Nebraska Reading First Winter Report 2005-2006

The Winter Progress Report offers an overview of student mid-year achievement. Student achievement will be interpreted through two separate comparisons. In each section we start with a comparison of this year’s winter achievement and last year’s mid-year achievement; a between cohorts comparison. This comparison will show whether the mid-year achievement of Reading First schools is higher than last year as we anticipated. A second comparison focuses on following student achievement from fall to winter of 2005-2006 school year. This within cohort comparison shows the sustainability of this year’s baseline

Stray field signatures of N\'eel textured skyrmions in Ir/Fe/Co/Pt multilayer films

Skyrmions are nanoscale spin configurations with topological properties that hold great promise for spintronic devices. Here, we establish their N\'eel texture, helicity, and size in Ir/Fe/Co/Pt multilayer films by constructing a multipole expansion to model their stray field signatures and applying it to magnetic force microscopy (MFM) images. Furthermore, the demonstrated sensitivity to inhomogeneity in skyrmion properties, coupled with a unique capability to estimate the pinning force governing dynamics, portends broad applicability in the burgeoning field of topological spin textures.Comment: 6 pages, 4 figures, significantly revised and upgraded. For the updated supplementary material please contact one of the corresponding author

Modeling of negative autoregulated genetic networks in single cells

We discuss recent developments in the modeling of negative autoregulated genetic networks. In particular, we consider the temporal evolution of the population of mRNA and proteins in simple networks using rate equations. In the limit of low copy numbers, fluctuation effects become significant and more adequate modeling is then achieved using the master equation formalism. The analogy between regulatory gene networks and chemical reaction networks on dust grains in the interstellar medium is discussed. The analysis and simulation of complex reaction networks are also considered.Comment: 15 pages, 4 figures. Published in Gen

How good is the Exponential Function discounting Formula? An Experimental Study

This paper estimates the degree of the exponential-function misvaluation, its variation with given product price level, and its expected growth rate. The paper examines whether other mathematical functions, such as linear, quadratic and cubic functions, conform to the discounting and compounding processes of individual decision makers. Using subjects familiar with the exponential function discounting formula, this study finds that individuals undervalue the compound interest discounting formula given by the exponential function and overvalue the simple interest discounting formula given by the linear function. These findings can be attributed to the overreaction, overconfidence, mental accounting and narrow-framing behaviors discussed in psychology.Exponential Discount Function; Experimental Subjective Discount Rates; Linear, Quadratic and Cubic Functions; overreaction, overconfidence, mental accounting and narrow-framing behavior; Economic Psychology.

Evidence for strong electron-phonon coupling and polarons in the optical response of La_{2-x}Sr_xCuO_4

The normal state optical response of La_{2-x}Sr_xCuO_4 is found to be consistent with a simple multi-component model, based on free carriers with strong electron-phonon interaction, localized polaronic states near 0.15 eV and a mid-infrared band at 0.5 eV. Normal state reflectance and absorbance of La_{1.83}Sr_{0.17}CuO_4 are investigated and their temperature dependence is explained. Both, the ac and dc response are recovered and the quasi-linear behavior of the optical scattering rate up to 3000- 4000 cm^{-1} is found to be consistent with strong electron-phonon interaction, which also accounts for the value of T_c. Although not strictly applicable in the superconducting state, our simple model accounts for the observed penetration depth and the optical response below T_c can be recovered by introducing a small amount of additional carriers. Our findings suggest that the optical response of La_{2-x}Sr_xCuO_4 could be explained both, in the normal and superconducting state, by a simple multi-fluid model with strong electron-phonon interaction if the gap symmetry and the temperature dependence of the 0.5 eV mid-infrared band are adequately taken into account.Comment: 22 pages, REVTeX, 12 figures in ps-fil

Non-Gaussian Resistance Noise near Electrical Breakdown in Granular Materials

The distribution of resistance fluctuations of conducting thin films with granular structure near electrical breakdown is studied by numerical simulations. The film is modeled as a resistor network in a steady state determined by the competition between two biased processes, breaking and recovery. Systems of different sizes and with different levels of internal disorder are considered. Sharp deviations from a Gaussian distribution are found near breakdown and the effect increases with the degree of internal disorder. However, we show that in general this non-Gaussianity is related to the finite size of the system and vanishes in the large size limit. Nevertheless, near the critical point of the conductor-insulator transition, deviations from Gaussianity persist when the size is increased and the distribution of resistance fluctuations is well fitted by the universal Bramwell-Holdsworth-Pinton distribution.Comment: 8 pages, 6 figures; accepted for publication on Physica

Chiral magnetic textures in Ir/Fe/Co/Pt multilayers: Evolution and topological Hall signature

Skyrmions are topologically protected, two-dimensional, localized hedgehogs and whorls of spin. Originally invented as a concept in field theory for nuclear interactions, skyrmions are central to a wide range of phenomena in condensed matter. Their realization at room temperature (RT) in magnetic multilayers has generated considerable interest, fueled by technological prospects and the access granted to fundamental questions. The interaction of skyrmions with charge carriers gives rise to exotic electrodynamics, such as the topological Hall effect (THE), the Hall response to an emergent magnetic field, a manifestation of the skyrmion Berry-phase. The proposal that THE can be used to detect skyrmions needs to be tested quantitatively. For that it is imperative to develop comprehensive understanding of skyrmions and other chiral textures, and their electrical fingerprint. Here, using Hall transport and magnetic imaging, we track the evolution of magnetic textures and their THE signature in a technologically viable multilayer film as a function of temperature ($T$) and out-of-plane applied magnetic field ($H$). We show that topological Hall resistivity ($\rho_\mathrm{TH}$) scales with the density of isolated skyrmions ($n_\mathrm{sk}$) over a wide range of $T$, confirming the impact of the skyrmion Berry-phase on electronic transport. We find that at higher $n_\mathrm{sk}$ skyrmions cluster into worms which carry considerable topological charge, unlike topologically-trivial spin spirals. While we establish a qualitative agreement between $\rho_\mathrm{TH}(H,T)$ and areal density of topological charge $n_\mathrm{T}(H,T)$, our detailed quantitative analysis shows a much larger $\rho_\mathrm{TH}$ than the prevailing theory predicts for observed $n_\mathrm{T}$.Comment: Major revision of the original version. The extensive Supplementary Information is available upon reques