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Abstract  

We show that every T 1 wN-space is expandable and as a corollary, we prove that a ϑ-refinable sym-wg T 1 space is paracompact and thus two problems of Chris Good are solved. We also investigate s-expandability, and for extremally disconnected spaces, a characterization of s-expandability is given in terms of covers, which gives an extension to a known result.

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Abstract  

The partition of uranium(VI) between nitric acid solutions and solutions of N,N-dibutyldodecanamide (DBDA) in kerosene has been investigated at varying concentrations of nitric acid, extractant, salting-out agent LiNO3 and at different temperatures. The mechanism of extraction is discussed in the light of the results obtained.

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Abstract  

A new diamide N,N,N,N-tetrahexylsuccinylamide (THSA) was synthesized, characterised and used for the extraction of U(V) and Th(IV) from nitric acid solutions in a diluent composed of 50% 1,2,4-trimethylbenzene (TMB) and 50% kerosene (OK). Extraction distribution coefficients of U(VI) and Th(IV) as a function of aqueous nitric acid concentration, extractant concentration and temperature have been studied. The composition of extracted species, equilibrium constants and enthalpies of extraction reactions have also been calculated. The IR spectra of saturated extraction of U(VI) and Th(IV) were recorded.

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Abstract  

Prompt k 0-factors relative to chlorine and relative g-emission intensities were determined for the strong non-1/v absorbers 113Cd, 149Sm, 151Eu,155Gd and 157Gd. Measurements were performed using the SNU-KAERI prompt gamma activation analysis (PGAA) facility at the Korea Atomic Energy Research Institute (KAERI). For proper experimental determination of the prompt k 0-factors, the effective g-factor and cadmium ratio were taken into account, in consideration of the effects from the non-1/v capture cross section and neutron spectrum in the thermal and epithermal energy region. By using the actual spectrum of the neutron beam in this study, the effective g-factor was obtained by calculation, and the influence of epithermal neutrons on the capture rate was corrected by measuring the cadmium ratio for each non-1/v target isotope. The measured prompt k 0-factors were used to check the consistency between the existing dataset of the absolute g-emission intensity and the 2200 m/s capture cross section for these isotopes.

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Abstract  

The development of a new radionuclide generator, based on118Te/118Sb, has been studied. The 3.5 minute118Sb daughter activity decays principally by positron emission and has potential use as a flow tracer. The118Te parent is conveniently produced by proton bombardment of antimony targets. A simple and efficient scheme for the separation of radiotellurium from proton-irradiated antimony targets has been developed, and thin-target cross sections for121Sb(p, 4n)118Te and competing reactions have been determined. For antimony targets irradiated with 46 MeV protons, the yields (mCi/g Ah) of118Te,119mTe and119Te were measured to be 0.71, 0.33 and 1.9, respectively. The adsorption and elution characteristics of activated carbon for tellurium have been evaluated for use as a column chromatography adsorbent in a118Te/118Sb generator. The conditions for optimal118Sb elution and minimal118Te breakthrough for promising systems are presented.

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Abstract  

Thermal behaviour of tri(O,O'-diisopropyldithiophosphate)cobalt(III), Co(dptp)3 and bis (O,O'-diethyldithiophosphate)nickel(II), Ni(detp)2 and its adducts with pyridine, Ni(detp)2(py)2 or 4-methylpyridine, Ni(detp)(mpy)2 in a dynamic nitrogen atmosphere was investigated by TG-DTG and DSC techniques, which showed a medium endothermic peak for the evolution process of pyridine(or 4-methylpyridine) and a strong exothermic peak for that of O,O'-diethyldithiophosphate. The thermal stability and decomposition patterns for these compounds were compared and interpreted in terms of structural features such as bond character and steric effects. The kinetic parameters and mechanisms of every decomposition stage involved for all these complexes were obtained employing the non-isothermal kinetic analysis method suggested by Malek et al., which showed the kinetics mechanism for pyrolysis of pyridine(or 4-methylpyridine) is an S-B empirical model with lower activation energy, while that of O,O'-dialkyldithiophosphate is a diffusion model. These results are in accord with the fact that two ligands are of different type.

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The hypothesis of niche differentiation with respect to resources is considered to be one of the most influential explanations for the maintenance of species diversity. The hypothesis has been examined extensively by testing its prediction of species-habitat association, which posits that the spatial distribution of species is highly correlated with environmental variables. However, we argue that widespread evidence of the species-habitat association lacks adequate rigor to justify the niche differentiation hypothesis. In this study, we tested whether and to what extent the observed species-habitat association could be caused by ecological processes other than niche differentiation, in a 20-ha subtropical forest plot. The niche differentiation hypothesis was evaluated by testing the species-habitat association and performing a cross-evaluation of the habitat-diversity expectation, which posits that a strong positive correlation exists between species diversity and habitat complexity. Failure to support the habitat-diversity expectation would at a minimum indicate that the niche differentiation hypothesis might not be the main underlying process of species distribution, despite prevalence of the species-habitat association in the same plot. Our analysis revealed that distributions of most species (86.11%) in the plot were significantly associated with at least one of eight topographical and soil nutrient variables. However, there was almost no significant positive correlation between species diversity and habitat complexity at various spatial scales in the same plot. The results indicate that additional caution is warranted when interpreting the species-habitat association from the niche differentiation perspective. A significant species-habitat association indicates only a species’ habitat preference. The association may reveal nothing about interspecific differences in habitat preference, which is a requirement of the niche differentiation hypothesis.

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Genetic structure of 142 parent lines of sorghum [Sorghum bicolor (L.) Moench] was analyzed using model-based approach based on SSR markers. Forty-one selected from 103 SSR markers were used to analyze the parent lines, which generated 189 alleles revealed by each marker ranging from 2 to 11 with an average of 4.6 per marker. The polymorphic information content (PIC) value was 0.543 with a range of 0.089 to 0.850. All the parent lines were assigned to 7 subgroups, named Kafir, Kaoliang, Feterita, Shallu, Hegari, Milo and Durra. Parent lines without clear pedigree record were clustered into their corresponding groups, and genetic components of each line were estimated by Q-values. Information of this study would be useful for breeders to conclude their genetic background and select appropriate parents for germplasm improvement and hybrid breeding, and thus improve the efficiency of breeding programs.

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Abstract  

Various techniques and methodologies of thermal conductivity measurement have been based on the determination of the rate of directional heat flow through a material having a unit temperature differential between its opposing faces. The constancy of the rate depends on the material density, its thermal resistance and the heat flow path itself. The last of these variables contributes most significantly to the true value of steady-state axial and radial heat dissipation depending on the magnitude of transient thermal diffusivity along these directions. The transient hot-wire technique is broadly used for absolute measurements of the thermal conductivity of fluids. Refinement of this method has resulted in a capability for accurate and simultaneous measurement of both thermal conductivity and thermal diffusivity together with the determination of the specific heat. However, these measurements, especially those for the thermal diffusivity, may be significantly influenced by fluid radiation. Recently developed corrections have been used to examine this assumption and rectify the influence of even weak fluid radiation. A thermal conductivity cell for measurement of the thermal properties of electrically conducting fluids has been developed and discussed.

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Summary  

The prompt k 0,H factors for B, N, Si, P, S and Cl were determined relative to the 2223.25 keV gamma-line from the 1H(n,γ) reaction. The measurements were performed at the SNU-KAERI Prompt Gamma Activation Analysis facility, of which the background was greatly reduced recently by upgrading the detection system to a Compton suppressed g-ray spectrometer with a BGO/NaI(Tl) guard detector and by improving the shield geometry. From the measured prompt k 0,H factors, the partial γ-ray production cross sections were determined using the latest cross section for H. The measured prompt k 0,H factors were tabulated and compared with the other reported data.

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