241 research outputs found
Disentangling superconducting and magnetic orders in NaFe_1-xNi_xAs using muon spin rotation
Muon spin rotation and relaxation studies have been performed on a "111"
family of iron-based superconductors NaFe_1-xNi_xAs. Static magnetic order was
characterized by obtaining the temperature and doping dependences of the local
ordered magnetic moment size and the volume fraction of the magnetically
ordered regions. For x = 0 and 0.4 %, a transition to a nearly-homogeneous long
range magnetically ordered state is observed, while for higher x than 0.4 %
magnetic order becomes more disordered and is completely suppressed for x = 1.5
%. The magnetic volume fraction continuously decreases with increasing x. The
combination of magnetic and superconducting volumes implies that a
spatially-overlapping coexistence of magnetism and superconductivity spans a
large region of the T-x phase diagram for NaFe_1-xNi_xAs . A strong reduction
of both the ordered moment size and the volume fraction is observed below the
superconducting T_C for x = 0.6, 1.0, and 1.3 %, in contrast to other iron
pnictides in which one of these two parameters exhibits a reduction below TC,
but not both. The suppression of magnetic order is further enhanced with
increased Ni doping, leading to a reentrant non-magnetic state below T_C for x
= 1.3 %. The reentrant behavior indicates an interplay between
antiferromagnetism and superconductivity involving competition for the same
electrons. These observations are consistent with the sign-changing s-wave
superconducting state, which is expected to appear on the verge of microscopic
coexistence and phase separation with magnetism. We also present a universal
linear relationship between the local ordered moment size and the
antiferromagnetic ordering temperature TN across a variety of iron-based
superconductors. We argue that this linear relationship is consistent with an
itinerant-electron approach, in which Fermi surface nesting drives
antiferromagnetic ordering.Comment: 20 pages, 14 figures, Correspondence should be addressed to Prof.
Yasutomo Uemura: [email protected]
The Atacama Cosmology Telescope: A Measurement of the Thermal Sunyaev-Zel'dovich Effect Using the Skewness of the CMB Temperature Distribution
We present a detection of the unnormalized skewness induced by the
thermal Sunyaev-Zel'dovich (tSZ) effect in filtered Atacama Cosmology Telescope
(ACT) 148 GHz cosmic microwave background temperature maps. Contamination due
to infrared and radio sources is minimized by template subtraction of resolved
sources and by constructing a mask using outlying values in the 218 GHz
(tSZ-null) ACT maps. We measure = -31 +- 6 \mu K^3 (measurement error
only) or +- 14 \mu K^3 (including cosmic variance error) in the filtered ACT
data, a 5-sigma detection. We show that the skewness is a sensitive probe of
sigma_8, and use analytic calculations and tSZ simulations to obtain
cosmological constraints from this measurement. From this signal alone we infer
a value of sigma_8= 0.79 +0.03 -0.03 (68 % C.L.) +0.06 -0.06 (95 % C.L.). Our
results demonstrate that measurements of non-Gaussianity can be a useful method
for characterizing the tSZ effect and extracting the underlying cosmological
information.Comment: 9 pages, 5 figures. Replaced with version accepted by Phys. Rev. D,
with improvements to the likelihood function and the IR source treatment;
only minor changes in the result
Microbial ligand costimulation drives neutrophilic steroid-refractory asthma
Funding: The authors thank the Wellcome Trust (102705) and the Universities of Aberdeen and Cape Town for funding. This research was also supported, in part, by National Institutes of Health GM53522 and GM083016 to DLW. KF and BNL are funded by the Fonds Wetenschappelijk Onderzoek, BNL is the recipient of an European Research Commission consolidator grant and participates in the European Union FP7 programs EUBIOPRED and MedALL. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD
The Atacama Cosmology Telescope: Data Characterization and Map Making
We present a description of the data reduction and mapmaking pipeline used
for the 2008 observing season of the Atacama Cosmology Telescope (ACT). The
data presented here at 148 GHz represent 12% of the 90 TB collected by ACT from
2007 to 2010. In 2008 we observed for 136 days, producing a total of 1423 hours
of data (11 TB for the 148 GHz band only), with a daily average of 10.5 hours
of observation. From these, 1085 hours were devoted to a 850 deg^2 stripe (11.2
hours by 9.1 deg) centered on a declination of -52.7 deg, while 175 hours were
devoted to a 280 deg^2 stripe (4.5 hours by 4.8 deg) centered at the celestial
equator. We discuss sources of statistical and systematic noise, calibration,
telescope pointing, and data selection. Out of 1260 survey hours and 1024
detectors per array, 816 hours and 593 effective detectors remain after data
selection for this frequency band, yielding a 38% survey efficiency. The total
sensitivity in 2008, determined from the noise level between 5 Hz and 20 Hz in
the time-ordered data stream (TOD), is 32 micro-Kelvin sqrt{s} in CMB units.
Atmospheric brightness fluctuations constitute the main contaminant in the data
and dominate the detector noise covariance at low frequencies in the TOD. The
maps were made by solving the least-squares problem using the Preconditioned
Conjugate Gradient method, incorporating the details of the detector and noise
correlations. Cross-correlation with WMAP sky maps, as well as analysis from
simulations, reveal that our maps are unbiased at multipoles ell > 300. This
paper accompanies the public release of the 148 GHz southern stripe maps from
2008. The techniques described here will be applied to future maps and data
releases.Comment: 20 pages, 18 figures, 6 tables, an ACT Collaboration pape
The Atacama Cosmology Telescope: Cosmological parameters from three seasons of data
We present constraints on cosmological and astrophysical parameters from
high-resolution microwave background maps at 148 GHz and 218 GHz made by the
Atacama Cosmology Telescope (ACT) in three seasons of observations from 2008 to
2010. A model of primary cosmological and secondary foreground parameters is
fit to the map power spectra and lensing deflection power spectrum, including
contributions from both the thermal Sunyaev-Zeldovich (tSZ) effect and the
kinematic Sunyaev-Zeldovich (kSZ) effect, Poisson and correlated anisotropy
from unresolved infrared sources, radio sources, and the correlation between
the tSZ effect and infrared sources. The power ell^2 C_ell/2pi of the thermal
SZ power spectrum at 148 GHz is measured to be 3.4 +\- 1.4 muK^2 at ell=3000,
while the corresponding amplitude of the kinematic SZ power spectrum has a 95%
confidence level upper limit of 8.6 muK^2. Combining ACT power spectra with the
WMAP 7-year temperature and polarization power spectra, we find excellent
consistency with the LCDM model. We constrain the number of effective
relativistic degrees of freedom in the early universe to be Neff=2.79 +\- 0.56,
in agreement with the canonical value of Neff=3.046 for three massless
neutrinos. We constrain the sum of the neutrino masses to be Sigma m_nu < 0.39
eV at 95% confidence when combining ACT and WMAP 7-year data with BAO and
Hubble constant measurements. We constrain the amount of primordial helium to
be Yp = 0.225 +\- 0.034, and measure no variation in the fine structure
constant alpha since recombination, with alpha/alpha0 = 1.004 +/- 0.005. We
also find no evidence for any running of the scalar spectral index, dns/dlnk =
-0.004 +\- 0.012.Comment: 26 pages, 22 figures. This paper is a companion to Das et al. (2013)
and Dunkley et al. (2013). Matches published JCAP versio
Enhancing carbon sequestration in soil with coal combustion products: a technology for minimising carbon footprints in coal-power generation and agriculture
Coal-fired power generation and agriculture account for more than half of global greenhouse gas emissions, but the coal fly ash (CFA) produced in the former can be a resource for reducing emissions from agriculture to minimise environmental footprints in both industries. Our aim in this study was to test how acidic and alkaline CFA addition could minimise loss of C and N from acidic soil, with or without added manure. We determined composition and structural characteristics of acidic and alkaline CFA for their capacity to adsorb organic carbon, but observed poor adsorption because of low concentrations of cenospheres and unburnt carbon as the primary absorbents in the ash. Addition of CFA had no impact on the loss of carbon or nitrogen from unmanured soil in which concentrations of these nutrients were low. Loss of carbon from manured soil was reduced by 36% with alkaline ashes and by 3-fold with acidic ashes; while loss of N was 30–50% lower with acidic ashes, but 28% higher with alkaline ashes, compared with no ash treatment. The increases in C sparing with CFA addition were achieved not by direct C absorption but by restraining microbial population and respiration, and potentially emissions. Alkaline CFA increased soil pH and if used to substitute just 10% of lime for ameliorating soil acidity would reduce CO2 emission associated with the mining of the lime and its eventual dissolution in soil by ~ 2.66 Tg or 2.8% of Australia’s annual agricultural emissions. High concentrations of oxides of phosphorus, silicon, titanium and clay particles in acidic ashes, and oxides of cations in alkaline ashes, were associated with potential for promoting C storage and acidity amelioration in soil
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