Emergence of Kinetic Behavior in Streaming Ultracold Neutral Plasmas

We create streaming ultracold neutral plasmas by tailoring the photoionizing laser beam that creates the plasma. By varying the electron temperature, we control the relative velocity of the streaming populations, and, in conjunction with variation of the plasma density, this controls the ion collisionality of the colliding streams. Laser-induced fluorescence is used to map the spatially resolved density and velocity distribution function for the ions. We identify the lack of local thermal equilibrium and distinct populations of interpenetrating, counter-streaming ions as signatures of kinetic behavior. Experimental data is compared with results from a one-dimensional, two-fluid numerical simulation.Comment: 8 pages, 6 figure

Creating Non-Maxwellian Velocity Distributions in Ultracold Plasmas

We present techniques to perturb, measure and model the ion velocity distribution in an ultracold neutral plasma produced by photoionization of strontium atoms. By optical pumping with circularly polarized light we promote ions with certain velocities to a different spin ground state, and probe the resulting perturbed velocity distribution through laser-induced fluorescence spectroscopy. We discuss various approaches to extract the velocity distribution from our measured spectra, and assess their quality through comparisons with molecular dynamic simulationsComment: 13 pages, 8 figure

Velocity Relaxation in a Strongly Coupled Plasma

Collisional relaxation of Coulomb systems is studied in the strongly coupled regime. We use an optical pump-probe approach to manipulate and monitor the dynamics of ions in an ultracold neutral plasma, which allows direct measurement of relaxation rates in a regime where common Landau-Spitzer theory breaks down. Numerical simulations confirm the experimental results and display non-Markovian dynamics at early times.Comment: 5 pages, 5 figure

High Resolution Ionization of Ultracold Neutral Plasmas

Collective effects, such as waves and instabilities, are integral to our understanding of most plasma phenomena. We have been able to study these in ultracold neutral plasmas by shaping the initial density distribution through spatial modulation of the ionizing laser intensity. We describe a relay imaging system for the photoionization beam that allows us to create higher resolution features and its application to extend the observation of ion acoustic waves to shorter wavelengths. We also describe the formation of sculpted density profiles to create fast expansion of plasma into vacuum and streaming plasmas

Disordered Kondo Nanoclusters: Effect of Energy Spacing

Exact diagonalization results for Kondo nanoclusters alloyed with mixed valence impurities show that tuning the {\it energy spacing}, $\Delta$, drives the system from the Kondo to the RKKY regime. The interplay of $\Delta$ and disorder gives rise to a $\Delta$ versus concentration T=0 phase diagram very rich in structure, where regions with prevailing Kondo or RKKY correlations alternate with domains of ferromagnetic order. The local Kondo temperatures, $T_K$, and RKKY interactions depend strongly on the local environment and are overall {\it enhanced} by disorder, in contrast to the hypothesis of ``Kondo disorder'' single-impurity models.Comment: 4pages 4 figuresDisordered Kondo Nanoclusters: Effect of Energy Spacin

Raman spectroscopy study of the interface structure in (CaCuO2)n/(SrTiO3)m superlattices

Raman spectra of CaCuO2/SrTiO3 superlattices show clear spectroscopic marker of two structures formed in CaCuO2 at the interface with SrTiO3. For non-superconducting superlattices, grown in low oxidizing atmosphere, the 425 cm-1 frequency of oxygen vibration in CuO2 planes is the same as for CCO films with infinite layer structure (planar Cu-O coordination). For superconducting superlattices grown in highly oxidizing atmosphere, a 60 cm-1 frequency shift to lower energy occurs. This is ascribed to a change from planar to pyramidal Cu-O coordination because of oxygen incorporation at the interface. Raman spectroscopy proves to be a powerful tool for interface structure investigation

Tailoring Graphene with Metals on Top

We study the effects of metallic doping on the electronic properties of graphene using density functional theory in the local density approximation in the presence of a local charging energy (LDA+U). The electronic properties are sensitive to whether graphene is doped with alkali or transition metals. We estimate the the charge transfer from a single layer of Potassium on top of graphene in terms of the local charging energy of the graphene sheet. The coating of graphene with a non-magnetic layer of Palladium, on the other hand, can lead to a magnetic instability in coated graphene due to the hybridization between the transition-metal and the carbon orbitals.Comment: 5 pages, 4 figure

La defensa de la conservación de las especies: el papel de los conflictos entre las leyes y las normas de la comunidad en diversas etapas de una acción comunicativa

New laws promoting species conservation in protected sites are often contested by local communities. Conflicts between the laws and community norms may explain this; yet the literature on normative conflicts has still not examined such laws-norms conflicts. It has moreover been inconclusive regarding the (negative or positive) relationship between normative conflicts and action, and has not studied how they affect engagement in communicative actions supporting the laws. A stage model (Trans-Theoretical Model) was used to clarify how two types of conflicts — between the law and community descriptive and injunctive norms, and between the latter two — are associated with transitions from awareness to engagement in communicative action. A survey of 342 residents in Portuguese Natura 2000 sites showed stronger normative conflicts at pre-action (versus post-action) stages. Additionally, conflict between injunctive and descriptive community norms is lower and more invariant across stages than conflict between them and the law, suggesting a higher relevance of the later for (dis)engagement in communicative action. We discuss the contributions a stage perspective may offer for improving the implementation of conservation laws.laws promoting species conservation in protected sites are often contested by local communities. Conflicts between the laws and community norms may explain this; yet the literature on normative conflicts has still not examined such laws-norms conflicts. It has moreover been inconclusive regarding the (negative or positive) relationship between normative conflicts and action, and has not studied how they affect engagement in communicative actions supporting the laws. A stage model (Trans-Theoretical Model) was used to clarify how two types of conflicts — between the law and community descriptive and injunctive norms, and between the latter two — are associated with transitions from awareness to engagement in communicative action. A survey of 342 residents in Portuguese Natura 2000 sites showed stronger normative conflicts at pre-action (versus post-action) stages. Additionally, conflict between injunctive and descriptive community norms is lower and more invariant across stages than conflict between them and the law, suggesting a higher relevance of the later for (dis)engagement in communicative action. We discuss the contributions a stage perspective may offer for improving the implementation of conservation laws.info:eu-repo/semantics/acceptedVersio

Cognitive polyphasia in the reception of legal innovations for biodiversity conservation

Cognitive polyphasia has mainly been used to address encounters between innovative scientific knowledge and local, traditional knowledge. Yet, change and innovation occur in many spheres of life, not just in the scientific one. In this paper we examine the encounter between new laws – or legal innovations – and local knowledge, and discuss how the normative force of new laws shapes communication and cognitive polyphasia. We specifically focus on the Generalisation phase of legal innovation, when new laws are translated into concrete practices, the social debate is more intense, and cognitive polyphasia is more likely to occur. We present empirical data from focus groups and interviews to illustrate how this happens for the specific case of the reception of new biodiversity conservation laws affecting communities living in protected sites. We also examine the positions of professionals from local mediating systems, illustrating how they manage the dilemmas linked to the introduction of new laws. The results illustrate the contexts of use of non-polyphasic and polyphasic interventions; they also show how polyphasia is expressed by two divergent argumentative formats (thematisation and conventionalisation), whose conjugation is indispensable for trying to contest the law while still respecting the normative meta-system. The findings are discussed taking into account the macro-societal consequences of cognitive polyphasia, trying to show how, at the societal level, it may contribute to slowing down social change. We also discuss how this is related to the enablement of emancipated representations, those where uncertainty and ambivalence more clearly emerge and sustain the negotiation of meaning