Electronic Structure and Lattice dynamics of NaFeAs

The similarity of the electronic structures of NaFeAs and other Fe pnictides has been demonstrated on the basis of first-principle calculations. The global double-degeneracy of electronic bands along X-M and R-A direction indicates the instability of Fe pnictides and is explained on the basis of a tight-binding model. The de Haas-van Alphen parameters for the Fermi surface (FS) of NaFeAs have been calculated. A $\mathbf{Q}_{M}=(1/2,1/2,0)$ spin density wave (SDW) instead of a charge density wave (CDW) ground state is predicted based on the calculated generalized susceptibility $\chi(\mathbf{q})$ and a criterion derived from a restricted Hatree-Fock model. The strongest electron-phonon (e-p) coupling has been found to involve only As, Na z-direction vibration with linear-response calculations. A possible enhancement mechanism for e-p coupling due to correlation is suggested

Pressure shift of the superconducting T_c of LiFeAs

The effect of hydrostatic pressure on the superconductivity in LiFeAs is investigated up to 1.8 GPa. The superconducting transition temperature, T_c, decreases linearly with pressure at a rate of 1.5 K/GPa. The negative pressure coefficient of T_c and the high ambient pressure T_c indicate that LiFeAs is the high-pressure analogue of the isoelectronic SrFe_2As_2 and BaFe_2As_2.Comment: 3 pages, 2 figure

Lower Critical Field, Anisotropy, and Two-Gap Features of LiFeAs

The magnetic properties of LiFeAs, as single crystalline and polycrystalline samples, were investigated. The lower critical field deduced from the vortex penetration of two single crystals appears to be almost isotropic with a temperature dependence closer to that of two-gap superconductors. The parameters extracted from the reversible magnetizations of sintered polycrystalline samples are in good agreement with those from the single crystal data.Comment: 19 pages, 5 figure

Greenland Ice Sheet surface melt amplified by snowline migration and bare ice exposure

Greenland Ice Sheet mass loss has recently increased because of enhanced surface melt and runoff. Since melt is critically modulated by surface albedo, understanding the processes and feedbacks that alter albedo is a prerequisite for accurately forecasting mass loss. Using satellite imagery, we demonstrate the importance of Greenland’s seasonally fluctuating snowline, which reduces ice sheet albedo and enhances melt by exposing dark bare ice. From 2001 to 2017, this process drove 53% of net shortwave radiation variability in the ablation zone and amplified ice sheet melt five times more than hydrological and biological processes that darken bare ice itself. In a warmer climate, snowline fluctuations will exert an even greater control on melt due to flatter ice sheet topography at higher elevations. Current climate models, however, inaccurately predict snowline elevations during high melt years, portending an unforeseen uncertainty in forecasts of Greenland’s runoff contribution to global sea level ris

Whistler mode startup in the Michigan Mirror Machine

Results of investigations of whistler mode ECRH plasma startup in the Michigan Mirror Machine are presented. Electron‐velocity‐distribution and plasma‐spatial‐distribution time evolution are characterized by measurements from axially and radially moveable Langmuir probes, an endloss current detector, an electron cyclotron emission radiometer, a foil‐filtered X‐ray detector, and a diamagnetic loop at the mirror midplane. Measurements of the buildup of both electron density and perpendicular pressure (nkT⟂) are compared to predictions from various numerical models. Both modeling and data suggest the creation of a highly anisotropic electron velocity distribution function with a ‘‘sloshing electron’’ axial density profile.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87352/2/204_1.pd

CAKβ/Pyk2 Kinase Is a Signaling Link for Induction of Long-Term Potentiation in CA1 Hippocampus

AbstractLong-term potentiation (LTP) is an activity-dependent enhancement of synaptic efficacy, considered a model of learning and memory. The biochemical cascade producing LTP requires activation of Src, which upregulates the function of NMDA receptors (NMDARs), but how Src becomes activated is unknown. Here, we show that the focal adhesion kinase CAKβ/Pyk2 upregulated NMDAR function by activating Src in CA1 hippocampal neurons. Induction of LTP was prevented by blocking CAKβ/Pyk2, and administering CAKβ/Pyk2 intracellularly mimicked and occluded LTP. Tyrosine phosphorylation of CAKβ/Pyk2 and its association with Src was increased by stimulation that produced LTP. Finally, CAKβ/Pyk2-stimulated enhancement of synaptic AMPA responses was prevented by blocking NMDARS, chelating intracellular Ca2+, or blocking Src. Thus, activating CAKβ/Pyk2 is required for inducing LTP and may depend upon downstream activation of Src to upregulate NMDA receptors

Pair-Hopping Mechanism for Layered Superconductors

We propose a possible charge fluctuation effect expected in layered superconducting materials. In the multireference density functional theory, relevant fluctuation channels for the Josephson coupling between superconducting layers include the interlayer pair hopping derived from the Coulomb repulsion. When interlayer single-electron tunneling processes are irrelevant in the Kohn-Sham electronic band structure calculation, the two-body effective interactions stabilize a superconducting phase. This state is also regarded as a valence-bond solid in a bulk electronic state. The hidden order parameters coexist with the superconducting order parameter when the charging effect of a layer is comparable to the pair hopping. Relevant materials structures favorable for the pair-hopping mechanism are discussed.Comment: 24 pages, 2 figures, to be published in J. Phys. Soc. Jpn. (2009

Molecular basis for DNA repair synthesis on short gaps by mycobacterial Primase-Polymerase C

Cells utilise specialized polymerases from the Primase-Polymerase (Prim-Pol) superfamily to maintain genome stability. Prim-Pol’s function in genome maintenance pathways including replication, repair and damage tolerance. Mycobacteria contain multiple Prim-Pols required for lesion repair, including Prim-PolC that performs short gap repair synthesis during excision repair. To understand the molecular basis of Prim-PolC’s gap recognition and synthesis activities, we elucidated crystal structures of pre- and post-catalytic complexes bound to gapped DNA substrates. These intermediates explain its binding preference for short gaps and reveal a distinctive modus operandi called Synthesis-dependent Template Displacement (STD). This mechanism enables Prim-PolC to couple primer extension with template base dislocation, ensuring that the unpaired templating bases in the gap are ushered into the active site in an ordered manner. Insights provided by these structures establishes the molecular basis of Prim-PolC’s gap recognition and extension activities, while also illuminating the mechanisms of primer extension utilised by closely related Prim-Pols