an empirical study on bug assignment automation using chinese bug data

Univ SE Calif, Ctr Syst & Software Engn, ABB, Microsoft Res, IEEE, ACMSIGSOFT, N Carolina State Univ Comp Sci

Assignment of absolute configuration of cyclic secondary amines by NMR techniques using Mosher's method: a general procedure exemplified with (-)-isoanabasine

A general procedure to determine the absolute configuration of cyclic secondary amines with Mosher's NMR method is demonstrated, with assignment of absolute configuration of isoanabasine as an example. Each Mosher amide can adopt two stable conformations (named rotamers) caused by hindered rotation around amide C-N bond. Via a three-step structural analysis of four rotamers, the absolute configuration of (-)-isoanabasine is deduced to be (R) on the basis of Newman projections, which makes it easy to understand and clarify the application of Mosher's method to cyclic secondary amines. Furthermore, it was observed that there was an unexpected ratio of rotamers of Mosher amide derived from (R)-isoanabasine and (R)-Mosher acid. This phenomenon implied that it is necessary to distinguish the predominant rotamer from the minor one prior to determining the absolute configuration while using this technique.

Complete assignment of H-1-NMR resonances of the king cobra neurotoxin CM-11

The king cobra(Ophiophagus hannah) neurotoxin CM-11 is long-chain peptide with 72 amino acid residues. Its complete assignment of H-1-NMR resonances was obtained using various 2D-NMR technologies, including DQF-COSY, clean-TOCSY and NOESY.

A NEW SCHEME FOR ASSIGNMENT OF A CANONICAL CONNECTION TABLE

A new algorithm for deriving canonical numbering of atoms in a molecular graph has been developed. Some graph invariants, such as node properties, degree (connectivity), topological path, the smallest node ring index, etc., are encoded together to partit

ASSIGNMENT OF C-13 NMR-SPECTRA OF POLYMER WITH SEMIEMPIRICAL METHOD - SURVEY OF SPECTRUM OF SECONDARY CARBON OF 1,2-PBD

In chain molecules of 1, 2-PBD, there are two kinds of gauche arrangements, which is the cause of making the spectrum of the secondary carbon in main chain of the polymer split. In such a complex system, the gauche arrangements of the secondary carbon and the tertiary carbon occupy an important position. Hence, the contribution of the tertiary carbon to the chemical shifts of the secondary carbon has a decisive effect on the sequence structure distribution. In comparison the contribution of vinyl groups is ...

NONINVASIVE GIANT PANDA PATERNITY EXCLUSION

Giant panda hair samples obtained by noninvasive methods served as a source of DNA for amplification of seven giant panda microsatellite loci utilizing the polymerase chain reaction. Thirteen giant pandas held in Chinese zoos were tested for identification of paternity. Some males listed as sires have been excluded as the biological father of captive-born giant pandas. Because of the death of some potential sires, paternity is still not assigned for some giant pandas, although there is a high likelihood that paternity assignment could be made if postmortem samples are available for genetic analysis. The DNA microsatellite variation assayed by the test we have developed provides a rapid, highly informative, and noninvasive method for paternity identification in giant pandas. (C) 1994 Wiley-Liss, Inc.

Four new terrestrial species of Marionina (Clitellata, Enchytraeidae) from China and re-examination of M. hoVbaueri Moller

Enchytraeid surveys were made in China, mainly along the Changjiang (Yangtze) River Basin, during the period 1991-1999. Among the findings, four terrestrial species of Marionina are new to science and well illustrate the taxonomic complexity of the genus as currently defined. Marionina sinica sp. n. is characterized by a specific chaetal distribution, the marionine pattern of the dorsal blood vessel, and elongate, fusiform, spermathecal ectal ducts. Marionina sacculata sp. n. is distinguished by the possession of a pair of pouch-like oesophageal appendages in IV, the lack of lateral chaetae in VII-XI, a marionine pattern of the dorsal blood vessel, and short spermathecal ectal ducts gradually expanding into spherical ampullae. Both M. sinica and M. sacculata have minute bodies (2-3 mm long in vivo) and lack spermathecal accessory glands. The former species shows its closest aYnities with the European M. brendae Rota, 1995, whereas the latter is closest to the German M. hoVbaueri Moller, 1971, for which an amended diagnosis is provided. Marionina seminuda sp. n. has only ventral chaetal bundles, distributed from III onwards and bisetose. It is similar to the Holarctic M. subterranea (Knollner, 1935) in lacking entirely the lateral chaetae and in having the brain incised posteriorly, the dorsal vessel bifurcating behind the pharynx, and coelomocytes containing opaque granules, but diVers from it in having the longest chaetae in preclitellar segments and gland cells distributed all over the spermathecal ectal ducts. Marionina righiana sp. n. is diagnosed by the location of the head pore on the prostomium, the absence of lateral chaetae from VIII ( VII or IX) onwards, the possession of free spermathecae extending backwards through one to four segments, the brain deeply incised posteriorly, the lumbricilline pattern of the dorsal blood vessel, and the opacity of coelomocytes in vivo. Prior to this study, members of the genus so atypical as M. righiana with respect to the position of the head pore and the structure of the spermathecae were known only from South American soils. Until the taxonomy of Marionina has been more thoroughly assessed and revised, the assignment of the four species to this large assemblage should be regarded as tentative.

Influence of dual incorporation of In and N on the luminescence of GaInNAs/GaAs single quantum wells

The optical properties of above- and below-band-edge transitions have been investigated by incorporating In atoms into GaNAs/GaAs single quantum wells. The experimental results show that with increasing In concentration the interband luminescence is improved and the luminescence intensity below the band edge in GaInNAs/GaAs decreases significantly. An interpretation is given that N atoms are preferable to form a covalent bond with In than with Ga atoms in a GaInNAs alloy, due to the compensation of the atomic-size difference between In and N atoms on the GaAs substrate. The photoreflectance spectra of the GaInNAs/GaAs single quantum well support the assignment of an intrinsic mechanism to the high-energy luminescence peak. (C) 2000 American Institute of Physics. [S0003- 6951(00)01752-6].

Hole levels and exciton states in CdS nanocrystals

We have studied the hole levels and exciton states in CdS nanocrystals by using the hole effective-mass Hamiltonian for wurtzite structure. It is found that the optically passive P-x state will become the ground hole state for small CdS quantum dots of radius less than 69 Angstrom. It suggests that the "dark exciton" would be more easily observed in the CdS quantum dots than that in CdSe quantum dots. The size dependence of the resonant Stokes shift is predicted for CdS quantum dots. Including the Coulomb interaction, exciton energies as functions of the dot radius are calculated and compared with experimental data.

Study of rapid carrier capture and relaxation in InAs/GaAs heterostructures

The rapid carrier capture and relaxation processes in InAs/GaAs quantum dots were studied at 77K by using a simple degenerate pump-probe technique. A rising process was observed in the transient reflectivity, following the initial fast relaxation associated with GaAs bulk matrix, and this rising process was assigned to be related to the carrier capture from the GaAs barriers to InAs layers. The assignment was modeled using Kramers-Kronig relation. By analyzing the rising process observed in the transient reflectivity, the carrier capture time constants were obtained. The measured capture times decrease with the increase of carrier concentration.

Exciton states and optical spectra in CdSe nanocrystallite quantum dots

By using the hole effective-mass Hamiltonian for semiconductors with the wurtzite structure, we have studied the exciton states and optical spectra in CdSe nanocrystallite quantum dots. The intrinsic asymmetry of the hexagonal lattice structure and the effect of spin-orbital coupling (SOC) on the hole states are investigated. It is found that the strong SOC limit is a good approximation for hole states. The selection rules and oscillator strengths for optical transitions between the conduction- and valence-band states are obtained. The Coulomb interaction of exciton states is also taken into account. In order to identify the exciton states, we use the approximation of eliminating the coupling of Gamma(6)(X, Y) with Gamma(1)(Z) states. The results are found to account for most of the important features of the experimental photoluminescence excitation spectra of Norris ct nl. However, if the interaction between Gamma(6)(X, Y) and Gamma(1)(Z) states is ignored, the optically passive P-x state cannot become the ground hole state for small CdSe quantum dots of radius less than 30 Angstrom. It is suggested that the intrinsic asymmetry of the hexagonal lattice structure and the coupling of Gamma(6)(X,Y) with Gamma(1)(Z) states are important for understanding the "dark exciton" effect.

Carrier capture into InAs/GaAs quantum dots detected by a simple degenerate pump-probe technique

We demonstrate that the carrier capture and relaxation processes in InAs/GaAs quantum dots can be detected by a simple degenerate pump-probe technique. We have observed a rising process in the transient reflectivity, following the initial fast relaxation in a GaAs matrix, and assigned this rising process to the carrier capture from the GaAs barriers to the InAs layers. The assignment was modeled using the Kramers-Kronig relations. The capture time was found to depend strongly on the InAs layer thickness as well as on the excitation density and photon energy. (C) 2000 Elsevier Science Ltd. All rights reserved.

Raman-forbidden mode and oxygen ordering in Bi2Sr2-xLaxCuO6+gamma single crystals annealed in oxygen

A Raman-forbidden phonon mode at about 840 cm(-1) is observed popularly on the surface of pun and La-doped Bi2Sr2-xLaxCuO6+y (0 less than or equal to x less than or equal to 0.8) single crystals annealed in oxygen. A remarkable excitation dependence of this additional line is found. Based on the properties of the structure of the Bi-O layer with excess oxygen atoms and the similarity in the appearance of the Raman-forbidden modes between RBa2Cu3Ox (R = Y, Nd, Gd, Pr) and Bi2Sr2-xLaxCuO6+y systems, we attribute the manifestation of this additional line to the ordering of the interstitial oxygen in the Bi-O layers. Our results provide Raman evidences for confirming that the ordering of the movable oxygen may exist universally in high-temperature superconductors.

Resonant magnetopolaron effects in GaAs/AlGaAs multiple quantum well structures

A detailed experimental study of electron cyclotron resonance (CR) has been carried out at 4.2 K in three modulation-doped GaAs/Al0.3Ga0.7As multiple quantum well samples in fields up to 30 T. A strong avoided-level-crossing splitting of the CR energies due to resonant magnetopolaron effects is observed for all samples near the GaAs reststrahlen region. Resonant splittings in the region of AlAs-like interface phonon modes of the barriers are observed in two samples with narrower well width and smaller doping concentration. The interaction between electrons and the AlAs interface optical phonon modes has been calculated for our specific sample structures in the framework of the memory-function formalism. The calculated results are in good agreement with the experimental results, which confirms our assignment of the observed splitting near the AlAs-like phonon region is due to the resonant magnetopolaron interaction of electrons in the wells with AlAs-like interface phonons. (C) 1998 Elsevier Science B.V. All rights reserved.