990 research outputs found
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
Extinctions and Correlations for Uniformly Discrete Point Processes with Pure Point Dynamical Spectra
The paper investigates how correlations can completely specify a uniformly
discrete point process. The setting is that of uniformly discrete point sets in
real space for which the corresponding dynamical hull is ergodic. The first
result is that all of the essential physical information in such a system is
derivable from its -point correlations, . If the system is
pure point diffractive an upper bound on the number of correlations required
can be derived from the cycle structure of a graph formed from the dynamical
and Bragg spectra. In particular, if the diffraction has no extinctions, then
the 2 and 3 point correlations contain all the relevant information.Comment: 16 page
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
Quantum theory of electromechanical noise and momentum transfer statistics
A quantum mechanical theory is developed for the statistics of momentum
transferred to the lattice by conduction electrons. Results for the
electromechanical noise power in the semiclassical diffusive transport regime
agree with a recent theory based on the Boltzmann-Langevin equation. All
moments of the transferred momentum are calculated for a single-channel
conductor with a localized scatterer, and compared with the known statistics of
transmitted charge.Comment: 10 pages, 2 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
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
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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
Quantum Dynamics in Non-equilibrium Strongly Correlated Environments
We consider a quantum point contact between two Luttinger liquids coupled to
a mechanical system (oscillator). For non-vanishing bias, we find an effective
oscillator temperature that depends on the Luttinger parameter. A generalized
fluctuation-dissipation relation connects the decoherence and dissipation of
the oscillator to the current-voltage characteristics of the device. Via a
spectral representation, this result is generalized to arbitrary leads in a
weak tunneling regime.Comment: 4 pages, 1 figur
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