Determining reflections for beam propagation algorithms

Reflections occur whenever different waveguide sections are concatenated. In this paper, we will give approximate formulas for determining the reflection coefficient. Starting with generalized transmission line equations we will derive general formulas where suitable approximations are introduced. These approximations allow the determination of the reflections with low numerical effort. The expressions were implemented in an FD-BPM algorithm to determine the field distribution in waveguide devices. For an application in CAD systems the reflection coefficient of the fundamental mode was computed with the approximate formulas. Numerical results were obtained for various concatenations of different waveguide sections. A comparison with the method of lines, a semi-analytic algorithm, shows a good agreement.     

Metastable atom‐activated dissociation mass spectrometry: leucine/isoleucine differentiation and ring cleavage of proline residues

Extensive backbone fragmentation resulting in a‐, b‐, c‐, x‐, y‐ and z‐type ions is observed of singly and doubly charged peptide ions through their interaction with a high kinetic energy beam of argon or helium metastable atoms in a modified quadrupole ion trap mass spectrometer. The ability to determine phosphorylation‐sites confirms the observation with previous reports and we report the new ability to distinguish between leucine and isoleucine residues and the ability to cleave two covalent bonds of the proline ring resulting in a‐, b‐, x‐, y‐, z‐ and w‐type ions. The fragmentation spectra indicate that fragmentation occurs through nonergodic radical ion chemistry akin to electron capture dissociation (ECD), electron transfer dissociation (ETD) and electron ionization dissociation mechanisms. However, metastable atom‐activated dissociation mass spectrometry demonstrates three apparent benefits to ECD and ETD: (1) the ability to fragment singly charged precursor ions, (2) the ability to fragment negatively charged ions and (3) the ability to cleave the proline ring that requires the cleavage of two covalent bonds. Helium metastable atoms generated more fragment ions than argon metastable atoms for both substance P and bradykinin regardless of the precursor ion charge state. Reaction times less than 250 ms and efficiencies approaching 5% are compatible with on‐line fragmentation, as would be desirable for bottom‐up proteomics applications. Copyright © 2009 John Wiley & Sons, Ltd.     

Offset approximation based on reparameterizing the path of a moving point along the base circle

This paper presents a novel algorithm for planar curve offsetting. The basic idea is to regard the locus relative to initial base circle, which is formed by moving the unit normal vectors of the base curve, as a unit circular arc first, then accurately to represent it as a rational curve, and finally to reparameterize it in a particular way to approximate the offset. Examples illustrated that the algorithm yields fewer curve segments and control points as well as C^1 continuity, and so has much significance in terms of saving computing time, reducing the data storage and smoothing curves entirely.     

Comparison of UV and charged aerosol detection approach in pharmaceutical analysis of statins

CAD (charged aerosol detector) has recently become a new alternative detection system in HPLC. This detection approach was applied in a new HPLC method for the determination of three of the major statins used in clinical treatment—simvastatin, lovastatin and atorvastatin.The method was optimized and the influence of individual parameters on CAD response and sensitivity was carefully studied. Chromatography was performed on a Zorbax Eclipse XDB C18 (4.6 mm × 75 mm, 3.5 μm), using acetonitrile and formic acid 0.1% as mobile phase. The detection was performed using both CAD (20 pA range) and DAD (diode array detector—238 nm) simultaneously connected in series. In terms of linearity, precision and accuracy, the method was validated using tablets containing atorvastatin and simvastatin.The CAD is designated to be a non-linear detector in a wide dynamic range, however, in this application and in the tested concentration range its response was found to be perfectly linear. The limits of quantitation (0.1 μg/ml) were found to be two times lower than those of UV detection.     

Size exclusion chromatography with Corona charged aerosol detector for the analysis of polyethylene glycol polymer

A technique of using size exclusion chromatography (SEC) with the Corona charged aerosol detector (CAD) was developed and evaluated in comparison with refractive index (RI) and evaporative light scattering detection (ELSD) for fast screening of polyethylene glycol (PEG), a polymer used in preparing pegylated pharmaceutical compounds. These detection techniques were used in the analysis of multiple lots of PEG reagents. CAD was found to provide more accurate impurity and polydispersity profiles of PEG reagents that better differentiate their quality, while RI was not suitable for this application due to its low sensitivity and ELSD led to underestimation of the impurity and polydispersity. The accuracy of polydispersity determination by SEC-CAD was validated against a commercial reference standard of known polydispersity. The SEC-CAD technique and the observed differences between the three detectors can also be applied to polymer analysis in general.     

Application of cinchona-sulfonate-based chiral zwitterionic ion exchangers for the separation of proline-containing dipeptide rotamers and determination of on-column isomerization parameters from dynamic elution profiles

The interconversion of cis and trans isomers of dipeptides containing C-terminal proline was studied by dynamic chromatography on zwitterionic chiral stationary phases at temperatures ranging from −15 °C to +45 °C The cis–trans isomers could be separated below 0 °C and above 0–10 °C plateau formation and peak coalescence phenomena occurred, which is characteristic for a dynamic process at the time-scale of partitioning. At and above room temperature, full coalescence was observed, which allowed separations of enantiomers without interference from interconversion effects. Analysis of the dynamic elution profiles of the interconverting peptides allowed the determination of isomerization rate constants and thermodynamic activation parameters (isomerization enthalpy, entropy and activation energy). In accordance with established results, isomerization rates and thermodynamic parameters were found to depend on the nature of the N-terminal amino acid. Isomerization barriers were only slightly lower than values determined with other methods but significant differences in the relative contributions of the activation enthalpy and entropy as well as isomerization rates pointed toward selector-moderated isomerization dynamics.     

光学仪器结构设计的CAD系统

本文介绍了在AutoCAD软体平台上用AutoLISP语言开发集参数化二维图形设计和有限元建模为一体的光学仪器结构设计CAD系统的方法。标准零件在数据库中以参数化图块的形式存储,典型部件则采用参数化拼解法以图形文件的形式存储,整个数据库服从树状结构。     

Injection level dependence of the gain, refractive index variation, and alpha (α) parameter in broad-area InGaAs deep quantum-well lasers

In this study, a single, simple and an accurate computer-aided design model is developed in order to obtain the injection level dependence of the critical quantities of broad-area (with a width of 50 μm or more) InGaAs deep quantum-well (QW) lasers. Each of these quantities (gain, refractive index variation, and alpha (α) parameter) requires lengthy mathematical calculations with the use of different theories, assumptions, approximations, and estimations of some parameter values. The model is based on artificial neural network (ANN) approach that the total computational time is in the order of microseconds for the whole quantities in order to get their accurate values. The results are in very good agreement with the previously obtained results from an InGaAs deep QW laser sample.     

Dynamic Programming Algorithms for Generating Optimal Strip Layouts

This paper presents dynamic programming algorithms for generating optimal strip layouts of equal blanks processed by shearing and punching. The shearing and punching process includes two stages. The sheet is cut into strips using orthogonal guillotine cuts at the first stage. The blanks are punched from the strips at the second stage. The algorithms are applicable in solving the unconstrained problem where the blank demand is unconstrained, the constrained problem where the demand is exact, the unconstrained problem with blade length constraint, and the constrained problem with blade length constraint. When the sheet length is longer than the blade length of the guillotine shear used, the dynamic programming algorithm is applied to generate optimal layouts on segments of lengths not longer than the blade length, and the knapsack algorithm is employed to find the optimal layout of the segments on the sheet. Experimental computations show that the algorithms are efficient.     

A Unified Approach to the Analysis of a Category of H-Plane Discontinuities

Based on the mode matching method, the generalized scattering parameters including the fundamental and higher order modes (multi-modes) are obtained for the discontinuity interface of a category of waveguide H-plane discontinuities. Then by using a general port-connection order-decrease method raised by the author, the whole discontinuity including the two interfaces and the intermediate part of finite length or zero length (as is the case for very thin inductive windows or irises) can be combined into one network, and the generalized scattering parameters of this network can be obtained from which the scattering parameters of the fundamental mode can be extracted. If needed, the equivalent circuit parameters can be calculated directly from the scattering parameters. Examples are given to show the validity and versatility of this new method for dielectric filled waveguide, inductive iris and/or window, E-plane metal and/or finline insert, and even the offset E-plane finline insert, etc.. Multiple inserts, windows and irises can also be analysed.