Zaitsev A.N.,Natural History Museum in London |
Williams C.T.,Natural History Museum in London |
Britvin S.N.,Saint Petersburg State University |
Kuznetsova I.V.,Saint Petersburg University for Technology and Design |
And 3 more authors.
Mineralogical Magazine | Year: 2010
Kerimasite, ideally Ca3Zr2(Fe3+ 2Si)O12, is a new calcium zirconium silicate-ferrite member of the garnet group from the extinct nephelinitic volcano Kerimasi and surrounding explosion craters in northern Tanzania. The mineral occurs as subhedral crystals up to 100 μm in size in calcite carbonatites, and as euhedral to subhedral crystals up to 180 μm in size in carbonatite eluvium. Kerimasite is light to dark-brown in colour and transparent with a vitreous lustre. No cleavage or parting was observed and the mineral is brittle. The calculated density is 4.105(1) g/cm3. The micro-indentation, VHN 25, ranges from 1168 to 1288 kg/mm2. Kerimasite is isotropic with n = 1.945(5). The average chemical formula of the mineral derived from electron microprobe analyses (sample K 94-25) and calculated for O = 12 and all Fe as Fe2O3 is (Ca3.00Mn 0.01Ce0.01Nd0.01)Σ3.03(Zr 1.72Nb0.14Ti0.08Mg0.02Y 0.02)Σ1.98(Fe3+ 1.23Si 0.86Al0.82Ti0.09)Σ3.00O 12. The largest Fe content determined in kerimasite is 21.6 wt.% Fe2O3 and this value corresponds to 1.66 a.p.f.u. in the tetrahedral site. Kerimasite is cubic, space group Ia3d with a = 12.549(1) Å , V = 1976.2(4) Å 3 and Z = 8. The five strongest powder-diffraction lines [d in Å , (I/Io), hkl] are: 4.441 (49) (220), 3.140 (91) (400), 2.808 (70) (420), 2.564 (93) (422) and 1.677 (100) (642). Single-crystal structure refinement revealed the typical structure of the garnet-group minerals. The name is given after the locality, Kerimasi volcano, Tanzania. © 2010 Mineralogical Society.
Andreeva O.A.,RAS Institute of Macromolecular Compounds |
Burkova L.A.,Saint Petersburg University for Technology and Design
Physics of the Solid State | Year: 2011
The mechanisms of chemical dedoping of conductive polypyrrole with the initial conductivity values differing by an order of magnitude have been studied using EPR spectroscopy. An analysis of the temperature dependences of the electrical resistance of the initial highly conductive samples and dedoped samples has revealed a transition from three-dimensional conduction in the initial samples to one-dimensional conduction in the dedoped samples. This transition is caused by the transformation of transverse bipolarons into longitudinal bipolarons and ipolarons. It has been established that transverse and longitudinal quasiparticles are stabilized by counterions involving iron ions in different spin states: the spin of iron in the counterion of a transverse bipolaron is 2 and iron is inactive in the EPR spectrum, whereas in the counterion of longitudinal quasiparticles, the spin of iron is 5/2 and iron becomes paramagnetic. © 2011 Pleiades Publishing, Ltd.
Perepelkin K.E.,Saint Petersburg University for Technology and Design
Fibre Chemistry | Year: 2010
The current types of ultrastrong and high-modulus fibres made from linear fibre-forming polymers - structure, principles of fabrication, properties, and basic areas of application - are examined. Most of the attention is focused on carbocyclic and heterocyclic para-aramid fibres, whose production capacities have reached 60,000 tons a year, the features of their structure and properties and areas of application. High-strength fibres made from other types of aromatic polymers (poly-p-phenylene benzobisoxazoles and thiazoles, polyarylates, polyvinyl alcohol, ultrahigh-molecular-weight polyethylene) are also briefly examined. © 2010 Springer Science+Business Media, Inc.
Andreeva O.A.,Russian Academy of Sciences |
Burkova L.A.,Saint Petersburg University for Technology and Design |
Podeshvo I.V.,Russian Academy of Sciences
Russian Journal of Physical Chemistry B | Year: 2015
Four aromatic amino acids (p-aminobenzoic, 4,6-diaminoisophthalic, o-aminobenzoic, and methylene-bis-anthranilic) were studied by FTIR spectroscopy. The first two molecules were found to exist in the solid phase exclusively in neutral form and the latter two in coexisting neutral and ionic forms. The shift of the tautomeric equilibrium from neutral molecule to zwitterion is determined by the character of substitution, molecular conformation, and the possibility of noncovalent bonds formed between the functional groups. The separation of charges becomes possible only if the conformers of the molecule include a structure with an OH….N intramolecular hydrogen bond. The proton is completely transferred from the acid group to the amino group when the strong intermolecular hydrogen bonds can stabilize the formed zwitterion. Otherwise, uncharged complexes with different degrees of proton transfer to the amino group are formed. © 2015, Pleiades Publishing, Ltd.
Vakulenko S.,Saint Petersburg University for Technology and Design |
Radulescu O.,Montpellier University
Fundamenta Informaticae | Year: 2012
We investigate the possibility of programming arbitrarily complex space-time patterns, and transitions between such patterns, by gene networks. We consider networks with two types of nodes. The u-nodes, called centers, are hyperconnected and interact one to another via u-nodes, called satellites. This centralized architecture realizes a bow-tie scheme and possesses interesting properties. Namely, this organization creates feedback loops that are capable to generate any prescribed patterning dynamics, chaotic or periodic, or stabilize a number of prescribed equilibrium states. We show that activation or silencing of a node can sharply switch the network dynamics, even if the activated or silenced node is weakly connected. Centralized networks can keep their flexibility, and still be protected against environmental noises. Finding an optimized network that is both robust and flexible is a computationally hard problem in general, but it becomes feasible when the number of satellites is large. In theoretical biology, this class of models can be used to implement the Driesch-Wolpert program, allowing to go from morphogen gradients to multicellular organisms.