in the latter case they are known as Bayesian networks). Our random fields are a generalization of probabilistic cellular automata (PCA) and their theory has features intermediate between that of discrete-time processes and the theory of statistical mechanical lattice fields. Its proper definition is based on the notion of partially ordered specification (POS), in close analogy to the theory of Gibbs measures. This paper contains two types of results. First, we present the basic elements of the general theory of PORFs: basic geometrical issues, definition in terms of conditional probability kernels, extremal decomposition, extremality and triviality, reconstruction starting from single-site kernels, relations between POM and Gibbs fields. Second, we prove three uniqueness criteria that correspond to the criteria known as uniform boundedness, Dobrushin uniqueness and disagreement percolation in the theory of Gibbs measures.     

Ordered hadron S-Matrix

An ordered hadron S-matrix is developed that accommodates an arbitrary number of “neighbors” for each particle. Automatic features are baryon-number conservation and zero triality. The ordered Hilbert space splits into a set of non-communicating sectors each characterized by a “skeleton” graph whose external edges can be given aquark interpretation. Selection rules are found that generalize the OZI rules.     

神光Ⅱ升级装置中靶场桁架的结构稳定性

 从提高结构稳定性的基本理论出发,利用有限元方法研究了靶场桁架结构稳定性。结果表明：影响大口径反射镜动态稳定性的主要因素为靶场桁架的第三阶模态振型,其薄弱环节为支撑立柱;通过在支撑立柱间增加横向加强筋、桁架立柱采用钢管混凝土结构等措施可有效提高桁架的结构稳定性;立柱截面最小方形空心型钢的尺寸为300 mm×6 mm。给出的靶场桁架的稳定性设计方案满足大口径反射镜的动态稳定性指标。     

Magnetic properties of Fe/Nd artificial superstructure films

Multilayered films with artificial superstructures were prepared by alternately depositing Fe and Nd in ultrahigh vacuum. The magnetic properties are studied from⁵⁷Fe Mössbauer spectroscopy. The hyperfine field in Fe layers and the direction of Fe magnetic moments depend on the Fe and Nd layer thicknesses. For films with certain Fe and Nd layer thicknesses, the direction of Fe magnetic moments is in-plane at 300 K but changes to be perpendicular at low temperatures. The direction of Fe magnetic moments is discussed in relation with the magnetization of interface Nd atoms.     

Influence of urea on polyvinyl alcohol molecular superstructure formation

Whiskers up to 1 cm in length were grown in polyvinyl alcohol (PVA) and urea solution. Raman and IR spectra discover an interaction between PVA and urea molecules. Optical and electronic microscopy data show that urea influences on PVA molecular superstructure formation. PVA whiskers prepared in urea solution can be used for organic semiconductors production which properties are determined by arrangement of polymer macromolecules.     

Ferromagnetism and superstructure in Ca1-xLaxB6

We critically investigate the model of a doped excitonic insulator, which has recently been invoked to explain some experimental properties of the ferromagnetic state in Ca1-xLaxB6. We demonstrate that the ground state of this model is intrinsically unstable towards the appearance of a superstructure. In addition, the model would lead to a phase separation of doped carriers into electron-enriched and neutral domains, which may be prevented by Coulomb forces only. Recent experiments indicate that a superstructure may indeed show up in this material.     

Normally Ordered and Antinormally Ordered Expansions of Some Exponential Operators in Hilbert Space

In this paper, the completeness relations of the fundamental representations in quantum mechanics, together with the "integration within orderd product" technique are exploited to derive normally ordered and antinormally ordered expansions of some exponential operators in Hilbert space. Applications of the normally ordered exponential operators to evaluating Feynman matrix element in coherent state representation are given, which seems to be a new approach.     

级数相位去包裹方法

提出了一个简单的相位去包裹方法－－条纹的极数相位去包裹算法,将其用来恢复物体的真实相位。与传统的条纹相位去包裹方法相比较,该方法能够消除光载频、物体边缘、阴影和盲点的影响。理论分析和实验结果证明该方法适用于条纹空间相位测量方法解调的包裹相位。     

Photoinduced superstructure in the low-temperature phase of a Peierls system

This paper is a theoretical study of the properties of the low-temperature phase of a Peierls system when nonequilibrium electron-hole pairs are excited in the phase. A microscopic theory is developed to show that at low temperatures a spatially nonuniform periodic structure with a modulated band gap forms in the thermodynamically nonequilibrium system considered. The critical temperature of formation of such a superstructure, the critical electron-hole pair concentration, the spatial period, and the percentage modulation are calculated. Zh. éksp. Teor. Fiz. 115, 1297–1314 (April 1999)     

Laser induced microrelief superstructure of Ag/ITO seed-mediated nanocomposites

The topography of indium tin oxide (ITO) films with incorporated silver nanoparticles and irradiated by single pulses of 18 ns Nd:YAG laser has been investigated. The study was carried out with two Ag/ITO films having resistances of 50 Ω/ITO sheet and 4 Ω/ITO sheet. The periodic structures in both samples were created after the laser treatment. The photo-induced periodic structures have a different character while the sheet resistance plays a major role in the growth process of these structures. The results of optical and non-linear optical investigations lead us to the conclusion that the temporary polarization of samples during laser treatment is responsible for the shape of periodic structures.     

Atomic configuration of microtwins in alloys having Ll2 superstructure

In the approximation of paired interatomic potentials of the Morse type, modeling is done on the atomic configuration and energy of formation of superstructure stacking faults and superstructure twinning stacking faults in the ordered alloys Cu₃Au and Ni₃Fe, and also in the intermetallide Ni₃Al. Features are observed in the local deformation of the crystal lattice defects near equilibrium (in terms of internal energy), and the principle difference in the state of the atomic surroundings of the examined plane defects is shown. In alloys of Cu₃Au and Ni₃Fe, calculations are done for different values of the long-range order parameter. A difference is detected in the variation of the energy of formation of superstructure twinning stacking faults in alloys of Cu₃Au and Ni₃Fe with the long-range order parameter. This difference correlates with experimental observation of the properties when varying the temperature in the alloys.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 31–36, November, 1987.     

Interaction of wide-spectrum electromagnetic pulses with materials containing a superstructure

The interaction of wide-spectrum electromagnetic pulses with materials containing a superstructure is considered. The effective equation is obtained, which has a form of classical one-dimensional sine-Gordon equation, perturbed by quantum transitions between minibands. Numerical solutions are presented, and a region is established, where transitions between minibands play a significant role in the electromagnetic pulse dynamics.     

State of two-dimensional long-period superstructure in the metastable Fe-Nd-B phase

We investigated using transmission electron microscopy (TEM) the state of a long-period superstructure (LPS) composed of a metastable D0₃ phase, which emerged during crystallisation of Fe₈₉Nd₇B₄ amorphous alloys [Konno, Uehara, Hirosawa, et al., Phil. Mag. A 79 2413 (1999)]. Diffraction studies showed that it is a two-dimensional (2D) LPS characterized by 1/4a ₀?111? antiphase boundaries (APBs) perpendicular to ?100? directions and 1/2a ₀?100? APBs perpendicular to ?110? directions, where a ₀ is the unit cell parameter of the D0₃ cell. Dark field images and high-resolution TEM showed that superperiods estimated from diffraction patterns, 3.2 and 2.4?nm, respectively, represent an average structure; and real arrangements of APBs are rather diverse in terms of both periodicity and APB planes. These observations indicate that the 2D LPS emerged in the following reaction sequence: amorphous?→?A2?→?D0₃ with 2D LPS?→?D0₃, where all the phases are metastable.