人工时效条件对重力铸造B356铝合金力学性能的影响（英文）

采用差示扫描热量法(DSC)、硬度测试和拉伸试验研究重力铸造B356铝合金的时效硬化行为。人工时效温度分别为155、165和180°C,热处理时间为40 min^32 h。DSC结果表明,样品在低于室温的条件下(约为-10°C)形成团簇。由于团簇形成影响主要强化相β′′的后续沉淀过程,因此可以推断,固溶处理后不及时进行人工时效处理将对合金的力学性能产生不利影响。同时证实,在人工时效过程中(分别在155°C时效16 h,165°C时效6 h和180°C时效4 h)当β′′相生成完全后,合金的硬度和拉伸强度达到最大。经最高时效温度处理的样品其力学性能随时效时间的延长而降低,这与共格β′′相向半共格β′相的转变相关。最后计算得到与β′′相沉淀相关的活化能为57.2 k J/mol。

重力铸造Sr变质B356铝合金的热处理工艺优化（英文）

近年来,采用某些铸造工艺使生产薄壁件成为可能,尺寸上已实现金属型铸造技术能实现小于4 mm的极限。因为这些铸件的安全边际量减小,有必要研究Al-7Si-Mg合金的T6热处理条件,以获得最佳的强度和延性组合。此外,必须优化与T6处理有关的成本和生产时间。采用实验研究优化了重力铸造Sr变质B356铝合金薄壁件的固溶强化和人工时效条件。分别选取530°C和550°C作为固溶处理温度,固溶2~8 h,随后水淬,165°C人工时效2~32 h。获得最佳的综合力学性能的热处理条件是:550°C固溶2 h,165°C人工时效28 h。DSC分析表明,β''相在人工时效过程中充分析出后,合金达到最佳力学性能。

可积谐振系统中的极端波事件研究进展

从微观角度上讲,单个极端异常波事件可视为可积模型方程的时空局域有理函数解.本文主要讨论了三类典型的可积谐振相互作用模型(即长波短波谐振方程,三波谐振相互作用方程,非线性薛定谔和麦克斯韦-布洛赫方程)的基阶Peregrine异常波解及其相关研究进展;明确指出了这些基阶异常波解形式具有普适性,可推广应用到多分量或更高阶的可积模型中;借助数值模拟,还展示了共存异常波、互补异常波、以及自感应透明Peregrine孤子等新颖动力学.

Dam-break Modeling in Alpine Valleys

Dam-break analysis is of great importance in mountain environment,especially where reservoirs are located upstream of densely populated areas and hydraulic hazard should be assessed for land planning purposes.Accordingly,there is a need to identify suitable operative tools which may differ from the ones used in flat flood-prone areas.This paper shows the results provided by a 1D and a 2D model based on the Shallow Water Equations(SWE) for dam-break wave propagation in alpine regions.The 1D model takes advantage of a topographic toolkit that includes an algorithm for pre-processing the Digital Elevation Model(DEM) and of a novel criterion for the automatic cross-section space refinement.The 2D model is FLO-2D,a commercial software widely used for flood routing in mountain areas.In order to verify the predictive effectiveness of these numerical models,the test case of the Cancano dam-break has been recovered from the historical study of De Marchi(1945),which provides a unique laboratory data set concerning the consequences of the potential collapse of the former Cancano dam(Northern Italy).The measured discharge hydrograph at the dam also provides the data to test a simplified method recently proposed for the characterization of the hydrograph following a sudden dam-break.

New Zealand Advances in Performance-Based Seismic Design

This paper provides a summary of the objectives and principles which underpin the 2004 edition of the New Zealand earthquake design standard, AS/NZS 1170 Part 5. As with many modern earthquake design standards, the New Zealand earthquake design standard recognizes that earthquake resistant design that only addresses life safety goals without addressing both operational continuity of essential facilities and damage control, falls short of public expectations. Such standards not longer meet societal expectations. The paper outlines how these issues have been addressed within New Zealand, and some of the issues addressed when preparing appendices to the standard to provide guidance for materials standard writers to ensure consistency with the proposed approach. Recognizing the significance of non-structural components and parts of buildings in both damage control and operational continuity has been an important step forward in attaining the performance levels required.

原位生成白炭黑对异戊橡胶补强性能与其制备方法和结构的相互关系

弹性体一般需要添加补强填料以提高其基本性能而得到商业应用。炭黑和白炭黑是应用最广的橡胶补强填料。一般说来,与炭黑填充胶料相比,白炭黑填充胶料的撕裂强度较大、耐磨性能和耐老化性能较好。此外,在轮胎工业中,当炭黑补强和白炭黑补强的两种轮胎耐磨性能和湿地抓着性能相同时，后者胎面胶的滚动阻力比前者更低。

High Temperature Oxidation as a Production Route for Electronic Materials

Oxidation of metallic components often results in degradation and structural failure,prevention is therefore an important topic.On the other hand,oxidation process creates new products such as metal oxides,can be used as a production route.A well-known process in semiconductor industry is that oxidation in dry or wet atmosphere is a popular way for growth of multi-functional SiO_2 films on Si wafers. Recently,oxidation processes under controlled conditions(atmosphere,temperature,and time) are used to prepare various oxides,carbides,or nitrides with micro-/nano-struetures,well-defined composition,dimension, shape and properties.The use of oxidation now includes thin film and nano-/micro-sized devices, and porous oxides for sensing and catalysis purposes.This paper introduces the research activities in the authors' group on applications of oxidation as a tool for synthesis of functional materials.

Evaluating soil erosion by water in a small alpine catchment in Northern Italy: comparison of empirical models

To quantify water erosion rates and annual soil loss in mountainous areas,two different empirical models were used to estimate the effects of soil erosion in a small mountain basin,the Guerna Creek watershed,located in the Central Southern Alps(Northern Italy).These two models,Revised Universal Soil Loss Equation(RUSLE) and Erosion Potential Model(EPM),were implemented in a Geographical Information System,accounting for the geographical,geomorphological,and weather-climate parameters,which are fundamental to evaluating the intensity and variability of the erosive processes.Soil characterization was supported by laboratory analysis.The results(computed soil loss of 87 t/ha/year and 11.1 m^(3)/ha/year,using RUSLE equation and EPM method,respectively,and sediment yield of 7.5 m^(3)/ha/year using EPM method) were compared to other studies reported in the literature for different case studies with similar topographic and climatic features,as well as to those provided by the European Soil Data Centre(ESDAC).In both cases,the agreement was satisfactory,showing consistency of the adopted procedures to the parametrization of the physical processes.

Nonlinear frequency conversion in optical nanoantennas and metasurfaces:materials evolution and fabrication

Nonlinear frequency conversion is one of the most fundamental processes in nonlinear optics.It has a wide range of applications in our daily lives,including novel light sources,sensing,and information processing.It is usually assumed that nonlinear frequency conversion requires large crystals that gradually accumulate a strong effect.However,the large size of nonlinear crystals is not compatible with the miniaturisation of modern photonic and optoelectronic systems.Therefore,shrinking the nonlinear structures down to the nanoscale,while keeping favourable conversion efficiencies,is of great importance for future photonics applications.In the last decade,researchers have studied the strategies for enhancing the nonlinear efficiencies at the nanoscale,e.g.by employing different nonlinear materials,resonant couplings and hybridization techniques.In this paper,we provide a compact review of the nanomaterials-based efforts,ranging from metal to dielectric and semiconductor nanostructures,including their relevant nanofabrication techniques.

A Theory of the Risk for Empirical CVaR with Application to Portfolio Selection

When decisions are based on empirical observations,a trade-off arises between flexibility of the decision and ability to generalize to new situations.In this paper,we focus on decisions that are obtained by the empirical minimization of the Conditional Value-at-Risk(CVa R)and argue that in CVa R the trade-off between flexibility and generalization can be understood on the ground of theoretical results under very general assumptions on the system that generates the observations.The results have implications on topics related to order and structure selection in various applications where the CVa R risk-measure is used.A study on a portfolio optimization problem with real data demonstrates our results.

Tuning the second-harmonic generation in AlGaAs nanodimers via non-radiative state optimization [Invited]

Dielectric nanocavities are emerging as a versatile and powerful tool for the linear and nonlinear manipulation of light at the nanoscale. In this work, we exploit the effective coupling of electric and toroidal modes in Al Ga As nanodimers to locally enhance both electric and magnetic fields while minimizing the optical scattering, thereby optimizing their second-harmonic generation efficiency with respect to the case of a single isolated nanodisk. We also demonstrate that proper near-field coupling can provide further degrees of freedom to control the polarization state and the radiation diagram of the second-harmonic field.

Enhanced second-harmonic generation from two-dimensional MoSe_(2) on a silicon waveguide

Two-dimensional transition-metal dichalcogenides(TMDCs)with intrinsically broken crystal inversion symmetry and large secondorder nonlinear responses have shown great promise for future nonlinear light sources.However,the sub-nanometer monolayer thickness of such materials limits the length of their nonlinear interaction with light.Here,we experimentally demonstrate the enhancement of the second-harmonic generation from monolayer MoSe_(2) by its integration onto a 220-nm-thick silicon waveguide.Such on-chip integration allows for a marked increase in the interaction length between the MoSe_(2) and the waveguide mode,further enabling phase matching of the nonlinear process.The demonstrated TMDC–silicon photonic hybrid integration opens the door to second-order nonlinear effects within the silicon photonic platform,including efficient frequency conversion,parametric amplification and the generation of entangled photon pairs.

Large eddy simulation of room fire spread using a medium scale compartment made of medium density fibreboard (MDF) panels

At present,there is a shortage of experimental and simulation studies on fire spread in medium-and large-scale compartments while the existing models of the fire spread are limited for typical engineering applications.This paper proposes a new model for large-scale fire spread on medium density fibreboard(MDF)panels.Validating the model with single burning item(SBI)experiments,it is found that the numerical simulation closely predicts the experimental heat release rate(HRR)with some error near the peak.The predicted heat flux and distance of lateral flame spread are consistent with the experiments and an existing model.The effects of kinetic properties and heat of combustion are identified through a sensitivity analysis.The decrease of activation energy and increase of pre-exponential factor make the MDF easier to pyrolyze and the increase of heat of combustion enhances the flame temperature and thus provide more heat feedback to the sample surface.The low activation energy(71.9 kJ/mol)and high heat of combustion(46.5 MJ/kg)of the model ensure the occurrence of flame spread.Furthermore,the model was validated using medium-scale compartment fire experiments and the results showed that the model can accurately predict the HRR after flashover(the error is within 7%).While the burner is ignited,the predictions of in-compartment gas temperature and heat flux are more accurate.However,when the burner is extinguished,the modelled in-compartment gas temperature is lower than the experimental values,resulting in a lower heat flux prediction.The model leads to easier flame spread;therefore,the modelled flame spreads faster in the compartment compared to the experiment,and thus the HRR increases more rapidly.

Femtosecond nonlinear losses in multimode optical fibers

Multimode optical fibers are attracting a growing interest for their capability to transport high-power laser beams,coupled with novel nonlinear optics-based applications.However,optical fiber breakdown occurs when beam intensities exceed a certain critical value.Optical breakdown associated with irreversible modifications of the refractive index,triggered by multiphoton absorption,has been largely exploited for fiber material microstructuration.Here we show that,for light beam intensities slightly below the breakdown threshold,nonlinear absorption strongly affects the dynamics of a propagating beam as well.We experimentally analyze this subthreshold regime and highlight the key role played by spatial self-imaging in graded-index fibers for enhancing nonlinear optical losses.We characterize the nonlinear power transmission properties of multimode fibers for femtosecond pulses propagating in the near-infrared spectral range.We show that an effective N-photon absorption analytical model is able to describe the experimental data well.

Appropriate solid waste management system in Quelimane (Mozambique):study and design of a small-scale center for plastic sorting with wastewater treatment

Appropriate solid waste management(SWM)strategies are necessary to avoid severe environmental and sanitary impacts,especially in low-income countries.Such strategies are most likely to succeed whether implementing actors are supported by scientific research.In this paper,the results of a collaboration between local authorities and researchers are presented and discussed that are the assessment of waste generation in the city of Quelimane(Mozambique),integrating existing and field-collected data and the design of a small-scale center for plastic sorting to complement the SWM system of the city.The center is expected to receive about 0.3-0.4 t/day of plastic waste(5%-7%of the overall amount of plastic waste daily produced in Quelimane).As long-term sustainability represents a typical issue,simplicity of operation was a leading principle in the design of the center;moreover,the design included a treatment plant(WWTP)for generated wastewater,whose management is usually neglected in such interventions.Among others,natural wastewater treatment(constructed wetlands)has been chosen for its affordability.Noteworthy,the so-conceived WWTP appears as a novelty in the scientific literature associated with small-scale plastic sorting plants.The system is designed to treat an average flow of 6 m3/day and consisted of a septic tank followed by a subsurface flow constructed wetland.Overall,the COD(chemical oxygen demand)and TSS(total suspended solids)removal higher than 80%and 90%were estimated,respectively.Based on this work,both the center and the WWTP were successfully realized,which are waiting to become operational.In the authors’opinion,the implemented procedure could become a reference for broader investigations and surveys.

A slug capturing method in unconventional scenarios: The 5ESCARGOTS code applied to non-Newtonian fluids, high viscous oils and complex geometries

Previous work showed that a one-dimensional,hyperbolic,transient five-equation two-fluid model can predict automatically the formation,growth,and subsequent development of slugs in horizontal and near-horizontal flow.This method was implemented in a finite volume numerical scheme e called 5ESCARGOTS code.Comparison with experimental data showed that it can be used to predict the flow pattern and statistical characteristics(slug velocity,length,and frequency).However,the capabilities of this approach have been tested only for water-air flows in a straight horizontal pipe.In this work,we validate the application of the code to some unconventional problems.Firstly,we test the possibility of slug capturing approach to describe and predict the relevant features of air/high viscosity oils or air/non-Newtonian fluids flows.Comparisons between some slug characteristics and empirical correlations,available in literature,are discussed.Then,we move from simple geometries toward more complex conditions that may be representative of actual application cases,also employing high viscous oils as liquid phase.Comparison against experimental data shows results in reasonable agreement.

Velocity profiles description and shape factors inclusion in a hyperbolic,one-dimensional,transient two-fluid model for stratified and slug flow simulations in pipes

In a previous work it has been shown that a one-dimensional,hyperbolic,transient five equations twofluid model is able to numerically describe stratified,wavy,and slug flow in horizontal and nearhorizontal pipes.Slug statistical characteristics can be numerically predicted with results in good agreement with experimental data and well-known empirical relations.In this model some approximated and simplified assumptions are adopted to describe shear stresses at wall and at phase interface.In this paper,we focus on the possibility to account for the cross sectional flow by inserting shape factors into the momentum balance equations of the aforementioned model.Velocity profiles are obtained by a pre-integrated model and they are computed at each time step and at each computational cell.Once that the velocity profiles are known,the obtained shape factors are inserted in the numerical resolution.In this way it is possible to recover part of the information lost due to the one-dimensional flow description.Velocity profiles computed in stratified conditions are compared against experimental profiles measured by PIV technique;a method to compute the velocity profile during slug initiation and growth has been developed and the computed velocity distribution in the liquid phase was compared against the one-seventh power law.