Intrinsic thermal vibrations of suspended doubly clamped single-wall carbon nanotubes

We report the observation of thermally driven mechanical vibrations of suspended doubly clamped carbon nanotubes, grown by chemical vapor deposition (CVD). Several experimental procedures are used to suspend carbon nanotubes. The vibration is observed as a blurring in images taken with a scanning electron microscope. The measured vibration amplitudes are compared with a model based on linear continuum mechanics.Comment: pdf including figures, see: http://www.unibas.ch/phys-meso/Research/Papers/2003/NT-Thermal-Vibrations.pd

On the modulation instability development in optical fiber systems

Extensive numerical simulations were performed to investigate all stages of modulation instability development from the initial pulse of pico-second duration in photonic crystal fiber: quasi-solitons and dispersive waves formation, their interaction stage and the further propagation. Comparison between 4 different NLS-like systems was made: the classical NLS equation, NLS system plus higher dispersion terms, NLS plus higher dispersion and self-steepening and also fully generalized NLS equation with Raman scattering taken into account. For the latter case a mechanism of energy transfer from smaller quasi-solitons to the bigger ones is proposed to explain the dramatical increase of rogue waves appearance frequency in comparison to the systems when the Raman scattering is not taken into account.Comment: 9 pages, 54 figure

Electromechanical instability in suspended carbon nanotubes

We have theoretically investigated electromechanical properties of freely suspended carbon nanotubes when a current is injected into the tubes using a scanning tunneling microscope. We show that a shuttle-like electromechanical instability can occur if the bias voltage exceeds a dissipation-dependent threshold value. An instability results in large amplitude vibrations of the carbon nanotube bending mode, which modify the current-voltage characteristics of the system

An ITPR1 Gene Deletion Causes Spinocerebellar Ataxia 15/16: A Genetic, Clinical and Radiological Description

The purpose of this study was to characterise a novel family with very slowly progressive pure spinocerebellar ataxia (SCA) caused by a deletion in the inositol 1,4,5-triphosphate receptor 1 (ITPR1) gene on chromosome 3. This is a detailed clinical, genetic, and radiological description of the genotype. Deletions in ITPR1 have been shown to cause SCA15/SCA16 in six families to date. A further Japanese family has been identified with an ITPR1 point mutation. The exact prevalence is as yet unknown, but is probably higher than previously thought. The clinical phenotype of the family is described, and videotaped clinical examinations are presented. Serial brain magnetic resonance imaging studies were carried out on one affected individual, and genetic analysis was performed on several family members. Protein analysis confirmed the ITPR1 deletion. Affected subjects display a remarkably slow, almost pure cerebellar syndrome. Serial magnetic resonance imaging shows moderate cerebellar atrophy with mild inferior parietal and temporal cortical volume loss. Genetic analysis shows a deletion of 346,487 bp in ITPR1 (the second largest ITPR1 deletion reported to date), suggesting SCA15 is due to a loss of ITPR1 function. Western blotting of lymphoblastoid cell line protein confirms reduced ITPR1 protein levels. SCA15 is a slowly or nonprogressive pure cerebellar ataxia, which appears to be caused by a loss of ITPR1 function and a reduction in the translated protein. Patients with nonprogressive or slowly progressive ataxia should be screened for ITPR1 defects

Characterization of defect structures in nanocrystalline materials by X-ray line profile analysis

X-ray line profile analysis is a powerful alternative tool for determining dislocation densities, dislocation type, crystallite and subgrain size and size-distributions, and planar defects, especially the frequency of twin boundaries and stacking faults. The method is especially useful in the case of submicron grain size or nanocrystalline materials, where X-ray line broadening is a well pronounced effect, and the observation of defects with very large density is often not easy by transmission electron microscopy. The fundamentals of X-ray line broadening are summarized in terms of the different qualitative breadth methods, and the more sophisticated and more quantitative whole pattern fitting procedures. The efficiency and practical use of X-ray line profile analysis is shown by discussing its applications to metallic, ceramic, diamond-like and polymer nanomaterials

Mortality and implant revision rates of hip arthroplasty in patients with osteoarthritis:registry based cohort study

Objectives To examine mortality and revision rates among patients with osteoarthritis undergoing hip arthroplasty and to compare these rates between patients undergoing cemented or uncemented procedures and to compare outcomes between men undergoing stemmed total hip replacements and Birmingham hip resurfacing. Design Cohort study. Setting National Joint Registry. Population About 275 000 patient records. Main outcome measures Hip arthroplasty procedures were linked to the time to any subsequent mortality or revision (implant failure). Flexible parametric survival analysis methods were used to analyse time to mortality and also time to revision. Comparisons between procedure groups were adjusted for age, sex, American Society of Anesthesiologists (ASA) grade, and complexity. Results As there were large baseline differences in the characteristics of patients receiving cemented, uncemented, or resurfacing procedures, unadjusted comparisons are inappropriate. Multivariable survival analyses identified a higher mortality rate for patients undergoing cemented compared with uncemented total hip replacement (adjusted hazard ratio 1.11, 95% confidence interval 1.07 to 1.16); conversely, there was a lower revision rate with cemented procedures (0.53, 0.50 to 0.57). These translate to small predicted differences in population averaged absolute survival probability at all time points. For example, compared with the uncemented group, at eight years after surgery the predicted probability of death in the cemented group was 0.013 higher (0.007 to 0.019) and the predicted probability of revision was 0.015 lower (0.012 to 0.017). In multivariable analyses restricted to men, there was a higher mortality rate in the cemented group and the uncemented group compared with the Birmingham hip resurfacing group. In terms of revision, the Birmingham hip resurfacings had a similar revision rate to uncemented total hip replacements. Both uncemented total hip replacements and Birmingham hip resurfacings had a higher revision rate than cemented total hip replacements. Conclusions There is a small but significant increased risk of revision with uncemented rather than cemented total hip replacement, and a small but significant increased risk of death with cemented procedures. It is not known whether these are causal relations or caused by residual confounding. Compared with uncemented and cemented total hip replacements, Birmingham hip resurfacing has a significantly lower risk of death in men of all ages. Previously, only adjusted analyses of hip implant revision rates have been used to recommend and justify use of cheaper cemented total hip implants. Our investigations additionally consider mortality rates and suggest a potentially higher mortality rate with cemented total hip replacements, which merits further investigation

Entropic Comparison of Atomic-Resolution Electron Tomography of Crystals and Amorphous Materials

Electron tomography bears promise for widespread determination of the three-dimensional arrangement of atoms in solids. However, it remains unclear whether methods successful for crystals are optimal for amorphous solids. Here, we explore the relative difficulty encountered in atomic-resolution tomography of crystalline and amorphous nanoparticles. We define an informational entropy to reveal the inherent importance of low-entropy zone-axis projections in the reconstruction of crystals. In turn, we propose considerations for optimal sampling for tomography of ordered and disordered materials.M. M. J. T is grateful for the support from the Leverhulme Trust and from the U.S. Department of Energy, Contract No. DE-AC02-06CH11357. R. K. L. acknowledges support from a Clare College Junior Research Fellowship. S. M. C. and P. A. M. acknowledge funding from the European Research Council under the European Union’s Seventh Framework Program (FP7/2007–2013)/ERC Grant Agreement No. 291522-3DIMAGE. C.-B. S. acknowledges support from the Leverhulme Trust project “Breaking the non-convexity barrier,” EPSRC Grant No. EP/M00483X/1, EPSRC Centre Grant No. EP/N014588/1, and CHiPS (the Horizon 2020 RISE project grant). R. T. acknowledges funding from EPSRC Grant No. EP/L016516/1 for the Cambridge Centre for Analysis. R. T. and C.-B. S. also acknowledge the Cantab Capital Institute for the Mathematics of Information. M. B. acknowledges the Isaac Newton Trust and the Leverhulme Trust Early Career Fellowship “Learning from mistakes: A supervised feedback-loop for imaging applications.

The strain energy and Young's Moduli of single-wall Carbon nanotubules calculated from the electronic energy-band theory

The strain energies in straight and bent single-walled carbon nanotubes (SWNTs) are calculated by taking account of the total energy of all the occupied band electrons. The obtained results are in good agreement with previous theoretical studies and experimental observations. The Young's modulus and the effective wall thickness of SWNT are obtained from the bending strain energies of SWNTs with various cross-sectional radii. The repulsion potential between ions contributes the main part of the Young's modulus of SWNT. The wall thickness of SWNT comes completely from the overlap of electronic orbits, and is approximately of the extension of $\pi$ orbit of carbon atom. Both the Young's modulus and the wall thickness are independent of the radius and the helicity of SWNT, and insensitive to the fitting parameters. The results show that continuum elasticity theory can serve well to describe the mechanical properties of SWNTs.Comment: 12 pages, 2 figure

Ab-initio structural, elastic, and vibrational properties of carbon nanotubes

A study based on ab initio calculations is presented on the estructural, elastic, and vibrational properties of single-wall carbon nanotubes with different radii and chiralities. We use SIESTA, an implementation of pseudopotential-density-functional theory which allows calculations on systems with a large number of atoms per cell. Different quantities like bond distances, Young moduli, Poisson ratio and the frequencies of different phonon branches are monitored versus tube radius. The validity of expectations based on graphite is explored down to small radii, where some deviations appear related to the curvature effects. For the phonon spectra, the results are compared with the predictions of the simple zone-folding approximation. Except for the known defficiencies of this approximation in the low-frequency vibrational regions, it offers quite accurate results, even for relatively small radii.Comment: 13 pages, 7 figures, submitted to Phys. Rev. B (11 Nov. 98