Experimental Research on the Impact of Ion Exchange and Infiltration on the Microstructure of Rare Earth Orebody

To detect the evolutional characteristics of pore structure in ore leaching process of ion-type rare earth, this paper analyzes the influence mechanism of ion exchange seepage action on the microstructure of orebody, and an experiment for remodeling rare earth saturated samples and ore leaching was designed. Using nuclear magnetic resonance technology obtains the pore structure T2 map of H2O and (NH4)2SO4 solution in the ore leaching process and inverts and reconstitutes the pore structure distribution image. The results of contrastive analysis experiments indicate that impact factors of the ore leaching process on the microstructure of rare earth orebodies include two aspects: solution seepage and ion exchange. The main factor of pore structure distribution is the ion exchange action, determined by a dual effect. The sole action of solution seepage leads to an increase in pore size, which means that pore size structure is changing from small and medium to macro. Ion exchange gives rise to the movement and restructuring of particles, which results in a decrease in pore sizes. The pore structure changes from loose to compact; in the entire ore leaching process, the ion exchange action advances in a layered shape along the direction of seepage, and the chemical replacement and physical seepage alternately impact the microstructure of the orebodies.

Analysis of the effects of vagal stimulation on the sinus venosus of the toad

In amphibians and mammals, vagal stimulation leads to the release of acetylcholine, ACh, which causes bradycardia. However, the responses to nerve stimulation are not well mimicked by exogenously applied ACh. These observations have led to the suggestion that there are subpopulations of muscarinic receptors on pacemaker cells and that during vagal stimulation neuronally released ACh caused slowing by suppressing inward current flow during diastole. After the generation of action potentials has been prevented by applying an organic calcium antagonist, vagal stimulation causes a hyperpolarization and an increase in membrane resistance: this observation suggests that the hyperpolarization results from a supression of inward, presumably Na + , current flow. In this study we describe the effects of vagal stimulation on membrane potentials recorded from arrested and beating hearts by using a computer model. The model of Noble & Noble ( Proc. R. Soc. Lond. B 222, 295 (1984)) was modified to describe the shape of amphibian pacemaker action potentials. A voltage-dependent Na conductance was included as well as two voltage-independent conductances, a background Na conductance and a background K conductance. Subsequently the hypothesis that the changes in membrane potential recorded during vagal stimulation from arrested preparations resulted from a reduction in Na conductance and this represented the sole action of vagally released ACh, was tested. If this were so, the changes in membrane conductance that occur during vagal inhibitory junction potentials recorded from arrested preparations should produce changes in pacemaker action potentials similar to those recorded experimentally from beating preparations. This was found to be the case. Thus the analyses are consistent with the idea that vagal inhibition of pacemaker cells results solely from a suppression of the two pacemaker sodium currents.

On the theory of the perturbations of the planets

The methods hitherto employed by mathematicians for determining the variations which the elements of the orbit of a planet undergo in consequence of perturbation, and for expressing these variations analytically in the manner best adapted for computation, are found to depend upon a theory in mechanics, of considerable intricacy, known by the name of the Variation of the Arbitrary Constants . In seeking the means for abridging the severe labour of the calculations, we must separate the general principles on which they are founded from the analytical processes by which they are carried into effect; and in some important problems great advantage is obtained by adapting the investigation to the particular circumstance of the case, and attending solely to the principles of the method in deducing the solution. The author suggests the possibility of simplifying physical astronomy by calling in the aid of only the usual principles of Dynamics, and by setting aside every formula or equation not absolutely necessary for arriving at the final results. The present paper contains a complete determination of the variable elements of the elliptic orbit of a disturbed planet, deduced from three differential equations, that follow readily from the mechanical conditions of the problem. In applying these equations the author observes, the procedure is the same whether a planet is urged by the sole action of the constant force of the sun, or is besides disturbed by the attraction of other bodies revolving round the luminary; the only difference being that, in the first case, the elements of the orbit are all constant, whereas in the other case they are all variable. The success of the method followed by the author is derived from a new differential equation between the time and the area described by the planet in its momentary plane, which greatly shortens the investigation by rendering it unnecessary to consider the projection of the orbit. But the solution given in the present paper, although it makes no reference to the analytical formulæ of the theory of the Variations of the Arbitrary Constants , is no less an application of that method and an example of its utility, and of the necessity of employing it in very complicated problems.