Direct Measurement of O(2)(a(1)D) and O(2)(X(3)?) in Chemical Oxygen-Iodine Lasers with use of Spontaneous Raman Imaging

A spontaneous Raman imaging system (SRIS) has been developed that can monitor chemical oxygen-iodine laser (COIL) singlet oxygen generator (SOG) performance in real time. This system permits one to monitor directly the SOG performance by measuring O(2)(a(1)D) and O(2)(X(3)?) simultaneously with a single intensified CCD array at the exit of an imaging monochromator. We present the results from tests conducted on a 0.25-mol SOG using a prototype Raman system. Performance and validation of a highly sensitive SRIS that was designed and built specifically for SOG diagnostics are discussed. Detection and possible interferences of other species relevant to COIL devices such as I(2) and Cl(2) are investigated.     

Dielectric and Piezoelectric Properties of (Na0.5Bi0.5)(Ti1–xMnx)O3 (x = 0–0.1) Modified Ceramics

Inorganic Materials - We have studied the crystal structure and dielectric and local piezoelectric properties of (Na0.5Bi0.5)(Ti1–xMnx)O3 (x = 0–0.1) modified sodium bismuth...     

An On-Line Technique for the Determination of the δ(18)O and δ(17)O of Gaseous and Dissolved Oxygen

Few studies have used the stable isotopic composition of O(2) as a tracer of gas transport or biogeochemical processes in environmental research. Here we demonstrate field sampling techniques for gaseous and dissolved O(2) and describe an analytical method for measuring δ(18)O and δ(17)O values of O(2) in air, soil gas, and water samples using continuous-flow isotope-ratio mass spectrometry (CF-IRMS). A Micromass CF-IRMS was altered to accommodate a sample gas injection port prior to a CO(2) and H(2)O trap and GC column. The GC column was a 1-m, 5-? molecular sieve column held at 35 °C. The resolved sample O(2) was introduced to the IRMS via an open split. δ(18)O and δ(17)O values were determined by measurement of O(2) isotopes at m/z 34/32 and 33/32 and comparison to a reference pulse of O(2). Repeated injections of atmospheric oxygen yielded a repeatability (±SD) of ±0.17‰ for δ(18)O and ±0.5‰ for δ(17)O. IRMS source linearity was excellent for O(2) over a sample size range of 60-400 μL. The smallest sample for routine δ(18)O and δ(17)O determinations was ～80 μL of O(2), with a sample analysis time of 180 s. Preliminary results from a riverine and soil gas study illustrate natural oxygen isotope fractionation processes.     

Visible photoluminescense of the (112¯0), (101¯1) and (0001) surfaces of ZnO nanofilms

Thin ZnO nanofilms 25 nm thick with (0001), $\left(11\overline{2}0\right)$ and $\left(10\overline{1}1\right)$ as surfaces were grown epitaxially on the NaCl (111) and (001) surfaces. The room temperature photoluminescence (PL) spectrum from the $\left(11\overline{2}0\right)$ nanofilm has a sharp UV emission but negligible green emission, indicating that it has good quality and low defect density. However, the PL spectra from the $\left(10\overline{1}1\right)$ and (0001) surface nanofilms have a broad green emission, and that of the $\left(10\overline{1}1\right)$ surface is stronger than the (0001) surface. The result supports that the surface oxygen vacancies are the probable origins of the green emission.     

(Cu0.5Tl0.5)(Ba2–yCay)(CaMg)(Cu3–x Znx)O10–δ (y = 0, 1; x = 0, 2, 2.5, 2.8, 3) and (MxTl1–x)(BaCa)(CaMg) Zn3O10–δ (M = Ag,K; x = 0, 0.5) Superconductors for the Studies the role of Spin Density Waves in the Mechanism of High Tc Superconductivity

Journal of Superconductivity and Novel Magnetism - (Cu0.5Tl0.5)(Ba2–yCay)(CaMg)(Cu3–xZnx)O10–δ (y?=?0, 1; x?=?0, 2, 2.5, 2.8, 3) and...     

Nanocrystalline NiFe2O4 and nanocomposites of (NiFe2O4)(1-x)(Al2O3)x (x = 0.25, 0.40): superparamagnetic behavior and Mössbauer spectroscopy

Nanocrystalline NiFe2O4 with different particle sizes and nanocomposites of (NiFe2O4)(1-x)(Al2O3)x (x = 0.25, 0.40) were prepared by using co-precipitation method. In this method two techniques viz., 'ultrasonication' and 'magnetic stirring' during co-precipitation were used. The as prepared samples were annealed at different temperatures to obtain samples with different particle sizes. The formation of the nanocrystalline spinel phases of all the samples were confirmed by X-ray diffraction (XRD) patterns. The sizes of the nanoparticles of all the samples were calculated from the broadening of the (311) line in the XRD pattern. The distribution of sizes are remarkably less in samples obtained from 'ultrasonication' technique compared to those obtained in 'magnetic stirring' technique. The different soft magnetic quantities viz., coercive field, magnetization, remanance, hysteresis losses etc. were extracted from the ac hysteresis loops observed at different frequencies. The variations of coercive field and hysteresis loss as functions of frequency and particle sizes have been studied. M?ssbauer spectra of the samples along with the hysteresis loops recorded at room temperature indicate the presence of superparamagnetic (SPM) relaxations of the nanoparticles. Also, SPM relaxations have been introduced in the samples annealed at higher temperature by encapsulating the nanoparticles in non-magnetic matrix of Al2O3 with 40% coating.     

Coupled Electron- and Proton-Transfer Processes in the Reduction of α-[P(2)W(18)O(62)](6)(-) and α-[H(2)W(12)O(40)](6)(-) As Revealed by Simulation of Cyclic Voltammograms

Quantitative analysis of the complex problem of coupled electron- and proton-transfer steps during reduction of the polyoxo anions α-[P(2)W(18)O(62)](6)(-) and α-[H(2)W(12)O(40)](6)(-) in aqueous NaCl (0.5 M) has been achieved by simulation of cyclic voltammograms (Rudolph, M.; Reddy, D. P.; Feldberg, S. W. Anal. Chem. 1994, 66, 589A) over wide ranges of anion concentration, pH, and scan rate. Since there are too many unknown parameters to attempt a one-step global form of simulation, a systematic, stepwise approach has been adopted by progressively accessing regimes of increasing voltammetric complexity. This protocol allows experimental behavior in each system over 5 orders of magnitude in proton concentration to be simulated by estimation of three protonation constants combined with experimentally determined reversible half-wave potentials for the two one-electron processes involved. Fast electron transfer and protonation kinetics are assumed. The importance of the values chosen for the diffusion coefficients of the proton and polyoxo anion species is considered. The simulations account for the fact that pairs of one-electron processes coalesce to give an apparent two-electron process in the pH range 1-6 for reduction of both anions.     

Effect of Doping and High-Temperature Annealing on the Structural and Electrical Properties of Zn_(1-X)Ni_XO(0≤X≤0.15) Powders

This paper reported the synthesis,crystal structure and electrical conductivity properties of Ni-doped ZnO powders(i.e.Zn 1 X Ni X O binary system,X=0,0.0025,0.005,0.0075 and in the range 0.01≤X≤0.15).Iphase samples,which were indexed as single phase with a hexagonal(wurtzite) structure in the Zn 1 X Ni X O binary system,were determined by X-ray diffraction(XRD).The widest range of the I-phase was determined as 0≤X≤0.03 at 1200 C;above this range the mixed phase was observed.The impurity phase was determined as NiO when compared with standard XRD data,using the PDF program.We focused on single I-phase ZnO samples which were synthesized at 1200 C because of the widest range of solubility limit at this temperature.It was observed that the lattice parameters a and c of the I-phase decreased with Ni doping concentration.The morphology of the I-phase samples was analyzed with a scanning electron microscope.The electrical conductivity of the pure ZnO and single I-phase samples were studied by using the four-probe dc method at temperatures between 100 and 950 C in air atmosphere.The electrical conductivity values of pure ZnO and 3 mol% Ni-doped ZnO samples at 100 C were 2×10 6 and 4.8×10 6 1 ·cm 1,and at 950 C they were 1.8 and 3.6 1 ·cm 1,respectively.In other words,electrical conductivity increased with Ni doping concentration.     

Relaxor behaviour of (Ba0·5Sr0·5)(Ti0·6Zr0·4)O3 ceramics

Ba_0·5Sr_0·5Ti_0·6Zr_0·4O₃ ceramic has been prepared through solid state reaction route. X-ray diffraction shows that the sample has cubic perovskite structure with space group Pm-3m at room temperature. Temperature dependent dielectric study of the ceramic has been investigated in the frequency range 50 Hz-1 MHz. The density of the sample is determined using Archimedes’ principle and is found to be ∼99% of X-ray density. The dielectric study revealed diffuse phase transition of second order. A broad dielectric anomaly coupled with the shift of dielectric maxima toward a higher temperature with increasing frequency indicates the relaxor-type behaviour in the ceramics. The index of relaxation (γ) and the broadening parameter (Δ) were estimated from a linear fit of the modified Curie-Weiss law. The value of γ ∼ 1·72 indicates the strong relaxor nature of the ceramic. A remarkably good fit to the Vogel-Fulcher relation further supports such a relaxor nature.     

Cobalt-mediated synthesis of 2-(4-pyridyl)benzimidazole. x-ray structures of Co[2-(4-pyridyl)benzimidazole]2(H2O)2(NO3)2 and [Co(isonicotinate)(4-pyridiniumcarboxylate)(H2O)(NO3)]∞

We have observed an unusual example of cobalt-mediated cyclization of 4-pyridinecarboxaldehyde and 2-nitroaniline to afford 2-(4-pyridyl)benzimidazole under hydro(solvo)thermal conditions. Reaction of Co(NO₃)₂·6H₂O with 4-pyridinecarboxaldehyde and 2-nitroaniline in ethanol at 120°C gave a cobalt(II) coordination compound, Co[2-(4-pyridyl)benzimidazole]₂(H₂O)₂(NO₃)₂, 1. In contrast, when the hydro(solvo)thermal reaction was carried out between Co(NO₃)₂·6H₂O and isonicotinic acid in the presence of 2-nitroaniline at 110°C, a one-dimensional Co(II) coordination polymer with the formula of [Co(isonicotinate)(4-pyridiniumcarboxylate)(H₂O)(NO₃)]_∞, 2, resulted. The X-ray single crystal structures of both 1 and 2 are described. Interestingly, the isonicotinic acid in 2 exists as a 4-pyridiniumcarboxylate tautomer, and the pyridinium hydrogen atom forms a very strong hydrogen bond to the carboxylate oxygen of the 4-pyridiniumcarboxylate on an adjacent metal center. 1 forms a three-dimensional polymeric network through hydrogen bonding interactions, while 2 exists as a 2-D bilayer polymeric network through hydrogen bonding interactions.     

1, 3-dipolar cycloaddition as a general route for functionalization of Fe(3)O(4) nanoparticles

Triazole formation by 1,?3-dipolar cycloaddition reactions has been used to functionalize the surface of Fe(3)O(4) nanoparticles. Fe(3)O(4) particle samples with diameters around 22 nm were synthesized without any additional stabilizer, and were then treated with silane coupling agent to react with propargyl acid. The alkynyl group on the Fe(3)O(4) surface provides better conjugation efficiency with azide derivative molecules, which led to their attachment through the formation of a 1,?2,?3-triazole ring.     

Dependence of the low-temperature specific heat of YBa2Cu3O7−δ on δ and magnetic field: The H1/2T term for H≠0; absence of evidence for a T2 term for H=0

Specific-heat measurements with improved precision on two new samples of YBa₂Cu₃O_7– with relatively low concentrations of paramagnetic centers are reported. For one sample the measurements were made for different values of . The data are analyzed, and the data reported earlier for another sample reanalyzed, with an improved fitting expression. In each case, the data give a well defined H^1/2T term in the mixed state. No persuasive evidence for a T² term in the superconducting state is found.     

Recognition for 3‐D objects based on the determination of the position and the orientation from a noisy single perspective view

Abstract

Recognizing 3‐D objects from 2‐D images has been an important area of research in computer vision. In this paper, an efficient method is developed to determine the position and the orientation of a 3‐D polyhedron in a noisy image. This method assumes that the direction of a straight line on an image can be determined from noisy data. A set of linear equations are used to determine the orientation of an object. In cases where there are not enough straight lines of an image presented, the constraint equations can be introduced and the iterative process is applied. However the iterative process is simple and the divergence is not a problem. After the orientation is determined, the straight lines, corresponding to the visible edges of the object, are used to determine the intersection points. From the intersections and the corresponding corners of the polyhedron, another set of linear equations are used to obtain the position of the object.

If the sum of the perpendicular distances, between the endpoints of the image projection of each model line and the corresponding image line, divided by the number of end‐points is less than a threshold, then the matching process is passed. It is shown, in this paper, that we cannot distinguish between geometrically similar objects without texture analysis from a single perspective view. Thus, the threshold, ?_i , which is determined by a scheme developed here, of model i is used to check whether the candidate model is accepted. Finally, all the concepts, presented in this paper, are illustrated through several examples given in this paper.     

High-temperature electrical conductivity and thermal expansion of SmBa2(Cu1-xFex 3O6+δ (x = 0–0.2)

The electrical conductivity and thermal expansion of SmBa₂(Cu_1-xFe_{x 3}O_6+δ (x = 0-0.2) were measured in air in the temperature range from 20 to 900°C. The linear thermal expansion coefficient was determined to be (12.8–13.5) × 10^-6 K^-1 in the temperature range from 20 to 350°C and (16.2–17.8) × 10^-6 K^-1 in the range from 350 to 800°C. Between 400 and 900°C, the conductivity of SmBa₂(Cu_1-xFe_x)₃O_6+δ was found to decrease with increasingx, mainly in the rangex = 0–0.1. This finding was interpreted in terms of the Fe occupancies on the Cu(1) and Cu(2) sites.     

Relaxor behaviour and dielectric properties of BiFeO3 doped Ba(Zr0·1Ti0·9)O3 ceramics

Ba_1???x Bi _x (Ti_0·9Zr_0·1)_1???x Fe _x O₃ ( x = 0–0·075) ceramics are prepared using a conventional solid state reaction method. X-ray diffraction shows the presence of a single phase. Addition of Bi^3?+? and Fe^3?+? strongly influences the crystal structure and dielectric properties of the ceramics. The evolution from a normal ferroelectric to a relaxor ferroelectric is emphasized. Ba_0·99Bi_0·01(Ti_0·9Zr_0·1)_0·99Fe_0·01O₃ ceramic shows a relaxor behaviour at room temperature with Δ T _m =12 K. P– E hysteresis loop of the composition, x = 0·007, shows a remanent polarization ( P _r ) of 0·5 μC/cm² with a coercive field ( E _C ) of 2 kV/cm. Raman spectra of all compounds are performed and correlated well with the X-ray diffraction and dielectric measurement results.     

Formation and characterization of the solid solutions (CrxFe1−x)2O3, 0⩽x⩽1

The solid solutions (Cr_xFe_1–x)₂O₃, 0 x 1, were prepared by traditional ceramic procedures. The samples were characterized using X-ray diffraction, Mössbauer, Fourier transform infra-red (FT-IR) and optical spectroscopic measurements. In the whole concentration range two phases exist phase F, -(Cr_xFe_1–x)₂O₃, which is isostructural with -Fe₂O₃ and phase C, which is closely related to Cr₂O₃. Phase F exists in samples heated up to 900°C, for 0 x 0.95. Phase C exists from x0.27 to x=1 for samples heated up to 900°C and from x0.65 to x=1 for samples heated up to 1200 °C. For samples heated up to 900 °C, the solubility limits were 27.5 ± 0.5 mol% of Cr₂O₃ in -Fe₂O₃ and 4.0 ± 0.5 mol % of -Fe₂O₃ in Cr₂O₃. For the samples heated at 1200 °C the diffraction peaks for the F and C phases in the two phase region were severely overlapped and thus the solubility limits could not be determined accurately as for previous samples. ⁵⁷Fe Mössbauer spectra of the samples heated up to 1200 °C showed significant broadening of spectral lines and a gradual decrease of the hyperfine magnetic field with increase of x up to 0.50. For x0.7, a paramagnetic doublet with collapsing sextet was observed. The spectra were interpreted in terms of an electronic relaxation effect; however, an agglomeration of iron ions which would contribute to the superparamagnetic effect could not be excluded. The FT-IR spectra showed transition effects in accordance with the X-ray diffraction results. The most intense absorption bands, observed for the samples heated up to 1200 °C, were located at 460 and 370 nm (22 000 and 27 000cm^–1) for x 0.5, 500 and 360 nm for x < 0.3, and might be correlated with the strong enhancement of the pair transitions through antiferromagnetic interactions. The intensification of the ⁶A₁ 4T₁ Fe³⁺ ions in all spectra and the development of the absorption at 13000 cm^–1 due to a metal-metal charge transfer (Cr³⁺ Fe³⁺) transition, might be explained by exchange coupling which has been observed in some spinel compounds.     

Effects of ceramic processing parameters on the microstructure and dielectric properties of (Ba1-xCax)(Ti0.99-y′ ZryMn0.01)O3 sintered in a reducing atmosphere

The effect of A/B ratio, sintering temperature, and oxygen partial pressure on microstructure and ceramic dielectric properties of 1 mol % MnO₂ doped (Ba,Ca)(Ti,Zr,)O₃ sintered in a reducing atmosphere were investigated. Microstructure is found to be closely related to processing parameters. With decreasing A/B ratio, decreasing oxygen partial pressure and increasing sintering temperature, grain growth is enhanced. Concurrent with the grain size reduction, the crystal structure transformed from tetragonal to pseudocubic at room temperature and the dielectric constant, the dissipation factor and Curie point all decreased. However, the effects of grain size give a marked discrepancy on breakdown. The effect of A/B ratio and sintering temperature both suggest that breakdown voltage is decreased with increasing grain size. However, the breakdown voltage in relation to grain size by changing the oxygen partial pressure seems to show no significant difference.     

Microstructure and superconductivity of highly ordered YBa(2)Cu(3)O(7-δ) nanowire arrays

In order to explore the fundamental properties of one-dimensional nanostructured high-temperature superconductors and enhance their promising applications, a universal and general method for the synthesis of high-quality YBa(2)Cu(3)O(7-δ) (YBCO) nanowire arrays is developed, which involves the combination of a novel sol-gel process to lower the crystallization temperature of YBCO, and porous anodic alumina (PAA) as an effective morphology-directing hard template. Field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM) results indicate that the as-prepared YBCO nanowires have average diameters of about 50?nm and lengths up to several microns. The structures of the samples were analysed by x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), energy-dispersive x-ray spectroscopy (EDX) and inductively coupled plasma (ICP) analysis, which indicate that the nanowires are well crystallized with orthorhombic YBCO-123 structure. The magnetization measurement under zero-field-cooled (ZFC) mode indicates that the superconducting transition temperature (T(c)) of the nanowires is about 92?K, which is in agreement with that of a bulk YBCO sample.     

Ho:YV0(4) solid-state saturable-absorber Q switch for a 2-µm Tm, Cr:Y(3)Al(5)O(12) laser

The holmium-doped yttrium orthovanadate (Ho:YVO(4)) crystal was shown to be an effective solid-state saturable-absorber Q switch for a flash-lamp-pumped Tm,Cr:Y(3)Al(5)O(12) laser operating at 2.017 μm. A single Q-switched laser pulse of 3.5 mJ in energy and 45 ns in duration was observed with a 1-mm-thick 4% Ho:YVO(4) solid-state saturable absorber, which was grown with the high-temperature-solution-growth method.