Recording of concave diffraction gratings in counterpropagating beams using meniscus blanks

The most technological way of recording blazed concave holographic gratings is by using the direct- and back-reflected beams. Usually plano-concave blanks are used for diffraction grating fabrication. To compensate the refraction at the plane back surface of the blank, one has to use additional elements or two-step recording mountings. Another solution is to use diffraction grating blanks having zero optical power. A number of gratings with different groove frequencies have been fabricated using concave—convex blanks. The theoretical investigation of the aberration properties of the recording mountings, and the experimental study of the grating properties are discussed. Using the CODE V program it is shown that a significant reduction in the aberration size of the virtual recording source can be achieved by optimization of the radius of curvature of the blank back surface. The experimental results confirm the possibility of achieving gratings that can be used in flat-field spectrometers with a limit of resolution of about 2–3 nm even in the case where an aberrated virtual recording source is used.     

PARAMETERS THAT DETERMINE TRIPALMITIN CRYSTALLIZATION IN SESAME OIL

The crystallization of tripalmitin (TP) in sesame oil (0.98, 1.80 and 2.62% w/v) was investigated under isothermal conditions using a cooling rate similar to the one achieved by industrial crystallizers (1 K/min) and utilizing a modification of the Avrami equation. It was concluded that z, the crystallization rate constant, and the associated energy of activation (Ea) values determined through Avrami's original equation yield erroneous results. Additional results indicated that the increase in supercooling at constant oil phase viscosity (e.g., 5.25–5.5 dynes/cm²) during crystallization, produced a higher degree of nucleation without an appreciable effect on TP crystal size. In contrast, as viscosity of the oil phase decreased at equal supercooling conditions (e.g., 22.0 - 22.5C) the main crystallization process evaluated through z and Ea was crystal growth. It was also concluded that the characteristic crystallization stages of induction time for nucleation, crystal nucleation and growth, and end of crystallization were evident in the viscosity profile of the solid fraction developed during TP crystallization. The predominance of any of these processes (i.e., nucleation or crystal growth) as a function of supercooling and viscosity of the oil phase determines, to a great extent, the rheological profile during crystallization and the final viscosity value of the crystal suspension.     

GATED COMMUNITIES AND SPATIAL INEQUALITY

ABSTRACT: In this article we analyze gated communities as a nexus of social and spatial relations within the context of urban inequality. We apply Tickamyer's (2000) sociological framework for incorporating space into the study of inequality, which allows us to substantiate the arguments that the process of gating increases urban inequality. The contributions of this article are three: (1) We generate a new systematic theoretical approach toward the study of gated communities, which we consider as middle range theory; (2) We argue that gated communities reproduce the existing levels of social stratification and that they also define a new, permanent differentiation order in the spatial organization of cities in the United States (in this respect we also arrive at six hypotheses, which can be tested in future research); (3) We introduce the term “gating machine,” where the combination of the interests and actions of local governments, real estate developers, the media, and consumers suggest that prevailing structural conditions assure the future proliferation of gated communities.     

Microbial characterisation and stability of a farmhouse natural fermented milk from Spain

This work reports the microbial characterisation of a farmhouse natural fermented milk (NFM) with good sensorial properties produced in Spain. Culturing and denaturing gradient gel electrophoresis (DGGE) analyses showed thatLactococcus lactissubsp.lactis and L. lactissubsp.cremoris(approximate levels of 10⁹ cfu/mL) were dominant in this NFM, whileLactobacillus plantarumappeared at a lower level (10⁶–10⁷ cfu/mL). Repetitive extragenic palindromic (REP)‐PCR typing of the isolates identified single strains each ofLc. lactissubsp.lactis, Lc. lactissubsp.cremorisandLb. plantarum. These three strains formed a stable microbial association which has been maintained for at least some decades.     

烧结温度对Q235钢搪瓷涂层组织结构及性能影响

通过一次涂搪法在 Q235 低碳钢表面制备出 700 ~ 900 ℃ 烧结的搪瓷涂层。 采用 XRD、SEM、EDS、显微维氏硬度计、落球装置及电化学工作站研究了涂层物相组成、组织形貌、微区成分、机械性能及腐蚀行为。 结果表明:搪瓷涂层在烧结过程中表面孔隙率持续减小,截面孔隙率则先减小后增大再减小;磨加物石英逐渐溶解在涂层硅氧四面体 [SiO₄ ]网络中,使涂层显微硬度和光泽度提高;涂层与基体界面处氧化层逐渐减小并最终消失,而 Fe 扩散区逐渐扩大并形成富含 Fe-Co 和 Fe-Ni 枝晶的密着层;涂层表面釉质层形成及内部腐蚀通道的闭合使其耐腐蚀性能显著提高。     

Studies of Silica-Structure Phases: I, GaPO4, GaAsO4, and GaSbO4

In the course of work on all compositions which would probably yield silica-structure phases, a detailed study was made of the A³⁺B⁵⁺O₄-type compounds with gallium as the trivalent element. Two forms of GaPO₄ exist corresponding to quartz and cristobalite; the quartz form has a thermal expansion of the low-quartz type and no stable α-β transition is found in this phase. It inverts stably to the cristobalite form at 933°± 4°C. The cristobalite form melts at 1670°C. and the liquid cannot be made to form a glass. The cristobalite form also has a metastable displacive transition at 616°± 2°C. GaAsO₄ exists only in a form corresponding to the lowquartz structure. It disproportionates into Ga₂O₃ and As₂O₅ at about 1000°C. GaSbO₄ could only be prepared in one form corresponding to the rutile structure. The influence of such phases on SiO₂ was determined by studying a few mixtures in the system SiO₂-GaPO₄. The SiO₂ end member appears to admit about 25% GaPO₄ into solid solution in the cristobalite phase at the highest temperature. Even under hydrothennal conditions, however, equilibrium cannot be easily attained at the lower temperatures in a few hundred hours. The results are presented in a not-impossible diagram for the system GaPO₄-SiO₂.