What Does the Construction Industry Value in Its Workers?

This paper briefly characterizes today’s United States (U.S.) construction workforce, and attempts to provide evidence for what the construction industry most values in its workers. It presents the social and demographic characteristics of a sample of 862 construction workers, from 19 project sites that were interviewed in 2002, as part of a research effort at the University of Texas at Austin, and compares them with broader-based Bureau of Labor Statistics data to establish the degree to which they represent the U.S. construction workforce. Via statistical analysis, the paper explores the relationships between workers’ attributes and how the industry compensates them as reflected in both hourly wages and average annual incomes. The statistical results reinforce what is known about the importance of years of experience; however, it also provides evidence of the importance of number of crafts each worker possessed, and computer knowledge. Less, but significant, evidence was obtained for the importance of the number of years spent with his/her current firm, craft training hours, age, or self-assessed performance.     

ITPMAP: An Improved Three-Pass Mutual Authentication Protocol for Secure RFID Systems

Radio frequency identification (RFID) is a wireless technology used in various applications to minimize the complexity of everyday life. However, it opens a large number of security and privacy issues that require to be addressed before its successful deployment. Many RFID authentication protocols are proposed in recent years to address security and privacy issues, and most of them are based on lightweight cryptographic techniques such as pseudo-random number generators (PRNGs), or bitwise logical operations. However, the existing RFID authentication protocols suffer from security weaknesses, and cannot solve most of the security and privacy problems. A new solution is necessary to address security and privacy issues. In this paper, an improved three-pass mutual authentication protocol (ITPMAP) for low-cost RFID tags is proposed to offer an adequate security level for RFID systems. The proposed ITPMAP protocol uses one PRNG on the tag side and heavy-weighted cryptographic techniques (i.e., digital signature and password-based encryption schemes) on the back-end server side instead of lightweight cryptographic techniques to address the security and privacy issues. The ITPMAP protocol is secure against various attacks such as cloning, spoofing, replay, and desynchronization attacks. Furthermore, as a proof of concept, the ITPMAP protocol is adopted to propose the design of three real-life RFID systems; namely: Signing and Verification of Graduation Certificate System, issuing and verification of e-ticketing system, and charging and discharging of prepaid card system. The Unified Modeling Language is used to demonstrate the design of the proposed ITPMAP protocol and systems. Java language is used for the implementation of the proposed systems. In addition, the “Mifare Classic” tags and readers are used as RFID apparatuses for the proposed systems.     

Flow condensation in parallel micro-channels – Part 2: Heat transfer results and correlation technique

This second part of a two-part study concerns heat transfer characteristics for FC-72 condensing along parallel, square micro-channels with a hydraulic diameter of 1 mm, which were formed in the top surface of a solid copper plate. Heat from the condensing flow was rejected to a counter flow of water through channels brazed to the underside of the copper plate. The FC-72 condensation heat transfer coefficient was highest near the channel inlet, where the annual liquid film is thinnest. The heat transfer coefficient decreased along the micro-channel because of the film thickening and eventual collapse of the annular regime. Notable heat transfer enhancement was observed for annular flow regions of the micro-channel associated with interfacial waves. Comparing the present data to predictions of previous annular condensation heat transfer correlations shows correlations intended for macro-channels generally provide better predictions than correlations intended specifically for mini/micro-channels. A new condensation heat transfer coefficient correlation is proposed for annular condensation heat transfer in mini/micro-channels. The new correlation shows excellent predictive capability based on both the present FC-72 data and a large database for mini/micro-channel flows amassed from eight previous sources.     

Accurate surface potential determination in Schottky diodes by the use of a correlated current and capacitance voltage measurements.Application to n-InP

Based on current voltage(I-V_g) and capacitance voltage(C-V_g) measurements,a reliable procedure is proposed to determine the effective surface potential V_d(V_g) in Schottky diodes.In the framework of thermionic emission,our analysis includes both the effect of the series resistance and the ideality factor,even voltage dependent. This technique is applied to n-type indium phosphide(n-InP) Schottky diodes with and without an interfacial layer and allows us to provide an interpretation of the observed peak on the C-V_g measurements.The study clearly shows that the depletion width and the flat band barrier height deduced from C-V_g,which are important parameters directly related to the surface potential in the semiconductor,should be estimated within our approach to obtain more reliable information.     

A multi-objective simulated annealing for the multi-criteria dial a ride problem

The paper describes a multi-objective mathematical model for Dial a Ride Problem (DRP) and an application of Multi-Objective Simulated Annealing (MOSA) to solve it. DRP is to take over the passenger from a place of departure to a place of arrival. In the DRP, customers send transportation requests to an operator. A request consists of a specified pickup location and destination location along with a desired departure or arrival time. The ultimate aim is to offer an alternative to displacement optimized individually and collectively. The DRP is classified as NP-hard problem that's why most research has been concentrated on the use of approximate methods to solve it. Indeed the DRP is a multi-criteria problem, the proposed solution of which aims to reduce both route duration in response to a certain quality of service provided. In this work, we offer our contribution to the study and solving the DRP in the application using the MOSA algorithm. Tests show competitive results on (Cordeau and Laporte, 2003a) benchmark datasets while improving processing times.     

Are Stacker Crane Problems easy? A statistical study

Many full truckload pick-up and delivery problems in the intermodal freight container transport industry can be modeled as Asymmetric Traveling Salesman Problems (ATSPs). Several authors have noted that while ATSPs are NP-hard, some instances are readily solved to optimality in only a short amount of time. Furthermore, the literature contains several references to the Stacker Crane Problem (SCP) as an “easy” problem amidst the ATSPs. We put this hypothesis to test by using statistical methods to build a model relating measurable distance matrix structures to the amount of time required by two existing exact solvers in finding solutions to over 500 ATSP instances. From this analysis we conclude that SCPs are not necessarily easier than other ATSPs, but a special subset of SCPs, termed drayage problems, are more readily solved. We speculate that drayage problems are “easy” because of a comparatively high number of zeros in symmetric locations within the distance matrix. In real-world drayage problems (i.e. the movement of containers a short distance to/from a port or rail terminal), these zeros correspond to the prevalence of jobs originating at or destined to a fixed number of freight terminals.     

Universal approach to predicting two-phase frictional pressure drop for adiabatic and condensing mini/micro-channel flows

Previous models and correlations for the prediction of pressure drop in adiabatic and condensing mini/micro-channel flows have been validated for only a few working fluids and relatively narrow ranges of relevant parameters. A universal predictive approach for these flows must be capable of tackling many fluids with drastically different thermophysical properties and very broad ranges of all geometrical and flow parameters of practical interest. To achieve this goal, a new consolidated database of 7115 frictional pressure gradient data points for both adiabatic and condensing mini/micro-channel flows is amassed from 36 sources. The database consists of 17 working fluids, hydraulic diameters from 0.0695 to 6.22 mm, mass velocities from 4.0 to 8528 kg/m² s, liquid-only Reynolds numbers from 3.9 to 89,798, flow qualities from 0 to 1, and reduced pressures from 0.0052 to 0.91. It is shown that, while a few prior models and correlations provide fair predictions of the consolidated database, their predictive accuracy is highly compromised for certain subsets of the database. A universal approach to predicting two-phase frictional pressure drop is proposed by incorporating appropriate dimensionless relations in a separated flow model to account for both small channel size and different combinations of liquid and vapor states. This approach is shown to provide excellent predictions of the entire consolidated database and fairly uniform accuracy against all parameters of the database. This approach is also capable of tackling single and multiple channels as well as situations involving significant flow deceleration due to condensation.     

Fuzzy rule based predictive model for cutting force in turning of reinforced PEEK composite

Carbon fiber reinforced plastics have gained large interest among the community of composites manufactures and consumers due to their excellent adaptability to various industrial applications. In particular, there exists a demand for optimizing machining conditions of mechanical parts made from poly ether ether ketone reinforced with 30% of carbon fiber when using TiN coated cutting tools. In this work, predictive models that describe the relationship between the independent machining variables: cutting speed, feed rate and depth of cut, and the criteria of machinability: cutting force, cutting power and specific cutting pressure were derived. This was achieved by using either classical response surface regression technique or by implementing fuzzy logic models which are based on the compositional rule of inference that establish a parametric relation between a given response and the independent input variables. Effectiveness of these models has been proved by analyzing their coefficients of correlation and by comparing predictions they give with experimental results.     

Effect of Anhydride Modification on the Thermal Stability of Cultivated Acacia mangium

Abstract

This paper tests the hypothesis that propionic and succinic anhydride modification will improve the thermal stability of cultivated Acacia mangium wood. The thermal stability of modified wood was characterized with thermogravimetric analysis. Evidence of modification was confirmed by Fourier transform infrared analysis. Our results show that chemical modification with anhydrides improves the thermal stability of the Acacia wood. The higher thermal stability of anhydride-modified Acacia wood compared with unmodified wood is attributed to the reduction in hydrophilic nature of the wood due to esterification. Succinylated wood has better thermal stability than propionylated wood based on the values of on-set degradation temperatures, the temperatures at which 30, 50, and 70% degradation occurred, and the activation energy. The improved thermal stability of modified wood compared with the unmodified wood will offer potential for better utilization of Acacia mangium.     

New T-Shape Polyurethanes: Synthesis,Thermal and Mechanical Properties

A series of new T-shaped polyurethanes were prepared from various diisocyanates and 2,5-dihydroxybenzelidene aniline (azomethine bisphenol). The latter compound was synthesized by the reaction of 2,5-dihydroxy-benzaldehyde with aniline. The structures of azomethine bisphenol and T-shaped polyurethane were confirmed by FT-IR, ¹H-NMR, ¹³C-NMR Spectroscopy and elemental analysis (CHN). The mechanical properties were characterized by tensile strength, tear strength and shore hardness. Thermal properties were also studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Mechanical and thermal studies showed that the synthesized polyurethanes possess good mechanical and thermal properties.