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排序方式: 共有39条查询结果,搜索用时 15 毫秒
1.
Underwater communication primarily utilizes propagation of acoustic waves in water. Its unique characteristics, including slow propagation speed and low data rates, pose many challenges to Media Access Control (MAC) protocol design. In most existing handshaking-based underwater MAC protocols, only an initiating sender can transmit data packets to its intended receiver after a channel reservation through a Request-to-Send (RTS)/Clear-to-Send (CTS) handshake. This conventional single-node transmission approach is particularly inefficient in underwater environments, as it does not account for long propagation delays. To improve channel utilization in high latency environments, we propose a novel approach that exploits the idle waiting time during a 2-way handshake to set up concurrent transmissions from multiple nodes. The sender can coordinate multiple first-hop neighbors (appenders) to use the current handshake opportunity to transmit (append) their data packets with partially overlapping transmission times. After the sender finishes transmitting its packets to its own receiver, it starts to receive incoming appended packets that arrive in a collision-free packet train. This not only reduces the amount of time spent on control signaling, but it also greatly improves packet exchange efficiency. Based on this idea, we propose an asynchronous, single-channel handshaking-based MAC protocol based on reverse opportunistic packet appending (ROPA). From extensive simulations (single- and multi-hop networks) and comparisons with several existing MAC protocols, including MACA-U, MACA-UPT, BiC-MAC, Slotted-FAMA, DACAP, unslotted Aloha, we show that ROPA significantly increases channel utilization and offers performance gains in throughput and delay while attaining a stable saturation throughput. 相似文献
2.
Huiguang Liang Ransi Nilaksha De Silva Wei Tsang Ooi Mehul Motani 《Multimedia Tools and Applications》2009,45(1-3):163-190
We collected mobility traces of avatars spanning multiple regions in Second Life, a popular user-created virtual world. We analyzed the traces to characterize the dynamics of the avatars’ mobility and behavior, both temporally and spatially. We discuss the implications of our findings on the design of peer-to-peer architecture, interest management, mobility modeling of avatars, server load balancing and zone partitioning, caching, and prefetching for user-created virtual worlds. 相似文献
3.
Fatty acid modified polyurethane dispersion for surface coatings: Effect of fatty acid content and ionic content 总被引:1,自引:0,他引:1
Ashish Patel Chintankumar Patel M.G. Patel Mehul Patel Ashok Dighe 《Progress in Organic Coatings》2010
The higher molecular weight fatty acid modified polyurethane–urea dispersions (PUDs) were prepared with effective utilization of fatty acid and ionic emulsifier. The PUDs were prepared using oligomer of linoleic fatty acid, dimethylol propionic acid (DMPA), linear polyester diol, isophorone diisocyanate (IPDI), triethylamine (TEA) and ethylenediamine (EDA) by prepolymer mixing method. Resultant PUDs had so-called controlled branched polymer structures. To incorporate fatty acid residues in the backbone of the polyurethane two types of oligomers were used which were synthesized by esterifying linoleic acid and phthalic anhydride (PA) with different monomers having different hydroxyl functionality i.e. trimethylol propane (TMP), pentaerythritol and neopentyl glycol (NPG). The oligomers were mixed with linear polyester diol in different proportions and used as polyol part in prepolymer for PUDs. Various compositional variations such as type of oligomer, content of oligomer and ionic emulsifier were studied for stability and compatibility with water. The PUDs were also examined by FTIR, AFM, GPC, particle size analyzer, viscometer, TGA, DMA and tensile tester to analyze structures and properties. Chemical, water and corrosion resistances of the dried films were also evaluated to study the effect of oligomer content in modified PUDs. These properties are found to be significantly affected by the content and type of oligomer as well as ionic content in the polymer. 相似文献
4.
ABSTRACTA theoretical model for the study of size dependent cohesive energy of face-centered cubic (fcc) nanomaterials has been developed by considering the cluster order and particle size of these materials. Using the newly developed theoretical model, cohesive energy of Au, Ag and Al nanomaterials have been calculated and compared with other theoretical models and existing experimental data. The comparison of theoretical findings of the present work indicates that present developed theoretical model is in good agreement with available experimental results which show the validity of our work. 相似文献
5.
Mohammad Mirhosseini Brandon Rodenburg Mehul Malik Robert W. Boyd 《Journal of Modern Optics》2014,61(1):43-48
AbstractFree-space communication allows one to use spatial mode encoding, which is susceptible to the effects of diffraction and turbulence. Here, we discuss the optimum communication modes of a system while taking such effects into account. We construct a free-space communication system that encodes information onto the plane-wave (PW) modes of light. We study the performance of this system in the presence of atmospheric turbulence, and compare it with previous results for a system employing orbital-angular-momentum (OAM) encoding. We are able to show that the PW basis is the preferred basis set for communication through atmospheric turbulence for a system with a large Fresnel number product. This study has important implications for high-dimensional quantum key distribution systems. 相似文献
6.
Joshi Vaibhav B. Raval Mehul S. Kuribayashi Minoru 《Multimedia Tools and Applications》2018,77(13):16597-16622
In digital era, privacy preservation and data size reduction are important issues and many applications handle them simultaneously. In this paper, authors introduce a novel application of reversible data hiding to protect privacy sensitive region in a color image while reducing its file size. The proposed work introduces entropy as a new performance criterion along with distortion, capacity for reversible data hiding. Evaluation metric of the proposed method is a file size of watermarked and losslessly compressed image. The proposed method preserves privacy and controls rise in image entropy by reversible data hiding.
相似文献7.
Mehul Barde Montoia Davis Shivani Rangari Hajeewaka C. Mendis Leonardo De La Fuente Maria L. Auad 《应用聚合物科学杂志》2018,135(27)
To prepare antibacterial, polymeric catheters for preventing catheter‐induced infections, sulfathiazole was loaded into polyurethane by solubilizing with solvents and the resultant films were cast. Fourier transform infrared spectroscopy confirmed the presence of sulfathiazole in the drug‐loaded polyurethane films. The thermal and mechanical properties of the films were assessed using differential scanning calorimetry and dynamic mechanical analysis. The drug‐loaded films were immersed in constantly stirred, deionized water at 37 °C for in vitro drug release study. The experimental data obtained from the in vitro drug release study were fit into mathematical models. Antibacterial efficiency of released sulfathiazole was evaluated by Escherichia coli growth inhibition test. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46467. 相似文献
8.
In the study of iron catalysts, careful passivation is necessary for study of microstructure by ex situ analytical techniques. The passivation procedure used in our study consists of heating the sample in He at the reaction temperature, cooling to room temperature and introducing small amounts of O2 (<1%) in a flowing He stream. A properly passivated sample shows no more than a few nm of surface Fe3O4 on-Fe, when examined in a high resolution TEM. Proper passivation is also characterized by an exotherm of no more than 2–3 K. We show that a Fischer-Tropsch catalyst carbided in CO will show substantial amounts of magnetite, if exposed to air without proper passivation. Such surface oxidation may cause errors in determining the relative amounts of the magnetite and carbide phases in Fischer-Tropsch catalysts, which are important for proper identification of the catalytically active phase. 相似文献
9.
Kiran N. Solanki Mark A. Tschopp Mehul A. Bhatia Nathan R. Rhodes 《Metallurgical and Materials Transactions A》2013,44(3):1365-1375
Material strengthening and embrittlement are controlled by complex intrinsic interactions between dislocations and hydrogen-induced defect structures that strongly alter the observed deformation mechanisms in materials. In this study, we reported molecular statics simulations at zero temperature for pure α-Fe with a single H atom at an interstitial and vacancy site, and two H atoms at an interstitial and vacancy site for each of the 〈100〉, 〈110〉, and 〈111〉 symmetric tilt grain boundary (STGB) systems. Simulation results show that the grain boundary (GB) system has a smaller effect than the type of H defect configuration (interstitial H, H-vacancy, interstitial 2H, and 2H-vacancy). For example, the segregation energy of hydrogen configurations as a function of distance is comparable between symmetric tilt GB systems. However, the segregation energy of the 〈100〉 STGB system with H at an interstitial site is 23 pct of the segregation energy of 2H at a similar interstitial site. This implies that there is a large binding energy associated with two interstitial H atoms in the GB. Thus, the energy gained by this H-H reaction is ~54 pct of the segregation energy of 2H in an interstitial site, creating a large driving force for H atoms to bind to each other within the GB. Moreover, the cohesive energy values of 125 STGBs were calculated for various local H concentrations. We found that as the GB energy approaches zero, the energy gained by trapping more hydrogen atoms is negligible and the GB can fail via cleavage. These results also show that there is a strong correlation between the GB character and the trapping limit (saturation limit) for hydrogen. Finally, we developed an atomistic modeling framework to address the probabilistic nature of H segregation and the consequent embrittlement of the GB. These insights are useful for improving ductility by reengineering the GB character of polycrystalline materials to alter the segregation and embrittlement behavior in α-Fe. 相似文献
10.
Karl Johnson Caitlin B. Biddell Hillary K. Hecht Kristen H. Lich Julie Swann Paul Delamater Maria Mayorga Julie Ivy Raymond L. Smith Mehul D. Patel 《突发事故与危机管理杂志》2023,31(2):259-272
This study sought to understand COVID-19-related organizational decisions were made across sectors. To gain this understanding, we conducted semi-structured interviews with organizational decision-makers in North Carolina about their experiences responding to COVID-19. Conventional content analysis was used to analyse the context, inputs, and processes involved in decision-making. Between October 2020 and February 2021, we interviewed 44 decision-makers from the following sectors: business (n = 4), community non-profit (n = 3), county government (n = 4), healthcare (n = 5), local public health (n = 5), public safety (n = 7), religious (n = 6), education (n = 7) and transportation (n = 3). We found that during the pandemic, organizations looked to scientific authorities, the decisions of peer organizations, data about COVID-19, and their own experience with prior crises. Interpretation of inputs was informed by current political events, societal trends, and organization mission. Decision-makers had to account for divergent internal opinions and community behaviour. To navigate inputs and contextual factors, organizations decentralized decision-making authority, formed auxiliary decision-making bodies, learned to resolve internal conflicts, learned in real time from their crisis response, and routinely communicated decisions with their communities. In conclusion, aligned with systems and contingency theories of decision-making, decision-making during COVID-19 depended on an organization's ‘fit’ within the specifics of their existing system and their ability to orient the dynamics of that system to their own goals. 相似文献