Polynomial algorithm for exact calculation of partition function for binary spin model on planar graphs

In this paper we propose and realize an algorithm for exact calculation of partition function for planar graph models with binary variables. The complexity of the algorithm is O(N ²) Experiments show good agreement with Onsager’s analytical solution for the two-dimensional Ising model of infinite size.     

Recovery of rare-earth elements from nitric acid solutions by fullerene black impregnated with diphenyl(dibutylcarbamoylmethyl)phosphine oxide

The distribution of microamounts of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y nitrates between aqueous HNO₃ solutions and fullerene black impregnated with diphenyl(dibutylcarbamoylmethyl)phosphine oxide (L) was studied. The influence exerted on the efficiency of REE recovery by the HNO₃ concentration in the aqueous phase and concentration of L in the sorbent phase was examined. The degree of REE recovery increases on adding HClO₄ to the aqueous phase.     

Use of doubly charged ions in the determination of certain rare earth elements in neodymium, samarium, europium, and their compounds by inductively coupled plasma mass spectrometry

It is proposed to use doubly charged ions of the rare earth elements (REEs) to be determined in samples of neodymium, samarium, europium, and gadolinium by inductively coupled plasma mass spectrometry (ICP-MS) in order to reduce spectral interferences caused by oxide and hydroxide matrix ions. Optimal conditions for the registration of the doubly charged ions of REEs (resolution, depth of plasma sampling, generator output power, and argon flow in a nebulizer) are developed. The limits of determination for the REEs determined using singly and doubly charged ions in the samples of Nd, Sm, Eu, and Gd are evaluated. It is shown that the use of the signal from the doubly charged ions of odd isotopes allows reducing the limits of determination for Dy, Ho, Tm, and Er in neodymium, samarium, europium, and their oxides by one to two orders of magnitude.     

Preconcentration of rare earth elements(III) by sorption from nitric acid solutions using carbamoylmethylphosphine oxide and an ionic liquid

Sorption of microamounts of rare earth elements(III) from HNO₃ solutions with complexing sorbents prepared by noncovalent immobilization of diphenyl(dibutylcarbamoylmethyl)phosphine oxide and an ionic liquid, 1-methyl-3-butylimidazolium bis[(trifluoromethyl)sulfonyl]imide, on the surface of carbon nanotubes was studied in relation to the component ratio in the sorbent and to the HNO₃ concentration in the aqueous phase. The efficiency of the recovery of rare earth elements considerably increases when the sorbent phase contains the ionic liquid.     

Stable Highly Enriched Isotopes in Routine Analysis of Rocks,Soils, Grounds,and Sediments by ICP-MS

Two procedures of acid digestion in an open system and in autoclaves are developed for routine ICP-AES and ICP-MS analysis of rocks, soils, grounds, and sediments. Proposed is a technique based on the use of stable highly enriched isotopes produced in Russia which enables the control (although with certain limitations) over the digestion procedure for each analyzed sample.     

Extraction of U(VI) and Th(IV) from nitric acid solutions with tetraaryl-substituted (<Emphasis Type="Italic">o</Emphasis>-phenyleneoxymethylene)diphosphine dioxides

Extraction of U(VI) and Th(IV) from HNO₃ solutions in the form of complexes with tetraarylsubstituted (o-phenyleneoxymethylene)diphosphine dioxides is studied. The effect of substituents at the P atoms in the extractant molecule on its extraction ability and selectivity is considered. The stoichiometry of the extractable complexes is determined. The possibility of U(VI) and Th(IV) preconcentration with a complexing sorbent prepared by noncovalent immobilization of tetra-p-tolyl-substituted (o-phenyleneoxymethylene)-diphosphine dioxide on a polymeric matrix is demonstrated.     

Flip-chip LEDs with deep mesa emitting at 4.2 µm

The spectral, current-voltage, and emission-current characteristics under forward and reverse biases, and the near-field emission pattern of flip-chip LEDs based on heterostructures with an InAsSb active layer (emission wavelength of 4.2 μm at 300 K) and a mesa of 40–50 μm in depth and 240 μm in diameter are analyzed. The possibility of raising the emission output by varying the configuration of the structure and selecting the optimal operation mode dependently on the working temperature are discussed. Original Russian Text ? N.V. Zotova, N.D. Il’inskaya, S.A. Karandashev, B.A. Matveev, M.A. Remennyi, N.M. Stus’, 2006, published in Fizika i Tekhnika Poluprovodnikov, 2006, Vol. 40, No. 6, pp. 717–723.     

Negative luminescence at 3.9 µm in InGaAsSb-based diodes

Current-voltage characteristics, as well as spectral and power-current characteristics, for the emission of InAsSbP/InGaAsSb double-heterostructure diodes grown on InAs substrates were measured under forward and reverse biases in the temperature range of 25–90°C. It was shown that the conversion efficiency for negative luminescence, which occurs due to the extraction of charge carriers from the regions adjacent to the p-n junction at temperatures ～90°C, is higher than the conversion efficiency for electroluminescence. Narrowing of the negative luminescence spectra in diodes with a built-in cavity was observed.     

Extraction of U(VI), Th(IV), and REE(III) from nitrate solutions with diaryl(dialkylcarbamoylalkyl)phosphine oxides containing a dialkylcarbamoylmethyl substituent in the alkylene bridge

The extraction of microamounts of U(VI), Th(IV), and REE(III) from HNO₃ and NH₄NO₃ solutions with solutions of diaryl(dialkylcarbamoylalkyl)phosphine oxides containing a dialkylcarbamoylmethyl substituent in the alkylene bridge was studied. The stoichiometry of the complexes extracted from nitric acid solutions with N,N,N',N'-tetrabutyl-2-(di-p-anisylphosphinyl)butanedioic diamide I was determined. The influence of the extractant structure and aqueous phase composition on the efficiency and selectivity of the extraction of U(VI), Th(IV), and REE(III) into the organic phase was examined. Introduction of the–CH₂C(O)NAlk₂ fragment into the methylene bridge of the diaryl(dialkylcarbamoylmethyl)phosphine oxide molecule considerably enhances the extraction of REE(III) from neutral nitrate solutions. Such modification of the extractant molecule only slightly influences the extraction of REE(III) from nitric acid solutions, but leads to a considerable increase in the U(VI) extraction and to a decrease in the Th(IV) extraction. The selectivity of the extraction of U(VI) and REE(III) is thus considerably increased.     

Extraction of rare earth elements(III) from HNO3 and HCl solutions with mixtures of carbamoylmethylphosphine oxides and picrolonic acid

Extraction of REE(III) microamounts from HNO₃ and HCl solutions with mixtures of mono- and bis-carbamoylmethylphosphine oxides with picrolonic acid in 1,2-dichloroethane was studied. The strong synergistic effect observed is due to increased hydrophobicity of the extractable complexes. The influence of the structure of carbamoylmethylphosphine oxides on the REE(III) extraction efficiency was considered, and the stoichiometry of the extractable complexes was determined. The possibility of REE(III) recovery and preconcentration from nitric acid solutions with a complexing sorbent prepared by noncovalent immobilization of the reagent mixture on the surface of a macroporous polymeric sorbent was demonstrated.