98 research outputs found
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Experimental demonstration of a squeezing-enhanced power-recycled Michelson interferometer for gravitational wave detection
No full textInterferometric gravitational wave detectors are expected to be limited by shot noise at some frequencies. We experimentally demonstrate that a power recycled Michelson with squeezed light injected into the dark port can overcome this limit. An improvement in the signal-to-noise ratio of 2.3 dB is measured and locked stably for long periods of time. The configuration, control, and signal readout of our experiment are compatible with current gravitational wave detector designs. We consider the application of our system to long baseline interferometer designs such as LIGO
A comparison of responses to single and repeated discrete choice questions
No full textAccording to neoclassical economic theory, a stated preference elicitation
format comprising a single binary choice between the status quo and one alternative is
incentive compatible under certain conditions. Formats typically used in choice
experiments comprising a sequence of discrete choice questions do not hold this property.
In this paper, the effect on stated preferences of expanding the number of binary choice
tasks per respondent from one to four is tested using a split sample treatment in an
attribute-based survey relating to the undergrounding of overhead electricity and
telecommunications wires. We find evidence to suggest that presenting multiple choice
tasks per respondent decreases estimates of expected willingness to pay. Preferences
stated in the first of a sequence of choice tasks are not significantly different from those
stated in the incentive compatible single binary choice task, but, in subsequent choice
tasks, responses are influenced by cost levels observed in past questions. Three
behavioural explanations can be advanced – weak strategic misrepresentation, reference
point revision and cost-driven value learning. The evidence is contrary to the standard assumption of truthful response with stable preferences
Observation of light localization in modulated Bessel optical lattices
No full textWe generate higher-order azimuthally modulated Bessel
optical lattices in photorefractive crystals by employing a phase-imprinting
technique. We report on the experimental observation of self-trapping and
nonlinear localization of light in such segmented lattices in the form of
ring-shaped and single-site states. The experimental results agree well with
numerical simulations accounting for an anisotropic and spatially nonlocal
nonlinear response of photorefractive crystals
Cerebrovascular disease associated with antiphospholipid antibodies: more questions than answers
No full textNeurological syndromes occur in a significant number of patients with antiphospholipid antibodies. The
optimal management for these patients however remains uncertain.
Our study is a descriptive analysis looking retrospectively at 45 patients who presented to the principal
tertiary referral centre in the Australian Capital Territory, with either cerebral arterial or venous
thrombosis for which there was no obvious cause for their presentation when initially reviewed. The
diagnosis was based on the clinical findings made by one of three neurologists attached to our centre.
Radiological findings and the presence of either IgM or IgG anticardiolipin antibodies, IgG anti-beta-2
glycoprotein 1 antibodies or a lupus anticoagulant were then documented.
In this group of patients three subgroups were identified:
1. Individuals that fulfilled the Sapporo Classification Criteria
2. Individuals with transiently positive antiphospholipid antibodies and
3. Individuals with persistently low positive antiphospholipid antibodies.
The most interesting of these three groups are those individuals with transiently positive antiphospholipid
antibodies. A potential cause for presentation was identified in only one patient of this group with
documented infective endocarditis and bacteraemia. Comparison with the other two groups suggested
that there was little in terms of clinical presentation, radiological findings or intercurrent risk factors for
thrombotic disease to distinguish between them. With disappearance of antiphospholipid antibodies, the
individuals within this group have not had further thrombotic events.
Our observations emphasise the problems that continue to exist in relation to the occurrence of
cerebrovascular disease in the context of antiphospholipid antibodies and the optimal management of
these stratified groups. Our findings also raise an as yet unanswered question as to the signficance of these
transiently positive antiphospholipid antibodies. In the absence of significant intercurrent risk factors our
findings would suggest that in the group we describe that they are likely to be of clinical significance
Tissue distribution of migration inhibitory factor and inducible nitric oxide synthase in falciparum malaria and sepsis in African children
No full textBACKGROUND:
The inflammatory nature of falciparum malaria has been acknowledged since increased circulating levels of tumour necrosis factor (TNF) were first measured, but precisely where the mediators downstream from this prototype inflammatory mediator are generated has not been investigated. Here we report on the cellular distribution, by immunohistochemistry, of migration inhibitory factor (MIF) and inducible nitric oxide synthase (iNOS) in this disease, and in sepsis.
METHODS:
We stained for MIF and iNOS in tissues collected during 44 paediatric autopsies in Blantyre, Malawi. These comprised 42 acutely ill comatose patients, 32 of whom were diagnosed clinically as cerebral malaria and the other 10 as non-malarial diseases. Another 2 were non-malarial, non-comatose deaths. Other control tissues were from Australian adults.
RESULTS:
Of the 32 clinically diagnosed cerebral malaria cases, 11 had negligible histological change in the brain, and no or scanty intravascular sequestration of parasitised erythrocytes, another 7 had no histological changes in the brain, but sequestered parasitised erythrocytes were present (usually dense), and the remaining 14 brains showed micro-haemorrhages and intravascular mononuclear cell accumulations, plus sequestered parasitised erythrocytes. The vascular walls of the latter group stained most strongly for iNOS. Vascular wall iNOS staining was usually of low intensity in the second group (7 brains) and was virtually absent from the cerebral vascular walls of 8 of the 10 comatose patients without malaria, and also from control brains. The chest wall was chosen as a typical non-cerebral site encompassing a range of tissues of interest. Here pronounced iNOS staining in vascular wall and skeletal muscle was present in some 50% of the children in all groups, including septic meningitis, irrespective of the degree of staining in cerebral vascular walls. Parasites or malarial pigment were rare to absent in all chest wall sections. While MIF was common in chest wall vessels, usually in association with iNOS, it was absent in brain vessels.
CONCLUSIONS:
These results agree with the view that clinically diagnosed cerebral malaria in African children is a collection of overlapping syndromes acting through different organ systems, with several mechanisms, not necessarily associated with cerebral vascular inflammation and damage, combining to cause death
Absolute cross sections for the ionization-excitation of helium by electron impact
No full textIn a recent publication we presented detailed experimental and theoretical results for the electron-impactinduced
ionization of ground-state helium atoms. The purpose of that work was to refine theoretical approaches
and provide further insight into the Coulomb four-body problem. Cross section ratios were presented for
transitions leading to excited states, relative to those leading to the ground state, of the helium ion. We now
build on that study by presenting individual relative triple-differential ionization cross sections TDCSs for an
additional body of experimental data measured at lower values of scattered-electron energies. This has been
facilitated through the development of new electron-gun optics which enables us to accurately characterize the
spectrometer transmission at low energies. The experimental results are compared to calculations resulting
from a number of different approaches. For ionization leading to He+ 1s2 1S, cross sections are calculated by
the highly accurate convergent close-coupling CCC method. The CCC data are used to place the relative
experimental data on to an absolute scale. TDCSs describing transitions to the excited states are calculated
through three different approaches, namely, through a hybrid distorted-wave+R-matrix close-coupling model,
through the recently developed four-body distorted-wave model, and by a first Born approximation calculation.
Comparison of the first- and second-order theories with experiment allows for the accuracy of the different
theoretical approaches to be assessed and gives insight into which physical aspects of the problem are most
important to accurately model
Net-gain from a parametric amplifier on a chalcogenide optical chip
No full textWe report first observation of net-gain from an optical
parametric amplifier in a planar waveguide. This was achieved in a lowloss
As2S3 planar waveguide, with a strong nonlinearity (γ ~ 10 /W/m) and
tailored anomalous dispersion yielding efficient Raman-assisted four-wave
mixing at telecom wavelengths. The experiments were in good agreement
with theory, and indicate a peak net-gain greater than +16 dB for the signal
and idler (+30 dB neglecting coupling losses) and a broad bandwidth
spanning 180 nm
Near-field imaging and frequency tuning of a high-Q photonic crystal membrane microcavity
No full textWe discuss experimental studies of the interaction between
a nanoscopic object and a photonic crystal membrane resonator of quality
factor Q=55000. By controlled actuation of a glass fiber tip in the near field
of the photonic crystal, we constructed a complete spatio-spectral map of
the resonator mode and its coupling with the fiber tip. On the one hand,
our findings demonstrate that scanning probes can profoundly influence the
optical characteristics and the near-field images of photonic devices. On the
other hand, we show that the introduction of a nanoscopic object provides
a low loss method for on-command tuning of a photonic crystal resonator
frequency. Our results are in a very good agreement with the predictions of
a combined numerical/analytical theory
Using active resonator impedance matching for shot-noise limited, cavity enhanced amplitude modulated laser absorption spectroscopy
No full textWe introduce a closed-loop feedback technique to actively
control the coupling condition of an optical cavity, by employing amplitude
modulation of the interrogating laser. We show that active impedance
matching of the cavity facilitates optimal shot-noise sensing performance
in a cavity enhanced system, while its control error signal can be used
for intra-cavity absorption or loss signal extraction. We present the first
demonstration of this technique with a fiber ring cavity, and achieved
shot-noise limited loss sensitivity. We also briefly discuss further use of
impedance matching control as a tool for other applications
The Anthropocene, global change and sleeping giants: where on Earth are we going?
No full textThe "climate problem" has come to the fore in public policy
debates over the last year or so. The continuing high
temperatures, the spate of intense tropical cyclones and
deepening droughts in some parts of the world have
focused attention on the issue of defining "dangerous climate
change" [1]. This is often conceptualised as an upper
limit to the rise in global mean temperature, for example,
2°C above pre-industrial levels, which in turn leads to a
back calculation of the permissible concentration of CO2
in the atmosphere and then to the trajectories of the corresponding
maximum anthropogenic carbon emissions