Tensor models and embedded Riemann surfaces

Tensor models and, more generally, group field theories are candidates for higher-dimensional quantum gravity, just as matrix models are in the 2d setting. With the recent advent of a 1/N-expansion for coloured tensor models, more focus has been given to the study of the topological aspects of their Feynman graphs. Crucial to the aforementioned analysis were certain subgraphs known as bubbles and jackets. We demonstrate in the 3d case that these graphs are generated by matrix models embedded inside the tensor theory. Moreover, we show that the jacket graphs represent (Heegaard) splitting surfaces for the triangulation dual to the Feynman graph. With this in hand, we are able to re-express the Boulatov model as a quantum field theory on these Riemann surfaces.Comment: 9 pages, 7 fi

Physical insight into reduced surface roughness scattering in strained silicon inversion layers

A seemingly anomalous enhancement of electron mobility in strained silicon inversion layers at high sheet densities has exposed a conspicuous gap between device physics theory and experiment in recent years. We show that the root of this discrepancy is due to a bulging effect in the electron \Delta 4 wavefunction at the silicon surface. This renders \Delta 4 electrons more susceptible to perturbations in surface structure thereby increasing surface roughness scattering for these states. Strain engineering utilized by the CMOS industry reduces the relative occupancy of the \Delta 4 states resulting in less overall surface roughness scattering in the channel. We show that the origin of this effect can be explained by moving beyond the effective mass approximation and contrasting the properties of the \Delta 2 and \Delta 4 wavefunctions in a representation that comprehends full crystal and Bloch state symmetry.Comment: 5 pages, 6 figures. Submitted to Applied Physics Letters on 4 April 2012. Update

Lessons learned from CHMP2B, implications for frontotemporal dementia and amyotrophic lateral sclerosis.

Frontotemporal dementia (FTD) and Amyotrophic Lateral Sclerosis (ALS) are two neurodegenerative diseases with clinical, genetic and pathological overlap. As such, they are commonly regarded as a single spectrum disorder, with pure FTD and pure ALS representing distinct ends of a continuum. Dysfunctional endo-lysosomal and autophagic trafficking, leading to impaired proteostasis is common across the FTD-ALS spectrum. These pathways are, in part, mediated by CHMP2B, a protein that coordinates membrane scission events as a core component of the ESCRT machinery. Here we review how ALS and FTD disease causing mutations in CHMP2B have greatly contributed to our understanding of how endosomal-lysosomal and autophagic dysfunction contribute to neurodegeneration, and how in vitro and in vivo models have helped elucidate novel candidates for potential therapeutic intervention with implications across the FTD-ALS spectrum

Microscopic Current Dynamics in Nanoscale Junctions

So far transport properties of nanoscale contacts have been mostly studied within the static scattering approach. The electron dynamics and the transient behavior of current flow, however, remain poorly understood. We present a numerical study of microscopic current flow dynamics in nanoscale quantum point contacts. We employ an approach that combines a microcanonical picture of transport with time-dependent density-functional theory. We carry out atomic and jellium model calculations to show that the time evolution of the current flow exhibits several noteworthy features, such as nonlaminarity and edge flow. We attribute these features to the interaction of the electron fluid with the ionic lattice, to the existence of pressure gradients in the fluid, and to the transient dynamical formation of surface charges at the nanocontact-electrode interfaces. Our results suggest that quantum transport systems exhibit hydrodynamical characteristics which resemble those of a classical liquid.Comment: 8 pages, 5 figures; Accepted for publication in Phys. Rev.

Lithologic Controls on Focused Erosion and Intraplate Earthquakes in the Eastern Tennessee Seismic Zone

We present a new geomorphic model for the intraplate eastern Tennessee seismic zone (ETSZ). Previous studies document that the Upper Tennessee drainage basin is in a transient state of adjustment to ~150 m of base level fall that occurred in the Late Miocene. Using quantitative geomorphology, we demonstrate that base level fall resulted in the erosion of ~3,500 km3 of highly erodibility rock in an ~70 km wide by ~350‐km‐long corridor in the Paleozoic fold‐thrust belt above the ETSZ. Models of modern incision rates show a NE‐SW trending swath of elevated erosion ~30 km southeast of the center of the ETSZ. Stress modeling shows that lithologically focused erosion has affected fault clamping stress on preexisting, favorably oriented faults. We argue that the lithologically controlled transient erosional response to base level fall in the Upper Tennessee basin has given rise to and is sustaining earthquake activity in the ETSZ

Sphingolipids Regulate Neuromuscular Synapse Structure and function in Drosophila

Sphingolipids are found in abundance at synapses and have been implicated in regulation of synapse structure, function and degeneration. Their precise role in these processes, however, remains obscure. Serine Palmitoyl-transferase (SPT) is the first enzymatic step for synthesis of sphingolipids. Analysis of the Drosophila larval neuromuscular junction revealed mutations in the SPT enzyme subunit, lace/SPTLC2 resulted in deficits in synaptic structure and function. Although neuromuscular junction (NMJ) length is normal in lace mutants, the number of boutons per NMJ is reduced to ~50% of the wild type number. Synaptic boutons in lace mutants are much larger but show little perturbation to the general ultrastructure. Electrophysiological analysis of lace mutant synapses revealed strong synaptic transmission coupled with predominance of depression over facilitation. The structural and functional phenotypes of lace mirrored aspects of Basigin (Bsg), a small Ig-domain adhesion molecule also known to regulate synaptic structure and function. Mutant combinations of lace and Bsg generated large synaptic boutons, while lace mutants showed abnormal accumulation of Bsg at synapses, suggesting that Bsg requires sphingolipid to regulate structure of the synapse. In support of this, we found Bsg to be enriched in lipid rafts. Our data points to a role for sphingolipids in the regulation and fine-tuning of synaptic structure and function while sphingolipid regulation of synaptic structure may be mediated via the activity of Bsg