7,577 research outputs found
The Rwenzori Mountains, a Paleoproterzoic crustal shear belt crossing the Albertine rift system
This contribution discusses the development of the Paleoproterozoic Buganda-Toro belt in the Rwenzori mountains and its influence on the western part of the East African Rift System in Uganda. The Buganda-Toro belt is composed of several thick-skinned nappes consisting of Archaean Gneisses and Palaeoproterozoic cover units that are thrusted northwards. The high Rwenzori mountains are located in the frontal unit of this belt with retrograde greenschist facies gneisses towards the north, which are unconformably overlain by metasediments and amphibolites. Towards the south the metasediments are overthrust by the next migmatitic gneiss unit that belongs to a crustal scale nappe. The southwards dipping metasedimentary and volcanic sequence in the high Rwenzori mountains shows an inverse metamorphic grade with greenschist facies conditions in the north and amphibolite facies conditions in the south. Early D1 deformation structures are overgrown by cordierite, which in turn grows into D2 deformation, representing the major northwards directed thrusting event. We argue that the inverse metamorphic gradient develops because higher grade rocks are exhumed in the footwall of a crustal scale nappe whereas the exhumation decreases towards the north away from the nappe leading to a decrease in metamorphic grade. The D2 deformation event is followed by a D3 E-W compression, a D4 with the development of steep shear zones with a NNE-SSW and SSE-NNW trend including the large Nyamwamba shear followed by a local D5 retrograde event and D6 brittle inverse faulting. The Paleoproterozoic Buganda-Toro belt is relatively stiff and crosses the NNE-SSW running rift system exactly at the node where the highest peaks of the Rwenzori mountains are situated and where the lake George rift terminates towards the north. Orientation of brittle and ductile fabrics show some similarities indicating that the cross-cutting Buganda-Toro belt influenced rift propagation and brittle fault development within the Rwenzori mountain and that this stiff belt may form part of the reason why the Rwenzori mountains are relatively high within the rift.
Keywords: East African Rift, Basement, Buganda Toro, Inverse Metamorphic Gradient, Microtectonics, Rwenzori mountain
Intercalation of graphene on SiC(0001) via ion-implantation
Electronic devices based on graphene technology are catching on rapidly and
the ability to engineer graphene properties at the nanoscale is becoming, more
than ever, indispensable. Here, we present a new procedure of graphene
functionalization on SiC(0001) that paves the way towards the fabrication of
complex graphene electronic chips. The procedure resides on the well-known
ion-implantation technique. The efficiency of the working principle is
demonstrated by the intercalation of the epitaxial graphene layer on SiC(0001)
with Bi atoms, which was not possible following standard procedures. Our
results put forward the ion-beam lithography to nanostructure and functionalize
desired graphene chips
Is Bigger Machinery the Answer?
The machinery used to operate a farm these days represents a substantial investment, and there\u27s a tendency to think big in terms of machinery. But don\u27t discount gains possible through improved machinery management
Long-Distance Contributions to D^0-D^0bar Mixing Parameters
Long-distance contributions to the - mixing parameters and
are evaluated using latest data on hadronic decays. In particular, we
take on two-body and decays to evaluate the contributions of
two-body intermediate states because they account for of hadronic
decays. Use of the diagrammatic approach has been made to estimate
yet-observed decay modes. We find that is of order a few
and of order from hadronic and modes. These are in good
agreement with the latest direct measurement of - mixing
parameters using the and decays by
BaBar. We estimate the contribution to from the modes using the
factorization model and comment on the single-particle resonance effects and
contributions from other two-body modes involving even-parity states.Comment: 18 pages and 1 figure; footnotes and references added; to appear in
Phys. Rev.
TeV neutrinos and gamma rays from pulsars
Recent studies suggest that pulsars could be strong sources of TeV muon
neutrinos provided positive ions are accelerated by pulsar polar caps to PeV
energies. In such a situation muon neutrinos are produced through the delta
resonance in interactions of pulsar accelerated ions with its thermal radiation
field. High energy gamma rays also should be produced simultaneously in pulsar
environment as both charged and neutral pions are generated in the interactions
of energetic hadrons with the ambient photon fields. Here we estimate TeV gamma
ray flux at Earth from few nearby young pulsars. When compared with the
observations we find that proper consideration of the effect of polar cap
geometry in flux calculation is important. Incorporating such an effect we
obtain the (revised) event rates at Earth due to few potential nearby pulsars.
The results suggest that pulsars are unlikely to be detected by the upcoming
neutrino telescopes. We also estimate TeV gamma ray and neutrino fluxes from
pulsar nebulae for the adopted model of particle acceleration.Comment: Six pages, accepted in MNRA
Tkachenko waves, glitches and precession in neutron star
Here I discuss possible relations between free precession of neutron stars,
Tkachenko waves inside them and glitches. I note that the proposed precession
period of the isolated neutron star RX J0720.4-3125 (Haberl et al. 2006) is
consistent with the period of Tkachenko waves for the spin period 8.4s. Based
on a possible observation of a glitch in RX J0720.4-3125 (van Kerkwijk et al.
2007), I propose a simple model, in which long period precession is powered by
Tkachenko waves generated by a glitch. The period of free precession,
determined by a NS oblateness, should be equal to the standing Tkachenko wave
period for effective energy transfer from the standing wave to the precession
motion. A similar scenario can be applicable also in the case of the PSR
B1828-11.Comment: 6 pages, no figures, accepted to Ap&S
Pulsar Constraints on Neutron Star Structure and Equation of State
With the aim of constraining the structural properties of neutron stars and
the equation of state of dense matter, we study sudden spin-ups, glitches,
occurring in the Vela pulsar and in six other pulsars. We present evidence that
glitches represent a self-regulating instability for which the star prepares
over a waiting time. The angular momentum requirements of glitches in Vela
indicate that at least 1.4% of the star's moment of inertia drives these
events. If glitches originate in the liquid of the inner crust, Vela's
`radiation radius' must exceed ~12 km for a mass of 1.4 solar masses.
Observational tests of whether other neutron stars obey this constraint will be
possible in the near future.Comment: 5 pages, including figures. To appear in Physical Review Letter
Microscopic theory of quadrupolar ordering in TmTe
We have calculated the crystal electric field of TmTe (T>T_Q) and have
obtained that the ground state of a Tm 4f hole is the doublet in
agreement with Mossbauer experiments. We study the quadrupole interactions
arising from quantum transitions of 4f holes of Tm. An effective attraction is
found at the L point of the Brillouin zone, . Assuming that the
quadrupolar condensation involves a single arm of we show that
there are two variants for quadrupole ordering which are described by the space
groups C2/c and C2/m. The Landau free energy is derived in mean-field theory.
The phase transition is of second order. The corresponding quadrupole order
parameters are combinations of and components. The obtained
domain structure is in agreement with observations from neutron diffraction
studies for TmTe. Calculated lattice distortions are found to be different for
the two variants of quadrupole ordering. We suggest to measure lattice
displacements in order to discriminate between those two structures.Comment: 10 pages, 2 figures, 5 tables; accepted by PR
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