First-passage times in complex scale-invariant media

How long does it take a random walker to reach a given target point? This quantity, known as a first passage time (FPT), has led to a growing number of theoretical investigations over the last decade1. The importance of FPTs originates from the crucial role played by first encounter properties in various real situations, including transport in disordered media, neuron firing dynamics, spreading of diseases or target search processes. Most methods to determine the FPT properties in confining domains have been limited to effective 1D geometries, or for space dimensions larger than one only to homogeneous media1. Here we propose a general theory which allows one to accurately evaluate the mean FPT (MFPT) in complex media. Remarkably, this analytical approach provides a universal scaling dependence of the MFPT on both the volume of the confining domain and the source-target distance. This analysis is applicable to a broad range of stochastic processes characterized by length scale invariant properties. Our theoretical predictions are confirmed by numerical simulations for several emblematic models of disordered media, fractals, anomalous diffusion and scale free networks.Comment: Submitted version. Supplementary Informations available on Nature websit

AtPDR12 contributes to lead resistance in arabidopsis

Arabidopsis ( Arabidopsis thaliana) contains about 130 ATP- binding cassette ( ABC) proteins, which are likely to contribute to the transport of diverse materials, including toxic substances. However, the substrates of ABC transporters remain unknown in most cases. We tested which ABC transporter is involved in detoxification of lead [ Pb( II)]. Among the many tested, we found that the message level of only AtPDR12 increased in both shoots and roots of Pb( II)- treated Arabidopsis, suggesting that it may be involved in the detoxification of Pb( II). AtPDR12- knockout plants ( atpdr12) were used to further test this possibility. In Pb( II)- containing medium, atpdr12 plants grew less well and had higher Pb contents than those of wild- type plants. In contrast, AtPDR12- overexpressing Arabidopsis plants were more resistant to Pb( II) and had lower Pb contents than wild- type plants. The mutant phenotypes and their Pb contents, as well as the localization of the GFP: AtPDR12 fusion protein at the plasma membrane, suggest that AtPDR12 functions as a pump to exclude Pb( II) and/ or Pb( II)- containing toxic compounds from the cytoplasm. Inhibition of glutathione synthesis by addition of buthionine sulfoximine to the growth medium exacerbated the Pb( II)- sensitive phenotype of atpdr12 plants, consistent with a glutathione- dependent detoxification mechanism operating in parallel with an AtPDR12- dependent mechanism. Thus, we propose that AtPDR12 is an ABC transporter that contributes to Pb( II) resistance in Arabidopsis.X11146sciescopu

AtATM3 is involved in heavy metal resistance in Arabidopsis

AtATM3, an ATP- binding cassette transporter of Arabidopsis ( Arabidopsis thaliana), is a mitochondrial protein involved in the biogenesis of iron-sulfur clusters and iron homeostasis in plants. Our gene expression analysis showed that AtATM3 is up-regulated in roots of plants treated with cadmium [Cd(II)] or lead ( II); hence, we investigated whether this gene is involved in heavy metal tolerance. We found that AtATM3-overexpressing plants were enhanced in resistance to Cd, whereas atatm3 mutant plants were more sensitive to Cd than their wild-type controls. Moreover, atatm3 mutant plants expressing 35S promoter-driven AtATM3 were more resistant to Cd than wild-type plants. Since previous reports often showed that the cytosolic glutathione level is positively correlated with heavy metal resistance, we measured nonprotein thiols (NPSH) in these mutant plants. Surprisingly, we found that atatm3 contained more NPSH than the wild type under normal conditions. AtATM3-overexpressing plants did not differ under normal conditions, but contained less NPSH than wild-type plants when exposed to Cd( II). These results suggest a role for AtATM3 in regulating cellular NPSH level, a hypothesis that was further supported by our gene expression study. Genetic or pharmacological inhibition of glutathione biosynthesis led to the elevated expression of AtATM3, whereas expression of the glutathione synthase gene GSH1 was increased under Cd( II) stress and in the atatm3 mutant. Because the closest homolog of AtATM3 in fission yeast (Schizosaccharomyces pombe), HMT1, is a vacuolar membrane-localized phytochelatin-Cd transporter, it is tempting to speculate that glutathione-Cd( II) complexes formed in the mitochondria are exported by AtATM3. In conclusion, our data show that AtATM3 contributes to Cd resistance and suggest that it may mediate transport of glutamine synthetase-conjugated Cd(II) across the mitochondrial membrane.X11123sciescopu

A structural study of effects of NiP seed layer on the magnetic properties of CoCrPt/Ti/NiP perpendicular magnetic films

The CoCrPt/Ti/NiP films for perpendicular magnetic recording were studied using X-ray scattering and anomalous X-ray scattering. When the NiP seed layer was used, the long range order of the texture peak of the magnetic film decreased and less Co Was associated with this Bragg order. The structural results were consistent with the observed increased coercivity and decreased magnetization due to the increased magnetic grain isolation caused by the presence of NiP seed layer. (C) 2002 Elsevier Science B.V. All rights reserved.X114sciescopu

Structural study of CoCrPt films by anomalous x-ray scattering and extended x-ray absorption fine structure

The correlation of elemental chemistry with the particular long-range order in question cannot be obtained by common conventional characterization techniques. Here we report a study of determining the elemental concentrations of the textured Bragg diffraction peak and the averaged local atomic environment of sputtered CoCrPt films using anomalous x-ray scattering and extended x-ray absorption fine structures. The elemental compositions of the textured peak in these polycrystalline nanostructured films differed from the average global film composition. The higher Cr concentration in the textured peak indicated that a significant amount of Cr did not segregate towards the grain boundaries as a result of the low sputtering temperature and pressure used. The structural observations were consistent with the magnetic results. (C) 2002 American Institute of Physics.open111414sciescopu

Long-range order and short-range order study on CoCrPt/Ti films by synchrotron x-ray scattering and extended x-ray absorption fine structure spectroscopy

The long-range order (LRO) and short-range order (SRO) of CoCrPt/Ti/NiP perpendicular media films were studied by synchrotron x-ray scattering and extended x-ray absorption fine structure (EXAFS) spectroscopy in order to correlate their effects with the magnetic properties. The thickness of the magnetic media films and the NiP seed layers were kept constant, whereas the Ti underlayer thickness was varied. The increase of out-of-plane coercivity and squareness was related to the increase in the crystallinity and texture of CoCrPt (002), which first increased and then decreased with increasing Ti thickness. The best magnetic properties were observed for the magnetic film grown on the 30 nm Ti underlayer. The improvement was associated with the local atomic environment in which a relatively ordered Co, and disordered Cr and Pt existed. This suggests that a higher degree of Co and Cr phase segregation contributed to the enhancement of the magnetic properties. The LRO and SRO results are consistent with the magnetic properties. (C) 2002 American Institute of Physics.open1189sciescopu

Structural effects of Ti underlayer on CoCrPt magnetic films

The effects of long-range and short-range orders of Ti underlayer thickness on the magnetic properties of sputtered Co72Cr21Pt7 films were investigated using synchrotron X-ray scattering and X-ray absorption near-edge structure spectroscopy. The results were consistent with that of magnetic measurements and X-ray photoelectron spectroscopy. For thin Ti underlayers (10 nm), the oxidation of Ti and significant mixing of other elements within this underlayer did not promote texture development, further resulting in poor texturing of magnetic films and undesirable magnetic properties. Increased crystallinity and texture of metallic Ti in thicker underlayers enhanced the magnetic peak alignment and its properties.X1144sciescopu

ADAMTS-2 functions as anti-angiogenic and anti-tumoral molecule independently of its catalytic activity.

ADAMTS-2 is a metalloproteinase that plays a key role in the processing of fibrillar procollagen precursors into mature collagen molecules by excising the amino-propeptide. We demonstrate that recombinant ADAMTS-2 is also able to reduce proliferation of endothelial cells, and to induce their retraction and detachment from the substrate resulting in apoptosis. Dephosphorylation of Erk1/2 and MLC largely precedes the ADAMTS-2 induced morphological alterations. In 3-D culture models, ADAMTS-2 strongly reduced branching of capillary-like structures formed by endothelial cells and their long-term maintenance and inhibited vessels formation in embryoid bodies (EB). Growth and vascularization of tumors formed in nude mice by HEK 293-EBNA cells expressing ADAMTS-2 were drastically reduced. A similar anti-tumoral activity was observed when using cells expressing recombinant deleted forms of ADAMTS-2, including catalytically inactive enzyme. Nucleolin, a nuclear protein also found to be associated with the cell membrane, was identified as a potential receptor mediating the antiangiogenic properties of ADAMTS-2