26,249 research outputs found
Predicting adaptive responses - simulating occupied environments
Simulation of building performance is increasingly being used in design practice to predict comfort of occupants in finished buildings. This is an area of great uncertainty: what actions does a person take when too warm or suffering from glare; how is comfort measured; how do groups of people interact to control environmental conditions, etc? An increasing attention to model these issues is evident in current research. Two issues are covered in this paper: how comfort can be assessed and what actions occupants are likely to make to achieve and maintain a comfortable status. The former issue describes the implementation of existing codes within a computational framework. This is non-trivial as information on local air velocities, radiant temperature and air temperature and relative humidity have to be predicted as they evolve over time in response to changing environmental conditions. This paper also presents a nascent algorithm for modelling occupant behaviour with respect to operable windows. The algorithm is based on results of several field studies which show the influence of internal and external temperatures on decision making in this respect. The derivation and implementation of the algorithm is discussed, highlighting areas where further effort could be of benefit
A strategic study of energy efficient and hybrid energy system options for a multi-family building in Korea
This study is to identify performance of energy efficiency measures and to match low-carbon and renewable energy (RE) systems supplies to demands in the context of multi-family residential buildings in Korea. An approach to the evaluation of the hybrid energy systems was investigated, including consideration of heat and power demand profiles, energy system combinations, building design options and strategies for matching supply to demand. The approach is encapsulated within an integrated software environment. Building energy simulation technology was exploited to make virtual energy use data. Low-carbon and RE system modelling techniques were used to predict energy supply profiles. A series of demand/supply matching-based analyses were made to identify the effect of energy efficient demand measures (e.g. roof-top gardens, innovative underfloor heating system) and evaluate the capacity utilisation factor from the hybrid energy systems. On the basis of performance information obtained at the conceptual design stage, the design team can pinpoint the most energy efficient demand/supply combination, and consequently, maximise the impact of hybrid energy systems adoption
Confined coherence in quasi-one-dimensional metals
We present a functional renormalization group calculation of the effect of
strong interactions on the shape of the Fermi surface of weakly coupled
metallic chains. In the regime where the bare interchain hopping is small, we
show that scattering processes involving large momentum transfers perpendicular
to the chains can completely destroy the warping of the true Fermi surface,
leading to a confined state where the renormalized interchain hopping vanishes
and a coherent motion perpendicular to the chains is impossible.Comment: 4 RevTex pages, 5 figures,final version as published by PR
Quantum Faraday Effect in Double-Dot Aharonov-Bohm Ring
We investigate Faraday's law of induction manifested in the quantum state of
Aharonov-Bohm loops. In particular, we propose a flux-switching experiment for
a double-dot AB ring to verify the phase shift induced by Faraday's law. We
show that the induced {\em Faraday phase} is geometric and nontopological. Our
study demonstrates that the relation between the local phases of a ring at
different fluxes is not arbitrary but is instead determined by Faraday's
inductive law, which is in strong contrast to the arbitrary local phase of an
Aharonov-Bohm ring for a given flux.Comment: Submitted to Phys. Rev. Let
Development and preliminary evaluation of a clinical guidance programme for the decision about prophylactic oophorectomy in women undergoing a hysterectomy
Objectives: To develop a decision analysis based and computerised clinical guidance programme
(CGP) that provides patient specific guidance on the decision whether or not to undergo a prophylactic
oophorectomy to reduce the risk of subsequent ovarian cancer and to undertake a preliminary pilot
and evaluation.
Subjects: Women who had already agreed to have a hysterectomy who otherwise had no ovarian
pathology.
Setting: Oophorectomy decision consultation at the outpatient or pre-admission clinic.
Methods: A CGP was developed with advice from gynaecologists and patient groups, incorporating
a set of Markov models within a decision analytical framework to evaluate the benefits of undergoing
a prophylactic oophorectomy or not on the basis of quality adjusted life expectancy, life expectancy,
and for varying durations of hormone replacement therapy. Sensitivity analysis and preliminary testing
of the CGP were undertaken to compare its overall performance with established guidelines and practice.
A small convenience sample of women invited to use the CGP were interviewed, the interviews
were taped and transcribed, and a thematic analysis was undertaken.
Results: The run time of the programme was 20 minutes, depending on the use of opt outs to default
values. The CGP functioned well in preliminary testing. Women were able to use the programme and
expressed overall satisfaction with it. Some had reservations about the computerised format and some
were surprised at the specificity of the guidance given.
Conclusions: A CGP can be developed for a complex healthcare decision. It can give evidence-based
health guidance which can be adjusted to account for individual risk factors and reflects a patient’s
own values and preferences concerning health outcomes. Future decision aids and support systems
need to be developed and evaluated in a way which takes account of the variation in patients’ preferences
for inclusion in the decision making process
The relation between accretion rates and the initial mass function in hydrodynamical simulations of star formation
We analyse a hydrodynamical simulation of star formation. Sink particles in
the simulations which represent stars show episodic growth, which is presumably
accretion from a core that can be regularly replenished in response to the
fluctuating conditions in the local environment. The accretion rates follow
, as expected from accretion in a gas-dominated
potential, but with substantial variations over-laid on this. The growth times
follow an exponential distribution which is tapered at long times due to the
finite length of the simulation. The initial collapse masses have an
approximately lognormal distribution with already an onset of a power-law at
large masses. The sink particle mass function can be reproduced with a
non-linear stochastic process, with fluctuating accretion rates , a distribution of seed masses and a distribution of growth times. All
three factors contribute equally to the form of the final sink mass function.
We find that the upper power law tail of the IMF is unrelated to Bondi-Hoyle
accretion.Comment: 13 pages, 13 figures, MNRAS accepte
Competitive accretion in embedded stellar cluster
We investigate the physics of gas accretion in young stellar clusters.
Accretion in clusters is a dynamic phenomenon as both the stars and the gas
respond to the same gravitational potential. Accretion rates are highly
non-uniform with stars nearer the centre of the cluster, where gas densities
are higher, accreting more than others. This competitive accretion naturally
results in both initial mass segregation and a spectrum of stellar masses.
Accretion in gas-dominated clusters is well modelled using a tidal-lobe radius
instead of the commonly used Bondi-Hoyle accretion radius. This works as both
the stellar and gas velocities are under the influence of the same
gravitational potential and are thus comparable. The low relative velocity that
results means that the tidal radius is smaller than the Bondi-Hoyle radius in
these systems. In contrast, when the stars dominate the potential and are
virialised, the Bondi-Hoyle radius is smaller than the tidal radius and thus
Bondi-Hoyle accretion is a better fit to the accretion rates.Comment: 11 pages, 11 figures, MNRAS in pres
The Origin of Episodic Accretion Bursts in the Early Stages of Star Formation
We study numerically the evolution of rotating cloud cores, from the collapse
of a magnetically supercritical core to the formation of a protostar and the
development of a protostellar disk during the main accretion phase. We find
that the disk quickly becomes unstable to the development of a spiral structure
similar to that observed recently in AB Aurigae. A continuous infall of matter
from the protostellar envelope makes the protostellar disk unstable, leading to
spiral arms and the formation of dense protostellar/protoplanetary clumps
within them. The growing strength of spiral arms and ensuing redistribution of
mass and angular momentum creates a strong centrifugal disbalance in the disk
and triggers bursts of mass accretion during which the dense
protostellar/protoplanetary clumps fall onto the central protostar. These
episodes of clump infall may manifest themselves as episodes of vigorous
accretion rate (\ge 10^{-4} M_sun/yr) as is observed in FU Orionis variables.
Between these accretion bursts, the protostar is characterized by a low
accretion rate (< 10^{-6} M_sun/yr). During the phase of episodic accretion,
the mass of the protostellar disk remains less than or comparable to the mass
of the protostar.Comment: 5 pages, 2 figures, accepted for publication in ApJ
Further developments in the conflation of CFD and building simulation
To provide practitioners with the means to tackle problems related to poor indoor environments, building simulation and computational fluid dynamics can usefully be integrated within a single computational framework. This paper describes the outcomes from a research project sponsored by the European Commission, which furthered the CFD modelling aspects of the ESP-r system. The paper summarises the form of the CFD model and describes the method used to integrate the thermal and flow domains
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