Materials science. The hardest known oxide

A material as hard as diamond or cubic boron nitride has yet to be identified, but here we report the discovery of a cotunnite-structured titanium oxide which represents the hardest oxide known. This is a new polymorph of titanium dioxide, where titanium is nine-coordinated to oxygen in the cotunnite (PbCl2) structure. The phase is synthesized at pressures above 60 gigapascals (GPa) and temperatures above 1,000 K and is one of the least compressible and hardest polycrystalline materials to be described.     

Delta-wing function of webbed feet gives hydrodynamic lift for swimming propulsion in birds

Most foot-propelled swimming birds sweep their webbed feet backwards in a curved path that lies in a plane aligned with the swimming direction. When the foot passes the most outward position, near the beginning of the power stroke, a tangent to the foot trajectory is parallel with the line of swimming and the foot web is perpendicular to it. But later in the stroke the foot takes an increasingly transverse direction, swinging towards the longitudinal axis of the body. Here we show that, early in the power stroke, propulsion is achieved mostly by hydrodynamic drag on the foot, whereas there is a gradual transition into lift-based propulsion later in the stroke. At the shift to lift mode, the attached vortices of the drag-based phase turn into a starting vortex, shed at the trailing edge, and into spiralling leading-edge vortices along the sides of the foot. Because of their delta shape, webbed feet can generate propulsive forces continuously through two successive modes, from drag at the beginning of the stroke, all the way through the transition to predominantly lift later in the stroke.     

Multiple phospholipase activation by OX1 orexin/hypocretin receptors

We investigated coupling of OX(1) receptors to phospholipase activation and diacylglycerol generation in Chinese hamster ovary (CHO) cells using both biochemical and fluorescence "real-time" methods. The results indicate that at lowest orexin-A concentrations (highest potency), diacylglycerol generated results from phospholipase D activity. At 10-100-fold higher orexin-A concentrations, phospholipase C is activated, likely hydrolyzing phosphatidylinositol (PI) or phosphatidylinositol monophosphate (PIP) but not phosphatidylinositol bisphosphate (PIP(2)). At further 7-fold higher orexin-A concentrations, PIP(2) is hydrolyzed, releasing both diacylglycerol and inositol-1,4,5-trisphosphate. Thus, OX(1) orexin receptors connect to multiple phospholipase activities, apparently composed of at least one phospholipase D and two different phospholipase C activities. At low agonist concentrations, diacylglycerol and phosphatidic acid are the preferred products, and interestingly, it seems that even the primarily activated phospholipase C mainly works to increase diacylglycerol and not inositol-1,4,5-trisphosphate.     

Fusion genes and rearranged genes as a linear function of chromosome aberrations in cancer

Cytogenetic aberrations have been reported in 45,000 human neoplasms. Structural balanced rearrangements are associated with distinct tumor subtypes with remarkable specificity and have been essential for identifying genes involved in tumorigenesis. All balanced rearrangements that have been characterized molecularly act by deregulating a gene in one of the breakpoints or by creating a fusion gene. Because most recurrent aberrations and rearranged genes have been found in hematological disorders, whereas numerous genomic imbalances have been identified in solid tumors, it has become generally accepted that there are pathogenetic differences between these neoplasms. We here show that in every tumor type, the numbers of recurrent balanced chromosome abnormalities, fusion genes and genes rearranged as a consequence of balanced aberrations are simply a function of the number of cases with an abnormal karyotype. Hence, there may not be any fundamental tissue-specific differences in the genetic mechanisms by which neoplasia is initiated.     

Observation of the dynamical Casimir effect in a superconducting circuit

One of the most surprising predictions of modern quantum theory is that the vacuum of space is not empty. In fact, quantum theory predicts that it teems with virtual particles flitting in and out of existence. Although initially a curiosity, it was quickly realized that these vacuum fluctuations had measurable consequences--for instance, producing the Lamb shift of atomic spectra and modifying the magnetic moment of the electron. This type of renormalization due to vacuum fluctuations is now central to our understanding of nature. However, these effects provide indirect evidence for the existence of vacuum fluctuations. From early on, it was discussed whether it might be possible to more directly observe the virtual particles that compose the quantum vacuum. Forty years ago, it was suggested that a mirror undergoing relativistic motion could convert virtual photons into directly observable real photons. The phenomenon, later termed the dynamical Casimir effect, has not been demonstrated previously. Here we observe the dynamical Casimir effect in a superconducting circuit consisting of a coplanar transmission line with a tunable electrical length. The rate of change of the electrical length can be made very fast (a substantial fraction of the speed of light) by modulating the inductance of a superconducting quantum interference device at high frequencies (>10 gigahertz). In addition to observing the creation of real photons, we detect two-mode squeezing in the emitted radiation, which is a signature of the quantum character of the generation process.