Two-dimensional performance of uniform irradiation with the use of an edge-softened lens array and spectral dispersion

A lens array composed of edge-softened elements is used to improve on-target irradiation uniformity in the Shenguang II Laser Facility, with which a Fresnel pattern of suppressed diffraction peaks is obtained. Additional uniformity can be reached by reducing short-wavelength interference speckles inside the pattern when the technique of smoothing by spectral dispersion is also used. Two-dimensional performance of irradiation is simulated and the results indicate that a pattern of steeper edges and a flat top can be achieved with this joint technique. (c) 2007 Optical Society of America.

Characteristics of high reflection mirror with an SiO2 top layer for multilayer dielectric grating

The high reflection (HR) mirror composed of dielectric stacks with excellent spectrum characteristics and high damage resistant ability is critical for fabricating multilayer dielectric (MLD) grating for pulse compressor. The selection of the SiO2 material as the top layer of the HR mirror for grating fabrication is beneficial for improving the laser-induced damage threshold of MLD grating as well as minimizing the standing-wave effect in the photoresist during the exposure process. Based on an (HLL) H-9 design comprising quarter-waves of HfO2 ( H) and half-waves of SiO2 ( L), we obtain an optimal design of the HR mirror for MLD grating, the SiO2 top layer of which is optimized with a merit function including both the diffraction efficiency of the MLD grating and the electric field enhancement in the grating. Dependence of the performance of the MLD grating on the fabrication error of the dielectric mirror is analysed in detail. The HR mirror is also fabricated by E-beam evaporation, which shows good spectral characteristics at the exposure wavelength of 413 nm and at the operation wavelength of 1053 nm and an average damage threshold of 10 J cm(-2) for a 12 ns pulse.

Increasing top-down suppression from prefrontal cortex facilitates tactile working memory

Navigated transcranial magnetic stimulation (TMS) combined with diffusion-weighted magnetic resonance imaging (DW-MRI) and tractography allows investigating functional anatomy of the human brain with high precision. Here we demonstrate that working memory (WM) processing of tactile temporal information is facilitated by delivering a single TMS pulse to the middle frontal gyrus (MFG) during memory maintenance. Facilitation was obtained only with a TMS pulse applied to a location of the MFG with anatomical connectivity to the primary somatosensory cortex (S1). TMS improved tactile WM also when distractive tactile stimuli interfered with memory maintenance. Moreover, TMS to the same MFG site attenuated somatosensory evoked responses (SEPs). The results suggest that the TMS-induced memory improvement is explained by increased top-down suppression of interfering sensory processing in S1 via the MFG-S1 link. These results demonstrate an anatomical and functional network that is involved in maintenance of tactile temporal WM. (C) 2009 Elsevier Inc. All rights reserved.

淡水生态系统中的TOP-DOWN效应与生物多样性保护

淡水生态系统中高营养级类群可以对低营养级类群产生强烈的影响，最终导致整个生态环境的改变，这一现象被称作下行（ｔｏｐｄｏｗｎ）效应。本文对ｔｏｐｄｏｗｎ的含义特别是鱼类所产生ｔｏｐｄｏｗｎ效应的结果进行了阐述，提出了ｔｏｐｄｏｗｎ效应还表现在当原来生态系统中的高营养级类群缺少时，也会造成生态系统结构与功能发生变化的观点。最后，根据淡水生态系统ｔｏｐｄｏｗｎ效应的特点，认为在淡水生态系统的生物多样性保护中，应注意高营养级类群的保护和谨慎地对待引种问题

Photodegradation dynamics of pure microcystin variants with illumination of fixed wavelength UV-lights

Photolysis of microcystins by UV irradiation and the effects of different environmental factors on efficiency of UV degradation were studied. The results indicated that the rates of the photolytical degradation reactions of microcystin-LR and RR-follow pseudo-first-order kinetic process. The results also showed that the concentrations of two microcystin variants decreased significantly by UV-C Irradiation; the wavelength and intensitiy of UV irradiation are two very important factors affecting the rate of degradation; temperature and pH value could also affect the half life of degradation rates. When irradiated by weaker UV-Iight, isomerization could be detected in the course of photolytical degradation. The concentrations of two isomers transformed from microcystin-LR reached its maximum at the third minute and decreased with the time afterwards. To simulate photolysis of microcystins in the field water body, microcystins with low concentration were used. It was found that UV-C illumination was capable of decomposing over 95% of microcystins within 40 min. In the presence of humic substances the photodecomposition slowed down to a certain extent. These results are valuable in using UV irradiation for elimination microcystins from raw water.

A Si-based tunable narrow-band flat-top filter with multiple-step-type Fabry-Perot cavity structure

In the optical network, the quick and accurate alignment with wavelength is an important issue during the channel detection. At this point, a filter having flat-top response characteristic is an effective solution. Based on multiple-step-type Fabry-Perot cavity structure, a novel all-Si-based thermooptical tunable flat-top filter with narrow-band has been fabricated, using our patent silicon-on-reflector bonding technology. The device demonstrated a 1-dB flat-top width of 1 nm, 3-dB band of 3 nm, free spectra range of 8 nm, and the tuning range of 4.6 nm was obtained under the applied voltage of 4 V.

Effect of the technology of implanting nitrogen into buried oxide on the radiation hardness of the top gate oxide for partially depleted SOIPMOSFET

The effect of implanting nitrogen into buried oxide on the top gate oxide hardness against total irradiation does has been investigated with three nitrogen implantation doses (8 x 10(15), 2 x 10(16) and 1 x 10(17) cm(-2)) for partially depleted SOI PMOSFET. The experimental results reveal the trend of negative shift of the threshold voltages of the studied transistors with the increase of nitrogen implantation dose before irradiation. After the irradiation with a total dose of 5 x 10(5) rad(Si) under a positive gate voltage of 2V, the threshold voltage shift of the transistors corresponding to the nitrogen implantation dose 8 x 10(15) cm(-2) is smaller than that of the transistors without implantation. However, when the implantation dose reaches 2 x 10(16) and 1 x 10(17) cm(-2), for the majority of the tested transistors, their top gate oxide was badly damaged due to irradiation. In addition, the radiation also causes damage to the body-drain junctions of the transistors with the gate oxide damaged. All the results can be interpreted by tracing back to the nitrogen implantation damage to the crystal lattices in the top silicon.

Stability of GaAs photocathodes under different intensities of illumination

The photocurrent curves of reflection-mode GaAs photocathodes as a function of time, when were illuminated by white light with an intensity of 0, 33 and 100 Ix, respectively, were measured using a multi-information measurement system. The calculated lifetimes of cathodes are 320, 160 and 75 min, respectively, showing that the stability of cathodes degraded with the increase of light intensity. The lifetime of cathode, illuminated by white light with an intensity of 100 Ix, while no photocurrent was being drawn during the illumination, was 100 min. Through comparison, we found that the influence of illumination on cathodes stability is greater than that of photocurrent. The quantum-yield curves of cathodes as a functions of time, when illuminated by white light with an intensity of 33 Ix, were measured also. The measured results show that the shape of the yield curves changes with increasing illumination time due to the faster quantum-yield degradation rate of low energy photons. Based on the revised quantum-efficiency equations for the reflection-mode cathodes, the variation of yield curves are analyzed to be due to the intervalley diffusion of photoelectrons and the evolution of the surface potential barrier profile of the photocathodes during degradation process.

Flat-top arrayed waveguide grating using a tapered multimode interferometer

A 40-channel 0.8-nm-spaced flat-top silica-based arrayed waveguide grating (AWG) with a tapered multimode interferometer (MMI) at the end of its input waveguide has been experimentally demonstrated for the first time. By adding the MMI, the 1-dB and 3-dB bandwidths are increased to 0.45 and 0.62 nm, respectively. The insertion loss (IS) of the device ranges from 3.8 to 6.8 dB. The IS uniformity is better than 3.0 dB. The crosstalk is better than -25 dB. Compared to the AWG with a rectangular MMI, the AWG with a tapered MMI shows better IS, crosstalk, and ripple. (c) 2006 Society of Photo-Optical Instrumentation Engineers.

Field-aided collection in GaInP2 top solar cells

This paper reports the study on a field-aided collection in p-on-n GaInP2 top cells. The cells were produced by metalorganic vapor phase epitaxy at a low gas pressure. In order to optimize the device configuration, numerical simulations have been performed for the impacts of field-aided collection on the performance of the top cells. On the basis of the modeling results, a modified p(+)-p(-)-n(-)-n(+) configuration is introduced for GaInP2 top cells. This modification has brought out improved photovoltaic performance of the top cells, with conversion efficiency EFF = 14.26% (AM0, 2 x 2 cm(2), 25degreesC). (C) 2003 Elsevier B.V. All rights reserved.