2,135 research outputs found
Considering the impact of situation-specific motivations and constraints in the design of naturally ventilated and hybrid buildings
A simple logical model of the interaction between a building and its occupants is presented based on the principle that if free to do so, people will adjust their posture, clothing or available building controls (windows, blinds, doors, fans, and thermostats) with the aim of achieving or restoring comfort and reducing discomfort. These adjustments are related to building design in two ways: first the freedom to adjust depends on the availability and ease-of-use of control options; second the use of controls affects building comfort and energy performance. Hence it is essential that these interactions are considered in the design process. The model captures occupant use of controls in response to thermal stimuli (too warm, too cold etc.) and non-thermal stimuli (e.g. desire for fresh air). The situation-specific motivations and constraints on control use are represented through trigger temperatures at which control actions occur, motivations are included as negative constraints and incorporated into a single constraint value describing the specifics of each situation. The values of constraints are quantified for a range of existing buildings in Europe and Pakistan. The integration of the model within a design flow is proposed and the impact of different levels of constraints demonstrated. It is proposed that to minimise energy use and maximise comfort in naturally ventilated and hybrid buildings the designer should take the following steps: 1. Provide unconstrained low energy adaptive control options where possible, 2. Avoid problems with indoor air quality which provide motivations for excessive ventilation rates, 3. Incorporate situation-specific adaptive behaviour of occupants in design simulations, 4. Analyse the robustness of designs against variations in patterns of use and climate, and 5. Incorporate appropriate comfort standards into the operational building controls (e.g. BEMS)
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Rapid ice aggregation process revealed through triple-wavelength Doppler spectra radar analysis
Rapid aggregation of ice particles has been identified by combining data from three co-located, vertically-pointing radars operating at different frequencies. A new technique has been developed that uses the Doppler spectra from these radars to retrieve the vertical profile of ice particle size distributions.
The ice particles grow rapidly from a maximum size of 0.75 mm to 5 mm while falling less than 500 m and in under 10 minutes. This rapid growth is shown to agree well with theoretical estimates of aggregation, with aggregation efficiency close to 1, and is inconsistent with other growth processes, e.g. growth by deposition, riming. The aggregation occurs in the middle of the cloud, and is not present throughout the entire lifetime of the cloud. However, the layer of rapid aggregation is very well defined, at a constant height, where the temperature is −15 °C, and lasts for at least 20 minutes (approximate horizontal distance: 24 km). Immediately above this layer, the radar Doppler spectra is bi-modal, which signals the formation of new small ice particles at that height. We suggest that these newly formed particles, at approximately −15 °C, grow dendritic arms, enabling them to easily interlock and accelerate the aggregation process. The estimated aggregation efficiency in the studied cloud is between 0.7 and 1, consistent with recent laboratory studies for dendrites at this temperature.
A newly developed method for retrieving the ice particle size distribution using the Doppler spectra allows these retrievals in a much larger fraction of the cloud than existing DWR methods. Through quantitative comparison of the Doppler spectra from the three radars we are able to estimate the ice particle size distribution at different heights in the cloud. Comparison of these size distributions with those calculated with more basic radar-derived values and more restrictive assumptions agree very well; however, the newly developed method allows size distribution retrieval in a larger fraction of the cloud because it allows us to isolate the signal from the larger (non-Rayleigh scattering) particles in the distribution and allows for deviation from the assumed shape of the distribution
Magnetic field dependence of superconducting energy gaps in YNi2B2C: Evidence of multiband superconductivity
We present results of in field directional point contact spectroscopy (DPCS)
study in the quaternary borocarbide superconductor YNi2B2C, which is
characterized by a highly anisotropic superconducting gap function. For I||a,
the superconducting energy gap (D), decreases linearly with magnetic field and
vanishes around 3.25T which is well below the upper critical field (Hc2~6T)
measured at the same temperature (2.2K). For I||c, on the other hand, D
decreases weakly with magnetic field but the broadening parameter (G) increases
rapidly with magnetic field with the absence of any resolvable feature above
3.5T. From an analysis of the field variation of energy gaps and the zero bias
density of states we show that the unconventional gap function observed in this
material could originate from multiband superconductivity.Comment: 19 pages including figures (final version
Anisotropic thermodynamics of d-wave superconductors in the vortex state
We show that the density of states and the thermodynamic properties of a 2D
d-wave superconductor in the vortex state with applied magnetic field
in the plane depend on the angle between and the order parameter nodes.
Within a semiclassical treatment of the extended quasiparticle states, we
obtain fourfold oscillations of the specific heat, measurement of which
provides a simple probe of gap symmetry. The frequency dependence of the
density of states and the temperature dependence of thermodynamic properties
obey different power laws for field in the nodal and anti-nodal direction. The
fourfold pattern is changed to twofold when orthorhombicity is considered.Comment: 5 pages, figures included, minor changes, published versio
High-pressure structural, elastic and electronic properties of the scintillator host material, KMgF_3
The high-pressure structural behaviour of the fluoroperovskite KMgF_3 is
investigated by theory and experiment. Density functional calculations were
performed within the local density approximation and the generalized gradient
approximation for exchange and correlation effects, as implemented within the
full-potential linear muffin-tin orbital method. In situ high-pressure powder
x-ray diffraction experiments were performed up to a maximum pressure of 40 GPa
using synchrotron radiation. We find that the cubic Pm\bar{3}m crystal symmetry
persists throughout the pressure range studied. The calculated ground state
properties -- the equilibrium lattice constant, bulk modulus and elastic
constants -- are in good agreement with experimental results. By analyzing the
ratio between the bulk and shear modulii, we conclude that KMgF_3 is brittle in
nature. Under ambient conditions, KMgF_3 is found to be an indirect gap
insulator with the gap increasing under pressure.Comment: 4 figure
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High intensity neutrino source superconducting solenoid cyrostat design
Fermi National Accelerator Laboratory (FNAL) is involved in the development of a 100 MeV superconducting linac. This linac is part of the High Intensity Neutrino Source (HINS) R&D Program. The initial beam acceleration in the front end section of the linac is achieved using room temperature spoke cavities, each of which is combined with a superconducting focusing solenoid. These solenoid magnets are cooled with liquid helium at 4.5K, operate at 250 A and have a maximum magnetic field strength of 7.5 T. The solenoid cryostat will house the helium vessel, suspension system, thermal shield, multilayer insulation, power leads, instrumentation, a vacuum vessel and cryogenic distribution lines. This paper discusses the requirements and detailed design of these superconducting solenoid cryostats
'We don't learn democracy, we live it!' : consulting the pupil voice in Scottish schools
As the education for citizenship agenda continues to impact on schools, there is a need to begin the discussion around examining the kind of initiatives that can push it forward. In Scotland the proposals should, it is argued, permeate the curriculum throughout the school. Yet there is the fear that the responsibility of all can become the responsibility of none. This paper examines, through case study research carried out by the authors, initiatives in schools designed to take forward the citizenship agenda in the light of children's rights. The first two relate to firstly the impact of pupil councils in primary schools and secondly the impact of discussing controversial issues in the primary classroom. The third outlines the impact on values and dispositions of developing more participatory, democratic practice in the classroom. The paper concludes by calling for both more initiatives of this type and more evaluation of their worth
High Pressure Insulator-Metal Transition in Molecular Fluid Oxygen
We report the first experimental evidence for a metallic phase in fluid
molecular oxygen. Our electrical conductivity measurements of fluid oxygen
under dynamic quasi-isentropic compression show that a non-metal/metal
transition occurs at 3.4 fold compression, 4500 K and 1.2 Mbar. We discuss the
main features of the electrical conductivity dependence on density and
temperature and give an interpretation of the nature of the electrical
transport mechanisms in fluid oxygen at these extreme conditions.Comment: RevTeX, 4 figure
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