Polar steroidal compounds from the Far-Eastern starfish Lethasterias nanimensis chelifera

In addition to the salts described previously (with a sulfated steroid as the anion and the alkaloid salsolinol as the cation), nine other steroidal compounds including three new compounds were isolated from the Far-Eastern starfish Lethasterias nanimensis chelifera collected near the coast of the Onekotan island (Kuril isles). A nonsteroidal compound found in this starfish is (1S,3S)-1-methyl-1,2,3,4-tetrahydro-lv2790t60104170p/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-carboline-3-carboxylic acid. The structures of the isolated compounds were determined by NMR spectroscopy and mass spectrometry.     

A Tsallis’ statistics based neural network model for novel word learning

We invoke the Tsallis entropy formalism, a nonextensive entropy measure, to include some degree of non-locality in a neural network that is used for simulation of novel word learning in adults. A generalization of the gradient descent dynamics, realized via nonextensive cost functions, is used as a learning rule in a simple perceptron. The model is first investigated for general properties, and then tested against the empirical data, gathered from simple memorization experiments involving two populations of linguistically different subjects. Numerical solutions of the model equations corresponded to the measured performance states of human learners. In particular, we found that the memorization tasks were executed with rather small but population-specific amounts of nonextensivity, quantified by the entropic index q. Our findings raise the possibility of using entropic nonextensivity as a means of characterizing the degree of complexity of learning in both natural and artificial systems.     

Reactions of cyclic α-methoxy nitrones with nucleophilic reagents

Reactions of cyclic lv2k71m3/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-methoxy nitrones, which are derivatives of imidazole or dihydroimidazole N-oxides, with amines, KOH, or KSH result in the replacement of the MeO group to form cyclic lv2k71m3/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">-amino nitrones, hydroxamic acids, or thiohydroxamic acids, respectively. Analogous reactions occur with C-nucleophiles.     

Crystal structure of 4-methylpyridinium 2,4-dinitrophenolate

A crystalline salt of 4-methylpyridinium 2,4-dinitrophenolate has been prepared and characterized by X-ray crystallography. The salt crystallizes in the monoclinic space group P2_1/c with a = 9.105(2), b = 7.617(2), c = 18.424(3) Å, lv9jcfrp18g/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0"> = 90.00, lv9jcfrp18g/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0"> = 101.19(1), lv9jcfrp18g/xxlarge947.gif" alt="gamma" align="MIDDLE" BORDER="0"> = 90.00°, V = 1253.5(5) ų, and Z = 4. In the title salt, the phenolate and pyridinium ion are held by bifurcated hydrogen bonds of N–H···O, and are arranged in an almost coplanar manner to each other due to two sets of CHO hydrogen bonds. The geometrical arrangement in the title salt is characterized by the formation of herringbone motif of 4-methylpyridinium 2,4-dinitrophenolate. The herringbone motif is stablized by CHO hydrogen bonds. The face-to-face interval between the phenolate and pyridinium ring is 3.3094 Å, in a range governed by lv9jcfrp18g/xxlarge960.gif" alt="pgr" align="BASELINE" BORDER="0">–lv9jcfrp18g/xxlarge960.gif" alt="pgr" align="BASELINE" BORDER="0"> interaction.     

Some problems in PTC theory: solvation,crystalline lattice strength,and topology

It was shown thatS _N2-type reactions both in solid-liquid and liquid-liquid systems can proceed at the interface through the formation of cyclic adsorption complexes. The conditions for the formation of the latter were formulated, and the kinetic and thermodynamic parameters of reaction with solid ionophoric salts were estimated. A linear relation between the energy of the crystalline lattice of the salt and its melting point was estimated, the latter being shown to be useful as a simplified estimation of the reactivity of solid salts in reactions where the crystalline lattice is destroyed. In solid-liquid systems the lv06h8657/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">benzenelv06h8657/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0"> effect of solvents was discussed. In highly basic nitrogen-containing solvents (pyridine,etc.), a substitution reaction proceeds in the absence of a PT catalyst. The role of hydration in liquid-liquid systems was discussed.Reviews published in this issue were prepared on the basis of lectures presented at the conference lv06h8657/xxlarge8220.gif" alt="ldquo" align="MIDDLE" BORDER="0">Phase Transfer Catalysis. New Ideas and Methodslv06h8657/xxlarge8221.gif" alt="rdquo" align="MIDDLE" BORDER="0"> (Moscow, March 21–25, 1994).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2085–2093, November, 1995.     

Ultra-sensitive in-beam \gamma -ray spectroscopy for nuclear astrophysics at LUNA

Ultra-sensitive in-beam lv3l1887k10pj220/10050_2009_5107_Article_IEq2.gif" alt="$ \gamma$" align="middle" border="0"> -ray spectroscopy studies for nuclear astrophysics are performed at the LUNA (Laboratory for Underground Nuclear Astrophysics) 400 kV accelerator, deep underground in Italy’s Gran Sasso laboratory. By virtue of a specially constructed passive shield, the laboratory lv3l1887k10pj220/10050_2009_5107_Article_IEq3.gif" alt="$ \gamma$" align="middle" border="0"> -ray background for lv3l1887k10pj220/10050_2009_5107_Article_IEq4.gif" alt="$\ensuremath E_{\gamma}$" align="middle" border="0"> < 3 MeV at LUNA has been reduced to levels comparable to those experienced in dedicated offline underground lv3l1887k10pj220/10050_2009_5107_Article_IEq5.gif" alt="$ \gamma$" align="middle" border="0"> -counting setups. The lv3l1887k10pj220/10050_2009_5107_Article_IEq6.gif" alt="$ \gamma$" align="middle" border="0"> -ray background induced by an incident lv3l1887k10pj220/10050_2009_5107_Article_IEq7.gif" alt="$ \alpha$" align="middle" border="0"> -beam has been studied. The data are used to evaluate the feasibility of sensitive in-beam experiments at LUNA and, by extension, at similar proposed facilities.