Estudio y comparación del esqueleto axial de un saurópodo (Dinosauria, Sauropodomorpha) procedente de la Formación Villar del Arzobispo (Titónico-Berriasiense) de Galve, Teruel

The great vertebrate fossil record, Tithonian-Barremian in age, found in the outcrops of Galve (Teruel, Spain), has been recently increased with the discovery of sauropod remains in Cuesta Lonsal locality. The dorsal vertebral record of this sauropod is described in this paper. It was found in the Villar del Arzobispo Formation, which means the transition between the Upper Jurassic shallow marine environments to the continental environments of the Lower Cretaceous in this area of the Iberian Range. Plesiomorphic characters are present in the studied material together with derived and eight autapomorphic characters. Comparison with most representative sauropod genera of all the clades, especially Losillasaurus giganteus, from the same Formation, and a cladistic analysis, allows the conclusion that the studied material belongs to a basal neosauropod not described yet, and different than Macronaria and Diplodocidae+Dicraeosauridae. Cladistic analysis also shows a politomy in Neosauropoda node, in which the Cuesta Lonsal sauropod is included. In the future a complete study of all the material of this sauropod will provide new data to the neosauropod origin and evolutive radiation that affected them. Key words: Sauropoda, Neosauropoda, axial squeleton, Tithonian-Berriasian, Galve.El abundante registro fósil de vertebrados del intervalo Titónico-Barremiense presente en los yacimientos de Galve, ha sido engrosado en los últimos años con el hallazgo de los restos de un saurópodo en el yacimiento de Cuesta Lonsal, del cual se describe y compara en este trabajo el registro vertebral dorsal. Proviene de la Formación Villar del Arzobispo, muy rica en restos directos e indirectos de dinosaurios, y que representa la transición entre los medios marinos someros de finales del Jurásico y los medios continentales de la base del Cretácico Inferior en esta zona de la Cordillera Ibérica. Del material estudiado destaca la presencia de caracteres plesiomórficos para los saurópodos, combinados con caracteres derivados y con ocho caracteres autapomórficos. Una comparación con los géneros más representativos de los diversos clados de saurópodos, y en especial con Losillasaurus giganteus, hallado en la misma formación geológica, y un análisis cladístico, permite concluir que el registro estudiado pertenece a un neosaurópodo basal sin describir y distinto de Macronaria y de Diplodocidae + Dicraeosauridae. El análisis cladístico muestra además una amplia politomía en el nodo Neosauropoda, en el que se incluye el saurópodo de Cuesta Lonsal, cuyo estudio completo aportará en el futuro nuevos datos sobre las relaciones filogenéticas que rodean al origen de los neosaurópodos y las radiaciones evolutivas que les afectaron. Palabras clave: Sauropoda, Neosauropoda, esqueleto axial, Titónico-Berriasiense, Galvé

Observation of a Distribution of Internal Transverse Magnetic Fields in a Mn12-Based Single Molecule Magnet

A distribution of internal transverse magnetic fields has been observed in single molecule magnet (SMM) Mn12-BrAc in the pure magnetic quantum tunneling (MQT) regime. Magnetic relaxation experiments at 0.4 K are used to produce a hole in the distribution of transverse fields whose angle and depth depend on the orientation and amplitude of an applied transverse ``digging field.'' The presence of such transverse magnetic fields can explain the main features of resonant MQT in this material, including the tunneling rates, the form of the relaxation and the absence of tunneling selection rules. We propose a model in which the transverse fields originate from a distribution of tilts of the molecular magnetic easy axes.Comment: 4 page

Low temperature microwave emission from molecular clusters

We investigate the experimental detection of the electromagnetic radiation generated in the fast magnetization reversal in Mn12-acetate at low temperatures. In our experiments we used large single crystals and assemblies of several small single crystals of Mn12-acetate placed inside a cylindrical stainless steel waveguide in which an InSb hot electron device was also placed to detect the radiation. All this was set inside a SQUID magnetometer that allowed to change the magnetic field and measure the magnetic moment and the temperature of the sample as the InSb detected simultaneously the radiation emitted from the molecular magnets. Our data show a sequential process in which the fast inversion of the magnetic moment first occurs, then the radiation is detected by the InSb device, and finally the temperature of the sample increases during 15 ms to subsequently recover its original value in several hundreds of milliseconds.Comment: changed conten

Incommensurate Transverse Anisotropy Induced by Disorder and Spin-Orbit-Vibron Coupling in Mn12-acetate

It has been shown within density-functional theory that in Mn$_{12}$-acetate there are effects due to disorder by solvent molecules and a coupling between vibrational and electronic degrees of freedom. We calculate the in-plane principal axes of the second-order anisotropy caused by the second effect and compare them with those of the fourth-order anisotropy due to the first effect. We find that the two types of the principal axes are not commensurate with each other, which results in a complete quenching of the tunnel-splitting oscillation as a function of an applied transverse field.Comment: Will be presented at MMM conference 200

Definitive spectroscopic determination of the transverse interactions responsible for the magnetic quantum tunneling in Mn12-acetate

We present detailed angle-dependent single crystal electron paramagnetic resonance (EPR) data for field rotations in the hard plane of the S=10 single molecule magnet Mn12-acetate. A clear four-fold variation in the resonance positions may be attributed to an intrinsic fourth order transverse anisotropy (O44). Meanwhile, a four-fold variation of the EPR lineshapes confirms a recently proposed model wherein disorder associated with the acetic acid of crystallization induces a locally varying quadratic (rhombic) transverse anisotropy (O22). These findings explain most aspects of the magnetic quantum tunneling observed in Mn12-acetate.Comment: 7 pages, including figures, accepted for publication in Phys. Rev. Let

Predictors of return to driving after stroke

OBJECTIVE: While returning to driving is a major concern for many stroke survivors, predicting who will return to driving after a stroke is often difficult for rehabilitation professionals. The primary aim of this study was to identify patient factors present at admission to an inpatient rehabilitation hospital that can be used to identify which patients with acute stroke will and will not return to driving. DESIGN: After comparing returners and non-returners on demographic and clinical characteristics, a logistic regression model with return to driving as the outcome variable was built using the backward stepwise method. RESULTS: Thirty-one percent (48/156) of patients who had been driving before their stroke had returned to driving six months post-stroke. The final regression model, using FIM cognition and lower extremity Motricity Index scores, predicted the driving outcome with an accuracy of 75% (107/143). CONCLUSIONS: Patients with lower FIM cognition and lower extremity Motricity Index scores at admission to inpatient rehabilitation are less likely to return to driving at six months. This model could be used by rehabilitation professionals to help counsel patients and their families and focus treatment goals

Magnetic qubits as hardware for quantum computers

We propose two potential realisations for quantum bits based on nanometre scale magnetic particles of large spin S and high anisotropy molecular clusters. In case (1) the bit-value basis states |0> and |1> are the ground and first excited spin states Sz = S and S-1, separated by an energy gap given by the ferromagnetic resonance (FMR) frequency. In case (2), when there is significant tunnelling through the anisotropy barrier, the qubit states correspond to the symmetric, |0>, and antisymmetric, |1>, combinations of the two-fold degenerate ground state Sz = +- S. In each case the temperature of operation must be low compared to the energy gap, \Delta, between the states |0> and |1>. The gap \Delta in case (2) can be controlled with an external magnetic field perpendicular to the easy axis of the molecular cluster. The states of different molecular clusters and magnetic particles may be entangled by connecting them by superconducting lines with Josephson switches, leading to the potential for quantum computing hardware.Comment: 17 pages, 3 figure

Dipolar ordering in Fe8?

We show that the low-temperature physics of molecular nanomagnets, contrary to the prevailing one-molecule picture, must be determined by the long-range magnetic ordering due to many-body dipolar interactions. The calculations here performed, using Ewald's summation, suggest a ferromagnetic ground state with a Curie temperature of about 130 mK. The energy of this state is quite close to those of an antiferromagnetic state and to a glass of frozen spin chains. The latter may be realized at finite temperature due to its high entropy.Comment: 7 pages, no figures, submitted to EP

High frequency resonant experiments in Fe8_8 molecular clusters

Precise resonant experiments on Fe$_{8}$ magnetic clusters have been conducted down to 1.2 K at various tranverse magnetic fields, using a cylindrical resonator cavity with 40 different frequencies between 37 GHz and 110 GHz. All the observed resonances for both single crystal and oriented powder, have been fitted by the eigenstates of the hamiltonian ${\cal H}=-DS_z^2+ES_x^2-g\mu_B{\bf H}\cdot {\bf S}$. We have identified the resonances corresponding to the coherent quantum oscillations for different orientations of spin S = 10.Comment: to appear in Phys.Rev. B (August 2000

Relaxation and Landau-Zener experiments down to 100 mK in ferritin

Temperature-independent magnetic viscosity in ferritin has been observed from 2 K down to 100 mK, proving that quantum tunneling plays the main role in these particles at low temperature. Magnetic relaxation has also been studied using the Landau-Zener method making the system crossing zero resonant field at different rates, alpha=dH/dt, ranging from 10^{-5} to 10^{-3} T/s, and at different temperatures, from 150 mK up to the blocking temperature. We propose a new Tln(Delta H_{eff}/tau_0 alpha) scaling law for the Landau-Zener probability in a system distributed in volumes, where Delta H_{eff} is the effective width of the zero field resonance.Comment: 13 pages, 4 postscript figure