147 research outputs found
Spherically Symmetric Static Solutions in General Relativity
No full textThis thesis studies spherically symmetric static solutions in general relativity.
The most general form of matter in general relativity compatible with staticity and spherical
symmetry is anisotropic fluid. We study all possible algorithms that can generate all solutions
of the anisotropic fluid system via quadrature using all possible pairs of the four basic
functions of the system as input functions. We also study sub-algorithms that generate all
solutions that are regular at the center and, for this, we revisit the conditions for central
regularity for both isotropic and anisotropic systems and obtain all possible sets of equivalent
initial conditions for regularity by combining the Einstein equations with the previouslyknown geometric conditions of regularity. Our study provides a reformulation of an existing
algorithm for the system and provides its first regularity analysis. A surprisingly simple
new algorithm for the anisotropic system follows from our study that aligns itself with the
regularity conditions. This concordance enables us to find solutions that satisfy all the
other hard-to-achieve conditions of physical acceptability. Anisotropy has increasingly been
shown to be physically relevant in recent times. We keep the well-studied isotropic system
as a special case and use it as a frame of reference for measuring the success of our study of
the anisotropic system.
We then study the hydrostatic equilibrium of static (an)isotropic fluid spheres. From the
condition of hydrostatic equilibrium, we explore maps between (an)isotropic solutions with
the same density profiles and develop solution-generating techniques to find new solutions
from existing ones. We compare and give physical interpretations of several equilibrium
configurations in terms of fluid variables and provide several examples where the solutiongenerating theorems can be utilized to find physically acceptable anisotropic solutions. This
include a new exact solution that satisfies all physically desirable conditions.
Finally, we study light propagation in Kottler, i.e., Schwarzschild-(anti-)de Sitter, spacetime.
The metric of this spacetime is known in canonical coordinates and, unlike its Λ = 0 version
(i.e, Schwarzschild metric), this metric was not known in isotropic coordinates (in which the
constant-time hypersurfaces are flat). We obtain the Kottler metric in isotropic coordinates.
This further enables us to plot the refractive indices of Kottler spacetime and show that the
invariance of Snell’s law in ordinary geometric optics is analogous to projective equivalence
in isotropic static coordinates.
We conclude with a summary and some future directions
VHF-UHF Measurements of Lightning
No full textUniversal software radio peripheral (USRP) was utilized to receive the radiation produced by lightning flashes in VHF and UHF bands, with the bandwidth ranging from 2MHz to 8MHz. The software radio was programmed to record this radiation by integrating GPS clock and absolute timing. Moreover, two USRP N210 were employed to simultaneously record data at VHF and UHF bands with different programmable gain settings. This data was compared with the data from National Lightning Detection Network (available as location, type and peak current of lightning) and the magnetic sensor operating at LF (30 to 300 kHz). The output of USRP is the antenna displacement current ∂E/∂t (uncalibrated) and of LF magnetic sensor is the induced voltage ∂B/∂t. From comparison, the following results were obtained. K processes or regular pulse bursts in both cloud and cloud to ground discharges were clearly visible at UHF-VHF-LF. These processes were even visible at VHF with 0 dB gain, if superimposed on high magnitude slow (electric field change) processes such as J process probably. Distant Narrow bipolar pulses were observed with significant magnitude at VHF. Initial breakdown in cloud discharge was strong at LF and VHF but not significant at UHF. Instead the short pulses, probably stepped leaders, with 1 to 2.5 µs of time duration produced high magnitudes at UHF (while LF pulses remained small yet visible). Moreover, in few cloud discharges some processes occurring during final stage produced strong VHF-UHF radiation.</p
Incorporation of curcumin in lipid based delivery systems and assessment of its bioaccessibility
No full textCurcumin, the major curcuminoid compound from turmeric (Curcuma longa) is a well-studied nutraceutical with many health promoting biological properties. The benefits of curcumin greatly dependon its solubilization (bioaccessibility) and subsequent absorption through cell lining so that it can reach systemic/general circulation. Unfortunately, curcumin has low water solubility and undergoes rapid metabolism on oral delivery. Lipids have shown to affect the absorption of poorly soluble nutraceuticals such as curcumin by enhancing solubilization in the intestinal milieu through alterations to the composition and character of the colloidal environment –e.g. vesicles, mixed micelles and micelles when delivered orally. Thus, the purpose ofthis study was to formulate threelipid-based delivery systems with curcuminoids –gel like emulsions, nanoemulsions andorganogels, and investigate their impact on in vitro solubilization or bioaccessibility. Curcumin was dissolved in MC T oil with the help of Span 20 to be used as the lipid phase. Gel-like emulsions, nanoemulsions andorganogelswere then formulated using the curcumin-MCT oil lipid phase using different types of sugar esters as organogelators and emulsifiers. The organogels and gel-like emulsions are viscoelastic in naturewith a solid dominant behaviorwhich was supported by the rheological data. Optical and fluorescence microscopic imaging helped understand the morphology ofcurcumin inthe lipidbased delivery systemsas well as the systems themselves. Digital scanning calorimetry was used to study the phase transitionsthat occurin the systems. The bioaccessibilityof the different lipid based delivery systemswas evaluated using in vitrolipolysis experiments (dynamic pH stat lipid digestion model). Results suggest that lipid based delivery systems have more bioaccessibility when compared to that of unformulated curcuminoids. The bioaccessibility of curcumin increased at least 6.4 folds when it was incorporated in a lipid based delivery system as compared to unformulated curcuminoids.O ut of the three systems tested, gel-like emulsions had the highest stability and thus can be good candidate for incorporation and delivery of curcumin.M.S.Includes bibliographical referencesby Kavitakumari H. Solank
Nanotechnology-based approaches for regenerative medicine and biosensing
No full textThe recent emergence of nanotechnology has set high expectations in many fields of science, especially in biology and medicine. Nanotechnology-based approaches are expected to solve key questions in the emerging field of regenerative medicine. Regenerative medicine essentially deals with regeneration of cells, ultimately leading to the formation of tissues and organs. For this purpose, stem cells, embryonic stem cells or adult stem cells, are thought to be ideal resources. However, many challenges need to be addressed before the full therapeutic potential of stem cells can be harnessed. Controlling the differentiation of stem cells into cells of a specific lineage is extremely vital and challenging. Addressing this challenge, in this work, novel nanotechnology-based approaches for controlling the differentiation of neural stem cells (NSCs) into neurons has been presented. Regeneration of damaged neurons, due to traumatic injuries or degenerative diseases, is extremely challenging. For this purpose, NSCs can be used as resources that can differentiate into neurons, thus having great potential in solving needs of many patients suffering from such conditions. For controlling the differentiation of stem cells, soluble cues (comprising of small molecules and biomolecules) and insoluble cues (cell-cell interactions and cell-microenvironment interactions) play a very important role. The delivery of soluble cues, such as genetic material, into stem cells is extremely challenging. The initial part of this work presents the use of nanomaterials for efficiently delivering soluble cues such as small molecules and small interfering RNA (siRNA) into NSCs for controlling their differentiation into neurons. However, for regenerative purposes, it is preferred that least amounts of the delivery vehicle be used. Thus, the following part of the thesis presents the development and applications of nanotechnology-based approaches for enhancing the differentiation of NSCs into neurons using insoluble cues. The cellular microenviroment, consisting for the extracellular matrix (ECM) was modified by the use of nanostructures, to deliver siRNA into NSCs to enhance neuronal differentiation. Nanotopography-mediated reverse uptake of only the siRNA molecules from the ECM was achieved by the NSCs. NSC differentiation was also controlled by the use of protein micropatterns, wherein the pattern geometry and size defined the fate of the NSCs. Lastly, graphene, in combination with nanoparticles was used as component of the ECM to not only enhance the differentiation of NSCs into neurons, but also align the axons of the differentiated NSCs, having significant implications for its use in regenerating injured spinal cords. The final portion of the thesis presents the applications of nanotechnology for developing highly sensitive and selective biosensors, for detecting biomarkers implicated in various diseases such as cancer and acute pancreatitis.Ph. D.Includes bibliographical referencesby Aniruddh P. Solank
Atomic scale investigation of grain boundary structure role on intergranular deformation in aluminium
No full textabstract: The role that grain boundary (GB) structure plays on the directional asymmetry of an intergranular crack (i.e. cleavage behaviour is favoured along one direction, while ductile behaviour along the other direction of the interface) was investigated using atomistic simulations for aluminium 〈1 1 0〉 symmetric tilt GBs. Middle-tension (M(T)) and Mode-I crack propagation specimens were used to evaluate the predictive capability of the Rice criterion. The stress–strain response of the GBs for the M(T) specimens highlighted the importance of the GB structure. The observed crack tip behaviour for certain GBs (Σ9 (2 2 1), Σ11 (3 3 2) and Σ33 (4 4 1)) with the M(T) specimen displayed an absence of directional asymmetry which is in disagreement with the Rice criterion. Moreover, in these GBs with the M(T) specimen, the dislocation emission from a GB source at a finite distance ahead of the crack tip was observed rather than from the crack tip, as suggested by the Rice criterion. In an attempt to understand discrepancy between the theoretical predictions and atomistic observations, the effect of boundary conditions (M(T), Mode-I and the edge crack) on the crack tip events was examined and it was concluded that the incipient plastic events observed were strongly influenced by the boundary conditions (i.e. activation of dislocation sources along the GB, in contrast to dislocation nucleation directly from the crack tip). In summary, these findings provide new insights into crack growth behaviour along GB interfaces and provide a physical basis for examining the role of the GB character on incipient event ahead of a crack tip and interface properties, as an input to higher scale models.This is an Author's Accepted Manuscript of an article published as Adlakha, I., Bhatia, M. A., Tschopp, M. A., & Solanki, K. N. (2014). Atomic scale investigation of grain boundary structure role on intergranular deformation in aluminium. PHILOSOPHICAL MAGAZINE, 94(30), 3445-3466. http://dx.doi.org/10.1080/14786435.2014.961585. Copyright Taylor & Francis, available online at: http://www.tandfonline.com/doi/abs/10.1080/14786435.2014.96158
Author′s reply for comment on "positive end-expiratory pressure valve malfunctioning detected by capnographic and airway pressure waveform"
No full textStructural and optical properties of hydrazine hydrate capped cadmium sulphide nanoparticles
No full textInvestigation on structural properties of M-type strontium hexaferrite synthesized in presence of neem and aloe-vera plant leaves extract
No full textAttitude Estimation of a Quadcopter with one fully damaged rotor using on-board MARG Sensors
No full textQuadcopters are becoming increasingly popular across diverse sectors such as mapping, photography, or surveillance. Since rotor damages occur frequently, it is essential to improve the attitude estimation and thus ultimately the ability to control a damaged quadcopter. The Control and Simulation group of TU Delft developed a quadcopter controller for the case of a single damaged rotor in an inside environment, where the attitude and position of the quadcopter are provided by an external system. In the present research, a novel attitude estimator called Adaptive Fuzzy Complementary Kalman Filter (AFCKF) has been developed and validated that works independently of any external systems. It is able to estimate the attitude of a quadcopter with one fully damaged rotor while only relying on the on-board sensors. The results show that the AFCKF is able to provide significantly better attitude estimates for flights with a damaged rotor than mainstream filters, estimating the roll and pitch of the quadcopter with an RMS error of less than 1.7 degrees and a variance of less than 2 degrees. It is the only filter that is able to track the quadcopter's yaw angle for the case of a damaged rotor, while showing only a comparatively small rise in the computational cost.Aerospace Engineerin
Dedicated Autonomous Wildlife Guardian Final Report
No full textAE3200 - Design Synthesis ExerciseAerospace Engineerin
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