SURFACE TEXTURES FOR ENHANCED LUBRICATION: FABRICATION AND CHARACTERIZATION TECHNIQUES

Theoretical and experimental results show that the performance of a load-bearing surface in hydrodynamic lubrication may be enhanced by engineering a definable surface texture onto the surface. These surface textures are in the form of protrusions (positive asperities) or cavities (negative asperities) of known size and geometry. The benefits of such surface textures include lower friction torque, higher load capacity and lower operating temperatures. This Thesis details a fabrication process to manufacture such surface textures/asperities on flat surfaces. The asperities are fabricated using a UV photolithography process followed by electroplating. A complete surface characterization is done to evaluate the effectiveness of the manufacturing process. From the characterization results, some errors in asperity geometry are identified and statistically quantified. These errors are found to be normally distributed and the random surface roughness is 1 to 3 orders of magnitude less than the deterministic feature size. The accuracy of the manufacturing process for fabricating the asperities was found to lie within 6.5 % of the desired value over all the errors studied. Finally, a sensitivity analysis is done to theoretically evaluate the effect of some of these errors in the hydrodynamic lubrication regime

Direct observation of interface and nanoscale compositional modulation in ternary III-As heterostructure nanowires

Straight, axial InAs nanowire with multiple segments of GaInAs were grown. High resolution X-ray energy-dispersive spectroscopy (EDS) mapping reveal the distribution of group III atoms at the axial interfaces and at the sidewalls. Significant Ga enrichment, accompanied by a structural change is observed at the GaInAs/InAs interfaces and a higher Ga concentration for the early grown GaInAs segments. The elemental map and EDS line profile infer Ga enrichment at the facet junctions between the sidewalls. The relative chemical potentials of ternary alloys and the thermodynamic driving force for liquid to solid transition explains the growth mechanisms behind the enrichment.Comment: 12 Pages, 4 figure

Lesinurad: a novel therapeutic option in the pharmacotherapy of gout

Gout is characterized by painful joint inflammation, most commonly in the first metatarsophalangeal joint, resulting from precipitation of monosodium urate crystals in a joint space. Current therapies for chronic gout include mainly allopurinol and febuxostat. Inspite of the availability of these medications for several years, a significant number of patients do not have adequate control of uric acid levels resulting in acute gout flares. Lesinurad is the most recent drug molecule approved by US FDA & EMA for the treatment of gout in patients with uncontrolled gout along with allopurinol. Lesinurad prevents reabsorption of uric acid from the renal tubules, resulting in uricosuria. The efficacy of the lesinurad was demonstrated in three randomized phase 3 controlled clinical trials where the drug was primarily evaluated in the setting of background therapy with allopurinol or febuxostat. There is a definite risk of nephrotoxicity with monotherapy and when the drug is used in patients who have inadequate renal function. The drug does appear to be relatively safe, though the inconclusive cardiovascular safety of the drug has prompted the regulatory agency to mandate post marketing trials to evaluate the safety of this molecule. Nevertheless, lesinurad does appear to have a lot of promise as a front line drug molecule in the control of hyperuricemia

Flibanserin: a serendipitous story

Female sexual disorders are increasingly being recognized in the population and hypoactive sexual desire disorder (HSDD) is one of the commonest sexual disorders among females. The prevalence of the disease varies between 10-20% in the Caucasian population. Testosterone is the only treatment that is approved by the European Medical Agency. Flibanserin is a drug that has been approved by the US FDA for HSDD among pre-menopausal women in 2015. Flibanserin is a 5-HT1A receptor agonist and 5-HT2A receptor antagonist that rebalances the neural circuitry involved in processing sexual desire by reducing serotonin activity and enhancing dopamine and epinephrine activity. The efficacy of the drug was confirmed in three pivotal randomized placebo control trials in premenopausal women who consumed the drug for 24 weeks. There was a significant improvement in the number of sexually satisfying events. The most common safety concerns for flibanserin as seen in clinical trials were somnolence, hypotension and syncope. The drug is prescribed at a dose of 100 mg once daily at bed time. The marginal efficacy of the drug coupled with other safety concerns, such as hypo-tensions have given room for much criticism over the drug’s approval by the FDA. Nevertheless, on a positive note the serendipitous discovery of flibanserin and its repurposing for HSDD is a compelling narrative in its drug development history. It remains to be seen if the long term safety of the molecule and the efficacy of the molecule in non-trial settings could make it an attractive pharmaco-therapeutic option for HSDD

Algebraic Properties of Parikh Matrices of Words under an Extension of Thue Morphism

The Parikh matrix of a word $w$ over an alphabet $\{a_1, \cdots , a_k \}$ with an ordering $a_1 < a_2 < \cdots a_k,$ gives the number of occurrences of each factor of the word $a_1 \cdots a_k$ as a (scattered) subword of the word $w.$ Two words $u,v$ are said to be $M-$equivalent, if the Parikh matrices of $u$ and $v$ are the same. On the other hand properties of image words under different morphisms have been studied in the context of subwords and Parikh matrices. Here an extension to three letters, introduced by S$\acute{e}\acute{e}$bold (2003), of the well-known Thue morphism on two letters, is considered and properties of Parikh matrices of morphic images of words are investigated. The significance of the contribution is that various classes of binary words are obtained whose images are $M-$equivalent under this extended morphism

Polarization retention loss in PbTiO3 ferroelectric films due to leakage currents

The relationship between retention loss in single crystal PbTiO3 ferroelectric thin films and leakage currents is demonstrated by piezoresponse and conductive atomic force microscopy measurements. It was found that the polarization reversal in the absence of an electric field followed a stretched exponential behavior 1−exp[−(t/k)^d] with exponent d>1, which is distinct from a dispersive random walk process with d<1. The latter has been observed in polycrystalline films for which retention loss was associated with grain boundaries. The leakage current indicates power law scaling at short length scales, which strongly depends on the applied electric field. Additional information of the microstructure, which contributes to an explanation of the presence of leakage currents, is presented with high resolution transmission electron microscopy analysis.