Exactly integrable family of generalized Hubbard models with twisted Yangian symmetry

A strongly correlated electron system with controlled hopping, in the line of the recently proposed generalized Hubbard models as candidates for high T_c-superconductors, is considered. The model along with a whole class of such systems are shown to be completely integrable with explicit quantum R-matrices and the Lax operators. Inspite of novelties in the Bethe ansatz solution, the final results do not deviate much from those of the standard Hubbard model. However, the symmetry of the model is changed to a recently discovered twisted Yangian symmetry.Comment: Latex, 10 pages, no figure, revised version to be published in Physics Letters

Algebraic approach in unifying quantum integrable models

A novel algebra underlying integrable systems is shown to generate and unify a large class of quantum integrable models with given $R$-matrix, through reductions of an ancestor Lax operator and its different realizations. Along with known discrete and field models a new class of inhomogeneous and impurity models are obtained.Comment: Revtex, 6 pages, no figure, revised version to be published in Phys. Rev. Lett., 199

Synthesis and Study of Chemo-Hydrothermally Derived Water-Soluble Chitosan and Chiosan-Metal Oxide Composites

Chitosan (CS) is a man-made sugar based biopolymer derived from chitin, the second most abundant natural polymer after cellulose. Chitin is sourced from crustacean species such as shrimps and crabs. The chemical structure of chitin contains N-Acetyl D-glucosamine monomer units which forms CS upon deacetylation. In CS, ?-(1-4) linked D-glucosamine units are randomly distributed. Approximately 75% - 80% sugar units contains primary amine groups in commercially available low molecular weight CS. Biodegradability, low toxicity, mucoadhesive and transfecting properties of CS polymer are attractive for applications as oral and nasal drug delivery systems. Chitosan polymer is water insoluble at neutral pH. To solubilize CS, dilute mineral acid (such as hydrochloric acid and nitric acid) or organic acid (such as acetic acid) is often used. CS contains both hydroxyl and primary amine groups in its structure. In acidic solution, the amine functional groups become protonated (positively charged). Positively charged CS remains stable only in low pH condition due to electrostatic repulsion of charged polymer segments. Therefore, by using a suitable anionic (negatively charged) cross-linker, stable CS particles (such as nanoparticles and microspheres) can be prepared. This is popularly known as ionic gelation method. Extensive studies have been done on the synthesis of drug loaded CS particles where particle integrity is maintained by ionic gelation using tripolyphosphate (TPP, an anionic cross-linker). Drug encapsulated CS-TPP composite particles are shown to maintain biodegradability and biocompatibility. The CS-TPP composite particles exhibits very limited dispersibility at neutral pH conditions specifically in neutral buffered conditions. A number of biomedical applications (including systemic drug formulations) however demands buffer-stable CS composite particles for achieving optimal therapeutic outcome. To overcome the above dispersibility issues, CS polymer and CS particles units have been chemically modified using water soluble motifs (such as water soluble polymer or ligands). This approach is very cumbersome and usually involves multiple purification steps. Chemical modification of natural CS chain introduces risks of compromising biodegradability and biocompatibility. Therefore, there is a strong need for developing a straightforward method of making water soluble CS and CS particles. Chapter 1 of this dissertation presents an overview of the CS polymer, various applications of CS polymers, methods of making CS polymers and CS particles, current limitations of synthesis methods for preparing stable chitosan particles at neutral pH conditions and finally delineates the scope of the proposed research work. Chapter 2 describes development of chemo-hydrothermal synthesis method for producing water soluble CS polymer and water dispersible CS composite particles. In this method, a chemical (depolymerizing agent) is used to treat CS polymer in a hydrothermal (high temperature and high pressure) condition. Two types of depolymerizing agents have been used, an inorganic acid (e.g. hydrochloric acid, HCl) and a bicarboxylic organic acid (e.g. tartaric acid, TA). In both cases, 100% depolymerized CS polymer was obtained. Chemical characteristics of the depolymerized CS were comparable to acid solubilized CS. CS polymer exhibits weak fluorescence. Interestingly, hydrothermally depolymerized CS shows strong fluorescence properties irrespective of the nature of depolymerizing agent used. TA not only depolymerized CS but also formed CS-TA composite particulate structures in solution via self-assembly. The CS-TA composite particles are stable in a wide pH range from 5 to 11. Detailed spectroscopic and microscopic studies have been done to understand the basic mechanism of particle formation and increase in fluorescence properties (i.e. structure-property relationship). Usefulness of CS-TA in solubilizing water-insoluble cargos (such as fluorescein isothiocyanate, FITC) has been demonstrated. Chapter 3 is focused on hydrothermal synthesis of mixed-valence copper (Cu) oxide loaded CS-TA composite particles and their characterization. Crystalline Cu oxide nanoparticles were coated with the CS-TA layer. Water dispersibility of Cu oxide greatly improved upon coating with CS-TA material. To demonstrate catalytic activity of Cu-oxide loaded CS-TA film in sequestering carbon dioxide (CO2), an electrochemical setup was used. Electrochemical reduction of CO2 was successfully demonstrated. It was observed that CS-TA environment not only maintained catalytic properties of Cu oxide but also allowed solution processing of Cu-oxide film onto the electrode surface. Chapter 4 discusses a convenient method of making monodispersed water dispersible Cu loaded chitosan nanoparticles (Cu-CS) using HCl depolymerized CS polymer. The purpose of this study was to investigate if there was any improvement in antibacterial properties of Cu-CS nanoparticles prepared using hydrothermally treated CS polymer. Interestingly, it was observed that the antibacterial efficacy of Cu was not compromised in Cu-CS nanoparticles. Moreover, the materials exhibited improvement in antibacterial efficacy against both Gram-negative and Gram-positive bacteria species. A plausible mechanism has been proposed to explain antibacterial results. Chapter 5 summarizes major findings of this dissertation research and presents future research directions

Optimum Placement of Long Gauge FBG Sensor in Reinforced Concrete Bridge: A Case Study

In the world today, civil infrastructure plays a major role in the advancement of the modern age. They are huge in scale, complex in their behaviour and create great impact in everyday life. To ensure safety of these structures, assessment of their structural integrity is an important and challenging task. The sole purpose of structural health monitoring is to detect damage in the structures and suggest suitable rehabilitation measures. Various sensors are employed to achieve the task of damage detection and establish a warning system to avoid failure of the structures. For large structures, long-gauge Fibre Bragg Grating (FBG) sensors which are sensitive to the global behaviour, can be suitably used for this purpose. However, health monitoring of a structure with large number of sensors is expensive and hence there is a need to optimize the number of sensors deployed to minimize the cost of the exercise without compromising on performance assessment. For this purpose, several optimization algorithms are available in literature. In this study, the Effective Independence Method (EIM) which optimizes the response of the structure based on modal analysis, is used to derive the Optimum sensor placement (OSP) protocol for a reinforced concrete (RC) bridge-deck in Poland, the geometry of which has been taken from literature. This will enable the placement of 40 long gauge FBG sensors in regions for efficient damage response in the bridge-deck. Further, the optimum orientation of the sensors is further validated with a finite element model of the bridge-deck, where a moving load is applied, and strains are recorded in the sensing fibre in both longitudinal (along length) and transverse (along breadth) alignments. It has been found that long gauge FBG sensors placed in the transverse direction are more efficient in damage detection than when they are placed longitudinally

The magnetic behavior of Cu-Ni-Co-Fe quaternary alloys prepared by Mechanical alloying

The Cu-Ni-Co-Fe alloys with average grain size~10nm have been prepared by mechanical alloying. The ball milled and annealed samples were characterized by XRD, HRTEM and magnetic measurement. In the case of ball milled sample, superior magnetic properties have been achieved for sample comprising dispersed magnetic phases in Cu-rich matrix. In the case of annealed sample magnetic properties are improved due to precipitation of hard magnetic phase Co(fcc) from single phase Cu-rich solid solution

Sub-micron sized saccharide fibres via electrospinning

In this work, the production of continuous submicron diameter saccharide fibres is shown to be possible using the electrospinning process. The mechanism for the formation of electrospun polymer fibres is usually attributed to the physical entanglement of long molecular chains. The ability to electrospin continuous fibre from a low molecular weight saccharides was an unexpected phenomenon. The formation of sub-micron diameter “sugar syrup” fibres was observed in situ using high speed video. The trajectory of the electrospun saccharide fibre was observed to follow that typical of electrospun polymers. Based on initial food grade glucose syrup tests, various solutions based on combinations of syrup components, i.e. mono-, di- and tri-saccharides, were investigated to map out materials and electrospinning conditions that would lead to the formation of fibre. This work demonstrated that sucrose exhibits the highest propensity for fibre formation during electrospinning amongst the various types of saccharide solutions studied. The possibility of electrospinning low molecular weight saccharides into sub-micron fibres has implications for the electrospinability of supramolecular polymers and other biomaterial

Chitosan coated copper-oxide nano particles: a novel electro-catalyst for CO2 reduction

We report here a simple one-pot method for the synthesis of copper-oxide based novel film forming electro catalysts for CO2 reduction. Water dispersible chitosan (CS)-CuO/Cu2O (CuxO) nano composites of diameter 10-20 nm were obtained by hydrothermal reactions of CS, CuSO4 center dot 5H(2)O and tartaric acid (TA). Here, TA acts as a multifunctional reagent as de-polymerizer of CS, ionic cross linker of depolymerised CS and complex forming ligand with Cu2+ ions. These CS coated CuxO nanoparticles were characterized by HRTEM, UV-VIS, AFM, FTIR and XPS. An ultra thin film of composite catalyst was deposited onto a Pt electrode by drop cast techniques and applied to study CO2 reduction by cyclic voltammetric techniques. The voltammogram shows a reduction peak at -0.665 V vs. RHE at pH 5.3 with a short hydrogen evolution tail indicating its better performance in terms of retarding the H-2 evolution reaction. This has been explained proposing a model of protonated CS on the electrode surface that repels incoming H+ ions at the electrode-electrolyte interface. This is the first time a film forming copper-oxide based nano composite material for efficient electro-catalytic reduction of CO2 in aqueous solution has been reported

Theoretical study of the electronic spectra of small molecules that incorporate analogues of the copper-cysteine bond

The copper-sulphur bond which binds cysteinate to the metal centre is a key factor in the spectroscopy of blue copper proteins. We present theoretical calculations describing the electronically excited states of small molecules, including CuSH, CuSCH_3, (CH_3)_2SCuSH, (imidazole)-CuSH and (imidazole)_2-CuSH, derived from the active site of blue copper proteins that contain the copper-sulphur bond in order to identify small molecular systems that have electronic structure that is analogous to the active site of the proteins. Both neutral and cationic forms are studied, since these represent the reduced and oxidised forms of the protein, respectively. For CuSH and CuSH^+, excitation energies from time-dependent density functional theory with the B97-1 exchange-correlation functional agree well with the available experimental data and multireference configuration interaction calculations. For the positive ions, the singly occupied molecular orbital is formed from an antibonding combination of a 3d orbital on copper and a 3pπ orbital on sulphur, which is analogous to the protein. This leads several of the molecules to have qualitatively similar electronic spectra to the proteins. For the neutral molecules, changes in the nature of the low lying virtual orbitals leads the predicted electronic spectra to vary substantially between the different molecules. In particular, addition of a ligand bonded directly to copper results in the low-lying excited states observed in CuSH and CuSCH_33 to be absent or shifted to higher energies