Analysis of the impact of craft labour availability on North American construction project productivity and schedule performance

The North American construction industry has experienced periods of craft shortages for decades. While this problem has received significant attention from researchers, less attention has been given to quantifying the impact of availability of craft labour on project performance. The primary contribution of the current work to the body of knowledge is the quantification of the relationship between craft labour availability and project performance, as measured by project productivity and schedule. Data from 97 construction projects completed in the U.S. and Canada between 2001 and 2014 were collected from two industry databases. The primary analysis shows that projects that experienced craft shortages underwent substantial and statistically lower productivity compared to projects that did not. The analysis also shows a significant growth in schedule overrun due to the craft labour shortages among the same population of projects. Further exploration by means of several regression analyses shows a statistically significant correlation between increased craft recruiting difficulty and lower project productivity and also higher schedule overruns in both project databases. The results are confirmed across both databases and serve as informative models that provide valuable insight for project management teams to perceive the risk that lack of skills poses on project productivity and time performance. Understanding the level of impact that craft shortages are having through robust statistical analyses is a first step in developing the motivation for industry leaders, communities and construction stakeholders to address this challenge.     

Real-time monitoring of color variations of apple slices and effects of pre-treatment and drying air temperature

An attempt was made to quantify the contribution of chemical pre-treatment on the color changes of apple slices during hot air drying. The monitored color attributes of apple slices were computed real time at drying air temperatures of 50, 60, and 70 °C. The apple slices dried in a computer vision system (CVS) assisted-hot air dryer both with and without pre-treatment. The quantities of measured color parameters for pre-treated (P.T.) samples were subtracted from the values obtained for untreated (U.T.) samples at the same water content. For this purpose, an artificial neural network was developed and used satisfactorily for mapping out the color parameters of P.T. samples at calculated moisture ratio for U.T. sample to compute the physio-chemically significant difference. From the results, it can be derived that a CVS seems to be a promising tool when it comes to detecting and monitoring the effects of various pre-treatments on being-processed foodstuffs .     

Target optimization for a 10-MeV E-beam neutron converter

Accelerator-based target design and optimization is an approach for neutron generation. The target plays an important role for a neutron source on an electron accelerator. For optimizing a neutron source using 10 MeV electron beams of Rhodotron-TT200, Pb, Ta, or W alloys with Be were calculated as photo-neutron converter. The neutron yield, flux and energy were simulated using the MCNPX code. The results indicate that a 10 MeV electron beam is capable of producing high-intensity neutron flux of 1013n·cm–2·s–1 with average energy of 0.8 MeV.     

A simple method to approximate the probability of error for equal gain combiner over independent fading channels

Using the Beaulieu series, the probability of error for equal gain combiner over independent fading channels can be formulated in the form of an infinite series. The computation of the coefficients of this series needs complicated integrations over fading envelope distribution. In this paper, a new approximation method is developed for the computation of the required coefficients of the error probability series, which needs only mean and variance of the fading envelope. Hence, the purposed method eliminates the need for complicated integrations while computing the required coefficients. This feature provides an interesting flexibility for our developed method, so that it can be used as a unified method for performance analysis of equal gain combiner over various independent fading channels, especially where the required integrations have no closed‐form solutions. To present an application for the proposed approximation method, the fading channel is modeled by three‐parameter generalized Gamma distribution (GG3), which is a generic model that covers many well‐known channel models for both multipath and shadow fading. The presented numerical results show good accuracy as well as low computational complexity of the presented method. Copyright © 2007 John Wiley & Sons, Ltd.     

Mobile ad hoc relaying for upward vertical handoff in hybrid WLAN/cellular systems

One of the main issues in hybrid wireless networks is vertical handoff. Dropping probability is one of the important parameters that must be considered in planning the wireless communication systems. However, there has not been much effort in dropping rate reduction in loosely coupled hybrid wireless networks. In loosely coupled WLAN/cellular systems the system administrator of the WLAN is different from the cellular one. Therefore, in these situations, reducing the dropping probability based on classical methods such as using reserved guard channels is difficult. A handoff from a WLAN to a cellular system occurs when a multi-mode device moves out of the WLANs coverage area. This is an upward vertical handoff in a hybrid network. In this paper, we propose to employ ad hoc relaying during the upward vertical handoff in a hybrid WLAN/cellular system. Two-hop and multi-hop relaying approaches, which we propose in this paper, improve the dropping probability regardless of the number of reserved channels. Simulation results support the effectiveness of the proposed methods. Also, practical routing protocols are proposed in order to implement the suggested relaying methods.     

Simulation of carbon nanotube FETs with linear doping profile near the source and drain contacts

We propose carbon nanotube field effect transistors (CNTFETs) in which the source and drain regions of the channel (carbon nanotube) have been doped nonuniformly. The MOSFET like CNTFETs (MOSCNTs) suffer from band to band tunneling which in turn causes the ambipolar conduction. In this paper, we propose a linear doping profile for the carbon nanotube (CNT) near the source and drain contacts. This reduces the gradient of each potential barrier at the interface between the intrinsic and doped parts of the CNT and suppresses the band to band tunneling and ambipolar conduction. The device has been simulated by solving coupled Poisson and Schrödinger equations. Non-equilibrium Green’s function (NEGF) method has been used to investigate the transport properties. The uncoupled mode space approach has been used to reduce the computational burden. The calculated energy band diagrams justified improved ambipolar behavior and lower off current.     

A new comprehensive genetic algorithm method for optimal overcurrent relays coordination

For optimal co-ordination of overcurrent relays, linear programming techniques such as simplex, two-phase simplex and dual simplex are used. Another way of optimal coordination program is using artificial intelligent system such as genetic algorithm (GA). In this paper, a powerful optimal coordination method based on GA is introduced. The objective function (OF) is developed to solve the problems of miscoordination and continuous or discrete time setting multiplier (TSM) or time dial setting (TDS). In other words; the novelty of the paper is the modification of the existing objective function of GA, by introducing a new parameter and adding a new term to OF, to handle miscoordination problems both for continues and discrete TSM or TDS. The method is applied to two different power system networks and from the obtained results it is revealed that the new method is efficient, accurate and flexible.     

Possibility of using chemical fertilizers instead of 9K medium in bioleaching process of low-grade sulfide copper ores

The possibility of applying chemical fertilizers as a source of nutrients for bacterial growth in bioleaching process was investigated. In the first part of the experiment the nutrient content of four sulfide copper ore samples was determined. The results confirmed that the amount of calcium, magnesium and sulfur were sufficient to support bacterial growth, whereas nitrogen, phosphorous and potassium were not sufficient. Therefore, N, P, and K from a chemical fertilizer source were applied to the sulfide copper ores to make a cost-effective bioleaching process. According to shake flask experiments by using mesophilic, iron-sulfur oxidizing bacteria, bacterial activity and copper recovery in some proposed media was satisfactory compared to 9K medium. Additionally, potassium had positive effect on the copper ore bioleaching while NO₃⁻ and Cl⁻ had inhibitory effect on the bacterial activity.     

Preparation of synthesized sulfide polymer through phase-transfer catalyzed polycondensation of ethylene dibromide and sodium tetrasulfide: characterization,thermal and rheological properties

Sulfide polymers were obtained through the interfacial polymerization of sodium tetrasulfide and ethylene dibromide. The polymerization process was carried out under interfacial condition using two phase-transfer catalysts: methyl-tributyl ammonium bromide and methyl-tributyl ammonium chloride. The polymer characteristics were examined by attenuated total reflectance- fourier transform infrared spectroscopy, elemental analysis (CHNS/O) and X-ray diffraction methods. Thermal characteristics were investigated by differential scanning calorimetry and thermogravimetric analysis methods. The rheological behavior of the synthesized sulfide polymer during curing reaction, and isothermal time dependency of elastic storage modulus, G^′, at different temperatures and constant shear frequency was studied using a stress-controlled rheometer. Moreover, the solvent resistance of synthesized polymer was investigated through the swelling method.     

Synthesis of 2-arylbenzothiazoles using nano BF3/SiO2 as a reusable and efficient heterogeneous catalyst under mild conditions

2-Arylbenzothiazoles were synthesized via condensation of 2-aminothiophenol and different aldehydes catalyzed by nano silica-supported boron trifluoride (nano BF₃/SiO₂) as an efficient and reusable catalyst in high yields and short reaction times. The reactions proceeded at room temperature under mild conditions to afford 2-arylbenzothiazole derivatives. The pure products were identified and characterized by physical and spectroscopic data such as IR, ¹H NMR, ¹³C NMR and Mass spectroscopy.