Specific and unspecific interactions in polar fluids in view of wideband dielectric far-infrared spectra

A simple molecular analytical theory of dielectric relaxation in strongly polar fluids is considered in terms of a semi- phenomenological approach. Theoretical spectra epsilon(v), a(v) of complex permittivity and absorption coefficient are fully determined by a form of intermolecular potential well, in which a dipole reorients. In a recent publication by VI. Gaiduk, O.F. Nielsen, and T.S. Perova [J. Molliq 95 (1002) 1-25] the wideband spectra of liquid H2O and D2O were described in terms of a composite model comprising the rectangular and the cosine squared potential wells. Much better results are achieved in this work, where the rectangular well is replaced by a well with a rounded bottom termed the hat-curved well. The spectrum of the auto-correlation function (ACF) is calculated for such a potential. The proposed theory of a composite model, comprising hat-curved and parabolic wells, is applied for liquid water. This model is capable for describing the Debye relaxation region, the second relaxation region in the submillimeter wavelength range, and the far infra-red (FIR) e(v), a(v) spectra, where an intense librational band and an additional weak band are placed, respectively, near 700 cm(-1) and 200 cm(-1). The latter band reflects the features of so-called specific (viz. directly related to H-bonds) interactions and the former band reflects the features of unspecific interactions. The physical mechanisms connected with these types of interactions are discussed in terms of two relevant types of water structure (types of molecular rotation). The proposed theory is also applied to a non-associated liquid in terms of one hat-curved potential well. (C) 2004 Elsevier B.V. All rights reserved.

Near-field distribution of optical transmission of periodic subwavelength holes in a metal film

Optical transmission of a two-dimensional array of subwavelength holes in a metal film has been numerically studied using a differential method. Transmission spectra have been calculated showing a significant increase of the transmission in certain spectral ranges corresponding to the excitation of the surface polariton Bloch waves on a metal surface with a periodic hole structure. Under the enhanced transmission conditions, the near-field distribution of the transmitted light reveals an intensity enhancement greater than 2 orders of magnitude in localized (similar to 40 nm) spots resulting from the interference of the surface polaritons Bragg scattered by the holes in an array.

State-Selective Photodissociation Dynamics of Formaldehyde: Near Threshold Studies of the H+HCO Product Channel

The laser-induced photodissociation of formaldehyde in the wavelength range 309<λ<330nm 309<λ<330nm has been investigated using H (Rydberg) atom photofragment translational spectroscopy. Photolysis wavelengths corresponding to specific rovibronic transitions in the A ˜ A 2 1 ←X ˜ A 1 1 ÃA21←X̃A11 2 1 0 4 3 0 201403 , 2 2 0 4 1 0 202401 , 2 2 0 4 3 0 202403 , 2 3 0 4 1 0 203401 , and 2 1 0 5 1 0 201501 bands of H 2 CO H2CO were studied. The total kinetic energy release spectra so derived can be used to determine partial rotational state population distributions of the HCO cofragment. HCO product state distributions have been derived following the population of various different N K a NKa levels in the A ˜ A 2 1 ÃA21 2 2 4 3 2243 and 2 3 4 1 2341 states. Two distinct spectral signatures are identified, suggesting competition between dissociation pathways involving the X ˜ A 1 1 X̃A11 and the a ˜ A 2 3 ãA23 potential energy surfaces. Most rovibrational states of H 2 CO(A ˜ A 2 1 ) H2CO(ÃA21) investigated in this work produceH+HCO(X ˜ A ′ 2 ) H+HCO(X̃A′2) photofragments with a broad kinetic energy distribution and significant population in high energy rotational states of HCO. Photodissociation via the A ˜ A 2 1 ÃA21 2 2 4 3 2243 1 1,1 11,1 (and 1 1,0 11,0 ) rovibronic states yields predominantly HCO fragments with low internal energy, a signature that these rovibronic levels are perturbed by the a ˜ A 2 3 ãA23 state. The results also suggest the need for further careful measurements of the H+HCO H+HCO quantum yield from H 2 CO H2CO photolysis at energies approaching, and above, the barrier to C–H bond fission on the a ˜ A 2 3 ãA23 potential energy surface.

Two-layer mm-wave FSS of linear slot elements with low insertion loss

The performance of a very low loss frequency selective surface (FSS) comprising two air spaced planar arrays of linear slot elements is reported. The beamsplitter generates a low loss passband response with a very sharp transmission roll-off with frequency. Simulated and measured results in the 30 GHz and 300 GHz wavebands are used to quantify the performance improvement compared to a conventional multilayer dielectrically backed conducting ring FSS. The paper also discusses the effect of the array dimensions on the passband width and filter roll-off rate.

Comparative analysis of the DC performance of DG MOSFETs on highly-doped and near-intrinsic silicon layers

A comparison of dc characteristics of fully depleted double-gate (DG) MOSFETs with respect to low-power circuit applications and device scaling has been performed by two-dimensional device simulation. Three different DG MOSFET structures including a conventional N+ polysilicon gate device with highly doped Si layer, an asymmetrical P+/N+ polysilicon gate device with low doped Si layer and a midgap metal gate device with low doped Si layer have been analysed. It was found that DG MOSFET with mid-gap metal, gates yields the best dc parameters for given off-state drain leakage current and highest immunity to the variation of technology parameters (gate length, gate oxide thickness and Si layer thickness). It is also found that an asymmetrical P+/N+ polysilicon gate DG MOSFET design offers comparable dc characteristics, but better parameter immunity to technology tolerances than a conventional DG MOSFET. (C) 2004 Elsevier Ltd. All rights reserved.

Near-infrared spectroscopy of PKS 1549-79: a protoquasar revealed?

We present a near-infrared (near-IR) spectrum of the nearby radio galaxy PKS 1549-79 (z = 0.153). These data were taken with the aim of testing the idea that this object contains a quasar nucleus that is moderately extinguished, despite evidence that its radio jet points close to our line of sight. We detect broad Paalpha emission (FWHM 1745 +/- 40 km s(-1)), relatively bright continuum emission, and a continuum slope consistent with a reddened quasar spectrum (3.1 <A(V) <7.3), all emitted by an unresolved point source. Therefore we conclude that we have, indeed, detected a hidden quasar nucleus in PKS 1549-79. Combined with previous results, these observations are consistent with the idea that PKS 1549-79 is a young radio source in which the cocoon of debris left over from the triggering events has not yet been swept aside by circumnuclear outflows.