281 research outputs found
An Electrochemically-mediated Gas Separation Process for Carbon Abatement
This work describes a promising alternative to conventional thermal processes for absorber/desorber processing of for removal of CO[subscript 2] from flue gas streams at fossil fuel fired power plants. Our electrochemically-mediated amine regeneration (EMAR) process offers the advantages of an electrical system coupled with the desirable high output purities typical of amine sorbents that are difficult to achieve with most electric systems such as pressure-swing sorption, membrane separation, and oxy-fuel combustion. Preliminary experimental results are presented that demonstrate the feasibility of using ethylenediamine as the CO[subscript 2] sorbent and copper electro-cycling to isothermally modulate the amine affinity for CO[subscript 2]. Cupric ions entirely deactivate ethylenediamine at a ratio of 2:1 diamine to copper. Open-circuit potential measurements at 50°C indicate the required energy to desorb CO[subscript 2] and regenerate the ethylenediamine is 18 kJ/mole CO[subscript 2] under open-circuit conditions. Kinetic over-potentials are sufficiently low to ensure acceptable energy losses. Lower energies can be achieved by increasing the temperature or by changing the amine.Siemens Corporation (CKI Research Fund)United States. Advanced Research Projects Agency-Energy (Research Grant DE-AR0000083
Post-combustion carbon dioxide capture using electrochemically mediated amine regeneration
Electrochemically mediated amine regeneration is a new post-combustion capture technology with the potential to exploit the excellent removal efficiencies of thermal amine scrubbers while reducing parasitic energy losses and capital costs. The improvements result from the use of an electrochemical stripping cycle, in lieu of the traditional thermal swing, to facilitate CO[subscript 2] desorption and amine regeneration; metal cations generated at an anode react with the amines, displacing the CO[subscript 2], which is then flashed off, and the amines are regenerated by subsequent reduction of the metal cations in a cathode cell. The advantages of such a process include higher CO[subscript 2] desorption pressures, smaller absorbers, and lower energy demands. Several example chemistries using different polyamines and copper are presented. Experimental results indicate an open-circuit efficiency of 54% (15 kJ per mole CO[subscript 2]) is achievable at the tested conditions and models predict that 69% efficiency is possible at higher temperatures and pressures. A bench scale system produced 1.6 mL min[superscript −1] CO[subscript 2] while operating at 0.4 volts and 42% Faradaic efficiency; this corresponds to a work of less than 100 kJ per mole.United States. Advanced Research Projects Agency-Energy (Grant DE-AR0000083
Electrochemically mediated separation for carbon capture
Carbon capture technology has been proposed as an effective approach for the mitigation of anthropogenic CO[subscript 2] emissions. Thermal-swing separation technologies based on wet chemical scrubbing show potential for facilitating CO[subscript 2] capture at industrial-scale carbon emitters; however, the total operational and capital costs resulting from the high energy consumption are prohibitive for their implementation. Electrochemically mediated processes are proposed to be the next generation of CO[subscript 2] separation technology that can enable carbon capture to be a more viable option for carbon mitigation in the near future. This technology utilizes electrochemically active sorbents that undergo significant changes in their molecular affinity for CO[subscript 2] molecules as they progress through an electrochemical cycle. This nearly isothermal separation process consumes electrical energy to facilitate effective CO[subscript 2] capture and regeneration processes under more benign conditions of sorption and desorption than in traditional continuous wet-scrubber operations. This electrically driven separation process has the potential to significantly reduce the difficulty of retrofitting CO[subscript 2] capture units to existing fossil fuel-fired power generators. The ease of installing an electrically driven separation system would also allow its application to other industrial carbon emitters. The design of such a system, however, requires careful consideration since it involves both heterogeneous electrochemical activation/deactivation of sorbents and homogeneous complexation of the activated sorbents with CO[subscript 2] molecules. Optimization of the energy efficiency requires minimizing the irreversibility associated with these processes. In this study, we use a general exergy analysis to evaluate the minimum thermodynamic work based on the system design and the electrochemical parameters of quinodal redox-active molecules. Using this thermodynamic framework, our results suggest that the proposed technology could capture CO[subscript 2] from a dilute post-combustion flue gas and regenerate CO[subscript 2] at 1 bar with high efficiency, if a two-stage design is effectively implemented.Siemens Corporation (Massachusetts Institute of Technology. Center of Knowledge Interchange Project Fund
Computer-controlled apparatus for automated development of continuous flow methods
An automated apparatus to assist in the development of analytical
continuous flow methods is described. The system is capable of
controlling and monitoring a variety of pumps, valves, and
detectors through an IBM PC-AT compatible computer. System
components consist of two types of peristaltic pumps (including a
multiple pump unit), syringe pumps, electrically and pneumatically
actuated valves, and an assortment of spectrophotometric and
electrochemical detectors. Details of the interface circuitry are given
where appropriate. To demonstrate the utility of the system, an
automatically generated response surface is presented for the flow
injection determination of iron(II) by its reaction with
1,10-phenanthroline
Underdiagnosis of mild cognitive impairment: A consequence of ignoring practice effects
INTRODUCTION: Longitudinal testing is necessary to accurately measure cognitive change. However, repeated testing is susceptible to practice effects, which may obscure true cognitive decline and delay detection of mild cognitive impairment (MCI).
METHODS: We retested 995 late-middle-aged men in a ∼6-year follow-up of the Vietnam Era Twin Study of Aging. In addition, 170 age-matched replacements were tested for the first time at study wave 2. Group differences were used to calculate practice effects after controlling for attrition effects. MCI diagnoses were generated from practice-adjusted scores.
RESULTS: There were significant practice effects on most cognitive domains. Conversion to MCI doubled after correcting for practice effects, from 4.5% to 9%. Importantly, practice effects were present although there were declines in uncorrected scores.
DISCUSSION: Accounting for practice effects is critical to early detection of MCI. Declines, when lower than expected, can still indicate practice effects. Replacement participants are needed for accurately assessing disease progression.Published versio
‘Reasonable Adjustments’ under the UK’s Equality Act 2010:An enquiry into the care and treatment provided to patients with intellectual disabilities following admission to acute hospital settings
Objectives To understand the views of qualified medical practitioners regarding “reasonable adjustments” and the quality of the care and treatment provided to adults with intellectual disabilities when admitted to acute hospitals as inpatients. Methods Semi‐structured interviews took place with 14 medical practitioners, seven from each of two acute hospitals, with a thematic analysis of the resulting data. Results All 14 medical practitioners reported problems in the diagnosis and treatment of patients with intellectual disabilities. Most participants attributed these difficulties to communication problems and/or behaviours that, in the context of a hospital ward, were non‐conforming. However, a minority reported that, because they were likely to have multiple comorbid health conditions, patients with intellectual disabilities were more complex. In addition, half of all these respondents reported making little use of “reasonable adjustments” introduced to improve the quality of the care received by this group of patients. Conclusions Medical practitioners should make better use of the “reasonable adjustments” introduced in the UK to address inequities in care and treatment received by patients with intellectual disabilities. However, training should also focus on the biomedical complexities often presented by these men and women
The WiggleZ Dark Energy Survey: the growth rate of cosmic structure since redshift z=0.9
We present precise measurements of the growth rate of cosmic structure for
the redshift range 0.1 < z < 0.9, using redshift-space distortions in the
galaxy power spectrum of the WiggleZ Dark Energy Survey. Our results, which
have a precision of around 10% in four independent redshift bins, are well-fit
by a flat LCDM cosmological model with matter density parameter Omega_m = 0.27.
Our analysis hence indicates that this model provides a self-consistent
description of the growth of cosmic structure through large-scale perturbations
and the homogeneous cosmic expansion mapped by supernovae and baryon acoustic
oscillations. We achieve robust results by systematically comparing our data
with several different models of the quasi-linear growth of structure including
empirical models, fitting formulae calibrated to N-body simulations, and
perturbation theory techniques. We extract the first measurements of the power
spectrum of the velocity divergence field, P_vv(k), as a function of redshift
(under the assumption that P_gv(k) = -sqrt[P_gg(k) P_vv(k)] where g is the
galaxy overdensity field), and demonstrate that the WiggleZ galaxy-mass
cross-correlation is consistent with a deterministic (rather than stochastic)
scale-independent bias model for WiggleZ galaxies for scales k < 0.3 h/Mpc.
Measurements of the cosmic growth rate from the WiggleZ Survey and other
current and future observations offer a powerful test of the physical nature of
dark energy that is complementary to distance-redshift measures such as
supernovae and baryon acoustic oscillations.Comment: 17 pages, 11 figures, accepted for publication by MNRA
The WiggleZ Dark Energy Survey: measuring the cosmic expansion history using the Alcock-Paczynski test and distant supernovae
Astronomical observations suggest that today's Universe is dominated by a
dark energy of unknown physical origin. One of the most notable consequences in
many models is that dark energy should cause the expansion of the Universe to
accelerate: but the expansion rate as a function of time has proven very
difficult to measure directly. We present a new determination of the cosmic
expansion history by combining distant supernovae observations with a
geometrical analysis of large-scale galaxy clustering within the WiggleZ Dark
Energy Survey, using the Alcock-Paczynski test to measure the distortion of
standard spheres. Our result constitutes a robust and non-parametric
measurement of the Hubble expansion rate as a function of time, which we
measure with 10-15% precision in four bins within the redshift range 0.1 < z <
0.9. We demonstrate that the cosmic expansion is accelerating, in a manner
independent of the parameterization of the cosmological model (although
assuming cosmic homogeneity in our data analysis). Furthermore, we find that
this expansion history is consistent with a cosmological-constant dark energy.Comment: 13 pages, 7 figures, accepted for publication by MNRA
The WiggleZ Dark Energy Survey: the transition to large-scale cosmic homogeneity
We have made the largest-volume measurement to date of the transition to
large-scale homogeneity in the distribution of galaxies. We use the WiggleZ
survey, a spectroscopic survey of over 200,000 blue galaxies in a cosmic volume
of ~1 (Gpc/h)^3. A new method of defining the 'homogeneity scale' is presented,
which is more robust than methods previously used in the literature, and which
can be easily compared between different surveys. Due to the large cosmic depth
of WiggleZ (up to z=1) we are able to make the first measurement of the
transition to homogeneity over a range of cosmic epochs. The mean number of
galaxies N(<r) in spheres of comoving radius r is proportional to r^3 within
1%, or equivalently the fractal dimension of the sample is within 1% of D_2=3,
at radii larger than 71 \pm 8 Mpc/h at z~0.2, 70 \pm 5 Mpc/h at z~0.4, 81 \pm 5
Mpc/h at z~0.6, and 75 \pm 4 Mpc/h at z~0.8. We demonstrate the robustness of
our results against selection function effects, using a LCDM N-body simulation
and a suite of inhomogeneous fractal distributions. The results are in
excellent agreement with both the LCDM N-body simulation and an analytical LCDM
prediction. We can exclude a fractal distribution with fractal dimension below
D_2=2.97 on scales from ~80 Mpc/h up to the largest scales probed by our
measurement, ~300 Mpc/h, at 99.99% confidence.Comment: 21 pages, 16 figures, accepted for publication in MNRA
Cosmological Constraints from the Clustering of the Sloan Digital Sky Survey DR7 Luminous Red Galaxies
We present the power spectrum of the reconstructed halo density field derived
from a sample of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey
Seventh Data Release (DR7). The halo power spectrum has a direct connection to
the underlying dark matter power for k <= 0.2 h/Mpc, well into the quasi-linear
regime. This enables us to use a factor of ~8 more modes in the cosmological
analysis than an analysis with kmax = 0.1 h/Mpc, as was adopted in the SDSS
team analysis of the DR4 LRG sample (Tegmark et al. 2006). The observed halo
power spectrum for 0.02 < k < 0.2 h/Mpc is well-fit by our model: chi^2 = 39.6
for 40 degrees of freedom for the best fit LCDM model. We find \Omega_m h^2 *
(n_s/0.96)^0.13 = 0.141^{+0.009}_{-0.012} for a power law primordial power
spectrum with spectral index n_s and \Omega_b h^2 = 0.02265 fixed, consistent
with CMB measurements. The halo power spectrum also constrains the ratio of the
comoving sound horizon at the baryon-drag epoch to an effective distance to
z=0.35: r_s/D_V(0.35) = 0.1097^{+0.0039}_{-0.0042}. Combining the halo power
spectrum measurement with the WMAP 5 year results, for the flat LCDM model we
find \Omega_m = 0.289 +/- 0.019 and H_0 = 69.4 +/- 1.6 km/s/Mpc. Allowing for
massive neutrinos in LCDM, we find \sum m_{\nu} < 0.62 eV at the 95% confidence
level. If we instead consider the effective number of relativistic species Neff
as a free parameter, we find Neff = 4.8^{+1.8}_{-1.7}. Combining also with the
Kowalski et al. (2008) supernova sample, we find \Omega_{tot} = 1.011 +/- 0.009
and w = -0.99 +/- 0.11 for an open cosmology with constant dark energy equation
of state w.Comment: 26 pages, 19 figures, submitted to MNRAS. The power spectrum and a
module to calculate the likelihoods is publicly available at
http://lambda.gsfc.nasa.gov/toolbox/lrgdr/ . v2 fixes abstract formatting
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