Universal Dynamical Steps in the Exact Time-Dependent Exchange-Correlation Potential

We show that the exact exchange-correlation potential of time-dependent density-functional theory displays dynamical step structures that have a spatially non-local and time non-local dependence on the density. Using one-dimensional two-electron model systems, we illustrate these steps for a range of non-equilibrium dynamical situations relevant for modeling of photo-chemical/physical processes: field-free evolution of a non-stationary state, resonant local excitation, resonant complete charge-transfer, and evolution under an arbitrary field. Lack of these steps in usual approximations yield inaccurate dynamics, for example predicting faster dynamics and incomplete charge transfer

A Mechanism for Cutting Carbon Nanotubes with a Scanning Tunneling Microscope

We discuss the local cutting of single-walled carbon nanotubes by a voltage pulse to the tip of a scanning tunneling microscope. The tip voltage ($\mid V \mid \ge$~3.8 eV) is the key physical quantity in the cutting process. After reviewing several possible physical mechanisms we conclude that the cutting process relies on the weakening of the carbon-carbon bonds through a combination of localized particle-hole excitations induced by inelastically tunneling electrons and elastic deformation due to the electric field between tip and sample. The carbon network releases part of the induced mechanical stress by forming topological defects that act as nucleation centers for the formation of dislocations that dynamically propagate towards bond-breaking.Comment: 7 pages, 6 postscript figures, submitted to PR

Partially observed bipartite network analysis to identify predictive connections in transcriptional regulatory networks

<p>Abstract</p> <p>Background</p> <p>Messenger RNA expression is regulated by a complex interplay of different regulatory proteins. Unfortunately, directly measuring the individual activity of these regulatory proteins is difficult, leaving us with only the resulting gene expression pattern as a marker for the underlying regulatory network or regulator-gene associations. Furthermore, traditional methods to predict these regulator-gene associations do not define the relative importance of each association, leading to a large number of connections in the global regulatory network that, although true, are not useful.</p> <p>Results</p> <p>Here we present a Bayesian method that identifies which known transcriptional relationships in a regulatory network are consistent with a given body of static gene expression data by eliminating the non-relevant ones. The Partially Observed Bipartite Network (POBN) approach developed here is tested using <it>E. coli </it>expression data and a transcriptional regulatory network derived from RegulonDB. When the regulatory network for <it>E. coli </it>was integrated with 266 <it>E. coli </it>gene chip observations, POBN identified 93 out of 570 connections that were either inconsistent or not adequately supported by the expression data.</p> <p>Conclusion</p> <p>POBN provides a systematic way to integrate known transcriptional networks with observed gene expression data to better identify which transcriptional pathways are likely responsible for the observed gene expression pattern.</p

STRUCTURAL INVESTIGATION OF A HIGH-CHROMIUM MATERIAL USED AS AN EXTERNAL, WORKING LAYER OF A BIMETALLIC MILL ROLLER

The bimetallic mill roller has been produced by the method of vertical axis centrifugal casting. The processes, accompanying the formation of the structure of the external (working) layer from high chromium material of the bimetallic roller have been investigated. A mathematical model for the geometry of the working layer was created. By using the MAGMA Soft software package, simulations of the processes of casting and crystallization have been made. A metallographic assessment of the microstructure has been made.

Glaciation and deglaciation of the Stump Cross area, Yorkshire Dales, northern England, determined by terrestrial cosmogenic nuclide (10Be) dating.

Terrestrial cosmogenic nuclide (l0Be) surface-exposure ages are reported for three glacially-transported gritstone boulders and one glacially-scoured exposure of gritstone bedrock in the vicinity of Stump Cross Caverns, North Yorkshire. Although the ages do not form a statistically consistent cluster, three of them nevertheless indicate that the transport and deposition of boulders was by ice of the last (Late Devensian) glaciation. The ages provide evidence for glacier ice at the Wharfe-Nidd interfluve, in contrast to previously held views that these uplands had remained above the level of the last ice sheet. The youngest of the three ages on boulders (-18.5 ka) is taken as the best estimate for déglaciation of the area. This is consistent both with surface-exposure ages from sites elsewhere around the southern margin of the Yorkshire Dales and with uranium-series dated speleothems in Stump Cross Caverns. Together these results reveal that déglaciation of the Dales was most likely well advanced by ~18-16 ka, facilitating the rejuvenation of surface and subsurface karstic processes