Permalloy-based carbon nanotube spin-valve

In this Letter we demonstrate that Permalloy (Py), a widely used Ni/Fe alloy, forms contacts to carbon nanotubes (CNTs) that meet the requirements for the injection and detection of spin-polarized currents in carbon-based spintronic devices. We establish the material quality and magnetization properties of Py strips in the shape of suitable electrical contacts and find a sharp magnetization switching tunable by geometry in the anisotropic magnetoresistance (AMR) of a single strip at cryogenic temperatures. In addition, we show that Py contacts couple strongly to CNTs, comparable to Pd contacts, thereby forming CNT quantum dots at low temperatures. These results form the basis for a Py-based CNT spin-valve exhibiting very sharp resistance switchings in the tunneling magnetoresistance, which directly correspond to the magnetization reversals in the individual contacts observed in AMR experiments.Comment: 3 page

Update on TAO moored ORG array

During the Coupled Ocean Atmosphere Response Experiment (COARE) six TAO moorings were equipped with optical rain gauges (ORG's). In late 1993 moorings deployed on the equator at 154E and 157.5E were recovered and not redeployed as they were augmentations to the TAO array for COARE only. In December 1993, four TAO moorings were equipped with ORG's: one each at 2N, 156E and 2S, 156E and ORG doublets on the equator at 0, 156E and 0, 165E. The 2N, 156E mooring has been lost. By the end of April all sites will have been serviced and six refurbished sensors will again be deployed in the same locations

Machine Scoring of Student Essays: Truth and Consequences

The current trend toward machine-scoring of student work, Ericsson and Haswell argue, has created an emerging issue with implications for higher education across the disciplines, but with particular importance for those in English departments and in administration. The academic community has been silent on the issue—some would say excluded from it—while the commercial entities who develop essay-scoring software have been very active. Machine Scoring of Student Essays is the first volume to seriously consider the educational mechanisms and consequences of this trend, and it offers important discussions from some of the leading scholars in writing assessment.https://digitalcommons.usu.edu/usupress_pubs/1138/thumbnail.jp

On Convergence of the Inexact Rayleigh Quotient Iteration with the Lanczos Method Used for Solving Linear Systems

For the Hermitian inexact Rayleigh quotient iteration (RQI), the author has established new local general convergence results, independent of iterative solvers for inner linear systems. The theory shows that the method locally converges quadratically under a new condition, called the uniform positiveness condition. In this paper we first consider the local convergence of the inexact RQI with the unpreconditioned Lanczos method for the linear systems. Some attractive properties are derived for the residuals, whose norms are $\xi_{k+1}$'s, of the linear systems obtained by the Lanczos method. Based on them and the new general convergence results, we make a refined analysis and establish new local convergence results. It is proved that the inexact RQI with Lanczos converges quadratically provided that $\xi_{k+1}\leq\xi$ with a constant $\xi\geq 1$. The method is guaranteed to converge linearly provided that $\xi_{k+1}$ is bounded by a small multiple of the reciprocal of the residual norm $\|r_k\|$ of the current approximate eigenpair. The results are fundamentally different from the existing convergence results that always require $\xi_{k+1}<1$, and they have a strong impact on effective implementations of the method. We extend the new theory to the inexact RQI with a tuned preconditioned Lanczos for the linear systems. Based on the new theory, we can design practical criteria to control $\xi_{k+1}$ to achieve quadratic convergence and implement the method more effectively than ever before. Numerical experiments confirm our theory.Comment: 20 pages, 8 figures. arXiv admin note: text overlap with arXiv:0906.223

Laser‐induced desorption of NO from NiO(100): Ab initio calculations of potential surfaces for intermediate excited states

In order to interpret the experimental results of the state resolved UV‐laser‐induced desorption of NO from NiO(100) (rotational and vibrational populations, velocity distributions of the desorbing NO molecules, etc.), we have performed ab initio complete active space self‐consistent field (CASSCF) and configuration interaction (CI) calculations for the interaction potential between NO and the NiO(100) surface in the electronic ground state and for those excited states which are involved in the desorption process. The NiO(100)–NO distance and the tilt angle between the NO axis and the surface normal have been varied. A cluster model containing a NiO8−5‐cluster embedded in a Madelung potential has been used for representing the NiO(100) surface. The excited states which are important for the desorption process, are charge transfer states of the substrate–adsorbate system, in which one electron is transferred from the surface into the NO‐2π‐orbital. The potential curves of these excited charge transfer states show deep minima (4 eV–5 eV) at surface/NO distances which are smaller than that in the ground state. The angular dependence of these potentials behaves similar as in the ground state. A semiempirical correction to the calculated excitation energies has been added which makes use of the bulk polarization of NiO. With this correction the charge transfer states are considerably stabilized. The lowest excitation energy amounts to about 4 eV which is in reasonable agreement with the onset of the laser desorption observed experimentally at about 3.5 eV. The density of the NO−‐like states is rather high, so that probably several excited states are involved in the desorption process. The potential energy curves for all of these states are quite similar, but the transitions from the ground state into different excited charge transfer states show strongly differing oscillator strengths, which are also strongly dependent on the surface/NO distance. This fact is important for the dynamics of the deexcitation process in the sense of a selection criterion for the states involved. The magnitude of the oscillator strengths is large in comparison with the excitation of NO in the gas phase, which might be an indication for the possibility of optical excitation processes. One dimensional wave packet calculations on two potential energy curves using fixed lifetimes for the excited state in each calculation have been performed and enable us to estimate the mean lifetime of the excited state to be 15 fs≤τ≤25 fs. This implies that the dynamics of the system is dominated by the attractive part of the excited state potential

Rates and Characteristics of Intermediate Mass Ratio Inspirals Detectable by Advanced LIGO

Gravitational waves (GWs) from the inspiral of a neutron star (NS) or stellar-mass black hole (BH) into an intermediate-mass black hole (IMBH) with mass between ~50 and ~350 solar masses may be detectable by the planned advanced generation of ground-based GW interferometers. Such intermediate mass ratio inspirals (IMRIs) are most likely to be found in globular clusters. We analyze four possible IMRI formation mechanisms: (1) hardening of an NS-IMBH or BH-IMBH binary via three-body interactions, (2) hardening via Kozai resonance in a hierarchical triple system, (3) direct capture, and (4) inspiral of a compact object from a tidally captured main-sequence star; we also discuss tidal effects when the inspiraling object is an NS. For each mechanism we predict the typical eccentricities of the resulting IMRIs. We find that IMRIs will have largely circularized by the time they enter the sensitivity band of ground-based detectors. Hardening of a binary via three-body interactions, which is likely to be the dominant mechanism for IMRI formation, yields eccentricities under 10^-4 when the GW frequency reaches 10 Hz. Even among IMRIs formed via direct captures, which can have the highest eccentricities, around 90% will circularize to eccentricities under 0.1 before the GW frequency reaches 10 Hz. We estimate the rate of IMRI coalescences in globular clusters and the sensitivity of a network of three Advanced LIGO detectors to the resulting GWs. We show that this detector network may see up to tens of IMRIs per year, although rates of one to a few per year may be more plausible. We also estimate the loss in signal-to-noise ratio that will result from using circular IMRI templates for data analysis and find that, for the eccentricities we expect, this loss is negligible.Comment: Accepted for publication in ApJ; revised version reflects changes made to the article during the acceptance proces