Semaphore Concept Research Articles

Landscape semaphore: Seeing mud and mangroves in the Brazilian Northeast

This paper explores how the amphibious landscapes of mangroves and mudflats of Northeast Brazil have been seen and re‐seen. The spatial and political ecologies of mangroves and mud interact with political aesthetics in specific ways. Reading landscapes as aesthetic encounters] with nature means recognising that ways of seeing are as historically and geographically specific as what they represent and produce. Thinking through the history of landscape from the Northeast exposes the coloniality of landscape thought but can also show how landscape has been reinvented and reconceptualised. Using Marilena Chauí’s concept of semaphore, we can place landscape's symbolic force within the colonial encounter. This opens up not only the intellectual history of how geographers use landscape, but the relationship between aesthetics and nature, and between perception and territory, in a specific place. Putting these creative and intellectual practices together can draw out the rich specificity of responses to a singular, changing landscape, and multiply geographical ways of interpreting, representing, and conceptualising landscape. Seeing amphibiously allows us to revel in landscape’s flexibility and stickiness. In this paper I pursue this argument through an analysis of cultural representations of the coastal landscape of the Brazilian Northeast. The Northeast’s place within the emergence of European landscape histories reminds us of the under‐emphasised coloniality of landscape. More importantly, in 20th‐century representations of the territory of the estuarine Atlantic coast we find a re‐calibration of perspective that is foreshortened, embodied, and muddied. They unsettle the fixities of colonial ways of seeing space, nature, and territory and amount to a regionally specific, counter‐hegemonic political aesthetics of nature.

Semaphore Based Data Aggregation and Similarity Findings for Underwater Wireless Sensor Networks

A critical factor of underwater sensor networks (UWSN) is to maintain energy consumption at minimum, as immediate battery replacement is difficult. This is achieved by reducing duplication of data with similarity functions. The construction of optimal clustering is to avoid data loss. In this article, similarity function-based data aggregation with a Semaphore process is applied to UWSN to retain the energy level at an advantage. Sensor nodes (SNs) are clustered in a Date Palm Tree approach. The Minkowski Distance model is used in Data Aggregation Nodes (DANs) to check similar measures of readings collected from cluster members. The Semaphore concept is executed in all DANs and cluster heads (CHs) to enhance network life and regulate excessive exploitation of energy levels of the SN, DANs, and CHs. The message queue (MQ) can be used to allow the packets transferred from the DANs to the cluster heads (CHs). The proposed algorithm SBDA with similarity measures would result in better link quality, reduction in redundancy, data delay, and would control the consumption of energy.

Real-Time Reconfigurations of Embedded Control Systems

This paper deals with the study of the reconfiguration of embedded control systems with safety following component-based approaches from the functional level to the operational level. The authors define the architecture of the Reconfiguration Agent which is modelled by nested state machines to apply local reconfigurations. They propose in this journal paper technical solutions to implement the whole agent-based architecture, by defining UML meta-models for both Control Components and also agents. To guarantee safety reconfigurations of tasks at run-time, they define service and reconfiguration processes for tasks and use the semaphore concept to ensure safety mutual exclusions. As a method to ensure the scheduling between periodic tasks with precedence and mutual exclusion constraints, the authors apply the priority ceiling protocol.

Efficient implementation of semaphores in controller area networks

Synchronization of concurrent activities by means of semaphores is widely adopted in industrial distributed systems. This paper presents some mechanisms which facilitate the efficient implementation of the popular semaphore concept in real-time networks based on the controller area network medium access technique. The advantages obtained by adopting the proposed solution are twofold. First, better performance can be obtained because most of the semaphore management mechanisms are moved from the application to the physical and data-link communication layers. Second, a fully distributed management scheme is implemented, and there is no need to place the semaphore control structures on a particular node in the network.

Semaphores revisited with MMS

The objective of this article is to realize an in-depth study of MMS semaphores. This article is not a tutorial on MMS semaphores although it does explain to some extent how MMS semaphores behave and can be utilized. What we are trying to achieve is a definitive clarification of the MMS semaphore concept in order to make its use easier to MMS programmers and to encourage its adoption in the industrial applications and products. We compare MMS semaphores to Dijkstra's classical semaphores and show that real differences exist. Other mechanisms are also discussed (monitors, CSP). Examples are provided to illustrate our analysis and references to the semaphore mechanism of some operating systems are given to ease the comparison. We come to the conclusion that MMS semaphores are flexible but cannot be utilized to solve all kinds of problems classical semaphores usually cope with. We also explain why the two kinds of semaphores provided by MMS are redundant.

Towards a derivational style of distributed system design ? An example

Rederivation of the train signalling protocol developed in the 19th century is used to illustrate the application of several formal techniques to assist in the derivation of an implementation of a simple distributed system from its specification. It was this train signalling protocol that gave rise to the now-familiar concept ofsemaphore. However, a study of the train system shows that there is much more to its protocol than simply the instantiation of the semaphore concept. The derivation makes use of several formal techniques including weakest precondition calculation, finite differencing, generalization, and weakening of invariants. Informal reasoning is used to treat concerns of availability of information, and availability of control. Opportunities for inserting additional robustness into the derived implementation are identified during the process. The objective is to demonstrate the degree to which an implementation can bederived, rather than merely verified after some unknown invention process.

A general purpose computer emulator

The emulator is organized as a set of four asynchronous units which carry out specific functions and which can work in a concurrent form. This units are: The Master Control, the Instruction Management, the Memory and the Data Management. The master control distributes the jobs that each unit should accomplish. The processor communication system is based in the Dijkstra's binary semaphore concept. In order to simplify the microinterpreters construction, the emulator has the following features: 1) A flexible and reformable structure with a variable length of processing; 2) A decoding and field e x traction mechanism for the instructions, based on an associative memory, a barrel shifter and a mask circuit; 3) A microin s truction set with a high-level semantic.

On a solution to the cigarette smoker's problem (without conditional statements)

This report discusses a problem first introduced by Patil, who has claimed that the cigarette smoker's problem cannot be solved using the P and V operations introduced by Dijkstra unless conditional statements are used. An examination of Patil's proof shows that he has established this claim only under strong restrictions on the use of P and V . These restrictions eliminate programming techniques used by Dijkstra and others since the first introduction of the semaphore concept. This paper contains a solution to the problem. It also discusses the need for the generalized operators suggested by Patil.