Phase Shifter for a 915 MHz Phased Array Hyperthermia System

This paper describes a design for an analog phase shifter operating at 915 MHz and suitable for use in a phased array microwave hyperthermia system. Here, the major operating constraint was minimization of amplitude variation over a 1800 phase shift, whereas previous phase shifters were designed to obtain a linear relationship between phase and control voltage. The result is a simple, inexpensive hybrid coupler phase shifter that operates over a narrow bandwidth and provides 180°of continuous phase shift with input powers up to 1 W.     

Temperature- and Field-Dependent Charge Relaxation in SiO2 Gate Insulators

Experimental results are presented for the time dependence of the relaxation of flat-band voltage shift (?VFB) induced by ionizing radiation in metaloxide-semiconductor (MOS) capacitors incorporating radiation-hard wet (pyrogenic H20) thermally-grown SiO2 gate insulators. ?VFB was observed from 0.4 ms to 800 s following short-pulse sample irradiation at temperatures from 79 to 295 K and with applied fields from -6 to + 6 MV/cm. The results illustrate the strong temperature and field dependences of hole transport in the SiO2 which is responsible for the early annealing of the radiation-induced ?VFB. Examples are given of the manner in which these data may be applied to estimate the response of radiation-hard MOS devices at various times after irradiation, particularly in the potentially troublesome low temperature (80-150 K) regime.     

Colors of the past: color image segmentation in historical topographic maps based on homogeneity

A novel approach to color image segmentation (CIS) in scanned archival topographic maps of the 19th century is presented. Archival maps provide unique information for GIS-based change detection and are the only spatially contiguous data sources prior to the establishment of remote sensing. Processing such documents is challenging due to their very low graphical quality caused by ageing, manual production and scanning. Typical artifacts are high degrees of mixed and false coloring, as well as blurring in the images. Existing approaches for segmentation in cartographic documents are normally presented using well-conditioned maps. The CIS approach presented here uses information from the local image plane, the frequency domain and color space. As a first step, iterative clustering is based on local homogeneity, frequency of homogeneity-tested pixels and similarity. By defining a peak-finding rule, “hidden” color layer prototypes can be identified without prior knowledge. Based on these prototypes a constrained seeded region growing (SRG) process is carried out to find connected regions of color layers using color similarity and spatial connectivity. The method was tested on map pages with different graphical properties with robust results as derived from an accuracy assessment.     

Apparatus for the measurement of the magnetization of steel

An improved method has been developed for measuring the magnetization of steel with great accuracy up to saturation. With toroidal samples it is not possible to reach the necessary field strength. Ellipsoidal samples are used, for which the magnetizing factor can be calculated exactly. The specimens are 200 mm long, have a maximum diameter of 10 mm, and are shaped accurately to within 0.01 mm. With this method magnetization curves can be obtained up to 10⁵A/m with an accuracy of better than 1%.     

X-band 0.5, 1, and 2 watt power amplifiers with markedimprovement in power-added efficiency

Very efficient X-band MESFET power amplifiers, showing greater power-added efficiency over a wider bandwidth than any X-band amplifiers of comparable output reported to date, are discussed. The amplifiers were designed with attention given to optimum bias, proper harmonic termination, and efficient power combining. These device and design issues are discussed, and a straightforward design method which achieved the increased levels of efficiency is described     

Evidence for dominant wild female chimpanzees investing more in sons

Parents are expected to invest more resources in the offspring gender that promises more grandchildren. In a variety of vertebrate species skewed sex ratio at birth and differential parental investment in sons and daughters have been documented. Wild chimpanzees, Pan troglodytesliving in the Tai National Park, Cote d'Ivoire, were followed for 15 years. This community followed the typical species pattern in that males showed natal philopatry and the sex ratio at birth was almost 1:1. An analysis of 33 inter-birth intervals revealed that dominant females invested about 2 years more in sons, whereas subdominant females invested about 11 months more in daughters. The first difference is significant. Sons of dominant females had higher survival than other youngsters. The benefit of such a facultative investment is discussed. The absence of such a differential investment by mothers in other chimpanzee populations is compatible with an explanation based on variations within the female-biased dispersal pattern in this species and the possible role of maternal condition.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour     

Fitting interrelated datasets: metabolite diffusion and general lineshapes

Objective

Simultaneous modeling of true 2-D spectroscopy data, or more generally, interrelated spectral datasets has been described previously and is useful for quantitative magnetic resonance spectroscopy applications. In this study, a combined method of reference-lineshape enhanced model fitting and two-dimensional prior-knowledge fitting for the case of diffusion weighted MR spectroscopy is presented.

Materials and methods

Time-dependent field distortions determined from a water reference are applied to the spectral bases used in linear-combination modeling of interrelated spectra. This was implemented together with a simultaneous spectral and diffusion model fitting in the previously described Fitting Tool for Arrays of Interrelated Datasets (FiTAID), where prior knowledge conditions and restraints can be enforced in two dimensions.

Results

The benefit in terms of increased accuracy and precision of parameters is illustrated with examples from Monte Carlo simulations, in vitro and in vivo human brain scans for one- and two-dimensional datasets from 2-D separation, inversion recovery and diffusion-weighted spectroscopy (DWS). For DWS, it was found that acquisitions could be substantially shortened.

Conclusion

It is shown that inclusion of a measured lineshape into modeling of interrelated MR spectra is beneficial and can be combined also with simultaneous spectral and diffusion modeling.

     

Phenylketonuria: findings at MR imaging and localized in vivo H-1 MR spectroscopy of the brain in patients with early treatment

PURPOSE: To characterize white matter changes in early-treated phenylketonuria (PKU) with magnetic resonance (MR) imaging and hydrogen-1 MR spectroscopy and to correlate these findings to biochemical control and brain function. MATERIALS AND METHODS: Fifty-one patients aged 12-33 years underwent T1-, T2-, and proton-density-weighted MR imaging and testing of intelligence, visual evoked potentials (VEPs), and neuropsychologic status (29 adult patients only). H-1 MR spectroscopy was performed in eight patients to determine brain metabolite concentrations, including phenylalanine (PHE) concentration, and brain compartmentation. RESULTS: MR imaging revealed a high frequency of supra- and infratentorial abnormalities. MR imaging grade, which was based on areas of high signal intensity on T2-weighted images, showed statistically significant correlation with long-term biochemical control and neuropsychologic test results but not with intelligence quotient or VEPs. H-1 MR spectroscopy revealed normal metabolite levels, except for increased PHE levels. It also showed enlarged cerebrospinal fluid-like compartments in affected white matter, related to plasma and brain concentrations of PHE and MR imaging grades. CONCLUSION: A synergistic use of MR imaging and MR spectroscopy may help elucidate both the pathogenesis of brain dysfunction and clinical treatment policies in PKU.