A Key and check-list to Kenya Orchids

Volume: XXI

2014 Murmuri Earthquake

We present source models for the August 2014 Murmuri (Dehloran) earthquake sequence in the Zagros Mountains of Iran. An Mw6.2 mainshock was followed by an aftershock sequence containing 5 events of Mw ≥ 5.4. Models of P and SH waveforms show that all events had dominantly thrust-faulting mechanisms, and had centroid depths that place them within the thick sedimentary sequence, above the crystalline basement. The combination of our estimated focal mechanisms, relative relocations of the event hypocentres, and the surface displacement patterns observed using InSAR, imply that the mainshock and largest aftershock ruptured different fault planes and both contributed to the surface deformation. The fault planes both slipped in horizontally-elongated patches, possibly due to rheological layering limiting the up- and down-dip extent of rupture. The slip vector of the Murmuri mainshock implies that the decollement beneath the Lorestan Arc is weaker than any such feature beneath the Dezful Embayment, providing an explanation for the plan-view sinuosity of the range-front of the Zagros Mountains.This work form part of the NERC- and ESRC-funded project ‘Earthquakes Without Frontiers’. JRE is funded by the NERC projects ‘COMET’ and ‘LiCS’.This is the author accepted manuscript. The final version is available from Oxford University Press via http://dx.doi.org/10.1093/gji/ggv36

Towards a Microscopic Model of Magnetoelectric Interactions in Ni3V2O8

We develop a microscopic magnetoelectric coupling in Ni$_3$V$_2$O$_8$ (NVO) which gives rise to the trilinear phenomenological coupling used previously to explain the phase transition in which magnetic and ferroelectric order parameters appear simultaneously. Using combined neutron scattering measurements and first-principles calculations of the phonons in NVO, we determine eleven phonons which can induce the observed spontaneous polarization. Among these eleven phonons, we find that a few of them can actually induce a significant dipole moment. Using the calculated atomic charges, we find that the required distortion to induce the observed dipole moment is very small (~0.001 \AA) and therefore it would be very difficult to observe the distortion by neutron-powder diffraction. Finally, we identify the derivatives of the exchange tensor with respect to atomic displacements which are needed for a microscopic model of a spin-phonon coupling in NVO and which we hope will be obtained from a fundamental quantum calculation such as LDA+U. We also analyze two toy models to illustrate that the Dzyaloskinskii-Moriya interaction is very important for coexisting of magnetic and ferroelectric order but it is not the only mechanism when the local site symmetry of the system is low enough.Comment: 20 pages, 10 figure

The origins of quark-hadron duality: How does the square of the sum become the sum of the squares?

Bloom-Gilman duality demonstrates empirically that the electroproduction of $N^*$'s at low momentum transfers averages smoothly around the scaling curve measured at large momentum transfers. The latter is proportional to the sum of the squares of the constituent charges whereas the former involves the coherent excitation of resonances and is driven by the square of summed constituent charges. We determine the minimal necessary conditions for this equality to be realised so that duality can occur and consider the implications for a range of processes that may be studied soon at CEBAF.Comment: 9 page

A Neutron Elastic Diffuse Scattering Study of PMN

We have performed elastic diffuse neutron scattering studies on the relaxor Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_3$ (PMN). The measured intensity distribution near a (100) Bragg peak in the (hk0) scattering plane assumes the shape of a butterfly with extended intensity in the (110) and (1$\bar{1}$0) directions. The temperature dependence of the diffuse scattering shows that both the size of the polar nanoregions (PNR) and the integrated diffuse intensity increase with cooling even for temperatures below the Curie temperature $T_C \sim 213$ K.Comment: Submitted to PR

Charmed and Bottom Baryons: a Variational Approach based on Heavy Quark Symmetry

The use of Heavy Quark Symmetry to study bottom and charmed baryons leads to important simplifications of the non-relativistic three body problem, which turns out to be easily solved by a simple variational ansatz. Our simple scheme reproduces previous results (baryon masses, charge and mass radii, $...$) obtained by solving the Faddeev equations with simple non-relativistic quark--quark potentials, adjusted to the light and heavy--light meson spectra. Wave functions, parameterized in a simple manner, are also given and thus they can be easily used to compute further observables. Our method has been also used to find the predictions for strangeness-less baryons of the SU(2) chirally inspired quark-quark interactions. We find that the one pion exchange term of the chirally inspired interactions leads to relative changes of the $\Lambda_b$ and $\Lambda_c$ binding energies as large as 90%.Comment: 20 pages, 5 figures. Revised version to be published in Nucl. Phys.