Controlled surface charging as a depth-profiling probe for mesoscopic layers

Probing the structure of material layers just a few nanometres thick requires analytical techniques with high depth sensitivity. X-ray photoelectron spectroscopy (XPS) provides one such method, but obtaining vertically resolved structural information from the raw data is not straightforward. There are several XPS depth-profiling methods, including ion etching, angle-resolved XPS (ref. 2) and Tougaard's approach, but all suffer various limitations. Here we report a simple, non-destructive XPS depth-profiling method that yields accurate depth information with nanometre resolution. We demonstrate the technique using self-assembled multilayers on gold surfaces; the former contain 'marker' monolayers that have been inserted at predetermined depths. A controllable potential gradient is established vertically through the sample by charging the surface of the dielectric overlayer with an electron flood gun. The local potential is probed by measuring XPS line shifts, which correlate directly with the vertical position of atoms. We term the method 'controlled surface charging' and expect it to be generally applicable to a large variety of mesoscopic heterostructures.     

Elevated UV-B radiation reduces genome stability in plants

Long-term depletion of the stratospheric ozone layer contributes to an increase in terrestrial solar ultraviolet-B radiation. This has deleterious effects on living organisms, such as DNA damage. When exposed to elevated ultraviolet-B radiation (UV-B; 280-315 nm), plants display a wide variety of physiological and morphological responses characterized as acclimation and adaptation. Here we show, using special sun simulators, that elevated solar UV-B doses increase the frequency of somatic homologous DNA rearrangements in Arabidopsis and tobacco plants. Increases in recombination are accompanied by a strong induction of photolyase and Rad51 gene expression. These genes are putatively involved in major DNA repair pathways, photoreactivation and recombination repair. In mutant Arabidopsis plants that are deficient in photoreactivating ultraviolet-induced cyclobutane pyrimidine dimers, recombination under elevated UV-B regimes greatly exceeds wild-type levels. Our results show that homologous recombination repair pathways might be involved in eliminating UV-B-induced DNA lesions in plants. Thus, increases in terrestrial solar UV-B radiation as forecasted for the early 21st century may affect genome stability in plants.     

Subduction erosion along the Middle America convergent margin

'Subduction erosion' has been invoked to explain material missing from some continents along convergent margins. It has been suggested that this form of tectonic erosion removes continental material at the front of the margin or along the underside of the upper (continental) plate. Frontal erosion is interpreted from disrupted topography at the base of a slope and is most evident in the wake of subducting seamounts. In contrast, structures resulting from erosion at the base of a continental plate are seldom recognized in seismic reflection images because such images typically have poor resolution at distances greater than approximately 5 km from the trench axis. Basal erosion from seamounts and ridges has been inferred, but few large subducted bodies--let alone the eroded base of the upper plate--are imaged convincingly. From seismic images we identify here two mechanisms of basal erosion: erosion by seamount tunnelling and removal of large rock lenses of a distending upper plate. Seismic cross-sections from Costa Rica to Nicaragua indicate that erosion may extend along much of the Middle America convergent margin.     

Interception of comet Hyakutake's ion tail at a distance of 500 million kilometres

Remote sensing observations and the direct sampling of material from a few comets have established the characteristic composition of cometary gas. This gas is ionized by solar ultraviolet radiation and the solar wind to form 'pick-up' ions, ions in a low ionization state that retain the same compositional signatures as the original gas. The pick-up ions are carried outward by the solar wind, and they could in principle be detected far from the coma (Sampling of pick-up ions has also been used to study interplanetary dust, Venus' tail and the interstellar medium.) Here we report the serendipitous detection of cometary pick-up ions, most probably associated with the tail of comet Hyakutake, at a distance of 3.4 AU from the nucleus. Previous observations have provided a wealth of physical and chemical information about a small sample of comets, but this detection suggests that remote sampling of comet compositions, and the discovery of otherwise invisible comets, may be possible.     

A multiple intelligent agent system for credit risk prediction via an optimization of localized generalization error with diversity

Company bankruptcies cost billions of dollars in losses to banks each year. Thus credit risk prediction is a critical part of a bank＇s loan approval decision process. Traditional financial models for credit risk prediction are no longer adequate for describing today＇s complex relationship between the financial health and potential bankruptcy of a company. In this work, a multiple classifier system （embedded in a multiple intelligent agent system） is proposed to predict the financial health of a company. In our model, each individual agent （classifier） makes a prediction on the likelihood of credit risk based on only partial information of the company. Each of the agents is an expert, but has limited knowledge （represented by features） about the company. The decisions of all agents are combined together to form a final credit risk prediction. Experiments show that our model out-performs other existing methods using the benchmarking Compustat American Corporations dataset.     

Impedance Studies on Starch-NH_4NO_3 Films

1 Results Starch is considered a suitable source material because of its inherent biodegradability,ready viability and relatively low cost[1].In the present work,polymer electrolytes based on starch have been prepared by the solution cast technique.The conductivity of the films is characterized using impedance spectroscopy at room temperatures.The imaginary impedance (Zi) versus real impedance (ZR) plot of pure starch films consists of a semicircle.The bulk resistance (Rb) was taken from the intercept o...