气候变暖日益加剧,近100年来全球地表平均气温已经上升近1.0℃。稻–麦两熟是苏、皖江淮地区的主流种植制度,但江淮稻–麦两熟种植制度对气候变暖的适应还不清楚。为此,我们利用34个气象站点和45个物候站点多年历史数据分析了江淮稻–...气候变暖日益加剧,近100年来全球地表平均气温已经上升近1.0℃。稻–麦两熟是苏、皖江淮地区的主流种植制度,但江淮稻–麦两熟种植制度对气候变暖的适应还不清楚。为此,我们利用34个气象站点和45个物候站点多年历史数据分析了江淮稻–麦两熟区气温升高特征和作物物候变化规律。研究表明,江淮地区增温幅度区域上南高北低,熟季间麦季高稻季低,月份间3月份最高。水稻季,江南地区播种期推迟3.4 d 10a^(–1)、淮南抽穗期提早2 d 10a^(–1)、淮北收获期推迟6.2 d 10a^(–1)。小麦季,江南播种期推迟6.4 d 10a^(–1)、全区域抽穗期和收获期有提早的趋势。稻–麦茬口期淮北缩短4.6 d 10a^(–1)、江南延长6.9 d 10a^(–1)。水稻、小麦各生育阶段平均温度没有显著变化、花后有效积温大多呈增加趋势。水稻季积温生产效率变化不大,小麦季积温生产效率提高了0.008~0.346 kg hm^(–2)℃^(–1)10a^(–1)。气温升高降低了江南和淮南地区小麦产量和淮南地区水稻产量,但增加了淮北地区小麦产量。研究结果表明江淮稻–麦两熟种植制度正逐步适应了气候变暖,通过合理改变播期可以减缓气候变暖对作物产量的负面影响;可为气候变化适应性栽培和耕作技术创新提供参考。展开更多
传统的勒索软件动态检测方法需要收集较长时间的软件行为,难以满足勒索软件及时检测的需求.本文从勒索软件及时检测的角度出发,提出了“勒索软件检测关键时间段(Critical Time Periods for Ransomware Detection,CTP)”的概念,并基于CT...传统的勒索软件动态检测方法需要收集较长时间的软件行为,难以满足勒索软件及时检测的需求.本文从勒索软件及时检测的角度出发,提出了“勒索软件检测关键时间段(Critical Time Periods for Ransomware Detection,CTP)”的概念,并基于CTP的要求提出了一种基于应用程序编程接口(Application Programming Interface,API)短序列的勒索软件早期检测方法(Ransomware Early Detection Method based on short API Sequence,REDMS).REDMS以软件在CTP内执行时所调用的API短序列为分析对象,通过n-gram模型和词频-逆文档频率算法对采集到的API短序列进行计算以生成特征向量,然后运用机器学习算法建立检测模型对勒索软件进行早期检测.实验结果显示,REDMS在API采集时段为前7s且使用随机森林算法时,分别能以98.2%、96.7%的准确率检测出已知和未知的勒索软件样本.展开更多
A spintronic near-field microwave imaging system without vector network analyzers is used to detect the distribution of microwaves,which are scattered by a sub-wavelength periodical metal wire grating.An ultra thin me...A spintronic near-field microwave imaging system without vector network analyzers is used to detect the distribution of microwaves,which are scattered by a sub-wavelength periodical metal wire grating.An ultra thin metal body with diameter of 100μm(λ/300)is observed by imaging illuminated by a 10 GHz shining source.An application with high sensitivity and resolution detection is proposed in the microwave region under a weak applied external static magnetic field.展开更多
The band structure and transmission coefficient of the two-dimensional ternary locally resonant phononic crystal are computed by the finite element method with the calculated frequency up to 120 kHz.The band gap in th...The band structure and transmission coefficient of the two-dimensional ternary locally resonant phononic crystal are computed by the finite element method with the calculated frequency up to 120 kHz.The band gap in the high frequency range is found and considered as the Bragg band gap in the locally resonant phononic crystal which has the locally resonant band gap in the low frequency range normally.Then,a composite phononic crystal by hybridizing the Bragg scattering phononic crystal and the locally resonant phononic crystal is proposed.Simultaneous Bragg and locally resonant band gaps are displayed and discussed for the composite phononic crystal.The results show that the simultaneous Bragg band gap and locally resonant band gap can be tuned.展开更多
We investigate the effects of the V/III ratio of a low-temperature GaN buffer layer on the growth of the overlaying nonpolar-plane GaN film grown on-plane sapphire by metal-organic chemical-vapor deposition(MOCVD).Wit...We investigate the effects of the V/III ratio of a low-temperature GaN buffer layer on the growth of the overlaying nonpolar-plane GaN film grown on-plane sapphire by metal-organic chemical-vapor deposition(MOCVD).With other experimental conditions keeping fixed,the low-temperature GaN buffer layers are grown under various V/III ratios of 1000,3000,6000 and 9000,respectively.The characteristics of the-plane GaN films are analyzed by scanning electron microscopy,high resolution x-ray diffraction,Raman spectrum,and low temperature photoluminescence.The results show that the V/III ratio of the buffer layer has significant effects on the crystal quality of the a-plane GaN film,and a V/III ratio of 6000 is found to be the most suitable condition to achieve pit-free flat GaN surface.展开更多
Si-doped Al_(0.4)Ga_(0.6)N(Si-Al_(0.4)Ga_(0.6)GN)epilayers grown on an AlGaN window layer(WL)with different Al contents are prepared using a high-quality A1N buffer layer by metal-organic chemical vapor deposition.Sur...Si-doped Al_(0.4)Ga_(0.6)N(Si-Al_(0.4)Ga_(0.6)GN)epilayers grown on an AlGaN window layer(WL)with different Al contents are prepared using a high-quality A1N buffer layer by metal-organic chemical vapor deposition.Surface morphology,crystalline quality and electric properties of these epilayers are investigated by using atomic force microscopy,x-ray diffraction,Raman scattering spectrum and Hall techniques.Results show that the surface morphology of these epilayers are mainly determined by the Si-doping level which,together with the effect of Al content of WL,also has an obvious impact on the electron concentrations.On the other hand,the insertion of AlGaN WL is helpful to the increase of Si doping level and conductivity of subsequently grown Si-Al_(0.4)Ga_(0.6)N epilayers.However,the insertion as well as the increase of Al content of WL result in increase of dislocation densities,compressive strain in Si-Al_(0.4)Ga_(0.6)N epilayers,and tilt of A1N subgrains at the top interface of the buffer layer.Further,the degradation of crystalline quality with the Al content of WL exerts a decisive influence on the conductivity of the Si-Al_(0.4)Ga_(0.6)N epilayers grown on WL with Al content of 0.6 through a dramatic decrease in electron mobility.展开更多
文摘气候变暖日益加剧,近100年来全球地表平均气温已经上升近1.0℃。稻–麦两熟是苏、皖江淮地区的主流种植制度,但江淮稻–麦两熟种植制度对气候变暖的适应还不清楚。为此,我们利用34个气象站点和45个物候站点多年历史数据分析了江淮稻–麦两熟区气温升高特征和作物物候变化规律。研究表明,江淮地区增温幅度区域上南高北低,熟季间麦季高稻季低,月份间3月份最高。水稻季,江南地区播种期推迟3.4 d 10a^(–1)、淮南抽穗期提早2 d 10a^(–1)、淮北收获期推迟6.2 d 10a^(–1)。小麦季,江南播种期推迟6.4 d 10a^(–1)、全区域抽穗期和收获期有提早的趋势。稻–麦茬口期淮北缩短4.6 d 10a^(–1)、江南延长6.9 d 10a^(–1)。水稻、小麦各生育阶段平均温度没有显著变化、花后有效积温大多呈增加趋势。水稻季积温生产效率变化不大,小麦季积温生产效率提高了0.008~0.346 kg hm^(–2)℃^(–1)10a^(–1)。气温升高降低了江南和淮南地区小麦产量和淮南地区水稻产量,但增加了淮北地区小麦产量。研究结果表明江淮稻–麦两熟种植制度正逐步适应了气候变暖,通过合理改变播期可以减缓气候变暖对作物产量的负面影响;可为气候变化适应性栽培和耕作技术创新提供参考。
文摘传统的勒索软件动态检测方法需要收集较长时间的软件行为,难以满足勒索软件及时检测的需求.本文从勒索软件及时检测的角度出发,提出了“勒索软件检测关键时间段(Critical Time Periods for Ransomware Detection,CTP)”的概念,并基于CTP的要求提出了一种基于应用程序编程接口(Application Programming Interface,API)短序列的勒索软件早期检测方法(Ransomware Early Detection Method based on short API Sequence,REDMS).REDMS以软件在CTP内执行时所调用的API短序列为分析对象,通过n-gram模型和词频-逆文档频率算法对采集到的API短序列进行计算以生成特征向量,然后运用机器学习算法建立检测模型对勒索软件进行早期检测.实验结果显示,REDMS在API采集时段为前7s且使用随机森林算法时,分别能以98.2%、96.7%的准确率检测出已知和未知的勒索软件样本.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11274330 and 10990103.
文摘A spintronic near-field microwave imaging system without vector network analyzers is used to detect the distribution of microwaves,which are scattered by a sub-wavelength periodical metal wire grating.An ultra thin metal body with diameter of 100μm(λ/300)is observed by imaging illuminated by a 10 GHz shining source.An application with high sensitivity and resolution detection is proposed in the microwave region under a weak applied external static magnetic field.
基金the National Natural Science Foundation of China(Nos 10832002 and 11072127)the National Basic Research Program of China(No 2011CB610305).
文摘The band structure and transmission coefficient of the two-dimensional ternary locally resonant phononic crystal are computed by the finite element method with the calculated frequency up to 120 kHz.The band gap in the high frequency range is found and considered as the Bragg band gap in the locally resonant phononic crystal which has the locally resonant band gap in the low frequency range normally.Then,a composite phononic crystal by hybridizing the Bragg scattering phononic crystal and the locally resonant phononic crystal is proposed.Simultaneous Bragg and locally resonant band gaps are displayed and discussed for the composite phononic crystal.The results show that the simultaneous Bragg band gap and locally resonant band gap can be tuned.
基金Supported by the National Natural Science Foundation of China under Grant No 60976042the Major Program of National Natural Science Foundation of China under Grant No 10990100the National Basic Research Program of China under Grant Nos 2010CB923204 and 2012CB619302。
文摘We investigate the effects of the V/III ratio of a low-temperature GaN buffer layer on the growth of the overlaying nonpolar-plane GaN film grown on-plane sapphire by metal-organic chemical-vapor deposition(MOCVD).With other experimental conditions keeping fixed,the low-temperature GaN buffer layers are grown under various V/III ratios of 1000,3000,6000 and 9000,respectively.The characteristics of the-plane GaN films are analyzed by scanning electron microscopy,high resolution x-ray diffraction,Raman spectrum,and low temperature photoluminescence.The results show that the V/III ratio of the buffer layer has significant effects on the crystal quality of the a-plane GaN film,and a V/III ratio of 6000 is found to be the most suitable condition to achieve pit-free flat GaN surface.
基金Supported by the National Basic Research Program of China under Grant No 2010CB923204the Major Program of the National Natural Science Foundation of China under Grant No 10990100+2 种基金the National Natural Science Foundation of China under Grant No 60976042the China Postdoctoral Science Foundation under Grant No 20100471172the Program for the New Century Excellent Talents in University of Ministry of Education of China under Grant No NCET-08-0214.
文摘Si-doped Al_(0.4)Ga_(0.6)N(Si-Al_(0.4)Ga_(0.6)GN)epilayers grown on an AlGaN window layer(WL)with different Al contents are prepared using a high-quality A1N buffer layer by metal-organic chemical vapor deposition.Surface morphology,crystalline quality and electric properties of these epilayers are investigated by using atomic force microscopy,x-ray diffraction,Raman scattering spectrum and Hall techniques.Results show that the surface morphology of these epilayers are mainly determined by the Si-doping level which,together with the effect of Al content of WL,also has an obvious impact on the electron concentrations.On the other hand,the insertion of AlGaN WL is helpful to the increase of Si doping level and conductivity of subsequently grown Si-Al_(0.4)Ga_(0.6)N epilayers.However,the insertion as well as the increase of Al content of WL result in increase of dislocation densities,compressive strain in Si-Al_(0.4)Ga_(0.6)N epilayers,and tilt of A1N subgrains at the top interface of the buffer layer.Further,the degradation of crystalline quality with the Al content of WL exerts a decisive influence on the conductivity of the Si-Al_(0.4)Ga_(0.6)N epilayers grown on WL with Al content of 0.6 through a dramatic decrease in electron mobility.
