Impact of Electron-Phonon Coupling on Near-Field Optical Spectra

The finite momentum transfer ($\boldsymbol{q}$) longitudinal optical response $\sigma^L(\boldsymbol{q},\omega)$ of graphene has a peak at an energy $\omega=\hbar v_F q$. This corresponds directly to a quasiparticle peak in the spectral density at momentum relative to the Fermi momentum $k_F -q$. Inclusion of coupling to a phonon mode at $\omega_E$ results, for $\omega<|\omega_E|$, in a constant electron-phonon renormalization of the bare bands by a mass enhancement factor $(1+\lambda)$ and this is followed by a phonon kink at $\omega_E$ where additional broadening begins. Here we study the corresponding changes in the optical quasiparticle peaks which we find to continue to directly track the renormalized quasiparticle energies until $q$ is large enough that the optical transitions begin to sample the phonon kink region of the dispersion curves where linearity in momentum is lost in the renormalized Dirac Fermion dispersion curves and the correspondence to a single quasiparticle energy is lost. Nevertheless there remains in $\sigma^L(\boldsymbol{q},\omega)$ features analogous to the phonon kinks of the dispersion curves which are observable through variation of $q$ and $\omega$.Comment: 6 pages, 5 figure

REDUCING TRANSPORTATION DAMAGE TO GRAPES AND STRAWBERRIES

In-transit vibration damage to grapes and strawberries results in reduced quality for the consumer and reduced profits for the produce industry. To solve this problem, the first step is to determine which vibrational frequencies are causing the damage. In various tests, grapes and strawberries were subjected to different frequencies at constant force levels. The effects of the vibration treatments were evaluated on the basis of grading, color analysis, firmness, respiration rate and ethylene production rate. The critical frequency was found to lie between 7.5 and 10 Hertz for both commodities. Color change and respiration rate were shown to be good indicators of damage in grapes. Strawberries did not show a significant effect due to color. Firmness was not affected by vibration in either commodity.Agribusiness,

Reclaiming human machine nature

Extending and modifying his domain of life by artifact production is one of the main characteristics of humankind. From the first hominid, who used a wood stick or a stone for extending his upper limbs and augmenting his gesture strength, to current systems engineers who used technologies for augmenting human cognition, perception and action, extending human body capabilities remains a big issue. From more than fifty years cybernetics, computer and cognitive sciences have imposed only one reductionist model of human machine systems: cognitive systems. Inspired by philosophy, behaviorist psychology and the information treatment metaphor, the cognitive system paradigm requires a function view and a functional analysis in human systems design process. According that design approach, human have been reduced to his metaphysical and functional properties in a new dualism. Human body requirements have been left to physical ergonomics or "physiology". With multidisciplinary convergence, the issues of "human-machine" systems and "human artifacts" evolve. The loss of biological and social boundaries between human organisms and interactive and informational physical artifact questions the current engineering methods and ergonomic design of cognitive systems. New developpment of human machine systems for intensive care, human space activities or bio-engineering sytems requires grounding human systems design on a renewed epistemological framework for future human systems model and evidence based "bio-engineering". In that context, reclaiming human factors, augmented human and human machine nature is a necessityComment: Published in HCI International 2014, Heraklion : Greece (2014

SIMULATED IN-TRANSIT VIBRATION DAMAGE TO FRESH MARKET RASPBERRIES

Agribusiness,

On the micro mechanics of one-dimensional normal compression

Discrete-element modelling has been used to investigate the micro mechanics of one-dimensional compression. One-dimensional compression is modelled in three dimensions using an oedometer and a large number of particles, and without the use of agglomerates. The fracture of a particle is governed by the octahedral shear stress within the particle due to the multiple contacts and a Weibull distribution of strengths. Different fracture mechanisms are considered, and the influence of the distribution of fragments produced for each fracture on the global particle size distribution and the slope of the normal compression line is investigated. Using the discrete-element method, compression is related to the evolution of a fractal distribution of particles. The compression index is found to be solely a function of the strengths of the particles as a function of size

The impact of category separation on unsupervised categorization

Most previous research on unsupervised categorization has used unconstrained tasks in which no instructions are provided about the underlying category structure or the stimuli are not clustered into categories. Few studies have investigated constrained tasks in which the goal is to learn pre-defined stimulus clusters in the absence of feedback. These studies have generally reported good performance when the stimulus clusters could be separated by a one-dimensional rule. The present study investigated the limits of this ability. Results suggest that even when two stimulus clusters are as widely separated as in previous studies, performance is poor if within-category variance on the relevant dimension is nonnegligible. In fact, under these conditions many participants failed even to identify the single relevant stimulus dimension. This poor performance is generally incompatible with all current models of unsupervised category learning

The Effects of Category Overlap on Information-Integration and Rule-Based Category Learning

Three experiments investigate whether the amount of category overlap constrains the decision strategies used in category learning, and whether such constraints depend on the type of category structures used. Experiments 1 and 2 used a category learning task requiring perceptual integration of information from multiple dimensions (information-integration task) and Experiment 3 used a task requiring the application of an explicit strategy (rule-based task). In the information-integration task, participants used perceptual-integration strategies at moderate levels of category overlap, but explicit strategies at extreme levels of overlap – even when such strategies were sub-optimal. In contrast, in the rule-based task, participants used explicit strategies regardless of the level of category overlap. These data are consistent with a multiple systems view of category learning, and suggest that categorization strategy depends on the type of task that is used, and on the degree to which each stimulus is probabilistically associated with the contrasting categories

Dynamic Failure in Amorphous Solids via a Cavitation Instability

The understanding of dynamic failure in amorphous materials via the propagation of free boundaries like cracks and voids must go beyond elasticity theory, since plasticity intervenes in a crucial and poorly understood manner near the moving free boundary. In this Letter we focus on failure via a cavitation instability in a radially-symmetric stressed material, set up the free boundary dynamics taking both elasticity and visco-plasticity into account, using the recently proposed athermal Shear Transformation Zone theory. We demonstrate the existence (in amorphous systems) of fast cavitation modes accompanied by extensive plastic deformations and discuss the revealed physics.Comment: 4 pages, 4 figure

Development of a coaxial plasma gun for space propulsion final report

Current sheet accelerators and pulsed plasma thrustors for spacecraft propulsio