La causalité adéquate chez Spinoza

L’objectif de cet article est de proposer une analyse de deux conceptions distinctes de la causalité chez Spinoza. Selon la première (« émanative ») la nature-dieu serait la cause directe de toute action qui a lieu au niveau des choses finies; tandis que, selon la seconde (« consécutive ») toute action finie ferait partie d’une chaîne infinie de causes (dont chacune est toutefois finie) qui est répandue dans la durée. Je montre que cette causalité-ci n’est ni illusoire ni simplement derivative, contre les suggestions de plusieurs travaux récents sur Spinoza. En deuxième lieu nous proposons un modèle pour la causalité consécutive qui assure la possibilité que les êtres finis puissent fonctionner comme des causes adéquates au sens spinoziste dans le champ physique. Ici l’analyse s’oppose à plusieurs chercheurs qui soutiennent qu’il existe une rupture entre les attributs de la pensée et de l’étendue dans le système spinoziste.This study addresses the problem of analyzing two distinct conceptions of causality in Spinoza. According to the first (" emanative ") god-nature is the direct cause of every action which occurs at the level of finite things; while, according to the second (" sequential "), every finite action would be part of an infinite chain of causes (each finite) extended into duration. I show that sequential causality is neither illusory nor simply derivative, contrary to the suggestions made by several recent studies of Spinoza. Secondly, I offer a model for sequential causality which assures the possibility that finite beings may function as adequate causes (in Spinoza’s sense) within the physical field. Here my analysis is opposed to those commentators who argue for a rupture in Spinoza between the attributes of thought and extension

Dynamics of charge-density waves in the presence of free carriers

The response of an unpinned, incommensurate charge-density wave (CDW) to external perturbations in the presence of free quasiparticles is studied. The CDW can act as a charged lattice but the proportion of the total charge density assigned to the CDW and to quasiparticles depends on the external conditions. If the collisions between quasiparticles can be ignored, the effective charge of the CDW is different in the static and dynamic limits. In the static limit the quasiparticles relax to screen spatial variations and the form is analogous to that used for superfluids. In the dynamic limit the quasiparticles do not renormalize the effective charge. In the presence of collisions the effective charge depends on the distribution of quasiparticles which in turn depends on the relative importance of various scattering rates. In general, a simple two-fluid model is not applicable

Purification and detection of entangled coherent states

In [J. C. Howell and J. A. Yeazell, Phys. Rev. A 62, 012102 (2000)], a proposal is made to generate entangled macroscopically distinguishable states of two spatially separated traveling optical modes. We model the decoherence due to light scattering during the propagation along an optical transmission line and propose a setup allowing an entanglement purification from a number of preparations which are partially decohered due to transmission. A purification is achieved even without any manual intervention. We consider a nondemolition configuration to measure the purity of the state as contrast of interference fringes in a double-slit setup. Regarding the entangled coherent states as a state of a bipartite quantum system, a close relationship between purity and entanglement of formation can be obtained. In this way, the contrast of interference fringes provides a direct means to measure entanglement.Comment: 9 pages, 6 figures, using Revtex

Andreev scattering in the asymmetric ladder with preformed bosonic pairs

We discuss the phase coherence which emanates from the ladder-like proximity effect between a ``weak superconductor'' with preformed bosonic pairs (here, a single-chain Luther-Emery liquid with superconducting correlations that decay approximately as $x^{-1}$) and a Fermi gas with unpaired fermions. Carefully studying tunneling mechanism(s), we show that the boson-mediated Cooper pairing between remaining unpaired electrons results in a quasi long-range superconductivity: Superconducting correlations decay very slowly as $x^{-\eta}$ with $\eta\approx 1/2$. This process is reminiscent of the coupling of fermions to preformed bosonic pairs introduced in the context of high-Tc cuprates.Comment: 5 pages, final version (To appear in PRB Rapid Communication

The Effect of Decorative Foil Stamping on Consumer Attention

Packaging plays a crucial role in communicating product benefits to consumers. Oftentimes, designers use high visibility enhancements to differentiate packaging within the competitive array. Although luxury brands commonly use enhanced graphical and printing techniques to convey high quality products, many private label package designers are also utilizing enhancements to attract attention to their products. This research sought to understand how incorporating foil stamping to the primary panel of fast moving consumer good packaging will affect consumer attention and purchase preference. Through the collection of quantitative data, consumer attention and purchase preference were evaluated. Three different products were selected for evaluation for the study: popcorn, cereal, and boxed pasta dinners. A total of 172 participants completed the study, which took place in a realistic and immersive shopping environment (CUshop™). Two eye tracking metrics were collected using mobile eye tracking technology. Participants completed a qualitative survey, which recorded basic demographic information. Significance tests were conducted to test for statistical differences in consumer attention behavior as well as purchase decision between the foil and control packages. It was determined that foil stamping did significantly (α =0.05) affect consumer attention towards the respective product compared to the control, yet the effect was not consistent. Eye tracking metrics varied across the products and categories tested; some foil stamped samples positively affected consumer attention, others negatively and some had no effect whatsoever. Results show that foil stamping can be a highly strategic influencer (both positively and negatively) on consumer attention and purchase decision. However, it is recommended that this enhancement be tested within an in-context environment to ensure it benefits the brand and product within the competitive array

Nuclear safety policy working group recommendations on nuclear propulsion safety for the space exploration initiative

An interagency Nuclear Safety Working Group (NSPWG) was chartered to recommend nuclear safety policy, requirements, and guidelines for the Space Exploration Initiative (SEI) nuclear propulsion program. These recommendations, which are contained in this report, should facilitate the implementation of mission planning and conceptual design studies. The NSPWG has recommended a top-level policy to provide the guiding principles for the development and implementation of the SEI nuclear propulsion safety program. In addition, the NSPWG has reviewed safety issues for nuclear propulsion and recommended top-level safety requirements and guidelines to address these issues. These recommendations should be useful for the development of the program's top-level requirements for safety functions (referred to as Safety Functional Requirements). The safety requirements and guidelines address the following topics: reactor start-up, inadvertent criticality, radiological release and exposure, disposal, entry, safeguards, risk/reliability, operational safety, ground testing, and other considerations

Truncation of a 2-dimensional Fermi surface due to quasiparticle gap formation at the saddle points

We study a two-dimensional Fermi liquid with a Fermi surface containing the saddle points $(\pi,0)$ and $(0,\pi)$. Including Cooper and Peierls channel contributions leads to a one-loop renormalization group flow to strong coupling for short range repulsive interactions. In a certain parameter range the characteristics of the fixed point, opening of a spin and charge gap and dominant pairing correlations are similar to those of a 2-leg ladder at half-filling. An increase of the electron density we argue leads to a truncation of the Fermi surface with only 4 disconnected arcs remaining.Comment: Reference added. RevTeX 4 pages incl. 4 ps file

Evolution of Magnetic and Superconducting Fluctuations with Doping of High-Tc Superconductors (An electronic Raman scattering study)

For YBa_2Cu_3O_{6+\delta} and Bi_2Sr_2CaCu_2O_8 superconductors, electronic Raman scattering from high- and low-energy excitations has been studied in relation to the hole doping level, temperature, and energy of the incident photons. For underdoped superconductors, it is concluded that short range antiferromagnetic (AF) correlations persist with hole doping and doped single holes are incoherent in the AF environment. Above the superconducting (SC) transition temperature T_c the system exhibits a sharp Raman resonance of B_1g symmetry and about 75 meV energy and a pseudogap for electron-hole excitations below 75 meV, a manifestation of a partially coherent state forming from doped incoherent quasi-particles. The occupancy of the coherent state increases with cooling until phase ordering at T_c produces a global SC state.Comment: 5 pages, 4 EPS figures; SNS'97 Proceedings to appear in J. Phys. Chem. Solid

Resistivity as a function of temperature for models with hot spots on the Fermi surface.

We calculate the resistivity $\rho$ as a function of temperature $T$ for two models currently discussed in connection with high temperature superconductivity: nearly antiferromagnetic Fermi liquids and models with van Hove singularities on the Fermi surface. The resistivity is calculated semiclassicaly by making use of a Boltzmann equation which is formulated as a variational problem. For the model of nearly antiferromagnetic Fermi liquids we construct a better variational solution compared to the standard one and we find a new energy scale for the crossover to the $\rho\propto T^2$ behavior at low temperatures. This energy scale is finite even when the spin-fluctuations are assumed to be critical. The effect of additional impurity scattering is discussed. For the model with van Hove singularities a standard ansatz for the Boltzmann equation is sufficient to show that although the quasiparticle lifetime is anomalously short, the resistivity $\rho\propto T^2\ln(1/T)$.Comment: Revtex 3.0, 8 pages; figures available upon request. Submitted to Phys. Rev. B

Midinfrared Conductivity in Orientationally Disordered Doped Fullerides

The coupling between the intramolecular vibrational modes and the doped conduction electrons in $M_3C_{60}$ is studied by a calculation of the electronic contributions to the phonon self energies. The calculations are carried out for an orientationally ordered reference solid with symmetry $Fm \bar{3} m$ and for a model with quenched orientational disorder on the fullerene sites. In both cases, the dispersion and symmetry of the renormalized modes is governed by the electronic contributions. The current current correlation functions and frequency dependent conductivity through the midinfrared are calculated for both models. In the disordered structures, the renormalized modes derived from even parity intramolecular phonons are resonant with the dipole excited single particle spectrum, and modulate the predicted midinfrared conductivity. The spectra for this coupled system are calculated for several recently proposed microscopic models for the electron phonon coupling, and a comparison is made with recent experimental data which demonstrate this effect.Comment: 32 pages + 9 postscript figures (on request), REVTeX 3.