Topology-aided cross-layer fast handoff designs for IEEE 802.11/mobile IP environments

This study first reviews state-of-the-art fast handoff techniques for IEEE 802.11 or Mobile IP networks. Based on that review, topology-aided cross-layer fast handoff designs are proposed for Mobile IP over IEEE 802.1.1 networks. Time-sensitive applications, such as voice over IP (VoIP), cannot tolerate the long layer-2 plus layer-3 handoff delays that arise in IEEE 802.11/Mobile IP environments. Cross-layer designs are increasingly adopted to shorten the handoff latency time. Handoff-related layer-2 triggers may reduce the delay between layer-2 handoff completion and the associated layer-3 handoff activation. Cross-layer topology information, such as the association between 802.11 access points and Mobile IP mobility agents, together with layer-2 triggers, can be utilized by a mobile node to start layer-3 handoff-related activities, such as agent discovery, address configuration, and registration, in parallel with or prior to those of layer-2 handoff. Experimental results indicate that the whole handoff. delay can meet the delay requirement of VoIP applications when layer-3 handoff activities occur prior to layer-2 handoffs.     

New voice over Internet protocol technique with hierarchical datasecurity protection

The authors propose a voice over Internet protocol (VoIP) technique with a new hierarchical data security protection (HDSP) scheme. The proposed HDSP scheme can maintain the voice quality degraded from packet loss and preserve high data security. It performs both the data inter-leaving on the inter-frame of voice for achieving better error recovery of voices suffering from continuous packet loss, and the data encryption on the intra-frame of voice for achieving high data security, which are controlled by a random bit-string sequence generated from a chaotic system. To demonstrate the performance of the proposed HDSP scheme, we have successfully verified and analysed the proposed approach through software simulation and statistical measures on several test voices     

Intermetallic formation in Sn3Ag0.5Cu and Sn3Ag0.5Cu0.06Ni0.01Ge solder BGA packages with immersion Ag surface finish

The intermetallic compounds formed in Sn3Ag0.5Cu and Sn3Ag0.5Cu0.06Ni0.01Ge solder BGA packages with Ag/Cu pads are investigated. After reflow, scallop-shaped η-Cu₆Sn₅ and continuous planar η-(cu_0.9Ni_0.1)₆Sn₅ intermetallics appear at the interfaces of the Sn3Ag0.5Cu and Sn3Ag0.5Cu0.06Ni0.01Ge solder joints, respectively. In the case of the Sn3Ag0.5Cu specimens, an additional ε-Cu₃Sn intermetallic layer is formed at the interface between the η-Cu₆Sn₅ and Cu pads after aging at 150°C, while the same type of intermetallic formation is inhibited in the Sn3Ag0.5Cu0.06Ni0.01Ge packages. In addition, the coarsening of Ag₃Sn precipitates also abates in the solder matrix of the Sn3Ag0.5Cu0.06Ni0.01Ge packages, which results in a slightly higher ball shear strength for the specimens.     

Spatiotemporal Magnetocaloric Microenvironment for Guiding the Fate of Biodegradable Polymer Implants

The degradation behavior of implants is significantly important for bone repair. However, it is still unprocurable to spatiotemporally regulate the degradation of the implants to match bone ingrowth. In this paper, a magneto-controlled biodegradation model is established to explore the degradation behavior of magnetic scaffolds in a magnetothermal microenvironment generated by an alternating magnetic field (AMF). The results demonstrate that the scaffolds can be heated by magnetic nanoparticles (NPs) under AMF, which dramatically accelerated scaffold degradation. Especially, magnetic NPs modified by oleic acid with a better interface compatibility exhibit a greater heating efficiency to further facilitate the degradation. Furthermore, the molecular dynamics simulations reveal that the enhanced motion correlation between magnetic NPs and polymer matrix can accelerate the energy transfer. As a proof-of-concept, the feasibility of magneto-controlled degradation for implants is demonstrated, and an optimizing strategy for better heating efficiency of nanomaterials is provided, which may have great instructive significance for clinical medicine.     

Rewritable Electrically Controllable Liquid Crystal Actuators

Conductive structures determine the functions and actuation modes of electrically responsive soft actuators. The rewritability of conductive structures is highly desirable but has not been realized in electro-driven actuators. Typically, once conductive pathways are established, they can hardly be modified; thus, the function of the actuator is permanently fixed. In this study, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is developed as a rewritable conductive coating for actuators composed of liquid crystalline elastomers (LCEs). This enables reconfigurable, adaptive, and precisely controllable electro-driven motions and the repeated use of the same actuator for various purposes without disposal. Moreover, different PEDOT:PSS layers can be coated onto different regions, thus enabling the assembly of different actuation behaviors in a monolithic actuator under a single input voltage. Unlike all previously reported soft actuators that respond to electricity and light, opposite shape changes in an actuator with a series circuit can be performed under these two stimuli. Furthermore, when combining LCEs with dynamic covalent bonds, the PEDOT:PSS-coated LCE (PEDOT:PSS-LCE) actuator can be reprogrammed based on two different mechanisms: rewriting the conductive PEDOT:PSS patterns and re-aligning the LCEs. This versatile method can be adapted to other types of actuators.     

Interfacial Reactions of Sn, Sn-3.0Ag-0.5Cu, and Sn-9Zn Lead-Free Solders with Fe-42Ni Substrates

Interfacial reactions between Sn, Sn-3.0 wt.%Ag-0.5 wt.%Cu (SAC), and Sn-9 wt.%Zn (SZ) lead-free solders and Fe-42 wt.%Ni (alloy 42) substrates at 240°C, 255°C, and 270°C were investigated in this study. FeSn₂, (Fe,Ni, Cu)Sn₂, and (Ni,Fe)₅Zn₂₁ phases were formed, respectively, at the interface in the Sn/alloy 42, SAC/alloy 42, and SZ/alloy 42 couples. As the reaction time and temperature were increased, the layered intermetallic compound (IMC) assumed two distinct structures, i.e., a thicker layer and a pillar-shaped IMC, in all couples. The IMC thickness of these couples increased with the increase of reaction time and temperature. The IMC thickness was also proportional to the square root of the reaction time. The interfacial reaction mechanism of these couples was diffusion controlled.     

Admission Control Algorithms for Revenue Optimization with QoS Guarantees in Mobile Wireless Networks

We propose and analyze call admission control algorithms integrated with pricing for revenue optimization with QoS guarantees to serve multiple service classes in mobile wireless networks. Traditional admission control algorithms make acceptance decisions for new and handoff calls to satisfy certain QoS constraints such as the dropping probability of handoff calls and the blocking probability of new calls being lower than a pre-specified threshold. We analyze a class of partitioning and threshold-based admission control algorithms that make acceptance/rejection decisions not only to satisfy QoS requirements but also to optimize the revenue of the system by taking prices and arrival/departure information of service calls into account. We show that for a “charge-by-time” pricing scheme, there exist optimal resource allocation settings under which the partitioning and threshold-based admission control algorithms would produce the maximum revenue obtainable by the system without sacrificing QoS requirements. Further, we develop a new hybrid admission control algorithm which outperforms both partitioning and threshold-based admission control algorithms over a wide range of input parameters characterizing the operating environment and service workload conditions. Methods for utilizing of the analysis results for realtime admission control for revenue optimization with QoS guarantees are described with numerical data given to demonstrate the applicability.     

Algorithms for supporting disconnected write operations for wireless Web access in mobile client-server environments

In a wireless mobile client-server environment, a mobile user may voluntarily disconnect itself from the Web server to save its battery life and avoid high communication prices. To allow Web pages to be updated while the mobile user is disconnected from the Web server, updates can be staged in the mobile host and propagated back to the Web server upon reconnection. In this paper, we analyze algorithms for supporting disconnected write operations for wireless Web access and develop a performance model to identify the optimal length of the disconnection period under which the cost of update propagation is minimized. The analysis result is particularly applicable to Web applications which allow wireless mobile users to modify Web contents while on the move. We show how the result can be applied to real-time Web applications such that the mobile user can determine the longest disconnection period such that it can still propagate updates to the server before the deadline so that a minimum communication cost is incurred.     

Error probability for orthogonal space-time block code diversity system using rectangular QAM transmission over Rayleigh fading channels

In this paper, theoretical symbol error probability (SEP) expressions are derived for orthogonal space-time block code (OSTBC) diversity systems employing arbitrary rectangular M-QAM transmission over flat Rayleigh fading channels. Independent fading between diversity channels is assumed. Channel average powers may be distinctive, identical, or mixed with both. The rectangular M-QAM results are extended to square M-QAM, M-PAM, and binary antipodal signaling. All derived expressions are in elementary forms without complicated high-order transcendental functions and unevaluated integrals and, hence, are strictly exact and can be readily simulated by the computer. Moreover, it is shown that mixed Rayleigh fading results can be readily extended to various Nakagami-m fading results. A four-transmit-antenna system with a half-rate OSTBC for 16-QAM signaling is used to demonstrate that the theoretical result is in excellent agreement with the Monte Carlo simulated result. From simulation curves, it is shown that, under the independent channel fading condition, channels with identical powers have better error rate performance than channels with distinctive powers.     

POLAROGRAPHIC CHARACTERIZATION OF AROMATIC STRUCTURES IN COAL LIQUID PRODUCTS

Reducible aromatic species in coal liquid products from five major processes (Synthoil, FMC COED, HRI H-Coal, PAMCO SRC, and Catalytic Inc. SRC) together with solvent elution chromatography fractions of a selected asphaltene has been evaluated. The half-wave potentials measurments are found to be consistant with other methods. The total polarographic reduction of measurement per average molecule for Synthoil solvent fractions, as measured by diffusion constant (i_d/C), increases in the following manner: gas oil → resin → asphaltene → carbene → carboid. The same trend was observed when color indices (I) and refractive indices (n₂₅) were individually studied.