1,321 research outputs found
Investigation of advanced navigation and guidance system concepts for all-weather rotorcraft operations
Results are presented of a survey conducted of active helicopter operators to determine the extent to which they wish to operate in IMC conditions, the visibility limits under which they would operate, the revenue benefits to be gained, and the percent of aircraft cost they would pay for such increased capability. Candidate systems were examined for capability to meet the requirements of a mission model constructed to represent the modes of flight normally encountered in low visibility conditions. Recommendations are made for development of high resolution radar, simulation of the control display system for steep approaches, and for development of an obstacle sensing system for detecting wires. A cost feasibility analysis is included
Developing an On-Line Interactive Health Psychology Module.
On-line teaching material in health psychology was developed which ensured a range of students could access appropriate material for their course and level of study. This material has been developed around the concept of smaller 'content chunks' which can be combined into whole units of learning (topics), and ultimately, a module. On the basis of the underlying philosophy that the medium is part of the message, we considered interactivity to be a key element in engaging the student with the material. Consequently, the key aim of this development was to stimulate and engage students, promoting better involvement with the academic material, and hence better learning. It was hoped that this was achieved through the development of material including linked programmes and supporting material, small Java Scripts and basic email, forms and HTML additions. This material is outlined as are some of the interactive activities introduced, and the preliminary student and tutor experience described
Energy demand on dairy farms in Ireland
peer-reviewedReducing electricity consumption in Irish milk production is a topical issue for 2 reasons. First, the introduction of a dynamic electricity pricing system, with peak and off-peak prices, will be a reality for 80% of electricity consumers by 2020. The proposed pricing schedule intends to discourage energy consumption during peak periods (i.e., when electricity demand on the national grid is high) and to incentivize energy consumption during off-peak periods. If farmers, for example, carry out their evening milking during the peak period, energy costs may increase, which would affect farm profitability. Second, electricity consumption is identified in contributing to about 25% of energy use along the life cycle of pasture-based milk. The objectives of this study, therefore, were to document electricity use per kilogram of milk sold and to identify strategies that reduce its overall use while maximizing its use in off-peak periods (currently from 0000 to 0900h). We assessed, therefore, average daily and seasonal trends in electricity consumption on 22 Irish dairy farms, through detailed auditing of electricity-consuming processes. To determine the potential of identified strategies to save energy, we also assessed total energy use of Irish milk, which is the sum of the direct (i.e., energy use on farm) and indirect energy use (i.e., energy needed to produce farm inputs). On average, a total of 31.73 MJ was required to produce 1kg of milk solids, of which 20% was direct and 80% was indirect energy use. Electricity accounted for 60% of the direct energy use, and mainly resulted from milk cooling (31%), water heating (23%), and milking (20%). Analysis of trends in electricity consumption revealed that 62% of daily electricity was used at peak periods. Electricity use on Irish dairy farms, therefore, is substantial and centered around milk harvesting. To improve the competitiveness of milk production in a dynamic electricity pricing environment, therefore, management changes and technologies are required that decouple energy use during milking processes from peak periods
Interacting crumpled manifolds
In this article we study the effect of a delta-interaction on a polymerized
membrane of arbitrary internal dimension D. Depending on the dimensionality of
membrane and embedding space, different physical scenarios are observed. We
emphasize on the difference of polymers from membranes. For the latter,
non-trivial contributions appear at the 2-loop level. We also exploit a
``massive scheme'' inspired by calculations in fixed dimensions for scalar
field theories. Despite the fact that these calculations are only amenable
numerically, we found that in the limit of D to 2 each diagram can be evaluated
analytically. This property extends in fact to any order in perturbation
theory, allowing for a summation of all orders. This is a novel and quite
surprising result. Finally, an attempt to go beyond D=2 is presented.
Applications to the case of self-avoiding membranes are mentioned
Trace-element abundances in the shallow lithospheric mantle of the North Atlantic Craton margin: implications for melting and metasomatism beneath Northern Scotland
Bulk rock geochemistry and major- and trace-element compositions of clinopyroxene have been determined for three suites of peridotitic mantle xenoliths from the North Atlantic Craton (NAC) in northern Scotland, to establish the magmatic and metasomatic history of subcontinental lithospheric mantle (SCLM) below this region. Spinel lherzolites from the southernmost locality (Streap Com'laidh) have non-NAC mantle compositions, while the two northern xenolith suites (Loch Roag and Rinibar) are derived from the thinned NAC marginal keel. Clinopyroxene compositions have characteristic trace-element signatures which show both 'primary' and 'metasomatic' origins. We use Zr and Hf abundances to identify ancient cryptic refertilization in 'primary' clinopyroxenes. We suggest that Loch Roag and Rinibar peridotite xenoliths represent an ancient Archaean-Palaeoproterozoic SCLM with original depleted cratonic signatures which were overprinted by metasomatism around the time of intrusion of the Scourie Dyke Swarm (âŒ2.4 Ga). This SCLM keel was preserved during Caledonian orogenesis, although some addition of material and/or metasomatism probably also occurred, as recorded by Rinibar xenoliths. Rinibar and Streap xenoliths were entrained in Permo-Carboniferous magmas and thus were isolated from the SCLM âŒ200 Ma before Loch Roag xenoliths (in an Eocene dyke). Crucially, despite their geographical location, lithospheric mantle peridotite samples from Loch Roag show no evidence of recent melting or refertilization during the Palaeogene opening of the Atlantic
Momentum-independent magnetic excitation continuum in the honeycomb iridate HLiIrO
In the search for realizations of Quantum Spin Liquids (QSL), it is essential
to understand the interplay between inherent disorder and the correlated
fluctuating spin ground state. HLiIrO is regarded as a spin liquid
proximate to the Kitaev-limit (KQSL) in which H zero-point motion and stacking
faults are known to be present. Bond disorder has been invoked to account for
the existence of unexpected low-energy spin excitations. Controversy remains
about the nature of the underlying correlated state and if any KQSL physics
survives. Here, we use resonant X-ray spectroscopies to map the collective
excitations in HLiIrO and characterize its magnetic state. We
uncover a broad bandwidth and momentum-independent continuum of magnetic
excitations at low temperatures that are distinct from the paramagnetic state.
The center energy and high-energy tail of the continuum are consistent with
expectations for dominant ferromagnetic Kitaev interactions between dynamically
fluctuating spins. The absence of a momentum dependence to these excitations
indicates a broken translational invariance. Our data support an interpretation
of HLiIrO as a disordered topological spin liquid in close
proximity to bond-disordered versions of the KQSL. Our results shed light on
how random disorder affects topological magnetic states and have implications
for future experimental and theoretical works toward realizing the Kitaev model
in condensed matter system
Basal-plane Incommensurate Phases in HCP Structures
An Ising model with competing interaction is used to study the appearance of
incommensurate phases in the basal plane of an hexagonal closed-packed
structure. The calculated mean-field phase diagram reveals various
1q-incommensurate and lock-in phases. The results are applied to explain the
basal-plane incommensurate phase in some compounds of the A'A"BX_4 family, like
K_2MoO_4, K_2WO_4, Rb_2WO4 and to describe the sequence of high-temperature
phase transitions in other compounds of this family.Comment: 8 pages, RevTeX + 4 ps figure
Reconstruction and subsurface lattice distortions in the (2 Ă 1)O-Ni(110) structure: A LEED analysis
LEED analysis of the reconstructed (2 Ă 1)O-Ni(110) system clearly favors the âmissing rowâ structure over the âsaw-toothâ and âbuckled rowâ models. By using a novel computational procedure 8 structural parameters could be refined simultaneously, leading to excellent R-factors (RZJ = 0.09, RP = 0.18). The adsorbed O atoms are located 0.2 Ă
above the long bridge sites in [001] direction, presumably with a slight displacement ( 0.1 Ă
) in [1 0] direction to an asymmetric adsorption site. The nearest-neighbor Ni---O bond lengths (1.77 Ă
) are rather short. The separation between the topmost two Ni layers is expanded to 1.30 Ă
(bulk value 1.25 Ă
), while that between the second and third layer is slightly contracted to 1.23 Ă
. The third layer is, in addition, slightly buckled (±0.05 Ă
). The results are discussed on the basis of our present general knowledge about the structure of adsorbate covered metallic surfaces
Critical adsorption on curved objects
A systematic fieldtheoretic description of critical adsorption on curved
objects such as spherical or rodlike colloidal particles immersed in a fluid
near criticality is presented. The temperature dependence of the corresponding
order parameter profiles and of the excess adsorption are calculated
explicitly. Critical adsorption on elongated rods is substantially more
pronounced than on spherical particles. It turns out that, within the context
of critical phenomena in confined geometries, critical adsorption on a
microscopically thin `needle' represents a distinct universality class of its
own. Under favorable conditions the results are relevant for the flocculation
of colloidal particles.Comment: 52 pages, 10 figure
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