低信噪比下的语音识别技术

传统的语音识别方法,信噪比较低时识别率也较低。为了使语音识别更具有环境适应性、抗噪性,从非齐次隐马尔可夫模型(nonhomogeneous Hidden Markov Model,HMM)出发,结合自适应函数链神经元网络,训练出适应环境变化的混合语音模型,并采用该混合模型进行语音识别。实验结果表明,该模型适用于含噪语音的识别,特别是在低信噪情况下,可以相对提高识别率。     

α,β-不饱和酮中C＝C双键的Ir催化的高对映选择性氢化

α-手性酮化合物是一类重要的合成中间体. 至今已有很多工作致力于在酮羰基α-位构建手性中心, 但由于产物易于消旋, 有效地不对称催化合成α-手性酮化合物的方法非常有限. 从结构看通过α,β-不饱和酮的还原是一个构建酮羰基α-位手性中心的直接方法, 但α,β-不饱和酮的还原往往是羰基而不是双键被还原. 中国科学院上海有机化学研究所侯雪龙小组发现, 利用Phosphinooxazoline (PHOX)为配体的Ir催化剂1能有效地催化氢化α,β-不饱和酮的碳碳双键, 反应可以在常压下进行, 产物ee值均大于97%. 这一方法提供了一个高效、简便的α-手性酮化合物的合成手段[在此论文寄至Angew. Chem.编辑部前一星期, 德国的Bolm, C.也投寄了相似工作: Angew. Chem. Int. Ed. 2008, 47, 8920].     

带弦圈的最小2宽直径

设k为正整数,G是简单k连通图.图G的k宽直径,dk(G),是指最小的整数ι使得对任意两不同顶点x,y∈V(G),都存在k条长至多为ι的内部不交的连接x和y的路.用C(n,t)表示在圈Gn上增加t条边所得的图.定义h(n,t):min{d2(C(n,t))}.本文给出了h(n,2)=[n/2].而且,给出了当t较大时h(n,t)的界.     

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在自行设计与建造的液态锂铅合金鼓泡器实验系统上,开展了气-液接触法提取液态锂铅合金中的氢。实验结果表明,氦气比氩气更适合作填料塔的载带气;塔温越高,塔出口端氢含量越大;载气流速对出口端氢含量的影响呈锯齿状,无明显规律。实验结果虽然与文献数据有差别,但可以认为采用气-液接触法提取液态锂铅中的氢同位素是可行的,提取效率是随液态锂铅在填料塔中滞留的时间增长而增大的。     

L-半胱氨酸/漆酶修饰的纳米金阴极对氧还原的电催化

以四氯金酸和L-半胱氨酸为原料,合成了L-半胱氨酸功能化纳米金粒子,将此纳米粒子修饰在金盘电极表面并共价偶联漆酶分子。 以循环伏安法研究了此固定漆酶电极在无氧磷酸盐缓冲液中电化学行为和催化氧还原能力,并进一步评估了其作为氧传感器使用的性能：以计时电流法测定其对氧气的检测限,与氧气的亲和力（以米氏常数表征）,研究了传感器的长期使用性、热稳定性和pH-催化电流关系。 结果表明,此固定漆酶电极可以实现漆酶活性中心T2与导电纳米粒子间的直接电子迁移而无需任何外加电子中介体（氧化还原峰的式电位为192.5 mV vs AgCl/Ag）,并在接近漆酶活性中心T3氧化还原式电位（780 mV vs NHE）附近发生氧还原;测得的固酶电极与氧气的亲和力较高（米氏常数为216.4 μmol/L）且检测限低达0.22 μmol/L,在4 ℃下保存60 d后活力仍然保持初始活力的大约78%。 但这种电极的热稳定性较差,受pH值影响较明显,在pH值近于生理条件时几乎完全丧失活力。     

有限变形的三维粘弹性本构模型(英文)

遗传积分形式与弹性元件和粘壶串并联表示的微分形式可以描述高聚物小变形情况下的粘弹性特性.文章以这些小变形的本构模型为起点,推出有限变形下的本构模型.一个有限变形过程分解成一系列微小变形子过程.小变形子过程中,应力的转动变化由弹性本构方程确定,主应力的变化由弹性元件和粘壶串并联结构的模型确定,这样提出了一个满足客观性原理的有限变形的粘弹性本构模型.模型材料参数随应变率而变,所以模型适合于从准静态到冲击载荷的较宽应变率范围.作为应用,计算了简单剪切有限变形,就建议的模型与现有的模型进行了比较,结果表明建议的模型能够描述高聚物有限变形情况下的粘弹性性质.     

肟醚碳负离子对氮杂环丙烷的开环反应

苯乙酮肟醚α碳负离子在添加 HMPA 的条件下,顺利实现了对单取代和环状氮杂环丙烷的开环,取得中等到良好的收率。四氢萘酮肟醚 α 碳负离子在该条件下也可以对部分氮杂环丙烷开环。反应中 HMPA 起到对锂离子的络合作用,可以在一定程度上增加碳负离子的亲核性。     

Higgs and Bottom Quarks Associated Production at High Energy Colliders in the Littlest Higgs Model with T-Parity

In the littlest Higgs Model with T-parity,we discuss the Higgs production in association with bottom quarks at the LHC and future electron-positron collider.We calculate the cross sections of production channels pp→bb H,bb→H and bg→b H at 14 Te V LHC and the cross sections of production channel e~+e~-→bb H in(un)polarized beams at the lowest order.In order to investigate the observability,we display some typical final state distributions in the Higgs to diphoton channel.     

Comparing potential-driven DBI-inspired non-minimal kinetic coupling(Dinkic) inflation with observational data

In our previous work [1], a new kind of inflation model was proposed, which has the interesting property that its perturbation equation of motion gets a correction of k4, due to the non-linearity of the kinetic term.Nonetheless, the scale-invariance of the power spectrum remains valid, both in large-k and small-k limits. In this paper, we investigate in detail the spectral index, the index running and the tensor/scalar ratio in this model, especially in the potential-driven case, and compare the results with the current PLANCK/BICEP observational data.We also discuss the tensor spectrum in this case, which is expected to be tested by future observations of primordial gravitational waves.     

Single-layer broadband planar antenna using ultrathin high-efficiency focusing metasurfaces

Phase gradient metasurfaces(PGMS) offer a fascinating ability to control the amplitude and phase of the electromagnetic(EM) waves on a subwavelength scale, resulting in new applications of designing novel microwave devices with improved performances. In this paper, a reflective symmetrical element, consisting of orthogonally I-shaped structures, has been demonstrated with an approximately parallel phase response from 15 GHz to 22 GHz, which results in an interesting wideband property. For practical design, a planar antenna is implemented by a well-optimized focusing metasurface and excited by a self-designed Vivaldi antenna at the focus. Numerical and experimental results coincide well. The planar antenna has a series of merits such as a wide 3-d B gain bandwidth of 15–22 GHz, an average gain enhancement of 16 d B, a comparable aperture efficiency of better than 45% at 18 GHz, and also a simple fabrication process. The proposed reflective metasurface opens up a new avenue to design wideband microwave devices.