The influence of tungsten on an amorphous-to-crystalline transition, leading to formation of anatase, and dielectric properties is examined for anodic oxides on Ti-W alloys. The structural change, ...which occurs at voltages of ~ 10 V on high-purity titanium, and provides sites for generation of high-pressure gas oxygen bubbles, is suppressed to progressively increased voltages by increasing tungsten content of the film. Phosphorus species, derived from the electrolyte, also hinder the change. The tungsten species are located in the inner ~80% of the film thickness as result of the faster migration of Ti+ ions relative to that of W6+ ions in the growing oxide. Although the reported permittivity of anodic tungsten oxide is higher than that of amorphous anodic titania, the permittivity of the films on alloys decreases gradually with increasing tungsten content.
Demonstrations of high voltage phenomena are among the most spectacular and visually beautiful illustrations of physics. Here, we describe a high potential generator (several hundred thousand volts) ...which is based on a resonant transformer, derived from a standard Tesla coil arrangement with high
Q
secondary coil. Control electronics have been implemented that allow the user to command single shot discharges, should they be required for a particular demonstration. We review the behavior of a coupled resonant system with relevance to the spark-gap excited Tesla circuit implemented in our generator. The importance of the
Q
factor in the secondary coil design is emphasized, but only with due regard to other design factors including the coupling coefficient and primary spark-gap, which in certain configurations can outweigh the benefits of achieving very high
Q.
Physics of the Theremin Skeldon, Kenneth D.; Reid, Lindsay M.; McInally, Viviene ...
American journal of physics,
11/1998, Letnik:
66, Številka:
11
Journal Article
Recenzirano
We discuss some of the interesting physics behind the design and operation of the Theremin electronic musical instrument. To complement the theory we present details of a parallel effort to construct ...two versions of this remarkable instrument. One of these designs remains fairly faithful to the traditional beat frequency oscillator approach that first inspired Theremin’s invention, while the other contains more modern electronics that helps make more reliable the setting up and use of the instrument. The emphasis on the physical principles continues into a comparison of the two instruments. Following completion, the Theremins have been extensively used in public and schools science exhibitions and in lecture demonstrations.
We describe an apparatus that will sense the vibration of a wineglass through the jitter induced on a laser beam reflected from the glass wall. A positive feedback system provides a high level ...sound-wave-train that maintains the vibration of the glass, while a light-emitting diode lighting panel, also deriving its signal from the feedback system, allows the motion of the glass to be clearly observed in a user-controllable way. The positive feedback signal, along with observations from some additional experiments, can be used to highlight some of the nonlinear aspects of the resonance. Although the apparatus is primarily intended as a demonstration exhibit, we have found it useful also as a physics teaching aid.
In this Letter we give simpler proofs of the famous results of Perko–Walter–Elmabsout theorem published in Proc. Amer. Math. Soc. 94 (1985) 301 and Celest. Mech. 41 (1988) 131.
The transport numbers of metal and oxygen species have been determined in amorphous anodic tantala films, using transmission electron microscopy to locate ion-implanted xenon marker layers within the ...films. The films were formed on sputtering-deposited tantalum at constant current density, in the range 0.01–10 mA
cm
−2, in 0.06 wt% H
3PO
4 solution at either 20 or 85 °C. The films grow by migration of metal and oxygen species through the film thickness, with formation of new film material at the film/electrolyte and metal/film interfaces respectively. The cation transport number,
t
+, increases due to either increase in current density or decrease in temperature: for current densities in the selected range,
t
+ increases from 0.18 to 0.32 at 20 °C, and from 0.14 to 0.29 at 85 °C. Low concentrations of phosphorus species, incorporated into an outer layer of the film, migrate inward during film growth. The migration rates are slower than those of oxygen species, by a factor in the range 0.2–0.3.
The effects of current density and temperature on the anodic films formed on tantalum in dilute H
3PO
4 (0.06%wt) solution have been studied by transmission electron microscopy, using ultramicrotomed ...sections, and Rutherford backscattering spectroscopy. Two-layered films have been identified, comprising an inner relatively pure Ta
2O
5 layer, adjacent to the metal/film interface, and an outer layer containing incorporated PO
4
3− anions. The total amount and depth of incorporated phosphorus species increase with increasing current density and decreasing temperature, in correspondence with the enhancement of the electric field. The formation conditions for the films include those relevant to the commercial anodising of tantalum for capacitors for which the extent of phosphorus incorporation is shown to be comparatively low.
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