Project Performance Control in Reconstruction Projects

Cost, schedule, and quality are the main indicators of performance in construction projects. These indicators are highly interrelated and require some balance and trade-off among them to achieve efficient overall control over project performance. Focusing on these performance indicators, the primary objective of this study is to investigate the use of conventional control techniques in projects involving reconstruction of occupied buildings. To facilitate this analysis, performance data have been collected, using a questionnaire survey, from 25 reconstruction and 15 new construction projects. The survey was followed by structured interviews with construction practitioners and project participants to elicit success-related factors and to identify some of the unique problems affecting the control of reconstruction projects. Using the collected data, performance comparison was conducted between new and reconstruction projects along with a detailed analysis of the suitability of existing techniques for the control of the cost, schedule, and quality in reconstruction projects.     

Comparison between a linear and a branched low-density polyethylene

Two low-density polyethylenes, a linear low-pressure (LLDPE) and a branched high-pressure (LDPE), have been compared. Their shear and extensional behavior and melt fracture phenomena have been investigated, and some mechanical and optical properties of their blown films have been measured. The rheological analysis showed major differences between the samples, both in shear viscosity and in elongational viscosity. The LLDPE exhibited two types of melt fracture, the first of which—a fine scale extrudate roughness—was not shown by the LDPE and appeared at a very low shear rate. The concomitance in LLDPE of a high shear viscosity and a low elongational viscosity and the presence of melt fracture at low shear rate resulted in its more difficult processing into film. The mechanical properties of the LLDPE film approached those of high-density polyethylene while the optical characteristics were in the range of LDPE. Such a coexistence of properties makes LLDPE an interesting material for film production.     

Discrete fractional Fourier transform based on the eigenvectors of tridiagonal and nearly tridiagonal matrices

The recent emergence of the discrete fractional Fourier transform (DFRFT) has caused a revived interest in the eigenanalysis of the discrete Fourier transform (DFT) matrix F with the objective of generating orthonormal Hermite–Gaussian-like eigenvectors. The Grünbaum tridiagonal matrix T—which commutes with matrix F—has only one repeated eigenvalue with multiplicity two and simple remaining eigenvalues. A detailed eigendecomposition of matrix T is performed with the objective of deriving two orthonormal eigenvectors—common to both the F and T matrices—pertaining to the repeated eigenvalue of T. The nearly tridiagonal matrix S first introduced by Dickinson and Steiglitz and later studied by Candan et al.—which commutes with matrix F—is rigorously proved to reduce to a 2×2 block diagonal form by means of a similarity transformation defined in terms of an involutary matrix P. Moreover explicit expressions are derived for the elements of the two tridiagonal submatrices forming the two diagonal blocks in order to circumvent the need for performing two matrix multiplications. Although matrix T has the merit of being tridiagonal and does not need the tridiagonalization step as matrix S, the simulation results show that the eigenvectors of matrix S better approximate samples of the Hermite–Gaussian functions than those of matrix T and moreover they have a shorter computation time due to the block diagonalization result. Consequently they can serve as a better basis for developing the DFRFT.     

In-House Delivery of Multiple-Small Reconstruction Projects

As compared with new construction, reconstruction of operational facilities exhibits a higher challenge, particularly when multiple projects are involved. For owner organizations involved in such projects, use of in-house resources versus outside contractors has been a major dilemma, with each approach having its potential benefits. This paper uses a real-life case study approach to investigate the delivery of 800 small reconstruction projects using in-house forces. Details are described related to the prioritization, budgeting, organization structure, and the mechanisms used for staff allocation. It was found that the main characteristics of projects that are best delivered by in-house forces include high urgency and inadequate scope definition. Outsourcing this type of projects exposes the owner to a large number of changes and their consequent cost overruns/delays. Based on the case study, the challenges facing in-house delivered projects and the factors that contribute to their success were investigated and outlined. To verify the findings a questionnaire survey among similar organizations is conducted and its results discussed.     

On modeling the solids conveying zone of a plasticating extruder

A model for the solids conveying zone of a plasticating extruder is presented. The flow of solid granules is studied in the framework of thermomechanics of media with affine structure, and assimilated to plane steady flow of an incompressible viscous fluid with spherical indeformable structure. Simple constitutive equations are accepted, along with those kinematical assumptions which stem directly from the geometry of the system. The resulting balance equations are given a dimensionless form, and integrated so as to arrive at closed-form solutions for velocity, spin and temperature of granules. A discussion of the influence of the adimensional parameters relevant to the problem is presented; this discussion is supplemented with some examples. Finally, various developments and refinements of the present model are proposed.     

Effect of morphology on stress relaxation of polypropylene

Samples of isotactic polypropylene having different morphologies and crystallinities were prepared and subjected to stress-relaxation experiments at different levels of strain. The relaxation moduli were determined in the range of temperature between – 20 and 40°C over a period of time from 1 to 1000 seconds. Using the time-temperature superposition principle, the activation energy values of the shift factors a_T were determined and the master curves were obtained for the various structures. Increasing crystallinity and/or crystalline aggregate size increases the relaxation modulus of the material and changes both shape and location of the spectrum of relaxation times so that no simple method can be found to correlate the various master curves.