Exploring the contributions of liquid-phase sulfur chemistry to the mass-independent sulfur fractionation of the Archean rock record

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 30-32).Archean sulfur mass-independent fractionation (S-MIF) has been widely recognized as one of the strongest indicators for the rise of atmospheric oxygen in the Early Proterozoic. A decade after its discovery, the wide-ranging implications of Archean sulfur MIF have been discussed extensively and despite a number of recent studies on the gas-phase chemistry of sulfur, no definite overall picture has emerged to date as to the precise origin and preservation of the Archean mass-independent sulfur signal. The interpretation of the Archean sulfur MIF as a strong constraint for atmospheric oxygen levels, however, requires a dominant atmospheric source of sulfur MIF. This study was aimed at investigating the potential contribution of the poorly explored mass-independent effects from liquid-phase sulfur chemistry and focused on sulfur isotope fractionation during liquid-phase photolytic breakdown of phenacylphenylsulfone (PPS) as a model system for initial investigation. Results confirm that MIF in this system is caused by the magnetic 33S isotope and excludes other mechanisms such as nuclear volume effects or vibronic coupling that would produce concomitant MIF in the 32S-34_3-3S triad. This provides a starting point for discussing the implications of magnetic isotope effects as a mechanism for mass-independent isotope fractionation in the chemical evolution of the sulfur cycle and suggests that liquid-phase processes such as the photolysis of PPS cannot constitute the principal source of mass-independent sulfur fractionation in the Archean.by Sebastian Hermann Kopf.S.M

China’s Recent Maritime Legislation. A Study of Consistency with the International Law of the Sea and the Political Context

No abstract available

From Geocycles to Genomes and Back

A holy grail for environmental microbiologists is being able to predict the effects of any given microbial community on a particular environment. In an era of increasingly dramatic changes in global climate, this goal is becoming evermore important. It is now well accepted that microorganisms have had and continue to have a profound influence on shaping the chemistry of the Earth. It would thus be both intellectually satisfying and practically useful if we could enumerate the microbial players in a specific locale, and, knowing their metabolic potential and how they regulate their various metabolisms, make predictions about how their presence would shape the geochemistry of that locale as it evolves in time

L'évolution climatique des villes européennes

La méthode des analogues climatiques consiste à déterminer un endroit doté aujourd'hui d'un climat comparable à celui que l'on prédit à la fin du siècle. Ce travail représente ainsi ce que signifie le changement climatique pour Paris et 8 autres grandes villes européennes. Dans le scénario du Hadley Centre, le climat de Paris entre 2070 et 2100 ressemble fortement au climat actuel de Badajoz, près de Cordoue : Capitale de l'Estremadure, dans le sud-ouest de l'Espagne, caractérisé par des étés brûlants et arides . Pour tenir compte des incertitudes, cet article compare les résultats de trois des principaux modèles climatiques européens. Du climat de Badajoz à celui des pays Baltes en passant par Rome, l'éventail des futurs possibles pour Paris est encore très ouvert

Ligand-Enhanced Abiotic Iron Oxidation and the Effects of Chemical versus Biological Iron Cycling in Anoxic Environments

This study introduces a newly isolated, genetically tractable bacterium (Pseudogulbenkiania sp. strain MAI-1) and explores the extent to which its nitrate-dependent iron-oxidation activity is directly biologically catalyzed. Specifically, we focused on the role of iron chelating ligands in promoting chemical oxidation of Fe(II) by nitrite under anoxic conditions. Strong organic ligands such as nitrilotriacetate and citrate can substantially enhance chemical oxidation of Fe(II) by nitrite at circumneutral pH. We show that strain MAI-1 exhibits unambiguous biological Fe(II) oxidation despite a significant contribution (~30–35%) from ligand-enhanced chemical oxidation. Our work with the model denitrifying strain Paracoccus denitrificans further shows that ligand-enhanced chemical oxidation of Fe(II) by microbially produced nitrite can be an important general side effect of biological denitrification. Our assessment of reaction rates derived from literature reports of anaerobic Fe(II) oxidation, both chemical and biological, highlights the potential competition and likely co-occurrence of chemical Fe(II) oxidation (mediated by microbial production of nitrite) and truly biological Fe(II) oxidation

Measurement of nitrous oxide isotopologues and isotopomers by the MAT 253 Ultra

The global budget of nitrous oxide is dominated by terrestrial and marine biological sources and atmospheric sinks. Details of the budget remain unclear, including the cause of increasing atmospheric N_2O concentrations. Marine sources of N_2O include denitrification and nitrification. Our understanding of the major microbial players in the nitrogen cycle has changed in recent years (for example, the nitrifying Archaea), and the overall contributions of these organisms to N_2O production and their isotopic signatures are poorly constrained [1]

L'évolution climatique des villes européennes

La méthode des analogues climatiques consiste à déterminer un endroit doté aujourd'hui d'un climat comparable à celui que l'on prédit à la fin du siècle. Ce travail représente ainsi ce que signifie le changement climatique pour Paris et 8 autres grandes villes européennes. Dans le scénario du Hadley Centre, le climat de Paris entre 2070 et 2100 ressemble fortement au climat actuel de Badajoz, près de Cordoue : Capitale de l'Estremadure, dans le sud-ouest de l'Espagne, caractérisé par des étés brûlants et arides . Pour tenir compte des incertitudes, cet article compare les résultats de trois des principaux modèles climatiques européens. Du climat de Badajoz à celui des pays Baltes en passant par Rome, l'éventail des futurs possibles pour Paris est encore très ouvert.changement climatique; impact

Shear behavior of DFDP-1 borehole samples from the Alpine Fault, New Zealand, under a wide range of experimental conditions

The Alpine Fault is a major plate-boundary fault zone that poses a major seismic hazard in southern New Zealand. The initial stage of the Deep Fault Drilling Project has provided sample material from the major lithological constituents of the Alpine Fault from two pilot boreholes. We use laboratory shearing experiments to show that the friction coefficient µ of fault-related rocks and their precursors varies between 0.38 and 0.80 depending on the lithology, presence of pore fluid, effective normal stress, and temperature. Under conditions appropriate for several kilometers depth on the Alpine Fault (100 MPa, 160 °C, fluid-saturated), a gouge sample located very near to the principal slip zone exhibits µ = 0.67, which is high compared with other major fault zones targeted by scientific drilling, and suggests the capacity for large shear stresses at depth. A consistent observation is that every major lithological unit tested exhibits positive and negative values of friction velocity dependence. Critical nucleation patch lengths estimated using representative values of the friction velocity-dependent parameter a−b and the critical slip distance D c , combined with previously documented elastic properties of the wall rock, may be as low as ~3 m. This small value, consistent with a seismic moment M o = ~4 × 1010 for an M w = ~1 earthquake, suggests that events of this size or larger are expected to occur as ordinary earthquakes and that slow or transient slip events are unlikely in the approximate depth range of 3–7 km

ACL surgery: reasons for failure and management

Abstract Despite the general success of anterior cruciate ligament reconstructions (ACL-R), there are still studies reporting a high failure rate. Orthopedic surgeons are therefore increasingly confronted with the treatment of ACL retears, which are often accompanied by other lesions, such as meniscus tears and cartilage damage and which, if overlooked, can lead to poor postoperative clinical outcomes. The literature shows a wide variety of causes for ACL-R failure. Main causes are further trauma and possible technical errors during surgery, among which the position of the femoral tunnel is thought to be one of the most important. A successful postoperative outcome after ACL-revision surgery requires good preoperative planning, including a thorough evaluation of patient's medical history, e.g. instability during daily or sports activity, increased general joint laxity, and hints for a low-grade infection. A careful clinical examination should be performed. Additionally, comprehensive imaging is necessary. Besides a magnetic resonance imaging, a CT scan is helpful to determine location of tunnel apertures and to analyze for tunnel enlargement. A lateral knee radiograph is helpful to determine the tibial slope. The range of surgical options for the treatment of ACL-R failure is broad today. Orthopedic surgeons and experts in Sports Medicine must deal with various possible associated injuries of the knee or unfavorable anatomical conditions for ACL-R. The aim of this review was to highlight predictors and reasons of failures of ACL-R as well as describe diagnostic procedures to individualize treatment strategies for improved outcome after revision ACL-R. Keywords: ACL reconstruction; ACL revision; ACL revision management; causes of graft failure

Pediatric Cystic Fibrosis Sputum Can Be Chemically Dynamic, Anoxic, and Extremely Reduced Due to Hydrogen Sulfide Formation

Severe and persistent bacterial lung infections characterize cystic fibrosis (CF). While several studies have documented the microbial diversity within CF lung mucus, we know much less about the inorganic chemistry that constrains microbial metabolic processes and their distribution. We hypothesized that sputum is chemically heterogeneous both within and between patients. To test this, we measured microprofiles of oxygen and sulfide concentrations as well as pH and oxidation-reduction potentials in 48 sputum samples from 22 pediatric patients with CF. Inorganic ions were measured in 20 samples from 12 patients. In all cases, oxygen was depleted within the first few millimeters below the sputum-air interface. Apart from this steep oxycline, anoxia dominated the sputum environment. Different sputum samples exhibited a broad range of redox conditions, with either oxidizing (16 mV to 355 mV) or reducing (−300 to −107 mV) potentials. The majority of reduced samples contained hydrogen sulfide and had a low pH (2.9 to 6.5). Sulfide concentrations increased at a rate of 0.30 µM H_2S/min. Nitrous oxide was detected in only one sample that also contained sulfide. Microenvironmental variability was observed both within a single patient over time and between patients. Modeling oxygen dynamics within CF mucus plugs indicates that anoxic zones vary as a function of bacterial load and mucus thickness and can occupy a significant portion of the mucus volume. Thus, aerobic respiration accounts only partially for pathogen survival in CF sputum, motivating research to identify mechanisms of survival under conditions that span fluctuating redox states, including sulfidic environments