CAD of Millimeter Wave Y-Junction Circulators with a Ferrite Sphere

A gradient optimization technique along with a definition of cost function is applied to the CAD of the circulator with a magnetized ferrite sphere for millimeter wave communications. A three-dimensional Finite-Difference Time-Domain (FDTD) approach for the analysis of this ferrite sphere based microstrip circulator is presented. The topology of the structure is enforced at each step of optimization and its physical dimensions are used as optimization variables. The cost function is defined using location of zeros and poles of the circulator's transmission, isolation, and reflection functions. Numerical tests show that the optimization process converges from an arbitrarily selected starting point with the new definition of the cost function.     

Nanotechnology Standards Initiatives at the IEEE

Journal of Nanoparticle Research -     

Synthesis and ion‐sensing phenomena of two new helical conjugated oligomers containing 1,10‐phenanthroline and oligo‐alkylthiophene

Two new 1,10‐phenanthroline (Phen) containing conjugated oligomers, oligo‐3,8‐bis(4‐octylthiophene‐2‐yl)‐1,10‐phenanthroline) (PDTPh) and oligo‐3,8‐bis‐(4‐octyl‐5‐(4‐ctylthiophene‐2‐yl)thiophene‐2‐yl)‐1,10‐phenanthroline) (PTTPh), as well as their corresponding monomers (OTPhOT and OTOTPhOTOT) were prepared and their metal ion‐sensing properties were investigated. The oligomers showed high thermal stability, good proccessibility, and gave varied color when reacted with different metal ions. Oligomers also showed distinct responses toward metal ions when compared with their corresponding monomers, suggesting that the ionochromic responses were determined by not only the coordinating ability of Phen unit but also the conformation of oligomer chains. Moreover, the differences in the ion‐sensing behaviors between OTPhOT and OTOTPhOTOT also suggested that the coordination ability of Phen depends on its substituents. The oligo‐alkylthiophene moieties in PDTPh and PTTPh acted as spacers to reorganize the conformation of the oligomer chains, as well as the electron donating groups to adjust the coordination ability of the Phen. These findings provide a clue for designing Phen‐containing ion‐sensors for specified ion‐sensing applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1586–1597, 2008     

Microwave switching behaviors of Fe/Ag/Fe/Ag epitaxial films

In this study, Fe/Ag/Fe/Ag ferromagnetic structures were epitaxially grown on a GaAs(1 0 0) substrate. Using the Network Analyzer (Agilent 8510C), FMR (ferromagnetic resonant) signals were observed in samples as the in-plane magnetic field was applied to either hard- or easy-axes. Of interest was that our sample demonstrated a FMR-switching behavior in hard-axis but not in easy-axis. The detecting data showed that the switch magnetic field was much smaller than what has been stated previously in Fe/Cu/Fe systems by other laboratories. In addition to the frequency switch in FMR, we also observed a magnetic reversal behavior in its M–H curve. Data presented that both of the FMR and magnetic reverse took place in the same direction (hard-axis).     

A heterocyclic analog of leucine-enkephalin

A series of di-, tri-, tetra- and pentapeptide analogs of leucine-enkephalin have been prepared in which the initial tyrosinylglycine fragment has been replaced by the 5,6-dihydro-5,5-dimethyl-2-oxo-3-phenyl-1(2H)-pyrazineacetic acid moiety.     

1-bromo-2-chlorocyclopropene--A new cycloproparene synthon. Synthesis of 1H-Cyclopropa[b]phenanthrene

Treatment of 1-bromo-2,2-dichloro(trimethylsilyl)cyclopropane (2) with tetra-$\text{n}$-butylammonium fluoride in tetrahydrofuran yields 1-bromo-2-chlorocyclopropene (1). 1H-Cyclopropa[b]phenanthrene (3) can be prepared by aromatization of the Diels-Alder adduct of 1 and 1,2-dimethylene-3,5,6,7,8,9-hexahydronaphthalene (6) using DDQ followed by potassium $\text{t}$-butoxide in tetrahydrofuran.     

Polydispersity effects on diffusion in polymers: Concentration profiles of d-polystyrene measured by forward recoil spectrometry

Forward recoil spectrometry is shown to be a useful technique for measuring diffusion of d-polymer chains in h-polymer melts. Concentration profiles of a deuterated diffusing species may be determined with a depth resolution of 80 nm and a sensitivity of 0.1 vol % d-polymer in h-polymer. Consequently diffusion coefficients as small as 10^?16 cm²/s can be readily measured. If polymer chains diffuse by a reptation mechanism, the concentration profile ø(x) of diffusing polydisperse polymer should be quite different from ø_m(x), the Fickian solution, which one obtains for monodisperse polymer. This idea was tested by measuring ø(x) of polydisperse d-polystyrene (d-PS) diffusing into h-PS. The results are in excellent agreement with the ø(x) predicted from the reptation model and the experimentally determined molecular weight distribution.     

Spatial distribution of sodium dimers generated by a laser microprobe

Spatial mapping of sodium dimers and sodium atoms produced in a laser-generated plume is reported. The distributions support a sputtering mechanism for atom production.     

Dimensional reduction of superstring models

Compactification of ten-dimensional supergravity on Calabi-Yau manifolds (as recently proposed by Candelas, Horowitz, Strominger, and the author) gives n=1 supergravity theories in four dimensions. This paper is devoted to working out the Kähler potential and superpotential which arise.