Generators of the ideal of an algebraic space curve

In this paper we show that the ideal of any algebraic curve in affine 3-space whose Jacobian matrix has rank at least 1 at every singular point of the curve can be generated by three polynomials and we give constructive procedures to compute such generators.     

UV-cured fluorinated coatings for plastics: effect of the photoinitiator and of the substrate filler on adhesion

A high-performance fluorinated acrylic coating, containing perfluoropolyether chains, was applied to polyethylene and polypropylene by means of the UV-curing technique. The conditions for a good adhesion onto the plastic substrates were studied. A chemical bonding between the cured network and both the substrates was achieved when the photopolymerization was performed in the presence of benzophenone as a photoinitiator: by hydrogen abstraction from the substrate, polymer radicals were formed and could then initiate the polymerization of the acrylic species; grafting experiments of hydroxyethylacrylate confirmed this mechanism. However, the grafting reaction did not take place when the plastic substrates contained carbon black as a filler, which acted as a radical scavenger. In this case, in fact the adhesion results are not good, similar to those obtained in presence of a cleavage-type photoinitiator.     

FGM and laminated doubly curved shells and panels of revolution with a free-form meridian: A 2-D GDQ solution for free vibrations

In this paper, the generalized differential quadrature (GDQ) method is applied to study the dynamic behavior of functionally graded materials (FGMs) and laminated doubly curved shells and panels of revolution with a free-form meridian. The First-order Shear Deformation Theory (FSDT) is used to analyze the above mentioned moderately thick structural elements. In order to include the effect of the initial curvature a generalization of the Reissner-Mindlin theory, proposed by Toorani and Lakis, is adopted. The governing equations of motion, written in terms of stress resultants, are expressed as functions of five kinematic parameters, by using the constitutive and kinematic relationships. The solution is given in terms of generalized displacement components of points lying on the middle surface of the shell. Simple Rational Bézier curves are used to define the meridian curve of the revolution structures. Firstly, the differential quadrature (DQ) rule is introduced to determine the geometric parameters of the structures with a free-form meridian. Secondly, the discretization of the system by means of the GDQ technique leads to a standard linear eigenvalue problem, where two independent variables are involved. Results are obtained taking the meridional and circumferential co-ordinates into account, without using the Fourier modal expansion methodology. Comparisons between the Reissner-Mindlin and the Toorani-Lakis theory are presented. Furthermore, GDQ results are compared with those obtained by using commercial programs such as Abaqus, Ansys, Nastran, Straus and Pro/Mechanica. Very good agreement is observed. Finally, different lamination schemes are considered to expand the combination of the two functionally graded four-parameter power-law distributions adopted. The treatment is developed within the theory of linear elasticity, when materials are assumed to be isotropic and inhomogeneous through the lamina thickness direction. A two-constituent functionally graded lamina consists of ceramic and metal those are graded through the lamina thickness. A parametric study is performed to illustrate the influence of the parameters on the mechanical behavior of shell and panel structures considered.     

THROO: a Tracked Hybrid Rover to Overpass Obstacles

In this paper, the design, simulation and experimental tests are presented for THROO: a Tracked Hybrid Rover, which has been developed to Overpass Obstacles. The proposed mobile robot has 3-DOFs and it is capable of straight motion, turning ability and two operations, namely rover-like motion with tracks on flat terrain and walking-like motion with track and legs to overpass obstacles to move on uneven terrain. The leg mechanism is composed of a four-bar linkage, which has been synthesized according to the desired features. In particular, the Burmester problem, which aims at finding the geometric parameters of a four-bar linkage required for a prescribed set of finitely separated poses are solved for the case understudy. Dynamic simulations have been carried out and a prototype has been built. The proposed results show the hybrid rover ability to overpass obstacles, for which size is comparable or greater than the track high.     

GradH‐Correction: guaranteed sizing gradation in multi‐patch parametric surface meshing

In this paper a new method, called GradH‐Correction, for the generation of multi‐patch parametric surface meshes with controlled sizing gradation is presented. Such gradation is obtained performing a correction on the size values located on the vertices of the background mesh used to define the control space that governs the meshing process. In the presence of a multi‐patch surface, like shells of BREP solids, the proposed algorithm manages the whole composite surface simultaneously and as a unique entity. Sizing information can spread from a patch to its adjacent ones and the resulting size gradation is independent from the surface partitioning. Theoretical considerations lead to the assertion that, given a parameter λ, after performing a GradH‐Correction of level λ over the control space, the unit mesh constructed using the corrected control space is a mesh of gradation λ in the real space (target space). This means that the length ratio of any two adjacent edges of the mesh is bounded between 1/λ and λ. Numerical results show that meshes generated from corrected control spaces are of high quality and good gradation also when the background mesh has poor quality. However, due to mesh generator imprecision and theoretical limitations, guaranteed gradation is achieved only for the sizing specifications and not for the generated mesh. Copyright © 2004 John Wiley & Sons, Ltd.     

Network and single user performance evaluation of a mobile data system over flat fading transmission channels

In this paper the contrasting effects of transmission impairments and capture on both the network and single user performance of a slotted Aloha system are investigated in a mobile radio environment, accounting for frequency non-selective random propagation phenomena, and employing the packet error probability in order to define packet losses and capture. With this study we demonstrate that it is possible to generalize in a real propagation context a method previously proposed in literature for evaluating the network behavior in terms of steady-state throughput, backlog and stability in conventional transmission conditions, i.e., when all the transmission channels were error-free and the collisions caused the loss of all the packets involved. Moreover, we indicate under which specific constraints on the terminal mobility we can apply this method to analytically predict the single user performance, which we show being an important design parameter. Through the numerical results reported we quantitatively point out that in the absence of coding capture increases system stability and moderately improves the overall system throughput and backlog. We also outline the trade-off between an increased capture gain obtained by means of coding and the corresponding system cost in terms of complexity and bandwidth occupancy. Furthermore, we demonstrate the unfairness which affects the single user performance and the consequent need for countermeasures in order not to discriminate among users differently located within the network; yet, this last solution is detrimental as regards the positive capture effects.This work was supported by M.U.R.S.T. and C.N.R. (Italy).     

Performance Evaluation of a Bluetooth-Based WLAN Adopting a Polling Protocol Under Realistic Channel Conditions

Even if Bluetooth has not been specifically designated for WLANs (Wireless Local Area Networks) and the interconnection of computers, the possibility of establishing low-cost wireless connections makes this technology attractive for this kind of context also. In this paper we assess, by means of a simulative approach that takes the complete physical and MAC level aspects into account, the performance of a Bluetooth-based WLAN adopting a roll-call polling protocol under realistic channel conditions, that is, in the presence of the typical impairments of indoor wireless communications (fading, etc); moreover, we propose an analytical formulation to derive the maximum throughput offered by a Bluetooth link and we suggest a call admission control technique based on the previous analytical considerations.     

Blood cell transplantation: report from an International Consensus Meeting

An International Consensus Meeting on blood cell transplantation took place in Heemskerk, The Netherlands on 27-29 June 1994. The term 'blood cell transplantation' was preferred to peripheral blood stem cell transplantation. The following issues were addressed: stem cell assessment and ex vivo expansion, techniques for stem cell mobilization, applications of blood cell transplantation, malignant cell contamination and allogeneic blood cell transplantation.