Contents of Volume 24 (2003)

Volume Contents

Contents of Volume 23 (2003)     

Stable model categories are categories of modules

A stable model category is a setting for homotopy theory where the suspension functor is invertible. The prototypical examples are the category of spectra in the sense of stable homotopy theory and the category of unbounded chain complexes of modules over a ring. In this paper we develop methods for deciding when two stable model categories represent ‘the same homotopy theory’. We show that stable model categories with a single compact generator are equivalent to modules over a ring spectrum. More generally stable model categories with a set of generators are characterized as modules over a ‘ring spectrum with several objects’, i.e., as spectrum valued diagram categories. We also prove a Morita theorem which shows how equivalences between module categories over ring spectra can be realized by smashing with a pair of bimodules. Finally, we characterize stable model categories which represent the derived category of a ring. This is a slight generalization of Rickard's work on derived equivalent rings. We also include a proof of the model category equivalence of modules over the Eilenberg-Mac Lane spectrum HR and (unbounded) chain complexes of R-modules for a ring R.     

Photoemission studies of clean and oxygen-covered Pt 6(111) × (100)

Employing the enhanced sensitivity obtained by using synchrotron radiation near the Cooper minimum for the 5d valence electrons, we have located the oxygen 2p and 2s levels for oxygen chemisorbed on a Pt 6(111) × (100) crystal. We find the oxygen 2p level located ?6 eV with a FWHM of 3 eV and the 2s at ?21.6 eV. A factor of four difference in saturation coverage is measured between temperatures of 300 and 120 K, but the position and width of the 2p level is independent of temperature. We observe also the 1b₁ orbital of weakly adsorbed H₂O molecules, which has pure O 2p parentage; from the intensity of this orbital, we are able to suggest why it is difficult to observe the oxygen 2p signal at low photon energies. In addition, we note a strong preferential attenuation in the Pt states near E_f for the adsorbed H₂O in spite of the weak nature of the bond.     

On stable geometries

Within the concept of projective lattice geometry we are considering the class of stable geometries which have also been introduced in [14]. The investigation of their basic properties will result in fundamental structure theorems which especially give a lattice-geometric characterization of free left modules of rank 6 over proper right Bezout rings of stable rank 2. This yields a proper generalization of previous results of ours.     

Perfect imaging through a disordered waveguide lattice

It is experimentally demonstrated that perfect imaging is possible in disordered wave guiding media, provided that the disorder is off-diagonal, i.e., that only the spacing varies randomly between the otherwise identical lattice sites. On-diagonal disorder or Kerr nonlinearity destroys the imaging.     

Laser-assisted one-step fabrication of homogeneous glass–silver composite

Glass doped with silver ions was fabricated using a dry technique and then irradiated at the scanning speed of 14 mm?s^?1 using a nanosecond pulsed Nd:YVO₄ laser operating at 355?nm. This led to the spatially selective, one-step precipitation of silver particles and fabrication of a homogeneously structured optical composite material: glass?Csilver composite. The optical and structural properties of such composite material can be designed at will, which could have potential impact on light/plasmon wave and sensing technologies, optoelectronics, and surface enhanced Raman spectroscopy.     

Systematic parametric investigation on the CVD process of polysiloxane nano- and microstructures

Amorphous polysiloxane nano- and microstructures with different shapes can be synthesized from trifunctional organosilane precursors. In the present study, various polysiloxane nano- and microstructures have been produced via a chemical vapor deposition process using ethyltrichlorosilane as precursor. The structure formation and shape are the result of a delicate interplay between temperature, absolute amount of water, and relative humidity. The impact of these reaction parameters during a chemical vapor deposition process has been examined. Experiments have been performed to find a correlation between the reaction conditions and the final shape. Scanning electron microscopy data show that different structures like polysiloxane microrings, microrods, sprouts, nanofilaments, and mixtures of them can be synthesized depending on the reaction conditions. Furthermore, the in-depth comparison of the nanofilament diameters illustrates the dominating influence of relative humidity on structure formation. There is a general trend that at a higher value of relative humidity, structures with a larger diameter are formed independent from the temperature. Here, we clearly differentiate between relative humidity as major and absolute amount of water and temperature as minor important adjusting screws defining the thickness and shape of the resulting nano- and microstructures. Based on these observations, we proof the mechanism of the initial step of structure formation. It is shown that nano- and micro-sized water droplets formed on the substrate surface are likely to act as starting points for structure formation. All results described here strongly confirm the recently published droplet assisted growth and shaping mechanism.     

A study of fused silica micro/nano patterning by focused-ion-beam

A dual-beam scanning electron microscopy (SEM)/focused-ion-beam (FIB) system was used to pattern fused silica substrates coated with a 15 nm thin Cr layer. The dimensions of fabricated features together with their surface morphology and profiles were investigated by SEM and atomic force microscopy (AFM). The study demonstrated that with the increase of the ion beam fluence the sputtering rate of the fused silica decreased non-linearly. Also, it was found that initially the sputtering rate increased with the increase of the beam current, after reaching a maximum value, it started decreasing when further beam current increment was performed. Compared with unprocessed areas, the surface finish of the features fabricated by FIB exhibited a significant improvement, and the ion fluence influence on the surface roughness of trenches with low aspect ratios could be considered as negligible. Using a fine beam probe, nano-gratings in the form of grooves with a width down to 54 nm and an aspect ratio higher than three were fabricated. The study showed that FIB machining could be an alternative technology to e-beam lithography for producing fused silica templates for UV nanoimprinting.     

Study of 19Na at SPIRAL

The excitation function for the elastic-scattering reaction p( ¹⁸Ne, p) ¹⁸Ne was measured with the first radioactive beam from the SPIRAL facility at the GANIL laboratory and with a solid cryogenic hydrogen target. Several broad resonances have been observed, corresponding to new excited states in the unbound nucleus ¹⁹Na. In addition, two-proton emission events have been identified and are discussed.     

Closure modeling in bridging regions of variable-resolution (VR) turbulence computations

Optimal utilization of computational resources mandates spatio-temporal variation in resolution for computing complex engineering flows. Closure modeling in regions bridging between different resolutions is rendered difficult due to changing interactions between resolved and unresolved fields. We develop a closure model for the bridging region based on energy conservation principles. Then we proceed to provide a proof of concept in decaying isotropic turbulence with temporally varying resolution. The simplicity of the flow permits a thorough examination of various aspects of the proposed closure not feasible in more complex flows. The results demonstrate the potential promise of the approach, but more validation studies need to be performed.While the present development is in the context of partially averaged Navier–Stokes (PANS) method, the closure principle should apply for other variable-resolution (VR) approaches.