Multi-objective optimization of the ecm process

Optimization of process parameters is helpful in efficient working of the process and, hence, in lowering the cost of machining. Optimization of ECM process parameters has been achieved by considering only one objective at a time from metal removal rate, geometrical accuracy, and total process cost. From a practical point of view, a solution of the ecm problem satisfying all three objectives simultaneously is highly desirable.In the proposed model, a multi-objective problem involving the ecm process is formulated producing highly nonlinearized equations. These are then linearized by regression analysis and converted into a goal programming format. Finally, the problem is solved by the partitioning algorithm.It is concluded that the tool, or cathode, remains safe at the optimal values of design variables obtained in the examples discussed. The optimal value of voltage when metal removal rate is the only objective, is found to be higher than the case when the geometrical accuracy requirement is also to be satisfied.     

Elastohydrodynamic analysis of a cylindrical journal bearing with a flexible bearing shell

The effect of the elastic deformation of a bearing shell was considered in the determination of the performance characteristics of a hydrodynamic journal bearing. The finite element method with an iteration scheme was employed to solve the Reynolds equation governing flow in the clearance space and the three-dimensional linear elasticity equations representing the displacement vector field in the bearing shell. For design convenience a nondimensional deformation coefficient ψ relating μ, E_m, U₀ , C, R_j and tis defined. The performance characteristics were obtained in terms of load-carrying capacity, fluid flow, power loss and attitude angle for an aspect ratio $\text{L}\text{D = 1}$, eccentricity ? = 0.6 and for a wide range of deformation coefficients. The results are compared for bearing materials having Poisson's ratio v equal to 0.3 and 0.4.     

A Generalization of the Poisson Distribution

A new generalization of the Poisson distribution, with two parameters λ₁ and λ₂, is obtained as a limiting form of the generalized negative binomial distribution. The variance of the distribution is greater than, equal to or smaller than the mean according as λ₂ is positive, zero or negative. The distribution gives a very close fit to supposedly binomial, Poisson and negative-binomial data and provides with a model suitable to most unimodel or reverse J-shaped distributions. Diagrams showing the variations in the form of the distribution for different values of λ₁ and λ₂ are given.     

Performance of genetic algorithms in search for water splitting perovskites

We examine the performance of genetic algorithms (GAs) in uncovering solar water light splitters over a space of almost 19,000 perovskite materials. The entire search space was previously calculated using density functional theory to determine solutions that fulfill constraints on stability, band gap, and band edge position. Here, we test over 2500 unique GA implementations in finding these solutions to determine whether GA can avoid the need for brute force search, and thereby enable larger chemical spaces to be screened within a given computational budget. We find that the best GAs tested offer almost a 6 times efficiency gain over random search, and are comparable to the performance of a search based on informed chemical rules. In addition, the GA is almost 10 times as efficient as random search in finding half the solutions within the search space. By employing chemical rules, the performance of the GA can be further improved to approximately 12–17 better than random search. We discuss the effect of population size, selection function, crossover function, mutation rate, fitness function, and elitism on the final result, finding that selection function and elitism are especially important to GA performance. In addition, we determine that parameters that perform well in finding solar water splitters can also be applied to discovering transparent photocorrosion shields. Our results indicate that coupling GAs to high-throughput density functional calculations presents a promising method to rapidly search large chemical spaces for technological materials.     

Sterile keratitis after corneal collagen crosslinking in a child

Corneal collagen crosslinking (CXL) is a non invasive technique used in halting the progression of keratoconus. Complications with this modality are rare. We report a case of an 8-year-old child who developed sterile infiltrates in the immediate postoperative period after uneventful corneal collagen crosslinking for keratoconus. The infiltrates resolved with topical steroid therapy. There was also present coexisting vernal keratoconjunctivitis (VKC) which was controlled with topical 2% cyclosporine A eye drops prior to crosslinking treatment. This case highlights importance of controlling VKC prior to CXL in keratoconus as it adds to the risk of developing post operative sterile keratitis.     

Self‐Assembly of π‐Conjugated Amphiphiles: Free Standing,Ordered Sheets with Enhanced Mobility

Oligo(p‐phenylenevinylenes) (OPVs) with amphiphilic character are synthesized and their self‐assembly characteristics studied. Careful studies point at two morphologically different states of assemblies, with one being two dimensional sheets and the other as rolled tubes. This is also the first time that self‐assembled sheets are achieved for OPVs. Morphological and photo‐physical studies reveal a unique aggregate to aggregate transition between rolled tubes and two dimensional sheets, which is outlined as a more thermodynamic aggregate. The thermodynamic aggregate (2D sheet) is better ordered and consists of chromophores that are better excitonically coupled. The mobilities of these aggregates are also studied for a field effect transistor device and as expected sheets supersede rolled tubes by a couple of orders. More interestingly, the mobility values obtained for the well ordered chromophores in sheets is three orders higher than any other self‐assembled OPV previously reported. It is hypothesized that the better π interactions enforced by the amphiphilic design and the resultant supramolecular organization is a prime factor for such a remarkable rise in mobilities.     

Rapid mixing chemical oxidative polymerization: an easy route to prepare PANI coated small-diameter CNTs/PANI nanofibres composite thin film

Composite thin film containing polyaniline (PANI) coated small diameter carbon nanotubes (SDCNTs)/PANI nanofibres (NFs) has been prepared using an easy in situ rapid mixing chemical oxidative polymerization method. SDCNTs thin film was obtained using thermal chemical vapour deposition method in a separate experiment, whilst PANI NFs are formed in situ during the synthesis of composite. In the composite, PANI coated SDCNTs are uniformly distributed among PANI NFs. The presence of SDCNTs during the composite synthesis does not influence the nucleation and growth of PANI NFs. Raman analysis shows a good interaction between PANI and SDCNTs. Room temperature d.c. electrical sheet resistance of SDCNTs/PANI NFs composite thin film surface is three orders lesser than that of PANI NFs thin film (PANI NFs have the same morphology as in the composite) synthesized using the same method but without the presence of SDCNTs.     

Catalytic effect of bis (cyclopentadienyl) nickel II on the improvement of the hydrogenation-dehydrogenation of Mg-MgH2 system

Bis(cyclopentadienyl) nickel II is one of the best precursors of nickel catalyst which remarkably improved the hydrogen absorption-desorption of Mg–MgH₂ system. The X-ray photoelectron spectroscopy (XPS) and Furrier Transformed Infrared Spectroscopy (FTIR) analyses revealed that bis (cyclopentadienyl) nickel II decomposed into metallic nickel during ball milling with MgH₂. The nickel thus formed has homogeneously doped over the Mg - MgH₂ surface. The Ni-doped Mg-MgH₂ have shown the excellent catalytic effect on hydrogen absorption-desorption. The catalyzed MgH₂ could desorb hydrogen below 225 °C (T_onset) under Ar flow, and absorb hydrogen at 50 °C under 1.5 MPa H₂ pressure. The hydrogen absorption-desorption temperatures are remarkably decreased as compared to the uncatalyzed Mg-MgH₂ system under the identical experimental conditions.