Functional Magnetic Resonance Imaging: a study of malnourished rats

Malnutrition is a main public health problem in developing countries. Incidence is increasing and the mortality rate is still high. Malnutrition can leads mayor problems that can be irreversible if it is present before brain development is completed. We used BOLD (blood oxygen level-dependent effect) Functional Magnetic Resonance Imaging to investigate the regions of brain activity in malnourished rats. The food competition method was applied to a rat model to provoke malnutrition during lactation. The weight increase is delayed even if there is plenty milk available. To localize those regions of activity resulting from the trigeminal nerve stimulation, the vibrissae-barrel axis was employed due to the functional and morphological correlation between the vibrissae and the barrels. BOLD response changes caused by the trigeminal nerve stimulation on brain activity of malnourished and control rats were obtained at 7T. Results showed a major neuronal activity in malnourished rats on regions like cerebellum, somatosensorial cortex, hippocampus, and hypothalamus. This is the first study in malnourished rats and illustrates BOLD activation in various brain structures

Grain Evolution across the Shocks in the L1448-mm Outflow

The recent detection of shock-precursors toward the very young L1448-mm outflow offers us the possibility to study the grain chemistry during the first stages of the shock evolution, constraining the molecules ejected from grains and the species formed in gas phase. Observations of key molecules in the grain chemistry such as SiO, CH3OH, SO, CS, H2S, OCS, and SO2 toward this outflow are presented. The line profiles and the derived abundances show three distinct velocity regimes that trace the shock evolution: the preshock, the shock-precursor and the postshock gas. The SiO, CH3OH, SO, and CS abundances are enhanced with respect to the quiescent gas by 1 order of magnitude in the shock-precursor component, and by 3 orders of magnitude in the postshock gas. The derived SiO and CH3OH abundances are consistent with the recent ejection of these molecules from grains. Since H2S is only enhanced in the shock-precursor component, and OCS and SO2 are undetected, SO and CS are the most abundant sulfur-bearing species in the grain mantles of L1448-mm. The ejection of mainly SO and CS rather than H2S or OCS from grains, suggests that the sulfur chemistry will depend on the chemical "history" of the grain mantles in outflows and hot cores.Comment: 4 pages, 2 figures, accepted for publication in ApJ

Anderson transition in low-dimensional disordered systems driven by nonrandom long-range hopping

The single-parameter scaling hypothesis predicts the absence of delocalized states for noninteracting quasiparticles in low-dimensional disordered systems. We show analytically and numerically that extended states may occur in the one- and two-dimensional Anderson model with a nonrandom hopping falling off as some power of the distance between sites. The different size scaling of the bare level spacing and the renormalized magnitude of the disorder seen by the quasiparticles finally results in the delocalization of states at one of the band edges of the quasiparticle energy spectrum. The delocalized nature of those eigenstates is investigated by numerical diagonalization of the Hamiltonian and by the supersymmetric method for disorder averaging, combined with a renormalization group analysis.Comment: 4 pages with 2 Postscript figures, revtex 4. To appear in Phys. Rev. Let

A Density Matrix Renormalization Group study of Excitons in Dendrimers

We introduce the density matrix renormalization group (DMRG) method as an efficient computational tool for one-exciton approximations with off-diagonal disorder. This method allows us to reduce the computational effort by targetting only a few low-lying eigenstates at each statistical sampling, in contrast to the exact diagonalization methods that compute the whole spectrum. As an application of the method, we study excitons in two families of branched molecules called dendrimers using a recently introduced simple model. We compute the absortion peaks for these dendrimers varying their generation number $g$ and number of wedges $w$.Comment: REVTEX4.b4 file, 12 pages, 12 ps Figure

Jet driven molecular outflows in Orion

We present high sensitivity and high angular resolution images of the high velocity (vLSR>30kms^-1) CO emission in the J=1-0 and J=2-1 lines of the Orion KL region. These results reveal the morphology of the high-velocity CO emission at the most extreme velocities. High velocity emission have been only detected in two regions: BN/KL (IRc2/I) and Orion-S. The Orion-S region contains a very young (dynamical age of 10^3years), very fast (~110kms^-1) and very compact (<0.16pc) bipolar outflow. From the morphology of the high-velocity gas we estimate that the position of the powering source must be ~20'' north of FIR4. For the IRc2/I molecular outflow the morphology of the moderate velocity (<60kms^-1) gas shows a weak bipolarity around IRc2/I. The gas at the most extreme velocities does not show any bipolarity around IRc2/I, if any, it is found ~30'' north from these sources. The blue and redshifted gas at moderate velocities shows similar spatial distribution with a systematic trend for the size of the high-velocity gas to decrease as the terminal radial velocity increases. The size-velocity relationship is fitted with a simple velocity law which considers a highly collimated jet and entrained material outside the jet moving in the radial direction. We also find that most of the CO outflowing at moderate velocities is located at the head of the jet. Our results and the spatial distribution and kinematics of the shock tracers in this outflow can be explained if the IRc2/I outflow is driven by a precessing jet oriented along the line of sight.Comment: 15 pages, 10 figure

Jets and high-velocity bullets in the Orion A outflows. Is the IRc2 outflow powered by a variable jet?

We present high sensitivity maps of the High Velocity (HV) CO emission toward the molecular outflows around IRc2 and Orion-S in the Orion A molecular cloud. The maps reveal the presence of HV bullets in both outflows with velocities between 40-80kms-1 from the ambient gas velocity. The blue and redshifted CO HV bullets associated with the IRc2 outflow are distributed in thin (12"-20", 0.02-0.04pc) elliptical ring-like structures with a size of ~10"x50" (0.02x0.1pc). The CO emission at the most extreme blue and redshifted velocities (EHV) peaks 20" north of source I, just inside the rings of the HV bullets. The low velocity H2O masers and the H2* bullets around IRc2 are located at the inner edges of the ring of CO HV bullets and surrounding the EHV CO emission. Furthermore, the high velocity H2O masers are very well correlated with the EHV CO emission. This morphology is consistent with a model of a jet driven molecular outflow oriented close to the line of sight. In the Orion-S outflow, the morphology of the CO HV bullets shows a bipolar structure in the southeast-northwest direction, and the H2O masers are found only at low velocities in the region between the exciting source and the CO HV bullets. The morphology of the CO HV bullets, the radial velocities and the spatial distribution of the H2O masers in both outflows, as well as the H2* features around IRc2, are consistent with a model in which these outflows are driven by a jet variable in direction.In this scenario, the large traverse velocity measured for the H2O masers in the IRc2 outflow, ~18kms-1, supports the evolutionary connection between the jet and the shell-like outflows.Comment: 4 pages, 2 figure

Single-Block Renormalization Group: Quantum Mechanical Problems

We reformulate the density matrix renormalization group method (DMRG) in terms of a single block, instead of the standard left and right blocks used in the construction of the superblock. This version of the DMRG, which we call the puncture renormalization group (PRG), makes easy and natural the extension of the DMRG to higher dimensional lattices. To test numerically this proposal, we study several quantum mechanical models in one, two and three dimensions. In 1D the performance of the standard DMRG is much better than its PRG version, however for 2D models the PRG is more efficient than the DMRG in a variety of circumstances. In 3D the PRG performs also quite well.Comment: RevTex4b4, 13 pages, two-column, 8 fig

A High Density Thin layer confining the HII region M42. HHT measurements

We present HHT observations in the N=3-2 rotational transition of the CN radical toward selected positions of the Trapezium region and of the molecular Ridge in the Orion molecular cloud. Two of the positions in the Ridge were also observed in the N=2-1 line of CN and 13CN. The N=3-2 CN lines have been combined with observations of the N=2-1 and N=1-0 transitions of CN, and of the N=2-1 of 13CN to estimate the physical conditions and CN abundances in the molecular gas. We analyze in detail the excitation of the CN lines and find that the hyperfine ratios of the N=3-2 line are always close to the Local Thermodynamic Equilibrium (LTE) optically thin values even in the case of optically thick emission. This is due to different excitation temperatures for the different hyperfine lines. From the line intensity ratios between the different CN transitions we derive H_2 densities of ~10^5cm^-3 for the molecular Ridge and of ~3x10^6cm^-3 for the Trapezium region. The CN column densities are one order of magnitude larger in the Ridge than in the Trapezium region, but the CN to H_2 ratio is similar both in the Trapezium and in the Ridge. The combination of the low CN column densities, high H_2 densities and relatively high CN abundances toward the Trapezium region requires that the CN emission arises from a thin layer with a depth along the line of sight of only \~5x10^15cm. This high density thin layer of molecular gas seems to be related with material that confines the rear side of the HII region Orion A. However the molecular layer is not moving as expected from the expansion of the HII region, but it is ``static'' with respect to the gas in the molecular cloud. We discuss the implication of a high density ``static'' layer in the evolution of an HII region.Comment: 16 pages, 5 figures,accepted for Ap

Magnetic Resonance Imaging with a Dielectric Lens

Recently, metamaterials have been introduced to improve the signal-to-noise ratio (SNR) of magnetic resonance images with very promising results. However, the use polymers in the generation of high quality images in magnetic resonance imaging has not been fully been investigated. These investigations explored the use of a dielectric periodical array as a lens to improve the image SNR generated with single surface coils. Commercial polycarbonate glazing sheets were used together with a circular coil to generate phantom images at 3 Tesla on a clinical MR imager.Comment: 1 page, 3 figures. Submitted to the Joint Annual Meeting ISMRM-ESMRMB 200

Fluctuations of work cost in optimal generation of correlations

We study the impact of work cost fluctuations on optimal protocols for the creation of correlations in quantum systems. We analyze several notions of work fluctuations to show that even in the simplest case of two free qubits, protocols that are optimal in their work cost (such as the one developed by Huber et al. [NJP 17, 065008 (2015)]) suffer work cost fluctuations that can be much larger than the work cost. We discuss the implications of this fact in the application of such protocols and suggest that, depending on the implementation, protocols that are sub-optimal in their work cost could beat optimal protocols in some scenarios. This highlights the importance of assessing the dynamics of work fluctuations in quantum thermodynamic protocols.Comment: 12 pages, 5 figures. RevTeX 4.1. V2: Updated with latest content and also match published versio