A Time-Slot Assignment Strategy for ATM Broadband Indoor Wireless Networks

The rapid development of wireless in-building communication systems, has widened the scope of supported applications. Remote terminals may be capable of producing broadband real-time traffic such as variable bit-rate (VBR) video or bursty data transfers. Consequently one of the important issues in indoor broadband wireless networks (IBWN) is employment of an efficient bandwidth management protocol. In such a protocol, both the effects of radio channel behavior and the traffic heterogeneity have to be considered. In this paper we present a bandwidth allocation scheme based on the interplay of the radio channel characteristics and the traffic parameters and requirements. In the proposed scheme the base station visits the terminals in a non-uniform cyclic fashion. The inter-visit interval and the amount of service which is provided to each user during a visit, is determined using the channel and traffic parameters based on an analytical approach. This system is evaluated by simulations and is found to provide improved performance in fulfilling the requirements of multimedia services in IBWN.     

The behaviour of aged three‐way catalytic converters in the different modes of legislated cycles

Automotive three‐way catalytic converters are routinely applied today in the elimination of carbon monoxide, urburned or partially burned hydrocarbons and nitrogen oxides from gasoline engine exhaust gas. Catalyst activity in this case is only indirectly assessed by means of the measurement of overall emissions during a legislated driving cycle. The specific structure of the driving cycles embodied in a legislated emissions test procedure, significantly affects catalyst performance. In addition, catalyst behaviour is affected by the levels of raw engine emissions and catalyst inlet temperatures. The latter are strongly influenced by exhaust system design. The above explain easily the difficulties arising when one wants to discriminate between the behaviour of different catalysts in a specific test procedure. The advent of reliable mathematical models of three‐way catalytic converter operation allows for a detailed analysis of catalyst performance over the full legislated cycle, which gives more insight into the catalytic activity itself. In this paper, a specific experimental and computational case study is employed to demonstrate the role of mathematical modelling in the detailed analysis of aged catalyst performance during the US and EU legislated test procedures. Copyright © 2000 John Wiley & Sons, Ltd.     

DYNAMIC FILTRATION MODELING IN FOAM FILTERS FOR DIESEL EXHAUST

Diesel Particulate Filters (DPFs) are probably the most effective means for trapping the exhaust emitted particulate from diesel engines. Foam type filters become a promising alternative to the common wall flow filters, since they are effective in filtering small size particles and provide a larger specific surface area for catalytic coatings. A mathematical model taking into account the significant phenomena during the dynamic filtration of foam fitters is developed. The model predicts the filtration efficiency and the induced backpressure as function of the geometric filter properties and operating conditions. A novel approach is employed which considers both “deep-bed” and “cake”filtration characteristics in the filter. Due to the particular structure properties of the foam filters it is necessary to define a characteristic parameter, which differentiates among different filter types. This parameter, which has a physical meaning, is easily derived by simple experimental measurements. The model is employed to. identify and understand the critical parameters of the phenomenon. Indicative parametric runs are presented, which illustrate the applicability of the model in system optimization procedures.     

THREE-WAY CATALYTIC CONVERTER MODELING AND APPLICATIONS

The advent of stricter U.S. and European exhaust emissions regulations has increased the need for reliable 3-way catalytic converter models supporting the design of demanding exhaust systems for low-emitting vehicles. Although a number of tunable models have been presented in the literature, their efficient performance in actual 3-way applicaions requires further development and validation. The major difficulties posed in such modeling efforts arise from the complexities in the reaction schemes and the respective rate expressions for the multitude of currently used catalyst formulations. This paper addresses the details of tuning and real world application of a two-dimensional catalytic converter model, which accounts for the HC (hydrocarbons) and CO oxidation, as well as NO reduction reactions. The model features a number of innovations regarding the catalyst transient behaviour modelling and the reaction kinetics scheme. The advanced oxygen storage submodel presented is capable of accounting for the redox and temperature dependence of the oxygen availability under transient operation. The redox sensitivity of the reaction scheme allows to get clearer insight in the “lambda-window” behavior of 3-way catalysts. It is concluded, that mathematical modelling may successfully describe important aspects of real world three-way catalytic converter operation under dynamic conditions, and thus, is a valid tool in exhaust aftertreatment systems optimization.     

Analytical calculation of local buckling and post-buckling behavior of isotropic and orthotropic stiffened panels

A methodology for the analytical assessment of local buckling and post-buckling behavior of isotropic and orthotropic stiffened plates is presented. The approach considers the stiffened panel segment located between two stiffeners, while the remaining panel is replaced by equivalent transverse and rotational springs of varying stiffness, which act as elastic edge supports. A two-dimensional Ritz displacement function (pb-2 Ritz) is utilized in the solution of the local buckling problem of isotropic and laminated symmetric composite panels with arbitrary edge boundary conditions. The buckling analysis of the segment provides an accurate and conservative prediction of the panel local buckling behavior. Consequently, the developed methodology is extended in the prediction of the post-buckling response of stiffened panels of which the skin has undergone local buckling. Of high importance for the calculation of the post-buckling behavior is the selection of appropriate boundary conditions for the structural members analyzed. A comparison of the present methodology results to respective finite element (FE) results has shown a satisfactory agreement.     

Combination chemotherapy with cisplatin-vinblastine in malignant mesothelioma

From June 1985 to March 1993, 20 consecutive patients with histologically proven malignant mesothelioma were treated with cisplatin 100 mg/m2 i.v. infusion on day 1 and vinblastine 6 mg/m2 i.v. on day 1 and 8. Treatment was repeated every 4 weeks until progression. All patients were evaluated clinically and by CT-scan and were staged (Stage IV), according to Butchard's criteria, on entry to the study. None had prior surgical excision. Eighty-one chemotherapy cycles were administered to 20 patients. One complete response, four partial responses, nine stable diseases and six progressions were noted. One partial responder entered complete response following an operation. Toxicity was acceptable and no treatment-related deaths occurred. The median survival for responders was 19.3 months; for patients with stable disease 15.7 months and for non-responders, 5.2 months. The mean duration of response was 13 months. We conclude that for this small group of patients, the combination cisplatin-vinblastine is effective, with acceptable toxicity in malignant mesothelioma. Further study with a larger number of patients is necessary.     

LMDS/LMCS hub interconnection alternatives and multiple access issues

LMDS/LMCS is a broadband wireless local loop, millimeter‐wave alternative to emerging integrated multiservice access networks. Significantly large amounts of bandwidth – in the order of one GHz of spectrum – are made available to residential subscribers or supported business users respectively that employ highly directional antennas and signal polarization to establish communication with a central hub. Besides the requirement for dynamic bandwidth allocation capabilities, these networks should be able to guarantee negotiated quality of service (QoS) levels to a number of constant‐length (ATM) – and possibly variable length (TCP/IP) – packet streams. In this context, we analyze the performance of contention, polling/probing and piggybacking mechanisms that will be used by the LMDS MAC protocol for the dynamic support of both real‐time and non‐real‐time traffic streams. More specifically, we focus on the end‐to‐end performance of a real‐time variable bit rate connection for which the LMDS link is only the access component of a multi‐link path through an ATM network. Results are presented on maximum end‐to‐end cell delays under a Weighted Round Robin service discipline and buffer requirements are calculated for no‐loss conditions. In parallel, we also consider the case in which variable length IP packet traffic is supported as such by the same wireless access network. Backbone interconnection alternatives of LMDS hubs, multiple access proposals and scheduling algorithms are addressed in this framework. This revised version was published online in July 2006 with corrections to the Cover Date.     

Performance evaluation of candidate MAC protocols for LMCS/LMDSnetworks

Broadband wireless access (BWA) offers attractive features such as ease and speed of deployment, fast realization of revenues, and low infrastructure cost. This paper focuses on medium access control (MAC) alternatives that can find application in an LMDS/LMCS network capable of supporting multimedia traffic. Multifrequency demand assignment TDMA-based schemes appear (at the moment) to be a suitable choice in this context. The selected protocol should be dynamically capable of providing multirate capabilities and quality-of-service guarantees. An obvious candidate for the aforementioned purpose is the LMDS-specific MAC proposal in the DAVIC 1.2 recommendation. For purposes of comparison, we also examine the evolving IEEE 802.14 MAC convergence protocol and MCNS (multimedia cable network system) DOCSIS (ITU J-112) MAC standard that are intended to support similar applications and services in an HFC (hybrid fiber coax) environment. The three protocols are examined under noiseless and noisy channel conditions. Previous results on LMDS channel characteristics are summarized and used for modeling noisy channel conditions. The candidate protocols are compared in terms of mean access delay, throughput, and collision multiplicity statistics, when contention of users is involved. The effect of dynamic slot allocation on the performance of the candidate protocols is also examined     

An investigation of shape memory alloys as actuating elements in aerospace morphing applications

Two innovative actuating concepts for aerospace morphing applications, based on shape memory alloys (SMAs), are proposed. The first concept investigates a composite plate incorporating embedded SMA wires. A nonlinear auto regressive with exogenous excitation model is proposed for controlling single-cycle/multi-cycle loading conditions of the SMA wires. The second actuating concept studies a novel rib configuration, which incorporates a compliant mechanism for enabling aerofoil's leading edge morphing. Different rib-compliant mechanism concepts are designed and analyzed. The most efficient rib concept is experimentally characterized. The experimental results from both actuating concepts showed good agreement with the respective numerical.