1,214 research outputs found
Frangible tube energy dissipation Patent
Energy dissipating shock absorbing system for land payload recovery or vehicle brakin
Break-up of metal tube makes one-time shock absorber, bars rebound
A frangible metal tube has the capability to dissipate the energy generated when a vehicle lands with excessive velocity. The tube is so placed that, at impact, it is forced against a die and, as it fragments, energy is absorbed
Weak ferromagnetism of antiferromagnetic domains in graphene with defects
Magnetic properties of graphene with randomly distributed magnetic
defects/vacancies are studied in terms of the Kondo Hamiltonian in the mean
field approximation. It has been shown that graphene with defects undergoes a
magnetic phase transition from a paramagnetic to a antiferromagnetic (AFM)
phase once the temperature reaches the critical point . The defect
straggling is taken into account as an assignable cause of multiple nucleation
into AFM domains. Since each domain is characterized by partial compensating
magnetization of the defects associated with different sublattices, together
they reveal a super-paramagnetic behavior in a magnetic field. Theory
qualitatively describe the experimental data provided the temperature
dependence of the AFM domain structure.Comment: 8 pages, 2 figure
Surface Polar Phonon Dominated Electron Transport in Graphene
The effects of surface polar phonons on electronic transport properties of
monolayer graphene are studied by using a Monte Carlo simulation. Specifically,
the low-field electron mobility and saturation velocity are examined for
different substrates (SiC, SiO2, and HfO2) in comparison to the intrinsic case.
While the results show that the low-field mobility can be substantially reduced
by the introduction of surface polar phonon scattering, corresponding
degradation of the saturation velocity is not observed for all three substrates
at room temperature. It is also found that surface polar phonons can influence
graphene electrical resistivity even at low temperature, leading potentially to
inaccurate estimation of the acoustic phonon deformation potential constant
Electron spin relaxation in carbon nanotubes
The long standing problem of inexplicably short spin relaxation in carbon
nanotubes (CNTs) is examined. The curvature-mediated spin-orbital interaction
is shown to induce fluctuating electron spin precession causing efficient
relaxation in a manner analogous to the Dyakonov-Perel mechanism. Our
calculation estimates longitudinal (spin-flip) and transversal (decoherence)
relaxation times as short as 150 ps and 110 ps at room temperature,
respectively, along with a pronounced anisotropic dependence. Interference of
electrons originating from different valleys can lead to even faster dephasing.
The results can help clarify the measured data, resolving discrepancies in the
literature.Comment: 9 pages, 3 figure
First Principles Analysis of Electron-Phonon Interaction in Graphene
The electron-phonon interaction in monolayer graphene is investigated by
using density functional perturbation theory. The results indicate that the
electron-phonon interaction strength is of comparable magnitude for all four
in-plane phonon branches and must be considered simultaneously. Moreover, the
calculated scattering rates suggest an acoustic phonon contribution that is
much weaker than previously thought, revealing the role of optical phonons even
at low energies. Accordingly it is predicted, in good agreement with a recent
measurement, that the intrinsic mobility of graphene may be more than an order
of magnitude larger than the high values reported in suspended samples.Comment: 12 pages, 4 figure
Parton distribution functions and quark orbital motion
Covariant version of the quark-parton model is studied. Dependence of the
structure functions and parton distributions on the 3D quark intrinsic motion
is discussed. The important role of the quark orbital momentum, which is a
particular case of intrinsic motion, appears as a direct consequence of the
covariant description. Effect of orbital motion is substantial especially for
polarized structure functions. At the same time, the procedure for obtaining
the quark momentum distributions of polarized quarks from the combination of
polarized and unpolarized structure functions is suggested.Comment: 17 pages, 2 figures, 1 table. Paper is accepted for publication in
Eur.Phys.J.
Ectodomain shedding of the hypoxia-induced carbonic anhydrase IX is a metalloprotease-dependent process regulated by TACE/ADAM17
Carbonic anhydrase IX (CA IX) is a transmembrane protein whose expression is strongly induced by hypoxia in a broad spectrum of human tumours. It is a highly active enzyme functionally involved in both pH control and cell adhesion. Its presence in tumours usually indicates poor prognosis. Ectodomain of CA IX is detectable in the culture medium and body fluids of cancer patients, but the mechanism of its shedding has not been thoroughly investigated. Here, we analysed several cell lines with natural and ectopic expression of CA IX to show that its ectodomain release is sensitive to metalloprotease inhibitor batimastat (BB-94) and that hypoxia maintains the normal rate of basal shedding, thus leading to concomitant increase in cell-associated and extracellular CA IX levels. Using CHO-M2 cells defective in shedding, we demonstrated that the basal CA IX ectodomain release does not require a functional TNFα-converting enzyme (TACE/ADAM17), whereas the activation of CA IX shedding by both phorbol-12-myristate-13-acetate and pervanadate is TACE-dependent. Our results suggest that the cleavage of CA IX ectodomain is a regulated process that responds to physiological factors and signal transduction stimuli and may therefore contribute to adaptive changes in the protein composition of tumour cells and their microenvironment
Strange particle production in 158 and 40 GeV/ Pb-Pb and p-Be collisions
Results on strange particle production in Pb-Pb collisions at 158 and 40
GeV/ beam momentum from the NA57 experiment at CERN SPS are presented.
Particle yields and ratios are compared with those measured at RHIC.
Strangeness enhancements with respect to p-Be reactions at the same beam
momenta have been also measured: results about their dependence on centrality
and collision energy are reported and discussed.Comment: Contribution to the proceedings of the "Hot Quarks 2004" Conference,
July 18-24 2004, New Mexico, USA, submitted to Journal of Physics G 7 pages,
5 figure
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