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M M Grady

Publications and source records attributed to M M Grady.

9 recordsLinked to original sources
PubMed2006

Searching for signatures of life on Mars: an Fe-isotope perspective.

Recent spacecraft and lander missions to Mars have reinforced previous interpretations that Mars was a wet and warm planet in the geological past. The role of liquid water in shaping many of the surface features on Mars has long been recognized. Since the presence of liquid water is essential for survival of life, conditions on early Mars might have been more favourable for the emergence and evolution of life. Until a sample return mission to Mars, one of the ways of studying the past environmental conditions on Mars is through chemical and isotopic studies of Martian meteorites. Over 35 individual meteorite samples, believed to have originated on Mars, are now available for lab-based studies. Fe is a key element that is present in both primary and secondary minerals in the Martian meteorites. Fe-isotope ratios can be fractionated by low-temperature processes which includes biological activity. Experimental investigations of Fe reduction and oxidation by bacteria have produced large fractionation in Fe-isotope ratios. Hence, it is considered likely that if there is/were any form of life present on Mars then it might be possible to detect its signature by Fe-isotope studies of Martian meteorites. In the present study, we have analysed a number of Martian meteorites for their bulk-Fe-isotope composition. In addition, a set of terrestrial analogue material has also been analysed to compare the results and draw inferences. So far, our studies have not found any measurable Fe-isotopic fractionation in bulk Martian meteorites that can be ascribed to any low-temperature process operative on Mars.

Biological Evolution↗
PubMed2004

A critical review of atypical antipsychotic utilization: comparing monotherapy with polypharmacy and augmentation.

The atypical antipsychotics risperidone, olanzapine, quetiapine, ziprasidone, and aripiprazole have become first-line treatment for schizophrenia because they reduce the positive symptoms of psychosis but do not have a high incidence of extrapyramidal symptoms. However, these agents, like other antipsychotics, may take as long as 16 or more weeks to produce a response, and even with prolonged treatment are unlikely to evoke responses greater than 50% improvement in symptoms. This has led to the experimental use of high atypical antipsychotic doses, antipsychotic polypharmacy, and augmentation with other psychotropic drugs, all of which occur commonly in clinical practice. This article reviews the current evidence for these increasingly common means of treating schizophrenia and psychosis, with particular emphasis on polypharmacy and augmentation. To date, there are only two controlled studies of antipsychotic polypharmacy involving an atypical antipsychotic; the rest of the data are uncontrolled trials and case reports that describe a mixture of positive and negative findings. One multicenter, double-blind trial shows a faster onset of action when divalproex is added to risperidone or olanzapine than with antipsychotic monotherapy. A small double-blind study demonstrates efficacy when lamotrigine is added to clozapine. The rest of the data on augmentation with anticonvulsants are uncontrolled, and most report adverse effects. With the exception of divalproex, there are currently no compelling data to justify the use of antipsychotic polypharmacy or augmentation. Existing evidence suggests that the best treatments for schizophrenia and psychosis may be long-term trials of a sequence of atypical antipsychotic monotherapies at therapeutic doses.

Acetates↗
PubMed1998

The origin of chondritic macromolecular organic matter: a carbon and nitrogen isotope study.

The N and C abundances and isotopic compositions of acid-insoluble carbonaceous material in thirteen primitive chondrites (five unequilibrated ordinary chondrites, three CM chondrites, three enstatite chondrites, a CI chondrite and a CR chondrite) have been measured by stepped combustion. While the range of C isotopic compositions observed is only delta 13C = 30%, the N isotopes range from delta 15N approximately -40 to 260%. After correction for metamorphism, presolar nanodiamonds appear to have made up a fairly constant 3-4 wt% of the insoluble C in all the chondrites studied. The apparently similar initial presolar nanodiamond to organic C ratios, and the correlations of elemental and isotopic compositions with metamorphic indicators in the ordinary and enstatite chondrites, suggest that the chondrites all accreted similar organic material. This original material probably most closely resembles that now found in Renazzo and Semarkona. These two meteorites have almost M-shaped N isotope release profiles that can be explained most simply by the super-position of two components, one with a composition between delta 15N = -20 and -40% and a narrow combustion interval, the other having a broader release profile and a composition of delta 15N approximately 260%. Although isotopically more subdued, the CI and the three CM chondrites all appear to show vestiges of this M-shaped profile. How and where the components in the acid-insoluble organics formed remains poorly constrained. The small variation in nanodiamond to organic C ratio between the chondrite groups limits the local synthesis of organic matter in the various chondrite formation regions to at most 30%. The most 15N-rich material probably formed in the interstellar medium, and the fraction of organic N in Renazzo in this material ranges from 40 to 70%. The isotopically light component may have formed in the solar system, but the limited range in nanodiamond to total organic C ratios in the chondrite groups is consistent with most of the organic material being, presolar.

Carbon↗
PubMed1998

A nitrogen and argon stable isotope study of Allan Hills 84001: implications for the evolution of the Martian atmosphere.

The abundances and isotopic compositions of N and Ar have been measured by stepped combustion of the Allan Hills 84001 (ALH 84001) Martian orthopyroxenite. Material described as shocked is N-poor ([N] approximately 0.34 ppm; delta 15N approximately +23%); although during stepped combustion, 15N-enriched N (delta 15N approximately +143%) is released in a narrow temperature interval between 700 degrees C and 800 degrees C (along with 13C-enriched C (delta 13C approximately +19%) and 40Ar). Cosmogenic species are found to be negligible at this temperature; thus, the isotopically heavy component is identified, in part, as Martian atmospheric gas trapped relatively recently in the history of ALH84001. The N and Ar data show that ALH84001 contains species from the Martian lithosphere, a component interpreted as ancient trapped atmosphere (in addition to the modern atmospheric species), and excess 40Ar from K decay. Deconvolution of radiogenic 40Ar from other Ar components, on the basis of end-member 36Ar/14N and 40Ar/36Ar ratios, has enabled calculation of a K-Ar age for ALH 84001 as 3.5-4.6 Ga, depending on assumed K abundance. If the component believed to be Martian palaeoatmosphere was introduced to ALH 84001 at the time the K-Ar age was set, then the composition of the atmosphere at this time is constrained to: delta 15N > or = +200%, 40Ar/36Ar < or = 3000 and 36Ar/14N > or = 17 x 10(-5). In terms of the petrogenetic history of the meteorite, ALH 84001 crystallised soon after differentiation of the planet, may have been shocked and thermally metamorphosed in an early period of bombardment, and then subjected to a second event. This later process did not reset the K-Ar system but perhaps was responsible for introducing (recent) atmospheric gases into ALH 84001; and it might mark the time at which ALH 84001 suffered fluid alteration resulting in the formation of the plagioclase and carbonate mineral assemblages.

Argon↗
PubMed1994

Record of fluid-rock interactions on Mars from the meteorite ALH84001.

Allan Hills (ALH) 84001 is the most recently recognized member of a suite of meteorites--the SNCs--that almost certainly originated on Mars. Several factors distinguish ALH84001 from the other SNC meteorites. Preliminary studies suggest that it may be older than other martian meteorites. Moreover, it contains abundant, zoned domains of calcium-iron-magnesium carbonate that are indigenous to the sample and thus may hold important clues regarding near-surface processes on Mars and the evolution of the martian atmosphere. We report here analyses of the carbon and oxygen stable-isotope compositions of the carbonates that place constraints on their formation conditions. Our results imply the presence of at least two chemically distinct carbonates--one Ca,Fe-rich, the other Mg-rich--that are enriched in 13C relative to terrestrial carbonates (delta 13C approximately +41/1000), consistent with martian atmospheric CO2 as the carbon source. The oxygen isotope compositions of the carbonates indicate that they precipitated from a low-temperature fluid in the martian crust. Combined with textural and bulk geochemical considerations, the isotope data suggest that carbonate deposition took place in an open-system environment in which the ambient temperature fluctuated.

Atmosphere↗
PubMed1993

Occupational exposure to bloodborne diseases and universal precautions: measurement of health care workers' self reported attitudes.

1. As the numbers of persons infected with bloodborne diseases continues to increase, it is paramount that all health care workers exhibit behaviors reflecting unerring compliance with universal precautions. 2. Physicians and RNs who are highly trained in bloodborne diseases and universal precautions, who have the tools available for universal precautions, and who are exposed to people with bloodborne diseases, are overwhelmingly not complying with universal precautions. 3. To better understand how attitudes impact behaviors, a valid and reliable tool was developed which measured health care workers' attitudes toward bloodborne diseases and universal precautions. 4. Training programs addressing attitudes and knowledge may help change health care workers' non-compliant behaviors into behaviors reflecting compliance with universal precautions.

Blood-Borne Pathogens↗
PubMed1989

The formation of weathering products on the LEW 85320 ordinary chondrite: evidence from carbon and oxygen stable isotope compositions and implications for carbonates in SNC meteorites.

Isotopic analysis of nesquehonite recovered from the surface of the LEW 85320 H5 ordinary chondrite shows that the delta 13C and delta 18O values of the two generations of bicarbonate (Antarctic and Texas) are different: delta 13C = +7.9% and +4.2%; delta 18O = +17.9% and 12.1% respectively. Carbon isotopic compositions are consistent with equilibrium formation from atmospheric carbon dioxide at -2 +/- 4 degrees C (Antarctic) and +16 +/- 4 degrees C (Texas). Oxygen isotopic data imply that the water required for nesquehonite precipitation was derived from atmospheric water vapour or glacial meltwater which had locally exchanged with silicates, either in the meteorite or in underlying bedrock. Although carbonates with similar delta 13C values have been identified in the SNC meteorites EETA 79001 and Nakhla, petrographic and temperature constraints argue against their simply being terrestrial weathering products.

Antarctic Regions↗