Thermodynamics and phase diagrams of lead-free solder materials

Many of the existing and most promising lead-free solders for electronics contain tin or tin and indium as a low melting base alloy with small additions of silver and/or copper. Layers of nickel or palladium are frequently used contact materials. This makes the two quaternary systems Ag–Cu–Ni–Sn and Ag–In–Pd–Sn of considerable importance for the understanding of the processes that occur during soldering and during operation of the soldered devices. The present review gives a brief survey on experimental thermodynamic and phase diagram research in our laboratory. Thermodynamic data were obtained by calorimetric measurements, whereas phase equilibria were determined by X-ray diffraction, thermal analyses and metallographic methods (optical and electron microscopy). Enthalpies of mixing for liquid alloys are reported for the binary systems Ag–Sn, Cu–Sn, Ni–Sn, In–Sn, Pd–Sn, and Ag–Ni, the ternary systems Ag–Cu–Sn, Cu–Ni–Sn, Ag–Ni–Sn, Ag–Pd–Sn, In–Pd–Sn, and Ag–In–Sn, and the two quaternary systems themselves, i.e. Ag–Cu–Ni–Sn, and Ag–In–Pd–Sn. Enthalpies of formation are given for solid intermetallic compounds in the three systems Ag–Sn, Cu–Sn, and Ni–Sn. Phase equilibria are presented for binary Ni–Sn and ternary Ag–Ni–Sn, Ag–In–Pd and In–Pd–Sn. In addition, enthalpies of mixing of liquid alloys are also reported for the two ternary systems Bi–Cu–Sn and Bi–Sn–Zn which are of interest for Bi–Sn and Sn–Zn solders.     

Preparation of smooth potassium hexatitanate nanofilms by sol–gel method

New nanosmooth potassium hexatitanate films have been prepared on crystalline Si (111) and ITO glass substrates by sol–gel method using Ti(n-OC₄H₉)₄ and CH₃COOK as precursors. Atomic force microscopy (AFM) topographic images were analyzed to select the optimal preparation conditions for the films. It is shown that the films consist of flat particles with the ratio of diameter to height around 11. The root mean square (RMS) roughness of the films based on the measurement of an area of 2,000 nm × 2,000 nm in AFM images is 6.4 nm. The crystal growth process of potassium hexatitanate film was characterized by XRD, Raman spectra, and TEM. The results showed that the crystal growth of potassium hexatitanate nanofilm is a confined growth mechanism. Electrochemical measurements demonstrated that the photocurrent of potassium hexatitanate film electrode is more stable than that of TiO₂ film electrode.     

Thermoluminescence characteristics of Sm<Superscript>3+</Superscript> doped NaYF<Subscript>4</Subscript> crystals

Thermoluminescence (TL) characteristics of NaYF₄ crystals doped with Sm³⁺ have been studied after γ-ray irradiation. Dependence of luminescence efficiency on Sm³⁺ concentration and radiation dose has been measured and possible applications of NaYF₄: Sm³⁺ as a novel phosphor for TL dosimetry have been investigated. The efficiency of 0·3 mole% Sm³⁺ doped NaYF₄ crystal has been found to be maximum and comparable with commercial thermoluminescence dosimetric (TLD) materials.     

Meshing of porous foam structures on the micro-scale

A semi-automatic block-structured grid generation technique for hexahedral meshing of porous open cell Kelvin foam structures for investigation of the pore scale fluid flow is presented. The performance of the algorithm is compared with a tetrahedral full automatic Delaunay meshing technique. In the first part of the paper the meshing strategies are explained. In the second part grid generation times, simulation times and the mesh quality are evaluated. For this Computational Fluid Dynamics (CFD) simulations for both a diffusion-dominated case (Re = 0.129) and a convection-dominated case (Re = 129) are carried out and analysed on four different cell resolutions of each mesh type. For the quality evaluation three different a posteriori error estimates are studied for the two mesh types on the different mesh sizes. The results are: the block-structured grid generation technique is about 10–20 times faster than the tetrahedral full automatic technique. While the mean field error estimates are comparable for both meshes, the maximum field error estimates for the block-structured meshes are only half of those for the tetrahedral meshes. Reaching simulation results of the same quality the hexahedral mesh needs about 20–40% less iterations with comparable mesh sizes. The time per iteration for the hexahedral meshes are up to 94% smaller than for the tetrahedral meshes. This makes the semi-automatic block-structured grid generation technique especially suitable for parameter studies and for the investigation of micro-scale flows in foam structures consisting of large quantities of Kelvin cells.     

Metaheuristic algorithms for solving two interconnected vehicle routing problems in a hospital complex

This paper addresses a real-life logistic problem arising in the hospital complex of Tours (France). The two-level vehicle routing problem has time windows, a heterogeneous fleet, and multi-depot, multi-commodity and split deliveries. The first level concerns the routing problem for a fleet of vehicles serving several hospital units that delivers medicines, clean linen, meals, various supplies, patient files and picks up waste and dirty linen. The second level concerns the problem of routing employees between buildings within a large hospital unit. Both levels are interconnected. In addition, decisions about sizing and planning the teams of drivers and warehouse employees have to be made. Two metaheuristic algorithms are proposed to solve the entire problem: a genetic algorithm and a tabu search. The algorithms are tested on 100 instances, randomly generated on the basis of real-life instances.     

A PATH PLANNING METHOD BASED ON CELLULAR AUTOMATA FOR COOPERATIVE ROBOTS

A Cellular Automaton-based technique suitable for solving the path planning problem in a distributed robot team is outlined. Real-time path planning is a challenging task that has many applications in the fields of artificial intelligence, moving robots, virtual reality, and agent behavior simulation. The problem refers to finding a collision-free path for autonomous robots between two specified positions in a configuration area. The complexity of the problem increases in systems of multiple robots. More specifically, some distance should be covered by each robot in an unknown environment, avoiding obstacles found on its route to the destination. On the other hand, all robots must adjust their actions in order to keep their initial team formation immutable. Two different formations were tested in order to study the efficiency and the flexibility of the proposed method. Using different formations, the proposed technique could find applications to image processing tasks, swarm intelligence, etc. Furthermore, the presented Cellular Automaton (CA) method was implemented and tested in a real system using three autonomous mobile minirobots called E-pucks. Experimental results indicate that accurate collision-free paths could be created with low computational cost. Additionally, cooperation tasks could be achieved using minimal hardware resources, even in systems with low-cost robots.     

Elevation,latitude and longitude decorrelation stretch of multi-temporal near-diurnal LST imagery

A method is presented for elevation, latitude and longitude decorrelation stretch of day (1:30 pm) minus night (1:30 am) monthly averaged land surface temperature (LST) differences captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) which correspond to near-diurnal LST (NDL) estimates. Principal components 1 and 2 (PC1 and PC2) account for 88.9% of the variance evident in NDL imagery. Multiple linear regression analysis of PC1 and PC2 quantifies the variance explained by elevation, latitude and longitude. Predicted and residual images of PC1 and PC2 account for 45.37% and the 43.53% of the variance, respectively. If dimension reduction (omit PC1 and PC2) is applied, then 43.53% of the variance that is independent of elevation, latitude and longitude will be subtracted from the reconstructed NDL data set. Selective variance reduction reconstructs the NDL imagery from the PC1 and PC2 residual images as well as the remaining PCs and thus only the portion of variance that is not related to elevation, latitude and longitude is taken into account. The reconstructed imagery shows the amount by which the standardized NDL value per pixel deviates from the predicted elevation, latitude and longitude. Clustering of the reconstructed data set identified positive and negative NDL anomalies in the USA and Mexico.     

Assessment of tectonic activity in a seismically locked segment of Himachal Himalaya

Bilaspur (31° 23′ 586′′ N; 76° 45′ 178′′ E) lies in the south-west Himachal close to the Main Boundary Thrust (MBT). Neotectonic studies carried out in this region have revealed that the area is traversed by several faults, many of which may be active. GPS studies carried out in the entire Himalayan region indicate crustal shortening leading to strain accumulation. This is manifest in enhanced tectonic activity in the form of major and minor earthquakes. However, there are certain areas where stress release has not been witnessed and these areas can fail in large magnitude earthquakes in the future. Bilaspur lies in the zone of strain accumulation. This zone is building up a slip deficit at the rate of 14 ± 1 mm year^?1. In the light of these revelations and the fact that Bilaspur houses one of the biggest water reservoirs of the country an attempt has been made to assess the implications of these observations.     

Parametric state feedback design of linear distributed-parameter systems

The parametric approach for the design of state feedback controllers has been formulated so far only for linear lumped-parameter systems. It yields an explicit parametric expression for the state feedback gain given the closed-loop eigenvalues and the set of corresponding parameter vectors. This contribution presents a parameterisation of state feedback controllers for linear distributed-parameter systems with scalar state and distributed control. By introducing the closed-loop eigenvalues and the parameter vectors as design parameters, an explicit expression for the state feedback is obtained. In contrast to the pure eigenvalue assignment, the parameterisation allows the assignment not only of the closed-loop eigenvalues but also of the closed-loop eigenfunctions. The usefulness of the proposed parametric approach is demonstrated by decoupling the transfer behaviour of a MIMO diffusion system with respect to its dominant modes.     

On relationships between the mechanical properties of recycled aggregate concrete: An overview

In this paper, a detailed investigation is conducted to analyze the relationships between the mechanical properties of recycled aggregate concrete (RAC). Based on a large number of experimental results published worldwide in literature from 1985 to 2004, an experimental database is developed with regard to the main mechanical properties of RAC. In particular, the relations between the compressive strength, the density, the splitting tensile strength, the flexural strength, and the elastic modulus are investigated and discussed in detail. It is found that the interrelationships between the mechanical properties of RAC could be quite different from those of normal concrete. Some improved new equations are proposed for the prediction of the relations between the mechanical properties of RAC based on the statistical regression analysis with the least squares method.