The Dallol Geothermal Area, Northern Afar (Ethiopia)-An Exceptional Planetary Field Analog on Earth.

The Dallol volcano and its associated hydrothermal field are located in a remote area of the northern Danakil Depression in Ethiopia, a region only recently appraised after decades of inaccessibility due to severe political instability and the absence of infrastructure. The region is notable for hosting environments at the very edge of natural physical-chemical extremities. It is surrounded by a wide, hyperarid salt plain and is one of the hottest (average annual temperatureDallol: 36-38°C) and most acidic natural systems (pHDallol ≈0) on Earth. Spectacular geomorphologies and mineral deposits produced by supersaturated hydrothermal waters and brines are the result of complex interactions between active and inactive hydrothermal alteration of the bedrock, sulfuric hot springs and pools, fumaroles and geysers, and recrystallization processes driven by hydrothermal waters, degassing, and rapid evaporation. The study of planetary field analog environments plays a crucial role in characterizing the physical and chemical boundaries within which life can exist on Earth and other planets. It is essential for the definition and assessment of the conditions of habitability on other planets, including the possibility for biosignature preservation and in situ testing of technologies for life detection. The Dallol area represents an excellent Mars analog environment given that the active volcanic environment, the associated diffuse hydrothermalism and hydrothermal alteration, and the vast acidic sulfate deposits are reminiscent of past hydrothermal activity on Mars. The work presented in this paper is an overview of the Dallol volcanic area and its hydrothermal field that integrates previous literature with observations and results obtained from field surveys and monitoring coupled with sample characterization. In so doing, we highlight its exceptional potential as a planetary field analog as well as a site for future astrobiological and exploration programs.

Bentonite-based organoclays as innovative flame retardants agents for SBS copolymer.

Two organophilic bentonites, based on nitrogen-containing compounds, have been synthesised via ion exchange starting from pristine bentonite with octadecyltrimethylammonium bromide (OTAB) and with synthetic melamine-derived N2,N4-dihexadecyl-1,3,5-triazine-2,4,6-triamine (DEDMEL). The chemical and morphological characterization of the organoclays was based on XRD, TEM, Laser Granulometry, X-Ray Fluorescence and CEC capacity. Copoly(styrene-butadiene-styrene)-nanocomposites (SBS-nanocomposites) were obtained by intercalation of the SBS-copolymer into these new organoclays by melt intercalation method. XRD and TEM analysis of the organoclays and of the micro/nano-composites obtained are presented. The effect of the organoclays on the SBS-nanocomposite's flammability properties was investigated using cone calorimeter. An encouraging decrease of 20% in the peak heat released rate (PHRR) has been obtained confirming the important role of melamine's based skeleton and its derived organoclays to act as effective fire retardants and for the improvement of this important functional property in SBS copolymers.

The sand seas of Titan: Cassini RADAR observations of longitudinal dunes.

The most recent Cassini RADAR images of Titan show widespread regions (up to 1500 kilometers by 200 kilometers) of near-parallel radar-dark linear features that appear to be seas of longitudinal dunes similar to those seen in the Namib desert on Earth. The Ku-band (2.17-centimeter wavelength) images show approximately 100-meter ridges consistent with duneforms and reveal flow interactions with underlying hills. The distribution and orientation of the dunes support a model of fluctuating surface winds of approximately 0.5 meter per second resulting from the combination of an eastward flow with a variable tidal wind. The existence of dunes also requires geological processes that create sand-sized (100- to 300-micrometer) particulates and a lack of persistent equatorial surface liquids to act as sand traps.

Inhibitory effect of synthetic histatin 5 on leukotoxin from Actinobacillus actinomycetemcomitans.

Actinobacillus actinomycetemcomitans is a gram-negative bacterium strongly implicated in the pathogenesis of juvenile periodontitis. This periodontal pathogen synthesizes a leukotoxin that destroys human polymorphonuclear leukocytes (PMNs), and this toxin is thought to be responsible for the virulence of A. actinomycetemcomitans. It was therefore of interest to assess whether major virulence factors of periodontal pathogens were neutralized by salivary components. This study focuses on the effect of histatins, components of the nonimmune oral defense system, on leukotoxin activity. Leukotoxin was extracted with polymyxin B from freshly grown anaerobic cultures of A. actinomycetemcomitans strain Y4. PMNs isolated from blood of healthy human volunteers were incubated in a cytotoxicity assay containing PMNs (10(7) cells/ml) and leukotoxin preparation (0-500 microg/ml) in Hanks' balanced salt solution at 37 degrees C for 0-120 min with or without synthetic histatin 5 (0-500 microM). Cytotoxicity was measured by release of lactate dehydrogenase (LDH) at different time intervals. Histatin 5 neutralized the toxic effect of the leukotoxin preparation in a concentration-dependent manner, with an IC(50) value of 150 microM. When PMNs were preincubated with histatin 5 (300 microM), washed and subsequently exposed to leukotoxin, no protective effect was observed. This observation suggests a mechanism of inhibition whereby histatin 5 either directly neutralizes the leukotoxin or interferes with the leukotoxin-PMN interaction. The inhibitory effect of histatin 5 on leukotoxic activity may suggest a new biological function of histatins in the oral cavity as a naturally occurring secondary antibiotic.

The effects of nicotine and age on replication and viability of human gingival fibroblasts in vitro.

The aim of the present study was to examine: (1) the effects of nicotine on human gingival fibroblasts (HGF); (2) differences between smokers (> or = 10 cigarettes/day at least for 5 years) and non-smokers; (3) differences between patients of different age. HGF were obtained, through biopsies during periodontal surgical procedures, from 15 patients which were divided in 4 groups: 4 patients, smokers aged < or = 25 years; 4 patients, non-smokers aged < or = 25 years; 3 patients, smokers aged > or = 40 years; 4 patients, non-smokers aged > or = 40 years. Nicotine has been tested in 3 different concentrations: 6 microg/ml; 60 microg/ml; 600 microg/ml. To assess cells viability, the neutral red (NR) test was used; to evaluate cell proliferation, the Hoechst test was employed. After 48 h of nicotine exposure, it was found that 600 microg/ml nicotine was strongly cytotoxic to HGF of all groups, with a significant reduction of both proliferation and viability of cells versus control. Comparison between groups of the same age: when comparing untreated HGF (i.e., control values) of smokers < or = 25 years versus non-smokers < or = 25 years, cell proliferation, but not viability, was found to be increased in smokers. Both viability and proliferation of control cells of smokers > or = 40 years were increased versus non-smokers > or = 40 years. HGF of non-smokers < or = 25 years, when exposed to nicotine 600 microg/ml, have less viability and proliferation than HGF of smokers of the same age. Comparison between groups of different age: In the smoker group, untreated HGF (i.e., control values) had similar viability and proliferation, irrespective of age, but nicotine 600 microg/ml kills more HGF in smokers < or = 25 years than in smokers > or = 40 years. In non-smokers, untreated HGF < or = 25 years replicate less, but are not less viable than HGF > or = 40 years. When challenged with nicotine 600 microg/ml, HGF < or = 25 years were less viable than HGF > or = 40 years. From this study, it appears that the smoking history and the patient age could be relevant for final evaluation of the results, since HGF from smokers are less sensitive to nicotine than HGF from non-smokers, and cells from older donors are more resistant to nicotine than cells from younger donors.

In vitro testing of the responses of human gingival fibroblasts and L-929 cells to nicotine.

Tobacco smoke is considered to be a major risk factor in the development of cardiac diseases and lung cancer. It has also been shown that periodontitis is more prevalent and more severe in smokers than in non-smokers. Nicotine, the major pyridine alkaloid in tobacco, has been shown to participate in periodontal disease, exerting both local and systemic effects. In the present study, the effects of nicotine (6µg/ml, 60µg/ml and 600µg/ml) on human gingival fibroblasts (HGF) were assessed by using various exposure protocols. The responses of HGF cultures obtained from smokers and non-smokers were compared to those found when using a continuous cell line (L-929). Neutral red uptake (NRU) and the measurement of DNA content with bis-benzimide dye were used to assess cell viability and cell number, respectively. NRU was the most sensitive technique for the detection of cytotoxic effects. L-929 cells were found to be affected by nicotine in the NRU assay, with a strong cytotoxic effect with 600µg/ml nicotine, and a "response" with 60µg/ml nicotine when prolonged or double challenge was applied. Non-smoker HGF and smoker HGF reacted to nicotine in different ways, depending on the concentrations and the exposure times used, but had identical reactions following double exposure. With the Hoechst DNA assay, 600µg/ml nicotine was found to affect the growth of non-smoker HGF after long or repeated exposure, while smoker HGF were affected only by repeated exposure; growth of L-929 cells was not affected. It was concluded that HGF from smokers are able to sustain higher concentrations of nicotine without adverse effects than are non-smoker HGF and L-929 cells. If this occurs in vivo, nicotine would not be considered to be a major toxicant to HGF in smokers.

Search for life on Mars.

A multi-user integrated suite of instruments designed to optimize the search for evidence of life on Mars is described. The package includes: -Surface inspection and surface environment analysis to identify the potential Mars landing sites, to inspect the surface geology and mineralogy, to search for visible surficial microbial macrofossils, to study the surface radiation budget and surface oxidation processes, to search for niches for extant life. -Subsurface sample acquisition by core drilling -Analysis of surface and subsurface minerals and organics to characterize the surface mineralogy, to analyse the surface and subsurface oxidants, to analyse the mineralogy of subsurface aliquots, to analyse the organics present in the subsurface aliquots (elemental and molecular composition, isotopes, chirality). -Macroscopic and microscopic inspection of subsurface aliquots to search for life's indicators (paleontological, biological, mineralogical) and to characterize the mineralogy of the subsurface aliquots. The study is led by ESA Manned Spaceflight and Microgravity Directorate.