Current-induced magnetic vortex core switching in a Permalloy nanodisk

We report on the switching of a magnetic vortex core in a sub-micron Permalloy disk, induced by a short current pulse applied in the film plane. Micromagnetic simulations including the adiabatic and non-adiabatic spin-torque terms are used to investigate the current-driven magnetization dynamics. We predict that a core reversal can be triggered by current bursts a tenth of a nanosecond long. The vortex core reversal process is found to be the same as when an external field pulse is applied. The control of a vortex core's orientation using current pulses introduces the technologically relevant possibility to address individual nanomagnets within dense arrays.Comment: 3 pages, 3 figure

Ammonia emissions from deciduous forest after leaf fall

The understanding of biochemical feedback mechanisms in the climate system is lacking knowledge in relation to bi-directional ammonia (NH3) exchange between natural ecosystems and the atmosphere. We therefore study the atmospheric NH3 fluxes during a 25-day period during autumn 2010 (21 October to 15 November) for the Danish beech forest Lille Bøgeskov to address the hypothesis that NH3 emissions occur from deciduous forests in relation to leaf fall. This is accomplished by using observations of vegetation status, NH3 fluxes and model calculations. Vegetation status was observed using plant area index (PAI) and leaf area index (LAI). NH3 fluxes were measured using the relaxed eddy accumulation (REA) method. The REA-based NH3 concentrations were compared to NH3 denuder measurements. Model calculations of the atmospheric NH3 concentration were obtained with the Danish Ammonia MOdelling System (DAMOS). The relative contribution from the forest components to the atmospheric NH3 flux was assessed using a simple two-layer bi-directional canopy compensation point model. A total of 57.7% of the fluxes measured showed emission and 19.5% showed deposition. A clear tendency of the flux going from deposition of −0.25 ± 0.30 μg NH3-N m−2 s−1 to emission of up to 0.67 ± 0.28 μg NH3-N m−2 s−1 throughout the measurement period was found. In the leaf fall period (23 October to 8 November), an increase in the atmospheric NH3 concentrations was related to the increasing forest NH3 flux. Following leaf fall, the magnitude and temporal structure of the measured NH3 emission fluxes could be adequately reproduced with the bi-directional resistance model; it suggested the forest ground layer (soil and litter) to be the main contributing component to the NH3 emissions. The modelled concentration from DAMOS fits well the measured concentrations before leaf fall, but during and after leaf fall, the modelled concentrations are too low. The results indicate that the missing contribution to atmospheric NH3 concentration from vegetative surfaces related to leaf fall are of a relatively large magnitude. We therefore conclude that emissions from deciduous forests are important to include in model calculations of atmospheric NH3 for forest ecosystems. Finally, diurnal variations in the measured NH3 concentrations were related to meteorological conditions, forest phenology and the spatial distribution of local anthropogenic NH3 sources. This suggests that an accurate description of ammonia fluxes over forest ecosystems requires a dynamic description of atmospheric and vegetation processes

Magnetization structure of a Bloch point singularity

Switching of magnetic vortex cores involves a topological transition characterized by the presence of a magnetization singularity, a point where the magnetization vanishes (Bloch point). We analytically derive the shape of the Bloch point that is an extremum of the free energy with exchange, dipole and the Landau terms for the determination of the local value of the magnetization modulus.Comment: 4 pages, 2 figure

Emotional Episodes Facilitate Word Recall

Dysphoric and nondysphoric college students described self-generated images of themselves interacting with the referents of neutral nouns; the nouns were paired with adjectives that changed their emotional meaning (e.g., cruise ship, cargo ship, sinking ship). On the subsequent unexpected test, the nouns from emotional pairings were more frequently recalled than were those from neutral pairings, regardless of their valence or congruence with the students\u27 mood. An examination of the initial descriptions revealed that emotional images were more distinctive, but not in a pattern correlated with recall of the corresponding nouns

Collisionless energy absorption in the short-pulse intense laser-cluster interaction

In a previous Letter [Phys. Rev. Lett. 96, 123401 (2006)] we have shown by means of three-dimensional particle-in-cell simulations and a simple rigid-sphere model that nonlinear resonance absorption is the dominant collisionless absorption mechanism in the intense, short-pulse laser cluster interaction. In this paper we present a more detailed account of the matter. In particular we show that the absorption efficiency is almost independent of the laser polarization. In the rigid-sphere model, the absorbed energy increases by many orders of magnitude at a certain threshold laser intensity. The particle-in-cell results display maximum fractional absorption around the same intensity. We calculate the threshold intensity and show that it is underestimated by the common over-barrier ionization estimate.Comment: 12 pages, 13 figures, RevTeX

Constructive Memory for Bizarre and Sensible Sentences

Sensible, interrelated sentences were presented with or without bizarre sentences that could be transformed to fit the context of the sensible sentences. Two experiments examined subjects\u27 ability to recognize or recall both types of sentences, either immediately or after 2 weeks. Bizarre sentences were frequently recognized at immediate testing; they were generally unavailable at delayed recognition and were never recalled verbatim. In addition, results indicated that transformations of bizarre sentences were stored in memory but were not well incorporated within the structure for the sensible material. These findings are consistent with a constructive approach to memory. Finally, the results suggest that processing bizarre information can lead to more accurate recognition and recall of the sensible context

Cognition, Emotion, and Memory: Some Applications and Issues

This chapter describes some ways in which the psychology of cognition, emotion, and memory can or might be applied in several practical settings. Recent years have seen a rapid growth in research on cognition and emotion and this research has been summarized in a variety of sources (e.g., Ellis & Ashbrook, 1988, 1989; Ellis, Varner, & Becker, in press; Fiedler & Forgas, 1988; lsen, 1984; Kuiken, 1989; Williams, Watts, MacLeod, & Mathews, 1988). Moreover, a new journal appeared in 1987, Cognition and Emotion, which is entirely devoted to relations among emotional states and the full range of cognitive processes typically studied by psychologists. Ellis and Ashbrook (1989) noted that although this research area has a much earlier history of activity, it lay relatively dormant until the mid-1970s. However, its growth has accelerated rapidly until it has now become an important and active area of research and theoretical development