2,971 research outputs found
Contrasting the capabilities of building energy performance simulation programs
For the past 50 years, a wide variety of building energy simulation programs have been developed, enhanced and are in use throughout the building energy community. This paper is an overview of a report, which provides up-to-date comparison of the features and capabilities of twenty major building energy simulation programs. The comparison is based on information provided by the program developers in the following categories: general modeling features; zone loads; building envelope and daylighting and solar; infiltration, ventilation and multizone airflow; renewable energy systems; electrical systems and equipment; HVAC systems; HVAC equipment; environmental emissions; economic evaluation; climate data availability, results reporting; validation; and user interface, links to other programs, and availability
âSo people know I'm a Sikhâ: Narratives of Sikh masculinities in contemporary Britain
This article examines British-born Sikh men's identification to Sikhism. In particular, it focuses on the appropriation and use of Sikh symbols amongst men who define themselves as Sikh. This article suggests that whilst there are multiple ways of âbeingâ a Sikh man in contemporary post-colonial Britain, and marking belonging to the Sikh faith, there is also a collectively understood idea of what an âidealâ Sikh man should be. Drawing upon Connell and Messerschmidt's discussion of locally specific hegemonic masculinities (2005. âHegemonic Masculinity: Rethinking the Concept.â Gender and Society 19 (6): 829â859), it is suggested that an ideal Sikh masculine identity is partly informed by a Khalsa discourse, which informs a particular performance of Sikh male identity, whilst also encouraging the surveillance of young men's activities both by themselves and by others. These Sikh masculinities are complex and multiple, rotating to reaffirm, challenge and redefine contextualised notions of hegemonic masculinity within the Sikh diaspora in post-colonial Britain. Such localised Sikh masculinities may both assert male privilege and reap patriarchal dividends (Connell, W. 1995. Masculinities. Cambridge: Polity Press), resulting in particular British Sikh hegemonic masculinities which seek to shape the performance of masculinity, yet in another context these very same performances of masculinity may also signify a more marginalised masculinity vis-Ă -vis other dominant hegemonic forms
Onion-shell model for cosmic ray electrons and radio synchrotron emission in supernova remnants
The spectrum of cosmic ray electrons, accelerated in the shock front of a supernova remnant (SNR), is calculated in the test-particle approximation using an onion-shell model. Particle diffusion within the evolving remnant is explicity taken into account. The particle spectrum becomes steeper with increasing radius as well as SNR age. Simple models of the magnetic field distribution allow a prediction of the intensity and spectrum of radio synchrotron emission and their radial variation. The agreement with existing observations is satisfactory in several SNR's but fails in other cases. Radiative cooling may be an important effect, especially in SNR's exploding in a dense interstellar medium
Self-Similar Evolution of Cosmic-Ray Modified Shocks: The Cosmic-Ray Spectrum
We use kinetic simulations of diffusive shock acceleration (DSA) to study the
time-dependent evolution of plane, quasi-parallel, cosmic-ray (CR) modified
shocks. Thermal leakage injection of low energy CRs and finite Alfv\'en wave
propagation and dissipation are included. Bohm diffusion as well as the
diffusion with the power-law momentum dependence are modeled. As long as the
acceleration time scale to relativistic energies is much shorter than the
dynamical evolution time scale of the shocks, the precursor and subshock
transition approach the time-asymptotic state, which depends on the shock sonic
and Alfv\'enic Mach numbers and the CR injection efficiency. For the diffusion
models we employ, the shock precursor structure evolves in an approximately
self-similar fashion, depending only on the similarity variable, x/(u_s t).
During this self-similar stage, the CR distribution at the subshock maintains a
characteristic form as it evolves: the sum of two power-laws with the slopes
determined by the subshock and total compression ratios with an exponential
cutoff at the highest accelerated momentum, p_{max}(t). Based on the results of
the DSA simulations spanning a range of Mach numbers, we suggest functional
forms for the shock structure parameters, from which the aforementioned form of
CR spectrum can be constructed. These analytic forms may represent approximate
solutions to the DSA problem for astrophysical shocks during the self-similar
evolutionary stage as well as during the steady-state stage if p_{max} is
fixed.Comment: 38 pages, 12 figures, ApJ accepte
Changes in Lumbo-Pelvic Coordination of Individuals with and without Low Back Pain when Wearing a Hip Orthosis
Individuals with low back pain demonstrate an abnormal lumbo-pelvic coordination compared to back-healthy individuals. This abnormal coordination presents itself as a reduction in lumbar contributions and an increase in pelvic rotations during a trunk forward bending and backward return task. This study investigated the ability of a hip orthosis in correcting such an abnormal lumbo-pelvic coordination by restricting pelvic rotation and, hence increasing lumbar contributions. The effects of the hip orthosis on the lumbo-pelvic coordination were investigated in 20 low back pain patients and 20 asymptomatic controls. The orthosis reduced pelvic rotation by 12.7° and increased lumbar contributions by 11%. Contrary to our expectation, orthosis-induced changes in lumbo-pelvic coordination were smaller in patients; most likely because our relatively young patient group had smaller unrestricted pelvic rotations compared to asymptomatic individuals. Considering the observed capability of a hip orthosis in causing the expected changes in lumbo-pelvic coordination when there is a relatively large pelvic contribution to trunk motion, application of a hip orthosis may provide a promising method of correcting abnormal lumbo-pelvic coordination, particularly among patients who demonstrate larger pelvic rotation, that warrants further investigation
Turbulent magnetic field amplification driven by cosmic-ray pressure gradients
Observations of non-thermal emission from several supernova remnants suggest
that magnetic fields close to the blastwave are much stronger than would be
naively expected from simple shock compression of the field permeating the
interstellar medium (ISM).
We present a simple model which is capable of achieving sufficient magnetic
field amplification to explain the observations. We propose that the cosmic-ray
pressure gradient acting on the inhomogeneous ISM upstream of the supernova
blastwave induces strong turbulence upstream of the supernova blastwave. The
turbulence is generated through the differential acceleration of the upstream
ISM which occurs as a result of density inhomogeneities in the ISM. This
turbulence then amplifies the pre-existing magnetic field.
Numerical simulations are presented which demonstrate that amplification
factors of 20 or more are easily achievable by this mechanism when reasonable
parameters for the ISM and supernova blastwave are assumed. The length scale
over which this amplification occurs is that of the diffusion length of the
highest energy non-thermal particles.Comment: 13 pages, 4 figures, 1 Table. Accepted for publication in MNRAS,
modified following referee comments and references adde
The Density Spike in Cosmic-Ray-Modified Shocks: Formation, Evolution, and Instability
We examine the formation and evolution of the density enhancement (density
spike) that appears downstream of strong, cosmic-ray-modified shocks. This
feature results from temporary overcompression of the flow by the combined
cosmic-ray shock precursor/gas subshock. Formation of the density spike is
expected whenever shock modification by cosmic-ray pressure increases strongly.
That occurence may be anticipated for newly generated strong shocks or for
cosmic-ray-modified shocks encountering a region of higher external density,
for example. The predicted mass density within the spike increases with the
shock Mach number and with shocks more dominated by cosmic-ray pressure. We
find this spike to be linearly unstable under a modified Rayleigh-Taylor
instability criterion at the early stage of its formation. We confirm this
instability numerically using two independent codes based on the two-fluid
model for cosmic-ray transport. These two-dimensional simulations show that the
instability grows impulsively at early stages and then slows down as the
gradients of total pressure and gas density decrease. Observational discovery
of this unstable density spike behind shocks, possibly through radio emission
enhanced by the amplified magnetic fields would provide evidence for the
existence of strongly cosmic-ray modified shock structures.Comment: 26 pages in Latex and 6 figures. Accepted to Ap
Comparison of Different Methods for Nonlinear Diffusive Shock Acceleration
We provide a both qualitative and quantitative comparison among different
approaches aimed to solve the problem of non-linear diffusive acceleration of
particles at shocks. In particular, we show that state-of-the-art models
(numerical, Monte Carlo and semi-analytical), even if based on different
physical assumptions and implementations, for typical environmental parameters
lead to very consistent results in terms of shock hydrodynamics, cosmic ray
spectrum and also escaping flux spectrum and anisotropy. Strong points and
limits of each approach are also discussed, as a function of the problem one
wants to study.Comment: 26 pages, 4 figures, published version (references updated
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