Incoherent dynamics of vibrating single-molecule transistors

We study the tunneling conductance of nano-scale quantum ``shuttles'' in connection with a recent experiment (H. Park et al., Nature, 407, 57 (2000)) in which a vibrating C^60 molecule was apparently functioning as the island of a single electron transistor (SET). While our calculation starts from the same model of previous work (D. Boese and H. Schoeller, Europhys. Lett. 54, 66(2001)) we obtain quantitatively different dynamics. Calculated I-V curves exhibit most features present in experimental data with a physically reasonable parameter set, and point to a strong dependence of the oscillator's potential on the electrostatics of the island region. We propose that in a regime where the electric field due to the bias voltage itself affects island position, a "catastrophic" negative differential conductance (NDC) may be realized. This effect is directly attributable to the magnitude of overlap of final and initial quantum oscillator states, and as such represents experimental control over quantum transitions of the oscillator via the macroscopically controllable bias voltage.Comment: 6 pages, LaTex, 6 figure

Structural analysis of Pt(1 1 1)c(√3 × 5)rect.–CO using photoelectron diffraction

Core level shift scanned-energy mode photoelectron diffraction using the two distinct components of the C 1s emission has been used to determine the structure of the Pt(1 1 1)c(√3 × 5)rect.–CO phase formed by 0.6 ML of adsorbed CO. The results confirm earlier assignments of these components to CO in atop and bridging sites, further confirm that the best structural model involves a 2:1 occupation ratio of these two sites, and provides quantitative structural parameter values. In particular the Pt–C chemisorption bondlengths for the atop and bridging sites are, respectively, 1.86 ± 0.02 Å and 2.02 ± 0.04 Å. These values are closely similar to those found in the 0.5 ML coverage c(4 × 2) phase, involving an atop:bridge occupation ratio of 1:1, obtained in earlier quantitative low energy electron diffraction studies. The results also indicate a clear tilt of the molecular axis of atop CO species in this compression phase, consistent with the finding of an earlier electron-stimulated desorption ion angular distribution investigatio

Harmonising and linking biomedical and clinical data across disparate data archives to enable integrative cross-biobank research

A wealth of biospecimen samples are stored in modern globally distributed biobanks. Biomedical researchers worldwide need to be able to combine the available resources to improve the power of large-scale studies. A prerequisite for this effort is to be able to search and access phenotypic, clinical and other information about samples that are currently stored at biobanks in an integrated manner. However, privacy issues together with heterogeneous information systems and the lack of agreed-upon vocabularies have made specimen searching across multiple biobanks extremely challenging. We describe three case studies where we have linked samples and sample descriptions in order to facilitate global searching of available samples for research. The use cases include the ENGAGE (European Network for Genetic and Genomic Epidemiology) consortium comprising at least 39 cohorts, the SUMMIT (surrogate markers for micro- and macro-vascular hard endpoints for innovative diabetes tools) consortium and a pilot for data integration between a Swedish clinical health registry and a biobank. We used the Sample avAILability (SAIL) method for data linking: first, created harmonised variables and then annotated and made searchable information on the number of specimens available in individual biobanks for various phenotypic categories. By operating on this categorised availability data we sidestep many obstacles related to privacy that arise when handling real values and show that harmonised and annotated records about data availability across disparate biomedical archives provide a key methodological advance in pre-analysis exchange of information between biobanks, that is, during the project planning phase

Effects of benthivorous fish on biogeochemical processes in lake sediments

1. Studies of aquatic environments have shown that community organisation may strongly affect ecosystem functioning. One common phenomenon is a change in nutrient level following a shift in the fish community composition. Although several hypotheses have been suggested, there is no consensus on which mechanisms are involved. Our study evaluated indirect effects of benthivorous fish on the biogeochemical processes at the sediment-water interface separately from direct effects caused by nutrient excretion or sediment resuspension. 2. We assigned field enclosures to three treatments representing typical pond communities; without fish, addition of approximately 10 small tench or addition of one large bream. After one summer, we monitored the water chemistry, benthic invertebrates and periphyton in the enclosures and sampled sediment cores for laboratory analysis of biochemical process rates (oxygen, phosphorus and nitrogen exchange between sediment and water, and denitrification rate). 3. Fish had strong negative effects on benthic invertebrates, but weaker effects on periphyton, organic content and porosity of the sediment. Moreover, there were significant positive fish effects on both phosphorus and nitrogen concentrations in the water. However, there were no general treatment effects on sediment processes that could explain the treatment effects on water chemistry in the enclosures. 4. Hence, overall treatment effects attenuated along the chain of interactions. We conclude that the observed effect of benthic fish on water chemistry was probably because of direct effects on nutrient excretion or resuspension of sediment. The similarity between bream and tench treatments suggests large niche complementarity despite their different habitat preferences

Fetal origins of adult disease: epidemiology and mechanisms

The past 10 years have provided unequivocal evidence that there are associations between birth size measures and future development of adult diseases, such as type 2 diabetes and coronary artery disease. Despite initial concern that bias or residual confounding in the analyses had produced these rather bizarre associations, the findings have now been reproduced in different cohorts by independent investigators from many parts of the world. The challenge for the next decade must be to discover the cellular and molecular mechanisms giving rise to these associations. If this aim is accomplished, it might be possible to devise strategies to reduce the impact of these disabling, chronic, and expensive diseases. The purpose of this review is to describe some of the relevant, important, and more recent epidemiological studies, and also to discuss potential mechanisms underpinning the associations.J Clin Pathol(J Clin Pathol 2000;53:822–828) Key Words: atherosclerotic vascular disease • type 2 diabetes • birth weigh