7940 research outputs found
Sort by
Chlorpyrifos Sensing Behavior of Metal Incorporated Zinc Oxide Nanowires Grown by Limited Volume Heating Technique
No full textIn the modern agricultural world, extensive usage of pesticides to preserve crops from pests has become one of the major concerns due to their neurotoxic property. Organophosphates (OP) are the most widely used pesticide due to their low cost and a broad spectrum of applications. Moreover, chlorpyrifos (CP), which belongs to the OP family, get readily accumulated in the ecosystem and as a result, their traces are remain in the environment due to their low solubility in water and high soil sorption coefficient. This residual amount of CP causes severe health problems for humans and other livestock. In order to detect these toxic compounds, there is a need for real-time, portable, low-cost sensors, where the response can be recorded by the variation in current-voltage behavior. Nanostructured metal oxide (Zinc oxide) have been found to exhibit interesting properties such as large surface-to-volume ratio, low cost, low temperature growth, non-toxic nature, which made ZnO a potential material for the development of chemical sensors. In this research work, high aspect ratio zinc oxide (ZnO) nanowires are grown using the custom-designed limited volume heating (LVH) technique, where the optimization of various growth parameters is carried out systematically. The morphological and structural characterizations have revealed the evolution of c-axis oriented ZnO NWs by LVH technique. The length and aspect ratio of the NWs, grown by LVH technique, is found to be around 9 μm and 300, respectively, which is nearly five times higher than that of the conventional growth technique. In addition, an effort has been made to further improve the CP sensing response of LVH grown NWs by incorporation of various metallic dopants like Al, Ti, Mn, Cu, and Ag. The LVH grown ZnO NWs are coated with metal thin film by RF sputtering (pre-deposition) technique followed by the heat treatment (drive-in) in inert ambient for thermal diffusion of metal dopants. The drive-in process is conducted at various temperatures below the melting point of respective metals. The metal film thickness is also varied as 15 nm, 30 nm, and 45 nm to study the effect of film thickness. Post-growth morphological and structural investigations of the NWs have been carried outby FESEM, HRTEM, and XRD techniques. Besides, the distribution of dopant in NWs is verified from elemental mapping images obtained by energy-dispersive X-ray spectroscopy measurement. Furthermore, microstructural and photoluminescence properties of metal incorporated ZnO NWs are investigated with various process parameters. Finally, the CP sensing behavior of metal incorporated ZnO NWs is carried out by studying the current-time response at room temperature for various concentrations of CP varying from 500 mg/kg to 6000 mg/kg. The as-grown ZnO NWs have shown the CP in/out current ratio around 5 and 38 for CP lethal dosage of 500 mg/kg and 6000 mg/kg, respectively. The CP sensing behavior of metal incorporated ZnO NWs is found to be significantly improved with metal type, thickness, and drive-in temperature. Among various metallic dopants, the highest CP sensor response has been observed for Cu incorporated NWs with a noteworthy improvement in current in/out ratio of around 768, for CP dosage of 6000 mg/kg. Besides, the response and recovery time of Cu incorporated ZnO NWs are found to be around 14 s and 5 s, respectively for CP concentration of 6000 mg/kg. The above research work opens the path for the fabrication of metal incorporated LVH grown nanostructures for low cost, portable, real-time CP sensors
Environmental Management of Koira Mining Region through Cumulative Impact Assessment Study
No full textThe iron and manganese ore rich zone of Sundargarh district of Odisha is known as the Koira mining sector, and currently there are 65 working mines. All the mines in Koira mining sector are regulated by a comprehensive set of policy and regulations both at the Central and State levels. Though impact assessment has been done for individual mines, no study has been carried out till date on environmental compliance status taking all the mines together. The environmental impact of a cluster is not only the cumulative effect of all the individual mines and industries but also it should take into account the symbiotic and indirect impact of a region as a whole. Adequacy of the conventional EIA methodology in addressing the overall impact in a cluster has remained questionable. An assessment of the cumulative effects from several industrial projects is an important tool in planning for genuine development (Dutta et al., 2004). Cumulative impact assessment is the process in which the effects of a proposed mine are considered in conjunction with other activities in the general area. A regional concentration of mines will cause cumulative impact beyond those arising from a single mine, e.g. high concentration of particulate matter, impact on surface water quality, severe draw down of water table, deterioration of soil quality etc. Negative groundwater impacts are intensified by several mines in an area and reduced stream flow that can reduce the volume of water available for agriculture. The present work therefore involves the development of a methodology to assess and forecast the environmental impact in a mining area comprising of a cluster of mines, based on which appropriate environmental management practices can be adopted. Air Quality Monitoring (AQM) was carried out at 5 different locations of Koira mining area. The air quality parameters monitored were PM10 and PM2.5, Sulphur Dioxide (SO2) and Oxides of Nitrogen (NOx). The PM2.5, SO2 and NOx concentration in Koira mining area were found to be below the limits prescribed by Central Pollution Control Board. However, the PM10 concentration was found to be above the permissible limit during the summer, as the average concentration was 108μg/m3. Similarly, the air quality index for the Koira mining area for most of the days was found to be satisfactory. However, on a few occasions, it was found to be moderately polluted. This indicates that the mining organizations present in this region have to make additional arrangement for control of particulate matter during summer. The poor air quality index may be attributed to respirable particulate matter and diesel emissions. The major source of the particulate matter is haul roads in mines and transportation roads. Restriction of trucks/dumpers speed and overhauling, and regular road maintenance and cleaning are essential in order to control dust pollution from transportation, together with water spraying on roads. Washing of dumpers/trucks’ wheels/body at an appropriate distance from site entrance, loading and unloading area protected from wind, minimization of drop heights, use of sheet or cover on loaded vehicles and application of water sprays to moisten transported material is also essential. Installation of sprinkling system along with application of binding agents, chemicals on unpaved roads are required. In addition, unpaved roads should be converted to black topped roads, with regular maintenance/ repair of roads to maintain compactness, gradient and drainage. Sweeping of unpaved roads and the imposition of speed limits on trucks and other vehicles was also useful. Regular maintenance of the machines that use diesel as fuel is expected to reduce the NOx emission, thereby improving the quality of air in the area. BOD across all the locations does not exceed the prescribed standard of 30 mg/l. Thus it can be safely assumed that, anthropogenic activities have not affected the steams within the study area. The higher iron content in surface water during monsoon can be attributed towards surface run off from adjoining mines and over burden dumps. The maximum iron content is observed at the downstream locations of Kundra Nala. The iron content of Class-A water as per IS-2296 is 0.3 and most of the stations exceeds this standard. Hence the water is suitable for drinking only after conventional treatment. Higher suspended solids in the surface water during monsoon season are natural consequences of surface runoff during monsoon All the 10 locations, in the study area show uniform variation in TDS levels. Ground water monitoring values during summer when compared to standards show that the pH at all the stations except stations GW2 is acidic. The observed values of iron vary from 0.23-2.65 mg/l while the permissible limit is 0.3 mg/l. The observed values of pH in post monsoon season also suggest the acidic nature of the ground water. The total hardness of ground water at the monitoring stations are within the permissible limits. However, the observed values of hardness are lower during monsoon than that of the summer season because of the ground water recharge. The iron content varies from 0.11 to 0.22 mg/l and is the highest for GW-6 monitoring station. The high iron values can be attributed to the rock formation in the region and groundwater infiltration from iron ore material in the region and overburdens. In the present study, 3.1% of the mining workers had hearing loss. 14% of the workers had refraction error which is similar to general population. But 1% of the workers have defective colour vision which points out the need of initial medical examination and suitable placing of workers. Only 7 workers had hernia. This may be due to statutory requirement of hernia repair for fitness to work. Strict compliance of Initial and periodic medical examinations as laid down in statutory regulations is the ideal way to assess health status of mining workers which can lead the way to prevention of diseases. Further studies with assessment of hazard exposure will be helpful in linking health findings. Regular health examinations, health education and use of personal protective equipment amongst the workers need to be encouraged. Implementation of engineering measures to control exposure will benefit the health and productivity of the miners. Enforcing legal regulations especially regarding environmental monitoring will ensure better working condition. Awareness programs regarding prevention of health hazards in mining industry should be conducted among workers for creating a healthy workforce. Finally, a cumulative environmental impact index (CEII) was developed drawing inference from the framework prescribed by CPCB and was applied to the Koira mining region having a cluster of iron and manganese mines. In order to apply the CEII, certain modifications were made in the original framework to determine the cumulative impact index of a predominantly mineral cluster. The CEII index value determined following the developed method was found out to be 56 which indicate that through there are a large number of mines in operation; still the area is not severely polluted. However, it may be noted that it is approaching the severely polluted criteria. Thus, it is high time that adequate attention may be given to control air, water and soil pollution, so that the index value could be further down which will establish minimal impact of mining in the area
Studies on Removal of Ammonia-Nitrogen from Industrial Wastewater using Inverse Fluidized Bed Biofilm Reactor
No full textAmong the several available biological means to treat industrial wastewaters, the use of inverse fluidized bed biofilm reactors (IFBBRs) has gained much attention in recent years. Compared to conventional fluidized bed reactors, IFBBRs have many unique benefits due to which these are widely used nowadays for the treatment of pollutants like ferrous iron, aniline, phenol, and sulphate. In the current work, nutrient pollutants of industrial wastewater particularly ammonia-nitrogen is treated for which hydrodynamics of an IFBBR were studied at first. Hydrodynamics with respect to phase holdups was studied by varying different parameters such as ratio of bed volume to reactor volume (Vb/Vr ratio) and superficial gas velocity. The developed correlations for the gas phase holdup have average absolute percent deviations of 7.90 & 7.39 suggesting good agreement of the predicted values with the experimentally observed values. Synthetic wastewater was treated in the present IFBBR using polypropylene balls and mixed culture. The inoculum was prepared from the sludge taken from the local steel industry’s wastewater treatment plant. The effects of different input parameters such as Vb/Vr ratio, superficial air velocity, initial concentration of NH4+-N, C/N ratio, temperature, and pH were studied. The output in terms of final concentration of NH4+-N in the wastewater was measured as per APHA standards for each experiment at pre-determined time intervals. Optimum operating condition was found to be at Vb/Vr ratio of 0.380, pH of 8.3, temperature of 300C, superficial gas velocity of 0.0085 m/s, and C/N ratio of 0.0. Complete removal of NH4+-N is achieved in this IFBBR at a faster rate. However, with the increase of C/N ratio from 0.0 to 2.5, the NH4+-N removal reduces by 30.96% to 52.18% for initial NH4+-N concentrations of 40 to 200 mg/l respectively. Percentage nitrification was found to be 96.2% for initial NH4+-N concentration of 40 mg/l which reduces with the increase of C/N ratios and initial NH4+-N concentrations. Fractional Factorial Design analysis has been used to predict the removal of NH4+-N and the rate of reaction of NH4+-N. In these cases the average absolute percent deviations were 11.75 and 7.89 respectively suggesting the proposed correlations to be better validated with the experimentally observed values. The kinetic parameters obtained were also found to be in the acceptable range. The performance of the present IFBBR was further found to be stable for semi-batch operations with NH4+-N loading rate of 40 to 200 mg/l/d. The local pond water was also treated in this IFBBR. The results obtained from the experiments were also found to be satisfactory implying the effectiveness of the IFBBR for wastewater treatment in general
Signal Analysis and Chatter Control Studies in Internal Turning Operations
No full textThe current manufacturing scenario with industry 4.0 and IoT standards produces a variety of highly precise and accurate products. In spite of several developments in manufacturing technology, the machining instabilities are still inevitable due to several operating factors like work material inhomogeneities, variation of chip cross-section, disturbances in tool or workpiece, environmental disturbances and so on. The vibration instability or chatter conditions results-in a relatively poor surface finish and reduced overall productivity. Particularly, in operations like internal turning and thin walled milling, the chatter vibrations have detrimental effect in achieving accurate products. Present work focuses on the development of some accurate models for dynamic analysis with regenerative and friction chatter forces to understand the machining stability in internal turning and proposes some control methodologies. A dynamic modeling of regenerative chatter is initially studied with one dimensional models and an improved friction-induced regenerative chatter model is developed using a two-degree of freedom (2-DOF) model of internal turning system by considering process damping forces along with nonlinear cubic stiffness terms. The proposed model is validated with the available cutting models using the stability boundary diagram obtained from linear stability analysis performed using the natural parameter continuation method. The stability lobes obtained from the proposed model outperforms and predicts stable zones with good accuracy. Then the nonlinear behaviour of cutting tool in 2-DOF model with Stribeck and regenerative effects under internal resonance and primary resonance conditions is investigated. The nonlinear responses and the cutting stability are determined using higher order multiple time scales method (MTSM). The results obtained from MTSM are validated with a numerical time integration solution. The effect of nonlinearities on the frequency responses and stability is studied further, and the system parameters for stable cutting operation are identified. As the boundaries predicted in the stability lobe diagrams are affected by many surrounding factors such as speed, temperature, tool wear, etc., their reliability is sometimes not acceptable. Therefore, signal based identification approaches are used. The raw signal contaminated by noise is first collected, and a denoising technique is applied, followed by some signal processing method. In the present work, a novel adaptive wavelet threshold (AWT) based wavelet denoising and improved complete ensemble empirical mode decomposition with adaptive noise (ICEEMDAN) approaches are proposed in order to identify the exact stability states and range of resonance frequency. Further, classification of cutting conditions is performed using an improved probabilistic neural network (PNN) model. The results are compared with the existing approaches and observed that the proposed methods are more accurate compared to the available standard approaches. Cutting experiments are conducted on AISI 1020 workpieces and the vibration signals are extracted practically and processed for the identification of stable states. Towards the design of damped boring bar configuration, the method of constrained layer damping (CLD) is employed with composite material damping layer. The viscoelastic damping layer effectiveness is enhanced by considering different volume fractions of silicon carbide nanoparticles embedded in the carbon-epoxy micro composite. Both analytical and experimental works are conducted to understand the passive vibration control ability of the system. Next, as an extension towards active control, the piezoelectric material is applied for the part of length in constrained layer with optimized damping layer configurations. The dynamic analysis and control of this boring bar is studied as a sandwich model subjected to cutting forces at the tool tip. Proportional derivative with sliding mode control law is used to estimate the required electric field for the piezoelectric materials to minimize the tool tip vibration amplitudes in an online manner. Results of the model are presented for different speeds of operation and unstable vibrations are minimized by proper selection of control gains and location of the piezoelectric patches along the tool length. Furthermore, the effectiveness of control scheme is tested in the presence of external disturbance signal added to the tool dynamics. The disturbance estimation model is developed with radial basis function neural network. Numerical simulations are conducted with finite element modeling of the tool. Overall, few new approaches are proposed for identification and control of chatter in internal turning operations
Consumer Brand Engagement and Brand Loyalty: Catalyzing Effect of Brand Relationship Quality
No full textUnderstanding the dynamics of focal consumer/brand relationships has garnered the attention of academic scholars and brand managers in the last three decades. Specifically, identifying the various means to create and maintain enduring relationships with consumers has been a popular research stream. In the marketing domain, the ‘engagement’ construct has been considered vital in comprehensively capturing the true nature of the consumer/brand relationship. Along these lines, consumer brand engagement (CBE) has emerged as a crucial predictor for brand-related outcomes and strategic imperative for establishing competitive advantage. Since 2010, a body of researchers conducted exploratory studies to understand the fundamentals of the engagement concept in the marketing area. Despite the ever-growing scholarly interest, there has been a dearth of empirical studies concerning CBE, which limits the knowledge about the measurement of the concept and its relational consequences. Based on the extensive literature review, the present study addresses the gaps through investigating the potent antecedents of CBE and its direct role in driving brand loyalty and indirectly/via brand relationship quality (mediator). Also, the study explores the moderating impact of consumer characteristics i.e. gender, age profile, and usage experience on enhancing brand loyalty. To satisfy the research objectives, the Indian automobile industry, especially passenger vehicles and two-wheeler brands were the main focus of interest. Survey research was carried out using a structured questionnaire; while, convenience and snowball sampling was followed to draw the respondent sample. The gathered responses were subjected to preliminary assessments for establishing normality and evaluating the associative nature of the study variables. Following these assessments, the proposed model was tested and validated through factor analysis and structural equation modeling. The findings reveal the antecedents (brand interactivity, consumer involvement, and self-brand image congruency) positively impact CBE. Further, the mediating role of brand relationship quality (BRQ) was supported. Also, age profiles and usage experience have a substantial moderating effect on the hypothesized paths. Additionally, the BRQ index based on the final set of six indicators effectively captures the conceptual domain of brand relationship quality and positively influences brand loyalty. These findings contribute to the limited literature on the CBE by empirically explaining its drivers and outcomes. From the managerial lens, the findings yield novel insights for developing targeted engagement and relationship-building strategies for automobile consumers
Exploration of New Eu(III) Complexes and their Applications in Light Emitting Diodes and Sensors: Combined Experimental and Theoretical Investigations
No full textThis thesis work mainly going to describe about the designing and synthesis of the ancillary ligand (antenna) for the Eu(III) based complexes and to investigate their application in red/white LEDs, sensors (temperature and vapoluminescence sensor) Chapter 1, represents a general introduction of lanthanides and its unique spectral properties and it application in various fields. The importance of Eu(III) complexes, antenna effect (DBM and ancillary ligand), the lanthanides (specially Eu(III)) application in Red/white LED, temperature sensor and vapoluminescence were systematically discussed. In addition, the recent progress of Eu(III) complexes for LEDs and sensors were also been discussed. The main objective and significance of the present work of the thesis were documented. Chapter 2, Narrow band red emitting phosphor plays vital role in high performance smart white LEDs. In this context, a series of new Eu(III) complexes have been synthesized with neutral ligand (C1functionalised Phenanthro-imidazole-based ancillary ligands substituted with functionalized phenyl moieties and DBM as an anionic ligand. All the newly synthesized Eu-complexes showed extremely narrow band red emission due to ED transition (5D0-7F2, both in solid and thin film) with high quantum efficiency. Combined experimental and theoretical study indicates that the energy transfer from ligand to metal ion is complete. Temperature dependent PL study in solution reveals that the red emission is retained (only the ED (5D0-7F2) intensity decreases with increasing temperature). Red LED and hybrid white LEDs were fabricated by using near UV LED chip with Eu-complexes and near UV/blue LED conjugated with yellow dye and Eu-complex mixture, respectively. Hybrid white LED (Eu(DBM)3PhenpCN-pCF3 + yellow dye) showed superior CRI (84%), CIE (x = 0.36, y = 0.39) (near UV based) and CRI (82%), CIE (x = 0.34, y = 0.36) (blue LED based). In addition, presently studied Eu-complexes showed excellent reversible on-off-on luminescence behavior with exposure of acid-base vapours. Detailed spectroscopic investigation reveals that the protonation of the Eu-complexes (ligands) plays key role in the on-off-on luminescence. Chapter 3, a series of luminescent ternary Eu(III) complexes were synthesized and studied their photophysical properties. PL emission spectra of ligands showed blue emission, whereas Eu(III) complex showed red emission in solid while in solution phase Eu(DBM)3Phen-pCH3-mCF3 are showing multiple emission (near white emission). Fabrication of LED has been done by conjugating the Eu-complex with near UV LED the obtained results are very close to National Television System Committee (NTSC) standard for pure red emission. LED fabrication of Eu(DBM)3Phen-pCH3-mCF3 with 1:50 ratio show near white emission with CIE, x = 0.35, y = 0.20. In addition, presently studied Eu(III) complex shows excellent sensing behavior in the thermo-sensor (in the range 303K-453K) and vapoluminescent sensor.
Chapter 4, Eu(III) complexes coordinated with phenanthroimidazole ligands based on fluorinated moieties (ancillary ligand) and DBM (anionic ligand) were designed and synthesized successfully. Eucomplexes in solid phase shown pure red emission (due to ED transitions) and solution slightly deviated (observed multiple emission) due to ligand emission in the EuIII complex. Solvatochromism study reveals that the Eu-complexes showed red emission along with the ligand emission peak (comparatively intense) in methanol and DMSO solution, which leads to obtain white emission. In addition, the lifetime of the fluorinated mCF3 ligand revealed high. Remarkable linear decrease in luminescence intensity with increasing the temperature, open up the new window to use this material as sensitive temperature sensor in the temperature range of 30−80oC. Fabricated red LEDs (InGaN) showed very close to the NTSC standard values for bright red emission. EuIII complexes exhibits on−off switching of photoluminescence via vapoluminescence process and observed best response to the acid-base (HCl-NH3) vapours. Chapter 5, a series of soft UV excitable new narrow-band red-emitting trivalent europium complexes were designed, synthesized and their photophysical properties were studied. The newly synthesized ancillary ligands showed deep blue emission with CIE y < 0.1. In contrast, the corresponding Eu(III) complexes shown extremely narrow-band red emission (in solid, solution [except pCF3 functionalized Eu(III) complex, it shown both ligand and Eu emission leads to nearly white emission] and thin-film) with wide excitation range (200-500 nm, where the near UV and blue LED emission occurs). Solvatochromism study reveals that the Eu-complexes showed multi-color emission. The hybrid white LED was fabricated by conjugating the near UV LED with yellow organic dye and 5-Eu complex, the results showed extremely high CRI (96%), CCT (4447 K) and the CIE color coordinate (x = 0.36, y = 0.35). In addition, the complexes were used for acid-base sensing. All the complexes showed very good reversible on-off-on luminescence behavior (exposure of complexes with HCl and NH3) and these complexes can find potential applications in anti-counterfeiting. Chapter 6, a series of smart luminescent Eu(III) complexes were synthesized by using C1-functionalize phenanthro-imidazole derivatives as a neutral ligand and DBM (anionic ligand). PL emission spectra of ligands showed blue to bluish-green emission, whereas their corresponding Eu-complexes shown multicolor emission in solution and red emission in solid state (solid as well as neat thin film).Energy transfer mechanism between ligand to Eu(III) ion is explained based on both theoretical (DFT and TD-DFT) and experimental study. The red LEDs were fabricated and found all the LEDs shown excellent color purity. Hybrid white LED was fabricated by conjugating the mixed phosphor dye (ligand and complex) with near UV LED shown superior white light emission (CCT (5298), CRI (80%), CIE (x = 0.337, y = 0.343)). In addition, dual emission Eu(III) complexes were explored for thermos-sensor (in the range 303 K – 353 K) applications. Paper based acid-base vapour sensor (exposure leads to switch in the emission color (bluishgreen to red)) of these complexes were explored and can also be used for anti-counterfeiting applications.
Chapter 7, Promoting from the structural flexibility and easy solution process capability, single component white light emitting pure organo-lanthanide complexes have considered as a promising candidate for solid state lighting. A series of ancillary ligand by using imidazo-bipyridyl derivatives and DBM, as anionic ligand are employed to synthesized ternary Eu(III) complex.The photophysical and electrochemical properties of the ligand and their Eu(III) complexes were carefully investigated and the energy transfer mechanism were understood by combined experimental and theoretical calculation. Multiple-emission from both ligand and Eu(III)-ion leads to single component white light emission. White light emitting diodes (LED)was fabricated by conjugating the Eu-complex with near UVLED, the results showed superior performance (CIE (x = 0.33, y = 0.33, close to NTSC standard for pure white emission), correlated color temperature CCT (5386 K) and color rendering index CRI (63%)).The selected Eu-complex was further coated on blue LED chip and the corresponding white LED showed CIE (x = 0.36, y = 0.35), CCT (4234K) and CRI (75%). In addition, taking benefit of dual characteristic emission of the Eu-complexes, the ratiometric sensing behavior was explored. The Eu(DBM)3L-mCF3 have the relative sensitivity value of 4.9% K-1 at 323 K. Chapter 8, spectral window of dual visible light emissions of molecular europium complex leads to white light can be modulated by design strategy. A Eu-complex with butterfly structure displays dual emission, leads to single phase white light emitting molecular complex with excellent colour quality. Such behaviour is not observed with an analogous Eu-complex with triangle structure (rather shows usual red emission), suggesting that the partial lighting up of Eu-ion along with ligand emission (controlled energy transfer from ligand to EuIII ion) is more imperative for the creation of white light. The white LED assembled using butterfly Eu phosphor as white emitter yields a bright pure white light with CRI (95%), CCT (5457 K) and CIE (x = 0.33, y = 0.33),whereas the triangle Eu-phosphor displays red light with CIE value of x = 0.58, y = 0.31. The fabricated white/red LED continued to emit a bright white/red light even more than a year. The present design strategy can be widely adapted to synthesis single phase white emitting Eu-phosphor as well as explored for temperature sensing and sensor for vapoluminescence. Chapter 9, deals the summary and conclusion as well as future perspective of the work. The present thesis works deals with rational design and synthesis of new and novel class of ancillary ligand and their corresponding Eu3+ complexes for white LEDs and sensor (temperature and vapoluminescence). In addition, Eu molecular complexes also been explored for single component white light emitter based white LEDs. The observations and the conclusions derived from the present investigations are summarized in this chapter
Structural, Magnetic, and Magnetoelectric Correlation in bulk, nano, and Doping Modified Trirutile Fe2TeO6
No full textIn this thesis, the correlation among lattice, spin, and charge degrees of freedom are investigated in bulk, nano, and doping modified inverse trirutile Fe2TeO6 (FTO). The bulk and doped materials are synthesized via solid-state reaction route. The nano polycrystalline FTO has been synthesized by the sol-gel process. Structural, magnetic, and magnetoelectric (ME) properties are studied for bulk material. The detailed investigations reveal of the rare existence of d5 off-centering, weak ferroelectric polarization and demonstrate its correlation with observed magnetism and ME coupling in the apparent centrosymmetric (P42/mnm) G type (TN~210 K) antiferromagnet FTO compound. The origin of ferroelectricity (FE) is associated with both lattice and asymmetric electron density distribution around the ion cores as concluded by ellipsoid analysis (EA) and charge density distribution analysis following the maximum entropy method (MEM). Apart from the surprising FE of d5 origin, the existence of d(5/2)-d(5/2) dimeric interaction to manifest broad maximum in the magnetic susceptibility above TN and change in spin dynamics at 150 K is evidentially reported. Simultaneous manifestations of all the correlated phenomena are probed via neutron diffraction, magnetization, heat capacity, and muon spectroscopic measurements. The emergence of magnetic order and the magnetoelectricity solely depends on the same ion (Fe3+) though unusual ME multiferroicity is found well above TN. ME coupling is observed in the spin-phonon coupling, magnetic field-dependent polarization, ME voltage, and magnetostrain measurements. Intrabilayer exchange coupling via the double oxygen bridged Fe-O1-Fe pathway is proposed to play a dominating role to exhibit the negative nonlinear ME behavior at 300 K. Interbilayer exchange via Fe-O2-Fe pathways dominantly determines the hysteretic nonlinear ME coupling below TN. The observation of renormalization of different Raman modes below 210 K suggests the existence of spin-phonon coupling in the material. The coupling strength is quantified in the range 0.1-1.2 cm-1 following the mean field approximation and two-spin cluster approximation. The spin-phonon coupling is realized to be mediated by asymmetric stretching of Fe-O2 in Fe-O2-Fe exchange pathways. The observed nonlinear ME coupling signifies magnetoelasticity as manifested in the temperature and magnetic field-dependent strain measurement. Hence, the rare existence of FE, magnetic order, and ME coupling induced by the same d5 ion is demonstrated in bulk FTO. Sol-gel synthesized nanocrystalline FTO sample is characterized for structural, magnetic, morphological, and ME properties. Higher distortion with diffuse p-d hybridization (Fe-O bond) in Fe3+ polyhedra is observed in nano FTO compared to the bulk material. Nano-spherical morphology with particle size 10-40 nm is observed in the synthesized samples. Signature of reduction in surface coordination is observed in XPS and Raman spectroscopy study. TN is observed to be shifted to 167 K from 210 K, as seen in bulk. The shift towards low temperature is explained by the finite size effect. The broad anomaly in magnetic susceptibility above TN is well ascribed by 5/2-5/2 dimeric interaction fitting. A weak ferromagnetic induction is observed due to reduced surface coordination in the nano sample. The room temperature ferroelectric and ME properties of the nano FTO change significantly due to the finite size effect, reduced surface coordination and diffuse nature of Fe-O covalent bonding. Polarization (Pr) value (0.098 μC/cm2) increases in nano-FTO. A nonmonotonous increase in the remanent polarization is noticed when an external magnetic field is applied to the sample. This is a clear indication of prevailing substantial ME coupling in the nano sample at room temperature. The quantification of magnetoelectricity is done by directly measuring the ME voltage (V) in the presence of a varying dc magnetic field (H), and the ME coefficients are obtained using a quadratic relation in H. The values so obtained for the first order (α/d), second-order (β/d), and third-order (γ/d) ME coefficients are ∼0.22 mV cm−1 Oe−1, ∼−1.70 × 10−2 mV cm−1Oe−2, and ∼0.72 × 10−6 mV cm−1Oe−3, respectively. Nb is doped (FTON5: 5% and FTON10: 10%) at the Te position to study the doping-induced modification based on a theoretically proposed strategy to increase TN. No change is observed up to 10% Nb doping. Instead, a weak ferromagnetic induction is observed on increasing Nb concentration. The remanent polarization decreases with increase Nb doping concentration. The nonlinear magnetic field dependency is fitted with the equation containing three terms, and the different coupling coefficients are obtained as; α/d~0.32 mVcm-1Oe-1, β/d~5.13×10-3mVcm-1Oe-2, γ/d~5.13×10-5 mVcm-1Oe-3. Similarly, for FTON5, the nonlinear fitting corresponds to value of coefficients as, α/d~0.15 mVcm-1Oe-1, β/d~1.65×10-3mVcm-1Oe-2, γ/d~6.40×10-5 mVcm-1Oe-3. In case of FTON10 linear voltage response is observed with, α/d~0.37 mVcm-1Oe-1, β/d~ 2.88×10-3mVcm-1Oe-2. Hence, new room temperature ME material with the unconventional ME coupling is reported in bulk and nanocrystalline FTO. The explored ME properties can be exploited to have potential technological applications
Effective Clinical Gait Analysis using Supervised Learning Techniques
No full textGait analysis has become a popular trend to solve critical problems in different application domains. It has demonstrated crucial significance in the clinical domain also. Quantification of gait pattern through subtle analysis of salient features have surpassed the pitfalls of prevailing qualitative assessment techniques. Computational intelligence techniques, specifically machine learning algorithms, have demonstrated competing performance in modeling non-linear data relationships of gait variables. Another issue that needs to be emphasized is the expensiveness of the prevailing gait assessment systems. High end sensors make the overall system costly, which is not affordable for most clinics, especially in a developing country. High expenditure causes limited expansion of gait laboratories across the world. Compulsorily pathologists follow the error-prone qualitative techniques to assess gait. Hence, a low-cost arrangement to analyze gait is hugely needed. This thesis has proposed four contributions to address some challenging problems of human gait in the clinical domain using some low-cost system setups. Few vital issues,like gait event detection, abnormality detection, feature assessment, etc., were explored and investigated. Basically, this thesis targets to construct a few affordable automatic gait abnormality detection systems after addressing some pre-requisite issues. Validation of a sensor before using it for clinical purposes is an important issue. Studies reported that the skeletal data stream of Kinect is not suitable to estimate joint kinematics. Although the joint angle time series follows the pattern of the corresponding ground truth, it differs substantially in terms of magnitude. Hence, as an alternative, the color image data stream of Kinect was investigated for joint kinematics in the first contribution. The point cloud feature of Kinect was used to extract lower limb joint positions, which were then converted to joint angles using extended Kalman filter and a kinematic model. The process was validated against the gold standard cameras. The obtained joint angles were significant to use for medical purposes. Event annotation is considered as an initial work for constructing a gait abnormality detection system. Most of the clinics follow the manual annotation technique of gait events on a time series data. However, this method is error-prone and laborious. On the contrary, automatic gait event detection systems are gradually becoming popular. This thesis proposes an event detection system using a state-space model. A multi-Kinect architecture for overground walking was established. Data were collected from both pathological and normal populations. A state-space model was constructed where the temporal evolution of gait signal was modeled by quantifying feature uncertainty. The inter-state transition frames were marked as the gait events. In addition, an attempt was made for treadmill gait also. Here, an unsupervised approach was proposed to detect gait events using a multi-Kinect system. Cerebral Palsy is a widespread disease across the world. The activity of daily life of patients suffers from distorted gait. Numerous features have been extracted to characterize the gait pattern of this population. However, there exists a high variability in the recommended features. Prior information on the most important gait feature would help to construct a population-specific gait abnormality detection system. Hence, a well-known statistical approach called meta-analysis, which is generally used in medical science to estimate the effect of an intervention, has been used to select the most important gait features in Cerebral Palsy population. Features were ranked according to their importance level. Automatic abnormality detection systems, specifically for the Cerebral Palsy patients, are expensive. On the other hand, systems based on a low-cost sensor, like Kinect, suffer from several problems. This thesis addresses some of those issues. A clinically relevant walking track was constructed using a multi-Kinect architecture. An algorithm to remove outliers from the multi-Kinect data has been proposed. Features, generally used to detect the Cerebral Palsy gait, are influenced by the gait velocity. A speed-invariant feature might be beneficial for such systems. Hence, this thesis used a handcrafted speed invariant feature and compared its performance against the best feature set. Different supervised models were established to construct the abnormality detection systems
Evolution of Porosity and Nanostructure in Preceramic Polymer Derived Nanoporous Particulates
No full textInert pyrolysis of Si-containing polymers affords multifunctional amorphous ceramics. Enhancing the textural properties of these materials, including porosity, surface area, and nanostructure, one can enable a wide range of applications in adsorption, gas storage, gas separation membranes, ultra-capacitors, bio-implants, and Li ion batteries. However, the control of pore size distribution and retention of the high surface area at higher temperatures are engineering challenges that need to be met by novel materials and processing methods. Polymer derived silicon particulate ceramics can be effectively used to meet the above challenges. Pyrolysis of the preceramic polymers leads to the escape of organic moieties followed by sintering, resulting in a very low specific surface area (SSA) of the final particulate ceramics produced. Current work explores a novel and versatile method for the fabrication of a high surface area ceramic hybrid with controlled porosity at higher temperatures. In a typical process, the hybrid ceramics are proposed to be fabricated by coating the liquid preceramic polymer solutions around particulate ceramics. The template limits shrinkage of the PDC coating leading to retention of SSA over 290 m2 g-1, and micro-mesoporous hierarchical pore size distribution (PSD). The first part of the work deals with crystalline oxide as templates. Nanoparticulate boehmite powders were used as templates around which preceramic polymer were coated yielding an alumina-SiOC core-shell structure stable at higher temperatures. The final microstructure of the SiOC produced depends on many factors such as the polymer composition and pyrolytic parameters such as final temperature, and heating rate. Thus, two kinds of polymers were used based on their carbon content and their architecture such as a silica rich polymethylsilsequioxane and a carbon rich polymethylphenylsilsequioxane. Additionally, the effect of various processing parameters including polymer ratio, heating rate, and pyrolysis temperature was studied. The evolution of the phase and porosity was extensively studied with varying parameters to find an adequate process to produce a micro-mesoporous nanostructure. Subsequently, amorphous nanocarbon particulates of similar particle size were chosen as templates owing to the versatility of the process. Similar studies were performed for the nanocarbon-SiOC hybrids. It was observed that the porosity evolution in SiOC depends on the process of its conversion from polymer to ceramic and not on the template chosen, making it generic and versatile. In the next part, nanostructured-PDC hybrid was further explored by selectively sacrificing the species present in the SiOC microstructure. The unique SiOC structure in the coating, comprising of SiO2 based nanodomains (1 nm–5 nm) and graphene type carbon layers provided opportunities to create porosity by eliminating SiO2 domains from the nanostructure. Such carbon hybrid materials, produced by HF etching the ceramic hybrids have shown SSA in excess of 900 m2 g-1 to 2000 m2 g-1 with a major part being microporous (<2 nm). High resolution transmission electron micrograph (HRTEM) imaging of the hybrids has shown observable microporosity. Interestingly, a wide range of pore sizes and their distribution can be tailored according to the desired need with subtle changes made in process parameters. The high SSA, optimal PSD, and the highly ordered carbon structures formed in the carbon hybrids made the material suitable for electrode materials in electrical double layer capacitors (EDLC). The results obtained gave the highest value achieved of 333 F g-1 in aqueous electrolyte. The nearly rectangular shapes obtained from the cyclic voltammetry graphs observed for the material made it ideal for a supercapacitor electrode. The effect of the microstructure, including the pore shape and volume in the carbon hybrids, was seen to affect their supercapacitive behavior
Functional Carbon Nanomaterials for Chemosensing and Therapeutic Application
No full textThe thesis entitled, “Functional Carbon Nanomaterial for Chemosensing and Therapeutic Application” is an embodiment of investigations aimed at development of simple easy synthetic methodologies for N-doped carbon quantum nanomaterials for specific applications. The thesis has been divided into seven chapters.
Proper selection of molecular precursors and surface passivating agents can produce N-doped carbon nanomaterials with high QY, biocompatibility, and long-term stability which may offer a wide variety of applications. For surface modification of nanocarbon, the functional sites on the surface can react with the terminal groups of organic, polymeric, inorganic or biological materials via covalent, electrostatic interactions or hydrogen bonds. The resulting conjugates of nanocarbon can combine both of their properties, which makes it possible for them to be applied in targeting-specific sensing, drug delivery and bioimaging. However, the number of reactive groups capping the surface, the ratio of reactive groups and the coupling molecules are hard to control which makes surface engineering process inaccessible. Therefore, development of rational surface modification strategies in nanocarbons and related biomedical applications are under continuous progress.
In chapter 2, hydrophilic functional carbon quantum dots (CQD) have been prepared following hydrothermal method. This CQD is utilized for flumioxazin pesticide detection following Cu catalyzed azide-alkyne click reaction. The same CQD is conjugated with γFe2O3-DMSA for selective detection as well as removal of mercury from contaminated water sample in chapter 3. This can also facilitate imaging and sensing in bacteria and living fish organs. In chapter 4, therapeutic CQD has been derived from papaya leaf which shows photothermal antimicrobial effect under exposure of NIR laser. These CQDs are incorporated in polyvinyl alcohol-melamine hydrogel and has shown NIR stimulated photothermal and photodynamic effect. In chapter 5, Nitrogen doped mesoporous carbon spheres (NMCS) have been prepared from pyrrole and substituted aniline following soft templating approach. The effect of molecular precursors on size, microstructure and phototherapeutic properties has been investigated in detail. In chapter
6, NMCS gated with a light sensitive supramolecular gate has been designed which can carry anticancer drug gemcitabine. Photothermal and photodynamic property of these NMCS has been investigated under 980 nm NIR laser irradiation. Cell killing efficacy due to combinatorial photo-chemo therapy is investigated in oral cancer FaDu and skin cancer B16F10 melanoma cell lines. Polymeric coating over NMCS surface avoids premature leakage in vitro. The utilization of upconverted radiation by substituted nitrobenzyl linker tend to decomposition followed by drug release under momentary laser irradiation has been studied in vitro. The photothermal conversion efficiency and quantum yield of ROS generation has been investigated for these NMCS. Overall multifunctional NMCS provide a justified platform for cancer treatment