Self-oscillations in field emission nanowire mechanical resonators: a nanometric DC-AC conversion

We report the observation of self-oscillations in a bottom-up nanoelectromechanical system (NEMS) during field emission driven by a constant applied voltage. An electromechanical model is explored that explains the phenomenon and that can be directly used to develop integrated devices. In this first study we have already achieved ~50% DC/AC (direct to alternative current) conversion. Electrical self-oscillations in NEMS open up a new path for the development of high speed, autonomous nanoresonators, and signal generators and show that field emission (FE) is a powerful tool for building new nano-components

Towards the Development of a Model of Vision: An Investigation into the Architectures and Mechanisms of Visual Perception

A conceptual model of visual perception has been developed using a multidisciplinary approach which combines both top-down and bottom-up descriptions of vision. Top-down psychological theories of visual perception have been investigated resulting in the development of a theory of perception which combines the best of existing accounts. Perception is defined in terms of a combination of "data driven" and "concept driven" explanations. Bottom-up neurophysiological descriptions have also been investigated to provide possible descriptions of structure and function for the development of a conceptual model based upon the theory. An attempt is made to provide a "complete" account of visual perception through the development of both the theory and conceptual model. Further it is envisaged that the development of such a model will provide new insight into the development of artificial vision systems and new algorithms for perceptual function in such systems

Open access - the rise and fall of a community-driven model of scientific communication

International audience•In 25 years, open access, i.e. free and unrestricted access to scientific information, has become a significant part of scientific communication. However, its success story should not conceal a fundamental change of its nature.•Open access started, together with the Web, at the grassroots, as a bottom-up, community-driven model of open journals and repositories. Today the key driving forces are no longer community-driven needs and objectives but commercial, institutional and political interests.•This development serves the needs of the scientific community insofar as more and more content becomes available through open journals and repositories. Yet, the fall of open access as a community-driven model is running the risk of becoming dysfunctional for the scientists and may create new barriers and digital divides

Building stock dynamics and its impacts on materials and energy demand in China

China hosts a large amount of building stocks, which is nearly 50 billion square meters. Moreover, annual new construction is growing fast, representing half of the world's total. The trend is expected to continue through the year 2050. Impressive demand for new residential and commercial construction, relative shorter average building lifetime, and higher material intensities have driven massive domestic production of energy intensive building materials such as cement and steel. This paper developed a bottom-up building stock turnover model to project the growths, retrofits and retirements of China's residential and commercial building floor space from 2010 to 2050. It also applied typical material intensities and energy intensities to estimate building materials demand and energy consumed to produce these building materials. By conducting scenario analyses of building lifetime, it identified significant potentials of building materials and energy demand conservation. This study underscored the importance of addressing building material efficiency, improving building lifetime and quality, and promoting compact urban development to reduce energy and environment consequences in China

Ambiguity and Conflict in Policy Implementation: The Case of the New Care Models (Vanguard) Programme in England

Policy driven change is challenging, with a significant gap between theory and practice. A key tension in enacting such change is achieving a balance between bottom-up development of local, context-specific approaches, and top-down, centrally determined policy solutions and their mutual sequencing. Ideal type models of the policy-making process envisage a rational ordered approach, driven by evidence and accompanied by ongoing evaluation of outcomes (Parsons, 1995, p77); however, the reality is far more complex. We examine the implementation and early operation of the New Care Models (NCM) Vanguard programme in England, using Matland’s (1995) ambiguity-conflict model, to explore the aims and expectations of the programme. We consider the relationship between top-down and bottom-up approaches to policy development and draw attention to the pressures coming from what was initially perceived as a permissive policy approach of encouraging experimentation, whilst also requiring rapid learning, scale and spread. We suggest that future programmes for large-scale policy implementation initiatives could be crafted differently to take account of the environment of implementation and render ambitions more realistic. Rather than aiming to create a set of definite products and templates, it may be that a set of principles for design and implementation should be developed and spread

The effectiveness of the United Nations\u27 use of communication to achieve development results: a genuine shift from top-down to bottom-up development approach? a case study from Egypt

This thesis focuses on â communication for development\u27 concepts and initiatives, in an attempt to, first, investigate the limits of the UN\u27s perceived shift from a top-down to a bottom-up development approach, and secondly, to evaluate the degree and extent of the effectiveness of its communication efforts to achieve development results. The main hypothesis is that communication, as a tool used to achieve development objectives, remains vastly underutilized within the UN system, partly owing to the lack of adopting a genuine people-centred, bottom-up approach in favour of top-down global strategies. The thesis first embarks on a review of the evolution of development approaches, with a focus on the role of the UN, followed by an analysis of different schools of â communication for development\u27, exploring the influence of the historical shift in global development thinking and the UN\u27s role in this field. The thesis then tackles a case study from the United Nations Development Programme in Egypt to investigate the degree to which such initiatives are community-driven versus corporate-dictated. Project evaluation analysis and a series of independent focus groups with target beneficiaries suggest that UNDP\u27s communication focus at the corporate level remains largely driven by a top-down diffusion model for the purpose of increasing its delivery of development aid and prospect mobilized resources. Based on the research findings, the thesis concludes with a proposed alternative framework for implementation at the project level to balance off this corporate top-down influence with more effective and measurable communication initiatives that promote participatory activities stemming from the community and serving their genuine development objectives

Field-driven dynamics of nematic microcapillaries

Polymer-dispersed liquid crystal (PDLC) composites have long been a focus of study for their unique electro-optical properties which have resulted in various applications such as switchable (transparent/translucent) windows. These composites are manufactured using desirable "bottom-up" techniques, such as phase separation of a liquid crystal/polymer mixture, which enable production of PDLC films at very large scales. LC domains within PDLCs are typically spheroidal, as opposed to rectangular for an LCD panel, and thus exhibit substantially different behaviour in the presence of an external field. The fundamental difference between spheroidal and rectangular nematic domains is that the former results in the presence of nanoscale orientational defects in LC order while the latter does not. Progress in the development and optimization of PDLC electro-optical properties has progressed at a relatively slow pace due to this increased complexity. In this work, continuum simulations are performed in order to capture the complex formation and electric field-driven switching dynamics of approximations of PDLC domains. Using a simplified elliptic cylinder (microcapillary) geometry as an approximation of spheroidal PDLC domains, the effects of geometry (aspect ratio), surface anchoring, and external field strength are studied through the use of the Landau--de Gennes model of the nematic LC phase.Comment: 22 pages, 9 figures, Physical Review