Showing papers by "Instituto Politécnico Nacional published in 1981"
TL;DR: A DNA sequence essential for the R64drd11 + ColK-mediated conjugal transfer of pBR322 has been located in a 540 bp HaeIII fragment between the vegetative origin of replication and the tetracycline resistance gene of this vector.
147 citations
TL;DR: A survey of the recent literature on the structural behaviour under variable repeated loads, with emphasis on developments which relaxed some of the above assumptions, but preserved the character of generalization of limit analysis typical of the ‘classical’ shakedown theory and methods of analysis and design.
118 citations
TL;DR: This work has shown that the reconstitution approach has proved to be valuable in efforts to understand the molecular mechanisms of membrane transport and energy transduction.
Abstract: Recent progress in membrane biology has brought us to a stage where it is possible to associate complex biological processes to identifiable membrane proteins. Technical advances in the biochemical characterization and purification of membrane proteins have contributed a wealth of structural information. The reconstitution approach has proved to be valuable in our efforts to understand the molecular mechanisms of membrane transport and energy transduction.
111 citations
TL;DR: In this paper, the authors present a discussion of some of the aspects of parameter characterization problems in the field of Geomechanics, and the influence of the number of input data and of the experimental errors affecting them on the results of characterization problems is discussed.
94 citations
TL;DR: The observations discussed in this article indicate that at the blister, junctions are really tight; (a) when transported fluid is allowed to escape through a permeable support, junications are also tight, but (c) when the support is impermeable the junctions allow ouabain and peroxidase through.
Abstract: The formation of blisters is a transient phenomenon that led Dr. Leighton to describe its observation with time-lapse photography in the MDCK monolayer to a "gently boiling oatmeal." One may ask why is it transient and why most areas are momentarily not blistering. The observations discussed in this article indicate that (a) at the blister, junctions are really tight; (b) when transported fluid is allowed to escape through a permeable support, junctions are also tight, but (c) when the support is impermeable the junctions allow ouabain and peroxidase through. This suggests that, if the attachment of the monolayer is strong enough, the accumulation of fluid (Figure 7) bursts the junctions. If, on the contrary, junctions withstand the pressure, factor 3 of Figure 7 prevails over the others, and a blister is formed. In all the rest of the monolayer junctions seem to be open. This is in keeping with the observation by Rabito et al.,27 that if the monolayers are prepared on weakened supports, blisters are much bigger than under control conditions. It also allows the measurement of ionic fluxes and labeling of pumping sites at the basolateral membrane. As a corollary, one may say that some of the factors known to affect blistering 26 may very well act through modifications in the occluding junctions.
69 citations
TL;DR: Polymers of this type may be considered as potential oligomeric drug-binding matrices because the benzotriazole or the imidazolyl residues can easily be exchanged.
Abstract: α-Hydroxysuccinyl-ω-hydroxysuccinyloxypoly(oxyethylene)s (succinic half-esters of poly-(ethylene glycol)s) (2) of different molecular weights were prepared, and transformed into the corresponding benzotriazole and imidazole derivatives 3 and 4. The benzotriazolyl or the imidazolyl residues in these polymers can easily be exchanged. This was proved with model compounds bearing hydroxyl or amino groups. Polymers of this type may be considered as potential oligomeric drug-binding matrices.
58 citations
TL;DR: In this article, a numerical approach is presented for the back calculation of the earth pressure acting on embedded or retaining structures, which is applicable to structures of any shape and requires a set of in situ measurements that may include displacements of points on the structure, values of concentrated forces, value of distributed loads at some locations.
Abstract: A numerical approach is presented for the ‘identification’ (or back calculation) of the earth pressure acting on embedded or retaining structures. The procedure is applicable to structures of any shape and requires a set of in situ measurements that may include displacements of points on the structure, values of concentrated forces, values of distributed loads at some locations, etc. Possible limiting values of the unknown loads, non-linear structural behaviour, varying accuracies of the input data are accounted for in the problem formulation. Depending upon the type of problem, the solution is reached by means of the unconstrained or constrained minimization of a suitably defined error function. As an example, the proposed approach is applied to the identification of the earth pressure acting on some typical geotechnical engineering structures.
49 citations
TL;DR: In this article, solid state transitions of the WO3γ-Al2O3 system have been investigated in the temperature range 873-1323 K. The formation of α-Al 2O3 and Al 2(WO4)3 phases and the thermal desorption of W(VI) attached to the γ-Al 3 surface have been studied as function of the treatment time.
43 citations
TL;DR: In this paper, BrMgCH2CH3 was added onto the erythro and threo aldehydes to give 6:4 and 8:2 selectivity, respectively.
40 citations
TL;DR: In this paper, a numerical procedure for the finite element solution of stress analysis problems involving non-linear creep of rocks is presented, belonging to the class of "evolutive" approaches.
37 citations
TL;DR: In this article, the influence of the stirrer clearance C on the hydrodynamics of agitated vesels, and particularly on the minimum stirrer velocity for the complete suspension of solid particles, NSUPjSUPs, may be considerable.
TL;DR: It is suggested that the viscosimetric evaluation of DNA disentanglement is probably the most sensitive method for studying DNA damage induced “in vivo” by chemical carcinogens.
TL;DR: In this article, the analysis of Fermi resonances in the CH-stretching and HCH-bending regions of the Raman spectra of trans-polymethylene chains and CD3CH3CD2 is proposed.
TL;DR: In this article, the quantitative shift reagent behavior of polymethoxylated flavones in the presence of Pr(fod) 3 has been studied and it has been shown that the degree of substitution in the neighborhood of the carbonyl group can be determined from the number of signals that are strongly shifted and broadened.
TL;DR: The structure and relative stereochemistry of rastevione (1a), the main constituent of the roots of S. serrata and S. rhombifolia, were deduced from chemical transformations combined with spectral data and by a single crystal X-ray diffraction study.
TL;DR: It is tentatively concluded that the active principles of Tullidora may enter the axons through the motor nerve terminals, and the distal segments of the motor nerves would then be preferentially affected and demyelination could result from axonal damage.
Abstract:
Peripheral nerve demyelination was induced in cats by oral administration of ether extracts of Tullidora (Karwinskia humboldtiana). Proteins from several hindlimb nerves, spinal roots, and dorsal columns of the spinal cord were subjected to slab gel electrophoresis and quantified by densitometry. In Tullidora-treated cats with severe motor disturbances, specific myelin proteins were reduced by at least 50% in motor nerves and less than 25% in cutaneous axons. There was a greater decrease of these proteins in the distal than in the cephalad segments of the sciatic nerve; no changes were detected either in the spinal roots or in the white matter of the spinal cord. Electron microscopy revealed intense demyelination in the motor nerves only. Both the density of the 100 A-thick neurofilaments and the relative proportion of a polypeptide with a molecular weight of 68,000 were considerably increased in the affected nerves. It is tentatively concluded that the active principles of Tullidora may enter the axons through the motor nerve terminals. The distal segments of the motor nerves would then be preferentially affected and demyelination could result from axonal damage.
TL;DR: In this paper, the synthesis of N-benzoyl-L -daunosamine from the C4 threo aldehyde (2b), prepared from D -threonine, through the intermediacy of the C7 adduct was reported.
TL;DR: In this article, the authors investigated the reduced extrapolation length Λ of a homeotropic nematic-liquid-crystal cell as a function of the reduced anchoring energy β and the reduced fieldu in the case of anisotropic elasticity.
Abstract: The reduced extrapolation length Λ of a homeotropic nematic-liquid-crystal cell has been theoretically investigated as a function of the reduced anchoring energy β and the reduced fieldu in the case of anisotropic elasticity. For a particular MBBA cell the experimental behaviour of both β and Λvs. the reduced temperature τ has been reported.
TL;DR: In this article, the assignment of all ring carbons of p-benzoquinones derived from perezone and from thymoquinone was completed using gated decoupled spectra.
Abstract: The assignment of all ring carbons of p-benzoquinones derived from perezone and from thymoquinone was completed using gated decoupled spectra. The long range proton-carbon couplings are discussed in terms of the degree of substitution of the quinone ring. The tautomeric interconversion of the two energetically equivalent forms of 2,5-dihydroxy-1,4-benzoquinones has been studied in various solvents and at several temperatures.
TL;DR: In this paper, the interpretation of the IR intensities of CH 3 CH 2 CH 3, CD 3 CD 2 CH 2 CD 3 and CH 3 CD 1 CH 3 in terms of bond parameters is discussed.
TL;DR: In this paper, the synthesis of N-benzoyl derivatives of L - arabino (10), L - xylo (13) and L - lyxo (L -vancosamine) from fermenting yeast from α-methylcinnamaldehyde and acetaldehyde is reported.
TL;DR: Aqueous titanium trichloride promotes reductive dimerization of benzoylcyanide in acetic acid and mixed pinacol reaction in acetone medium.
TL;DR: In this article, the low-temperature infrared spectrum of solid malonaldehyde (MA) is analyzed and discussed and it is shown that the open chain s-trans conformation is stabilized by the formation of a strong intermolecular H-bond.
TL;DR: 13C NMR data are presented for the psilostachyinolides, psilOSTachyin C, p silostachy in, canambrin, pSilostachyIn B, altamisin, pPaulitin and isopaulitin, obtained from Ambrosia cumanensis H.B.C. and AmbrosIA canescens (Gray).
Abstract: 13C NMR data are presented for the psilostachyinolides, psilostachyin C, psilostachyin, canambrin, psilostachyin B, altamisin, paulitin and isopaulitin, obtained from Ambrosia cumanensis H.B.K., Ambrosia psilostachya D.C. and Ambrosia canescens (Gray).
TL;DR: In this article, free-radical decomposition of diazonium salts catalyzed by titanous or titanous and ferrous salts in the presence of β-substituted α,β-unsaturated carbonyl compounds leads to 1,4-diaryl pyrazole derivatives.
TL;DR: In this article, α-methylcinnamaldehyde (1b), acetaldehyde and fermenting bakers'yeast, at pH 5, the R α-ketol (6) was obtained in ca. 15% yield, togheter with unreacted.
TL;DR: In this paper, the radiative corrections to first order in $\ensuremath{\alpha}$ to the three-body semileptonic decays of pseudoscalar mesons are treated in a general fashion, which is suitable for model-independent experimental analysis.
Abstract: The radiative corrections to first order in $\ensuremath{\alpha}$ to the three-body semileptonic decays of pseudoscalar mesons, ${M}_{l3}$, are treated in a general fashion, which is suitable for model-independent experimental analysis. Special attention is paid to the energy dependence of the form factors involved. No approximation is made about the smallness of the four-momentum transfer. As an application an expression for the energy spectrum of the charged lepton is derived. The procedure developed in this paper is valid for ${\ensuremath{\pi}}_{e3}$, ${K}_{l3}^{\ifmmode\pm\else\textpm\fi{}}$, ${D}_{l3}^{\ifmmode\pm\else\textpm\fi{}}$, or any charged ${M}_{l3}$ decay, $l$ being an electron or a muon, provided hard bremsstrahlung photons are experimentally discriminated.
TL;DR: Together with the new (+)-epoxydon monoacetate, 3-methylidene-6-methoxy-1,4-benzodioxan-2-one and 2-(2-hydroxy-5- methoxyphenoxy)-acrylic acid, has been isolated and identified from the mycelium of Mycosphaerella ligulicola grown on Sabouraud-maltose 4 %-agar.