420 research outputs found
MONTANA - THE NEW R.V. SALES CAPITAL OF THE U.S.
No full textMotor home travelers across the country are flocking to Montana to purchase their luxury R.V.s as the vehicles are not subject to sales tax and registration fees are minimal. Some see this activity as tax evasion, but taxation expert Walter Hellerstein says its perfectly legal. To read the complete story, see The New York Times. The article title is The draw of Montana for the R.V. set? It\u27s not the Scenery. It was published on 8/17/05, and the author is Jim Robbins
MONTANA - THE NEW R.V. SALES CAPITAL OF THE U.S.
No full textMotor home travelers across the country are flocking to Montana to purchase their luxury R.V.s as the vehicles are not subject to sales tax and registration fees are minimal. Some see this activity as tax evasion, but taxation expert Walter Hellerstein says its perfectly legal. To read the complete story, see The New York Times. The article title is The draw of Montana for the R.V. set? It\u27s not the Scenery. It was published on 8/17/05, and the author is Jim Robbins
ST2249-MRSA-III: a second major recombinant methicillin-resistant Staphylococcus aureus clone causing healthcare infection in the 1970s
No full textTyping of healthcare-associated methicillin-resistant Staphylococcus aureus (MRSA) from Australia in the 1970s revealed a novel clone, ST2249-MRSA-III (CC45), present from 1973 to 1979. This clone was present before the Australian epidemic caused by the recombinant clone, ST239-MRSA-III. This study aimed to characterize the genome of ST2249-MRSA-III to establish its relationship to other MRSA clones. DNA microarray analysis was conducted and a draft genome sequence of ST2249 was obtained. The recombinant structure of the ST2249 genome was revealed by comparisons to publicly available ST239 and ST45 genomes. Microarray analysis of genomic DNA of 13 ST2249 isolates showed gross similarities with the ST239 chromosome in a segment around the origin of replication and with ST45 for the remainder of the chromosome. Recombination breakpoints were precisely determined by the changing pattern of nucleotide polymorphisms in the genome sequence of ST2249 isolate SK1585 compared with ST239 and ST45. One breakpoint was identified to the right of oriC, between sites 1014 and 1065 of the gene D484_00045. Another was identified to the left of oriC, between sites 1185 and 1248 of D484_01632. These results indicate that ST2249 inherited approximately 35.3% of its chromosome from an ST239-like parent and 64.7% from an ST45-like parent. ST2249-MRSA-III resulted from a major recombination between parents that resemble ST239 and ST45. Although only limited Australian archival material is available, the oldest extant isolate of ST2249 predates the oldest Australian isolate of ST239 by 3 years. It is therefore plausible that these two recombinant clones were introduced into Australia separately
Neighbor discovery in energy harvesting wireless sensor networks
No full textHomes, offices and vehicles are getting networked. This will enable context aware, autonomous operation of many support systems that could be controlled remotely. To achieve this there would be a large number of tiny devices -- sensors and actuators -- which are networked and they are termed generally as Internet of Things (IoT) devices. In future, they will be powered through harvested energy from the ambience to enable perennial lifetime and minimal manual maintenance. Some examples of energy sources are photovoltaic panels and piezoelectric crystals. Several challenges arise due to the nature of sources of energy. One of these challenges is that the devices (nodes) leave and re-enter networks due to fluctuating availability of harvested energy. This energy condition requires the adaptation of special means at every layer of the communication model. For example, as a result of fluctuating energy levels, the neighbor table maintained at each node changes quite often leading to complications in forming and maintaining routes. In fact initial neighbor discovery (ND) itself is a difficult task. Further, usage of directional antennas would affect the time taken to complete ND. Given the spatio-temporal variations in energy availability in harvesting environments, there are benefits of energy prediction. With the help of prediction, resource allocation within a single system and splitting of tasks between nodes in a network would be enhanced. In order to identify the various parameters that affect ND we first describe a generic analytical model of an energy harvesting device. Next, we study a network of these devices through exhaustive simulation study considering these various parameters. We demonstrate the benefits and challenges of using directional antennas for ND. We present a scheme that nodes could use to discover their neighbors during initial deployment and another scheme that could be used for subsequent discovery on re-entry into the network. We show that a dedicated ND protocol is necessary for energy harvesting networks and that directional ND is beneficial in these networks under some circumstances. Finally, we present light-weight energy prediction solutions that can be used to improve the performance of the ND process in particular.TelecommunicationElectrical EngineeringElectrical Engineering, Mathematics and Computer Scienc
Topology Control in Energy-harvesting Wireless Sensor Networks
No full textAmbient energy-harvesting technology is a promising approach to keep wireless sensor networks (WSNs) operating perennially. Depending on the harvesting source, nodes can either be active (alive) or inactive (dead) at any instant in such Energy-Harvesting WSNs (EH-WSNs). Thus, even in a static deployment of EH-WSNs, the network topology is no longer static. A popular method to increase energy-efficiency in WSNs is by employing topology control algorithms. Most of the topology control algorithms in the literature focus only on the transmission power while constructing a static topology without taking into account the residual energy of the nodes. Consequently, they cannot handle the situation when nodes have different energy levels, and when the number of active nodes varies with time in EH-WSN. Since the number of nodes alive in EH-WSNs is varying there is no possibility of having a centralized solution. To address this issue, we present two localized energy based topology control algorithms, viz., EBTC-1 and EBTC-2. EBTC-1 is for convergecast applications of WSNs and EBTC-2 is for a generic scenario where all nodes are required to be strictly connected. In some cases, to ensure fault tolerance the network may be required to be k-connected. While typical topology control algorithms select a particular number of neighbors, the distinguishing feature of both these algorithms is that they select neighbors based on energy levels, and render the global topology strongly-connected. Simulation results confirm that EBTC-1 and EBTC-2 reduce the transmission power and they let nodes have neighbors with high remaining energy. Results show that our proposed algorithms increase at least 33% in the remaining energy per neighbor. In addition, in terms of energy consumption and fault-tolerance, our proposed algorithms typically achieve 1-connected topology using 74% less energy compared to K-Neigh.Embedded SystemsSoftware and Computer TechnologyElectrical Engineering, Mathematics and Computer Scienc
Allocation of Opportunistic Spectrum for Cognitive Radio Ad hoc Networks
No full textCognitive Radios (CRs) address the problems of spectrum scarcity and under-utilization of the spectrum. However, realizing a CR network is neither easy nor straight-forward. The link layer in CR Ad hoc Networks is responsible for allocating suitable channels, out of the currently available channels. It is also responsible for setting up communication between nodes. Further, the spectrum efficiency should be maximized in a fair way. The problem of spectrum allocation can be modeled as a graph-theoretic problem. The selection of channels amongst the CR nodes in the network is an NP class problem. We prove this is, in fact, an NP complete problem. We propose a time-slotted system. In such a system, the schedule length needs to be kept to a minimum for higher spectrum utilization. We analyze the problem to determine conditions for an optimal allocation. We use edge coloring as a tool to analyze and propose heuristics. In ad hoc networks, distributed solutions are preferred due to the lack of infrastructure. We propose two distributed algorithms: (i) clique based, and (ii) localized heuristic algorithms. We compare the results of these heuristics with the algorithm proposed in literature. We also find the worst case bounds for these algorithms. For efficiency purposes, it is required to have a constant number of slots per frame. In such cases, producing a valid schedule is not enough since unfairness of allocation will eventually arise. To address this issue, we modify the edge coloring and clique based heuristics to produce valid fair schedules. Finally, we briefly consider the advantages of having a joint spectrum sensing-allocation scheme at the link layer. When the spectrum sensing scheme at the PHY layer is not completely reliable, a link layer scheme can help in reducing the false alarms and miss-detections. We, further constrain the system by limiting the number of channels that can be sensed within a frame. We present the spectrum utilization with this joint sensing-allocation policy.Wireless and Mobile CommunicationsTelecommunicationsElectrical Engineering, Mathematics and Computer Scienc
Anthrachinon uit koolteer
No full textDocument(en) uit de collectie Chemische ProcestechnologieDelftChemTechApplied Science
Allelic variation in genes encoding Panton–Valentine leukocidin from community-associated Staphylococcus aureus
No full textABSTRACTCommunity-associated methicillin-resistant Staphylococcus aureus isolates characteristically contain the genes for Panton–Valentine leukocidin (PVL), which is a proposed virulence factor. To determine whether different alleles of the PVL genes lukS-PV and lukF-PV occur, and whether they are associated with specific genetic lineages of S. aureus, sequences from 28 S. aureus isolates, representing four different multilocus sequence types, and bacteriophages SLT and PVL were compared. Seven nucleotide polymorphisms were identified, which defined three groups of the lukS-PV and lukF-PV sequence. Only one polymorphism resulted in an amino-acid change. Bacteriophage SLT and isolates of bacteriophage type 80/81 contained the prototypic (founder) lukS-PV and lukF-PV sequence. The alleles were not lineage-specific
Performance and fairness enhancement in ZigBee networks
No full textZigBee is a robust wireless communication standard which is based on physical and MAC layer on IEEE 802.15.4. ZigBee is also critically limited by the low data rate standard when there are many source nodes in the network. How to fairly and efficiently access the network and delivery the packets should be considered as one of the crucial issues. The simulation results illustrate that packet delivery ratio and delay are the most important measures for performance analysis in ZigBee. To obtain a better behavior of ZigBee network, we propose three methods which can significantly improve the packet delivery ratio and satisfy the requirements for fairness. Firstly, packet aggregation is introduced to ZigBee networks to aggregate data in an energy efficient manner so that network lifetime is enhanced. When there are too many nodes in the network, not all the nodes get the same chance to access the network and successfully transmit the packets. Three fairness metrics are introduced to evaluate the fairness among all the nodes. Intra-cluster and inter-cluster fairness are two proposed methods to enhance fairness based on packet aggregations. With intra-cluster fairness methods, cluster head should delay the packets and process the packets from the other node when the number of received packets from one source node is more than the average level. After intra-cluster fairness, different clusters still have fairness issue. Inter-cluster fairness should be designed to achieve absolute fairness among all the end devices. The simulations results show that our new methods could make the way of accessing the network and transmitting the packets efficient and fair as we have expected.Wireless and Mobile CommunicationsTelecommunicationsElectrical Engineering, Mathematics and Computer Scienc
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