A constrained Potts antiferromagnet model with an interface representation

We define a four-state Potts model ensemble on the square lattice, with the constraints that neighboring spins must have different values, and that no plaquette may contain all four states. The spin configurations may be mapped into those of a 2-dimensional interface in a 2+5 dimensional space. If this interface is in a Gaussian rough phase (as is the case for most other models with such a mapping), then the spin correlations are critical and their exponents can be related to the stiffness governing the interface fluctuations. Results of our Monte Carlo simulations show height fluctuations with an anomalous dependence on wavevector, intermediate between the behaviors expected in a rough phase and in a smooth phase; we argue that the smooth phase (which would imply long-range spin order) is the best interpretation.Comment: 61 pages, LaTeX. Submitted to J. Phys.

Low field hysteresis in disordered ferromagnets

We analyze low field hysteresis close to the demagnetized state in disordered ferromagnets using the zero temperature random-field Ising model. We solve the demagnetization process exactly in one dimension and derive the Rayleigh law of hysteresis. The initial susceptibility a and the hysteretic coefficient b display a peak as a function of the disorder width. This behavior is confirmed by numerical simulations d=2,3 showing that in limit of weak disorder demagnetization is not possible and the Rayleigh law is not defined. These results are in agreement with experimental observations on nanocrystalline magnetic materials.Comment: Extended version, 18 pages, 5 figures, to appear in Phys. Rev.

Spin states of the first four holes in a silicon nanowire quantum dot

We report measurements on a silicon nanowire quantum dot with a clarity that allows for a complete understanding of the spin states of the first four holes. First, we show control of the hole number down to one. Detailed measurements at perpendicular magnetic fields reveal the Zeeman splitting of a single hole in silicon. We are able to determine the ground-state spin configuration for one to four holes occupying the quantum dot and find a spin filling with alternating spin-down and spin-up holes, which is confirmed by magnetospectroscopy up to 9T. Additionally, a so far inexplicable feature in single-charge quantum dots in many materials systems is analyzed in detail. We observe excitations of the zero-hole ground-state energy of the quantum dot, which cannot correspond to electronic or Zeeman states. We show that the most likely explanation is acoustic phonon emission to a cavity between the two contacts to the nanowire.Comment: 24 pages, 8 figures, both including supporting informatio

Determination of early summer pasture conditions to optimize forage and calf productivity and profitability

Forages can be valuable elements in a sustainable production system. The date when animals are first allowed to graze on pastures can impact the quality and amount of forages available. This study explored various factors that influence successful grazing

Dynamics of Metal Centers Monitored by Nuclear Inelastic Scattering

Nuclear inelastic scattering of synchrotron radiation has been used now since 10 years as a tool for vibrational spectroscopy. This method has turned out especially useful in case of large molecules that contain a M\"ossbauer active metal center. Recent applications to iron-sulfur proteins, to iron(II) spin crossover complexes and to tin-DNA complexes are discussed. Special emphasis is given to the combination of nuclear inelastic scattering and density functional calculations

Ipl1/aurora kinase suppresses S-CDK-driven spindle formation during prophase I to ensure chromosome integrity during meiosis

Cells coordinate spindle formation with DNA repair and morphological modifications to chromosomes prior to their segregation to prevent cell division with damaged chromosomes. Here we uncover a novel and unexpected role for Aurora kinase in preventing the formation of spindles by Clb5-CDK (S-CDK) during meiotic prophase I and when the DDR is active in budding yeast. This is critical since S-CDK is essential for replication during premeiotic S-phase as well as double-strand break induction that facilitates meiotic recombination and, ultimately, chromosome segregation. Furthermore, we find that depletion of Cdc5 polo kinase activity delays spindle formation in DDR-arrested cells and that ectopic expression of Cdc5 in prophase I enhances spindle formation, when Ipl1 is depleted. Our findings establish a new paradigm for Aurora kinase function in both negative and positive regulation of spindle dynamics

Ultrathin compound semiconductor on insulator layers for high performance nanoscale transistors

Over the past several years, the inherent scaling limitations of electron devices have fueled the exploration of high carrier mobility semiconductors as a Si replacement to further enhance the device performance. In particular, compound semiconductors heterogeneously integrated on Si substrates have been actively studied, combining the high mobility of III-V semiconductors and the well-established, low cost processing of Si technology. This integration, however, presents significant challenges. Conventionally, heteroepitaxial growth of complex multilayers on Si has been explored. Besides complexity, high defect densities and junction leakage currents present limitations in the approach. Motivated by this challenge, here we utilize an epitaxial transfer method for the integration of ultrathin layers of single-crystalline InAs on Si/SiO2 substrates. As a parallel to silicon-on-insulator (SOI) technology14,we use the abbreviation "XOI" to represent our compound semiconductor-on-insulator platform. Through experiments and simulation, the electrical properties of InAs XOI transistors are explored, elucidating the critical role of quantum confinement in the transport properties of ultrathin XOI layers. Importantly, a high quality InAs/dielectric interface is obtained by the use of a novel thermally grown interfacial InAsOx layer (~1 nm thick). The fabricated FETs exhibit an impressive peak transconductance of ~1.6 mS/{\mu}m at VDS=0.5V with ON/OFF current ratio of greater than 10,000 and a subthreshold swing of 107-150 mV/decade for a channel length of ~0.5 {\mu}m

Security and Privacy Issues in Wireless Mesh Networks: A Survey

This book chapter identifies various security threats in wireless mesh network (WMN). Keeping in mind the critical requirement of security and user privacy in WMNs, this chapter provides a comprehensive overview of various possible attacks on different layers of the communication protocol stack for WMNs and their corresponding defense mechanisms. First, it identifies the security vulnerabilities in the physical, link, network, transport, application layers. Furthermore, various possible attacks on the key management protocols, user authentication and access control protocols, and user privacy preservation protocols are presented. After enumerating various possible attacks, the chapter provides a detailed discussion on various existing security mechanisms and protocols to defend against and wherever possible prevent the possible attacks. Comparative analyses are also presented on the security schemes with regards to the cryptographic schemes used, key management strategies deployed, use of any trusted third party, computation and communication overhead involved etc. The chapter then presents a brief discussion on various trust management approaches for WMNs since trust and reputation-based schemes are increasingly becoming popular for enforcing security in wireless networks. A number of open problems in security and privacy issues for WMNs are subsequently discussed before the chapter is finally concluded.Comment: 62 pages, 12 figures, 6 tables. This chapter is an extension of the author's previous submission in arXiv submission: arXiv:1102.1226. There are some text overlaps with the previous submissio

Solid stress facilitates spheroid formation: potential involvement of hyaluronan

When neoplastic cells grow in confined spaces in vivo, they exert a finite force on the surrounding tissue resulting in the generation of solid stress. By growing multicellular spheroids in agarose gels of defined mechanical properties, we have recently shown that solid stress inhibits the growth of spheroids and that this growth-inhibiting stress ranges from 45 to 120 mmHg. Here we show that solid stress facilitates the formation of spheroids in the highly metastatic Dunning R3327 rat prostate carcinoma AT3.1 cells, which predominantly do not grow as spheroids in free suspension. The maximum size and the growth rate of the resulting spheroids decreased with increasing stress. Relieving solid stress by enzymatic digestion of gels resulted in gradual loss of spheroidal morphology in 8 days. In contrast, the low metastatic variant AT2.1 cells, which grow as spheroids in free suspension as well as in the gels, maintained their spheroidal morphology even after stress removal. Histological examination revealed that most cells in AT2.1 spheroids are in close apposition whereas a regular matrix separates the cells in the AT3.1 gel spheroids. Staining with the hyaluronan binding protein revealed that the matrix between AT3.1 cells in agarose contained hyaluronan, while AT3.1 cells had negligible or no hyaluronan when grown in free suspension. Hyaluronan was found to be present in both free suspensions and agarose gel spheroids of AT2.1. We suggest that cell–cell adhesion may be adequate for spheroid formation, whereas solid stress may be required to form spheroids when cell–matrix adhesion is predominant. These findings have significant implications for tumour growth, invasion and metastasis

Genome-wide Polygenic Burden of Rare Deleterious Variants in Sudden Unexpected Death in Epilepsy

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