Er：Yb：YCOB晶体制备及其激光二极管抽运激光特性

研究了Er：Yb：YCa4O(BO3)3(简称Er：Yb：YCOB)的多晶制备和单晶生长，用提拉法生长出光学质量优良的Er：Yb：YCOB单晶，测量了其吸收光谱和荧光光谱，分析了其能级和泵浦原理，并进行了以激光二极管为抽运源的激光试验，实现了Er：Yb：YCOB晶体的在1．55μn附近110mW的激光输出，且斜效率达18．9％。     

Combination of carbon isotope ratio with hydrogen isotope ratio determinations in sports drug testing

Carbon isotope ratio (CIR) analysis has been routinely and successfully applied to doping control analysis for many years to uncover the misuse of endogenous steroids such as testosterone. Over the years, several challenges and limitations of this approach became apparent, e.g., the influence of inadequate chromatographic separation on CIR values or the emergence of steroid preparations comprising identical CIRs as endogenous steroids. While the latter has been addressed recently by the implementation of hydrogen isotope ratios (HIR), an improved sample preparation for CIR avoiding co-eluting compounds is presented herein together with newly established reference values of those endogenous steroids being relevant for doping controls. From the fraction of glucuronidated steroids 5β-pregnane-3α,20α-diol, 5α-androst-16-en-3α-ol, 3α-Hydroxy-5β-androstane-11,17-dione, 3α-hydroxy-5α-androstan-17-one (ANDRO), 3α-hydroxy-5β-androstan-17-one (ETIO), 3β-hydroxy-androst-5-en-17-one (DHEA), 5α- and 5β-androstane-3α,17β-diol (5aDIOL and 5bDIOL), 17β-hydroxy-androst-4-en-3-one and 17α-hydroxy-androst-4-en-3-one were included. In addition, sulfate conjugates of ANDRO, ETIO, DHEA, 3β-hydroxy-5α-androstan-17-one plus 17α- and androst-5-ene-3β,17β-diol were considered and analyzed after acidic solvolysis. The results obtained for the reference population encompassing n?=?67 males and females confirmed earlier findings regarding factors influencing endogenous CIR. Variations in sample preparation influenced CIR measurements especially for 5aDIOL and 5bDIOL, the most valuable steroidal analytes for the detection of testosterone misuse. Earlier investigations on the HIR of the same reference population enabled the evaluation of combined measurements of CIR and HIR and its usefulness regarding both steroid metabolism studies and doping control analysis. The combination of both stable isotopes would allow for lower reference limits providing the same statistical power and certainty to distinguish between the endo- or exogenous origin of a urinary steroid.     

ID-based cryptography using symmetric primitives

A general method for deriving an identity-based public key cryptosystem from a one-way function is described. We construct both ID-based signature schemes and ID-based encryption schemes. We use a general technique which is applied to multi-signature versions of the one-time signature scheme of Lamport and to a public key encryption scheme based on a symmetric block cipher which we present. We make use of one-way functions and block designs with properties related to cover-free families to optimise the efficiency of our schemes.      

Stable, red laser pumped, multi-kilohertz Alexandrite laser

Operation of a miniature Alexandrite laser pulse-pumped at 671 nm by a Q-switched, frequency-doubled, diode-pumped Nd:GdVO₄ laser is reported. Average power output ∼150 mW at 765 nm with optical-to-optical slope efficiencies of 28% has been demonstrated for gain-switched operation of the Alexandrite laser at 80 kHz. Q-switched pump-pulse stacking has been used to reduce output pulse width by a factor of 6 and increase peak power by a factor of 38 over gain-switched operation.     

Study of the fluence dependent interplay between laser induced material removal mechanisms in metals: Vaporization, melt displacement and melt ejection

Three quantitative methods, namely profilometry, high speed imaging and recoil momentum measurements using a ballistic pendulum, are used to determine the interplay of vaporization, melt displacement and melt ejection on nanosecond laser induced material removal. At low to moderate fluences (<7 J cm⁻²) material removal occurs via vaporization and melt displacement in aluminium. At high fluences (>7 J cm⁻²), material removal occurs predominantly via the explosive ejection of liquid droplets from the melt pool.     

Nonnegative matrix factorization for spectral data analysis

Data analysis is pervasive throughout business, engineering and science. Very often the data to be analyzed is nonnegative, and it is often preferable to take this constraint into account in the analysis process. Here we are concerned with the application of analyzing data obtained using astronomical spectrometers, which provide spectral data, which is inherently nonnegative. The identification and classification of space objects that cannot be imaged in the normal way with telescopes is an important but difficult problem for tracking thousands of objects, including satellites, rocket bodies, debris, and asteroids, in orbit around the earth. In this paper, we develop an effective nonnegative matrix factorization algorithm with novel smoothness constraints for unmixing spectral reflectance data for space object identification and classification purposes. Promising numerical results are presented using laboratory and simulated datasets.     

Self-Frequency-Doubling Ytterbium Lasers

Ytterbium-doped self-frequency-doubling lasers offer high efficiency, tunable, visible and near-infrared, cw and pulsed operation from compact devices. We review the performance of ytterbium-doped yttrium aluminium borate (Yb:YAB) self-frequency-doubling lasers. Because of the detailed dynaMisc of the interaction of the nonlinear pulse shaping process for mode-locking or for Q-switching self-frequency-doubled lasers, we observe pulse lengthening in each process when frequency doubling is optimised, with high average output power. However, for continuous wave operation, the self-frequency doubling process may be optimised to give highly efficient, robust, widely-tunable output in the visible as well as fundamental output in the infrared.     

Recent developments in the use of isotope ratio mass spectrometry in sports drug testing

According to the annual report of the World Anti-Doping Agency, steroids are the most frequently detected class of doping agents. Detecting the misuse of endogenously occurring steroids, i.e. steroids such as testosterone that are produced naturally by humans, is one of the most challenging issues in doping control analysis. The established thresholds for urinary concentrations or concentration ratios such as the testosterone/epitestosterone quotient are sometimes inconclusive owing to the large biological variation in these parameters.