Non-commutative stopping times

Imperial Users onl

Optimal Battery Operations and Design Considering Capacity Fade Mechanisms

Safely and capacity fade are the key issues that restrict the use of the lithium-ion battery for many applications. These issues are being tackled in a variety of ways. This dissertation focuses on using detailed continuum-level electrochemical models to study transport, kinetics, and mechanical processes in the lithium-ion batteries. These models can be used to quantify the effect of capacity fade mechanisms (side reactions and mechanical degradation) and improve the safety aspects of the lithium ion batteries. Three capacity-fade mechanisms—solid electrolyte interface side reaction, lithium-plating side reaction and mechanical degradation due to intercalation-induced stresses—are considered in the dissertation. Monitoring and control of plating side reaction is also very critical for battery safety. Two main focus areas of the dissertation are: 1) Optimal battery operation (design of charging/discharging protocols) considering three capacity fade mechanisms mentioned previously along with safety issues 2) Rational battery design (choice of porosity, thicknesses of electrodes, etc.) considering discharge capacity and capacity fade mechanism

DESIGN OF ADVANCED ION-EXCHANGE MEMBRANES AND THEIR PERFORMANCE ASSESSMENT FOR DOWNSTREAM CHROMATOGRAPHIC BIOSEPARATIONS

This doctoral research focuses on the design, development and characterization of advanced ion-exchange membranes and their performance evaluation as process chromatography media for downstream bioseparations. Chromatography is a widely used unit operation in the biopharmaceutical industry for the downstream purification of protein therapeutics. The rapid developments in biotechnology and the pharmaceutical potential of biomolecules have increased the worldwide demand for protein therapeutics dramatically. Considering that 50−90% of the total cost of bioprocesses is due to the downstream recovery and purification, high-productivity and high-resolution separation techniques that will enable cost-effective production are essential to the biopharmaceutical industry. In recent years, membrane chromatography has been promoted as a promising alternative to more conventional packed-bed resin chromatography. Although the potential for membrane chromatography is great, the historically lower binding capacity of membranes compared to resin media has limited its broad implementation. Therefore, primary objectives of this dissertation were to prepare advanced weak and strong anion-exchange membranes with ultrahigh and completely reversible protein binding capacities and to demonstrate the high-throughput and high resolution that these membranes enable in the separation of a target protein from a complex media (cell lysate). The research presented here pertains to the use of atom transfer radical polymerization (ATRP) to prepare surface-modified weak and strong anion-exchange membranes for chromatographic bioseparations. Surface-initiated atom transfer radical polymerization (ATRP) was used to graft poly(2-dimethylaminoethyl methacrylate), (poly(DMAEMA)), and poly([2-(methacryloyloxy)ethyl]trimethylammonium chloride), (poly(MAETMAC)), nanolayers from the internal pore surfaces of commercial regenerated microporous membranes. Characterization of physicochemical and performance properties of newly designed, surface-modified membranes was performed using various analytical techniques. The central theme of my research was to investigate how polymer architecture influences the separation performance properties of surface-modified ion-exchange membranes. In one study, the grafting density and average molecular weight of polymer chains grown from the membrane pore surfaces were varied independently and optimized to prepare weak anion-exchange membranes with ultra-high and completely reversible dynamic binding capacity. The effects of polymer grafting density, average molar mass of polymer and linear flow velocity on the dynamic binding capacity were studied. This study yielded weak anion-exchange membranes with very high volumetric protein binding capacities (static binding capacity∼140 mg BSA/mL and dynamic capacity ∼130 mg/mL) at high linear flow velocities (\u3e350 cm/h) and relatively low transmembrane pressure drop (\u3c3 bar). In a second study, a systematic evaluation was performed on the role of polymer molecular architecture on the separation performance of strong anion-exchange membranes. Anion-exchange membranes with different polymer chain densities were prepared using surface-initiated ATRP. The effect of polymer chain density, and, thus the, degree of polymer grafting, on the mass transfer resistances and accessibility of large biopolymers (IgG and DNA) was studied. From this detailed study, I have prepared a unique protocol to design strong Q-type anion-exchange membranes with unusually high volumetric protein binding capacities (dynamic binding capacity ∼140 mg IgG/mL and ∼27 mg DNA/mL) at high linear flow velocities (\u3e190 cm/h) and relatively low transmembrane pressure drop (\u3c3.5 bar). Overall, findings from my Doctor of Philosophy (PhD) studies strengthen the argument that membrane chromatography can be a higher capacity and higher throughput process than resin chromatography. Finally, I evaluated the protein separation performance of my newly designed anion-exchange membrane adsorber and compared it to a commercial membrane adsorber and resin column. One aspect of this study was to compare the protein separation performance of membrane chromatography with resin column chromatography. Anion-exchange chromatography was used under salt-gradient and pH-gradient elution to separate anthrax protective antigen protein from periplasmic Escherichia coli lysate. Overall, this part of the work demonstrates that membrane chromatography is a high-capacity, high-throughput, high-resolution separation technique, and that resolution in membrane chromatography can be higher than resin column chromatography under preparative conditions and at much higher (15 times higher than widely used resin column) volumetric throughput

Automatic face recognition using stereo images

Face recognition is an important pattern recognition problem, in the study of both natural and artificial learning problems. Compaxed to other biometrics, it is non-intrusive, non- invasive and requires no paxticipation from the subjects. As a result, it has many applications varying from human-computer-interaction to access control and law-enforcement to crowd surveillance. In typical optical image based face recognition systems, the systematic vaxiability arising from representing the three-dimensional (3D) shape of a face by a two-dimensional (21)) illumination intensity matrix is treated as random vaxiability. Multiple examples of the face displaying vaxying pose and expressions axe captured in different imaging conditions. The imaging environment, pose and expressions are strictly controlled and the images undergo rigorous normalisation and pre-processing. This may be implemented in a paxtially or a fully automated system. Although these systems report high classification accuracies (>90%), they lack versatility and tend to fail when deployed outside laboratory conditions. Recently, more sophisticated 3D face recognition systems haxnessing the depth information have emerged. These systems usually employ specialist equipment such as laser scanners and structured light projectors. Although more accurate than 2D optical image based recognition, these systems are equally difficult to implement in a non-co-operative environment. Existing face recognition systems, both 2D and 3D, detract from the main advantages of face recognition and fail to fully exploit its non-intrusive capacity. This is either because they rely too much on subject co-operation, which is not always available, or because they cannot cope with noisy data. The main objective of this work was to investigate the role of depth information in face recognition in a noisy environment. A stereo-based system, inspired by the human binocular vision, was devised using a pair of manually calibrated digital off-the-shelf cameras in a stereo setup to compute depth information. Depth values extracted from 2D intensity images using stereoscopy are extremely noisy, and as a result this approach for face recognition is rare. This was cofirmed by the results of our experimental work. Noise in the set of correspondences, camera calibration and triangulation led to inaccurate depth reconstruction, which in turn led to poor classifier accuracy for both 3D surface matching and 211) 2 depth maps. Recognition experiments axe performed on the Sheffield Dataset, consisting 692 images of 22 individuals with varying pose, illumination and expressions

A Critical Study of the Novels of Amitav Ghosh

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मैत्रेयी पुष्पा के उपन्यासों में नारी पात्र

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Synthetic Ion Channels: A New Class of Membrane Disruptor and Efflux Pump Inhibitor for the Recovery of Antibiotic Potency

Antibiotic resistance has become a world-wide health care crisis. In 2013 there were 50,000 deaths in U.S. and EU, associated with hospital acquired bacterial infections. This problem is exacerbated by the lack of new antibiotics in development. Here, we report that synthetic amphiphiles represent a new class of adjuvants that rescue antibiotic potency against multidrug resistant bacteria. Hydraphiles are amphiphiles, designed and synthesized in Gokel lab, that show many of the same properties as protein ion channels. Hydraphiles were previously shown to have antimicrobial activity against Escherichia coli, Bacillus subtilis and Saccharomyces cerevisiae. Here, we report that hydraphiles recover the activity of tetracycline and fluoroquinolones (ciprofloxacin, norfloxacin) against E. coli, Klebsiella pneumoniae, Staphylococcus aureus bacteria. At sub-lethal concentrations, hydraphiles do not inhibit bacterial growth, show synergy with existing antibiotics and transport K+ ions. Controls confirmed that the structure and function of hydraphiles are critical for its activity. Our investigation shows that hydraphiles can inhibit antibiotic efflux pumps and increase the bacterial membrane permeability. The outer membranes of Gram negative bacteria provide for an attractive target for antibiotic development. We showed that benzyl C14 hydraphile localize in the cell membrane of E. coli and human embryonic kidney (HEK-293) cells. However, hydraphile only increases the permeability of bacterial membranes. An advantage of this approach is that bacteria cannot readily develop resistance to membrane-active amphiphiles as observed with benzyl C14 hydraphiles. Our results show that hydraphiles inhibited the activity of norA efflux pump in S. aureus. As a result, the accumulation of the substrate/antibiotic increases in the S. aureus cytoplasm. This increases the antibiotic potency. At sub-lethal concentration of benzyl C14 hydraphile, the survival of three different mammalian cells was 80-100%. Overall, we report a novel adjuvant platform that could be used to rescue the efficacy of existing antibiotics for the treatment of life-threatening bacterial infections

Growth and Characterization of some Bio-material Crystals

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Optimal charge/discharge profiles of mechanically constrained lithium-ion batteries

The cost and safety related issues of lithium-ion batteries require proactive charge and discharge profiles that can efficiently utilize the battery. Detailed electrochemical engineering based models that incorporate all of the key physics affecting the internal states of a lithium-ion battery are modeled using a system of coupled nonlinear partial differential equations. Careful choice of numerical discretization schemes and mathematical reformulation approaches can reduce the computational cost of these models to implement them in control relevant applications. The progress made in understanding the capacity fade mechanisms has paved the way for inclusion of that knowledge in deriving optimal charging/discharging profiles. Derivation of optimal charging/discharging profiles using physics based models enable us to provide constraints that can minimize local nonideal behavior and maximize efficiency locally and globally. This presentation will discuss derivation of optimal charging/discharging profiles which restrict various driving forces that accelerate capacity fade in a battery (e.g., temperature rise, over-potential for parasitic side reactions, intercalation induced stresses in solid phase) with minimal compromise on the amount of charge stored