Effect of hot acid etching on the mechanical strength of ground YAG laser elements

High-power pumped Nd:YAG elements may exceed their tensile strength under high thermally induced stress. Providing extra strength to such rods is essential for their employment in high-power lasers. The tensile strength of YAG elements was increased by chemical etching in concentrated phosphoric acid. The highest tensile strength was achieved by etching of fine-ground YAG components: an average for slabs, and for rods, which are 3.6 times and 5 times higher than those of non-etched elements, respectively. The measurements were carried out by four-point flexure strength test. We have established a dependency among the micro-roughness of YAG elements, the surface morphology obtained by etching, and the tensile strength: the tensile strength of the etched element improves for finer after-etch surface texture, which is obtained for finer initial micro-roughness.

To assure the withstanding of Nd:YAG rods under high thermal gradients, a new approach was employed, namely, increasing the pump-power applied to the Nd:YAG rod till fracture. Our results show an increase by more than 2.7 times in tensile strength of etched Nd:YAG rods as compared to standard commercial rods, which corresponds to a thermal loading of excess of 434 W/cm.     

Radiothermoluminescence of surface layers of n-tetracosane crystals

A radiothermoluminescence (RTL) curve of surface layers of n-tetracosane crystals has been obtained, which appear to be similar but not identical to the RTL of the evacuated sample or the sample with CCl₄. Since CCl₄ does not penetrate the crystal, the difference between the RTL curves of the evacuated sample and the one with CCl₄ represents the RTL of crystal surface layers. The RTL curve of tetracosane with the scavenger is that of RTL of intracrystalline areas of the alkane. The difference in shape between the surface and bulk RTL curves is manifested well in the ratio of the RTL curves for the surface and the evacuated sample.     

A novel pathogen detection system based on high‐resolution CE‐SSCP using a triblock copolymer matrix

Although CE‐SSCP analysis combined with 16S ribosomal RNA gene‐specific PCR has enormous potential as a simple and versatile pathogen detection technique, low resolution of CE‐SSCP causes the limited application. Among the experimental conditions affecting the resolution, the polymer matrix is considered to be most critical to improve the resolution of CE‐SSCP analysis. However, due to the peak broadening caused by the interaction between hydrophobic moiety of polymer matrices and DNA, conventional polymer matrices are not ideal for CE‐SSCP analysis. A poly(ethyleneoxide)‐poly(propyleneoxide)‐poly(ethyleneoxide) (PEO‐PPO‐PEO) triblock copolymer, with dynamic coating ability and a propensity to form micelles to minimize exposure of hydrophobic PPO block to DNA, can be an alternative matrix. In this study, we examined the resolution of CE‐SSCP analysis using the PEO‐PPO‐PEO triblock copolymer as the polymer matrix and four same‐sized DNA fragments of similar sequence content. Among 48 commercially available PEO‐PPO‐PEO triblock copolymers, three were selected due to their transparency in the operable range of viscosity and PEO₁₃₇PPO₄₃PEO₁₃₇ exhibited the most effective separation. Significant improvement in resolution allowed discrimination of the similar sequences, thus greatly facilitated CE‐SSCP analysis compared to the conventional polymer matrix. The results indicate that PEO‐PPO‐PEO triblock copolymer may serve as an ideal matrix for high‐resolution CE‐SSCP analysis.     

Homogeneously alloyed CdSxSe1-x nanocrystals: synthesis, characterization, and composition/size-dependent band gap

Alloy nanocrystals provide an additional degree of freedom in selecting desirable properties for nanoscale engineering because their physical and optical properties depend on both size and composition. We report the pyrolytic synthesis of homogeneously alloyed CdS(x)Se(1-x) nanocrystals in all proportions. The nanocrystals are characterized using UV-visible absorption spectroscopy, transmission electron microscopy, X-ray diffractrometry, and Rutherford backscattering spectrometry to determine precisely structure, size, and composition. The dependence of band gap on nanocrystal size and composition is elucidated, yielding a bowing constant of 0.29, in agreement with bulk values. In addition, the morphology of the resultant nanocrystals can be altered by changing the reaction conditions, generating structures ranging from homogeneous, spherical nanocrystals to one-dimensional gradient nanorods.     

Extending Pummerer reaction chemistry. Asymmetric synthesis of spirocyclic oxindoles via chiral indole-2-sulfoxides

The conversion of (Ss)-3-(omega-allylsilane and silyl enol ether)indole-2-sulfoxides to spirocyclic indolenines and then to oxindoles proceeds, in favorable cases, with moderate levels of chirality transfer from sulfur to C3 of the indole core. A mechanistic model, which features either an Sn2'-like additive Pummerer sequence or a tight ion pair generated by an Sn1-like vinylogous Pummerer transform, is proposed to rationalize the sense of asymmetric induction.     

Probing a very narrow Z' boson with CDF and D0 Data

The CDF and D0 data of nearly 475 pb(-1) in the dilepton channel is used to probe a recent class of models, Stueckelberg extensions of the standard model (StSM), which predict a Z' boson whose mass is of topological origin with a very narrow decay width. A Drell-Yan analysis for dilepton production via this Z' shows that the current data put constraints on the parameter space of the StSM. With a total integrated luminosity of 8 fb(-1), the very narrow can be discovered up to a mass of about 600 GeV. The StSM Z' will be very distinct since it can occur in the region where a Randall-Sundrum graviton is excluded.     

The Temporal Ultraviolet Limit for Complex Bosonic Many-body Models

We consider the partition function for a many-body model consisting of a weakly coupled gas of bosons at any temperature T > 0 and any chemical potential μ, but with both infrared and ultraviolet cutoffs imposed in both temporal and spatial directions. We take the limit as the ultraviolet cutoff in the temporal direction is removed and develop a representation for the limit that, hopefully, provides a suitable starting point for controlling the limit as the infrared cutoffs are removed.     

On Heyde’s Theorem for Probability Distributions on a Discrete Abelian Group

Let X be a countable discrete Abelian group containing no elements of order 2. Let α be an automorphism of X. Let ξ₁ and ξ₂ be independent random variables with values in the group X and distributions μ₁ and μ₂. The main result of the article is the following statement. The symmetry of the conditional distribution of the linear form L₂ = ξ₁ + αξ₂ given L₁ = ξ₁ + ξ₂ implies that μ _j are shifts of the Haar distribution of a finite subgroup of X if and only if α satisfies the condition Ker(I + α)= {0}. Some generalisations of this theorem are also proved.     

An interplay between the processes of condensation and ordering in open submonolayers of adsorbed atoms

We study the coupled processes of condensation and ordering in open atomic submonolayers adsorbed on the (001) crystal plane of a bcc alloy. The system of interstitial adsorption sites is viewed as consisting of two equivalent square sublattices. It is established that at sufficiently low substrate temperatures in a certain range of pressures of the surrounding vapor and under the repulsive character of lateral adatom–adatom interaction the adlayer may exhibit positional long-range order. A P–T diagram is constructed showing the stability region of the ordered surface phase. A system of kinetic equations is derived, which permits to analyze numerically the simultaneous evolution of the long-range order parameter and the adsorbate film coverage in the course of establishment of thermodynamic equilibrium. The processes of adsorption and surface ordering prove to be substantially interdependent. Evolution of the long-range order parameter is shown to bear a distinct threshold character. The equilibrium ordered state is attained via formation of a kinetically-slowed disordered surface phase. In evolutionary curves this is manifested by the two-stage variation of coverage. Reasons for such type of the coverage temporal evolution are suggested.     

Cyclization Cascade of Allenyl Azides: Synergy Between Theory and Experiment

Collaborative work between experimentalists and computational chemists have demonstrated a stong synergy which allowed the rationalization of allenyl azide chemistry and permited the development of an efficient synthetic tool aimed at the preparation of several alkaloids. Saturated allenyl azides undergo a reaction cascade involving key diradical intermediates that follow the Curtin-Hammett model whereas unsaturated allenyl azides form indolidene intermediates that furnish the final indole products via electrocyclic ring closure events taking place out of the Curtin-Hammett regime. The regiochemistry of the reaction cascade with the latter substrates can be manipulated by Cu(I) addition to the reaction mixture.