EPR study of vanadium-loaded yttrium-cerium-zirconium solid solutions

5YO_1.5-10CeO₂-85ZrO₂ solid solution doped with vanadium was studied by means of electron paramagnetic resonance (EPR). The nature of the vanadium species formed by treatment of samples with O₂, CO, and H₂ was investigated. Three types of paramagnetic V⁴⁺ ions found in samples evacuated at 723 K have been attributed to tetragonally compressed octahedral complexes of vanadyl type with different interionic V–O distances. Two of them are supposed to be located on the surface of the oxide support, whereas the third type is in the bulk of the solid. EPR spectroscopy of all CO reduced samples showed the presence of isolated mononuclear V⁴⁺ species. Reducing treatment of the samples with H₂ also provoked the formation of aggregated V⁴⁺ species. The later species formed either by the agglomeration of surface isolated V⁴⁺ ions during high-temperature treatment or the reduction of polymerized V⁵⁺ species present in as-prepared samples. Obtained results can be used for the better understanding of vanadium effect on catalysts properties.     

First Spectra from a New, Wide Band, Hybrid Digital Correlator Spectrometer for the First-HIFI Instrument

We have designed and built a new, wide band, modulable resolution spectrometer, in view of full astronomical qualifying tests, and to prepare future models for the FIRST satellite's heterodyne instrument. Our spectrometer, a hybrid digital Autocorrelator, offers flexibility in terms of bandwidth (from 170MHz to 680MHz) and resolution (from 700kHz to 3MHz). This spectrometer required the development of a dedicated analog filter bank, homemade samplers, and the design of full custom GaAs integrated circuits. Laboratory tests have shown excellent agreement with expected performances and observations performed with the IRAM 30-m radiotelescope have qualified its capabilities. Despite the relatively limited number of channels of our current prototype compared to others spectrometers, the main advantages are its stability (inherent to digital technique), and its spectral versatility. Recent microelectronics advances and rad-tolerance of our spectrometer components are used to prepare a new, compact, and low power consumption autocorrelator in view of a flight model for HIFI, the heterodyne instrument on the ESA cornerstone mission FIRST.     

Transformation of the quasicrystalline phase Al-Cr-Fe induced by rapid solidification

A quasicrystalline phase, Q, with icosahedral symmetry was detected by X-ray diffraction and transmission electron microscopy in Al-3Cr-xFe (x=0 1 or 3 at %) alloys elaborated by hot extrusion of rapidly solidified powders. Chemical microanalysis showed the average composition of this phase to be 75 ± 0.5% Al, 12 ± 1%Cr, 12 ± 1% Fe. Annealing treatments led to its transformation into the equilibrium phases Al₁₃Cr₂ and Al₁₃Fe₄, directly at high temperature, or through a metastable and unknown phase, X, at intermediate temperature. This transformation was followed by X-ray diffraction, calorimetry and in situ electron microscopy. The convergent-beam technique was used for characterization of the X phase.     

A new iterative soft-output Viterbi algorithm and its application to the “dicode” channel

We present an iterative soft-output decoding algorithm for serially concatenated coding systems. It has better performance than the conventional noniterative decoding algorithm. When applied together with an outer convolutional code to the dicode channel with partial response (1 — D), we obtain an additional coding gain of about 1 dB at a bit-error rate of 10^-4 after two iterations. This new algorithm can also be applied advantageously to satellite communication and fading channels.     

Surface wave excitation on a microstrip ring antenna

A theoretical analysis of the excitation of surface waves on a microstrip ring antenna is presented. The problem is formulated using dyadic Green's functions in a layered medium with magnetic-type equivalent current sources. The integral equation for the fields is solved in the wave number complex plane so that the fields from space and surface waves are obtained separately. The space wave radiation efficiency is calculated for the TM₁₁, TM₁₂, and TM₁₃ modes for various values of the normalized dielectric substrate thickness, d/λ₀. It is noted that the TM₁₃ mode radiates more efficiently than the TM₁₁ and TM₁₂ modes. The results are of importance in the design of these antennas     

Experimental study on simulated molten jet-coolant interactions

Molten fuel-coolant interactions in a jet contact mode was studied with respect to the safety of liquid-metal-cooled fast breeder reactors (LMFBRs). From a series of molten Wood's metal (melting point 79 °C) jet-water interaction experiments, several distinct modes of interaction behaviors were observed for various combinations of initial temperature conditions of the two fluids. A semi-empirical model for a minimum film boiling temperature criterion was developed and used to reasonably explain the different interaction modes. It was concluded that energetic jet-water interactions are only possible under relatively narrow initial thermal conditions. Preliminary extrapolation of the present results to a UO₂-sodium system suggests that mild interactions and coolable debris formation should be most likely in LMFBRs.     

Interrelationships between strains of Salmonella enteritidis belonging to phage types 4, 7, 7a, 8, 13, 13a, 23, 24 and 30

Cyclin A is a nuclear protein which is part of a kinase complex with either p34cdc2 or p33cdk2. Cyclin A is required in higher eukaryotic cells at the G1/S and the G2/M transitions. To examine the relationship between cyclin A and DNA replication, we simultaneously labeled exponentially growing HeLa cells for the distribution of cyclin A and proliferating cell nuclear antigen (PCNA). We have now demonstrated, by means of immunoelectron microscopy, that cyclin A is located at the sites of DNA replication visualized by both BrdU and PCNA labeling. Thus cyclin A may play a significant role in the phosphorylation of proteins at or near the sites of DNA replication.     

Surface organometallic chemistry on metals. Application to chemicals and fine chemicals

Some applications of surface organometallic chemistry on metals to catalysis are presented, showing the great importance of the modification of a metallic surface by organometallic compounds on its catalytic properties. The selective hydrogenation of α–β unsaturated aldehydes such as citral (Z and E) can be achieved on rhodium–tin catalysts. While rhodium alone is relatively unselective, geraniol (and nerol) can be obtained selectively (> 98%) without a significant loss of activity by use of a rhodium–tin catalyst showing a typical ligand effect of the organotin fragment on the surface. Similarly, in the isomerization of (+) 3-carene into (+) 2-carene or the dehydrogenation of butan–2–ol into methyl ethyl ketone, the selectivity into the desired product is increased by introduction of small amounts of tin which will form adatoms poisoning unselective sites. An alloying effect of tin is also presented in the dehydrogenation reaction of isobutane in isobutene. This revised version was published online in June 2006 with corrections to the Cover Date.