Incommensurate and commensurate magnetic long-range order in metallic REPd3 compounds of rare earths (RE=Nd,Tb, Dy,Er, Tm,Yb)

Compared to previous bulk magnetic measurements unusual magnetic ordering phenomena were detected by systematic neutron scattering experiments performed in the temperature range of 7 mKT300 K on the series of cubic metallic compounds REPd₃ of the rare earths RE=Nd, Tb, Dy, Er, Tm and Yb. Except for ErPd₃ withT _N =3 K the observed critical temperatures are compatible with the de Gennes scaling. The complexity of long-range magnetic ordering increases with decreasing 4f ⁿ occupancy, ranging from ferro- or ferrimagnetism in YbPd₃ and DyPd₃ via commensurate antiferromagnetic ordering in ErPd₃ and TmPd₃ [k=(1/2, 1/2, 0)] to incommensurate antiferromagnetic ordering of modulated type in TbPd₃ and NdPd₃. Both RKKY interactions, crystalline electric field, hybridization with 4d states of Pd as well as nuclear spin polarization in the case of RE=Nd appear to be of importance for the magnetic properties of REPd₃ systems.     

Formation pathways and structure—Property interrelationship of 3-imino-1-methyl-5,5-dialkyl-4,7,7-tricyano-2-oxabicyclo-[2.2.1]heptane derivatives

The problems of the structure—property interrelationship of 3-imino-2-oxabicyclo[2.2.1]heptane derivatives are discussed on the basis of x-ray diffraction studies (XDS). A pathway for the formation of the bicyclic compounds is proposed, and the realization of spirans in the reaction of sym-tetracyanoethane with conjugated cyclic systems containing s-cis C=C and C=O fragments is substantiated. The factors responsible for the syn orientation of the oxygen atom and the N-substituent of the imino group are analyzed. It is shown that a change in the steric hindrance in the bicyclic compounds leads to a change in the conformation of the latter. The reasons for the shortening of the C_sp3-C_sp3, C_sp3-C_sp and C=N exo bonds and the correlation of the XDS and IR spectroscopic data are examined. From the XDS data for N-bromo-substituted imines, a model for Br⁺...NC electrophilic attack was proposedCommunication 16 from the series Chemistry of 1,1,2,2-tetracyanoethane. See [1] for Communication 15.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 519–526, April, 1991.     

Acetals of lactams and acid amides. 67. Polarographic behavior of enamines of the indoles series in anhydrous DMF

The polarographic behavior of derivatives of 2-aminomethyleneindoxyl and 3-aminomethyleneoxindole in anhydrous DMF has been studied and the results compared with data on the polarographic reduction of substituted aminomethyleneacetophenones and of related enaminoketones and eneaminoamides. It is established that the ease of reduction is determined by the nature of the substituent on the enamine and indole nitrogen atoms and also by the presence or absence of an -methyl group in the -position of the eneamines (for noncyclic enaminoketones).For Communication 66, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 642–648, May, 1991.     

Isopropylation of indoline

The composition of the reaction products was ascertained, and the kinetics of the alkylation of indoline with isopropyl alcohol in 90% sulfuric acid at 60C were studied. The reactivities of indoline and its carbocyclic analogs are compared.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 920–922, July, 1991.     

Ethyl α-cyanoacrylate in the Michael reaction

Ethyl -cyanocarylate undergoes the Michael reaction with strong CH-acids (pK _a < 13) in the presence of strong basic amines such as butylamine, piperidine, and triethylamine. Only polymerization of ethyl -cyanoacrylate occurs under the same conditions with weaker CH-acids in the presence of less basic amines such as aniline, N-methylaniline, and pyridine.A. N. Nesmeyanov Institute of Organometallic Compounds, Russian Academy of Sciences, 117813 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2449–2452, October, 1992.     

Two-dimensional nuclear Overhauser enhancement NMR experiments on pelargonidin-3-glucopyranoside, an anthocyanin of low molecular mass.

Pelargonidin-3-glucoside has been isolated from the acidified methanolic extract of strawberries (Fragaria anannassa variety Corona) by successive application of an ion-exchange resin, droplet-counter chromatography and gel filtration. The pigment in acidified methanolic solution was studied by means of the two-dimensional nuclear Overhauser enhancement NMR technique, and the sugar unit was found to be attached to the 3-position on the aglycone. At +20 degrees C the pigment was found to be in the extreme narrowing limit where the NOESY cross-peaks are negative. However, at -20 degrees C this low-mass anthocyanin could be studied in the slow motion regime where the NOESY cross-peaks are positive. With a mixing time of 0.3 s, the glucose H1"-H4" proton pair was measured in the initial cross-relaxation rate and their cross-peak volume corresponded to the H1"-H4" distance found in a 4C1 chair conformation.     

A partially observed control problem for Markov chains

A finite state, continuous time Markov chain is considered and the solution to the filtering problem given when the observation process counts the total number of jumps. The Zakai equation for the unnormalized conditional distribution is obtained and the control problem discussed in separated form with this as the state. A new feature is that, because of the correlation between the state and observation process, the control parameter appears in the diffusion coefficient which multiplies the Poisson noise in the Zakai equation. By introducing a Gâteaux derivative the minimum principle, satisfied by an optimal control, is derived. If the optimal control is Markov, a stochastic integrand can be obtained more explicitly and new forward and backward equations satisfied by the adjoint process are obtained.This research was partially supported by NSERC Grant A7964, the Air Force Office of Scientific Research, United States Air Force, under Contract AFOSR-86-0332, and the U.S. Army Research Office under Contract DAAL03-87-0102.     

Experiments in Solving Mixed Integer Programming Problems on a Small Array of Transputers

The time-consuming process of solving large-scale Mixed Integer Programming problems using the branch-and-bound technique can be speeded up by introducing a degree of parallelism into the basic algorithm. This paper describes the development and implementation of a parallel branch-and-bound algorithm created by adapting a commercial MIP solver. Inherent in the design of this software are certain ad hoc methods, the use of which are necessary in the effective solution of real problems. The extent to which these ad hoc methods can successfully be transferred to a parallel environment, in this case an array of at most nine transputers, is discussed. Computational results on a variety of real integer programming problems are reported.     

Existence of Cesàro limit of bounded solution of evolution equation in banach space

An existence criterion for the Cesàro limit of a bounded solution y(t) of the problem dy(t)/dt = Ay(t), y(0)=y₀, t [O, ), where A is a closed linear operator with dense domain of definition D(A) in a reflexive Banach space E, is obtained under the condition that there exists a sufficiently small interval (O, ) belonging to the set of the regular points (A) of the operator A.Translated from Ukrayins'kyy Matematychnyy Zhurnal, Vol. 44, No. 9, pp. 1279–1280, September, 1992.     

Inverse problems of the theory of separately continuous mappings

The present paper investigates the problem of constructing a separately continuous function defined on the product of two topological spaces that possesses a specified set of points of discontinuity and the related special problem of constructing a pointwise convergent sequence of continuous functions that possesses a specified set of points of nonuniform convergence and set of points of discontinuity of a limit function. In the metrizable case the former problem is solved for separable F-sets whose projections onto every cofactor is of the first category. The second problem is solved for a pair of embedded F.Translated from Ukrayins'kyy Matematychnyy Zhurnal, Vol. 44, No. 9, pp. 1209–1220, September, 1992.