卫星影像“邻近效应”PSF校正方法

将传感器接收到的信号TOAS(the top of the atmosphere signals)转换成反映地表目标特性的反射信号是遥感信息定量化的关键环节之一。在假定大气干扰已经被排除的条件下,由于像元之间“邻近效应”的存在,被观测目标像元的反射信号(DN值中)包含了背景地物像元散射的贡献。这种贡献的大小与背景像元的反射率值大小成正比,同时与距离目标像元的远近相关。据Carder(1995),Christtopher(1998)等的研究结果,当空间分辨率大于250 m时, “邻近效应”的影响作用超过混合像元影响作用。随着卫星遥感空间分辨率和应用遥感信息定量化程度要求的提高,“邻近效应”及其校正已经开始受到遥感界的重视。近来,我们在国家自然科学基金的支持下,开展这方面的工作。介绍了我们选择北京地区Landsat5 TM数据为例,利用辐射传输模型原理,对影像中存在的“邻近效应”进行了分析和校正,试图理解“邻近效应”的一般影响特征。

超导“邻近效应”与电子能态分布研究

运用稳恒条件和动量守恒定律说明了稳恒电路中,穿过任意横截面的全部载流子的定向运动总动量在数值上是守恒的;比较了超导薄膜中和正常导体的外表面层中载流子的能态,用以上的两个结果解释了超导“邻近效应”.

Detailed Routing Algorithm with Optical Proximity Effects Constraint

We present a detailed routing algorithm considering the optical proximity effect. The light intensity is calculated beforehand and stored in look-up tables. These costs are used as a constraint to guide the sequential routing. The routing algorithm is based on constructed force directed Steiner tree routing to enhance routing efficien- cy. Experimental results on industrial benchmark circuits show that the presented routing algorithm can obtain much improvement considering optical effects short runtime.

An All-E-Beam Lithography Process for the Patterning of 2D Photonic Crystal Waveguide Devices

We present an all-e-beam lithography （EBL） process for the patterning of photonic crystal waveguides. The whole device structures are exposed in two steps. Holes constituting the photonic crystal lattice and defects are first exposed with a small exposure step size （less than 10nm）. With the introduction of the additional proximity effect to compensate the original proximity effect, the shape, size, and position of the holes can be well controlled. The second step is the exposure of the access waveguides at a larger step size （about 30nm） to improve the scan speed of the EBL. The influence of write-field stitching error can be alleviated by replacing the original waveguides with tapered waveguides at the joint of adjacent write-fields. It is found experimentally that a higher exposure efficiency is achieved with a larger step size;however,a larger step size requires a higher dose.

Acoustic higher-order topology derived from first-order with built-in Zeeman-like fields

Higher-order topological insulators(HOTIs),with topological corner or hinge states,have emerged as a thriving topic in the field of topological physics.However,few connections have been found for HOTIs with well-explored first-order topological insulators.Recently a proposal asserted that a significant bridge can be established between the HOTIs and Z2 topological insulators.When subjected to an inplane Zeeman field,corner states,the signature of the HOTIs,can be induced in a Z2 topological insulator.Such Zeeman fields can be produced,for example,by the ferromagnetic proximity effect or magnetic atom doping,which drastically increases the experimental complexity.Here,we show that a phononic crystal,designed as a bilayer of coupled acoustic cavities,exactly hosts the Kane-Mele model with built-in in-plane Zeeman fields.The helical edge states along the zigzag edges are gapped,and the corner states,localized spatially at the corners of the samples,appear in the gap.This verifies the Zeeman field induced higher-order topology.We further demonstrate the intriguing contrast properties of the corner states at the outer and inner corners in a hexagonal ring-shaped sample.

Evidence for nematic superconductivity of topological surface states in PbTaSe2

Spontaneous symmetry breaking has been a paradigm to describe the phase transitions in condensed matter physics.In addition to the continuous electromagnetic gauge symmetry,an unconventional superconductor can break discrete symmetries simultaneously,such as time reversal and lattice rotational symmetry.In this work we report a characteristic in-plane 2-fold behaviour of the resistive upper critical field and point-contact spectra on the superconducting semimetal PbTaSe2 with topological nodal-rings,despite its hexagonal lattice symmetry(or D3 h in bulk while C3 v on surface,to be precise).The 2-fold behaviour persists up to its surface upper critical field Hc2R even though bulk superconductivity has been suppressed at its bulk upper critical field Hc2HC<<Hc2R,signaling its probable surface-only electronic nematicity.In addition,we do not observe any lattice rotational symmetry breaking signal from field-angle-dependent specific heat within the resolution.It is worth noting that such surface-only electronic nematicity is in sharp contrast to the observation in the topological superconductor candidate,CuxBi2Se3,where the nematicity occurs in various bulk measurements.In combination with theory,superconducting nematicity is likely to emerge from the topological surface states of PbTaSe2,rather than the proximity effect.The issue of time reversal symmetry breaking is also addressed.Thus,our results on PbTaSe2 shed new light on possible routes to realize nematic superconductivity with nontrivial topology.