636 research outputs found
The Keck+Magellan Survey for Lyman Limit Absorption I: The Frequency Distribution of Super Lyman Limit Systems
We present the results of a survey for super Lyman limit systems (SLLS;
defined to be absorbers with 19.0 <= log(NHI) <= 20.3 cm^-2) from a large
sample of high resolution spectra acquired using the Keck and Magellan
telescopes. Specifically, we present 47 new SLLS from 113 QSO sightlines. We
focus on the neutral hydrogen frequency distribution f(N,X) of the SLLS and its
moments, and compare these results with the Lyman-alpha forest and the damped
Lyman alpha systems (DLA; absorbers with log(NHI) >= 20.3 cm^-2). We find that
that f(N,X) of the SLLS can be reasonably described with a power-law of index
alpha = -1.43^{+0.15}_{-0.16} or alpha = -1.19^{+0.20}_{-0.21} depending on
whether we set the lower N(HI) bound for the analysis at 10^{19.0} cm^-2 or
10^{19.3}$ cm^-2, respectively. The results indicate a flattening in the slope
of f(N,X) between the SLLS and DLA. We find little evidence for redshift
evolution in the shape of f(N,X) for the SLLS over the redshift range of the
sample 1.68 < z < 4.47 and only tentative evidence for evolution in the zeroth
moment of f(N,X), the line density l_lls(X). We introduce the observable
distribution function O(N,X) and its moment, which elucidates comparisons of HI
absorbers from the Lyman-alpha through to the DLA. We find that a simple three
parameter function can fit O(N,X) over the range 17.0 <= log(NHI) <=22.0. We
use these results to predict that f(N,X) must show two additional inflections
below the SLLS regime to match the observed f(N,X) distribution of the
Lyman-alpha forest. Finally, we demonstrate that SLLS contribute a minor
fraction (~15%) of the universe's hydrogen atoms and, therefore, an even small
fraction of the mass in predominantly neutral gas.Comment: 15 pages, 10 figures, accepted to the Astrophysical Journal. Revision
includes updated reference
PND99 Comparison of Patients With Relapsing Remitting Multiple Sclerosis (Rrms) Treated With Disease Modifying Treatments (Dmt) In Europe (Eu) And The United States (Us)
Deuterium at high-redshift: Primordial abundance in the zabs = 2.621 damped Ly-alpha system towards CTQ247
The detection of neutral deuterium in the low-metallicity damped
Lyman-{\alpha} system at zabs = 2.621 towards the quasar CTQ247 is reported.
Using a high signal-to-noise and high spectral resolution (R = 60000) spectrum
from the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph, we
precisely measure the deuterium-to-oxygen ratio log N(DI)/N(OI) = 0.74+/-0.04,
as well as the overall oxygen abundance, log N(OI)/N(HI)=-5.29+/-0.10 (or
equivalently [O/H]=-1.99+/-0.10 with respect to the solar value). Assuming
uniform metallicity throughout the system, our measurement translates to (D/H)
= (2.8+0.8 -0.6)x10^-5. This ratio is consistent within errors (<0.4sigma) with
the primordial ratio, (D/H)p = (2.59+/-0.15)x10^-5, predicted by standard
Big-Bang Nucleosynthesis using the WMAP7 value of the cosmological density of
baryons (100 Omega_b h^2 = 2.249+/-0.056). The DI absorption lines are observed
to be broader than the OI absorption lines. From a consistent fit of the
profiles we derive the turbulent broadening to be 5.2 km/s and the temperature
of the gas to be T = 8800+/-1500 K, corresponding to a warm neutral medium.Comment: Accepted for publication in A&A Letter
The Deuterium to Hydrogen Abundance Ratio Towards a Fourth QSO: HS0105+1619
We report the measurement of the primordial D/H abundance ratio towards QSO
\object. The column density of the hydrogen in the Lyman limit
system is high, \lnhi \cmm, allowing for the deuterium to
be seen in 5 Lyman series transitions. The measured value of the D/H ratio
towards QSO \object is found to be D/H. The
metallicity of the system showing D/H is found to be solar,
indicating that the measured D/H is the primordial D/H within the measurement
errors. The gas which shows D/H is neutral, unlike previous D/H systems which
were more highly ionized. Thus, the determination of the D/H ratio becomes more
secure since we are measuring it in different astrophysical environments, but
the error is larger because we now see more dispersion between measurements.
Combined with prior measurements of D/H, the best D/H ratio is now D/H, which is 10% lower than the previous value. The new
values for the baryon to photon ratio, and baryonic matter density derived from
D/H are and \ob
respectively.Comment: Minor text and reference changes. To appear in the May 10, 2001 issue
of the Astrophysical Journa
Script development as a ‘wicked problem’
© 2018 Intellect Ltd Article. Both a process and a set of products, influenced by policy as well as people, and incorporating objective agendas at the same time as subjective experiences, script development is a core practice within the screen industry –yet one that is hard to pin down and, to some extent, define. From an academic research perspective, we might say that script development is a ‘wicked problem’ precisely because of these complex and often contradictory aspects. Following on from a recent Journal of Screenwriting special issue on script development (2017, vol. 8:3), and in particular an article therein dedicated to reviewing the literature and ‘defining the field’, an expanded team of researchers follow up on those ideas and insights. In this article, then, we attempt to theorize script development as a ‘wicked problem’ that spans a range of themes and disciplines. As a ‘wicked’ team of authors, our expertise encompasses screenwriting theory, screenwriting practice, film and television studies, cultural policy, ethnography, gender studies and comedy. By drawing on these critical domains and creative practices, we present a series of interconnected themes that we hope not only suggests the potential for script development as a rich and exciting scholarly pursuit, but that also inspires and encourages other researchers to join forces in an attempt to solve the script development ‘puzzle’
Early-universe constraints on a time-varying fine structure constant
Higher-dimensional theories have the remarkable feature of predicting a time
(and hence redshift) dependence of the `fundamental' four dimensional constants
on cosmological timescales. In this paper we update the bounds on a possible
variation of the fine structure constant alpha at the time of BBN (z =10^10)
and CMB (z=10^3). Using the recently-released high-resolution CMB anisotropy
data and the latest estimates of primordial abundances of 4He and D, we do not
find evidence for a varying alpha at more than one-sigma level at either epoch.Comment: 5 pages, 1 figure, minor misprints corrected, references added. The
analysis has been updated using new BOOMERanG and DASI data on CMB anisotrop
Constraining The Universal Lepton Asymmetry
The relic cosmic background neutrinos accompanying the cosmic microwave
background (CMB) photons may hide a universal lepton asymmetry orders of
magnitude larger than the universal baryon asymmetry. At present, the only
direct way to probe such an asymmetry is through its effect on the abundances
of the light elements produced during primordial nucleosynthesis. The relic
light element abundances also depend on the baryon asymmetry, parameterized by
the baryon density parameter (eta_B = n_B/n_gamma = 10^(-10)*eta_10), and on
the early-universe expansion rate, parameterized by the expansion rate factor
(S = H'/H) or, equivalently by the effective number of neutrinos (N_nu = 3 +
43(S^2 - 1)/7). We use data from the CMB (and Large Scale Structure: LSS) along
with the observationally-inferred relic abundances of deuterium and helium-4 to
provide new bounds on the universal lepton asymmetry, finding for eta_L, the
analog of eta_B, 0.072 +/- 0.053 if it is assumed that N_nu = 3 and, 0.115 +/-
0.095 along with N_nu = 3.3^{+0.7}_{-0.6}, if N_nu is free to vary
Precision Primordial He Measurement with CMB Experiments
Big bang nucleosynthesis (BBN) and the cosmic microwave background (CMB) are
two major pillars of cosmology. Standard BBN accurately predicts the primordial
light element abundances (He, D, He and Li), depending on one
parameter, the baryon density. Light element observations are used as a
baryometers. The CMB anisotropies also contain information about the content of
the universe which allows an important consistency check on the Big Bang model.
In addition CMB observations now have sufficient accuracy to not only determine
the total baryon density, but also resolve its principal constituents, H and
He. We present a global analysis of all recent CMB data, with special
emphasis on the concordance with BBN theory and light element observations. We
find and
(fraction of baryon mass as He) using CMB data alone, in agreement with
He abundance observations. With this concordance established we show that
the inclusion of BBN theory priors significantly reduces the volume of
parameter space. In this case, we find
and . We also find that the inclusion of deuterium
abundance observations reduces the and ranges by a factor
of 2. Further light element observations and CMB anisotropy experiments
will refine this concordance and sharpen BBN and the CMB as tools for precision
cosmology.Comment: 7 pages, 3 color figures made minor changes to bring inline with
journal versio
The primordial Helium-4 abundance determination: systematic effects
By extrapolating to O/H = N/H = 0 the empirical correlations Y-O/H and Y-N/H
defined by a relatively large sample of ~ 45 Blue Compact Dwarfs (BCDs), we
have obtained a primordial 4Helium mass fraction Yp= 0.2443+/-0.0015 with dY/dZ
= 2.4+/-1.0. This result is in excellent agreement with the average Yp=
0.2452+/-0.0015 determined in the two most metal-deficient BCDs known, I Zw 18
(Zsun/50) and SBS 0335-052 (Zsun/41), where the correction for He production is
smallest. The quoted error (1sigma) of < 1% is statistical and does not include
systematic effects. We examine various systematic effects including collisional
excitation of Hydrogen lines, ionization structure and temperature fluctuation
effects, and underlying stellar HeI absorption, and conclude that combining all
systematic effects, our Yp may be underestimated by ~ 2-4%. Taken at face
value, our Yp implies a baryon-to-photon number ratio eta = 4.7x10^-10 and a
baryon mass fraction Omega_b h^2_{100} = 0.017+/-0.005 (2sigma), consistent
with the values obtained from deuterium and Cosmic Microwave Background
measurements. Correcting Yp upward by 2-4% would make the agreement even
better.Comment: 12 pages, 5 PS figures, to appear in "Matter in the Universe", ed P.
Jetzer, K. Pretzl and R. von Steiger, Kluwer, Dordrecht (2002
Access to Artemisinin-Based Anti-Malarial Treatment and its Related Factors in Rural Tanzania.
Artemisinin-based combination treatment (ACT) has been widely adopted as one of the main malaria control strategies. However, its promise to save thousands of lives in sub-Saharan Africa depends on how effective the use of ACT is within the routine health system. The INESS platform evaluated effective coverage of ACT in several African countries. Timely access within 24 hours to an authorized ACT outlet is one of the determinants of effective coverage and was assessed for artemether-lumefantrine (Alu), in two district health systems in rural Tanzania. From October 2009 to June 2011we conducted continuous rolling household surveys in the Kilombero-Ulanga and the Rufiji Health and Demographic Surveillance Sites (HDSS). Surveys were linked to the routine HDSS update rounds. Members of randomly pre-selected households that had experienced a fever episode in the previous two weeks were eligible for a structured interview. Data on individual treatment seeking, access to treatment, timing, source of treatment and household costs per episode were collected. Data are presented on timely access from a total of 2,112 interviews in relation to demographics, seasonality, and socio economic status. In Kilombero-Ulanga, 41.8% (CI: 36.6-45.1) and in Rufiji 36.8% (33.7-40.1) of fever cases had access to an authorized ACT provider within 24 hours of fever onset. In neither of the HDSS site was age, sex, socio-economic status or seasonality of malaria found to be significantly correlated with timely access. Timely access to authorized ACT providers is below 50% despite interventions intended to improve access such as social marketing and accreditation of private dispensing outlets. To improve prompt diagnosis and treatment, access remains a major bottle neck and new more innovative interventions are needed to raise effective coverage of malaria treatment in Tanzania
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