Reduction of Np(V) with Fe(II) in weakly acidic solutions containing H<Subscript>2</Subscript>C<Subscript>2</Subscript>O<Subscript>4</Subscript>

The kinetics of the reaction of Np(V) with Fe(II) in dilute perchloric and nitric acid solutions containing H₂C₂O₄ was studied by spectrophotometry. In the range pH 1–2, the reaction rate is described by the equation d[Np(V)]/dt = k[Np(V)][Fe(II)][H₂C₂O₄]²[H⁺]^−1.6, k = 182 mol^−1.4 l^1.4 s⁻¹. The activation energy in the range 25–45°C is 26 kJ mol⁻¹. The reaction mechanism involves formation of Fe(II) and Np(V) oxalate complexes, followed by their reaction with the participation of the H⁺ ion.     

Crystal structure and electrical properties of CaNaBi<Subscript>2</Subscript>Nb<Subscript>3</Subscript>O<Subscript>12</Subscript> ceramics

Monophasic CaNaBi₂Nb₃O₁₂ powders were synthesized via the conventional solid-state reaction route. Rietveld refinement of the X-ray powder diffraction (XRD) data and selected area electron diffraction (SAED) studies confirmed the phase to be a three-layer Aurivillius oxide associated with an orthorhombic B2cb space group. The dielectric properties of the ceramics have been studied in the 300–800 K temperature range at various frequencies (1 kHz to 1 MHz). A dielectric anomaly was observed at 676 K for all the frequencies corresponding to the ferroelectric to paraelectric phase transition as it was also corroborated by the high temperature X-ray diffraction studies. The incidence of the polarization–electric field (P vs. E) hysteresis loop demonstrated CaNaBi₂Nb₃O₁₂ to be ferroelectric.     

Antibody-based Detection of <Emphasis Type="Italic">Escherichia coli</Emphasis> O157:H7 and <Emphasis Type="Italic">Salmonella enterica</Emphasis> Serovar Typhimurium Grown in Low-shear Modeled Microgravity

With the advent of prolonged spaceflights, it is important to determine if antibody-based assays can be used to monitor food and water for bacterial contaminants. In the present work, a ground-based high aspect ratio vessel (HARV) was used to determine if low shear modeled microgravity (LSMMG) alters antibody-binding to E. coli O157:H7 and Salmonella enterica serovar Typhimurium. Antibody–bacteria binding was similar under LSMMG and normal gravity because there was no difference in amount of captured bacteria measured by colony forming units (CFU) between assays conducted in the HARV and a conventional roller flask. The ability of E. coli O157:H7 and Salmonella Typhimurium grown in LSMMG to bind specific antibodies was also studied. After incubations of 4, 18 or 36 h in the HARV or a shaking incubator, bacteria were harvested for enzyme-linked immunosorbent assays (ELISA). In the E. coli O157:H7 ELISA using a goat polyclonal primary antibody, LSMMG did not alter the linear range of detection (10⁵–10⁷ cells/ml) nor the signal to noise ratio at any bacterial concentration. Although insignificant changes in signal to noise ratios were evident, LSMMG did not alter the range of detection (10⁵–10⁷ cells/ml) for Salmonella Typhimurium in ELISAs using either a polyclonal or a monoclonal antibody. These results suggest that immunoassays may be used in spacecrafts because LSMMG does not have significant deleterious effects on antibody-binding to bacteria nor does it significantly alter surface antigens necessary for antibody-based methods.     

Experimental and theoretical analysis of selective hydrogenation of <Emphasis Type="Italic">p</Emphasis>-nitroanisole to <Emphasis Type="Italic">p</Emphasis>-anisidine over Pd/C: kinetics and catalyst deactivation

The selective reduction of nitro compounds to the corresponding amines in multi-functional moieties is attempted in a variety of industries using polluting processes including iron–acid and sulfide/polysulfide reduction processes. In the current work, selective hydrogenation of p-nitroanisole (PNA) to p-anisidine (PA) has been carried out using supported metal catalysts. 5% Pd/C was found to be highly effective in comparison with other metal catalysts used. Kinetic interpretation has been made by studying the important process parameters using 5% Pd/C as the catalyst. The experimental results show that conversion of PNA reaches 100% under the appropriate reaction conditions. The reaction was found to be 100% selective towards PA. It was possible to determine both the rate constant and adsorption equilibrium constant for the reaction. The activation energy of reaction and free energy of adsorption were found to be 10.25 and –2.4 kcal mol^–1, respectively, indicating that the reaction is Langmuir-Hinshelwood kinetically controlled. The catalyst was found to be deactivated due to the blocking of channels by product precipitation, which was considered as independent deactivation. A deactivation model was developed and it was found to fit the data very well. A complete theoretical and experimental analysis is presented. Electronic Publication     

Microstructure and magnetic properties of Ni<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> synthesized by combustion reaction

An investigation was made of samples having a chemical formula of Ni_1−x Zn _x Fe₂O₄, where x = 0.3, 0.5 and 0.7. The samples were prepared by the reaction combustion synthesis method and sintered at 1,200 °C/2 h in a static air atmosphere. The influence of the Zn concentration on the relative density, microstructure and magnetic properties of the samples was studied. X-ray diffraction, scanning electron microscopy and magnetic hysteresis loop tracer were used to analyze the compositions. The samples were found to have a spinel cubic structure, sintered density of 92.9%–98.8% of the corresponding X-ray density, homogeneous microstructure with grain size ranging from 1.37 to 3.36 μm, maximum flux density of 0.16–0.35 T, field coercivity ranging from 17 to 168 A/m, and loss hysteresis of 1.5–105 W/kg. Increased grain growth, with fine pores inside the grains, was found to occur as the Zn concentration increased. The overall findings are discussed here in light of the existing understanding of these systems.     

Ab initio study of structural,electronic, phase diagram,and optical properties of CdSe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript><Emphasis Type="Italic">1−x</Emphasis></Subscript> semiconducting alloys

Based on the self-consistent ab initio full potential-linearized augmented plane wave method, the structural, electronic, optical, and thermodynamic properties of CdSe _x Te_1−x ternary semiconductor alloys have been investigated. The exchange–correlation potential was calculated using both the generalized gradient approximation (GGA) by Perdew–Burke–Ernzerhof (PBE) and the GGA by Engel–Vosko (EV-GGA). The ground-state properties are determined for the cubic bulk materials CdSe, CdTe, and their mixed crystals at various concentrations (x = 0.25, 0.5, and 0.75). Deviation of the lattice parameter from Vegard’s law and the bulk modulus from linear concentration dependence has been examined. The microscopic origins of the band-gap bowing parameter have been discussed. Moreover, the refractive index and the optical dielectric constant for CdSe _x Te_1−x are studied using different models. Besides, the thermodynamic stability of the alloys of interest is investigated by means of the miscibility critical temperature.     

Mechanical Properties of (Cu<Subscript>0.5</Subscript>Tl<Subscript>0.5</Subscript>)-1223 Substituted by Pr

Cu_0.5Tl_0.5Ba₂Ca_2−x Pr _x Cu₃O_10−δ superconducting samples, with 0≤x≤0.15, were prepared by a single-step solid state reaction on a form of rectangular bar. The prepared samples were characterized using X-ray powder diffraction (XRD) and scanning electron microscope (SEM). The room temperature Vickers microhardness was measured at different loads (0.25–3 N). The experimental results were analyzed using Meyer’s law, Hays–Kendall approach, elastic/plastic deformation model, proportional specimen resistance model, and the indentation-induced cracking (IIC) model. Surprising results were obtained and showed that all samples in the form of rectangular bars exhibited reverse indentation size effect in contrary with those in the form of discs. Vickers microhardness values were decreased as Pr-content increased that consisting with the porosity results. Furthermore, the Young’s modulus was determined using the dynamic resonance technique. A relation between Young’s modulus (E) and Vickers microhardness (H _V) was obtained.     

Electrical and magnetic properties of (BiNa)<Subscript>1/2</Subscript>(FeV)<Subscript>1/2</Subscript>O<Subscript>3</Subscript>

Potential multiferroic material, (BiNa)_1/2(FeV)_1/2O₃, synthesized using solid-state route is investigated. The phase formation was confirmed by X-ray diffraction and surface morphology by scanning electron microscopy (SEM). Structural data reveal the single phase formation corroborated by SEM. The grain distribution is uniform with an average grain size of 3·6 μm. Electrical properties were investigated in a frequency range (1 kHz–1 MHz) by complex impedance spectroscopy (CIS) technique. The material showed negative temperature coefficient of resistance (NTCR) reflecting semiconductor behaviour. A.C. conductivity was found to obey Johnscher’s law. Conductivity mechanism is discussed and activation energy estimated (1·17 eV) for the conduction process is associated with Fe^3 +→ Fe^2 + variable state. The M–H curve showed the presence of ferromagnetism in the studied material.     

Enhanced Superconducting Properties of Air-Processed GdBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>7-δ</Subscript> Single Domains with BaCO<Subscript>3</Subscript>/BaCuO<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript> Addition

Single domain GdBa₂Cu_7-δ (Gd123) bulk superconductors were fabricated in air by top-seeding melt-texture growth. Performance of the air-processed Gd123 was successfully enhanced by addition of both BaCO₃ and BaCuO_2−x , which suppress the formation of Gd_1+x Ba_2−x Cu₃O_7-δ solid solutions. The optimum doping amount ranges from 0.05 to 0.15, M BaCO₃ and 0.05 to 0.1, M BaCuO_2−x per molar Gd123. The distribution of the second phase particles was observed by scanning electron microscopy. A narrow band formed by Gd₂BaCuO₅ particle concentration appeared around the seeding zone in both a–b plane and c-growth sector in Gd123 single grain. Trapped magnetic field density reached 0.67, T for sample with 24 mm in diameter and 8, mm in thickness and a high critical current density J _c up to 91,200, A/cm² was achieved at 77, K under self-field.     

Phase developments and dielectric responses of barium substituted four-layer CaBi<Subscript>4</Subscript>Ti<Subscript>4</Subscript>O<Subscript>15</Subscript> Aurivillius

In this paper, mixed Ca–Ba oxide Ca_1 − x Ba _x Bi₄Ti₄O₁₅ (CBBT) ceramics, fabricated by the improved traditional ceramics process were investigated by doping concentrations of Ba ion up to x =\emph{x} {=} 0·9 (in steps of 0·1). At room temperature, an orthorhombic crystal system was confirmed using XRD, and their parameter was obtained using the Rietveld method. Dielectric properties and phase transitions were studied and are explained in terms of lattice response of these ceramics. A shift in ferroelectric–paraelectric phase transition (T_C\emph{T}_{C}) to lower temperatures and a corresponding decrease in permittivity peak with increasing concentration of Ba^2 + are also observed. The ferroelectric–paraelectric phase transition of CBBT compounds is of normal type in nature, differing from the relaxor characteristic of BBT. The decrease of orthorhombicity in the lattice structure by the larger Ba^2 + ion incorporation, indicating an approach of a and b, results in lower Curie temperature. Appearance of anomalous loss peaks of Ba-rich compounds at 530°C reveals a phase transition development trend from ferroelectric orthorhombic structure to the paraelectric orthorhombic structure. Relationship of polarization with lattice response is discussed.     

Crossover Behavior of Variable Range Hopping in Bi-Doped C<Subscript>60</Subscript>

Abstract: Mott variable-range hopping (VRH) is characterized by an exp [1/T ^1/4] behavior in the temperature dependence of resistivity and is generally observed near the metal–insulator transition as electron screening increases and the Coulomb gap disappears near the metallic phase, while Efros–Shklovskii VRH, characterized by exp [1/T ^1/2], is found deeper in the insulating region. We have investigated the transport properties of Bi-doped fullerene C₆₀. Samples were prepared via solid state reaction in a sealed quartz tube near 600°C. The resistivity data can be fit with a single function exp [1/T ^υ ] (υ=1/4 or 1/2, depending on the Bi concentration) over the entire temperature range below 300 K and over 5–6 orders of magnitude in resistivity. υ changes from 1/4 to 1/2 as the Bi concentration increases, suggesting a crossover from Mott VRH to intergranular tunneling at higher Bi concentration. The thermoelectric Seebeck coefficient was also measured and is about 20 μV/K at room temperature. It decreases with decreasing temperature. The thermal conductivity of the doped samples is extremely low.     

Formation,thermal, optical and physical properties of GeS<Subscript>2</Subscript>–Ga<Subscript>2</Subscript>S<Subscript>3</Subscript>–AgCl novel chalcohalide glasses

Novel GeS₂–Ga₂S₃–AgCl chalcohalide glasses had been prepared by melt-quenching technique, and the glass-forming region was determined by XRD, which indicated that the maximum of dissolvable AgCl was up to 65 mol%. Thermal and optical properties of the glasses were studied by differential scanning calorimetry (DSC) and Visible-IR transmission, which showed that most of GeS₂–Ga₂S₃–AgCl glasses had strong glass-forming ability and broad region of transmission (about 0.45–12.5 μm). With the addition of AgCl, the glass transition temperature, Tg decreases distinctly, and the short-wavelength cut-off edge (λ_vis) of the glasses also shifts to the long wavelength gradually. However, the glass-forming ability of the glass has a complicated evolutional trend depended on the compositional change. In addition, the values of the Vickers microhardness, H _v , which decrease with the addition of AgCl, are high enough for the practical applications. These excellent properties of GeS₂–Ga₂S₃–AgCl glasses make them potentially applied in the optoelectronic field, such as all-optical switch, etc.     

Growth rate of Nb<Subscript>3</Subscript>Sn for reactive diffusion between Nb and Cu–9.3Sn–0.3Ti alloy

In order to examine experimentally the growth behavior of Nb₃Sn during reactive diffusion between Nb and a bronze with the α + β two-phase microstructure, a sandwich (Cu–Sn–Ti)/Nb/(Cu–Sn–Ti) diffusion couple was prepared from pure Nb and a ternary Cu–Sn–Ti alloy with concentrations of 9.3 at.% Sn and 0.3 at.% Ti by a diffusion bonding technique. Here, α is the primary solid-solution phase of Cu with the face-centered cubic structure, and β is the intermediate phase with the body-centered cubic structure. The diffusion couple was isothermally annealed at temperatures between T = 923 and 1,053 K for various times up to 843 h. Owing to annealing, the Nb₃Sn layer is formed along each (Cu–Sn–Ti)/Nb interface in the diffusion couple, and grows mainly into Nb. Hence, the migration of the Nb₃Sn/Nb interface governs the growth of the Nb₃Sn layer. The mean thickness of the Nb₃Sn layer is proportional to a power function of the annealing time. The exponent of the power function is close to unity at T = 923 K, but takes values of 0.8–0.7 at T = 973–1,053 K. Consequently, the interface reaction at the migrating Nb₃Sn/Nb interface is the rate-controlling process for the growth of the Nb₃Sn layer at T = 923 K, and the interdiffusion across the Nb₃Sn layer as well as the interface reaction contributes to the rate-controlling process at T = 973–1,053 K. Except the effect of Ti, the growth rate of the Nb₃Sn layer is predominantly determined by the activity of Sn in the bronze and thus the concentration of Sn in the α phase. As a result, the growth rate is hardly affected by the volume fraction of the β phase, though the final amount of the Nb₃Sn layer may depend on the volume fraction.     

Study of structure and properties of ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Glasses of the ternary system ZnO–Bi₂O₃–P₂O₅ were prepared and studied in two compositional series 50ZnO–xBi₂O₃–(50 − x)P₂O₅ and (50 − y)ZnO–yBi₂O₃–50P₂O₅. Two distinct glass-forming regions were found in the 50ZnO–xBi₂O₃–(50 − x)P₂O₅ glass series with x = 0–10 and 20–35 mol.% Bi₂O₃. All prepared Bi₂O₃-containing glasses reveal a high chemical durability. Small additions of Bi₂O₃ (∼5 mol.%) improve thermal stability of glasses. All glasses crystallize on heating within the temperature range of 505–583 °C. Structural studies by Raman and ³¹P MAS NMR spectroscopies showed the rapid depolymerisation of phosphate chains within the first region with x = 0–15 and the presence of isolated Q⁰ phosphate units within the second region with x = 20–35. Raman studies showed that bismuth is incorporated in the glass structure in BiO₆ units and their vibrational bands were observed within the spectral region of 350–700 cm⁻¹. The evolution of properties and the spectroscopic data are both in accordance with a network former effect of Bi₂O₃.     

Using computer simulation techniques to design a tellurium-123 target for <Superscript>123</Superscript>I production

The production of ¹²³I from ¹²³Te by the ^l23Te(p, n)¹²³I reaction at various target enrichments (99.9, 91, 85.4, and 70.1%) was simulated using ALICE and SRIM programs. The ¹²³I production feasibility by the above reaction was evaluated. The calculations give more accurate results for proton beam energy of less than 30 MeV. The cross sections of all tellurium reactions with proton were calculated at 0–30 MeV proton beam energy with ALICE program, and the yield of ¹²³I was calculated by analytical methods. Our prediction for ¹²³I production via bombardment of ¹²³Te (99.9%) with a proton beam energy of 5–15 MeV is about 7.2 mCi μA⁻¹ h⁻¹. Published in Russian in Radiokhimiya, 2008, Vol. 50, No. 5, pp. 460–463. The text was submitted by the authors in English.     

An Experimental Study of the <Emphasis Type="Italic">pVTx</Emphasis> Properties for Aqueous Solutions of Ammonia Focusing on the Maximum Density Region

An experimental study of the pressure–volume–temperature-composition (pVTx) properties for the aqueous solution of ammonia, namely NH₃–H₂O mixtures, has been conducted with the use of a constant-volume apparatus, especially focusing on the maximum density behavior, in the range of temperatures from 253 to 309 K, pressures from 0.47 to 16.93 MPa, densities from 950 to 1007 kg · m⁻³ and compositions from 0 to 0.1436 mole fraction of ammonia. The behavior of the maximum densities for the aqueous solution of ammonia has been investigated for the first time by the present experimental study, and the available equations of state do not represent the pVTx properties of the present measured data adequately near the maximum density region. Paper presented at the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder, Colorado, U.S.A.     

Electrical and optical properties of InSbSe<Subscript>3</Subscript> amorphous thin films

Electrical conductivity, I–V characteristics and optical properties are investigated for InSbSe₃ amorphous thin films of different thicknesses prepared by thermal evaporation at room temperature. The composition of both the synthesized material and thin films were checked by energy dispersive X-ray spectroscopy (EDX). X-ray analysis indicated that all samples under investigation have amorphous structure. The dc electrical conductivity was measured in the temperature range (303–393 K) and thickness range (149–691 nm). The activation energy ΔE _σ was found to be independent of film thickness in the investigated range. The obtained I–V characteristic curves for the investigated samples are typical for memory switches. The switching voltage increases linearly with film thickness in the range (113–750 nm), while it decreases exponentially with temperature in the range (303–393 K). The switching process can be explained according to an electrothermal process initiated by Joule-heating of the current channel. Measurements of transmittance and reflectance in the spectral range (400–2,500 nm) are used to calculate optical constants (refractive index n and absorption index k). Both n and k are practically independent of film thickness in the investigated range (149–691 nm). By analysis of the refractive index n the high frequency dielectric constant ε_∞ was determined via two procedures and was found to have the values of 9.3 and 9.15. Beyond the absorption edge, the absorption is due to allowed indirect transitions with energy gap of 1.46 eV independent on film thickness in the investigated range.     

Microwave assisted enzyme catalysis for synthesis of <Emphasis Type="Italic">n-</Emphasis>butyl dipheyl methyl mercapto acetate in non-aqueous media

n-Butyl dipheyl methyl mercapto acetate is an important pharmaceutical intermediate, having applications in the synthesis of Modafinil, a CNS stimulant drug. The current process is highly polluting and requires alternate green processes. Synthesis of it was carried out via lipase in the presence of microwave irradiation. Optimization of reaction conditions, such as catalyst loading, mole ratio of reactants, reaction temperature, water concentration and reusability of catalysts under the microwave irradiation was done. Among all, the commercially available lipases Novozym 435 was found best and gives the conversion 34% in 24 h at 60°C. A ping–pong bi–bi model with substrate n-butanol inhibition at higher concentration was found to be suitable for kinetics of the reaction.     

Bibliometric characteristics of the journal <Emphasis Type="Italic">Science</Emphasis>: Pre-Koshland,Koshland and post-Koshland period

During the period 1985–1995 Daniel Koshland was Editor-in-Chief of the journal Science. As such he exerted a huge influence on all aspects related to content and lay-out of the journal. This study compares Science’s bibliometric characteristics between three periods: a pre-Koshland (1975–1984) period, the Koshland period (1985–1995) and the post-Koshland period (1996–2006). The distributions of document types, the country/territory and institutional distribution of authors, co-authorship data and disciplinary impact measured by subject categories of citations are studied. These bibliometric characteristics unveil some of the changes the journal went through under the leadership of Daniel Koshland.     

In situ X-ray study of order–disorder phase transitions in Cu–Al–Be melt spun ribbons

The disorder–order phase transitions in Cu–Al–Be shape memory alloys were studied by in-situ X-ray diffraction. Isothermal measurements in an inert gas chamber were made on ribbons of Cu–Al–Be alloys, obtained by melt spinning. A position sensitive detector was used for a fast record of the X-ray signal on a θ–θ geometry diffractometer. Each ribbon was used as the heating element, avoiding the need of a heating sample holder and obtaining a better measurement of the temperature with a thermocouple attached directly to the ribbon. The order transition was followed at different temperatures after a high temperature annealing (700 °C) in the disordered β-phase region. A first order transition was observed from disordered β (A2) to ordered β ₁ (DO₃), without prior β (B2) ordering. No precipitation was detected during this fast measuring procedure.