Top

Summary

A spinning top, or simply a top, is a toy with a squat body and a sharp point at the bottom, designed to be spun on its vertical axis, balancing on the tip due to the gyroscopic effect. Once set in motion, a top will usually wobble for a few seconds, spin upright for a while, then start to wobble again with increasing amplitude as it loses energy, and finally tip over and roll on its side. Tops exist in many variations and materials, chiefly wood, metal, and plastic, often with a metal tip. They may be set in motion by twirling a handle with the fingers, by pulling a rope coiled around the body, or by means of a built-in auger (spiral plunger). Such toys have been used since antiquity in solitary or competitive games, where each player tries to keep one's top spinning for as long as possible, or achieve some other goal. Some tops have faceted bodies with symbols or inscriptions, and are used like dice to inject randomness into games, or for divination and ritual purposes. The ubi

Official source

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Piezoelectric energy harvesters (PEHs) convert mechanical energy from vibrations into electrical energy. They have become popular in energy-autonomous IoT systems. However, the total energy extracted by a PEH is highly sensitive to matching between the PEH impedance and the energy extraction circuit. Prior solutions include the use of a full-bridge rectifier (FBR) and a so-called synchronous electric-charge extraction (SECE) [1], and are suitable for non-periodic vibrations. However, their extraction efficiency is low since the large internal capacitance C p (usually 10's of nF) of the PEH (Fig. 27.2.1) prevents the output voltage from reaching its maximum power point (MPP) under a typical sinusoidal and transient excitation (V MPP = 1/2·I p R p ). A recently proposed technique [2,3,4], called bias-flip, achieves a higher extraction efficiency by forcing a predetermined constant voltage at the PEH output, V p , which is then flipped every half-period of the assumed sinusoidal excitation (Fig. 27.2.1, top left). To flip V p , the energy in capacitor C p is extracted using either a large external inductor [2,3] or capacitor arrays [4]. It is then restored with the opposite polarity (Fig. 27.2.1, top). However, V MPP of the PEH varies with sinusoidal current I p ; hence, the two fixed values of V p in the flip-bias technique either over or underestimate V MPP for much of the oscillation cycle (pattern filled regions in Fig. 27.2.1, top right). In addition, none of the prior approaches compensate for V MPP -waveform amplitude changes, due to input intensity variations or decaying oscillations after an impulse, further degrading efficiency.

IEEE2019

Investigation and modification of the magnetism of epitaxial Fe structures

Diego Repetto

In this thesis, the magnetic and structural properties of layered epitaxial film systems and clusters are presented. A main achievement is the investigation of the direct correlation between magnetism and structural or morphological details of ultrathin films. For this purpose, the film structure has been accessed directly by means of surface science methods. The effect of structural changes on the magnetism were observed in-situ by magneto-optical techniques. First, epitaxial Fe films grown at low temperature (∼ 120K) on Cu(100) have been investigated. Such layers assume an fcc-crystal structure due to their interaction with the underlying Cu substrate. Within this work it is shown that the morphology of these films can be altered by annealing treatments. The thermally-induced morphological changes have direct consequences for domain wall propagation and result in increased coercivity and in modified surface anisotropy. Flat fcc-Fe layers on Cu(100) have been used as templates to form fcc-Fe/Cu/Fe trilayers with coupled perpendicular magnetization. Such systems might be of relevance for data storage applications. The perpendicular coupling is ascribed to the realignment of the magnetization of the bottom Fe layer within the stray field produced by the top Fe layer magnetization. The magnetic coupling has been investigated as a function of the thickness of the top and the bottom Fe layer as well as the Cu spacer thickness. It was found that the magneto-static interaction is a direct consequence of the fcc-structure of both Fe layers and the interface roughness. It is demonstrated that Fe films with fcc-structure and perpendicular magnetization can also be prepared on other fcc-templates, such as Pt substrates. Monatomic steps on the substrate surface are exploited to steer the growth of the film and with it the magnetism. Despite significant differences in the morphology and the atomic structure of Fe films on flat Pt(111) and stepped Pt(997), the critical thickness for the spin reorientation transition is similar on the two surfaces. However, the local atomic arrangement above three monolayer film thickness determines in-plane easy magnetization axis parallel to the step edges. For all layered systems investigated in this thesis, epitaxial strain is a the driving force which influences the film structure and triggers structural transitions. The strain dependence of the morphology and the magnetism was probed by a comparative study of Fe deposited on Pt substrates with and without a noble gas buffer layer. The formation of relaxed Fe clusters during Xe layer desorption is favored in the absence of the overlayer-substrate interaction. Striking differences in the magnetic anisotropy between the systems are attributed to magneto-elastic contributions. Measurements of the blocking temperature of the Fe clusters allow estimating the cluster size. All samples have been investigated under ultra high vacuum conditions. The study of the sample magnetic properties study was done by in-situ magneto-optical Kerr effect measurements and Kerr microscopy. Structural characterization was done by low energy electron diffraction and, in collaboration with other scientists, by scanning tunnelling microscopy.

EPFL2006

Analog circuit design is often the bottleneck when designing mixed analog-digital systems. A Top-Down, Constraint-Driven Design Methodology for Analog Integrated Circuits presents a new methodology based on a top-down, constraint-driven design paradigm that provides a solution to this problem. This methodology has two principal advantages: (1) it provides a high probability for the first silicon which meets all specifications, and (2) it shortens the design cycle. A Top-Down, Constraint-Driven Design Methodology for Analog Integrated Circuits is part of an ongoing research effort at the University of California at Berkeley in the Electrical Engineering and Computer Sciences Department. Many faculty and students, past and present, are working on this design methodology and its supporting tools. The principal goals are: (1) developing the design methodology, (2) developing and applying new tools, and (3) proving' the methodology by undertaking industrial strength' design examples. The work presented here is neither a beginning nor an end in the development of a complete top-down, constraint-driven design methodology, but rather a step in its development. This work is divided into three parts. Chapter 2 presents the design methodology along with foundation material. Chapters 3-8 describe supporting concepts for the methodology, from behavioral simulation and modeling to circuit module generators. Finally, Chapters 9-11 illustrate the methodology in detail by presenting the entire design cycle through three large-scale examples. These include the design of a current source D/A converter, a Sigma-Delta A/D converter, and a video driver system. Chapter 12 presents conclusions and current research topics. A Top-Down, Constraint-Driven Design Methodology for Analog Integrated Circuits will be of interest to analog and mixed-signal designers as well as CAD tool developers.

Springer Verlag1997

Investigation and modification of the magnetism of epitaxial Fe structures

Diego Repetto

EPFL2006