Nordic Electricity Congestion's Arrangement as a Model for Europe: Physical Constraints or Operators' Opportunity

Nordic Electricity Congestion's Arrangement as a Model for Europe: Physical Constraints or Operators' Opportunit

Rheo-acoustic gels: Tuning mechanical and flow properties of colloidal gels with ultrasonic vibrations

Colloidal gels, where nanoscale particles aggregate into an elastic yet fragile network, are at the heart of materials that combine specific optical, electrical and mechanical properties. Tailoring the viscoelastic features of colloidal gels in real-time thanks to an external stimulus currently appears as a major challenge in the design of "smart" soft materials. Here we introduce "rheo-acoustic" gels, a class of materials that are sensitive to ultrasonic vibrations. By using a combination of rheological and structural characterization, we evidence and quantify a strong softening in three widely different colloidal gels submitted to ultrasonic vibrations (with submicron amplitude and frequency 20-500 kHz). This softening is attributed to micron-sized cracks within the gel network that may or may not fully heal once vibrations are turned off depending on the acoustic intensity. Ultrasonic vibrations are further shown to dramatically decrease the gel yield stress and accelerate shear-induced fluidization. Ultrasound-assisted fluidization dynamics appear to be governed by an effective temperature that depends on the acoustic intensity. Our work opens the way to a full control of elastic and flow properties by ultrasonic vibrations as well as to future theoretical and numerical modeling of such rheo-acoustic gels.Comment: 21 pages, 14 figure

Non-dynamic origin of the acoustic attenuation at high frequency in glasses

The sound attenuation in the THz region is studied down to T=16 K in glassy glycerol by inelastic x-ray scattering. At striking variance with the decrease found below 100 K in the GHz data, the attenuation in the THz range does not show any T dependence. This result i) indicates the presence of two different attenuation mechanisms, active respectively in the high and low frequency limits; ii) demonstrates the non-dynamic origin of the attenuation of THz sound waves, and confirms a similar conclusion obtained in SiO2 glass by molecular dynamics; and iii) supports the low frequency attenuation mechanism proposed by Fabian and Allen (Phys.Rev.Lett. 82, 1478 (1999)).Comment: 3 pages, 5 Figures, To be published in PR

Nordic electricity congestion's arrangement as a model for Europe : physical constraints or operators' opportunism?

Congestion on power grids seems a physical reality, a "hard" fact easy to check. Our paper models a different idea: congestion signal may be distorted by transmission system operators (TSOs), which puts the European integrated electricity market at risk. 1ʻ when the TSOs share the revenue produced by congestion's pricing they have an incentive in distorting data. 2ʻ because congestion signals are not physical data but "home made" conventions, TSOs could be able distorting them. 3ʻ when congestion appears on cross border lines that link several countries with their own regulatory mechanisms, the settlement of this incentive's problem necessitates a high degree of coordination. Congestion puts undoubtedly the threat of a collapse on interconnected grids. The "capacity constrained situations" have therefore to be avoided. Congestion signalling depends on norms set by TSOs and a signal is given when the power flows attain the "secure" limits set by TSOs. These security norms are not stable and invariable because some flexibility is needed by the very nature of the power flows and because lines physical capacity limits are not constant. Therefore TSOs are defining the congestion signal on a variable, complex and non transparent constraint and may manipulate it for their own interests. In Nordic countries the "Light Handed Regulation" makes this opportunistic behaviour more likely. We need a more effective congestion regulatory mechanism.Supported by the MIT Center for Energy and Environmental Policy Research

Sigmoid Neural Transfer Function Realised by Percolation

An experiment using the phenomenon of percolation has been conducted to demonstrate the implementation of neural functionality (summing and sigmoid transfer). A simple analog approximation to digital percolation is implemented. The device consists of a piece of amorphous silicon with stochastic bit-stream optical inputs, in which a current percolating from one end to the other defines the neuron output, also in the form of a stochastic bit stream. Preliminary experimental results are presented

Elastic consequences of a single plastic event : a step towards the microscopic modeling of the flow of yield stress fluids

With the eventual aim of describing flowing elasto-plastic materials, we focus on the elementary brick of such a flow, a plastic event, and compute the long-range perturbation it elastically induces in a medium submitted to a global shear strain. We characterize the effect of a nearby wall on this perturbation, and quantify the importance of finite size effects. Although for the sake of simplicity most of our explicit formulae deal with a 2D situation, our statements hold for 3D situations as well.Comment: submitted to EPJ

Predicting lung cancer recurrence from circulating tumour DNA. Commentary on 'Phylogenetic ctDNA analysis depicts early-stage lung cancer evolution'

No abstract available

Thermochemical recovery technology for improved modern engine fuel economy – part 1: analysis of a prototype exhaust gas fuel reformer

Exhaust gas fuel reforming has the potential to improve the thermal efficiency of internal combustion engines, as well as simultaneously reduce gaseous and particulate emissions.</p