不同积雪深度与面积对积雪覆盖遥感反演的影响

针对利用多源遥感数据进行积雪覆盖监测的需要,在分析不同深度与面积的积雪实测光谱基础上,探讨了在利用NDSI方法进行积雪覆盖遥感监测时,不同积雪深度对其的影响,并以HJ-1B卫星以及MODIS卫星为例,研究了不同积雪面积对遥感积雪反演的影响。结果表明,积雪深度几乎对遥感积雪覆盖监测的结果没有影响,而在积雪面积方面,受所使用的遥感影像空间分辨率的制约,对遥感积雪监测的结果有一定影响。     

Toward a new elastic-decohesive model of Arctic sea ice

This paper argues for a new constitutive model, an elastic-decohesive model for sea ice. The model is motivated by examining satellite observations of the Arctic processed to show ice deformation in the form of divergence, shear and vorticity. The model is implemented numerically in the material-point method and used to predict motion and deformation of sea ice by simulating a region of the Beaufort Sea. The model is able to capture the qualitative and statistical behavior of localized deformation seen in the observations.     

Determination of trace level of perchlorate in Antarctic snow and ice by ion chromatography coupled with tandem mass spectrometry using an automated sample on-line preconcentration method

A new ion chromatography coupled with tandem mass spectrometry（IC-ESI-MS/MS） method,with automated sampling and on-line preconcentration,has been developed for the determination of perchlorate in Antarctic snow and ice at low part-per-trillion（ng/L） levels.To the best of our knowledge, this is the first time that an analytical method is used for the determination of perchlorate in Antarctic snow and ice.The IC-ESI-MS/MS instrumentation consisted of an ICS2000 ion chromatography（IC） system coupled to an API3200 electrospray tandem mass spectrometer（ESI-MS/MS）.On-line preconcentration was realized through a six-port injector valve,a TAC-ULP1 concentrator column and an AS auto-sampler.Multiple reaction monitoring（MRM） mode was used to quantify the perchlorate anion.The transition of ³⁵Cl¹⁶O₄^-（m/z 98.9） into ³⁵Cl¹⁶O₃^-（m/z 82.9） was monitored for quantifying the main analyte,and the transition of ³⁷Cl¹⁶O₄^-（m/z 100.9） into ³⁷Cl¹⁶O₃^-（m/z 84.9） was monitored for examining a proper isotopic abundance ratio of ³⁵Cl to ³⁷Cl,which was used as a confirmation tool.The limit of detection（LOD） and limit of quantitation（LOQ） for the method was 0.2 ng/ L and 0.5 ng/L,respectively.And this new method exhibited acceptable accuracy and precision for samples at ng/L levels.All the tested snow and ice samples were found to contain measurable amount of perchlorate,ranging from 10 ng/L to 340 ng/L.     

Minimum vertex cover problem for coupled interdependent networks with cascading failures

This paper defines and analyzes a generalization of the classical minimum vertex cover problem to the case of two-layer interdependent networks with cascading node failures that can be caused by two common types of interdependence. Previous studies on interdependent networks mainly addressed the issues of cascading failures from a numerical simulations perspective, whereas this paper proposes an exact optimization-based approach for identifying a minimum-cardinality set of nodes, whose deletion would effectively disable both network layers through cascading failure mechanisms. We analyze the computational complexity and linear 0–1 formulations of the defined problems, as well as prove an LP approximation ratio result that generalizes the well-known 2-approximation for the classical minimum vertex cover problem. In addition, we introduce the concept of a “depth of cascade” (i.e., the maximum possible length of a sequence of cascading failures for a given interdependent network) and show that for any problem instance this parameter can be explicitly derived via a polynomial-time procedure.     

电容感应式冰厚监测系统在南极海冰监测中的应用

为了实现对南极的实时自动化监测,设计并研制了电容式冰厚监测系统,系统于2012年3月至8月对南极中山站附近的近岸海冰进行了连续6个月的厚度自动化监测,通过对监测数据的对比分析,得到了监测系统的准确度与相对偏差.结果证明系统用于高精度定点监测海冰厚度是可行的,并对系统监测南极海冰的不足与今后改进研究的内容进行了讨论.     

单形和3维立方体乘积上小覆盖的等变协边类的个数

本文研究了小覆盖的等变协边分类.利用示性函数和Stong同态确定了单形和3维立方体乘积上小覆盖的等变协边类的个数,推广了现有文献中的相关结果.     

最大度为5的图的Alcuin数

1000多年前,英国著名学者Alcuin曾提出过一个古老的渡河问题,即狼、羊和卷心菜的渡河问题.最近,Prisner和Csorba等人把这一问题推广到任意的"冲突图"G=(V,E)上,考虑了一类情况更一般的运输计划问题.现在监管者欲运输V中的所有"物品/点"渡河,这里V的两个点邻接当且仅当这两个点为冲突点.冲突点是指不能在无人监管的情况下留在一起的点.特别地,Alcuin渡河问题可转化成"冲突路"P_3上是否存在可行运输方案问题.图G的Alcuin数是指图G具有可行运输方案(即把V的点代表的"物品"全部运到河对岸)时船的最小容量.最大度为5且覆盖数至少为5的图和最大度Δ(G)≤4且覆盖数不小于Δ(G)-1的图的Alcuin数已经被确定.本文给出最大度为4且覆盖数不超过2和最大度为5且覆盖数不超过4的图的Alcuin数.至此,最大度不超过5的图的Alcuin数被完全确定.     

均匀电场对冰晶结构及生长的影响

Homogeneous crystallization of supercooled water under electric field with strength ranging from 4.0 to 40.0 V·nm^-1 was investigated by using molecular simulation technique. The liquid-solid transition was successfully obtained based on ice component analysis using the CHILL algorithm. The analysis suggested that the produced crystalline was cubic ice dominant. The influence of the field strength on the structure and the growth rate of the ice was studied. The results revealed that the presence of an electric field drove the system to crystallize rapidly into dense and distorted cubic ice. The density of the crystals increased as a function of the field strength, from 0.98 to 1.08 g·cm^-3. The growth rate of the ice nucleus increased along with the field strength according to the characteristic time derived from the Avrami equation which ranged from 0.254 to 5.513 ns. This type of acceleration can be partially attributed to the enhancement of the rotational dynamics of the water molecules. Moreover, by monitoring the formation history of the cubic ice, we found that the defective ice acted as a transition state linking the liquid water and the cubic ice.     

Macroscopic Free‐Standing Hierarchical 3D Architectures Assembled from Silver Nanowires by Ice Templating

As macroscopic three dimensional (3D) architectures show increasing significance, much effort has been devoted to the hierarchical organization of 1D nanomaterials into serviceable macroscopic 3D assemblies. How to assemble 1D nanoscale building blocks into 3D hierarchical architectures is still a challenge. Herein we report a general strategy based on the use of ice as a template for assembling 1D nanostructures with high efficiency and good controllability. Free‐standing macroscopic 3D Ag nanowire (AgNW) assemblies with hierarchical binary‐network architectures are then fabricated from a 1D AgNW suspension for the first time. The microstructure of this 3D AgNW network endows it with electrical conductivity and allows it to be made into stretchable and foldable conductors with high electromechanical stability. These properties should make this kind of macroscopic 3D AgNW architecture and it composites suitable for electronic applications.