440 research outputs found
Kinks, rings, and rackets in filamentous structures
Carbon nanotubes and biological filaments each spontaneously assemble into
kinked helices, rings, and "tennis racket" shapes due to competition between
elastic and interfacial effects. We show that the slender geometry is a more
important determinant of the morphology than any molecular details. Our
mesoscopic continuum theory is capable of quantifying observations of these
structures, and is suggestive of their occurrence in other filamentous
assemblies as well.Comment: This paper was originally published in PNAS 100: 12141-12146 (2003).
The present version has corrected Eq. 3, A1, and A2, and some minor typo
Structural stability and energetics of single-walled carbon nanotubes under uniaxial strain
A (10x10) single-walled carbon nanotube consisting of 400 atoms with 20
layers is simulated under tensile loading using our developed O(N) parallel
tight-binding molecular-dynamics algorithms. It is observed that the simulated
carbon nanotube is able to carry the strain up to 122% of the relaxed tube
length in elongation and up to 93% for compression. Young s modulus, tensile
strength, and the Poisson ratio are calculated and the values found are 0.311
TPa, 4.92 GPa, and 0.287, respectively. The stress-strain curve is obtained.
The elastic limit is observed at a strain rate of 0.09 while the breaking point
is at 0.23. The frequency of vibration for the pristine (10x10) carbon nanotube
in the radial direction is 4.71x10^3 GHz and it is sensitive to the strain
rate.Comment: 11 pages, 8 figure
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Impact of rabies vaccination history on attainment of an adequate antibody titre among dogs tested for International Travel Certification, Israel - 2010-2014
Rabies is endemic in wildlife or domestic carnivore populations globally. Infection of domestic dogs is of particular concern in many areas. In regions where domestic animals are at risk of exposure to rabies virus, dogs should be routinely vaccinated against rabies to protect both pet and human populations. Many countries require demonstration of an adequate level of serum rabies neutralizing antibodies to permit entry of dogs during international travel. We analysed rabies titres of dogs seeking travel certification in Israel to assess demographic and vaccine history factors associated with antibody titres below the acceptable threshold for travel certification. Having received only one previous rabies vaccination and a longer duration since the most recent vaccination was received were primary risk factors for not achieving an adequate rabies virus neutralizing antibody titre for travel certification. These risk factors had stronger effects in younger animals, but were consistent for dogs of all ages. In particular, these findings reiterate the importance of administering at least two rabies vaccinations (the primo vaccination and subsequent booster) to ensure population-level protection against rabies in dogs globally
Single- and multi-walled carbon nanotubes viewed as elastic tubes with Young's moduli dependent on layer number
The complete energy expression of a deformed single-walled carbon nanotube
(SWNT) is derived in the continuum limit from the local density approximation
model proposed by Lenosky {\it et al.} \lbrack Nature (London) {\bf 355}, 333
(1992)\rbrack and shows to be content with the classic shell theory by which
the Young's modulus, the Poisson ratio and the effective wall thickness of
SWNTs are obtained as TPa, , , respectively.
The elasticity of a multi-walled carbon nanotube (MWNT) is investigated as the
combination of the above SWNTs of layer distance and the
Young's modulus of the MWNT is found to be an apparent function of the number
of layers, , varying from 4.70TPa to 1.04TPa for N=1 to .Comment: 4 pages, 1 figur
Nonlinear resonance in a three-terminal carbon nanotube resonator
The RF-response of a three-terminal carbon nanotube resonator coupled to
RF-transmission lines is studied by means of perturbation theory and direct
numerical integration. We find three distinct oscillatory regimes, including
one regime capable of exhibiting very large hysteresis loops in the frequency
response. Considering a purely capacitive transduction, we derive a set of
algebraic equations which can be used to find the output power (S-parameters)
for a device connected to transmission lines with characteristic impedance
.Comment: 16 pages, 8 figure
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.
Testing T Invariance in the Interaction of Slow Neutrons with Aligned Nuclei
The study of five-fold (P even, T odd) correlation in the interaction of slow
polarized neutrons with aligned nuclei is a possible way of testing the time
reversal invariance due to the expected enhancement of T violating effects in
compound resonances. Possible nuclear targets are discussed which can be
aligned both dynamically as well as by the "brute force" method at low
temperature. A statistical estimation is performed of the five-fold correlation
for low lying p wave compound resonances of the Sb, Sb and
I nuclei. It is shown that a significant improvement can be achieved
for the bound on the intensity of the fundamental parity conserving time
violating (PCTV) interaction.Comment: 22 pages, 5 figures, published versio
Polyelectrolyte microcapsules as a tool to enhance photosensitizing effect of chlorin E6
The inclusion of chlorin E6 in polymer capsules reduced dark toxicity and increased the photosensitizing effect compared to the free form of ClE
Dislocations and Grain Boundaries in Two-Dimensional Boron Nitride
A new dislocation structure-square-octagon pair (4|8) is discovered in
two-dimensional boron nitride (h-BN), via first-principles calculations. It has
lower energy than corresponding pentagon-heptagon pairs (5|7), which contain
unfavorable homo-elemental bonds. Based on the structures of dislocations,
grain boundaries (GB) in BN are investigated. Depending on the tilt angle of
grains, GB can be either polar (B-rich or N-rich), constituted by 5|7s, or
un-polar, composed of 4|8s. The polar GBs carry net charges, positive at B-rich
and negative at N-rich ones. In contrast to GBs in graphene which generally
impede the electronic transport, polar GBs have smaller bandgap compared to
perfect BN, which may suggest interesting electronic and optic applications
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
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