Noncontact measurement of high-temperature surface tension and viscosity of bulk metallic glass-forming alloys using the drop oscillation technique

High-temperature surface tension and viscosities for five bulk metallic glass-forming alloys with widely different glass-forming abilities are measured. The measurements are carried out in a high-vacuum electrostatic levitator using the drop oscillation technique. The surface tension follows proportional mathematical addition of pure components' surface tension except when some of the constituent elements have much lower surface tension. In such cases, there is surface segregation of the low surface tension elements. These alloys are found to have orders of magnitude higher viscosity at their melting points compared to the constituent metals. Among the bulk glass-forming alloys, the better glass former has a higher melting-temperature viscosity, which demonstrates that high-temperature viscosity has a pronounced influence on glass-forming ability. Correlations between surface tension and viscosity are also investigated

Evaporative segregation in 80 percent Ni-20 percent Cr and 60 percent Fe-40 percent Ni alloys

The phenomenon of evaporative segregation in binary alloys has been investigated through a study of some experimental evaporation data relating to the Ni-Cr and Ni-Fr systems. In normal evaporation it is assumed that (1) the evaporating alloy is always homogeneous, (2) the vapor is instantly removed, and (3) the alloy follows Raoult's law. The solutions of the evaporation equations for the two most important cases are presented and experimental data are analyzed with these equations. The difference between observed and calculated values of evaporation constants lies within one order of magnitude. This is surprising because of the major assumptions stated above. Experimental results have shown that the evaporation time and final solute concentration are logarithmically related, further supporting our evaporation equations. It is further shown that neglecting the nonlogarithmic term in these evaporation equations may introduce considerable errors in the analysis

Overheating threshold and its effect on time–temperature-transformation diagrams of zirconium based bulk metallic glasses

A pronounced effect of overheating is observed on the crystallization behavior for the three zirconium-based bulk metallic glasses: Zr41.2Ti13.8Cu12.5Ni10Be22.5, Zr57Cu15.4Ni12.6Al10Nb5, and Zr52.5Cu17.9Ni14.6Al10Ti5. A threshold overheating temperature is found for each of the three alloys, above which there is a drastic increase in the undercooling level and the crystallization times. Time–temperature-transformation (TTT) diagrams were measured for the three alloys by overheating above their respective threshold temperatures. The TTT curves for Zr41.2Ti13.8Cu12.5Ni10Be22.5 and Zr57Cu15.4Ni12.6Al10Nb5 are very similar in shape and scale with their respective glass transition temperatures, suggesting that system-specific properties do not play a crucial role in defining crystallization kinetics in these alloys. The critical cooling rates to vitrify the alloys as determined from the TTT curves are about 2 K/s for Zr41.2Ti13.8Cu12.5Ni10Be22.5 and 10 K/s for Zr57Cu15.4Ni12.6Al10Nb5. The measurements were conducted in a high-vacuum electrostatic levitator

Overheating threshold and its effect on time–temperature-transformation diagrams of zirconium based bulk metallic glasses

A pronounced effect of overheating is observed on the crystallization behavior for the three zirconium-based bulk metallic glasses: Zr41.2Ti13.8Cu12.5Ni10Be22.5, Zr57Cu15.4Ni12.6Al10Nb5, and Zr52.5Cu17.9Ni14.6Al10Ti5. A threshold overheating temperature is found for each of the three alloys, above which there is a drastic increase in the undercooling level and the crystallization times. Time–temperature-transformation (TTT) diagrams were measured for the three alloys by overheating above their respective threshold temperatures. The TTT curves for Zr41.2Ti13.8Cu12.5Ni10Be22.5 and Zr57Cu15.4Ni12.6Al10Nb5 are very similar in shape and scale with their respective glass transition temperatures, suggesting that system-specific properties do not play a crucial role in defining crystallization kinetics in these alloys. The critical cooling rates to vitrify the alloys as determined from the TTT curves are about 2 K/s for Zr41.2Ti13.8Cu12.5Ni10Be22.5 and 10 K/s for Zr57Cu15.4Ni12.6Al10Nb5. The measurements were conducted in a high-vacuum electrostatic levitator

Charged analogue of Finch-Skea stars

We present solutions to the Einstein-Maxwell system of equations in spherically symmetric gravitational fields for static interior spacetimes with a specified form of the electric field intensity. The condition of pressure isotropy yields three category of solutions. The first category is expressible in terms of elementary functions and does not have an uncharged limit. The second category is given in terms of Bessel functions of half-integer order. These charged solutions satisfy a barotropic equation of state and contain Finch-Skea uncharged stars. The third category is obtained in terms of modified Bessel functions of half-integer order and does not have an uncharged limit. The physical features of the charged analogue of the Finch-Skea stars are studied in detail. In particular the condition of causality is satisfied and the speed of sound does not exceed the speed of light. The physical analysis indicates that this analogue is a realistic model for static charged relativistic perfect fluid spheres.Comment: 17 pages, To appear in Int. J. Mod. Phys.

Some anatomical features of a radiation-induced grape variegata

Some anatomical and a few distinguishing morphological featmes of radiation-induced Pusa Seedless variegata have been described. The chloropliyll deficient sectors, which were identical on the two surfaces of the leaves, were usually thinner than the green sectors and thinness was either due to the reduced number of mesophyll layers or smaller cells or both. The yellow colouration of chlorotic sectors seemed to be mainly due to thinness of the sectors and to some extent due to lack of sufficient chlorophyll.Anatomische Merkmale bei einer Rebe mit strahlungsinduzierter ScheckungAnatomische und kennzeichnende morphologische Eigenschaften einer strahlungsinduzierten gescheckten Mutante der Rebsorte Pusa Seedless werden beschrieben. Die chlorophyllarmen Sektoren beider Blattseiten, die sich deckten, waren gewöhnlich dünner als die grünen Bezirke. Dies war entweder auf eine verringerte Anzahl Mesophyllschichten oder durch kleinere Zellen oder durch beide Ursachen bedingt. Die Gelbfärbung der chlorotischen Sektoren scheint hauptsächlich auf ihre verminderte Dicke und in gewissem Umfang auf Chlorophyllmangel zurückzuführen zu sein

Morphological descriptions of some induced systematic mutants of grapes (Vitis vinifera L.)

During mutation induction studies on grapes (Vitis vinifera L.) conducted from 1967 to 1969 a large number of systematic, chlorophyll and other types of somatic mutants were isolated in Bhokri cultivar after N-nitroso-methyl urethane and gamma radiation treatments. The vegetative characters of 18 systematic mutants have been described under 6 main groups and 12 names. Some of these, viz. 'heptalobed' and 'foliolate' types, which have an increased number of lobes may be rare ones. A large number of systematic mutants had leaves with deeper sinuses and very acute and long teeth. On the contrary, there was one mutant (closed-petiolar sinus type), induced by NMUt, whose leaves were finely serrated and almost devoid of lateral sinuses, besides being thick and reflexed. Other mutants had glossy foliage or were dwarf with small, narrow leaves.Morphologische Beschreibung einiger experimentell ausgeloster systematischer Mutanten von Reben (Vitis vinifera L.)An Reben (Vitis vinifera L., Sorte Bhokri) wurden 1967-1969 Untersuchungen über die Auslösung von Mutationen angestellt. Nach Behandlung mit N-Nitroso-methyl-urethan (NMUt) und Gammastrahlen wurde eine große Zahl von systematischen Chlorophyll- und anderen somatischen Mutanten isoliert. Die morphologischen Eigenschaften von 18 systematischen Mutanten werden beschrieben und die Mutanten unter 12 Bezeichnungen in 6 Hauptgruppen eingeteilt. Einige von ihnen, und zwar die ,,siebenlappigen" und die ,,fiederspaltigen" Typen, die eine erhöhte Anzahl von Blattlappen aufweisen, dürften selten vorkommen. Eine große Anzahl systematischer Mutanten hatte Blätter mit tieferen Buchten und sehr spitzen und langen Zähnen. Im Gegensatz hierzu hatte eine durch NMUt ausgelöste Mutante (mit geschlossener Stielbucht) fein gesägte Blätter - fast ohne Nebenbuchten; außerdem waren sie dick und nach oben gewölbt. Andere Mutanten hatten glänzende Blätter oder waren zwergwüchsig mit kleinen schmalen Blättern

Reconstructing the primordial power spectrum from the CMB

We propose a straightforward and model independent methodology for characterizing the sensitivity of CMB and other experiments to wiggles, irregularities, and features in the primordial power spectrum. Assuming that the primordial cosmological perturbations are adiabatic, we present a function space generalization of the usual Fisher matrix formalism, applied to a CMB experiment resembling Planck with and without ancillary data. This work is closely related to other work on recovering the inflationary potential and exploring specific models of non-minimal, or perhaps baroque, primordial power spectra. The approach adopted here, however, most directly expresses what the data is really telling us. We explore in detail the structure of the available information and quantify exactly what features can be reconstructed and at what statistical significance.Comment: 43 pages Revtex, 23 figure