Solution approaches to the course timetabling problem

University course timetabling is one of the most important administrative activities that take place in all academic institutions. In this work, we go over the main points of recent papers on the timetabling problem. We concentrate on university timetabling and introduce hard and soft constraints as well as most currently used objective functions. We also discuss some solution methods that have been applied by researchers. Finally, we raise more questions to be explored in future studies. We hope the directions lead to new researches that cover all aspects of the problem and result in high-quality timetables.     

Analysis and optimization of the asynchronous modulated light detection pixel

Detection of modulated light signals transmitted by active image markers can be used in object localization tasks and machine vision applications. The asynchronous demodulation pixel is able to detect the signal transmitted by these modulated markers. The modulated marker position in a two-dimensional pixel array can be used to identify the marker location in the field. In this paper the asynchronous demodulation pixel is analyzed and its operation is investigated in the presence of non-ideal effects such as parasitic elements, device mismatches and process variations. The effect of demodulator bias conditions and different switch pulsing techniques are examined and a modified demodulator controlling method is presented to increase the dynamic range and sensitivity of the pixel compared with the common operation schemes. The different demodulator structures are also simulated as 64 × 64 pixel array sensors using a 0.18 μm standard CMOS process and their operation is compared regarding sensitivity, filter transfer function, pixel size and power consumption.     

Improvement in corrosion resistance of commercial pure titanium for the enhancement of its biocompatibility

A new surface modification protocol encompassing an anodization treatment has been developed to improve the surface properties of biomedical titanium. Anodization in presence of nickel sulfate is one of a good way to improve the resistance of commercial pure titanium (cp‐Ti) in phosphate saline buffer solution (PSB). The potentiostatic behavior of anodized titanium in sulfuric acid with nickel sulfate differed markedly from that of titanium anodized in sulfuric acid free from nickel sulfate. Polarization and electrochemical impedance spectroscopy (EIS) recorded an increase in the corrosion resistance of the passive film. Scanning electron microscopy (SEM) and energy diffraction X‐ray (EDX) analysis were used to investigate the morphology and structure of the anodized film in absence and in presence of nickel sulfate. On the other hand, sealed anodized titanium samples exposed to PSB for up to 3 days have been studied by EIS to obtain detailed information concerning the electrochemical properties of sealed anodized titanium. An equivalent circuit that reproduces the impedance results of porous cp‐Ti oxide (TiO₂) films is proposed. These observations indicate that anodization of cp‐Ti in presence of nickel sulfate and sealing the anodized film can serve as a simple low‐temperature method to enhance the corrosion resistance of cp‐Ti when used as an implant material.     

Improving the quality of surface in the polishing process with the magnetic abrasive powder polishing using a high-frequency induction heating source on CNC table

In this research, polishing flat surfaces has been done by using a completely new and innovative method. In this method, rotary magnetic tool that carry magnetic abrasive powders, is placed in a very strong thermal induction field, and magnetic rotary tool frequently change its direction from clockwise (CW) to counterclockwise (CCW) and CCW to CW. The frequency of changing rotation direction is an important parameter of this innovation method. The intended pieces for polishing operations have been placed on a synchronic two-axis Cartesian CNC table, and the gap between rotary magnetic tool and the sheet surface can be controlled by a power transmission screw operating in the direction of the vertical axis. Several experiments have proved high performance of the new proposed method in the process of polishing.     

Spontaneous Formation of Liquid Crystals in Ultralarge Graphene Oxide Dispersions

A novel process is developed to synthesize graphene oxide sheets with an ultralarge size based on a solution‐phase method involving pre‐exfoliation of graphite flakes. Spontaneous formation of lyotropic nematic liquid crystals is identified upon the addition of the ultralarge graphene oxide sheets in water above a critical concentration of about 0.1 wt%. It is the lowest filler content ever reported for the formation of liquid crystals from any colloid, arising mainly from the ultrahigh aspect ratio of the graphene oxide sheets of over 30 000. It is proposed that the self‐assembled brick‐like graphene oxide nanostructure can be applied in many areas, such as energy‐storage devices and nanocomposites with a high degree of orientation.     

Novel solution for acceleration motion of a vertically falling spherical particle by HPM–Padé approximant

In this paper the acceleration motion of a vertically falling spherical particle in incompressible Newtonian media is investigated. The velocity is evaluated by using homotopy perturbation method (HPM) and Padé approximant which is an analytical solution technique. The current results are then compared with those derived from HPM and the established fourth order Runge–Kutta method in order to verify the accuracy of the proposed method. It is found that this method can achieve more suitable results in comparison to HPM.     

Nano-AlN particle reinforced Mg composites: microstructural and mechanical properties

In this study, nano-AlN particles were introduced into pure Mg matrix through the powder metallurgy technique incorporating microwave assisted two-directional sintering followed by hot extrusion. The effect of varying volume fraction of nano-AlN addition on the microstructural and mechanical properties of pure Mg was investigated. Microstructural characterisation revealed marginal grain refinement due to the fairly uniform distribution of AlN nano-particulates. X-ray diffraction results indicated basal texture weakening in Mg/0·2AlN composite. Tensile property measurements revealed an overall increase in strength properties and ductility. Among the developed composites, Mg/0·8AlN displayed superior strength (～30% improvement) and Mg/0·2AlN showed enhanced ductility (～80% enhancement). Under compressive loading, the developed Mg/AlN nanocomposite formulations exhibited improved strength properties without significant effect on compressibility.     

A modified thermodynamic insight to deliquescence of a void‐containing nanocrystal confirmed by MD simulation

Existence of voids in crystalline structures can affect their physical and chemical properties considerably. When the size of the crystal reaches to nanoscale, experimental determination of its void fraction is difficult. In this work, a molecular dynamics approach is introduced to find equilibrium void fractions of a simple cubic (CsCl) and fcc (KCl) nanocrystals by determination of their deliquescence relative humidity (DRH) for different sizes and void fractions and extrapolation of the results to the bulk limit. To confirm the simulation results, the size dependency of DRH to the nanoparticle size was studied thermodynamically by inclusion of size‐dependent density of water nanodroplet which leads to a simple homographic equation. This method proposes the equilibrium void percents of CsCl and KCl nanoparticles to be 10 and 15%, respectively, which are obtained by extrapolation of the results to the bulk limit. The success of obtained Möbius function was also confirmed by fitting it to experimental data for deliquescence of NaCl nanoparticles which implies the importance of considering density of water nanodroplet as a size dependent quantity. Also, using the mentioned thermodynamic approach, void dependency of deliquescence for the nanoparticles was found to be as a quasi‐linear trend which is compatible with the simulation results. It is noticeable that the approach used this work for determination of equilibrium void fraction is only valid if the utilized force fields are accurate. © 2016 American Institute of Chemical Engineers AIChE J, 62: 4066–4077, 2016     

Electron back-scattered diffraction and nanoindentation analysis of nanostructured Al tubes processed by multipass tubular-channel angular pressing

Microstructural evolution and mechanical properties of nanostructured 1060 aluminum alloy tubes processed by tubular-channel angular pressing (TCAP) process were investigated using electron back-scattered diffraction (EBSD), transmission electron microscopy (TEM) and nanoindentation analyzes. EBSD scans revealed a homogeneous ultrafine grained microstructure after the third passes of the TCAP process. Apart from that the mean grain sizes of the TCAP processed tubes were refined to 566 nm, 500 nm and 480 nm respectively after the first, second and third passes. The results showed that after the three TCAP passes, the grain boundaries with a high angle comprised 78% of all the boundaries. This is in comparison to the first pass processed sample that includes approximately 20% HAGBs. The TEM inspection afforded an appreciation of the role of very low-angle misorientation boundaries in the process of refining microstructure. Nanoindentation results showed that hardness was the smallest form of an unprocessed sample while the largest form of the processed sample after the three passes of TCAP indicated the highest resistant of the material. In addition, the module of elasticity of the TCAP processed samples was greater from that of the unprocessed sample.     

The conditional mean spectra by disaggregating the eta spectral shape indicator

Conditional spectra are a recent development in this field, which utilizes the advantages of spectral shape indicators, for example, epsilon and eta. The application of an eta indicator in conditional spectra calculations depends mainly on calculating the peak ground velocity epsilon, data about which are not readily available in the current literature. This issue has been solved by linear regression between the conventional epsilon and the peak ground velocity epsilon. However, not enough attention has been paid in the literature to the disaggregation of the eta indicator. For this reason, the disaggregation of seismic hazard based on the use of an eta indicator has been investigated in this paper, based on a simplified linear seismic source. The obtained results were compared with the available approach in the literature, which shows that this refinement has a meaningful effect on the conditional spectra specifically in the short period range. Furthermore, eta‐based conditional spectra are used at different hazard levels to select ground‐motion records. A three‐storeyed building is then analysed, and the corresponding annual probability of failure is calculated based on the full dataset as well as on the records, which were selected based on conditional spectra.