Abstract:. In the recent years a significant progress was achieved in the field of design and fabrication of optical systems based on freeform optical surfaces. They provide a possibility to build fast, wide-angle and high-resolution systems, which are very compact and free of obscuration. However, the field of freeform surfaces design techniques still remains underexplored. In the present paper we use the mathematical apparatus of orthogonal polynomials defined over a square aperture, which was developed before for the tasks of wavefront reconstruction, to describe shape of a mirror surface. Two cases, namely Legendre polynomials and generalization of the Zernike polynomials on a square, are considered. The potential advantages of these polynomials sets are demonstrated on example of a three-mirror unobscured telescope with F/#=2.5 and FoV=7.2x7.2°. In addition, we discuss possibility of use of curved detectors in such a design.
À partir de l'analyse de plus de 2 000 prises de retraite chez les "cols bleus" et les "cols blancs" d'une grande municipalité, au cours de la décennie 1973-1983, il s'avère que les cols bleus perçoivent une rente inférieure, jouissent de leur vie à la retraite moins longtemps et meurent plus jeunes que les cols blancs. Le cheminement causal dégagé pour expliquer cette situation fait s'entrecroiser les effets complexes et conjugués de la réglementation du régime de retraite privé en vigueur, des conditions de travail ainsi que des itinéraires professionnels différentiels.From the analysis of more than 2000 retirement decisions by blue-collar and white-collar workers in a large municipality in the decade from 1973-1983, it is demonstrated that blue-collar workers receive a smaller pension, take advantage of their retirement for a shorter period of time, and die younger than white-collar workers. The causal progression proposed to explain this situation brings together the complex and combined effects of regulations concerning private pension plans now in force, of working conditions, and of differential occupational itineraries.A partir del análisis de más de 2 000 jubilaciones entre los obreros y los empleados de una gran municipalidad, en el curso del decenio 1973-1983, se revela que los obreros perciben una renta inferior, disfrutan de la vida de jubilados menos tiempo y mueren más jóvenes que los empleados. El recorrido causal puesto en relieve para explicar esta situación hace entrecruzarse los efectos complejos y conjugados de la reglamentación del régimen de jubilación privado en vigor, de la misma manera que de las condiciones de trabajo e itinerarios profesionales diferentes
Written assessment items were developed to probe students' understanding of a variety of direct current (DC) resistive electric circuit concepts. The items were used to explore the mental models that grade 3-8 students use in explaining the direction of electric current and how electric current is affected by different configurations of simple battery and bulb circuits. Consistency of applying mental models in different, but equivalent, circuits was also analyzed. Students analyses of current flow direction was categorized into one of two mental models: (1) bidirectional and (2) unidirectional. We found an increase in the consistency of current flow direction mental model use coinciding with grade 4 instruction of batteries and bulbs, however, the proportion of students using a bidirectional flow model was similar in grades 3-8.
wafer stacking technologies offer new possibilities in terms of device architecture and miniaturization [1][2][3]. To stack wafers, reliable throughsilicon vias (TSVs) and interconnections must be processed into ultrathin wafers, and such processing is made possible by new methods for wafer handling. Of the different wafer-level bonding techniques, temporary wafer bonding adhesives can offer a variety of properties sufficient for withstanding the TSV processes: flow properties, mechanical strength, thermal stability, chemical resistance, and easy debonding and cleaning processes. This paper demonstrates that, contrary to tapes and waxes currently used for temporary bonding, a new removable high-temperature adhesive meets all the requirements named above for reliable TSV processing on 8-inch active wafers. We will first describe formation of TSVs with aspect ratios of 1:1 and 2:1 into thinned wafers.
IntroductionTo be successful, 3-D ultrathin wafer stacking technologies require the development of reliable through-die interconnects with varying aspect ratios depending on the application. This type of integration poses forward new challenges in the development of new TSV processes suitable for thin-wafer handling technologies.It has already been demonstrated in a previous publication [4] that a temporary bonding process using new hightemperature adhesives could provide an innovative and robust solution to produce functional 1:1 aspect ratio TSVs in 70-micron-thick silicon wafers. This first result showed that in addition to presenting sufficient thermal and mechanical properties to withstand all the backside process steps, the high-temperature adhesive enables easy bonding, debonding, and cleaning processes.Although encouraging, these first results obtained on plain silicon wafers were not completely representative of TSV integration in industrial products. Indeed, due to the presence of several metallization and passivation layers, an active CMOS-containing wafer can present a different deformation behavior compared to a plain wafer when heated, which can weaken its adhesion to the temporary layer during the process. Therefore the purpose of this paper is to assess the TSV creation on temporarily bonded complex active wafers.In the first part of this paper, we will assess the full TSV realization on device wafers thinned to 70 microns thanks to a temporary bonding process. The active wafers used were
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