Developmental nmda receptor dysregulation in the infantile neuronal ceroid lipofuscinosis mouse model

Protein palmitoylation and depalmitoylation alter protein function. This post-translational modification is critical for synaptic transmission and plasticity. Mutation of the depalmitoylating enzyme palmitoyl-protein thioesterase 1 (PPT1) causes infantile neuronal ceroid lipofuscinosis (CLN1), a pediatric neurodegenerative disease. However, the role of protein depalmitoylation in synaptic maturation is unknown. Therefore, we studied synapse development in Ppt1-/- mouse visual cortex. We demonstrate that the developmental N-methyl-D-aspartate receptor (NMDAR) subunit switch from GluN2B to GluN2A is stagnated in Ppt1-/- mice. Correspondingly, Ppt1-/- neurons exhibit immature evoked NMDAR currents and dendritic spine morphology in vivo. Further, dissociated Ppt1-/- cultured neurons show extrasynaptic, diffuse calcium influxes and enhanced vulnerability to NMDA-induced excitotoxicity, reflecting the predominance of GluN2B-containing receptors. Remarkably, Ppt1-/- neurons demonstrate hyperpalmitoylation of GluN2B as well as Fyn kinase, which regulates surface retention of GluN2B. Thus, PPT1 plays a critical role in postsynapse maturation by facilitating the GluN2 subunit switch and proteostasis of palmitoylated proteins

Soil Moisture Initialization Error and Subgrid Variability of Precipitation in Seasonal Streamflow Forecasting

Offline simulations over the conterminous United States (CONUS) with a land surface model are used to address two issues relevant to the forecasting of large-scale seasonal streamflow: (i) the extent to which errors in soil moisture initialization degrade streamflow forecasts, and (ii) the extent to which a realistic increase in the spatial resolution of forecasted precipitation would improve streamflow forecasts. The addition of error to a soil moisture initialization field is found to lead to a nearly proportional reduction in streamflow forecast skill. The linearity of the response allows the determination of a lower bound for the increase in streamflow forecast skill achievable through improved soil moisture estimation, e.g., through satellite-based soil moisture measurements. An increase in the resolution of precipitation is found to have an impact on large-scale streamflow forecasts only when evaporation variance is significant relative to the precipitation variance. This condition is met only in the western half of the CONUS domain. Taken together, the two studies demonstrate the utility of a continental-scale land surface modeling system as a tool for addressing the science of hydrological prediction

Numerical study of the lattice vacancy effects on the single-channel electron transport of graphite ribbons

Lattice vacancy effects on electrical conductance of nanographite ribbon are investigated by means of the Landauer approach using a tight binding model. In the low-energy regime ribbons with zigzag boundary provide a single conducting channel whose origin is connected with the presence of edge states. It is found that the chemical potential dependence of conductance strongly depends on the difference ($\Delta$) of the number of removed A and B sublattice sites. The large lattice vacancy with $\Delta\neq 0$ shows $2\Delta$ zero-conductance dips in the single-channel region, however, the large lattice vacancy with $\Delta=0$ has no dip structure in this region. The connection between this conductance rule and the Longuet-Higgins conjecture is also discussed

Terahertz and infrared spectroscopic evidence of phonon-paramagnon coupling in hexagonal piezomagnetic YMnO3

Terahertz and far-infrared electric and magnetic responses of hexagonal piezomagnetic YMnO3 single crystals are investigated. Antiferromagnetic resonance is observed in the spectra of magnetic permeability mu_a [H(omega) oriented within the hexagonal plane] below the Neel temperature T_N. This excitation softens from 41 to 32 cm-1 on heating and finally disappears above T_N. An additional weak and heavily-damped excitation is seen in the spectra of complex dielectric permittivity epsilon_c within the same frequency range. This excitation contributes to the dielectric spectra in both antiferromagnetic and paramagnetic phases. Its oscillator strength significantly increases on heating towards room temperature thus providing evidence of piezomagnetic or higher-order couplings to polar phonons. Other heavily-damped dielectric excitations are detected near 100 cm-1 in the paramagnetic phase in both epsilon_c and epsilon_a spectra and they exhibit similar temperature behavior. These excitations appearing in the frequency range of magnon branches well below polar phonons could remind electromagnons; however, their temperature dependence is quite different. We have used density functional theory for calculating phonon dispersion branches in the whole Brillouin zone. A detailed analysis of these results and of previously published magnon dispersion branches brought us to the conclusion that the observed absorption bands stem from phonon-phonon and phonon- paramagnon differential absorption processes. The latter is enabled by a strong short-range in-plane spin correlations in the paramagnetic phase.Comment: subm. to PR

Low-Energy Effective Hamiltonian and the Surface States of Ca_3PbO

The band structure of Ca_3PbO, which possesses a three-dimensional massive Dirac electron at the Fermi energy, is investigated in detail. Analysis of the orbital weight distributions on the bands obtained in the first-principles calculation reveals that the bands crossing the Fermi energy originate from the three Pb-p orbitals and three Ca-dx2y2 orbitals. Taking these Pb-p and Ca-dx2y2 orbitals as basis wave functions, a tight-binding model is constructed. With the appropriate choice of the hopping integrals and the strength of the spin-orbit coupling, the constructed model sucessfully captures important features of the band structure around the Fermi energy obtained in the first-principles calculation. By applying the suitable basis transformation and expanding the matrix elements in the series of the momentum measured from a Dirac point, the low-energy effective Hamiltonian of this model is explicitely derived and proved to be a Dirac Hamiltonain. The origin of the mass term is also discussed. It is shown that the spin-orbit coupling and the orbitals other than Pb-p and Ca-dx2y2 orbitals play important roles in making the mass term finite. Finally, the surface band structures of Ca_3PbO for several types of surfaces are investigated using the constructed tight-binding model. We find that there appear nontrivial surface states that cannot be explained as the bulk bands projected on the surface Brillouin zone. The relation to the topological insulator is also discussed.Comment: 11 page

Quasiparticle transport equation with collision delay. II. Microscopic Theory

For a system of non-interacting electrons scattered by neutral impurities, we derive a modified Boltzmann equation that includes quasiparticle and virial corrections. We start from quasiclassical transport equation for non-equilibrium Green's functions and apply limit of small scattering rates. Resulting transport equation for quasiparticles has gradient corrections to scattering integrals. These gradient corrections are rearranged into a form characteristic for virial corrections

Cooperative mixing induced surface roughening in bilayer metals: a possible novel surface damage mechanism

Molecular dynamics simulations have been used to study a collective atomic transport phenomenon by repeated Ar$^+$ irradiations in the Ti/Pt interfacial system. The ion-induced injection of surface atoms to the bulk, the ejection of bulk atoms to the top layers together with surface erosion is strongly enhanced by interfacial mixing. This process leads to a dense interfacial material, and broadening of the interface region. The process scales with the relative difference of the atomic masses. We find that surface roughening and interfacial mixing is strongly coupled via an enhanced counterflow material transport normal to the surface which might be a novel surface damage mechanism. This cooperative phenomenon is active when the bilayer system is subjected to a high dose ion irradiation (multiple ion irradiations) and leads to surface cavity growth.Comment: 6 pages, 6 figures. accepted in Nucl. Instrum. Meth.