Modal mineralogy of the H-group chondrites : progressive effects of metamorphism

For several ordinary chondrite mineral phases, CIPW normative abundances are noticeably higher than modal abundances The discrepancy may result in part from the failure of the CIPW calculation to account for the A1 and Ca enriched mesostasis phase found in ordinary chondrites. The discrepancy is relatively uniform among the analyzed chondrites and may not significantly affect certain petrologie trends that were uncovered using normative calculations. Specifically, the norm trend suggesting oxidation with increasing metamorphism (McSween and Labotka, 1993) is supported by Fe enrichment in H chondrite olivine and low-Ca pyroxene, and an increase in modal H chondrite olivine abundance. The chemical and mineralogical data for H5 and H6 values commonly overlap, possibly a result of our small sample size or the misclassification of one or more chondrites. However,overlap also appears in L and LL chondrite data (e.g., Gastineau, 2000; McSween and Labotka, 1993) and may actually be the result of the gradational nature of ordinary chondrite metamorphism. Petrologie trends may be more apparent from analyses of a wider range of petrologic types, as opposed to observations of adjacent petrologie types. Plagioclase abundance did not appear to increase from type 5 to type 6 in our meteorites,suggesting that plagioclase had crystallized completely by type 5. While mesostasis remains in type 6 chondrites, the plagioclase component appears to have devitrified during type 5 metamorphism. Geothermometers that rely on plagioclase crystallizing during type 6 metamorphism may not be valid However, the leading alternative — the pyroxene geothermometer — has its own pitfalls when applied to ordinary chondrites, including the possibility that high-Ca pyroxene may not have been completely equilibrated. The high-Fe chondrite Bumwell, while unique among the known ordinary chondrites, may not represent a specimen from a previously unsampled parent body. Many of the trends in our study indicate that Bumwell petrologic characteristics lie outside of the present range for Hchondrites. However, in several trends, the gap between H chondrite and Bumwell values is smaller than the gaps between other ordinary chondrite petrologic groups. Hopefully, additional low-FeO falls will be collected, and classifications can be determined in light of petrologic types other than type 4. Because normative and modal data are not identical, previous applications of normative data to asteroid spectroscopy should be revisited While trends and overall conclusions probably will not need adjustment, the spectral data sets may need to be re-evaluated Since overall conclusions should persist in the light of new modal data, we still believe that asteroid 6 Hebe represents the best candidate for an H chondrite parent body

Electron Capture in Charge-Tagged Peptides. Evidence for the Role of Excited Electronic States

International audienceElectron capture dissociation (ECD) was studied with doubly charged dipeptide ions that were tagged with fixed-charge tris-(2,4,6-trimethoxyphenyl)phosphonium-methylenecarboxamido (TMPP-ac) groups. Dipeptides GK, KG, AK, KA, and GR were each selectively tagged with one TMPP-ac group at the N-terminal amino group while the other charge was introduced by protonation at the lysine or arginine side-chain groups to give (TMPP-ac-peptide + H)2+ ions by electrospray ionization. Doubly tagged peptide derivatives were also prepared from GK, KG, AK, and KA in which the fixed-charge TMPP-ac groups were attached to the N-terminal and lysine side-chain amino groups to give (TMPP-ac-peptide-ac-TMPP)2+ dications by electrospray. ECD of (TMPP-ac-peptide + H)2+ resulted in 72% to 84% conversion to singly charged dissociation products while no intact charge-reduced (TMPP-ac-dipeptide + H)+• ions were detected. The dissociations involved loss of H, formation of (TMPP + H)+, and N–C(alpha) bond cleavages giving TMPP-CH2CONH2+ (c0) and c1 fragments. In contrast, ECD of (TMPP-ac-peptide-ac-TMPP)2+ resulted in 31% to 40% conversion to dissociation products due to loss of neutral TMPP molecules and 2,4,6-trimethoxyphenyl radicals. No peptide backbone cleavages were observed for the doubly tagged peptide ions. Ab initio and density functional theory calculations for (Ph3P-ac-GK + H)2+ and (H3P-ac-GK + H)2+ analogs indicated that the doubly charged ions contained the lysine side-chain NH3+ group internally solvated by the COOH group. The distance between the charge-carrying phosphonium and ammonium atoms was calculated to be 13.1-13.2 Å in the most stable dication conformers. The intrinsic recombination energies of the TMPP+-ac and (GK + H)+ moieties, 2.7 and 3.15 eV, respectively, indicated that upon electron capture the ground electronic states of the (TMPP-ac-peptide + H)+• ions retained the charge in the TMPP group. Ground electronic state (TMPP-ac-GK + H)+• ions were calculated to spontaneously isomerize by lysine H-atom transfer to the COOH group to form dihydroxycarbinyl radical intermediates with the retention of the charged TMPP group. These can trigger cleavages of the adjacent N–C(alpha) bonds to give rise to the c1 fragment ions. However, the calculated transition-state energies for GK and GGK models suggested that the ground-state potential energy surface was not favorable for the formation of the abundant c0 fragment ions. This pointed to the involvement of excited electronic states according to the Utah-Washington mechanism of ECD

Quantitation of Human Immunodeficiency Virus Provirus and Circulating Virus: Relationship with Immunologic Parameters

Virologic and seroimmunologic parameters were determined in 56 persons infected with human immunodeficiency virus (HIV). The provirus level varied from 10 to 100,000/106 CD4+ lymphocytes, and genomic HIV RNA was detectable in 39 of 56 patients at a relative concentration varying from 10 to >250 copies/ml, of serum. Provirus expressed as copies per 106 CD4+ lymphocytes and as circulating virus per milliliter of serum increased with disease progression and decrease of CD4+ cell concentration. The mean provirus concentration expressed per milliliter of blood varied little among categories of patients with various levels of CD4+ cells, but there was a progressive increase of circulating HIV genomic RNA. These virologic data suggest that during the course of HIV infection, an increasing proportion of the remaining CD4+ lymphocytes harbor the HIV genome and produce infectious virus. Finally, there was a marked correlation between increased provirus and genomic RNA concentration and three seroimmunologic markers: decrease in CD4+cell count, p24 antigenemia, and disappearance of antibodies to HIV core antige

Research on mother tongue's learning strategies of pupils in Singapore

AbstractWith information and communication technology used widely in the primary school in Singapore, it will be focused how to use ICT to support the pupils to learn mother tongue. Chinese is one of mother tongue popular in Singapore. Previous research show that language learning effects have very much related to learning strategies. Thus, we would like to explore the current status of those pupils’ Chinese language learning strategies. According to Oxford's classification, the language learning strategy includes six categories: compensation, meta-cognitive, cognitive, social, memory, and affective strategies. We used the inventory SILL to know more about these strategies. We want to solve three questions: What about their strategies in learning Chinese? How are their language learning strategies influenced by their personal characters? Which of their strategies should be supported with ICT to teach?After the survey, we found that those pupils had good scores on the compensation, meta-cognitive, cognitive, and social strategies, but insufficient on the memory strategy and affective strategy. Female pupils are better than male in all six strategies. Male and female pupils have significant differences between cognitive, compensation, meta-cognitive, and affective strategy. Pupils have significant difference only in affective strategy between pupils of fourth and fifth grade. No significant difference in other strategies among three grades. Referenced to related research on ICT, we consider that teachers should integrate ICT in the classroom to increase the exercise of memory strategy and induce their affective strategy

Memphis Tours: la excelencia en el servicio

Desde el primer momento Memphis Tours de El Cairo me sorprendió por el trato personalizado. Tan pronto como hice contacto para saber que me ofrecían, el Señor Mohamed Besheer me contestó absolviendo preguntas, haciendo sugerencias y con mucha paciencia armando la visita mía que llegaría vía Madrid y la de mi primo Jorge que llegaba de Beirut. Se agregó al clásico recorrido de las Pirámides de Gize y la navegación por el Nilo, una visita a Memfis y la pirámide escalonada de Soser para el día en que estaría aún solo en El Cairo por asunto de frecuencia de vuelos

From orogenic collapse to rifting, structures of the South China Sea

The opening of the South China Sea has been a matter of debate for many years because of its internal structure, the differences between the conjugate margins and the variations of rifting and spreading directions. Although it is considered as being a back-arc basin, it is not sitting directly above a subduction zone, and the rifting process lasted for an unusually long duration. Among the specific characteristics is the early phase of rifting which took place early in place of the former Yanshanian andean-type mountain range. This stage is marked by narrow basins filled with deformed conglomerate, and initiated around 70My ago within a framework where the oblique subduction …published_or_final_versio