变栅距光栅实现啁啾脉冲光谱整形

为了充分利用放大介质的增益带宽，获得脉宽更短，功率更高的输出脉冲，需要将输入到主放大链的种子脉冲进行光谱整形来补偿放大过程中的增益窄化效应。提出了利用变栅距反射光栅实现中心波长1053nm，谱宽6nm啁啾脉冲的光谱整形。运用严格的光栅衍射耦合波理论分析光栅的衍射特性，发现该方案不会引入相位畸变。分别计算和分析了刻槽深度、入射角大小、光栅周期以及入射光波长的变化对衍射效率的影响，通过选取适当的光栅参量可获得0．5％～84％的光谱调制深度。

Proposed visible emission line space solar coronagraph

The outer atmosphere of the sun called the corona has been observed during total solar eclipse for short periods (typically <6 min), from as early as the eighteenth century. In the recent past, space-based instruments have permitted us to study the corona uninterruptedly. In spite of these developments, the dynamic corona and its high temperature (1-2 million K) are yet to be Ally understood. It is conjectured that their dynamic nature and associated energetic events are possible reasons behind the high temperature. In order to study these in detail, a visible emission line space solar coronagraph is being proposed as a payload under the small-satellite programme of the Indian Space Research Organisation. The satellite is named as Aditya-1 and the scientific objectives of this payload are to study: (i) the existence of intensity oscillations for the study of wave-driven coronal heating; (ii) the dynamics and formation of coronal loops and temperature structure of the coronal features; (iii) the origin, cause and acceleration of coronal mass ejections (CMEs) and other solar active features, and (iv) coronal magnetic field topology and three-dimensional structures of CMEs using polarization information. The uniqueness of this payload compared to previously flown space instruments is as follows: (a) observations in the visible wavelength closer to the disk (down to 1.05 solar radii); (b) high time cadence capability (better than two-images per second), and (c) simultaneous observations of at least two spectral windows all the time and three spectral windows for short durations.

Double-line-density gratings structure for compression and generation of double femtosecond laser pulses

Grating pairs are widely used for pulse compression and stretching. Normally, the two gratings are identical. We propose a very simple structure with double-line-density reflective gratings for pulse compression and generation of double pulses, which has the advantages of no material dispersion, compact in volume, simple in structure, etc. The use of reflective Dammann gratings fully demonstrated the principle of this structure. The output pulses are well verified by a standard frequency-resolved optical gating apparatus. This structure will be highly interesting in ultrashort pulse compression and other more practical applications of femtosecond laser pulses. (c) 2007 Optical Society of America.

Even aberration measurement of lithographic projection system based on optimized phase-shifting marks

In the present paper, we propose a novel method for measuring the even aberrations of lithographic projection optics by use of optimized phase-shifting marks on the test mask. The line/space ratio of the phase-shifting marks is optimized to obtain the maximum sensitivities of Zernike coefficients corresponding to even aberrations. Spherical aberration and astigmatism can be calculated from the focus shifts of phase-shifting gratings oriented at 0 degrees, 45 degrees, 90 degrees and 135 degrees at multiple illumination settings. The PROLITH simulation results show that, the measurement accuracy of spherical aberration and astigmatism obviously increase, after the optimization of the measurement mark. (C) 2008 Elsevier B.V. All rights reserved.

Seasonal changes in the distribution of dissolved organic nitrogen in coastal and open-ocean waters in the North East Pacific: sources and sinks

The distribution of dissolved organic nitrogen (DON) and nitrate were determined seasonally (winter, spring and summer) during three years along line P, i.e. an E-W transect from the coast of British Columbia, Canada, to Station P (50degreesN, 145degreesW) in the subarctic North East Pacific Ocean. In conjunction, DON measurements were made in the Straits of Juan de Fuca and Georgia within an estuarine system connected to the NE Pacific Ocean. The distribution of DON at the surface showed higher values of 4-17 muM in the Straits relative to values of 4-10 muM encountered along line P, respectively. Along line P, the concentration of DON showed an inshore-offshore gradient at the surface with higher values near the coast. The equation for the conservation of DON showed that horizontal transport of DON (inshore-offshore) was much larger than vertical physical mixing. Horizontal advection of DON-rich waters from the coastal estuarine system to the NE Pacific Ocean was likely the cause of the inshore-offshore gradient in the concentration of DON. Although the concentration of DON was very variable in space and time, it increased from winter to summer, with an average build up of 4.3 muM in the Straits and 0.7 muM in the NE subarctic Pacific. This implied seasonal DON sources of 0.3 mmol N m(-2) d(-1) at Station P and 1.5 mmol N m(-2) d(-1) in the Straits, respectively. These seasonal DON accumulation rates corresponded to about 15-20% of the seasonal nitrate uptake and suggested that there was a small seasonal build up of labile DON at the surface. However, the long residence times of 180-1560 d indicated that the most of the DON pool in surface waters was refractory in two very different productivity regimes of the NE Pacific. (C) 2002 Elsevier Science Ltd. All rights reserved.

Gaussian anamorphosis in the analysis step of the EnKF: a joint state-variable/observation approach

The analysis step of the (ensemble) Kalman filter is optimal when (1) the distribution of the background is Gaussian, (2) state variables and observations are related via a linear operator, and (3) the observational error is of additive nature and has Gaussian distribution. When these conditions are largely violated, a pre-processing step known as Gaussian anamorphosis (GA) can be applied. The objective of this procedure is to obtain state variables and observations that better fulfil the Gaussianity conditions in some sense. In this work we analyse GA from a joint perspective, paying attention to the effects of transformations in the joint state variable/observation space. First, we study transformations for state variables and observations that are independent from each other. Then, we introduce a targeted joint transformation with the objective to obtain joint Gaussianity in the transformed space. We focus primarily in the univariate case, and briefly comment on the multivariate one. A key point of this paper is that, when (1)-(3) are violated, using the analysis step of the EnKF will not recover the exact posterior density in spite of any transformations one may perform. These transformations, however, provide approximations of different quality to the Bayesian solution of the problem. Using an example in which the Bayesian posterior can be analytically computed, we assess the quality of the analysis distributions generated after applying the EnKF analysis step in conjunction with different GA options. The value of the targeted joint transformation is particularly clear for the case when the prior is Gaussian, the marginal density for the observations is close to Gaussian, and the likelihood is a Gaussian mixture.

Chain scission resists for extreme ultraviolet lithography based on high performance polysulfone-containing polymers

A series of polymers with a comb architecture were prepared where the poly(olefin sulfone) backbone was designed to be highly sensitive to extreme ultraviolet (EUV) radiation, while the well-defined poly(methyl methacrylate) (PMMA) arms were incorporated with the aim of increasing structural stability. It is hypothesized that upon EUV radiation rapid degradation of the polysulfone backbone will occur leaving behind the well-defined PMMA arms. The synthesized polymers were characterised and have had their performance as chain-scission EUV photoresists evaluated. It was found that all materials possess high sensitivity towards degradation by EUV radiation (E0 in the range 4–6 mJ cm−2). Selective degradation of the poly(1-pentene sulfone) backbone relative to the PMMA arms was demonstrated by mass spectrometry headspace analysis during EUV irradiation and by grazing-angle ATR-FTIR. EUV interference patterning has shown that materials are capable of resolving 30 nm 1:1 line:space features. The incorporation of PMMA was found to increase the structural integrity of the patterned features. Thus, it has been shown that terpolymer materials possessing a highly sensitive poly(olefin sulfone) backbone and PMMA arms are able to provide a tuneable materials platform for chain scission EUV resists. These materials have the potential to benefit applications that require nanopattering, such as computer chip manufacture and nano-MEMS.

A hybrid cascaded multilevel inverter with supercapacitor direct integration for wind power systems

This paper presents a grid-side inverter based supercapacitor direct integration scheme for wind power systems. The inverter used in this study consists of a conventional two-level inverter and three H-bridge modules. Three supercapacitor banks are directly connected to the dc-links of H-bridge modules. This approach eliminates the need for interfacing dc-dc converters and thus considerably improves the overall efficiency. However, for the maximum utilization of super capacitors their voltages should be allowed to vary. As a result of this variable voltage space vectors of the hybrid inverter get distributed unevenly. To handle this issue, a modified PWM method and a space vector modulation method are proposed and they can generate undistorted current even in the presence of unevenly distributed space vectors. A supercapacitor voltage balancing method is also presented in this paper. Simulation results are presented to validate the efficacy of the proposed scheme, modulation methods and control techniques.

Effect of soil variability on the bearing capacity of clay and in slope stability problems

Site-specific geotechnical data are always random and variable in space. In the present study, a procedure for quantifying the variability in geotechnical characterization and design parameters is discussed using the site-specific cone tip resistance data (qc) obtained from static cone penetration test (SCPT). The parameters for the spatial variability modeling of geotechnical parameters i.e. (i) existing trend function in the in situ qc data; (ii) second moment statistics i.e. analysis of mean, variance, and auto-correlation structure of the soil strength and stiffness parameters; and (iii) inputs from the spatial correlation analysis, are utilized in the numerical modeling procedures using the finite difference numerical code FLAC 5.0. The influence of consideration of spatially variable soil parameters on the reliability-based geotechnical deign is studied for the two cases i.e. (a) bearing capacity analysis of a shallow foundation resting on a clayey soil, and (b) analysis of stability and deformation pattern of a cohesive-frictional soil slope. The study highlights the procedure for conducting a site-specific study using field test data such as SCPT in geotechnical analysis and demonstrates that a few additional computations involving soil variability provide a better insight into the role of variability in designs.

Molecular Caches: A caching structure for dynamic creation of application-specific Heterogeneous cache regions

CMPs enable simultaneous execution of multiple applications on the same platforms that share cache resources. Diversity in the cache access patterns of these simultaneously executing applications can potentially trigger inter-application interference, leading to cache pollution. Whereas a large cache can ameliorate this problem, the issues of larger power consumption with increasing cache size, amplified at sub-100nm technologies, makes this solution prohibitive. In this paper in order to address the issues relating to power-aware performance of caches, we propose a caching structure that addresses the following: 1. Definition of application-specific cache partitions as an aggregation of caching units (molecules). The parameters of each molecule namely size, associativity and line size are chosen so that the power consumed by it and access time are optimal for the given technology. 2. Application-Specific resizing of cache partitions with variable and adaptive associativity per cache line, way size and variable line size. 3. A replacement policy that is transparent to the partition in terms of size, heterogeneity in associativity and line size. Through simulation studies we establish the superiority of molecular cache (caches built as aggregations of molecules) that offers a 29% power advantage over that of an equivalently performing traditional cache.

Caribbean connectivity: implications for Marine Protected Area Management. Proceedings of a Special Symposium, 9-11 November 2006, 59th Annual Meeting of the Gulf and Caribbean Fisheries Institute, Belize City, Belize

Executive Summary: Tropical marine ecosystems in the Caribbean region are inextricably linked through the movement of pollutants, nutrients, diseases, and other stressors, which threaten to further degrade coral reef communities. The magnitude of change that is occurring within the region is considerable, and solutions will require investigating pros and cons of networks of marine protected areas (MPAs), cooperation of neighboring countries, improved understanding of how external stressors degrade local marine resources, and ameliorating those stressors. Connectivity can be broadly defined as the exchange of materials (e.g., nutrients and pollutants), organisms, and genes and can be divided into: 1) genetic or evolutionary connectivity that concerns the exchange of organisms and genes, 2) demographic connectivity, which is the exchange of individuals among local groups, and 3) oceanographic connectivity, which includes flow of materials and circulation patterns and variability that underpin much of all these exchanges. Presently, we understand little about connectivity at specific locations beyond model outputs, and yet we must manage MPAs with connectivity in mind. A key to successful MPA management is how to most effectively work with scientists to acquire the information managers need. Oceanography connectivity is poorly understood, and even less is known about the shape of the dispersal curve for most species. Dispersal kernels differ for various systems, species, and life histories and are likely highly variable in space and time. Furthermore, the implications of different dispersal kernels on population dynamics and management of species is unknown. However, small dispersal kernels are the norm - not the exception. Linking patterns of dispersal to management options is difficult given the present state of knowledge. The behavioral component of larval dispersal has a major impact on where larvae settle. Individual larval behavior and life history details are required to produce meaningful simulations of population connectivity. Biological inputs are critical determinants of dispersal outcomes beyond what can be gleaned from models of passive dispersal. There is considerable temporal and spatial variation to connectivity patterns. New models are increasingly being developed, but these must be validated to understand upstream-downstream neighborhoods, dispersal corridors, stepping stones, and source/sink dynamics. At present, models are mainly useful for providing generalities and generating hypotheses. Low-technology approaches such as drifter vials and oceanographic drogues are useful, affordable options for understanding local connectivity. The “silver bullet” approach to MPA design may not be possible for several reasons. Genetic connectivity studies reveal divergent population genetic structures despite similar larval life histories. Historical stochasticity in reproduction and/or recruitment likely has important, longlasting consequences on present day genetic structure. (PDF has 200 pages.)

基于多台阶反射光栅的飞秒脉冲压缩装置

反射式光栅对是一种具有负色散性质的器件,可用于飞秒激光脉冲的压缩和展宽,具有无材料色散的优点。给出了一种基于多台阶反射光栅的脉冲压缩装置。该装置为倍密度光栅结构,由两个周期分别为40μm和20μm的四台阶反射式光栅组成。实验得到的衍射效率可以达到70%以上,输入脉冲经过两个光栅的衍射后会按原路返回,从而达到色散补偿的效果。利用此压缩装置,脉冲宽度为66.8 fs的输入脉冲压缩至接近傅里叶变换极限脉冲,即46.6 fs,由此证明只要多台阶光栅效率足够高,此装置就有可能成为不同于棱镜对进行飞秒脉冲腔内和腔外压缩的另一种途径。

The role of substrate, flow and larval supply to recruitment of the red abalone (Haliotis rufescens)

Precipitous declines in wild populations of the red abalone Haliotis rufescens and the eventual closure of the commercial and southern recreational fishery have led to renewed interest in supplementing wild stocks with hatchery-raised individuals. Most work to date has focused on releasing small juveniles and has had limited success. Although much is known about larval settlement, juvenile survivorship and growth of abalone, there is scanty information on natural processes in the field. The failure of many regulated fisheries worldwide suggests that both the larval and juvenile stages may be important in determining the future population, and that early juvenile mortality is more important than previously believed. This paper presents a series of experiments designed to examine factors and mechanisms that could affect settlement, survivorship, and growth of larvae and early post-settlers in the field. Laboratory trials under different flow regimes showed that red abalone larvae settled preferentially on substrates encrusted with coralline algae, and that settlement was rapid when exposed to crusts compared to other surfaces. Urchin grazing of films appeared to facilitate abalone settlement but only when urchins were removed. Initial field experiments showed that released larvae settled on natural cobble rock, and that settlement was at least one order of magnitude greater when settlement habitats were tented. I then examined post-settlement survivorship at one and two days after settlement, and found that although there was a large amount of variation, on average 10% of released larvae were found as newly-settled recruits after 1 day. Survivorship and growth of recruits were followed over at least one month in both Spring and Fall. Abalone settled at higher densities, survived better and grew faster in the warmer Fall months than in the Spring. The density of month-old abalone recruits was correlated with density of naturally-occurring gastropods in the Spring, but not in the Fall. These results suggest that settlement and survivorship can be extremely variable across space and time, and that oceanographic and local biotic conditions play a role and should be considered when planning larval seeding.

Denitrification and inference of nitrogen sources in the karstic Floridan Aquifer

Aquifer denitrification is among the most poorly constrained fluxes in global and regional nitrogen budgets. The few direct measurements of denitrification in groundwaters provide limited information about its spatial and temporal variability, particularly at the scale of whole aquifers. Uncertainty in estimates of denitrification may also lead to underestimates of its effect on isotopic signatures of inorganic N, and thereby confound the inference of N source from these data. In this study, our objectives are to quantify the magnitude and variability of denitrification in the Upper Floridan Aquifer (UFA) and evaluate its effect on N isotopic signatures at the regional scale. Using dual noble gas tracers (Ne, Ar) to generate physical predictions of N2 gas concentrations for 112 observations from 61 UFA springs, we show that excess (i.e. denitrification-derived) N2 is highly variable in space and inversely correlated with dissolved oxygen (O2). Negative relationships between O2 and δ15N NO3 across a larger dataset of 113 springs, well-constrained isotopic fractionation coefficients, and strong 15N:18O covariation further support inferences of denitrification in this uniquely organic-matter-poor system. Despite relatively low average rates, denitrification accounted for 32 % of estimated aquifer N inputs across all sampled UFA springs. Back-calculations of source δ15N NO3 based on denitrification progression suggest that isotopically-enriched nitrate (NO3-) in many springs of the UFA reflects groundwater denitrification rather than urban- or animal-derived inputs. © Author(s) 2012.

Generation of a train of ultrashort pulses from a compact birefringent crystal array

A linear array of n calcite crystals is shown to allow the generation of a high contrast (> 10: 1) train of 2(n) high energy (> 100 mu J) pulses from a single ultrafast laser pulse. Advantage is taken of the pulse-splitting properties of a single birefringent crystal, where an incident laser pulse can be split into two pulses with orthogonal polarizations and equal intensity, separated temporally in proportion to the thickness of the crystal traversed and the difference in refractive indices of the two optic axes. In the work presented here an array of seven calcite crystals of sequentially doubled thickness is used to produce a train of 128 pulses, each of femtosecond duration. Readily versatile properties such as the number of pulses in the train and variable mark-space ratio are realized from such a setup. (c) 2007 Optical Society of America