Negative and Nonlinear Response in an Exactly Solved Dynamical Model of Particle Transport

We consider a simple model of particle transport on the line defined by a dynamical map F satisfying F(x+1) = 1 + F(x) for all x in R and F(x) = ax + b for |x| < 0.5. Its two parameters a (`slope') and b (`bias') are respectively symmetric and antisymmetric under reflection x -> R(x) = -x. Restricting ourselves to the chaotic regime |a| > 1 and therein mainly to the part a>1 we study not only the `diffusion coefficient' D(a,b), but also the `current' J(a,b). An important tool for such a study are the exact expressions for J and D as obtained recently by one of the authors. These expressions allow for a quite efficient numerical implementation, which is important, because the functions encountered typically have a fractal character. The main results are presented in several plots of these functions J(a,b) and D(a,b) and in an over-all `chart' displaying, in the parameter plane, all possibly relevant information on the system including, e.g., the dynamical phase diagram as well as invariants such as the values of topological invariants (kneading numbers) which, according to the formulas, determine the singularity structure of J and D. Our most significant findings are: 1) `Nonlinear Response': The parameter dependence of these transport properties is, throughout the `ergodic' part of the parameter plane (i.e. outside the infinitely many Arnol'd tongues) fractally nonlinear. 2) `Negative Response': Inside certain regions with an apparently fractal boundary the current J and the bias b have opposite signs.Comment: corrected typos and minor reformulations; 28 pages (revtex) with 7 figures (postscript); accepted for publication in JS

UNDER-REPORTING OF CATCHES OF SOUTH COAST ROCK LOBSTER PALINURUS GILCHRISTI, WITH IMPLICATIONS FOR THE ASSESSMENT AND MANAGEMENT OF THE FISHERY

Under-reporting of fishery catches can severely affect the precision of stock assessment estimates, which require accurate information on catch and catch rate. Under-reporting of catches of South Coast rock lobster Palinurus gilchristi over the past decade was estimated from verified daily catch rates and the number of days spent at sea by the commercial fleet. The malpractice increased sharply between the 1997/98 and 2000/01 fishing seasons. The index of abundance for the resource (standardized catch per unit effort) increased by 2&#37 for 1998/99, 12&#37 for 1999/00 and 14&#37 for 2000/01, after eliminating under-reported information from the input data. An agestructured production model, with the adjusted abundance index as an input, and including known and estimated over-catches between 1991/92 and 2000/01, increased the maximum sustainable yield estimate from 360 to 390 tons tail mass. The Total Allowable Catch (TAC) management regulation that was historically used in the fishery failed to address over-harvesting as a result of poor compliance. A combined TAC and Total Allowable Effort management strategy was introduced in 2000/01 to restrict fishing effort (days at sea) on the basis of quota size and vessel efficiency. Changes in management strategy, which include cancellation of the license of a fishing company responsible for systematic under-reporting and over-harvesting, decrease in fishing effort, reduction in over-capacity of vessels and other infrastructure and stabilization of trap catch rates have improved the outlook for the fishery

Analisi delle prestazioni energetiche delle coperture ventilate

Le esigenze sul contenimento dei consumi energetici degli edifici richiedono un involucro performante nella stagione invernale ed estiva. Un involucro progettato in modo sbagliato, può favorire, nella stagione invernale, la crescita di muffe sulla superficie interna e la condensazione interstiziale che diminuiscono sensibilmente le condizioni di comfort. Questi due fenomeni, inoltre, sono causa frequente di contenzioso civile nel settore delle costruzioni. Nell'ultimo decennio, la diffusione degli impianti di condizionamento ha determinato un sensibile aumento dei consumi di energia elettrica con particolare riguardo alla stagione estiva. Di qui nasce l’esigenza di utilizzo di tecniche passive come la ventilazione delle intercapedini d’aria nelle pareti. Nel presente lavoro si è posto l’obiettivo di valutare i vantaggi conseguibili con l’impiego delle coperture ventilate (piane o a falde) sia nella stagione invernale che quella estiva. Sono stati affrontati problemi tipici della stagione invernale, come muffa e condensa interstiziale, per due coperture piane di frequente utilizzo nell'edilizia per tre diverse località e zone climatiche. Consistenti fenomeni di condensa interstiziale insieme alle esigenze della legislazione vigente (prescrizione sulla totale assenza della condensa interstiziale) hanno richiesto la necessità di intervento. In particolare si può intervenire ventilando l’intercapedine d’aria. Sono state calcolate le portate minime di ventilazione necessarie a evitare la condensa e mostrato un apparecchio tipo con il quale esse possono essere generate. È stata studiata la variazione delle portate d’aria nelle coperture piane in base ad alcuni parametri termo igrometrici (es.: temperatura esterna, umidità relativa esterna e la produzione di vapore all'interno dell’ambiente). Nella stagione estiva è stato calcolato il risparmio energetico conseguibile con due tipologie di coperture ventilate a falde sia nel caso di ventilazione naturale, data dall'effetto camino, sia nel caso della ventilazione forzata, realizzata con un aspiratore. Sono stati calcolati i parametri termici dinamici delle coperture con l’intercapedine d’aria chiusa (non ventilata) e confrontati con le coperture ventilate

39 Gasification of char particles with CO2 AND H2O

Gasification of large char particles with CO2 and H2O has been investigated both experimentally and with model studies. A local volumetric rate model is derived that takes into account the chemical reaction rate and the effective diffusivity being a function of the local carbon conversion and therefore a function of time and position within the particle. The model includes shrinking unreacted core and homogeneous reaction as extreme cases. Chemical reaction rates of powdered deal wood char were measured for different CO2 and/or H2O concentrations (0.05 - 2 mol/m3) and as a function of the carbon conversion and temperature (1073 - 1273 K) by means of a modified thermobalance. In separate single particle tests the effective diffusivity has been determined for different carbon conversions. A specially designed single particle reactor has been used for local carbon conversions. measurement within 0,04 m particles. Carbon conversion profiles obtained differ from those predicted by the shrinking core and homogeneous reaction extremes but could be very well explained by the local volumetric rate model. As an example results obtained from a 3 kg/h co-current moving bed wood gasifier are presented. Char conversion, particle diameter and temperature profiles agree well with the reduction zone model based on the local volumetric-rate particle model

Thought for Food: the impact of ICT on agribusiness

This report outlines the impact of ICT on the food economy. On the basis of a literature review from four disciplines - knowledge management, management information systems, operations research and logistics, and economics - the demand for new ICT applications, the supply of new applications and the match between demand and supply are identified. Subsequently the impact of new ICT applications on the food economy is discussed. The report relates the development of new technologies to innovation and adoption processes and economic growth, and to concepts of open innovations and living lab

Northern Hemisphere Glaciation during the Globally Warm Early Late Pliocene

The early Late Pliocene (3.6 to ~3.0 million years ago) is the last extended interval in Earth's history when atmospheric CO2 concentrations were comparable to today's and global climate was warmer. Yet a severe global glaciation during marine isotope stage (MIS) M2 interrupted this phase of global warmth ~3.30 million years ago, and is seen as a premature attempt of the climate system to establish an ice-age world. Here we propose a conceptual model for the glaciation and deglaciation of MIS M2 based on geochemical and palynological records from five marine sediment cores along a Caribbean to eastern North Atlantic transect. Our records show that increased Pacific-to-Atlantic flow via the Central American Seaway weakened the North Atlantic Current and attendant northward heat transport prior to MIS M2. The consequent cooling of the northern high latitude oceans permitted expansion of the continental ice sheets during MIS M2, despite near-modern atmospheric CO2 concentrations. Sea level drop during this glaciation halted the inflow of Pacific water to the Atlantic via the Central American Seaway, allowing the build-up of a Caribbean Warm Pool. Once this warm pool was large enough, the Gulf Stream–North Atlantic Current system was reinvigorated, leading to significant northward heat transport that terminated the glaciation. Before and after MIS M2, heat transport via the North Atlantic Current was crucial in maintaining warm climates comparable to those predicted for the end of this century

Ultrafast quasiparticle relaxation dynamics in normal metals and heavy fermion materials

We present a detailed theoretical study of the ultrafast quasiparticle relaxation dynamics observed in normal metals and heavy fermion materials with femtosecond time-resolved optical pump-probe spectroscopy. For normal metals, a nonthermal electron distribution gives rise to a temperature (T) independent electron-phonon relaxation time at low temperatures, in contrast to the T^{-3}-divergent behavior predicted by the two-temperature model. For heavy fermion compounds, we find that the blocking of electron-phonon scattering for heavy electrons within the density-of-states peak near the Fermi energy is crucial to explain the rapid increase of the electron-phonon relaxation time below the Kondo temperature. We propose the hypothesis that the slower Fermi velocity compared to the sound velocity provides a natural blocking mechanism due to energy and momentum conservation laws.Comment: 10 pages, 11 figure