Image guide couplers with dielectric coupling elements and radiation reduction

Directional couplers in image guide technique for millimeter-wave circuits are discussed, and steps to improve their properties are demonstrated. The simple two-line-9 dB coupler with periodical coupling is compared to a design with an intermediate dielectric coupling element to reduce the frequency dependence. Radiation from the waveguide bends can be reduced significantly by inserting absorber materials at critical points. Experimental results for a-3 dB coupler are also given.     

Image guide couplers with isotropic and anisotropic coupling elements

Among other waveguide elements directional couplers are required in integrated millimeterwave circuits in image guide technique. Hereby an I-guide is used which consists of a dielectric slab between two conducting plates on which the electric field is perpendicularily. Flat coupling behaviour and better isolation can be reached by use of a dielectric coupling element and absorber materials. Thereby the frequency dependence is reduced significantly. Further the coupling can be steered by an additional premagnetized ferrite slab. In this way switched couplers can be realized.     

Systematic investigations of anthocyanin–metal interactions by Raman spectroscopy

The FT‐Raman spectra of the chloride salts of pelargonidin‐3‐glucoside, cyanidin‐3‐glucoside and delphinidin‐3‐glucoside, their structures at pH 5.0 and their interaction with aluminium and ferric ions are presented for the first time and discussed with regard to their spectroscopic response. Two marker bands at approximately 1510 and 1330/1350 cm⁻¹ and one band at approximately 1330/1350 cm⁻¹ were identified being characteristic for the formation of ferric and aluminium chelates, respectively, of cyanidin‐3‐glucoside and delphinidin‐3‐glucoside. In contrast, pelargonidin‐3‐glucoside, exhibiting one single hydroxyl group in the B‐ring, did not form metal chelates, which could be clearly demonstrated by missing marker bands. The formation of anthocyanin–metal chelates was also verified in model systems containing commercial sugar beet pectin and a pectic polysaccharide fraction isolated thereof, respectively. In addition, the absence of anthocyanin–metal chelates in systems prepared with citrate buffer was confirmed, and the effects of low and high methoxylated citrus pectins on chelate formation were studied. Copyright © 2012 John Wiley & Sons, Ltd.     

250 W end-pumped Nd:YAG laser with direct pumping into the upper laser level

A high-power longitudinally pumped Nd:YAG laser using direct pumping into the upper laser level is demonstrated. With an absorbed pump power of 438 W an output power of 250 W was realized, which results in an optical-to-optical efficiency of 57%. To the best of our knowledge, this is the first demonstration of a high-output power 885 nm pumped laser design.     

Assessment of mitral regurgitation by magnetic resonance imaging

To evaluate the potential of magnetic resonance imaging (MRI) in detection and quantification of mitral regurgitation, 26 pts. with echocardiographically or angiographically documented mitral regurgitation were examined using a 0.5 Tesla superconducting magnet. In each patient a multislice-multiphase study in a sagittal-coronal double angulated projection (four-chamber view equivalent) was performed to assess left and right ventricular volumes, ejection fraction and regurgitant fraction. Additionally a blood flow sensitive cine-study (fast field echo: FFE) was done to visualize direction and area of regurgitant jet. MRI data were compared with quantitative and qualitative assessment of mitral regurgitation by angiography, 2D echocardiography, Doppler sonography and color flow mapping. Using the FFE mode MRI was able to detect the regurgitant jet as a typical signal loss within the left atrium in all patients. The ratio of regurgitant jet area/left atrium area as determined by MRI showed a correlation with a comparable ratio from color Doppler sonography of R = 0.87 (p < 0.001). There was also good agreement in semiquantitative grading of mitral regurgitation between MRI and angiography (R = 0.77, p < 0.001). The determination of left and right ventricular stroke volume allowed the calculation of the regurgitant fraction, which showed a correlation with invasively determined regurgitation fraction of R = 0.84 (p < 0.001). These data provide additional information that MRI may be useful as a noninvasive technique to detect and quantify mitral regurgitation.     

Aberrant default mode network in subjects with amnestic mild cognitive impairment using resting-state functional MRI

Amnestic mild cognitive impairment (aMCI) is a syndrome associated with faster memory decline than normal aging and frequently represents the prodromal phase of Alzheimer's disease. When a person is not actively engaged in a goal-directed task, spontaneous functional magnetic resonance imaging (fMRI) signals can reveal functionally connected brain networks, including the so-called default mode network (DMN). To date, only a few studies have investigated DMN functions in aMCI populations. In this study, group-independent component analysis was conducted for resting-state fMRI data, with slices acquired perpendicular to the long axis of the hippocampus, from eight subjects with aMCI and eight normal control subjects. Subjects with aMCI showed an increased DMN activity in middle cingulate cortex, medial prefrontal cortex and left inferior parietal cortex compared to the normal control group. Decreased DMN activity for the aMCI group compared to the normal control group was noted in lateral prefrontal cortex, left medial temporal lobe (MTL), left medial temporal gyrus, posterior cingulate cortex/retrosplenial cortex/precuneus and right angular gyrus. Although MTL volume difference between the two groups was not statistically significant, a decreased activity in left MTL was observed for the aMCI group. Positive correlations between the DMN activity and memory scores were noted for left lateral prefrontal cortex, left medial temporal gyrus and right angular gyrus. These findings support the premise that alterations of the DMN occur in aMCI and may indicate deficiencies in functional, intrinsic brain architecture that correlate with memory function, even before significant MTL atrophy is detectable by structural MRI.     

Method for measuring chemical diffusion coefficients in solids

Experiments were performed with temperature programmed desorption of hydrogen and deuterium adsorbates on small platinum spheres. Beyond the expected desorption peak of these adsorbates at around 300 K sample temperature an additional desorption peak at higher temperatures was observed. This additional peak is explained by the diffusion of hydrogen or deuterium atoms from the inside of the spheres to their surfaces with final desorption from these surfaces. The visibility of this second high temperature desorption peak is supported by a small diameter of the platinum spheres. Platinum spheres with diameters around 64 μm were used. The sample temperature at which the second peak was observed depends on the parameters: diameter of the platinum spheres, heating rate of the sample and chemical diffusion coefficient of hydrogen or deuterium in platinum. A theory, which assumes that the chemical diffusion coefficient can be described with an Arrhenius ansatz, was developed to simulate the occurrence of the second peak. The combination of these kinds of experiments with the theory gives a method to measure chemical diffusion coefficients. This method can be called temperature programmed diffusion. At 510 K sample temperature the diffusion coefficient 1.61×10⁻¹² m²/s of hydrogen in platinum and the diffusion coefficient 1.40×10⁻¹² m²/s of deuterium in platinum was measured.     

Neutral Hexacoordinate Phosphorus: Substituted Carbodiimide Phosphoranes and Other Chelated Substituted 2-Pyridine Derivatives

Abstract

A series of neutral hexacoordinate λ⁶ phosphorus compounds of the general formula X_4-n(CF₃)_nPN(R)C(C1)N(R) (n = 0, 1, 2, 3; R = cyclohexyl, isopropyl) has been prepared. The parent compounds are obtained by “insertion” of carbodiimide into the P-C1 bond of λ⁵-chlorophosphorane. Substituted pyridines also react readily with λ⁵ chloro and fluoro phosphoranes to form 2-methylamino, thio and oxopyridine chelates of the form X₄P(Epy) (E = 0, NMe and S; X = F, Cl) in which the phosphorus achieves six coordination through acceptance of the pyridine nitrogen. Selected reactions and the fluxional behavior of the λ⁶ systems are discussed.