alpha-tocopherol is essential for acquired chill-light tolerance in the cyanobacterium Synechocystis sp strain PCC 6803

Unlike Escherichia coli, the cyanobacterium Synechocystis sp. strain PCC 6803 is insensitive to chill (5 degrees C) in the dark but rapidly losses viability when exposed to chill in the light (100 mu mol photons m(-2) s(-1)). Preconditioning at a low temperature (15 degrees C) greatly enhances the chill-light tolerance of Synechocystis sp. strain PCC 6803. This phenomenon is called acquired chill-light tolerance (ACLT). Preconditioned wild-type cells maintained a substantially higher level of alpha-tocopherol after exposure to chill-light stress. Mutants unable to synthesize alpha-tocopherol, such as slr1736, slr1737, slr0089, and slr0090 mutants, almost completely lost ACLT. When exposed to chill without light, these mutants showed no or a slight difference from the wild type. When complemented, the slr0089 mutant regained its ACLT. Copper-regulated expression of slr0090 from P-petE controlled the level of et-tocopherol and ACLT. We conclude that alpha-tocopherol is essential for ACLT of Synechocystis sp. strain PCC 6803. The role of a-tocopherol in ACLT may be based largely on a nonantioxidant activity that is not possessed by other tocopherols or pathway intermediates.

Evaluation of soot particles of biomass fuels with endocrine-modulating activity in yeast-based bioassay

Exposure to indoor air pollution (IAP) from the combustion of biomass fuels is an important cause of morbidity and mortality in developing countries. In the work discussed in this paper we evaluated the endocrine activity of soot particles from biomass fuels by using yeast bioassay. These pollutants could have beta-galactosidase activity with a relative potency (RP) about 10(-7)-10(-9) that of estradiol. Soot particles from wood and straw combustion only partially induced beta-galactosidase activity whereas others produced fully inductive activity in the yeast assay system. These pollutants did not have estrogen antagonist and progesterone agonist activity within the defined concentration range. However, these pollutants require 2-4 orders of magnitude higher IC50 to inhibit the activity of progesterone in a similar dose-response manner to mifepristone. We therefore propose that the endocrine activity of some environmental pollutants may be because of inhibition of the progesterone receptor (hPR). GC-MS results showed that substituted polycyclic aromatic hydrocarbon (PAH) compounds, substituted phenolic compounds and derivatives, aromatic carbonyl compounds, and phytosteroids in these soot particles may be mimicking endogenous hormones.

Multimode resonances in metallically confined square-resonator microlasers

Directional emission InP/AlGaInAs square-resonator microlasers with a side length of 20 mu m are fabricated by standard photolithography and inductively coupled-plasma etching technique. Multimode resonances with about seven distinct mode peaks in a free-spectral range are observed from 1460 to 1560 nm with the free-spectral range of 12.1 nm near the wavelength of 1510 nm, and the mode refractive index versus the photon energy E (eV) as 3.07152+0.18304E are obtained by fitting the laser spectra with an analytical mode wavelength formula derived by light ray method. In addition, mode field pattern is simulated for cold cavity by two dimensional finite-difference time-domain technique.

Relationship between the electric performance and the photoluminescence spectra of resonant tunnelling diodes

Resonant tunnelling diodes with different structures were grown. Their photoluminescence spectra were investigated. By contrast, the luminescence in the quantum well is separated from that of other epilayers. The result is obtained that the exciton of the luminescence in the quantum well is partly come from the cap layer in the experiment. So the photoluminescence spectrum is closely related to the electron transport in the resonant tunnelling diode structure. This offers a method by which the important performance of resonant tunnelling diode could be forecast by analysing the integrated photoluminescence intensities.

Vertical PIN ultraviolet photodetectors based on 4H-SiC homoepilayers

Vertical PIN ultraviolet photodetectors based on 4H-SiC homoepilayers are presented. The growth of the 4H-SiC homoepilayers was carried out in a LPCVD system. The size of the active area of the photodetector was 300 x 300 mu m(2). The dark and illuminated I-V characteristics were measured at reverse biases from 0 V to 30 V at room temperature. The illuminated current was at least two orders of magnitude higher than the dark current at a bias of below 12 V. The photoresponse was measured from 200 nm to 400 nm at different reverse biases and the peak values of the photo response were located at 3 10 nm. The calculated spectral detectivity D* was shown to be higher than 10(13) cmHz(1/2)/W from 260 to 360 nm with a peak value of 5.9 x 10(13) cmHz(1/2) /W at 310 nm. The peak value of the photoresponse was hundreds of times higher than the response at 400 nm, which showed the device had good visible blind performance. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

1064nm RCE探测器光电响应特性分析

对1064nm谐振腔增强型（RCE）光电探测器（PD）的光电响应特性进行了分析研究．利用MBE生长技术得到有源区分别为量子阱和量子点的1064nm RCE探测器的外延片，并对制作的探测器进行了各种光电特性测试．结果表明量子阱结构的RCE探测器量子效率峰值达到57％，谱线半宽6～7nm，峰值波长1059nm；而量子点结构的RCE探测器量子效率峰值达到30％，谱线半宽5nm，峰值波长1056nm．通过分析量子效率和吸收系数之间的关系，对两种结构器件的吸收进行了比较，发现虽然量子点探测器的吸收小，但通过合理设计共振腔等方法也可以达到较高的量子效率．两种结构的器件都有很好的I-V特性．

Second-Order Raman Scattering from n- and p-Type 4H-SiC

The results of second-order Raman-scattering experiments on n- and p-type 4H-SiC are presented,covering the acoustic and the optical overtone spectral regions.Some of the observed structures in the spectra are assigned to particular phonon branches and the points in the Brillouin zone from which the scattering originates.There exists a doublet at 626/636cm-1 with energy difference about 10cm-1 in both n- and p-type 4H-SiC,which is similar to the doublet structure with the same energy difference founded in hexagonal GaN,ZnO, and AlN.The cutoff frequency at 1926cm-1 of the second-order Raman is not the overtone of the A1(LO) peak of the n-type doping 4H-SiC,but that of the undoping one.The second-order Raman spectrum of 4H-SiC can hardly be affected by doping species or doping density.

成骨细胞铺展形状和面积对其凋亡的影响

<正>骨组织内的三种细胞(即骨细胞、成骨细胞和破骨细胞)控制着骨的形成与吸收。骨细胞位于胞外矿物质沉积形成的骨陷窝内,而成骨细胞与破骨细胞位于骨小梁的表面。成骨细胞在向骨细胞进行分化的过程中,首先大量分泌细胞外基质逐渐将自身束缚在一个狭小的空间内,并最终在这种狭小的空间中分化为骨细胞。另一方面,成骨细胞紧密排列在骨小梁的表面,细胞间距离约为1μm,当分化为骨细胞后,细胞间距离