Tunable Transient Decay Times in Nonlinear Systems: Application to Magnetic Precession

The dynamical motion of the magnetization plays a key role in the properties of magnetic materials. If the magnetization is initially away from the equilibrium direction in a magnetic nanoparticle, it will precess at a natural frequency and, with some damping present, will decay to the equilibrium position in a short lifetime. Here we investigate a simple but important situation where a magnetic nanoparticle is driven non-resonantly by an oscillating magnetic field, not at the natural frequency. We find a surprising result that the lifetime of the transient motion is strongly tunable, by factors of over 10,000, by varying the amplitude of the driving field.Comment: EPL Preprin

The effect of transverse magnetic correlations on a coupled order parameter: shifted transition temperatures and thermal hysteresis

We use a Green's function method with Random Phase Approximation to show how magnetic correlations may affect electric polarization in multiferroic materials with magnetic-exchange-type magnetoelectric coupling. We use a model spin 1/2 ferromagnetic ferroelectric system but our results are expected to apply to multiferroic materials with more complex magnetic structures. In particular, we find that transverse magnetic correlations result in a change in the free energy of the ferroelectric solutions leading to the possibility for thermal hysteresis of the electric polarization above the magnetic Curie temperature. Although we are motivated by multiferroic materials, this problem represents a more general calculation of the effect of fluctuations on coupled order parameters

The High Arctic in Extreme Winters: Vortex, Temperature, and MLS and ACE-FTS Trace Gas Evolution

The first three Canadian Arctic Atmospheric Chemistry Experiment (ACE) Validation Campaigns at Eureka (80° N, 86° W) were during two extremes of Arctic winter variability: Stratospheric sudden warmings (SSWs) in 2004 and 2006 were among the strongest, most prolonged on record; 2005 was a record cold winter. New satellite measurements from ACE-Fourier Transform Spectrometer (ACE-FTS), Sounding of the Atmosphere using Broadband Emission Radiometry, and Aura Microwave Limb Sounder (MLS), with meteorological analyses and Eureka lidar and radiosonde temperatures, are used to detail the meteorology in these winters, to demonstrate its influence on transport and chemistry, and to provide a context for interpretation of campaign observations. During the 2004 and 2006 SSWs, the vortex broke down throughout the stratosphere, reformed quickly in the upper stratosphere, and remained weak in the middle and lower stratosphere. The stratopause reformed at very high altitude, above where it could be accurately represented in the meteorological analyses. The 2004 and 2006 Eureka campaigns were during the recovery from the SSWs, with the redeveloping vortex over Eureka. 2005 was the coldest winter on record in the lower stratosphere, but with an early final warming in mid-March. The vortex was over Eureka at the start of the 2005 campaign, but moved away as it broke up. Disparate temperature profile structure and vortex evolution resulted in much lower (higher) temperatures in the upper (lower) stratosphere in 2004 and 2006 than in 2005. Satellite temperatures agree well with Eureka radiosondes, and with lidar data up to 50–60 km. Consistent with a strong, cold upper stratospheric vortex and enhanced radiative cooling after the SSWs, MLS and ACE-FTS trace gas measurements show strongly enhanced descent in the upper stratospheric vortex during the 2004 and 2006 Eureka campaigns compared to that in 2005

Field trips, friendships and societies: Exploring student engagement in the School of Earth and Environment, University of Leeds.

Student engagement in Higher Education is increasingly seen as having a critical influence on achievement and overall university experience. However, engagement is predominantly evaluated through survey instruments, and in-depth studies of small student populations that explore the dynamics of the construct, and diversity of student experiences are currently lacking. This paper addresses this gap by exploring student perspectives of the factors impacting student engagement in the School of Earth and Environment, [University]. Focus groups were held with students across six degree programmes and four years of study and data were analysed using Kahu’s (2013) conceptual framework of engagement, antecedents and consequences. Findings emphasise prominent feedback loops between and within the various elements of the framework. In the School of Earth and Environment, key enablers of positive feedback loops are field trips, friendships and societies, which interact dynamically with inter alia increased sense of belonging and community. These, in turn, lead to motivation, confidence, deeper learning, further positive relationships and further engagement. Future student engagement initiatives should therefore seek to nurture and develop community to promote positive engagement feedback loops

Assimilation of the Microwave Limb Sounder Radiances

It has been shown that the assimilation of limb-sounder data can significantly improve the representation of ozone in NASA's GEOS Data Assimilation Systems (GEOS-DAS), particularly in the stratosphere. The studies conducted so far utilized retrieved data from the MIPAS, POAM, ILAS and EOS Microwave Limb Sounder (EOS MLS) instruments. Direct assimilation of the radiance data can be seen as the natural next step to those studies. The motivation behind working with radiances is twofold. First, retrieval algorithms use a priori data which are either climatological or are obtained from previous analyses. This introduces additional uncertainty and, in some cases, may lead to "self-contamination"- when the a priori is taken from the same assimilation system in which subsequently ingests the retrieved observations. Second, radiances can be available in near real time thus providing an opportunity for operational assimilation, which could help improve the use of infrared radiance instruments from operational satellite instruments. In this presentation we summarize our ongoing work on an implementation of the assimilation of EOS MLS radiances into the GEOS-5 DAS. This work focuses on assimilation of band 7 brightness temperatures which are sensitive to ozone. Our implementation uses the MLS Callable Forward Model developed by the MLS team at NASA JPL as the observation operator. We will describe our approach and recent results which are not yet final. In particular, we will demonstrate that this approach has a potential to improve the vertical structure of ozone in the lower tropical stratosphere as compared with the retrieved MLS product. We will discuss the computational efficiency of this implementation

Bodies, building and bricks: Women architects and builders in eight eco-communities in Argentina, Britain, Spain, Thailand and USA

Eco-building is a male domain where men are presumed to be better builders and designers, more men than women build and women find their design ideas and contributions to eco-building are belittled. This article suggests that a focus on bodies, embodiment and the ‘doing’ of building is a potentially productive way to move beyond current gender discrimination. This article makes three key interventions using empirical material from eight case studies of eco-communities in Britain, Thailand, Spain, the USA and Argentina. First, it uses a focus on eco-communities to illustrate the enduring persistence of gender divisions in architecture and building. Second, by using multi-site examples of eco-communities from diverse countries this article finds more commonalities than differences in gender discrimination across cultures and nationalities. Third, it outlines three spaces of opportunity through which more gender-neutral approaches are being developed in eco-building: (1) in challenging the need for ‘strong’ bodies, (2) by practising more embodied ways of building and (3) by making visible women's bodies in building. The ‘doing’ and manual aspect of eco-building is unfamiliar for many (not just women) and interviewees commented on the need to (re)learn how to be practical and to understand the physical possibilities (and limitations) of their bodies