On the behaviour of solid particles in a horizontal boundary layer with turbulence and saltation effects

 A horizontal turbulent boundary layer of air carrying heavy solid particles is investigated experimentally. Mean and r.m.s. velocities of air and particles are measured by LDA, and particle mass flux distributions are obtained by means of a sampling method. The influence of the saltation mechanism is revealed by the large particle r.m.s. velocity in the near-wall region, and by the velocity lag of the particles in the outer region of the boundary layer, which is shown to be closely related to their free fall velocity. The present original results are discussed and compared with available experimental data concerning other kinds of horizontal flows. Received: 17 June 1996/Accepted: 3 April 1997     

Vibrations of bonded beams with a single lap adhesive joint

The natural frequencies and loss factors of the coupled longitudinal and flexural vibrations of a system consisting of a pair of parallel and identical elastic cantilevers which are lap-jointed by viscoelastic material over a length a_c from their free ends have been investigated. A complete set of equations of motion and boundary conditions governing the vibration of the system are derived. The solution of these equations, subject to satisfying the boundary conditions, yields the desired natural frequencies and associated composite loss factors. The numerical results have been compared with those from two other approximate methods.     

Terahertz Time-Domain Spectroscopy of Solids: A Review

Recent development of the terahertz time domain spectroscopy (THz-TDS) and its application to solids have been reviewed. This spectroscopy is unique in that the time-domain wave forms are measured at first and the complex optical constants are deduced directly by the Fourier transformation of them without resort to the Kramers-Kronig analysis. Various types of the THz-TDS systems are briefly described. Applications of the THz-TDS to various solids, i.e., semiconductors, superconductors, polymers, photonic crystals, and so on are also presented to demonstrate how widely this spectroscopy is applicable to characterization of solids.     

Pepsinogen secretion from cultured rat gastric mucosal cells

Rat gastric mucosal cells were isolated with the aid of 0.1% collagenase and Dispase. Pepsinogen secretion from these cells was stimulated by carbachol, cholecystokinin octapeptide (CCK(S)-8) and pentagastrin, but not by histamine. Attempts to obtain a sufficient number of cells using a higher concentration of Dispase resulted in disappearance of the responses to secretagogues. However, when gastric mucosal cells thus prepared were cultured for 24 h in a CO2 incubator, they were found to respond not only to carbachol, CCK(S)-8 and pentagastrin, but also to histamine, resulting in an increase in pepsinogen secretion. The secretagogue-induced pepsinogen secretion was inhibited by its antagonist in a dose-dependent manner. These results suggest that the receptor present in chief cells for pepsinogen secretion was destroyed during the isolation procedure and regenerated during culture.     

Reconfigurable Photonic Crystal Reversibly Exhibiting Single and Double Structural Colors

Unlike absorption-based colors of dyes and pigments, reflection-based colors of photonic crystals, so called “structural colors”, are responsive to external stimuli, but can remain unfaded for over ten million years, and therefore regarded as a next-generation coloring mechanism. However, it is a challenge to rationally design the spectra of structural colors, where one structure gives only one reflection peak defined by Bragg's law, unlike those of absorption-based colors. Here, we report a reconfigurable photonic crystal that exhibits single-peak and double-peak structural colors. This photonic crystal is composed of a colloidal nanosheet in water, which spontaneously adopts a layered structure with single periodicity (407 nm). After a temperature-gradient treatment, the photonic crystal segregates into two regions with shrunken (385 nm) and expanded (448 nm) periodicities, and thus exhibits double reflection peaks that are blue- and red-shifted from the original one, respectively. Notably, the transition between the single-peak and double-peak states is reversible.