Molecular phase space transport in water:non-stationary random walk model

Molecular transport in phase space is crucial for chemical reactions because it defines how pre-reactive molecular configurations are found during the time evolution of the system. Using Molecular Dynamics (MD) simulated atomistic trajectories we test the assumption of the normal diffusion in the phase space for bulk water at ambient conditions by checking the equivalence of the transport to the random walk model. Contrary to common expectations we have found that some statistical features of the transport in the phase space differ from those of the normal diffusion models. This implies a non-random character of the path search process by the reacting complexes in water solutions. Our further numerical experiments show that a significant long period of non-stationarity in the transition probabilities of the segments of molecular trajectories can account for the observed non-uniform filling of the phase space. Surprisingly, the characteristic periods in the model non-stationarity constitute hundreds of nanoseconds, that is much longer time scales compared to typical lifetime of known liquid water molecular structures (several picoseconds).

Computational mechanics reveals nanosecond time correlations in molecular dynamics of liquid systems

Statistical complexity, a measure introduced in computational mechanics has been applied to MD simulated liquid water and other molecular systems. It has been found that statistical complexity does not converge in these systems but grows logarithmically without a limit. The coefficient of the growth has been introduced as a new molecular parameter which is invariant for a given liquid system. Using this new parameter extremely long time correlations in the system undetectable by traditional methods are elucidated. The existence of hundreds of picosecond and even nanosecond long correlations in bulk water has been demonstrated. © 2008 Elsevier B.V. All rights reserved.

Could lichens grow on Mars?

Lichens meet some but not all of the criteria that must be fulfilled by inhabitants of Mars. They could withstand many aspects of the hostile environment especially if they live within the rocks as they do in the dry valleys of Antarctica. Lichens, however, are dual organisms and we have to presuppose the successful establishment of a variety of microorganisms on Mars and especially algae and fungi. To date, the evidence for the existence of microorganisms in Martian meteorites is controversial and there is no conclusive evidence of present life on the surface. In addition, if endolithic lichens have evolved on Mars and are alive today they would be subjected to a considerably more hostile environment than the extreme environments on Earth, which are regarded as at the limit of tolerance of present day lichens. The lack of liquid water over most of the surface and the problem of obtaining sufficient nitrogen resources are particular problems for Martian lichens. Further landings on Mars, scheduled for 2005 and future missions are likely to increase substantially our knowledge of the Martian surface and the possibilities for life by attempting to bring back samples of rock and minerals. In addition, the use of techniques such as Laser Raman technology and the development of gas chromatographic methods for use in space increase the probability that an answer to the question of whether lichens have existed on Mars will be obtained in the near future.

The icephobic performance of alkyl-grafted aluminum surfaces

This work analyzes the anti-icing performance of flat aluminum surfaces coated with widely used alkyl-group based layers of octadecyltrimethoxysilane, fluorinated alkylsilane and stearic acid as they are subjected to repeated icing/deicing cycles. The wetting properties of the samples upon long-term immersion in water are also evaluated. The results demonstrate that smooth aluminum surfaces grafted with alkyl groups are prone to gradual degradation of their hydrophobic and icephobic properties, which is caused by interactions and reactions with both ice and liquid water. This implies that alkyl-group based monolayers on aluminum surfaces are not likely to be durable icephobic coatings unless their durability in contact with ice and/or water is significantly improved.