Magnetic shape memory and giant magnetocaloric effect in Heusler alloys

The results of theoretical and experimental investigations of the phase transitions in ferromagnetic Heusler alloys with a thermoelastic martensitic transition are briefly discussed.     

High order implicit method for odes stiff systems

This paper presents a new difference scheme for numerical solution of stiff systems of ODE’s. The present study is mainly motivated to develop an absolutely stable numerical method with a high order of approximation. In this work a double implicit A-stable difference scheme with the sixth order of approximation is suggested. Another purpose of this study is to introduce automatic choice of the integration step size of the difference scheme which is derived from the proposed scheme and the one step scheme of the fourth order of approximation. The algorithm was tested by means of solving the Kreiss problem and a chemical kinetics problem. The behavior of the gas explosive mixture (H ₂ + O₂) in a closed space with a mobile piston is considered in test problem 2. It is our conclusion that a hydrogen-operated engine will permit to decrease the emitted levels of hazardous atmospheric pollutants.     

The role of structural and nonstructural water in oxyfluoride K<Subscript>2</Subscript>WO<Subscript>2</Subscript>F<Subscript>4</Subscript> · H<Subscript>2</Subscript>O

X-ray structural and polarization optical investigations have been performed, and birefringence and rotation angles of the optical indicatrix φ _b and φ _c of the K₂WO₂F₄ · H₂O crystal have been measured in the temperature range of 100–600 K. The structure and symmetry of compounds at room temperature have been refined. It has been established that the layered crystal K₂WO₂F₄ · H₂O can exist in two states (A and B) depending on the atmospheric humidity and undergoes the sequence of reversible and irreversible phase transformations G ₃ ↔ G ₂ → G ₁ → G ₀. The sequences of changes in the phase symmetry P [`1]\bar 1 ↔ C2/m → P4/nmm for samples A and m ↔ C2/m → P4/nmm for samples B have been found. The second-order proper ferroelastic phase transition (P [`1]\bar 1 ↔ C2/m) at T ₀₃ = 270–290 K (G ₃ ↔ G ₂) is accompanied by twinning and appearance of the shift deformation x ₆. The crystal system of the substance for the B crystals remains invariable after the second-order phase transition G ₃ ↔ G ₂. The irreversible first-order phase transition G ₂ → G ₁ occurs in a temperature range T ₀₂ ≈ 350–380 K; it is accompanied by the loss of the crystallization water, which then is reduced easily from the atmosphere for a day. The substance decomposes at T ₀₁ ≈ 510 K (G ₁ → G ₀). The distinction between the A and B crystals has been explained by the presence or absence of free water in interlayer spacings.     

The heat capacity and density of solutions of barium and tetrabutylammonium iodides in N-methylpyrrolidone at 298.15 K

The heat capacity and density of solutions of barium and tetrabutylammonium iodides in N-methylpyrrolidone (MP) were studied at 298.15 K by calorimetry and densimetry. The standard partial molar heat capacities and volumes (\(\overline {C_{p^2 }^ \circ } \) and \(\overline {V_2^ \circ } \)) of the electrolytes in MP were calculated. The standard heat capacities \(\overline {C_{pi}^ \circ } \) and volumes \(\overline {V_i^ \circ } \) of the Ba²⁺ and (C₄H₉)₄N⁺ ions in solution in MP at 298.15 K were determined. With the tetrabutylammonium ion, these values were in agreement with those calculated on the basis of the tetraphenylarsonium-tetraphenyl borate and tetraphenylphosphonium-tetraphenyl borate assumptions. The results are discussed in relation to the special features of solvation in solutions of the salts studied.     

Structural Features of Silatranes and Germatranes

In stabilization of the endo configuration of silatranes and germatranes, a major role is played not only by the Si (or Ge) and N atoms, but also by oxygen and other atoms of the atrane core, which is manifested in molecular orbital parameters. Calculation of the system of interacting methyltrimethoxysilane and trimethylamine shows that the energy of the system grows as the distance between the Si and N atoms is decreased from 5 to 2 Å. The Si-N interaction in methylsilatrane, according to the calculations and precision X-ray diffraction studies, is the interaction of filled electronic shells and is electrostatic in nature. Analysis of the thermodynamic functions of formation of 1-methyl- and 1-hydroxysilatranes and -germatranes reveals an increase in the enthalpy and the decisive contribution of the entropy factors to stabilization of the reaction products. A ¹H NMR study of ethylgermatrane in aqueous solution revealed its equilibrium with the hydro- lyzed form. The transition state in the first step of hydrolysis of methyl- and hydroxysilatranes and -germatranes was studied by methods of quantum chemistry (AM1, PM3; basis sets STO-3G, 6-31G, 6-31G*, 6-31G** B3LYP method).     

Intepretation der konduktometrischen Titrationskurven der sauren Kaolinitformen

Ohne Zusammenfassung     

Reactive epoxy-functionalized thin films by a pulsed plasma polymerization process

A novel plasma functionalization process based on the pulsed plasma polymerization of allyl glycidyl ether is reported for the generation of robust and highly reactive epoxy-functionalized surfaces with well-defined chemical properties. Using a multitechnique approach including X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS), infrared spectroscopy (FT-IR), atomic force microscopy (AFM) and ellipsometry, the effect of the plasma deposition parameters on the creation and retention of epoxy surface functionalities was characterized systematically. Under optimal plasma polymerization conditions (duty cycle: 1 ms/20 ms and 1 ms/200 ms), reactive uniform films with a high level of reproducibility were prepared and successfully used to covalently immobilize the model protein lysozyme. Surface derivatization was also carried out with ethanolamine to probe for epoxy groups. The ethanolamine blocked surface resisted nonspecific adsorption of lysozyme. Lysozyme immobilization was also done via microcontact printing. These results show that allyl glycidyl ether plasma polymer layers are an attractive strategy to produce a reactive epoxy functionalized surface on a wide range of substrate materials for biochip and other biotechnology applications.     

Study of the Gilding Technology of the “Idol” from the 10th Century Mound “Chernaya Mogila” (“Black Grave”)

Crystallography Reports - A unique artifact—the “idol” from the 10th century mound “Chernaya Mogila” (“Black Grave”), a famous Old Rus’ site, has...     

The peculiarities of physical network formation in carboxyl-containing poly(dimethylcarbosiloxane)

An unusual effect of physical network formation during heating or at room temperature alter previous heating was found for originally liquid poly(dimethylcarbosiloxane) containing 0.5 – 2.5 mol% of side carboxyl groups by means of the measurement of its Theological properties. The reason for this behaviour is supposed to be the predominance of intramolecular hydrogen bonding of COOH groups in original polymer and the intra– to Intermolecular bonds rearrangement during heating. The alternative reason can be the microphase separation with domains of COOH groups. The reversibility of the network is confirmed by the decrease in the elasticity modulus, development of irreversible deformation on further heating and by break-up of Junctions on the addition of small amounts of polar liquids.