Optimization of Resource Allocation and Leveling Using Genetic Algorithms

Resource allocation and leveling are among the top challenges in project management. Due to the complexity of projects, resource allocation and leveling have been dealt with as two distinct subproblems solved mainly using heuristic procedures that cannot guarantee optimum solutions. In this paper, improvements are proposed to resource allocation and leveling heuristics, and the Genetic Algorithms (GAs) technique is used to search for near-optimum solution, considering both aspects simultaneously. In the improved heuristics, random priorities are introduced into selected tasks and their impact on the schedule is monitored. The GA procedure then searches for an optimum set of tasks' priorities that produces shorter project duration and better-leveled resource profiles. One major advantage of the procedure is its simple applicability within commercial project management software systems to improve their performance. With a widely used system as an example, a macro program is written to automate the GA procedure. A case study is presented and several experiments conducted to demonstrate the multiobjective benefit of the procedure and outline future extensions.     

Factors contributing to early age shrinkage cracking of slag concretes subjected to 7-days moist curing

The objective of this study was to investigate all the factors contributing to early age shrinkage cracking in concrete, namely, shrinkage, tensile creep, tensile elastic modulus, tensile strength of concretes, and to study the effect of slag as a binder on these factors. The above-mentioned factors were measured in early age concretes made with 0, 35, 50 and 65% level replacement of ordinary Portland cement by slag. All the concretes studied were moist cured for 7-days. It was found that, at lower slag replacement levels (0, 35 and 50%), the tensile strength decreased with increasing slag replacement. However, this is more than compensated by decreasing tensile elastic modulus and shrinkage. There was no significant change found in tensile creep with the changing slag levels. The study shows that the influence of the tensile elastic modulus is a major consideration for early age cracking of slag concretes.     

Evaluation and Carbon Fiber Reinforced Polymer Strengthening of Existing Garage: Case Study

The concrete-repair fiber reinforced polymer technology emerged in the United States during the past 10 years. Since 1995, carbon fiber reinforced polymer (CFRP) has been applied to strengthen concrete decks of a troubled posttensioned garage in Atlanta. During the construction of the garage, design deficiencies were found. A remedial repair, involving heavily?reinforced, 7.6 cm (3 in.) thick Gunite (Shotcrete) beams, applied to the underside of the slab between drop panels in the east-west (E-W) direction, was developed in 1984. Since then, delamination of Gunite beams and other structural problems repeatedly occurred. Epoxy injection and other limited repairs were done over the years in an attempt to remediate the problems. In 2000, due to the growing delamination concerns, backed up with nondestructive impact-echo testing results, and due to the newest set of structural analyses that showed additional design deficiencies, Simpson Gumpertz & Heger developed a new and comprehensive remedial program. The first phase of this program included an in-depth mechanical in?situ load test program to study the strength and stiffness performance of the existing typical slab spans, including the effects of Gunite beams, the loss of Gunite beams due to delamination, and the CFRP?strengthing of spans. The tests showed that the CFRP repair of E-W spans with delaminated Gunite beams is warranted and that it performs well. The performance of the existing typical spans in the north-south direction was found to be acceptable without any repairs. Further monitoring of the performance of Gunite beams is required, and additional CFRP strengthening will be done periodically. In addition, structural deficiencies of the typical second-level end bays were repaired using additional steel framing supports.     

Combined crease recovery finishing and pigment printing

The combined application of crease recovery finishing (using a dimethyloldihydroxyethylene urea-based finish) and pigment printing is evaluated in this study. The use of a small amount of ammonium chloride in a combined print–finish process induces significant pigment print paste viscosity losses. However, the catalyst 2-aminoethanesulphonic acid produces negligible viscosity reduction when used in the combined print–finish process, coupled with the desired levels of finish and pigment print performance. Similar dry crease recovery, breaking load, colour strength and colour fastness properties are achieved by using 2-aminoethanesulphonic acid in the combined print–finish process relative to the conventional print–finish process.     

Life-Cycle Cost Analysis using Deterministic and Stochastic Methods: Conflicting Results

Life-cycle cost analysis is an essential approach to differentiating alternative rehabilitation strategies for steel bridge paint systems. An economic analysis (EA), which is a deterministic method, and the Markov decision process (MDP), which is a stochastic method, were used to carry out the life-cycle cost analysis. These analyses were applied to data from two state Departments of Transportation. The deterioration curves for steel bridge paint condition rating against age were constructed. Different rehabilitation scenarios were proposed for steel bridge paint. The EA and the MDP were used to analyze and differentiate among the proposed rehabilitation scenarios. The results of the EA were different from those of MDP for the two data sets. MDP favored the “do nothing” scenario until the end of paint life and then a complete repainting. EA indicated that the scenario “do spot repairs at state 3 of the paint life” and repeat that until the end of the bridge life was superior. The results were analyzed to determine the reason for the conflict.     

Synthesis and thermal cure of high molecular weight polybenzoxazine precursors and the properties of the thermosets

High molecular weight polybenzoxazine precursors have been synthesized from aromatic or aliphatic diamine and bisphenol-A with paraformaldehyde. The precursors were obtained as soluble white powder. Molecular weight was estimated from the size exclusion chromatography to be several thousands. The structure of the precursors was confirmed by IR, ¹H NMR and elemental analysis, indicating the presence of cyclic benzoxazine structure. The ratio of the ring-closed benzoxazine structure and the ring-opened structure in the high molecular weight precursor was estimated from ¹H NMR spectrum and also from the exotherm of DSC, showing that the ratio of the ring-closed benzoxazine structure was 77–98%. The precursor solution was cast on glass plate, giving transparent and self-standing precursor films, which was thermally cured up to 240 °C to give brown transparent polybenzoxazine films. The toughness of the crosslinked polybenzoxazine films from the high molecular weight precursors was greatly enhanced compared with the cured film from the typical low molecular weight monomer. Tensile measurement of the polybenzoxazine films revealed that polybenzoxazine from aromatic diamine exhibited the highest strength and modulus. While, polybenzoxazine from longer aliphatic diamine had higher elongation at break. The viscoelastic analyses showed that the glass transition temperature of the polybenzoxazines derived from the high molecular weight precursors were as high as 238–260 °C. Additionally, these novel polybenzoxazine thermosets showed excellent thermal stability.     

铁对粉末冶金法制备铝基复合材料微观组织和力学性能及磁学性能的影响(英文)

研究铁对粉末冶金法制备铝基复合材料微观组织、力学性能及磁学性能的影响。利用机械混合制备含0,5%,10%和15%Fe(质量分数)的铝基复合材料。Al-Fe混合粉末经压制后在真空炉中600°C烧结1 h。XRD结果表明:在含有5%和10%Fe的试样中只有Fe和Al的衍射峰,而含有15%Fe的试样中则存在Al和Al13Fe4的衍射峰。实验结果表明:随着Fe含量的增加,材料的致密度和导热性变差。复合材料中的Fe可以提高其强度和硬度。材料的强化机制包括基体的晶粒细化,Fe颗粒的均匀分布以及Al13Fe4金属间化合物的形成。含有5%Fe试样的磁化强度为0.3816×10-3A·m2/g,对于含有10%Fe的试样,其磁化强度增加至0.6597×10-3A·m2/g,而对于含有15%Fe试样,其磁化强度降低至0.0702×10-3A·m2/g。这是由于在高铁试样中形成了反磁性的Al13Fe4金属间化合物导致磁化强度降低。     

Influence of High-Pressure Coolant Assistance on the Machinability of the Titanium Alloy Ti555–3

The origin of this article is the quantification of productivity gains and the improvement in surface integrity seen for a recent titanium alloy that is seeing increasing use in the aeronautical industry. The Ti555–3 titanium alloy, which is starting to find greater application in the aeronautical field, exhibits certain difficulties in terms of machining. High Pressure Coolant (HPC) assisted turning consists of projecting a high pressure coolant jet between the chip and the tool. Comparisons are made between assisted turning using variable jet pressure and conventional turning (dry and classical lubrication). It is shown that it is possible to improve productivity by using HPC-assisted machining. The results highlight good chip fragmentation and a great improvement of tool life with HPC assistance. Surface integrity is also shown to be improved, through surface roughness parameters that decrease, and surface residual stresses that become more compressive. These effects have been attributed to the thermo-mechanical action of the coolant jet resulting in lower cutting forces, lower coefficient of friction and lower temperature in the cutting zone.     

A crystal-tolerant fully integrated CMOS low-IF dual-band GPS receiver

This paper presents the design of a dual-band L1/L2 GPS receiver, that can be easily integrated in portable devices (mainly GSM mobile phones). For the ease of integration with GSM wireless systems the receiver can tolerate most of the common GSM crystals, besides the GPS crystals, this will eliminate the need to use another crystal on board. A new frequency plan is presented to satisfy this requirement. A low-IF receiver architecture is used for dual-band operation with analog on-chip image rejection. The receiver is composed of a narrow-band LNA for each band, dual down-conversion mixers, a variable-gain channel filter, a 2-bit analog-to-digital converter, and a fully integrated frequency synthesizer including an on-chip VCO and loop filter. The complex filter can accept IF frequency variation of 10% around 4.092 MHz which allows the use of the commonly used 10/13/26 MHz GSM crystals and all the GPS crystals. The synthesizer generates the LO signals for both L1/L2 bands with an average phase noise of −95 dBc/Hz. The receiver exhibits maximum gain of 112 and 115 dB, noise figures of 4 and 3.6 dB, and input compression points of −76 and −79 dBm for L1 and L2, respectively. An on-chip variable-gain channel filter provides IF image rejection greater than 25 dB and gain control range over 80 dB. The receiver is designed in 0.13 μm CMOS technology and consumes 18 mW from a 1.2-V supply.     

Risk-Based Evaluation for Meeting Future Water Demand of the Brahmaputra Floodplain Within Bangladesh

A risk-based evaluation is performed for meeting future water demands in the Brahmaputra Floodplain Area within Bangladesh (BFA). This evaluation is carried out using three risk-based performance indicators: reliability, resiliency and vulnerability. The vulnerability indicator has been redefined incorporating the aspect of a supply failure. The analysis includes the impacts of climate change on both water demands and resources, and the generation of synthetic flows of the Brahmaputra River using time series models. The simulated values of the indicators reveal that the expected demand of the BFA up to the year 2050 can be supplied with the proposed Brahmaputra Barrage inside Bangladesh under the ‘no change’ in climatic condition, provided that the groundwater remains usable. However, if groundwater becomes unusable due to widespread arsenic contamination and/or a climate change occurs, it would not be possible to meet the future water demand of the region with high reliability, moderate resiliency and low vulnerability.