Dynamic job shop scheduling for missed due date performance

In this research, missed due date in terms of mean absolute lateness (MAL) and mean square lateness (MSL) has been considered as a performance criterion and a scheduling study has been performed to improve the missed due date performance in dynamic, stochastic, multi machine job shop environments. In the study, a new due date assignment model was proposed and a new dynamic dispatching rule was developed. The results indicate that the proposed due date assignment model is very successful for improving the missed due date performance and the developed dispatching rule is also very successful for meeting the assigned due dates.     

Determination of hot crack susceptibility in various kinds of steels

The aim of this investigation was to study the hot crack susceptibility of some Turkish and German structural steel plates with a modified varestraint-transvarestraint test method. Testing was accomplished using a Tungsten Inert Gas (TIG) welding process. The results of this study revealed that total crack length increases as welding current increases or punch radius or welding speed decreases. An attempt is made to provide explanations for these phenomena.     

Nucleation of stress-induced martensites in a Ti/Mo-based alloy

The formation of stress-induced α ″ martensite in a metastable β Ti-Mo-based alloy has been studied using X-ray diffraction and transmission electron microscopy. The martensite nucleates heterogeneously at pre-existing sub-grain boundaries by dissociation of the boundary dislocations which bow out on inclined planes. The growth of martensite laths from the resultant stacking faults occurs by the motion of interfacial disconnections: the steps at the cores of these defects account for the apparent discrepancy between the 112 glide plane for the initial partial dislocation and the 334 habit plane for the martensite laths.Professor died on March 12th 2004.     

Acoustic Detection of Phase Transitions at the Nanoscale

Materials near structural phase transitions find applications in a wide range of devices. Typically, phase transitions are determined macroscopically through measurements of relevant order parameters and related property coefficients. Here, a method for understanding electric field induced phase transitions in ferroelectrically active materials at the nanometer scale via acoustic detection with band‐excitation piezoresponse force microscopy (BE‐PFM) is introduced. Specifically, the field‐induced rhombohedral (R) to tetragonal (T) phase transition in single crystal 0.72PbMg_1/3Nb_2/3O₃‐0.28PbTiO₃ (PMN‐PT) is mapped. It is shown that due to sample heterogeneity, some regions are more prone to the R–T transition, and display signatures in the acquired piezoresponse loops, as well as pronounced softening in the elastic modulus (monitored via the resonant frequency and calibrated with models of cantilever dynamics) that occurs just prior to phase switching. Landau–Devonshire thermodynamic theory confirms the stability of the tetragonal phase under applied fields in PMN‐PT, while phase‐field modeling suggests that the transition evolves smoothly in the probed volume of the tip, both in agreement with the BE‐PFM results. These results confirm the validity and utility of utilizing acoustic changes at phase transitions to detect their onset in nanoscale probed volumes, allowing spatial mapping of their onset with unprecedented resolution.     

Regional unemployment in Turkey

High unemployment rates are a concern for a country, existence of high regional unemployment differentials is another. Turkey has both. This paper using spatial and nonparametric techniques documents the wide regional unemployment disparities in Turkey from 1980 to 2000. Data indicate that the provincial unemployment rates are quite persistent and the gap across different regions widens even further with spatial clusters emerging across the country. The evidence indicates that human capital and demand deficiency are the sources of observed disparity across provinces. Furthermore, the sources of unemployment differentials have changed over time.     

Aspects of the Electrocaloric Behavior of Ferroelectric Thin Films: A Review of the Predictions of the Landau-Ginzburg Theory

A thermodynamic model is used to investigate the electrocaloric response of thin film perovskite ferroelectrics under the influence of differing electrical, thermal and mechanical boundary conditions including bias and driving field, temperature, lateral clamping and misfit strain. A comparison of the electrothermal properties of ferroelectric solid solutions comprised of BaTiO₃, PbTiO₃ and/or SrTiO₃ illustrates the influence of composition on electrocaloric properties. Computations made for (001) textured polycrystalline BaTiO₃ films on IC-friendly substrates quantify the effects of thermal stresses. The combined results provide insights concerning how the deposition temperature, substrate material and composition can be adjusted to obtain desired electrocaloric response.     

Polarization, piezoelectric properties, and elastic coefficients of In x Ga1−x N solid solutions from first principles

III-nitrides GaN and InN, and In _x Ga_1−x N solid solutions are polarizable semiconductors that crystallize in the prototypical wurtzite (W) structure. We present here the results of a density functional theory study carried out to determine the spontaneous polarization, piezoelectric coefficients, and elastic coefficients of In _x Ga_1−x N alloys as a function of In the concentration x. To calculate these properties, we construct three distinct hexagonal/orthorhombic equivalent In _x Ga_1−x N supercells that are derived from the disordered W unit cell of GaN and InN. These include an ordered W lattice (P6₃ mc/Pmc2₁) and orthorhombic O-16 and O-32 lattices with Pmn2₁/Pna2₁ or P2₁ symmetry, respectively. Depending on the crystal structure, spontaneous polarization as a function of the In concentration x shows a downward bowing (W), a linear interpolation (O-16), and an upward bowing (O-32) between −0.033 C/m² and −0.043 C/m², the spontaneous polarizations of the end components GaN and InN, respectively. The composition dependence of the effective basal plane and out of plane (along the [0001] direction) piezoelectric coefficients (e _// and e ₃₃, respectively) in the W and O-16 structure is non-linear and varies between e _// = −0.287 C/m² and e ₃₃ = 0.598 C/m² for GaN, and e _// = −0.455 C/m² and e ₃₃ = 1.044 C/m² for InN. While the bulk modulus of In _x Ga_1−x N in the W and O-16 structures follows Vegard’s law from 170 GPa (x = 0) to 124 GPa (x = 1), in the O-32 structure it shows a strong downward bowing for compositions 0 < x < 0.5.     

Coenzyme Q10 supplementation and diastolic heart functions in hemodialysis patients: A randomized double‐blind placebo‐controlled trial

Coenzyme Q10 (CoQ10) supplementation has been shown to improve diastolic heart function in various patient cohorts. Systolic and diastolic dysfunctions are common in patients with end‐stage renal disease. Favorable effects of CoQ10 on cardiac functions are yet to be seen in hemodialysis patients. We aimed to evaluate effect of CoQ10 supplementation on diastolic function in a cohort of maintenance hemodialysis patients. This was a prospective, double‐blind, placebo‐controlled, crossover study in which all patients received placebo and oral CoQ10 200 mg/d during the 8 weeks in each phase, with a 4‐week washout period. Participants underwent conventional and tissue Doppler echocardiography before and after each study phase. Parameters characterizing left ventricle diastolic function and other standard echocardiographic measurements were recorded. Twenty‐eight patients were randomized, but 22 patients completed study protocol. Intraventricular septum (IVS) thickness and left ventricle mass were significantly decreased in CoQ10 group (P = 0.03 and P = 0.01, respectively). Myocardial peak systolic and early diastolic velocities derived from IVS were significantly increased (P = 0.048 and P = 0.04, respectively). Isovolumetric relaxation time and E/Em ratio calculated for IVS also significantly reduced in CoQ10 group (p = 0.02 and p = 0.04, respectively). There was no significant difference in any of the studied echocardiographic parameters in placebo group. The results of this study showed that CoQ10 supplementation did not significantly improved diastolic heart functions compared with placebo in maintenance hemodialysis patients.     

GRASP with path relinking for a multiple objective sequencing problem for a mixed-model assembly line

This research presents a new application of greedy randomised adaptive search procedure (GRASP) to address a production sequencing problem for mixed-model assembly line in a just-in-time (JIT) production system in two different cases. In the former case, small size sequencing problems are considered and two objectives are presented; minimisation of setups and optimisation of stability of material usage rates. These two objectives are inversely correlated with each other, so simultaneous optimisation of both is challenging. This type of problem is NP-hard. The GRASP, with path relinking, searches for efficient frontier where simultaneous optimisation of number of setups and usage rates is desired. Several test problems are solved via GRASP and its performance is compared to solutions obtained via complete enumeration and simulated annealing (SA), tabu search (TS) and genetic algorithms (GA) approaches from the literature. Experimental results reveal that the GRASP with path relinking provides near-optimal solutions in terms of the two objectives and its ‘average inferiority%’ and ‘average percentile’ performances are superior to that of other heuristics. In the latter case, the goal is to explore varying the emphasis of these two conflicting objectives. Larger sequencing problems are considered and solved via GRASP with path relinking. Its objective function values are compared to the solutions obtained via a SA approach from the literature. Experimental results show that GRASP also provides good performance on large size problems and its percentage improvement is better than that of SA. Overall results also show, however, that the GRASP performs poorly with regard to CPU time.