Abnormal temperature dependent photoluminescence of self-assembled InAs/GaAs surface quantum dots with high areal density

We have investigated temperature dependent photoluminescence of both buried and surface self-assembled InAs/GaAs quantum dots with an areal density up to similar to 10(11)/cm(2). Different from the buried quantum dots, the peak energy of surface quantum dots shows a blueshift relative to the bulk material variation from 15 to 130K. Besides the line width and the integrated intensity both first decrease and then increase in this temperature interval. The observed phenomena can be explained by carrier trapping effects by some shallow localized centers near the surface quantum dots.

Effect of electron-electron scattering on spin dephasing in a high-mobility low-density two-dimensional electron gas

By utilizing time-resolved Kerr rotation techniques, we have investigated the spin dynamics of a high-mobility low density two-dimensional electron gas in a GaAs/Al0.35Ga0.65As heterostructure in the dependence on temperature from 1.5 to 30 K. It is found that the spin relaxation/dephasing time under a magnetic field of 0.5 T exhibits a maximum of 3.12 ns around 14 K, which is superimposed on an increasing background with rising temperature. The appearance of the maximum is ascribed to that at the temperature where the crossover from the degenerate to the nondegenerate regime takes place, electron-electron Coulomb scattering becomes strongest, and thus inhomogeneous precession broadening due to the D'yakonov-Perel' mechanism becomes weakest. These results agree with the recent theoretical predictions [J. Zhou et al., Phys. Rev. B 15, 045305 (2007)], which verify the importance of electron-electron Coulomb scattering to electron spin relaxation/dephasing.

Spin dynamics of electrons in the first excited subband of a high-mobility low-density two-dimensional electron system

We report on time-resolved Kerr rotation measurements of spin coherence of electrons in the first excited subband of a high-mobility low-density two-dimensional electron system in a GaAs/Al0.35Ga0.65As heterostructure. While the transverse spin lifetime (T-2(*)) of electrons decreases monotonically with increasing magnetic field, it has a nonmonotonic dependence on the temperature and reaches a peak value of 596 ps at 36 K, indicating the effect of intersubband electron-electron scattering on the electron-spin relaxation.

High precision mass measurement and LPT

A Penning trap, which can measure the atomic masses with the highest precision, is one of the most important facilities in nuclear physics research nowadays. The precision mass data play an important role in the studies of nuclear models, mass formulas, nuclear synthesis processes in the nuclear astrophysics, symmetries of the weak interaction and the conserved vector current (CVC) hypothesis. The status of high precision mass measurement around the world, the basic principle of Penning trap and the basic information about the LPT (Lanzhou Penning Trap) are introduced.

High resolution mass spectrometric alveolar proteomics: Identification of surfactant protein SP-A and SP-D modifications in proteinosis and cystic fibrosis patients

In the present study, one- and two-dimensional gel electrophoresis combined with high resolution Fourier transform-ion cyclotron resonance mass spectrometry (FT-ICR MS) have been applied as powerful approaches for the proteome analysis of surfactant proteins SP-A and SP-D, including identification of structurally modified and truncation forms, in bronchoalveolar lavage fluid from patients with cystic fibrosis, chronic bronchitis and pulmonary alveolar proteinosis. Highly sensitive micro preparation techniques were developed for matrix-assisted laser desorption/ionization (MALDI) FT-ICR MS analysis which provided the identification of surfactant proteins at very low levels. Owing to the high resolution, FT-ICR MS was found to provide substantial advantages for the structural identification of surfactant proteins from complex biological matrices with high mass determination accuracy. Several protein bands corresponding to SP-A and SP-D were identified by MALDI-FT-ICR MS after electrophoretic separation by one- and two-dimensional gel electrophoresis, and provided the identification of structural modifications (hydroxy-proline) and degradation products.

Capillary liquid chromatographic-high-resolution mass spectrometric analysis of ribonucleotides

A method of capillary HPLC-high-resolution MS was developed for the trace analysis of ATP, GTP, dATP and dGTP Dimethylhexylamine (DMHA) was used as ion-pairing agent for the HPLC retention and separation of the nucleotides and positive ion electrospray time-of-flight MS was used for the detection. The application of capillary HPLC allowed minimal usage of DMHA while providing excellent peak retention and resolution, which significantly reduced the ion suppression in electrospray ionization-MS analysis and thus increased the sensitivity. Adduct ions of nucleotides and DMHA were used as quantitative ions in order to achieve the best sensitivity. DMHA concentration at 5 mM in the aqueous mobile phase at pH 7 was found to be the optimal conditions for the C Is capillary column. The method was applied to determine ATP level in cultured C6 glioma cells that were treated with toxic concentrations of Zn. The results showed that the cellular ATP level decreased from 2.7 pmol/cell (<10% cell death) in average control cell samples to 0.36 pmol/cell as the concentration of Zn increased to 120 mg/l (>35% cell death) in culture medium.

Studies on the nature of the macromolecular condensed state of "nascent" ultra high molar mass polyethylene

Ultra high molar mass polyethylene (UHPE) powder as polymerized in a slurry process has been studied, in its nascent state, after recrystallization on rapid cooling from the melt and after hot compression molding to a film, by DSC, effect of annealing the recrystallized specimen at 120 similar to 130 degreesC, morphology by polarizing optical microscopy and small angle X-ray scattering. Based on the experimental results obtained the macromolecular condensed state of the nascent UHPE powder is a rare case of a multi-chain condensed state of non-interpenetrating chains, involving interlaced extended chain crystalline layers and relaxed parallel chain amorphous layers. On melting, a nematic rubbery state of nanometer size domain resulted. The nematic-isotropic transition temperature was judged from literature data to be at least 220 degreesC, possibly higher than 300 degreesC, the exact temperature is however not sue because of chain degradation at such high temperatures. The recrystallization process from the melt is a crystallization from a nematic rubbery state. The drop of remelting peak temperature by 10 K of the specimen recrystallized from its melt as compared to the nascent state has its origin in the decrease both of the crystalline chain stem length and of the degree of crystallinity. The remelting peak temperature could be returned close to that of the nascent state by annealing at 120 similar to 130 degreesC.

Interplay effects of temperature and injection power on photoluminescence of InAs/GaAs quantum dot with high and low areal density

In this report, we have investigated the temperature and injection power dependent photoluminescence in self-assembled InAs/GaAs quantum dots (QDs) systems with low and high areal density, respectively. It was found that, for the high-density samples, state filling effect and abnormal temperature dependence were interacting. In particular, the injection power-induced variations were most obvious at the temperature interval where carriers transfer from small quantum dots (SQDs) to large quantum dots (LQDs). Such interplay effects could be explained by carrier population of SQDs relative to LQDs, which could be fitted well using a thermal carrier rate equation model. On the other hand, for the low density sample, an abnormal broadening of full width at half maximum (FWHM) was observed at the 15-100 K interval. In addition, the FWHM also broadened with increasing injection power at the whole measured temperature interval. Such peculiarities of low density QDs could be attributed to the exciton dephasing processes, which is similar to the characteristic of a single quantum dot. The compared interplay effects of high-and low-density QDs reflect the difference between an interacting and isolated QDs system.

Lung alveolar proteomics of bronchoalveolar lavage from a pulmonary alveolar proteinosis patient using high-resolution FTICR mass spectrometry

High-resolution Fourier transform ion cyclotron resonance (FTICR) mass spectrometry was developed and applied to the proteome analysis of bronchoalveolar lavage fluid (BALF) from a patient with pulmonary alveolar proteinosis. With use of 1-D and 2-D gel electrophoresis, surfactant protein A (SP-A) and other surfactant-related lung alveolar proteins were efficiently separated and identified by matrix-assisted laser desorption/ionization FTICR mass spectrometry . Low molecular mass BALF proteins were separated using a gradient 2-D gel. An efficient extraction/precipitation system was developed and used for the enrichment of surfactant proteins. The result of the BALF proteome analysis show the presence of several isoforms of SP-A, in which an N-non-glycosylierte form and several proline hydroxylations were identified. Furthermore, a number of protein spots were found to contain a mixture of proteins unresolved by 2-D gel electrophoresis, illustrating the feasibility of high-resolution mass spectrometry to provide identifications of proteins that remain unseparated in 2-D gels even upon extended pH gradients.

Secondary electron time detector for mass measurements at CSRe

The Isochronous Mass Spectrometry is a high accurate mass spectrometer. A secondary electrons time detector has been developed and used for mass measurements. Secondary electrons from a thin carbon foil are accelerated by ail electric field and deflected 180 degrees by a magnetic field onto a micro-channel plate. The time detector has been tested with alpha particles and a time resolution of 197 ps (FWHM) was obtained in the laboratory. A mass resolution around 8 x 10(-6) For Delta m/m was achieved by using this time detector in a pilot mass measurement experiment.

Characterization of triterpenoidic saponin mixture in crude extracts from leaves of Acanthopanax senticosus Harms by saponin structural correlation and mass spectrometry

Eighteen triterpenoidic saponins in crude extracts from leaves of Acanthopanax senticous Harms have been investigated by electrospray ionization multi-stage tandem mass spectrometry and high-resolution mass spectrometry. In ESI-MS spectra, predominant [M + Na](+) ions in the positive ion mode have been observed for molecular mass information. Meanwhile, specific structural correlations between these ions are firstly found. The 18 peaks (ions) can be classified into three groups (group D, E, and F with mass increase) with each group including six peaks. There is a mass difference of 132 Da between group D and E for each corresponding peak in turn (for example peak 1 to peak 7), indicating one more pentose residue was attached to saponins in group E than those corresponding in group D. The mass difference of 146 Da between group E and F implies one more deoxy-hexose attached to saponins in group F than those corresponding in group E. The structural correlations of the corresponding ions are confirmed by tandem mass spectrometry and high-re solution mass spectrometry. These structural features can not only facilitate the rapid characterization of the native known saponins in crude plant extracts, thus avoiding tedious derivation and separation of saponins, but also help find novel compounds of the same type in a specific medicinal plant.

Effects of cell density, light intensity and mixing on Undaria pinnatifida gametophyte activity in a photobioreactor

An on-line controlled 7 1 sterilizable photobioreactor was used for the optimisation of a culture of gametophytes of Undaria pinnatifida. The gametophytes, which had been stored for three years in a culture cabinet at 16 degreesC, could rapidly grow in the photobioreactor under controlled conditions. The rate of increase of dissolved oxygen and pH were used to monitor the photosynthetic activity. Optimal gametophytes density changed varying the light intensity. The optimal cell densities were 3.24 and 3.45 g FW l(-1) when the cultures were exposed to 61.7 and 82.3 muE m(-2) s(-1), respectively. The optimal cell density was higher under a high photon flux density (PFD) than under low PFD. On the other hand, the optimal light intensities were different for different cell density cultures. The light saturation point was higher at high cell density cultures than at low cell density cultures. The optimal rotational speed was 150 rpm for high cell density culture in the photobioreactor. (C) 2003 Elsevier B.V. All rights reserved.