Synthesis of the proposed structure of phaeosphaeride A

The first total synthesis of the proposed structure of phaeosphaeride A has been achieved via six-membered-ring formation by means of an intramolecular vinyl-anion aldol reaction as the key step. This synthesis suggests a revised configurational assignment for phaeosphaeride A.     

Kinetics of thermal decomposition of MCO3 to MO (M=Ca,Sr and Ba)

The kinetics of the thermal decompositions of CaCO₃, SrCO₃ and BaCO₃ into their oxides were studied by thermogravimetry at constant and linearly increasing temperatures. The kinetics of the isothermal decompositions of calcium and strontium carbonates were described by the lawR _n =1–(1–)^1/n , wheren=1.8 and 1.2, respectively. The kinetics of the non-isothermal decompositions of the two carbonates, analysed by the Ozawa and Coats-Redfern methods, were in keeping with the isothermal kinetics. True kinetic compensation laws were established for each decomposition of the two carbonates, including the data under both isothermal and non-isothermal conditions.As concerns the decompositions of BaCO₃, however, there was some difference between the kinetic features relating the isothermal and non-isothermal conditions. A true kinetic compensation law was not established in this case.

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Zusammenfassung Die Kinetik der thermischen Zersetzung von CaCO₃, SrCO₃ und BaCO₃ zu den Oxiden wurden durch Thermogravimetrie bei konstanter und linear ansteigender Temperatur untersucht. Die Kinetik der isothermen Zersetzung von Calcium- und Strontium-carbonat folgt dem GesetzR _n =1–(1 –)^1/n, won=1,8 bzw. 1,2. Die Kinetik der nichtisothermen nach den Methoden von Ozawa und Coats-Redfern analysierten Zersetzung der zwei Carbonate ist in Übereinstimmung mit der isothermen Zersetzung. Wahre kinetische Kompensationsgesetze wurden für die Zersetzung der beiden Carbonate erhalten, einschließlich der sich sowohl auf isotherme als auch auf nichtisotherme Bedingungen beziehenden Daten. Was die Zersetzung von Bariumcarbonat betrifft, so wurden einige Unterschiede im kinetischen Verhalten bei der Zersetzung unter isothermen und nichtisothermen Bedingungen festgestellt. Ein wahres kinetisches Kompensationsgesetz konnte in diesem Falle nicht ermittelt werden.

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, . R _n =1–(1–)^1/n , , , 1,8 1,2. , -, . « » , . , , . - «» .

     

Numerical solutions to the time-dependent Bloch equations revisited

The purpose of this study was to demonstrate a simple and fast method for solving the time-dependent Bloch equations. First, the time-dependent Bloch equations were reduced to a homogeneous linear differential equation, and then a simple equation was derived to solve it using a matrix operation. The validity of this method was investigated by comparing with the analytical solutions in the case of constant radiofrequency irradiation. There was a good agreement between them, indicating the validity of this method. As a further example, this method was applied to the time-dependent Bloch equations in the two-pool exchange model for chemical exchange saturation transfer (CEST) or amide proton transfer (APT) magnetic resonance imaging (MRI), and the Z-spectra and asymmetry spectra were calculated from their solutions. They were also calculated using the fourth/fifth-order Runge-Kutta-Fehlberg (RKF) method for comparison. There was also a good agreement between them, and this method was much faster than the RKF method. In conclusion, this method will be useful for analyzing the complex CEST or APT contrast mechanism and/or investigating the optimal conditions for CEST or APT MRI.     

Molecular field model for -Mn5Ge2

A calculation is made on the thermomagnetic curves of an N-type ferrimagnet -Mn₅Ge₂, based on the molecular field theory using the magnetic structure determined by the neutron diffraction. The resultant magnetization calculated as a function of temperature reproduces the features of the experimental curve.     

Field-induced functions of porous Si as a confined system

Electroluminescent porous Si (PS) diodes exhibit various useful functions under a high-electric field. The experimental PS diodes are composed of thin semitransparent metal films, PS layers (about 500 nm thick in minimum), p- or n-type Si substrates and ohmic back contacts. Definite nonlinear electrical behavior (negative resistance and nonvolatile bistable memory effects) and cold electron emission phenomena appear in these PS diodes associated with the EL emission. Both the negative resistance and memory effects are related to the charging of Si nanocrystallites by field-induced carrier injection. The electron emission observed in the PS diodes formed on n+–Si substrates is caused by hot electrons tunnelling through the top contact. By an appropriate structural control of PS, the effective drift length under a high-field conduction is significantly increased, and then electrons are emitted ballistically. These functions reflect the activity of PS as a nanocrystalline confined system.     

Supersymmetric nonlinear sigma models constrained on non-compact manifold

A detailed analysis by 1/n expansion is presented of supersymmetric nonlinear sigma models in two dimensions withU(n) symmetry in which the scalar fields are constrained on a non-compact manifold. The theories are ultraviolet finite. In the massless version of the models no mass scale is generated and gauge bosons fail to get dynamics while this is possible provided the theory contains a mass scale. The effects of introduction of the “Ø-term” into supersymmetric theories are also discussed. In particular, it is argued that supersymmetry is broken by the Ø-term only in finite supersymmetric theories. Finally, a singular behavior in the massless limit in these models is pointed out.     

Kinetics of self-decomposition and hydrogen atom transfer reactions of substituted phthalimide N-oxyl radicals in acetic acid

Kinetic data have been obtained for three distinct types of reactions of phthalimide N-oxyl radicals (PINO(.)) and N-hydroxyphthalimide (NHPI) derivatives. The first is the self-decomposition of PINO(.) which was found to follow second-order kinetics. In the self-decomposition of 4-methyl-N-hydroxyphthalimide (4-Me-NHPI), H-atom abstraction competes with self-decomposition in the presence of excess 4-Me-NHPI. The second set of reactions studied is hydrogen atom transfer from NHPI to PINO(.), e.g., PINO(.) + 4-Me-NHPI <=> NHPI + 4-Me-PINO(.). The substantial KIE, k(H)/k(D) = 11 for both forward and reverse reactions, supports the assignment of H-atom transfer rather than stepwise electron-proton transfer. These data were correlated with the Marcus cross relation for hydrogen-atom transfer, and good agreement between the experimental and the calculated rate constants was obtained. The third reaction studied is hydrogen abstraction by PINO(.) from p-xylene and toluene. The reaction becomes regularly slower as the ring substituent on PINO(.) is more electron donating. Analysis by the Hammett equation gave rho = 1.1 and 1.8 for the reactions of PINO(.) with p-xylene and toluene, respectively.     

New interpolation technique for the CIP method on curvilinear coordinates

We propose a new interpolation technique for the CIP method applied to curvilinear coordinates. The CIP method can hardly maintain third-order accuracy on curvilinear coordinates. The reason for the degeneracy in accuracies has not been discussed in detail. This paper reveals the problems of the CIP method on curvilinear coordinates and presents an improved CIP method to solve the advection equation accurately. The features of the presented method are: (1) the metric computation on the upwind stencil is defined in the same manner as in the advection phase of the CIP method; and (2) gradient values in the physical domain in the computation on the curvilinear coordinates are used. Various test problems show that the improved CIP method has approximate third-order accuracy.     

Comparative study on the thermal behavior of structural concretes of sodium-cooled fast reactor

Journal of Thermal Analysis and Calorimetry - Thermal behaviors of two different siliceous concretes used in a sodium-cooled fast reactor were comparatively investigated in a temperature range from...     

Synthesis of maremycins A and D1 via cycloaddition of a nitrone with (E)-3-ethylidene-1-methylindolin-2-one

A concise synthesis of maremycins A and D1 has been accomplished via cycloaddition of a chiral cyclic nitrone with ( E)-3-ethylidene-1-methylindolin-2-one as a key step. This synthesis clarifies the stereochemistry of the maremycins and is suitable for large-scale synthesis for biological screening.