Mixed molecular and atomic phase of dense hydrogen

We used Raman and visible transmission spectroscopy to investigate dense hydrogen (deuterium) up to 315 (275) GPa at 300 K. At around 200 GPa, we observe the phase transformation, which we attribute to phase III, previously observed only at low temperatures. This is succeeded at 220 GPa by a reversible transformation to a new phase, IV, characterized by the simultaneous appearance of the second vibrational fundamental and new low-frequency phonon excitations and a dramatic softening and broadening of the first vibrational fundamental mode. The optical transmission spectra of phase IV show an overall increase of absorption and a closing band gap which reaches 1.8 eV at 315 GPa. Analysis of the Raman spectra suggests that phase IV is a mixture of graphenelike layers, consisting of elongated H2 dimers experiencing large pairing fluctuations, and unbound H2 molecules.     

Crystal and molecular structure of Zoapatanolide B,a sesquiterpene lactone

The crystal and molecular structure of the natural product Zoapatanolide B has been determined by X-ray crystallographic analysis. The compound, obtained from the leaves ofMontanoa tomentosa, is a heliangolide sesquiterpene lactone. The two molecules of the asymmetric unit are linked together by hydrogen bonding and this results in conformational differences when the ester side chains (at C(9)) are compared.     

Isomorphous dichloro‐ and dibromo(2‐methyl‐2‐phenyl­propyl)­phenylstannane,both displaying the same intramolecular π–π interaction at 120 K

The title compounds, di­chloro‐ and di­bromo­neophyl­phenyl­tin, [SnCl₂(C₆H₅)(C₁₀H₁₃)] and [SnBr₂(C₆H₅)(C₁₀H₁₃)], respectively, are remarkable for the `U' shape of the mol­ecules, whereby the two phenyl groups are brought face‐to‐face in an arrangement that permits intermolecular C—H⋯π bonds to connect the mol­ecules into layers parallel to (100). Intermolecular Sn–halide bonds are notably absent from the structures.     

Control of a coupled map lattice model for vortex shedding in the wake of a cylinder

The flow behind a vibrating flexible cable at low Reynolds numbers can exhibit complex wake structures such as lace-like patterns, vortex dislocations and frequency cells. These structures have been observed in experiments and numerical simulations, and are predicted by a previously developed low-order coupled map lattice (CML). The discrete (in time and space) CML models consist of a series of diffusively coupled circle map oscillators along the cable span. Motivated by a desire to modify the complex wake patterns behind flexible vibrating cables we have studied the addition of control terms into the highly efficient CML models and explored the resulting dynamics. Proportional, adaptive proportional and discontinuous non-linear (DNL) control methods were used to derive the control laws. The first method employed occasional proportional feedback. The adaptive method used spatio-temporal feedback control. The DNL method used a discontinuous feedback linearization procedure, and the controller was designed for the resulting linearized system using eigenvalue assignment. These techniques were applied to a modeled vortex dislocation structure in the wake of a vibrating cable in uniform freestream flow. Parallel shedding patterns were achieved for a range of forcing frequency-forcing amplitude combinations studied to validate the control theory. The adaptive proportional and DNL methods were found to be more effective than the proportional control method due to the incorporation of a spatially varying feedback gain across the cylinder span. The DNL method was found to be the most efficient controller of the low-order CML model. The required control level across the cable span was correlated to the 1/1 lock-on behavior of the temporal circle map.     

The development of information storage materials — How microscopy can help?

The response of giant magnetoresistance (GMR) devices depends critically on the film microstructure, with parameters such as layer thickness and interfacial abruptness being crucial. This paper presents results obtained using high resolution electron microscopy (HREM), chemical mapping and atom probe microanalysis. Local variations in the magnetic properties are induced by the microstructure and also when the films are patterned to form small elements. These lead to changes in the magnetization reversal mechanism. Some results of the studies of the magnetization reversal carried out using in situ in Lorentz transmission electron microscopy (LTEM) magnetizing experiments are also included.