A Lightweight Distributed Solution to Content Replication in Mobile Networks

Performance and reliability of content access in mobile networks is conditioned by the number and location of content replicas deployed at the network nodes. Facility location theory has been the traditional, centralized approach to study content replication: computing the number and placement of replicas in a network can be cast as an uncapacitated facility location problem. The endeavour of this work is to design a distributed, lightweight solution to the above joint optimization problem, while taking into account the network dynamics. In particular, we devise a mechanism that lets nodes share the burden of storing and providing content, so as to achieve load balancing, and decide whether to replicate or drop the information so as to adapt to a dynamic content demand and time-varying topology. We evaluate our mechanism through simulation, by exploring a wide range of settings and studying realistic content access mechanisms that go beyond the traditional assumptionmatching demand points to their closest content replica. Results show that our mechanism, which uses local measurements only, is: (i) extremely precise in approximating an optimal solution to content placement and replication; (ii) robust against network mobility; (iii) flexible in accommodating various content access patterns, including variation in time and space of the content demand.Comment: 12 page

A Gossip-based optimistic replication for efficient delay-sensitive streaming using an interactive middleware support system

While sharing resources the efficiency is substantially degraded as a result of the scarceness of availability of the requested resources in a multiclient support manner. These resources are often aggravated by many factors like the temporal constraints for availability or node flooding by the requested replicated file chunks. Thus replicated file chunks should be efficiently disseminated in order to enable resource availability on-demand by the mobile users. This work considers a cross layered middleware support system for efficient delay-sensitive streaming by using each device's connectivity and social interactions in a cross layered manner. The collaborative streaming is achieved through the epidemically replicated file chunk policy which uses a transition-based approach of a chained model of an infectious disease with susceptible, infected, recovered and death states. The Gossip-based stateful model enforces the mobile nodes whether to host a file chunk or not or, when no longer a chunk is needed, to purge it. The proposed model is thoroughly evaluated through experimental simulation taking measures for the effective throughput Eff as a function of the packet loss parameter in contrast with the effectiveness of the replication Gossip-based policy.Comment: IEEE Systems Journal 201

Adaptive Square-Shaped Trajectory-Based Service Location Protocol in Wireless Sensor Networks

In this paper we propose an adaptive square-shaped trajectory (ASST)-based service location method to ensure load scalability in wireless sensor networks. This first establishes a square-shaped trajectory over the nodes that surround a target point computed by the hash function and any user can access it, using the hash. Both the width and the size of the trajectory are dynamically adjustable, depending on the number of queries made to the service information on the trajectory. The number of sensor nodes on the trajectory varies in proportion to the changing trajectory shape, allowing high loads to be distributed around the hot spot area

Autonomous Gossiping: A self-organizing epidemic algorithm for selective information dissemination in mobile ad-hoc networks

We introduce autonomous gossiping (A/G), a new genre epidemic algorithm for selective dissemination of information in contrast to previous usage of epidemic algorithms which flood the whole network. A/G is a paradigm which suits well in a mobile ad-hoc networking (MANET) environment because it does not require any infrastructure or middleware like multicast tree and (un)subscription maintenance for publish/subscribe, but uses ecological and economic principles in a self-organizing manner in order to achieve its selectivity. The trade-off of using an infrastructure-less self-organizing mechanism like A/G is that it does not guarantee completeness deterministically as is one of the original objectives of alternate selective dissemination schemes like publish/subscribe. We argue that such incompleteness is not a problem in many non-critical real-life civilian application scenarios and realistic node mobility patterns, where the overhead of infrastructure maintenance may outweigh the benefits of completeness, more over, at present there exists no mechanism to realize publish/subscribe or other paradigms for selective dissemination in MANET environments. A/G's reliance and hence vulnerability on cooperation of mobile nodes is also much less as compared to other possible schemes using routing information, since it does not expect node philanthropy for forwarding/carrying information, but only cooperation to the extent that nodes already carrying the information pass it on to other suitable ones. Thus autonomous gossiping is expected to be a light-weight infrastructure-less information dissemination service for MANETs, and hence support any-to-many communication (flexible casting) without the need to establish and maintain separate routing information (e.g., multicast trees)

Energy-Efficient Querying of Wireless Sensor Networks

Due to the distributed nature of information collection in wireless sensor networks and the inherent limitations of the component devices, the ability to store, locate, and retrieve data and services with minimum energy expenditure is a critical network function. Additionally, effective search protocols must scale efficiently and consume a minimum of network energy and memory reserves. A novel search protocol, the Trajectory-based Selective Broadcast Query protocol, is proposed. An analytical model of the protocol is derived, and an optimization model is formulated. Based on the results of analysis and simulation, the protocol is shown to reduce the expected total network energy expenditure by 45.5 percent to 75 percent compared to current methods. This research also derives an enhanced analytical node model of random walk search protocols for networks with limited-lifetime resources and time-constrained queries. An optimization program is developed to minimize the expected total energy expenditure while simultaneously ensuring the proportion of failed queries does not exceed a specified threshold. Finally, the ability of the analytical node model to predict the performance of random walk search protocols in large-population networks is established through extensive simulation experiments. It is shown that the model provides a reliable estimate of optimum search algorithm parameters

Towards Efficient File Sharing and Packet Routing in Mobile Opportunistic Networks

With the increasing popularity of portable digital devices (e.g., smartphones, laptops, and tablets), mobile opportunistic networks (MONs) [40, 90] consisting of portable devices have attracted much attention recently. MONs are also known as pocket switched networks (PSNs) [52]. MONs can be regarded as a special form of mobile ad hoc networks (MANETs) [7] or delay tolerant networks (DTNs) [35, 56]. In such networks, mobile nodes (devices) move continuously and meet opportunistically. Two mobile nodes can communicate with each other only when they are within the communication range of each other in a peer-to-peer (P2P) manner (i.e., without the need of infrastructures). Therefore, such a network structure can potentially provide file sharing or packet routing services among portable devices without the support of network infrastructures. On the other hand, mobile opportunistic networks often experience frequent network partition, and no end-to-end contemporaneous path can be ensured in the network. These distinctive properties make traditional file sharing or packet routing algorithms in Internet or mobile networks a formidable challenge in MONs. In summary, it is essential and important to achieve efficient file sharing and packet routing algorithms in MONs, which are the key for providing practical and novel services and applications over such networks. In this Dissertation, we develop several methods to resolve the aforementioned challenges. Firstly, we propose two methods to enhance file sharing efficiency in MONs by creating replicas and by leveraging social network properties, respectively. In the first method, we investigate how to create file replicas to optimize file availability for file sharing in MONs. We introduce a new concept of resource for file replication, which considers both node storage and meeting frequency with other nodes. We theoretically study the influence of resource allocation on the average file access delay and derive a resource allocation rule to minimize the average file access delay. We also propose a distributed file replication protocol to realize the deduced optimal file replication rule. In the second method, we leverage social network properties to improve the file searching efficiency in MONs. This method groups common-interest nodes that frequently meet with each other into a community. It takes advantage of node mobility by designating stable nodes, which have the most frequent contact with community members, as community coordinators for intra-community file request forwarding, and highly-mobile nodes that visit other communities frequently as community ambassadors for inter-community file request forwarding. Based on such a community structure, an interest-oriented file searching scheme is proposed to first search local community and then search the community that is most likely to contain the requested file, leading to highly efficient file sharing in MONs. Secondly, we propose two methods to realize efficient packet routing among mobile nodes and among different landmarks in MONs, respectively. The first method utilizes distributed social map to route packets to mobile nodes efficiently with a low-cost in MONs. Each node builds its own social map consisting of nodes it has met and their frequently encountered nodes in a distributed manner. Based on both encountering frequency and social closeness of two linked nodes in the social map, we decide the weight of each link to reflect the packet delivery ability between the two nodes. The social map enables more accurate forwarder selection through a broader view and reduces the cost on information exchange. The second method realizes high-throughput packet routing among different landmarks in MONs. It selects popular places that nodes visit frequently as landmarks and divides the entire MON area into sub-areas represented by landmarks. Nodes transiting between two landmarks relay packets between the two landmarks. The frequency of node transits between two landmarks is measured to represent the forwarding capacity between them, based on which routing tables are built on each landmark to guide packet routing. Finally, packets are routed landmark by landmark to reach their destination landmarks. Extensive analysis and real-trace based experiments are conducted to support the designs in this Dissertation and demonstrate the effectiveness of the proposed methods in comparison with the state-of-art methods. In the future, we plan to further enhance the file sharing and packet routing efficiency by considering more realistic scenarios or including more useful information. We will also investigate the security and privacy issues in the proposed methods

Isolation, cultivation and characterization of cells originating from tumor and tumor margin of patients with basal cell carcinoma in vitro

Homeostaza kože direktno zavisi od mehanizma kontinuiranog obnavljanja ćelijske populacije kože i njene sposobnosti regeneracije. U epidermisu je prisutna posebna populacija ćelija zadužena za proces samoobnavljanja kože, tzv. epidermalne matične ćelije koje imaju sposobnost proliferacije, migracije, diferencijacije i programirane ćelijske smrti. Ukoliko dođe do narušavanja ravnoteže između ovih procesa, može doći do maligne transformacije zdrave matične ćelije u kancersku matičnu ćeliju. Poznato je da za hemorezistenciju, metastaziranje i recidiviranje tumora odgovornost nosi posebna populaciju tumorskih ćelija koje se nazivaju kancerske matične ćelije. Istraživanja pokazuju da bazocelularni karcinom kože vodi poreklo od matičnih ćelija ispupčenja folikula dlake, infundibuluma dlake i interfolikularnog epidermisa. Bazocelularni karcinom (BCK) je najčešći maligni tumor kože, pa i ako retko metastazira karakteriše ga invazivni rast pri čemu infiltriše okolne strukture i dovodi do ozbiljnih funkcionalnih i estetskih defekata. U literaturi se kao jedan od ključnih faktora odgovornih za recidiviranje navodi neadekvatna širina margine resekcije tumora. Istraživanja su pokazala da je za primarne BCK na koži lica veličine do 20 mm preporučena širina margine 3 mm. Cilj ovog istraživanja bio je identifikacija i karakterizacija subpopulacije ćelija sa osobinama matičnosti izolovanih iz BCK-a i bliske margine od 3 mm, ispitivanjem proliferativnog, klonogenog i migratornog potencijala, analizom ekspresije embrionalnih, mezenhimskih i tumorskih markera, analizom biohemijske strukture ćelija, ispitivanjem sposobnosti diferencijacije u više ćelijskih linija kao i stepena otpornosti ćelija na dejstvo citostatika. U istraživanju je učestvovalo 13 pacijenata sa primarnim bazocelularnim karcinomom na koži lica veličine do 20 mm. Nakon detaljno uzete anamneze i potpisanog informisanog pristanka pristupalo se hirurškoj eksciziji tumorske promene, koja se smatra zlatnim standardom u terapiji BCK-a. Iz svih ekscidiranih uzorka za izolaciju ćelija uzet je deo tumorskog tkiva, tkiva bliske margine (udaljene 3 mm od makroskopske granice tumora) i deo zdrave kože obuhvaćen oblikom resekcije (udaljen od makroskopske granice tumora više od 5 mm), dok je preostali deo tkiva poslat na histopatološku analizu. Za karakterizaciju ćelija u kulturi korišćeni su testovi proliferacije, migracije, formiranja kolonija, sfera i ramanska spektroskopija. Markeri kancerskih matičnih ćelija (KMĆ) analizirani su ,,Real-Time PCR” metodom i protočnom citometrijom...renewal and regeneration and the epidermis harbors a special cell population responsible for the process of self-renewal and regeneration of the skin, so called epidermal stem cells that have the ability to proliferate, migrate, differentiate, and undergo programmed cell death. If imbalance between these processes occurs, malignant transformation of healthy stem cell into the cancerous stem cell may happen. It is also known that a specific population of tumor cells called cancer stem cells is responsible for the hemoresistance, metastasis, and recurrence. Studies have shown that skin basal cell carcinoma is caused by stem cells of hair follicle, hair infundibulum and interfollicular epidermis. Basocellular carcinoma (BCC) is the most common malignant tumor of the skin, but it rarely gives metastases It is characterized by invasive growth, infiltrating surrounding structures and leading to serious functional and aesthetic defects. In the literature, inadequate margins are indicated as one of the key factors responsible for tumor recurrences. Studies have shown that for the primary facial skin BCC of less than 20 mm a margin of 3 mm is recommended. The aim of this study was to identify and characterize the cell subpopulation with stem characteristics whithin BCC and its margins (3 mm close) by testing proliferative, clonogenic and migratory potential, by analyzing the expression of embryonic, mesenchymal and tumor markers, by analizing biochemical structure of cells, by examining the differentiation potential of generated cell lines and by testing the degree of chemo-resistance. The study included 13 patients with primary BCC of face skin of less than 20 mm. Following a detailed anamnesis and a signed informed consent, the surgical excision which is considered a gold standard in BCC therapy, was done. A portion of the tumor tissue, of close margin (3 mm from the macroscopic tumor limit), and of healthy skin included in the resecion (at least 5mm from the macroscopic tumor limit), were obtained from all the patients. The remaining of the tissue was subjected to histopathological analysis. For cell phenotype characterization, tests of proliferation, colony formation, scratch assay, and sphere formation were used..

Mobile Datenbanken - heute, morgen und in 20 Jahren. Tagungsband zum 8. Workshop des GI-Arbeitskreises "Mobile Datenbanken und Informationssysteme" am 28.2.2005 im Rahmen der BTW 2005 in Karlsruhe

Der Workshop Mobile Datenbanken heute, morgen und in 20 Jahren ist der nunmehr achte Workshop des GI Arbeitskreises Mobile Datenbanken und Informationssysteme. Der Workshop findet im Rahmen der BTW 2005, der GI Fachtagung für Datenbanksysteme in Business, Technologie und Web, vom 28. Februar bis zum 01. März 2005 in Karlsruhe statt. Das Workshopprogramm umfasst zwei eingeladene Vorträge sowie sieben wissenschaftliche Beiträge, die vom Programmkomitee aus den Einreichungen ausgewählt wurden. Für den zweiten Workshoptag, der im Zeichen intensiver Diskussionen stehen soll, wurden zwei weitere Einreichungen als Diskussionsgrundlage ausgewählt. Inhaltlich spannt der Workshop einen weiten Bogen: Von fast schon klassischen Fragen aus dem Kernbereich mobiler Datenbanken, wie etwa der Transaktionsbearbeitung in diesen Systemen, bis hin zu neuen Multimediaanwendungen auf mobilen Geräten und von der Anfragebearbeitung in Ad-hoc-Netzen bis zur Analyse des Stands der Technik beim Entwurf mobiler Anwendungen. Diese Breite spiegelt die Breite der Fragestellungen, die bei der Betrachtung von mobiler Informationsnutzung zu Tage treten, wider. Wir hoffen mit unserem Workshop einen Beitrag zum besseren Verständnis dieser Fragestellungen zu liefern und ein Forum zum Austausch von Fragen, Lösungsansätzen und Problemstellungen zwischen Praktikern und Forschern aus dem universitären Umfeld zu bieten