Tube-wave propagation in a fluid-filled borehole generated by a single point force applied to the surrounding formation

Propagation of tube waves in an infinite fluid-filled borehole, generated by a single-force point source placed in the elastic surrounding formation, is analyzed in the long-wave approximation. Integral representations of the precise solution are obtained both for fast and slow formations. An asymptotic analysis of tube-wave propagation in the fluid-filled borehole is performed on the basis of these two integral representations. The complete asymptotic wave field in the borehole fluid for a fast formation consists of P and SV phases and the lowest eigenmode of the Stoneley wave (tube wave). For a slow formation the conical Stoneley wave (Mach wave) is generated. It appears only behind the critical angle defined by the ratio of the S wave velocity in the formation to the low-frequency Stoneley wave velocity and decays weakly with an offset. Asymptotic wave forms are in good agreement with wave forms obtained by straightforward calculations.     

Liquid crystalline polymers

The suitabilities of thermo-optometry and differential scanning calorimetry for the characterization of certain copolyethers were compared. Under certain conditions, such polymers do not exhibit the endotherm signal corresponding to the solid/liquid crystalline transition in the DSC curves. Thermo-optometry provides evidence of these phase transitions into the liquid crystalline state, and is a very useful additional method.     

Grafting with acrylonitrile with the redox system cellulose xanthogenate–hydrogen peroxide

The possibility of obtaining modified cellulose products by reacting cellulose xanthogenate in solutions containing oxidizers and acrylonitrile was studied. The ability of the cellulose xanthogenate–hydrogen peroxide redox system to initiate graft copolymerization of acrylonitrile on the cellulose was demonstrated. The influence of various factors on the processes was investigated. An attempt was made to clarify the nature of the reactions involved.     

1-Aryl-6-azauracile, 7. Mitt.: Herstellung einiger funktioneller Derivate der 1-Phenyl-6-azauracil-5-carbonsäure

Zusammenfassung In der vorliegenden Arbeit wird die Herstellung des Chlorids (1), von Estern (2a, 2b), Amiden (3a-3g), des N-Hydroxyamids (3h) und Hydrazids (3i) der 1-Phenyl-6-azauracil-5-carbonsäure beschrieben.     

Synthesis of pentafluorophenylmethylamines via silicon Mannich reaction

[reaction: see text] The three-component coupling of aldehydes, secondary amines, and methoxytris(pentafluorophenyl)silane, MeOSi(C(6)F(5))(3), affording pentafluorophenylmethylamines has been described. The generation of the five-coordinate silicate intermediate is believed to be the key feature responsible for the efficiency of the reaction.     

Magnetoelectric switching of exchange bias

The perpendicular exchange bias field, H(EB), of the magnetoelectric heterostructure Cr2O3(111)/(Co/Pt)(3) changes sign after field cooling to below the Néel temperature of Cr2O3 in either parallel or antiparallel axial magnetic and electric freezing fields. The switching of H(EB) is explained by magnetoelectrically induced antiferromagnetic single domains which extend to the interface, where the direction of their end spins controls the sign of H(EB). Novel applications in magnetoelectronic devices seem possible.     

Brine rejection from freezing salt solutions: a molecular dynamics study

The atmospherically and technologically very important process of brine rejection from freezing salt solutions is investigated with atomic resolution using molecular dynamics simulations. The present calculations allow us to follow the motion of each water molecule and salt ion and to propose a microscopic mechanism of brine rejection, in which a fluctuation (reduction) of the ion density in the vicinity of the ice front is followed by the growth of a new ice layer. The presence of salt slows down the freezing process, which leads to the formation of an almost neat ice next to a disordered brine layer.     

Direct observation of long-range assisted formation of Ag clusters on Si(111)7 x 7

Formation of Ag clusters on reconstructed surface Si(111)7 x 7 was for the first time observed in real time during deposition by means of scanning tunneling microscopy. The sequences of images taken at room temperature show mechanisms controlling the growth and behavior of individual Ag adatoms. Obtained data reveal new details of attractive interaction between adsorbates occupying adjacent half-unit cells of the 7 x 7 reconstruction. Time evolution of growth characteristics was simulated by means of a simple model. The growth scenario observed in vivo is discussed with respect to previously reported models based on data obtained after finishing the deposition--post-mortem.     

Forces between a single atom and its distant mirror image

An excited-state atom whose emitted light is backreflected by a distant mirror can experience trapping forces, because the presence of the mirror modifies both the electromagnetic vacuum field and the atom's own radiation reaction field. We demonstrate this mechanical action using a single trapped barium ion. We observe the trapping conditions to be notably altered when the distant mirror is translated across an optical wavelength. The well-localized barium ion enables the spatial dependence of the forces to be measured explicitly. The experiment has implications for quantum information processing and may be regarded as the most elementary optical tweezers.