The primordial deuterium abundance at z = 2.504 from a high signal-to-noise spectrum of Q1009+2956

The spectrum of the $z_{\rm em} = 2.63$ quasar Q1009+2956 has been observed extensively on the Keck telescope. The Lyman limit absorption system $z_{\rm abs} = 2.504$ was previously used to measure D/H by Burles & Tytler using a spectrum with signal to noise approximately 60 per pixel in the continuum near Ly {\alpha} at $z_{\rm abs} = 2.504$. The larger dataset now available combines to form an exceptionally high signal to noise spectrum, around 147 per pixel. Several heavy element absorption lines are detected in this LLS, providing strong constraints on the kinematic structure. We explore a suite of absorption system models and find that the deuterium feature is likely to be contaminated by weak interloping Ly {\alpha} absorption from a low column density H I cloud, reducing the expected D/H precision. We find D/H = $2.48^{+0.41}_{-0.35}\times10^{-5}$ for this system. Combining this new measurement with others from the literature and applying the method of Least Trimmed Squares to a statistical sample of 15 D/H measurements results in a "reliable" sample of 13 values. This sample yields a primordial deuterium abundance of (D/H)$_{\rm p} = (2.545 \pm 0.025)\times10^{-5}$. The corresponding mean baryonic density of the Universe is $\Omega_{\rm b}h^2 = 0.02174\pm0.00025$. The quasar absorption data is of the same precision as, and marginally inconsistent with, the 2015 CMB Planck (TT+lowP+lensing) measurement, $\Omega_{\rm b}h^2 = 0.02226\pm0.00023$. Further quasar and more precise nuclear data are required to establish whether this is a random fluctuation.Comment: accepted by MNRAS, 18 pages, 12 figures, 6 table

Thissavros Hydropower Plant Managing Geotechnical Problems in the Construction

The Thissavros hydropower and pumped storage project on the Nestos river in northern Greece involved construction of a 172 m high rockfill dam and an underground power house with 300 MW installed capacity. Bedrock at the site consists of gneiss with complex geological structure and complicated hydrogeological conditions. On the right abutment, the dam partially rests on a large landslide and the toe of another large landslide extends into the plunge pool from the left bank. Initial excavations activated the dormant slides. Unloading, buttressing and drainage successfully stabilized the landslides. Core material for the dam is a silty sand and required special precautions in design and construction. Starting with an extremely rapid reservoir filling the dam has performed highly satisfactorily. The power house had to be excavated in a relatively unfavorable geological orientation but application of structural discontinuity analysis avoided wedge failures

Primordial deuterium abundance at z=2.504 towards Q1009+2956

The z_abs = 2.504 Lyman Limit absorption system (LLS) towards Q1009+2956 has previously been used to estimate the primordial deuterium abundance. Since the initial measurement by Burles & Tytler, this quasar has been observed extensively with the Keck telescope, providing a substantial increase in signal-to-noise (from 60 to 147 at continuum level of Ly-alpha at z_abs=2.504). We explore a set of different models for the absorption system and find that the deuterium feature is contaminated by Ly-alpha absorption from a low column density H I cloud. This significantly limits precision to which one can estimate the D/H ratio in this LLS. Our final result for this system D/H =2.48^{+0.41}_{-0.35}*10^{-5} has the same relative uncertainty of 17% as the previous estimate by Burles & Tytler despite the far higher signal-to-noise of our dataset. A weighted mean of 13 D/H measurements available in the literature (including our result) gives the primordial deuterium abundance of (D/H)_p = (2.545 +/- 0.025)*10^{-5} and the corresponding baryon density of the Universe of Omega_b h^2 = 0.02174 +/- 0.00025 marginally inconsistent with the 2015 Planck CMB data.Comment: 7 pages, 3 figures, conference proceedings from PhysicA.SPb 201

Digging Deeper: Bioturbation increases the preserved sulfur isotope fractionation

Bioturbation enhances mixing between the seafloor and overlying ocean due to changes the redox state of the sediment and influences the biogeochemical cycling of redox-sensitive elements such as sulfur. Before the widespread appearance of burrowing fauna over the Proterozoic-Phanerozoic transition, marine sediments were largely undisturbed and transport of material across the sediment-water interface was diffusion-dominated. Through both a microcosm experiment and numerical model, we show that the effect of bioturbation on marine sediments is to enhance the drawdown of sulfate from the water column into the sediment and thus “open-up” the sedimentary system. The key finding is that bioturbation increases the difference between the isotopic signature of seawater sulfate and pore water sulfide, the latter of which is preserved in sedimentary sulfide minerals. Our study empirically demonstrates a long-held assumption and helps identify the isotopic impact of bioturbation in the geological record and its environmental effects in modern marine systems

The MESSy aerosol submodel MADE3 (v2.0b): description and a box model test

We introduce MADE3 (Modal Aerosol Dynamics model for Europe, adapted for global applications, 3rd generation; version: MADE3v2.0b), an aerosol dynamics submodel for application within the MESSy framework (Modular Earth Submodel System). MADE3 builds on the predecessor aerosol submodels MADE and MADE-in. Its main new features are the explicit representation of coarse mode particle interactions both with other particles and with condensable gases, and the inclusion of hydrochloric acid (HCl) / chloride (Cl) partitioning between the gas and condensed phases. The aerosol size distribution is represented in the new submodel as a superposition of nine lognormal modes: one for fully soluble particles, one for insoluble particles, and one for mixed particles in each of three size ranges (Aitken, accumulation, and coarse mode size ranges). <br><br> In order to assess the performance of MADE3 we compare it to its predecessor MADE and to the much more detailed particle-resolved aerosol model PartMC-MOSAIC in a box model simulation of an idealised marine boundary layer test case. MADE3 and MADE results are very similar, except in the coarse mode, where the aerosol is dominated by sea spray particles. Cl is reduced in MADE3 with respect to MADE due to the HCl / Cl partitioning that leads to Cl removal from the sea spray aerosol in our test case. Additionally, the aerosol nitrate concentration is higher in MADE3 due to the condensation of nitric acid on coarse mode particles. MADE3 and PartMC-MOSAIC show substantial differences in the fine particle size distributions (sizes &lesssim; 2 μm) that could be relevant when simulating climate effects on a global scale. Nevertheless, the agreement between MADE3 and PartMC-MOSAIC is very good when it comes to coarse particle size distributions (sizes &gtrsim; 2 μm), and also in terms of aerosol composition. Considering these results and the well-established ability of MADE in reproducing observed aerosol loadings and composition, MADE3 seems suitable for application within a global model

Investigating the enabling factors influencing occupational therapists’ adoption of assisted living technology

Introduction Research into technology adoption has focused on older adults’ motivations, with less exploration of the perspective of healthcare providers, including occupational therapists, who are often described as the gatekeepers to assisted living technology. Method This qualitative study utilized semi-structured interviews and focus groups with 20 occupational therapists in England and Scotland. The goal was to identify those enabling factors necessary for occupational therapists to adopt assisted living technology. Results Five themes emerged regarding the enablers needed to support the adoption of assisted living technology by occupational therapists, including: (1) a positive client–therapist relationship; (2) affordability; (3) time; (4) increased awareness, education, and training; and (5) usability features of the assisted living technology. Conclusion With an aging population and the increasing role that technology is playing globally in older adults’ lives, it has never been more important for occupational therapists to harness the potential of new, developing, and existing technologies to support people to live and age as well as possible. To accomplish this, however, requires that occupational therapists are equipped with the time, training, and education necessary to offer their clients assisted living technologies that are client-centered, usable, and affordabl

Continuous melting of compact polymers

The competition between chain entropy and bending rigidity in compact polymers can be addressed within a lattice model introduced by P.J. Flory in 1956. It exhibits a transition between an entropy dominated disordered phase and an energetically favored crystalline phase. The nature of this order-disorder transition has been debated ever since the introduction of the model. Here we present exact results for the Flory model in two dimensions relevant for polymers on surfaces, such as DNA adsorbed on a lipid bilayer. We predict a continuous melting transition, and compute exact values of critical exponents at the transition point.Comment: 5 pages, 1 figur

Global atmospheric budget of acetaldehyde: 3-D model analysis and constraints from in-situ and satellite observations

We construct a global atmospheric budget for acetaldehyde using a 3-D model of atmospheric chemistry (GEOS-Chem), and use an ensemble of observations to evaluate present understanding of its sources and sinks. Hydrocarbon oxidation provides the largest acetaldehyde source in the model (128 Tg a&lt;sup&gt;&amp;minus;1&lt;/sup&gt;, a factor of 4 greater than the previous estimate), with alkanes, alkenes, and ethanol the main precursors. There is also a minor source from isoprene oxidation. We use an updated chemical mechanism for GEOS-Chem, and photochemical acetaldehyde yields are consistent with the Master Chemical Mechanism. We present a new approach to quantifying the acetaldehyde air-sea flux based on the global distribution of light absorption due to colored dissolved organic matter (CDOM) derived from satellite ocean color observations. The resulting net ocean emission is 57 Tg a&lt;sup&gt;&amp;minus;1&lt;/sup&gt;, the second largest global source of acetaldehyde. A key uncertainty is the acetaldehyde turnover time in the ocean mixed layer, with quantitative model evaluation over the ocean complicated by known measurement artifacts in clean air. Simulated concentrations in surface air over the ocean generally agree well with aircraft measurements, though the model tends to overestimate the vertical gradient. PAN:NO&lt;sub&gt;x&lt;/sub&gt; ratios are well-simulated in the marine boundary layer, providing some support for the modeled ocean source. We introduce the Model of Emissions of Gases and Aerosols from Nature (MEGANv2.1) for acetaldehyde and ethanol and use it to quantify their net flux from living terrestrial plants. Including emissions from decaying plants the total direct acetaldehyde source from the land biosphere is 23 Tg a&lt;sup&gt;&amp;minus;1&lt;/sup&gt;. Other terrestrial acetaldehyde sources include biomass burning (3 Tg a&lt;sup&gt;&amp;minus;1&lt;/sup&gt;) and anthropogenic emissions (2 Tg a&lt;sup&gt;&amp;minus;1&lt;/sup&gt;). Simulated concentrations in the continental boundary layer are generally unbiased and capture the spatial gradients seen in observations over North America, Europe, and tropical South America. However, the model underestimates acetaldehyde levels in urban outflow, suggesting a missing source in polluted air. Ubiquitous high measured concentrations in the free troposphere are not captured by the model, and based on present understanding are not consistent with concurrent measurements of PAN and NO&lt;sub&gt;x&lt;/sub&gt;: we find no compelling evidence for a widespread missing acetaldehyde source in the free troposphere. We estimate the current US source of ethanol and acetaldehyde (primary + secondary) at 1.3 Tg a&lt;sup&gt;&amp;minus;1&lt;/sup&gt; and 7.8 Tg a&lt;sup&gt;&amp;minus;1&lt;/sup&gt;, approximately 60{%} and 480% of the corresponding increases expected for a national transition from gasoline to ethanol fuel