1,135 research outputs found
The Validity of the Modified Star Excursion Balance Test as a Predictor of Knee Extensor and Hip Abductor Strength
Objectives: To test the construct validity of the modified Star Excursion Balance Test (SEBT) in predicting the strength of knee extensors and hip abductors and to compare performance between dominant and non-dominant legs. Strength, as measured using hand held dynamometry, has been used as one of a variety of measures in order to subgroup patients with patellofemoral pain. This method is not well received in clinical practice due to time constraints and cost. In contrast, the SEBT is a quick and simple functional measure of dynamic stability. This study examined the validity of the SEBT as an alternate strength measure. Design: Within subject correlation. Each participant recorded maximum isometric contractions for hip abduction and knee extension using a HHD and performed the modified SEBT, on both legs, within one test period. Paired t tests were used to compare dominant and non-dominant legs and Pearsonâs correlation analyses were used to explore for associations. Setting: Non-clinical environment, Participants: Eighteen healthy male amateur runnerâs between 18 and 39 years old (mean age 36.1 years). Main outcome measures: Knee and hip moments normalised for leg length (Nm/m) for the HHD and percent of leg length reach score for each SEBT reach as well as a composite of all three. Results: There was no significant difference between dominant and non-dominant legs for all the tests (knee extension p = 0.72, hip abduction p = 0.90, SEBT composite p = 0.86) therefore data was combined into one set. There was no significant relationship between either hip abduction strength (r = 0.28, p = 0.11), or knee extension strength (r= 0.16, p = 0.17), with any combination of the SEBT. A moderate relationship (r = 0.52, p = 0.38) between hip abduction and SEBT posterolateral reach was seen, however, this was not statistically significant. Conclusion: There was no statistically significant association between either knee extension or hip abduction strength with the modified SEBT. This suggests that strength is unlikely to be a primary construct of the test and the SEBT is not a useful replacement for the HHD when testing strength
Untangling cosmic magnetic fields: Faraday tomography at metre wavelengths with LOFAR
14 pages, 6 figures. Accepted for publication in "The Power of Faraday Tomography" special issue of GalaxiesThe technique of Faraday tomography is a key tool for the study ofmagnetised plasmas in the new era of broadband radio-polarisation observations. In particular, observations at metre wavelengths provide significantly better Faraday depth accuracies compared to traditional centimetre-wavelength observations. However, the effect of Faraday depolarisationmakes the polarised signal very challenging to detect at metre wavelengths (MHz frequencies). In this work, Faraday tomography is used to characterise the Faraday rotation properties of polarised sources found in data from the LOFAR Two-Metre Sky Survey (LoTSS). Of the 76 extragalactic polarised sources analysed here, we find that all host a radio-loud AGN (Active Galactic Nucleus). The majority of the sources (~64%) are large FRII radio galaxies with a median projected linear size of 710 kpc and median radio luminosity at 144 MHz of 4 Ă 10 26 W Hz -1 (with ~13% of all sources having a linear size > 1 Mpc). In several cases, both hotspots are detected in polarisation at an angular resolution of ~20'. One such case allowed a study of intergalactic magnetic fields on scales of 3.4 Mpc. Other detected source types include an FRI radio galaxy and at least eight blazars. Most sources display simple Faraday spectra, but we highlight one blazar that displays a complex Faraday spectrum, with two close peaks in the Faraday dispersion function.Peer reviewe
LOFAR early-time search for coherent radio emission from GRB 180706A
© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society.The nature of the central engines of gamma-ray bursts (GRBs) and the composition of their relativistic jets are still under debate. If the jets are Poynting flux dominated rather than baryon dominated, a coherent radio flare from magnetic re-connection events might be expected with the prompt gamma-ray emission. There are two competing models for the central engines of GRBs; a black hole or a newly formed milli-second magnetar. If the central engine is a magnetar it is predicted to produce coherent radio emission as persistent or flaring activity. In this paper, we present the deepest limits to date for this emission following LOFAR rapid response observations of GRB 180706A. No emission is detected to a 3 limit of 1.7 mJy beam at 144 MHz in a two-hour LOFAR observation starting 4.5 minutes after the gamma-ray trigger. A forced source extraction at the position of GRB 180706A provides a marginally positive (1 sigma) peak flux density of mJy. The data were time-sliced into different sets of snapshot durations to search for FRB like emission. No short duration emission was detected at the location of the GRB. We compare these results to theoretical models and discuss the implications of a non-detection.Peer reviewedFinal Accepted Versio
An intergalactic medium temperature from a giant radio galaxy
© 2022 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/).The warm-hot intergalactic medium (warm-hot IGM, or WHIM) pervades the filaments of the Cosmic Web and harbours half of the Universe's baryons. The WHIM's thermodynamic properties are notoriously hard to measure. Here we estimate a galaxy group - WHIM boundary temperature using a new method. In particular, we use a radio image of the giant radio galaxy (giant RG, or GRG) created by NGC 6185, a massive nearby spiral. We analyse this extraordinary object with a Bayesian 3D lobe model and deduce an equipartition pressure -- among the lowest found in RGs yet. Using an X-ray-based statistical conversion for Fanaroff-Riley II RGs, we find a true lobe pressure . Cosmic Web reconstructions, group catalogues, and MHD simulations furthermore imply an -scale IGM density . The buoyantly rising lobes are crushed by the IGM at their inner side, where an approximate balance between IGM and lobe pressure occurs: . The ideal gas law then suggests an IGM temperature , or , at the virial radius -- consistent with X-ray-derived temperatures of similarly massive groups. Interestingly, the method is not performing at its limit: in principle, estimates are already possible -- rivalling the lowest X-ray measurements available. The technique's future scope extends from galaxy group outskirts to the WHIM. In conclusion, we demonstrate that observations of GRGs in Cosmic Web filaments are finally sensitive enough to probe the thermodynamics of galaxy groups and beyond.Peer reviewe
Automated parametric neutronics analysis of the Helium Cooled Pebble Bed breeder blanket with BeââTi
The Helium Cooled Pebble Bed (HCPB) breeder blanket is being developed as part of the European Fusion Programme. Part of the programme is to investigate blanket designs relevant for future demonstration fusion power plants. This paper presents neutronics analyses of the HCPB with an alternative neutron multiplier, Be12Ti which is incorporated into the design, replacing the current Be multiplier. A parameter study was performed for a range of geometries to identify the optimal heights of the lithium ceramic and neutron multiplier pebble beds. Automated creation of CAD models followed by conversion to constructive solid geometry (CSG) and unstructured mesh (UM) geometry allows the models to be useful for both neutronics simulations and engineering simulations. In this neutronics study simulations were performed using MCNP 6.1 to find the tritium breeding ratio, energy multiplication and the volumetric heat loads of different blanket designs. Combinations of geometry parameters and material choices that resulted in adequate TBR values were identified and will be further investigated with automated engineering simulations. This paper provides insight, supported by neutronics analysis, on the validity of the design and comments on some of the potential advantages and disadvantages of using Be12Ti in the Helium Cooled Pebble Bed (HCPB) breeder blanket. Blankets with Be12Ti neutron multiplier were found to produce less tritium but higher energy multiplication when compared to blankets with Be neutron multiplier
Microwave observations of spinning dust emission in NGC6946
We report new cm-wave measurements at five frequencies between 15 and 18GHz
of the continuum emission from the reportedly anomalous "region 4" of the
nearby galaxy NGC6946. We find that the emission in this frequency range is
significantly in excess of that measured at 8.5GHz, but has a spectrum from
15-18GHz consistent with optically thin free-free emission from a compact HII
region. In combination with previously published data we fit four emission
models containing different continuum components using the Bayesian spectrum
analysis package radiospec. These fits show that, in combination with data at
other frequencies, a model with a spinning dust component is slightly preferred
to those that possess better-established emission mechanisms.Comment: submitted MNRA
Discovery of inverse-Compton X-ray emission and estimate of the volume-averaged magnetic field in a galaxy group
Observed in a significant fraction of clusters and groups of galaxies,
diffuse radio synchrotron emission reveals the presence of relativistic
electrons and magnetic fields permeating large-scale systems of galaxies.
Although these non-thermal electrons are expected to upscatter cosmic microwave
background photons up to hard X-ray energies, such inverse-Compton (IC) X-ray
emission has so far not been unambiguously detected on cluster/group scales.
Using deep, new proprietary XMM-Newton observations (200 ks of clean
exposure), we report a 4.6 detection of extended IC X-ray emission in
MRC 0116+111, an extraordinary group of galaxies at . Assuming a
spectral slope derived from low-frequency radio data, the detection remains
robust to systematic uncertainties. Together with low-frequency radio data from
GMRT, this detection provides an estimate for the volume-averaged magnetic
field of G within the central part of the group. This
value can serve as an anchor for studies of magnetic fields in the largest
gravitationally bound systems in the Universe.Comment: 11 pages, 7 figures, accepted for publication in MNRA
Polarised radio pulsations from a new T dwarf binary
Brown dwarfs display Jupiter-like auroral phenomena such as magnetospheric
H emission and coherent radio emission. Coherent radio emission is a
probe of magnetospheric acceleration mechanisms and provides a direct
measurement of the magnetic field strength at the emitter's location, both of
which are difficult to access by other means. Observations of the coldest brown
dwarfs (spectral types T and Y) are particularly interesting as their
magnetospheric phenomena may be very similar to those in gas-giant exoplanets.
Here we present 144 MHz radio and infrared adaptive optics observations of the
brown dwarf WISEP J101905.63+652954.2 made using the LOFAR and Keck telescopes
respectively. The radio data shows pulsed highly circularly polarised emission
which yields a rotation rate of hr. The infrared imaging
reveals the source to be a binary with a projected separation of
mas between components of spectral type T5. and T7.. With a
simple "toy model" we show that the radio emission can in principle be powered
by the interaction between the two dwarfs with a mass-loss rates of at least
times the Jovian value. WISEP J101905.63+652954.2 is interesting because
it is the first pulsed methane dwarf detected in a low radio-frequency search.
Unlike previous gigahertz-frequency searches that were only sensitive to
objects with kiloGauss fields, our low-frequency search is sensitive to surface
magnetic fields of Gauss and above which might reveal the coldest
radio-loud objects down to planetary mass-scales.Comment: Accepted for publication in A&
NGC 326: X-shaped no more
We present new 144-MHz LOFAR observations of the prototypical âX-shapedâ radio galaxy NGC 326, which show that the formerly known wings of the radio lobes extend smoothly into a large-scale, complex radio structure. We argue that this structure is most likely the result of hydrodynamical effects in an ongoing group or cluster merger, for which pre-existing X-ray and optical data provide independent evidence. The large-scale radio structure is hard to explain purely in terms of jet reorientation due to the merger of binary black holes, a previously proposed explanation for the inner structure of NGC 326. For this reason, we suggest that the simplest model is one in which the merger-related hydrodynamical processes account for all the source structure, though we do not rule out the possibility that a black hole merger has occurred. Inference of the black hole-black hole merger rate from observations of X-shaped sources should be carried out with caution in the absence of deep, sensitive low-frequency observations. Some X-shaped sources may be signposts of cluster merger activity, and it would be useful to investigate the environments of these objects more generally
Remnant radio-loud AGN in the Herschel-ATLAS field
Only a small fraction of observed active galactic nuclei (AGN) display large-scale radio emission associated with jets, yet these radio-loud AGN have become increasingly important in models of galaxy evolution. In determining the dynamics and energetics of the radio sources over cosmic time, a key question concerns what happens when their jets switch off. The resulting âremnant' radio-loud AGN have been surprisingly evasive in past radio surveys, and therefore statistical information on the population of radio-loud AGN in their dying phase is limited. In this paper, with the recent developments of Low-Frequency Array (LOFAR) and the Very Large Array, we are able to provide a systematically selected sample of remnant radio-loud AGN in the Herschel-ATLAS field. Using a simple core-detection method, we constrain the upper limit on the fraction of remnants in our radio-loud AGN sample to 9âperâcent, implying that the extended lobe emission fades rapidly once the core/jets turn off. We also find that our remnant sample has a wide range of spectral indices (â1.5 â©œ α1400150 â©œ â0.5), confirming that the lobes of some remnants may possess flat spectra at low frequencies just as active sources do. We suggest that, even with the unprecedented sensitivity of LOFAR, our sample may still only contain the youngest of the remnant population
- âŠ