Quadratic forms in skew normal variates

In this paper first a characterization of the multivariate skew normal distribution is given. Then the joint moment generating functions of two quadratic forms, and a linear compound and a quadratic form in skew normal variates, have been derived and conditions for their independence are given. Distribution of the ratios of quadratic forms in skew normal variates has also been studied.     

External calibration in gas chromatography-combustion-isotope ratio mass spectrometry measurements of endogenous androgenic anabolic steroids in sports doping control

An alternative calibration procedure for the Gas Chromatography–Combustion–Isotope Ratio Mass Spectrometry (GC–C–IRMS) measurements of the World Antidoping Agency (WADA) Accredited Laboratories is presented. To alleviate the need for externally calibrated CO₂ gas for GC–C–IRMS analysis of urinary steroid metabolites, calibration using an external standard mixture solution of steroids with certified isotopic composition was investigated. The reference steroids of the calibration mixture and routine samples underwent identical instrumental processes. The calibration standards bracketed the entire range of the relevant δ¹³C values for the endogenous and exogenous steroids as well as their chromatographic retention times. The certified δ¹³C values of the reference calibrators were plotted in relation to measured m/z¹³CO₂/¹²CO₂ (i.e. R(45/44)) mass spectrometric signals of each calibrator. δ¹³C values of the sample steroids were calculated from the least squares fit through the calibration curve. The effect of the external calibration on δ¹³C values, using the same calibration standards and set of urine samples but different brands of GC–C–IRMS instruments, was assessed by an interlaboratory study in the WADA Accredited Laboratories of Sydney, Australia and Athens, Greece. Relative correspondence between the laboratories for determination of androsterone, etiocholanolone, 5β-androstane-3α,17β-diacetate, and pregnanediacetate means were SD(δ¹³C) = 0.12‰, 0.58‰, −0.34‰, and −0.40‰, respectively. These data demonstrate that accurate intralaboratory external calibration with certified steroids provided by United States Antidoping Agency (USADA) and without external CO₂ calibration is feasible and directly applicable to the WADA Accredited Laboratories for the harmonization of the GC–C–IRMS measurements.     

高速多光谱 TDI CCD 成像电路系统

为实现多光谱TDI CCD的高速高信噪比成像,利用可空间应用的多光谱TDI CCD传感器研制出了高性能成像电路系统。该系统以现场可编程门阵列（ FPGA）为核心逻辑单元,带有RS422外围通信控制接口,并采用CAMERALINK接口输出图像数据。系统具有动态推扫成像的能力,可同时输出全色和彩色两种模式的图像数据。利用灰度条纹的靶标对传感器的3个多光谱（ R、G、B）感光区标定白平衡,利用彩色条纹的靶标对系统进行成像测试,在驱动频率为15 MHz的情况下,系统单片CCD输出的图像数据率达到1.2 Gbps。试验结果表明,获取全色图像的信噪比达到了53.56 dB,各多光谱图像的信噪比较高的也在40 dB以上,满足空间对地高分辨多光谱遥感成像的技术指标要求,对高速空间多光谱遥感相机的研制具有借鉴意义。     

The detection and estimation of the change point in a disccrete-time stochastic system

A piecewise-constant process containing a single jump is observed under noise in the context of discrete time. The conditional density and maximum a posteriori (MAP) estimator of the jump time as well as the Bayes detector of the jump itself are determined using the powerful measure transformation approach. The Bayes detector provides a convenient sequential detection rule for practical on-line implementation. An asymptotic result for the distribution of the MAP estimator's estimation error and the corresponding convergence rate are derived. This result provides a reference measure of optimal performance for jump-time estimators in discrete-time stochastic systems that does not depend on the jump time's prior distribution     

Cooperative diversity performance of selection relaying over correlated shadowing

The study of relaying systems has found renewed interest in the context of cooperative diversity for communication channels suffering from fading. In particular, dual-hop relaying with diversity combining of the relayed and direct path at the receiver has practical importance and can be considered as a building block for forming larger communication systems. This paper presents novel analytical expressions and numerical results on cooperative diversity performance using selection relaying over correlated lognormal channels for both SC and MRC techniques at the receiver. In addition, an exact framework for comparing the performance and efficiency of the medium access protocol and relay capabilities (TDMA/half-duplex, SDMA/full-duplex) is proposed. Finally, based on the analysis and novel mathematical expressions for the outage probability, we investigate the impact of the lognormal parameters (including correlation) on the cooperative system performance and its efficiency.     

Selective Determination of Itraconazole in the Presence of Its Oxidative Degradation Product by A New Spectrophotometric Method

A simple, specific, accurate and precise spectrophotometric stability indicating method is developed for determination of itraconazole in the presence of its oxidative degradation product and in pharmaceutical formulations. A newly developed spectrophotometric method called ratio difference method by measuring the difference in amplitudes between 230 and 265 nm of ratio spectra. The calibration curve is linear over the concentration range of 5～25 μg·mL-1 with mean percentage recovery of 99.81±1.002. Selective quantification of itraconazole, singly in bulk form, pharmaceutical formulations and in the presence of its oxidative degradation product is demonstrated. The results have been statistically compared with a pharmacopeial method.     

大气CO2反演的地表反射率影响分析与比值反演方法

近红外波段空基大气CO₂反演是一个病态问题,地表特征的不确定性是其重要的影响因素之一。针对大气CO₂高精度反演的需求,研究了地表反射率两大不确定性因素对大气CO₂反演的影响程度,提出了比值光谱法对这种影响进行校正。比值光谱法中CO₂无吸收通道(off-line)的选择至关重要,通过比较和分析多种off-line通道的选择方法,发现多通道多点平均法因多数据平均可降低随机误差的优势,获得的off-line通道对应的反演精度最高,而且离散程度也小。比值光谱法结合多通道多点平均法选取出的off-line通道对地表反射率的不确定性影响有明显的校正效果,有利于大气CO₂反演精度的提高。     

Dielectric inserts for sensitivity and RF magnetic field enhancement in NMR volume coils

A method for enhancing the signal to noise ratio (SNR) in NMR volume coils is described. By introducing inserts made of low-loss, high dielectric constant material into specific locations in the coil, the SNR can often be enhanced by up to 20%, while B₁ homogeneity is hardly affected. A model for predicting the limit of the SNR improvement is also presented. The model accurately predicts the SNR gain obtained in both numerical simulations and experiment. An experiment was conducted on a mini-MRI system. Experimental results are in very good agreement with the simulations in regard to both SNR improvement and B₁ enhancement in transmission. Inserts made of ultra high dielectric constant materials can be as thin as few millimeters, thus, conveniently fitting into existing coil-sample gaps in volume coils.     

受干扰光谱信息中矿物颜料粒径信息的获取

矿物颜料的准确配色是实现文物壁画高品质修复,颜色高保真还原的关键技术。矿物颜料颗粒的粒径大小是影响矿物颜料颜色信息和光谱反射率信息的一个重要因素。准确获取壁画表面的矿物颜料光谱反射率信息,是实现颜料颗粒粒径信息识别的有效途径。但是,由于壁画表面矿物颜料部分采样点的光谱信息受到了干扰,无法与不同粒径的矿物颜料的光谱数据库准确匹配,因此也无法从采集的光谱信息中获取有效的粒径信息。针对受干扰的颜料光谱信息,提出利用比值导数法对其进行处理。把光谱信息从光谱反射率空间转换到比值导数光谱空间进行匹配,降低光谱中的干扰信息,增强矿物颜料颗粒本身的光谱特征信息。以壁画中常用的不同粒径的石青和石绿矿物颜料为实验对象,制成色块样本,以基底和白色颜料为主要影响因素,对文中提出的方法进行测试。光谱角度量的结果和光谱曲线图的匹配结果显示,在比值导数光谱空间,获得了满意的光谱匹配精度。验证了文中提出的分析方法可以解决实验中受干扰颜料光谱匹配不准确而无法获得粒径信息的问题,能够为壁画修复过程中矿物颜料的配色提供准确的粒径信息参考。     

激光光镊拉曼光谱仪信噪比测量研究

通过对激光光镊拉曼光谱仪系统信噪比测量分析研究表明：在一定条件下,平均背景噪声随冷却温度降低而缓慢减小,在激发波长不变时对应的信噪比逐渐增加;曝光时间的延长使系统信噪比以不同比例线性增加;激光输入功率和系统信噪比成正比．这为单细胞拉曼光谱测量与分析提供了有力的实验依据．