224,673 research outputs found

    Current screens

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    The architecture of screen design, including LCD, LED and DLP projection, is analysed in terms of the political economy and their aesthetics and phenomenological impacts, in association with the use of codecs as constraining as well as enabling tools in the control and management of visual data transmission

    Progress in leptonic and semileptonic decays in lattice QCD

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    The status of lattice calculations of heavy quark phenomenology is reviewed. Particular emphasis is placed on the understanding and control of the calculational uncertainties. The ensuing implications for constraining the CKM matrix elements are discussed.Comment: 7 pages, talk given at DPF'99 Conference, Jan. 5-9 1999, Los Angeles, C

    A Robust Consensus Algorithm for Current Sharing and Voltage Regulation in DC Microgrids

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    In this paper a novel distributed control algorithm for current sharing and voltage regulation in Direct Current (DC) microgrids is proposed. The DC microgrid is composed of several Distributed Generation units (DGUs), including Buck converters and current loads. The considered model permits an arbitrary network topology and is affected by unknown load demand and modelling uncertainties. The proposed control strategy exploits a communication network to achieve proportional current sharing using a consensus-like algorithm. Voltage regulation is achieved by constraining the system to a suitable manifold. Two robust control strategies of Sliding Mode (SM) type are developed to reach the desired manifold in a finite time. The proposed control scheme is formally analyzed, proving the achievement of proportional current sharing, while guaranteeing that the weighted average voltage of the microgrid is identical to the weighted average of the voltage references.Comment: 12 page

    A Graph Theory Approach for Regional Controllability of Boolean Cellular Automata

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    Controllability is one of the central concepts of modern control theory that allows a good understanding of a system's behaviour. It consists in constraining a system to reach the desired state from an initial state within a given time interval. When the desired objective affects only a sub-region of the domain, the control is said to be regional. The purpose of this paper is to study a particular case of regional control using cellular automata models since they are spatially extended systems where spatial properties can be easily defined thanks to their intrinsic locality. We investigate the case of boundary controls on the target region using an original approach based on graph theory. Necessary and sufficient conditions are given based on the Hamiltonian Circuit and strongly connected component. The controls are obtained using a preimage approach

    Lunar Ascent and Orbit Injection via Neighboring Optimal Guidance and Constrained Attitude Control

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    Future human or robotic missions to the Moon will require efficient ascent path and accurate orbit injection maneuvers, because the dynamical conditions at injection affect the subsequent phases of spaceflight. This research focuses on the original combination of two techniques applied to lunar ascent modules, i.e., (1) the recently introduced variable-time-domain neighboring optimal guidance (VTD-NOG), and (2) a constrained proportional-derivative (CPD) attitude control algorithm. VTD-NOG belongs to the class of feedback implicit guidance approaches aimed at finding the corrective control actions capable of maintaining the spacecraft sufficiently close to the reference trajectory. CPD pursues the desired attitude using thrust vector control while constraining the rate of the thrust deflection angle. The numerical results unequivocally demonstrate that the joint use of VTD-NOG and CPD represents an accurate and effective methodology for guidance and control of lunar ascent path and orbit injection in the presence of nonnominal flight conditions

    Controllability of structural brain networks.

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    Cognitive function is driven by dynamic interactions between large-scale neural circuits or networks, enabling behaviour. However, fundamental principles constraining these dynamic network processes have remained elusive. Here we use tools from control and network theories to offer a mechanistic explanation for how the brain moves between cognitive states drawn from the network organization of white matter microstructure. Our results suggest that densely connected areas, particularly in the default mode system, facilitate the movement of the brain to many easily reachable states. Weakly connected areas, particularly in cognitive control systems, facilitate the movement of the brain to difficult-to-reach states. Areas located on the boundary between network communities, particularly in attentional control systems, facilitate the integration or segregation of diverse cognitive systems. Our results suggest that structural network differences between cognitive circuits dictate their distinct roles in controlling trajectories of brain network function

    Constraining Public Employee Speech: Government’s Control of Its Workers’ Speech to Protect Its Own Expression

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    This Article identifies a key doctrinal shift in courts\u27 treatment Of public employees\u27 First Amendment claims-a shift that imperils the public\u27s interest in transparent government as well as the free speech rights of more than twenty million government workers. In the past, courts interpreted the First Amendment to permit governmental discipline of public employee speech on matters of public interest only when such speech undermined the government employer\u27s interest in efficiently providing public services. In contrast, courts now increasingly focus on-and defer to-government\u27s claim to control its workers\u27 expression to protect its own speech. More specifically, courts increasingly permit government to control its employees\u27 expression at work, characterizing this speech as the government\u27s own for which it has paid with a salary. This trend frustrates a meaningful commitment to republican government by allowing government officials to punish, and thus deter, whistleblowing and other valuable on-the-job speech that would otherwise facilitate the public\u27s ability to hold the government politically accountable for its choices. Courts also increasingly consider government workers to be speaking as employees even when away from work, deferring to the government\u27s assertion that its association with employees who engage in certain off-duty expression undermines its credibility in communicating its own contrary views. Implicit in courts\u27 reasoning is the premise that a public entity\u27s employment relationship with an individual who engages in certain expression communicates a substantive message to the public that the government is entitled to control. Courts\u27 unfettered deference to such claims would permit government agencies to fire workers for any unpopular or controversial off-duty speech to which the public might object, potentially enforcing orthodox expression as a condition of public employment. To be sure, government speech is as valuable as it is inevitable. But taken together, these trends lead to the rejection of government workers\u27 First Amendment claims in a growing number of cases that undermine workers\u27 free speech rights as well as the public\u27s interest in transparent government. Because of this shift\u27s normatively troubling implications, this Article proposes a new constitutional framework for public employee speech cases that attends more carefully to what it is that government seeks to communicate and whether that message is actually impaired by employee speech. It thus proposes a less deferential approach to assessing government\u27s expressive claims to its workers\u27 speech both on and off the job, exploring both categorical and contextual frameworks for identifying more precisely the comparatively small universe of workers\u27 speech that actually threatens government\u27s own expression
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