A New Exposed-terminal-free MAC Protocol for Multi-hop Wireless Networks

AbstractThis article presents a new multichannel medium access control (MAC) protocol to solve the exposed-terminal (ET) problem for efficient channel sharing in multi-hop wireless networks. It uses request-to-send and clear-to-send (RTS/CTS) dialogue on a common channel and flexibly opts for conflict-free traffic channels to carry out the data packet transmission on the basis of a new channel selection scheme. The acknowledgment (ACK) packet for the data packet transmission is sent back to the sender over another common channel thus completely eliminating the exposed-terminal effects. Any adjacent communication pair can take full advantage of multiple traffic channels without collision and the spatial reuse of the same channel is extended to other communication pairs which are even within 2 hops from them. In addition, the hidden-terminal effect is also considerably reduced because most of possible packet collisions on a single channel are avoided due to traffic load balance on multichannels. Finally, a performance comparison is made between the proposed protocol and other typical MAC protocols. Simulation results evidence its obvious superiority to the MAC protocols associated with other channel selection schemes and traditional ACK transmission scheme as well as cooperative asynchronous multichannel MAC (CAM-MAC) protocol in terms of four performance indices: total channel utilization, average channel utilization, average packet delay, and packet dropping rate

Sediment Transport using Grain Size Trend Analysis: A Case Study in SW of Portugal

As a embayed coast, the main sediment sources are fluvial discharges, sea-cliff erosion and sand carried by longshore currents [1]. The particles are transported in suspended load or bedload pattern under the coactions of tidal currents and waves. In response to sediment transport processes, the spatial variations in the grain-size parameters exist, that reflect the net particles transport trend and the dynamic conditions. Thus, the grain size trend analysis was developed to study the net sediment transport. The study area is an embayed coast from Troia to Sines in SW of Portugal. There is a cape in the south end while the north end is a mountain belt with 35 km in length and 500 m in height [2]. A river with small discharge lies in the north. The tidal range varies between 1.5~3.5 m while the swell and winds from the west and northwest are dominant [3]. Therefore, the study area is sheltered from persist winds from north in summer and exposed to the storm waves from southwest in winter. The surfical sediment was sampled in the shallow water in 1980, 1983 and 1985, respectively. In order to obtain the important sediment source and sediment transport trend, three approaches were used: (1) the EOF (Empirical Orthogonal Function) analysis technique; (2) the McLaren Model; (3) grain size trend analysis. The wave is dominant in the study area. The result of EOF analysis shows that the most important sediment source is cliff erosion. The sediment eroded from cliffs during storms and high waves was transported off-shore and southward in the south part during high energy effect, in the north part that was carried by longshore current northwards and deposit at the left of the estuarine. The mud discharged from the river met with the west waves and deposited at the lee side of the mountain belt. It would be concluded that the sediment was disturbed and transported perpendicular to the shoreline by the southwest storm waves in winter and along the shoreline by persist wind in summer. Keywords: Grain size trend analysis; EOF; embayed coast; SW Portuga

Preparation and properties of desulfurization gypsum-slag hydraulic cementitious materials

AbstractDesulfurization gypsum is the desulphurization products of wet FGD process in coal-fired power plants. However, it has not been widely used by far. In order to expand the application scope of desulphurization gypsum, desulphurization gypsum-industrial waste composite cementing material, a new type of hydraulic cementing material prepared by a lot of desulphurization gypsum, granulated blast furnace slag and some activator is studied in this paper. Its performance is also studied

Global Value Chain Restructuring in the trade of Knocked Down products

Trade in knocked down products embodies the international division of labour and the distribution characteristics of the global value chains. The value chain of the trade in knocked down products is defined in this paper through the analysis of the process of the intra-product international division of labour. Firstly, the value chain of knocked down products is divided into two parts, i.e. the value chain of product design and production and the value change of product assembly and sale. Then, the necessary conditions are deduced to realize the reconstruction of the value chain. The tariff escalation policy of the importing country is the main reason for the disruption of the product value chain and the value shifting to the importing country. Finally, the areas of value chain disruption in the cases of various modes of trade in knocked down products are established. As a result, the research on the restructuring of the value chain in the trade in knocked down products will help companies choose a high value link in the value chain from the global distribution perspective

Planning analysis for locally advanced lung cancer: dosimetric and efficiency comparisons between intensity-modulated radiotherapy (IMRT), single-arc/partial-arc volumetric modulated arc therapy (SA/PA-VMAT)

<p>Abstract</p> <p>Purpose</p> <p>To analyze the differences between the intensity-modulated radiotherapy (IMRT), single/partial-arc volumetric modulated arc therapy (SA/PA-VMAT) techniques in treatment planning for locally advanced lung cancer.</p> <p>Materials and methods</p> <p>12 patients were retrospectively studied. In each patient's case, several parameters were analyzed based on the dose-volume histograms (DVH) of the IMRT, SA/PA-VMAT plans respectively. Also, each plan was delivered to a phantom for time comparison.</p> <p>Results</p> <p>The SA-VMAT plans showed the superior target dose coverage, although the minimum/mean/maximum doses to the target were similar. For the total and contralateral lungs, the higher V_5/10, lower V_20/30and mean lung dose (MLD) were observed in the SA/PA-VMAT plans (<it>p </it>< 0.05, respectively). The PA-VMAT technique improves the dose sparing (V₂₀, V₃₀and MLD) of the controlateral lung more notably, comparing to those parameters of the IMRT and SA-VMAT plans respectively. The delivered monitor units (MUs) and treatment times were reduced significantly with VMAT plans, especially PA-VMAT plans (for MUs: mean 458.3 <it>vs</it>. 439.2 <it>vs</it>. 435.7 MUs, <it>p </it>< 0.05 and for treatment time: mean 13.7 <it>vs</it>. 10.6 <it>vs</it>. 6.4 minutes, <it>p </it>< 0.01).</p> <p>Conclusions</p> <p>The SA-VMAT technique achieves highly conformal dose distribution to the target. Comparing to the IMRT plans, the higher V_5/10, lower V_20/30and MLD were observed in the total and contralateral lungs in the VMAT plans, especially in the PA-VMAT plans. The SA/PA-VMAT plans also reduced treatment time with more efficient dose delivering. But the clinical benefit of the VMAT technique for locally advanced lung cancer needs further investigations.</p

Sediment sources and transport pathway identification based on grain-size distributions on the SW coast of Portugal

Espichel-Sines is an embayed coast in SW Portugal, consisting of two capes at both extremities, a tidal inlet and associated ebb tidal delta, a barrier spit, sandy beaches, sea cliffs, and a submarine canyon. Beach berm, backshore, near shore and inner shelf sediment samples were taken. Samples were analyzed for their grain-size compositions. This study ranks the hypothetical sediment sources influences on the sediment distributions in the study area using the multivariate Empirical Orthogonal Function (EOF) techniques. Transport pathways in this study were independently identified using the grain size trend analysis (GSTA) technique to verify the EOF findings. The results show that the cliff-erosion sediment is composed of pebbles and sand and is the most important sediment source for the entire embayment. The sediment at the inlet mouth is a mixture of pebbles, sand, silt, and clay, which is a minor sediment source that only has local influence. The overall grain-size distributions on the shelf are dominated by the sand except for the high mud content around the tidal delta front in the northern embayment. Sediment transport patterns on the inner shelf at the landward and north sides of the canyon head are landward and northward along the barrier spit, respectively. On the south side of the canyon head, the prevailing sediment transport is seaward. Sediment transport occurs in both directions along the shore

Cellulose-starch hybrid films plasticized by aqueous ZnCl2 solution

Starch and cellulose are two typical natural polymers from plants that have similar chemical structures. The blending of these two biopolymers for materials development is an interesting topic, although how their molecular interactions could influence the conformation and properties of the resultant materials has not been studied extensively. Herein, the rheological properties of cellulose/starch/ZnCl2 solutions were studied, and the structures and properties of cellulose-starch hybrid films were characterized. The rheological study shows that compared with starch (containing mostly amylose), cellulose contributed more to the solution’s viscosity and has a stronger shear-thinning behavior. A comparison between the experimental and calculated zero-shear-rate viscosities indicates that compact complexes (interfacial interactions) formed between cellulose and starch with ≤50 wt % cellulose content, whereas a loose structure (phase separation) existed with ≥70 wt % cellulose content. For starch-rich hybrid films prepared by compression molding, less than 7 wt % of cellulose was found to improve the mechanical properties despite the reduced crystallinity of the starch; for cellulose-rich hybrid films, a higher content of starch reduced the material properties, although the chemical interactions were not apparently influenced. It is concluded that the mechanical properties of biopolymer films were mainly affected by the structural conformation, as indicated by the rheological results. View Full-Tex