Bioremediation of contaminated soil beds and groundwater — A simulation study

Pollution has reached levels which demand immediate attention and scientific and technological solutions are required on an urgent basis. We are concerned in this paper with bioremediation of soil and groundwater, i.e. the use of indigenous micro-organisms to clean up soil beds and groundwater contaminated with organic pollutants. To achieve managedin situ bioremediation in practice, treated water is recycled with added nutrients into the ground so that oxygen and nitrogen are carried with the water to the subsurface regions. Sorption, convective-dispersive flow and chemical and biological transformations are the chief processes involved that have to be modelled. Here we discuss a simulation model developed to aid in designing an efficient system that maximizes the rate of biodegradation. Simulation models are a must in this case since laboratory experiments take time periods of the order of months. An unusual feature of this simulation model is that it is governed by coupled partial and ordinary differential equations. Partial differential equations (PDEs) model the diffusion and biodegradation processes occurring in the micropores of soil aggregates while ordinary differential equations (ODEs) describe the bioremediation in the interstitial spaces between soil aggregates, both partial and ordinary differential equations being nonlinear. The model is applied to the case of high initial contaminant concentrations. This work is part of a joint project with Regional Research Laboratory, Jorhat and has been carried out in close cooperation with N N Dutta. Discussions with K S Yajnik have been very useful.     

A study of Mg and Cu additions on the foaming behaviour of Al–Si alloys

Aluminium casting alloys containing Mg and Cu in addition to Si were investigated with respect to their potential to be foamed. The kinetics of foam expansion of different alloys was studied and the resulting structures were characterised. Of the stages of evolution of foams, namely (i) pore nucleation, (ii) foam growth in the semisolid state, (iii) further expansion in the fully liquid state, the latter two were explored. Expansion in the semisolid state could be related to the available liquid fraction. Mg-containing Al–Si alloys yielded a less coarse and more uniform pore structure than the other alloys investigated. However, achieving a high volume expansion required restriction to a narrow process window and led to the suggestion of AlMg4Si8 as a practical alloy.     

A preliminary study on optimizing the heat treatment of high strength Al–Cu–Mg–Zn alloys

The design of critical aerospace alloys is primarily built on optimizing strength and ductility, both of which can be enhanced by controlling the alloying element additions as well as heat treatment conditions. The 7075 alloy is one such aerospace alloy. The main objective of this study was to optimize the 7075 strength. Several experimental alloys were prepared and tensile test bars were cast using an ASTM B-108 type permanent metallic mold. The as-cast samples were then solution heat-treated at 470 °C for times up to 48 h. The solution heat-treated bars were also aged in order to improve the alloy strength through precipitation hardening. Line scans for Mg, Cu and Zn were obtained from the various heat-treated alloy samples using an electron probe microanalyzer equipped with Energy Dispersive X-ray (EDX) and Wavelength Dispersive Spectroscopic (WDS) facilities. Peaks corresponding to the Mg, Cu and Zn concentrations in the as-cast samples disappeared after solution treatment, reflecting optimized homogeneity structures. The newly developed versions of the 7075 alloy displayed an ultimate tensile strength (UTS) of ∼1 GPa.     

A Mössbauer study of the oxidation of Fe-Ni alloys at 535 and 635°C

Fe⁵⁷ transmission Mössbauer spectroscopy, supported by metallography, SEM and X-ray diffraction analysis, has been employed to study the oxidation of Fe-Ni alloys at 535 and 635° C in 1 atm. of air. With increasing Ni content of the alloy, the composition of the scale changed and the oxidation rate decreased. For an alloy containing 0.9% Ni, the oxide scale produced at 535° C was Fe₃O₄ covered by a thin outer layer of-Fe₂O₃, while at 635° C FeO was additionally present as a major phase. The scale formed on a 10% Ni alloy at both 535 and 635° C was similar to that observed for the 0.9% Ni alloy oxidized at 535° C (i.e. of Fe₃O₄ and-Fe₂O₃), although the-Fe₂O₃ layer tended to be relatively thicker. For a 49% Ni alloy, the scale at both 535 and 635° C comprised an inner layer of Ni _x Fe_3–x O₄ (withx0.5, on average) and an outer layer of-Fe₂O₃, of similar thickness. Finally, on an 83% Ni alloy oxidized at 635° C, the scale consisted of roughly equally thick layers of NiO (next to the metal) and NiFe₂O₄, and a thin outer covering of-Fe₂O₃. The decrease in oxidation rate with increasing Ni content of the alloy is discussed briefly in relation to the changing composition of the scale and diffusion in the alloy.     

Examination of the specific features of the electron density of states of weakly nonstoichiometric Fe–V–Al alloys through the analysis of low-temperature heat capacity

The results of a comparative study of low-temperature heat capacity and resistivity of weakly nonstoichiometric Fe–V–Al alloys with their composition varied (in iron, vanadium, and aluminum atoms individually) with respect to the stoichiometric Fe₂Val alloy are reported. The electron density of states near the Fermi energy is estimated for the studied alloys. The data confirming the presence of a narrow pseudogap at the Fermi level in alloys enriched with vanadium and the lack of such a pseudogap in alloys enriched with iron or aluminum are obtained.     

Effects of kanban withdrawal policies and other factors on the performance of JIT systems—a simulation study

This paper presents the results of a simulation study of a just–in–time (JIT) production control system and its performance under different operational conditions. In particular, the effects of two different kanban withdrawal policies on such performance measures as throughput rate, station utilizations and total work in process levels are investigated. Also, simulation experiments are carried out to determine the effects of processing time variability, number of different types of kanbans allowed at each station and production line length on the mentioned performance measures of JIT production control method. The simulation experiments were carried out for production lines in which processing times of stations were assumed to follow gamma and Erlang distributions.     

Microstructure characterisation and CTE study of Fe—42Ni—Nb invar alloys

Invar alloy has low coefficient of thermal expansion; however, the week strength always limits its application. To circumvent this problem, the authors have designed Fe—42%Ni—Nb invar alloy using midfrequency vacuum induction melting technique. The microstructures of this alloy were characterised by means of XRD, SEM and TEM. The multicomponent composition (NiFeCMnNb) is chosen such that upon chill casting of the alloy the liquid undergoes a metastable reaction, forming a strengthening NbC precipitated phase on γ-(Fe, Ni) solid solution. As a result, the alloy achieves the low coefficient of thermal expansion α_30–100=6·14 × 10^?6 K^?1 ranged from room temperature to 100°C. The results show: in NiFe invar alloys, the primary phases are γ-(NiFe), FeNi₃) Ni and Fe₂C; and with the addition of carbon, manganese and rare earth niobium, NiFeCMnNb invar alloy achieves such primary phases as γ-(NiFe) and Nb_yC_x; and TEM structure consists of superfine structure and its matrix is γ-(NiFe).     

A Monte Carlo simulation for the study of the influence of the thickness of the source in 3H β-ray spectroscopy

A Monte Carlo simulation for the study of the influence of the thickness of the radioactive source in β-ray spectroscopy is presented in this paper. We make use of the Bethe-Bloch formula for ionization loss and Rutherford scattering cross section to trace the tracks of the β particles from a randomly sampled point source of given energy, which has been implanted in an aluminum coating with copper backing. We have studied seven groups of β rays with momenta from 119.14262 to 139.12328 keV/c. There are the peak shift, the broadening of the line width and the low energy tail. Their momentum dependences have been found. The program can be applied to similar cases with minor modification.     

A study of the composition and microstructure of nanodispersed Cu–Ni alloys obtained by different routes from copper and nickel oxides

Mixtures of CuO and NiO were prepared by two different techniques, and then the oxides were reduced with H₂. Method A involved the preparation of mechanical mixtures of CuO and NiO using different milling and pelletizing processes. Method B involved the chemical synthesis of the mixture of CuO and NiO. The route used to prepare the copper and nickel oxide mixture was found to have great influence on the characteristics of bimetallic Cu–Ni particles obtained. Observations performed using the X-ray diffraction (XRD) technique showed that although both methods led to the Cu–Ni solid solution, the diffractogram of the alloy obtained with method A revealed the presence of NiO together with the alloy. The temperature-programmed reduction (TPR) experiments indicated that the alloy is formed at lower temperatures when using method B. The scanning electron microscopy (SEM) studies revealed notable differences in the morphology and size distribution of the bimetallic particles synthesized by different routes. The results of the electron probe microanalysis (EPMA) studies evidenced the existence of a small amount of oxygen in both cases and demonstrated that the alloy synthesized using method B presented a homogeneous composition with a Cu–Ni ratio close to 1:1. On the contrary, the alloy obtained using method A was not homogeneous in all the volume of the solid. The homogeneity depended on the mechanical treatment undergone by the mixture of the oxides.     

On the glass-forming ability of Ni–P binary alloys

The composition dependence of glass-forming ability (GFA) of Ni–P binary alloys was systematically examined by fabricating ribbons of different thicknesses, and the microhardness of the glassy ribbon was measured. The eutectic alloy Ni_80.4P_19.6 has the best GFA and the highest microhardness in glassy state. As the alloy composition is deviated from the eutectic composition, both GFA and microhardness decrease, accompanied with an increasing full width at half maximum of the main broad peak in the X-ray diffraction spectrum of the glassy ribbon. All these results indicate a close correlation among microstructure, GFA and microhardness for the metallic glass.     

Optimization of composition and heat treatment design of Mg–Sn–Zn alloys via the CALPHAD method

This work is focused on the application of the calculation of phase diagrams method for alloy and heat treatment design. We analyzed the influence of Zn content on the precipitation of Mg₂Sn in Mg–Sn–Zn alloys. A comparison with previous studies in the Mg–Sn–Zn system was made according to the published results and computational thermochemistry simulations. The phase evolution in the Mg–Sn–Zn system was evaluated for the different compositions, and the simulations were used for precise alloy and heat treatment design. The composition of the ternary alloy was set as Mg–8wt%Sn–1.25wt%Zn. The Sn and Zn content was designed and confirmed to be within the α-Mg solubility limit at the solution treatment temperature. The addition of Zn and the heat treatment applied resulted in the enhancement and refinement of the Mg₂Sn precipitation. Three Vickers micro-hardness maxima were detected: precipitation of metastable Mg–Zn phases, heterogeneous precipitation of Mg₂Sn on the Mg–Zn precipitates, and Mg₂Sn precipitation in the α-Mg matrix. The CT simulations were found to be a valuable alloy design tool.     

A study on the influence of Mo, Al and Si additions on the microstructure of annealed dual phase Cr–Ta alloys

The effects of additions of 5 at.% Mo, Al and Si on the long-term annealed microstructures of a two phase Cr–Cr₂Ta alloy have been studied. Following 200 h at 1300 °C, the lamellar eutectic constituent of all the alloys disintegrated into discrete particles of the Laves phase embedded within a Cr-rich solid solution phase, along with the formation of fine Laves phase precipitates. One of the predominant differences between the three alloying additions was the extent of the C14 to C15 polytypic transformation of the Cr₂Ta-based Laves phase. With Mo and Al additions, the Cr₂Ta Laves phase transformed from C14 to either C15 or intermediate hexagonal polytypes following 200 h annealing at 1300 °C. In contrast, Si additions stabilised the C14 polytype, with no transformation to other polytypes observed after prolonged annealing at 1000, 1100 and 1300 °C.     

Effect of heat treatment and Fe content on the microstructure and mechanical properties of die-cast Al–Si–Cu alloys

The effect of solution and ageing heat treatment on the microstructure and mechanical properties of the die-cast Al–9 wt.%Si–3.5 wt.%Cu alloys containing 0.1–1.0 wt.% Fe was investigated. The results showed that the dendritic primary α-Al phase was varied from 20 to 100 μm in size and the globular α-Al grains were smaller than 10 μm in size. The Fe-rich intermetallics exhibited coarse compact or star-like shapes with the sizes from 10 to 20 μm and the fine compact particles at an average size of 0.75 μm. The solution treatment of the alloys could be achieved in a short period of time, typically 30 min at 510 °C, which dissolved the Cu-rich intermetallics into the primary α-Al phase and spheroidised the eutectic Si phase. During the subsequent ageing treatment, numerous fine precipitates of θ′ and Q′ phases were formed to provide effective strengthening to the α-Al phase, significantly improving the mechanical properties. Therefore, Fe content in the die-cast Al–Si–Cu alloys needs to be controlled at a low level in order to obtain the improved ductility and strength under solution and aged condition.     

A simulation model of the Triple Helix of university–industry–government relations and the decomposition of the redundancy

A Triple Helix (TH) network of bi- and trilateral relations among universities, industries, and governments can be considered as an ecosystem in which uncertainty can be reduced when functions become synergetic. The functions are based on correlations among distributions of relations, and therefore latent. The correlations span a vector space in which two vectors (P and Q) can be used to represent forward “sending” and reflexive “receiving,” respectively. These two vectors can also be understood in terms of the generation versus reduction of uncertainty in the communication field that results from interactions among the three bi-lateral channels of communication. We specify a system of Lotka–Volterra equations between the vectors that can be solved. Redundancy generation can then be simulated and the results can be decomposed in terms of the TH components. Furthermore, we show that the strength and frequency of the relations are independent parameters in the model. Redundancy generation in TH arrangements can be decomposed using Fourier analysis of the time-series of empirical studies. As an example, the case of co-authorship relations in Japan is re-analyzed. The model allows us to interpret the sinusoidal functions of the Fourier analysis as representing redundancies.     

Atomic-scale study of compositional and structural evolution of early-stage grain boundary precipitation in Al–Cu alloys through phase-field crystal simulation

Journal of Materials Science - Interfacial solute clustering is an essential step preceding grain boundary (GB) precipitation. Both states, i.e., clusters and precipitates, alter the mechanical,...     

Reformulation of the Nosé–Hoover thermostat for heat conduction simulation at nanoscale

This paper investigates the heat conduction phenomena at nanoscale by reformulating the Nosé–Hoover thermostat for nonequilibrium molecular dynamics simulation. Inspired by the Nosé–Hoover mechanics, the feedback temperature force caused by the temperature control is reformulated to a more general level, aiming at (1) controlling the temperature locally at several distinct spots and (2) eliminating the rigid-body translation and rotation which are unexpectedly introduced into the system due to the feedback temperature force, so that accurate trajectories of atoms can be generated and the heat conduction simulation at nanoscale can be performed successfully. Correspondingly, the definition of temperature is modified; the expression of the Hamiltonian is generalized. To demonstrate the capability and feasibility of this newly formulated algorithm, we studied heat conduction phenomenon in a beam-like finite size specimen via our in-house developed computer code. The results, temperature distributions across the specimen, are shown to reach steady state after a period of time which cannot be achieved by the original Nosé–Hoover thermostat. Also, it is concluded that the heat conduction at nanoscale exhibits the same feature of Fourier’s law at macroscopic scale, namely that the heat flux is linearly proportional to the temperature gradient, if the temperature is averaged over a sufficiently large time interval and large spatial region. The thermal conductivity can thereafter be calculated based on the linear relation between the heat flux and the temperature gradient. It is found that the obtained numerical value of thermal conductivity matches the experimental result very well.     

The effects of heat treatment on the microstructure and mechanical property of laser melting deposition γ-TiAl intermetallic alloys

Ti–47Al–2.5V–1Cr and Ti–40Al–2Cr (at.%) intermetallic alloys was fabricated by the laser melting deposition (LMD) manufacturing process. The microstructure was characterized by optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The room-temperature (RT) tensile properties and Vickers hardness of the as-deposited and heat-treated specimens were evaluated on longitudinal directions. Results shows that full density columnar grain with fully lamellar (FL) microstructure consisted of γ-TiAl and α₂-Ti₃Al was formed in the as-deposited γ-TiAl samples. The room-temperature tensile strength of the as-deposited Ti–47Al–2.5V–1Cr alloy is up to approximately 650 MPa in the longitudinal direction and 600 MPa for the as-deposited Ti–40Al–2Cr alloy, while the tensile elongation is approximately 0.6% at most. Different microstructure types were obtained in the Ti–47Al–2.5V–1Cr and Ti–40Al–2Cr alloy after heat treatment. The stress–strain curve and the tensile fracture sub-surface indicate that the fracture manner of the as-deposited and heat-treated specimens was inter-granular manner.     

On the growth of the minority phase during downward transient directional solidification of hypomonotectic and monotectic Al–Pb alloys

Al–Pb alloys were solidified under non steady heat flow conditions using a casting assembly in order to promote vertical downward directional solidification. The downward configuration enables the effects of gravity-driven convection on the final microstructure to be evaluated since the collective movement of Pb-rich particles downwards is favored, due to density differences between the two coexisting liquid phases. Investigations have been made of the obtained solidification structures. Growth rates (v) and cooling rates ( \mathop T^· \mathop T\limits^{\cdot} ) of the Al–Pb alloys solidified downwards were experimentally determined by the cooling curves recorded along the casting length. The monotectic structure was characterized by metallography and a microstructural transition has been observed in all cases. The microstructure was characterized by well-distributed Pb-rich droplets in the aluminum-rich matrix from the casting cooled surface up to a certain position in the casting, followed by a mixture of fibers and strings of pearls from this point to the bottom of the casting. The increase in alloy lead content delays the formation of fibers for alloys solidified downwards, which occurs for v < 0.48 mm/s and v < 0.15 mm/s for Al–0.9 wt%Pb and Al–1.2 wt%Pb alloys, respectively. Experimental power laws relating the interphase spacing, λ, to v and characterized by −2.0 and −6.5 exponents, were found to represent the growth of droplets and fibers, respectively, for both alloys solidified downwards.     

Rudolph Clausius – A pioneer of the modern theory of heat

Rudolph Clausius (1822–1888) played an important role in advancing the theory of heat during the 19th century. His contributions concerned the development of the two fundamental principles of heat as well as the microscopic approach of kinetic theory where he introduced the new concept of the mean free path. He always strictly separated these two fields. When Clausius took up his studies the idea that heat belonged to the so-called imponderables which were weightless and invisible had not yet disappeared. Carnot had still used that idea for his well-known cycle. Clausius was able to make the Carnot-cycle compatible with the concept of heat as a kind of motion.His research opened the way for thermodynamics later chiefly advocated by Planck as well as for modern statistical physics mainly connected with the names of Maxwell and Boltzmann. Scientific education and research of Clausius will be discussed here in the context of the development of the theory of heat. As he published most of his important papers on this subject already during the first two decades of his career we confine on this period. Clausius began his studies in Berlin in 1840, habilitated there in 1850 and was appointed at the newly founded Polytechnical School in Zürich in 1855. It will be shown that Clausius remained an outsider in the physics community of his time as he himself did not perform any research experiments.     

Interaction between sulfate-reducing bacteria and aluminum alloys——Corrosion mechanisms of 5052 and Al-Zn-In-Cd aluminum alloys

Microbiologically influenced corrosion caused by sulfate-reducing bacteria(SRB) poses a serious threat to marine engineering facilities.This study focused on the interaction between the corrosion behavior of two aluminum alloys and SRB metabolic activity.SRB growth curve and sulfate variation with and with aluminum were performed to find the effect of two aluminum alloys on SRB metabolic activity.Corrosion of 5052 aluminum alloy and Al-Zn-In-Cd aluminum alloy with and without SRB were performed.The results showed that both the presence of 5052 and Al-Zn-In-Cd aluminum alloy promoted SRB metabolic activity,with the Al-Zn-In-Cd aluminum alloy having a smaller promotion effect compared with 5052 aluminum alloy.The electrochemical results suggested that the corrosion of the Al-Zn-In-Cd aluminum alloy was accelerated substantially by SRB.Moreover,SRB led to the transformation of Al-Zn-In-Cd aluminum alloy corrosion product from Al(OH)3 to Al2 S3 and NaAlO2.