调制n型掺杂ZnSe/BeTe Ⅱ型量子阱结构的发光特性

报道了调制n型掺杂ZnSe/BeTe/ZnSe Ⅱ型量子阱(type-II QW)在极低温至室温(14—296K)条件下的各种光学性质. 反射光谱显示了对于非掺杂样品,激子(X)的跃迁起着支配作用,而只有在掺杂样品的光谱里展示了一个典型的负的带电激子(X^-)的跃迁特征. PL光谱及其直线偏振度P_l都显著地依赖于n型掺杂量和平行于QW生长方向的外加电场. 这个特征被认为是由n型掺杂导致了内秉电场(built 关键词： 光致发光 二维电子气 带电激子 Ⅱ型量子阱     

Low radiation loss Y-junctions in planar dielectric optical waveguides

A simple structure is proposed to reduce radiation losses of Y-junctions in planar optical waveguides by decreasing refractive indices near the branching regions. The losses of the properly designed Y-junctions can be reduced by around an order of magnitude compared with those of conventional ones when the branching angles are large.     

Synthesis of 1-benzothiepine and 1-benzazepine derivatives as orally active CCR5 antagonists

Quaternary ammonium benzocycloheptene compound 1 has previously been reported as a clinical candidate for an injectable CCR5 antagonist. In order to develop an orally active CCR5 antagonist, derivatives of tertiary amine benzocycloheptene 2, the chemical precursor to 1, were investigated. The benzocycloheptene ring was converted to benzothiepine and benzazepine rings and it was found that these changes could enhance the potency of tertiary amine derivatives. In particular, the 1-benzothiepine-1,1-dioxide 11b and the N-methyl-1-benzazepine 18 showed increased activity and good preliminary pharmacokinetic properties. The synthesis of 1-benzothiepine and 1-benzazepine derivatives and their activity are described.     

Bending losses of a doubly clad slab waveguide

This communication considers the bending losses of a doubly clad slab waveguide in which the core has the largest refractive index and the inner cladding has the lowest. It is found that the bending losses are drastically reduced by inserting a low-index inner cladding between the core and the outer cladding.     

Nanotube phonon waveguide

We find that the high thermal conductivity of carbon nanotubes remains intact under severe structural deformations while the corresponding electrical resistance and thermoelectric power show compromised responses. Similar robust thermal transport against bending is found for boron nitride nanotubes. Surprisingly, for both systems the phonon mean free path exceeds the characteristic length of structural ripples induced by bending and approaches the theoretical limit set by the radius of curvature. The robustness of heat conduction in nanotubes refines the ultimate limit that is far beyond the reach of ordinary materials.     

Three new monoterpenoids from the fruit of Genipa americana

Three new monoterpenoids, called genipacetal, genipamide, and genipaol, were isolated from the fruit of Genipa americana L. (Rubiaceae), along with the four known iridoids genipin, gardendiol, deacetyl asperulosidic acid methyl ester, and shanzhiside. Their chemical structures were determined on the basis of spectroscopic data.     

Four new triterpene glycosides from Nigella damascena

Four new triterpene glycosides, named nigellosides A, B, C, and D, were from the air-dried aerial parts of Nigella damascena L. (Ranunculaceae), and the structures were elucidated on the basis of spectroscopic data including 2D NMR spectra and chemical evidence. Their chemical structures have been characterized as 3-O-alpha-L-rhamnopyranosyl-(1-->2)-alpha-L-arabinopyranosyl gypsogenin 28-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl ester, 3-O-beta-D-glucopyranosyl-(1-->3)-alpha-L-rhamnopyranosyl-(1-->2)-alpha-L-arabinopyranosyl gypsogenin 28-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl ester, 3-O-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-xylopyranosyl hederagenin 28-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl ester, and 3-O-beta-D-glucopyranosyl-(1-->3)-alpha-L-rhamnopyranosyl-(1-->2)-beta-D-xylopyranosyl hederagenin 28-beta-D-glucopyranosyl-(1-->6)-beta-D-glucopyranosyl ester.     

Synthesis and properties of bio‐based polyurethanes bearing hydroxy groups derived from alditols

Four kinds of bio‐based polyurethanes bearing hydroxy groups in the pendants were synthesized by the polyaddition of D ‐mannitol‐ and D,L ‐erythritol‐derived diols (1,2:5,6‐di‐O‐isopropylidene‐D ‐mannitol and 1,2‐O‐isopropylidene‐D,L ‐erythritol) with hexamethylene diisocyanate and methyl (S)‐2,6‐diisocyanatohexanoate and the subsequent deprotection of the isopropylidene groups. They were hydrolyzed much more quickly than the corresponding protected polyurethanes at 50 °C and pH 7.0, although their hydrolytic degradation rate was lower than that of polyurethanes with saccharic and glucuronic lactone groups, which had been reported in our previous articles. The introduction of D ‐mannitol units to the polyether‐polyurethanes containing poly(oxytetramethylene) glycol units also enhanced their hydrolyzibility. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Chemical modification of chain end in nylon 4 and improvement of its thermal stability

Two kinds of nylon 4 having an acyllactam group at one or both chain ends were synthesized by the anionic ring‐opening polymerization of 2‐pyrrolidone using N‐benzoyl‐2‐pyrrolidone (BP) or N,N′‐isophthaloylbis‐2‐pyrrolidone (IPP) and potassium tert‐butoxide as an initiator and a catalyst, respectively, and carefully isolated with the suppression of moisture adsorption. The acyllactam at one chain end in the low molecular weight of nylon 4 was quantitatively converted to other functional groups such as carboxy, amine and so on, which were confirmed by matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI TOF) mass spectroscopy. Terminal acyllactam groups telechelating in the nylon 4 at both chain ends were also modified to carboxy and amino groups. From the thermogravimetric analysis (TGA), thermal decomposition point of the modified nylon 4 was increased in comparison with that of the original acyllactam‐type nylon 4, although the acyllactam chain end caused the backbiting depolymerization accompanied with the generation of 2‐pyrrolidone monomer. The direct heating of the acyllactam‐telechelic low molecular weight of nylon 4 mixed with the diamine in bulk also led to improve its thermal stability significantly by the chain extension through the polyaddition reaction. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011