The mass spectrometric [M ? C2H4O]+ process in cyclic ketones. I—the nature of the C2H4O losss in bicyclo[3.3.1]nonan-2-one and 3-one

Although the loss of a C₂H₄O molecule from the molecular ions of the isomeric bicyclo[3.3.1]nonan-2- and 3-ones gives rise to the base peak at m/e 94 in both spectra, deuterium labelling results show that the processes leading to this ion are markedly different in the two cases. While the 2-one follows essentially (>80%) the same [M ? C₂H₄O]+ fragmentation pathway described for other 2-alkylcyclohexanones, the 3-one exhibits a more complex decomposition pathway in which one α-hydrogen is transferred away from the departing C₂ unit and three hydrogen atoms are subsequently rearranged to the eliminated C₂H₄O molecule. Similar competing fragmentation schemes have been invoked to explain deuterium labelling results in cycloheptanone, 2-methylcycloheptanone and cyclooctanone.     

光纤几何参数的自动检测仪

叙述了光纤几何参数的自动测试方法,光纤断面通过显微光学系统成像,由CCD摄像头接收,并通过图像采集系统传输到计算机中,供进一步处理,介绍了测量原理及数学模型,采用了图像增强,图像分割等处理技术,消除图像噪声,从光纤断面图像中提取有效信息,采用不同的算法,精确计算了光纤几何参数,编制了实用化软件,提供了实测结果及二三维图示,根据上述原理与技术研制的仪器,操作简便,测量精度高。     

大容量长距离传输用低非线性效应非零色散位移光纤

利用非等温等离子体化学气相沉积 (PCVD)工艺制备了一种适合于大容量高速率长途干线网与城域网的中芯下陷型纤芯结构非零色散位移光纤。该光纤的有效面积大于 95 μm2 ,在 15 5 0nm波段的色散值约为9ps/(nm·km) ,有效的抑制了传输过程中光非线性效应的产生。通过对光纤剖面结构的优化设计 ,光纤的 15 5 0nm处的传输损耗降到约 0 .2 1dB/km ,与传统单模光纤的熔接损耗低于 0 .11dB ,且在直径为 6 0mm圆筒上绕 10 0圈后在 14 6 0nm到 16 2 5nm波长范围所引起的附加弯曲损耗均低于 0 .0 2dB/km。同时 ,该光纤色散斜率低于0 .0 6 5 ps/(nm2 ·km) ,偏振模色散 (PMD)小于 0 .0 5 ps·km-1/2 。此外 ,由于光纤的零色散点移到了 14 30nm以下 ,使波分复用 (WDM)传输在S波段 (14 6 0～ 15 30nm)、C波段 (15 30～ 15 6 5nm)、L(15 6 5～ 16 2 5nm)波段上都兼容。     

High-speed, high-resolution optical coherence tomography retinal imaging with a frequency-swept laser at 850 nm

High-speed, high-resolution optical coherence tomography (OCT) imaging of the human retina is demonstrated using a frequency-swept laser at 850 nm. A compact external cavity semiconductor laser design, optimized for swept-source ophthalmic OCT, is described. The laser enables an effective 16 kHz sweep rate with >10 mm coherence length and a tuning range of approximately 35 nm full width at half-maximum, yielding an axial resolution of <7 micro m in tissue.     

Effects of hydrophilic and hydrophobic counterions on the Coulombic interactions in perfluorosulfonate ionomers

Attenuated total reflectance FTIR spectroscopy was used to compare the influence of hydrophilic and hydrophobic counterions on the vibrational behavior of the sulfonate and perfluoroether groups in 1100 equivalent weight (EW) Nafion^® and 808 EW Dow perfluorosulfonate ionomer membranes. For dry, Na⁺-form membranes, the infrared band attributed to the —SO₃^? symmetric stretching vibration was found to shift to higher frequencies with an increase in the degree of neutralization. In contrast, neutralization with tetrabutlyammonium ions caused the —SO₃^? vibrational band to shift to lower frequencies with increasing neutralization. This behavior is attributed to a diminished polarization of the —SO₃^? groups by the hydrophobic and diffusely charged TBA⁺ cations, relative to the strong polarization observed with Na⁺ ions. Vibrational bands attributed to perfluoroether groups in close proximity to the sulfonate groups were also found to be influenced by Coulombic interactions within the clusters. The frequency shifts of these bands followed a trend that was virtually identical to that observed for the —SO₃^? symmetric stretch. This behavior is attributed to a combination of through-space, dipolar field effects, and through-bond inductive effects, from the neighboring ionic groups. In Nafion^®, the ether groups directly attached to the backbone are shielded from the Coulombic interactions within the clusters, while the ether groups within three bonds of the terminal ionic groups are very sensitive to the state of polarization of the sulfonate anion. ©1995 John Wiley & Sons, Inc.     

Ortho effects in mass spectrometric fragmentation processes

The mass spectra of the phenylhydrazones and 2,4-dinitrophenylhydrazones of ortho substituted benzaldehydes and acetophenones (X = I, Br, Cl, OCH₃, OH) show characteristic [M ? X]⁺ ions which allow the ortho derivatives to be distinguished from their meta and para isomers.     

A simple passive collector for direct measurement of radon flux from soil

A simple technique for measurement of the soil-atmosphere radon flux has been developed by fastening a charcoal canister inside a PVC cylindrical container. This device, which is deployed at the ground surface for approximately 16 hours, captures radon emanating from the soil by adsorption onto the charcoal surface. After recovery of the canister and measurement of the radon daughter activity on a NaI detector, the radon flux may be calculated if the adsorption efficiency of radon onto the charcoal is known. This parameter was determined by exposure of charcoal canisters to²²⁶Ra-spiked barium palmitate filter sources for timed intervals. Since this compound is known to emanate 100% of the²²²Rn generated during radium decay, it forms a useful flux standard. The accuracy of our flux measurements was assessed by comparison to a more established technique, the enclosed-chamber or accumulator method. Concentration measurements were made for the chamber over a less than 2-hour period while the canister flux measurements were based on single overnight deployments. The experiment was repeated 5 times at two different sites and the two techniques generally agreed within a 95% confidence interval.