SBS改性再生型木塑复合材料及其耐水性能

为了充分利用城市固体废弃物中的各项资源，本项工作将固体废弃物中的高密度聚乙烯（HDPE）回收后与废弃的木纤维、苯乙烯-丁二烯-苯乙烯（SBS）进行复合，成功地制备出SBS／再生型木塑复合材料，并进行了力学性能测试和水煮试验。结果表明，SBS的加入使木塑复合材料的冲击韧性得到显著改善，同时，复合材料的弯曲强度和弯曲模量没有明显的影响，表明SBS可以作为木塑复合材料的增韧剂。SBS／木塑复合材料经过8周、60℃的水煮后，复合材料的吸水率和厚度膨胀率均有所增加，弯曲模量和冲击韧性分别平均下降14．4％、10．8％。水煮试验初期复合材料的弯曲强度逐渐降低，然后又逐渐增大，第8周后弯曲强度增加的幅度约10％。木塑复合材料的冲击破坏模式以界面脱粘为主，而加入SBS后，复合材料的破坏以纤维断裂和基体断裂为主。     

Modeling visuospatial reasoning

I apply my proposed modification of Soar/Spatial/Visual System and Kosslyn’s (1983) computational operations on images to problems within a 2 × 2 taxonomy that classifies research according to whether the coding involves static or dynamic relations within an object or between objects (Newcombe & Shipley, 2015). I then repeat this analysis for problems that are included in mathematics and science curricula. Because many of these problems involve reasoning from diagrams Hegarty’s (2011) framework for reasoning from visual-spatial displays provides additional support for organizing this topic. Two more relevant frameworks specify reasoning at different levels of abstraction (Reed, 2016) and with different combinations of actions and objects (Reed, 2018). The article concludes with suggestions for future directions.     

Near Infrared Spectrometer for the Near Earth Asteroid Rendezvous Mission

The Near-Infrared Spectrometer (NIS) instrument on the Near-Earth Asteroid Rendezvous (NEAR) spacecraft is designed to map spectral properties of the mission target, the S-type asteroid 433 Eros, at near-infrared wavelengths diagnostic of the composition of minerals forming S asteroids. NIS is a grating spectrometer, in which light is directed by a dichroic beam-splitter onto a 32-element Ge detector (center wavelengths, 816–1486 nm) and a 32-element InGaAs detector (center wavelengths, 1371–2708 nm). Each detector reports a 32-channel spectrum at 12-bit quantization. The field-of-view is selectable using slits with dimensions calibrated at 0.37° × 0.76° (narrow slit) and 0.74° × 0.76° (wide slit). A shutter can be closed for dark current measurements. For the Ge detector, there is an option to command a 10x boost in gain. A scan mirror rotates the field-of-view over a 140° range, and a diffuse gold radiance calibration target is viewable at the sunward edge of the field of regard. Spectra are measured once per second, and up to 16 can be summed onboard. Hyperspectral image cubes are built up by a combination of down-track spacecraft motion and cross-track scanning of the mirror. Instrument software allows execution of data acquisition macros, which include selection of the slit width, number of spectra to sum, gain, mirror scanning, and an option to interleave dark spectra with the shutter closed among asteroid observations. The instrument was extensively characterized by on-ground calibration, and a comprehensive program of in-flight calibration was begun shortly after launch. NIS observations of Eros will largely be coordinated with multicolor imaging from the Multispectral Imager (MSI). NIS will begin observing Eros during approach to the asteroid, and the instrument will map Eros at successively higher spatial resolutions as NEAR's orbit around Eros is lowered incrementally to 25 km altitude. Ultimate products of the investigation will include composition maps of the entire illuminated surface of Eros at spatial resolutions as high as 300 m.     

高超声速飞行器推进模块的设计参数分析

通过斜激波理论、准一维工程估算和特征线方法建立了一个与飞行器机体一体化的推进系统模块的气动分析模型,其中采用参考温度法估算模块的粘性效应。在此基础上分别研究了飞行器前体长度、前缘角及推进模块宽度等关键设计参数对推进模块气动性能的影响。结果表明:增大模块前体长度将使模块的升力、净推力和比冲先增后降;增加前缘角将增加升力,但降低净推力;增加模块宽度会导致等效升力下降。因此,在设计此类高超声速巡航飞行器时,应采用模块化的推进系统并折衷选择前体长度和前缘角的大小。      

Time-Delay Integration Imaging with ICON’s Far-Ultraviolet Imager

A Time-Delay Integration (TDI) image acquisition and processing system has been developed to capture ICON’s Far Ultraviolet (FUV) Spectrographic Imager data. The TDI system is designed to provide variable-range motion-compensated imaging of Earth’s nightside ionospheric limb and sub-limb scenes viewed from Low Earth Orbit in the 135.6 nm emission of oxygen with an integration time of 12 seconds. As a pre-requisite of the motion compensation the TDI system is also designed to provide corrections for optical distortions generated by the FUV Imager’s optical assembly. On the dayside the TDI system is used to process 135.6 nm and 157.0 nm wavelength altitude profiles simultaneously. We present the TDI system’s design methodology and implementation as an FPGA module with an emphasis on minimization of on-board data throughput and telemetry. We also present the methods and results of testing the TDI system in simulation and with Engineering Ground Support Equipment (EGSE) to validate its performance.

     

防风网对煤堆遮风效果的风洞实验研究

为了考察防风网对堆场煤堆的遮风效果,进行了防风网与煤堆之间区域的流场可视化实验。使用风洞模拟大气边界层条件,并将开孔率为38.5%的防风网模型布置在煤堆模型前方。实验中采用粒子成像测速(PIV)系统测量了防风网和堆场区域的平均风速分布,并且获得了煤堆表面的摩擦风速分布,进一步估算煤堆起尘量的变化情况。实验发现,防风网可有效降低煤堆表面迎风区域的摩擦风速,而对背风面的流场分布影响较小。研究结果可为防风网的遮护作用提供一定的实验支持。     

再生型木塑复合材料的研究

为了充分利用城市固体废弃物中的各项资源,本项工作将固体废弃物中的高密度聚乙烯(H igh dens itypo lyethy lene,HDPE)回收后与废弃的木纤维进行复合,成功地制备出再生型木塑复合材料。研究了木纤维长度、含量以及相容剂对木塑复合材料热性能和力学性能的影响。通过扫描电子显微镜观察了复合材料的冲击断口形貌,分析了此类复合材料的断裂机制。结果表明:木纤维的加入使HDPE的结晶温度降低,结晶速度减慢;相容剂的加入大大改善了木纤维与基体树脂之间的界面结合。随着木纤维含量的增加,木塑复合材料的弯曲强度升高,冲击强度下降。     

Space: a third great age of discovery

The world has known three great ages of exploration-the circumnavigation of the globe, with its attendant discovery of new lands; the traversing and cataloguing of the newly-found continents; and the exploration of the uninhabited regions of Antarctica, the deep ocean basins and outer space. The author points to the culturally and historically determined nature of discovery, which has thus far been largely a Western phenomenon, but emphasizes the qualitatively different character of space which takes the Earth, rather than any particular part of it, as its starting point, and which sets forth to chart regions that are most probably abiotic.     

Life before RNA

The hypothesis that life originated and evolved from linear informational molecules capable of facilitating their own catalytic replication is deeply entrenched. However, widespread acceptance of this paradigm seems oblivious to a lack of direct experimental support. Here, we outline the fundamental objections to the de novo appearance of linear, self-replicating polymers and examine an alternative hypothesis of template-directed coding of peptide catalysts by adsorbed purine bases. The bases (which encode biological information in modern nucleic acids) spontaneously self-organize into two-dimensional molecular solids adsorbed to the uncharged surfaces of crystalline minerals; their molecular arrangement is specified by hydrogen bonding rules between adjacent molecules and can possess the aperiodic complexity to encode putative protobiological information. The persistence of such information through self-reproduction, together with the capacity of adsorbed bases to exhibit enantiomorphism and effect amino acid discrimination, would seem to provide the necessary machinery for a primitive genetic coding mechanism.