Theory of percolation and tunneling regimes in nanogranular metal films

Nanogranular metal composites, consisting of immiscible metallic and insulating phases deposited on a substrate, are characterized by two distinct electronic transport regimes depending on the relative amount of the metallic phase. At sufficiently large metallic loadings, granular metals behave as percolating systems with a well-defined critical concentration above which macroscopic clusters of physically connected conductive particles span the entire sample. Below the critical loading, granular metal films are in the dielectric regime, where current can flow throughout the composite only via hopping or tunneling processes between isolated nanosized particles or clusters. In this case transport is intrinsically non-percolative in the sense that no critical concentration can be identified for the onset of transport. It is shown here that, although being very different in nature, these two regimes can be described by treating percolation and hopping on equal footing. By considering general features of the microstructure and of the electrical connectedness, the concentration dependence of the dc conductivity of several nanogranular metal films is reproduced to high accuracy within an effective medium approach. In particular, fits to published experimental data enable us to extract the values of microscopic parameters that govern the percolation and tunneling regimes, explaining thus the transport properties observed in nanogranular metal films.Comment: 11 pages, 8 figures + Supplemental material with 5 figure

Story of Use: Analysis of Film Narratives to Inform the Design of Object Interactions

Not only is using a product an experience, it is an interaction and it is narrative in nature. This work in progress paper describes the narrative theory background for this statement, in particular schemata theory and the concepts of agency, tellability and narrativity, then describes methods that are being used in the project to analyse film narratives and apply these to the design of tellable physical products

Signal coverage approach to the detection probability of hypothetical extraterrestrial emitters in the Milky Way

The lack of evidence for the existence of extraterrestrial life, even the simplest forms of animal life, makes it is difficult to decide whether the search for extraterrestrial intelligence (SETI) is more a high-risk, high-payoff endeavor than a futile attempt. Here we insist that even if extraterrestrial civilizations do exist and communicate, the likelihood of detecting their signals crucially depends on whether the Earth lies within a region of the galaxy covered by such signals. By considering possible populations of independent emitters in the galaxy, we build a statistical model of the domain covered by hypothetical extraterrestrial signals to derive the detection probability that the Earth is within such a domain. We show that for general distributions of the signal longevity and directionality, the mean number of detectable emitters is less than one even for detection probabilities as large as 50\%, regardless of the number of emitters in the galaxy.Comment: 9 pages, 5 figure

Spin-orbit scattering in d-wave superconductors

When non-magnetic impurities are introduced in a d-wave superconductor, both thermodynamic and spectral properties are strongly affected if the impurity potential is close to the strong resonance limit. In addition to the scalar impurity potential, the charge carriers are also spin-orbit coupled to the impurities. Here it is shown that (i) close to the unitarity limit for the impurity scattering, the spin-orbit contribution is of the same order of magnitude than the scalar scattering and cannot be neglected, (ii) the spin-orbit scattering is pair-breaking and (iii) induces a small id_xy component to the off-diagonal part of the self-energy.Comment: 9 pages, 3 postscript figures, euromacr.tex-europhys.sty, submitted to Europhysics Letter

The Ta-Da Series: A Technique for Generating Surprising Designs Based on Opposites and Gut Reactions

Chapter in an edited collection, originally presented at the 5th international Design and Emotion Conference in Gothenburg, Sweden

Cinematic Narratives of Product Interaction Experiences: Methods for Cross-Media Fertilisation of the Design Process

This paper outlines the initial phases of a practice-based PhD research project; it outlines methods that will be used to analyse the role of objects within cinematic narratives and how these narrative roles could be translated into methods for designing products to enrich the experience of using the products. The starting point for this project is the hypothesis that any interaction between a user and an object will be remembered and interpreted in a user's mind as a form of narrative. This project therefore tries to harness narrative structures and devices from other media to inform the design of products that can specifically cater to these narrative qualities inherent in the way we experience products. This paper outlines methods for opening up the dialogue about these cross-media narrative comparisons, to assist in generating design work which focuses on the narrative qualities of product experience

The Ta-Da Series: presentation of a technique and its use in generating a series of surprising designs

Surprise is an emotion that is used very explicitly in personal interactions and in narrative media, yet it is not used in the same way within design. This case study presents a technique devised and used to apply the results of theoretical research on surprise to the creation of a series of surprising objects. The designs in this series are very different in the way they function, yet they are derived from the same technique, based on cultural expectations, gut reactions and pleasant surprise. To begin with, the design process involved studying what is expected of objects, and identifying what the main characteristics of a specific category of objects are. What do we expect when we approach a lamp? And in particular, are there any signs which we can use to reinforce these expectations? The second step is to find the opposite of those characteristics and turn them into design concepts. In this case a lamp needs to make light in order to be a lamp, so its main connotation cannot be opposed. But there are other connotations that are not necessarily intrinsic in lamps but which we all tend to associate with lamps, and those are connotations and those are connotations about breakable materials and fragility. The design therefore plays with these expectations by creating a lamp that at first sight has some connotations of a typology of lamp that is both common and extremely breakable; in this way it reinforces the feeling of fragility. But the lamp itself is made of rubber, so if it fell it wouldn’t break but bounce. In addition to this, the technique uses inbuilt gut reactions and fears to reinforce the surprising effect. The lamp only turns on when it is placed on the edge of the table; in this way the lamp will always be in a precarious position, not only reinforcing the feeling of instability, but playing with the user’s gut reactions: though the owner knows that the lamp will not break, it is hard to shed the ingrained reaction of wanting to move it to the middle of the table. By using these gut reactions, the lamp creates a playful sense of suspense, and pleasant surprise when one discovers, or remembers, that the lamp is made of rubber and it is meant to fall. This same technique is applied to three designs, the On-Edge Lamp, the (Un-) Stable Stool and the Impolite Coffee Tables. These three designs will be presented and the differences and similarities between the designs will be outlined

Continuum percolation of polydisperse hyperspheres in infinite dimensions

We analyze the critical connectivity of systems of penetrable $d$-dimensional spheres having size distributions in terms of weighed random geometrical graphs, in which vertex coordinates correspond to random positions of the sphere centers and edges are formed between any two overlapping spheres. Edge weights naturally arise from the different radii of two overlapping spheres. For the case in which the spheres have bounded size distributions, we show that clusters of connected spheres are tree-like for $d\rightarrow \infty$ and they contain no closed loops. In this case, we find that the mean cluster size diverges at the percolation threshold density $\eta_c\rightarrow 2^{-d}$, independently of the particular size distribution. We also show that the mean number of overlaps for a particle at criticality $z_c$ is smaller than unity, while $z_c\rightarrow 1$ only for spheres with fixed radii. We explain these features by showing that in the large dimensionality limit the critical connectivity is dominated by the spheres with the largest size. Assuming that closed loops can be neglected also for unbounded radii distributions, we find that the asymptotic critical threshold for systems of spheres with radii following a lognormal distribution is no longer universal, and that it can be smaller than $2^{-d}$ for $d\rightarrow\infty$.Comment: 11 pages, 5 figure

Vacant Lot Greening Options in Buffalo

The main goals of PUSH (People United for Sustainable Housing) and its development subsidiary, the Buffalo Neighborhood Stabilization Corporation (BNSC), are to mobilize residents to create strong neighborhoods with quality affordable housing, to expand local hiring opportunities, and to advance economic justice in Buffalo