Impedance boundary method of moments with extended boundaryconditions

An improved impedance boundary method of moments is proposed to accurately and efficiently determine the propagation characteristics of multilayer planar optical waveguides whose refractive index profiles contain large step index changes or a graded-index region combined with step index changes. Extended impedance boundary conditions are used in the impedance boundary method of moments to replace regions in the waveguide structure which have refractive index discontinuities. Two methods for determining the extended boundary conditions include the standard transfer matrix method and a procedure utilizing a cascaded transmission line representation with successive calculation of input impedances. Simulation results show significantly improved convergence rates in the determination of propagation constants     

Intrathecal granuloma complicating chronic spinal infusion of morphine. Report of three cases

OBJECTIVE: To assess the frequency of methotrexate (MTX)-induced pancytopenia in rheumatoid arthritis (RA). METHODS: A MEDLINE literature search was conducted to identify articles published during the last 15 years (1980-1995) that presented data on MTX-associated pancytopenia. Two case reports of our own experience are also presented. In addition, articles that examined risk factors associated with MTX-related pancytopenia were identified. RESULTS: A total of 70 patients with pancytopenia related to MTX therapy were identified (68 reported in the literature, 2 from our own experience). Sixty-one of the patients were described in published case reports, 7 patients were from 5 long-term prospective studies. In many of these cases, predisposing factors for the development of pancytopenia were described. The 5 long-term prospective studies reported toxicity data on patients who had been treated with MTX for at least 13 weeks. A total of 511 patients were included in the prospective trials, yielding an overall incidence of pancytopenia of 1.4% (7 of 511). Of the 70 cases reported, 12 patients died (17%). Most of them had impaired renal function, hypoalbuminemia, concurrent infection, and/or concomitant medication with more than 5 drugs. The minimal cumulative MTX dose leading to fatal pancytopenia was 10 mg, observed in one of our patients. CONCLUSION: Pancytopenia is not an uncommon side effect of low-dose pulse MTX therapy in RA. It can lead to serious complications, including death.     

Diversity in publications [From the Editor's Desk]

It is common wisdom that diversity can make a group strong. Approaching a problem or situation from multiple perspectives increases the chances of finding longterm, effective solutions. Several years ago at the National Institute of Standards and Technology (NIST), during one of our diversity training sessions, we learned that the ancient Incas were able to survive for centuries on a diet rich in potatoes because they grew a diverse variety of the tubers. As growing conditions changed year to year (drought, wet, or short growing seasons), there was generally one or another type of potato that would survive. We were told that the Irish, on the other hand, focused exclusively on one type of potato that appeared to be well suited to their environment, but when that one variety became susceptible to disease, the terrible Irish potato famine occurred.     

Systematic Error of the Nose-to-Nose Sampling-Oscilloscope Calibration

We use traceable swept-sine and electrooptic-sampling-system-based sampling-oscilloscope calibrations to measure the systematic error of the nose-to-nose calibration, and compare the results to simulations. Our results show that the errors in the nose-to-nose calibration are small at low frequencies, but significant at high frequencies.     

Measurement Bandwidth Extension Using Multisine Signals: Propagation of Error

We describe a post-processing technique that extends the effective measurement bandwidth of narrowband vector receivers by phase aligning overlapping measurements. We study the repeatability of the method and the propagation of errors as increasing numbers of bands are stitched together. The method can be used to find phase errors both in the excitation band of frequencies, as well as in distortion products, for periodic multisine signals.      

Application notes: multisine signals for wireless system test and design

Multisine signals are used in the laboratory and in the field to provide a periodic, well-characterized waveform that can simulate complex modulated radio frequency (RF) signals. In the field of wireless telecommunications, multisines are often used to provide realistic test signals that have statistics similar to various types of digitally modulated signals. It is concluded that the multisine approach is well suited for evaluating a nonlinear system excited by real communication signals. Multisine signals enable to gather important information about the in-band distortion and to excite long-term memory effects by generating baseband components. They are periodic and straightforward to characterize, making them ideal for identifying both magnitude and phase distortion during test and verification. Using multisines to simulate standard wireless system excitations and figures of merit allows for very good laboratory nonlinear distortion measurement setups.     

The Sampling Oscilloscope as a Microwave Instrument

Most of the equipment required is readily available in most microwave labs: a vector network analyzer, a microwave signal generator, and, of course, a sampling oscilloscope. In this paper, the authors summarize many of the corrections discussed in " Terminology for high-speed sampling-oscilloscope calibration" [Williams et al., 2006] and "Magnitude and phase calibrations for RF, microwave, and high-speed digital signal measurements" [Remley and Hale, 2007] that are necessary for metrology-grade measurements and Illustrate the application of these oscilloscopes to the characterization of microwave signals.     

A versatile impedance boundary method of moments computationaltechnique for solving the one-dimensional Schrodinger equation withapplication to quantum well and quantum wire problems

A versatile and efficient computational technique for use in the analysis of quantum wells (QWs) and a class of quantum wires with arbitrary potential profiles is presented. This expansion technique is an extension of the impedance boundary method of moments (IBMOM), which was first developed for analysis of planar optical waveguide structures. The similarity in formulation of the electromagnetic problem and the QW problem is exploited, Eigenenergies or quasi-eigenenergies, wave functions and, for quantum wires with separable wave functions, conductance are determined. No discretization or step approximation is required of potential profiles which can be described in functional form. Computational results are presented to demonstrate the accuracy and efficiency of the technique