钾钠铌酸锶钡系列晶体自泵浦位相共轭镜的研究

报道了钾钠铌酸锶（ＫＮＳＢＮ）晶体系列自泵浦位相共轭反射镜的最新研究结果。ＫＮＳＢＮ：Ｃｕ、ＫＮＳＢＮ：Ｃｏ和ＫＮＳＢＮ：Ｃｅ自泵浦位相共轭反射镜的反射率分别可达７３％、７３％和８４．３％，ＫＮＳＢＮ：Ｃｕ自泵浦位相共轭反射镜的响应时间在低功率下达２００ｍｓ。     

How crystals that sense and respond to their environments could evolve

An enduring mystery in biology is how a physical entity simple enough to have arisen spontaneously could have evolved into the complex life seen on Earth today. Cairns-Smith has proposed that life might have originated in clays which stored genomes consisting of an arrangement of crystal monomers that was replicated during growth. While a clay genome is simple enough to have conceivably arisen spontaneously, it is not obvious how it might have produced more complex forms as a result of evolution. Here, we examine this possibility in the tile assembly model, a generalized model of crystal growth that has been used to study the self-assembly of DNA tiles. We describe hypothetical crystals for which evolution of complex crystal sequences is driven by the scarceness of resources required for growth. We show how, under certain circumstances, crystal growth that performs computation can predict which resources are abundant. In such cases, crystals executing programs that make these predictions most accurately will grow fastest. Since crystals can perform universal computation, the complexity of computation that can be used to optimize growth is unbounded. To the extent that lessons derived from the tile assembly model might be applicable to mineral crystals, our results suggest that resource scarcity could conceivably have provided the evolutionary pressures necessary to produce complex clay genomes that sense and respond to changes in their environment.

Bending diamonds by femtosecond laser ablation

We present a new method based on femtosecond laser ablation for the fabrication of statically bent diamond crystals. Using this method, curvature radii of 1 m can easily be achieved, and the curvature obtained is very uniform. Since diamond is extremely tolerant to high radiation doses, partly due to its densely packed lattice, such bent crystals are optimal solutions for crystal-based collimation and/or extraction. Furthermore, using interlaced ablation on both sides, the technique opens for the possibility of constructing a crystalline undulator based on the best material known, to approach the enormous beam densities required for lasing operation of such a device.     

Modeling the Anisotropic Deformation Response of β‐HMX Molecular Crystals

In this paper, we develop a computational model for the anisotropic plastic response of β‐HMX molecular crystals based upon experimental data. While phenomenological models of β‐HMX currently exist, they are inadequate as they cannot account for the orientation dependence of the observed response. The proposed model, on the other hand, successfully predicts the experimentally observed highly anisotropic and orientation dependent yield surfaces of β‐HMX molecular crystals having different crystal orientations. The model also correctly predicts the anisotropic plastic yielding of β‐HMX under uniaxial compression at different temperatures along different crystallographic directions. The model presented in this paper may be extended to predict the yielding and elastic–plastic deformation of other energetic molecular crystals.     

Dynamic nuclear polarization in crystals of Nd:LaAlO3, a polarized La target for a test of time-reversal invariance

Dynamic nuclear polarization (DNP) has been performed in a magnetic field of 2.35 T at a temperature below 0.3 K in crystals of Nd³⁺ :LaAlO₃. A Q-meter NMR-system was used to measure the polarization of the ²⁷Al and ¹³⁹La nuclei and allowed to characterize the quality of the crystals. The ¹³⁹La polarizations of +47.5% and −56.5% achieved represent an important step in the development of a polarized ¹³⁹La target for a test of time reversal invariance in low-energy neutron reactions.     

GROWTH RATES OF POTASSIUM SULPHATE CRYSTALS OF DIFFERENT SURFACE QUALITIES IN THE SIZE RANGE FROM 10-100 μm

Growth rate data of surface-integration controlled growing potassium sulphate crystals in the size range. 10-100μm are presented. The experiments were carried out in an agitated vessel crystallizer. The crystal growth rates were calculated from the shift of the population distributions with time as measured by a Coulter-Counter. In particular the effect of different surface qualities on the growth rates was investigated and clearly demonstrated. The existence of a growth rate dispersion (GRD) was shown for crystals in an agitated crystallizer. This is a new observation since previously this effect was only investigated for stagnant solutions in the case of the above mentioned range of crystal sizes.     

Reduced Sensitivity RDX Obtained From Bachmann RDX

In recent years much interest has been generated in a quality of reduced sensitivity RDX (RS‐RDX), like I‐RDX^® which, when incorporated in cast cure and even pressable plastic bonded explosives (PBX compositions), can confer reduced shock sensitivity as measured through gap test. At crystal level, lot of work has been done to try to determine which property or properties may explain the behaviour of the corresponding cast PBX composition. But up to now, and despite an international inter‐laboratory comparison (Round Robin) of seven lots of RDX from five different manufacturers conducted from 2003 to 2005, even if some techniques lead to interesting results, there is no dedicated specification to apply to RS‐RDX. This quality (I‐RDX^®) has proved to retain its low sensitivity even after ageing, which does not seem to be the case for standard RDX produced by the Bachmann process (when re‐crystallized under I‐RDX conditions in order to obtain RS‐RDX). It has been shown that the higher sensitivity of RDX produced by the Bachmann process, or the evolution of sensitivity after ageing of RS‐RDX produced from Bachmann RDX may be linked to the presence of octogen (HMX) during the crystallization process. In order to check such hypothesis, low HMX content RDX produced by the Bachmann process has been prepared and evaluated in cast PBX composition (PBX N 109). Results of the characterization of such quality of RDX and its evaluation in cast PBX composition as well as ageing behaviour are presented and discussed; there are indications that removal of HMX from Bachmann RDX may lead to RS‐RDX, which retains its RS character even after ageing.     

Spectral Absorptivity and Thermal Conductivity of BGO and BSO Melts and Single Crystals

The present work describes the results of spectral absorptivity, α, and thermal conductivity, λ, studies for compound oxides Bi₄Ge₃O_12, Bi₁₂GeO_20, Bi₄Si₃O_12, and Bi₁₂SiO₂₀ in molten and monocrystalline states. The data for the spectral absorptivity were obtained by placing the sample onto a mirror and using the transmission method. To obtain the data on the thermal conductivity of crystals, the stationary method of two identical samples was used. The data for the thermal conductivity of melts were obtained by a new stationary relative method in which the thermal conductivity of the crystal is used as a reference. Special attention is focused on numerical and experimental error analysis at high temperature. The studies have shown that α in the range of a transmission band strongly depends on crystal purity. It varies from 0.0005 cm⁻¹ to 0.03 cm⁻¹ for Bi₄Ge₃O₁₂ and reaches 0.15 cm⁻¹ for Bi₄Si₃O₁₂. It was found that α is significantly greater for melts than for crystals, reaching (150 to 200) cm⁻¹ for the Bi₄Ge₃O₁₂ melt. The thermal conductivity of the melts under investigation was found to be much smaller than that of the corresponding crystals.