Improved efficiency of a pulsed optical parametric oscillator by delayed double-pass pump

By delaying the second pass of the pump of a singly resonant optical parametric oscillator, the conversion efficiency can be improved. We show the experimental results of an intracavity-doubled singly resonant parametric oscillator pumped by a Q-switched laser. Using 0.49 mJ of pump energy at 532 nm from a diode-pumped Nd:YAG laser, 0.085 mJ of 488 nm was obtained with the optimum delay for the second pass of the pump, giving a conversion efficiency of 17%. The improvement over the case of a single-pass pump was 85%, and the improvement over the double-pass pump with a small delay was 40%.     

Stereospecific polymerization of benzyl α-(alkoxymethyl) acrylates

α-(Alkoxymethyl) acrylates, such as methyl α-(phenoxymethyl) acrylate, benzyl α-(methoxymethyl)acrylate (BMMA), benzyl α-(benzyloxymethyl)acrylate, and benzyl α-(tert-butoxymethyl)acrylate, were synthesized, and their polymerizability and the stereoregularity of the polymers obtained by radical and anionic methods were investigated. The radically obtained polymers were found to be atactic by ¹³C- and ¹H-NMR analyses, but the polymers obtained with lithium reagents in toluene at −78°C were highly isotactic. Further, it is noteworthy that isotactic polymers were also produced with lithium reagents even in tetrahydrofuran. Effects of polymerization temperature and counter cation on stereoregularity were clearly observed in the polymerization of BMMA, and a potassium reagent afforded an almost atactic polymer. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 721–726, 1997     

Polymerization of monomers containing functional silyl groups. 12. Anionic polymerization of styrene derivatives para-substituted with pentamethyldisilyl (Si-Si), heptamethyltrisilyl (Si-Si-Si), and nonamethyltetrasilyl (Si-Si-Si-Si) groups

Three styrene derivatives, para-substituted pentamethyldisilyl (Si-Si), heptamethyltrisilyl (Si-Si-Si), and nonamethyltetrasilyl (Si-Si-Si-Si) groups 1 - 3 were synthesized and polymerized in tetrahydrofuran (THF) at −78°C and in benzene at 40°C. The polymerizations of 1 and 2 in THF were found to proceed without transfer and termination reactions to afford stable living polymers. The Si-Si and Si-Si-Si bonds are found to be completely stable under the conditions. Under the same conditions, novel block copolymers with well-defined structures were synthesized by sequential addition of 1 or 2 and styrene. By contrast, side reactions occurred during the polymerizations of 1 and 2 in benzene at 40°C, although polymer yields were quantitative. More seriously, polymer was not obtained in the polymerization of 3 both in THF and in benzene. Thus, the effect of chain length of the oligosilyl group is found to be critical in the anionic polymerization of 1 - 3 .     

Effect of partial oxidation and repolarization of TiC-derived nanoporous carbon electrodes on supercapacitor performance using a pH-neutral aqueous electrolyte

Journal of Solid State Electrochemistry - The present study considers TiC-derived carbon (CDC) and its partially oxidized derivative (ox-red-CDC) as potential electrode materials for pH-neutral...     

Preparation of polypseudorotaxane composed of linear and cyclic polyethylene oxides and its application to solid polymer electrolyte

The mixture of linear polyethylene glycol with molecular weight of 20,000 (l-PEG_20K) and cyclic polyethylene glycol with molecular weight of 1,000 (c-PEG_1K) was ultrasonicated in acetonitrile. After evaporating the solvent, the residue was analyzed by DSC to show a remarkable decrease of crystallization temperature. Such a large crystallization suppression was not observed when linear polyethylene glycol with molecular weight of 1,000 (l-PEG_1K) was added instead of c-PEG_1K. Further, the mixture of cyclic polyethylene glycols (c-PEG_6K and c-PEG_1K) did not exhibit a significant crystallization suppression. These experimental results indicated that formation of polypseudorotaxane through ultrasonication-assisted ring penetration played an important role in the crystallization suppression. Ionic conductivities of the polypseudorotaxane-based polymer electrolytes prepared from polyethylene oxide with molecular weight of 600,000 (PEO_600K) and c-PEG_1K showed conductivity enhancement especially at low Li salt concentration.     

Synthesis of Tetra-Substituted Trifluoromethyl-3,1-Benzoxazines by Transition-Metal-Catalyzed Decarboxylative Cyclization of N-Benzoyl Benzoxazinones

Efficient synthesis of N,O-heterocyclic tetra-substituted trifluoromethyl-3,1-benzoxazines via a transition-metal-catalyzed decarboxylative intramolecular cyclization was achieved. The decarboxylation of N-benzoyl trifluoromethyl-benzoxazinones generated the amide oxygen nucleophile, allowing a selective internal C₁-attack on Pd- or Cu-coordinated zwitterions, affording medicinally attractive tetra-substituted vinyl- or ethynyl-trifluoromethyl-3,1-benzoxazines. This protocol can be applied to the synthesis of perfluoroalkyl- and non-fluorinated 3,1-benzoxazines.     

Synthesis and asymmetric anionic polymerization of substituted 7‐aryl‐2,6‐dimethyl‐1,4‐benzoquinone methides

Substituted 7‐aryl‐2,6‐dimethyl‐1,4‐benzoquinone methides which have an electron‐donating methoxy substituent at the para‐position (p‐OMe, 2a ) or an electron‐withdrawing chloro one at the para‐ (p‐Cl, 2b ), meta‐ (m‐Cl, 2c ) , and ortho‐positions (o‐Cl, 2d ) of the benzene ring were synthesized, and their asymmetric anionic polymerizations using the complex of lithium 4‐isopropylphenoxide with (?)‐sparteine were carried out in toluene at 0 °C. The polymers with negative specific rotation were obtained for all of four monomers, and the polymer obtained from 2a showed smaller specific rotation value than that of polymer having no substituent (p‐H, 1 ) on the phenyl group and the polymers obtained from 2b–d showed larger ones. It was found that the kind of a substituent and its substitution position on the phenyl group affect significantly the optical activity of polymers. The largest specific rotation value of [α]₄₃₅= ?153.2° was obtained in the polymerization of 2d with an ortho‐chloro substituent. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 437–444     

Anticipation effect in pedestrian dynamics: Modeling and experiments

In this paper, we propose the anticipation floor field (AFF) as an extension of the floor field (FF) model, which is one of the successful models in describing pedestrian dynamics. The AFF focuses on non-local interaction between pedestrians, which has not been taken into account in the FF model based on local rules. We have conducted several experiments, as well as simulations of counter flow to show the validity of our model. It is found that strength and range of anticipation significantly affect pedestrian dynamics, and there is an optimal strength of anticipation to realize the smoothest counter flow.