Luminescence decay of distant donor-acceptor pairs in phosphorous-doped ZnTe

Luminescence decay of isolated donor-acceptor pairs has been measured over the range of pair distance R ～ 180 Å in phosphorous-doped ZnTe. Analysis of the recombination rate as a function of the pair distance suggests an asymptotic behaviour of the acceptor envelope function of the type exp(-r/a_A), with $\text{a}{}_{\mathrm{A}}\text{= 40 ± 10}\text{A}\text{?}$. This effective Bohr radius would correspond to an hydrogenic mass $\text{m}{}^1\text{= (0.13 ± 0.03)}\text{m}{}_{\mathrm{o}}$, which is close to the light hole mass as measured from cyclotron resonance experiments, $\text{m}{}^1\text{= (0.154 ± 0.005)}\text{m}{}_{\mathrm{o}}$. A discussion on the validity of the isolated donor-acceptor pair model is also given.     

化学沉淀法制备硒化铅薄膜

采用化学沉淀的方法沉淀PbSe薄膜,分别加入缓冲剂联氨(方法A)和碘化钾(方法B)。对反应原理进行了分析,对制备过程进行了优化,分别制备出了高质量的PbSe薄膜。采用XRD、SEM、EDS以及红外光谱测试对所制备样品进行了分析。结果表明,两种方法制备均为PbSe多晶薄膜,方法A制备薄膜结晶质量更好,择优生长方向明显;薄膜颗粒度、表面粗糙度都小于方法B;两种薄膜的Pb元素与Se元素比例接近化学计量比,方法B含有少量I元素;两种方法制备样品的吸收边相对带边跃迁都发生蓝移。     

Large magnetic entropy change in Nd<Subscript>2/3</Subscript>Sr<Subscript>1/3</Subscript>MnO<Subscript>3</Subscript>

In order to search for new materials for the application of magnetic refrigeration, the polycrystalline perovskite compound Nd_2/3Sr_1/3MnO₃ was prepared by a solid-state method. The dependence of the magnetization on the applied field and temperature was measured near the Curie temperature. In terms of Maxwells equation, the temperature dependence of the absolute value of the isothermal magnetic entropy change |S_M| at various applied fields from 1 T to 5 T was determined. The results showed that a large magnetic entropy change was observed in this compound. The maximum magnetic entropy change |S_M^max|can reach 3.25 J/kgK with an applied field of 1 T at the Curie temperature of 257.5 K, which equals that of Gd. At 5 T applied field, it is 7.57 J/kgK. Such good magnetocaloric properties make this compound a promising candidate for the application of magnetic refrigeration in the room-temperature range. PACS 74.25.Ha; 75.30.-m; 75.30.Sg; 75.50.-y; 75.60.-d     

润滑油对基于制冷循环的喷雾冷却系统性能的影响

针对高功率固体激光器的散热需求,设计了一种基于制冷循环的喷雾冷却系统,并对其换热性能进行研究。由于制冷系统的压缩机需要润滑,冷却液中不可避免地会混有润滑油。润滑油会对冷却液的粘度、表面张力产生影响,并可能产生油膜,从而对冷却液的换热过程产生强化或抑制。因此,通过实验研究,分析了润滑油对喷雾冷却换热性能的影响。实验结果表明,冷却液中存在润滑油,会增大冷却液流经喷嘴过程中的阻力,减小流量,但根据本系统的应用情况,可以忽略;在低热流密度时,含有一定量的润滑油更有利于热源表面温度的均匀分布,高热流密度时,2%(质量分数)的含油量对温度分布不均的影响可以忽略;润滑油的存在可以提高临界热流密度,使得系统的散热能力得到提高,更有利于其在高功率固体激光器散热领域的应用。     

Search for carbon stars and DZ white dwarfs in SDSS spectra survey through machine learning

Carbon stars and DZ white dwarfs are two types of rare objects in the Galaxy.In this paper,we have applied the label propagation algorithm to search for these two types of stars from Data Release Eight(DR8)of the Sloan Digital Sky Survey(SDSS),which is verified to be efcient by calculating precision and recall.From nearly two million spectra including stars,galaxies and QSOs,we have found 260 new carbon stars in which 96 stars have been identified as dwarfs and 7 identified as giants,and 11 composition spectrum systems(each of them consists of a white dwarf and a carbon star).Similarly,using the label propagation method,we have obtained 29 new DZ white dwarfs from SDSS DR8.Compared with PCA reconstructed spectra,the 29 findings are typical DZ white dwarfs.We have also investigated their proper motions by comparing them with proper motion distribution of 9,374 white dwarfs,and found that they satisfy the current observed white dwarfs by SDSS generally have large proper motions.In addition,we have estimated their efective temperatures by fitting the polynomial relationship between efective temperature and g-r color of known DZ white dwarfs,and found 12 of the 29 new DZ white dwarfs are cool,in which nine are between 6,000 K and 6,600 K,and three are below 6,000 K.     

Efficient three-step entanglement concentration for an arbitrary four-photon cluster state

We propose an entanglement concentration protocol to concentrate an arbitrary partially-entangled four-photon cluster state.As a pioneering three-step entanglement concentration scheme,our protocol only needs a single-photon resource to assist the concentration in each step,which makes this protocol more economical.With the help of the linear optical elements and weak cross-Kerr nonlinearity,one can obtain a maximally-entangled cluster state via local operations and classical communication.Moreover,the protocol can be iterated to obtain a higher success probability and is feasible under current experimental conditions.     

光纤非相干合成光束在湍流大气中的传输实验研究

进行了六路100 W量级光纤非相干合成光束在实际大气湍流中的传输实验,将六路光斑直径为9 mm的单模光纤光束分别扩束,扩束后的光斑直径为90 mm。基于倾斜镜的合束系统来控制各路光束的指向,在不同强度的湍流条件中,通过主镜口径为440 mm的发射系统水平聚焦传输至470 m处。倾斜控制系统闭环工作时,一倍衍射极限内的桶中功率占目标处总功率的比值是开环工作时的1.7倍左右,随着大气湍流的强度变弱,此比值变大。     

心率变异性的异方差特征研究

心率变异性数据具有非平稳和瞬时波动的特点,本文提出了采用自回归条件异方差(ARCH)分析方法分析这种波动.分析方法采用自回归移动平均模型消除序列的趋势和相关性,采用F检验法判断残差序列中是否存在ARCH效应,同时给出接受ARCH效应的概率.对充血性心衰竭病人和正常人的心率波动序列进行分析,两类人群ARCH特征接受概率及其变化率的统计值有较大差异,表明该方法可以区分不同的群体,为心电信息学研究提供了一种新的方法.     

马氏过程经验测度的大偏差上界

本文研究了ω拓扑下马氏过程经验测度的一致大偏差上界.利用非紧度量βω(P)的性质,证明了马氏过程经验测度在(M1(E),ω)满足一致好的大偏差上界,当且仅当rω(P)＝0,推广了吴黎明[10]中的定理6.1.     

Optimal uncertainty size in distributionally robust inverse covariance estimation

In a recent paper, Nguyen et al. (2018) built a distributionally robust estimator for the precision matrix of the Gaussian distribution. The distributional uncertainty size is a key ingredient in the construction of this estimator. We develop a statistical theory which shows how to optimally choose the uncertainty size to minimize the associated Stein loss. Surprisingly, rather than the expected canonical square-root scaling rate, the optimal uncertainty size scales linearly with the sample size.