Formation and peculiarities of heterogeneity in polyethylene samples obtained by extrusion

Three-layer structure was observed in the polyethylene strips obtained under definite conditions of extrusion, with the high degree of orientation of the core layer being most remarkable. The wide-and small-angle X-ray investigation of the different layers of the strips and the pole figures analysis were performed. In the outer layers a texture is formed. Crystalline structure formed in the core is characterized by almost regular cylindrical arrangement of a and b axes around the extrusion direction. The c axes direction almost coincides with the extrusion direction. In the core of the extruded strand, lamellae are arranged in parallel stacks. The angle value between the normal to the lamellae surface direction and the extrusion direction is about 30°.     

Catalytic Decomposition of Organic Anions in Alkaline Radioactive Waste: 1. EDTA Oxidation

Decomposition of ethylenediaminetetraacetate in alkaline solutions with H₂O₂, Na₂S₂O₈, NaClO, and NaBrO was studied titrimetrically. EDTA is oxidized in solutions heated above 60°C in the presence of cobalt salts at stepwise addition of excess H₂O₂. The reaction between persulfate and EDTA has an induction period decreasing with increasing NaOH concentration and temperature and with decreasing initial EDTA content or with adding AgNO₃, K₄Fe(CN)₆, or NaNO₂. The process involves thermal dissociation of the persulfate ions into radical ions and the subsequent development of a chain reaction. Hypochlorite ions oxidize EDTA in 0.5-5.0 M NaOH at 25-60°C. The process efficiency can be improved by fractional addition of the oxidant in the presence of Co(II) or Ni(II) salts. EDTA is oxidized in alkaline solutions with hypobromite ions only on heating to 95°C. Salts of Co(II), Ni(II), and Cu(II) accelerate the process.     

Microphase structure features of network block polymer over a wide temperature range

Changes in the microheterogeneous structure of a network block polymer based on diene and epoxy blocks have been studied using the small-angle X-ray scattering technique with a position sensitive detector. The formation of a three-dimensional chemical bond network is shown to result in microphase separation of chemically distinct blocks. The resulting microphase structure is stabilized by the three-dimensional network which prevents the establishment of a thermodynamic equilibrium in the system over a wide temperature range.     

Interaction of U(VI), Np(VI), and Pu(VI) ions with unsaturated heteropolytungstates of the 17th and 11th series in aqueous solutions

The stability constants of the complexes of U(VI), Np(VI), and Pu(VI) with the heteropolyanions (HPAs) P₂W₁₇O ₆₁ ^10? , SiW₁₁O ₃₉ ^8? , and PW₁₁O ₃₉ ^7? in solutions with pH from ?0.3 (2 M H⁺) to 5–5.5 in the presence of Na or K salts (up to 2 M) and without them were measured. All the complexes have exclusively the 1: 1 composition; their stability constants β^M(VI) in neutral solutions at a low ionic strength are close to 10⁸ 1 mol^?1. In 0.1–2.0 M acid solutions, log β^M(VI) for the complexes with P₂W₁₇O ₆₁ ^10? is within 1.4–3.9. The slope of the pH dependence of log β^M(VI) does not exceed 1.75; this fact suggests that no more than two protons are displaced from HPA upon complexation in acid solutions. In the presence of 1–2 M sodium salts, the β^M(VI) values reach a maximum at pH ～3 and drastically decrease with a further increase in pH. Actinides(VI) interact with HPAs appreciably more weakly than do actinides(III), which is apparently due to the fact that the denticity of HPAs in the complexes with An(VI), apparently, does not exceed 2.     

Formal oxidation potentials of actinide couples in K<Subscript>10</Subscript>P<Subscript>2</Subscript>W<Subscript>17</Subscript>O<Subscript>61</Subscript> solutions

The formal oxidation potentials of the M(VI)/M(V), M(V)/M(IV), and M(IV)/M(III) couples for actinides from U to No and of the M(IV)/M(III) couples for some actinides in 1 M H⁺ or 1 M Na⁺ (pH ～5–5.5) solutions containing K₁₀P₂W₁₇O₆₁ were calculated from the data on stability of complexes of f element ions with the unsaturated heteropolytungstate anion P₂W₁₇O ₆₁ ^10? . In some cases, the previously accepted values were subjected to major revision, especially the potentials of the An(V)/An(IV) couples. Problems arising in measuring the potentials of the couples involving Np(III) and Pu(III) which react with the heteropolyanion to form a heteropoly blue are discussed. The potentials of some M(III)/M(II) couples are estimated.     

Accurate event-driven motion compensation in high-resolution PET incorporating scattered and random events

With continuing improvements in spatial resolution of positron emission tomography (PET) scanners, small patient movements during PET imaging become a significant source of resolution degradation. This work develops and investigates a comprehensive formalism for accurate motion-compensated reconstruction which at the same time is very feasible in the context of high-resolution PET. In particular, this paper proposes an effective method to incorporate presence of scattered and random coincidences in the context of motion (which is similarly applicable to various other motion correction schemes). The overall reconstruction framework takes into consideration missing projection data which are not detected due to motion, and additionally, incorporates information from all detected events, including those which fall outside the field-of-view following motion correction. The proposed approach has been extensively validated using phantom experiments as well as realistic simulations of a new mathematical brain phantom developed in this work, and the results for a dynamic patient study are also presented.      

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.     

The reaction Pu(VI) + Fe(CN)<Stack><Subscript>6</Subscript><Superscript>3−</Superscript></Stack> ⇄ Pu(VII) + Fe(CN)<Stack><Subscript>6</Subscript><Superscript>4−</Superscript></Stack> in NaOH solutions

A spectrophotometric study showed that, in 5 M NaOH, Pu(VII) prepared by ozonation of Pu(VI) is reduced with excess K₄Fe(CN)₆. The Pu(VII) content can be estimated from the amount of the Fe(CN)₆³⁻ formed. In NaOH solutions of concentration exceeding 8 M, the Fe(CN)₆³⁻ ion oxidizes Pu(VI). In 10.3 M NaOH, the tenfold excess of K₃Fe(CN)₆ fully converts 1 mM Pu(VI) to the heptavalent state within 4 min (rate constant 1.3 l mol⁻¹ s⁻¹ at 20°C). With an increase in the NaOH concentration, the oxidation rate increases, and smaller excess of K₃Fe(CN)₆ is required. This oxidant is consumed not only for Pu(VI) oxidation but also in reactions with H₂O and OH⁻ ions. Pu(VII) is unstable and is slowly reduced with water and with products of decomposition of iron complexes.