TPTVer： A Trusted Third Party Based Trusted Verifier for Multi-Layered Outsourced Big Data System in Cloud Environment

Cloud computing is very useful for big data owner who doesn't want to manage IT infrastructure and big data technique details. However, it is hard for big data owner to trust multi-layer outsourced big data system in cloud environment and to verify which outsourced service leads to the problem. Similarly, the cloud service provider cannot simply trust the data computation applications. At last,the verification data itself may also leak the sensitive information from the cloud service provider and data owner. We propose a new three-level definition of the verification, threat model, corresponding trusted policies based on different roles for outsourced big data system in cloud. We also provide two policy enforcement methods for building trusted data computation environment by measuring both the Map Reduce application and its behaviors based on trusted computing and aspect-oriented programming. To prevent sensitive information leakage from verification process,we provide a privacy-preserved verification method. Finally, we implement the TPTVer, a Trusted third Party based Trusted Verifier as a proof of concept system. Our evaluation and analysis show that TPTVer can provide trusted verification for multi-layered outsourced big data system in the cloud with low overhead.

二维石墨炔/金属氢氧化物异质结用于高效析氧反应

析氧反应(OER)是能量转换过程中重要的半反应,开发高效、稳定、低成本的析氧反应催化剂具有重要的意义.本文报道了一种简单的原位可控生长的方法,在铜双金属氢氧化物纳米片表面原位生长石墨炔薄膜,形成了新型石墨炔/金属氢氧化物异质结界面结构,并通过改变化学组成的方法,实现对其电催化OER活性和稳定性的有效提升.研究结果显示Ni_(0.74)Cu_(0.26)LDH@GDY/NF具有最佳OER催化性能.电流密度为10 mA cm^(-2)时的过电位仅为292 mV,且具有优异的长期稳定性,比如在6000圈连续的循环测试后OER活性几乎无衰减.实验结果表明,石墨炔的引入可以有效增加活性表面积和活性位点,促进电荷转移提高导电性,且能够高效保护催化剂不被腐蚀,从而提高整体催化性能.

Diurnal and Seasonal Variations of Thermal Stratification and Vertical Mixing in a Shallow Fresh Water Lake

Among several influential factors, the geographical position and depth of a lake determine its thermal structure. In temperate zones, shallow lakes show significant differences in thermal stratification compared to deep lakes. Here,the variation in thermal stratification in Lake Taihu, a shallow fresh water lake, is studied systematically. Lake Taihu is a warm polymictic lake whose thermal stratification varies in short cycles of one day to a few days. The thermal stratification in Lake Taihu has shallow depths in the upper region and a large amplitude in the temperature gradient,the maximum of which exceeds 5°C m–1. The water temperature in the entire layer changes in a relatively consistent manner. Therefore, compared to a deep lake at similar latitude, the thermal stratification in Lake Taihu exhibits small seasonal differences, but the wide variation in the short term becomes important. Shallow polymictic lakes share the characteristic of diurnal mixing. Prominent differences on the duration and frequency of long-lasting thermal stratification are found in these lakes, which may result from the differences of local climate, lake depth, and fetch. A prominent response of thermal stratification to weather conditions is found, being controlled by the stratifying effect of solar radiation and the mixing effect of wind disturbance. Other than the diurnal stratification and convection, the representative responses of thermal stratification to these two factors with contrary effects are also discussed. When solar radiation increases, stronger wind is required to prevent the lake from becoming stratified. A daily average wind speed greater than 6 m s–1 can maintain the mixed state in Lake Taihu. Moreover, wind-induced convection is detected during thermal stratification. Due to lack of solar radiation, convection occurs more easily in nighttime than in daytime. Convection occurs frequently in fall and winter, whereas long-lasting and stable stratification causes less convection in summer.

Graphene-driving strain engineering to enable strain-free epitaxy of AlN film for deep ultraviolet light-emitting diode

The energy-efficient deep ultraviolet(DUV)optoelectronic devices suffer from critical issues associated with the poor quality and large strain of nitride material system caused by the inherent mismatch of heteroepitaxy.In this work,we have prepared the strain-free AlN film with low dislocation density(DD)by graphene(Gr)-driving strain-pre-store engineering and a unique mechanism of strain-relaxation in quasi-van der Waals(QvdW)epitaxy is presented.The DD in AlN epilayer with Gr exhibits an anomalous sawtooth-like evolution during the whole epitaxy process.Gr can help to enable the annihilation of the dislocations originated from the interface between AlN and Gr/sapphire by impelling a lateral two-dimensional growth mode.Remarkably,it can induce AlN epilayer to pre-store sufficient tensile strain during the early growth stage and thus compensate the compressive strain caused by hetero-mismatch.Therefore,the low-strain state of the DUV light-emitting diode(DUV-LED)epitaxial structure is realized on the strain-free AlN template with Gr.Furthermore,the DUV-LED with Gr demonstrate 2.1 times enhancement of light output power and a better stability of luminous wavelength compared to that on bare sapphire.An in-depth understanding of this work reveals diverse beneficial impacts of Gr on nitride growth and provides a novel strategy of relaxing the vital requirements of hetero-mismatch in conventional heteroepitaxy.