Chemical abundances in the inner 5 kpc of the Galactic disk

High-resolution, high signal-to-noise spectral data are presented for four young B-type stars lying towards the Galactic Centre. Determination of their atmospheric parameters from their absorption line profiles, and uvby photometric measurement of the continua indicate that they are massive objects lying slightly out of the plane, and were probably born in the disk between 2.5-5 kpc from the Centre. We have carried out a detailed absolute and differential line-by-line abundance analyses of the four stars compared to two stars with very similar atmospheric parameters in the solar neighbourhood. The stars appear to be rich in all the well sampled chemical elements (C, N, Si, Mg, S, Al), except for oxygen. Oxygen abundances derived in the atmospheres of these four stars are very similar to that in the solar neighbourhood. If the photospheric composition of these young stars is reflective of the gaseous ISM in the inner Galaxy, then the values derived for the enhanced metals are in excellent agreement with the extrapolation of the Galactic abundance gradients previously derived by Rolleston et al. (2000) and others. However, the data for oxygen suggests that the inner Galaxy may not be richer than normal in this element, and the physical reasons for such a scenario are unclear.

Compact ridge waveguide filter with parallel and series-coupled resonators

A novel 3rd-order compact E-plane ridge waveguide filter is presented. Miniaturization is achieved upon introducing a configuration of parallel-coupled E-plane ridge waveguide resonators. Furthermore, the proposed filter allows for transmission zeros at finite frequencies. Fabrication simplicity and mass producibility of standard E-plane filters is maintained. The numerical and experimental results are presented to validate the proposed configuration. A miniaturisation factor of 2 and very sharp upper cutoff are achieved. 2005 Wiley Periodicals, Inc.

Novel periodically loaded ridged waveguide resonators

Novel periodically loaded E-plane waveguide resonators are presented in this paper. The proposed resonators make use of the slow-wave effect in order to achieve significantly increased loaded Q values for resonators of constant volume, as compared to their homogeneous counterparts, without introducing any complexity in the fabrication process. Numerical and experimental results are presented to validate the argument. (C) 2003 Wiley Periodicals, Inc.

Novel periodically loaded multilayer resonators

In this paper novel 3D periodic multilayer structures are investigated in MIC technology, and a periodically loaded multilayer waveguide resonant structure is proposed. This is a very compact structure and still maintains simple fabrication process. The resonator is designed at 10 and 28 GHz. The simulated results of this resonator, which is obtained from commercial FEM software package HFSS, are confirmed by experimental results. The experiments are based oil the same resonator structure, only at 10 GHz. By modifying the conventional waveguide resonator, with the proposed structure, a minimum 30% shorter resonator can be achieved, which is very important at filter applications. (C) 2002 Wiley Periodicals, Inc.

Chemical evolution of protoplanetary disks - the effects of viscous accretion, turbulent mixing and disk winds

We calculate the chemical evolution of protoplanetary disks considering radial viscous accretion, vertical turbulent mixing, and vertical disk winds. We study the effects on the disk chemical structure when different models for the formation of molecular hydrogen on dust grains are adopted. Our gas-phase chemistry is extracted from the UMIST Database for Astrochemistry (Rate06) to which we have added detailed gas-grain interactions. We use our chemical model results to generate synthetic near- and mid-infrared local thermodynamic equilibrium line emission spectra and compare these with recent Spitzer observations. Our results show that if H2 formation on warm grains is taken into consideration, the H2O and OH abundances in the disk surface increase significantly. We find that the radial accretion flow strongly influences the molecular abundances, with those in the cold midplane layers particularly affected. On the other hand, we show that diffusive turbulent mixing affects the disk chemistry in the warm molecular layers, influencing the line emission from the disk and subsequently improving agreement with observations. We find that NH3, CH3OH, C2H2, and sulfur-containing species are greatly enhanced by the inclusion of turbulent mixing. We demonstrate that disk winds potentially affect the disk chemistry and the resulting molecular line emission in a manner similar to that found when mixing is included.

Quality factor of E-plane periodically loaded waveguide resonators and filter applications

The quality factor of microwave resonators miniaturised by virtue of periodic loading is assessed. Five X-band resonators in E-plane technology with different miniaturisation factors have been designed to resonate at approximately the same frequency. The loaded quality factor is extracted from the fractional bandwidth and subsequently employed to estimate the unloaded quality factor. The study reveals that the unloaded quality factor drops approximately linearly with the miniaturisation. Subsequently design guidelines for E-plane filters with periodically loaded resonators are provided by means of an example involving a fifth-order filter. Full-wave simulated and experimental results are presented to validate the study.

Quantum ground state of self-organized atomic crystals in optical resonators

Cold atoms, driven by a laser and simultaneously coupled to the quantum field of an optical resonator, may self-organize in periodic structures. These structures are supported by the optical lattice, which emerges from the laser light they scatter into the cavity mode and form when the laser intensity exceeds a threshold value. We study theoretically the quantum ground state of these structures above the pump threshold of self-organization by mapping the atomic dynamics of the self-organized crystal to a Bose-Hubbard model. We find that the quantum ground state of the self-organized structure can be the one of a Mott insulator, depending on the pump strength of the driving laser. For very large pump strengths, where the intracavity-field intensity is maximum and one would expect a Mott-insulator state, we find intervals of parameters where the phase is compressible. These states could be realized in existing experimental setups.