942 resultados para reflection holograms


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This paper examines the epistemological bases for the inclusion of stakeholders in policy research. While it concedes that the input of stakeholders provides essential expert and experiential knowledge for the understanding of complex policies and programmes, it contends that the approach which assumes that all interpretations of policy including those of stakeholders should be afforded equal validity, which we term relativist perspectivism, undermines the possibility of robust research by allowing power to replace methodological rigour as the primary research dynamic. It is noted that this problem tends to be more acute when the research is qualitative. A study into the gendered effects of Common Agricultural Policy reforms is used as an illustrative example of how research can be compromised by relativist perspectivism. It is argued that realist research methodologies uniquely provide the capacity to maintain epistemological robustness, while also being able to take due account of the perspectives of stakeholders.

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A pin diode-loaded active doubly periodic flat strip FSS is shown to act as a dynamic screen. It is shown that by means of d.c. bias control, we can utilize the screen in, (1) transmission mode as a dual band electromagnetic shutter, or with the inclusion of a ground plane in reflection mode, (is (2) it dual band refection canceller. (3) an amplitude shift keying (ASK) spatial modulator. The properties of the FSS are characterized using a specially designed parallel plate waveguide simulator that permits normal incidence excitation of the FSS under test. (C) 2009 Wiley Periodicals. Inc. Microwave Opt Technol Lett 51: 2059-2061, 2009; Published online in Wiley Inter-Science (www. interscience.wiley.com). DOI 10.1002/mop.24547

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A scheme to obtain brilliant x-ray sources by coherent reflection of a counter-propagating pulse from laser-driven dense electron sheets is theoretically and numerically investigated in a self-consistent manner. A radiation pressure acceleration model for the dynamics of the electron sheets blown out from laser-irradiated ultrathin foils is developed and verified by PIC simulations. The first multidimensional and integral demonstration of the scheme by 2D PIC simulations is presented. It is found that the reflected pulse undergoes Doppler-upshift by a factor 4?z2, where ?z = (1- vz2/c2)-1/2 is the effective Lorentz factor of the electron sheet al ong its normal direction. Meanwhile the pulse electric field is intensified by a factor depending on the electron density of the sheet in its moving frame ne/?, where ? is the full Lorentz factor.

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This paper is written by democratic educators who stand for the idea that is it worth developing, through classrooms and schools, a socially just (egalitarian), anti-discriminatory society where interdependent relationships are valued. This paper significantly develops some of the ideas explored in the authors’ earlier contribution concerned with progress in Northern Ireland towards educational inclusion, and how this might more effectively advance in a post-conflict transforming society. In particular, the paper poses the ‘so what’ question, and it responds by exploring the practical implications of six key ideas thought essential for transforming learning environments supportive of cultural diversity, equity and excellence for all. In addition, it includes examples of how school staff, along with collaborating partners, might utilize these key principles in order to facilitate school improvement.

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This paper examines the DC power requirements of PIN diodes which, with suitable applied DC bias, have the potential to reflect or to permit transmission of millimetre wave energy through them by the process of inducing a semiconductor plasma layer in the i-region. The study is conducted using device level simulation of SOI and bulk PIN diodes and reflection modelling based on the Drude conduction model. We examined five diode lengths (60–140 µm) and seven diode thicknesses (4–100 µm). Simulation output for the diodes of varying thicknesses was subsequently used in reflection modelling to assess their performance for 100 GHz operation. It is shown that substantially high DC input power is required in order to induce near total reflection in SOI PIN diodes at 100 GHz. Thinner devices consume less DC power, but reflect less incident radiation for given input power. SOI diodes are shown to have improved carrier confinement compared with bulk diodes.

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The potential of employing a millimetre-wave MMIC reflection amplifier as a building block for a retrodirective reflectarray is investigated. With this in mind the phase conjugating behaviour of the device is experimentally quantified at 21 GHz.

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The mid-infrared optical response of c-axis thin films of YBa2Cu3O7-delta has been studied using Otto-configuration attenuated total reflectance. The measured reflectance-angle characteristics are dominated by a strong absorption feature due to the excitation of surface plasmons, and can be modeled to determine the a-b plane dielectric function. The results show that while epsilon(i,) and therefore sigma(r), are temperature independent, \epsilon(r)\ exhibits a moderate decrease with generalized Drude analysis shows that the plasma frequency is independent of temperature, but decreases with decreasing doping. The scattering rate increases with temperature, and also increases with decreasing doping, consistent with stronger coupling in the underdoped regime. The mass-enhancement is small but increases to 30-40% at delta = 0.6. Difficulties in reconciling the results with some current theories of high-T-c materials are discussed. Finally, the surface plasmon propagation lengths and penetration depths are shown to vary systematically with doping. (C) 2003 Elsevier B.V. All rights reserved.