Various Scale Levels of the Gel-to-Glass Transformation

The gel-to-glass transition in SiO₂ xerogels prepared by inorganic sol-gel synthesis was studied. The evolution of the molecular structure is traced using the infrared and lowfrequency Raman spectroscopy methods. The elastic moduli of the samples as well as the pore wall moduli at various stages of heat treatment are determined from the data on Brillouin scattering. The formation of monolithic glass on the macroscopic level manifests itself within a narrow temperature range by the dramatic increase of Young's modulus to the accepted value for fused silica. This phenomenon coincides with structural transformations on the molecular scale: (i) the definite correlation radius (the long-range order sphere) appears; (ii) local distortions of the silica network relax. The presence of structural defects influences the kinetics of vitreous SiO₂ formation during xerogel heat treatment.     

Learning rules of a card game from video

This paper presents a framework for automatically learning rules of a simple game of cards using data from a vision system observing the game being played. Incremental learning of object and protocol models from video, for use by an artificial cognitive agent, is presented. iLearn??a novel algorithm for inducing univariate decision trees for symbolic datasets is introduced. iLearn builds the decision tree in an incremental way allowing automatic learning of rules of the game.     

Standardized tests fail to assess the effects of antibiotics on environmental bacteria

Pharmaceuticals are designed and used because of their specific biological effects. Over the past decade, compounds from various classes of pharmaceuticals have been detected in the environment. Concern has grown about the adverse effects pharmaceuticals in the environment might potentially have on human and ecological health. A sound risk assessment is therefore urgently needed for pharmaceuticals. Standardized tests for assessing the effects of chemicals on environmental organisms are widely used for this purpose. However it is questionable whether classical standardized tests give reliable data needed for environmental risk assessment. In this study we investigated the suitability of the respiration inhibition test OECD 209 for the assessment of the effects of antibiotics, disinfectants and cytotoxics on sewage sludge bacteria. We found that inhibition concentrations can strongly depend on the test period and the type of compound. We conclude that tests to assess the effects of pharmaceuticals on environmental organisms such as bacteria have to be evaluated before their results can be used in environmental risk assessment.     

DC and AC characteristics of delta-doped GaAs FET

Molecular-beam-epitaxy-grown GaAs field-effect transistors (FETs) using a delta-doped channel are discussed. FETs having gate lengths of 1.3 μm showed transconductances as high as 290 mS/mm at a current density of 200 mA/mm. The measured f_T was 14.5 GHz and the extracted f_max was 30 GHz. These results are the best reported in a FET with this material structure having a delta-doped channel     

DC and RF performance of GaAs MESFET fabricated on silicon substrate using epitaxial lift-off technique

GaAs MESFETs have been fabricated on a silicon substrate using a molecular beam epitaxy grown film detached from its growth substrate and attached on a silicon substrate covered with a dielectric. The device processing is done on the silicon substrate. The MESFETs exhibit I/sub DSS/=130 mA/mm, g/sub m/=135 mS/mm and for 1.3 mu m gate length unity current gain cut-off frequency f/sub T/ of 12 GHz. Excellent device isolation with subpicoampere leakage currents is obtained.<>     

Monolithic multiple wavelength surface emitting laser arrays

A two-dimensional (2-D) surface emitting laser array emitting 140 unique, nonredundant, uniformly separated, single-mode wavelengths in the 980-nm regime is described. The wavelength separation between neighboring lasers is as small as 0.3 nm. A large total wavelength span of 43 nm was obtained without compromising the performance of the lasers. All 140 lasers have nearly the same threshold currents, voltages, and resistances. The techniques used are generic and can be readily extended to both longer and shorter wavelength lasers. The authors also report the first wavelength division multiplexing system experiment using part of this laser array. A BER (bit-error ratio) of 10 ^-9 at 155 Mb/s was obtained with simultaneous operation of four lasers at a wavelength separation of 1.5 nm. Negligible optical and electrical crosstalk was observed between the lasers     

Grafted GaAlAs rib waveguides on an InP substrate

Rib waveguides were fabricated on a 1.4 mu m thick GaAlAs epilayer granted on the surface of a semi-insulating InP substrate by epitaxial lift-off. Single-mode waveguides with propagation losses (<7 dB/cm) lower than heteroepitaxially grown counterparts have been achieved. TEM analysis on the GaAlAs/InP interface indicates surface scattering as one of the main loss mechanisms.<>