Showing papers by "Instituto Politécnico Nacional published in 1979"
TL;DR: An analytical solution to the problem of modeling bandpass nonlinear channels and evaluating the performance of digital communication systems operating on them is presented and basic advantages are the generality it offers to the analysis and the fact that it allows accurate evaluation of the error probability in a short computer time.
Abstract: An analytical solution to the problem of modeling bandpass nonlinear channels and evaluating the performance of digital communication systems operating on them is presented. A method based on a Volterra series representation of the overall channel is first proposed, which allows one to extend to nonlinearities with memory the well-known concepts of complex envelope of bandpass signals and low-pass equivalent of bandpass linear systems. The general results previously mentioned are then applied to digital satellite communication systems operating over nonlinear channels. The effect of a nonlinear amplifier located in the satellite is considered, in combination with that of transmitting and receiving filters located in the Earth stations. In addition, both uplink and downlink noise are taken into account. Basic advantages of this approach are the generality it offers to the analysis and the fact that it allows accurate evaluation of the error probability in a short computer time.
293 citations
TL;DR: This review describes how recent developments have sustained the expectation that by characterizing these substances, and their physiological actions upon the liver, a precise explanation of fundamental regulatory mechanisms would emerge.
222 citations
TL;DR: In this paper, photoemissive detection of arbitrary quantized radiation fields is studied with incorporation of the nontrivial effects of detector quantum efficiency and the increase in homodyne signal-to-noise ratio obtained by use of TCS radiation yields significant performance gains in both linear modulation and antipodal signal detection.
Abstract: In Part I of this three-part study, it was shown that novel quantum states, called two-photon coherent states (TCS), have significant potential for improving free-space optical communications. Because TCS radiation does not possess a classical analog, i.e., its diagonal P -representation is highly singular, the semiclassical conditional Poisson process model for direct detection is not applicable to TCS reception. In this paper, photoemissive detection of arbitrary quantized radiation fields is studied with incorporation of the nontrivial effects of detector quantum efficiency. General theorems are derived permitting the application of classical point process results to the detection and estimation of signals in arbitrary quantum states. These general theorems are applied to determining the performance of TCS optical communication systems that employ direct, heterodyne, or homodyne detection in binary decision as well as in linear modulation problems. It is shown that the use of TCS radiation with direct detection or heterodyne detection results in minimal performance increments over comparable coherent-state systems. Homodyne detection, however, can achieve the full TCS signal-to-noise ratio improvement predicted in Part I of this study. The increase in homodyne signal-to-noise ratio obtained by use of TCS radiation yields significant performance gains in both linear modulation and antipodal signal detection.
219 citations
TL;DR: In this paper, the authors studied the relationship between elastoplastic stress-strain relations with the current yield surface and the elastic modulus and showed that the rate response uniqueness and material stability of the elasticity modulus can be interpreted in mechanical terms using standard compression tests and for particular forms of constitutive laws.
192 citations
TL;DR: In this paper, the optimum geometry for strip cathodes or grids in MWPC for avalanche localization along the anode wires through measurement of induced pulses is calculated, and the resolution limits due to electronic noise are established as a function of the required time resolution.
123 citations
TL;DR: There is a variation in the relative amounts of these proteins in different batches of cells which may relate to the nutritional status of the organisms.
77 citations
TL;DR: It is suggested that decorrelation of MS activity by gamma influence may improve the fidelity of the information transmitted by the Ia MS ensemble by filtering distortion harmonics, as well as damping tremor oscillations in the stretch reflex loop.
64 citations
55 citations
TL;DR: In this article, the complete stress and strain response of elastic-perfectly plastic structures subjected to proportional loading up to collapse is determined by a method essentially consisting of a linear programming procedure supplemented by an additional rule which enforces a complementarity relation among variables at each pivotal step (restricted basis entry).
49 citations
TL;DR: In this article, a soil mechanics oriented theory of the hysteretic behaviour of materials under alternating loading is presented, focusing on the behaviour within the yield locus. But the authors do not consider the effects of the load on the soil.
46 citations
TL;DR: In this article, the requirements for desirable technological properties of semiconductors for photovoltaic conversion are discussed and two criteria are suggested for the selection of materials that could guide the search towards low melting compounds made of cheap component elements: (1) a deviation from ideality vs. energy gap diagram for the prediction of energy gaps from the knowledge of melting temperatures or viceversa; (2) the use of the Parthe-Goryunova-Mooser-Pearson criteria for compounds of which only their chemical formula is known but not their structure.
01 Jan 1979
TL;DR: It is demonstrated that STS or DTS activated amides offer new opportunities to prepare polymer drug adducts with a main backbone degradable to safe metabolites in the body fluids.
Abstract: Succinic esters of starch and dextrane (STS and DTS) have been prepared and transformed into the corresponding imidazolides. These are difficult to isolate in a pure state. Without previous isolation, however, they react smoothly with alcohols or amines giving the corresponding polymeric esters or amides. STS benzotriazolide has also been prepared, and isolated in a pure state. It has been found to have the same reactivity towards alcohols and amines than other previously described polymeric benzotriazolides. These results demonstrate that STS or DTS activated amides offer new opportunities to prepare polymer drug adducts with a main backbone degradable to safe metabolites in the body fluids.
TL;DR: A method is presented allowing direct and continuous estimation of the excitability changes of single fiber terminal arborizations within the central nervous system and can accurately determine input-output curves of single units requiring relatively small current variations.
TL;DR: The structure of di-1,5-cyclooctadienesilver tetrafluoroborate was determined from single crystal X-ray diffraction data as discussed by the authors, where the silver atom is four coordinated to the olefinic ends of the two cyclooctadiene molecules in a modified tetrahedral coordination described as "cubical".
TL;DR: It is concluded that the C-terminal group is also blocked and a neurodepressing hormone has been isolated and purified to homogeneity from aqueous extracts of 2000 eyestalks of the Mexican crayfish Procambarus bouvieri (Ortmann).
Abstract: 1. A neurodepressing hormone has been isolated and purified to homogeneity from aqueous extracts of 2000 eyestalks of the Mexican crayfish Procambarus bouvieri (Ortmann).
2. Purification was achieved by gel filtration on Sephadex G-25 and G-15, and preparative paper electrophoresis at four pH values (1.8, 3.6, 6.0 and 10.0).
3. The recovery of hormone activity was 85% and the specific activity was 4.0 × 104 times that of the starting material.
4. The hormone is a thermostable peptide of approximately 1200 molecular weight and composed of neutral amino acids.
5. No N-terminal group could be found. From its electrophoretic behavior it is concluded that the C-terminal group is also blocked.
01 Jan 1979
TL;DR: A list of 149 species o[ fungi is presented, of which 120 are reported for first time from the State of Hidalgo, in the Zacualtipan-Tehuetlan region, in Mexico.
Abstract: A list of 149 species o[ fungi is presented, of which 120 are reported for first time from the State of Hidalgo. The material was colected from six localities of the Zacualtipan-Tehuetlan region, in the State oE Hidalgo (Mexico).
TL;DR: In this paper, the absorption curve was resolved into two components pertaining to the primary and the scattered beam, respectively, and the shape of the curve was given in terms of the mylar mass absorption coefficient and of the atomic number of the scatterer.
Abstract: Implantation in mylar of positrons from22Na was investigated in «broad beam» arrangement. The absorption curve was resolved into two components pertaining to the primary and the scattered beam, respectively. Here the shape of the curve is given in terms of the mylar mass absorption coefficient and of the atomic number of the scatterer. The role played by the scattered positrons in populating the surface layers is outlined.
TL;DR: Evidence is presented that receptors for pancreatic hormones change differently when liver is damaged and during its regeneration following CCl 4 intoxication, similar to changes reported previously in fetal liver development or following partial hepatectomy of adult rat.
TL;DR: In this paper, four γ-hydroxybutenolide sesquiterpenes have been isolated from Lactarius scrobiculatus, L. blennius and L. pallidus.
TL;DR: In un ejemplar juvenil monstruoso, with bicefalia funcional de Rhinoptera steindachneri Evermann and Jenkins, colectado en la Costa Occidental de Baja California Sur, se hace una descripcion morfologica y anatomica detallada, ofreciendose ademas datos morfometricos as mentioned in this paper.
Abstract: Con base en un ejemplar juvenil monstruoso, con bicefalia funcional de Rhinoptera steindachneri Evermann y Jenkins, colectado en la Costa Occidental de Baja California Sur, se hace una descripcion morfologica y anatomica detallada, ofreciendose ademas datos morfometricos. Se discute brevemente acerca de este fenomeno que aparentemente no es muy comun en los Elasmobranquios, a juzgar por la gran cantidad de literatura que existe sobre anomalias y defectos de esta clase, que mayormente se refieren a peces oseos. El estudio se complementa con una serie de fotografias que muestran claramente las estructuras mencionadas en el texto.
TL;DR: It is postulated that the observed conduction block is a consequence of demyelination, and the medial gastrocnemius and soleus muscles of paralyzed hind limbs showed mechanical properties similar to those observed after denervation.
TL;DR: The tadpole spinal cord is a useful preparation in which to study the dynamic properties ofnormal non-transformed glia as influenced by a changing neuronal population, whereas the frog FT is a unique preparation for the study of some properties of normal glia largely in the absence of neurons.
TL;DR: Two new metabolites, dimethyl 2-(2-ethenyl-5-hydroxy-4H-1-benzopyran-4-onyl-3)-malonate and methyl 2-methoxy-8-Hydroxy-9-oxo-9H-xanthene- 1-carboxylate, have been isolated and identified from the mycelium of Mycosphaerella rosigena grown on potato-agar.
TL;DR: In this paper, the diterpene trachylobane and a series of derivatives have been completely analyzed by FT 13C NMR spectroscopy and the results are discussed in comparison with the experimental data.
Abstract: The diterpene trachylobane and a series of derivatives have been completely analysed by FT 13C NMR spectroscopy. All 13C frequencies for trachylobanol have been unambiguously assigned by experimental techniques, i.e. by proton single-frequency selective decoupling and shift reagent experiments. Shift calculations have been performed for the parent compound by using known methods. The results are discussed in comparison with the experimental data. Satisfactory agreement between predicted and experimental values has been obtained.
TL;DR: In this paper, the authors give necessary and sufficient conditions for linearly independent vectors to hold in the presence of arbitrary matrices, and some consequences of this result are also presented.
TL;DR: Stingrays swim with an active elevation-depression sequence of the pectoral fin resembling an extension-flexion sequence, and immediately following high decerebration, stingrays are capable of locomotion, and the pattern of muscle activity closely resembles that of intact animals.
TL;DR: In this paper, the authors derived consequences of a condition for the equality of two star products given by the second author and studied another method for the same problem which consists of comparing the components, in an appropriate basis, of the star products involved.
TL;DR: In this paper, the dependence of the fluorescence decay law both on the degree of DNA saturation by the dye and on the ionic strength of the solutions is investigated, and it is shown that the quinacrine mustard molecules intercalating the DNA base pairs exhibit two different fluorescence behaviors which make them either donors or acceptors in a Forster energy transfer mechanism.
Abstract: —Measurements of time-resolved fluorescence of Micrococcus lysodeikticus DNA stained with quinacrine mustard are presented in this paper. In particular, the dependence of the fluorescence decay law both on the degree of DNA saturation by the dye and on the ionic strength of the solutions is investigated. It is shown that the quinacrine mustard molecules intercalating the DNA base pairs exhibit two different fluorescence behaviors which make them either donors or acceptors in a Forster energy transfer mechanism. A mathematical formulation of this mechanism allows us to interpret all the experimental fluorescence decay curves. In addition, some new properties of the external binding mode are obtained.