Effect of the mold temperature on the electrical properties of carbon-black-loaded polystyrene/SB block copolymer blends

The electrical resistivities of a carbon-black-filled styrene–butadiene block copolymer (SB) and their blends with polystyrene were measured as a function of carbon content for specimens compression-molded at 200 and 250°C. The insulator–conductor point transition was greatly influenced by the mold temperature. This behavior associated to the scanning electronic microscopy investigations suggests the presence of some amount of the filler at the interface. A strong interaction between the filler and the polymer was also observed. The formation of bound rubber and a coherent rubber–filler gel depend on the molding conditions and the carbon black content in the composites. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 825–833, 1998     

Analysis of co‐axial transmission lines with arbitrary cross‐section

A numerical model for the determination of electromagnetic fields and characteristic impedance of co‐axial cables with arbitrary cross‐section is developed, based on dyadic Green's functions and the moment method. The advantages of the method are generality, simplicity and accuracy of its results. Besides this, the fields are represented as series over orthogonal functions, which can be useful in the solution of some problems, such as discontinuity between lines of different cross sections. A numerical application to cables of rectangular cross‐section shows the accuracy of the method. Copyright © 1999 John Wiley & Sons, Ltd.     

Computing the correlation dimension on a network of workstations

We present a parallel algorithm for computing the correlation dimension (D₂) from a time series generated by a dynamic system, using the method of correlation integrals, which essentially requires the computation of distances among a set of points in the state space. The parallelization is suitable for coarse-grained multiprocessor systems with distributed memory and is carried out using a virtually shared memory model. The algorithm simultaneously gives all the correlation integrals at various state space dimensions needed to estimate the D₂. Two versions are discussed: the first computes all distances between points; the second computes only distances less than a fixed ϵ, and employs a box-assisted approach and linked lists for an efficient search of neighbouring points. The algorithms, coded in Fortran 77, are tested on a heterogeneous network of workstations consisting of various DEC Alphas of different powers, interconnected by Ethernet; the Network Linda parallel environment is used. A detailed analysis of performance is carried out using the generalization of speed-up and efficiency for heterogeneous systems. The algorithms are fully asynchronous and so intrinsically balanced. In almost all the situations they provide a unitary efficiency. The second version greatly reduces the computational work, thus making it possible to tackle D₂ estimation even for medium and high-dimensional systems, where an extremely large number of points is involved. The algorithms can also be employed in other applicative contexts requiring the efficient computation of distances among a large set of points. The method proposed for the analysis of performance can be applied to similar problems. © 1998 John Wiley & Sons, Ltd.     

Failure Analysis of a Cyclic Contact Testing Machine Pin

The goal of this paper is to investigate the failure of a mandrel pin mounted on a rolling contact test bench. For this purpose, different methods of analysis were conducted, including metallography and stress analysis. The stress values in the failed pin were determined by Finite Elements. The high notch effect and the incorrect mounting of the specimens were identified as the failure causes. A pin design change is proposed to reduce the maximum stress even in the case of incorrect specimen mounting.     

Relatives in the same university faculty: nepotism or merit?

In many countries culture, practice or regulations inhibit the co-presence of relatives within the university faculty. We test the legitimacy of such attitudes and provisions, investigating the phenomenon of nepotism in Italy, a nation with high rates of favoritism. We compare the individual research performance of “children” who have “parents” in the same university against that of the “non-children” with the same academic rank and seniority, in the same field. The results show non-significant differences in performance. Analyses of career advancement show that children’s research performance is on average superior to that of their colleagues who did not advance. The study’s findings do not rule out the existence of nepotism, which has been actually recorded in a low percentage of cases, but do not prove either the most serious presumed consequences of nepotism, namely that relatives who are poor performers are getting ahead of non-relatives who are better performers. In light of these results, many attitudes and norms concerning parental ties in academia should be reconsidered.     

Topological Fiber Entropy for Linear Flows on Vector Bundles

For linear flows on vector bundles, it is shown that the topological entropy of lower dimensional subspaces in the fibers is determined by the Morse spectrum over chain recurrent components of the induced flows on Grassmann bundles.     

Hollow carbon nanostructures obtained from hydrothermal carbonization of lignocellulosic biomass

Here we describe a new method for obtaining carbon nanocages at relatively low temperatures using a low-cost lignocellulosic waste material as carbon precursor. Coconut coir dust has been submitted to hydrothermal carbonization in the presence of clays minerals such as sepiolite, attapulgite, and montmorillonite followed by a demineralization step. Just after hydrothermal treatment, the samples prepared in the absence of the clays presented a sponge-like morphology as typically described for hard-plant tissues submitted to this treatment while the samples heated in the presence of clays were fundamentally heterogeneous. After chemical etching with hydrofluoric acid, the sample free from clays exhibited irregular round-shaped particles with poorly defined cavities. For samples containing clays, on the other hand, the chemical etching lead to well-defined carbon nanocages as long as the particles were successfully etched such as attapulgite and montmorillonite. For sepiolite, however, the presence of residual inorganic particles was observed along with irregularly shaped hollow nanostructures. Finally, Raman measurements revealed the typical features of amorphous carbons.     

Optimization of Design and Performance of Solid‐Liquid Separators: A Thickener Hydrocyclone

Studies on hydrocyclones have evolved over recent years and various configurations of this device have been proposed in the literature for different purposes. Herein, an innovative geometrical configuration of hydrocyclones was developed by means of the response surface technique, combined with an optimization algorithm and supported by a computational fluid dynamics complementary study. The results obtained with these optimization techniques were validated by experimental data. The optimized hydrocyclone configuration is characterized by low energy consumption, i.e., low Euler number, with a small underflow‐to‐throughput ratio and can be used as a thickener hydrocyclone.