Imaging with unfocused regions of focused ultrasound beams

This article gives an analytical, computational, and experimental treatment of the spatial resolution encoded in unfocused regions of focused ultrasound beams. This topic is important in diagnostic ultrasound since ultrasound array systems are limited to a single transmit focal point per acoustic transmission, hence there is a loss of spatial resolution away from the transmit focus, even with the use of dynamic receive focusing. It is demonstrated that the spatial bandwidth of a Gaussian-apodized beam is approximately constant with depth, which means that there is just as much encoded spatial resolution away from the transmit focus as there is in the focal region. The practical application of this principle is discussed, an algorithm for retrospectively focusing signals from unfocused regions of fixed-focus beams is presented, and a quantitative comparison between the authors' methods and dynamic-receive beamforming is provided.     

滴汞电极2.5次微分电分析法测定天然水中痕量钛

天然水中钛的定量分析有分光光度法、极谱法、催化波法等方法。微分电分析法尚未见报导。本文得出了以0.02M苦杏仁酸-4%氯酸钾(pH=3)为底液时,钛在滴汞电极上2.5次微分电分析法催化波,峰形明晰、干扰少、线性范围为1×10^-10-1×10^-7g/ml钛。可直接用于天然水中痕量钛的测定。     

高效率连续激光二极管泵浦Cr∶LiSAF激光器

报道了500mW激光二极管端面泵浦Cr∶LiSAF激光器连续运转的实验研究结果.特别是在分析了泵浦光与腔模的耦合情况后,提出了一套与泵浦源相适应的准直聚焦系统,提高了耦合效率.实验对两种不同掺杂浓度和不同形状的Cr∶LiSAF晶体进行了研究,在850nm的中心波长处获得最大输出功率分别为20mW和13mW,斜效率分别为10.3%和7.8%,并对实验结果作了讨论.     

Development and validation of a high-performance liquid chromatography tandem mass spectrometry assay for atorvastatin, ortho-hydroxy atorvastatin, and para-hydroxy atorvastatin in human, dog, and rat plasma

A liquid chromatographic/mass spectrometric method to quantitate atorvastatin (AT) and its active metabolites ortho-hydroxy (o-AT) and para-hydroxy (p-AT) atorvastatin in human, dog, and rat plasma was validated. The method consisted of washing plasma samples at high pH with diethyl ether and subsequently extracting the analytes and two internal standards, [d ₅]-atorvastatin ([d ₅]-AT) and [d ₅]-ortho-hydroxy atorvastatin ([d ₅]-o-AT), from acidified plasma by using diethyl ether. The ether layer was evaporated to dryness and the residue reconstituted in ammonium acetate (20 mM, pH 4.0)-acetonitrile-isopropanol (60:40:1, v/v/v). Chromatographic separation of analytes was achieved by using a YMC J’Sphere H80 (C-18) 150 × 2 mm, 4 μm particle size, column with a mobile phase consisting of acetonitrile-0.1% acetic acid, (70:30, v/v). Analytes were detected by using MS/MS. Sample introduction and ionization was by electrospray ionization in the positive ion mode. The method proved suitable for routine quantitation of AT, o-AT, and p-AT over the concentration range of 0.250 to 25.0 ng/mL. Approximate retention time ranges of p-AT, o-AT, [d ₅]-o-AT, AT, and [d ₅]-AT were 2.27 ± 0.21, 3.36 ± 0.23, 3.54 ± 0.46, 4.12 ± 0.61, and 4.65 ± 0.65 min, respectively. No peaks interfering with quantitation were observed throughout the validation processes. Mean recoveries of AT, o-AT, and p-AT from plasma ranged 100%–107%, 70.6%–104%, and 47.6%–85.6%, respectively. Mean recoveries of the [d ₅]-AT and [d ₅]-o-AT internal standards ranged 98.0%–99.9% and 97.3%–97.9%, respectively. Interassay precision, based on the percent relative deviation for replicate quality controls for AT, o-AT, and p-AT, was ≤7.19%, 8.28%, and 12.7%, respectively. Interassay accuracy for AT, o-AT, and p-AT was ±10.6%, 5.86%, and 15.8%, respectively. AT, o-AT, and p-AT in human, dog, and rat plasma quality controls were stable to three freeze-thaw cycles. AT, o-AT, and p-AT were stable frozen for 127, 30 and 270 days in human, dog, and rat plasma quality control samples, respectively. Human plasma quality control samples containing AT, o-AT, and p-AT were stable for at least 4 days at ambient room temperature and 37 °C. The lower limit of quantitation for all analytes was 0.250 ng/mL for a 1.0-mL sample aliquot.     

Towards a Useful Philosophy of Biochemistry: Sketches and Examples

Scientific development influences philosophical thought, and vice versa. If philosophy is to be of any use to the production, evaluation or application of biochemical knowledge, biochemistry will have to explicate its needs. This paper concentrates on the need for a philosophical analysis of methodological challenges in biochemistry, above all the problematic relation between in vitro experiments and the desire for in vivo knowledge. This problem receives much attention within biochemistry, but the focus is on practical detail. It is discussed how a theoretical analysis can go beyond a naïve understanding of scientific success and failure in such cases. Several examples are presented to elucidate this issue, including the methodological implications of the precautionary principle, the possible interplay between theoretical methodology of biochemistry and the science studies, and the methodological complexities related to experimental protocol standardisation and use of instruments and kits.     

自蔓延高温合成氮化铝晶须形态和生长机理研究(2)

在对自蔓延高温合成方法制得的AIN晶须形态研究的基础上,采用高分辩电镜等技术,对AIN晶须进行了生长机理研究,结果表明,晶须头部的小液滴显示氮化铝晶须可由VLS机制生成.光滑晶须头部的出现、过饱和度与晶须直径的关系、侧面的二次生长、生长台阶的出现,这些都说明VS机制在起作用.虽然在AIN晶须中发现层错和位错,但经过分析认为,它们都不是氮化铝晶须的生长机制.     

37 fs、 0.94 μm钛宝石自锁模激光器的研究

报道了低增益区Ｔｉ＾３＋：Ａｌ２Ｏ３红外飞秒激光器的连续及自锁模运转情况,采用四镜折叠像散补偿腔,对于连续波运转,泵浦阈值功率为５．８Ｗ,其调谐范围为０．９－０．９７μｍ。     

Iterative computation of derivatives of repeated eigenvalues and the corresponding eigenvectors

Recently the authors proposed a simultaneous iteration algorithm for the computation of the partial derivatives of repeated eigenvalues and the corresponding eigenvectors of matrices depending on several real variables. This paper analyses the properties of that algorithm and extends it in several ways. The previous requirement that the repeated eigenvalue be dominant is relaxed, and the new generalized algorithm given here allows the simultaneous treatment of simple and repeated eigenvalues. Methods for accelerating convergence are examined. Numerical results support our theoretical analysis. Copyright © 2000 John Wiley & Sons, Ltd.