Near-infrared study of short-range disorder of OH and F in monoclinic amphiboles.

Amphiboles were synthesized along the joins tremolite–fluorotremolite, richterite–fluororichterite and potassic-richterite–potassic-fluororichterite at 750 8C and 1 kbar P(H2O). Infrared spectra of the amphiboles were recorded in the principal OH-stretching region. Amphiboles of the tremolite–fluorotremolite series show one-mode behavior, a single band due to a local MgMgMg-OH-AM (M 5 vacancy) arrangement; this behavior is consistent with no coupling between NNN (next-nearest-neighbor) O3 anions either through the O3- O3 edge or across the vacant A-site cavity. The amphiboles of the richterite-fluororichterite and potassic-richterite–potassic-fluororichterite series show two-mode behavior, two bands due to the local arrangements MgMgMg-OH-ANa-OH and MgMgMg-OH-ANa-F (and their K equivalents); this behavior is consistent with coupling between NNN O3 anions across the filled A-site cavity through Na or K that occupies the A-site. A mathematical model is developed to describe local (OH,F) ordering in amphiboles as a function of F content. The variation in infrared band intensities is consistent with complete short-range disorder of OH and F in the synthetic amphiboles of the richterite-fluororichterite and potassicrichterite- potassic–fluororichterite series

The CFHT Open Star Cluster Survey II -- Deep CCD Photometry of the Old Open Star Cluster NGC 6819

We present analysis of deep CCD photometry for the very rich, old open star cluster NGC 6819. These CFH12K data results represent the first of nineteen open star clusters which were imaged as a part of the CFHT Open Star Cluster Survey. We find a tight, very rich, main-sequence and turn-off consisting of over 2900 cluster stars in the V, B-V color-magnitude diagram (CMD). Main-sequence fitting of the un-evolved cluster stars with the Hyades star cluster yields a distance modulus of (m-M)v = 12.30 +/- 0.12, for a reddening of E(B-V) = 0.10. These values are consistent with a newly calculated theoretical stellar isochrone of age 2.5 Gyrs, which we take to be the age of the cluster. Detailed star counts indicate a much larger cluster extent (R = 9.5' +/- 1.0'), by a factor of ~2 over some previous estimates. Incompleteness tests confirm a slightly negatively sloped luminosity function extending to faint (V ~ 23) magnitudes which is indicative of a dynamically evolved cluster. Further luminosity function and mass segregation tests indicate that low mass objects (M < 0.65Mo) predominate in the outer regions of the cluster, 3.5 < R < 9.5. The estimation of the number of white dwarfs in NGC 6819 are in good agreement with the observed number. For those white dwarf candidates which pass both a statistical and image classification tests, we show comparisons to white dwarf isochrones and cooling models which suggest the need for spectroscopy to confirm the white dwarf nature of the brighter objects.Comment: 15 Figures and 6 Tables available in higher resolution from ADS. Accepted for Publication in AJ -- Kalirai et al. 2001b, 122, 266. Update

BNa–BLi solid-solution in A-site-vacant amphiboles: synthesis and cation ordering along the ferri-clinoferroholmquistite–riebeckite join.

Amphiboles were hydrothermally synthesized at 500 ∞C and 4 kbar in the system Li2O-Na2OFeO- Fe2O3-SiO2-H2O, with nominal compositions along the riebeckite [■Na2Fe3 2+ Fe2 3+Si8O22(OH)2]-ferri-clinoferroholmquistite [■Li2Fe3 2+Fe2 3+Si8O22(OH)2] join, where the exchange vector is NaLi–1 at the B-site. Experimental products were characterized by powder XRD and SEM-EDAX, confirming very high amphibole yield along the join (>95%, plus minor quartz). The XRD patterns can be indexed in C2/m, and the refined cell parameters show linear variation as a function of composition. For the BLi end-member, the IR spectrum shows a single sharp main band centered at 3614 cm–1, which is assigned to the FeFeFe-OH-A■ configuration. With increasing BNa in the mineral, this band broadens and shifts 4 cm–1 to higher frequencies. This effect can be attributed to the change in M4 site occupancy. Minor ANa (partial solid-solution toward arfvedsonite) is also observed with increasing sodium in the system. Mössbauer spectroscopy confirms the cation distribution provided by IR data, and shows that a small, but significant amount of Fe2+ occurs at M4 along the join. Infrared spectroscopy shows that the Li end-member has a very ordered structure, whereas intermediate compositions show local heterogeneities associated with the presence of two different B sites occupied by Na or Li

The OH-F substitution in synthetic pargasite at 1.5 kbar, 850 °C.

Amphiboles were synthesized at 1.5 kbar PH2O and 850 °C along the join pargasite-fluoropargasite. Structural variations in the amphibole as a function of F have been characterized by a combination of SEM-EDS, X-ray powder diffraction, and infrared spectroscopy. SEM-EDS analyses show that, for increasing F in the system, there is a decrease in Altot in the amphibole and a significant decrease of F incorporation in the structure. In agreement with the EDS data, the variation in cell parameters and IR spectra show that incorporation of F in pargasite is restricted to about 1.0 atoms per formula unit (apfu). The OH-stretching spectra show fine structure caused by F replacing OH at the O3 anion site, and are consistent with two-mode behavior typical of A-site-filled amphiboles. The agreement between calculated and observed relative band intensities suggests complete short-range disorder of OH and F at the O3 anion site

Site occupancies in synthetic monoclinic amphiboles: Rietveld structure refinement and infrared spectroscopy of (nickel, magnesium, cobalt)-richterite.

Amphiboles were synthesized at 750 8C, 1 kbar (H2O) on the binary joins (nickel, magnesium)-richterite and (magnesium, cobalt)-richterite. Structural variations and site occupancies were characterized by Rietveld structure refinement, with final RBragg indices in the range 4–9%, and by powder infrared spectroscopy in the principal OH-stretching region. Site-occupancy refinement of Ni-Mg and Mg-Co distributions give the partition coefficients over M1,3 and M2 where KM21 5 (M21/Mg)M1,3/(M21/Mg)M2, and M21 5 Ni21 or Co21, K 5 2.98 6 0.37 and K 5 1.34 6 0.31. Both Kd Ni Co values are greater than 1.0, d d whereas [6]r(Ni21 ) , [6]r(Mg) , [6]r(Co21 ); this indicates that cation size is not the primary factor affecting the ordering of Ni-Mg and Mg-Co over the octahedral sites. The infrared spectra of intermediate binary compositions show fine structure caused by ordering of Ni- Mg or Mg-Co over the M1,3 sites and by ordering of Na and M (vacancy) at the A site; thus intermediate compositions show an eight-band spectrum in the principal OHstretching region. Precise band intensities were derived by nonlinear least-squares fitting of Gaussian band shapes to the observed spectra. The relative observed intensities of the combinations of bands 3IA1 2IB1 IC and IB 1 2IC 1 3ID are in accord with the equations o o o o o o of Burns and Strens (1966), indicating that there is no significant variation in molar absorptivity with frequency (energy) for individual bands within a single sample (spectrum). Combined with the results of Skogby and Rossman (1991) on polarized single-crystal infrared spectra of amphiboles, this result suggests that different local configurations of M1,3 cations in amphiboles couple such that the transition probabilities of the associated OH groups are equal

Instituições e críticas na produção de tabaco do Rio Grande do Sul/Brasil: Mudanças e reafirmações institucionais

This study focuses on issues surrounding tobacco production in Brazil, seeking to understand the changes occurred in tobacco farming out of criticisms and changes in the environment. Based on the theoretical and methodological conceptions from Sociology of Critique and institutionalist theories, semi-structured interviews were conducted with relevant actors in the central region of Rio Grande do Sul, adding to documentary analysis, with a view to analyze the institutional changes that have been occurring in tobacco production. First, devices of local and global criticism were identified, as well as the transformations that engender uncertainty in the tobacco farming environment. In this set of disputes, as responses to criticism, it was possible to map the institutions that have been supporting tobacco growing. Based on this, the transformations in the actions of tobacco companies were analyzed, which appeared to be mainly semantic, aimed at requalifying the Integrated Tobacco Production System and, thus, reaffirming the institutions that support tobacco growing. Findings showed that, in the environment of tobacco-growing family farmers, institutional changes are heterogeneous, affecting both the connections with and interpretations about tobacco. As a result, some farmers are being excluded from the system, and they need government support to change their realities.Este estudio aborda la problemática situación que rodea la producción de tabaco en Brasil, con el objetivo de comprender los cambios en el escenario del cultivo del tabaco a partir de críticas y cambios en el entorno. A partir de la concepción teórica y metodológica de la Sociología Crítica y las teorías institucionalistas, se realizaron entrevistas semiestructuradas en la región central de Rio Grande do Sul y análisis documental con el objetivo de analizar los cambios institucionales que se han venido produciendo en la producción de tabaco. Primero, se identificaron los dispositivos de crítica local y global, así como las transformaciones que generan el entorno incierto en el que se inserta la producción de tabaco. En esta lista de disputas, como respuesta a las críticas, fue posible mapear las instituciones que han estado apoyando el cultivo de tabaco en RS. Con base en ello, se analizaron las transformaciones en la actuación de las empresas tabacaleras, principalmente semánticamente, recalificando el Sistema Integrado de Producción de Tabaco (SIPT) y, así, reafirmando las instituciones que apoyan el cultivo del tabaco. Como resultado principal, se encontró que, en el entorno de los agricultores familiares productores de tabaco, los cambios institucionales son heterogéneos, con cambios en los vínculos e interpretaciones sobre el tabaco. Por otro lado, en base a la conducta de las empresas tabacaleras y un grupo de agricultores que apuestan por esta perspectiva de futuro, se estima que habrá una selección de los productores más “aptos” para el sistema y la nueva legalidad. y requisitos del mercado. Como resultado, los productores están siendo excluidos del sistema que necesitan el apoyo del gobierno para cambiar sus realidades.Este estudo versa sobre a situação problemática em torno da produção de tabaco no Brasil, com o intuito de compreender as mudanças no cenário da fumicultura a partir das críticas e das transformações no ambiente. Com base na concepção teórica e metodológica da Sociologia da Crítica e de teorias institucionalistas, foram realizadas entrevistas semiestruturadas na região central do Rio Grande do Sul e análise documental com o objetivo de analisar as mudanças institucionais que vêm ocorrendo na produção de tabaco. Primeiramente, foram identificados os dispositivos das críticas locais e globais, bem como as transformações que geram o ambiente de incerteza em que a fumicultura está inserida. Nessa relação de disputas, como respostas às críticas, foi possível mapear as instituições que vêm sustentando a fumicultura no RS. Partindo disso, foram analisadas as transformações nas ações das empresas fumageiras, principalmente de forma semântica, requalificando o Sistema Integrado de Produção de Tabaco (SIPT) e, assim, reafirmando as instituições que sustentam a fumicultura. Como principal resultado verificou-se que, no ambiente dos agricultores familiares produtores de tabaco, as mudanças institucionais são heterogêneas, com mudanças nos vínculos e nas interpretações sobre o tabaco. Por outro lado, com base na conduta das empresas fumageiras e de um grupo de agricultores que apostam nessa perspectiva de futuro, estima-se que ocorrerá uma seleção dos produtores mais “aptos” ao sistema e às novas exigências legais e de mercado. Como consequência disso, produtores estão sendo excluídos do sistema os quais necessitam de um apoio governamental para a mudança de suas realidades

Scattering in PT-symmetric quantum mechanics

A general formalism is worked out for the description of one-dimensional scattering in non-hermitian quantum mechanics and constraints on transmission and reflection coefficients are derived in the cases of P, T, or PT invariance of the Hamiltonian. Applications to some solvable PT-symmetric potentials are shown in detail. Our main original results concern the association of reflectionless potentials with asymptotic exact PT symmetry and the peculiarities of separable kernels of non-local potentials in connection with hermiticity, T invariance and PT invariance.Comment: 41 pages, to appear in Ann. Phy

Controls at the starting point for preventing accidents in the road transport of dangerous products / Controles no ponto de partida para prevenção de acidentes no transporte rodoviário de produtos perigosos

This article discusses activities related to the prevention of road accidents with dangerous products that precede trips by tank truck drivers. The Brazilian normative framework (laws, decrees, and norms), the Haddon Matrix as a systemic prevention model, and the premises of the Olho Vivo nas Estradas Program of the Brazilian Chemical Industry Association constitute the conceptual bases of the research. The empirical approach consists of semi-structured interviews with drivers of a fuel distributor who travel along the BR-116. The results indicate that the company has training practices and disclosure of recent accidents. The workgroup dominates the normative knowledge and preventive procedures, being the main concern of the interviewees with the carelessness practiced by drivers who travel the roads in all types of vehicles (trucks, automobiles, motorcycles)