bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dithiobiuretes in reactions with electrophilic acetylenes. New derivatives of 1,3,5-dithiazines,-thiadiazines and-triazines as the products of competing reactions of nucleophilic cycloaddition
Authors: Glotova Tatýana , Protsuk Nadezhda , Albanov Alexander , Lopyrev Valentin , Dolgushin Gennadii 
Published: August 2006

AbstractThe nucleophilic addition of 2,4-dithiobiurete, 1- and 1,4-substituted 2,4-dithiobiuretes (2 a-e) with benzoylacetylene (1) has been studied. 2-(Benzoylmethyl)-4-(R1-imino)-6-(R2-imino)dihydro-4H-1,3,5-dithiazinium perchlorates (3 a-e) are obtained in glacial acetic acid (AcOH) in the presence of equimolar quantities of HClO4. The reaction of benzoylacetylene with 1,5-diphenyl-2,4-dithiobiurete in either of MeOH, C6H6, or MeCN solvents proceeds non-selectively to give a mixture of products such as 2-(benzoylmethyl)-4,6-di(phenylimino)dihydro-4H-1,3,5-dithiazine (5), 2-(benzoylmethyl)-4-(β-benzoylvinyl)thio-3-phenyl-6-(phenylimino)-3,6-dihydro-2H-1,3,5-thiadiazine (8), 2-(benzoylmethyl)-1,3-diphenylhexahydro-1,3,5-triazine-4,6-dithione (7) and N-(β-benzoylvinyl)-N-phenylthioureas (6).
Synthesis of 4-aryloxy-7-nitrobenzofurazan derivatives from 4-chloro-7-nitrobenzofurazan and various phenoxide anions (including pharmaceuticals) in the presence of crown ethers
Authors: Bem Marioara , Caproiu Miron , Stoicescu Dan , Constantinescu Titus , Balaban Alexandru 
Published: August 2006

Abstract4-Chloro-7-nitrobenzofurazan reacts by nucleophilic substitution with phenoxide anions derived from estriol (2c), ethynylestradiol (2d), phenol (3e), guaiacol (3f), 2,6-dimethoxyphenol (3g), eugenol (3h), isoeugenol (3i), the cytostatic Etoposide (4), and Reichardt’s betaine (5) in the presence of crown ethers affording the corresponding 4-aryloxy-7-nitrobenzofurazan derivatives 6c, 6d, 7e-7i, 8, and 9. The structure of these compounds was confirmed by NMR spectra. Hydrophobicity/hydrophilicity parameters were investigated by reverse phase thin-layer chromatography.
Preliminary observations on the copolymerisation of acceptor monomer:donor monomer systems under microwave irradiation
Authors: Fellows Christopher 
Published: August 2006

AbstractThe mechanistic rationalisation of specific ‘microwave effects’ previously reported in a range of chemical reactions suggests that they may be observable in the freeradical copolymerisation of comonomer pairs capable of forming donor-acceptor complexes. Polymerisation under microwave irradiation is carried out for several comonomer pairs with weak donor-acceptor interactions, and no acceleration in rate or change in degree of alternation attributable to changes in propagation are observed. An increase in reaction rate of 150–200 % is observed for all systems, with trends in molecular weight suggesting this was due to an increase in radical flux. This is consistent with earlier reports of rate enhancement for free-radical polymerisations using the initiator 2,2′-azobis-isobutyronitrile, and it is proposed that microwave irradiation may reduce the amount of geminate radical recombination.
Synthesis, characterization and structure of the Bis(methyl-cyclopentadienyl)vanadium(IV) carboxylates
Authors: Vinklarek Jaromír , Honzíĉek Jan , Císařová Ivana , Pavliŝta Martin , Holubová Jana 
Published: August 2006

AbstractThe 1,1’-dimethylvanadocene dichloride ((C5H4CH3)2VCl2) reacts in aqueous solution with various carboxylic acids giving two different types of complexes. The 1,1’-dimethylvanadocene complexes of monocarboxylic acids (C5H4CH3)2V(OOCR)2 (R=H,CCl3, CF3, C6H5) contain two monodentate carboxylic ligands, whereas oxalic and malonic acids act as chelate compounds of the formula (C5H4CH3)2V(OOC-A-COO) (A=−, CH2). The structure of the (C5H4CH3)2 V(OOCCF3)2 complex was determined by single crystal X-ray diffraction analysis. The isotropic and anisotropic EPR spectra of all the complexes prepared were recorded. The obtained EPR parameter values were found to be in agreement with proposed structures.
Moravia: A 3-, 8-connected cubic structural pattern in space group Pm3m
Authors: Bucknum Michael , Castro Eduardo 
Published: August 2006

AbstractThis paper describes the crystal structure of a novel, hypothetical 3-,8-connected cubic structural pattern with the binary stoichiometry A3B8. The novel pattern lies in space group Pm3m, number 221. It possesses the Wells point symbol (4468812)3(43)8 and has the Wellsean Schläfli index (6, 4.3636). It is derived from the Andreini space filling arrangement of octahedra and cuboctahedra by replacing the areas where there are face-sharing of the polyhedra with the inscription of 3-connected, trigonal planar vertices, and retaining the points where the polyhedra share vertices in cube coordination. The structure-type could be representative of a binary metal oxide in which the metal cation attains a relatively high oxidation state of 51/3+. Possible metal oxide models for the structure-type include M3O8 (where M is a Group 6 or 7 elements).
Aromatic λ3 heterocycles XIV. Fosfinine-ether macrocyclesheterocycles XIV. Fosfinine-ether macrocycles
Authors: Pacureanu Liliana , Mracec Mircea 
Published: August 2006

AbstractThe geometry and electronic structure of several phosphinine-ether macrocycles were investigated at semiempirical level. The calculated geometries are in good agreement with experimental data. Compared to phosphinine, the coordinative abilities of phosphinineether macrocycles based on energy considerations suggest a little lowered π acceptor character, while π donor character is improved. The molecular environment causes a significant mixing of phosphinine and phenyl substituent π levels. The geometry and electronic properties of phosphinine-ether macrocycles can provide significant host coordination properties for guest species.
Thermodynamic model of crystallization and melting of small particles
Authors: Samsonov Vladimir , Malkov Oleg 
Published: August 2006

Abstract
The size dependence of the nanocrystal melting temperature has been investigated based on a nonequilibrium thermodynamics approach. An expression has been derived for the melting temperature that, contrary to the classical Tomson formula, takes into account the metastable character of the crystal nucleus-melt shell equilibrium. Quantitative estimations have been carried out for small spherical particles of aluminum, tin, and lead.
Glass-forming ability and thermal stability of Fe62Nb8−xZrxB30 and Fe72Zr8B20 amorphous alloys?
Authors: Shapaan M. , Lábár J. , Varga L. , Lendvai J. 
Published: August 2006

Abstract
Glass-forming ability (GFA) and thermal stability of Fe62Nb8B30, Fe62Nb6Zr2B30 and Fe72Zr8B20 at % amorphous alloys were investigated by calorimetric (DSC and DTA) measurements. The crystallization kinetics was studied by DSC in the mode of continuous versus linear heating and it was found that both the glass transition temperature, Tg, and the crystallization peak temperature, Tp, display strong dependence on the heating rate. The partial replacement of Nb by Zr leads to lower Tg and Tx temperatures and causes a decrease of the supercooled liquid region. JMA analysis of isothermal transformation data measured between Tg and Tx suggests that the crystallization of the Fe62Nb8B30 and Fe62Nb6Zr2B30 amorphous alloys take place by three-dimensional growth with constant nucleation rate. Nb enhances the precipitation of the metastable Fe23B6 phase and stabilizes it up to the third crystallization stage. Zr addition increases the lattice constant of Fe23B6 and, at the same time, decreases the grain size.
Critical fields of a superconducting cylinder
Authors: Zharkov G. 
Published: August 2006

Abstract
The self-consistent solutions of the nonlinear Ginzburg-Landau equations, which describe the behavior of a superconducting mesoscopic cylinder in an axial magnetic field H (provided there are no vortices inside the cylinder), are studied. Different, vortex-free states (M-, e-, d-, p-), which exist in a superconducting cylinder, are described. The critical fields (H
1, H
2, H
p, H
i, H
r), at which the first or second order phase transitions between different states of the cylinder occur, are found as functions of the cylinder radius R and the GL-parameter
$$\kappa $$
. The boundary
$$\kappa _c (R)$$
, which divides the regions of the first and second order (s, n)-transitions in the icreasing field, is found. It is found that at R→∞ the critical value, is
$$\kappa _c = 0.93$$
. The hysteresis phenomena, which appear when the cylinder passes from the normal to superconducting state in the decreasing field, are described. The connection between the self-consistent results and the linearized theory is discussed. It is shown that in the limiting case
$$\kappa \to {1 \mathord{\left/ {\vphantom {1 {\sqrt 2 }}} \right. \kern-\nulldelimiterspace} {\sqrt 2 }}$$
and R ≫ λ (λ is the London penetration length) the self-consistent solution (which correponds to the socalled metastable p-state) coincides with the analitic solution found from the degenerate Bogomolnyi equations. The reason for the existence of two critical GL-parameters
$$\kappa _0 = 0.707$$
and
$$\kappa _0 = 0.93$$
in, bulk superconductors is discussed.
Higher harmonics in the voltage on a superconducting wire carrying AC electrical current
Authors: Tebano Riccardo , Gömöry Fedor 
Published: August 2006

AbstractThe problem of determining the harmonic content in the voltage that appears on a superconducting wire carrying cosine-like AC current was resolved theoretically, using two approaches. First, the Fourier components of the voltage spectrum were found by numerical integration. Importance of individual terms was established, leading to two conclusions: a) it is the cosine component of the 3rd harmonic that represents the bulk of harmonic distortion, b) for the practical purposes it is sufficient to consider higher harmonics with n ≤ 7. Then, the analytical formulas were derived. While for the sine components a general expression containing an infinite series was found, closed-form formulas were derived for the cosine components of the harmonics 1, 3, 5, 7. Consequences of the results to the experimental technique used to study the AC transport properties of superconductors are discussed.
The characteristic X-ray spectra of free atoms of metals
Authors: Antsiferov P. 
Published: August 2006

AbstractThe article presents the results of a study of characteristic X-ray spectra of free atoms by means of a new simple technique. A pulsed electron beam was used for evaporation and to create inner-shell vacancies in free atoms of metals. The spectra were obtained with the help of an X-ray monochromator which allowed precise comparison between the free-atoms spectra and corresponding solid-state spectra. The shifts of the peaks were measured and found to be in the range Δλ/λ≈10−5–10−4. The K-, L- and M-series spectra were studied. A number of the free-atoms spectra revealed structure which was not resolved in the solid-state spectra and which is of interest for atomic structure calculation applications. This electron beam technique for the investigation of X-ray characteristic spectra of free atoms can be used for the refinement of X-ray wavelength standards.
Nematic ordering problem as the polymer problem of the excluded volume
Authors: Yakunin A. 
Published: August 2006

AbstractBased on a solution of the polymer excluded volume problem, a technique is proposed to estimate some parameters at the isotropic-nematic liquid crystal phase transition (the product of the volume fraction of hard sticks and the ratio of the stick length, L, to its diameter, D; the maximum value of this ratio at which one cannot regard the stick as hard). The critical exponents are estimated. The transition of a swelling polymer coil to ideal is revealed as the polymerization degree of a macromolecule increases. The entanglement concentration obtained agrees with experimental data for polymers with flexible chains. The number of monomers between neighbor entanglements is assumed to be the ratio L/D. A comparison of the theory with other ones and recent experimental data is made.
Nonlinear dynamics of mechanical system with external excitation
Authors: Ryczek Bogusław 
Published: August 2006

Abstract
This paper attends to the problem of vibration of a self-excited mechanical system with a relatively complicated, history dependent dry friction model. The experimentally identified friction model allows description of various cases of stationary and transient motion. The system is composed of a lumped mass that interacts with a belt by means of dry friction. The system is additionally subjected to an external harmonic excitation through elastic element. The main objective of the experimental research has been focused on the analysis of the system behaviour for various values of the excitation frequency. This paper includes also computer simulation of the vibration of the considered system and comparison between the results of experimental and theoretical analysis. The comparison enables the assumed friction model for steel-polyester pair to be verified. It was another goal of the investigations.
Hochschild Cohomology of skew group rings and invariants
Authors: Marcos E. , Martínez-Villa R. , Martins Ma. 
Published: August 2006

Abstract
Let A be a k-algebra and G be a group acting on A. We show that G also acts on the Hochschild cohomology algebra HH
⊙
(A) and that there is a monomorphism of rings HH
⊙
(A)
G→HH
⊙
(A[G]). That allows us to show the existence of a monomorphism from HH
⊙
(Ã)
G into HH
⊙
(A), where Ã is a Galois covering with group G.
Toxicological evaluation of exposed SPMD membranes
Authors: Kočí Vladimír , Mlejnek Martin , Kochánková Lucie 
Published: August 2006

Abstract
This article is focused on bioassay evaluation of exposed SPMDs. Toxicity testing of SPMD extract is a suitable complementary parameter to chemical analysis. Vtox as an integrative parameter describing toxic properties of extract from membrane and thus a level of contamination of assessed ambient is presented here. Two examples of practical use of Vtox is demonstrated: a course of toxicity throw wastewater treatment plant with industrial inlets and increase of toxicity in surface water body caused by leakages of POPs from industrial plant.
Modeling and simulation of free radical polymerization of styrene under semibatch reactor conditions
Authors: Curteanu Silvia 
Published: August 2006

Abstract
The first part of this approach is concerned with the elaboration of a radical polymerization model of styrenne, based on a kinetic diagram that includes chemical and thermal initiation, propagation, termination by recombination and chain transfer to the monomer. Furthermore, volume contraction during polymerization is considered, as well as the gel and glass effects. The mathematical formalism that describes the model in terms of moments is explored in detail. The model was then used to predict the changes in monomer conversion and molecular weight after intermediate addition of initiator and monomer. The results of this operation are dependent on the conditions of the reaction mass, quantity, and moment of substance addition. Therefore, the simulations were performed at different times with respect to the gel effect; before, during and after this phenomenon, and also with respect to different temperatures and initiators. Increasing the initiator concentration before the gel effect leads to an earlier appearance of the phenomenon and to a decrease in molecular weight. The ratio
$$\bar M_w /\bar M_n $$
reveals a polydispersity index smaller for the intermediate addition of initiator. No significant changes take place during or after the gel effect. If along with the initiator, unreacted monomver (used to dissolve the initiator) enters the reactor, a small dip in conversion is observed. The general conclusion of this paper reveals the intermediate addition of initiator as a method to control polymer properties and to prevent the “dead-end” polymerization of styrene.
A study of sample mineralization methods for arsenic analysis of blood and urine by hydride generation and graphite furnace atomic absorption spectrometry
Authors: Sysalova Jirina , Spevackova Vera 
Published: August 2006

AbstractMineralization procedures for blood and urine suitable for the determination of arsenic by Hydride Generation Atomic Absorption Spectrometry (HGAAS) are studied on model samples, and the results are utilized in biological monitoring investigations. The objective of this work is to obtain good total As recoveries for both matrices regardless of added As species (As(III), As(V), DMA, MMA, AsB, or AsC). Prior to the HGAAS analyses, preparation procedures were controlled under optimised conditions by graphite furnace atomic absorption spectrometry (GFAAS). Two preparation procedures for urine give As recoveries close to 100% by HGAAS: a) dry ashing at 420°C with Mg(NO3)2 on a hot plate, and b) microwave oven decomposition with (NH4)2S2O8. For blood samples, As recoveries by HGAAS range between 95 and 108% for all species when using dry ashing after a pretreatment of samples with HNO3 and H2O2 in a microwave oven. Wet digestion with (NH4)2S2O8 in a microwave oven gives recoveries very near 100% for Asinorg. and MMA. For other As species in spiked blood samples, recoveries of less than 20% As are found. Precision and detection limits obtained by both techniques are evaluated as well. For arsenic concentrations of 20 μg dm−3 or more in blood and urine, a chemical modifier is recommended for GFAAS analysis; it may or may not be proceeded by a mineralization step. For low As levels encountered in the unexposed population, the HGAAS technique provides reliable results only if a very complete mineralization procedure is used.
Simple synthesis of 3-acyl-5-alkyl(aryl)isoxazoles from terminal alkynes and nitrates of alkaline metals or ammonium
Authors: Rogachev Victor , Filimonov Victor , Kulmanakova Julya , Yusubov Mehman , Bender Wolfgang 
Published: August 2006

Abstract
A simple and general synthesis of 3-acyl-5-alkyl(aryl)isoxazoles by reaction of terminal alkynes with nitrates in acetic acid in the presence of SO3 or alkaline salts is described.
New transformation of cycloalkanone acetals by peracids α,ω-dicarboxylic acids synthesis
Authors: Terent'ev Alexander , Chodykin Sergey 
Published: August 2006

Abstract
A new process of oxidation of cycloalkanone acetals under the action of in situ generated performic acid has been found. The main products of the reaction are α, ω-dicarboxylic acids obtained with the yield up to 77% depending on the size of acetals ring. The process has been explored and optimized on the example of the dodecanedioic acid synthesis (a valuable industrial product).
Dehydrogenation studies of dihydronicotinamide adenine dinucleotide (NADH) with methylene blue in the presence of the copper hexcyanoferrate(II) complex and light
Authors: Tewari Brij 
Published: August 2006

Abstract
The effects of copper ferrocyanide and light on the dehydrogenation rate of NADH by methylene blue is studied. The results suggest that the dehydrogenation rate of NADH with methylene blue is enhanced by copper ferrocyanide. Light also affects the reaction rate.
Organic-inorganic hybrid materials based on N=C=O functionalised silan modified with titanium and zirconium
Authors: Ivanova Yordanka , Dimitriev Yanko , Gerganova Tsvetelina , Bryaskova Raina , Fernandes Maria , Miranda Salvado Isabel 
Published: August 2006

Abstract
This work investigates the influence of the precursor trimethylsilil isocyanate on the sol-gel synthesis of hybrid materials. The obtained Si−O−C−N network is additionally modified by titanium and zirconium alcoxypropoxides in the range of 10 to 30 wt. %. The structure of the obtained hybrid materials before and after pyrolysis up to 1100°C was investigated by methods of XRD, FTIR and 29Si MAS NMR. We established that the hybrid structure was stable up to 600°C based on IR study. The structural transformation of the hybrid materials into oxycarbonitrogen system started at 800°C. The network of the hybrids modified by titanium remained stable and amorphous up to the final temperature of the pyrolysis (1100°C) compared to the gels modified by more than 10 wt.% Zr. It was confirmed by XRD analysis that the last mentioned are nanocomposite materials, built from carbooxynitrogen vitreous matrix and ZrO2-nanocrystals (tetragonal). The NMR method verified the presence of heterometallic bonds (Si−O−Ti and Si−O−Zr) and Q4, ZrQ3 or TiQ3, NSiO3 and D structural units in the gels.
Indirect spectrophotometric determination of diltiazem hydrochloride in pure form and pharmaceutical formulations
Authors: El-Didamony Akram 
Published: August 2006

Abstract
Three simple, accurate, and sensitive spectrophotometric methods (A, B and C) have been described for the indirect assay of diltiazem hydrochloride (DIL.HCl), either in pure form or in pharmaceutical formulations. The first method (A) is based on the oxidation of DIL.HCl by N-bromosuccinimide (NBS) and determination of unconsumed NBS by measuring the decrease in absorbance of amaranth dye (AM) at a suitable λmax=521 nm. Other methods (B) and (C) involve the addition of excess cerric ammonium sulfate (CAS) and subsequent determination of the unconsumed oxidant by a decrease in the red color of chromotrope 2R (C2R) at a suitable λmax=528 nm or a decrease in the orange-pink color of rhodamine 6G (Rh6G) at λmax=525 nm, respectively. Regression analysis of Beer-Lambert plots showed good correlation in the concentration ranges 3.0–9.0, 3.5–7.0 and 3.5–6.3 μg ml−1 for methods A, B and C, respectively. The apparent molar absorptivity, Sandell's sensitivity, detection and quantification limits were calculated. The proposed methods have been applied successfully for the analysis of the drug in its pure form and its dosage form. No interference was observed from a common pharmaceutical adjuvant. Statistical comparison of the results with the reference method shows excellent agreement and indicates no significant difference in accuracy and precision.
Synthesis and identification of immunogen medroxyprogesterone acetate residues in edible foods and preparation of the Antisera
Authors: Xu C. , Peng C. , Hao K. , Jin Z. , Yang S. 
Published: August 2006

AbstractMedroxyprogesterone acetate (MPA), relative molecular mass is only 344.5 and it has no immunogenecity. The methods of the carbodiimides and the mixed anhydride were both adopted to couple MPA with bovine serum albumin, the carrier protein. The coupling rates of conjugate using the above methods were estimated to be 14 and 20 by ultraviolet spectrophotometry. The coupling was successful according to the analysis of SDS-PAGE illustration. New Zealand white rabbits were immunized with the conjugate the coupling rate of which was 14, and blood was collected after five periods of immunities. Then the titre of antiserum was tested to be 2.6 × 105 by indirect ELISA, which further identified the success of coupling.
Nitrous oxide emissions from waste incineration
Authors: Svoboda K. , Baxter D. , Martinec J. 
Published: August 2006

AbstractEU energy and environmental policy in waste management leads to increasing interest in developing methods for waste disposal with minimum emissions of greenhouse gases and minimum environmental impacts.From the point of view of nitrous oxide (N2O) emissions, waste incineration and waste co-combustion is very acceptable method of waste disposal. Two factors are important for attaining very low N2O emissions from waste incineration, particularly for waste with higher nitrogen content (e.g. sewage sludge, leather, etc.): temperature of incineration over 900°C and avoiding selective noncatalytic reduction (SNCR) de-NOx method based on urea. For reduction of N2O emissions retrofitting such plants to ammonia-based SNCR is recommendable. The modern selective catalytic reduction facilities for de-NOx at waste incineration plants are only negligible source of N2O.