Exchange Vector Research Articles

Likelihood ratio ordering of order statistics, mixtures and systems

Let X = ( X 1 , X 2 , … , X n ) be an exchangeable random vector, and denote X 1 : i = min { X 1 , X 2 , … , X i } and X i : i = max { X 1 , X 2 , … , X i } , 1 ⩽ i ⩽ n . These order statistics represent the lifetimes of the series and the parallel systems, respectively, with component lifetimes X i . In this paper we obtain conditions under which X 1 : i (or X i : i ) decreases (increases) in i in the likelihood ratio (lr) order. An even more general result involving general (that is, not necessary exchangeable) random vectors is also derived for general series (or parallel) systems. We show that the series (parallel) systems are not necessarily lr-ordered even if the components are independent. The likelihood ratio order can be characterized in terms of Glaser's function, defined by η ( t ) = - f ′ ( t ) / f ( t ) where f is the density function. This function is also a very useful tool to study the shape of hazard (or failure) rate and the mean residual life functions (see Glaser, R.E., 1980. Bathtub and related failure rate characterizations. J. Amer. Statist. Assoc. 75 (371), 667–672). It is also useful to study the likelihood ratio ordering and the increasing (or decreasing) likelihood ratio ILR (DLR) class. In this paper we also study properties of Glaser's function of mixtures. Specifically, we study ordering properties, monotonicity and the limiting behaviour. We show that, under some conditions, the limiting behaviour is similar to that of the strongest member (in the likelihood ratio order) of the mixture. We also consider the case of finite negative mixtures (i.e. mixtures which have some negative coefficients) which is applied to study Glaser's function of general coherent systems and order statistics and, in particular, the likelihood ratio ordering of coherent systems. The results are illustrated through a series of examples.

Micas of the muscovite–lepidolite series from Karibib pegmatites, Namibia

AbstractMicas of the muscovite–lepidolite series are main constituents of the evolved pegmatites from the Okatjimukuju-Kaliombo portion of the Karibib belt, Namibia. The compositional variations shown by the micas from the intermediate zones are mainly controlled by the Li3Al-1□-2 and SiLi2Al-2□-1 substitution schemes, whereas for the micas from the core margins and the replacement bodies, only the first of these two exchange vectors seems to operate. The chemical composition of the micas not only depends on the degree of pegmatite evolution, but also on the position in the internal zonation of the pegmatite. Micas from the core margins and the replacement units are generally richer in F, Li, Rb, Cs and Zn than those from the intermediate zones. In general, the contents of these elements increase with decreasing K/Rb ratio. However, some data departing from this general trend are also observed, which could be related to subsolidus processes. Some pegmatite bodies show a complete internal evolution, developed from the margins to the core zone, which is reflected in the chemical composition of the micas. The regional distribution of pegmatites does not define a zonation, because an overlapping of pegmatites with different degrees of evolution occurs. This could be due to the high level of evolution attained by most of the rare-element pegmatites, and to their topography with respect to a dome structure of the basement.

Negative Selection with the Diphtheria toxin A fragment Gene Improves Frequency of Cre-Mediated Cassette Exchange in ES Cells

The Cre-lox system is an important tool for genetic manipulation in embryonic stem cells. We previously reported that the cassette exchange strategy using the mutant lox66/71 and lox2272 combination showed high recombination efficiency and stability. However, the efficiency was strongly affected by the position of chromosomal target lox sites. To enrich successful cassette exchange events, even in clones showing lower recombination efficiency, we have improved exchange vector. The Diphtheria toxin A fragment gene was placed in the un-exchanged region for negative selection and the puromycin N-acetyltransferase gene, instead of the neomycin phosphotransferase gene, was used for positive selection. By reducing random integration, the frequency of successful cassette exchange increased up to 2-4 fold. Furthermore, by adding the third lox site to induce intrarmolecular recombination, the recombination efficiency of cassette exchange itself was improved, and the frequency increased to maximum 5 fold, in which the percentage of exchanged clones reached to 50-70%. This strategy should be useful for other recombinase-mediated cassette exchanges.

A rare garnet-tourmaline-sillimanite-biotite-ilmenite-quartz assemblage from the granulite-facies region of south-central Massachusetts

A rare lithology consisting of garnet-tourmaline-sillimanite-biotite-ilmenite-quartz has been found within the granulite-facies region of south-central Massachusetts. The homogeneous, Ti-rich oxy-dravitic tourmaline, X Mg = Mg/(Mg + Fe) = 0.72.0.77, falls into the alkali group, and is similar in composition to lower grade tourmaline found in corresponding metapelitic rocks in Maine. Charge-balancing calculations and binary diagrams suggest that, like biotite in the region, tourmaline has undergone deprotonation by means of the exchange vectors AlOR -1 (OH) -1 and TiO 2 R -1 (OH) -2 , where R represents Fe + Mg. The restriction of a concordant tourmaline-rich horizon in otherwise tourmaline-free rocks of this granulite-facies region suggests that either: (1) B, released during prograde fluid-absent dehydration reactions of muscovite and biotite, was locally available in a fluid phase or melt for later crystallization near the peak of granulite-facies metamorphism along pathways that provided a conduit for fluid migration; or (2) that this is simply a B-rich compositional horizon (tourmalinite) that survived anatexis and granulite-facies metamorphism and that records the incipient conditions of tourmaline breakdown and subsequent recrystallization near or post-peak metamorphism.

Y,REE,Nb,Ta,Ti-oxide (AB 2O 6) minerals from REL–REE euxenite-subtype pegmatites of the Třebíč Pluton, Czech Republic; substitutions and fractionation trends

Aeschynite-group minerals (AGM) and euxenite-group minerals (EGM) occur in REL–REE euxenite-subtype pegmatites from the Třebíč Pluton, Czech Republic. They form strongly metamictized, light brown to black, equigranular to needle-like, subhedral to anhedral grains enclosed in blocky K-feldspar and less commonly in albite, and blocky quartz, and in the graphic unit (quartz and K-feldspar). Both AGM and EGM are homogeneous to slightly heterogeneous in BSE images. They are not commonly associated with the other primary Y,REE,Ti,Nb-bearing minerals, i.e. allanite-(Ce), monazite-(Ce), titanite, and ilmenite, which occur within the same textural-paragenetic unit. Aeschynite-(Y), aeschynite-(Ce), aeschynite-(Nd), nioboaeschynite-(Ce), tantalaeschynite-(Ce), vigezzite and polycrase-(Y) were identified using EMP and canonical discrimination analysis [Ercit, T.S., 2005a. Identification and alteration trends of granitic–pegmatite-hosted (Y,REE,U,Th)–(Nb,Ta,Ti) oxide minerals: a statistical approach. Can. Mineral. 43, 4 1291–1303.]. The exchange vector ACa B(Nb,Ta) A(Y,REE) − 1 BTi − 1 or its combination with the exchange vector ACa 2 B(Nb,Ta) 3 A(U,Th) − 1 A(Y,REE) − 1 BTi − 3 have been elucidated for the AGM. The exchange vector ACa A(U,Th) A(Y,REE) − 2 is predominant in the EGM. The AGM are enriched in HREE, whereas LREE are concentrated in the EGM. Weak to none-existent geochemical fractionations, as expressed by the U/(U + Th), Y/(Y + REE), Ta/(Ta + Nb) and (Nb + Ta)/(Ti + Nb + Ta) ratios, were noted for single grains from both the AGM and EGM, as well as in grains of polycrase-(Y) from four different textural-paragenetic units located in the Vladislav pegmatite. Simultaneous increase of U/(U + Th) and Y/(Y + REE) in the AGM during fractionation is typical. The Ta/(Ta + Nb) fractionation is usually weak and contradicts the Y/(Y + REE) and U/(U + Th) fractionation trends. This unusual behavior of Nb and Ta may be controlled by associated Ti-rich minerals (titanite, ilmenite, rutile), the composition of parental melt and/or by elevated F activity. The AGM and EGM from pegmatites of the Třebíč Pluton are quite similar in composition to those from REL–REE euxenite-subtype pegmatites in the Trout Creek Pass, Chaffee County, Colorado, USA, which are generally Ca,U,Th-depleted, show lower Ta/(Ta+Nb), and lower variation in HREE/LREE.

Compositional evolution and substitutions in disseminated and nodular tourmaline from leucocratic granites: Examples from the Bohemian Massif, Czech Republic

Two distinct textural types of tourmaline have been distinguished in leucocratic granites of the Bohemian Massif (Moldanubicum, Saxothuringicum): (i) commonly euhedral disseminated tourmaline (DT) crystallized during relatively early stage of the granite consolidation, and (ii) typically interstitial nodular tourmaline (NT) formed during the stage transitional from late solidus to early subsolidus crystallization. The following substitutions (exchange vectors) participated in tourmaline from the studied granites: (1) X□ YAl XNa − 1 YR 2+ − 1 in the DT granites from the Moldanubicum; (2) X□ YAl 3 WO 2 XNa − 1 YR 2+ − 3 W(OH) − 2 and (6) XNa YR 2+WF X□ − 1 YAl − 1 WOH − 1 in the DT and NT granites from the Saxothuringicum. Tourmaline in the NT granites from the Moldanubicum yielded a complicated pattern indicating participation of several substitutions such as (1), (2) and (3) X□ YAl 2 WO XNa − 1 YR 2+ − 2 W(OH) − 1 . Very similar chemical compositions and similar fractionation trends in both DT and NT tourmaline types indicate crystallization in a quasi-closed system from early solidus to early subsolidus stage of granite consolidation. Substitutions in tourmaline from NT granites in the Moldanubicum are more similar to substitutions in tourmaline from Li-poor granitic pegmatites in the same region relative to tourmaline from DT granites. Plotting up EMP analyses of tourmaline indicates that a combination of two ternary diagrams Al–Fe–Mg and Na–Ca– X-site vacancy, coupled with simple plots involving single cations (elements) such as Na/Al, F/Na, Fe/Mg, characterizes both their chemical composition as well as the probable substitution mechanisms. Complex diagrams such as R1 + R2 versus R3 do not enable a proper investigation of the compositional evolution in the X-site and W-site and oversimplify the real substitutions. As a consequence the use of specific diagrams for specific tourmaline compositions (e.g., Ca-rich, Li-rich) is recommended.

Arsenian monazite-(Ce) and xenotime-(Y), REE arsenates and carbonates from the Tisovec-Rejkovo rhyolite, Western Carpathians, Slovakia: Composition and substitutions in the (REE,Y)XO 4 system (X = P, As, Si, Nb, S)

A unique REE–Y–(Th)–P–As–(Si)–(Nb)–(S) accessory assemblage was identified in a small body of Lower Triassic A-type rhyolite of the Silicic Superunit near Tisovec-Rejkovo, Central Slovakia. Arsenian monazite-(Ce)–phosphatian gasparite-(Ce) and arsenian xenotime-(Y)–phosphatian chernovite-(Y) solid solutions in association with REE carbonates (bastnäsite, parisite, röntgenite?, synchysite) and rare cerianite-(Ce) form anhedral to subhedral grains and aggregates (≤ 0.3 mm), scattered in the groundass or as intergrowths with zircon and Fe–Ti oxides. Compositions show a wide AsP − 1 substitution in monazite–gasparite and xenotime–chernovite solid solutions; atom. % As/(As+P) = 0.00 to 0.73 and 0.10 to 0.94, respectively. The presence of S in monazite–gasparite s.s. (≤ 0.14 apfu), together with Ca enrichment indicates “clinoanhydrite“ substitution, CaS(REE,Y) − 1 (P,As) − 1 , rather than the incorporation of brabantite, along the CaTh(REE,Y) − 2 exchange vector. Moreover, the Th- and Nb-rich members reveal thorite and fergusonite substitutions, ThSi(Y,REE) − 1 (P,As) − 1 and Nb(P,As) − 1 , respectively. The As-rich REE phases originated probably during the post-magmatic alteration of primary monazite-(Ce) and xenotime-(Y) by As-rich, high fO 2 fluids, whereas cerianite-(Ce) and the REE carbonates are products of a later hydrothermal overprint of the rhyolite by CO 2-rich solutions.

Garnet reequilibration and growth in the eclogite facies and geodynamical evolution near peak metamorphic conditions

Caledonian eclogite-facies metamorphism partially reworking Grenvillian granulite-facies anorthosite allows us to study the processes of garnet reequilibration at high pressure and to reconstruct the evolution of the unit near metamorphic peak conditions. Our results indicate that eclogite-facies metamorphism happened in two successive phases: first, inherited granulitic garnet was fractured and reequilibrated from their boundaries (crystal or fracture rims); then eclogite-facies minerals were crystallised in the fractures as overgrowths on inherited garnets. The reequilibration of inherited garnets is achieved through Fe2+Mg−1 exchange, whereas eclogite-facies garnets crystallised during the subsequent phase are notably richer in Ca than un- and re-equilibrated granulitic garnet. Pseudosection construction shows that this lack in Ca reequilibration cannot be related to variations in thermodynamic conditions (a H2O, reacting system composition) between the two phases. From the compilation of the available data, the reequilibration of granulitic garnet seems to be controlled by the inefficient intra- and inter-granular transport properties of Ca compared to Fe2+ and Mg. While these kinetic factors confine garnet reequilibration to Fe2+Mg−1 exchange, the extent of reequilibration along this exchange vector is controlled by partitioning with adjacent omphacite. On the contrary to the diffusional reequilibration of granulitic garnet that lasted for several My according to our modelling of the diffusional relaxation, the strong compositional gradients between eclogite-facies and reequilibrated garnets, which are almost unaffected by diffusional reequilibration, provide evidence that rapid exhumation followed the crystallisation of eclogite-facies minerals. We propose that the movement reversal itself, from burial to exhumation, and associated deformation and fluid flow, triggered this crystallisation event. The resulting evolution near metamorphic peak conditions is therefore strongly asymmetrical: on the one hand, the prograde diffusional relaxation profiles indicate slow movement during the last stages of burial, whereas the unaffected retrograde overgrowth indicates fast exhumation rates.

Angular dependence of potassium K-edge XANES spectra of trioctahedral micas: Significance for the determination of the local structure and electronic behavior of the interlayer site

The X-ray absorption angle-dependent behavior at the potassium K -edge has been determined for two end-members and two intermediate trioctahedral micas, which are representative of the Fe2+Mg−1, Fe3+Al−1, SiAl−1FeLi−1, and F−1OH exchange vectors, using horizontally polarized synchrotron radiation. Experimental spectra are interpreted by the multiple scattering theory following decomposition according to the angular dependence approach of Brouder (1990). The experimental spectra sum up anisotropic effects deriving from in-plane and out-of-plane photoelectron interactions with the potassium near- and next-near neighbors up to the fifth/sixth coordination sphere. For the first time, the absorption edge of a low Z atom is decomposed so as to produce two partial patterns giving, respectively, the full in-plane absorption spectrum (σ||) and the full out-of-plane spectrum (σ⊥). They fully describe the complete X-ray absorption dichroic behavior of layered compounds, of which mica is a prototype. σ|| essentially reflects the arrangement of the atoms located in the mica interlayer space and facing tetrahedral sheets. Differences among the four micas depend on structural changes induced by the adaptation of their tetrahedral sheets to the increasing sizes of their octahedral sheet due to chemical substitutions (i.e., the Fe2+Mg−1 vector, mainly) and to chemical changes at the octahedral anion site (F−1OH vector). By contrast, σ⊥ reflects multiple-scattering interactions entering deep into the mica structure, beyond the tetrahedral sheet and well into the octahedral sheet. Such contributions reflect both changes in the anions coordinating the octahedral cations and increasing total amount of heavy atoms (essentially Fe), and differ based on electronic properties such as oxidation states (e.g., Fe2+ and Fe3+). Therefore, angle-dependent XANES spectroscopy is one of the rare spectroscopic techniques able not only to detect, but also to quantify structural effects in the atoms at the medium- to long-range order.

Suicide vectors for antibiotic marker exchange and rapid generation of multiple knockout mutants by allelic exchange in Gram-negative bacteria

Allelic exchange is frequently used in bacteria to generate knockout mutants in genes of interest, to carry out phenotypic analysis and learn about their function. Frequently, understanding of gene function in complex processes such as pathogenesis requires the generation of multiple mutant strains. In Pseudomonads and other non-Enterobacteriaceae, this is a time-consuming and laborious process based on the use of suicide vectors and allelic exchange of the appropriate mutant version of each gene, disrupted by a different antibiotic marker. This often implies the generation of a series of mutants for each gene, each disrupted by a different antibiotic marker, in order to obtain all possible double or multiple mutant combinations. In this work, we have modified this method by developing a set of 3 plasmid derivatives from the previously described suicide vector for allelic exchange, pKAS32, to make antibiotic marker exchange easier and thus accelerate the entire process. Briefly, the construction of each single gene knockout mutant is carried out by allelic exchange of the chromosomal gene with a mutant allele disrupted by the insertion of a kanamycin resistance cassette. When a double mutant strain is required, antibiotic marker exchange is performed in either one of the single mutants, using any of the three plasmid derivatives that carry the kanamycin resistance gene disrupted by either a chloramphenicol, gentamycin, or streptomycin resistance cassette. The single mutant strain, carrying now an antibiotic resistance marker other than kanamycin, can be used to introduce a second mutation using the original plasmid constructs, to generate a double mutant. The process can be repeated sequentially to generate multiple mutants. We have validated this method by generating strains carrying different combinations of mutations in genes encoding different transcriptional regulators of the Hrp type III secretion system in Pseudomonas syringae. We have also tested the genetic organisation and stability of the resulting mutant strains during growth in laboratory conditions as well as in planta.

Hazard rate ordering of order statistics and systems

LetX= (X1,X2, …,Xn) be an exchangeable random vector, and writeX(1:i)= min{X1,X2, …,Xi}, 1 ≤i≤n. In this paper we obtain conditions under whichX(1:i)decreases iniin the hazard rate order. A result involving more general (that is, not necessarily exchangeable) random vectors is also derived. These results are applied to obtain the limiting behaviour of the hazard rate function of the lifetimes of various coherent systems in reliability theory. The notions of the Samaniego signatures and the minimal signatures of such systems are extensively used in the paper. An interesting relationship between these two signatures is obtained. The results are illustrated in a series of examples.

Hazard rate ordering of order statistics and systems

Let X = (X1, X2, …, Xn) be an exchangeable random vector, and write X(1:i) = min{X1, X2, …, Xi}, 1 ≤ i ≤ n. In this paper we obtain conditions under which X(1:i) decreases in i in the hazard rate order. A result involving more general (that is, not necessarily exchangeable) random vectors is also derived. These results are applied to obtain the limiting behaviour of the hazard rate function of the lifetimes of various coherent systems in reliability theory. The notions of the Samaniego signatures and the minimal signatures of such systems are extensively used in the paper. An interesting relationship between these two signatures is obtained. The results are illustrated in a series of examples.

Parvo-mangano-edenite, parvo-manganotremolite, and the solid solution between Ca and Mn2+ at the M4 site in amphiboles

This work reports the crystal-chemical characterization of Mn-rich amphiboles from the Grenville Marble of the Arnold mine, Fowler, St. Lawrence Co., New York (U.S.A.), which were previously described by Benimoff et al. (1991) as “manganoan silicic edenite”. According to the new nomenclature scheme for monoclinic amphiboles (Leake et al. 2004) the ideal composition of reference, A Na B (CaMn) C Mg 5 T (Si 7 Al)O 22 (OH) 2 with Ca > 1 apfu, is an end-member of the newly defined Group 5, and is named parvo-mangano-edenite. Re-examination of the original rock specimen showed significant inter- and intra-crystalline compositional variations, which can be expressed by the A Na -1 T Al -1 A ⃞ 1 T Si 1 and B Mn 2 B Ca -2 exchange vectors. The first vector leads to parvo-manganotremolite, ideally A ⃞ B (CaMn) C Mg 5 T Si 8 O 22 (OH) 2 with Ca > 1. The second mechanism was never found to reach Mn dominance; however, crystal-chemical analysis does not provide any evidence of structural limits, and thus the magno-calcic counterparts of the Group 5 amphiboles of this work may occur in similar but Mn-richer genetic environments. The presence of Mn at the B site helps to stabilize the charge arrangement of edenite. The parvo-mangano-edenite crystal with composition closest to the end-member, i.e., A(Na 0.74 K 0.02 )B(Ca 1.27 Mn 0.73 )C(Mg 4.51 Mn 2+ 0.28 Fe 2+ 0.05 Fe 3+ 0.03 Al 0.12 Ti 0.01 )T(Si 7.07 Al 0.93 )O 22 (OH) 2 , has a = 9.8260(5), b = 18.0487(9), c = 5.2840(4) Å, β = 104.55(1)º, V = 907.1 Å 3 (Z = 2); the calculated density is 3.11 g/cm 3 . The parvo-mangano tremolite crystal, with composition A (Na 0.44 K 0.01 ) B (Ca 1.13 Mn 0.83 Na 0.04 ) C (Mg 4.69 Mn 2+ 0.21 Fe 2+ 0.03 Fe 3+ 0.01 Al 0.06 ) T (Si 7.52 Al 0.48 )O 22 (OH) 2 , has a = 9.7807(5), b = 18.0548(9), c = 5.2928(4) Å, β = 104.19(1)º, V = 906.1 Å 3 (Z = 2); the calculated density is 3.08 g/cm 3 . The different compositions are virtually indistinguishable under the optical microscope, but can be identified by a measure of their unit-cell parameters. The single-crystal FTIR spectrum of parvo-mangano-edenite in the OH-stretching region shows two main absorptions at 3711 and 3671 cm -1 , plus shoulders at 3695, 3660, and 3641 cm -1 , respectively. FTIR spectroscopy indicates extensive short-range-order of cations in these amphiboles.

Mechanisms and geochemical significance of Si–Al substitution in zeolite solid solutions

Rock-forming zeolites often exhibit complex solid solutions reflecting isomorphous substitutions between Si and Al in tetrahedral framework sites, between charge-balancing extraframework cations, and between water molecules and vacancies. Although the number of moles of charge on extraframework cations in a zeolite must equal the moles of Al in order to maintain charge balance, the relationships between Si–Al and extraframework substitutions vary considerably across this mineral group. Review of available compositional data suggests that there are three main modes of Si–Al substitution in zeolites: 1) coupled CaAl–NaSi substitution; 2) coupled substitution of a single extraframework cation plus Al for Si; and 3) completely uncoupled substitution among extraframework cations and Si and Al on tetrahedral sites. Among zeolites that exhibit the latter two modes of solid solution, Si–Al substitution can be described by an SiO 2 (± H 2O) compositional exchange vector from a hypothetical, pure-silica endmember composition. Recent calorimetric, structural, and theoretical investigations suggest that Si–Al substitution follows a non-ideal, athermal solution model characterized by no excess enthalpies of mixing and negative excess entropies of mixing. Because Si–Al exchange in these minerals can be explicitly or implicitly described by exchange of an SiO 2 component, the Si/Al ratio in their framework can be predicted solely as a function of temperature, pressure, and the chemical potential of SiO 2. Application of this model leads to calculated Si/Al ratios in stilbite (coexisting with albite), analcime, and chabazite consistent with observed mineral compositions and parageneses in very low-grade metamorphic environments. Coexistence of silica polymorphs with zeolites containing SiO 2· nH 2O exchange vectors potentially provides a means of performing thermobarometric calculations in very low-grade metamorphic and diagenetic environments.

Potassium coordination in trioctahedral micas investigated by K-edge XANES spectroscopy

Fine-grained homogeneous powder samples of thirteen trioctahedral micas, mostly intermediate members of the phlogopite – annite solid solution series, and samples close to the phlogopite, fluor-phlogopite and tetra-ferriphlogopite end members have been examined at the potassium K-edge by X-ray absorption fine structure spectroscopy. The interlayer K+ cation is in a coordination that is certainly lower than 12, in contrast to what is expected from the ideal hexagonal symmetry model of the mica structure, and approaches – but it does not reach – coordination 6, as it should be when the effective ligands are the three nearest outer bridging oxygens of two facing upper and lower tetrahedral sheets. The observed range of coordinations implies that only some of the three inner bridging oxygen atoms in each sheet are involved, thus leading to 6±(1 … 6) effective configurations depending on the composition of the individual mica terms. The effective coordination number was found to vary continuously with composition from 11 to 7 and to be related to the tetrahedral rotation angle (α) according to two different linear relationships for the phlogopite – annite series (Fe2+Mg−1 exchange vector, involving the octahedral sheet only) and the phlogopite – tetra-ferriphlogopite series (Fe3+Al−1 vector, involving the tetrahedral sheet), respectively. Substitutions affecting either the A cation in the interlayer or the X anion in the octahedral sheet also affect the observed trends. In particular, the latter substitution effect is best seen in two near end member phlogopites, where the fluorine to hydroxyl substitution (F− (OH)−−1 exchange vector), which greatly changes the α tetrahedral rotation angle is, reflected in the experimental K XANES spectra by modifying not only the energy but also the intensities of most multiple scattering features.

High atmosphere‐ocean exchange of organic carbon in the NE subtropical Atlantic

The air‐sea exchange of organic carbon (OC) remains largely unexplored, except for few organic compounds comprising a small fraction of the total aerosol and gaseous OC in the atmosphere. Observations of high atmospheric concentrations and diffusive air‐sea exchanges for such individual organic compounds, suggest that air‐sea exchange of total OC may contribute significantly to the oceanic carbon budget. Here we quantify the atmosphere‐ocean exchanges of total OC in the NE Subtropical Atlantic. Average net gaseous diffusive air‐water fluxes averaged –31 and –25 mmol C m−2 d−1 for the spring and fall, respectively, exceeding measured OC inputs by dry aerosol deposition (FDDOC, −0.98 mmol C m−2 d−1) and net CO2 exchange (FCO2, −6.3 mmol C m−2 d−1). These fluxes are important to understand the regional carbon budget of the NE Subtropical Atlantic, and depict the atmosphere as a major dynamic vector for OC exchange with the ocean.

Upregulation of Proinflammatory Proteins Through NF-κB Pathway by Shed Membrane Microparticles Results in Vascular Hyporeactivity

Microparticles are membrane vesicles with procoagulant and proinflammatory properties released during cell activation, including apoptosis. The present study was designed in dissecting the effects evoked by microparticles on vascular reactivity. Microparticles from either apoptotic T lymphocytic cells or from plasma of diabetic patients with vascular complications induced vascular hyporeactivity in response to vasoconstrictor agents in mouse aorta. Hyporeactivity was reversed by nitric oxide (NO) synthase plus cyclooxygenase-2 inhibitors, and associated with an increased production of vasodilatory products such as NO and prostacyclin. Microparticles induced an upregulation of proinflammatory protein expressions, inducible NO-synthase and cyclooxygenase-2, mainly in the medial layer of the vessels as evidenced by immunochemical staining. In addition, microparticles evoke NF-kappaB activation probably through the interaction with the Fas/Fas Ligand pathway. Finally, in vivo treatment of mice with lymphocyte-derived MPs induces vascular hyporeactivity, which was reversed by the combination of NO and cyclooxygenase-2 inhibitors. These data provide a rationale to explain the paracrine role of microparticles as vectors of transcellular exchange of message in promoting vascular dysfunction during inflammatory diseases.

Synthesis and crystal-chemistry of alkali amphiboles in the system Na2O-MgO-FeO-Fe2O3-SiO2-H2O as a function of fO2

This paper reports the results of hydrothermal synthesis in the system Na 2 O-MgO-FeO-Fe 2 O 3 -SiO 2 -H 2 O. Four samples of stoichiometric magnesioriebeckite composition, ideally □Na 2 Mg 3 Fe 3+ 2 Si 8 O 22 (OH) 2 , were run at 700–800 °C, 0.4 GPa, and redox conditions varying from NNO (Nickel–Nickel Oxide) to NNO + 2.3 log f O 2 . Powder XRD and SEM-EDX show a high (>85%) amphibole yield for all samples; however, in no case was the end-member composition attained. EMP analyses show that the amphiboles obtained deviate strongly from nominal stoichiometry toward magnesio-arfvedsonite [NaNa 2 Mg 4 Fe 3+ Si 8 O 22 (OH) 2 ]. Powder XRD patterns were indexed in the space group C 2/ m ; refined cell-parameters reflect variations in the amphibole composition, and the cell volume is correlated linearly with the A-site occupancy. Mossbauer spectra show that in all samples, Fe 3+ is completely ordered at M2, whereas Fe 2+ occurs at the M1, M3, and M4 sites. The Fe 3+ /Fe 2+ ratio is a function of f O 2 : for increasing oxidation conditions, there is significant increase in M2 Fe 3+ and decrease in Fe 2+ , notably in M4 Fe 2+ . Mossbauer spectra also show significant variation in M1 Fe 2+ and M3 Fe 2+ quadrupole splitting as a function of the Fe 3+ content in the amphibole. IR spectra in the OH-stretching region show a well-resolved quadruplet at frequencies −1 , assigned to octahedral M1,3 (Mg, Fe 2+ )-OH- A □ configurations, and a broad band consisting of four overlapping components related to M1,3 (Mg, Fe 2+ ) configurations associated with occupied A-sites. Quantitative evaluation of the relative band intensities suggests a linear increase of A-site occupancy with decreasing f O 2 of synthesis. The composition of the amphiboles synthesized, can be best described by a combination of the C (Mg,Fe 2+ ) 1 B (Mg,Fe 2+ ) 1 C Fe 3+ −1 B Na −1 and the A Na 1 C (Mg,Fe 2+ ) 1 A □ −1 C Fe 3+ −1 exchange vectors. The experimental trend is in accord with the trend documented for natural amphiboles, and suggests that the amphibole composition can in fact be used to monitor changes in f O 2 during crystallization.

Ca-Fe3+-rich, Si-undersaturated buchite from Zelenky, North-Bohemian Brown Coal Basin, Czech Republic

Si-undersaturated Ca-Fe-rich buchite produced by fossil burning of a coal seam occurs in porcelanite deposit at Želenky in the North-Bohemian Brown Coal Basin, Czech Republic. Buchite is highly inhomogeneous, dense (ρ = 2.9–3.1 g/cm 3 ), strongly magnetic rock (10 −2 −10 −1 [SI]) composed of melilite, clinopyroxene (esseneite), spinel-group minerals, hematite, Ca 2 SiO 4 , calcite, aragonite, anorthite, anhydrite, perovskite, barite, two calcium ferrites - orthorhombic Ca 2 Fe 2 3+ O 5 (srebrodolskite) and CaFe 4 3+ O 7 , barium hexaferrite - BaFe 12 3+ O 19 , along with other several poorly identified phases. Clinopyroxene is rich in esseneite component (19–63 mol. %) and in a hypothetical end-member CaFe 3+ Fe 3+ SiO 6 (up to 25 mol. %) due to Fe 3+ substitution in tetrahedral sites (up to 0.26 apfu), and also in a hypothetical component Ca(Fe 2+ Mg) 0.5 Ti 0.5 AlSiO 6 (2–36 mol. %) due to incorporation of Ti (0.012–0.18 apfu), in M1 site. Melilite shows a wide compositional variability (mol. %): gehlenite 21–93, ferrigehlenite 0–34, akermanite 1–49, ferroakermanite 0–25, soda-melilite 0–15. Spinel-group minerals show solid solutions of Mf 12–80, Mt 1–62, Sp 2–68, Hc 0–21 (mol. %). Srebrodolskite, orthorhombic Ca 2 (Fe 3+ Al) 2 O 5 is widely substituted by Si and Ti. There are negative correlations among Fe + Al vs. Si + Ti ( R 2 = 0.998), and Ca (or R 2+ ) vs. total vacancy ( R 2 = 0.94), which are consistent with an exchange vector 2R 4+ □2R 3+ -1 Ca -1 , and suggest a hypothetical end-member Ca □ (SiTi) 2 O 5 . Calcium ferrite associated with srebrodolskite, ideally CaFe 4 3+ O 7 , shows extensive compositional variability: Ca 0.6–0.8 Fe 3+ 2.7–3.6 Al 0.1–0.6 Mg 0.2–0.6 Si 0.1–0.5 O 7 . First natural occurrence of barium hexaferrite, (Ba 0.6–1.1 Ca 0.1–0.2 )(Fe 3+ 10.0–11.7 Al 0.3–0.9 Ti 0.1–0.6 Mg 0.1–0.4 Mn 0.0–0.2 ) O 19 , ideally BaFe 3+ 12 O 19 , is reported. Variations of magnetic susceptibility with temperature were also investigated. Buchite originated by fusion of Tertiary clay and residual ash with overlying Quaternary sediments (loess loam with carbonate horizon) during fossil combustion of Miocene coal seam.

A Mössbauer and FTIR study of synthetic amphiboles along the magnesioriebeckite – ferri-clinoholmquistite join

A series of amphiboles along the magnesioriebeckite—□Na2Mg3Fe3+ 2Si8O22(OH)2– ferri-clinoholmquistite—□Li2Mg3Fe3+ 2Si8O22(OH)2 - join, defined by the BLiB Na−1 exchange vector, were hydrothermally synthesized at 700°C, 0.4 GPa, NNO + 1 redox conditions. Powder XRD and SEM-EDAX showed a very high (> 90%) amphibole yield for all samples. X-ray patterns were indexed in the C2/m space group; refined cell-parameters show a linear decrease of a and β as a function of chemistry. IR spectra in the OH-stretching region show four main and rather sharp bands; these are assigned to Mg and Fe2+ at M(1,3), and indicate that the obtained amphiboles depart from the nominal octahedral composition (M1,3Mg3). The IR spectra also show that there is an increasing filling-up of the A-site for increasing Na in the system (increasing solid-solution toward, arfvedsonite). Mossbauer spectra show four well-defined quadrupole doublets which are assigned to Fe3+ at M2 and to Fe2+ at M1, M3 and M4, respectively. The Fe3+/Fe2+ content derived from fitted peak areas show variable Fe3+ concentration along the series. Mossbauer spectra also show a distinct alteration of 57Fe hyperfine parameters with changing Na–Li at M4. The most evident variation is observed for the quadrupole splitting of Fe3+ at M2, which increases by ≈50% from ferri-clinoholmquistite to magnesio-riebeckite; this suggest that the M2 octahedron in ferri-clinoholmquistite is much closer to the ideal geometry than the M2 octahedron in magnesio-riebeckite. Mossbauer spectra show also a well-defined increase in the Fe2+ quadrupole splitting of the M1 and M3 octahedra, which is attributed to the Na–Li distribution at the B-sites.