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61.
Studies were conducted to determine the fate of 15alpha-hydroxyprogesterone in human placental tissue. Tritiated 15alpha-hydroxyprogesterone was perfused through normal human placentas in situ at the time of Cesarean section and incubated with a 10,000x g microsomal supernate of the placenta in vitro. In both systems the substrate, but no additional metabolites were identified. These findings indicate that 15alpha-hydroxyprogesterone is not metabolized during its passage in the human term placenta, and suggests that because of its fetal origin clinical measurements of 15alpha-hydroxyprogesterone may provide a valuable index to the status of fetal viability. 相似文献
62.
63.
FE Leon-S G Pradilla AM Chavez MA DeLeon OL Rueda J Bayona 《Canadian Metallurgical Quarterly》1998,38(7):419-422
Nurses must share their research and experiences with colleagues in order that areas of practice are debated and improved. Assessing the suitability of a piece of work for a journal and following simple ground rules will increase the likelihood of publication. 相似文献
64.
Juan A. Morales‐Rueda Elena Dibildox‐Alvarado Miriam A. Charó‐Alonso Richard G. Weiss Jorge F. Toro‐Vazquez 《European Journal of Lipid Science and Technology》2009,111(2):207-215
The thermo‐mechanical properties of organogels developed by a complex mixture of n‐alkanes present in candelilla wax (CW) were investigated and compared with the ones of organogels developed by a pure n‐alkane, dotriacontane (C32). In both cases, the liquid phase used was safflower oil high in triolein (SFO) and the variables studied were two levels of gelator concentration (1 and 3%), cooling rates of 1 and 10 °C/min, and two gel setting temperatures, 5 and 25 °C (Tset). Based on comparisons of the organogels made with C32, the presence of minor molecular components in CW had a profound effect on the crystal habit of the n‐alkanes in CW‐based organogels, and therefore on their physical properties. Thus, independent of the cooling rate and Tset, C32 showed a higher solubility and higher self‐assembly capability in the SFO than CW. Nevertheless, for the same gelator concentration and time‐temperature conditions, C32 organogels had lower G' profiles than CW organogels. Additionally, independent of the type of gelator, more stable organogel structures were developed at Tset = 5 °C and using the lower cooling rate. The rheological behavior of the organogels was explained considering the formation of a rotator phase by the n‐alkanes, its solid‐solid transition, and their dependence as a function of the cooling rate and Tset. The results here obtained showed that it is possible to gelate SFO through organogelation with CW and without the use of trans fats. 相似文献
65.
New features of 23S ribosomal RNA folding: the long helix 41-42 makes a "U-turn" inside the ribosome
PV Baranov OL Gurvich AA Bogdanov R Brimacombe OA Dontsova 《Canadian Metallurgical Quarterly》1998,4(6):658-668
23S rRNA from Escherichia coli was cleaved at single internucleotide bonds using ribonuclease H in the presence of appropriate chimeric oligonucleotides; the individual cleavage sites were between residues 384 and 385, 867 and 868, 1045 and 1046, and 2510 and 2511, with an additional fortuitous cleavage at positions 1117 and 1118. In each case, the 3' terminus of the 5' fragment was ligated to radioactively labeled 4-thiouridine 5'-,3'-biphosphate ("psUp"), and the cleaved 23S rRNA carrying this label was reconstituted into 50S subunits. The 50S subunits were able to associate normally with 30S subunits to form 70S ribosomes. Intra-RNA crosslinks from the 4-thiouridine residues were induced by irradiation at 350 nm, and the crosslink sites within the 23S rRNA were analyzed. The rRNA molecules carrying psUp at positions 867 and 1117 showed crosslinks to nearby positions on the opposite strand of the same double helix where the cleavage was located, and no crosslinking was detected from position 2510. In contrast, the rRNA carrying psUp at position 384 showed crosslinking to nt 420 (and sometimes also to 416 and 425) in the neighboring helix in 23S rRNA, and the rRNA with psUp at position 1045 gave a crosslink to residue 993. The latter crosslink demonstrates that the long helix 41-42 of the 23S rRNA (which carries the region associated with GTPase activity) must double back on itself, forming a "U-turn" in the ribosome. This result is discussed in terms of the topography of the GTPase region in the 50S subunit, and its relation to the locations of the 5S rRNA and the peptidyl transferase center. 相似文献
66.
Adsorption of adenine on Au(1 1 1) and Au(1 0 0) electrodes is studied by cyclic voltammetry, impedance and chronoamperometric measurements in 0.1 M and 0.01 M KClO4 and in 0.5 M NaF solutions. The experiments performed with flame-annealed electrodes at different contact potentials, scan potential limits and scan rates, suggest different adsorption behaviour on the unreconstructed and reconstructed surface domains. This is confirmed by comparing the results obtained with electrochemically annealed unreconstructed and with flame-annealed reconstructed surfaces. In both cases the initial electrode surface state is characterised by the Epzc values. The adsorption on reconstructed surfaces takes place at more positive potentials than on the unreconstructed surfaces and induces the lifting of the reconstruction.The thermodynamic analysis is performed on the chronoamperometric data for adenine desorption on well characterised unreconstructed Au(1 1 1) surfaces. To this end a new methodology of the chronoamperometric experiments is introduced. Quantitative thermodynamic adsorption parameters such as surface tension, Gibbs surface excess, Gibbs energy of adsorption, potential versus Gibbs excess slope and electrosorption valency are determined. Weak chemisorption of adenine is inferred with a molecular orientation independent on the coverage and on the electrode potential. It is proposed that adsorbed adenine molecules adopt a tilted orientation at the surface to facilitate the coordination to the gold atoms. 相似文献
67.
Increase of the final setting time of brushite cements by using chondroitin 4-sulfate and silica gel 总被引:1,自引:0,他引:1
Tamimi-Mariño F Mastio J Rueda C Blanco L López-Cabarcos E 《Journal of materials science. Materials in medicine》2007,18(6):1195-1201
Chondroitin 4-sulfate (C4S) is a bioactive glycosaminoglycan with inductive properties in bone and tissue regeneration. Dicalcium
phosphate dehydrate cements (known as brushite) are biocompatible and resorbable materials used in bone and dental surgery.
In this study we analyzed the effect of C4S on the setting of a calcium phosphate cement and the properties of the resulting
material. Brushite based cement powder was synthesised by mixing monocalcium phosphate with β-tricalcium phosphate and sodium
pyrophosphate. When the concentration of C4S, in the liquid added to the cement powder, was between 1 and 8% the cement final
setting time increases. Furthermore, the cement diametral tensile strength remains unaffected when solutions with concentrations
of C4S below 5% were used, but decreases at higher C4S concentrations. Calorimetric analysis showed that the cements prepared
with C4S alone and in combination with silica gel have a greater content of hydrated water. We concluded from our study that
the addition of small amounts of C4S increases the cement setting time without affecting its diametral tensile strength and
at the same time improves the cement’s hydrophilicity. 相似文献
68.
Jaime J. Hernández Mari-Cruz García-Gutiérrez Daniel R. Rueda Tiberio A. Ezquerra Richard J. Davies 《Composites Science and Technology》2012
Homogeneous and stable thin films of poly(butylene terephthalate) PBT and its nanocomposites based on single wall carbon nanotubes (SWCNTs) were prepared by spin coating. PBT thin films show crystalline structures for thicknesses above 40 nm, consisting of submicrometer size 2D-spherulites. In the case of nanocomposites, carbon nanotubes act as nucleating agents and provide a template for the crystallization of PBT. This gives rise to hybrid shish-kebab structures, even in the thinnest films (∼10 nm thick). Melting and recrystallization provoke the crystallization of PBT and its nanocomposites, and can be used to control morphology. For PBT thin films, the orientation of crystalline lamellae undergoes a transformation, changing from a disposition perpendicular to the substrate (“edge-on”) to a parallel arrangement (“flat-on”) after recrystallization. In the case of the nanocomposites, the CNT influence on the polymer crystallization morphology in thin films is less significant than in the bulk due to the effect of the substrate interactions. Using Raman microscopy it is possible to directly observe both, the degree of dispersion and the location of carbon nanotubes in the films. The results reveal that bigger agglomerates act as more effective nucleating points than isolated bundles of SWCNTs during crystallization of the polymer matrix. 相似文献
69.
Borja Fernández-d’Arlas Umar Khan Lorena Rueda Loli Martin Jose A. Ramos Jonathan N. Coleman Maria L. González Angel Valea Iñaki Mondragon Maria A. Corcuera Arantxa Eceiza 《Composites Science and Technology》2012
A comparative study of the influence of processing route on polyurethanes (PUs)/multiwalled carbon nanotube (MWCNT) composites mechanical and electrical properties and also morphology was undergone employing two differentiated processing methods, solvent casting and buckypaper infiltration, for producing PU composites with low, medium and high mass fractions of acid treated MWCNT, and with no covalent linkages between the matrix and the nanotubes. As for example, with a MWCNT mass fraction of ∼18 wt.% the second method produced stiffer (270 MPa), lighter (948 kg m−3) and more electrically conductive (1.8 S cm−1) composite while the first one gave softer (111 MPa) and more ductile (141%) materials. These properties differences are related to the different PU/MWCNT dispositions obtained through each synthesis route. Nanotubes percolating concentration is found to be crucial on composite properties evolution and a preferential interaction of MWCNT with PU hard segments is observed for solvent cast composites. 相似文献
70.
González-García L Parra-Barranco J Sánchez-Valencia JR Barranco A Borrás A González-Elipe AR García-Gutiérrez MC Hernández JJ Rueda DR Ezquerra TA 《Nanotechnology》2012,23(20):205701
This paper reports a thorough microstructural characterization of glancing angle deposited (GLAD) TiO(2) thin films. Atomic force microscopy (afm), grazing-incidence small-angle x-ray scattering (GISAXS) and water adsorption isotherms have been used to determine the evolution of porosity and the existence of some correlation distances between the nanocolumns constituting the basic elements of the film's nanostructure. It is found that the deposition angle and, to a lesser extent, the film thickness are the most important parameters controlling properties of the thin film. The importance of porosity and some critical dimensions encountered in the investigated GLAD thin films is highlighted in relation to the analysis of their optical properties when utilized as antireflective coatings or as hosts and templates for the development of new composite materials. 相似文献