A Polynomial Time Solution to Minimum Forwarding Set Problem in Wireless Networks under Unit Disk Coverage Model

Network-wide broadcast (simply broadcast) is a frequently used operation in wireless ad hoc networks (WANETs). One promising practical approach for energy-efficient broadcast is to use localized algorithms to minimize the number of nodes involved in the propagation of the broadcast messages. In this context, the minimum forwarding set problem (MFSP) (also known as multipoint relay (MPR) problem) has received a considerable attention in the research community. Even though the general form of the problem is shown to be NP-complete, the complexity of the problem has not been known under the practical application context of ad hoc networks. In this paper, we present a polynomial time algorithm to solve the MFSP for wireless network under unit disk coverage model. We prove the existence of some geometrical properties for the problem and then propose a polynomial time algorithm to build an optimal solution based on these properties. To the best of our knowledge, our algorithm is the first polynomial time solution to the MFSP under the unit disk coverage model. We believe that the work presented in this paper will have an impact on the design and development of new algorithms for several wireless network applications including energy-efficient multicast, broadcast, and topology control protocols for WANETs and sensor networks.     

The ratio of crystallinity and thermodynamical interactions of polycaprolactone with some aliphatic esters and aromatic solvents by inverse gas chromatography

Summary The retention diagrams of benzene, toluene, ethyl benzene, chloro benzene, n-propyl benzene, isopropyl benzene, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate and isoamyl acetate on the polycaprolactone were plotted at temperatures between 70 and 140^oC by inverse gas chromatography technique. Percent crystallinity of polycaprolactone were obtained at temperatures below melting point from the retention diagrams of benzene, toluene and ethyl benzene. It was concluded that the data obtained by inverse gas chromatography were comparable those of obtained by differential scanning calorimetry. Specific retention volume, V_g^o, Flory-Huggins polymer-solvent interaction parameters, ₁₂, the weight fraction activity coefficients of the solvents at infinite dilution, ₁, effective exchange energy parameters, X_eff were determined. Later, the partial molar heat of sorption, H_1,sorp and the partial molar heat of mixing, H₁ were obtained from the slope of the logarithm of specific retention volume, Ln V_g^o versus 1/T plot and from the slope of the logarithm of the weight fraction activity coefficients, ₁versus 1/T plot, respectively.     

A Distributed Approach for Monitoring Multicast Service Availability

With the deployment of native multicast in commercial networks, multicast is getting closer to becoming a ubiquitous service in the Internet. The success of this deployment largely depends on the availability of good management tools and systems. One of the most important management tasks for multicast is to verify the availability of the service to its users. This task is usually referred to as reachability monitoring. Reachability monitoring requires a number of monitoring stations to work together to collect this information in a distributed manner in the interdomain scale. In this paper we present a general architecture for multicast reachability monitoring systems and focus on three critical functions: agent configuration, monitoring, and feedback collection. For each component, we provide a number of alternative approaches to implement the required functionality and discuss their advantages and disadvantages. Then, we focus on the feedback collection component. To a large extent, it determines the complexity and the overhead of a monitoring system. Using simulations, we compare a number of alternative approaches for feedback collection and make suggestions on when to use each. We believe our work provides insight into the issues and considerations in designing and developing multicast reachability monitoring systems.     

Characterization of nanocrystalline Ni–Cu thin films electrodeposited onto ITO coated glass substrates: effect of pretreatment current density

In this work, Ni–Cu films were grown onto indium tin oxide coated glass substrates without and with galvanostatic pretreatment process at different current densities. In all cases, Ni–Cu films were electrodeposited at a constant deposition potential of ?1,800 mV versus saturated calomel electrode. After that, the surface morphology and structural properties of electrodeposited Ni–Cu films in dependence of pretreatment current density were studied. X-ray diffraction analysis showed that all films have face-centered cubic structure and consist of segregated two Ni-rich and Cu-rich phases regardless of pretreatment current density. The compositional analysis carried out by energy dispersive X-ray spectroscopy revealed that all films contain almost 90 wt% Ni and 10 wt% Cu. The average crystallite size decreased with decreasing pretreatment current density towards more negative values without inducing significant changes in the composition of the films. It was found that the preferred orientation of all films is in the [111] direction regardless of pretreatment current density. The effect of galvanostatic pretreatment process on the surface morphology investigated using a scanning electron microscopy and an atomic force microcopy were also discussed by means of obtained results.     

Mechanical,chemical, thermal,and rheological properties of recycled PA6/ABS binary and PA6/PA66/ABS ternary blends

The effects of multiple injection molding cycles on the chemical and mechanical properties of PA6/ABS and PA6/PA66/ABS blends are investigated. The chemical structures of both PA6/ABS binary and PA6/PA66/ABS ternary blends do not alter after recycling process. For PA6/ABS binary blend, it is found that the tensile strength, strain at break, elastic modulus, impact strength, flexural strength, and modulus of recycled blend decrease by 6.49%, 15.19%, 21.00%, 9.41%, 7.09%, and 8.25%, respectively, while MFI increases by 23.59% as compared with the virgin blend. After five recycling process for PA6/PA66/ABS ternary blend, the tensile strength, strain at break, and impact strength of recycled blend decrease by 18.00%, 50.80%, and 87.27%, respectively. However, flexural strength and modulus of PA6/PA66/ABS blend increase slightly. For virgin PA6/PA66/ABS blend, MFI value was 7.7 g/10 min and with recycling this value showed an important increase to 31.56 g/10 min after five cycles. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40810.     

Copolymer of ketonic resin–polyacrylonitrile

The polymerization of acrylonitrile in the presence of Ce(IV) salts and ketonic resin such as methyl ethyl ketone/formaldehyde and cyclohexanone/formaldehyde resin was investigated. Block copolymer of ketonic resin–polyacrylonitrile was produced. The effect of Ce(IV) concentration, temperature, time, and monomer concentration on the yield and molecular weight was studied. Maximum yield was obtained at 50°C and ceric ammonium nitrate concentration of 0.033 mol/L.     

Tracetree: a scalable mechanism to discover multicast tree topologies in the Internet

The successful deployment of multicast in the Internet requires the availability of good network management solutions. Discovering multicast tree topologies is an important component of this task. Network managers can use topology information to monitor and debug potential multicast forwarding problems. In addition, the collected topology has several other uses, for example, in reliable multicast transport protocols, in multicast congestion control protocols, and in discovering network characteristics. We present a mechanism for discovering multicast tree topologies using the forwarding state in the network. We call our approach tracetree. First, we present the basic operation of tracetree. Then, we explore various issues related to its functionality (e.g., scalability, security, etc.). Next, we provide a detailed evaluation by comparing it to the currently available alternatives. Finally, we discuss a number of deployment issues. We believe that tracetree provides an efficient and scalable mechanism for discovering multicast tree topologies and therefore fills an important void in the area of multicast network management.     

Energy conservation in compressed‐air systems

In this paper, we evaluate and quantify the energy losses associated with compressed‐air systems, and their costs to manufacturers. We also show how to reduce the cost of compressed air in existing facilities by making some modifications with attractive payback periods. Among the measures, we investigate to reduce the compressed air are: (1) repairing air leaks, (2) installing high‐efficiency motors, (3) reducing the average air inlet temperature by using outside air (4) reducing compressor air pressure. We also illustrate the potential saving associated with each measure by using realistic examples. Copyright © 2002 John Wiley & Sons, Ltd.     

Transport and Mechanical Properties of High-ZT Mg2.08Si0.4−x Sn0.6Sb x Thermoelectric Materials

Mg₂(Si,Sn) compounds are promising candidate low-cost, lightweight, nontoxic thermoelectric materials made from abundant elements and are suited for power generation applications in the intermediate temperature range of 600 K to 800 K. Knowledge on the transport and mechanical properties of Mg₂(Si,Sn) compounds is essential to the design of Mg₂(Si,Sn)-based thermoelectric devices. In this work, such materials were synthesized using the molten-salt sealing method and were powder processed, followed by pulsed electric sintering densification. A set of Mg_2.08Si_0.4?x Sn_0.6Sb _x (0 ≤ x ≤ 0.072) compounds were investigated, and a peak ZT of 1.50 was obtained at 716 K in Mg_2.08Si_0.364Sn_0.6Sb_0.036. The high ZT is attributed to a high electrical conductivity in these samples, possibly caused by a magnesium deficiency in the final product. The mechanical response of the material to stresses is a function of the elastic moduli. The temperature-dependent Young’s modulus, shear modulus, bulk modulus, Poisson’s ratio, acoustic wave speeds, and acoustic Debye temperature of the undoped Mg₂(Si,Sn) compounds were measured using resonant ultrasound spectroscopy from 295 K to 603 K. In addition, the hardness and fracture toughness were measured at room temperature.