67,490 research outputs found
The response of self-graviting protostellar discs to slow reduction in cooling timescale: the fragmentation boundary revisited
A number of previous studies of the fragmentation of self-gravitating
protostellar discs have modeled radiative cooling with a cooling timescale
(t_{cool}) parameterised as a simple multiple (beta_{cool}) of the local
dynamical timescale. Such studies have delineated the `fragmentation boundary'
in terms of a critical value of beta_{cool} (beta_{crit}), where the disc
fragments if beta_{cool} < beta_{crit}. Such an approach however begs the
question of how in reality a disc could ever be assembled with beta_{cool} <
beta_{crit}. Here we adopt the more realistic approach of gradually reducing
beta_{cool}, as might correspond to changes in thermal regime due to secular
changes in the disc density profile. We find that when beta_{cool} is gradually
reduced (on a timescale longer than t_{cool}), the disc is stabilised against
fragmentation, compared with models in which beta_{cool} is reduced rapidly. We
therefore conclude that a disc's ability to remain in a self-regulated,
self-gravitating state (without fragmentation) is partly dependent on its
thermal history, as well as its current cooling rate. Nevertheless, a slow
reduction in t_{cool} appears only to lower the fragmentation boundary by about
a factor two in t_{cool} and thus only permits maximum alpha values
(parameterising the efficiency of angular momentum transfer in the disc) that
are about a factor two higher than determined hitherto. Our results therefore
do not undermine the notion of a fundamental upper limit to the heating rate
that can be delivered by gravitational instabilities before the disc is subject
to fragmentation. An important implication of this work, therefore, is that
self-gravitating discs can enter into the regime of fragmentation via secular
evolution and it is not necessary to invoke rapid (impulsive) events to trigger
fragmentation.Comment: accepted for publication in MNRA
Helmet weight simulator
A device for providing acceleration cues to the helmet of a simulator pilot is described. Pulleys are attached to both shoulders of the pilot. A cable is attached to both sides of the helmet and extends through the pulleys to a takeup reel that is controlled by a torque motor. Control signals are applied to a servo system including the torque motor, the takeup reel and a force transducer which supplies the feedback signal. In one embodiment of the invention the force transducer is in the cable and in another it is in the takeup reel
Beta lives - some statistical perspectives on the capital asset pricing model
This note summarizes some technical issues relevant to the use of the idea of excess return in empirical modelling. We cover the case where the aim is to construct a measure of expected return on an asset and a model of the CAPM type is used. We review some of the problems and show examples where the basic CAPM may be used to develop other results which relate the expected returns on assets both to the expected return on the market and other factors
Condition matters: pupil voices on the design and condition of secondary schools
This research was produced by Sheffield Hallam University. The project aimed to inform the creation of a national schools Facilities Management network and an ongoing programme to research and benchmark the impact of school condition and design on pupils
Ionisation-induced star formation II: External irradiation of a turbulent molecular cloud
In this paper, we examine numerically the difference between triggered and
revealed star formation. We present Smoothed Particle Hydrodynamics (SPH)
simulations of the impact on a turbulent 10^4 solar-mass molecular cloud of
irradiation by an external source of ionising photons. In particular, using a
control model, we investigate the triggering of star formation within the
cloud. We find that, although feedback has a dramatic effect on the morphology
of our model cloud, its impact on star formation is relatively minor. We show
that external irradiation has both positive and negative effects, accelerating
the formation of some objects, delaying the formation of others, and inducing
the formation of some that would not otherwise have formed. Overall, the
calculation in which feedback is included forms nearly twice as many objects
over a period of \sim0.5 freefall times (\sim2.4 Myr), resulting in a
star--formation efficiency approximately one third higher (\sim4% as opposed to
\sim3% at this epoch) as in the control run in which feedback is absent.
Unfortunately, there appear to be no observable characteristics which could be
used to differentiate objects whose formation was triggered from those which
were forming anyway and which were simply revealed by the effects of radiation,
although this could be an effect of poor statistics.Comment: 12 pages, 9 figures, accepted by MNRA
Frequency-dependent polarizabilities of alkali atoms from ultraviolet through infrared spectral regions
We present results of first-principles calculations of the
frequency-dependent polarizabilities of all alkali atoms for light in the
wavelength range 300-1600 nm, with particular attention to wavelengths of
common infrared lasers. We parameterize our results so that they can be
extended accurately to arbitrary wavelengths above 800 nm. This work is
motivated by recent experiments involving simultaneous optical trapping of two
different alkali species. Our data can be used to predict the oscillation
frequencies of optically-trapped atoms, and particularly the ratios of
frequencies of different species held in the same trap. We identify wavelengths
at which two different alkali atoms have the same oscillation frequency.Comment: 6 pages, 2 figure
A pilot study of the S-MAP (Solutions for Medications Adherence Problems) intervention for older adults prescribed polypharmacy in primary care: Study protocol
Background: Adhering to multiple medications as prescribed is challenging for older patients (aged ≥ 65 years) and a difficult behaviour to improve. Previous interventions designed to address this have been largely complex in nature but have shown limited effectiveness and have rarely used theory in their design. It has been recognised that theory ('a systematic way of understanding events or situations') can guide intervention development and help researchers better understand how complex adherence interventions work. This pilot study aims to test a novel community pharmacy-based intervention that has been systematically developed using the Theoretical Domains Framework (12-domain version) of behaviour change. Methods: As part of a non-randomised pilot study, pharmacists in 12 community pharmacies across Northern Ireland (n = 6) and London, England (n = 6), will be trained to deliver the intervention to older patients who are prescribed ≥ 4 regular medicines and are non-adherent (self-reported). Ten patients will be recruited per pharmacy (n = 120) and offered up to four tailored one-to-one sessions, in the pharmacy or via telephone depending on their adherence, over a 3-4-month period. Guided by an electronic application (app) on iPads, the intervention content will be tailored to each patient's underlying reasons for non-adherence and mapped to the most appropriate solutions using established behaviour change techniques. This study will assess the feasibility of collecting data on the primary outcome of medication adherence (self-report and dispensing data) and secondary outcomes (health-related quality of life and unplanned hospitalisations). An embedded process evaluation will assess training fidelity for pharmacy staff, intervention fidelity, acceptability to patients and pharmacists and the intervention's mechanism of action. Process evaluation data will include audio-recordings of training workshops, intervention sessions, feedback interviews and patient surveys. Analysis will be largely descriptive. Discussion: Using pre-defined progression criteria, the findings from this pilot study will guide the decision whether to proceed to a cluster randomised controlled trial to test the effectiveness of the S-MAP intervention in comparison to usual care in community pharmacies. The study will also explore how the intervention components may work to bring about change in older patients' adherence behaviour and guide further refinement of the intervention and study procedures. Trial registration: This study is registered at ISRCTN: https://doi.org/10.1186/ISRCTN7383153
Colliders and Brane Vector Phenomenology
Brane world oscillations manifest themselves as massive vector gauge fields.
Their coupling to the Standard Model is deduced using the method of nonlinear
realizations of the spontaneously broken higher dimensional space-time
symmetries. Brane vectors are stable and weakly interacting, and therefore
escape particle detectors unnoticed. LEP and Tevatron data on the production of
a single photon in conjunction with missing energy are used to delineate
experimentally excluded regions of brane vector parameter space. The additional
region of parameter space accessible to the LHC as well as a future lepton
linear collider is also determined by means of this process.Comment: 12 pages, 13 figure
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