2,187 research outputs found
A Scanning Hall Probe Microscope for high resolution, large area, variable height Magnetic Field Imaging
International audienceWe present a Scanning Hall Probe Microscope operating in ambient conditions. One of the unique features of this microscope is the use of the same stepper motors for both sample positioning as well as scanning, which makes it possible to have a large scan range (few mm) in x and y directions, with a scan resolution of 0.1 µm. Protocols have been implemented to enable scanning at different heights from the sample surface. The z range is 35 mm. Microstructured Hall probes of size 1-5 µm have been developed. A minimum probe-sample distance < 2 µm has been obtained by the combination of new Hall probes and probe-sample distance regulation using a tuning fork based force detection technique. The system is also capable of recording local B(z) profiles. We discuss the application of the microscope for the study of micro-magnet arrays being developed for applications in micro-system
Introducing a method for mapping recreational experience
The provision of recreational opportunities forms an important and long-standing urban planning and management objective. However, considering a range of experiences encountered when in such spaces currently does not form part of existing open space assessment tools in the UK. In this paper, 'rec-mapping', an innovative method of analysing and mapping positive recreational experiences in urban green spaces, is explored and piloted within the UK planning context. Originating in the Nordic countries, this on-site method can provide urban planners and designers with data about the extent to which specific green spaces provide and support a range of recreational experiences. The exploration reported here is based on a short review of the method's background and an application in two test sites in Sheffield, south Yorkshire, in early summer 2010. This paper critically appraises the application of rec-mapping at smaller spatial scales and recommends further explorations within the UK planning context, as the method adds to existing open space assessment by providing a unique layer of information to analyse more fully the recreational qualities of urban green spaces
Children’s interactions with water in city centres: a case study from Sheffield, UK
Children’s experiences of outdoor environments have been studied now for more than 40 years yet no research has specifically focussed on children’s experiences of water play in constructed spaces of city centres. This article discusses the development of an observational mapping tool, called TOWEC, to record the interaction of children with water. It then reports findings and analysis from observations over a year-long period of 3,399 children interacting with water in the award winning public open space of the Peace Gardens in the centre of the City of Sheffield, UK. The findings reveal that children undertake both active and passive activities associated with the constructed water features and that these activities are influenced by gender, age and temperature, but not ethnicity. The water features were not designed for children to play in but the children realise the potential affordance that the water features provide
Fabrication of magnetocaloric La(Fe,Si) thick films
La(Fe,Si)-based compounds are considered to be very promising
magnetocaloric materials for magnetic refrigeration applications. Many studies
have focused on this material family but only in bulk form. In this paper, we
report the fabrication of thick films of La(Fe,Si), both with and
without post-hydriding. These films exhibit magnetic and structural properties
comparable to those of bulk materials. We also observe that the ferromagnetic
phase transition has a negative thermal hysteresis, a phenomenon not previously
found in this material but which may have its origins in the availability of a
strain energy reservoir, as in the cases of other materials in which negative
thermal hysteresis has been found. Here, it appears that the substrate acts to
store strain energy. Our exploratory study demonstrates the viability of thick
films of the La(Fe,Si) phase and motivates further work in the area,
while showing that additional perspectives can be gained from reducing the
dimensionality of magnetocaloric materials in which the magneto-volume effect
is large.Comment: 16 pages, 3 figure
Winds and tides of the Extended Unified Model in the mesosphere and lower thermosphere validated with meteor radar observations
The mesosphere and lower thermosphere (MLT) is a critical region that must be accurately reproduced in general circulation models (GCMs) that aim to
include the coupling between the lower and middle atmosphere and the thermosphere. An accurate representation of the MLT is thus important for
improved climate modelling and the development of a whole atmosphere model. This is because the atmospheric waves at these heights are particularly
large, and so the energy and momentum they carry is an important driver of climatological phenomena through the whole atmosphere, affecting
terrestrial and space weather. The Extended Unified Model (ExUM) is the recently developed version of the Met Office's Unified Model which has been
extended to model the MLT. The capability of the ExUM to model atmospheric winds and tides in the MLT is currently unknown. Here, we present the
first study of winds and tides from the ExUM. We make a comparison against meteor radar observations of winds and tides from 2006 between 80 and
100 km over two radar stations – Rothera (68∘ S, 68∘ W) and Ascension Island (8∘ S, 14∘ W). These
locations are chosen to study tides in two very different tidal regimes – the equatorial regime, where the diurnal (24 h) tide dominates, and the
polar regime, where the semi-diurnal (12 h) tide dominates. The results of this study illustrate that the ExUM is capable of reproducing
atmospheric winds and tides that capture many of the key characteristics seen in meteor radar observations, such as zonal and meridional wind
maxima and minima, the increase in tidal amplitude with increasing height, and the decrease in tidal phase with increasing height. In particular, in
the equatorial regime some essential characteristics of the background winds, tidal amplitudes and tidal phases are well captured but with
significant differences in detail. In the polar regime, the difference is more pronounced. The ExUM zonal background winds in austral winter are
primarily westward rather than eastward, and in austral summer they are larger than observed above 90 km. The ExUM tidal amplitudes here are in
general consistent with observed values, but they are also larger than observed values above 90 km in austral summer. The tidal phases are
generally well replicated in this regime. We propose that the bias in background winds in the polar regime is a consequence of the lack of in situ
gravity wave generation to generate eastward fluxes in the MLT. The results of this study indicate that the ExUM has a good natural capability for
modelling atmospheric winds and tides in the MLT but that there is room for improvement in the model physics in this region. This highlights the
need for modifications to the physical parameterization schemes used in the model in this region – such as the non-orographic spectral gravity wave
scheme – to improve aspects such as polar circulation. To this end, we make specific recommendations of changes that can be implemented to improve
the accuracy of the ExUM in the MLT.</p
High performance hard magnetic NdFeB thick films for integration into Micro-Electro-Mechanical-Systems
5m thick NdFeB films have been sputtered onto 100 mm Si substrates using
high rate sputtering (18 m/h). Films were deposited at ≤ 500 C and
then annealed at 750 C for 10 minutes. While films deposited at temperatures up
to 450 C have equiaxed grains, the size of which decreases with increasing
deposition temperature, the films deposited at 500 C have columnar grains. The
out-of-plane remanent magnetization increases with deposition temperature,
reaching a maximum value of 1.4 T, while the coercivity remains constant at
about 1.6 T. The maximum energy product achieved (400 kJ/m3) is comparable to
that of high-quality NdFeB sintered magnets
Investment Opportunities Forecasting: Extending the Grammar of a GP-based Tool
In this paper we present a new version of a GP financial forecasting tool, called EDDIE 8. The novelty of this version is that it allows the GP to search in the space of indicators, instead of using pre-specified ones. We compare EDDIE 8 with its predecessor, EDDIE 7, and find that new and improved solutions can be found. Analysis also shows that, on average, EDDIE 8's best tree performs better than the one of EDDIE 7. The above allows us to characterize EDDIE 8 as a valuable forecasting tool
Entangled Electronic States in Multiple Quantum-Dot Systems
We present an analytically solvable model of colinear, two-dimensional
quantum dots, each containing two electrons. Inter-dot coupling via the
electron-electron interaction gives rise to sets of entangled ground states.
These ground states have crystal-like inter-plane correlations and arise
discontinously with increasing magnetic field. Their ranges and stabilities are
found to depend on dot size ratios, and to increase with .Comment: To appear in Physical Review B (in press). RevTeX file. Figures
available from [email protected]
CHIMPS: the <sup>13</sup>CO/C<sup>18</sup>O (<i>J</i> = 3 → 2) Heterodyne Inner Milky Way Plane Survey
We present the 13CO/C18O (J = 3 → 2) Heterodyne Inner Milky Way Plane Survey (CHIMPS) which has been carried out using the Heterodyne Array Receiver Program on the 15 m James Clerk Maxwell Telescope (JCMT) in Hawaii. The high-resolution spectral survey currently covers |b| ≤ 0.5° and 28° ≲ l ≲ 46°, with an angular resolution of 15 arcsec in 0.5 km s-1 velocity channels. The spectra have a median rms of ˜0.6 K at this resolution, and for optically thin gas at an excitation temperature of 10 K, this sensitivity corresponds to column densities of NH2 ˜ 3 × 1020 cm-2 and NH2 ˜ 4 × 1021 cm-2 for 13CO and C18O, respectively. The molecular gas that CHIMPS traces is at higher column densities and is also more optically thin than in other publicly available CO surveys due to its rarer isotopologues, and thus more representative of the three-dimensional structure of the clouds. The critical density of the J = 3 → 2 transition of CO is ≳104 cm-3 at temperatures of ≤20 K, and so the higher density gas associated with star formation is well traced. These data complement other existing Galactic plane surveys, especially the JCMT Galactic Plane Survey which has similar spatial resolution and column density sensitivity, and the Herschel infrared Galactic Plane Survey. In this paper, we discuss the observations, data reduction and characteristics of the survey, presenting integrated-emission maps for the region covered. Position-velocity diagrams allow comparison with Galactic structure models of the Milky Way, and while we find good agreement with a particular four-arm model, there are some significant deviations
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