Isotope-selective excitation of 41Ca isotope in Doppler-free two-photon continuous-wave excitation: a case study

Seven schemes are studied theoretically for Doppler-free two-photon excitation of rare (41)Ca isotope using single-mode continuous-wave lasers. The ionization efficiencies and optical selectivities for all the schemes are calculated for various powers of the excitation and ionization lasers and for various focusing conditions of the two lasers. To maximize the ionization efficiencies and the optical selectivities, wavelength-dependent Stark compensation is used. Certain laser wavelengths of the ionization step termed as magic wavelengths are identified for compensating the Stark shift induced by the excitation laser. The effects of the Stark-shift-induced asymmetry and its reversal by selecting the appropriate magic wavelength for the ionization step for various excitation and ionization laser intensities are investigated. The ionization efficiency and optical selectivity for the best scheme after Stark compensation are found to be 8.4 x 10(-4) and approximately 9 x 10(3), respectively.     

Determination of the ionization state of 11-thioundecyl-1-phosphonic acid in self-assembled monolayers by chemical force microscopy

The present article describes the preparation and preliminary characterization of a novel phosphate-functionalized self-assembled monolayer (SAM) and the determination of the surface ionization states of the phosphate headgroup in aqueous solutions by chemical force microscopy (CFM). The phosphate headgroup used was PO(OH)2, a diprotic acid. The adhesion force between an AFM probe and a flat substrate, both of which were chemically modified with the same phosphate SAM, was also measured as a function of pH and ionic strength. At low ionic strength (10(-4) M), two peaks were observed in the force titration curve (adhesion force versus pH) at pH 4.5 and 8.4. The two peaks are positioned 2.4 and 1.2 pH units higher, respectively, than the acid dissociation constants obtained for the phosphate group free in aqueous solution. At high ionic strength (10(-1) M), the adhesion forces were reduced by 1 order of magnitude and the peaks were replaced by shoulders similar to those previously reported for acid force titrations. On the basis of JKR theory, the surface pKa values of the phosphate group in high ionic strength solutions were found to be 4.5 and 7.7, respectively. However, in light of the effects of ionic strength on the force titration curves, we discuss the applicability of JKR theory to nanoscopic measurements of adhesion force and surface pKa.     

Electron impact ionization of (1s2s2p)4 P j autoionization states of the lithium atom

Electron spectroscopy using intersecting electron and atomic beams was used for the first time to measure the electron excitation function of the (1s2s2p)⁴ P _1/2,3/2 autoionization states of the lithium atom in the range of collision energies between the level excitation threshold and 90 eV with an energy resolution better than 0.4 eV and a magic observation angle θ=54.7°. An analysis of the intense near-threshold structure observed revealed for the first time that autodetachment states of the negative lithium ion having excitation thresholds of 58.2±0.1 and 59.5±0.1 eV exist in the autoionization energy range. Pis’ma Zh. Tekh. Fiz. 25, 62–67 (July 12, 1999)     

Magnetic structure and spin-glass state of Fe1-x Zn x Cr2S4 spinels

Fe_1-x Zn _x Cr₂S₄ (0 <x < 1) solid solutions were synthesized and their magnetic properties and structure were investigated. The magnetic phase diagram of the solid-solution system was constructed. The results reveal a ferrimagnetic-spin glass-antiferromagnetic compositional transition in the FeCr₂S₄-ZnCr₂S₄ system.     

Correlation of C1s chemical state intensities with the O1s intensity in the XPS analysis of anodically oxidized glass-like carbon samples

An XPS study of anodic oxidized glass-like carbon (GC) was conducted in order to investigate the inconsistency between O_1s/C_1s and oxygen concentration (Ocal.) calculated from the curve fitting results of the C_1s spectrum. Consideration of the asymmetric peak shape of the C_1s spectrum is normally done in order to obtain precise curve fitting results. However, it was found that the 2nd-carbon peak should also be taken into consideration in the curve fitting process in addition to the effect of asymmetric peak shape of carbon to obtain a consistent value of O_1s/C_1s. The 2nd graphitic peak is normally located +0.7–+0.8 eV away from the original C_1s spectrum. The ratio of the 2nd graphitic peak area in the C_1s spectrum increased as the electrical charge increased. However, the peak shapes of C_1s spectra of anodic oxidized GC after heat treatment at 1500 °C in argon atmosphere were almost the same as the C_1s of untreated GC. Although the origin of the 2nd graphitic peak is not well understood, it may be related to the amount of oxygen on the GC surface.     

Influence of charge state on product ion mass spectra and the determination of 4S/6S sulfation sequence of chondroitin sulfate oligosaccharides

Electrospray ionization-Fourier transform ion cyclotron resonance tandem mass spectrometry is used to study the influence of charge state on the product ion spectra of chondroitin sulfate oligosaccharides for determination of the sulfate position on N-acetylgalactosamine residues. Sustained off-resonance irradiation collision-induced dissociation and infrared multiphoton dissociation are investigated for tandem mass spectrometry of chondroitin sulfate. Product ion spectra were obtained for ions of varying charge states from (4,5)-unsaturated (delta-unsaturated), reduced delta-unsaturated, and saturated oligosaccharides from chondroitin sulfate A and chondroitin sulfate C, separately. It was observed that ions in which the charge (z) is less than the number of sulfates dissociate to produce predominantly even-numbered B(n), C(n), Y(n), and Z(n) ions, and that odd-numbered fragment ions are observed for ions that have z equal to the number of sulfates. Sulfate adducted ions were observed in the product ion spectra of singly charged tetramer and hexamer oligosaccharides. This sulfate adduction was determined to result from migration of neutral sulfate during excitation.     

Absolute intensity measurements of the (11(1)0)II <--00(0)0 band of 12C16O2 at 5.2 microm

A nonlinear least-squares fitting procedure has been used to derive absolute intensities for lines in the P, R, and Q branches of the (11(1)0)II <-- 00(0)0 band of 12Cl602 (band center = 1932 cm(-1)) from long-path 0.01-cm(-1) resolution laboratory spectra. The spectral data were recorded at room temperature and low pressure (<10 Torr) with the Fourier transform spectrometer in the McMath solar telescope complex at Kitt Peak National Observatory. The observed line intensities were analyzed to derive the vibrational band intensity and F-factor coefficients. To obtain a good fit to the data, it was necessary to include terms in the expression for the F factor, which account for Coriolis-type and Fermi-type interactions and centrifugal distortion effects.     

Influence of NH4Cl on the < 1 0 0> directed growth and properties of ADP crystal

Good quality, pure and ammonium chloride added < 1 0 0> directed ADP single crystals with different sizes were grown by Sankaranarayanan-Ramasamy method with the vision to improve the properties of the crystal. The grown crystals have cylindrical morphology and the crystals were subjected to UV-Vis., DTA, microhardness, laser damage threshold, dielectric, piezoelectric and SHG studies. The addition of ammonium chloride improves the quality and yields crystals with transparency more than 80% in minimum duration of growth. Higher laser damage threshold and mechanical stability were observed in ammonium chloride added ADP crystals. Low dielectric loss shows that the grown crystal contains minimum defects. Good piezoelectric behaviour was observed for the grown crystals. The SHG efficiency of the crystals was obtained using Nd-YAG laser, which is approximately 3 times that of pure ADP and shows the suitability of the ingot for nonlinear optical applications.     

基于Ca(H_2P0_4)_2/H_3PO_4无机复合质子膜的燃料电池的制备

以Ca(H2PO4)2.H2O粉末和H3PO4水溶液合成的无机复合质子膜作为电解质,制备低温燃料电池,评价了无机质子膜的质子传导率以及所制成的燃料电池的输出性能。结果表明,在80℃、70%RH条件下,其质子传导率可以达到3.5×10-2S/cm,所制成的燃料电池在60℃时输出功率达到11.5mW/cm2。     

Synthesis and characterization of spinel Co3O4 octahedra enclosed by the {1 1 1} facets

Spinel Co₃O₄ octahedra synthesized by a facile redox-precipitation method were investigated for the complete oxidation of methane. XRD analysis showed that the spinel structural Co₃O₄ octahedra had a relatively strong (1 1 1) diffraction peak as compared with that of the irregular shaped Co₃O₄ nanoparticles prepared by a conventional precipitation method. The results of methane combustion test demonstrated that the Co₃O₄ octahedra had no catalytic activity at 300-500 °C, while the Co₃O₄ irregular nanoparticles were highly active at the same reaction conditions. HRTEM studies revealed that the Co₃O₄ octahedra were predominantly exposed by the low Miller-index {1 1 1} facets with the lowest surface energy, and the Co₃O₄ irregular nanoparticles were exposed by various crystal facets. The results exhibited that the {1 1 1} facets with the low surface energy of the Co₃O₄ octahedra resulted in the inert catalytic activity in the methane oxidation reaction.     

Effect of the charge state (z = -1, 0, +1) on the nuclear magnetic resonance of monodisperse Au25[S(CH2)2Ph]18(z) clusters

Monodisperse Au(25)L(18)(0) (L = S(CH(2))(2)Ph) and [n-Oct(4)N(+)][Au(25)L(18)(-)] clusters were synthesized in tetrahydrofuran. An original strategy was then devised to oxidize them: in the presence of bis(pentafluorobenzoyl) peroxide, the neutral or the negatively charged clusters react as efficient electron donors in a dissociative electron-transfer (ET) process, in the former case yielding [Au(25)L(18)(+)][C(6)F(5)CO(2)(-)]. As opposed to other reported redox methods, this dissociative ET approach is irreversible, easily controllable, and clean, particularly for NMR purposes, as no hydrogen atoms are introduced. By using this approach, the -1, 0, and +1 charge states of Au(25)L(18) could be fully characterized by (1)H and (13)C NMR spectroscopy, using one- and two-dimensional techniques, in various solvents, and as a function of temperature. For all charge states, the NMR results and analysis nicely match recent structural findings about the presence of two different ligand populations in the capping monolayer, each resonance of the two ligand families displaying distinct NMR patterns. The radical nature of Au(25)L(18)(0) is particularly evident in the (1)H and (13)C NMR patterns of the inner ligands. The NMR behavior of radical Au(25)L(18)(0) was also simulated by DFT calculations, and the interplay between theory and experiments revealed a fundamental paramagnetic contribution coming from Fermi contact shifts. Interestingly, the NMR patterns of Au(25)L(18)(-) and Au(25)L(18)(+) were found to be quite similar, pointing to the latter cluster form as a diamagnetic species.     

Preparation of hydroxyapatites via the MSO4 sulphates (M = Ca,Sr, Pb and Eu)

Hydroxyapatites of Ca, Sr and Pb have been prepared by a reaction of the sulphates of these metals with sodium phosphate arsenate or vanadate respectively in a strongly basic solution. X-ray diffraction and IR spectroscopy proved the formation of hydroxyapatites. DTA and TG data indicate the presence of one water molecule in Ca₅(PO₄)₃OH lost at 110°C.     

Mechanochemically assisted room temperature solid state metathesis reaction for the synthesis of MMoO4 (M = Ca, Sr and Ba)

This communication reports a novel mechanochemically assisted room temperature solid state metathesis reaction for the synthesis of submicron-size alkaline-earth molybdates crystallizing in a tetragonal Scheelite structure. The solids were characterized by powder XRD, FTIR, TGA, DTA, SEM, EDAX and TEM to ascertain their composition, phase homogeneity and morphology.     

Critical current density of the superconductor YBa1·5Ca0·5Cu3O7\t-\gd

The real and imaginary (lossy) components of a.c. susceptibility of high-T _c superconductor YBa_1·5Ca_0·5Cu₃O_7−δ were measured as a function of temperature for different a.c. fields and frequencies. From the lossy component of the a.c. susceptibility the transport critical current density and its temperature dependence have been computed on the basis of Kim’s critical state model.     

双相不锈钢1Cr18Ni11Si4AITi标准中的问题探讨

双相不锈钢1Cr18Ni11Si4AlTi由前苏联研制,目前在我国某些特殊行业中有重要的作用.根据我国现有标准GJB2294-95和GB/T1220-92组织生产,发现按标准中现行成分设计、热处理制度生产的产品与标准要求的力学性能(屈服强度σ0.2)需达到的规定值存在较大差异,很难达到所需要的屈服强度.通过完善相关成分和工艺参数,获得了满意的金相组织和优良的综合力学性能.通过试验探讨了生产实际与标准中的部分规定存在的差距.     

Some properties of the solid solutions EuxSr1−xNb4O11 and EuxSr1−xTa4O11

Two solid solutions Eu_xSr_1?xNb₄O₁₁ and Eu_xSr_1?xTa₄O₁₁ have been prepared. Electrical and magnetic properties of these solid solutions were investigated. Electrical conductivity in the niobate system was found to be much higher than that in the tantalate analog. The specimen Eu_0.1Sr_0.9Nb₄O₁₁ was most transmitting in the solid solutions in the range of 77–450K.