Atmospheric Deposition of Sulfur and Base Cations to European Forests

To simulate acidification processes in forests (soils), it is important to know as well as possible the atmospheric input. Large scale models have recently been improved to take better into account the differences in deposition between forests and other surfaces. In this report measurements of sulfur-fluxes onto the forest floor (54 case studies) are compared with deposition fluxes as calculated by the EMEP-model and by the RAINS modifications on this model. The value of the filtering parameter used in RAINS at this moment is discussed. A new quantitative basis for the filtering effect of different tree species is given. Fluxes of base cations are compared to sulfur fluxes to quantify the neutralizing effects of base cations. There appears to be no direct proportional relationship between base cation and sulfur fluxes onto the forest floor. It is proposed to study the possibility of linking, within the RAINS model, basic cation deposition with the amount and magnitude of several sources of basic cations

Sulfur deposition onto European forests: throughfall data and model estimates

The assessment of atmospheric sulfur deposition to forest is difficult because of its complex aerodynamic structure. Therefore, atmospheric deposition of sulfur to forest is often estimated by means of measuring throughfall fluxes onto the forest floor. In this paper, reported measurements of throughfall fluxes in European forests are analyzed. These fluxes are compared to deposition to bulk collectors located in nearby open land, to get an idea of the filtering efficiency of forests. In addition, fluxes are compared with deposition estimates from a long‐range transport model of air pollutants, linked to an emission generation model. According to reported measurements from 52 European conifer stands, we found that the sulfur flux was 3.8 ± 2.3 times greater onto the forest floor than onto precipitation collectors. In a similar data set of 13 deciduous stands this ratio was 2.3 ± 0.9. The ratio of throughfall flux to model estimate was 1.8 ± 0.9 in coniferous stands and 0.9 ± 0.3 in deciduous stands. For sites that are located in moderately to highly sulfur polluted areas, it is assumed that throughfall fluxes give a good estimation of the atmospheric sulfur deposition. We conclude that (1) sulfur deposition to forests is 1.5 to 6 times higher than deposition to smooth receptor surfaces due to an efficient filtering by the forest canopy, (2) average annual sulfur deposition at a given location is 50–100% greater on conifers than on deciduous trees, (3) the existing European scale model that links sulfur deposition to the pollution generation processes is quite accurate as far as deciduous forests are concerned, and (4) the model underestimates deposition to coniferous forest

Atmospheric Deposition of Sulfur, Nitrogen and basic Cations onto European Forests : Observations and Model Calculations

Measurements of sulfur and nitrogen deposition by means of the throughfall method are compared with model estimates. The sulfur model appears to estimate deposition to deciduous forests very well, but underestimates deposition to conifers by 30 to 40%. The NH4-N deposition to forest is underestimated by the applied model. The model predictions of NO3-N deposition do not show any bias against observations, but are not better correlated with observations than NH4 calculations. Reduced nitrogen compounds are the dominant nitrogen form in throughfall in ammonia polluted areas and contribute up to 50% of the total nitrogen deposition in other areas. Deposition of alkaline material to forests is estimated by applying different methods. Basic cation deposition neutralizes about 31% of the acid sulfur deposition to forest, on the average. Because of the large spatial variability of base cation deposition, it is recommended to develop a model for atmospheric transport and deposition of calcium- and magnesium-bearing particles

The interacting nature of dwarf galaxies hosting superluminous supernovae

(Abridged) Type I superluminous supernovae (SLSNe I) are rare, powerful explosions whose mechanism and progenitors remain elusive. SLSNe I show a preference for low-metallicity, actively star-forming dwarf galaxies. We investigate whether the hosts of SLSNe I show increased evidence for interaction. We use a sample of 42 SLSN I images obtained with $\textit{HST}$ and measure the number of companion galaxies by counting the objects detected within a given radius from the host. As a comparison, we used two Monte Carlo-based methods to estimate the expected average number of companion objects in the same images, as well as a sample of 32 galaxies that have hosted long gamma-ray bursts (GRBs). About 50% of SLSN I hosts have at least one major companion (within a flux ratio of 1:4) within 5 kpc. The average number of major companions per SLSN I host galaxy is $0.70^{+0.19}_{-0.14}$. Our Monte Carlo comparison methods yield a lower number of companions for random objects of similar brightness in the same image or for the SLSN host after randomly redistributing the sources in the same image. The Anderson-Darling test shows that this difference is statistically significant independent of the redshift range. The same is true for the projected distance distribution of the companions. The SLSN I hosts are, thus, found in areas of their images, where the object number density is greater than average. SLSN I hosts have more companions than GRB hosts ($0.44^{+0.25}_{-0.13}$ companions per host distributed over 25% of the hosts) but the difference is not statistically significant. The difference between their separations is, however, marginally significant. The dwarf galaxies hosting SLSNe I are often part of interacting systems. This suggests that SLSNe I progenitors are formed after a recent burst of star formation. Low metallicity alone cannot explain this tendency.Comment: Accepted for publication in A&A. In v2 replaced graphs with higher quality PDF version

Terror from the Sky: Unconventional Linguistic Clues to the Negrito Past

Within recorded history. most Southeast Asian peoples have been of southern Mongoloid physical type, whether they speak Austroasiatic, Tibeto-Burman, Austronesian, Tai-Kadai, or Hmong-Mien languages. However, population distributions suggest that this is a post-Pleistocene phenomenon and that for tens of millennia before the last glaciation ended Greater Mainland Southeast Asia, which included the currently insular world that rests on the Sunda Shelf, was peopled by short, dark-skinned, frizzy-haired foragers whose descendants in the Philippines came to be labeled by the sixteenth-century Spanish colonizers as negritos, a term that has since been extended to similar groups throughout the region. There are three areas in which these populations survived into the present so as to become part of written history: the Philippines, the Malay Peninsula, and the Andaman Islands. All Philippine negritos speak Austronesian languages, and all Malayan negritos speak languages in the nuclear Mon-Khmer branch of Austroasiatic, but the linguistic situation in the Andamans is a world apart. Given prehistoric language shifts among both Philippine and Malayan negritos, the prospects of determining whether disparate negrito populations were once a linguistically or culturally unified community would appear hopeless. Surprisingly, however, some clues to a common negrito past do survive in a most unexpected way

Trypanocidal and leishmanicidal activity of six limonoids

Six limonoids [kotschyienone A and B (1, 2), 7-deacetylgedunin (3), 7-deacetyl-7-oxogedunin (4), andirobin (5) and methyl angolensate (6)] were investigated for their trypanocidal and leishmanicidal activities using bloodstream forms of Trypanosoma brucei and promastigotes of Leishmania major. Whereas all compounds showed anti-trypanosomal activity, only compounds 1–4 displayed anti-leishmanial activity. The 50% growth inhibition (GI 50) values for the trypanocidal and leishmanicidal activity of the compounds ranged between 2.5 and 14.9 μM. Kotschyienone A (1) was found to be the most active compound with a minimal inhibition concentration (MIC) value of 10 μM and GI 50 values between 2.5 and 2.9 μM. Only compounds 1 and 3 showed moderate cytotoxicity against HL-60 cells with MIC and GI 50 values of 100 μM and 31.5–46.2 μM, respectively. Compound 1 was also found to show activity against intracellular amastigotes of L. major with a GI 50 value of 1.5 μM. The results suggest that limonoids have potential as drug candidates for the development of new treatments against trypanosomiasis and leishmaniasis

Chlorpromazine and amitriptyline are substrates and inhibitors of the acrb multidrug efflux pump

Efflux is an important mechanism in Gram-negative bacteria conferring multidrug resistance. Inhibition of efflux is an encouraging strategy to restore the antibacterial activity of antibiotics. Chlorpromazine and amitriptyline have been shown to behave as efflux inhibitors. However, their mode of action is poorly under-stood. Exposure of Salmonella enterica serovar Typhimurium and Escherichia coli to chlorpromazine selected for mutations within genes encoding RamR and MarR, regu-lators of the multidrug tripartite efflux pump AcrAB-TolC. Further experiments with S. Typhimurium containing AcrB D408A (a nonfunctional efflux pump) and chlor-promazine or amitriptyline resulted in the reversion of the mutant acrB allele to the wild type. Together, this suggests these drugs are AcrB efflux substrates. Subsequent docking studies with AcrB from S. Typhimurium and E. coli, followed by molecular dynamics simulations and free energy calculations showed that chlorpromazine and amitriptyline bind at the hydrophobic trap, a preferred binding site for substrates and inhibitors within the distal binding pocket of AcrB. Based on these simulations, we suggest that chlorpromazine and amitriptyline inhibit AcrB-mediated efflux by in-terfering with substrate binding. Our findings provide evidence that these drugs are substrates and inhibitors of AcrB, yielding molecular details of their mechanism of action and informing drug discovery of new efflux inhibitors. IMPORTANCE Efflux pumps of the resistance nodulation-cell division (RND) super-family are major contributors to multidrug resistance for most of the Gram-negative ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acineto-bacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) pathogens. The development of inhibitors of these pumps would be highly desirable; how-ever, several issues have thus far hindered all efforts at designing new efflux in-hibitory compounds devoid of adverse effects. An alternative route to de novo design relies on the use of marketed drugs, for which side effects on human health have been already assessed. In this work, we provide experimental evidence that the antipsychotic drugs chlorpromazine and amitriptyline are inhibi-tors of the AcrB transporter, the engine of the major RND efflux pumps in Escherichia coli and Salmonella enterica serovar Typhimurium. Furthermore, in silico calculations have provided a molecular-level picture of the inhibition mechanism, allowing rationalization of experimental data and paving the way for similar studies with other classes of marketed compounds