Orientation imaging microscopy in two-dimensional crystals via undersampled microscopy

A novel microscopy analysis technique is presented, with applications in imaging two-dimensional grains and grain boundaries. The method allows the identification of grain shapes and orientations from large area micrographs, via the moiré pattern obtained in a raster image. The observed moiré pattern originates from the aliasing between a micrographs regular sampling raster and the inherent periodicity of the elements forming the grain under study. The technique presented is very general, allowing grain analysis via many types of microscopy. We demonstrate it in this paper by using Tapping Mode Atomic Force Microscopy and Scanning Electron Microscopy on diblock copolymer thin films. PACS 68.37.Ps; 68.37.Hk; 68.37.Ef; 68.55.Jk; 61.72.Ff; 61.72.Mm     

Ultrasonic pulsed Doppler transoesophageal measurement of aortic haemodynamics in humans.

Centreline blood velocity and exterior wall motion were measured in the descending aorta of humans using an oesophageal probe, a pulsed ultrasound Doppler velocity meter and an ultrasonic echo tracking system. The development of a method for easily measuring haemodynamics in the thoracic region using an oesophageal probe will provide an essentially non-invasive method for the assessment of cardiac function and the nature of blood vessels in that region. Detailed anatomical studies of the thorax were conducted by cross-sectioning of the thorax of a cadaver. Blood velocity waveforms were recorded from the descending aorta both during rest and exercise. In one volunteer, the peak centreline velocity increased from a resting value of approximately 30 cm s-1 to an exercise value of approximately 50 cm s-1. Vessel diameter waveforms similar to those for pressure were also recorded showing diameter changes of 1.8 mm. The accuracy and resolution of the technique would be improved by multicrystal probes and multigate ultrasonic flowmeters allowing for accurate calculation of the Doppler angle, imaging of vascular flow regions, and measurement of pulse wave velocity.     

Regiodirected phosphorylation of 2,2′,7,7′-tetrahydroxydinaphthylmethane

The phosphorylation of 2,2′,7,7′-tetrahydroxydinaphthylmethane was studied and the influence of molecule pre-organization on the regioselectivity of functionalization was investigated. The reactions of 2,2′,7,7′-tetrahydroxydinaphthylmethane with phosphorous amides containing 1-3 amide bonds gave oligophosphorylated derivatives differing in the number and the nature of phosphorus fragments and in the size of phosphorus rings: tetraphosphorus macrocycles containing one 24-membered and two eight-membered phosphorus rings, triphosphorus compounds containing a phosphocine ring and two acyclic phosphorus fragments, and tetraphosphorylated derivatives with four phosphorus groups in the molecule. The possibility of controlling the regioselectivity of phosphorylation by using reagents differing in the number and activity of P-N bonds was demonstrated.     

How noise statistics impact models of enzyme cycles

Theoretical tools for adequately treating stochastic effects are important for understanding their role in biological processes. Although master equations provide rigorous means for investigating effects associated with fluctuations of discrete molecular copy numbers, they can be very challenging to treat analytically and numerically. Approaches based on the Langevin approximation are often more tractable, but care must be used to ensure that it is justified in each situation. Here, we examine a model of an enzyme cycle for which noise qualitatively alters the behavior of the system: fluctuations in the population of an enzyme can result in amplification and multistability in the distribution of its product. We compare master equation and Langevin treatments of this system and show that results derived previously with a white noise Langevin equation [M. Samoilov et al., Proc. Natl. Acad. Sci. U.S.A. 102, 2310 (2005)] are inconsistent with the master equation. A colored noise Langevin equation captures some, but not all, of the essential physics of the system. The advantages and disadvantages of the Langevin approximation for modeling biological processes are discussed.     

Direct imaging of polyethylene crystallites within block copolymer microdomains

Ruthenium tetroxide (RuO₄) is a versatile agent for imparting mass density contrast to saturated hydrocarbon polymers. We have successfully employed RuO₄ to examine the microdomain and crystallite morphologies of poly(ethylene‐block‐vinylcyclohexane) semicrystalline–glassy diblock copolymers via transmission electron microscopy (TEM). Ultrathin sections cut from blocks stained with RuO₄ showed excellent contrast in TEM, revealing the individual polyethylene crystallites that formed within the preexisting block copolymer microdomains. The size and orientation of the crystallites, which previously could only be inferred from scattering data, are readily apparent in the micrographs. Moreover, such imaging directly reveals the lateral extent of the crystallites and the number of crystallites lying within the cross section of each microdomain. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2564–2570, 2000     

Laser stimulation of low-temperature dissociative recombination of electrons and oxygen molecular ions

A theory of dissociative recombination of slow electrons and molecular ions in a strong monochromatic light field is developed. The theory takes into account interference between various reaction channels and is constructed in a rigid basis adiabatic with respect to rotation (the approximation of a fixed molecular axis). The mathematical apparatus of the theory is based on the stationary formalism of the matrix of radiation collisions, whose poles correspond to “quasi-energy” states of a composite system. Along with transitions into dissociative configurations, field-induced nonadiabatic transitions into bound intermediate states of valence (non-Rydberg) configurations are considered. As a particular application of the theory, the e^? + O ₂ ⁺ (²Π _g ) → $ O(^{2s_1 + 1} l_1 ) + O(^{2s_2 + 1} l_2 ) A theory of dissociative recombination of slow electrons and molecular ions in a strong monochromatic light field is developed. The theory takes into account interference between various reaction channels and is constructed in a rigid basis adiabatic with respect to rotation (the approximation of a fixed molecular axis). The mathematical apparatus of the theory is based on the stationary formalism of the matrix of radiation collisions, whose poles correspond to “quasi-energy” states of a composite system. Along with transitions into dissociative configurations, field-induced nonadiabatic transitions into bound intermediate states of valence (non-Rydberg) configurations are considered. As a particular application of the theory, the e⁻ + O₂⁺(²Π _g ) → reaction is analyzed. A study of this reaction requires detailed information about the potential curves of the states participating in it with taking into account the external electromagnetic field (l and s are the electronic angular momenta and reaction product spins). For this purpose, the general problem is divided into three stages. At the first stage, the theoretical approach is formulated, and at the second stage, the corresponding potential curves are calculated and the main reaction mechanisms are determined. The third stage should include calculations of the total and differential cross sections. This work is concerned with the first two stages; that is, the adiabatic potential curves of the singlet and triplet dissociative states of the O₂^** oxygen molecule are calculated, a classification of all possible transition types is given, and reaction mechanisms in the presence of monochromatic laser radiation are determined. The frequency regions of external radiation in which these mechanisms are most effective are found. Original Russian Text ? S.O. Adamson, R.J. Buenker, G.V. Golubkov, M.G. Golubkov, A.I. Dement’ev, 2009, published in Khimicheskaya Fizika, 2009, Vol. 28, No. 4, pp. 26–42.