Multiplication of the depth of detectability using γ11n arrays

The depth from which one can get information has always been a crucial parameter in the geophysical exploration. This paper deals with the depth of detectability (DD) of 2D electric resistivity tomography configurations. DD is the maximal depth from which a given model body is detectable in the presence of a given noise level. Based on previous DDcalculations for conventional electrode arrays it is shownin this paper that there is a nearly linear relation between the maximumvalue of their parameter-sensitivity (PS) maps and their DD values. Studying the PS maps of other arrays, as well, we found that many of them have higher PSmax values than those of the conventional arrays. These so-called γ11n arrays are therefore expected to have larger DD values, too. The performed DD-calculations have confirmed this expectation. γ11n arrays are linear geoelectric arrays where γ refers to the CPCP order of the current (C) and potential (P) electrodes whilst the subscript numbers refer to the distance of the neighbouring electrodes. In case of the studied prismand dyke models the γ11n arrays – if n is larger or equal to 2 – consistently produced higher DD-values than the best conventional arrays. The DD value of these arrays can be even 2–3 times larger than that of the best conventional array value. Such an increase in the DD value is especially useful if the available place for measurements is limited, e.g. due to infrastructural conditions. Anomalies in large depth, for example, which are not seen by traditionally used arrays, may become detectable using γ11n arrays as it was verified also by numerical studies. These arrays require moreover less measurement than most conventional arrays resulting in shorter measuring time

Diffúzió és szegregáció nanoszerkezetekben = Diffusion and segregation in nanonstructures

Szimulációkból, majd kísérletileg is megmutattuk, hogy ha a diffúziós együttható erősen függ a koncentrációtól, akkor az eredetileg éles határfelület lineárisan (nem parabolikusan, ahogyan azt a klasszikus Fick I. egyenletből várnánk) tolódik el nanoskálán fázisszeparálódó (Ni-Au) rendszerben, sőt eredetileg elmosódott határfelület kiélesedhet még ideális (korlátlan kölcsönös oldhatóságú) szilárd rendszerekben is (pl. Mo-V rendszer). Szimulációkból ugyancsak megmutattuk, hogy a kiélesedés akkor is végbemegy, ha a diffúziós feszültségek hatását figyelembe vesszük. Megmutattuk, hogy a nanoskálán végtelen gyors kinetikát jósoló jól ismert diffúziós paradoxon feloldható: egy kezdeti éles koncentrációprofil esetén a határfelület véges diffúziós permeabilitása határozza meg az áramot, amely kezdetben jó közelítéssel állandó és ez lineáris kinetikához vezethet. A fenti eredmények a nanoskálájú szilárdtest reakciók értelmezésében fontosak lehetnek. Az irodalomban korábban közölt, túl egyszerűsített, egyenletnél általánosabbat adtunk meg a szegregáció által stabilizált szemcseméret hőmérsékletfüggésére és ennek érvényességét a rendelkezésre álló adatokból igazoltuk. | It has been shown, both from simulation and experiments, that - if the diffusion coefficient has strong composition dependence - an initially sharp interface shifts linearly (not by a parabolic law, expected from the classical Fick I. equation) on nanoscale, and an initially diffuse interface can become sharper even in ideal (mutually completely soluble) systems (e.g. Mo/V system). It was also obtained from simulations that this sharpening takes place even if the effect of stresses, of diffusional origin, is taken into account. We have shown that the well-known diffusion paradox, predicting infinitely fast kinetics at the nanoscale, can be resolved: for an initially abrupt composition profile the flux crossing the interface is determined by the finite diffusion permeability of the interface. This is, in a good approximation, is constant at the beginning and this leads to a linear kinetics. These results can be important in the interpretation of solid state reaction on the nanoscale. General (more general than the oversimplified one published in the literature recently) relation between the segregation stabilized grain size and the temperature was derived and its validity is confirmed on the basis of available experimental data