34 research outputs found
Sterols sense swelling in lipid bilayers
In the mimetic membrane system of phosphatidylcholine bilayers, thickening
(pre-critical behavior, anomalous swelling) of the bilayers is observed, in the
vicinity of the main transition, which is non-linear with temperature. The
sterols cholesterol and androsten are used as sensors in a time-resolved
simultaneous small- and wide angle x-ray diffraction study to investigate the
cause of the thickening. We observe precritical behavior in the pure lipid
system, as well as with sterol concentrations less than 15%. To describe the
precritical behavior we introduce a theory of precritical phenomena.The good
temperature resolution of the data shows that a theory of the influence of
fluctuations needs modification. The main cause of the critical behavior
appears to be a changing hydration of the bilayer.Comment: 11 pages, 7 ps figures included, to appear in Phys.Rev.
The formation and fate of internal waves in the South China Sea
Internal gravity waves, the subsurface analogue of the familiar surface gravity waves that break on beaches, are ubiquitous in the ocean. Because of their strong vertical and horizontal currents, and the turbulent mixing caused by their breaking, they affect a panoply of ocean processes, such as the supply of nutrients for photosynthesis1, sediment and pollutant transport2 and acoustic transmission3; they also pose hazards for man-made structures in the ocean4. Generated primarily by the wind and the tides, internal waves can travel thousands of kilometres from their sources before breaking5, making it challenging to observe them and to include them in numerical climate models, which are sensitive to their effects6,7. For over a decade, studies8-11 have targeted the South China Sea, where the oceans' most powerful known internal waves are generated in the Luzon Strait and steepen dramatically as they propagate west. Confusion has persisted regarding their mechanism of generation, variability and energy budget, however, owing to the lack of in situ data from the Luzon Strait, where extreme flow conditions make measurements difficult. Here we use new observations and numerical models to (1) show that the waves begin as sinusoidal disturbances rather than arising from sharp hydraulic phenomena, (2) reveal the existence of >200-metre-high breaking internal waves in the region of generation that give rise to turbulence levels >10,000 times that in the open ocean, (3) determine that the Kuroshio western boundary current noticeably refracts the internal wave field emanating from the Luzon Strait, and (4) demonstrate a factor-of-two agreement between modelled and observed energy fluxes, which allows us to produce an observationally supported energy budget of the region. Together, these findings give a cradle-to-grave picture of internal waves on a basin scale, which will support further improvements of their representation in numerical climate predictions
MIBiG 3.0: a community-driven effort to annotate experimentally validated biosynthetic gene clusters
Microbial Biotechnolog
Mechanical stimulation of bone cells using fluid flow
This chapter describes several methods suitable for mechanically stimulating monolayers of bone cells by fluid shear stress (FSS) in vitro. Fluid flow is generated by pumping culture medium through two parallel plates, one of which contains a monolayer of cells. Methods for measuring nitric oxide production by bone cells in response to FSS are also described
Osteoblast isolation from murine calvaria and long bones
This chapter describes the isolation of primary mouse osteoblasts from adult mouse calvaria and long bones, as well as the process of isolation of bone cells from neonatal mouse calvaria. Osteoblasts from adult mouse bone are obtained as outgrowth from collagenase-treated bone pieces. Isolation of osteoblasts from neonatal calvaria is achieved by sequential enzymatic digestion of the bone matrix. Because of differences in origin and isolation method, each of the primary bone cell cultures described will have their own characteristics
Isolation of primary avian osteocytes
Osteocytes can be isolated from chicken calvaria using mild EDTA treatment alternating with collagenase treatment. The cell population obtained contains both osteoblasts and osteocytes. A pure population of osteocytes is obtained following immunomagnetic separation with the osteocyte-specific monoclonal antibody MAb OB7.3