In Situ Resistance Measurements of Strained Carbon Nanotubes

We investigate the response of multi-walled carbon nanotubes to mechanical strain applied with an Atomic Force Microscope (AFM) probe. We find that in some samples, changes in the contact resistance dominate the measured resistance change. In others, strain large enough to fracture the tube can be applied without a significant change in the contact resistance. In this case we observe that enough force is applied to break the tube without any change in resistance until the tube fails. We have also manipulated the ends of the broken tube back in contact with each other, re-establishing a finite resistance. We observe that in this broken configuration the resistance of the sample is tunable to values 15-350 kW greater than prior to breaking.Comment: Submitted to Applied Physics Letter

Hands-on tools for nanotechnology

A review of several experiments and techniques in the nanometer domain is given. The covered experiments and techniques are a sampling of the results obtained to date in the nanometer domain through an interdisciplinary collaboration that include computer scientists, materials scientists, social scientists and educators. The nano Manipulator provides a hands-on paradigm for materials science, biological science, educational methods and distance collaborations are being explored as well as providing a varied set of hard driving problems for computer science

Controlled placement of an individual carbon nanotube onto a microelectromechanical structure

We report on the precise placement of a single carbon nanotube (CNT) onto a microlectromechanial system (MEMS) structure. Using a hybrid atomic force microscope/scanning electron microscope (AFM/SEM) system, an individual multiwalled CNT was retrieved from a cartridge by the AFM tip, translated to a MEMS device, and then placed across a gap between an actuating and a stationary structure. Progress toward a resistance versus stress/strain measurement on a CNT will be discussed, including SEM images of a MEMS structure we have designed specifically for such a measurement. © 2002 American Institute of Physics

Ontogenetic and spatial variability in trophic biomarkers of juvenile saffron cod (Eleginus gracilis) from the Beaufort, Chukchi and Bering Seas

Climate models indicate the Arctic will undergo dramatic environmental change with forecasted increases in temperature and river runoff. Saffron cod (Eleginus gracilis) is abundant in nearshore waters and appears in the diet of many Arctic sea birds and marine mammals; however, little is known about its early ecology and consequently how they might be affected by environmental changes. We aimed to characterize the mechanisms of spatial and ontogenetic variation in trophic biomarkers (lipid classes, fatty acids and bulk C and N stable isotopes) of saffron cod from the Western Arctic, Chukchi and Bering Seas. Size-standardized analyses showed a significant difference in lipid condition metrics and trophic biomarkers as a function of survey location. Both ontogeny and sampling location played an important role in determining lipid stores with elevated levels in both small offshore juveniles (75 mm). Higher lipid storage in Arctic juveniles was associated with elevated levels of diatom fatty acid markers, but not with nearshore carbon input. Increased lipids were found in age-1 juveniles from Prudhoe Bay in the Western Beaufort that were feeding at a lower trophic level than similarly sized age-0 juveniles from surface trawls in the Bering Sea. The use of otolith annuli revealed two discrete patterns of growth that help explain the trade-offs between energy storage and rapid growth that diverge between the Arctic and Bering Sea. Laboratory temperature-growth experiments confirmed that saffron cod have a eurythermal growth response and are able to store excess lipids at temperatures as high as 20°C.Keywords: Arctic, Nutrition, Fatty acids, Saffron cod, Lipids, OntogenyKeywords: Arctic, Nutrition, Fatty acids, Saffron cod, Lipids, Ontogen

Bomb-produced radiocarbon validation of growth-increment crossdating allows marine paleoclimate reconstruction

The bivalve Pacific geoduck (Panopea generosa) has been used in the eastern North Pacific Ocean to create proxies for environmental factors such as temperature and oceanographic conditions. This type of research depends upon accurate age determination of Pacific geoducks, which historically was based on shell growth-increment counts. A recent study comparing age estimates generated by the dendrochronology (tree-ring science) procedure of crossdating to those estimated from growth-increment counts found a significant difference between the methods for geoduck older than 30 years. Compared to the traditional age determination method of counting growth increments, the crossdating method estimates a greater longevity in this species, with some individuals living in excess of 150 years. In the present study, the accuracy of each method was independently assessed using bomb-produced radiocarbon (C-14) techniques. Specimens whose birth years were estimated to be within the era of the bomb-produced marine C-14 increase and where the differences between ages estimated by the two methods were greatest were selected for C-14 analysis. The difference between age estimates from traditional growth-increment counts and those from crossdating was evaluated using their respective C-14 chronologies in comparisons to a reference chronology as a standard. The comparisons relied on Bayesian nonlinear models using Markov Chain Monte Carlo simulation. This method of analysis showed that with a 50% probability geoducks were aged correctly when using the crossdating method, compared to the growth increment counts which had a 50% probability of underestimating the age by 4 years. Therefore, the crossdated age estimates were found to be more accurate than increment counts. Furthermore, these results provide new confidence in using Pacific geoduck biochronologies for paleoclimate and paleoenvironmental reconstruction. Published by Elsevier B.V.Keywords: Age determination, Pacific geoduck, Bomb-produced radiocarbon, Bayesian models, Shell growth-increment counts, Crossdating, Panopea generos

Response of Methicillin-Resistant Staphylococcus aureus to Amicoumacin A

Amicoumacin A exhibits strong antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA), hence we sought to uncover its mechanism of action. Genome-wide transcriptome analysis of S. aureus COL in response to amicoumacin A showed alteration in transcription of genes specifying several cellular processes including cell envelope turnover, cross-membrane transport, virulence, metabolism, and general stress response. The most highly induced gene was lrgA, encoding an antiholin-like product, which is induced in cells undergoing a collapse of Δψ. Consistent with the notion that LrgA modulates murein hydrolase activity, COL grown in the presence of amicoumacin A showed reduced autolysis, which was primarily caused by lower hydrolase activity. To gain further insight into the mechanism of action of amicoumacin A, a whole genome comparison of wild-type COL and amicoumacin A-resistant mutants isolated by a serial passage method was carried out. Single point mutations generating codon substitutions were uncovered in ksgA (encoding RNA dimethyltransferase), fusA (elongation factor G), dnaG (primase), lacD (tagatose 1,6-bisphosphate aldolase), and SACOL0611 (a putative glycosyl transferase). The codon substitutions in EF-G that cause amicoumacin A resistance and fusidic acid resistance reside in separate domains and do not bring about cross resistance. Taken together, these results suggest that amicoumacin A might cause perturbation of the cell membrane and lead to energy dissipation. Decreased rates of cellular metabolism including protein synthesis and DNA replication in resistant strains might allow cells to compensate for membrane dysfunction and thus increase cell survivability

Managing collaboration in the nanoManipulator

We designed, developed, deployed, and evaluated the Collaborative nanoManipulator (CnM), a system supporting remote collaboration between users of the nanoManipulator interface to atomic force microscopes. To be accepted by users, the shared nanoManipulator application had to have the same high level of interactivity as the single user system and the application had to support a user’s ability to interleave working privately and working collaboratively. This paper briefly describes the entire collaboration system, but focuses on the shared nanoManipulator application. Based on our experience developing the CnM, we present: a method of analyzing applications to characterize the requirements for sharing data between collaborating sites, examples of data structures that support collaboration, and guidelines for selecting appropriate synchronization and concurrency control schemes