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  • 1
    Electronic Resource
    Electronic Resource
    Quantitative structure-activity relationships by neural networks and inductive logic programming. II. The inhibition of dihydrofolate reductase by triazines (1994)
    Springer
    Journal of computer aided molecular design 8 (1994), S. 421-432 
    Details
    ISSN: 1573-4951
    Keywords: QSAR ; Artificial intelligence ; Neural networks ; DHFR inhibitors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary One of the largest available data sets for developing a quantitative structure-activity relationship (QSAR) — the inhibition of dihydrofolate reductase (DHFR) by 2,4-diamino-6,6-dimethyl-5-phenyl-dihydrotriazine derivatives — has been used for a sixfold cross-validation trial of neural networks, inductive logic programming (ILP) and linear regression. No statistically significant difference was found between the predictive capabilities of the methods. However, the representation of molecules by attributes, which is integral to the ILP approach, provides understandable rules about drug-receptor interactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00125376
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  • 2
    Electronic Resource
    Electronic Resource
    Quantitative structure-activity relationships by neural networks and inductive logic programming. I. The inhibition of dihydrofolate reductase by pyrimidines (1994)
    Springer
    Journal of computer aided molecular design 8 (1994), S. 405-420 
    Details
    ISSN: 1573-4951
    Keywords: QSAR ; Artificial intelligence ; Neural networks ; DHFR inhibitors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Neural networks and inductive logic programming (ILP) have been compared to linear regression for modelling the QSAR of the inhibition of E. coli dihydrofolate reductase (DHFR) by 2,4-diamino-5-(substitured benzyl)pyrimidines, and, in the subsequent paper [Hirst, J.D., King, R.D. and Sternberg, M.J.E., J. Comput.-Aided Mol. Design, 8 (1994) 421], the inhibition of rodent DHFR by 2,4-diamino-6,6-dimethyl-5-phenyl-dihydrotriazines. Cross-validation trials provide a statistically rigorous assessment of the predictive capabilities of the methods, with training and testing data selected randomly and all the methods developed using identical training data. For the ILP analysis, molecules are represented by attributes other than Hansch parameters. Neural networks and ILP perform better than linear regression using the attribute representation, but the difference is not statistically significant. The major benefit from the ILP analysis is the formulation of understandable rules relating the activity of the inhibitors to their chemical structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00125375
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  • 3
    Electronic Resource
    Electronic Resource
    Feature construction with Inductive Logic Programming: A Study of Quantitative Predictions of Biological Activity Aided by Structural Attributes (1999)
    Springer
    Data mining and knowledge discovery 3 (1999), S. 37-57 
    Details
    ISSN: 1573-756X
    Keywords: constructive induction ; indicator variables ; ILP ; QSAR ; drug design ; scientific discovery
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract Recently, computer programs developed within the field of Inductive Logic Programming (ILP) have received some attention for their ability to construct restricted first-order logic solutions using problem-specific background knowledge. Prominent applications of such programs have been concerned with determining “structure-activity” relationships in the areas of molecular biology and chemistry. Typically the task here is to predict the “activity” of a compound (for example, toxicity), from its chemical structure. A summary of the research in the area is: (a) ILP programs have largely been restricted to qualitative predictions of activity (“high”, “low” etc.); (b) When appropriate attributes are available, ILP programs have equivalent predictivity to standard quantitative analysis techniques like linear regression. However ILP programs usually perform better when such attributes are unavailable; and (c) By using structural information as background knowledge, an ILP program can provide comprehensible explanations for biological activity. This paper examines the use of ILP programs as a method of “discovering” new attributes. These attributes could then be used by methods like linear regression, thus allowing for quantitative predictions while retaining the ability to use structural information as background knowledge. Using structure-activity tasks as a test-bed, the utility of ILP programs in constructing new features was evaluated by examining the prediction of biological activity using linear regression, with and without the aid of ILP learnt logical attributes. In three out of the five data sets examined the addition of ILP attributes produced statistically better results. In addition six important structural features that have escaped the attention of the expert chemists were discovered. The method used here to construct new attributes is not specific to the problem of predicting biological activity, and the results obtained suggest a wider role for ILP programs in aiding the process of scientific discovery.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1009815821645
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  • 4
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    Vanadium K Xanes Studies of EET79001 Impact-Melt Glasses Revisited (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Some impact-melt glasses in shergottites are rich in Martian atmospheric noble gases and sulfur suggesting a possible association with regolith-derived secondary mineral assemblages in the shocked samples. Previously, we studied two glasses, # 506 (Lith C in Lith A) and # 507 (Lith C in Lith B) from EET79001 [1,2] and suggested that sulfur initially existed as sulfate in the glass precursor materials and, on shock-melting of the precursors, the sulfate was reduced to sulfides in the shock glasses. To examine the validity of this hypothesis, we used V K microXANES techniques to measure the valence states of vanadium in the Lith C glasses from Lith A and Lith B in EET79001 [3] to complement and com-pare with previous analogous measurements on,78 glass (Lith C in Lith A) [4,5]. We reported the preliminary results in [3]. Vanadium is ideal for addressing the redox issue because it has multiple valence states and is a well-studied element. Vanadium in basalts exists mostly as V(sup 3+), V(sup 4+) and V(sup 5+) in terrestrial samples, mainly as V(sup 3+) with minor V(sup 2+) and minor V(sup 4+) in lunar samples and as roughly equal mixtures of V(sup 3+) and V(sup 4+) in Martian meteorites. In this report, we discuss the application of the V K XANES results to decipher the nature of shock reduction occurring in the silicate glasses during the impact process.
    Keywords: Geophysics
    Type: JSC-CN-35350 , Lunar and Planetary Science Conference; Mar 21, 2016 - Mar 25, 2016; The Woodlands, TX; United States
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  • 5
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    Al-Mg Isotope Study of Allende 5241 (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The defining characteristic of type B1 CAIs is a large (.5- 3mm) concentric melilite mantle [1]. In [2] we presented two isochrons from separate traverses across the melilite mantle of Allende EK 459-5-1. The primary petrographic differences between the traverses was the preservation of strong oscillatory zoning. The traverse that crossed the distinctive oscillatory zone produced a pristine internal isochron, while the other that did not have a strongly preserved oscillatory zone produced a disturbed isochron indicated by more scatter (higher MSWD) and a positive (delta)26Mg* intercept. The implication simply being that the oscillatory zone may represent varying conditions during the mantle formation event. We targeted a similar texture in Allende 5241 using the same methodology in an attempt to achieve similar results.
    Keywords: Geophysics
    Type: JSC-CN-35195 , Lunar and Planetary Science Conference; Mar 21, 2016 - Mar 25, 2016; The Woodlands, TX; United States
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  • 6
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    CAIs in Semarkona (LL3.0) (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Calcium, Aluminum-rich inclusions (CAIs) are the first forming solids of the Solar system. Their observed abundance, mean size, and mineralogy vary quite significantly between different groups of chondrites. These differences may reflect the dynamics and distinct cosmochemical conditions present in the region(s) of the protoplanetary disk from which each type likely accreted. Only about 11 such objects have been found in L and LL type while another 57 have been found in H type ordinary chondrites, compared to thousands in carbonaceous chondrites. At issue is whether the rare CAIs contained in ordinary chondrites truly reflect a distinct population from the inclusions commonly found in other chondrite types. Semarkona (LL3.00) (fall, ~691 g) is the most pristine chondrite available in our meteorite collection. Here we report petrography and mineralogy of 3 CAIs from Semarkona
    Keywords: Geophysics
    Type: JSC-CN-35196 , Lunar and Planetary Science Conference; Mar 21, 2016 - Mar 25, 2016; The Woodlands, TX; United States
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  • 7
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    Particle Size Distributions Obtained Through Unfolding 2D Sections: Towards Accurate Distributions of Nebular Solids in the Allende Meteorite (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Size distributions of nebular solids in chondrites suggest an efficient sorting of these early forming objects within the protoplanetary disk. The effect of this sorting has been documented by investigations of modal abundances of CAIs (e.g., [1-4]) and chondrules (e.g., [5-8]). Evidence for aerodynamic sorting in the disk is largely qualitative, and needs to be carefully assessed. It may be a way of concentrating these materials into planetesimal-mass clumps, perhaps 100 fs of ka after they formed. A key parameter is size/density distributions of particles (i.e., chondrules, CAIs, and metal grains), and in particular, whether the radius-density product (rxp) is a better metric for defining the distribution than r alone [9]. There is no consensus between r versus rxp based models. Here we report our initial tests and preliminary results, which when expanded will be used to test the accuracy of current dynamical disk models.
    Keywords: Geophysics
    Type: JSC-CN-25638 , 43rd Lunar aud Plauetary Science Conference; Mar 19, 2012 - Mar 23, 2012; The Woodlands, TX; United States
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  • 8
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    Dissolution of Olivine, Siderite, and Basalt at 80 Deg C in 0.1 M H2SO4 in a Flow Through Process: Insights into Acidic Weathering on Mars (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The occurrence of jarosite, other sulfates (e.g., Mg-and Ca-sulfates), and hematite along with silicic-lastic materials in outcrops of sedimentary materials at Meridiani Planum (MP) and detection of silica rich deposits in Gusev crater, Mars, are strong indicators of local acidic aqueous processes [1,2,3,4,5]. The formation of sediments at Meridiani Planum may have involved the evaporation of fluids derived from acid weathering of Martian basalts and subsequent diagenesis [6,7]. Also, our previous work on acid weathering of basaltic materials in a closed hydro-thermal system was focused on the mineralogy of the acid weathering products including the formation of jarosite and gray hematite spherules [8,9,10]. The object of this re-search is to extend our earlier qualitative work on acidic weathering of rocks to determine acidic dissolution rates of Mars analog basaltic materials at 80 C using a flow-thru reactor. We also characterized residual phases, including poorly crystalline or amorphous phases and precipitates, that remained after the treatments of olivine, siderite, and basalt which represent likely MP source rocks. This study is a stepping stone for a future simulation of the formation of MP rocks under a range of T and P.
    Keywords: Geophysics
    Type: JSC-CN-25629 , 43rd Lunar and Planetary Science Conference; Mar 19, 2012 - Mar 23, 2012; The Woodlands, TX; United States
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  • 9
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    Laboratory Shock Experiments on Basalt - Iron Sulfate Mixes at Approximately 40-50 GPa and Their Relevance to the Martian Regolith Component Present in Shergottites (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Basaltic shergottites such as Shergotty, Zagami and EET79001 contain impact melt glass pockets that are rich in Martian atmospheric gases [1] and are known as gas-rich impact-melt (GRIM) glasses. These glasses show evidence for the presence of a Martian regolith component based on Sm and Kr isotopic studies [2]. The GRIM glasses are sometimes embedded with clusters of innumerable micron-sized iron-sulfide blebs associated with minor amounts of iron sulfate particles [3, 4]. These sulfide blebs are secondary in origin and are not related to the primary igneous sulfides occurring in Martian meteorites. The material comprising these glasses arises from the highly oxidizing Martian surface and sulfur is unlikely to occur as sulfide in the Martian regoilith. Instead, sulfur is shown to occur as sulfate based on APXS and Mossbauer results obtained by the Opportunity and Spirit rovers at Meridiani and Gusev [5]. We have earlier suggested that the micron-sized iron sulfide globules in GRIM glasses were likely produced by shock-reduction of iron sulfate occurring in the regolith at the time when the GRIM glasses were produced by the meteoroid impact that launched the Martian meteorites into space [6]. As a result of high energy deposition by shock (approx. 40-60 GPa), the iron sulfate bearing phases are likely to melt along with other regolith components and will get reduced to immiscible sulfide fluid under reducing conditions. On quenching, this generates a dispersion of micron-scale sulfide blebs. The reducing agents in our case are likely to be H2 and CO which were shock-implanted from the Martian atmosphere into these glasses along with the noble gases. We conducted lab simulation experiments in the Lindhurst Laboratory of Experimental Geophysics at Caltech and the Experimental Impact Laboratory at JSC to test whether iron sulfide globules can be produced by impact-driven reduction of iron sulfate by subjecting Columbia River Basalt (CRB) and ferric sulfate mixtures to shock pressures between 40 and 50 GPa under reducing conditions. The experimental products from the recovered samples were analyzed by SEM and microprobe techniques at JSC.
    Keywords: Geophysics
    Type: JSC-CN-25635 , 43rd Lunar and Planetary Science Conference; Mar 19, 2012 - Mar 23, 2012; The Woodlands, TX; United States
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  • 10
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    Indigenous Carbon Embedded in Apollo 17 Black Volcanic Glass Surface Deposits (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The assessment of indigenous organic matter in returned lunar samples was one of the primary scientific goals of the Apollo program. The levels of such organic material were expected to be and found to be small. Previous work on this topic includes Murphy et al. [1] who reported the presence of anthropogenic organics with sub-ppm concentrations in Apollo 11 fines. In Apollo 12 samples, Preti et al. [2] detected low levels, 〈 10 ppb or below, of more complex organic material that may have been synthesized by abrupt heating during analysis. Kvenvolden et al. [3] detected porphyrin-like pigments at the ng to pg level in an Apollo 11 bulk sample. Hodgson et al. [4] and Ponnamperuma et al. [5] suggested that most if not all porphyrins were synthesized from rocket fuel during module landing. Chang et al. [6] reported indigenous carbon ranging from 5-20 g/g in the form of metal carbides in Apollo 11 fines. Hare et al. [7] reported amino acids at he 50 ng/g level in Apollo 11 samples but suggested the results may be explained as contamination. More recently, Clemett et al. [8] reported simple polycyclic aromatic hydrocarbons at concentrations of 〈 1ppm in an Apollo 16 soil. Low concentrations of lunar organics may be a consequence not only of its paucity, but also its heterogeneous distribution. If the sample size required for a measurement is large relative to the localization of organics, detection is limited not by ultimate sensitivity but rather by the ability to distinguish an indigenous signature from background contamination [9].
    Keywords: Geophysics
    Type: JSC-CN-25667 , 43rd Lunar aud Plauetary Science Conference; Mar 19, 2012 - Mar 23, 2012; The Woodlands, TX; United States
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