Analysis of the CH3D Nonad from 2000 to 3300 cm

As part of the simultaneous analysis of line positions and intensities of the first two polyads of monodeuterated methane, the results achieved for the region 3-5 μm are reported. It involves the three highest fundamentals, (ν₁, ν₂, ν₄), overlapped by overtone (2ν₃, 2ν₅, 2ν₆) and combination (ν₃+ν₆, ν₃+ν₅, ν₅+ν₆) bands. The theoretical model was based on the global tensorial model implemented in the MIRS package. Some 10 000 line positions and 2400 line intensities have been modeled to ±0.000 88 cm⁻¹ and ±3.6% respectively, using measurements obtained at 0.0056 and 0.011 cm⁻¹ resolution with the Fourier transform spectrometer at National Solar Observatory located at Kitt Peak. The strongest band in this polyad is ν₄(E) at 3016.7 cm⁻¹ with a strength of 6.3×10⁻¹⁸ cm⁻¹/(molecule cm⁻²) at 296 K; the weakest band is 2ν₃(E) at 2597.7 cm⁻¹ with a strength of 1.9×10⁻²⁰ cm⁻¹/(molecule cm⁻²) at 296 K. The total calculated absorption arising from the CH₃D nonad is 8.95×10⁻¹⁸ cm⁻¹/(molecule cm⁻²) at 296 K.     

Subcellular mass determination by <Superscript>4</Superscript>He<Superscript>+</Superscript> energy-loss micro-spectrometry

The scanning transmission ion microscope (STIM) has been used to determine the intracellular mass of human cultured cells. A 4He+ microbeam of 2.0 MeV energy was chosen to obtain enhanced ion-energy-loss sensitivity through the micron-thick freeze-dried cells. Local sample mass calculation, based on energy-loss conversion by use of appropriate matrix stopping powers, was performed by use of dedicated software. The method was validated with epoxy resin sections and polymer foil as analogues of biological samples in the range of (intra)cellular thickness, 150 to 3000 nm. STIM analysis resulted in less than 5% error in mass determination. 4He+ energy-loss micro-spectrometry was performed on freeze-dried human ovarian cancer cells, the mean areal mass obtained was 120 microg cm(-2) (200 microg cm(-2) in the nucleus and 250 microg cm(-2) in nucleoli). This method is particularly useful for mass normalization of X-ray fluorescence yields resulting from particle-induced X-ray emission microanalysis (micro-PIXE). When performed successively these two ion-beam micro-analytical methods enable the mapping of true element concentrations within single cells.     

Nature of the high-pressure transition in Fe2O3 hematite

We present a new method to separate the crystallographic and electronic phase transitions in hematite using x-ray emission spectroscopy and x-ray diffraction. Our observations, based on the behavior of a metastable high-pressure phase in the stability domain of the low-pressure phase, show that the electronic transition is preempted by the crystallographic transition. The former occurs only afterwards in the high-pressure phase, possibly as a result of a Mott transition. The idea that the electronic transition drives the transition in hematite is therefore invalidated. Such methods should help elucidate the mechanics and the driving forces behind a number of first-order high-pressure phase transitions.     

Left-divisibility and word problems in single relation monoids

LetM be a monoid presented by <Σ;u=v> whereu andv are words on the finite alphabet Σ./ Deciding the world problem forM is still an open question, though it seems decidable and partial results exist. The remaining cases to solve are presentations of the form <a, b; bva=aua>,u, v∈{a, b}^⋆ The word problem is then closely related to the left-divisibility problem, as shown by S.I. Adjan who introduced a procedure that “almost” allows to decide the problem. The main contribution, due to Adjan and Oganesjan, states that ifbva is an unbordered factor ofaua then the word problem is deciable. We restrict Adjan's procedure to study the case whenbva is unbordered, which allows us to extend Adjan and Oganesjan's theorem. More specifically, we show (Proposition 4.24) that the word problem is decidable for presentations <a, b; bva=aua> with the only following condition: Inbva, the leftmost train ofb is strictly longer than the others. The following corollary naturally holds: The word problem is decidable for presentations of the form <a, b; b ^m a ⁿ =aua>,u∈{a, b}^⋆,m, n>0     

Phonon replica of excited level of free exciton in CdS

We report here the first experimental observation of the flourescence of a LO phonon replica from the A_n=2 excitonic level in cadmium sulfide. A very simple theoretical interpretation is given. We present also experimental data about phonon replicas in the case of forbidden transitions.     

Gamma-ray spectra and sensitivities for 2.8 MeV neutron activation analysis

The use of 2.8 MeV neutrons produced by the D(d, n)³He reaction should be taken into consideration in some applications of radioactivation analysis. The low number of elements activable by these neutrons makes possible to minimize the matrix interference and the background below the characteristic photopeaks. The very low dead-time of the spectrometric measurements permits the use of the maximum neutron flux available now and in the future. The purpose of this paper is to define experimentally the sensitivity of determination for the 16 main elements activable with a 400 keV Van de Graaff accelerator at a 2.8 MeV neutron flux of 2·10⁶ n·cm⁻²·sec⁻¹ on the sample.     

Étude de la déformation d'un liquide magnétique

Sans résumé     

Correlations between acidity, surface structure, and catalytic activity of niobium oxide supported on zirconia

The development of the acidity and the relationship between acidity, catalytic activity, and the surface structure for niobium oxide supported on zirconia were investigated for a series of solids. The catalysts were active for 2-propanol dehydration only above a threshold in Nb loading. The acidity was studied by infrared spectroscopy of adsorbed 2,6-dimethylpyridine as a probe molecule, and the onset of activity was correlated with that of the formation of relatively strong Br?nsted acid sites. The variation in the abundance of these sites also correlated with the catalytic activity. Raman, IR, and UV spectroscopy results indicated that the active sites were related to polymeric Nb surface species. These results were compared to those previously reported for the WO(x)/ZrO(2) catalysts.     

Dynamics of traveling waves in the transverse section of a laser

We analyze the general features of the formation and interaction of transverse traveling waves and the appearance of filamentation in broad area semiconductor lasers with current profiling. For small apertures, the emitted profile is symmetric consisting of two counterpropagating transverse traveling waves, both emanating from the center of the device. For larger apertures, the emission becomes asymmetric as one of the traveling waves expands to occupy an increased area while the other occupies the remaining, smaller spatial region. In both devices, the pattern becomes unstable at higher injection currents due to optical filamentation, although an intermediate state is present in the wider device whereby the dominant wave undergoes a Hopf bifurcation before filamentation occurs.     

Optical spin hall effect

A remarkable analogy is established between the well-known spin Hall effect and the polarization dependence of Rayleigh scattering of light in microcavities. This dependence results from the strong spin effect in elastic scattering of exciton polaritons: if the initial polariton state has a zero spin and is characterized by some linear polarization, the scattered polaritons become strongly spin polarized. The polarization in the scattered state can be positive or negative dependent on the orientation of the linear polarization of the initial state and on the direction of scattering. Very surprisingly, spin polarizations of the polaritons scattered clockwise and anticlockwise have different signs. The optical spin Hall effect is possible due to strong longitudinal-transverse splitting and finite lifetime of exciton polaritons in microcavities.