Dynamic renormalization group study of a generalized continuum model of crystalline surfaces

We apply the Nozieres-Gallet dynamic renormalization group (RG) scheme to a continuum equilibrium model of a d-dimensional surface relaxing by linear surface tension and linear surface diffusion, and which is subject to a lattice potential favoring discrete values of the height variable. The model thus interpolates between the overdamped sine-Gordon model and a related continuum model of crystalline tensionless surfaces. The RG flow predicts the existence of an equilibrium roughening transition only for d = 2 dimensional surfaces, between a flat low-temperature phase and a rough high-temperature phase in the Edwards-Wilkinson (EW) universality class. The surface is always in the flat phase for any other substrate dimensions d > 2. For any value of d, the linear surface diffusion mechanism is an irrelevant perturbation of the linear surface tension mechanism, but may induce long crossovers within which the scaling properties of the linear molecular-beam epitaxy equation are observed, thus increasing the value of the sine-Gordon roughening temperature. This phenomenon originates in the non-linear lattice potential, and is seen to occur even in the absence of a bare surface tension term. An important consequence of this is that a crystalline tensionless surface is asymptotically described at high temperatures by the EW universality class.Comment: 22 pages, 5 figures. Accepted for publication in Physical Review

Universality in the Screening Cloud of Dislocations Surrounding a Disclination

A detailed analytical and numerical analysis for the dislocation cloud surrounding a disclination is presented. The analytical results show that the combined system behaves as a single disclination with an effective fractional charge which can be computed from the properties of the grain boundaries forming the dislocation cloud. Expressions are also given when the crystal is subjected to an external two-dimensional pressure. The analytical results are generalized to a scaling form for the energy which up to core energies is given by the Young modulus of the crystal times a universal function. The accuracy of the universality hypothesis is numerically checked to high accuracy. The numerical approach, based on a generalization from previous work by S. Seung and D.R. Nelson ({\em Phys. Rev A 38:1005 (1988)}), is interesting on its own and allows to compute the energy for an {\em arbitrary} distribution of defects, on an {\em arbitrary geometry} with an arbitrary elastic {\em energy} with very minor additional computational effort. Some implications for recent experimental, computational and theoretical work are also discussed.Comment: 35 pages, 21 eps file

Enhanced stability of the square lattice of a classical bilayer Wigner crystal

The stability and melting transition of a single layer and a bilayer crystal consisting of charged particles interacting through a Coulomb or a screened Coulomb potential is studied using the Monte-Carlo technique. A new melting criterion is formulated which we show to be universal for bilayer as well as for single layer crystals in the case of (screened) Coulomb, Lennard--Jones and 1/r^{12} repulsive inter-particle interactions. The melting temperature for the five different lattice structures of the bilayer Wigner crystal is obtained, and a phase diagram is constructed as a function of the interlayer distance. We found the surprising result that the square lattice has a substantial larger melting temperature as compared to the other lattice structures. This is a consequence of the specific topology of the defects which are created with increasing temperature and which have a larger energy as compared to the defects in e.g. a hexagonal lattice.Comment: Accepted for publication in Physical Review

Langevin Simulation of Thermally Activated Magnetization Reversal in Nanoscale Pillars

Numerical solutions of the Landau-Lifshitz-Gilbert micromagnetic model incorporating thermal fluctuations and dipole-dipole interactions (calculated by the Fast Multipole Method) are presented for systems composed of nanoscale iron pillars of dimension 9 nm x 9 nm x 150 nm. Hysteresis loops generated under sinusoidally varying fields are obtained, while the coercive field is estimated to be 1979 $\pm$ 14 Oe using linear field sweeps at T=0 K. Thermal effects are essential to the relaxation of magnetization trapped in a metastable orientation, such as happens after a rapid reversal of an external magnetic field less than the coercive value. The distribution of switching times is compared to a simple analytic theory that describes reversal with nucleation at the ends of the nanomagnets. Results are also presented for arrays of nanomagnets oriented perpendicular to a flat substrate. Even at a separation of 300 nm, where the field from neighboring pillars is only $\sim$ 1 Oe, the interactions have a significant effect on the switching of the magnets.Comment: 19 pages RevTeX, including 12 figures, clarified discussion of numerical technique

New insights into the genetic etiology of Alzheimer's disease and related dementias

Characterization of the genetic landscape of Alzheimer's disease (AD) and related dementias (ADD) provides a unique opportunity for a better understanding of the associated pathophysiological processes. We performed a two-stage genome-wide association study totaling 111,326 clinically diagnosed/'proxy' AD cases and 677,663 controls. We found 75 risk loci, of which 42 were new at the time of analysis. Pathway enrichment analyses confirmed the involvement of amyloid/tau pathways and highlighted microglia implication. Gene prioritization in the new loci identified 31 genes that were suggestive of new genetically associated processes, including the tumor necrosis factor alpha pathway through the linear ubiquitin chain assembly complex. We also built a new genetic risk score associated with the risk of future AD/dementia or progression from mild cognitive impairment to AD/dementia. The improvement in prediction led to a 1.6- to 1.9-fold increase in AD risk from the lowest to the highest decile, in addition to effects of age and the APOE ε4 allele

STI-induced damage and hot-carrier reliability in the narrow width short channel NMOSFET fabricated using global strained-Si technology

10.1109/ESSDER.2005.1546702Proceedings of ESSDERC 2005: 35th European Solid-State Device Research Conference2005533-53

A panel study on the effects of a Chinese medicinal suppository, Vigconic VI-28, on insulin-like growth factor 1 and homocysteine in healthy men

Metadata onlyChanges in serum homocysteine (Hcy), often related to stroke and vascular dementia, are negatively correlated with changes in serum insulin-like growth factor 1 (IGF-1) and growth hormone (GH) replacement decreases Hcy levels in men with GH deficiency. Very little information on the effects of Chinese medicines on GH and Hcy is available in the literature published in English. In this study, the effects of a Chinese medicine suppository, Vigconic VI-28 (VI-28), consisting of concentrated extracts of a composite mixture of herbal materials, on serum IGF-1 and Hcy were studied. In vivo observations after treatment with Chinese medicines have often indicated changes in biochemical profiles of measurable parameters related to those changes in endocrine secretions. Thirty six healthy males (age 47-66) were under observation over a 16-week schedule after using VI-28 suppository from 0 to 12 weeks. Blood specimens were taken monthly (except at the end of week 8) for analysis of Hcy and IGF-1 levels. Compared with week 0, IGF-1 levels (192.5 ± 66.4 ng/ml) were significantly elevated at week 4 (211.7 ± 80.5, p < 0.05) and week 12 (226.6 ± 95.2 ng/ml, p = 0.01). No significant changes were observed for Hcy for the whole cohort from week 0 to week 16. When the cohort was divided into 2 groups using a Hcy level of 13.0 µmol/l as the cut-off, a significant (p < 0.05) difference in IGF-1 was observed between the 2 groups at week 12 only. The mean IGF-1 of 14 subjects with higher Hcy levels was lower than that of the 22 subjects with lower Hcy. We believe that VI-28 may exert a regulatory effect on the relationship between Hcy and IGF-1, at least in subjects with relatively low levels of Hcy. In addition, we also observed an apparent association of hyperhomocysteinemia (Hcy greater than or equal to 13.0 mcmol/l) with decreased IGF-1

Enhanced performance in 50 nm N-MOSFETs with silicon-carbon source/drain regions

Technical Digest - International Electron Devices Meeting, IEDM1069-1071TDIM

SDODEL MOSFET for performance enhancement

10.1109/LED.2004.843215IEEE Electron Device Letters263205-207EDLE