Reaction of tricarbonyl(dienal)iron complexes with B-allyldiisopinocampheylborane

Addition of allyldiisopinocampheylborane to racemic (dienal)iron complexes, followed by oxidation, affords diastereomeric (1,4,6-trien-3-ol)iron complexes with moderate to low enantioselectivity. The high enantioselectivity typically observed for this allylborane reagent is attenuated by steric interaction between the Fe(CO)3 group and the chiral isopinocampheyl groups. Further diminution of the enantioselectivity is observed for dienal complexes in which one rotomer predominates

Numerical Simulations of a High-Resolution RANS-FVDM Scheme for the Design of a Gas Turbine Centrifugal Compressor

The aero-thermodynamic design and performance of a compressor need to conquer many vital challenges like it is a gas-driven turbo-machinery component, involvement of extensive iterative process for the convergence of the design, enormous design complexity due to three-dimensional flow phenomena, and multiflow physics embedded within a dynamic state-of-the-art. In this chapter, a strong attempt is made to address the above-cited technical issues to achieve an optimized design and performance of a centrifugal compressor with backward swept blade profile producing total pressure ratio of 5.4 with an ingested mass flow rate of 5.73 kg/s. A mean-line design methodology was implemented to configure sizing of the compressor. An optimum grid size was well validated by carrying out computational analysis with three different mesh sizes within the same framework. Finally, a detailed three-dimensional numerical simulation was performed using Reynolds-averaged Navier-Stokes equations based on finite volume discretization method (RANS-FVDM) scheme. Consequently, the polytropic efficiency, total-to-total efficiency, stagnation pressure ratio at a fixed rotational speed, and the overall design and aero-thermodynamic performance of the centrifugal compressor are validated

Black Hole Simulations: From Supercomputers to Your Laptop

In this thesis, I will present various advancements in the modeling of binary black holes (BBHs): two black holes (BHs) that are in orbit around each other. The BHs lose energy to gravitational waves, causing them to spiral towards each other until they eventually merge and leave behind a single BH. BBHs are primary sources for ground based detectors such as the Laser Interferometer Gravitational-Wave Observatory (LIGO). As the BHs are about to merge, they are moving at about half the speed of light and the spacetime is highly dynamical. All analytical methods break down at this stage, and numerical relativity (NR) simulations of the full Einstein’s equations are necessary. These simulations, however, are very expensive, with each simulation taking a month on a supercomputer. For direct data analysis applications with LIGO, we need a model that can be evaluated in a fraction of a second. Therefore, several approximate but fast models that are calibrated to NR simulations have been developed over the years. Surrogate modeling provides a more powerful alternative: trained directly against the NR simulations without added assumptions, these models can reproduce the simulations as accurately as the simulations themselves, while taking only a fraction of a second to evaluate on a laptop. In short, surrogate models take BBH NR simulations from supercomputers to your laptop, without a loss of accuracy. In this thesis, I will present several state-of-the-art surrogate models including (i) the first NR based surrogate model to span the full range of frequencies for ground based detectors, (ii) the first surrogate model for the mass, spin, and kick velocity of the final black hole after merger, and (iii) extension of an existing precessing surrogate model to higher mass ratios. In addition, I will present some work in improving the BBH initial data used in NR simulations, as well as in understanding the systematic biases introduced by approximate waveform models in LIGO data analysis. As we head into the imminent era of high-precision gravitational wave astronomy, accurate yet fast models such as surrogate models will play a crucial role in maximizing the science output of our detectors.</p

Comparative study of two biggest mineral wastes in South Africa for mine reclamation: A geotechnical study

Abstract : Laboratory investigations were conducted on two mineral wastes to assess their geotechnical properties for mine backfilling. Composite Coal Fly Ash (CFA) sludge recovered from CFA and acid mine drainage (AMD) reaction (ratios 1:2 and 1:3) and gold mine tailings (GMT) with 3 % cement were evaluated at varying curing ages. Both samples showed favourable characteristics for use in mine reclamation. However, solid/liquid ratios should be maintained to ensure maximum strength. The results show that CFA can be recommended for mine reclamation due to it geotechnical properties. The use of GMT is possible, however blending with higher percentages of cement should be considered

Evaluation of South African gold tailings as a mine backfilling material

Abstract : This paper presents the results of laboratory investigations conducted on gold mine tailings (GMT) to assess their chemical, mineralogical, leaching and geotechnical characteristics as well their acid generating potential in view of assessing its suitability as an alternative backfilling solution in mine reclamation. Chemical characterisation revealed that GMT is dominated by Si, Al and Fe with notable amounts of Cr, Zr, Zn, Pb, Ce, As, Ba, Ni, V, Sr, Nd, Cu, U and Co. Mineralogical characterisation revealed a composition of silicate minerals with secondary minerals such as jarosite, goethite and hematite. Acid base accounting (ABA) results showed that GMT are acid generating. During column leach experiments, leaching of elements and SO42- was significant at initial stages and became negligible thereafter. GMT composites exhibited moderate strength parameters. The effect of curing age and addition of cement contributed to the shear strength of the material. Furthermore, GMT showed favourable characteristics for use in mine backfilling; however, solid/liquid ratios should be maintained to ensure maximum strength. The use of GMT for backfilling is therefore possible; however, blending with higher percentages of cement and alkaline materials such as coal fly ash should be considered to chemically stabilise the material

A multifactorial obesity model developed from nationwide public health exposome data and modern computational analyses

Summary Statement of the problem Obesity is both multifactorial and multimodal, making it difficult to identify, unravel and distinguish causative and contributing factors. The lack of a clear model of aetiology hampers the design and evaluation of interventions to prevent and reduce obesity. Methods Using modern graph-theoretical algorithms, we are able to coalesce and analyse thousands of inter-dependent variables and interpret their putative relationships to obesity. Our modelling is different from traditional approaches; we make no a priori assumptions about the population, and model instead based on the actual characteristics of a population. Paracliques, noise-resistant collections of highly-correlated variables, are differentially distilled from data taken over counties associated with low versus high obesity rates. Factor analysis is then applied and a model is developed. Results and conclusions Latent variables concentrated around social deprivation, community infrastructure and climate, and especially heat stress were connected to obesity. Infrastructure, environment and community organisation differed in counties with low versus high obesity rates. Clear connections of community infrastructure with obesity in our results lead us to conclude that community level interventions are critical. This effort suggests that it might be useful to study and plan interventions around community organisation and structure, rather than just the individual, to combat the nation’s obesity epidemic

Amending the anisotropy barrier and luminescence behavior of heterometallic trinuclear linear M-II-Ln(III)-M-II (Ln(III)=Gd, Tb, Dy; M-II=Mg/Zn) complexes by change from divalent paramagnetic to diamagnetic metal ions

The sequential reaction of a multisite coordinating compartmental ligand LH4 [2-(2-hydroxy-3-(hydroxymethyl)-5-methylbenzylideneamino)-2-methylpropane-1,3-diol] with appropriate lanthanide salts followed by the addition of Mg(NO3)2·6H2O or Zn(NO3)2·6H2O in a 4:1:2 stoichiometric ratio in the presence of triethylamine affords a series of isostructural heterometallic trinuclear complexes containing [Mg2Ln]3+ [Ln = Dy (1), Gd (2) and Tb (3)] and [Zn2Ln]3+ [Ln = Dy (4), Gd (5) and Tb (6)] cores. The formation of 1-6 is demonstrated by X-ray crystallography as well as ESI-MS spectra. All complexes are isostructural possessing a linear trimetallic core with a central lanthanide ion. In this article we have discussed the comprehensive studies, involving synthesis, structure, magnetism and photophysical properties on this family of trinuclear [Mg2Ln]3+ and [Zn2Ln]3+ heterometallic complexes. Complexes 1 and 4 show slow relaxation of the magnetization below 12 K under zero applied direct-current field, but without reaching a neat maximum which is due to the overlapping with a faster quantum tunnelling relaxation mediated through dipole-dipole and hyperfine interactions. Under a small applied direct-current field of 1000 Oe the quantum tunneling was almost suppressed and temperature and frequency dependent peaks were observed, thus confirming the SMM behavior of complexes 1 and 4. The fit of the high-temperature relaxation times to the Arrhenius equation affords an effective energy barrier for the reversal of the magnetization of Ueff =72(2) K with o = 8 x 10-9 s for the SR process and Ueff = 61(2) K with o = 4 x 10-7 s for the FR process for 1 whereas for 4, an effective energy barrier for the reversal of the magnetization Ueff = 67(3) K with o = 4.5 x 10-8 s. To rule out the involvement of intermolecular collaborative interactions in the dynamic of relaxation, we have performed ac susceptibility measurements on 1:10 Dy:Y magnetic diluted samples of of 1 and 4, named as 1' and 4'. Interestingly, the diluted compounds 1' and 4' exhibits SMM behavior under zero magnetic field, thus suggesting that their relaxation processes are single molecular in origin and arise from the M-Dy-M unit. Ab initio CASSCF+RASSI calculations carried out on 1 and 4 confirm that the magnetic anisotropy is axial along the M-Dy-M axis and that the relaxation process occurs through the first excited energy level. Furthermore, the chromophoric [LH3]2- ligand is able to act as an 'antenna' group which was found to be effective in the selective sensitization of the emissions of TbIII-based complexes 3 and 6. The emission quantum yields and the luminescence lifetimes at room temperature are 11.7 % and 0.606 ms for 3, 22.7 % and 0.799 ms for 6

Experimental study and analysis of lubricants dispersed with nano Cu and TiO2 in a four-stroke two wheeler

The present investigation summarizes detailed experimental studies with standard lubricants of commercial quality known as Racer-4 of Hindustan Petroleum Corporation (India) dispersed with different mass concentrations of nanoparticles of Cu and TiO2. The test bench is fabricated with a four-stroke Hero-Honda motorbike hydraulically loaded at the rear wheel with proper instrumentation to record the fuel consumption, the load on the rear wheel, and the linear velocity. The whole range of data obtained on a stationery bike is subjected to regression analysis to arrive at various relationships between fuel consumption as a function of brake power, linear velocity, and percentage mass concentration of nanoparticles in the lubricant. The empirical relation correlates with the observed data with reasonable accuracy. Further, extension of the analysis by developing a mathematical model has revealed a definite improvement in brake thermal efficiency which ultimately affects the fuel economy by diminishing frictional power in the system with the introduction of nanoparticles into the lubricant. The performance of the engine seems to be better with nano Cu-Racer-4 combination than the one with nano TiO2