Unreachable Destinations Research Articles

Enhanced Multi-UAV Formation Control and Obstacle Avoidance Using IAAPF-SMC

In response to safety concerns pertaining to multi-UAV formation flights, a novel obstacle avoidance method based on an Improved Adaptive Artificial Potential field (IAAPF) is presented. This approach enhances UAV obstacle avoidance capabilities by utilizing segmented attraction potential fields refined with adaptive factors and augmented with virtual forces for inter-UAV collision avoidance. To further enhance the control and stability of multi-UAV formations, a Sliding Mode Control (SMC) method is integrated into the IAAPF-based obstacle avoidance framework. Renowned for its robustness and ability to handle system uncertainties and disturbances, the SMC method is combined with a feedback control system that utilizes inner and outer loops. The outer loop generates the desired path based on the leader’s state and control commands, while the inner loop tracks these trajectories and adjusts the follower UAVs’ motions. This design ensures that obstacle feedback is accounted for before the desired state information is received, enabling effective obstacle avoidance while maintaining formation integrity. Integrating leader-follower formation control techniques with SMC-based multi-UAV obstacle avoidance strategies ensures the effective convergence of the formation velocity and spacing to predetermined values, meeting the cooperative obstacle avoidance requirements of multi-UAV formations. Simulation results validate the efficacy of the proposed method in reaching otherwise unreachable destinations within obstacle-rich environments, while ensuring robust collision avoidance among UAVs.

STALB: A Spatio-Temporal Domain Autonomous Load Balancing Routing Protocol

Due to vehicle mobility, the topology of Vehicle Ad-hoc Networks (VANETs) may change dynamically. High mobility, limited bandwidth, and dynamic network topology pose challenges for communication in the Internet of Vehicles (IoVs). Literature works have attempted to promote efficient (e.g., lower end-to-end latency) message forwarding. However, due to the uncertain direction of message forwarding and vehicle mobility, they suffer from unreachable destinations and unstable connections. This paper explores the efficient method of message forwarding to alleviate network congestion in IoVs. We propose a Spatio-Temporal domain Autonomous Load Balancing (STALB) routing protocol. Specifically, STALB is a trajectory-based method for controlling the direction of message forwarding. STALB can significantly reduce the end-to-end latency and overload ratio, since it considers the local status of network relay devices (i.e., buffer score, congestion status) from the spatio-temporal domain. Then, we present a path reconstruction mechanism, which ensures that messages are forwarded to destinations within limited Time-To-live (TTL). Extensive simulation results show that STALB significantly outperforms other baseline methods (BSaW, TDOR, and TBHGR) regarding overhead ratio, average delivery latency, and average buffer time. Especially, the delivery rate of STALB can reach 99.9% under the sparse network scenario (4,500 messages), at least 0.7% higher than other baseline methods. Similarly, the average delivery delay of STALB is at least 84.31% lower than that of other baseline methods under the dense network scenario (18,000 messages).

“The sky is the limit. So I just hope, one day, I will reach my destiny:” hope, uncertainty, and disillusionment among LGBTQ + migrants in South Africa

ABSTRACT This qualitative study utilized arts-based methods to explore how LGBTQ + migrants in South Africa reconcile their expectations with their post-migration realities. Twenty-six pictures, created by LGBTQ + migrants (ages 19-39), were analyzed with their accompanying narratives to document participants’ experiences. Thematic and narrative analyses starting with the sensitizing concepts of hope, uncertainty, and disillusionment yielded three themes: (a) Yearning for freedom and acceptance before and after migration; (b) Dealing with uncertainty, disillusionment, and the grim realities of being an LGBTQ + migrant; and (c) Retaining hope for the future amid pain and struggle. Feeling isolated, participants yearned for societal acceptance and freedom to be themselves. This motivated their migration, but once in South Africa, they faced many social-structural challenges and developed feelings of disillusionment. Still, several retained hope, imagining safety and freedom not as an unreachable destination but as a future yet to come. Research and practice implications are discussed.

The Delay Measurement and Analysis of Unreachable Hosts of Internet

Delay related metrics are significant quality of service criteria for the performance evaluation of networks. Almost all delay related measurement and analysis studies take into consideration the reachable sources of Internet. However, unreachable sources might also shed light upon some problems such as worm propagation. In this study, we carry out a delay measurement study of unreachable destinations and analyse the delay dynamics of unreachable nodes. 2. Internet Control Message Protocol (ICMP) destination unreachable Internet Control Message Protocol-Destination Unreachable (ICMP T3) packets are considered for the delay measurement according to their code types which shows network un reach ability, host un reach ability, port un reach ability, etc. Measurement results show that unreachable sources exhibit totally different delay behaviour compared to reachable IP hosts. A significant part of the unreachable hosts experiences extra 3 seconds Round Trip Time (RTT) delay compared to accessible hosts mostly due to host un reach ability. It is also seen that, approximately 79% of destination un reach ability causes from host un reach ability. Obtained Hurst parameter estimation results reveal that unreachable host RTTs show lower Hurst degree compared to reachable hosts which is approximately a random behaviour. Unreachable sources exhibit totally different distributional characteristic compared to accessible ones which is best fitted with Phased Bi-Exponential distribution.

Modes of transport and rhythms of mobility in Bernard B. Dadié’s Un Nègre à Paris (1959) and Tété-Michel Kpomassie’s L’Africain du Groenland (1981)

ABSTRACT This article discusses Bernard B. Dadié’s Un Nègre à Paris (1959; 1994) and Tété-Michel Kpomassie’s L’Africain du Groenland ([1981] (2015); 2001) by focusing on their portrayals of transport and rhythms of mobility, and in so doing enhances the dialogue between travel writing studies and mobilities research. The texts’ representations of mobility practices and the rhythms thereof contribute to the production of the traveller figure (tourist; Arctic adventurer) and the destination (colonial metropolis; Arctic periphery). Dadié’s portrayals of transport produce a poetics of mobility that conveys a sense of speed and hurry but also of not being in the rhythm of the colonial metropolis, which eventually transforms into a critical attitude towards assimilationist impulses. Kpomassie’s travelogue captures the idea of an unreachable destination and the traveller’s struggle to pursue the journey despite obstacles, but also attests to the productive qualities of inertia as well as to the eurythmy of Arctic mobilities.

Improving Routing Convergence With Centrality: Theory and Implementation of Pop-Routing

One of the key features of a routing protocol is its ability to recover from link or node failures, recomputing routes efficiently without creating temporary loops. Indeed, in real conditions, there is always a trade-off between the overhead due to the periodic generation of control messages and route convergence time. This paper formalizes the problem of the choice of timers for control message generation as an optimization problem that minimizes the route convergence time, constrained to a constant signaling overhead. The solution requires the knowledge of nodes’ centrality in the topology and can be obtained with a computational complexity low enough to allow on-line computation of the timers. Results on both synthetic and real topologies show a significant decrease of the transient duration with the consequent performance gain in terms of reduced number of unreachable destinations and routing loops. Our proposal is general and it can be applied to enhance any link-state routing protocol, albeit it is more suited for wireless networks. As a concrete example, we present the extension of OLSRv2 with our proposal, named Pop-Routing, and discuss its performance and the stability of centrality metrics in three large-scale real wireless mesh networks. This exhaustive analysis on traces of the topology evolution of real networks for one entire week shows that pop-routing outperforms the non-enhanced protocol in every situation, even when it runs with sub-optimal timers due to centrality computation on stale information.

Island as an Unreachable Destination: Umberto Eco’s The Island of the Day Before (1994)

An island, owing to its very isolation, has accumulated layers of significances as an image, and turned out in course of time to be a multivalent sign, which has been adapted by writers and artists across lands and ages to articulate a rich spectrum of ideas, discourses, and counterdiscourses. In our times Umberto Eco, in a story, located in the mid-seventeenth century, and placed upon a non-space – neither land, nor water, nor air – for its backdrop, has offered yet another unusual approach to this unique signifier by means of installing a fresh paradigm of voyage and [non]arrival at an island, Umberto Eco’s The Island of the Day Before is a story about a search for ‘Terra Incognita’, for ‘the Island not Found’, and an impossible venture, ‘to find the Unfindable’. In spite of the crowded ideas, obscure references and antique time-space continuum the book exerts its own charm upon today’s reader. Some of the perennial themes addressed here are love, life, death, ‘Time’ and God, – and the unreachable island, which is so near, yet remains so far, serves as the pivotal point of this revolving, multi-modal mirror. By means of a superb feat of imaginative flight the dream-element of the situation has been reinforced by the metanarrator as he goes on reconstructing the scraps left behind by the precursor micro-narrator. The hyperreality of Roberto’s specific oxymoronic island , along with its ‘distant proximity’, is accentuated by the dream-tenor of the narrative as well as by covert/and overt mythical allusions, which have been lying strewn about unmistakably. Myths embrace and intersect one another across disparate cultural frames. Eco presents a fantasy island in the garb of mystic knowledge disseminated by a supposedly medieval theologiancum- scientist. The micro-narrator’s search is simultaneously about the Island of Solomon and the longitude, the hundred-eightieth meridian, both belonging to the ‘terra incognita’. The theological notion and the (pseudo) scientific concepts (of the 17th century) seem to be interchangeable variables in the context. At one level it is about ‘the Island not found’, not findable, and the protagonist’s paradoxical voyage for the same. How could one reach the unreachable! And yet, who knows! The reader is left only to imagine and wonder about this postmodern Odysseus who has no home, no kin, no land to rest his feet upon, no mission (which has been lost, along with the wrecked ship, in course of the voyage), and finally no destination even.

An Improved Path Planning Method Based on Artificial Potential Field for a Mobile Robot

Abstract To solve the problem of local minima and unreachable destination of the traditional artificial potential field method in mobile robot path planning, chaos optimization is introduced to improve the artificial potential field method. The potential field function was adopted as a target function of chaos optimization, and a kind of “two-stage” chaos optimization was used. The corresponding movement step and direction of the robot were achieved by chaos search. Comparison of the improved method proposed in this paper and the traditional artificial potential field method is performed by simulation. The simulation results show that the improved method gets rid of the drawbacks, such as local minima and unreachable goal. Furthermore, the improved method is also verified by building up a physical platform based on “Future Star” robot. The success of the physical experiment indicates that the improved algorithm is feasible and efficient for mobile robot path planning.

Mobile Indoor Navigation Assistance for Mobility Impaired People

Mobility impaired people are often confronted with barriers along their chosen routes which lead to unreachable destinations and frustration. In order to assist this user group with finding barrier-free outdoor and indoor routes, we have developed a mobile application for Android devices which computes barrier-free routes between two locations on the basis of a personal profile. During our research, we tried to find other options to locate the user inside of a building, returning precise positions which can be calculated in real time without a high computing power and additional hardware. The starting position of a route is computed by using Bluetooth 4.0 transmitters which send UUIDs which was adapted by including the geo location of the transmitter into them. This allows us to compute the exact position of the user by trilateration of the signal strength of each transmitter. The ending point of the route is individually chosen by the user and is also returned as a geo location. Because we are using geo locations in decimal format, the results of our calculations can be displayed on every digital geographical map. The main difference to other solutions is, that we don’t use a special coordinate system for every building, instead we use the geolocations, which represent the coordinate system of the world and therefore, our developed technology can generally support a wide range of projects in the field of navigation. In addition, the result of our calculation can be displayed on every digital geographical map and is easily calculable to other widely used standards like WGS84, the common standard for current navigation devices. Instead of using special coordinate systems for every building, we use the geolocations, which represent the coordinate system of the entire world. That way, we are not only independent of additional coordinate information, but our navigation assistance works indoors as well as outdoors, as outdoor routing is based on the same geoid data. This makes our approach useable for a wide area of interests. This paper presents an innovative way to track users anywhere on our planet - even if they are inside of buildings - without using satellite communication for the determination of the position.

Path Reecovery in 6LoWPAN Routing Protocol

6LoWPAN has become a new technology to provide the Internet connectivity to the traditional wireless sensor network (WSN). In order to route the delivered packet from originator to destination nodes, the simplified Ad-hoc On- Demand Distance Vector (AODV) routing protocol for 6LoWPAN with 6LoWPAN Ad-Hoc On-Demand Distance Vector Routing (LOAD) has been introduced. However, the conceptual LOAD routing protocol has yet proposed any path recovery mechanism in 6LoWPAN. In this paper, an originator recognition (OR) path recovery mechanism is proposed for the 6LoWPAN LOAD-based routing protocol. In this proposed mechanism, the participated nodes will memorize the originator address attached within data packet during the data transmission. When a link break happens on destination path, the LOAD protocol message will be amended by inserting an identity key, which is a memorial of originator address, in the generated route error (RERR) message before transmitted towards the originator for the failure notification. This identity key is then used by the originator to initialize path recovery in order to retransmit the failed data packet to the unreachable destination node. Instead of using MAC address in the LOAD routing protocol, IP address is used in the proposed Originator Recognition (OR) path recovery mechanism (OR-LOAD) routing protocol which is designed for the global routing. The proposed OR-LOAD routing protocol has been examined under noisy 6LoWPAN environment in Qualnet simulator. Its performance is then evaluated and compared to AODV routing protocol in terms of packet delivery ratio and average energy consumption. The simulation results show that the proposed OR-LOAD outperforms AODV with packet delivery ratio of 19.4%, and with comparable average energy consumption in both routing protocols.

Unicast-based fault-tolerant multicasting in wormhole-routed hypercubes

A unicast-based fault-tolerant multicasting method is proposed for hypercubes, which can still work well when the system contains enough faults. A multicast message may be unable to reach a destination if Hamming distance between the destination and the multicast source is large enough. A multicast message fails if any one of the destinations is unreachable from the source. An effective destination ordering scheme of the destinations is proposed for one-port systems first, it is extended to all-port systems for unicast-based fault-tolerant multicasting. Unreachable destinations from the source based on the local safety information are forwarded to a reachable destination, where the multicast message can be routed reliably. Destination ordering is completed based on Hamming distance. A multiple round p-cube routing scheme is presented for a deadlock-free fault-tolerant routing for each unicast step in hypercubes, where the same virtual channel is used for each round of p-cube routing. Sufficient simulation results are presented by comparing with the previous methods.

The Visual Quest in Jean Lorrain's Monsieur de Phocas

In his 1901 novel, Monsieur de Phocas, Jean Lorrain illustrates the Decadent aesthetic of narcissism, relating the desire to look to the desire to display, and establishing the complementarity of scopophilia and exhibitionism. For Lorrain's character, life is a search for mythical,forbidden things. Reflected in the directionless narrative, the hero embarks for exotic places. Privileging the unlocatable object and unreachable destination, he enjoys the trip, the search, the visual quest.A pointless journey, Lorrain's narrative only ends with its transcription, whenlife's dynamism is exchanged for a retrospective travelogue. Wanderlust gives way to exhaustion and ennui, becoming a recitation bequeathed to reader-offspring. Having documented the itinerary of the character's roving eye, the story is frozen in the performance of its disclosure. Lorrain'shero stops living in order to narrate, abandoning the wish to see in order to indulge the wish to show.

Design and simulation of a supplemental protocol for BGP

Internet policy routing has attracted a lot of attention in the last decade and it is believed that this topic will become even more important in the foreseeable future. The growing diversity of the Internet brings in many organizations under different authorities with conflicting interests. Each such organization forms an Autonomous System (AS), with its own policy regulating network traffic across its boundaries to protect valuable network resources. As a result, a policy violation at any intermediate AS may cause a packet to be silently dropped before reaching its destination. The Border Gateway Protocol (BGP) was introduced to solve this packet-dropping problem in the mid-1990s, followed by a series of revisions. Currently, BGP is the dominant protocol in this field. However, BGP is a distance-vector and hop-by-hop protocol, resulting in a loss of reachability information for some destinations, even though feasible routes to those destinations may physically exist. Unreachable destinations under BGP are not necessarily truly unreachable. To overcome this deficiency, this paper presents a source policy route discovery protocol to supplement BGP. Simulation results show that almost all the false negative unreachable destinations can be resolved by the proposed protocol.