Limited Scale-Free Overlay Topologies for Unstructured Peer-to-Peer Networks

In unstructured peer-to-peer (P2P) networks, the overlay topology (or connectivity graph) among peers is a crucial component in addition to the peer/data organization and search. Topological characteristics have profound impact on the efficiency of a search on such unstructured P2P networks, as well as other networks. A key limitation of scale-free (power-law) topologies is the high load (i.e., high degree) on a very few number of hub nodes. In a typical unstructured P2P network, peers are not willing to maintain high degrees/loads as they may not want to store a large number of entries for construction of the overlay topology. Therefore, to achieve fairness and practicality among all peers, hard cutoffs on the number of entries are imposed by the individual peers, which limits scale-freeness of the overall topology, hence limited scale-free networks. Thus, it is expected that the efficiency of the flooding search reduces as the size of the hard cutoff does. We investigate the construction of scale-free topologies with hard cutoffs (i.e., there are not any major hubs) and the effect of these hard cutoffs on the search efficiency. Interestingly, we observe that the efficiency of normalized flooding and random walk search algorithms increases as the hard cutoff decreases.     

Fuzzy logic control of vehicle suspensions with dry friction nonlinearity

We design and investigate the performance of fuzzy logic-controlled (FLC) active suspensions on a nonlinear vehicle model with four degrees of freedom, without causing any degeneration in suspension working limits. Force actuators were mounted parallel to the suspensions. In this new approach, linear combinations of the vertical velocities of the suspension ends and accelerations of the points of connection of the suspension to the body have been used as input variables. The study clearly demonstrates the effectiveness of the fuzzy logic controller for active suspension systems. Suspension working space degeneration is the most important problem in various applications. Decreasing the amplitudes of vehicle body vibrations improves ride comfort. Body bounce and pitch motion of the vehicle are presented both in time domain when travelling over a ramp-step road profile and in frequency domain. The results are compared with those of uncontrolled systems. At the end of this study, the performance and the advantage of the suggested approach and the improvement in ride comfort are discussed.     

The problem of human response to blast induced vibrations in tunnel construction and mitigation of vibration effects using cautious blasting in half-face blasting rounds

Blast induced ground vibrations generated by explosives in tunnel construction may cause structural damages in or close to urban areas. Therefore, the aim in blasting must be to suppress the vibration effects and mitigate the possible hazard on structures. But the psychological character of human response to vibrations involves highly subjective attitudes about what kind of environment is “acceptable” even if no structural damage is occurred. Therefore, we utilize the method of cautious blasting for half-faces that is environmentally friendly, and easy to utilize for tunnel construction. Small charges in this method are detonated sequentially to produce minimum side effects. This method is tested in a tunnel construction in Istanbul with numerous experimental shots. In these experiments, the duration and also quantity of explosives are carefully controlled. Regarding human response, better results are obtained with short durations (about 300 ms) compared to long durations (9000 or 480 ms). The quantity of maximum co-operating explosive charge decreases from 3.088 to 1.744 kg while the vibration levels defined as peak particle velocity (PPV) become more tolerable around 300 ms shot durations.     

Different control applications on a vehicle using fuzzy logic control

In this paper, the active suspension control of a vehicle model that has five degrees of freedom with a passenger seat using a fuzzy logic controller is studied. Three cases are taken into account as different control applications. In the first case, the vehicle model having passive suspensions with an active passenger seat is controlled. In the second case, active suspensions with passive passenger seat combination are controlled. In the third case, both the passenger seat and suspensions have active controllers. Vibrations of the passenger seat in the three cases due to road bump input are simulated. At the end of the study, the results are compared in order to select the combination that supplies the best ride comfort.     

The near-net-shape manufacturing of affordable titanium components for the M777 lightweight howitzer

The U.S. Marines’ and U.S. Army’s next-generation, titanium-intensive M777 howitzer offers reduced weight, increased mobility, and improved survivability over its aging, M198 steel-based predecessor. The National Center for Excellence in Metalworking Technology (NCEMT), operated by Concurrent Technologies Corporation, is helping to meet M777 program goals for cost, performance, and production schedule by developing near-net-shape manufacturing routes for traditionally machined and welded components. Under two projects sponsored by the Navy Manufacturing Technology Program, the NCEMT has developed investment cast spade and saddle components as well as flowformed tubes and forged bell housings. This paper summarizes the results of the two ongoing projects. For more information, contact Kevin L. Klug, Concurrent Technologies Corporation, 100 CTC Drive, Johnstown, PA 15904; (814) 269-2868; e-mail klugk@ctc.com.     

Elucidation of key aroma enhancement in cloudy lemon juices by the addition of peel oil using GC–MS-Olfactometry

Volatile substances play a crucial role in the consumer preference of lemon juices. The effects of heat treatment and addition of lemon peel oil to lemon juice (Citrus limon Burm. cv. Kutdiken) on the aroma compounds were elucidated for the first time. Total phenolic, antioxidant activity, acidity, pH and colour properties were also studied. Results revealed that the aroma of the juice samples comprised mostly the terpene compounds. Limonene, γ-terpinene, β-pinene and α-pinene were the influential terpenes responsible for the distinctive odour of the lemon juice. The addition of the lemon peel oil increased the amounts of the aroma and aroma-active compounds. Besides, the heat treatment had a positive effect on the total phenolics and the antioxidant activity but it caused significant reduction of the aroma compounds. Sensory analysis revealed that the most preferred sample was the juice with lemon peel oil added after pasteurisation.