Confinement Effectiveness in Rectangular Concrete Columns with Fiber Reinforced Polymer Wraps

An innovative mechanistic based method for passive confinement efficiency estimation is proposed based on the extension to rectangular sections of the pulley model previously proposed by the writers. A refined finite element model was developed using a nonlinear concrete constitutive law in order to analyze stresses in columns passively confined with fiber reinforced polymer wraps. Rectangular and square cross sections of variable corner radii were investigated with reference to a circular cross section. Results showed an increase in corner stresses with sharper corner radii, a localization of failure at the corners, and a decrease in confinement effectiveness with an increase in the rectangularity of the cross section or an increase in corner sharpness. A rigorous numerical method for calculating geometric confinement efficiency factors is proposed and typical factors are calculated and compared with the predictions of the simple pulley model showing good agreement.     

A collaborative defense mechanism against SYN flooding attacks in IP networks

SYN flooding exploits the Transmission Control Protocol (TCP) three-way handshake process by sending many connection requests using spoofed source IP addresses to a victim's host. This keeps that host from handling legitimate requests, causing it to populate its backlog queue with forged TCP connections. In this article, we propose a novel defense mechanism that makes use of the edge routers that are associated with the spoofed IP addresses’ networks to determine whether the incoming SYN–ACK segment is valid. This is accomplished by maintaining a matching table of the outgoing SYNs and incoming SYN–ACKs and also by using the ARP protocol. If an incoming SYN–ACK segment is not valid, the edge router resets the connection at the victim's host, freeing up an entry in the victim's backlog queue, and enabling it to accept other legitimate incoming connection requests. We also present a communication protocol to encourage collaboration between various networks to protect each other. We evaluated the performance of our proposed approach and studied its impact on the network. Our experimental and simulation results showed the efficiency of our proposed collaborative defense mechanism.     

Data predistortion techniques using intersymbol interpolation

Two data predistortion techniques are presented that compensate for high-power amplifier (HPA) nonlinearities in digital microwave radio systems by employing quadrature amplitude-modulation (QAM) signal formats. The first one is a T/2-spaced predistortion technique that ensures distortion-free HPA output at two points per symbol interval T. The second is a T/3-spaced predistortion technique which cancels nonlinear distortion at the HPA output at three points per symbol interval. As opposed to conventional data predistortion, which can only compensate for warping of the signal constellation, the new techniques are effective against intersymbol interference. Using the 64- and 256-QAM signal constellations, it is shown that the proposed techniques lead to a very efficient utilization of the available HPA power. It is shown that, of the two techniques, the T/3-spaced data predistortion employs narrower transmit-pulse shaping and achieves higher protection against adjacent-channel interference at the expense of some additional complexity     

Frequent use of menfegol spermicidal vaginal foaming tablets associated with a high incidence of genital lesions

Menfegol is a spermicide with in vitro activity against human immunodeficiency virus (HIV). A randomized placebo-controlled safety study covered the use of menfegol foaming tablets for 14 days at increasing frequencies of insertion by 125 prostitutes in Dakar, Senegal. The frequencies of colposcopically diagnosed genital lesions were 5.0%, 11.8%, 27.8%, 49.7%, and 29.4% among menfegol recipients when tablets were used once every other day or 1, 2, 4, or 8 times a day, respectively (P < .05). Among placebo recipients, frequencies were 11.1% and 23.5% when tablets were used < 8 times daily and 8 times daily, respectively. There was no association between subjective genital symptoms and the incidence of colposcopically detected lesions. The high incidence of genital lesions when menfegol foaming tablets were used more than once daily suggests that their frequent use should not be recommended to prevent HIV transmission. In use at low frequency, the tablets' toxicity might be balanced by anti-HIV properties. Safety studies on vaginal microbicides should use objective methods, such as colposcopy, to assess the incidence of lesions.     

Comments on `measurement of Ada overhead in OSI-stylecommunications systems'

The commenter disagrees with the comparison method used and questions the usefulness of the results obtained in the above named work by N.R. Howes and A.C. Weaver (see ibid., vol.15, no.12, p.1507-17, 1989). It is claimed that the comparison method is weak because Howes and Weaver did not take into account: the impact of control flow within a protocol, the coordination required between multiple entities executing within a layer and which share the services of a lower layer, and optimizations of R.J.A. Buhr's architecture (1984) which would have improved its performance efficiency     

Analyse des performances du codage multiniveau pour modulations à grand nombre d’états

In this paper, we analyze the performance of multilevel coding for high level QAM constellations. After the presentation of the encoder principle, we focus our study on a sub-optimal decoder which can be implemented very simply. We analyze the performance of the presented technique in terms of asymptotic gain and bit error rate characteristics. Finally, a pratical application in digital microwave radio links is considered, and one- and two-level coded 128-QAM are studied. At a bit error rate of 10^-8, it is shown that a 4 dB coding gain can be reached with moderate decoder complexity. These coding schemes are therefore very attractive for high-capacity microwave links applications.