Tessaleno C. Devezas

Anisotropy field of small magnetic particles as measured by resonance

The anisotropy field as measured by resonance is calculated for a coherent assembly of small magnetic particles possessing both crystal and shape anisotropy. The theoretical results are compared with experimental data on precipitated cobalt and magnesioferrite particles.

The biological determinants of long-wave behavior in socioeconomic growth and development

In this paper, it is claimed that the effective causality of long-term macroeconomic rhythms, most commonly referred to as long waves or Kondratieff waves, is founded in our biological realm. The observed patterns of regularity in human affairs, manifest as socioeconomic rhythms and recurrent phenomena, are constrained and codetermined by our natural human biological clocks, themselves the result of instructions impressed in the human genome and human cognitive capacity by the physical regularity of fixed cosmic cycles. Considering that a long wave can be conceived as an evolving learning dissipative structure consisting of two successive logistic structural cycles, an innovation cycle and a consolidation cycle, and applying considerations from population dynamics, chaos theory and logistic growth dynamics, a Generational-Learning Model is proposed that permits comprehension of the unfolding and time duration of the phenomenon. The proposed model is based on two kinds of biological constraints that impose the rhythm of collective human behavior — generational and cognitive. The generational consist of biologically based rhythms, namely, the Aggregate Virtual Working Life Tenure and the Aggregate Female Fecundity Interval, both subsets of the normative human life span or human life cycle. The cognitive consist of a limiting learning growth rate, manifest in the alternating sequence of two succeeding learning phases, a new knowledge phase and a consolidation phase. It is proposed that the syncopated beats of succeeding effective generational waves and the dynamics of the learning processes determine the long-wave behavior of socioeconomic growth and development. From the relationship between the differential and the discrete logistic equations, it is demonstrated that the unfolding of each structural cycle of a long wave is controlled by two parameters: the diffusion-learning rate δ and the aggregate effective generation tG, whose product maintained in the interval 3<δtG<4 (deterministic chaos) grants the evolution and performance of social systems. Moreover, it is speculated that the triggering mechanism of this long-term swinging behavior may result from the cohesion loss of a given technoeconomic system in consequence of reaching a threshold value of informational entropy production.

Power law behavior and world system evolution: A millennial learning process

Abstract Is social change on the scale of the human species a millennial learning process? The authors answer in the affirmative, demonstrating that world system evolution, viewed as a cascade of multilevel, nested, and self-similar, Darwinian-like processes ranging in “size” from one to over 250 generations, exhibits power law behavior, which is also known as self-organized criticality. World social organization, poised as it is on the boundary between order and chaos, is neither subcritical nor supercritical, and that allows for flexibility, which is a necessary condition of evolution and learning, and these in turn account for the major transitions marking world history and serving as the general framework for long-range forecasting. A literature review confirms the close affinity between evolution and learning, mathematical analysis reveals the crucial role of the learning rate as pacemaker of evolutionary change, and empirical evidence supports the concept of a cascade of evolutionary processes. The general equation describing world system emergence shows it to be a project whose current period is now 80% complete, suggesting that its major features might now be in place.

The nonlinear dynamics of technoeconomic systems: An informational interpretation

Abstract In this paper, a cybernetic framework is proposed that may help in understanding the specifics of the timely unfolding of recurrent social phenomena, as well as provide a basis for their application as useful forecasting tools for futures studies. The long-wave behavior in technoeconomic development was chosen to apply this theoretical framework. The time evolution of a technoeconomic system is described discretely as a logistically growing number of “interactors” adopting an emerging set of basic social and technological innovations. By using the logistic function as the probabilistic distribution of individuals exchanging and processing information in a finite niche of available information, it is possible to demonstrate that the rate of information entropy change exhibits a “wavy” aspect evidenced by a four-phased behavior denoting the unfolding of a complete long wave. The entire unfolding process, divided into two cycles, an innovation cycle and a consolidation cycle, is analyzed, and two very important threshold points are identified and discussed. The present theoretical analysis suggests that the technoeconomic system is not a purely chaotic process, but exhibits a limit-cycle behavior, whose basic mechanism is the periodical deployment and filling of information in a “leeway” field of active information. The pace of the process, and hence the duration of the long wave, is determined by two biological control parameters, one cognitive, driving the rate of exchanging and processing information at the microlevel, and the other generational, constraining the rate of transfer of knowledge (information integrated into a context) between successive generations at the macrolevel. Moreover, it is speculated that social systems mimic living systems as efficient negentropic machines, and making use of Prigogines entropy balance equation for open systems, it is suggested that its cyclical behavior is probably the best way to follow natures efficiency strategy.

Mechanical Characterization of Composites with Embedded Optical Fibers

The purpose of this investigation is to evaluate quantitatively and comparatively the effect of embedding optical fibers (OF) on the mechanical behavior of a carbon fiber-epoxy composite in order to verify whether their presence can possibly degrade the mechanical performance of the host material. The existing literature on this subject is not conclusive about the nature and intensity of this effect. Adding more reliable data to our systematic study contributes to this discussion favoring the conclusion about a harmful influence as a consequence of optical fiber embedment. Three kinds of mechanical tests have been performed in this work: impact tests, static flexural tests, and fatigue tests. The results of some experiments point to a possible detrimental influence related to the presence of the OF, being it different in nature and intensity for each of these tests. The mechanical behavior in static loading conditions seems to be not significantly affected as a consequence of the presence of the OF, while that in impact and fatigue tests are strongly affected, even though this influence being physically distinct from each other. Based on these results, some discussion is made about the possible failure mechanisms that can explain the detected differences.

Fatigue damage of carbon–epoxy laminates with embedded optical fibres

Abstract The present paper is concerned with the fatigue behaviour ofcarbon-epoxy laminates with embedded optical fibres subjected to bending loads. The main goal of this investigation was to evaluate quantitatively the effect of the presence of optical fibres within the host structure on its whole fatigue behaviour. Two optical fibre positions were investigated: in the mid-plane of the laminate and near the surface subjected to loading. Two distinct geometries of the ply stacking sequence were also considered, namely unidirectional and crossply. In order to evaluate the fatigue life and the fatigue damage, two different loading levels were used, both at 6 Hz frequency, room temperature and R = 0.1. Fatigue damage was monitored using dynamic stiffness decay and acoustic emission techniques. Failure mechanisms were analysed by means of optical and scanning microscopy. The results obtained lead to the conclusion that the embedding of optical fibres markedly prejudices the fatigue performance of the material only for certain configurations. It was also possible to speculate on the fatigue failure mechanisms, and to relate them with relevant experimental parameters, such as the lay-up geometry and optical fibre position.

Exploring the Use of Cork Based Composites for Aerospace Applications

Aerospace components are characterized by having high strength to weight ratios in order to obtain lightweight structures. Recently, different types of sandwich components using composite materials have been developed with the purpose of combining the effect of reinforced face-sheets with low weight core materials, such as honeycombs and foams. However, these materials must combine damage tolerance characteristics with high resistance under both static and dynamic loads. Cork composites can be considered as an alternative material for sandwich components since cork is a natural material with some remarkable properties, such as high damage tolerance to impact loads, good thermal and acoustic insulation capacities and excellent damping characteristics for the suppression of vibrations. The experiments carried out in this investigation were oriented in order to optimize the specific strength of cork based composites for sandwich components. Static bending tests were performed in order to characterize the mechanical strength of different types of cork agglomerates which were obtained considering distinct production variables. The ability to withstand dynamic loads was also evaluated from a set of impact tests using carbon-cork sandwich specimens. The results from experimental tests showed that cork agglomerates performance depends on the cork granulate size, the type of reinforcing elements and the bonding procedure used for the cohesion with the matrix material.

The Portuguese as System-builders in the Fifteenth and Sixteenth Centuries: A Case Study on the Role of Technology in the Evolution of the World System

Abstract World system evolution may be viewed as a cascade of multilevel, nested, self-similar and Darwinian-type processes poised on the boundary between order and chaos that allows for innovation. A framework developed by Devezas-Modelski opens the door to conceptualizing globalization as part of that evolutionary cascade, and as a process of system-building of which the Portuguese enterprises of the fifteenth and sixteenth centuries provide an illuminating case. Analysis is focused on two components of that cascade: the Portuguese long cycle, and the two (economic) K-waves and their related innovations. In this period preceding the Industrial Revolution, innovations focused on navigation and shipbuilding and formed the technical support for such activities. Quantitative analysis of empirical evidence on Portuguese expeditions and naval-military campaigns, the global network of bases, and of scarce data on the gold and pepper trades in this period supports the notion of long cycles and K-waves as system-building, and the more general conception of globalization as an evolutionary learning process.

The Evolutionary Trajectory of the World System toward an Age of Transition

Devezas and Modelski (2003) have shown that world system evolution consists in a cascade of multilevel, nested, and self-similar (fractal), Darwinian-like processes ranging in time from one to 250 generations, exhibiting power law behavior, which is also known as self-organized criticality.

MPT Influence on the Rheological Behaviour of Self-Flow Refractory Castables

The success of a refractory castable is largely due to the quality of its properties and ease of application. Self-flow refractory castables (SFRC), with high flowability index (>130%), can be easily accommodated in a mould without the application of external energy, being ideal for the manufacture of monolithic linings. SFRC castables without cement require a matrix of very fine particles, which guarantees improved rheological behaviour and performs the role of the binder in the absence of the refractory cement. The presence of the aggregate (coarse particles) hinders the flowability index, but improves the castable mechanical strength and reduces firing shrinkage, and also contributes to the reduction of the castable costs. The control of the maximum paste thickness (MPT) allows the reduction of the coarse particles interference, minimizing the number of contact points among the grains and avoiding the formation of an aggregate skeleton that impairs the flowability of the mixture. In the present work, 100% alumina SFRCs without cement were produced with a fixed matrix of fine particles, whose particle size distribution was optimized using statistical techniques (mixtures design and triangular response surfaces). Different aggregate particle size distributions were used, with several MPT values, with the objective of evaluating which was the mean distance that maximized the flowability index, simultaneously ensuring good mechanical strength for the refractory castable. Ensuring a minimum surface area of 2.22m2/g, the mixtures reach the self-flow turning point with a minimum water content and the maximum flowability is obtained for an aggregate particle size distribution modulus of q=0.22, and consequently an optimized MPT value. SFRC with high mechanical strength (>60MPa) were obtained.