Kinetic response of ionospheric ions to onset of auroral electric fields

Examination of the exact analytic solution of a kinetic model of collisional interaction of ionospheric fions with atmospheric neutrals in the Bhatnagar-Gross-Krook approximation, shows that the onset of intense auroral electric fields in the topside ionosphere can produce the following kinetic effects: (1) heat the bulk ionospheric ions to approximately 2 eV, thus driving them up to higher altitudes where they can be subjected to collisionless plasma processes; (2) produce a nonMaxwellian superthermal tail in the distribution function; and (3) cause the ion distribution function to be anisotropic with respect to the magnetic field with the perpendicular average thermal energy exceeding the parallel thermal energy

A randomized controlled trial to compare aesthetic outcomes of immediately placed implants with and without immediate provisionalization

IntroductionThere are mixed results regarding the aesthetic advantage of immediate provisionalization of dental implants. Therefore, this study aimed to compare facial mucosal level of single immediately placed implants with and without immediate provisionalization.MethodsSingle implants were immediately placed to replace a hopeless maxillary anterior or premolar tooth in 40 subjects. Each implant was randomly assigned to receive a nonâ occluding temporary crown or a healing abutment after implant placement. At 4 months, these implants were permanently restored and followed up for 12 months. Clinical and radiographic parameters were measured and compared.ResultsThe implant survival rate at 12 months in the test and control group was 90% and 100%, respectively. Midâ facial mucosal marginal level and papilla height changes were minimal within groups, and no significant differences were found between the two groups. The amount of marginal bone remodelling was modest, with no significant difference between the two groups. Radiographic bone changes were not statistically different between the groups, except for the vertical crestal bone resorption.ConclusionImmediate implant placement with or without provisionalization can achieve stable vertical soft tissue level for 12 months as compared to preâ extraction level. However, immediate provisionalization was not able to improve the aesthetic outcome further.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/151807/1/jcpe13171.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/151807/2/jcpe13171_am.pd

Kondo Effect in Fermi Systems with a Gap: A Renormalization Group Study

We present the results of a Wilson Renormalization Group study of the single-impurity Kondo and Anderson models in a system with a gap in the conduction electron spectrum. The behavior of the impurity susceptibility and the zero-frequency response function, $T>$ are discussed in the cases with and without particle-hole symmetry. In addition, for the asymmetric Anderson model the correlation functions, $<\vec S \cdot\vec \sigma (0)>$,$$, and$$ are computed.Comment: 10 pages, 10 figure

Divergences in QED on a Graph

We consider a model of quantum electrodynamics (QED) on a graph. The one-loop divergences in the model are investigated by use of the background field method.Comment: 14 pages, no figures, RevTeX4. References and typos adde

Strain and field modulation in bilayer graphene band structure

Using an external electric field, one can modulate the bandgap of Bernal stacked bilayer graphene by breaking A-~B symmetry. We analyze strain effects on the bilayer graphene using the extended Huckel theory and find that reduced interlayer distance results in higher bandgap modulation, as expected. Furthermore, above about 2.5 angstrom interlayer distance, the bandgap is direct, follows a convex relation to electric field and saturates to a value determined by the interlayer distance. However, below about 2.5 angstrom, the bandgap is indirect, the trend becomes concave and a threshold electric field is observed, which also depends on the stacking distance.Comment: 3 pages, 5 figures - v1 and v2 are the same, uploaded twice - v3, some typos fixed and a reference adde

Nonvolatile memory with molecule-engineered tunneling barriers

We report a novel field-sensitive tunneling barrier by embedding C60 in SiO2 for nonvolatile memory applications. C60 is a better choice than ultra-small nanocrystals due to its monodispersion. Moreover, C60 provides accessible energy levels to prompt resonant tunneling through SiO2 at high fields. However, this process is quenched at low fields due to HOMO-LUMO gap and large charging energy of C60. Furthermore, we demonstrate an improvement of more than an order of magnitude in retention to program/erase time ratio for a metal nanocrystal memory. This shows promise of engineering tunnel dielectrics by integrating molecules in the future hybrid molecular-silicon electronics.Comment: to appear in Applied Physics Letter

Collimating lenses from non-Euclidean transformation optics

Based on the non-Euclidean transformation optics, we design a thin metamaterial lens that can achieve wide-beam radiation by embedding a simple source (a point source in three-dimensional case or a line current source in two-dimensional case). The scheme is performed on a layer-by-layer geometry to convert curved surfaces in virtual space to flat sheets, which pile up and form the entire lens in physical space. Compared to previous designs, the lens has no extreme material parameters. Simulation results confirm its functionality.Comment: 12 pages, 6 figure

Effects of electrostatic screening on the conformation of single DNA molecules confined in a nanochannel

Single T4-DNA molecules were confined in rectangular-shaped channels with a depth of 300 nm and a width in the range 150-300 nm casted in a poly(dimethylsiloxane) nanofluidic chip. The extensions of the DNA molecules were measured with fluorescence microscopy as a function of the ionic strength and composition of the buffer as well as the DNA intercalation level by the YOYO-1 dye. The data were interpreted with scaling theory for a wormlike polymer in good solvent, including the effects of confinement, charge, and self-avoidance. It was found that the elongation of the DNA molecules with decreasing ionic strength can be interpreted in terms of an increase of the persistence length. Self-avoidance effects on the extension are moderate, due to the small correlation length imposed by the channel cross-sectional diameter. Intercalation of the dye results in an increase of the DNA contour length and a partial neutralization of the DNA charge, but besides effects of electrostatic origin it has no significant effect on the bare bending rigidity. In the presence of divalent cations, the DNA molecules were observed to contract, but they do not collapse into a condensed structure. It is proposed that this contraction results from a divalent counterion mediated attractive force between the segments of the DNA molecule.Comment: 38 pages, 10 figures, accepted for publication in The Journal of Chemical Physic

Search in weighted complex networks

We study trade-offs presented by local search algorithms in complex networks which are heterogeneous in edge weights and node degree. We show that search based on a network measure, local betweenness centrality (LBC), utilizes the heterogeneity of both node degrees and edge weights to perform the best in scale-free weighted networks. The search based on LBC is universal and performs well in a large class of complex networks.Comment: 14 pages, 5 figures, 4 tables, minor changes, added a referenc