Overlap Of Zones Research Articles

Development of reflexes from skin grafts in Rana pipiens: Influence of size and position of grafts

Skin grafts of various sizes, shapes, and positions were transposed between back and belly of frog tadpoles at midlarval stages. The aim of the experiments was to determine the effect of size and position of the graft on the development of reflexes evoked by light mechanical stimulation of the graft. Normal reflex movements of a limb were aimed at the stimulated point, and misdirected reflexes were aimed at the original position of the grafted skin rather than at the point of stimulation. At first only normal reflexes were evoked from all types of grafts. Grafts smaller than 40 mm 2 continued to give only normal responses. After a period of normal reflexes lasting a variable number of days after metamorphosis, misdirected reflexes were elicited from a small region of larger grafts. The position of this region was in the area of overlap of reflexogenous zones of forelimbs and hindlimbs. In larger grafts, the zone giving rise to misdirected reflexes spread gradually at a rate of about 1 mm per day until it occupied almost the entire graft. In those cases, the percentage of misdirected reflexes evoked from the graft was directly proportional to the graft area. Receptive fields of cutaneous nerves were mapped electrophysiologically. It was observed that nerves supplying the large grafts did not innervate surrounding skin and vice versa, but nerves grew across the margins of small grafts. The mechanism of exclusion of surrounding nerves by large grafts is not known. We concluded that misdirected reflexes developed after transposing pieces of back and belly skin in midlarval tadpoles, only if the area of the graft exceeded 40 mm 2 after metamorphosis, and if the graft crossed the boundaries of fore- and hindlimb reflexogenous zones.

Axial ratios and solubility limits of H.C.P. η and ε phases in the systems CdMn and ZnMn

Solubility limits and lattice parameters have been determined across the terminal solid solutions in the systems CdMn and ZnMn and across the ε phase in ZnMn. Increases in axial ratio across the η solid solutions are attributed to an increase in the overlap across the {00.2} faces of the Jones zone, indicating that manganese acts as divalent in these solutions. A change in the slope of the axial ratio-versus-composition plot at 78 at.% Zn is attributed to the onset of the {00.2} zone overlap, as found in the ε brasses, and indicates that in the ε phase manganese acts as univalent. These changes in the electronic configuration of manganese are related to its atomic volume in the various environments.

Superconducting transition temperatures in ε-phase PbBi alloys

Superconducting transition temperatures across the ε-phase in PbBi show an accelerated rise near e/ a = 4.28. This charge in d T c /d c is attributed to a {10.2} Brillouin zone overlap, the presence of which is confirmed by an increase in the axial ratio of the hexagonal cell.

Specific Heats of Zirconium Alloys at Low Temperatures

The specific heats of dilute alloys of silver, cadmium, indium, tin, and antimony in hexagonal zirconium were measured from 1.2 to 4.5 deg K. For each alloy the specific heat obeyed the relation c = gamma T + BETA T/sup 3/ within the experimental error. All of these solutes increased gamma linearly with concentration and d gamma /dx was linearly related to the chemical valence of the solute. The increase in gamma in the tinzirconium alloys showed that all electrons outside closed shells cannot be treated as equivalent in the rigid band model of alloying. All of these solutes increased the density af states of zirconium, providing evidence for a zone overlap in the zirconium d band and for a small number of electrons in a new band. All of the solutes increased the lattice specific heat and the Debye temperature was a linear function of solute concentration for each of these alloy systems. The function d theta /dx was not simply related to the solute valence but showed a close correlation with the magnitude of the rate of change of the distance between atoms at 000 and 1/3, 2/ 3, and 1/2 of the hexagonal cell. Additions of tinmore » to zirconium did not change the average interaction potential of the BCS theory appreciably. (auth)« less

Insoluble Residues in a Portion of the Ordovician Cynthiana Formation, North-Central Kentucky

ABSTRACT Re-examination of the Cynthiana Formation in Kentucky has been undertaken to relate the various named members stratigraphically and geographically. As a part of this work, a detailed study of insoluble residues from a horizon of this formation, a sequence of alternating shales and limestone, was undertaken to test the feasibility of correlation. High lateral variability of all aspects of both heavy and light fractions and overlap of zones within the vertical range of the insolubles make detailed correlations impossible. Correlation can only be made when a new heavy mineral suite or a new species appears. Size, good sorting, maturity and limited heavy mineral content of the rock indicate deposition in a shallow sea quite distant from the source area, a metamorphosed terrane of fairly high rank. Zircon, calcium garnet, amphiboles, and pyroxenes are the principal species found in the heavy fraction. Abraded and fragmental zircons are found to have a wide range of sizes whereas euhedral zircons are restricted to the silt sizes and are believed to have a bentonitic origin.

The soft X-Ray emission spectra of sodium, beryllium, boron silicon, and lithium

Abstract Emission hand forms of several elements obtained with a photon-counting spectrometer are compared with previously published spectra. The sodium L23,I(E)vs λ curve departs from the free electron perabola at energies than about 1 ev from the Fermi limit in accord with the theoretical form. The sodium extrapolated band width is 2.6 ± 0.3 ev. In beryllium K there is no contribution of p states from the bottom of the overlapping second zone. Zone overlap is estimated at 1–2 ev. The extrapolated band width for boron K is estimated at 14.1 ± 0.8 ev. The L23 band of silicon differs from those previously published but is apparently not affected by the temperature or the purity of the silicon. The extrapolated width is 13.4 ± 0.8 ev. A strong line at 253 A and a blue fluorescence which accompanies the lithium K spectrum are shown to be connected with the reaction with lithium of hydrocarbon molecules not condensed by the cold trap.

Single-crystal elastic constants of magnesium and magnesium alloys

The adiabatic elastic constants of single crystals of magnesium and dilute alloys of magnesium with Ag, In, and Sn have been measured by the ultrasonic pulse-echo technique. The values obtained for pure magnesium are: C 11 = 0.597, C 33 = 0.617, C 44 = 0.164, C 12 = 0.262, C 13 = 0.217, all expressed in units of 10 12 dyne cm −2. The alloy results show that within the experimental uncertainty all constants exhibit a smooth behavior as the electron concentration is increased to 2.020 per atom, through the critical region where zone overlap is thought to occur in the c direction. At most, a small change in slope could be read into the data for C 11 + 2 C 33 + C 12 − 4 C 13 at the critical electron atom ratio of 2.01. This behavior is in contrast to what might be expected from an extension of Leigh's predictions for the elastic constants of aluminium alloys.

Transport Properties of Dilute Binary Magnesium Alloys

Unusual lattice parameter behavior in dilute binary magnesium alloys has been observed by Raynor and others, and has been attributed to a Brillouin zone overlap phenomenon suggested by Jones. The primary purpose of this paper is to show that if the overlap model is even only qualitatively correct, measurements of electron transport properties should be sensitive to electron overlap. Such measurements have been made on the resistivity, temperature variation of resistivity, Hall coefficient, and thermoelectric power. Monovalent and divalent additions to magnesium are found to cause the Hall coefficient and thermoelectric power to vary monotonically with composition, but trivalent and quadrivalent additions cause these measurements to go through extrema associated with the zone overlap. It is proposed that both the Hall coefficient and the thermoelectric power may be expressed as the sum of two contributions. One contribution is directly related and therefore is linear to electron concentration. The other contribution arises essentially from everything else, particularly the perturbations upon the ion core potential when a foreign atom is introduced into the lattice. This latter contribution may be obtained directly from measurements on the magnesium-cadmium system. A simple subtraction then provides the electronic contribution for the alloy under question. A band picture is invoked to qualitatively justify this approach. Finally, this paper also demonstrates that Matthiessen's rule and Linde's rule are not valid for dilute magnesium alloys.

Lattice Constants and Brillouin Zone Overlap in Dilute Magnesium Alloys

The lattice constants of primary solid solutions of indium, aluminum, and cadmium in magnesium have been determined as a function of composition. A sharp change in ($\frac{c}{a}$) has been found only for magnesium-indium. The linearity of the ($\frac{c}{a}$) vs concentration curve for magnesium-aluminum has suggested that electron zone overlap does not necessarily lead to axial ratio anomalies and that changes in short-range order may be needed to explain such anomalies.

Brillouin Zone Investigation of Mg Alloys. I. Hall Effect and Conductivity

The Brillouin zone structure of hexagonal metal, in particular magnesium as calculated by Jones, has been examined by Hall measurements. The theory predicts a strong dependence on alloying, and the Hall data obtained on alloys of magnesium with aluminum or silver seem to corroborate Jones' theory. In the case of the silver alloys, the absolute value of the Hall constant decreases linearly as a function of alloying addition (0.1 at percent silver decreases the Hall constant by 5 percent). In the aluminum alloys the effect is not so great (0.1 at percent aluminum decreases the Hall constant by \ensuremath{\sim}2 percent) and a break in the Hall constant versus composition curve is detected. This break can be interpreted as being due to Brillouin zone overlap in the $c$ direction.Familiar conductivity rules for alloys are examined in the light of Jones' theory and it is shown that deviations from these rules are to be expected for the alloys of divalent hexagonal metals. A broad experimental program is outlined.