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Showing papers by "Instituto Superior Técnico published in 1978"


Journal ArticleDOI
21 Sep 1978-Nature
TL;DR: The combined use of both X-ray crystallography and NMR is reported to identify MET-7 and HIS-106 as the two ligands of the haem iron of cytochrome b562.
Abstract: X-RAY crystallography and nuclear magnetic resonance (NMR) are the two most powerful physical techniques for studying macromolecular structure. They are often used to complement one another in the study of a particular molecule. Crystallographic results have been of tremendous help in the NMR peak assignments which are subsequently used to obtain structural information in solution1,2. We report the combined use of both X-ray crystallography and NMR to identify MET-7 and HIS-106 as the two ligands of the haem iron of cytochrome b562.

40 citations


Journal ArticleDOI
TL;DR: It is shown that, besides the speed and angle estimation, simultaneous global range passive tracking is possible and simple expressions and graphical displays are presented that can be used as design tools in practical passive tracking problems.
Abstract: This paper studies passive problems where the receiver extracts from the source radiated signature information concerning the parameters defining the relative source/receiver geometry. A model encompassing the fundamental global and local characteristics for passive positioning and navigation is presented. It considers narrow-band signals, imposes linear constraints on the geometry, and exhibits explicitly the symmetry between the space and time aspects. The analysis concentrates on questions of global geometry identifiability, emphasizing the passive global range acquisition. The maximum-likelihood processor is analyzed by studying the ambiguity structure associated with inhomogeneous passive narrowband tracking. Bounds on the global and local mean-square error performance are studied and tested via Monte Carlo simulations. By considering two limiting geometries, a distant and a close observer, simple approximate expressions for the mean-square errors are presented and compared to the exact bounds. Herein the study is restricted to stationary geometries where the source is located by an extended array (spatial diversity). Subsequent papers generalize the study to moving sources (temporal diversity) and to coupled geometries.

35 citations


Journal ArticleDOI
TL;DR: In this paper, the total vapour pressure of liquid mixtures of krypton + ethene at the triple point temperature of Krypton (115.77 K) as a function of composition, of the excess molar volumes of the mixtures at the same temperature, and of excess enthalpy at 117.7 K.

15 citations


Journal ArticleDOI
TL;DR: Aires-Barros et al. as discussed by the authors found a possible correlation between the weathering indices obtained from samples of one type of sedimentary rock, a greywacke, altered to various degrees and those obtained after laboratory aging tests on the same rocks.
Abstract: The aim of this work is to find a possible correlation between the weathering indices obtained from samples of one type of sedimentary rock, a greywacke, altered to various degrees and those obtained after laboratory aging tests on the same rocks. In a first part the process of natural alteration is studied taking samples of three different alteration stages. These samples were collected in a vertical borehole and the natural weathering process was followed by geochemical and petrological observations. Geochemical calculations were made, in order to obtain the amount of gain and loss of chemical elements. The quantification of the weathering through the application of weathering indices and finally an attempt was made to apply an alterability index to these rocks. Samples of the same rocks were submitted to laboratory thermal fatigue tests (Aires-Barros et al. 1975), in order to follow the alteration by laboratory aging and to obtain weatherability indices. Physical values of sonic velocity, porosity, permeability and swelling were also determined. The presentation of the corresponding results forms the second part of this paper. In the third part, the values obtained in the two preceding parts are compared in order to test the laboratory work and to determine the correlation between the “one laboratory year test” and natural weathering.

11 citations


Journal ArticleDOI
TL;DR: In this paper, the stability against small perturbations of a certain class of nonlinear wave solutions of the equations that describe a cold unmagnetized plasma was studied. But the stability was not considered for the case of the transverse linearly polarized waves in an electron-positron plasma.
Abstract: This is part 2 of a paper concerned with the stability against small perturbations of a certain class of nonlinear wave solutions of the equations that describe a cold unmagnetized plasma. It refers to transverse linearly polarized waves in an electron-positron plasma. A numerical method, based on Floquet's theory of linear differential equations with periodic coefficients, is used to solve the perturbation equations and obtain the instability growth rates. All the three possible types of perturbations are discussed for a typical value of the (large) amplitude of the nonlinear wave: electrically longitudinal slightly unstable modes (with maximum growth rate γ approximately equal to 0·07ω 0 , where ω 0 is the frequency of the nonlinear wave); purely transverse moderately unstable modes (with γ ≃ 0·26ω 0 ); and highly unstable electrically transverse modes (with γ ≃ l·5ω 0 ).

6 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of ionizing particles on the radioluminescence yield of aromatic scintillators is studied and an expression giving the specific luminescence dS/dx as a function of the charge number z and of the incident particle specific energy loss has been derived.
Abstract: 2014 The influence of the nature of ionizing particles on the radioluminescence yield of aromatic scintillators is studied. Both prompt and delayed scintillation components are considered. An expression giving the specific luminescence dS/dx as a function of the charge number z and of the incident particle specific energy loss has been derived, following a track model published before, that is consistent with recent conclusions about the nature, evolution and distribution of the primary excitations created by an ionizing particle in the organic scintillator. The good agreement between the theoretical curves derived in this paper and the experimental ones previously reported provided us with a means of evaluating the different parameters included in the proposed expressions. The numerical values of these parameters agree with those of other authors and are theoretically discussed and justified. LE JOURNAL DE PHYSIQUE TOME 39, MAI 1978,

4 citations


Journal ArticleDOI
TL;DR: The concept of ion pain was introduced by Bjørnström as discussed by the authors, who recognized that the concept was helpful for studying the conductability of ctrrain saline solutions, and used it to identify the ion pain.
Abstract: In 1926 Bjcrnrm [31 tmroduced the concept of ion pain because he recognized t h thts concept was helpful for studying adeqquately the conductvtry of ctrrain saline solutions. By ion pair is meam che species which results from the association of as anion with a cation.

4 citations