Lateral Walking-Induced Forces on Footbridges

In the last several years many cases of large amplitude horizontal vibrations of footbridges have been observed, due to dynamic interaction between the walkers and the footbridge, which may occur when some conditions on the bridge mass, frequency and damping, as well as on the crowd density are met. Such interaction is an intriguing phenomenon, as it is associated with the dynamics of a complex system made of a structure and a number of walkers, the dynamics of the latter being governed by physiology and psychology. Provided this complexity, in this paper a preliminary step is made toward the modeling of the interaction forces exerted by a crowd to a footbridge. The results of an experimental investigation of the lateral forces exerted by one walker to a fixed floor are presented, and used to calibrate a deterministic and stochastic lateral loading models of footbridges, to be used in the case in which no interaction takes place. The results presented are also the background data for more sophisticated dynamic models allowing for bridge-crowd interaction.     

Vibrational analysis of functionalized polyolefins/poly(vinylchloride) blends

Polyolefins functionalized with diethylmaleate were mixed with poly(vinylchloride) (PVC) in different compositions. Intermolecular interactions involving the carbonyl groups of the side chains of the functionalized polyolefins and methine hydrogens of PVC were investigated by means of infrared spectroscopy. The major flexibility of the ester groups attached to the backbone chains, with respect to polyesters, seems to increase the capability of such groups to interact with groups of more polar polymers, thus allowing prediction of easier miscibility, which however also depends on the starting polyolefin structure and function-alization degree.     

Layered Video and Differentiated Coding for Adaptive QoS in Mixed Wired-Satellite Networks

Mobile networks are becoming nothing but a way to allow ubiquitous access to multimedia services. To allow efficient use of resources, new systems provide flexible bandwidth and different error protection techniques to match channel behavior. As the backbone network is increasingly becoming based on packet techniques and in particular on IP and related transport protocols, end to end service quality must be analyzed considering both the fixed and the mobile part. Source scalability may help in coping with a mixed and heterogeneous environment. In this work we present some results of a transmission chain comprising a scalable MPEG-2 coder, an IP network and a radio access exploiting the availability of satellites. It is shown that for a given target rate, differentiated coding can be exploited to achieve decodability and good quality at a channel SNR much lower that single layer streams. This revised version was published online in July 2006 with corrections to the Cover Date.     

A low cost calibration conditioner for dynamic strain gauge measurements

A conditioner for dynamic strain measurements that allows for a series of calibration signals with periodic and predefined time occurrence, during the whole period in which the measurements have to be carried out, is presented in this work. The calibration signals, having suitable size ratios between them, allow one to evaluate the linearity of the entire measurement chain.     

Vacuum-u.v. circular dichroism of optically active isotactic poly-α-olefins

Summary Circular dichroism of isotactic samples of poly-(S)-4-methyl-1-hexene and poly-(R)-3,7-dimethyl-1-octene, have been measured in the vacuum ultraviolet spectral region (200-140 nm). The c.d. band at about 160. nm accounts for the optical activity in the visible region and reflects the presence of one screw sense helical conformation of the sample examined.The authors thank Prof. W.C. Johnson, Jr., Department of Biochemistry and Biophysics, Oregon State University, for allowing them to use the vacuum u.v. spectrometer. This work has been partially supported by a N.A.T.O. grant, and by Ministero Pubblica Istruzione (MPI), Roma — Italy.     

A new experimental approach to the investigation of contact forces at an interface

The piezoelectric films recently developed permit the design of very efficient thin sensors which are suited to interesting applications in contact problems, not only in industrial robotics but also in experimental research. After a brief introduction exemplifying the electrical principles, the primary aspects of the technique are presented and discussed with reference to possible structural engineering applications. A rather simple example regarding the interaction between a steel bar and a block of concrete is also presented. The bar is excited by dynamic cyclic loads having variable frequency. The reliability of forces detected via a PVDF sensor is evaluated by comparing the results with those obtained in parallel by means of a dynamometer strain-gauge. The comparison is promising, even if some technological problems must be resolved before this experimental technique may be applied extensively.

---

Resume L'étude expérimentale des forces qui se manifestent à une interface équivaut souvent à un problème technique insoluble car chaque appareillage influe de manière significative sur le comportement mécanique. En outre, si l'interface se situe dans un continuum, l'utilisation de transducteurs ou d'extensomètres devient aussi plus complexe. Dans tous les cas, les mesures peuvent se faire éventuellement à proximité de l'interface, mais non à l'interface. Des améliorations techniques récentes dans le domaine de la robotique permettent d'utiliser des films de polymères piézoélectriques (fluoride de polyvinylidène, PVDF). En raison de l'épaisseur de ce capteur qui ne dépasse pas quelques micromètres, le comportement mécanique n'est pas perturbé. Le principle électrique est typique du transducteur piézoélectrique: les charges crées par le film piézoélectrique sollicité sont concentrées sur les surfaces métallisées qui le recouvrent. Cette technique permet d'étudier de nombreux problèmes structurels. S'il s'agit de béton armé, par exemple, il est intéressant d'examiner la répartition de la pression sur un appui de poutre ou bien à la surface d'un boulon d'ancrage, les contraintes interfaciales aussi bien d'une barre d'armature chargée axialement et transversalement, que de goujons dans des structures composites. Un exemple simple montre la fiabilité de la nouvelle technique: une haute barre d'adhérence enrobée dans un bloc de béton est mise sous charge dynamique. On compare la force détectée par le capteur PVDF placé à l'interface barre d'acier-barre d'enrobage avec celle qui est mesurée au moyen du dynamomètre traditionnel placé parallèlement au support. La comparaison, établie à différentes fréquences, est satisfaisante. Cependant, pour utiliser cette nouvelle technique sur une grande échelle, il convient de résoudre quelques problèmes techniques: l'améioration de la conductivité électrique des connexions entre les surfaces métallisées de la couche sensible et les fils d'entrée et de sortie la prévention d'une éventuelle perforation du film par des particules de granulats siliceux qui sont un des constituants de base des mortiers et bétons; l'évaluation de la sensibilité d'un capteur multicouches à l'écrasement inévitable du matériau à proximité d'une barre d'acier, avec une microfissuration locale et un glissement limité. La recherche se poursuit tant au niveau technologique qu'électronique.

     

The effect of support morphology on the reaction of oxidative dehydrogenation of ethane to ethylene at short contact times

The oxidative dehydrogenation of ethane is carried out in short contact time reactors over Pt and LaMnO₃ based catalysts supported on a large number of different ceramic substrates (45, 60 and 80 ppi foam monoliths and 200, 400, 600, 900 and 1200 cpsi honeycomb monoliths). Experimental results, obtained under the same conditions at varying the C₂H₆/O₂ ratio, showed that the highest performance in terms of ethylene selectivity and yield is always attained on LaMnO₃ catalysts. Furthermore, the results are significantly influenced by the morphology and cell density of the support, with 45 and 60 ppi foams and 400 and 600 cpsi honeycombs giving the best performance. The experimental results are explained by means of geometrical and fluid dynamic considerations on the support, and by means of a 2D mathematical model, which clearly indicates an optimal intermediate cell density for maximising ethylene selectivity and yield.     

利用新型合成仪器解决系统级测试难题

当今世界电子元件及产品正在加速发展，在大多数商业应用中，从设计到生产的周期现已缩短为只有六个月。而且，设备的内容及拓朴结构已经从单一功能元件迁移到多功能元件，进而还会迁移到整个子系统和系统中，在迁移时通常采用单个组件方案的形式（例如，用于智能电话和iPhone之类的设备）。现在，对于多载波功率放大器（MCPA）和软件定义的无线电（SDR）而言，直接软件控制和设备配置已司空见惯。例如RFIC之类的设备只能在混合信号环境中及实时条件下操作和测试。     

Assessing pre- and post-deformation in the southern Arava Valley segment of the Dead Sea Transform, Israel by differential interferometry

Differential radar interferometry, using archived ERS data over the region of the Dead Sea Transform, allows to detect ground movement (subsidence or uplift) in playas within the southern Arava Valley segment of the Dead Sea Rift. These measurements are consistent with a mean displacement rate of about 0.4 cm/month, in the direction of the radar beam, during the 8-month period preceding the Nuweiba earthquake of 22 November 1995. In the 3 years following the earthquake, the measured rate was smaller by a factor of 10. These movements are not related to salt diapirs or water pumping activities in the area. The exact location, along faults, suggests a possible correlation with pre-seismic and post-seismic fault deformation.A simple fault model consistent with the observed phenomena associates the observed subsidence/uplift to right and left stepping en-echelon fault patterns related to inter-seismic tensional accumulation along the faults. Further observations are necessary on this site and similar fault areas to corroborate the correlation between seismic activity and the observed phenomena. Monitoring of these sites should continue with differential Global positioning system (GPS) measurements and radar interferometric analysis using Envisat and Radarsat as well as archived data (including J-ERS).