Analysis of a tripartite entanglement distribution switch

Queueing Systems - We study a quantum switch that distributes tripartite entangled states to sets of users. The entanglement switching process requires two steps: First, each user attempts to...     

Effect of absorbed pump power on the quality of output beam from monolithic microchip lasers

The dependence of the beam propagation factor (M ² parameter) with the absorbed pump power in the case of monolithic microchip laser under face-cooled configuration is extensively studied. Our investigations show that the M ₂ parameter is related to the absorbed pump power through two parameters (α and β) whose values depend on the laser material properties and laser configuration. We have shown that one parameter arises due to the oscillation of higher order modes in the microchip cavity and the other parameter accounts for the spherical aberration associated with the thermal lens induced by the pump beam. Such dependency of M ² parameter with the absorbed pump power is experimentally verified for a face-cooled monolithic microchip laser based on Nd³⁺ -doped GdVO₄ crystal and the values of α and β parameters were estimated from the experimentally measured data points.     

Modification of magnetic anisotropy in metallic glasses using high-energy ion beam irradiation

Heavy ion irradiation in the electronic stopping power region induces macroscopic dimensional change in metallic glasses and introduces magnetic anisotropy in some magnetic materials. The present work is on the irradiation study of ferromagnetic metallic glasses, where both dimensional change and modification of magnetic anisotropy are expected. Magnetic anisotropy was measured using Mössbauer spectroscopy of virgin and irradiated Fe₄₀Ni₄₀B₂₀ and Fe₄₀Ni₃₈Mo₄B₁₈ metallic glass ribbons. 90 MeV ¹²⁷I beam was used for the irradiations. Irradiation doses were 5×10¹³ and 7.5×10¹³ ions/cm². The relative intensity ratios D ₂₃ of the second and third lines of the Mössbauer spectra were measured to determine the magnetic anisotropy. The virgin samples of both the materials display in-plane magnetic anisotropy, i.e., the spins are oriented parallel to the ribbon plane. Irradiation is found to cause reduction in magnetic anisotropy. Near-complete randomization of magnetic moments is observed at high irradiation doses. Correlation is found between the residual stresses introduced by ion irradiation and the change in magnetic anisotropy.     

Parametric Excitation of the Electron-Acoustic Wave in a Multiply Ionized Plasma

Parametric excitation of the electron-acoustic wave (EAW) has been analysed using a hydrodynamical model. The plasma has been assumed to consist of multiply charged ions. The ratio (α) of the hotter ion concentration to that of the electrons is a sensitive parameter. The condition for the occurrence of the EAW is well satisfied for the smaller values of α. The growth rate of the instability gets enhanced by increasing α and the charge state of the hotter ions. The values of α can be varied within short range only.     

Where is the sodium in self-assembled monolayers of single-stranded DNA?

Monolayers of single-stranded DNA (ssDNA) immobilized on surfaces form the basis of a number of important biotechnology applications, including DNA microarrays and biosensors. The organization of ssDNA as layer on a solid substrate allows one to investigate various properties of the DNA in a controlled manner and to use DNA for analytical applications as well as for exploring futuristic schemes for molecular electronics. It is commonly assumed that the adsorbed DNA layer contains some structural water and the cations. Here we show, based on XPS studies, that when monolayers of ssDNA are formed from sodium phosphate buffer and washed thoroughly, no Na+ signal is detected. A finite concentration of ions is observed when the DNA is made from a solution of Mg2+ ions, but it is still only a fifth of what it would be if all the phosphate ions were fully neutralized by the metal cations.     

Catalytic properties of vanadium bronzes, I. Decomposition of isopropanol

Decomposition of isopropanol on V₂O₅ and the bonzes Li_0.02V₂O₅, Na_0.02V₂O₅, Na_0.06V₂O₅, Li_0.33V₂O₅, and Na_0.33V₂O₅ has been studied in the temperature range 168–300°C. The main reaction was found to be dehydration to propene with negligible dehydrogenation to acetone on the first four catalysts. Dehydration on these catalysts increased with the alkali metal content, but the energy of activation remained unchanged. On the last two catalysts, dehydration and dehydrogenation proceeded at comparable rates. A tentative mechanism for the dehydration of isopropanol is proposed, based on the effect of the product on the initial rate, the electric conductivity of the catalysts and their ESR spectra.

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V₂O₅ : Li_0,02V₂O₅, Na_0,02V₂O₅, Na_0,06V₂O₅, Li_0,33V₂O₅ Na_0,33V₂O₅ 186–300°C. . , . . , , .

     

Recombination reactions of oxygen atoms on an anodized aluminum plasma reactor wall, studied by a spinning wall method

We have studied the recombination of O atoms on an anodized Al surface in an oxygen plasma, using a new "spinning wall" technique. With this method, a cylindrical section of the wall of the plasma reactor is rotated and the surface is periodically exposed to an oxygen plasma and then to a differentially pumped mass spectrometer (MS). By varying the substrate rotation frequency (r), we vary the reaction time (t(r)), that is, the time between exposure of the surface to O atoms in the plasma and MS detection of desorbing O(2) (t(r) = 1/2r). As t(r) is increased from 0.7 to 40 ms, the O(2) desorption signal decreases by a factor of 2 for an O-atom flux of 1 x 10(16) cm(-2) s(-1) and by a factor of 6 when the O flux is 1 x 10(17) cm(-2) s(-1). The O(2) signal decay is highly nonexponential, slowing at longer times and reaching zero signal as r --> 0. A model of O-atom recombination is compared with these time-dependent results. The model assumes adsorption occurs at surface sites with a range of binding energies. O can detach from these sites, become mobile, and diffuse along the surface. This leads to desorption of O, reattachment at free adsorption sites, and recombination to form O(2) that promptly desorbs. With several adjustable parameters, the model reproduces the observed shapes of the O(2) desorption decay curves and the lack of detectable desorption of O and predicts a high O-atom recombination coefficient on anodized aluminum.     

Solid state properties and catalytic behavior of the α- and β-vanadium bronzes

Decomposition of isopropanol (IPA) on V₂O₅, Li_0.02V₂O₅, Na_0.02V₂O₅, Na_0.06V₂O₅, Li_0.33V₂O₅, and Na_0.33V₂O₅ has been studied in the temperature range 186–300°C. The first four catalysts (α-phase) show predominately dehydration, whereas the last two (β-phase) have comparable dehydration and dehydrogenation activity. Dehydration activity increases with alkali metal concentration within the α-phase, but falls sharply on the β-phase catalysts. This difference is attributed to the different rate determining steps for the reaction on the α- and β-phase catalysts. X-ray and ir spectral data show that the β-phase catalysts are much more stable than the α-phase. A mechanism for the dehydration of IPA based on the electrical resistivity, ESR spectra, and kinetic data has been proposed.     

Liquids and liquid mixtures: Deduction of the BGY equation considering the angular distribution function

The Born→Green→Yvon equation for molecular fluid has been deduced considering the orientational distribution functions. The isotropic and anisotropic parts of the distribution function have been separated. The expressions deduced can be used in the case of mixtures and for the non-central type of intermolecular potential energy.     

Patterning porous matrices and planar substrates with quantum dots

Silica hydrogels and planar substrates were patterned with CdS nanoparticles using a photolithographic method based on the photo dissociation of thiols and cadmium-thiolate complexes. Silica hydrogels were prepared via a standard base-catalyzed route. The solvent was exchanged with an aqueous solution of CdSO₄ and 2-mercaptoethanol, and the samples were then exposed to a focused ultraviolet beam. Planar substrates were patterned by illuminating a precursor solution spin coated on the substrates. CdS nanoparticles formed in the illuminated spots, and had a diameter below about 2 nm. The diameter of the spots illuminated by the UV beam could be varied from a few hundred to a few μm, on both hydrogels and planar substrates. Samples were characterized with transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and optical absorption, photoluminescence and Raman spectroscopies. All these techniques confirmed the chemical identity of the CdS nanoparticles. To investigate the mechanism of nanoparticle formation, we took absorption spectra of the precursor solution as a function of irradiation time. In unirradiated solutions, we noticed a maximum at 250 nm, characteristic of Cd-thiolate complexes. The absorption at 250 nm decreased with increasing irradiation time. A new band appeared at 265 nm for exposures around 5 min, and that band shifted to 290 nm in samples exposed for 10 min. A yellow precipitate formed after about 30 min. XRD showed that the precipitate was cubic CdS, with a mean particle size of 1.4 nm. We attribute formation of CdS to the photodissociation of the thiols and of the Cd-thiolates. UV irradiation of these precursors yields a series of species that can react with Cd²⁺, such as RS^·, S²⁻ and H₂S. Small CdS nanoparticles form in the initial stages of illumination, and present absorption bands in the 265–290 nm region. These CdS aggregates grow, coalesce and precipitate for longer irradiation times.