3,024 research outputs found
Upper Limits on the 21 cm Power Spectrum at z = 5.9 from Quasar Absorption Line Spectroscopy
We present upper limits on the 21 cm power spectrum at calculated
from the model-independent limit on the neutral fraction of the intergalactic
medium of derived from dark
pixel statistics of quasar absorption spectra. Using 21CMMC, a Markov chain
Monte Carlo Epoch of Reionization analysis code, we explore the probability
distribution of 21 cm power spectra consistent with this constraint on the
neutral fraction. We present 99 per cent confidence upper limits of
to over a range of from 0.5 to $2.0\
h{\rm Mpc}^{-1}kz=5.9$ in excess of this value is highly suggestive of residual foreground
contamination or other systematic errors affecting the analysis.Comment: 5 pages, 1 figure, accepted to MNRAS letter
Constraints on the temperature of the intergalactic medium at z=8.4 with 21-cm observations
We compute robust lower limits on the spin temperature, , of the
intergalactic medium (IGM), implied by the upper limits on the 21-cm
power spectrum recently measured by PAPER-64. Unlike previous studies which
used a single epoch of reionization (EoR) model, our approach samples a large
parameter space of EoR models: the dominant uncertainty when estimating
constraints on . Allowing to be a free parameter and
marginalizing over EoR parameters in our Markov Chain Monte Carlo code 21CMMC,
we infer (corresponding approximately to ) for
a mean IGM neutral fraction of . We
further improve on these limits by folding-in additional EoR constraints based
on: (i) the dark fraction in QSO spectra, which implies a strict upper limit of
; and (ii) the
electron scattering optical depth,
measured by the Planck satellite. By restricting the allowed EoR models, these
additional observations tighten the approximate lower limits on the
spin temperature to K. Thus, even such preliminary 21-cm
observations begin to rule out extreme scenarios such as `cold reionization',
implying at least some prior heating of the IGM. The analysis framework
developed here can be applied to upcoming 21-cm observations, thereby providing
unique insights into the sources which heated and subsequently reionized the
very early Universe.Comment: 7 pages, 1 figure, accepted to MNRAS (matches online version
Volume and surface propellant heating in an electrothermal radio-frequency plasma micro-thruster
The temporal evolution of neutral gas temperature over the first 5 min of operation for an electrothermal radio-frequency micro-thruster with nitrogen (N2) propellant was measured using rovibrational band matching of the second positive N2 system. Three distinct periods of gas heating were identified with time constants of τ 1 = 8 × 10⁻⁵ s, τ 2 = 8 s, and τ 3 = 100 s. The fast heating (τ 1) is attributed to volumetric heating processes within the discharge driven by ion-neutral collisions. The slow heating (τ 3) is from ion neutralization and vibrational de-excitation on the walls creating wall heating. The intermediate heating mechanism (τ 2) is yet to be fully identified although some theories are suggested.This research was partially funded by the Australian
Space Research Program (APT project) and the Australian
Research Council Discovery Project (No. DP140100571)
Isolation of 39 polymorphic microsatellite loci and the development of a fluorescently labelled marker set for the Eurasian badger
We have isolated 78 microsatellite loci from the Eurasian badger (Meles meles). Of the 52 loci characterized, 39 were found to be polymorphic. A fluorescently labelled primer set was developed to enable individual-specific 17-locus genotypes to be obtained efficiently
ASD and PDA closure with CeraTM and CeraFlexTM devices
Introduction and aim: Percutaneous closure of congenital cardiac defects is common practice. The aim of the study was to describe our experience in closing PDAs, PFOs and an ASD using the new CeraTM and CeraFlexTM devices. Methods: Twenty patients were included in this retrospectivereview. All patients underwent device closure with the Cera TM and CeraFlexTM devices. Results: All attempts at device closure were successful (n=20). Indications included PDA (n=16), ASD (n=1) and PFO (n=3). Median age at procedure was: PDA 1y 10mo (4mo - 10y 4mo), ASD 27y and PFO 50y 9mo (38y - 70y). Median weight at procedure was: PDA 10.5kg (4.9kg - 70kg), ASD 56kg and PFO 82.5kg (80kg - 113kg). Periprocedural complications consisted of embolisation of 2 PDA devices, which could be repositioned. Conclusion: The CeraTM and CeraFlexTM devices are effective for closure of PDAs, ASDs and PFOs
Stenting the arterial duct: Practical aspects and review of outcomes
Cyanotic congenital heart lesions with duct-dependent pulmonary blood fl ow often require early intervention. Surgical palliation remains the treatment of choice, but is associated with substantial morbidity and mortality. Ductal stent implantation is becoming a recognised alternative to maintain pulmonary blood fl ow. Results of ductal stenting have improved and outcomes are good. We discuss the outcomes of published data and the practical aspects of ductal stenting
Exchange anisotropy pinning of a standing spin wave mode
Standing spin waves in a thin film are used as sensitive probes of interface
pinning induced by an antiferromagnet through exchange anisotropy. Using
coplanar waveguide ferromagnetic resonance, pinning of the lowest energy spin
wave thickness mode in Ni(80)Fe(20)/Ir(25)Mn(75) exchange biased bilayers was
studied for a range of IrMn thicknesses. We show that pinning of the standing
mode can be used to amplify, relative to the fundamental resonance, frequency
shifts associated with exchange bias. The shifts provide a unique `fingerprint'
of the exchange bias and can be interpreted in terms of an effective
ferromagnetic film thickness and ferromagnet/antiferromagnet interface
anisotropy. Thermal effects are studied for ultra-thin antiferromagnetic
Ir(25)Mn(75) thicknesses, and the onset of bias is correlated with changes in
the pinning fields. The pinning strength magnitude is found to grow with
cooling of the sample, while the effective ferromagnetic film thickness
simultaneously decreases. These results suggest that exchange bias involves
some deformation of magnetic order in the interface region.Comment: 7 pages, 7 figure
Direct measurement of neutral gas heating in a radio-frequency electrothermal plasma micro-thruster
Direct measurements and modelling of neutral gas heating in a radio-frequency (13.56 MHz)
electrothermal collisional plasma micro-thruster have been performed using rovibrational band
matching of the second positive system of molecular nitrogen (N2) for operating pressures of
4.5 Torr down to 0.5 Torr. The temperature measured with decreasing pressure for 10 W power
input ranged from 395 K to 530 K in pure N2 and from 834 K to 1090 K in argon with 1% N2. A
simple analytical model was developed which describes the difference in temperatures between the
argon and nitrogen discharges.Aspects of this research made use of software developed
by the Inversion Laboratory (ilab). Ilab is part of the
Auscope AGOS project—an initiative of the Australian
Government funded through the Education Investment Fund
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