虾青素的功能及应用进展

虾青素是一种类胡萝卜素,具有抗氧化、增强免疫和预防癌症等功效。现对国内外在虾青素的功能及应用方面的研究进展作一综述。     

基于SWAT模型的南沙河流域日流量过程研究

由于南沙河流域缺乏长系列实测径流资料,采用SWAT模型(Soil and Water AssessmentTool,土壤和水评价工具)分析北京南沙河流域干支流共16个断面不同水平年(P=50%、P=75%和P=95%)天然情况下的日流量过程。根据流域的DEM图(Digital Elevation Model,数字高程模型)、土地利用规划及土壤类型等大量流域基本资料建模,模型参数经实测流量过程率定后确定。运行模型可得到南沙河的日流量过程并经合理性分析,认为日流量过程基本符合天然来水情况。可供南沙河流域水质还清规划使用。     

Transient liquid-phase assisted spark-plasma sintering and dry sliding wear of B4C ceramics fabricated from B4C nanopowders

With the motivation of developing B₄C composites with superior wear resistance for tribological applications, an ultrafine-grained (～200?300 nm) B₄C composite was fabricated, characterized microstructurally, and tested mechanically and tribologically. First, a well-dispersed powder mixture of B₄C nanopowders (～40 nm) with coarse Ti-Al powders (～38 μm) as transient liquid-phase sintering additives was environmentally-friendly prepared by aqueous colloidal processing, optimized by measurements of the zeta potential of dilute suspensions and rheological studies of concentrated suspensions. Second, the powder mixture obtained by freeze-drying was densified by spark-plasma sintering (SPS), identifying the optimal SPS temperature (1850°C) by measurements of density, hardness, and toughness. Third, the dry sliding-wear behaviour of the optimal superhard B₄C composite (～31.5 GPa) was investigated by pin-on-disk tests and observations of the worn surface, determining its specific wear rate (～4.4·10^?8 mm³/(N·m)) as well as wear mode (two-body abrasion) and mechanism (plastic deformation). And lastly, the wear behaviour of the ultrafine-grained B₄C composite was compared with that of a reference fine-grained (～0.7?0.9 μm) B₄C composite, finding that both have the same mode and mechanism of wear but with the former being more resistant than the latter (～2.3·10⁷ vs 1.9·10⁷ (N·m)/mm³). Implications for the fabrication of B₄C tribocomponents with greater superior wear resistance are discussed.     

地球同步轨道空间双轴追日跟踪系统设计

为了实现在地球同步轨道上空间太阳能采集系统高精度对日定向,本文设计了基于C8051F040芯片的高精度双轴太阳跟踪控制器。该控制器首先根据当前时刻和空间位置获得太阳的基本位置,然后根据光能感应探测器的探测结果对太阳跟踪角度的偏差进行自动定位和校准。本系统地面实验效果良好,跟踪精度能够优于0.5%。     

碳热还原法制备SiC纳米线及其结构表征

采用简单的碳热还原法,以碳粉和Si02微粉分别作为碳源和硅源,在1550℃高温真空气氛箱式炉中制备SiC纳米线。并利用X射线衍射（XI国）、扫描电镜（SEM）和透射电镜（TEM）、傅里叶变换红外（FTIR）等测试手段对反应产物进行组分、形貌和结构表征。研究结果表明：产物为直线六棱柱形状的β-SiC纳米线,直径在50～300nm之间,纳米线内部含有较多的堆垛层错;纳米线主要以气-固（VS）机制生长。     

双螺杆泵螺杆成型铣刀廓形求解及验证

根据双螺杆泵螺杆螺旋面端面截形型线方程,利用成形铣削原理和坐标变换理论,从成形铣刀与螺杆工件的相对运动关系出发,建立基本的铣刀刀刃廓形方程。利用Matlab软件对设计刀具过程中的三角超越方程等非线性方程进行求解,得到铣刀回转面轴截形,然后以铣刀回转面轴截形为已知条件,反求螺杆螺旋面端截形,验证铣刀廓形求解方法的正确性。     

画法几何中的一种求解方法——直径圆周角法

文中以实例的形式,对画法几何中的定位、距离及角度等综合性强的典型实例,尤其是对看似用一般方法（除投影变换以外的方法）难以解决的一些实例,对其进行空间常规解题分析,并给出空间解题模型,而后给出利用直径圆周角法的空间解题模型及图解方法,比较结果表明,直径圆周角法作图简单。     

Craniocervical junction tuberculosis: a rare but dangerous disease

BACKGROUND: Mycobacterium tuberculosis of the cervical spine is a rare but dangerous manifestation of extra-pulmonary tuberculosis. The clinical picture ranges from early, nonspecific, insidious symptoms to severe neurological complications and death, attributed to craniocervical junction instability and cervicomedullary compression. The different lines of management include antituberculous medication with traction and external fixation or adjunctive surgery (debridement and stabilization) in patients with severe or persistent neurological complications and/or vertebral instability. METHODS: We describe two patients with advanced craniocervical junction tuberculosis. The early clinical picture was nonspecific in Case 1 and obscured by psychiatric illness in Case 2. The detailed clinical and radiological findings, and the management, will be described. Involvement of the occipital condyles and foramen magnum, which has not been reported previously, will be demonstrated. RESULTS: Both cases underwent transoral biopsy, aspiration, and debridement of retropharyngeal abscess (granuloma). Histological and tissue culture studies proved the abscesses were tuberculous and anti-tuberculous medications were started. Case 1 showed complete resolution of the clinical and radiological findings. Case 2 developed cardiorespiratory arrest while in a halo jacket. He was resuscitated but remained quadriplegic and semiconscious; he developed nosocomial gram negative pneumonia. He was referred back to his local hospital where he died 1 year later. CONCLUSIONS: Tuberculosis is an infrequent but notable cause of cervicomedullary compression. It should be suspected in patients with infective spondylitis who are immunocompromised or reside in an area highly endemic for tuberculosis. Management strategies include antituberculosis medication, transoral biopsy and drainage of the abscess, traction and external fixation, posterior decompression, and internal fixation, according to the clinical and radiological findings.     

ADP-ribosylation of serum proteins: evaluation as a potential tumor marker

The low-affinity p75 receptor for nerve growth factor (p75NGFR) has been implicated in mediating neuronal cell death in vitro. A recent in vitro study from our laboratory showed that the death of sensory neurons can be prevented by reducing the levels of p75NGFR with antisense oligonucleotides. To determine if p75NGFR also functions as a death signal in vivo, we have attempted to reduce its expression in peripheral sensory neurons by applying antisense oligonucleotides to the proximal end of the transected sciatic or median and ulnar nerves. We report here that antisense oligonucleotides, when applied to the proximal stump of a transected peripheral nerve, are retrogradely transported and effectively reduce p75NGFR protein levels in sensory neurons located in the dorsal root ganglia. Furthermore, treatment of the proximal nerve stump with antisense p75NGFR oligonucleotides significantly reduced the loss of these axotomized sensory neurons. These findings further support the view that p75NGFR is a death signaling molecule and that it signals death in axotomized neurons in the neonatal sensory nervous system.