Charge Density Wave Ratchet

We propose to operate a locally-gated charge density wave as an electron pump. Applying an oscillating gate potential with frequency $f$ causes equally spaced plateaux in the sliding charge density wave current separated by $\Delta I=2eNf,$ where $N$ is the number of parallel chains. The effects of thermal noise are investigated.Comment: To be published in Applied Physics Letter

Estimating Effects and Making Predictions from Genome-Wide Marker Data

In genome-wide association studies (GWAS), hundreds of thousands of genetic markers (SNPs) are tested for association with a trait or phenotype. Reported effects tend to be larger in magnitude than the true effects of these markers, the so-called ``winner's curse.'' We argue that the classical definition of unbiasedness is not useful in this context and propose to use a different definition of unbiasedness that is a property of the estimator we advocate. We suggest an integrated approach to the estimation of the SNP effects and to the prediction of trait values, treating SNP effects as random instead of fixed effects. Statistical methods traditionally used in the prediction of trait values in the genetics of livestock, which predates the availability of SNP data, can be applied to analysis of GWAS, giving better estimates of the SNP effects and predictions of phenotypic and genetic values in individuals.Comment: Published in at http://dx.doi.org/10.1214/09-STS306 the Statistical Science (http://www.imstat.org/sts/) by the Institute of Mathematical Statistics (http://www.imstat.org

Wood Anatomy of Metasequoia - Separation from Glyptostrobus and Function/Structure Considerations

This thesis is part of a broader cooperative study aimed at understanding Paleo-forest dynamics -- namely those of the Eocene period in the Canadian High Arctic. Wood of the dominant tree species -- Metasequoia -- that grew on Axel Heiberg Island, Nunavut, Canada is the focus of this research. The text is divided into two chapters written as articles to be submitted to the International Association of Wood Anatomists Journal (IAWA). The first chapter of this text is a direct result of classifying the fossil wood of Axel Heiberg. The wood of Glyptostrobus is similar to that of Metasequoia. Because both trees grew on the same sites, it was vital to be able to separate the wood of these species. We obtained extant wood samples of these relatively rare woods from herbaria around the world, tested previously published descriptions, and report observations that more consistently separate these species. The second chapter of this text discusses the xylem strategies of Metasequoia. Because Metasequoia is a tall tree with a high water demand, its wood must be sufficiently strong, and provide the canopy with enough water to meet its needs. A microscopic analysis of tracheid parameters provides evidence for postulating strength and hydraulic conductance functions. The results indicate that Metasequoia possesses unique specific gravity and microfibril angle trends that may be adaptive strategies for this species at its unique high latitude sites. We have shown that as Metasequoia trees increase in diameter and height, they produce tracheids that concomitantly strengthen and potentially improve hydraulic efficiency. This finding provides a new perspective on the strengthhydraulic conductance compromise proposed by other researchers, and demonstrates a strategy of strength enhancement that does not involve significant latewood production

Spin-torque switching: Fokker-Planck rate calculation

We describe a new approach to understanding and calculating magnetization switching rates and noise in the recently observed phenomenon of "spin-torque switching". In this phenomenon, which has possible applications to information storage, a large current passing from a pinned ferromagnetic (FM) layer to a free FM layer switches the free layer. Our main result is that the spin-torque effect increases the Arrhenius factor $\exp(-E/kT)$ in the switching rate, not by lowering the barrier $E$, but by raising the effective spin temperature $T$. To calculate this effect quantitatively, we extend Kramers' 1940 treatment of reaction rates, deriving and solving a Fokker-Planck equation for the energy distribution including a current-induced spin torque of the Slonczewski type. This method can be used to calculate slow switching rates without long-time simulations; in this Letter we calculate rates for telegraph noise that are in good qualitative agreement with recent experiments. The method also allows the calculation of current-induced magnetic noise in CPP (current perpendicular to plane) spin valve read heads.Comment: 11 pages, 8 figures, 1 appendix Original version in Nature format, replaced by Phys. Rev. Letters format. No substantive change

Strong Effects of Weak Localization in Charge Density Wave/Normal Metal Hybrids

Collective transport through a multichannel disordered conductor in contact with charge-density-wave electrodes is theoretically investigated. The statistical distribution function of the threshold potential for charge-density wave sliding is calculated by random matrix theory. In the diffusive regime weak localization has a strong effect on the sliding motion.Comment: To be published in Physical Review

Genetic architecture of body size in mammals

Much of the heritability for human stature is caused by mutations of small-to-medium effect. This is because detrimental pleiotropy restricts large-effect mutations to very low frequencies

Calculating energy derivatives for quantum chemistry on a quantum computer

Modeling chemical reactions and complicated molecular systems has been proposed as the `killer application' of a future quantum computer. Accurate calculations of derivatives of molecular eigenenergies are essential towards this end, allowing for geometry optimization, transition state searches, predictions of the response to an applied electric or magnetic field, and molecular dynamics simulations. In this work, we survey methods to calculate energy derivatives, and present two new methods: one based on quantum phase estimation, the other on a low-order response approximation. We calculate asymptotic error bounds and approximate computational scalings for the methods presented. Implementing these methods, we perform the world's first geometry optimization on an experimental quantum processor, estimating the equilibrium bond length of the dihydrogen molecule to within 0.014 Angstrom of the full configuration interaction value. Within the same experiment, we estimate the polarizability of the H2 molecule, finding agreement at the equilibrium bond length to within 0.06 a.u. (2% relative error).Comment: 19 pages, 1 page supplemental, 7 figures. v2 - tidied up and added example to appendice