Broadband double-layered coplanar patch antennas with adjustable CPW feeding structure

In this paper, we have presented the double-layered coplanar patch antennas of enhanced impedance bandwidth and adjustable conductor-backed coplanar waveguide feed lines. The proposed structure retains the advantage of laying the coplanar patch and coplanar waveguide (CPW) feed line on the same surface, which makes direct integration with other devices easier. In addition, the substrate thickness of the radiating patch can be adjusted to achieve a wider impedance bandwidth while the dimensions of the CPW feed line are kept unchanged. Simulation has been done by using commercial electromagnetic (EM) simulation software. Four testing antennas, which have centre frequency at about 10 GHz, were designed. The four testing antennas had the same total thickness, but different thickness combinations. From the measured return loss, gain, and radiation patterns of the antennas, it was demonstrated that different thickness combinations do not affect the characteristics of the antennas seriously. Therefore, the dimensions of the CPW feed structure of the antennas can be adjusted individually and can be selected for different applications

J/Psi and Psi' Suppression in Hadronic Matter

We present a microscopic calculation of the breakup cross sections of $J/\psi$ and $\psi'$ on pions and nucleons as a function of the kinetic energy. These cross sections are used for the investigation of the $J/\psi$ to continuum and $\psi'/J/\psi$ ratios in ultrarelativistic heavy ion collisions. The contribution of produced comoving pions to the $\psi'/J/\psi$ signal is calculated. While this model can account for the data, the uncertainties in the parameter values do not allow to exclude the possibility of additional sources for charmonium absorption, like a resonance gas or the quark gluon plasma.Comment: LaTeX, 6 pages including 2 EPS files, to be published in Prog. Part. Nucl. Phys., [email protected]

Direct Observation of Non-Monotonic dx2-y2-Wave Superconducting Gap in Electron-Doped High-Tc Superconductor Pr0.89LaCe0.11CuO4

We performed high-resolution angle-resolved photoemission spectroscopy on electron-doped high-Tc superconductor Pr0.89LaCe0.11CuO4 to study the anisotropy of the superconducting gap. The observed momentum dependence is basically consistent with the dx2-y2-wave symmetry, but obviously deviates from the monotonic dx2-y2 gap function. The maximum gap is observed not at the zone boundary, but at the hot spot where the antiferromagnetic spin fluctuation strongly couples to the electrons on the Fermi surface. The present experimental results unambiguously indicate the spin-mediated pairing mechanism in electron-doped high-Tc superconductors.Comment: 4 pages, 4 figure

Scanning tunneling microscopy and spectroscopy studies of graphite edges

We studied experimentally and theoretically the electronic local density of states (LDOS) near single step edges at the surface of exfoliated graphite. In scanning tunneling microscopy measurements, we observed the $(\sqrt{3} \times \sqrt{3}) R 30^{\circ}$ and honeycomb superstructures extending over 3$-$4 nm both from the zigzag and armchair edges. Calculations based on a density-functional derived non-orthogonal tight-binding model show that these superstructures can coexist if the two types of edges admix each other in real graphite step edges. Scanning tunneling spectroscopy measurements near the zigzag edge reveal a clear peak in the LDOS at an energy below the Fermi energy by 20 meV. No such a peak was observed near the armchair edge. We concluded that this peak corresponds to the "edge state" theoretically predicted for graphene ribbons, since a similar prominent LDOS peak due to the edge state is obtained by the first principles calculations.Comment: 4 pages, 6 figures, APF9, Appl. Surf. Sci. \bf{241}, 43 (2005

Photoredox-Mediated Metal-Free C–h Alkylation And Dual Catalysis

Over the past decade, a resurgence of interest in photo-induced electron transfer has resulted in a new class of organic transformations. The ability to harness over 60 kcal/mol of visible light energy to activate redox-labile substrates—via the intermediacy of a photoredox catalyst—has enabled reactions under extraordinarily mild conditions compared to alternative two-electron modes of activation. Recent research efforts have broadened the scope of trifluoroborate coupling partners, employed 1,4-dihydropyridines (DHPs) in mono- and dual-catalytic manifolds, and accessed new chemical space via C–H functionalization pathways. First, the development of alkyltrifluoroborates as latent radicals for C–H alkylation of heteroarenes under photocatalytic conditions is described. Notably, the catalytic generation of carbon-centered radicals and the BF3 byproduct accomplishes a regioselective and atom-economical approach to the classical Minisci reaction. Subsequent reports disclose DHPs as unique radical precursors that do not require the use of a photocatalyst to effect a single-electron oxidation. Instead, DHPs are oxidized in the presence persulfate, facilitated by their low oxidation potentials. Furthermore, photoredox/Ni dual catalysis protocols have been developed to overcome several inherent limitations of palladium-catalyzed cross-couplings [i.e., forcing reaction conditions, limited scope for C(sp3)–C(sp2) bond formation] by invoking a single-electron transmetalation pathway. Within the area of photoredox/Ni catalysis, a library of natural and unnatural aryl chromanones are accessed from the corresponding trifluoroboratochromanones and aryl bromides. In an effort to expand the radical toolbox by utilizing feedstock chemicals (e.g., aldehydes) to access radicals inspired the exploration of DHPs as radical partners in the dual catalytic paradigm. Exploiting the one-step procedure to access highly functionalized DHPs, a library of monosaccharide DHPs were synthesized and employed in the dual catalytic cross-coupling procedure with aryl bromides. In summary, the mild, photoredox-mediated C–H alkylation of heteroarenes represents a late-stage functionalization strategy to rapidly access highly functionalized motifs. Additionally, photoredox/Ni dual catalysis has enabled the modular synthesis of functionalized aryl chromanones and monosaccharides. Throughout these reported studies, it is clear the controlled and catalytic nature of photoredox catalysis enables previously challenging transformations and is primed for significant advancements in the near future