A prospectus for a theory of variable variability

It is proposed that the kind of stellar variability exhibited by the Sun in its magnetic activity cycle should be considered as a prototype of a class of stellar variability. The signature includes long 'periods' (compared to that of the radial fundamental model), erratic behavior, and intermittency. As other phenomena in the same variability class we nominate the liminosity fluctuations of ZZ Ceti stars and the solar 160 m oscillation. We discuss the possibility that analogous physical mechanisms are at work in all these cases, namely instabilities driven in a thin layer. These instabilities should be favorable to grave modes (in angle) and should arise in conditions that may allow more than one kind of instability to occur at once. The interaction of these competing instabilities produces complicated temporal variations. Given suitable idealizations, it is shown how to begin to compute solutions of small, but finite, amplitude

Maximal adaptive-decision speedups in quantum-state readout

The average time $T$ required for high-fidelity readout of quantum states can be significantly reduced via a real-time adaptive decision rule. An adaptive decision rule stops the readout as soon as a desired level of confidence has been achieved, as opposed to setting a fixed readout time $t_f$. The performance of the adaptive decision is characterized by the "adaptive-decision speedup," $t_f/T$. In this work, we reformulate this readout problem in terms of the first-passage time of a particle undergoing stochastic motion. This formalism allows us to theoretically establish the maximum achievable adaptive-decision speedups for several physical two-state readout implementations. We show that for two common readout schemes (the Gaussian latching readout and a readout relying on state-dependent decay), the speedup is bounded by $4$ and $2$, respectively, in the limit of high single-shot readout fidelity. We experimentally study the achievable speedup in a real-world scenario by applying the adaptive decision rule to a readout of the nitrogen-vacancy-center (NV-center) charge state. We find a speedup of $\approx 2$ with our experimental parameters. In addition, we propose a simple readout scheme for which the speedup can, in principle, be increased without bound as the fidelity is increased. Our results should lead to immediate improvements in nanoscale magnetometry based on spin-to-charge conversion of the NV-center spin, and provide a theoretical framework for further optimization of the bandwidth of quantum measurements.Comment: 18 pages, 11 figures. This version is close to the published versio

Anomalous exponents at the onset of an instability

Critical exponents are calculated exactly at the onset of an instability, using asymptotic expansiontechniques. When the unstable mode is subject to multiplicative noise whose spectrum at zero frequency vanishes, we show that the critical behavior can be anomalous, i.e. the mode amplitude X scales with departure from onset \mu as $~ \mu^\beta$ with an exponent $\beta$ different from its deterministic value. This behavior is observed in a direct numerical simulation of the dynamo instability and our results provide a possible explanation to recent experimental observations

Milk consumption rates and student attitudes, selected schools, Hamilton County, Tennessee, 1964

This study will attempt: 1. To ascertain the amount of milk consumed by fifth eighth. and eleventh grade students in selected schools in Hamilton County. 2. To determine the relationship between family income and milk consumption of fifth, eighth, and eleventh grade students in selected schools in Hamilton County. 3. To determine the attitudes toward milk of those students in selected schools in Hamilton County. 4. To determine the relationship, if any, between their attitudes toward milk and their milk consumption. 5. To point out to those in the milk industry the effect of these changing attitudes of adolescents on the consumption of milk

Initial Investigations of Possible Historic Chinese Habitation of Site 24SA0122 (Poacher Gulch)

Ryan, Jennifer A., M.A. December 2006 Anthropology Abstract of Initial Investigations of Possible Historic Chinese Habitation of Site 24SA2122 (Poacher Gulch) Chair: Dr. Kelly Dixon Site 24SA0122 is composed of a historic cabin footprint, road, trail, and masonry terraces. It is located in Poacher Gulch, a narrow North East trending drainage in Western Montana. The focus of this work has been on researching the masonry locus, and attempting to sift facts from scant documentary evidence about the area in order to create a National Register of Historic Places nomination for this site. The site is very similar to known Overseas Chinese gardening and mining loci in Idaho (Fee 1991). Archeological explorations undertaken by a joint team of Passport in Time volunteers from the Lolo National Forest and students from the University of Montana in the fall of 2006 were inconclusive. Future study of the area is planned for 2007, again as a joint venture between the University of Montana and the Lolo National Forest. Research goals included determining who inhabited the site, what it was used for, and creating a chronology of use for the Poacher Gulch Area. Investigations are still ongoing, but currently a rich folklore of Chinese in the area, combined with the strong visual similarity of the masonry locus to Idaho’s Chinese Gardens, makes it possible to infer that the site’s builders may have been Chinese. This work summarizes archeological and historical investigations undertaken at this site in 2005 and 2006

Fault-tolerant Quantum Communication with Minimal Physical Requirements

We describe a novel protocol for a quantum repeater which enables long distance quantum communication through realistic, lossy photonic channels. Contrary to previous proposals, our protocol incorporates active purification of arbitrary errors at each step of the protocol using only two qubits at each repeater station. Because of these minimal physical requirements, the present protocol can be realized in simple physical systems such as solid-state single photon emitters. As an example, we show how nitrogen vacancy color centers in diamond can be used to implement the protocol, using the nuclear and electronic spin to form the two qubits.Comment: 4 pages, 3 figures. V2: Minor modifications. V3: Major changes in the presentation and new titl

Effect of helicity and rotation on the free decay of turbulent flows

The self-similar decay of energy in a turbulent flow is studied in direct numerical simulations with and without rotation. Two initial conditions are considered: one non-helical (mirror-symmetric), and one with maximal helicity. The results show that, while in the absence of rotation the energy in the helical and non-helical cases decays with the same rate, in rotating flows the helicity content has a major impact on the decay rate. These differences are associated with differences in the energy and helicity cascades when rotation is present. Properties of the structures that arise in the flow at late times in each time are also discussed.Comment: 4 pages, 4 figure

Thermal Effects on the Magnetic Field Dependence of Spin Transfer Induced Magnetization Reversal

We have developed a self-aligned, high-yield process to fabricate CPP (current perpendicular to the plane) magnetic sensors of sub 100 nm dimensions. A pinned synthetic antiferromagnet (SAF) is used as the reference layer which minimizes dipole coupling to the free layer and field induced rotation of the reference layer. We find that the critical currents for spin transfer induced magnetization reversal of the free layer vary dramatically with relatively small changes the in-plane magnetic field, in contrast to theoretical predictions based on stability analysis of the Gilbert equations of magnetization dynamics including Slonczewski-type spin-torque terms. The discrepancy is believed due to thermal fluctuations over the time scale of the measurements. Once thermal fluctuations are taken into account, we find good quantitative agreement between our experimental results and numerical simulations.Comment: 14 pages, 4 figures, Submitted to Appl. Phys. Lett., Comparison of some of these results with a model described by N. Smith in cond-mat/040648

Spherical single-roll dynamos at large magnetic Reynolds numbers

This paper concerns kinematic helical dynamos in a spherical fluid body surrounded by an insulator. In particular, we examine their behaviour in the regime of large magnetic Reynolds number \Rm, for which dynamo action is usually concentrated upon a simple resonant stream-surface. The dynamo eigensolutions are computed numerically for two representative single-roll flows using a compact spherical harmonic decomposition and fourth-order finite-differences in radius. These solutions are then compared with the growth rates and eigenfunctions of the Gilbert and Ponty (2000) large \Rm asymptotic theory. We find good agreement between the growth rates when \Rm>10^4, and between the eigenfunctions when \Rm>10^5.Comment: 36 pages, 8 figures. V2: incorrect labels in Fig3 corrected. The article appears in Physics of Fluids, 22, 066601, and may be found at http://pof.aip.org/phfle6/v22/i6/p066601_s1 . (Copyright 2010 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics