Anisotropic Anomalous Diffusion assessed in the human brain by scalar invariant indices

A new method to investigate anomalous diffusion in human brain is proposed. The method has been inspired by both the stretched-exponential model proposed by Hall and Barrick (HB) and DTI. Quantities extracted using HB method were able to discriminate different cerebral tissues on the basis of their complexity, expressed by the stretching exponent gamma and of the anisotropy of gamma across different directions. Nevertheless, these quantities were not defined as scalar invariants like mean diffusivity and fractional anisotropy, which are eigenvalues of the diffusion tensor. We hypotesize instead that the signal may be espressed as a simple stretched-exponential only along the principal axes of diffusion, while in a generic direction the signal is modeled as a combination of three different stretched-exponentials. In this way, we derived indices to quantify both the tissue anomalous diffusion and its anisotropy, independently of the reference frame of the experiment. We tested and compare our new method with DTI and HB approaches applying them to 10 healty subjects brain at 3T. Our experimental results show that our parameters are highly correlated to intrinsic local geometry when compared to HB indices. Moreover, they offer a different kind of contrast when compared to DTI outputs. Specifically, our indices show a higher capability to discriminate among different areas of the corpus callosum, which are known to be associated to different axonal densities.Comment: 21 pages, 6 figures, 2 table

Energy metabolism and glutamate-glutamine cycle in the brain: a stoichiometric modeling perspective

Background: The energetics of cerebral activity critically relies on the functional and metabolic interactions between neurons and astrocytes. Important open questions include the relation between neuronal versus astrocytic energy demand, glucose uptake and intercellular lactate transfer, as well as their dependence on the level of activity. Results: We have developed a large-scale, constraint-based network model of the metabolic partnership between astrocytes and glutamatergic neurons that allows for a quantitative appraisal of the extent to which stoichiometry alone drives the energetics of the system. We find that the velocity of the glutamate-glutamine cycle (Vcyc) explains part of the uncoupling between glucose and oxygen utilization at increasing Vcyc levels. Thus, we are able to characterize different activation states in terms of the tissue oxygen-glucose index (OGI). Calculations show that glucose is taken up and metabolized according to cellular energy requirements, and that partitioning of the sugar between different cell types is not significantly affected by Vcyc. Furthermore, both the direction and magnitude of the lactate shuttle between neurons and astrocytes turn out to depend on the relative cell glucose uptake while being roughly independent of Vcyc. Conclusions: These findings suggest that, in absence of ad hoc activity-related constraints on neuronal and astrocytic metabolism, the glutamate-glutamine cycle does not control the relative energy demand of neurons and astrocytes, and hence their glucose uptake and lactate exchange. © 2013 Massucci et al.; licensee BioMed Central Ltd

High-k/InGaAs interface defects at cryogenic temperature

Oxide defects in the high-k/InGaAs MOS system are investigated. The behaviour of these traps is explored from room temperature down to 10 K. This study reveals that the exchange of free carriers between oxide states and either the conduction or the valence band is strongly temperature dependant. The capture and emission of electrons is strongly suppressed at 10 K as demonstrated by the collapse of the capacitance frequency dispersion in accumulation for n-InGaAs MOS devices, though hysteresis in the C-V sweeps is still present at 10 K. Phonon assisted tunnelling processes are considered in the simulation of electrical characteristics. The simulated data match very well the experimental characteristics and provide energy and spatial mapping of oxide defects. The multi phonon theory also help explain the impedance data temperature dependence. This study also reveals an asymmetry in the free carrier trapping between n and p type devices, where hole trapping is more significant at 10 K

Toward neuronal current spectroscopy at Ultra-Low field NMR

Centro Studi e Ricerche "E. Fermi", Rome, Italy. Email: [email protected] Physikalish-Technische Bundesanstalt (PTB), Abbestr. 2-12, 10587 Berlin, Germany University of Leipzig, Leipzig, Germany Neurophysics Group, Dept. of Neurology, Campus Benjamin Franklin, Charite/University Medicine, Berlin, Germany Dip. di Fisica, Universita di Roma "La Sapienza", Piazzale Aldo Moro, 5, 00185, Rome, Ital

Simulating the vibrational quantum dynamics of molecules using photonics

Advances in control techniques for vibrational quantum states in molecules present new challenges for modelling such systems, which could be amenable to quantum simulation methods. Here, by exploiting a natural mapping between vibrations in molecules and photons in waveguides, we demonstrate a reprogrammable photonic chip as a versatile simulation platform for a range of quantum dynamic behaviour in different molecules. We begin by simulating the time evolution of vibrational excitations in the harmonic approximation for several four-atom molecules, including H2CS, SO3, HNCO, HFHF, N4 and P4. We then simulate coherent and dephased energy transport in the simplest model of the peptide bond in proteins—N-methylacetamide—and simulate thermal relaxation and the effect of anharmonicities in H2O. Finally, we use multi-photon statistics with a feedback control algorithm to iteratively identify quantum states that increase a particular dissociation pathway of NH3. These methods point to powerful new simulation tools for molecular quantum dynamics and the field of femtochemistry