828 research outputs found
Modeling the evolution of aerosol particles in a ship plume using PartMC-MOSAIC
This study investigates the evolution of ship-emitted aerosol
particles using the stochastic particle-resolved model
PartMC-MOSAIC (Particle Monte Carlo model-Model for Simulating Aerosol Interactions and Chemistry). Comparisons of our results with observations from the
QUANTIFY (Quantifying the Climate Impact of Global
and European Transport Systems) study in 2007 in the English Channel and the Gulf of Biscay
showed that the model was able to reproduce the observed evolution
of total number concentration and the vanishing of the nucleation
mode consisting of sulfate particles. Further process analysis
revealed that during the first hour after emission, dilution reduced
the total number concentration by four orders of magnitude, while
coagulation reduced it by an additional order of
magnitude. Neglecting coagulation resulted in an overprediction of
more than one order of magnitude in the number concentration of
particles smaller than 40 nm at a plume age of 100 s. Coagulation
also significantly altered the mixing state of the particles,
leading to a continuum of internal mixtures of sulfate and black
carbon. The impact on cloud condensation nuclei (CCN) concentrations
depended on the supersaturation threshold <i>S</i> at which CCN activity
was evaluated. For the base case conditions, characterized
by a low formation rate of secondary aerosol species, neglecting
coagulation, but simulating condensation, led to an
underestimation of CCN concentrations of about 37% for <i>S</i> = 0.3%
at the end of the 14-h simulation. In contrast, for
supersaturations higher than 0.7%, neglecting coagulation
resulted in an overestimation of CCN concentration, about 75% for
<i>S</i> = 1%. For <i>S</i> lower than 0.2% the differences between
simulations including coagulation and neglecting coagulation were
negligible. Neglecting condensation, but simulating coagulation
did not impact the CCN concentrations below 0.2% and resulted in
an underestimation of CCN concentrations for larger
supersaturations, e.g., 18% for <i>S</i> = 0.6%. We also explored the
role of nucleation for the CCN concentrations in the ship
plume. For the base case the impact of nucleation on CCN
concentrations was limited, but for a sensitivity case with higher
formation rates of secondary aerosol over several hours, the CCN
concentrations increased by an order of magnitude for
supersaturation thresholds above 0.3%
Three-dimensional geometric morphometrics of thorax-pelvis covariation and its potential for predicting the thorax morphology: A case study on Kebara 2 Neandertal
The skeletal torso is a complex structure of outstanding importance in understanding human body shape evolution, but reconstruction usually entails an element of subjectivity as researchers apply their own anatomical expertise to the process. Among different fossil reconstruction methods, 3D geometric morphometric techniques have been increasingly used in the last decades. Two-block partial least squares analysis has shown great potential for predicting missing elements by exploiting the covariation between two structures (blocks) in a reference sample: one block can be predicted from the other one based on the strength of covariation between blocks. The first aim of this study is to test whether this predictive approach can be used for predicting thorax morphologies from pelvis morphologies within adult Homo sapiens reference samples with known covariation between the thorax and the pelvis. The second aim is to apply this method to Kebara 2 Neandertal (Israel, ∼60 ka) to predict its thorax morphology using two different pelvis reconstructions as predictors. We measured 134 true landmarks, 720 curve semilandmarks, and 160 surface semilandmarks on 60 3D virtual torso models segmented from CT scans. We conducted three two-block partial least squares analyses between the thorax (block 1) and the pelvis (block 2) based on the H. sapiens reference samples after performing generalized Procrustes superimposition on each block separately. Comparisons of these predictions in full shape space by means of Procrustes distances show that the male-only predictive model yields the most reliable predictions within modern humans. In addition, Kebara 2 thorax predictions based on this model concur with the thorax morphology proposed for Neandertals. The method presented here does not aim to replace other techniques, but to rather complement them through quantitative prediction of a virtual 'scaffold' to articulate the thoracic fossil elements, thus extending the potential of missing data estimation beyond the methods proposed in previous works
Reply to comment from Liotta and Rizzo on “Evolution of CO2 , SO2 , HCl and HNO3 in the volcanic plumes from Etna” by Voigt et al. [Geophys. Res. Lett.; 41, doi:10.1002/2013GL058974]
Editor’s Note:
The following comment and reply arise from an article
published in Geophysical Research Letters by Voigt
et al. (2014). The article addresses a volcanology topic,
and the commenters take issue with some conclusions
and offer an analysis of their own. Voigt and co-authors
have responded.
Why is this comment-and-reply being published in
the Bulletin? It is because Geophysical Research
Letters is one of a number of journals that do not offer
any published forum for discussion of the papers they
publish. This is a matter of editorial policy and a
decision for each journal.
The Bulletin of Volcanology does provide a forum for
discussion of articles published. When contacted by
Marcello Liotta with the request that the Bulletin consider
hosting a discussion of the Voigt et al. volcanology article in
GRL, I agreed to do so if the GRL authors were willing to
engage with the comment. Voigt and co-authors were willing
to do so and have been allowed a small amount of additional
space to summarize for Bulletin readers the key points of the
GRL paper under discussion before responding directly to the
comment from Liotta and Rizzo.
I hope that Bulletin readers find the discussion and reply of
interest
Local Dynamics and Strong Correlation Physics I: 1D and 2D Half-filled Hubbard Models
We report on a non-perturbative approach to the 1D and 2D Hubbard models that
is capable of recovering both strong and weak-coupling limits. We first show
that even when the on-site Coulomb repulsion, U, is much smaller than the
bandwith, the Mott-Hubbard gap never closes at half-filling in both 1D and 2D.
Consequently, the Hubbard model at half-filling is always in the
strong-coupling non-perturbative regime. For both large and small U, we find
that the population of nearest-neighbour singlet states approaches a value of
order unity as as would be expected for antiferromagnetic order. We
also find that the double occupancy is a smooth monotonic function of U and
approaches the anticipated non-interacting limit and large U limits. Finally,
in our results for the heat capacity in 1D differ by no more than 1% from the
Bethe ansatz predictions. In addition, we find that in 2D, the heat capacity vs
T for different values of U exhibits a universal crossing point at two
characteristic temperatures as is seen experimentally in a wide range of
strongly-correlated systems such as , , and . The
success of this method in recovering well-established results that stem
fundamentally from the Coulomb interaction suggests that local dynamics are at
the heart of the physics of strongly correlated systems.Comment: 10 pages, 16 figures included in text, Final version for publication
with a reference added and minor corrections. Phys. Rev. B, in pres
Assessing thoraco‐pelvic covariation in Homo sapiens and Pan troglodytes: A 3D geometric morphometric approach
Objectives
Understanding thoraco‐pelvic integration in Homo sapiens and their closest living relatives (genus Pan) is of great importance within the context of human body shape evolution. However, studies assessing thoraco‐pelvic covariation across Hominoidea species are scarce, although recent research would suggest shared covariation patterns in humans and chimpanzees but also species‐specific features, with sexual dimorphism and allometry influencing thoraco‐pelvic covariation in these taxa differently.
Material and Methods
N = 30 adult H. sapiens and N = 10 adult Pan troglodytes torso 3D models were analyzed using 3D geometric morphometrics and linear measurements. Effects of sexual dimorphism and allometry on thoraco‐pelvic covariation were assessed via regression analyses, and patterns of thoraco‐pelvic covariation in humans and chimpanzees were computed via Two‐Block Partial Least Squares analyses.
Results
Results confirm the existence of common aspects of thoraco‐pelvic covariation in humans and chimpanzees, and also species‐specific covariation in H. sapiens that is strongly influenced by sexual dimorphism and allometry. Species‐specific covariation patterns in chimpanzees could not be confirmed because of the small sample size, but metrics point to a correspondence between the most caudal ribs and iliac crest morphology that would be irrespective of sex.
Conclusions
This study suggests that humans and chimpanzees share common aspects of thoraco‐pelvic covariation but might differ in others. In humans, torso integration is strongly influenced by sexual dimorphism and allometry, whilst in chimpanzees it may not be. This study also highlights the importance not only of torso widths but also of torso depths when describing patterns of thoraco‐pelvic covariation in primates. Larger samples are necessary to support these interpretations
Nearly universal crossing point of the specific heat curves of Hubbard models
A nearly universal feature of the specific heat curves C(T,U) vs. T for
different U of a general class of Hubbard models is observed. That is, the
value C_+ of the specific heat curves at their high-temperature crossing point
T_+ is almost independent of lattice structure and spatial dimension d, with
C_+/k_B \approx 0.34. This surprising feature is explained within second order
perturbation theory in U by identifying two small parameters controlling the
value of C_+: the integral over the deviation of the density of states
N(\epsilon) from a constant value, characterized by \delta N=\int d\epsilon
|N(\epsilon)-1/2|, and the inverse dimension, 1/d.Comment: Revtex, 9 pages, 6 figure
Isosbestic points in the spectral function of correlated electrons
We investigate the properties of the spectral function A(omega,U) of
correlated electrons within the Hubbard model and dynamical mean-field theory.
Curves of A(omega,U) vs. omega for different values of the interaction U are
found to intersect near the band-edges of the non-interacting system. For a
wide range of U the crossing points are located within a sharply confined
region. The precise location of these 'isosbestic points' depends on details of
the non-interacting band structure. Isosbestic points of dynamic quantities
therefore provide valuable insights into microscopic energy scales of
correlated systems.Comment: 16 pages, 5 figure
Vertical profile of peroxyacetyl nitrate (PAN) from MIPAS-STR measurements over Brazil in February 2005 and its contribution to tropical UT NOy partitioning
We report on the retrieval of PAN (CH<sub>3</sub>C(O)OONO<sub>2</sub>) in the upper tropical troposphere from limb measurements by the remote-sensor MIPAS-STR on board the Russian high altitude research aircraft M55-Geophysica. The measurements were performed close to Araçatuba, Brazil, on 17 February 2005. The retrieval was made in the spectral range 775–820 cm<sup>−1</sup> where PAN exhibits its strongest feature but also more than 10 species interfere. Especially trace gases such as CH<sub>3</sub>CCl<sub>3</sub>, CFC-113, CFC-11, and CFC-22, emitting also in spectrally broad not-resolved branches, make the processing of PAN prone to errors. Therefore, the selection of appropriate spectral windows, the separate retrieval of several interfering species and the careful handling of the water vapour profile are part of the study presented. <br><br> The retrieved profile of PAN has a maximum of about 0.14 ppbv at 10 km altitude, slightly larger than the lowest reported values (<0.1 ppbv) and much lower than the highest reported in the literature (0.65 ppbv). Besides the NO<sub>y</sub> constituents measured by MIPAS-STR (HNO<sub>3</sub>, ClONO<sub>2</sub>, HO<sub>2</sub>NO<sub>2</sub>, PAN), the in situ instruments aboard the Geophysica provide simultaneous measurements of NO, NO<sub>2</sub>, and the sum NO<sub>y</sub>. Comparing the sum of in-situ and remotely derived NO+NO<sub>2</sub>+HNO<sub>3</sub>+ClONO<sub>2</sub>+HO<sub>2</sub>NO<sub>2</sub>+PAN with total NO<sub>y</sub> a deficit of 30–40% (0.2–0.3 ppbv) in the troposphere remains unexplained whereas the values fit well in the stratosphere
Intercomparison of aircraft instruments on board the <i>C-130</i> and <i>Falcon 20</i> over southern Germany during EXPORT 2000
International audienceIn the summer 2000 Export aircraft campaign (European eXport of Precursors and Ozone by long-Range Transport), two comprehensively instrumented research aircraft measuring a variety of chemical species flew wing tip to wing tip for a period of one and a quarter hours. During this interval a comparison was undertaken of the measurements of nitrogen oxide (NO), odd nitrogen species (NOy), carbon monoxide (CO) and ozone (O3). The comparison was performed at two different flight levels, which provided a 10-fold variation in the concentrations of both NO (10 to 1000 parts per trillion by volume (pptv)) and NOy (200 to over 2500 pptv). Large peaks of NO and NOy observed from the Falcon 20, which were at first thought to be from the exhaust of the C-130, were also detected on the 4 channel NOx,y instrument aboard the C-130. These peaks were a good indication that both aircraft were in the same air mass and that the Falcon 20 was not in the exhaust plume of the C-130. Correlations and statistical analysis are presented between the instruments used on the two separate aircraft platforms. These were found to be in good agreement giving a high degree of correlation for the ambient air studied. Any deviations from the correlations are accounted for in the estimated inaccuracies of the instruments. These results help to establish that the instruments aboard the separate aircraft are reliably able to measure the corresponding chemical species in the range of conditions sampled and that data collected by both aircraft can be co-ordinated for purposes of interpretation
Nanoparticle Release from Thermal Decomposition of Polymer Nanocomposites and the Biological Potential of the Emissions
Adding nanoparticles to polymers improves the properties significantly, such as UV resistance or even electrical conductivity. The growing use of these composite materials leads to a higher amount in disposals eventually. Within the circular economy there are two ways of handling: the recycling by shredding and reuse and the thermal treatment by combustion in municipal waste incinerators. In both cases there is nearly no information about the behavior of the nanoparticles and possible release scenarios. In this study a laboratory burner is used as a flexible set up to incinerate the polymer nanocomposites. The flue gas containing a complex mixture of combustion gases and particles is characterized by different particle analysers, PAH analysis, VOC analysis and TEM. The biological impact is studied by using a VITROCELL Automated ALI exposure station. Hereby, cells of the adenocarcino cell line A549 as well as a reconstituted bronchial epithelium (MucilAir, Epithelix) were exposed for 4 hours to the aerosols emitted from the combustion process. Within the exposure process, cells were exposed to the native aerosol, an aerosol under conditions to increase particle deposition via high voltage as well as a filtered aerosol, and therefore the sole gaseous phase. Furthermore, each exposure included a so-called clean air control, where cells where exposed to filtered air. The exposure was followed by a 21 h post-incubation before the cytotoxic effects were determined via LDH-release. To reveal if possible adverse effects are caused by the used nano-scaled filling material, all used nanomaterials did also undergo the same combustion process as a single material. Cytotoxicity studies showed no increased cytotoxic effects after the combustion of the sole nano-scaled filling materials. However, combustion of PE containing materials resulted in an enhanced LDH-release, and therefore cytotoxicity, in both cell culture models. Since no difference between exposures of unfiltered and filtered aerosols was apparent, it suggested that the observed cytotoxicity is due to the combustion induced gaseous phase
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