975 resultados para 312.235
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本文采用几何形态测量的方法对产自和政地区的鬣狗科Hyaenictitherium, Ictitherium, Adcrocuta和旁鬣狗科Dinocrocuta的材料进行研究,分析了这4个属保存完好的头骨标本的侧面形态。与东非大草原现生食肉动物的头骨整体形态分布的比较和分析表明,和政的鼬鬣狗(Ictitherium)和鬣型鼬鬣狗(Hyaenictitherium)的头骨形状分布介于现生斑鬣狗(Crocuta crocuta)、犬科猎狗(Lycaon pictus)和金豺(Canis aureus)之间,为二者似豺生态形态的解释提供了几何形态测量证据。再者,上述两属化石鬣狗的形状分布与现生斑鬣狗的幼年个体形状重叠,表明现生斑鬣狗头骨的发育机制可能是在鼬鬣狗祖先类型的异速生长规律基础上的持续发育,进而演化出现有的粗壮形态。此外,巨鬣狗(Dinocrocuta)和副鬣狗(Adcrocuta)的头骨形状与现生的斑鬣狗在几何形态测量空间内有普遍重叠的现象,指示了这些异时出现的种类具有相似的生态形态,因而可能占据相近的生态位。结果还显示巨鬣狗和斑鬣狗的幼年个体形状相近,以及两者从幼年到成年发育的形状变化过程也具有相似的规律。因而,巨鬣狗和斑鬣狗之间的趋同演化不仅表现在成年头骨的粗壮程度上,而且在幼年发育模式中也存在平行演化现象。现生发育学与行为生态学已经证实,相对其他大型食肉动物,现生斑鬣狗发育粗壮头骨形态的机制不是以增速生长,而是以延长发育期来实现的。由此推断,巨鬣狗的发育期有可能和现生鬣狗相当(35个月),也可能由于具有相对粗壮和巨大的头骨形态,其发育期会延长些。当然,这个新解释仍需要更多的化石数据和发育研究来证实。
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The interfacial behavior of the single quantum well (SQW) GaAs/AlxGa1-xAs electrode in HQ/BQ and Fc/Fc(+) electrolytes was characterized respectively by studying the quantum confined Stark effect and Franz-Keldysh oscillation with electrolyte electroreflectance spectroscopy. The interaction of the surface state of the SQW electrode with redox species and its effects on the distribution of external bias at the interface of the SQW electrode are discussed.
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作为未来新型光电子器件的有源区材料,采用能带工程形成的各种半导体量子点,以其所具有的许多独特光电特性而日益显示出潜在的重要应用。着重评述了量子点激光器、量子点红外光探测器和量子点单光子发射器件在近3至5年内取得的最新进展,并对存在的问题进行了分析和讨论。最后,提出了进一步改善器件性能的几种可能途径。
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对MTJ (磁隧道结)的GMR(巨磁阻)效应进行了分析。MTJ的结构、形态和工作条件会对GMR效应产生不同的影响。提出了一种4×1位MTJ MRAM(磁存储器)的电路结构,每个MRAM的存储单元由一个MTJ和一个MOSFET构成,用MTJ两磁极磁化方向的相对取向表示所存储的数据,数字线和位线电流产生磁场的共同作用可完成MRAM数据的写入。
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阐述了电子回旋共振等离子体化学气相沉积法淀积半导体器件端面光学膜的优良特性。介绍了淀积反射率小于10~(-4)的1310nm半导体激光器端面增透膜技术,并对这种技术的优点和两端淀积增透膜后的激光器特性进行了讨论。
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于2010-11-23批量导入
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The photoluminescence from ZnS1-xTex alloy with 0 < x < 0.3 was investigated under hydrostatic pressure up to 7 GPa. Two peaks were observed in the alloys with x < 0.01, which are related to excitons bound to isolated Te isoelectronic impurities (Te-1 centers) and Te pairs (Te-2 centers), respectively. Only the Te-2 related emissions were observed in the alloys with 0.01 < x < 0.03. The emissions in the alloys with 0.03 < x < 0.3 are attributed to the excitons bound to the Te-n (n greater than or equal to 3) cluster centers. The pressure coefficient of the Te-1 related peak is 89(4) meV/GPa, about 40% larger than that of the band gap of ZnS. On the other hand, the pressure coefficient of the Te-2 related emissions is only 52(4) meV/GPa, about 15% smaller than that of the ZnS band gap. A simple Koster-Slater model has been used to explain the different pressure behavior of the Te-1 and Te-2 centers. The pressure coefficient of the Te-3 centers is 62(2) meV/GPa. Then the pressure coefficients of the Te-n centers decrease rapidly with further increasing Te composition.
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Excitation-power dependence of hydrostatic pressure coefficients (dE/dP) of InxGa1-xN/InyGa1-yN multiple quantum wells is reported. When the excitation power increases from 1.0 to 33 mW, dE/dP increases from 26.9 to 33.8 meV/GPa, which is an increase by 25%. A saturation behavior of dE/dP with the excitation power is observed. The increment of dE/dP with increasing carrier density is explained by an reduction of the internal piezoelectric field due to an efficient screening effect of the free carriers on the field.
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采用312-D最优饱和设计,在丘陵半干旱区开展了连续4年的田间试验,深入地研究了春小麦水肥祸合效应。水肥单因子对产量和水分利用效率(WUE)有显著影响,大小顺序为:水>磷>氮,其中三个因子对产量的提高均是正效应,而对WUE的提高,氮、磷施用量是正效应,过量灌溉是负效应;两因子间祸合作用的强弱顺序为:氮与水祸合>氮与磷祸合>磷与水祸合,其中氮与磷祸合,以及氮与水祸合对提高产量和认心E均表现为极显著相互促进作用,而磷与水祸合表现为不显著的相互替代作用。水肥祸合通过提高气孔导度(Gs)、蒸腾速率(Tr)、叶表面相对湿度(RH)、叶内水浓度(Hi)和降低胞间COZ浓度(Ci),来提高叶片光合速率(Pn)。氮素营养缺乏引起叶片“光合午休”现象的发生,增加施氮量可以避免“光合午休”现象的发生。籽粒产量与灌浆期叶片Pn呈正相关。水肥单因子对叶片Pn影响的大小顺序是:氮>磷>水;因子间藕合作用强弱顺序为:氮与水棍合>磷与水祸合>氮与磷祸合。水肥优化管理是提高产量、叶片Pn及WUE的重要途径。中等用量的氮、磷、水藕合可以达到高产、高效,获得较高的WUE和叶片Pn,实现节水高产高效与较高叶片Pn的统一,为春小麦科学灌溉施肥提供了理论依据。