Synthesis and characterization of 8-methoxy-2''- deoxyadenosine-containing oligonucleotides to probe the syn glycosidic conformation of 2''-deoxyadenosine within DNA

BACKGROUND: Rectal motor activity is incompletely understood. The aim of this study was to characterize the patterns of rectal motor activity and to examine their diurnal variation and their relationships to proximal colonic activity and to meals. METHODS: We performed a 30-h ambulatory motility study by recording pressure activity at multiple sites in the colon in 18 normal subjects. RESULTS: During 288 h of recording, discrete bursts of tonic and phasic activity were seen in the rectum of all subjects at night and during the day lasting > or = 3 min, with a predominant frequency of 3 waves/min: periodic rectal motor activity (PRMA). Nocturnally, the number of cycles and the proportion of time occupied by this activity were greater (p < 0.001) and the inter-cycle interval was shorter (p < 0.008) compared with daytime, but the cycle duration was similar. Only 4 versus 5% (nocturnal vs daytime) of cycles propagated aborad, whereas 36 versus 14% (p < 0.01) propagated retrogradely, 16 versus 47% (p < 0.01) occurred simultaneously, and 44 versus 34% were confined to the rectum. There was considerable intra- and intersubject variability. PRMA was not related to meals or to anal motor activity, but 81% of nocturnal and 94% of daytime cycles occurred within 5 min of a motor event in the more proximal colon. CONCLUSIONS: PRMA is a characteristic feature of the normal rectum and is more frequent at night. The temporal association with motor events in the proximal colon suggests that PRMA is triggered by the arrival of stool or gas in the rectum. Because most cycles are either segmental or are propagated retrogradely, PRMA may serve as an intrinsic braking mechanism that prevents untimely flow of colonic contents, particularly during sleep.     

Effect of opsonins on the uptake of magnetic starch microspheres by rat Kupffer cells

The influence of various sera and proteins on the uptake of a superparamagnetic colloid (magnetic starch microspheres (MSM); particle size, 200 nm; crystal size, 10 nm) by the isolated and perfused rat liver has been studied. It is demonstrated that the capture of MSM is slightly reduced by the addition of rat blood to the protein-free perfusion medium but highly reduced by newborn calf serum (NCS). The SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) analysis of proteins adsorbed on the nanoparticles incubated in NCS reveals major coating by albumin and IgG. The addition of bovine IgG to the perfusion fluid reduces the rate of MSM uptake in the same extent that NCS, whereas fetal calf serum that contains only traces of IgG weakly alters the MSM clearance. Finally, complemented and decomplemented NCS exhibit the same influence on the MSM hepatic extraction. It is concluded that although lectins are largely involved in the uptake of MSM administered in the absence of proteins, opsonins receptors are implicated when the perfusion medium contains relevant blood components.     

The clustering and coarsening of carbon multiplets during the aging of martensite from mössbauer spectroscopy: The preprecipitation stage of epsilon carbide

Mössbauer spectra of as-quenched and aged martensite (9.5 at. pct C) are analyzed in terms of seven Fe environments, the abundances of which evolve with aging time. Besides the atoms of the matrix (A), Fe atoms which are first nearest neighbors of an isolated interstitial can only be distinguished by their quadrupole shift depending upon whether they lie in a direction perpendicular (B _a) or parallel to thec axis (B _c); classC atoms have two carbon neighbors whileD orE belong to an ordered phase; classF atoms have three carbon neighbors. The carbon multiplet model, based on interstitials residing exclusively in octahedral sites, an elastic stability of theC-C 1/2«111” doublet and a diffusion path for carbon in (001)α' can explain all the features observed: a first step attributed to the clustering of isolated multiplets, and a second step to the coarsening into extended multiplets which leads to the emergence of a new ordered iron carbide (B2 monoclinic with parallelepiped cell of 5.73, 6.74, and 8.60 Å) which transformsin situ into ε-carbide (~Fe₉C₄) (η carbide as long as it is coherent with the matrix). The positions of carbon atoms in Fe₉C₄ are specified and a synopsis with related phenomena is drawn.     

Understanding wash efficiency and chloride transfer in copper solvent extraction

Carryover of entrained aqueous from primary leaching operations into copper electrowinning electrolytes introduces impurities that can affect cathode quality and cause corrosion. As a result, more operations are introducing wash stages in their solvent extraction circuits in an attempt to dilute these entrainments with high-quality water. For more information, contact D.J. Burkhardt, Fluor Daniel, 7th Floor 1075, West Georgia Street, Vancouver, B.C. V6E 4M7, Canada; (604) 488-2113; fax (604) 488-2021; e-mail Debra.Burkhardt@fluor.com.     

Zr-二十面体准晶-十次准晶伪三元系中非晶的形成

分析了块状非晶与稳定准晶结构上的异同点，选择两种稳定准晶(二十面体准晶和十次准晶)相互混合，在保持准晶二十面体基本结构单元的基础上，增加元素组成的混乱度，再添加有利于形成高配位多面体的元素Zr，用急冷方法制备出非晶合金．对此非晶合金的热力学测试表明，该非晶形成能力和稳定性与Inoue的Zr65Al7.5Cu17.5Ni10非晶相近．     

Solution scattering structural analysis of the 70 S Escherichia coli ribosome by contrast variation. I. Invariants and validation of electron microscopy models

Solutions of selectively deuterated 70 S Escherichia coli ribosomes and of free 30 S and 50 S subunits were studied by neutron scattering using contrast variation. The integrity of the partially deuterated particles was controlled by parallel X-ray measurements. Integral parameters of the entire ribosome, of its subunits and of the protein and rRNA moieties were evaluated. The data allow an experimental validation of the two most recent electron microscopy reconstructions of the 70 S ribosome presented by the groups of J. Frank (Albany) and of M. van Heel & R. Brimacombe (Berlin). For each reconstruction, integral parameters and theoretical scattering curves from the 70 S and its subunits were calculated and compared with the experimental data. Although neither of the two models yields a comprehensive agreement with the experimental data, Frank's model provides a better fit. For the 50 S subunit of van Heel & Brimacombe's model the fit with the experimental data improves significantly when the internal channels and tunnels are filled up. The poorer fit of the latter model is thus caused by its "sponge"-like structure which may partly be due to an enhancement of high frequency contributions in some of the steps of the three-dimensional image reconstruction. It seems therefore unlikely that the ribosome has a "sponge"-like structure with a pronounced network of channels.     

A novel Computer-Aided Tree Species Identification method based on Burst Wind Segmentation of 3D bark textures

Terrestrial Laser Scanning (TLS) systems have gained increasing popularity in the forestry domain and are today widely used for the automatic measurement of forest inventory attributes. Nevertheless, to the best of our knowledge the problem of tree species recognition from TLS data has received very little attention from the scientific community. It is in this context that we present a novel Computer-Aided Tree Species Identification method based on 3D bark texture analysis. The novelty of our approach resides in the following three key points: (1) 3D salient regions extraction using a new morphological segmentation method that we have called Burst Wind Segmentation, (2) the extraction and pre-annotation of a collection of typical 3D bark patterns, known as scars, from each of the tree species. The pre-annotated scars are stored in a dictionary that we have called ScarBook and they are used as a reference for the comparison of the 3D salient segmented regions, (3) a wide variety of advanced shape, saliency, curvature and roughness features are extracted from the 3D salient segmented regions. To study the performance of our method, an experiment has been carried out on a dataset composed of 969 patches which correspond to 30 cm long segments of the trunk at breast height. Six species among the most dominant species in European forests have been tested with patches of different diameter at breast height values so as to study the identification accuracy with respect to age. The results obtained are very encouraging and promising and they confirm the possibility of identifying tree species using TLS data.     

Surface characterization of zirconium titanate (ZrTiO4) powder by measurements of electrical photoconductance and photoassisted oxygen isotope exchange

The photosensitivity of a ZrTiO₄ sample (33 m²/g) prepared by a sol-gel method has been assessed in the presence of O₂ by both photoconductance and oxygen isotope exchange (OIE) measurements at room temperature at wavelengths > 290 nm. For oxygen pressures < ca. 13.3 Pa, the steady-state photoconductance of ZrTiO₄ was unaffected by , which indicated that the direct recombination of the photoproduced charges played the dominant role. At higher pressures, varied as the reciprocal of , which was consistent with the fact that the electronic equilibrium was then governed by O₂ + e^– O ₂ ^– . OIE over ZrTiO₄ occurred predominantly via the overall mechanism which involves the exchange of two surface oxygen atoms for each exchange act. It was very slow as compared with OIE over photocatalytically active anatase samples which, in addition, occurs via another mechanism. These results allow one to predict that this ZrTiO₄ sample is a poorly active photocatalyst for oxidations involving gaseous oxygen, and further illustrate the interest of and OIE measurements to evaluate the photosensitivity of semiconductor oxide samples.     

Alumina supported tungsten hydrides, new efficient catalysts for alkane metathesis

Silica and alumina supported tantalum and tungsten hydrides were tested in alkane metathesis, for comparison of their catalytic properties. In propane metathesis [W]–H/Al₂O₃ proves to be twice more efficient than the usual [Ta]–H/SiO₂ catalyst which is still better than [Ta]–H/Al₂O₃ and [W]–H/SiO₂. Tungsten based catalysts lead to a narrower distribution in the products selectivity and to a higher amount of linear products than [Ta]–H/SiO₂. [W]–H/Al₂O₃ is also a better catalyst than [Ta]–H/SiO₂ for butane metathesis but is less efficient with ethane. Whereas the results in the case of propane or butane can involve the higher initial activity and a lower deactivation of the tungsten catalyst, in the case of ethane, mechanistic or kinetic aspects can be envisaged in particular concerning the difficulty to dehydrogenate ethane into ethylene.