Showing papers by "Instituto Politécnico Nacional published in 1982"
TL;DR: In this paper, the Navier-Stokes equations for a steady incompressible viscous flow have been explicitly written in this frame of reference, and the flow in a helical pipe has been studied, and, formdii 5f curvature and torsion small compared with the radius of the pipe, the flow has been considered as a perturbed Poiseuille flow.
Abstract: An orthogonal coordinate system along a generic spatial curve has been introduced, and the Navier-Stokes equations for a steady incompressible viscous flow have been explicitly written in this frame of reference. As an application the flow in a helical pipe has been studied, and, formdii 5f curvature and torsion small compared with the radius of the pipe, the flow has been considered as a perturbed Poiseuille flow. The result is that for curvatures and torsions of the same order and for low Reynolds number the curvature induces on the flow a first-order effect on the parameter e =κa, where κ is the curvature and a the radius of the pipe, while the effect of the torsion on the flow is of the second order in E. This last result disagrees with those of Wang (1981), who, adopting a non-orthogonal coordinate system, found a first-order effect of torsion on the flow.
270 citations
TL;DR: When CB is added to sealed monolayers there is a gradual drop in the electrical resistance across the monolayer, accompanied by a slow disorganization of the microfilament pattern of these cells, including a disturbance of a ring of cortical microfilaments that is normally associated with the junctions.
Abstract: In MDCK cell monolayers the opening and resealing of occluding junctions can be induced by removal and restoration of calcium to the external medium. The overall changes in permeability of the occluding junctions in the monolayer can be monitored by the drop and recovery of the total transepithelial electrical resistance. We have investigated the effects of cytochalasin B (CB) on this process. When CB is added to sealed monolayers there is a gradual drop in the electrical resistance across the monolayer. This drop is accompanied by a slow disorganization of the microfilament pattern of these cells, including a disturbance of a ring of cortical microfilaments that is normally associated with the junctions. Cells in open monolayers treated with CB will not reseal and have an altered filament distribution. These cells do not have a continuous cortical ring.
We have used a voltage scanning technique that uses a microelectrode to measure the resistance at selected points along the junction which surrounds a single cell. In untreated, closed monolayers, the junction is heterogeneous with alternating points of high and low conductance. In closed monolayers treated with CB, although there are low conductance points, we have observed an increased frequency of high conductance points that correlates with the change in the overall conductance. The frequency of high conductance points along the junction and the overall conductance both increase with time of exposure to CB.
In an effort to understand the molecular basis for the permeability changes induced by EGTA and CB, we have looked for differences in the protein components of the cell membranes of open, closed, and CB-treated MDCK monolayers. This was done by radioiodinating the surface membrane proteins under control and experimental conditions that bring about permeability changes. No significant differences in the labeled protein patterns were found under these conditions. These results suggest that the permeability changes involve only a structural rearrangement of membrane components. In addition we have observed that about 36% of the surface label remains bound to the insoluble cytoskeletons obtained from cells in control and experimental conditions that alter the permeability of the tight junctions. The iodinated proteins attached to the CS include polypeptides with Mr of ≥ 120K daltons as well as peptides with Mr = 56K, 50K, 36K, and 18K daltons.
116 citations
TL;DR: In this paper, the absorption and fluorescence properties of hematoporphyrin derivative in different solvent systems are investigated and the presence of a large amount of stable aggregates is demonstrated.
77 citations
TL;DR: In this article, a photoactivation mechanism of hematoporphyrin derivative is presented, based on the sequential absorption of two photons, leads to the production of cytotoxic radicals of HpD.
46 citations
TL;DR: In this paper, the reduction power of the redox system with increasing the pH is discussed, and the stereoselectivity observed in terms of Ti(IV) bridging control.
46 citations
TL;DR: In this paper, multicomponent molybdate catalysts consisting of Fe2(MoO4)3 with different amounts of Bi or Te were used for the oxidation of propylene to acrolein and characterized by means of DT, TG, and DSC analyses, surface area measurements, X-ray diffraction, and ir, Raman, diffuse reflectance, and Xray photoelectron spectroscopy.
45 citations
TL;DR: In this paper, the synthesis of 2,6-dideoxy sugars L -digitoxose (14), 2-deoxy-L -fucose (15) and L -mycarose (16) from the C4 and C5 chiral synthons through the intermediacy of the C7 adducts was reported.
39 citations
TL;DR: In the decerebrate cat the antidromic responses of C fibers are reduced, but not abolished, by reversible spinalization produced by cooling or by sectioning the thoracic spinal cord, which suggests in addition that in the deception preparation the presynaptic effectiveness of the C fiber input may be tonically decreased by supraspinal influences.
39 citations
TL;DR: Isoparvifolinone (2a), 8-hydroxypereflorine (3a), and diperezone (5) and the known sesquiterpenes cyperene and parvifoline (1a) were isolated from the roots of Perezia alamani var. oolepis.
38 citations
TL;DR: Ungar and Keller as discussed by the authors showed that when a mechanical mixture of two solid and crystalline n-alkanes of slightly different length is annealed at temperatures below the melting point of the shorter compound a mixed crystal is obtained.
34 citations
TL;DR: The previously unknown curcuquinol monoisovalerate and the known sesquiterpenes cyperene, cyperone, parvifoline, perezone, and α- and β-pipitzol were found in the roots of Perezia carpholepis.
TL;DR: In this article, an approximate method to study the monokinetic linear transport equation is outlined, starting from its integral form, rather than the integro-differential one, and the approximate solution may be deduced either analytically, in simple cases, or numerically by means of typical space discretization techniques, associated to proper boundary conditions.
TL;DR: Measurements of time‐resolved fluorescence microscopy of hematoporphyrin‐derivative in single cells of mice tissue, in HeLa cells, and in solution find that the presence of HpD stabilizes cell auto‐fluorescence and the fluorescence decay time is different in cells as compared with solution.
Abstract: This work presents measurements of time-resolved fluorescence microscopy of hematoporphyrin-derivative (HpD) in single cells of mice tissue (both tumor and normal cells), in HeLa Cells, and in solution. The measurements were performed using a pulsed-laser microfluorometer with high spatial and temporal resolution. In agreement with the results obtained with other techniques, it has been found that the tumor cells examined present an HpD uptake about five times higher than that of the normal cells of the corresponding tissue and that, within a cell, HpD become localized mainly in the cytoplasm. It has also been found that the fluorescence decay time is different in cells as compared with solution, and that the presence of HpD stabilizes cell auto-fluorescence. These results are discussed.
TL;DR: In this article, title compound (3b), prepared in concentrated CHCl3 or benzene solution and spectroscopically characterized, is shown to be an useful intermediate for the synthesis of sinapyl alcohol (1b) and its derivatives.
TL;DR: In this paper, the electron impact mass spectrometric behavior of a series of macrocyclic-acyclic polyether-ester compounds containing an isoxazole, benzene or pyridine ring is discussed in detail with the aid of exact mass measurements and metastable ions (linked scans B/E and B2/E).
Abstract: The electron impact mass spectrometric behaviour of a series of macrocyclic-acyclic polyether-ester compounds containing an isoxazole, benzene or pyridine ring is discussed in detail with the aid of exact mass measurements and metastable ions (linked scans B/E and B2/E). The nature of unusual [M+H]+ species, present in the crown moieties only, is elucidated by means of low electron energy measurements and labelling experiments. The field desorption spectra show only intense peaks corresponding to [M+H]+ species and rule out the presence of dimeric moieties.
TL;DR: Aqueous titanium trichloride reductively removes cyano and halo groups from the correspondingly substituted pyridines by a two electron-transfer process and promotes reduction of pyridsyl-ketones and aldehydes to glycols under very simple experimental conditions as discussed by the authors.
TL;DR: In this paper, an analysis of the non-linear creep effects around a deep circular tunnel driver in "squeezing" ground is presented, and the basic operations of the "evolutive" procedure adopted for time integration are outlined.
Abstract: An analysis is presented of the non-linear creep effects around a deep circular tunnel driver in "squeezing" ground. The time-dependent behaviour of the geotechnical medium is described by means or a simple viscoplastic rheological model capable of approximating primary, secondary and Tertiary creep behaviours. It is shown that Tertiary creep can be allowed for by providing a suitable law governing the variation of some material parameters (such as viscosity) with stresses and strains. The basic operations of the "evolutive" procedure adopted for time integration are outlined. Along each time integration step, quadratic variations of the stress and strain fields and linear variations of the material parameters are assumed. The results of various finite element analyses are presented concerning both lined and unlined cases. For the lined cases, the influence of the liner stiffness and of the time elapsed between the end of excavation and the liner installation is considered. (Author/TRRL)
TL;DR: The C4 erythro and threo diols were converted either into the chiral epoxides (13) and (15) or into the enantiomers (14, 15, and 16) as mentioned in this paper.
TL;DR: In this article, the temperature dependence of νi, Δν and the integrated band area for a few solid amides are studied for the γ(NH) mode in the infra-red.
Abstract: The temperature dependence of νi, Δν and the integrated band area for a few solid amides are studied for the γ(NH) mode in the infra-red. A general theoretical discussion of these structureless broad γ(NH) bands is presented. The bands are accounted for in terms of coupling of the γ(NH) mode with longitudinal as well as transversal low-frequency phonons.
01 Jan 1982
TL;DR: The role played in this context by direct search methods, least squares procedures and quadratic and nonlinear programming for identifying parameters in purely numerical models, linear models and linear complementarity models, respectively is concerned.
Abstract: Parameters which characterize geotechnical systems and are representative of the behaviour of soil or rock masses are often known with a high degree of uncertainty A way of reducing uncertainties and thus improving the mathematical models for analysis and design purposes is provided by a systematic adjustment of parameters so that theoretical predictions through the model match observational data This identification or “inverse” problem frequently implies recourse to techniques of mathematical optimization and particularly of mathematical programming This paper concerns the role played in this context by direct search methods, least squares procedures and quadratic and nonlinear programming for identifying parameters in purely numerical models, linear models and linear complementarity models, respectively A procedure of statistical identification is briefly mentioned at the end The scope is not to survey the field but merely to elucidate some aspects and potentialities of identification methods in geomechanics on the basis of a variety of recent results on particular problems
TL;DR: In this article, the dielectric function of liquid tin was calculated using a quantum-theoretical approach which involves the electron-ion pseudopotential and the structure factor of the liquid.
Abstract: The dielectric function of liquid tin was calculated using a quantum-theoretical approach which involves the electron-ion pseudopotential and the structure factor of the liquid. Empirical structure factors determined at several temperatures were used in the calculations. The results agree with published experimental data in the whole temperature range.
TL;DR: In this article, Aspergillus flavus was tested for their ability to produce aflatoxins, but only NRRL-6549 produced detectable amounts of B1, and smoking delayed but did not prevent mold growth.
Abstract: Aspergillus flavus NRRL-6549 and NRRL-6550 were tested for their ability to produce aflatoxins, but only NRRL-6549 produced detectable amounts of B1. Summer sausages prepared and inoculated with NRRL-6549 were smoked and held at 10 or 30°C for 3 or 6 wk at low or high humidities. Mold growth occurred on both inoculated and uninoculated sausages, the amount increasing with time, temperature and humidity. Smoking delayed but did not prevent mold growth. At 3 wk, aflatoxins were detected only in unsmoked inoculated sausages held at 30°C and high relative humidity. After 6 wk, B1 was found only in unsmoked inoculated sausages held at 10°C and high humidity, but at 30°C was present at 2.6–6.6 μg/kg in all inoculated samples at both low and high humidities.
TL;DR: In this paper, the vibrational density of states in the CC stretching region of polyacetylene upon doping was calculated, depending on the type of structural defects introduced.
TL;DR: The results with purified ATPase-inhibitor protein and (F1--ATPase)-inhibitors complex indicate that the activation process in the liposomes is due to the abolition of the inhibitory action of the inhibitor protein bound to a large fraction of the extracted ATPases.
Abstract: Protein-lipid complexes were transferred directly from mitochondria and submitochondrial particles into hexane and ether. The protein-lipid residue left after solvent removal from these extracts was used to form liposomes which display low-temperature-resistant ATPase activity. Centrifugation experiments indicate that the ATPase activity is associated to the vesicles. Most of the F1-ATPases appear to be accessible to the external water phase of the liposomes. The ATPase activity of these particles was insensitive to dicyclohexylcarbodiimide and oligomycin. Incubation of these vesicles at room temperature activated (4--10-fold) the ATPase through a process that is partially sensitive to phenylmethylsulfonyl fluoride. The results with purified ATPase-inhibitor protein and (F1--ATPase)-inhibitor complex indicate that the activation process in the liposomes is due to the abolition of the inhibitory action of the inhibitor protein bound to a large fraction of the extracted ATPases. Liposomes prepared from hexane extracts obtained from submitochondrial particles having different levels of ATPase activity displayed an activation ratio which correlated with the number of ATPases that are inhibited by the inhibitor protein in the submitochondrial particles. The extraction of mitochondrial ATPase and its incorporation into liposomes followed by activity measurements may be used to judge the number of ATPases that in a given preparation contain the inhibitor protein in its inhibiting site.
TL;DR: In this article, two nonlinear regression models, applied to winter daily SO2concentration data and to corresponding meteorological data from the metropolitan area of Vienna, are described, and sensitivity tests of model fitting performance are carried out by using various data sets for the estimation of regression coefficients.
TL;DR: Sets of electrooptical parameters suitable for longer n-paraffins and less constrained than those already used to fit the IR intensities of CH 4 and C 2 H 6 and their deuterated derivatives, are presented and discussed in this paper.
Abstract: Sets of electrooptical parameters (eop's), suitable for longer n-paraffins and less constrained than those already used to fit the IR intensities of CH 4 and C 2 H 6 and their deuterated derivatives, are presented and discussed. The technique adopted in the least-squares refinement of eop's from experimental data is discussed in detail.
TL;DR: It is shown that a centered finite differences approximation of the image differentials is mandatory to obtain good performances in the estimation of movements in television images.
TL;DR: In this paper, it was shown that the radiative corrections to the semileptonic decays of hyperons can be dealt with by a direct extension of a procedure originally introduced by Sirlin for neutron decay.
Abstract: Up to a certain accuracy, it is shown that the radiative corrections to the semileptonic decays of hyperons can be dealt with by a direct extension of a procedure originally introduced by Sirlin for neutron decay. We then compute the radiative corrections to the differential decay rate of polarized hyperons. From this expression the radiative corrections to rates and angular coefficients are obtained. We obtain a result suitable for model-independent analysis of experiments that improve the experimental accuracy on the determination of the differential decay rate up to 1 or 2 %.