Materials chemistry: macroporous crystalline vanadium oxide foam

Porous inorganic solids can be synthesized in complex forms, and here we describe a simple method to create an ultralight, macroporous, crystalline vanadium oxide foam by bubbling oxygen gas produced in situ through a viscous vanadium oxide gel. This foaming process could be extended to other metal oxides.     

Mercury's capture into the 3/2 spin-orbit resonance as a result of its chaotic dynamics

Mercury is locked into a 3/2 spin-orbit resonance where it rotates three times on its axis for every two orbits around the sun. The stability of this equilibrium state is well established, but our understanding of how this state initially arose remains unsatisfactory. Unless one uses an unrealistic tidal model with constant torques (which cannot account for the observed damping of the libration of the planet) the computed probability of capture into 3/2 resonance is very low (about 7 per cent). This led to the proposal that core-mantle friction may have increased the capture probability, but such a process requires very specific values of the core viscosity. Here we show that the chaotic evolution of Mercury's orbit can drive its eccentricity beyond 0.325 during the planet's history, which very efficiently leads to its capture into the 3/2 resonance. In our numerical integrations of 1,000 orbits of Mercury over 4 Gyr, capture into the 3/2 spin-orbit resonant state was the most probable final outcome of the planet's evolution, occurring 55.4 per cent of the time.     

Semaphorin 7A promotes axon outgrowth through integrins and MAPKs

Striking parallels exist between immune and nervous system cellular signalling mechanisms. Molecules originally shown to be critical for immune responses also serve neuronal functions, and similarly neural guidance cues can modulate immune function. We show here that semaphorin 7A (Sema7A), a membrane-anchored member of the semaphorin family of guidance proteins previously known for its immunomodulatory effects, can also mediate neuronal functions. Unlike many other semaphorins, which act as repulsive guidance cues, Sema7A enhances central and peripheral axon growth and is required for proper axon tract formation during embryonic development. Unexpectedly, Sema7A enhancement of axon outgrowth requires integrin receptors and activation of MAPK signalling pathways. These findings define a previously unknown biological function for semaphorins, identify an unexpected role for integrins and integrin-dependent intracellular signalling in mediating semaphorin responses, and provide a framework for understanding and interfering with Sema7A function in both immune and nervous systems.     

Seismic hazard in the Marmara Sea region following the 17 August 1999 Izmit earthquake

On 17 August 1999, a destructive magnitude 7.4 earthquake occurred 100 km east of Istanbul, near the city of Izmit, on the North Anatolian fault. This 1,600-km-long plate boundary slips at an average rate of 2-3 cm yr(-1), and historically has been the site of many devastating earthquakes. This century alone it has ruptured over 900 km of its length. Models of earthquake-induced stress change combined with active fault maps had been used to forecast that the epicentral area of the 1999 Izmit event was indeed a likely location for the occurrence of a large earthquake. Here we show that the 1999 event itself significantly modifies the stress distribution resulting from previous fault interactions. Our new stress models take into account all events in the region with magnitudes greater than 6 having occurred since 1700 as well as secular interseismic stress change, constrained by GPS data. These models provide a consistent picture of the long term spatio-temporal behaviour of the North Anatolian fault and indicate that two events of magnitude equal to, or greater than, the Izmit earthquake are likely to occur within the next decades beneath the Marmara Sea, south of Istanbul.     

Osculating Circle with Microscopes Within Microscopes

Classically, an osculating circle at a point of a planar curve is introduced technically, often with formula giving its radius and the coordinates of its center. In this note, we propose a new and intuitive definition of this concept: among all the circles which have, on the considered point, the same tangent as the studied curve and thus seem equal to the curve through a microscope, the osculating circle is this that seems equal to the curve through a microscope within microscope.     

“Eratosthenes' measurement of the earth reconsidered”

Communicated by C. Wilson     

Gene therapy: is IL2RG oncogenic in T-cell development?

The gene IL2RG encodes the gamma-chain of the interleukin-2 receptor and is mutated in patients with X-linked severe combined immune deficiency (X-SCID). Woods et al. report the development of thymus tumours in a mouse model of X-SCID after correction by lentiviral overexpression of IL2RG and claim that these were caused by IL2RG itself. Here we find that retroviral overexpression of IL2RG in human CD34+ cells has no effect on T-cell development, whereas overexpression of the T-cell acute lymphoblastic leukaemia (T-ALL) oncogene LMO2 leads to severe abnormalities. Retroviral expression of IL2RG may therefore not be directly oncogenic--rather, the restoration of normal signalling by the interleukin-7 receptor to X-SCID precursor cells allows progression of T-cell development to stages that are permissive for the pro-leukaemic effects of ectopic LMO2.