基于遥感的秦岭近20年生态环境空间格局变化研究

生态环境变化可由遥感的植被变化显示,利用RS和GIS技术、Landtrendr算法,提取秦岭地区近20年土地利用格局、植被覆盖变化趋势以及林地扰动与恢复情况,并对其变化驱动力进一步讨论。结果表明,近20年来,秦岭地区土地利用以林地为主,植被覆盖整体为增加趋势,城市区域为减少趋势;Landtrendr监测显示秦岭林地扰动事件多发生于市区,西安市开发早于其他地区,分类结果较好;且人为活动干扰是林地变化主要驱动力。上述结果表明秦岭生态文明建设取得一定成效,可为秦岭生态环境保护提供科学依据。

Modeling wave attenuation by vegetation with accompanying currents in SWAN

Coastal wetlands such as salt marshes and mangroves provide important protection against stormy waves.Accurate assessments of wetlands’capacity in wave attenuation are required to safely utilize their protection services.Recent studies have shown that tidal currents have a significant impact on wetlands’wave attenuation capacity,but such impact has been rarely considered in numerical models,which may lead to overestimation of wave attenuation in wetlands.This study modified the SWAN(Simulating Waves Nearshore)model to account for the effect of accompanying currents on vegetation-induced wave dissipation.Furthermore,this model was extended to include automatically derived vegetation drag coefficients,spatially varying vegetation height,and Doppler Effect in combined current-wave flows.Model evaluation against an analytical model and flume data shows that the modified model can accurately simulate wave height change in combined current-wave flows.Subsequently,we applied the new model to a mangrove wetland on Hailing Island in China with a special focus on the effect of currents on wave dissipation.It is found that the currents can either increase or decrease wave attenuation depending on the ratio of current velocity to the amplitude of the horizontal wave orbital velocity,which is in good agreement with field observations.Lastly,we used Hailing Island site as an example to simulate wave attenuation by vegetation under hypothetical storm surge conditions.Model results indicate that when currents are 0.08–0.15 m/s and the incident wave height is 0.75–0.90 m,wetlands’wave attenuation capacity can be reduced by nearly 10%compared with pure wave conditions,which provides implications for critical design conditions for coastal safety.The obtained results and the developed model are valuable for the design and implementation of wetland-based coastal defense.The code of the developed model has been made open source,in the hope to assist further research and coastal management.

Mangrove forests as a nature-based solution for coastal flood protection:Biophysical and ecological considerations

Nature-based coastal protection is increasingly recognised as a potentially sustainable and cost-effective solution to reduce coastal flood risk.It uses coastal ecosystems such as mangrove forests to create resilient designs for coastal flood protection.However,to use mangroves effectively as a nature-based measure for flood risk reduction,we must understand the biophysical processes that govern risk reduction capacity through mangrove ecosystem size and structure.In this perspective,we evaluate the current state of knowledge on local physical drivers and ecological processes that determine mangrove functioning as part of a nature-based flood defence.We show that the forest properties that comprise coastal flood protection are well-known,but models cannot yet pinpoint how spatial heterogeneity of the forest structure affects the capacity for wave or surge attenuation.Overall,there is relatively good understanding of the ecological processes that drive forest structure and size,but there is a lack of knowledge on how daily bed-level dynamics link to long-term biogeomorphic forest dynamics,and on the role of combined stressors influencing forest retreat.Integrating simulation models of forest structure under changing physical(e.g.due to sea-level change)and ecological drivers with hydrodynamic attenuation models will allow for better projections of long-term natural coastal protection.

基于NSCT-DCT-DWT-SVD联合数字水印算法

针对现有已提出的相关数字水印算法在不同攻击下存在的问题,提出一种将非下采样Contourlet变换NSCT(Non-subsampled Contourlet Transform)和DCT-DWT-SVD联合的数字水印算法。该算法将原始的宿主图像进行非下采样Contourlet变换得到与原始图像大小相同的低频子带,将低频子带进行离散小波变换分解,并对小波分解的低频部分与Arnold变换后的水印进行离散余弦变换。将变换得到的新区域与变换后的水印信息图像进行奇异值分解,将两者分解得到的奇异值矩阵相结合,作为最终的水印嵌入主成分。实验结果表明,该算法可以有效地抵抗JEPG压缩﹑椒盐噪声﹑泊松噪声﹑滤波等不同类型的攻击,在确保水印不可见性的同时具有较高的原始图像保真性。

Femtosecond strong-field coherent control of nonresonant ionization with shaped pulses

The strong-field coherent control of the nonresonant ionization of nitrous oxide using shaped pulses is investigated.We study the dependence of periodic coherent oscillation of the total ionization yield on the variation of laser phase parameters. The physical mechanism of the strong-field coherent control is investigated experimentally and theoretically by the nonresonant spectral phase interferences in the frequency domain. We show that the intense shaped pulses with broadband and off-resonance can be used as a robust strong-field coherent control method.

Pressure-Induced Structural Transitions of the Zinc Sulfide Nano-particles with Different Sizes

ZnS nano-particles with average sizes of 10 nm and 5 nm were fabricated by sol-gel method, and their pressure-induced phase transformations were in-situ examined in a diamond anvil cell by energy dispersive X-ray diffraction （EDXD） from ambient pressure to 35.0 GPa. From the obtained interplanar spacing data,the volume compression ratios were derived at different pressures, and then the bulk modulus and its pressure derivative were obtained by fitting to the Murnaghan equation. It is found that both ZnS nano-particles initially in the zinc-blende phase transformed to cubic NaCl structure in the presence of pressure and the transition was reversible when the pressure was released. Moreover, it is suggested that a smaller particle size will induce a larger transition pressure.

Adsorption Behavior of CH2 and CH3 on Metal Clusters CUn （n=1-6）

Using density functional theory with generalized gradient approximation and hybrid functional, we studied the properties of energy, charge population, and vibration of CH2 and CH3 adsorbed on Cun （n=1-6） clusters. The results show that the DFT calculation with the hybrid functional matches the experimental results better in both cases. The calculation results indicate that the adsorption of CH2 is stronger than that of CH3. During adsorption, the charges transfer from Cu to CH2 or CH3. The obtained vibrational frequencies for different modes of CH2 and CH3 adsorbed on Cun agree well with the experimental results for the adsorption on Cu（111） surface.

一种安全可行的数字水印协议

针对已提出的数字版权维护协议中存在的买方频繁参与交易,以及过多第三方参与的问题,提出一种安全高效的数字水印协议。该协议引入具有同态性的Paillier加密算法以及虹膜识别技术,解决了匿名、未绑定、盗版追踪等相关安全问题。并且交易过程中参与方之间的通信数据均采用加密、数字签名认证等形式表示,以确保通信数据的保密性与完整性。除此之外,买方选用交易应用程序完成信息传递、购买的操作,使得协议更加贴近日常的交易模式,易于实现。

BIM技术对工程造价影响的研究

随着社会信息化的发展,越来越多的领域都力求信息化管理,而具有模拟性的BIM技术的到来也为建筑行业带来了重大的变革。众所周知,建筑工程具备单一性及复杂性,因此想要测算其成本需要大量的数据,而这些数据的准确性和及时性都会影响到整个工程的成本管理,传统计量计价的方式会耗费大量的人力及精力,直接增加工程成本,且数据的准确性也有待考量,因此,将BIM技术运用于工程造价中,能够更好更迅速进行成本计算,便于成本管理。

Coherent control of fragmentation of methyl iodide by shaped femtosecond pulse train

Coherent control of fragmentation of CH_3I using shaped femtosecond pulse train is investigated.The dissociation processes can be modulated by changing the separation of the shaped pulse train, and the yield of I^+under the irradiation of the optimal pulse is significantly increased compared with that using the transform-limited pulse.We discuss the control mechanism of dissociation processes with coherent interference in time domain.A three-pulse control model is proposed to explain the counterintuitive experimental results.

国际工程变更索赔管理经验

在国际工程项目实施过程中避免不了会发生变更,工程索赔作为合同管理重要的组成部分,是建设方与施工方工程项目管理的重要组成部分,因此,如何正确利用项目自身资源,巧妙地进行变更索赔成为当前工程实施方面不可避免的话题。以斯里兰卡K坝为例,阐述国际工程变更索赔管理和相应问题及解决措施,做好国际工程项目变更索赔管理工作。

如何在国际工程项目中与监理进行有效沟通

在国外项目“小业主大监理”的管理模式下⑴,业主的管理职能主动后退,监理的职能往前方延伸,加之中西方工作方式、文化习俗、思维方式、价值标准方面存在巨大差异,监理的重要地位不言而喻。在国际工程项目中,承包商应掌握好与监理工程师的沟通艺术,对项目顺利实施至关重要。

水利水电施工合同管理与成本控制研究

当前我国水利水电施工技术不断发展,且逐渐走向海外,承接了一系列的海外大规模水利水电施工工程,而这类工程的合同管理和成本控制工作具有一定的特殊性。以此为主题,讨论了合同管理和成本控制之间的关系,详细论述了如何做好两类工作的具体措施,促进相关项目管理水平提升。

Preparation of Fe-As alloys by mechanical alloying and vacuum hot-pressed sintering:microstructure evolution,mechanical properties,and mechanisms

Arsenic materials have attracted great attention due to their unique properties.However,research concerning iron-arsenic(Fe-As) alloys is very scarce due to the volatility of As at low temperature and the high melting point of Fe.Herein,a new Fe-As alloy was obtained by mechanical alloying(MA) followed by vacuum hot-pressed sintering(VHPS).Moreover,a systematic study was carried out on the microstructural evolution,phase composition,leaching toxicity of As,and physical and mechanical properties of Fe-As alloys with varying weight fractions of As(20%,25%,30%,35%,45%,55%,65%,and 75%).The results showed that pre-alloyed metallic powders(PAMPs) have a fine grain size and specific supersaturated solid solution after MA,which could effectively improve the mechanical properties of Fe-As alloys by VHPS.A high density(> 7.350 g·cm^(-3)),low toxicity,and excellent mechanical properties could be obtained for FeAs alloys sintered via VHPS by adding an appropriate amount of As,which is more valuable than commercial Fe-As products.The Fe-25% As alloy with low toxicity and a relatively high density(7.635 g·cm^(-3)) provides an ultra-high compressive strength(1989.19 MPa),while the Fe-65% As alloy owns the maximum Vickers hardness(HVo.5 899.41).After leaching by the toxicity characteristic leaching procedure(TCLP),these alloys could still maintain good mechanical performance,and the strengthening mechanisms of Fe-As alloys before and after leaching were clarified.Changes in the grain size,micro structure,and phase distribution induced significant differences in the compressive strength and hardness.