504 research outputs found
Large-to small-scale dynamo in domains of large aspect ratio: kinematic regime
The Sun’s magnetic field exhibits coherence in space and time on much larger scales than
the turbulent convection that ultimately powers the dynamo. In this work, we look for numerical
evidence of a large-scale magnetic field as the magnetic Reynolds number, Rm, is
increased. The investigation is based on the simulations of the induction equation in elongated
periodic boxes. The imposed flows considered are the standard ABC flow (named after
Arnold, Beltrami & Childress) with wavenumber ku = 1 (small-scale) and a modulated ABC
flow with wavenumbers ku = m, 1, 1 ± m, where m is the wavenumber corresponding to
the long-wavelength perturbation on the scale of the box. The critical magnetic Reynolds
number Rcrit
m decreases as the permitted scale separation in the system increases, such that
Rcrit
m ∝ [Lx /Lz]
−1/2. The results show that the α-effect derived from the mean-field theory
ansatz is valid for a small range of Rm after which small scale dynamo instability occurs and the
mean-field approximation is no longer valid. The transition from large- to small-scale dynamo
is smooth and takes place in two stages: a fast transition into a predominantly small-scale
magnetic energy state and a slower transition into even smaller scales. In the range of Rm
considered, the most energetic Fourier component corresponding to the structure in the long
x-direction has twice the length-scale of the forcing scale. The long-wavelength perturbation
imposed on the ABC flow in the modulated case is not preserved in the eigenmodes of the
magnetic field
Double-diffusive instabilities of a shear-generated magnetic layer
Previous theoretical work has speculated about the existence of
double-diffusive magnetic buoyancy instabilities of a dynamically evolving
horizontal magnetic layer generated by the interaction of forced vertically
sheared velocity and a background vertical magnetic field. Here we confirm
numerically that if the ratio of the magnetic to thermal diffusivities is
sufficiently low then such instabilities can indeed exist, even for high
Richardson number shear flows. Magnetic buoyancy may therefore occur via this
mechanism for parameters that are likely to be relevant to the solar
tachocline, where regular magnetic buoyancy instabilities are unlikely.Comment: Submitted to ApJ
The Evolution of a Double Diffusive Magnetic Buoyancy Instability
Recently, Silvers, Vasil, Brummell, & Proctor (2009), using numerical
simulations, confirmed the existence of a double diffusive magnetic buoyancy
instability of a layer of horizontal magnetic field produced by the interaction
of a shear velocity field with a weak vertical field. Here, we demonstrate the
longer term nonlinear evolution of such an instability in the simulations. We
find that a quasi two-dimensional interchange instability rides (or "surfs") on
the growing shear-induced background downstream field gradients. The region of
activity expands since three-dimensional perturbations remain unstable in the
wake of this upward-moving activity front, and so the three-dimensional nature
becomes more noticeable with time.Comment: 9 pages; 3 figures; accepted to appear in IAU symposium 27
An investigation into the relationship between the systemic inflammatory response and survival: a Glasgow Inflammation Outcome study
Inflammation has been shown to play an integral role in a number of different disease processes. There is evidence that measurements of the systemic immune/inflammatory response are associated with mortality in patients with certain malignancies, as well as those with atherosclerotic disease. A variety of readily available inflammation-based prognostic scores, combining serum constituents of the systemic immune/inflammatory response, have been suggested for use in these patient groups. However, it is unclear whether systemic inflammation-based scores are universally associated with mortality across all tumour types and whether this relationship persists in atherosclerotic conditions including cardiovascular and cerebrovascular disease. The optimal constituents of such a score are also still to be determined. The present thesis further examines these topics with specific reference to:
1. The relationship between the presence of cancer, an inflammation-based prognostic score and biochemical parameters in a large group of unselected patients.
2. The relationship between an inflammation-based prognostic score and cancer survival in patients with malignancies at a number of different sites.
3. A comparison of commonly available inflammation-based prognostic scores in patients with cancer.
4. The prognostic value of a derived neutrophil to lymphocyte ratio, commonly available in patients with cancer undergoing chemotherapy.
5. The optimal serum constituents of the systemic inflammation-based Glasgow Prognostic Score (optimised) in patients with cancer.
6. The optimal constituents and prognostic value of a systemic inflammation-based score for predicting cardiovascular, cerebrovascular and all-cause mortality
Iron Age to Medieval entomogamous vegetation and Rhinolophus hipposideros roost in south-eastern Wales (UK)
Karst cave systems are well developed in Wales (UK) and, in some instances, constitute important bat roosts. Ogof Draenen, near Blaenavon in south-east Wales, is the most recent major cave discovery (1994) with already > 70 km of passages explored spanning a vertical range of 148 m. With the exception of one small chamber (Siambre Ddu) located directly above the main Ogof Draenen system, very few bats have been noticed inside. Extensive accumulations of guano, attributable to Rhinolophus hipposideros, are however found in parts of the Ogof Draenen system. In places covering many square meters and sometimes building heaps > 0.5 m thick, these represent volumes not yet found in any other cave system in the British Isles. Although the date of the abandonment of the main Ogof Draenen system as a bat roost remains unknown, six radiocarbon dates on guano from Ogof Draenen place the occupation in the Iron Age to Medieval period at least. Palynological analysis was undertaken on ten samples distributed through the cave. Comparisons were made with a moss polster and a lake mud sample from the area to provide a first approximation of the regional modern pollen rain and with two modern guano samples, one from Siambre Ddu and one from Agen Allwedd cave (5 km to the north-west) to provide a temporal comparison with the fossil guano. Agen Allwedd cave currently is one of the largest active roosts for Lesser Horseshoe bats in Britain and lies close to the present northern limit of this endangered species in Europe. The main results are that the cave appears to have been used both as a summer and a winter roost; most of the Ogof Draenen guano is formed within c.1600 14C years and, if the largest heap is continuous, it has accumulated within 750 14C years, i. e. 0.16 mm.year-1; the fossil guano samples reflect a relatively closed oak forest with more abundant ivy (Hedera) and holly (Ilex) than at present; insect-pollinated plants such as Ilex, Acer, Hedera and Impatiens glandulifera are over–represented in the guano samples; in addition to the usual causes of bat roost decline (pesticides, pollution), in the case of Ogof Draenen, we may add entrance blocked by rock collapse and decline of the local forest cover as well as change in its composition
Nonlinear Competition Between Small and Large Hexagonal Patterns
Recent experiments by Kudrolli, Pier and Gollub on surface waves,
parametrically excited by two-frequency forcing, show a transition from a small
hexagonal standing wave pattern to a triangular ``superlattice'' pattern. We
show that generically the hexagons and the superlattice wave patterns bifurcate
simultaneously from the flat surface state as the forcing amplitude is
increased, and that the experimentally-observed transition can be described by
considering a low-dimensional bifurcation problem. A number of predictions come
out of this general analysis.Comment: 4 pages, RevTex, revised, to appear in Phys. Rev. Let
The modified Glasgow prognostic score in prostate cancer: results from a retrospective clinical series of 744 patients
<p>Background: As the incidence of prostate cancer continues to rise steeply, there is an increasing need to identify more accurate prognostic markers for the disease. There is some evidence that a higher modified Glasgow Prognostic Score (mGPS) may be associated with poorer survival in patients with prostate cancer but it is not known whether this is independent of other established prognostic factors. Therefore the aim of this study was to describe the relationship between mGPS and survival in patients with prostate cancer after adjustment for other prognostic factors.</p>
<p>Methods: Retrospective clinical series on patients in Glasgow, Scotland, for whom data from the Scottish Cancer Registry, including Gleason score, Prostate Specific Antigen (PSA), C-reactive protein (CRP) and albumin, six months prior to or following the diagnosis, were included in this study.</p>
<p>The mGPS was constructed by combining CRP and albumin. Five-year and ten-year relative survival and relative excess risk of death were estimated by mGPS categories after adjusting for age, socioeconomic circumstances, Gleason score, PSA and previous in-patient bed days.</p>
<p>Results: Seven hundred and forty four prostate cancer patients were identified; of these, 497 (66.8%) died during a maximum follow up of 11.9 years. Patients with mGPS of 2 had poorest 5-year and 10-year relative survival, of 32.6% and 18.8%, respectively. Raised mGPS also had a significant association with excess risk of death at five years (mGPS 2: Relative Excess Risk = 3.57, 95% CI 2.31-5.52) and ten years (mGPS 2: Relative Excess Risk = 3.42, 95% CI 2.25-5.21) after adjusting for age, socioeconomic circumstances, Gleason score, PSA and previous in-patient bed days.</p>
<p>Conclusions: The mGPS is an independent and objective prognostic indicator for survival of patients with prostate cancer. It may be useful in determining the clinical management of patients with prostate cancer in addition to established prognostic markers.</p>
A system and methodologies for absolute QE measurements from the vacuum ultraviolet through the NIR
In this paper we present our system design and methodology for making
absolute quantum efficiency (QE) measurements through the vacuum ultraviolet
(VUV) and verify the system with delta-doped silicon CCDs. Delta-doped
detectors provide an excellent platform to validate measurements through the
VUV due to their enhanced UV response. The requirements for measuring QE
through the VUV are more strenuous than measurements in the near UV and
necessitate, among other things, the use of a vacuum monochromator, good dewar
chamber vacuum to prevent on-chip condensation, and more stringent handling
requirements.Comment: The following article has been submitted to/accepted by the Review of
Scientific Instruments. After it is published, it will be found at
http://rsi.aip.org
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