1,279 research outputs found
Viscoelasticity of crystal- and bubble-bearing rhyolite melts
The effect of non-deformable inclusions on the frequency-dependent rheology of a rhyolite melt plus crystals has been investigated using a sinusoidal torsion deformation device for measurements of shear viscosity and modulus in the frequency range of 5 mHz to 20 Hz at temperatures of 750–1050°C. The relaxed shear viscosity and unrelaxed shear modulus of rhyolite magma (rhyolite melt plus crystals plus bubbles) decreases with increasing bubble content and increases with the addition of crystals. At a crystal concentration of about 45% a relaxed value of the shear viscosity is not attainable. The presence of rigid inclusions results in an imaginary component of the shear modulus that becomes more symmetrical and shifted to the low-frequency—high-temperature range with respect to that for a crystal-free melt. The slope of log(Q−1) (internal friction) as a function of the dimensionless variable log(ωτ), is unaffected in the low-temperature—high-frequency range of crystals, with Q−1 ≈ 1/(ωτ)0.5 (the same as for bubble- and crystal-free rhyolite). For the present type of suspension, the internal friction is practically constant and independent of log(ωτ) in the high-temperature—low-frequency limit (ωτ 1). The shape of the Cole-Cole diagram becomes symmetrical and can be described as a Caputo body with parameter γ ≈ 0.45, whereas for bubble-bearing and inclusion-free rhyolite melts the shape of diagram relates to the β-relaxation exponent with β ≈ 0.5. The present work demonstrates that magma may or may not follow a power-law rheology depending on the relative volume proportion between crystals and bubbles
Low-energy effects in brane worlds: Liennard-Wiechert potentials and Hydrogen Lamb shift
Testing extra dimensions at low-energies may lead to interesting effects. In
this work a test point charge is taken to move uniformly in the 3-dimensional
subspace of a (3+)-brane embedded in a (3++1)-space with compact and
one warped infinite spatial extra dimensions. We found that the electromagnetic
potentials of the point charge match standard Liennard-Wiechert's at large
distances but differ from them close to it. These are finite at the position of
the charge and produce finite self-energies. We also studied a localized
Hydrogen atom and take the deviation from the standard Coulomb potential as a
perturbation. This produces a Lamb shift that is compared with known
experimental data to set bounds for the parameter of the model. This work
provides details and extends results reported in a previous Letter.Comment: Manuscript (LaTeX) and 2 figure files (eps format) used by the
manuscript LaTeX fil
Low scale gravity as the source of neutrino masses?
We address the question whether low-scale gravity alone can generate the
neutrino mass matrix needed to accommodate the observed phenomenology. In
low-scale gravity the neutrino mass matrix in the flavor basis is characterized
by one parameter (the gravity scale M_X) and by an exact or approximate flavor
blindness (namely, all elements of the mass matrix are of comparable size).
Neutrino masses and mixings are consistent with the observational data for
certain values of the matrix elements, but only when the spectrum of mass is
inverted or degenerate. For the latter type of spectra the parameter M_{ee}
probed in double beta experiments and the mass parameter probed by cosmology
are close to existing upper limits.Comment: 10 pages, 1 figur
Spectral conditions for positive maps
We provide a partial classification of positive linear maps in matrix algebras which is based on a family of spectral conditions. This construction generalizes celebrated Choi example of a map which is positive but not completely positive. It is shown how the spectral conditions enable one to construct linear maps on tensor products of matrix algebras which are positive but only on a convex subset of separable elements. Such maps provide basic tools to study quantum entanglement in multipartite systems
Strange stars in Krori-Barua space-time
The singularity space-time metric obtained by Krori and Barua\cite{Krori1975}
satisfies the physical requirements of a realistic star. Consequently, we
explore the possibility of applying the Krori and Barua model to describe
ultra-compact objects like strange stars. For it to become a viable model for
strange stars, bounds on the model parameters have been obtained. Consequences
of a mathematical description to model strange stars have been analyzed.Comment: 9 pages (two column), 12 figures. Some changes have been made. " To
appear in European Physical Journal C
The effect of wire electrical discharge machining on the fatigue life of Ti-6Al-2Sn-4Zr-6Mo aerospace alloy
AbstractThe paper details experimental data for the fatigue behaviour of aeroengine alloy Ti-6Al-2Sn-4Zr-6Mo following wire electrical discharge machining (WEDM), with minimum damage generator technology and optimised trim pass strategies. Comparative results for flank milled samples are also given together with associated micrographs detailing workpiece subsurface integrity and fracture initiation. Despite a marginally higher S-N response for the milled specimens compared to the wire machined samples when subject to a finishing regime, linear regression statistical analysis suggested no significant difference in performance at the 5% level based on slope responses. Micrographs showing sample crack initiation sites and fatigue crack growth paths suggest a 40- 50μm altered zone in fracture surfaces for milled specimens with fatigue striations defining the crack path. For WEDM surfaces, crack initiation was in some cases due to defects below the machined surface, with secondary cracks probably due to local stresses
The Landau Pole and decays in the 331 bilepton model
We calculate the decay widths and branching ratios of the extra neutral boson
predicted by the 331 bilepton model in the framework of two
different particle contents. These calculations are performed taken into
account oblique radiative corrections, and Flavor Changing Neutral Currents
(FCNC) under the ansatz of Matsuda as a texture for the quark mass matrices.
Contributions of the order of are obtained in the branching
ratios, and partial widths about one order of magnitude bigger in relation with
other non- and bilepton models are also obtained. A Landau-like pole arise at
3.5 TeV considering the full particle content of the minimal model (MM), where
the exotic sector is considered as a degenerated spectrum at 3 TeV scale. The
Landau pole problem can be avoid at the TeV scales if a new leptonic content
running below the threshold at TeV is implemented as suggested by other
authors.Comment: 20 pages, 5 figures, LaTeX2
Strong 3D correlations in vortex system of Bi2212:Pb
The experimental study of magnetic flux penetration under crossed magnetic
fields in Bi2212:Pb single crystal performed by magnetooptic technique (MO)
reveals remarkable field penetration pattern alteration (flux configuration
change) and superconducting current anisotropy enhancement by the in-plane
field. The anisotropy increases with the temperature rise up to . At an abrupt change in the flux behavior is found; the
correlation between the in-plane magnetic field and the out-of-plane magnetic
flux penetration disappears. No correlation is observed for . The
transition temperature does not depend on the magnetic field strength.
The observed flux penetration anisotropy is considered as an evidence of a
strong 3D - correlation between pancake vortices in different CuO planes at . This enables understanding of a remarkable pinning observed in
Bi2212:Pb at low temperatures.Comment: 8 pages, 9 figure
Guest Editorial: Space Information Networks: Technological Challenges, Design Issues, and Solutions
It has been expected that the space information networks (SIN),
as an extension of the terrestrial network, would provide high-speed,
high-capacity, global continuous communication, and data transmission
services anywhere for anyone at any time. With rapid advances
in relevant technologies (e.g., satellite miniaturization technology,
reusable rocket launch technology, and semiconductor technology),
low-orbit satellites, drones, and airships can be integrated into
the SIN to supply more comprehensive network connectivity. The
standard development organizations including 3GPP, ITU, and ETSI
already starts corresponding standardization activities to support nonterrestrial
networks in SIN. It can be foreseen that SIN will be
expanded to provide not only telephone services but also various
kinds of Internet services, and it is thus able to serve many more
users with different demands
- …