Nonlinear Bloch waves and balance between hardening and softening dispersion.

The introduction of nonlinearity alters the dispersion of elastic waves in solid media. In this paper, we present an analytical formulation for the treatment of finite-strain Bloch waves in one-dimensional phononic crystals consisting of layers with alternating material properties. Considering longitudinal waves and ignoring lateral effects, the exact nonlinear dispersion relation in each homogeneous layer is first obtained and subsequently used within the transfer matrix method to derive an approximate nonlinear dispersion relation for the overall periodic medium. The result is an amplitude-dependent elastic band structure that upon verification by numerical simulations is accurate for up to an amplitude-to-unit-cell length ratio of one-eighth. The derived dispersion relation allows us to interpret the formation of spatial invariance in the wave profile as a balance between hardening and softening effects in the dispersion that emerge due to the nonlinearity and the periodicity, respectively. For example, for a wave amplitude of the order of one-eighth of the unit-cell size in a demonstrative structure, the two effects are practically in balance for wavelengths as small as roughly three times the unit-cell size.

Flow stabilization by subsurface phonons.

The interaction between a fluid and a solid surface in relative motion represents a dynamical process that is central to the problem of laminar-to-turbulent transition (and consequent drag increase) for air, sea and land vehicles, as well as long-range pipelines. This problem may in principle be alleviated via a control stimulus designed to impede the generation and growth of instabilities inherent in the flow. Here, we show that phonon motion underneath a surface may be tuned to passively generate a spatio-temporal elastic deformation profile at the surface that counters these instabilities. We theoretically demonstrate this phenomenon and the underlying mechanism of frequency-dependent destructive interference of the unstable flow waves. The converse process of flow destabilization is illustrated as well. This approach provides a condensed-matter physics treatment to fluid-structure interaction and a new paradigm for flow control.

Isolation of stem cells from the mid gut epithelium of Culex pipiens mosquitoes (Diptera: Culicidae).

Stem cells are undifferentiated cells that remarkable ability to self-renew and produce differentiated cells that support normal development and tissue homeostasis. The authors isolated spherical stem cells from the midgut epithelium of the late third larval instars of Culex pipiens mosquitoes. In vitro, cultivated epithelial stem cells were able to proliferate and differentiate in fresh culture for 48 hr in absence of 20- hydroxyecdysone (20-E). The stem cells were the most common cells in the initial culture. One hundred of epithelial stem cells had been cultured. After 24 hr became 132 cells, 78% was undifferentiated stem cells and 8.3% &13.7% was enterocytes and goblet cells respectively. This ratio slightly decreased after de 48 hr to be 74% undifferentiated stem cells, 4.5% enterocytes and 5.6% goblet cells. After 72 hr the undifferentiated stem cells were not able to proliferate .The most differentiated goblet and enterocytes survived few days then died.

Sexual life in Pharaonic Egypt: towards a urological view.

Sex is a basic human need, common to all people at all times. It is evident that the ancient Egyptians were real human beings, not only a people who built massive pyramids and made mummies of their dead. The ancient Egyptians had a rich and varied sexual life, which they found an opportunity to describe in words and pictures. As in the other early primitive civilizations, erotic matters were of prime importance and became an integral part of life. In Pharaonic times, the Egyptians described impotence and recorded several methods to increase the sexual power. In the present paper, we will shed light on some aspects of the sexual life in ancient Egypt that may be interesting to the urologists, including ancient Egyptian concepts of sex and erotic matters, their own way of treatment of impotence and Min, the Egyptian fertility God.