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941.
942.
Routing for disruption tolerant networks: taxonomy and design 总被引:5,自引:0,他引:5
Thrasyvoulos Spyropoulos Rao Naveed Bin Rais Thierry Turletti Katia Obraczka Athanasios Vasilakos 《Wireless Networks》2010,16(8):2349-2370
Communication networks, whether they are wired or wireless, have traditionally been assumed to be connected at least most
of the time. However, emerging applications such as emergency response, special operations, smart environments, VANETs, etc.
coupled with node heterogeneity and volatile links (e.g. due to wireless propagation phenomena and node mobility) will likely
change the typical conditions under which networks operate. In fact, in such scenarios, networks may be mostly disconnected,
i.e., most of the time, end-to-end paths connecting every node pair do not exist. To cope with frequent, long-lived disconnections,
opportunistic routing techniques have been proposed in which, at every hop, a node decides whether it should forward or store-and-carry a message.
Despite a growing number of such proposals, there still exists little consensus on the most suitable routing algorithm(s)
in this context. One of the reasons is the large diversity of emerging wireless applications and networks exhibiting such
“episodic” connectivity. These networks often have very different characteristics and requirements, making it very difficult,
if not impossible, to design a routing solution that fits all. In this paper, we first break up existing routing strategies
into a small number of common and tunable routing modules (e.g. message replication, coding, etc.), and then show how and when a given routing module should be used, depending on the set of network characteristics exhibited by the wireless application. We further attempt to create a taxonomy for intermittently connected networks. We
try to identify generic network characteristics that are relevant to the routing process (e.g., network density, node heterogeneity, mobility patterns) and dissect different
“challenged” wireless networks or applications based on these characteristics. Our goal is to identify a set of useful design guidelines that will enable one to choose an appropriate routing protocol for the application or network in hand. Finally, to demonstrate
the utility of our approach, we take up some case studies of challenged wireless networks, and validate some of our routing
design principles using simulations. 相似文献
943.
Huang C.-Y. Huang T.-S. Cheng C.-Y. Chen Y.-C. Wan C.-T. Rao M. V. M. Su Y.-K. 《Photonics Technology Letters, IEEE》2010,22(5):305-307
944.
By heating H3BO3 with urea in 1 : 6 molar ratio, nanoparticles and nanotubes of BN are obtained. The urea–boric acid reaction can also be exploited to obtain graphene analogues of BN, with the number of layers depending on the relative proportions of the two reactants. Synthesis with a high proportion of urea yields a product containing graphene analogues of BN with an average of 2 layers. The surface area of BN increases with the decreasing number of layers, and the high-surface-area BN also exhibits high CO2 adsorption. Few-layer BN can be solubilized by interaction with Lewis bases. Nanopans and nanosheets formed by graphene-like BN are generated by the vapor phase reaction of NH3 and BBr3 at 1223 K. Nanopans of BN, being reported for the first time, have a bottom comprising single-layer BN and a wall of 0.7 nm height. The average inner volume of the nanopan is around 400 nm3. 相似文献
945.
Anwesha Maity Dipul Kalita Tarun Kumar Kayal Tridip Goswami Omprakash Chakrabarti Himadri Sekhar Maiti Paruchuri Gangadhar Rao 《Ceramics International》2010,36(1):323-331
Synthesis of SiC ceramic from processed cellulosic bio-precursor was investigated. Bamboo (Bambusa tulda Roxb.) plants abundantly available in the Jorhat district of Assam, India, were selected for extraction of fibers following Kraft pulping method and bleached bamboo pulp fibers were suitably cast in the form of rectangular boards. Coir fibers available in the Alleppy district of Kerala, India, were initially digested with dilute alkali, mixed with cellulose acetate solution, air dried and then hot-pressed at 140 ± 5 °C under 2.0–2.5 MPa pressure to make rectangular boards. Well-characterized processed bio-precursors were pyrolysed at ~800 °C under flowing N2 atmosphere to prepare the bio-carbonaceous preforms (carbon templates) which showed nearly uniform shrinkages in all directions. Coir fiber composite board carbon showed lower pyrolytic weight loss (~66%), higher density (0.49 g cm?3), lower porosity (~58%) and narrower pore diameter (10 μm) compared to the cast bamboo pulp fiber board carbon. The carbon samples showed perfect retention of fibrous morphological features of hierarchically grown bio-structures. Ceramization of carbon templates could be done by reactive melt silicon infiltration into porous channels at ~1600 °C under vacuum. The final ceramics were adequately dense (%theoretical density > 99%), showed negligible linear dimensional changes (indicating net-dimension formation capability), presence of crystalline Si and SiC phases and duplex microstructure with complete preservation of fibrous architecture of plant bio-structure. The Si/SiC ceramic composite synthesized from coir fiber board gave room temperature 3-point flexural strength and Young's modulus values of 121 MPa and 276 GPa, respectively. Both the ceramic composites showed adequate oxidation resistance during heating at 1300 °C for 7 h in air. 相似文献
946.
Daniel Lepek Jose Manuel Valverde Robert Pfeffer Rajesh N. Dave 《American Institute of Chemical Engineers》2010,56(1):54-65
We show experimental results on a proposed technique to enhance the fluidization of nanoparticle beds. This technique consists of the application of an alternating electric field to the nanofluidized bed. Three different field configurations have been tested: co‐flow field, cross‐flow field, and variable field configurations. Nanoparticle agglomerates are naturally charged by contact and tribo charging mechanisms and therefore are agitated by the action of the externally applied field, which enhance fluidization. According to our observations, the best results are obtained for the variable field configuration. In this configuration, the electric field strength is higher at the bottom of the bed, whereas it is almost negligible at the free surface. Thus, the larger agglomerates, which tend to sink at the bottom of the bed due to stratification, and usually impede uniform fluidization, are strongly agitated. It is thought that the strong agitation of the bigger agglomerates that usually sink to the bottom of the bed contributes to further homogenize the distribution of the gas flow within the bed by destabilizing the development of gas channels close to the gas distributor. On the other hand, the smaller agglomerates at the vicinity of the free surface are just weakly excited. Consequently, fluidization is greatly enhanced, whereas at the same time excessive elutriation is avoided. It is demonstrated that this technique is even suitable to achieve highly expanded fluidization of unsieved nanopowder samples even though the fluidization state returns to be heterogeneous upon the electric field being turned off. © 2009 American Institute of Chemical Engineers AIChE J, 2010 相似文献
947.
S. Uma M. Chidambaram A. Seshagiri Rao Chang Kyoo Yoo 《Chemical engineering science》2010,65(3):1065-1075
This paper presents a simple cascade controller in the enhanced modified Smith predictor structure for control of integrating processes. The proposed structure consists of two control loops, a secondary inner loop and a primary outer loop. The method has totally three controllers of which the secondary loop has one controller and the primary loop has two controllers. The secondary loop controller is designed using IMC technique. The primary loop set-point tracking and disturbance rejection controllers are designed using direct synthesis method. The primary set-point tracking controller is designed as a PID with lag filter and the primary disturbance rejection controller is designed as a PD with lead-lag filter. Simulation studies have been carried out on various cascade integrating processes with/without zero. The present method gives significant disturbance rejection both in the inner and outer loops and also shows significant improvement when compared to the recently reported methods. 相似文献
948.
Sabine Douxchamps François-Lionel Humbert Rein van der Hoek Martin Mena Stefano M. Bernasconi Axel Schmidt Idupulapati Rao Emmanuel Frossard Astrid Oberson 《Nutrient Cycling in Agroecosystems》2010,88(3):447-462
Canavalia brasiliensis (canavalia), a drought tolerant legume, was introduced into the smallholder traditional crop-livestock production system of the Nicaraguan hillsides as green manure to improve soil fertility or as forage during the dry season for improving milk production. Since nitrogen (N) is considered the most limiting nutrient for agricultural production in the target area, the objective of this study was to quantify the soil surface N budgets at plot level in farmers fields over two cropping years for the traditional maize/bean rotation and the alternative maize/canavalia rotation. Mineral fertilizer N, seed N and symbiotically fixed N were summed up as N input to the system. Symbiotic N2 fixation was assessed using the 15N natural abundance method. Nitrogen output was quantified as N export via harvested products. Canavalia derived in average 69% of its N from the atmosphere. The amount of N fixed per hectare varied highly according to the biomass production, which ranged from 0 to 5,700 kg ha?1. When used as green manure, canavalia increased the N balance of the maize/canavalia rotation but had no effect on the N uptake of the following maize crop. When used as forage, it bears the risk of a soil N depletion up to 41 kg N ha?1 unless N would be recycled to the plot by animal manure. Without N mineral fertilizer application, the N budget remains negative even if canavalia was used as green manure. Therefore, the replenishment of soil N stocks by using canavalia may need a few years, during which the application of mineral N fertilizer needs to be maintained to sustain agricultural production. 相似文献
949.
A three-dimensional zinc arsenate with an interrupted zeolitic framework (?IIO), [C4N3H16]2[Zn5(AsO4)4(HAsO4)2], I has been synthesized solvothermally. The structure is built up from ZnO4, AsO4 and HAsO4 tetrahedral units connected alternatively through their vertices forming the 3-D structure possessing one-dimensional channels bound by 10 T-atoms (T = Zn, As). The framework density of the structure is 10.4 T-atoms which indicates considerable openness in its structure. 相似文献
950.
Rajesh Patel VishnuP. Srivastava Lal DharS. Yadav 《Advanced Synthesis \u0026amp; Catalysis》2010,352(10):1610-1614
The first procedure to access N‐tosylimines directly from alcohols under mild and neutral conditions is reported. The protocol involves saccharin‐lithium bromide‐catalyzed oxidation of alcohols to aldehydes/ketones with chloramine‐T followed by their condensation with the in situ generated oxidation by‐product p‐toluenesulfonamide in the same reaction vessel to afford N‐tosylimines in 40–90% overall yields. The present work opens up a new and efficient synthetic route to N‐tosyimines directly from alcohols in a one‐pot procedure. 相似文献