A structural, infrared, and Mossbauer spectral study of rosemaryite, NaMnFe3+Al(PO4)(3)

in European Journal of Mineralogy (2006), 18(6, NOV-DEC), 775-785

Rosemaryite, ideally NaMnFe(3+)AI(PO4)(3), has been collected in the Buranga pegmatite, Rwanda. A single-crystal structure refinement was performed to R-1 = 4.01 %, in the P2(1)/n space group, with a = 12 ... [more ▼]

Rosemaryite, ideally NaMnFe(3+)AI(PO4)(3), has been collected in the Buranga pegmatite, Rwanda. A single-crystal structure refinement was performed to R-1 = 4.01 %, in the P2(1)/n space group, with a = 12.001(2), b = 12.396(1), c = 6.329(1) angstrom, beta 114.48(1)degrees, Vol. = 856.9(2) angstrom(3), Z = 4. The crystal structure and cation distributions are similar to those of ferrorosemaryite, NaFe2+Fe3+Al(PO4)(3), and qingheiite, Na2MnMgAl(PO4)(3), but aluminium predominantly occurs in the M(2a) site, not in the M(2b) site as observed in ferrowyllieite, Na2Fe22+Al(PO4)(3). The topologies of the X(1a) and X(1b) crystallographic sites are identical to those found in ferrorosemaryite, and correspond to a distorted octahedron and to a distorted cube, respectively. The [7+1]-coordinated X(2) site is a very distorted gable disphenoid, similar to the A(2)' site of the alluaudite structure. Mossbauer spectra have been obtained from 4.2 to 295 K, and fitted with a model including two Fe3+ and two Fe2+ doublets. The Fe2+ component corresponding to 2/3 of the Fe2+ spectral area and having a smaller quadrupole splitting of 2.63 mm/s at 15 K, is assigned to the Fe2+ on the M(2a) site, and the Fe2+ component with the larger quadrupole splitting of 3.17 mm/s at 15 K, is assigned to the Fe2+ on the M(1) site. Fe3+ is located only at the M(2a) and M(2b) sites, and the Fe3+ component corresponding to 3/4 of the Fe3+ and exhibiting the larger quadrupole spitting of 0.77 mm/s at 15 K, is most likely associated with Fe3+ on the M(2b) site. The infrared spectrum of rosemaryite shows absorption bands at 3450 and 1624 cm(-1), bands that arise from the vibrational modes of H2O and confirm the presence of water in the channels of the wyllieite structure. A comparison of both the Mossbauer spectra and structural data of rosemaryite with those of other phosphates of the alluaudite and wyllieite groups, is also presented. [less ▲]

Structural, Magnetic and Mössbauer Spectral Study of the Electronic Spin-state Transition in {Fe[HC(3-Mepz)2(5-Mepz)]2}(BF4)2

in Inorganic Chemistry (2009), 48

The complex {Fe[HC(3-Mepz)2(5-Mepz)]2}(BF4)2 (pz = pyrazolyl ring) has been prepared by the reaction of HC(3-Mepz)2(5-Mepz) with Fe(BF4)2·6H2O. The solid state structures obtained at 294 and 150 K show a ... [more ▼]

The complex {Fe[HC(3-Mepz)2(5-Mepz)]2}(BF4)2 (pz = pyrazolyl ring) has been prepared by the reaction of HC(3-Mepz)2(5-Mepz) with Fe(BF4)2·6H2O. The solid state structures obtained at 294 and 150 K show a distorted iron(II) octahedral N6 coordination environment with the largest deviations arising from the restrictions imposed by the chelate rings. At 294 K the complex is predominately high-spin with Fe–N bond distances averaging 2.14 Å, distances that are somewhat shorter than expected for a purely high-spin iron(II) complex because of the presence of an admixture of ca. 70 (I get 80 from both mag and X-ray, 3/15, where 3 is the subtraction of 2.14 and 2.17 and 15 1.99 and 2.14 and from Figure 3b) percent high-spin and 30 (20) percent low-spin iron(II). At 294 K the twisting of the pyrazolyl rings from the ideal C3v symmetry averages only 2.2o, a much smaller twist than has been observed previously in similar complexes. At 150 K the Fe–N bond distances average 1.99 Å, indicative of an almost fully low-spin iron(II) complex; the twist angle is only 1.3o, as expected for a complex with these Fe–N bond distances. The magnetic properties show that the complex undergoes a gradual change from low-spin iron(II) below 85 K to high-spin iron(II) at 400 K. The 4.2 to 60 K Mössbauer spectra correspond to a fully low-spin iron(II) complex but, upon further warming, the iron(II) begins to undergo spin-state relaxation on the Mössbauer time scale such that, at 155 and 315 K, the complex is 7.5 and 65 percent high-spin in the absence of any adjustment for the differing low-spin and high-spin recoil-free fractions. I would replace the previous sentence with the red. I see no reason to give the % from the Mössbauer in the abstract as it is likely a bit low as discussed in detail – neither the mag data nor X-ray data have the recoil issue. The last sentence in the abstract is the key information. OK The 4.2 to 60 K Mössbauer spectra correspond to a fully low-spin-iron(II) complex but, upon further warming above 85 K the iron(II) begins to undergo spin-state relaxation between the low- and high-spin forms on the Mössbauer time scale. At 155 and 315 K the complex exhibits spin-state relaxation rates of 0.36 and 7.38 MHz, respectively, and an Arrhenius plot of the logarithm of the relaxation rate yields an activation energy of 670 ± 40 cm–1 for the spin-state relaxation. [less ▲]

A structural, magnetic, and Mossbauer spectral study of several Na-Mn-Fe-bearing alluaudites

in Physics and Chemistry of Minerals (2004), 31(8), 487-506

The synthesis and the chemical, structural, magnetic, and Mossbauer spectral characterization of three synthetic alluaudites, Na2Mn2Fe(PO4)(3), NaMn Fe-2(PO4)(3) and (Na2MnFeFeIII)-Fe-II(PO4)(3), and a ... [more ▼]

The synthesis and the chemical, structural, magnetic, and Mossbauer spectral characterization of three synthetic alluaudites, Na2Mn2Fe(PO4)(3), NaMn Fe-2(PO4)(3) and (Na2MnFeFeIII)-Fe-II(PO4)(3), and a natural sample with the nominal composition of NaMn Fe-2(PO4)(3), collected in the Buranga pegmatite, Rwanda, are reported. All four compounds have the expected alluaudite monoclinic C2/c structure with the general formula [A(2)A(2)'][A(1)A(1)'A(1)(2)'']M(1)M(2)(2)(PO4)(3) in which manganese(II) is on the M(1) site and manganese(II), iron(III) and, in some cases, iron(II) on the M(2) site. The X-ray structure of Na2Mn2Fe(PO4)(3) also indicates a partially disordered distribution of Na-I and Mn-II on the M(1) and A(1) crystallographic sites. All four compounds are paramagnetic above 40 K and antiferromagnetically ordered below. Above 40 K the effective magnetic moments of NaMnFe2(PO4)(3) and Na2MnFeII Fe-III(PO4)(3) are those expected of high-spin manganese(II) and iron(III) with the (6)A(1g) electronic ground state and high-spin iron(II) with the T-5(2g) electronic ground state. In contrast, the effective magnetic moment of Na2Mn2Fe(PO4)(3) is lower than expected as a result of enhanced antiferromagnetic exchange coupling by the manganese(II) on the M(2) site. The Mossbauer spectra of all four compounds have been measured from 4.2 to 295 K and have been found to be magnetically ordered below 40 K for Na2Mn2Fe(PO4)(3) and similar to35 K for the remaining compounds. The Mossbauer spectra of Na2Mn2Fe(PO4)(3) exhibit the two expected iron(III) quadrupole doublets and/or magnetic sextets expected for a random distribution of manganese(II) and iron(III) ions on the M(2) site. Further, the Mossbauer spectra of (Na2MnFeFeIII)-Fe-II(PO4)(3) exhibit the two iron(II) and two iron(III) quadrupole doublets and/or magnetic sextets expected for a random distribution of iron(II) and iron(III) on the M(2) site. Surprisingly, the synthetic and natural samples of NaMnFe2(PO4)(3) have 19 and 10% of iron(II) on the M(2) site; apparently the presence of some iron(II) stabilizes the alluaudite structure through the reduction of iron(III)-iron(III) repulsion. The temperature dependence of the iron(II) quadrupole splitting yields a 440 to 600 cm(-1) low-symmetry component to the octahedral crystal field splitting at the M(2) site. The iron(II) and iron(III) hyperfine fields observed at 4.2 K are consistent with the presence of antiferromagnetic ordering at low temperatures in all four compounds. [less ▲]

Structurally conserved C-RFa revealed prolactin releasing activity in vitro and gene expression changes in pituitary of seasonally acclimatized carp.

in Biological Research (2012), 45(2), 183-92

Here we show the cloning and characterization of a novel homolog of prepro C-RFa cDNA from Cyprinus carpio. The deduced preprohormone precursor of 115 amino acids leads to a mature bioactive peptide of 20 ... [more ▼]

Here we show the cloning and characterization of a novel homolog of prepro C-RFa cDNA from Cyprinus carpio. The deduced preprohormone precursor of 115 amino acids leads to a mature bioactive peptide of 20 amino acids with identical sequence to other teleost C-RFa. Modeling of the mature C-RFa peptide highlighted significant similarity to homologous human PrRP20, specifically the conserved amphipathic system defined by the C-terminal alpha-helix. Clearly, the synthetic C-RFa peptide stimulated prolactin release from primary cultured fish pituitary cells. For the first time, significant variation was shown in C-RFa mRNA and protein levels in the hypothalamus and pituitary between summer- and winter-acclimatized carp. Furthermore, C-RFa protein distribution in carp central nervous tissue was visualized by immunodetection in fibers and cells in hypothalamus, olfactory tract, cerebellum and pituitary stalk. In conclusion, we demonstrated the structure conservation of C-RFa in teleosts and mammals and immunopositive cells and fibers for C-RFa in brain areas. Finally, the increase of C-RFa expression suggests the participation of this hypothalamic factor in the mechanism of modulation in PRL expression in carp. [less ▲]

Structuration dans les milieux granulaires

Master's dissertation (2005)

L'objet de ce travail est l'étude des milieux granulaires soumis des oscillations sinusoïdales et des phénomènes de structurations qui peuvent s'y produire. Trois parties le composent : la première partie ... [more ▼]

L'objet de ce travail est l'étude des milieux granulaires soumis des oscillations sinusoïdales et des phénomènes de structurations qui peuvent s'y produire. Trois parties le composent : la première partie est une introduction générale o quelques propriétés des granulaires sont exposés et où quelques structures dissipatives sont comparées. La deuxième partie présente les différents modèles permettant de décrire les phénomènes de structurations dont traite le travail. La dernière partie consiste en une étude expérimentale réalisée au laboratoire du GRASP. L'étude des différents modèles a montré que, contrairement aux fluides ou aux solides, des équations d'évolution de la densité, la vitesse et la température n'étaient pas parfaitement établies, ceci étant du à la nature fortement dissipative des milieux granulaires. Une analyse du système a également révélé qu'une description de type "milieu continu" n'est pas parfaitement justifiée, car la séparation entre les échelles microscopiques et macroscopiques est assez floue dans les milieux granulaires. L'étude expérimentale a permis de reproduire la plupart des structurations décrites dans la littérature, malgré les nombreuses imperfections du dispositif employé (vibrations fournies par un haut-parleur). Quelques mesures de longueur d'onde des "patterns" en fonction de la fréquence ont été réalisées. L'étude des comportements d'une couche constituée de deux matériaux granulaires différents a révélé que les mêmes structurations que dans la couche homogène se produisent, les plus gros grains se plaçant sur au-dessus des plus petits. En conclusion, les milieux granulaires en général et des phénomènes de structuration en particulier sont des domaines très vastes en plein développements. Les aspects théorique, numérique et expérimental méritent chacun de faire l'objet de recherche. Ce travail permet de faire le point sur les connaissances actuelles dans le domaine et ouvre de nombreuses perspectives d'étude. [less ▲]

Structuration de la diversité génétique du genre Milicia: taxonomie, phylogéographie, dynamique des populations

Doctoral thesis (2012)

Characterizing population genetic structure using phylogeographic approach contributes to understanding of evolutionary processes that affect plant populations. The present study investigated how past ... [more ▼]

Characterizing population genetic structure using phylogeographic approach contributes to understanding of evolutionary processes that affect plant populations. The present study investigated how past environmental variations can shape the spatial genetic diversity of an African timber tree species, Milicia excelsa (Welw) C.C. Berg. Given that plant responses to disturbances are closely linked to life history traits, this research also aimed to describe relationships between the reproductive traits of M. excelsa and its population genetic structure. Phylogeographic analyses were performed throughout the range of M. excelsa using nuclear and chloroplastic markers. Ecological characterization was conducted for a single population located in south-East Cameroon. Since M. excelsa is similar to the other species of its genus, M. regia (A. Chev) C.C. Berg, we first performed a morphogenetic comparison of these two taxa. The results confirmed an important morphological similarity between the two species with very rare discriminating criteria. In fact Bayesian assignment methods and reproductive isolation patterns suggest the occurrence of interspecific hybridization, which appeared to be unidirectional: hybrids displayed the M. regia morphotype. Because M. regia is known to be more adapted to humid tropical forests, one may expect it to occur in the Congo basin zone. However, its range is restricted to the western part of West Africa while M. excelsa occurs from Guinea-Conakry to Zimbabwe. Interestingly, in the case of M. excelsa, Central and West African specimens had no shared haplotype. This result was unexpected because long gene dispersal distances were found in Cameroonian populations, as expected from the behaviours of the main dispersal animals we identified, the bat Eidolon helvum and the parrots Psittacus erithacus and Agapornis swindernianus. In general, despite the likelihood for long distance seed dispersal, distinct genetic clusters were identified over West and Central Africa and their location may support the forest refugia hypothesis. In addition a phylogeographical signal was detected in chloroplast DNA indicating a prolonged separation between West and Central Africa populations with an accumulation of new mutations. At a smaller spatial scale, patterns of genetic structure also seemed to be weakly influenced by divergent reproduction times among sympatric individuals. The level of genetic diversity in the study populations falls within the range of values calculated for other tropical tree species. If phylogeography helps to infer population history, it also requires ecological or biological information to confirm some uncertainties. Such detailed data were often lacking to completely interpret numerous of our results. The present study raised new questions and led to new perspectives for further investigation both in phylogeography and botany. [less ▲]

Structuration du territoire pour répondre aux objectifs de réduction des émissions des gaz à effets de serre

in Teller, Jacques (Ed.) La dimension territoriale des politiques énergétiques et de réduction des GES (2010, November)

Nous présentons ici une recherche relative à l’impact de la structuration du territoire sur les émissions de gaz à effets de serre (GES). Trois champs de variables ont été prospectés à cette fin : les ... [more ▼]

Nous présentons ici une recherche relative à l’impact de la structuration du territoire sur les émissions de gaz à effets de serre (GES). Trois champs de variables ont été prospectés à cette fin : les variables territoriales bien sûr, mais également socio-économiques et technologiques, Celles-ci ont permis l’élaboration d’un cadastre énergétique des émissions dans deux domaines principaux de l’aménagement du territoire: la mobilité et le bâti. Il ressort de ces analyses que des gains d’émissions de GES appréciables sont envisageables à court à et à long terme, notamment dans le domaine du bâti. Cependant, ils ne peuvent être interprétés sans une réflexion de nature territoriale. La Wallonie est de fait caractérisée par une forte périurbanisation combinée à un très faible recyclage du parc bâti. Ces caractéristiques structurelles du territoire imposent aujourd’hui de formuler des réponses adaptées à différents types d’urbanisation (urbain, rural, périurbain). [less ▲]

Structuration spatiale des marches fonciers et production de l’urbanisation morphologique. Application à la Belgique et à ses nouveaux espaces résidentiels

Conference (2005, June 28)

Structure à conserver et aménagement à prévoir pour le conservation de la loutre en Région wallonne

Learning material (2012)

La loutre d’Europe est un mammifère protégé devenu rare en Région wallonne. Autrefois, l’espèce était pourtant présente sur l’ensemble des réseaux hydrographiques du pays. Très exigeante par rapport à la ... [more ▼]

La loutre d’Europe est un mammifère protégé devenu rare en Région wallonne. Autrefois, l’espèce était pourtant présente sur l’ensemble des réseaux hydrographiques du pays. Très exigeante par rapport à la qualité de son habitat et de sa nourriture, la loutre constitue un excellent témoin de l’état de santé de nos rivières. Mais si la population de loutre d’Europe paraît chez nous aujourd’hui au bord de l’extinction, on constate que d’autres populations européennes sont en pleine progression, notamment à partir de la France (Massif central) et de l’Allemagne. Elle gagne du terrain chaque année, amenuisant la distance qui nous sépare des autres populations européennes. Ce guide propose l’identification des abris potentiels pour la loutre ainsi que des aménagements des cours d’eau propices à son retour, puisqu’on pourrait l’espérer, à partir des populations européennes, d’ici 15 ou 20 ans. [less ▲]

Structure and behavior of rat primary and secondary Schwann cells in vitro

in Experimental Cell Research (1981), 131(2), 283-297

The structure and motility of isolated rat primary (I) Schwann cells (SC) have been compared to that of subcultured (II) SC during and after mitotic stimulation. I SC contain myelin components which ... [more ▼]

The structure and motility of isolated rat primary (I) Schwann cells (SC) have been compared to that of subcultured (II) SC during and after mitotic stimulation. I SC contain myelin components which persist for 2 weeks in serum-free medium while they rapidly disappear in medium containing serum and high glucose concentration. These components were never detected in II SC. Both I SC and II SC after their mitotic phase are spindle-shaped, contain many intermediate and actin filaments, have no basement membrane but show intense migratory and undulatory activities. Rare fibroblasts in I cultures are recognized by their extremely variable shape, the presence of Thy 1.1 antigen in their membrane and their intense edge ruffling alternating with abrupt translocation. In contrast, I SC movements consist of intracellular translocation of nuclei along SC processes, which retract and extend constantly, and in slow rhythmic undulation episodes (2.3 ± 0.2/min) alternating with migration at 135 ± 50 μ/h. The total number of these episodes per day in serum-free medium is rigorously identical for different cells (166.3 ± 0.2) and this uniformity of frequency suggests a genotypic basis. Cycles, consisting of an undulation episode followed by a resting interval, have mean durations of 8.6 ± 4.1 min and a sharp peak of occurrence at 6 min, with exponential distribution of the longer periods. Motility of II SC is considerably inhibited during mitotic stimulation by cholera toxin and a pituitary extract while SC phenotype has changed to a flat multipolar cell with prominent Golgi and ribosomes. Migration is reduced to 24 ± 2 μ/h and only 2% of the SC show pulsations of the same periodicity as the I SC undulations. A dramatic increase in pulsation frequency occurs 6–12 h after removal of mitogenic factors when 80% of II SC start pulsating twice as fast for 2–3 days. When mitoses cease, SC quickly recover their SC phenotype with rhythmic undulations while migration speed increased to 92 ± 20 μ/h. Thus, in spite of dramatic modification of shape, structure and behavior during mitotic stimulation, SC subsequently recover their unique motility pattern which might be essential for their myelinating function [less ▲]