2,865 research outputs found
Monolithically integrated active optical devices
Considerations relevant to the monolithic integration of optical detectors, lasers, and modulators with high speed amplifiers are discussed. Some design considerations for representative subsystems in the GaAs-AlGaAs and GaInAs-InP materials systems are described. Results of a detailed numerical design of an electro-optical birefringent filter for monolithic integration with a laser diode is described, and early experimental results on monolithic integration of broadband MESFET amplifiers with photoconductive detectors are reported
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
An XMM-Newton observation of Ton S180: Constraints on the continuum emission in ultrasoft Seyfert galaxies
We present an XMM-Newton observation of the bright, narrow-line, ultrasoft
Seyfert 1 galaxy Ton S180. The 0.3-10 keV X-ray spectrum is steep and curved,
showing a steep slope above 2.5 keV (Gamma ~ 2.3) and a smooth, featureless
excess of emission at lower energies. The spectrum can be adequately
parameterised using a simple double power-law model. The source is strongly
variable over the course of the observation but shows only weak spectral
variability, with the fractional variability amplitude remaining approximately
constant over more than a decade in energy. The curved continuum shape and weak
spectral variability are discussed in terms of various physical models for the
soft X-ray excess emission, including reflection off the surface of an ionised
accretion disc, inverse-Compton scattering of soft disc photons by thermal
electrons, and Comptonisation by electrons with a hybrid thermal/non-thermal
distribution. We emphasise the possibility that the strong soft excess may be
produced by dissipation of accretion energy in the hot, upper atmosphere of the
putative accretion disc.Comment: 9 pages, accepted for publication in MNRA
Holocene floodplain aggradation in the central Grampian Highlands, Scotland
Radiocarbon ages for samples of organic material within and overlying the highest Holocene floodplain and fan terraces in Glen Feshie and Glen Tromie imply sediment aggradation after âŒ4.3 cal ka and probably incision after âŒ3.7 cal ka, and in the Edendon Valley aggradation after âŒ2.8 cal ka, with incision after âŒ2.7 cal ka. The timing of sediment aggradation at all three sites postdates the onset of pine forest decline (âŒ4.8 cal ka) at nearby high-level sites, and coincides with wet periods characterised by high water tables. This coincidence in timing suggests that forest decline may have caused upstream extension of the tributary network, headwater incision and flashier flood responses, and that increased rainfall enhanced sediment discharge from headwater tributaries, with consequent sediment accumulation downstream on low-gradient fans and floodplains. More speculatively, exhaustion of readily entrained sediment from headwater areas may have stimulated subsequent floodplain and fan incision. Our results show that the highest Holocene terrace (the Main Holocene Terrace) is a diachronous feature, even in valleys emanating from the same upland source area, and support the conclusions of simulation models that predict marked increases in sediment discharge when deforestation is succeeded by an episode of increased rainfall.Peer reviewe
A two-component ionized reflection model of MCG--6-30-15
Ionized reflection has often been considered as the explanation for the
unusual Fe K variability observed in MCG--6-30-15. In this paper, we test this
model using a 325 ks observation of MCG--6-30-15 by XMM-Newton and BeppoSAX.
The data are fit between 2.5 and 80 keV with the constant density models of
Ross & Fabian. The best fit ionized reflection model requires the Fe K line to
be split into two reprocessing events: one from the inner disc to build up the
red wing, and the other from the outer accretion disc to fit the blue horn. The
implied geometry is a disc which becomes strongly warped or flared at large
radii. A good fit was obtained with a solar abundance of iron and a reflection
fraction (R) of unity for the inner reflector. The combination of the two
reflection spectra can appear to have R>2 as required by the BeppoSAX data. The
inner reflector has an ionization parameter \log \xi =3.8, but the outer one is
neutral with an inner radius ~70 gravitational radii (r_g), corresponding to a
light crossing time of about an hour for a 10^7 Msun black hole. Applying this
model to time-resolved spectra shows that the inner reflector becomes more
ionized as the source brightens. This reduces the strength of the red wing at
high flux states. The X-ray source is constrained to arise from a narrow
annulus at ~5 r_g, with only 6 per cent of the 2-10 keV flux due to the outer
reprocessor. This amount of localized energy generation is extremely difficult
to produce without resorting to other energy sources such as the black hole
spin. In fact, all the Fe K models fit to XMM-Newton spectra of MCG--6-30-15
require a large increase in energy production at the inner edge of the
accretion disc.Comment: 11 pages, 7 figuers, MNRAS in pres
XMM-Newton discovery of a sharp spectral feature at ~7 keV in the Narrow-Line Seyfert 1 galaxy 1H 0707-495
We report the first detection of a sharp spectral feature in a Narrow-Line
Seyfert 1 galaxy. Using XMM-Newton we have observed 1H0707-495 and find a drop
in flux by a factor of more than 2 at a rest-frame energy of ~7 keV without any
detectable narrow Fe K alpha line emission. The energy of this feature suggests
a connection with the neutral iron K photoelectric edge, but the lack of any
obvious absorption in the spectrum at lower energies makes the interpretation
challenging. We explore two alternative explanations for this unusual spectral
feature: (i) partial covering absorption by clouds of neutral material and (ii)
ionised disc reflection with lines and edges from different ionisation stages
of iron blurred together by relativistic effects. We note that both models
require an iron overabundance to explain the depth of the feature. The X-ray
light curve shows strong and rapid variability, changing by a factor of four
during the observation. The source displays modest spectral variability which
is uncorrelated with flux.Comment: 5 pages incl. 6 figures, accepted for publication in MNRA
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