Operation, system architectures, and physical Layer design considerations of distributed MAC protocols for UWB

Impulse-based ultra wideband (I-UWB) is an attractive radio technology for large ad hoc and sensor networks due to its robustness to harmful multipath effects, sub-centimeter ranging ability, simple hardware, and low radiated power. To scale to large sizes, networks often implement distributed medium access control (MAC) protocols. However, most MAC protocols for I-UWB are centralized, and they target small wireless personal area networks and cellular networks. We propose three distributed MAC protocols suitable for I-UWB. Two multichannel protocols, called multichannel pulse sense multiple access (M-PSMA) and multichannel ALOHA achieve high aggregate throughput. A busy-signal protocol, called busy-signal multiple access (BSMA), reduces the energy wasted from re-transmitted packets. This paper describes the three protocols in terms of the protocol's operation, the supporting system architecture, and the I-UWB physical layer. Physical layer simulations confirm the feasibility of implementing the proposed systems and also provide parameters for network simulations. Network simulations show that the throughput of M-PSMA exceeds that of a centralized time-division multiple-access protocol and that the energy efficiency of BSMA far surpasses that of other distributed protocols.     

Proximity Detection – Schutzeinrichtung für Gefahrenzonen im Untertageberg- und Tunnelbau: Stand der Technik und Notwendigkeiten der Weiterentwicklung

The restricted space in underground work sites in mining and tunnelling always entails the potential of collisions between men and machinery. Despite work rules and safety training, accidents of this category are still too frequent and therefore technical safety systems to avoid such collisions have been asked for and developed. In the United States of America and South Africa a rising number of such proximity detection systems are in operation and allow a first review of the impact on safety of miners. This article presents the state of the art and based on the existing operational experience some of the necessary further developments in this field.     

Monies,economies and democracy: cultivating ambivalence in the co-design of digital currencies

ABSTRACT

Systematised collaborative design of complementary currencies is still a largely unexplored area that offers underutilised opportunities for supporting a fair and sustainable sharing economy. Future currency design necessitates attention to the systemic factors and the social particularities in which new monetary alternatives, i.e. ‘monies’, and the technological solutions that serve these alternatives, are created. This paper argues for a socially and contextually sensitive design of complementary currency innovation. It considers the technological conditions and the tendencies to exploitation from contemporary capitalism. Based on the literature review, we propose collaborative design of complementary currencies with particularist and inclusive approaches. New directions for open-ended economic innovation are explored in finding opportunities in the future-oriented Transition Design, supported by an empathic and ambivalent design mindset.     

“92.8”高含沙洪水在黄河下游演进特性分析

“92.8”洪水位异常高的主要原因:一是前期连续几年枯水,造成河床严重淤积;二是本场洪水边滩淤积,河道过水面积减小。花园口站洪峰流量大于上站的主要原因是:主槽强烈冲刷,水位大幅度下降,漫滩水迅速回归主槽。     

Multi-objective Topology Optimization of Thermo-mechanical Compliant Mechanisms

The material characteristics of a structure will change with temperature variation,and will induce stress within the structure.Currently,the optimal design for the topology of compliant mechanisms is mainly performed in single physical field.However,when compliant mechanisms work in high temperature environments,their displacement outputs are generated not only by mechanical load,but also by the temperature variation which may become the prominent factor.Therefore,the influence of temperature must be considered in the design.In this paper,a novel optimization method for multi-objective topology of thermo-mechanical compliant mechanisms is presented.First,the thermal field is analyzed with finite-element method,where the thermal strain is taken into account in the constitutive relation,and the equivalent nodal thermal load is derived with the principle of virtual work.Then the thermal load is converted into physical loads in elastic field,and the control equation of the thermo-mechanical compliant mechanism is obtained.Second,the mathematical model of the multi-objective topology optimization is built by incorporating both the flexibility and stiffness.Meanwhile,the coupling sensitivity function and the sensitivity analysis equations of thermal steady-state response are derived.Finally,optimality criteria algorithm is employed to obtain numerical solution of the multi-objective topology optimization.Numerical examples show that the compliant mechanisms have better performance and are more applicable if the temperature effect is taken into account in the design process.The presented modeling and analysis methods provide a new idea and an effective approach to topology optimization of compliant mechanisms in electrothermic coupling field and multiphysics fields.     

Regulatory Power,Network Tools and Market Behaviour: Transforming Practices in Norwegian Urban Planning

Planning changes can be initiated formally through revisions of statutory rules; alternatively changes can arise informally through amendments to everyday planning activities. This article explains how local planning authorities in Norway introduce new planning practices relating to the management of land and planning procedures. The observed new practices have been introduced even though the formal hierarchical structure of the planning law has stayed unchanged. They are analysed as outcomes of the changing use of tools under the three models for co-ordinating behaviour: hierarchy understood as government, market and network. First, the existing planning system is analysed to explain the legal possibilities for changing planning practices informally. Two categories of practices are then discussed: the use of the detailed development plan as an implementation instrument, and the use of the regulatory power in framing interconnections and responsibilities towards stakeholders. The main conclusion is that regulatory tools have lost some strength in favour of tools under the network model, and that the observed changes in planning practices are mostly a result of mutual dependencies between these two models for co-ordinating behaviour.     

The intriguing role of spanish language vocabulary knowledge in predicting English reading comprehension.

This study explored a holistic model of English reading comprehension among a sample of 135 Spanish-English bilingual Latina and Latino 4th-grade students This model took into account Spanish language reading skills and language of initial literacy instruction. Controlling for language of instruction, English decoding skill, and English oral language proficiency, the authors explored the effects of Spanish language alphabetic knowledge, fluency, vocabulary knowledge, and listening comprehension on English reading comprehension. Results revealed a significant main effect for Spanish vocabulary knowledge and an interaction between Spanish vocabulary and English fluency, such that faster English readers benefited more from Spanish vocabulary knowledge than their less fluent counterparts. This study demonstrates the existence of literary skills transfer from the 1st to the 2nd language, as well as limits on such transfer. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Katalytischer wasserstoff-/sauerstoff-rekombinator mit selbstbegrenzung

Lead-acid cells evolve hydrogen and oxygen gasses during the charging mode, which results in a water loss. Gas recombination devices extend the water refilling periods due to the recombination reactionH₂ + $\text{1}\text{2}$O₂ → H₂O The recombination devices consist of: aerosol retainer, charcoal filter, catalyst, condenser, gas storage and vents. Theoretical models describing the self-limiting behaviour of the catalyst and the heat flow conditions in the device were developed.Design specifications of component requirements for a 435-W recombination device, which is capable of recombining 182 l/h stoichiometric oxyhydrogen gas, were also developed. Tests with the system (recombination device-lead-acid cell) showed that a maintenance-free and nearly gastight operation was achieved. The use of catalytic recombination devices improves the economy and safety of battery operation.