机器学习在紫外法测定硝酸盐氮浓度中的应用

紫外分光光度法(UV法)由于较传统化学方法具有效率高操作简便、无二次污染且可现场原位测试等优点,近些年来被广泛应用到水质参数的测试中。硝酸盐氮是工业废水中的主要污染物之一。基于UV法测量水体中硝酸盐氮浓度的标准方法是分别测量水样在220nm和275nm处的吸光度,然后用275 nm处的吸光度对220 nm处的吸光度进行校正,进而绘制出校正后的吸光度与硝酸盐氮浓度的标准曲线。然而,当硝酸盐氮浓度升高时,标准法所采用的朗伯比尔定律的线性关系以及不同物质吸光度叠加的线性不能很好地满足,在实际的实验测试中也发现,很难建立硝酸盐氮在220 nm处的吸收模型。为了克服单波长或双波长方法的缺陷,将硝酸盐氮吸收峰范围的各个波长的吸光特性引入到模型的建立之中。同时,为了降低模型的复杂度,在建立模型之前先对吸光度数据进行主成分分析,将输入数据的维度数从107压缩到4,然后对压缩后的数据使用局部加权线性回归法建模,该吸收模型对于训练样本和测试样本都有较好的预测结果,且能够适应高浓度时吸光度与浓度的非线性关系,测量上限可达几百mg·L-1。另外,此方法的原理和流程也适用于其他水质参数吸收模型的建立。     

New physics hints in B decays and collider outlook

There are currently two hints for new physics involving CP violation in b → s transitions: ΔS ≡ S _f − S _J ^ϕK ≠ 0, and difference in direct CP asymmetry ΔA _Kπ ≡ A _K+π ⁰ − A _K+π ⁻ ≠ 0. We explore the two scenarios with a large and unique new CP phase in b ↔ s transitions. Motivated by ΔS ≠ 0, we update on the right-handed strange-beauty squark sb _1R at TeV scale. Motivated by ΔA _Kπ ≠ 0, we explore sequential fourth generation t′ and b′ quarks. Both scenarios can survive constraints such as SM level b → sγ, sll and B _s mixing, and predict sizable CP violation in B _s mixing. The fourth generation picture predicts sizable K _L → π ⁰ vv. Direct search for sb _R, b′ and t′ at hadronic colliders, such as Tevatron Run II and LHC, can complement further CP violation studies at these machines, as well as at the future Super B factory.     

Influence of the electric characteristics of II–VI semiconductor material on the electroluminescence of lanthanide complex

The organic-inorganic combined structural device (ITO/PVK:Eu/ZnS/Al) is fabricated based on layered optimization scheme. II–VI semiconductor material ZnS is acted as an electron function (transporting and acceleration) layer. The hot electrons which have been accelerated in the ZnS layer directly impact excitation europium ions through resonant energy transfer and then recombine with injected holes to form excitons in PVK or EuTTA₂(N-HPA)Phen. Europium (Eu) ions may also be excited by intramolecular energy transfer from ligands. There are two kinds of excitation mechanisms: impacted excitation and injected recombination for the combined structural device. The electroluminescence (EL) intensity of the combined structural device is strongly improved and reaches up to 381 cd/m² at 20 V compared with the pure organic structural device. It may be an effective method to improve the EL intensity of the lanthanide complex by using electric characteristics of inorganic semiconductor materials.     

Optical mm-wave generation by using external modulator based on optical carrier suppression

In this paper, we have theoretically investigated the transmission performance of the optical millimeter (mm)-wave generated by using an external modulator based on optical carrier suppression for the first time. According to our theory, the data signals carried by the optical mm-wave are transmitted in the dispersion fiber without fading but are degraded greatly because of the time shift of the code edges, which still limits the transmission distance. The experimental results agree well with our theory.     

Mode-locked performance of hybrid soliton pulse source utilizing fiber grating external cavity lasers

Mode-locking characteristic of hybrid soliton pulse source (HSPS) utilizing linearly chirped raised-cosine flat top apodized fiber Bragg grating (FBG) is investigated by using coupled-mode equations. It is found that the fundamental repetition frequency range of HSPS is significantly extended by using linearly chirped raised-cosine flat top apodized FBG instead of linearly chirped Gaussian apodized FBG. The range of repetition frequencies over which proper mode-locking is obtained is 2-3.3 GHz with linearly chirped raised-cosine flat top apodized grating whereas this range is 2.1-2.95 GHz with linearly chirped Gaussian apodized grating.     

空间非均匀场下核间距对不对称分子谐波发射的影响

数值研究了空间非均匀场下核间距离对于不对称分子HeH2+发射高次谐波以及阿秒脉冲的影响。计算结果表明,通过适当调节HeH2+分子离子的核间距离以及空间非均匀参数,不仅谐波发射的截止能量得到了延伸,而且单一的短量子路径也被选择出来对谐波发射起作用。随后适当引入第二束控制激光场,谐波截止能量得到了进一步扩展,形成了两个带宽分别在431eV和372eV的连续平台区。 最后,通过适当的叠加谐波,可获得脉宽为31as-65as的一系列阿秒X射线光源。     

少周期非均匀场下原子空间位置对高次谐波发射的影响

本文通过数值求解含时薛定谔方程,研究了少周期非均匀激光脉冲作用下氦原子选取不同的空间位置时高次谐波的发射情况.通过对原子在纳米结构空隙中心附近区域不同空间位置上的高次谐波发射情况的研究发现,非均匀激光场中,即使原子处在中心附近的很小的区域内,原子的空间位置也直接影响着高次谐波发射.随着空间内原子坐标的增大,高次谐波的截止得到扩展,且谐波平台区并非单向扩展,而是向两端同时的扩展.通过时频分析和半经典三步模型研究了高次谐波发射的物理机制,并对获得的物理现象给出合理的解释.     

基于密度泛函理论的叶绿素A性质的研究

在液相环境中,采用密度泛函理论(DFT)、含时密度泛函理论(TD-DFT)、Multiwfn波函数分析软件,在pbepbe/6-311g(d)基组水平上,计算并分析了叶绿素A的结构、紫外光谱和电子—空穴分布,结果表明:pbepbe/6-311g(d)方法是计算叶绿素A紫外吸收光谱更精确的方法;叶绿素A分子的吡咯环与取代基相互作用的过程中,吡咯环Ⅳ受侧链"尾巴"的影响最大;理论计算的紫外光谱与实验数据吻合较好,其中635.71 nm和446.87 nm处的两个吸收峰可认为是叶绿素A的特征吸收峰;侧链或取代基团在叶绿素A激发过程中是给电子体,卟啉"头"既是电子供体,也是电子受体.     

二次谐波中大相位失谐下入射啁啾脉冲对相位的影响

讨论了在大相位失谐下,基波为频率啁啾脉冲的二次谐波产生过程,结果表明选取合适的啁啾参量可以使二次谐波的光强提高,但同时会使其波形和相位发生变化.三波相位的畸变主要取决于入射的基波啁啾脉冲,而与相位匹配的失谐量关系不大.     

Ultrafast dynamics in the excited hydrogen atom transfer states of ammonia clusters

Neutral ammonia clusters (NH₃)_m are photo-excited to the electronic state by a deep UV femtosecond laser pump pulse. Within a few hundred femtoseconds a significant fraction of the clusters rearrange to form an H-transfer state (NH₃)_m-2NH₄(3s)NH₂ with the subunit NH₄ in its 3s electronic ground state. This state is then electronically excited by a time-delayed infrared control pulse of variable wavelength. Finally, a third (probe) pulse in the UV ionizes the clusters for detection. The lifetime of the excited (NH₃)_m-2NH₄(3p)NH₂ states is found to vary between 2.7 and 0.13 ps depending on cluster size and excitation energy. It increases drastically upon deuteration. The corresponding cluster size-dependent photoelectron spectra allow us to disentangle the underlying energetics of the excitation and ionization process and reveal additional processes, such as nonresonant ionization or dissociative ionization. The experimental findings suggest that the excited H-transfer ammonia complexes with m > 2 are deactivated by an internal conversion process back to the electronically lowest H-transfer state followed by fast dissociation. Received 22 September 2001 and Received in final form 31 January 2002