Diffuse Reflection of Light

This thesis describes an attempt to determine the feasibility of measuring the ozone content in the air by absorption of light over a long path

Beyond the myth of legality? Framing effects and public reactions to high court decisions in Europe

How do people respond to different decision-making processes in high courts? One long-standing view suggests that citizens expect courts to be neutral arbiters of legal controversies. Although the relevance of such “myth of legality” has been challenged, we know very little about the relationship between the portrayals of the motives of courts and justices and public attitudes in civil law countries. We explore this question in a pair of experiments in Norway and Portugal where we isolate the effects of different institutional frames from outcome favorability. We find that while partisan frames are detrimental to fairness perceptions and acceptance of decisions, depictions of judicial decision-making that emphasize policy goals do not adversely affect citizens’ responses in comparison with legalistic frames. The results suggest that, even in civil law systems, preserving the myth of legality may not be a necessary condition to elicit public support for judicial decisions

Copper Alloy-Impregnated Carbon-Carbon Hybrid Composites for Electronic Packaging Applications

Porous carbon-carbon preforms, based on three-dimensional networks of PAN (Polyacrylonitrile)-based carbon fibers and various volume fractions of chemical vapor-deposited (CVD) carbon, were impregnated by oxygen-free, high-conductivity (OFHC) Cu, Cu-6Si-0.9Cr, and Cu-0.3Si-0.3Cr (wt pct) alloys by pressure infiltration casting. The obtained composites were characterized for their coefficient of thermal expansion (CTE) and thermal conductivity (K) along the through-thickness and two in-plane directions. One composite, with a 28 vol pct Cu-0.3Si-0.3Cr alloy, showed outstanding potential for thermal management applications in electronic applications. This composite exhibited approximately isotropic thermal expansion properties (CTE = 4 to 6.5 ppm/K) and thermal conductivities (k greater than or equal to 260 W/m K)

Calculation of the Casimir Force between Similar and Dissimilar Metal Plates at Finite Temperature

The Casimir pressure is calculated between parallel metal plates, containing the materials Au, Cu, or Al. Our motivation for making this calculation is the need of comparing theoretical predictions, based on the Lifshitz formula, with experiments that are becoming gradually more accurate. In particular, the finite temperature correction is considered, in view of the recent discussion in the literature on this point. A special attention is given to the case where the difference between the Casimir pressures at two different temperatures, T=300 K and T=350 K, is involved. This seems to be a case that will be experimentally attainable in the near future, and it will be a critical test of the temperature correction.Comment: 23 latex pages, 12 figures. Introductory section expanded, 4 new references. To appear in J. Phys. A: Math. Ge

On the Temperature Dependence of the Casimir Effect

The temperature dependence of the Casimir force between a real metallic plate and a metallic sphere is analyzed on the basis of optical data concerning the dispersion relation of metals such as gold and copper. Realistic permittivities imply, together with basic thermodynamic considerations, that the transverse electric zero mode does not contribute. This results in observable differences with the conventional prediction, which does not take this physical requirement into account. The results are shown to be consistent with the third law of thermodynamics, as well as being consistent with current experiments. However, the predicted temperature dependence should be detectable in future experiments. The inadequacies of approaches based on {\it ad hoc} assumptions, such as the plasma dispersion relation and the use of surface impedance without transverse momentum dependence, are discussed.Comment: 14 pages, 3 eps figures, revtex4. New version includes clarifications and new reference. Accepted for publication in Phys. Rev.

Casimir Force on Real Materials - the Slab and Cavity Geometry

We analyse the potential of the geometry of a slab in a planar cavity for the purpose of Casimir force experiments. The force and its dependence on temperature, material properties and finite slab thickness are investigated both analytically and numerically for slab and walls made of aluminium and teflon FEP respectively. We conclude that such a setup is ideal for measurements of the temperature dependence of the Casimir force. By numerical calculation it is shown that temperature effects are dramatically larger for dielectrics, suggesting that a dielectric such as teflon FEP whose properties vary little within a moderate temperature range, should be considered for experimental purposes. We finally discuss the subtle but fundamental matter of the various Green's two-point function approaches present in the literature and show how they are different formulations describing the same phenomenon.Comment: 24 pages, 11 figures; expanded discussion, one appendix added, 1 new figure and 10 new references. To appear in J. Phys. A: Math. Theo

Vacuum fluctuation forces between ultra-thin films

We have investigated the role of the quantum size effects in the evaluation of the force caused by electromagnetic vacuum fluctuations between ultra-thin films, using the dielectric tensor derived from the particle in a box model. Comparison with the results obtained by adopting a continuum dielectric model shows that, for film thicknesses of 1-10 nm, the electron confinement causes changes in the force intensity with respect to the isotropic plasma model which range from 40% to few percent depending upon the film electron density and the film separation. The calculated force shows quantum size oscillations, which can be significant for film separation distances of several nanometers. The role of electron confinement in reducing the large distance Casimir force is discussed

Thermal corrections to the Casimir effect

The Casimir effect, reflecting quantum vacuum fluctuations in the electromagnetic field in a region with material boundaries, has been studied both theoretically and experimentally since 1948. The forces between dielectric and metallic surfaces both plane and curved have been measured at the 10 to 1 percent level in a variety of room-temperature experiments, and remarkable agreement with the zero-temperature theory has been achieved. In fitting the data various corrections due to surface roughness, patch potentials, curvature, and temperature have been incorporated. It is the latter that is the subject of the present article. We point out that, in fact, no temperature dependence has yet been detected, and that the experimental situation is still too fluid to permit conclusions about thermal corrections to the Casimir effect. Theoretically, there are subtle issues concerning thermodynamics and electrodynamics which have resulted in disparate predictions concerning the nature of these corrections. However, a general consensus has seemed to emerge that suggests that the temperature correction to the Casimir effect is relatively large, and should be observable in future experiments involving surfaces separated at the few micrometer scale.Comment: 21 pages, 9 eps figures, uses iopart.cls. Final version to be published in New Journal of Physics, contains Conclusion and clarified remark

Casimir forces and non-Newtonian gravitation

The search for non-relativistic deviations from Newtonian gravitation can lead to new phenomena signalling the unification of gravity with the other fundamental interactions. Various recent theoretical frameworks indicate a possible window for non-Newtonian forces with gravitational coupling strength in the micrometre range. The major expected background in the same range is attributable to the Casimir force or variants of it if dielectric materials, rather than conducting ones, are considered. Here we review the measurements of the Casimir force performed so far in the micrometre range and how they determine constraints on non-Newtonian gravitation, also discussing the dominant sources of false signals. We also propose a geometry-independent parameterization of all data in terms of the measurement of the constant c. Any Casimir force measurement should lead, once all corrections are taken into account, to a determination of the constant c which, in order to assess the accuracy of the measurement, can be compared with its more precise value known through microscopic measurements. Although the last decade of experiments has resulted in solid demonstrations of the Casimir force, the situation is not conclusive with respect to being able to discover new physics. Future experiments and novel phenomenological analysis will be necessary to discover non-Newtonian forces or to push the window for their possible existence into regions of the parameter space which theoretically appear unnatural.Comment: Also available at http://www.iop.org/EJ/abstract/1367-2630/8/10/23