Impulse-response function of splanchnic circulation with model-independent constraints: theory and experimental validation

Modeling physiological processes using tracer kinetic methods requires knowledge of the time course of the tracer concentration in blood supplying the organ. For liver studies, however, inaccessibility of the portal vein makes direct measurement of the hepatic dual-input function impossible in humans. We want to develop a method to predict the portal venous time-activity curve from measurements of an arterial time-activity curve. An impulse-response function based on a continuous distribution of washout constants is developed and validated for the gut. Experiments with simultaneous blood sampling in aorta and portal vein were made in 13 anesthetized pigs following inhalation of intravascular [O-15] CO or injections of diffusible 3-O[ C-11] methylglucose (MG). The parameters of the impulse-response function have a physiological interpretation in terms of the distribution of washout constants and are mathematically equivalent to the mean transit time ( T) and standard deviation of transit times. The results include estimates of mean transit times from the aorta to the portal vein in pigs: (T) over bar = 0.35 +/- 0.05 min for CO and 1.7 +/- 0.1 min for MG. The prediction of the portal venous time-activity curve benefits from constraining the regression fits by parameters estimated independently. This is strong evidence for the physiological relevance of the impulse-response function, which includes asymptotically, and thereby justifies kinetically, a useful and simple power law. Similarity between our parameter estimates in pigs and parameter estimates in normal humans suggests that the proposed model can be adapted for use in humans.

Mean anisotropy of homogeneous Gaussian random fields and anisotropic norms of linear translation-invariant operators on multidimensional integer lattices

Sensitivity of output of a linear operator to its input can be quantified in various ways. In Control Theory, the input is usually interpreted as disturbance and the output is to be minimized in some sense. In stochastic worst-case design settings, the disturbance is considered random with imprecisely known probability distribution. The prior set of probability measures can be chosen so as to quantify how far the disturbance deviates from the white-noise hypothesis of Linear Quadratic Gaussian control. Such deviation can be measured by the minimal Kullback-Leibler informational divergence from the Gaussian distributions with zero mean and scalar covariance matrices. The resulting anisotropy functional is defined for finite power random vectors. Originally, anisotropy was introduced for directionally generic random vectors as the relative entropy of the normalized vector with respect to the uniform distribution on the unit sphere. The associated a-anisotropic norm of a matrix is then its maximum root mean square or average energy gain with respect to finite power or directionally generic inputs whose anisotropy is bounded above by a≥0. We give a systematic comparison of the anisotropy functionals and the associated norms. These are considered for unboundedly growing fragments of homogeneous Gaussian random fields on multidimensional integer lattice to yield mean anisotropy. Correspondingly, the anisotropic norms of finite matrices are extended to bounded linear translation invariant operators over such fields.

Discrete element modelling of power draw of tumbling mills

The power required to operate large mills is typically 5-10 MW. Hence, optimisation of power consumption will have a significant impact on overall economic performance and environmental impact. Power draw modelling results using the discrete element code PFC3D have been compared with results derived from the widely used empirical Model of Morrell. This is achieved by calculating the power draw for a range of operating conditions for constant mill size and fill factor using two modelling approaches. fThe discrete element modelling results show that, apart from density, selection of the appropriate material damping ratio is critical for the accuracy of modelling of the mill power draw. The relative insensitivity of the power draw to the material stiffness allows selection of moderate stiffness values, which result in acceptable computation time. The results obtained confirm that modelling of the power draw for a vertical slice of the mill, of thickness 20% of the mill length, is a reliable substitute for modelling the full mill. The power draw predictions from PFC3D show good agreement with those obtained using the empirical model. Due to its inherent flexibility, power draw modelling using PFC3D appears to be a viable and attractive alternative to empirical models where necessary code and computer power are available.

Low input tillage/cropping systems for limited resource areas

Agriculture in limited resource areas is characterized by small farms which an generally too small to adequately support the needs of an average farm family. The farming operation can be described as a low input cropping system with the main energy source being manual labor, draught animals and in some areas hand tractors. These farming systems are the most important contributor to the national economy of many developing countries. The role of tillage is similar in dryland agricultural systems in both the high input (HICS) and low input cropping systems (LICS), however, wet cultivation or puddling is unique to lowland rice-based systems in low input cropping systems. Evidence suggest that tillage may result in marginal increases in crop yield in the short term, however, in the longer term it may be neutral or give rise to yield decreases associated with soil structural degradation. On marginal soils, tillage may be required to prepare suitable seedbeds or to release adequate Nitrogen through mineralization, but in the longer term, however, tillage reduces soil organic matter content, increases soil erodibility and the emission of greenhouse gases. Tillage in low input cropping systems involves a very large proportion of the population and any changes: in current practices such as increased mechanization will have a large social impact such as increased unemployment and increasing feminization of poverty, as mechanization may actually reduce jobs for women. Rapid mechanization is likely to result in failures, but slower change, accompanied by measures to provide alternative rural employment, might be beneficial. Agriculture in limited resource areas must produce the food and fiber needs of their community, and its future depends on the development of sustainable tillage/cropping systems that are suitable for the soil and climatic conditions. These should be based on sound biophysical principles and meet the needs of and he acceptable to the farming communities. Some of the principle requirements for a sustainable system includes the maintenance of soil health, an increase in the rain water use efficiency of the system, increased use of fertilizer and the prevention of erosion. The maintenance of crop residues on the surface is paramount for meeting these requirements, and the competing use of crop residues must be met from other sources. These requirements can be met within a zonal tillage system combined with suitable agroforestry, which will reduce the need for crop residues. It is, however, essential that farmers participate in the development of any new technologies to ensure adoption of the new system. (C) 2001 Elsevier Science B.V. All rights reserved.

An advanced method for eliminating impacts from frequency deviations in power system signal processing

Frequency deviation is a common problem for power system signal processing. Many power system measurements are carried out in a fixed sampling rate assuming the system operates in its nominal frequency (50 or 60 Hz). However, the actual frequency may deviate from the normal value from time to time due to various reasons such as disturbances and subsequent system transients. Measurement of signals based on a fixed sampling rate may introduce errors under such situations. In order to achieve high precision signal measurement appropriate algorithms need to be employed to reduce the impact from frequency deviation in the power system data acquisition process. This paper proposes an advanced algorithm to enhance Fourier transform for power system signal processing. The algorithm is able to effectively correct frequency deviation under fixed sampling rate. Accurate measurement of power system signals is essential for the secure and reliable operation of power systems. The algorithm is readily applicable to such occasions where signal processing is affected by frequency deviation. Both mathematical proof and numerical simulation are given in this paper to illustrate robustness and effectiveness of the proposed algorithm. Crown Copyright (C) 2003 Published by Elsevier Science B.V. All rights reserved.

Translating policy: Power and action in Australia's country towns

Controversies In its present condition, rural Australia is characterised by a discourse of decline that sees country towns and regions as places of demoralisation and despair. From a Foucauldian governmentality perspective, those who live in these spaces are not so much 'powerless' to the demands of urban-based governments and global capital, as rendered governable according to the socio-political ambitions of late capitalism. While important insights have been derived from such analyses, it is argued in this paper that excessive attention is often paid to the power of the state with little concern for the various ways in which local people engage with, and transform the strategies and effects of state power. Rather than utilising the concept of resistance to make sense of these interactions, a sociology of translation is adopted from the Actor Network Theory literature. Applied to two case examples, it shows how governmental policies and programmes are frequently the outcome of the interactions and negotiations that take place between all those enrolled in the actor-network.

O treaty-making power na Constituição brasileira de 1988: uma análise comparativa do poder de celebrar tratados à luz da dinâmica das relações internacionais

O presente trabalho teve por objetivo estudar o modo pelo qual a Constituição brasileira de 1988 disciplina a competência dos poderes constituídos para a celebração de tratados. Buscou-se analisar, dessa forma, o relacionamento dos poderes Legislativo e Executivo no que tange ao procedimento de celebração de tratados internacionais.

Brazil: an emerging military power? The problem of the use of force in Brazilian international relations in the 21st century

The central goal of this paper is thinking about the Brazilian military power and its linking to the international ambitions of the country in the 21st century. After a comparative analysis to other BRICs and with a historical one about Brazil's strategic irrelevance, we aim to establish what the minimum military capacity Brazil would need in order to meet the country's latest international interests. Similarly, it will be discussed if the National Strategy of Defense, approved in 2008, and the recent strategic agreements signed with France represent one more step toward this minimum military capacity.

A harder edge: reframing Brazil's power relation with Africa

Brazil's rapprochement with Africa during the last decade has been mostly explained as an attempt to improve political dialogue, raise economic interactions, and provide technical cooperation assistance. This article, however, argues that such framework does not sufficiently account for the use of Brazilian material resources in order to attain harder strategic goals towards the continent. By focusing on defense cooperation ties, it highlights an important niche in South-South relations that has also grown exponentially, with important consequences on how Brazil exerts power across the Atlantic.

Rio Branco, grand strategy and naval power

This article addresses Baron of Rio Branco's grand strategy and the role played by the naval reorganization program (1904-1910) in this context. The ensuing case study determined the domestic and international constraints that affected the program, as well as the worldview of the patron of Brazilian diplomacy regarding military power's instrumentality to foreign policy.

Swords into ploughshares? China's Soft Power strategy in Southeast Asia and its challenges1

Since the 1990s, alongside China's economic growth, the international community has fostered a general anxiety towards a "China threat." In order to relieve itself from suspicion, China adopted the dual strategies of "harmonious worldview" and "good neighbor policy." The strategies led to the use of soft power in China's foreign policy. China aimed to reduce security concerns implied by the threat theory by supporting an image that caters to international peace and development. This article seeks to explain how China achieves its interests in Southeast Asia through the use of soft power. The authors address the concepts of "harmonious worldview" and "good neighbor policy" and how the twin strategies and soft power have shaped China's foreign policy in recent years. This article aims to provide insights into China's policy options in Southeast Asia in the near future.

China's rising Soft Power: the role of rhetoric in constructing China-Africa relations

As China turns increasingly to the cultivation of soft power in the course of developing its foreign policy, the use of political rhetoric and its explicit and implicit audiences become more and more important, both on a bilateral level and within the international arena at large. Using the case of China's relations with African countries, this article examines key themes within China's diplomatic narrative regarding its role on the African continent and contrasts with Western and African responses.