Spectral method for exploring patterns of diblock copolymers

A numerical method in Fourier-space is developed to solve the polymeric self-consistent field equations. The method does not require a priori symmetric information. More significantly, periodic structure can be adjusted automatically during the iteration process. In this article, we apply our method to AB linear diblock copolymer melt, thus reproduce all known stable phases, and reveal some meta-stable phases. It is worthy to point out that we also give an efficient strategy to estimating initial values for diblock copolymer system. Finally, by comparing with Matsen–Schick’s method, we show some advantages of our method.     

Thermodynamic modeling of the Al2O3–B2O3–SiO2 system

A complete literature review, critical evaluation, and thermodynamic modeling of the phase diagrams and thermodynamic properties of all oxide phases in the ternary Al₂O₃–B₂O₃–SiO₂ system at 1 bar pressure are presented. The molten oxide phase is described by the Modified Quasichemical Model and the Gibbs energy of the mullite solid solution is modeled using the Compound Energy Formalism. A set of optimized internally consistent thermodynamic functions for all the phases is presented. With the thermodynamic dataset, all available and reliable thermodynamic and phase equilibrium data can be reproduced within experimental error limits from 25 °C to above the liquidus temperatures. In addition, the reasonable predictions obtained for phase relations in the experimentally unexplored composition ranges suggest that the thermodynamic database can be used along with appropriate Gibbs energy minimization routines to calculate thermodynamic properties, phase equilibria, and phase diagrams of interest.     

乙烯醋酸乙烯酯/聚氯乙烯共混体系相容性、相逆转及其物理力学性能研究

<正> 硬质聚氯乙烯(PVC)由于韧性较差通常要用改性剂改善其抗冲击性能。但要使改性剂能有效起到作用,必须考虑它与PVC之间的相容性及其配比等对共混物性能的影响。本工作从动态力学及其他物理力学性能,研究了含48%醋酸乙烯(VAc)的乙烯醋酸乙烯酯共聚物(EVA)与PVC共混时组分之间的相容性及其配比对体系相逆转及其物理力学性能的影响。 样品:PVC采用北京化工二厂生产的SX-4型粉料。EVA粒料中的VAc重量含量为48%。将这两种料按不同的比例,加上助剂(二盐基亚磷酸铅、三盐基硫酸铅、硬     

The chirality of exceptional points

Exceptional points are singularities of the spectrum and wave functions of a Hamiltonian which occur as functions of a complex interaction parameter. They are accessible in experiments with dissipative systems. We show that the wave function at an exceptional point is a specific superposition of two configurations. The phase relation between the configurations is equivalent to a chirality which should be detectable in an experiment. Received 9 April 2001 and Received in final form 19 July 2001     

Composition and polyamorphism in supercooled yttria-alumina melts

By extending recent work on liquid-liquid transitions in supercooled yttria-alumina AYx liquids we draw attention to the compositional dependence of the structure factor of the high density liquid, arguing that this is sufficiently sensitive to discriminate between liquids at the level of a few %. Comparing structure factor differences between liquids of different compositions and in the same liquid AY20 between high and low temperatures straddling the transition at 1788 K between a high density liquid (HDL) and a low density liquid (LDL) enables compositional phase separation to be ruled out. It points instead to kinetic changes in polyhedral configurational order being the drivers for this polyamorphic transformation. Rotor behaviour observed in levitated liquid drops used in the high temperature experiments enables the reversibility of the LLT transition (LLT) and the associated changes in entropy and density to be identified. Evidence for critical-like behaviour in the structural relaxation time and in the fluctuation correlation length is presented. By re-examining recent work which failed to find the structural and thermal signatures for the LLT in liquid AY20 at 1788 K we present evidence for the LLT occurring instead in liquid AY15 at 1940 K, suggesting that the liquid-liquid transition temperature in AYx liquids decreases with increasing yttria content.     

Frustration and defects in non-periodic solids

Geometrical frustration arises whenever a local preferred configuration (lower energy for atomic systems, or best packing for hard spheres) cannot be propagated throughout space without defects. A general approach, using unfrustrated templates defined in curved space, have been previously applied to analyse a large number of cases like complex crystals, amorphous materials, liquid crystals, foams, and even biological organizations, with scales ranging from the atomic level up to macroscopic scales. In this paper, we discuss the close sphere packing problem, which has some relevance to the structural problem in amorphous metals, quasicrystals and some periodic complex metallic structures. The role of sets of disclination line defects is addressed, in particular with comparison with the major skeleton occurring in complex large-cell metals (Frank–Kasper phases). An interesting example of 12-fold symmetric quasiperiodic Frank–Kasper phase, and its disclination network, is also described.     

CO2 laser gas assisted nitriding of Ti-6Al-4V alloy

Laser gas assisted nitriding of Ti-6Al-4V alloy is carried out and nitride compounds formed and their concentration in the surface vicinity are examined. SEM, XRD and XPS are accommodated to examine the nitride layer characteristics. Microhardness across the nitride layer is measured. Temperature field and nitrogen distribution due to laser irradiation pulse is predicted. It is found that the nitride layer appears like golden color; however, it becomes dark gold color once the laser power irradiation is increased. The δ-TiN and ?-TiN are dominant phases in the surface vicinity. The needle like dendrite structure replace with the feathery like structure in the surface region due to high nitrogen concentration. No porous or microcracks are observed in the nitrided layer, except at high power irradiation, in this case, elongated cracks are observed in the surface region where the nitrogen concentration is considerably high.     

Metastable states,the adiabatic theorem and parity violating geometric phases I

A system of metastable plus unstable states is discussed. The mass matrix governing the time development of the system is supposed to vary slowly with time. The adiabatic limit for this case is studied and it is shown that only the metastable states obtain the analogs of the dynamical and geometrical phase factors familiar from stable states. Abelian and non-Abelian geometric phase factors for metastable states are defined.     

Diamond Composites with TiC,SiC and Ti 3 SiC 2 Bonding Phase

The problems connected with producing diamond composites with 30 wt.% of bonding phase in form of: SiC, TiC, and Ti 3 SiC 2 are presented in the paper. Increasing the fraction of the bonding phase within the composite generally helps to reduce internal stresses. Composites were sintered at pressure 8.0 - 0.2 GPa and temperature of 2070 - 50 K using the Bridgman type high pressure apparatus. Interactions in the diamond-SiC, the diamond-TiC, and the diamond-Ti 3 SiC 2 systems were studied by means of transmission electron microscope (TEM) and X-ray diffraction. Density was measured pycnometrically. The wear resistance studies of these composites were carried out using pin - on disc type laboratory equipment. Hardness was measured with Vickers apparatus. Results of measurements of physical and mechanical properties are reported.     

Geometric phase of a qubit interacting with a squeezed-thermal bath

We study the geometric phase of an open two-level quantum system under the influence of a squeezed, thermal environment for both non-dissipative as well as dissipative system-environment interactions. In the non-dissipative case, squeezing is found to have a similar influence as temperature, of suppressing geometric phase, while in the dissipative case, squeezing tends to counteract the suppressive influence of temperature in certain regimes. Thus, an interesting feature that emerges from our work is the contrast in the interplay between squeezing and thermal effects in non-dissipative and dissipative interactions. This can be useful for the practical implementation of geometric quantum information processing. By interpreting the open quantum effects as noisy channels, we make the connection between geometric phase and quantum noise processes familiar from quantum information theory.