530 research outputs found
Torsional response and stiffening of individual multi-walled carbon nanotubes
We report on the characterization of torsional oscillators which use
multi-walled carbon nanotubes as the spring elements. Through
atomic-force-microscope force-distance measurements we are able to apply
torsional strains to the nanotubes and measure their torsional spring constants
and effective shear moduli. We find that the effective shear moduli cover a
broad range, with the largest values near the theoretically predicted value.
The data also suggest that the nanotubes are stiffened by repeated flexing.Comment: 4 page
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
Atomic Scale Sliding and Rolling of Carbon Nanotubes
A carbon nanotube is an ideal object for understanding the atomic scale
aspects of interface interaction and friction. Using molecular statics and
dynamics methods different types of motion of nanotubes on a graphite surface
are investigated. We found that each nanotube has unique equilibrium
orientations with sharp potential energy minima. This leads to atomic scale
locking of the nanotube.
The effective contact area and the total interaction energy scale with the
square root of the radius. Sliding and rolling of nanotubes have different
characters. The potential energy barriers for sliding nanotubes are higher than
that for perfect rolling. When the nanotube is pushed, we observe a combination
of atomic scale spinning and sliding motion. The result is rolling with the
friction force comparable to sliding.Comment: 4 pages (two column) 6 figures - one ep
Highly responsive core-shell microactuator arrays for use in viscous and viscoelastic fluids
We present a new fabrication method to produce arrays of highly responsive polymer-metal core-shell magnetic microactuators. The core-shell fabrication method decouples the elastic and magnetic structural components such that the actuator response can be optimized by adjusting the core-shell geometry. Our microstructures are 10 μm long, 550 nm in diameter, and electrochemically fabricated in particle track-etched membranes, comprising a poly(dimethylsiloxane) core with a 100 nm Ni shell surrounding the upper 3–8 μm. The structures can achieve deflections of nearly 90° with moderate magnetic fields and are capable of driving fluid flow in a fluid 550 times more viscous than water
Deregulated expression of aurora kinases is not a prognostic biomarker in papillary thyroid cancer patients.
Abstract
A number of reports indicated that Aurora-A or Aurora-B overexpression represented a negative prognostic factor in several human malignancies. In thyroid cancer tissues a deregulated expression of Aurora kinases has been also demonstrated, butno information regarding its possible prognostic role in differentiated thyroid cancer is available. Here, weevaluated Aurora-A and Aurora-B mRNA expression and its prognostic relevance in a series of 87 papillary thyroid cancers (PTC), with a median follow-up of 63 months. The analysis of Aurora-A and Aurora-B mRNA levels in PTC tissues, compared to normal matched tissues, revealed that their expression was either up-or down-regulatedin the majority of cancer tissues. In particular, Aurora-A and Aurora-B mRNA levels were altered, respectively, in 55 (63.2%) and 79 (90.8%) out of the 87 PTC analyzed. A significant positive correlation between Aurora-A and Aurora-B mRNAswas observed (p=0.001). The expression of both Aurora genes was not affected by the BRAF(V600E) mutation. Univariate, multivariate and Kaplan-Mayer analyses documented the lack of association between Aurora-A or Aurora-B expression and clinicopathological parameterssuch as gender, age, tumor size, histology, TNM stage, lymph node metastasis and BRAF status as well asdisease recurrences or disease-free interval. Only Aurora-B mRNA was significantly higher in T(3-4) tissues, with respect to T(1-2) PTC tissues. The data reported here demonstrate that the expression of Aurora kinases is deregulated in the majority of PTC tissues, likely contributing to PTC progression. However, differently from other human solid cancers, detection of Aurora-A or Aurora-B mRNAs is not a prognostic biomarker inPTC patients
Nanoscale study of conduction through carbon nanotube networks
We present local conductance measurements of carbon nanotube networks with nanometer scale resolution and show that there are discrete drops in conductance that correspond to junctions of metallic nanotubes and semiconducting nanotubes. The anomalies of these networks compared to thin films are shown, and a new method of discerning between semiconducting and metallic single-wall carbon nanotubes is demonstrated
Simple and efficient method for carbon nanotube attachment to scanning probes and other substrates
We present a fast, high yield, low cost method for the production of scanning probes with aligned carbon nanotubes protruding from the ends. The procedure is described and images of undercut films are used to demonstrate the improved probe quality for topography measurements. A magnetophoretic model of the attachment and alignment processes is discussed
Atomistic Simulations of Nanotube Fracture
The fracture of carbon nanotubes is studied by atomistic simulations. The
fracture behavior is found to be almost independent of the separation energy
and to depend primarily on the inflection point in the interatomic potential.
The rangle of fracture strians compares well with experimental results, but
predicted range of fracture stresses is marketly higher than observed. Various
plausible small-scale defects do not suffice to bring the failure stresses into
agreement with available experimental results. As in the experiments, the
fracture of carbon nanotubes is predicted to be brittle. The results show
moderate dependence of fracture strength on chirality.Comment: 12 pages, PDF, submitted to Phy. Rev.
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