Influence of temperature and substrate concentration on bacterial growth yield in Seine River water batch cultures

The growth of natural bacterial assemblages was monitored in 3-liter reactors under various temperature and substrate concentration conditions. The oxygen concentration was continuously monitored, and subsamples were taken at short time intervals to determine bacterial number and biomass. The rate of bacterial mortality was also determined. Bacterial growth yield was calculated as the ratio of net production (increase in biomass corrected for mortality) to gross production (net production plus oxygen consumption expressed in carbon units). Averaging 33%, the growth yield did not show any trend with temperatures in the range of 8 to 25 degrees C but increased with the concentration of dissolved organic carbon in the range of 2 to 12 mg of C.liter-1.     

Insight into signal transduction: structural alterations in transmembrane helices probed by multi-1 ns molecular dynamics simulations

The hypothesis of structural alteration in transmembrane helices for signal transduction process is viewed by molecular dynamics simulation techniques. For the c-erbB-2 transmembrane domain involved in oncogenicity, the occurrence of conformational changes has been previously described as transition from the alpha to pi helix. This dynamical feature is thoroughly analyzed for the wild phenotype and oncogenic sequences from a series of 18 simulations carried out on one nanosecond time scale. We show that these structural events do not depend upon the conditions of simulations like force field or starting helix coordinates. We demonstrate that the oncogenic mutations Val659 Glu, Gln and Asp do not prevent the transition. Furthermore, we show that beta branched residues, in conjunction with Gly residues in the c-erbB-2 sequence, act as destabilizers for the alpha helix structure, pi deformations are tightly related to other local structural motifs found in soluble and membrane proteins. These structural alterations are discussed in term of structure-activity relationships for the c-erbB-2 activating mechanism mediated by transmembrane domain dimerization.     

Détermination du coefficient d'écoulement des gravillons

The angularity of aggregates of alluvial origin is a subject that systematically arises when one touches upon problems of intergranular friction in pavement courses and making concrete. The authors describe a test, based on measurement of the flow time of the material which tends to quantify this parameter. In particular, this test permits to determine the “indice de concassage” of the material without knowing the conditions of its elaboration and the real granularity of the material before crushing. Realization of measures and behaviour investigation of composite materials should make it possible to establish quickly new specifications in this field.     

Structure cristalline de la phase haute temperature de PbSO4.2PbO A 973K

Full profile X-ray powder diffraction structure refinements have been performed on the two polymorphs of the PbSO₄.2PbO phase. Both structures can be described as infinite double-chains of edge-sharing OPb₄ tetrahedra linked by the sulfate groups and running parallel to the (010) direction for the low temperature phase, and parallel to the (001) direction for the high temperature one. The mechanism of the phase transition may be described as a rotation of the sulfate group about one of its pseudo-ternary axis. The space group adopted for the refinement of the structure of the high temperature phase is Cmcm.     

Etude des phases ferroelastiques de Pb3V2O8 : Determination de la maille cristalline de la phase α ferroelectrique basse temperature

The cell parameters of the ferroelastic and ferroelectric phase of Pb₃V₂O₈ (T < 262 K) have been determined by very accurate X-ray powder diffractometry ; at 77 K, $\text{a}\text{= 7.460 (1)}\text{A}\text{?}$, $\text{b}\text{= 6.191 (1)}\text{A}\text{?}$, $\text{c}\text{= 9.348 (1)}\text{A}\text{?}$ and $\text{β = 116.63 (1)}\text{A}\text{?}$. This monoclinic cell is characterized by Z = 2 and the space group is A2. Thermal expansion tensors have been measured versus temperature for the three phases α (T < 262K), β (262K < T < 360 K) and γ (T > 360 K). The intermediate phase β is characterized by an important thermal expansion anisotropy and its molecular volume is higher than that of the two other phases α and γ.     

Dielectric Breakdown of Porous MgAl2O4

The effects of controlled porosity on the dielectric breakdown of sintered MgAl₂O₄ were measured using an acoustic emission technique. Results are compared to a statistical model relating dielectric strength to a random distribution of spherical pores and the probability of pores aligned in a vertical column. Data are in good agreement with the model when only maximum pore size is considered .     

A 1D- and 2D-NMR Study of an Anionic Surfactant/Neutral Polymer Complex

NMR chemical shifts and linewidth measurements were examined for mixtures of sodium 10-phenyldecanoate (Na ω-PhDec) in deuterated aqueous solutions in the presence of varying compositions of poly(ethylene oxide) (PEO) polymers of 2000 and 4000 molecular weight. In addition, variable temperature NMR spectra and NMR spin lattice relaxation times (T ₁) were obtained for the PEO-4000/Na ω-PhDec system as a function of varying polymer concentrations. As expected, the polymer/surfactant systems exhibit the behaviour typical of that of an anionic surfactant/neutral polymer system with well defined critical aggregation concentrations (CMC) corresponding to the formation of polymer/surfactant complexes below the CMC of the free surfactant. The ¹H-NMR linewidths acquired for the Na ω-PhDec/PEO-4000 system before and after the CMC region of the surfactant indicate that the maximum in the linewidth of the PEO proton peak is reached at approximately twice the CMC of the free surfactant. 2D-NMR NOESY measurements on this system exhibit cross peaks between the PEO protons and the protons on the surfactant backbone, consistent with the location of the phenyl group in the micellar interior. All these NMR experiments are interpreted in terms of the structure of the polymer/surfactant complexes as a function of the system composition.