Scaling of the turbulence transition threshold in a pipe

We report the results of an experimental investigation of the transition to turbulence in a pipe over approximately an order of magnitude range in the Reynolds number Re. A novel scaling law is uncovered using a systematic experimental procedure which permits contact to be made with modern theoretical thinking. The principal result we uncover is a scaling law which indicates that the amplitude of perturbation required to cause transition scales as O(Re-1).     

Supershell structure in alkali metal nanowires

Nanowires are formed by indenting and subsequently retracting two pieces of sodium metal. Their cross section gradually reduces upon retraction and the diameters can be obtained from the conductance. In previous work we have demonstrated that when one constructs a histogram of diameters from large numbers of indentation-retraction cycles such histograms show a periodic pattern of stable nanowire diameters due to shell structure in the conductance modes. Here, we report the observation of a modulation of this periodic pattern, in agreement with predictions of a supershell structure.     

Metalorganic vapour phase epitaxy of mercury cadmium telluride

The present review covers the fundamental factors involved in the the metalorganic vapour phase epitaxy of mercury cadmium telluride. In addition recent significant developments which could have an important influence on the future of the technology are discussed. The topics covering these developments include growth techniques, photoepitaxy, in-situ monitoring, “new” precursors, substrates and layer quality. The review highlights the advanced nature of the technology, which inspite of currently-addressed limitations has an important future.     

Pattern transformation triggered by deformation

Periodic elastomeric cellular solids are subjected to uniaxial compression and novel transformations of the patterned structures are found upon reaching a critical value of applied load. The results of a numerical investigation reveal that the pattern switch is triggered by a reversible elastic instability. Excellent quantitative agreement between numerical and experimental results is found and the transformations are found to be remarkably uniform across the samples. It is proposed that the mechanism will also operate at much smaller scales opening the possibility for imprinting complex patterns at the nanoscale or switching photonic and phononic crystals in a controlled way.     

Flow in a symmetric channel with an expanded section

We consider the flow in a symmetric two-dimensional channel with an expanded section. By examining the effect of varying the ratio of the inlet and outlet channel widths, we are able to place the earlier results of Mizushima et al. (Phys. Fluids 8 (1996) 2933) within an entire spectrum of nonlinear phenomena. Laboratory experiments support predicted behaviour in two regions of parameter space and highlight the importance of imperfections in the experimental apparatus.     

Quantum mechanics: cleaning up metaphysical baggage

The dynamic electronic structure of atoms and molecules can be directly observed by means of the (e, 2e) reaction, which measures the distribution of energies and momenta of two electrons in coincidence after a knockout reaction initiated by an electron beam of known momentum incident on a molecular gas target. The molecular state for each event is identified by the electron separation energy. The recoil momentum for each event is known from the difference of measured initial and final momenta. It has been verified that values of this momentum are equal under suitable conditions to the momentum of the electron in the target immediately before knockout. Thus the spherically-averaged electron momentum distribution for each molecular orbital is measured. This is directly related to molecular orbitals calculated by the methods of quantum chemistry. Properties obtained by this method for different types of molecules are discussed.     

Steric structure of N-allylphthalimide oxide and thiooxide

Conclusions N-Allylphthalimide oxide and thiooxide exist predominantly in the gauche conformation based on the C-C_ring bond, with a syn orientation of the phthalimide group and heteroatom of the three-membered ring. The phthalimide radical protrudes from the plane of N-C-C_ring by an angle of 60°.Translated from Investiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 664–667, March, 1979.The authors thank A. M. Salikhov for taking the IR spectra of the studied compounds.     

Identification of a set of genes showing regionally enriched expression in the mouse brain

Background

We have recorded responses from single neurons in murine visual cortex to determine the effectiveness of the input from the two murine cone photoreceptor mechanisms and whether there is any unique selectivity for cone inputs at this higher region of the visual system that would support the possibility of colour vision in mice. Each eye was stimulated by diffuse light, either 370 (strong stimulus for the ultra-violet (UV) cone opsin) or 505 nm (exclusively stimulating the middle wavelength sensitive (M) cone opsin), obtained from light emitting diodes (LEDs) in the presence of a strong adapting light that suppressed the responses of rods.

Results

Single cells responded to these diffuse stimuli in all areas of striate cortex. Two types of responsive cells were encountered. One type (135/323 – 42%) had little to no spontaneous activity and responded at either the on and/or the off phase of the light stimulus with a few impulses often of relatively large amplitude. A second type (166/323 – 51%) had spontaneous activity and responded tonically to light stimuli with impulses often of small amplitude. Most of the cells responded similarly to both spectral stimuli. A few (18/323 – 6%) responded strongly or exclusively to one or the other spectral stimulus and rarely in a spectrally opponent manner.

Conclusion

Most cells in murine striate cortex receive excitatory inputs from both UV- and M-cones. A small fraction shows either strong selectivity for one or the other cone mechanism and occasionally cone opponent responses. Cells that could underlie chromatic contrast detection are present but extremely rare in murine striate cortex.