3,651 research outputs found
Constraints on the distribution of absorption in the X-ray selected AGN population found in the 13H XMM-Newton/Chandra deep field
We present an analysis of the X-ray properties of sources detected in the 13H
XMM-Newton deep (200ks) field. In order to constrain the absorbed AGN
population, we use extensive Monte Carlo simulations to directly compare the
X-ray colours of observed sources with those predicted by several model
distributions. We have tested the simplest form of the AGN unified scheme,
whereby the intrinsic XLF of absorbed AGN is set to be the same as that of
their unabsorbed brethren, coupled with various model distributions of
absorption. The best fitting of these models sets the fraction of AGN with
absorbing column NH, proportional to (logNH)^8. We have also tested two
extensions to the unified scheme: an evolving absorption scenario, and a
luminosity dependent model distribution. Both of these provide poorer matches
to the observed X-ray colour distributions than the best fitting simple unified
model. We find that a luminosity dependent density evolution XLF reproduces
poorly the 0.5-2 keV source counts seen in the 13H field. Field to field
variations could be the cause of this disparity. Computing the simulated X-ray
colours with a simple absorbed power-law + reflection spectral model is found
to over-predict, by a factor of two, the fraction of hard sources that are
completely absorbed below 0.5 keV, implying that an additional source of
soft-band flux must be present for a number of the absorbed sources. Finally,
we show that around 40% of the 13H sample are expected to be AGN with NH>10^22
cm^-2.Comment: 13 pages, 9 figures, Accepted for publication in MNRA
What Have We Learned from Policy Transfer Research? Dolowitz and Marsh Revisited
Over the last decade, policy transfer has emerged as an important concept within public policy analysis, guiding both theoretical and empirical research spanning many venues and issue areas. Using Dolowitz and Marsh's 1996 stocktake as its starting point, this article reviews what has been learned by whom and for what purpose. It finds that the literature has evolved from its rather narrow, state-centred roots to cover many more actors and venues. While policy transfer still represents a niche topic for some researchers, an increasing number have successfully assimilated it into wider debates on topics such as globalisation, Europeanisation and policy innovation. This article assesses the concept's position in the overall ‘tool-kit’ of policy analysis, examines some possible future directions and reflects on their associated risks and opportunities
The MAP Satellite Feed Horns
We present the design, manufacturing methods, and characterization of 20
microwave feed horns currently in use on the Microwave Anisotropy Probe (MAP)
satellite. The nature of the cosmic microwave background (CMB) anisotropy
requires a detailed understanding of the properties of every optical component
of a microwave telescope. In particular, the properties of the feeds must be
known so that the forward gain and sidelobe response of the telescope can be
modeled and so that potential systematic effects may be computed. MAP requires
low emissivity, azimuthally symmetric, low-sidelobe feeds in five microwave
bands (K, Ka, Q, V, and W) that fit within a constrained geometry. The beam
pattern of each feed is modeled and compared with measurements; the agreement
is generally excellent to the -60 dB level (80 degrees from the beam peak).
This agreement verifies the beam-predicting software and the manufacturing
process. The feeds also affect the properties and modeling of the microwave
receivers. To this end, we show that the reflection from the feeds is less than
-25 dB over most of each band and that their emissivity is acceptable. The
feeds meet their multiple requirements.Comment: 9 pages with 7 figures, of which 2 are in low-resolution versions;
paper is available with higher quality figures at
http://map.gsfc.nasa.gov/m_mm/tp_links.htm
Effect of hyperon bulk viscosity on neutron-star r-modes
Neutron stars are expected to contain a significant number of hyperons in
addition to protons and neutrons in the highest density portions of their
cores. Following the work of Jones, we calculate the coefficient of bulk
viscosity due to nonleptonic weak interactions involving hyperons in
neutron-star cores, including new relativistic and superfluid effects. We
evaluate the influence of this new bulk viscosity on the gravitational
radiation driven instability in the r-modes. We find that the instability is
completely suppressed in stars with cores cooler than a few times 10^9 K, but
that stars rotating more rapidly than 10-30% of maximum are unstable for
temperatures around 10^10 K. Since neutron-star cores are expected to cool to a
few times 10^9 K within seconds (much shorter than the r-mode instability
growth time) due to direct Urca processes, we conclude that the gravitational
radiation instability will be suppressed in young neutron stars before it can
significantly change the angular momentum of the star.Comment: final PRD version, minor typos etc correcte
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National Diet and Nutrition Survey Rolling programme Years 9 to 11 (2016/2017 to 2018/2019) - A survey carried out on behalf of Public Health England and the Food Standards Agency
The National Diet and Nutrition Survey Rolling Programme (NDNS RP) is a continuous crosssectional survey, designed to assess the diet, nutrient intake and nutritional status of the general population aged 1.5 years and over living in private households in the UK. A representative sample of around 1,000 people (500 adults and 500 children) take part in the
NDNS RP each year.
Fieldwork for Years 9 to 11 of the NDNS RP was carried out between April 2016 and June 2019. The survey comprised an interview, a 4-day estimated diet diary, physical measurements and a blood and urine sample. Results are used by government to monitor progress toward diet
and nutrition objectives of UK Health Departments and to develop policy interventions.
The foods, nutrients and blood and urine measures presented in this report were selected for their nutritional and public health relevance to current dietary concerns in the UK. Results are analysed for 7 age groups: 1.5 to 3 years; 4 to 10 years; 11 to 18 years; 19 to 64 years; 65
years and over; 65 to 74 years and 75 years and over, split by sex in all except the youngest age group.
The report includes:
• descriptive statistics of food consumption, nutrient intake and nutritional status
including proportion of the population meeting government recommendations for
NDNS RP Years 9 to 11 (2016/17 to 2018/19) and comparison with results from years
7&8 (2014/15 to 2015/16).
• trends over time in relation to food consumption, nutrient intakes and nutritional status
in the UK for the first 11 years of the NDNS RP (2008/09 to 2018/19)PHE and Food Standards Agenc
Instrumental and Analytic Methods for Bolometric Polarimetry
We discuss instrumental and analytic methods that have been developed for the
first generation of bolometric cosmic microwave background (CMB) polarimeters.
The design, characterization, and analysis of data obtained using Polarization
Sensitive Bolometers (PSBs) are described in detail. This is followed by a
brief study of the effect of various polarization modulation techniques on the
recovery of sky polarization from scanning polarimeter data. Having been
successfully implemented on the sub-orbital Boomerang experiment, PSBs are
currently operational in two terrestrial CMB polarization experiments (QUaD and
the Robinson Telescope). We investigate two approaches to the analysis of data
from these experiments, using realistic simulations of time ordered data to
illustrate the impact of instrumental effects on the fidelity of the recovered
polarization signal. We find that the analysis of difference time streams takes
full advantage of the high degree of common mode rejection afforded by the PSB
design. In addition to the observational efforts currently underway, this
discussion is directly applicable to the PSBs that constitute the polarized
capability of the Planck HFI instrument.Comment: 23 pages, 11 figures. for submission to A&
Magnetic field decay in neutron stars: from Soft Gamma Repeaters to "weak field magnetars"
The recent discovery of the "weak field, old magnetar", the soft gamma
repeater SGR 0418+5729, whose dipole magnetic field is less than 7.5 \times
10^{12} G, has raised perplexing questions: How can the neutron star produce
SGR-like bursts with such a low magnetic field? What powers the observed X-ray
emission when neither the rotational energy nor the magnetic dipole energy are
sufficient? These observations, that suggest either a much larger energy
reservoir or a much younger true age (or both), have renewed the interest in
the evolutionary sequence of magnetars. We examine, here, a phenomenological
model for the magnetic field decay: B_dip} \propto (B_dip)^{1+a} and compare
its predictions with the observed period, P,the period derivative, \dot{P}, and
the X-ray luminosity, L_X, of magnetar candidates. We find a strong evidence
for a dipole field decay on a timescale of \sim 10^3 yr for the strongest (\sim
10^{15} G) field objects, with a decay index within the range 1 \leq a < 2 and
more likely within 1.5\lesssim a \lesssim 1.8. The decaying field implies a
younger age than what is implied by the spinown age. Surprisingly, even with
the younger age, the energy released in the dipole field decay is insufficient
to power the X-ray emission, suggesting the existence of a stronger internal
field, B_int. Examining several models for the internal magnetic field decay we
find that it must have a very large (> 10^{16} G) initial value. Our findings
suggest two clear distinct evolutionary tracks -- the SGR/AXP branch and the
transient branch, with a possible third branch involving high-field radio
pulsars that age into low luminosity X-ray dim isolated neutron stars.Comment: 47 pages, 11 figures, accepted for publication on MNRAS, in pres
Cosmological CPT Violation and CMB Polarization Measurements
In this paper we study the possibility of testing Charge-Parity-Time Reversal
(CPT) symmetry with cosmic microwave background (CMB) experiments. We consider
two kinds of Chern-Simons (CS) term, electromagnetic CS term and gravitational
CS term, and study their effects on the CMB polarization power spectra in
detail. By combining current CMB polarization measurements, the seven-year
WMAP, BOOMERanG 2003 and BICEP observations, we obtain a tight constraint on
the rotation angle deg (), indicating a
detection of the CPT violation. Here, we particularly take the
systematic errors of CMB measurements into account. After adding the QUaD
polarization data, the constraint becomes deg at 95%
confidence level. When comparing with the effect of electromagnetic CS term,
the gravitational CS term could only generate TB and EB power spectra with much
smaller amplitude. Therefore, the induced parameter can not be
constrained from the current polarization data. Furthermore, we study the
capabilities of future CMB measurements, Planck and CMBPol, on the constraints
of and . We find that the constraint of
can be significantly improved by a factor of 15. Therefore, if this rotation
angle effect can not be taken into account properly, the constraints of
cosmological parameters will be biased obviously. For the gravitational CS
term, the future Planck data still can not constrain very well, if
the primordial tensor perturbations are small, . We need the more
accurate CMBPol experiment to give better constraint on .Comment: 11 pages, 5 figures, 4 tables, Accepted for publication in JCA
Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Angular Power Spectra
We present the temperature and polarization angular power spectra of the
cosmic microwave background (CMB) derived from the first 5 years of WMAP data.
The 5-year temperature (TT) spectrum is cosmic variance limited up to multipole
l=530, and individual l-modes have S/N>1 for l<920. The best fitting
six-parameter LambdaCDM model has a reduced chi^2 for l=33-1000 of
chi^2/nu=1.06, with a probability to exceed of 9.3%. There is now significantly
improved data near the third peak which leads to improved cosmological
constraints. The temperature-polarization correlation (TE) is seen with high
significance. After accounting for foreground emission, the low-l reionization
feature in the EE power spectrum is preferred by \Delta\chi^2=19.6 for optical
depth tau=0.089 by the EE data alone, and is now largely cosmic variance
limited for l=2-6. There is no evidence for cosmic signal in the BB, TB, or EB
spectra after accounting for foreground emission. We find that, when averaged
over l=2-6, l(l+1)C^{BB}_l/2\pi < 0.15 uK^2 (95% CL).Comment: 29 pages, 13 figures, accepted by ApJ
High-Efficiency Resonant RF Spin Rotator with Broad Phase Space Acceptance for Pulsed Polarized Cold Neutron Beams
We have developed a radio-frequency resonant spin rotator to reverse the
neutron polarization in a 9.5 cm x 9.5 cm pulsed cold neutron beam with high
efficiency over a broad cold neutron energy range. The effect of the spin
reversal by the rotator on the neutron beam phase space is compared
qualitatively to RF neutron spin flippers based on adiabatic fast passage. The
spin rotator does not change the kinetic energy of the neutrons and leaves the
neutron beam phase space unchanged to high precision. We discuss the design of
the spin rotator and describe two types of transmission-based neutron spin-flip
efficiency measurements where the neutron beam was both polarized and analyzed
by optically-polarized 3He neutron spin filters. The efficiency of the spin
rotator was measured to be 98.0+/-0.8% on resonance for neutron energies from
3.3 to 18.4 meV over the full phase space of the beam. As an example of the
application of this device to an experiment we describe the integration of the
RF spin rotator into an apparatus to search for the small parity-violating
asymmetry A_gamma in polarized cold neutron capture on para-hydrogen by the
NPDGamma collaboration at LANSCE
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