Security warning system monitors up to fifteen remote areas simultaneously

Security warning system consisting of 15 television cameras is capable of monitoring several remote or unoccupied areas simultaneously. The system uses a commutator and decommutator, allowing time-multiplexed video transmission. This security system could be used in industrial and retail establishments

Nonlinear dynamics and surface diffusion of diatomic molecules

The motion of molecules on solid surfaces is of interest for technological applications, but it is also a theoretical challenge. We study the deterministic and thermal diffusive dynamics of a dimer moving on a periodic substrate. The deterministic motion of the dimer displays strongly nonlinear features and chaotic behavior. The dimer thermal diffusive dynamics deviates from simple Arrhenius behavior, due to the coupling between vibrational and translational degrees of freedom. In the low-temperature limit the dimer diffusion can become orders of magnitude larger than that of a single atom, as also found experimentally. The relation between chaotic deterministic dynamics and stochastic thermal diffusion is discussed.Comment: 4 pages, 4 figure

Power law load dependence of atomic friction

We present a theoretical study of the dynamics of a tip scanning a graphite surface as a function of the applied load. From the analysis of the lateral forces, we extract the friction force and the corrugation of the effective tip-surface interaction potential. We find both the friction force and potential amplitude to have a power law dependence on applied load with exponent $\sim 1.6$. We interpret these results as characteristic of sharp undeformable tips in contrast to the case of macroscopic and elastic microscopic contacts.Comment: 4 pages, 4 figure

Fantastic reconstruction: postcolonial artists and the colonial archive

The context paper addresses works submitted that are informed by postcolonial theoretical debates about multiculturalism, racial identification, essentialism, cultural hybridity and mimicry that prevailed in the cultural milieus of New York and London in the 1980s and early 1990s. Race is addressed in all these works as a language and racialisation is treated as a social and psychic process. The practice that is addressed in the context paper is interdisciplinary, involving performance, video and curating, as well as writing that assesses how these works engage the public in a dialogue about race as a signifying practice and about the seductive qualities of racial imagery. Central to the works submitted is the notion of the archive, and more particularly the colonial archive. The context paper singles out the pertinent conceptualizations of the archive in relation to the postcolonial theories and practices under consideration. Those most relevant to the works submitted are the writings of Edward Said, Michel Foucault and Allan Sekula. The colonial archive is understood as actual repositories of official representations of colonised peoples, as well as a structuring principle that demarcates the possible articulations of subaltern selfhood. The context paper treats the artistic works submitted as attempts to work through postcolonial theories via critically informed lived experiences, which is to say via praxis. What is proposed is that performative re- enactment and interaction with audiences offers an important means of exploring how racialised cultural discourses actually operate in and shape understanding of the world. The principal argument for the originality of the works submitted is that the reflexive use of performances foregrounding the constructed nature of racial identity through re-enactment and simulation constitutes an innovative approach to postcolonial praxis. The context paper also summarizes relevant aspects of the historical context in which the submitted works were produced. During that period, the author was associated with artists and art collectives that were actively engaged in a postcolonial critique of cultural institutions and Eurocentric aesthetics in the United States and Britain. The multicultural activism of that period concentrated on developing ways to combine experimental techniques with a "new cultural politics of difference" in the words of cultural theorist Cornel West. Multicultural activists were concerned not only with critiquing the stereotyping of racial minorities in mainstream media and art history, but also with putting forward a notion of race as a social construct and a symbolic practice. The works submitted address the ways that racial tropes from colonial discourse, such as "the primitive" reasserted themselves in the contemporary discourses of state-sponsored and corporate multiculturalism. The context statement focuses on three major cultural projects and nine essays that engage with the notion of race as a language. Those cultural projects are: my caged Amerindian performance, Two Undiscovered Amerindians Visit the West (1992-1994), featured in the video The Couple in the Cage (1993); my video a/k/a Mrs.George Gilbert (2004); and my curatorial project Only Skin Deep: Changing Visions of the American Self (2003). The essays address either these works or others by artists who share a concern with racial representation. The context statement outlines the theoretical underpinnings that inform these works. I discuss how these works have been informed by structuralist and post-structuralist theories of language and discursive practice; psychoanalytic theories of racial identification and fantasy and postcolonial models of cultural interpretation. The conclusion incorporates retrospective commentary on the shortcomings in my approach and in my original understanding of audience reception, particularly in relation to credulity and the suspension of disbelief

Rheological properties vs Local Dynamics in model disordered materials at Low Temperature

We study the rheological response at low temperature of a sheared model disordered material as a function of the bond rigidity. We find that the flow curves follow a Herschel-Bulkley law, whatever is the bond rigidity, with an exponent close to 0.5. Interestingly, the apparent viscosity can be related to a single relevant time scale $t_{rel}$, suggesting a strong connection between the local dynamics and the global mechanical behaviour. We propose a model based on the competition between the nucleation and the avalanche-like propagation of spatial strain heterogeneities. This model can explain the Herschel-Bulkley exponent on the basis of the size dependence of the heterogeneities on the shear rate.Comment: 9 pages, 7 figure

Random sequential adsorption and diffusion of dimers and k-mers on a square lattice

We have performed extensive simulations of random sequential adsorption and diffusion of $k$-mers, up to $k=5$ in two dimensions with particular attention to the case $k=2$. We focus on the behavior of the coverage and of vacancy dynamics as a function of time. We observe that for $k=2,3$ a complete coverage of the lattice is never reached, because of the existence of frozen configurations that prevent isolated vacancies in the lattice to join. From this result we argue that complete coverage is never attained for any value of $k$. The long time behavior of the coverage is not mean field and nonanalytic, with $t^{-1/2}$ as leading term. Long time coverage regimes are independent of the initial conditions while strongly depend on the diffusion probability and deposition rate and, in particular, different values of these parameters lead to different final values of the coverage. The geometrical complexity of these systems is also highlighted through an investigation of the vacancy population dynamics.Comment: 9 pages, 9 figures, to be published in the Journal of Chemical Physic

The development of the Silurian trilobite Aulacopleura koninckii reconstructed by applying inferred growth and segmentation dynamics: A case study in paleo-evo-devo

Fossilized growth series provide rare glimpses into the development of ancient organisms, illustrating descriptively how size and shape changed through ontogeny. Occasionally fossil preservation is such that it is feasible to test alternative possibilities about how ancient development was regulated. Here we apply inferred developmental parameters pertaining to size, shape, and segmentation in the abundant and well-preserved 429 Myr old trilobite Aulacopleura koninckii that we have investigated previously to reconstruct the post-embryonic ontogeny of this ancient arthropod. Our published morphometric analyses associated with model testing have shown that: specification of the adult number of trunk segments (polymorphic in this species) was determined precociously in ontogeny; that growth regulation was targeted (i.e., compensatory), such that each developmental stage exhibited comparable variance in size and shape; and that growth gradients operating along the main body axis, both during juvenile and adult ontogeny, resulted from a form of growth control based on positional specification. While such developmental features are common among extant organisms, our results represent the oldest evidence for them within Metazoa. Herein, the novel reconstruction of the development of Aulacopleura koninckii permits visualization of patterns of relative and absolute growth and segmentation as never before possible for a fossilized arthropod ontogeny. By conducting morphometric analysis of appropriate data sets it is thus possible to move beyond descriptive ontogenetic studies and to address questions of high interest for evolutionary developmental biology using data from fossils, which can help elucidate both how developmental processes themselves evolve and how they affect the evolution of organismal body patterning. By extending similar analyses to other cases of exceptional preservation of fossilized ontogeny, we can anticipate beginning to realize the research program of “paleo-evo-devo.

Non trivial behavior of the linear response function in phase ordering kinetics

Drawing from exact, approximate and numerical results an overview of the properties of the out of equilibrium response function in phase ordering kinetics is presented. Focusing on the zero field cooled magnetization, emphasis is on those features of this quantity which display non trivial behavior when relaxation proceeds by coarsening. Prominent among these is the dimensionality dependence of the scaling exponent $a_{\chi}$ which leads to failure of the connection between static and dynamic properties at the lower dimensionality $d_L$, where $a_{\chi}=0$. We also analyse the mean spherical model as an explicit example of a stochastic unstable system, for which the connection between statics and dynamics fails at all dimensionalities.Comment: 10 pages, 2 figures. Contribution to the International Conference "Perspectives on Quantum Field Theory, Statistical Mechanics and Stochastics" in honour of the 60th birthday of Francesco Guerr