236 research outputs found
Fracture of a biopolymer gel as a viscoplastic disentanglement process
We present an extensive experimental study of mode-I, steady, slow crack
dynamics in gelatin gels. Taking advantage of the sensitivity of the elastic
stiffness to gel composition and history we confirm and extend the model for
fracture of physical hydrogels which we proposed in a previous paper (Nature
Materials, doi:10.1038/nmat1666 (2006)), which attributes decohesion to the
viscoplastic pull-out of the network-constituting chains. So, we propose that,
in contrast with chemically cross-linked ones, reversible gels fracture without
chain scission
Resonance properties and microstructure of ultracompliant metallic nanoelectromechanical systems resonators synthesized from Al-32 at. % Mo amorphous-nanocrystalline metallic composites
This study details the resonance properties of 20 nm thick nanoelectromechanical system scale cantilevers fabricated from a metallic Al-32 at. %Mo nanocomposite. The advantage of the Al-32 at. %Mo alloy is that its strength and near-atomic surface smoothness enable fabrication of single-anchored metallic cantilevers with extreme length-to-thickness ratios, as high as 400:1. This yields uniquely compliant structures with exquisite force sensitivity. For example, an 8 ??m long, 20 nm thick Al-32 at. %Mo device has a spring constant of K280 ??Nm. We show through transmission electron microscope analysis and continuum modeling that the relevant damping mechanisms are related to the device microstructure.open3
Tuning the resonant frequency of single-walled carbon nanotube bundle oscillators through electron-beam-induced cross-link formations
Performance of Monolayer Graphene Nanomechanical Resonators with Electrical Readout
The enormous stiffness and low density of graphene make it an ideal material
for nanoelectromechanical (NEMS) applications. We demonstrate fabrication and
electrical readout of monolayer graphene resonators, and test their response to
changes in mass and temperature. The devices show resonances in the MHz range.
The strong dependence of the resonant frequency on applied gate voltage can be
fit to a membrane model, which yields the mass density and built-in strain.
Upon removal and addition of mass, we observe changes in both the density and
the strain, indicating that adsorbates impart tension to the graphene. Upon
cooling, the frequency increases; the shift rate can be used to measure the
unusual negative thermal expansion coefficient of graphene. The quality factor
increases with decreasing temperature, reaching ~10,000 at 5 K. By establishing
many of the basic attributes of monolayer graphene resonators, these studies
lay the groundwork for applications, including high-sensitivity mass detectors
The Importance of Edge Effects on the Intrinsic Loss Mechanisms of Graphene Nanoresonators
We utilize classical molecular dynamics simulations to investigate the
intrinsic loss mechanisms of monolayer graphene nanoresonators undergoing
flexural oscillations. We find that spurious edge modes of vibration, which
arise not due to externally applied stresses but intrinsically due to the
different vibrational properties of edge atoms, are the dominant intrinsic loss
mechanism that reduces the Q-factors. We additionally find that while hydrogen
passivation of the free edges is ineffective in reducing the spurious edge
modes, fixing the free edges is critical to removing the spurious edge-induced
vibrational states. Our atomistic simulations also show that the Q-factor
degrades inversely proportional to temperature; furthermore, we also
demonstrate that the intrinsic losses can be reduced significantly across a
range of operating temperatures through the application of tensile mechanical
strain.Comment: 15 pages, 5 figures. Accepted for publication in Nano Letter
Protein kinase Cδ expression in breast cancer as measured by real-time PCR, western blotting and ELISA
The protein kinase C (PKC) family of genes encode serine/threonine kinases that regulate proliferation, apoptosis, cell survival and migration. Multiple isoforms of PKC have been described, one of which is PKCδ. Currently, it is unclear whether PKCδ is involved in promoting or inhibiting cancer formation/progression. The aim of this study was therefore to investigate the expression of PKCδ in human breast cancer and relate its levels to multiple parameters of tumour progression. Protein kinase Cδ expression at the mRNA level was measured using real-time PCR (n=208) and at protein level by both immunoblotting (n=94) and ELISA (n=98). Following immunoblotting, two proteins were identified, migrating with molecular masses of 78 and 160 kDa. The 78 kDa protein is likely to be the mature form of PKCδ but the identity of the 160 kDa form is unknown. Levels of both these proteins correlated weakly but significantly with PKCδ concentrations determined by ELISA (for the 78 kDa form, r=0.444, P<0.005, n=91 and for the 160 kDa form, r=0.237, P=0.023, n=91) and with PKCδ mRNA levels (for the 78 kDa form, r=0.351, P=0.001, n=94 and for the 160 kDa form, r=0.216, P=0.037, n=94). Protein kinase Cδ mRNA expression was significantly higher in oestrogen receptor (ER)-positive compared with ER-negative tumours (P=0.007, Mann–Whitney U-test). Increasing concentrations of PKCδ mRNA were associated with reduced overall patient survival (P=0.004). Our results are consistent with a role for PKCδ in breast cancer progression
Optimized testing strategy for the diagnosis of GAA-FGF14 ataxia/spinocerebellar ataxia 27B
Dominantly inherited GAA repeat expansions in FGF14 are a common cause of spinocerebellar ataxia (GAA-FGF14 ataxia; spinocerebellar ataxia 27B). Molecular confirmation of FGF14 GAA repeat expansions has thus far mostly relied on long-read sequencing, a technology that is not yet widely available in clinical laboratories. We developed and validated a strategy to detect FGF14 GAA repeat expansions using long-range PCR, bidirectional repeat-primed PCRs, and Sanger sequencing. We compared this strategy to targeted nanopore sequencing in a cohort of 22 French Canadian patients and next validated it in a cohort of 53 French index patients with unsolved ataxia. Method comparison showed that capillary electrophoresis of long-range PCR amplification products significantly underestimated expansion sizes compared to nanopore sequencing (slope, 0.87 [95% CI, 0.81 to 0.93]; intercept, 14.58 [95% CI, − 2.48 to 31.12]) and gel electrophoresis (slope, 0.84 [95% CI, 0.78 to 0.97]; intercept, 21.34 [95% CI, − 27.66 to 40.22]). The latter techniques yielded similar size estimates. Following calibration with internal controls, expansion size estimates were similar between capillary electrophoresis and nanopore sequencing (slope: 0.98 [95% CI, 0.92 to 1.04]; intercept: 10.62 [95% CI, − 7.49 to 27.71]), and gel electrophoresis (slope: 0.94 [95% CI, 0.88 to 1.09]; intercept: 18.81 [95% CI, − 41.93 to 39.15]). Diagnosis was accurately confirmed for all 22 French Canadian patients using this strategy. We also identified 9 French patients (9/53; 17%) and 2 of their relatives who carried an FGF14 (GAA)≥250 expansion. This novel strategy reliably detected and sized FGF14 GAA expansions, and compared favorably to long-read sequencing
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