12,048 research outputs found
Two hundred fifty years of aerosols and climate: the end of the age of aerosols
Carbonaceous and sulfur aerosols have a substantial global and regional
influence on climate, resulting in a net cooling to date, in addition to
their impact on health and ecosystems. The magnitude of this influence has
changed substantially over the past and is expected to continue to change
into the future. An integrated picture of the changing climatic influence of
black carbon, organic carbon and sulfate over the period 1850 through 2100,
focusing on uncertainty, is presented using updated historical inventories
and a coordinated set of emission projections. We describe, in detail, the
aerosol emissions from the RCP4.5 scenario and its associated reference
scenario. While aerosols have had a substantial impact on climate over the
past century, we show that, by the end of the 21st century, aerosols
will likely be only a minor contributor to radiative forcing due to
increases in greenhouse gas forcing and a net global decrease in pollutant
emissions. This outcome is even more certain under a successful
implementation of a policy to limit greenhouse gas emissions as low-carbon
energy technologies that do not emit appreciable aerosol or SO<sub>2</sub> are
deployed
Spin Hall Conductance of the Two Dimensional Hole Gas in a Perpendicular Magnetic Field
The charge and spin Hall conductance of the two-dimensional hole gas within
the Luttinger model with and without inversion symmetry breaking terms in a
perpendicular magnetic field are studied, and two key phenomena are predicted.
The sign of the spin Hall conductance is modulated periodically by the external
magnetic field, which means a possible application in the future. Furthermore,
a resonant spin Hall conductance in the two-dimensional hole gas with a certain
hole density at a typical magnetic field is indicated, which implies a likely
way to firmly establish the intrinsic spin Hall effect. The charge Hall
conductance is unaffected by the spin-orbit coupling.Comment: accepted for publication in Phys. Rev. B; 6 pages, 4 figure
The formation of disinfection by-products from the chlorination and chloramination of amides
This study examined the potential of six aliphatic and aromatic amides, commonly found in natural waters or used as chemical aids in water treatment, to act as organic precursors for nine haloacetamides (HAcAms), five haloacetonitriles (HANs), regulated trihalomethanes (THMs) and haloacetic acids (HAAs) upon chlorination and chloramination. The impact of key experimental conditions, representative of drinking water, including pH (7 & 8), retention time (4 & 24 h) and bromide levels (0 & 100 ÎŒg/L), on the generation of the target DBPs was investigated. The highest aggregate DBP yields upon chlor(am)ination were reported for the aromatic and hydrophobic hydroxybenzamide; 2.7% ± 0.1% M/M (chlorination) and 1.7% M/M (chloramination). Increased reactivity was observed in aliphatic and hydrophilic compounds, acrylamide (2.5 ± 0.2% M/M) and acetamide (1.3 ± 0.2% M/M), in chlorination and chloramination, respectively. The addition of bromide increased average DBP yields by 50â70%. Relative to chlorination, the application of chloramines reduced DBP formation by 66.5% (without Brâ) and by 46.4% (with Brâ). However, bromine incorporation in HAAs and HAcAms was enhanced following chloramination, of concern due to the higher toxicological potency of brominated compounds
On holographic dark-energy models
Different holographic dark-energy models are studied from a unifying point of
view. We compare models for which the Hubble scale, the future event horizon or
a quantity proportional to the Ricci scale are taken as the infrared cutoff
length. We demonstrate that the mere definition of the holographic dark-energy
density generally implies an interaction with the dark-matter component. We
discuss the relation between the equation-of-state parameter and the energy
density ratio of both components for each of the choices, as well as the
possibility of non-interacting and scaling solutions. Parameter estimations for
all three cutoff options are performed with the help of a Bayesian statistical
analysis, using data from supernovae type Ia and the history of the Hubble
parameter. The CDM model is the clear winner of the analysis.
According to the Bayesian Information Criterion (), all holographic models
should be considered as ruled out, since the difference to the
corresponding CDM value is . According to the Akaike Information
Criterion (), however, we find for models with
Hubble-scale and Ricci-scale cutoffs, indicating, that they may still be
competitive. As we show for the example of the Ricci-scale case, also the use
of certain priors, reducing the number of free parameters to that of the
CDM model, may result in a competitive holographic model.Comment: 37 pages, 11 figures, 3 tables, statistical analysis improved,
accepted for publication in Phys.Rev.
Large-scale surface reconstruction energetics of Pt(100) and Au(100) by all-electron DFT
The low-index surfaces of Au and Pt all tend to reconstruct, a fact that is
of key importance in many nanostructure, catalytic, and electrochemical
applications. Remarkably, some significant questions regarding their structural
energies remain even today, in particular for the large-scale quasihexagonal
reconstructed (100) surfaces: Rather dissimilar reconstruction energies for Au
and Pt in available experiments, and experiment and theory do not match for Pt.
We here show by all-electron density-functional theory that only large enough
"(5 x N)" approximant supercells capture the qualitative reconstruction energy
trend between Au(100) and Pt(100), in contrast to what is often done in the
theoretical literature. Their magnitudes are then in fact similar, and closer
to the measured value for Pt(100); our calculations achieve excellent agreement
with known geometric characteristics and provide direct evidence for the
electronic reconstruction driving force.Comment: updated version - also includes EPAPS information as auxiliary file;
related publications can be found at http://www.fhi-berlin.mpg.de/th/th.htm
A cohort study of influences, health outcomes and costs of patients' health-seeking behaviour for minor ailments from primary and emergency care settings
To compare health-related and cost-related outcomes of consultations for symptoms suggestive of minor ailments in emergency departments (EDs), general practices and community pharmacies
The Cosmic Microwave Background & Inflation, Then & Now
Boomerang, Maxima, DASI, CBI and VSA significantly increase the case for
accelerated expansion in the early universe (the inflationary paradigm) and at
the current epoch (dark energy dominance), especially when combined with data
on high redshift supernovae (SN1) and large scale structure (LSS). There are
``7 pillars of Inflation'' that can be shown with the CMB probe, and at least
5, and possibly 6, of these have already been demonstrated in the CMB data: (1)
a large scale gravitational potential; (2) acoustic peaks/dips; (3) damping due
to shear viscosity; (4) a Gaussian (maximally random) distribution; (5)
secondary anisotropies; (6) polarization. A 7th pillar, anisotropies induced by
gravity wave quantum noise, could be too small. A minimal inflation parameter
set, \omega_b,\omega_{cdm}, \Omega_{tot}, \Omega_Q,w_Q,n_s,\tau_C, \sigma_8},
is used to illustrate the power of the current data. We find the CMB+LSS+SN1
data give \Omega_{tot} =1.00^{+.07}_{-.03}, consistent with (non-baroque)
inflation theory. Restricting to \Omega_{tot}=1, we find a nearly scale
invariant spectrum, n_s =0.97^{+.08}_{-.05}. The CDM density, \Omega_{cdm}{\rm
h}^2 =.12^{+.01}_{-.01}, and baryon density, \Omega_b {\rm h}^2 =
>.022^{+.003}_{-.002}, are in the expected range. (The Big Bang nucleosynthesis
estimate is 0.019\pm 0.002.) Substantial dark (unclustered) energy is inferred,
\Omega_Q \approx 0.68 \pm 0.05, and CMB+LSS \Omega_Q values are compatible with
the independent SN1 estimates. The dark energy equation of state, crudely
parameterized by a quintessence-field pressure-to-density ratio w_Q, is not
well determined by CMB+LSS (w_Q < -0.4 at 95% CL), but when combined with SN1
the resulting w_Q < -0.7 limit is quite consistent with the w_Q=-1 cosmological
constant case.Comment: 20 pages, 8 figures, in Theoretical Physics, MRST 2002: A Tribute to
George Libbrandt (AIP), eds. V. Elias, R. Epp, R. Myer
A Limit on the Polarized Anisotropy of the Cosmic Microwave Background at Subdegree Angular Scales
A ground-based polarimeter, PIQUE, operating at 90 GHz has set a new limit on
the magnitude of any polarized anisotropy in the cosmic microwave background.
The combination of the scan strategy and full width half maximum beam of 0.235
degrees gives broad window functions with average multipoles, l = 211+294-146
and l = 212+229-135 for the E- and B-mode window functions, respectively. A
joint likelihood analysis yields simultaneous 95% confidence level flat band
power limits of 14 and 13 microkelvin on the amplitudes of the E- and B-mode
angular power spectra, respectively. Assuming no B-modes, a 95% confidence
limit of 10 microkelvin is placed on the amplitude of the E-mode angular power
spectrum alone.Comment: 4 pages, 3 figures, submitted to Astrophysical Journal Letter
Cosmological predictions from the Misner brane
Within the spirit of five-dimensional gravity in the Randall-Sundrum
scenario, in this paper we consider cosmological and gravitational implications
induced by forcing the spacetime metric to satisfy a Misner-like symmetry. We
first show that in the resulting Misner-brane framework the Friedmann metric
for a radiation dominated flat universe and the Schwarzschild or anti-de Sitter
black holes metrics are exact solutions on the branes, but the model cannot
accommodate any inflationary solution. The horizon and flatness problems can
however be solved in Misner-brane cosmology by causal and noncausal
communications through the extra dimension between distant regions which are
outside the horizon. Based on a semiclassical approximation to the
path-integral approach, we have calculated the quantum state of the
Misner-brane universe and the quantum perturbations induced on its metric by
brane propagation along the fifth direction. We have then considered testable
predictions from our model. These include a scale-invariant spectrum of density
perturbations whose amplitude can be naturally accommodated to the required
value 10, and a power spectrum of CMB anisotropies whose
acoustic peaks are at the same sky angles as those predicted by inflationary
models, but having much smaller secondary-peak intensities. These predictions
seem to be compatible with COBE and recent Boomerang and Maxima measurementsComment: 16 pages, RevTe
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