Determination of rare-earth elements by the simultaneous gamma-neutron activation analyses using a microtron

The combination of photon and neutron activation provides an effective method of analysis of rare earths and other elements. A mixed -neutron field is obtained with electron-to-gamma /e/ and gamma-to-neutron /n/ converters combined with a lucite moderator. The samples are activated simultaneously. The sensitivities of this method have been compared with neutron activation in a graphite moderator cube using the same microtron. The advantages and shortcomings of the method are discussed.Dedicated to Prof. V.D. Nefedov on the occasion of his 70th birthday     

Einige Reaktionen der Siliciumtetrahalogenid-Pyridin-Additionsverbindungen

Zusammenfassung Siliciumtetrahalogenid-Pyridin-Addukte reagieren mit Halogenwasserstoffen schon bei Raumtemp. unter Pyridin-Übertragung (vgl. Rk. 1) und, bei positiverem Halogen am Silicium, unter gleichzeitigem Halogenaustausch (vgl. Rk. 2). Analoge Austauschreaktionen finden zwischen Siliciumhalogeniden und Pyridiniumhalogeniden statt (vgl. Rk. 3). Gemischte Silicium-halogenide ließen sich auf diesem Wege nicht darstellen; die Dismutationsneigung gemischter Siliciumhalogenide wird durch Anwesenheit von Pyridinium-Ionen offensichtlich verstärkt. Gegenüber SO₂, SO₃, NH₃ oder H₂S zeigen die Additionsverbindungen eine etwas größere Reaktionsbereitschaft als die freien Siliciumhalogenide.

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The silicontetrahalogenide-pyridine addition compounds react with hydrogen halogenides at room temperature according equation (1), in case of more positive halogen atoms on silicon with simultaneous exchange of the halogen atoms (equ. 2). Analogous exchange reactions are to be observed between silicon halogenides and pyridinium halogenides (equ. 3). It was not possible to prepare mixed silicon halogenides by this method. The addition compounds seem to react with SO₂, SO₃, NH₃ and H₂S somewhat easier than the free silicon halogenides.

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67. Mitt.:U. Wannagat, K. Hensen undF. Vielberg, Mh. Chem.99, 431, (1968).

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Zugleich 8. Mitt. über Verbindungen von Nichtmetallhalogeniden mit Pyridin und seinen Homologen; 7. Mitt. vgl.

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Mit Auszügen aus den DissertationenH. Voß, F. Vielberg undK. Hensen, Techn. Hochschule Aachen 1954 bzw. 1956 bzw. 1962, und der DiplomarbeitP. Petesch, Techn. Hochschule Aachen 1958.     

Synthesis of new 14-membered macrolide antibiotics via a novel ring contraction metathesis

[reaction: see text] A novel ring opening ring closing metathesis (ROM-RCM) was demonstrated for cyclic conjugated dienes, effecting the excision of a C(2)H(2) unit and a net ring contraction. Applying the ring contraction metathesis, new 14-membered ring macrolide antibiotics were synthesized in a single step from existing 16-membered ring macrolides. This new class of macrolide antibiotics will provide access to new therapeutics for the treatment of macrolide-resistant bacterial infections.     

Microcalorimeter arrays for ultra-high energy resolution X- and gamma-ray detection

Microcalorimeter detectors provide superior energy resolution for the detection of X-rays and gamma-rays. The technology utilizes a cryogenic transition-edge sensor (TES) coupled to a tin bulk absorber. We are working on fabrication methods for the production of arrays with many sensors. In this paper, we present data collected with an array of microcalorimeters using as many as 26 sensor elements simultaneously. Advances in sensor design have extended the useful dynamic range to photon energies up to ～200 keV, while providing resolution performance in the 80–90 eV FWHM range, significantly better than planar high-purity germanium. These sensor arrays have applications in the measurement of nuclear materials. We present data collected from ¹⁵³Gd, a highly-enriched uranium sample, and a plutonium isotopic standard source. We also demonstrate clean separation of the ²³⁵U 185.715 keV peak from the ubiquitous ²²⁶Ra 186.211 keV background peak interference.     

Effect of BaTiO3 on the aging process of PLA fibers obtained by centrifugal spinning

This study focused on the fabrication of a composite of polylactic acid fibers reinforced with barium titanate (BT) and obtained by centrifugal spinning. Different concentrations of inorganic powder (5, 10, and 15 wt%) have been added to the polymeric solution and the samples have been studied to monitor any modification in chemical, morphological, thermal, and mechanical properties. Subsequently, samples have been subjected to UV/O₃ irradiation at two different times (5 and 10 min) with the aim to verify the resistance to aging, which is considered a key factor for medical applications and outdoor. The presence of BT influenced strongly the structure of the fibers in many aspects. Samples with the lowest amount of BT showed a clear decrease of chemical and consequently of mechanical properties manifested with the breakage of the fibers subjected to treatment. The other composites apparently showed similar chemical properties comparing with the one without fillers but the mechanical properties clearly decreased. However, what emerged from the study is a clear stability during the aging tests promoted by the presence of BT. The samples with 10 and 15 wt% of BT presented chemical, thermal, and mechanical stabilities differently from the other samples. These results suggested that the fillers clearly modified the degree of crystallinity acting as nucleation agents and promoting the development of a stable crystalline phase during the treatment.     

Regularization of a final value problem for a nonlinear biharmonic equation

In this paper, we consider the nonlinear biharmonic equation. The problem is ill‐posed in the sense of Hadamard. To obtain a stable numerical solution, we consider a regularization method. We show rigourously, with error estimates provided, that the corresponding regularized solutions converge to the true solution strongly in uniformly with respect to the space coordinate under some a priori assumptions on the solution.     

A Method of Manufacturing Highly Conductive Composite Materials by Coating Surfaces of Nonconductors with Fine Particulate Conductive Substances

 A widely applicable aqueous dip-coating process termed substrate induced coagulation (SIC) suitable for coating various types of substrates (e.g. polar and unpolar polymers, inorganic glasses, metals) with fine particulate materials (e.g. carbon blacks, small particle size SiO₂ or TiO₂) has been developed. This process is based on the interaction of a conditioner (water soluble polymers or polyelectrolytes, e.g. proteins, polyvinylalcohols, polyacrylates with low charge density) which is adsorbed on the substrate with a surfactant-stabilized dispersion containing some additional electrolyte. Employing dispersions of conductive particles, the resulting coatings can be used as a conductive starting layer for electroplating. Such layers are fairly rinse-proof and may be applied in the metallization process of through holes in printed wiring boards or for the production of highly conductive composite materials from coated particles. SIC has also been used to improve the distribution of carbon in composite battery electrodes such as MnO₂/C.     

QUANTUM DEFECT THEORY: RYDBERG STATES OF THE NO MOLECULES

The NO molecule.in Rydberg states consists of a closed shell molecular ion and an excited electron in a Rydberg molecular bital. It is a comparatively simple but non-trivial excited molecule. Here, we present our theoretical calculation of the quantum defects of these Rydberg states. The theoretical results are in good agreement with the experimental data.