Cryodessiccation et réactivité des solides minéraux divisés: exemple d''echantillons pulvérulents d''oxyde de nickel ex-hydroxyde ou ex-nitrate

Nickel oxide samples are prepared from freeze-dried colloïdal or aqueous solutions of nickel hydroxide or nickel nitrate; a good homogenization of the particle size is observed, but no change is obtained in the reactivity of the products if compared with the usual heat-dried solids; this is due to the fact that, in spite of the utmost division of the solids by rapid congelation and then freeze-drying, the benefit of that operation is lost during the successive reactions leading to oxide and processes and conditions which have their own effect in fixing the particle size and reactivity of the final solid.     

Electrochemical behaviour of lead chloride (PbCl2) in dimethylsulphoxide (DMSO)—II. a chronopotentiometric study

In our earlier electrode kinetic studies (chronopotentiometric) of lead chloride (PbCl₂) in dimethylsulfoxide (DMSO), the points in the plot of E, vs log (τ^1/2 ? t^1/2) were linear in the form of a wave. This situation was similar to that observed by Delahay in the chronopotentionmetric reduction of chromate ion (aqueous medium) and thought to be due to a prekinetic step. To verify the presence of a prekinetic step in our case a survey of iτ^1/2vs i for a wider range of lead chloride concentration was started. But a distortion observed in the initial part of the curve (from 4·0 mM PbCl₂) was another point of similarity with that of chromate ion. This led us to consider the polarographic and chronopotentiometric reduction behaviour of CrO^2?₄ in two different electrolytes sodium hydroxide and sodium carbonate. Such considerations justify the presence of a prekinetic step in electrochemical reduction of chromate. Such a prekinetic step, probably the dissociation of PbCl₂, is verified and Kk^1/2₂ values for this coupled chemical reaction are determined according to the transition time expressions of Delahay and Dracka.     

Stability analysis of adaptively controlled systems subject to bounded disturbances

An approach for studying stability of adaptively controlled systems subject to bounded disturbances with unknown statistics is given. A shorter proof of some results established for minimum phase systems is also given; new results are established for nonminimum phase systems. In each case, the uniform boundedness of all signals is proven under a condition that is discussed. Examples of adaptive schemes that can be treated with this approach are given.     

An approach to testing specifications

An approach to testing the consistency of specifications is explored, which is applicable to the design validation of communication protocols and other cases of step-wise refinement. In this approach, a testing module compares a trace of interactions obtained from an execution of the refined specification (e.g., the protocol specification) with the reference specification (e.g., the communication service specification). Nondeterminism in reference specifications presents certain problems. Using an extended finite state transition model for the specifications, a strategy for limiting the amount of nondeterminacy is presented. An automated method for constructing a testing module for a given reference specification is discussed. Experience with the application of this testing approach to the design of a transport protocol and a distributed mutual exclusion algorithm is described.     

Etude au microscope electronique des phenomenes de transition de phases dans des monocristaux d'oxyde V2O3 pur et dope au chrome

An investigation by electron microscopy confirms the low temperature transition in single crystal of V₂O₃ and V_2?xCr_xO₃ (x = 0,048). The twin planes were identified in the corundun structure as (1 1 2 0)_M. An explanation is proposed.     

In-pile creep study on mixed oxide (U,Pu)O2

The in-pile creep of a mixed oxide UO₂-PuO₂ under compression was studied up to fission rate of $\text{6 × 10}{}^{13}\text{f cm}{}^{\mathrm{?3}}\text{s}{}^{\mathrm{?1}}$, for stresses up to 26.5 MN m^?2, at temperatures ranging from 700 to 900°C. The results obtained agree with those of other authors. The creep rate is proportional to the applied stress and to the fission yield. However, it is athermal within the temperature range explored and is not affected by the burn-up, which has so far reached 30000 MWd t^?1 (3.6% FIMA). When the sample is under compression the fuel swells under the action of the fission products formed in the oxide during its irradiation. The swelling rate is about that commonly accepted for a clad fuel element. Finally it seems that the oxide swells more when free from stress than when subjected to a stress field, but this point has to be confirmed.     

Neuromuscular blocking drugs and heart rate changes after direct nerve stimulation and during classical conditioning in cats.

2 experiments investigated cardiovascular responses to several common neuromuscular blocking compounds. Exp I, employing 16 male cats, assessed ganglionic transmission in sympathetic and parasympathetic systems controlling heart rate and blood pressure after dextrotubocurarine chloride (TC), dimethyl dextrotubocurarine iodide (DTI), succinylcholine chloride (SC), or saline. Cardiovascular responses to sympathetic stimulation were essentially unaffected at drug levels that blocked evoked electromyograms; however, vagally evoked bradycardia and corresponding blood pressure decrease were blocked by TC and reduced by DTI and SC. Exp II compared heart responses of 12 male cats under the same blocking compounds during differential classical aversive conditioning. Differential conditioned responses and unconditioned responses occurred under DTI, less under SC, but not under TC. However, Ss trained under TC and tested under DTI showed differential conditioned responses. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lois de comportement elastique isotropes en grandes deformations

We give a characterization of isotropic hyperelastic materials: there exists a potential of the logarithm of the Almansi-Euler strain tensor, the derivative of which provides us with the Cauchy stress tensor.