Information versus Communication in Course Management System participation

Web resources in Latin American higher education institutions have been reported to show a much stronger emphasis on Information than on Communication. A Course Management System (CMS), according to Social Constructivism framework, is an opportunity for fostering learning through interaction in a virtual environment for learning; hence, stimulating the use of a CMS for communication purposes seems quite appropriate. A quantitative analysis of 63.06% of the virtual classrooms was conducted, using the users log database to describe five variables: Participation, Informational Interaction Level, Communicational Interaction Level, and the use of Informational Resources and Communicational Resources in the CMS. An assessment of the first 2 years of implementation of Moodle in a campus confirmed prominence levels of interaction and resources that favor Information over Communication purposes in the use of the CMS. It is not conclusive whether this necessarily implies more or better learning; a profound qualitative study would be needed to answer these questions. Teachers and students show different behaviors in the face of this new ICT campus resource, while faculty members appear to have behaved in an erratic manner, students show steady levels of CMS usage.     

Empowerment: An ideal long-term goal: But what about now?

Comments on the article by H. Amaro (see record 1995-34352-001) regarding the problem of women's risk for HIV infection. The authors argue that Amaro's article has a major shortcoming in the argument that rather than focusing on current realities, long-term ideal solutions are emphasized. The authors believe that empowerment-based solutions contradict the current realities of many dyadic relationships. The authors found that dyadic sociocultural issues in both college students and adolescents are far too complex to be framed in terms of the individualistic change models cited by Amaro. The authors agree that empowerment may be the ideal ultimate solution, but that a more immediate strategy is also necessary. Thus, they advocate focusing on the woman's right to protect herself against HIV infection and pregnancy by methods that would not require the knowledge nor the consent of her partner. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Water governance, resilience and global environmental change - a reassessment of integrated water resources management (IWRM).

Integrated Water Resource Management (IWRM) is gaining increased acceptance among water policy makers and researchers as a way to create more effective governance institutions, leading towards integrated water development solutions for poverty alleviation, while addressing social, economic and environmental aspects of water challenges. However, global environmental change poses fundamental challenges to water policy makers as it implies vast scientific, and hence, policy uncertainty; its implications for international water governance initiatives remain unspecified, effectively hindering dialogue on how current IWRM initiatives should be modified. This paper addresses the lag between our growing understanding of resilient interconnected freshwater resources (and their governance) and the reforms being promoted by policy makers. In particular, there is a need to rethink some of IWRM's key components to better tackle the challenges posed by the complex behaviour of interconnected social-ecological systems and global environmental change.     

On parameter estimation for excitation control of synchronous generators

This paper deals with the problem of identification of the network parameters and the desired equilibrium in applications of excitation control for synchronous generators. Our main contribution is the construction of a new non‐linear identifier that provides asymptotically consistent estimates (with guaranteed transient bounds) of the line impedance and the equilibrium for the classical three‐dimensional flux‐decay model of a single generator connected to an infinite bus. This model is non‐linear, and non‐linearly parameterized, and the equilibria depend also non‐linearly on the unknown parameters. The proposed estimator can be used, adopting a certainty equivalent approach, to make adaptive any power system stabilizer that relies on the knowledge of these parameters. The behaviour of the scheme is illustrated in two simulated case studies with the interconnection and damping assignment passivity‐based controller recently proposed by the authors. Copyright © 2004 John Wiley & Sons, Ltd.     

Spatially adaptive subsampling of image sequences

In a spatially adaptive subsampling scheme, the subsampling lattice is adapted to the local spatial frequency content of an image sequence. In this paper, we use rate-distortion theory to show that spatially adaptive subsampling gives a better performance than subsampling with a fixed sampling lattice. A new algorithm that optimally assigns sampling lattices to different parts of the image is presented. The proposed spatially adaptive subsampling method can be applied within a motion-compensated coding scheme as well. Experiments show an increased performance over fixed lattice subsampling.     

An energy-shaping approach to the design of excitation control of synchronous generators

In this paper we discuss the estimation of the domain of attraction of equilibria in power systems and propose a new passivity-based controller design methodology for excitation control of synchronous generators. The methodology goes beyond the widely popular damping injection (L_gV) schemes, to actually shape the total energy function via modification of the energy transfer between the mechanical and electrical components of the system. Applying the procedure it is shown that a, properly tuned, linear state feedback enlarges both the estimates and the actual domain of attraction, thus increasing critical clearing time for faults. This is illustrated in two case studies, including a benchmark comparison with the classical control scheme.     

Transient stabilization of multimachine power systems with nontrivial transfer conductances

We provide a solution to the long-standing problem of transient stabilization of multimachine power systems with nonnegligible transfer conductances. More specifically, we consider the full 3n-dimensional model of the n-generator system with lossy transmission lines and loads and prove the existence of a nonlinear static state feedback law for the generator excitation field that ensures asymptotic stability of the operating point with a well-defined estimate of the domain of attraction provided by a bona fide Lyapunov function. To design the control law we apply the recently introduced interconnection and damping assignment passivity-based control methodology that endows the closed-loop system with a port-controlled Hamiltonian structure with desired total energy function. The latter consists of terms akin to kinetic and potential energies, thus has a clear physical interpretation. Our derivations underscore the deleterious effects of resistive elements which, as is well known, hamper the assignment of simple "gradient" energy functions and compel us to include nonstandard cross terms. A key step in the construction is the modification of the energy transfer between the electrical and the mechanical parts of the system which is obtained via the introduction of state-modulated interconnections that play the role of multipliers in classical passivity theory.     

Perfluorooctyl Bromide Polymeric Capsules as Dual Contrast Agents for Ultrasonography and Magnetic Resonance Imaging

Polymeric capsules with a thick shell made of biodegradable and biocompatible polymer and a liquid core of perfluorooctyl bromide (PFOB) were evaluated for stability as well as for ultrasound and magnetic resonance imaging (MRI) contrast enhancement. The method of preparation allows the mean capsule diameter to be regulated between 70 nm and 25 µm and the capsule thickness‐to‐radius ratio from 0.25 to 0.54. Capsule diameter remains stable at 37 °C in phosphate buffer for at least 4 and 6 h for nanocapsules and microcapsules, respectively. The in vitro ultrasound signal‐to‐noise ratio (SNR) was measured from 40 to 60 MHz for 6 µm and 150 nm capsules: the SNR increases with capsule concentration up to 20–25 mg mL⁻¹, and then reaches a plateau that depends on capsule diameter (13.5 ± 1.5 dB for 6 µm and 6 ± 2 dB for the 150 nm capsules). The ultrasound SNR is stable for up to 20 min for microcapsules and for several hours for nanocapsules. For nanocapsules, the thinner the shell, the larger the SNR and the more compressible the capsules. Nanocapsule suspensions imaged in vitro with a commercial ultrasound imaging system (normal and tissue harmonic imaging modes, 7–14 MHz probe) were detected down to concentrations of 12.5 mg mL⁻¹. Injections of nanocapsules (200 µg ml⁻¹) in mice in vivo reveal that the initial bolus passage presents significant ultrasound enhancement of the blood pool during hepatic imaging (7–14 MHz probe, tissue harmonic imaging mode). ¹⁹F‐MRI images were obtained in vitro at 9.4T using spin‐echo and gradient echo sequences and allow detecting nanocapsules in suspension (50 mg mL⁻¹). In conclusion, these results show initial feasibility for development of these capsules toward a dual‐modality contrast agent.     

Correlations Among Neutron Yield and Dynamical Discharge Characteristics Obtained from Electrical Signals in a 400?J Plasma Focus

Dynamical discharge characteristics and their relation with the total neutron yield emitted from a 400 J plasma focus operating in deuterium gas are presented. The dynamical nature of the plasma focus is obtained merely from the analysis of the voltage and current electrical signals without considering any particular geometry for the plasma sheath. It is calculated that large neutron yields are obtained when plasma inductance, mechanical energy and plasma voltage at pinching time have larger values. In contrast, no correlations are found among neutron yields either with plasma propagation velocities or quantities at the beginning of the radial phase. There is also found that the current sheath geometry changes according to the gas pressure, having larger curvature for lower pressures. The calculations also provide estimations of sheath thicknesses at the detachment from the insulator in the range of 0.5–1 mm, being thicker for larger neutron yield.