Uranium isotopes fingerprint biotic reduction.

Knowledge of paleo-redox conditions in the Earth's history provides a window into events that shaped the evolution of life on our planet. The role of microbial activity in paleo-redox processes remains unexplored due to the inability to discriminate biotic from abiotic redox transformations in the rock record. The ability to deconvolute these two processes would provide a means to identify environmental niches in which microbial activity was prevalent at a specific time in paleo-history and to correlate specific biogeochemical events with the corresponding microbial metabolism. Here, we demonstrate that the isotopic signature associated with microbial reduction of hexavalent uranium (U), i.e., the accumulation of the heavy isotope in the U(IV) phase, is readily distinguishable from that generated by abiotic uranium reduction in laboratory experiments. Thus, isotope signatures preserved in the geologic record through the reductive precipitation of uranium may provide the sought-after tool to probe for biotic processes. Because uranium is a common element in the Earth's crust and a wide variety of metabolic groups of microorganisms catalyze the biological reduction of U(VI), this tool is applicable to a multiplicity of geological epochs and terrestrial environments. The findings of this study indicate that biological activity contributed to the formation of many authigenic U deposits, including sandstone U deposits of various ages, as well as modern, Cretaceous, and Archean black shales. Additionally, engineered bioremediation activities also exhibit a biotic signature, suggesting that, although multiple pathways may be involved in the reduction, direct enzymatic reduction contributes substantially to the immobilization of uranium.

Effect of Fentanyl on Block Characteristics as Adjuvant to Intrathecal Bupivacaine for Lower Limb Surgeries.

BACKGROUND: Regional anesthesia is the preferred technique for most of lower abdominal and lower limb surgeries as it allows the patient to remain awake and minimize the problems associated with airway management. Hyperbaric bupivacaine 0.5%, although extensively used for spinal anesthesia, has a limitation of short duration. The addition of fentanyl, a synthetic lipophilic opioid, is known to prolong postoperative analgesia. AIMS: We aimed to study the effect of the addition of different doses of fentanyl to hyperbaric bupivacaine about hemodynamic changes, the extent of sensory and motor block, duration of analgesia, and complications that occur during the procedure. SETTINGS AND DESIGN: This study was a prospective, comparative, randomized, and double-blind study. MATERIALS AND METHODS: Patients were randomly allocated to three groups of 30 each. Group I (n [number of patients] = 30) received bupivacaine 0.5% heavy 2.0 mL diluted up to 2.5 mL with normal saline. Group II (n = 30) received bupivacaine 0.5% heavy 2.0 mL and fentanyl 20 µg diluted up to 2.5 mL with normal saline, and Group III (n = 30) received bupivacaine 0.5% heavy 2.0 mL and fentanyl 50 µg diluted up to 2.5 mL with normal saline. STATISTICAL ANALYSIS: The data were analyzed using Chi-square and Student's t-test. RESULTS AND CONCLUSIONS: The onset of sensory and motor block was early in Group III in comparison to Group I and Group II (P < 0.05). The duration of analgesia was significantly longer in Group III, followed by Group II, and least in Group I. None of the patients in Groups I and II had any complications such as hypotension, nausea, vomiting, bradycardia, and pruritus. However, the incidence of hypotension, nausea, and pruritus was more in Group III. 2 mg intrathecal bupivacaine with 20 µg fentanyl provides reliable and satisfactory sensory and motor block without increasing the incidence of side effects.

Astrobiological stoichiometry.

Chemical composition affects virtually all aspects of astrobiology, from stellar astrophysics to molecular biology. We present a synopsis of the research results presented at the "Stellar Stoichiometry" Workshop Without Walls hosted at Arizona State University April 11-12, 2013, under the auspices of the NASA Astrobiology Institute. The results focus on the measurement of chemical abundances and the effects of composition on processes from stellar to planetary scales. Of particular interest were the scientific connections between processes in these normally disparate fields. Measuring the abundances of elements in stars and giant and terrestrial planets poses substantial difficulties in technique and interpretation. One of the motivations for this conference was the fact that determinations of the abundance of a given element in a single star by different groups can differ by more than their quoted errors. The problems affecting the reliability of abundance estimations and their inherent limitations are discussed. When these problems are taken into consideration, self-consistent surveys of stellar abundances show that there is still substantial variation (factors of ∼ 2) in the ratios of common elements (e.g., C, O, Na, Al, Mg, Si, Ca) important in rock-forming minerals, atmospheres, and biology. We consider how abundance variations arise through injection of supernova nucleosynthesis products into star-forming material and through photoevaporation of protoplanetary disks. The effects of composition on stellar evolution are substantial, and coupled with planetary atmosphere models can result in predicted habitable zone extents that vary by many tens of percent. Variations in the bulk composition of planets can affect rates of radiogenic heating and substantially change the mineralogy of planetary interiors, affecting properties such as convection and energy transport.