| 1. |
- Niemi, MEK, et al.
(författare)
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- 2021
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swepub:Mat__t
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| 2. |
- Kanai, M, et al.
(författare)
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- 2023
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swepub:Mat__t
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| 3. |
- Murari, A., et al.
(författare)
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A control oriented strategy of disruption prediction to avoid the configuration collapse of tokamak reactors
- 2024
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Ingår i: Nature Communications. - 2041-1723 .- 2041-1723. ; 15:1
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Tidskriftsartikel (refereegranskat)abstract
- The objective of thermonuclear fusion consists of producing electricity from the coalescence of light nuclei in high temperature plasmas. The most promising route to fusion envisages the confinement of such plasmas with magnetic fields, whose most studied configuration is the tokamak. Disruptions are catastrophic collapses affecting all tokamak devices and one of the main potential showstoppers on the route to a commercial reactor. In this work we report how, deploying innovative analysis methods on thousands of JET experiments covering the isotopic compositions from hydrogen to full tritium and including the major D-T campaign, the nature of the various forms of collapse is investigated in all phases of the discharges. An original approach to proximity detection has been developed, which allows determining both the probability of and the time interval remaining before an incoming disruption, with adaptive, from scratch, real time compatible techniques. The results indicate that physics based prediction and control tools can be developed, to deploy realistic strategies of disruption avoidance and prevention, meeting the requirements of the next generation of devices.
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| 4. |
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| 5. |
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| 6. |
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| 7. |
- Andreoni, I., et al.
(författare)
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Follow Up of GW170817 and Its Electromagnetic Counterpart by Australian-Led Observing Programmes
- 2017
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Ingår i: Publications Astronomical Society of Australia. - : Cambridge University Press (CUP). - 1323-3580 .- 1448-6083. ; 34
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Forskningsöversikt (refereegranskat)abstract
- The discovery of the first electromagnetic counterpart to a gravitational wave signal has generated follow-up observations by over 50 facilities world-wide, ushering in the new era of multi-messenger astronomy. In this paper, we present follow-up observations of the gravitational wave event GW170817 and its electromagnetic counterpart SSS17a/DLT17ck (IAU label AT2017gfo) by 14 Australian telescopes and partner observatories as part of Australian-based and Australian-led research programs. We report early- to late-time multi-wavelength observations, including optical imaging and spectroscopy, mid-infrared imaging, radio imaging, and searches for fast radio bursts. Our optical spectra reveal that the transient source emission cooled from approximately 6 400 K to 2 100 K over a 7-d period and produced no significant optical emission lines. The spectral profiles, cooling rate, and photometric light curves are consistent with the expected outburst and subsequent processes of a binary neutron star merger. Star formation in the host galaxy probably ceased at least a Gyr ago, although there is evidence for a galaxy merger. Binary pulsars with short (100 Myr) decay times are therefore unlikely progenitors, but pulsars like PSR B1534+12 with its 2.7 Gyr coalescence time could produce such a merger. The displacement (similar to 2.2 kpc) of the binary star system from the centre of the main galaxy is not unusual for stars in the host galaxy or stars originating in the merging galaxy, and therefore any constraints on the kick velocity imparted to the progenitor are poor.
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| 8. |
- Bhat, N. D. R., et al.
(författare)
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Observations of Low-frequency Radio Emission from Millisecond Pulsars and Multipath Propagation in the Interstellar Medium
- 2018
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Ingår i: Astrophysical Journal, Supplement Series. - : American Astronomical Society. - 1538-4365 .- 0067-0049. ; 238:1
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Tidskriftsartikel (refereegranskat)abstract
- Studying the gravitational-wave sky with pulsar timing arrays (PTAs) is a key science goal for the Square Kilometre Array (SKA) and its pathfinder telescopes. With current PTAs reaching sub-microsecond timing precision, making accurate measurements of interstellar propagation effects and mitigating them effectively has become increasingly important to realize PTA goals. As these effects are much stronger at longer wavelengths, low-frequency observations are most appealing for characterizing the interstellar medium (ISM) along the sight lines toward PTA pulsars. The Murchison Widefield Array (MWA) and the Engineering Development Array (EDA), which utilizes MWA technologies, present promising opportunities for undertaking such studies, particularly for PTA pulsars located in the southern sky. Such pulsars are also the prime targets for PTA efforts planned with the South African MeerKAT, and eventually with the SKA. In this paper we report on observations of two bright southern millisecond pulsars, PSR J0437-4715 and PSR J2145-0750, made with these facilities; MWA observations sampled multiple frequencies across the 80-250 MHz frequency range, while the EDA provided direct-sampled baseband data to yield a large instantaneous usable bandwidth of similar to 200 MHz. Using these exploratory observations, we investigate various aspects relating to pulsar emission and ISM properties, such as spectral evolution of the mean pulse shape, scintillation as a function of frequency, chromaticity in interstellar dispersion, and flux density spectra at low frequencies. Systematic and regular monitoring observations will help ascertain the role of low-frequency measurements in PTA experiments, while simultaneously providing a detailed characterization of the ISM toward the pulsars, which will be useful in devising optimal observing strategies for future PTA experiments.
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| 9. |
- Horsley, S. A. R., et al.
(författare)
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Removing singular refractive indices with sculpted surfaces
- 2014
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 4, s. 4876-
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Tidskriftsartikel (refereegranskat)abstract
- The advent of Transformation Optics established the link between geometry and material properties, and has resulted in a degree of control over electromagnetic fields that was previously impossible. For waves confined to a surface it is known that there is a simpler, but related, geometrical equivalence between the surface shape and the refractive index, and here we demonstrate that conventional devices possessing a singularity-that is, the requirement of an infinite refractive index-can be realised for waves confined to an appropriately sculpted surface. In particular, we redesign three singular omnidirectional devices: the Eaton lens, the generalized Maxwell Fish-Eye, and the invisible sphere. Our designs perfectly reproduce the behaviour of these singular devices, and can be achieved with simple isotropic media of low refractive index contrast.
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| 10. |
- Smail, R. E., et al.
(författare)
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Constraining beyond the standard model nucleon isovector charges
- 2023
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Ingår i: Physical Review D. - : American Physical Society (APS). - 2470-0010 .- 2470-0029. ; 108:9
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Tidskriftsartikel (refereegranskat)abstract
- At the TeV scale, low-energy precision observations of neutron characteristics provide unique probes of novel physics. Precision studies of neutron decay observables are susceptible to beyond the Standard Model (BSM) tensor and scalar interactions, while the neutron electric dipole moment, dn, also has high sensitivity to new BSM CP-violating interactions. To fully utilize the potential of future experimental neutron physics programs, matrix elements of appropriate low-energy effective operators within neutron states must be precisely calculated. We present results from the QCDSF/UKQCD/CSSM Collaboration for the isovector charges gT, gA and gS of the nucleon, ς and Ξ baryons using lattice QCD methods and the Feynman-Hellmann theorem. We use a flavor symmetry breaking method to systematically approach the physical quark mass using ensembles that span five lattice spacings and multiple volumes. We extend this existing flavor-breaking expansion to also account for lattice spacing and finite volume effects in order to quantify all systematic uncertainties. Our final estimates of the nucleon isovector charges are gT=1.010(21)stat(12)sys,gA=1.253(63)stat(41)sys and gS=1.08(21)stat(03)sys renormalized, where appropriate, at μ=2 GeV in the MS¯ scheme.
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| 11. |
- Smail, R. E., et al.
(författare)
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Tensor Charges and their Impact on Physics Beyond the Standard Model
- 2022
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Ingår i: Proceedings of Science. - : Sissa Medialab Srl.
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Konferensbidrag (refereegranskat)abstract
- The nucleon tensor charge, gT, is an important quantity in the search for beyond the Standard Model tensor interactions in neutron and nuclear β-decays as well as the contribution of the quark electric dipole moment (EDM) to the neutron EDM. We present results from the QCDSF/UKQCD/CSSM collaboration for the tensor charge, gT, using lattice QCD methods and the Feynman-Hellmann theorem. We use a flavour symmetry breaking method to systematically approach the physical quark mass using ensembles that span three lattice spacings.
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| 12. |
- Batelaan, M., et al.
(författare)
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Nucleon Form Factors from the Feynman-Hellmann Method in Lattice QCD
- 2022
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Ingår i: Proceedings of Science. - : Sissa Medialab Srl.
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Konferensbidrag (refereegranskat)abstract
- Lattice QCD calculations of the nucleon electromagnetic form factors are of interest at both the high and low momentum transfer regions. For high momentum transfers especially there are open questions which require more intense study, such as the potential zero crossing in the proton's electric form factor. We will present recent progress from the QCDSF/UKQCD/CSSM collaboration on the calculation of these form factors using the Feynman-Hellmann method in lattice QCD. The Feynman-Hellmann method allows for greater control over excited states which we take advantage of by going to high values of the momentum transfer. In this proceeding we present results of the form factors up to 6 GeV2, using Nf = 2 + 1 flavour fermions for three different pion masses in the range 310-470 MeV. The results are extrapolated to the physical pion mass through the use of a flavour breaking expansion.
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| 13. |
- Bickerton, J. M., et al.
(författare)
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Patterns of flavour symmetry breaking in hadron matrix elements involving u, d and s quarks
- 2022
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Ingår i: Proceedings of Science. - : Sissa Medialab Srl.
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Konferensbidrag (refereegranskat)abstract
- Using an SU(3)-flavour symmetry breaking expansion between the strange and light quark masses, we determine how this constrains the extrapolation of baryon octet matrix elements and form factors. In particular we can construct certain combinations, which fan out from the symmetric point (when all the quark masses are degenerate) to the point where the light and strange quarks take their physical values. As a further example we consider the vector amplitude at zero momentum transfer for flavour changing currents.
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| 14. |
- De La Motte, S. A., et al.
(författare)
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Measurements of SU(3) f symmetry breaking in B meson decay constants
- 2022
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Ingår i: Proceedings of Science. - : Sissa Medialab Srl.
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Konferensbidrag (refereegranskat)abstract
- We present updates from QCDSF/UKQCD/CSSM on the SU(3) f breaking in B meson decay constants. The b-quarks are generated with an anisotropic clover-improved action, and are tuned to match properties of the physical B and B∗ mesons. Configurations are generated with m = 1/3(2ml + ms) kept constant to control symmetry breaking effects. Various sources of systematic uncertainty will be discussed, including those from continuum extrapolations and extrapolations to the physical point. We also present new efforts to calculate fB and fBs using weighted averages across multiple time fitting regions. The use of an automated weighted averaging technique over multiple fitting ranges allows for timely tuning of the b-quark and reduces the impact of systematic errors from fitting range biases in calculations of fB and fBs.
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| 15. |
- Mitchell-Thomas, R. C., et al.
(författare)
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Lenses on curved surfaces
- 2014
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Ingår i: Optics Letters. - 0146-9592 .- 1539-4794. ; 39:12, s. 3551-3554
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Tidskriftsartikel (refereegranskat)abstract
- This Letter presents a theory that allows graded index lenses to be mapped onto arbitrary rotationally symmetric curved surfaces. Examples of the Luneburg and Maxwell fish-eye lens are given, for numerous surfaces, always resulting in isotropic permittivity requirements. The performance of these lenses is initially illustrated with full-wave simulations utilizing a waveguide structure. A transformation of the refractive index profiles is then performed to design surface-wave lenses, where the dielectric layer is not only isotropic but also homogenous, demonstrating the applicability and ease of fabrication.
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| 16. |
- Mitchell-Thomas, R. C., et al.
(författare)
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The anti-fish eye cloak for surface wave antennas
- 2014
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Ingår i: 8th European Conference on Antennas and Propagation, EuCAP 2014. - 9788890701849 ; , s. 267-268
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Konferensbidrag (refereegranskat)abstract
- In this paper a new lens, named the anti-fish eye lens, is proposed and its relation to the Maxwell fish eye lens is described. This novel lens is then applied to cloak an object positioned underneath it, to electromagnetic waves that are confined to the surface. The performance of the lens in reforming the cylindrical wave fronts is illustrated with numerical simulations. This lens has direct applications for surface wave antennas that are conformal to curved structures to remove the influence of the curvature, the consequence of which would detrimentally affect the directivity because of the distortion of the wavefronts. Therefore, using this technique, the performance of surface wave antennas on curved surfaces can be equivalent to those on flat surfaces.
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| 17. |
- Quevedo-Teruel, Oscar, et al.
(författare)
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Conformal surface lenses from a bed of nails
- 2014
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Ingår i: 8th European Conference on Antennas and Propagation, EuCAP 2014. - 9788890701849 ; , s. 269-270
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Konferensbidrag (refereegranskat)abstract
- This paper presents a validation of a fast method for calculating the propagation constant of a periodic bed of nails structure. These results are compared to full wave simulation results, showing good agreement. This method is then employed to design a Luneburg lens which is conformal to the surface of a sphere. The index distribution required to create this conformal lens was calculated using an optical path technique. This work has applications for the design of communication systems for vehicles and airborne platforms.
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| 18. |
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| 19. |
- Chen, Qiao, et al.
(författare)
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A General Solution for Double-Layer Gradient-Index and Geodesic Lenses with Rotational Symmetry
- 2023
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Ingår i: 2023 17TH EUROPEAN CONFERENCE ON ANTENNAS AND PROPAGATION, EUCAP. - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- A double-layer lens consists of a pair of rotationally symmetric index profiles or geodesic lens shapes connected by a reflecting mirror partially covering their common periphery. Such a lens can provide a focus in each layer, and a wave travelling between the foci explores both layers. Here, we concentrate on the case with one layer being homogeneous or flat, and derive a general solution for the lens profiles by solving a Luneburg-like inverse problem with pre-specified foci inside or outside the lens, and different background indices in two layers. We demonstrate four examples of interest in ray-tracing plots. These lenses may find application in communications, sensing, and imaging from millimeter waves up to the optical bands.
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| 20. |
- Chen, Qiao, et al.
(författare)
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Double-layer geodesic and gradient-index lenses
- 2022
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- A double-layer lens consists of a first gradient-index/geodesic profile in an upper waveguide, partially surrounded by a mirror that reflects the wave into a lower guide where there is a second profile. Here, we derive a new family of rotational-symmetric inhomogeneous index profiles and equivalent geodesic lens shapes by solving an inverse problem of pre-specified focal points. We find an equivalence where single-layer lenses have a different functionality as double-layer lenses with the same profiles. As an example, we propose, manufacture, and experimentally validate a practical implementation of a geodesic double-layer lens that is engineered for a low-profile antenna with a compact footprint in the millimeter wave band. Its unique double-layer configuration allows for two-dimensional beam scanning using the same footprint as an extension of the presented design. These lenses may find applications in future wireless communication systems and sensing instruments in microwave, sub-terahertz, and optical domains. A double-layer lens consists of a first gradient-index/geodesic profile in an upper waveguide, partially surrounded by a mirror that reflects the wave into a lower guide where there is a second profile. A family of such lens profiles are derived.
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| 21. |
- Horsley, Alex R, et al.
(författare)
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Effects of cystic fibrosis lung disease on gas mixing indices derived from alveolar slope analysis.
- 2008
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Ingår i: Respiratory physiology & neurobiology. - : Elsevier BV. - 1569-9048. ; 162:3, s. 197-203
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Tidskriftsartikel (refereegranskat)abstract
- S(cond) and S(acin) are derived from analysis of concentration-normalized phase III slopes (Sn(III)) of a multiple breath inert gas washout. Studies in healthy and COPD subjects suggest these reflect ventilation heterogeneity in conducting and acinar airway zones respectively, but similar studies in cystic fibrosis (CF) are lacking. S(cond), S(acin) and lung clearance index (LCI, a measure of overall gas mixing efficiency) were measured in 22 adults and 18 children with CF and 17 adult and 29 child controls. Plethysmography and gas transfer measurements were performed in adults, and spirometry in all subjects. S(cond) was elevated in almost all CF patients, including children with mild disease and normal LCI. However, S(cond) did not correlate with other measurements and appeared to reach a maximum; further increase in ventilation heterogeneity being restricted to S(acin). The nature and/or severity of CF lung disease may invalidate assumptions underlying the ability to separate phase III slope analysis of ventilation heterogeneity into proximal and peripheral components, and LCI may be a better indicator of gas mixing in this population.
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| 22. |
- Horsley, A R, et al.
(författare)
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Lung clearance index is a sensitive, repeatable and practical measure of airways disease in adults with cystic fibrosis.
- 2008
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Ingår i: Thorax. - : BMJ. - 1468-3296 .- 0040-6376. ; 63:2, s. 135-40
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Lung clearance index (LCI) is a sensitive marker of early lung disease in children but has not been assessed in adults. Measurement is hindered by the complexity of the equipment required. The aims of this study were to assess performance of a novel gas analyser (Innocor) and to use it as a clinical tool for the measurement of LCI in cystic fibrosis (CF). METHODS: LCI was measured in 48 healthy adults, 12 healthy school-age children and 33 adults with CF by performing an inert gas washout from 0.2% sulfur hexafluoride (SF6). SF6 signal:noise ratio and 10-90% rise time of Innocor were compared with a mass spectrometer used in similar studies in children. RESULTS: Compared with the mass spectrometer, Innocor had a superior signal:noise ratio but a slower rise time (150 ms vs 60 ms) which may limit its use in very young children. Mean (SD) LCI in healthy adults was significantly different from that in patients with CF: 6.7 (0.4) vs 13.1 (3.8), p<0.001. Ten of the patients with CF had forced expiratory volume in 1 s > or = 80% predicted but only one had a normal LCI. LCI repeats were reproducible in all three groups of subjects (mean intra-visit coefficient of variation ranged from 3.6% to 5.4%). CONCLUSIONS: Innocor can be adapted to measure LCI and affords a simpler alternative to a mass spectrometer. LCI is raised in adults with CF with normal spirometry, and may prove to be a more sensitive marker of the effects of treatment in this group.
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| 23. |
- McCall, Martin, et al.
(författare)
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Roadmap on transformation optics
- 2018
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Ingår i: Journal of Optics. - : IOP Publishing. - 2040-8978 .- 2040-8986. ; 20:6
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Forskningsöversikt (refereegranskat)abstract
- Transformation optics asks, using Maxwell's equations, what kind of electromagnetic medium recreates some smooth deformation of space? The guiding principle is Einstein's principle of covariance: that any physical theory must take the same form in any coordinate system. This requirement fixes very precisely the required electromagnetic medium. The impact of this insight cannot be overestimated. Many practitioners were used to thinking that only a few analytic solutions to Maxwell's equations existed, such as the monochromatic plane wave in a homogeneous, isotropic medium. At a stroke, transformation optics increases that landscape from 'few' to 'infinity', and to each of the infinitude of analytic solutions dreamt up by the researcher, there corresponds an electromagnetic medium capable of reproducing that solution precisely. The most striking example is the electromagnetic cloak, thought to be an unreachable dream of science fiction writers, but realised in the laboratory a few months after the papers proposing the possibility were published. But the practical challenges are considerable, requiring meta-media that are at once electrically and magnetically inhomogeneous and anisotropic. How far have we come since the first demonstrations over a decade ago? And what does the future hold? If the wizardry of perfect macroscopic optical invisibility still eludes us in practice, then what compromises still enable us to create interesting, useful, devices? While three-dimensional (3D) cloaking remains a significant technical challenge, much progress has been made in two dimensions. Carpet cloaking, wherein an object is hidden under a surface that appears optically flat, relaxes the constraints of extreme electromagnetic parameters. Surface wave cloaking guides sub-wavelength surface waves, making uneven surfaces appear flat. Two dimensions is also the setting in which conformal and complex coordinate transformations are realisable, and the possibilities in this restricted domain do not appear to have been exhausted yet. Beyond cloaking, the enhanced electromagnetic landscape provided by transformation optics has shown how fully analytic solutions can be found to a number of physical scenarios such as plasmonic systems used in electron energy loss spectroscopy and cathodoluminescence. Are there further fields to be enriched? A new twist to transformation optics was the extension to the spacetime domain. By applying transformations to spacetime, rather than just space, it was shown that events rather than objects could be hidden from view; transformation optics had provided a means of effectively redacting events from history. The hype quickly settled into serious nonlinear optical experiments that demonstrated the soundness of the idea, and it is now possible to consider the practical implications, particularly in optical signal processing, of having an 'interrupt-without-interrupt' facility that the so-called temporal cloak provides. Inevitable issues of dispersion in actual systems have only begun to be addressed. Now that time is included in the programme of transformation optics, it is natural to ask what role ideas from general relativity can play in shaping the future of transformation optics. Indeed, one of the earliest papers on transformation optics was provocatively titled 'General Relativity in Electrical Engineering'. The answer that curvature does not enter directly into transformation optics merely encourages us to speculate on the role of transformation optics in defining laboratory analogues. Quite why Maxwell's theory defines a 'perfect' transformation theory, while other areas of physics such as acoustics are not apparently quite so amenable, is a deep question whose precise, mathematical answer will help inform us of the extent to which similar ideas can be extended to other fields. The contributors to this Roadmap, who are all renowned practitioners or inventors of transformation optics, will give their perspectives into the field's status and future development.
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| 24. |
- Taquet, Maxime, et al.
(författare)
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Post-acute COVID-19 neuropsychiatric symptoms are not associated with ongoing nervous system injury
- 2024
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Ingår i: BRAIN COMMUNICATIONS. - 2632-1297. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- A proportion of patients infected with severe acute respiratory syndrome coronavirus 2 experience a range of neuropsychiatric symptoms months after infection, including cognitive deficits, depression and anxiety. The mechanisms underpinning such symptoms remain elusive. Recent research has demonstrated that nervous system injury can occur during COVID-19. Whether ongoing neural injury in the months after COVID-19 accounts for the ongoing or emergent neuropsychiatric symptoms is unclear. Within a large prospective cohort study of adult survivors who were hospitalized for severe acute respiratory syndrome coronavirus 2 infection, we analysed plasma markers of nervous system injury and astrocytic activation, measured 6 months post-infection: neurofilament light, glial fibrillary acidic protein and total tau protein. We assessed whether these markers were associated with the severity of the acute COVID-19 illness and with post-acute neuropsychiatric symptoms (as measured by the Patient Health Questionnaire for depression, the General Anxiety Disorder assessment for anxiety, the Montreal Cognitive Assessment for objective cognitive deficit and the cognitive items of the Patient Symptom Questionnaire for subjective cognitive deficit) at 6 months and 1 year post-hospital discharge from COVID-19. No robust associations were found between markers of nervous system injury and severity of acute COVID-19 (except for an association of small effect size between duration of admission and neurofilament light) nor with post-acute neuropsychiatric symptoms. These results suggest that ongoing neuropsychiatric symptoms are not due to ongoing neural injury. COVID-19 is associated with raised neural injury markers and neuropsychiatric sequelae. It is unknown whether post-acute neural injury is linked to neuropsychiatric symptoms. Taquet et al. showed that there was no robust link between the two, suggesting that neuropsychiatric symptoms of post-acute COVID illness are not caused by ongoing neural injury.
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