Doctor of Philosophy

dissertationMicrowave/millimeter-wave imaging systems have become ubiquitous and have found applications in areas like astronomy, bio-medical diagnostics, remote sensing, and security surveillance. These areas have so far relied on conventional imaging devices (empl

W-band sparse synthetic aperture for computational imaging

journal articleWe present a sparse synthetic-aperture, active imaging system at W-band (75 - 110 GHz), which uses sub-harmonic mixer modules. The system employs mechanical scanning of the receiver module position, and a fixed transmitter module. A vector network analyzer provides the back end detection. A full-wave forward model allows accurate construction of the image transfer matrix. We solve the inverse problem to reconstruct scenes using the least squares technique. We demonstrate far-field, diffraction limited imaging of 2D and 3D objects and achieve a cross-range resolution of 3 mm and a depth-range resolution of 4 mm, respectively. Furthermore, we develop an information-based metric to evaluate the performance of a given image transfer matrix for noise-limited, computational imaging systems. We use this metric to find the optimal gain of the radiating ele­ ment for a given range, both theoretically and experimentally in our system

Cyclodienyl 1,3 - Dianionic Synthons: A Novel Synthesis of 5,5 - Dimethyl - 1,3 - Bis - (trimethylsilyl) Cyclohexa - 1,3 - Diene and its Diels - Alder [π4s+π2s] Cycloadditions with Six Dienophiles

The synthesis of 5,5-dimethyl-1,3-bis(trimethylsilyl)cyclohexa-1,3-diene: a novel cyclic 1,3-dianionic synthon is reported by the Wurtz-Fittig coupling reaction of 1,3-dichloro-5,5-dimethylcyclohexa-1,3-diene with metallic sodium and chlorotrimethylsilane in anhydrous ether solvent. The compound on further Diels-Alder [π4s+π2s] cycloaddition with five N-substituted maleimides gave five novel cycloadducts: the N-substituted 11,11-dimethyl-1,8-bis(trimethylsilyl)-4- azatricyclo[5.2.2.02,6]undec-8-ene-3,5-diones; and reaction with maleic anhydride yielded the novel 11,11-dimethyl-1,8- bis(trimethylsilyl)-4-oxotricyclo[5.2.2.02,6]undec-8-ene-3,5-dione in 94-97% overall yields

Next-generation sequencing for endocrine cancers : Recent advances and challenges

Contemporary molecular biology research tools have enriched numerous areas of biomedical research that address challenging diseases, including endocrine cancers (pituitary, thyroid, parathyroid, adrenal, testicular, ovarian, and neuroendocrine cancers). These tools have placed several intriguing clues before the scientific community. Endocrine cancers pose a major challenge in health care and research despite considerable attempts by researchers to understand their etiology. Microarray analyses have provided gene signatures from many cells, tissues, and organs that can differentiate healthy states from diseased ones, and even show patterns that correlate with stages of a disease. Microarray data can also elucidate the responses of endocrine tumors to therapeutic treatments. The rapid progress in next-generation sequencing methods has overcome many of the initial challenges of these technologies, and their advantages over microarray techniques have enabled them to emerge as valuable aids for clinical research applications (prognosis, identification of drug targets, etc.). A comprehensive review describing the recent advances in next-generation sequencing methods and their application in the evaluation of endocrine and endocrine-related cancers is lacking. The main purpose of this review is to illustrate the concepts that collectively constitute our current view of the possibilities offered by next-generation sequencing technological platforms, challenges to relevant applications, and perspectives on the future of clinical genetic testing of patients with endocrine tumors. We focus on recent discoveries in the use of next-generation sequencing methods for clinical diagnosis of endocrine tumors in patients and conclude with a discussion on persisting challenges and future objectives

mmWave Spatial-Temporal Single Harmonic Switching Transmitter Arrays for High back-off Beamforming Efficiency

This paper presents a spatial-temporal single harmonic switching (STHS) transmitter array architecture with enhanced efficiency in the power back-off (PBO) region. STHS is an electromagnetic and circuit co-designed and jointly optimized transmitter array that realizes beamforming and back-off power generation at the same time. The temporal dimension is originally added in STHS to achieve back-off efficiency enhancement, which can be combined with conventional power back-off enhancement methods such as Doherty amplifiers and envelope tracking. The design is validated through a simulation of a two-stage power amplifier in 65-nm CMOS at 77 GHz, which achieves a peak drain efficiency (DE) of 24.2%, a 22% DE at 3-dB PBO, 16% DE at 6-dB PBO, and 10.2% at 9-dB PBO. The efficiency exhibits a 57% improvement at 3-dB PBO, 100% improvement at 6-dB PBO, and 190% improvement at 9-dB PBO compared with class A/B amplifier

Formulation of Sodium Alginate Nanospheres Containing Amphotericin B for the Treatment of Systemic Candidiasis

Purpose: The aim of this work was to formulate sodium alginate nanospheres of amphotericin B by controlled gellification method and to evaluate the role of the nanospheres as a “passive carrier” in targeted antifungal therapy. Methods: Sodium alginate nanospheres of amphotericin B were prepared by controlled gellification method, and the particle size analysis was carried out by scanning electron microscopy. The carrier capacity of sodium alginate was evaluated in terms of drug to polymer ratio. In vitro release study was carried out on all drug loaded nanospheres by the dialysis method. Release kinetics of drug from different drug loaded nanospheres was also determined. The in vivo antifungal efficacy of nanospheres bound drug vis-à-vis the free drug was evaluated in candidiasis- induced mice models. Results: Preparation of nanospheres through controlled gellification method yielded particles with a size range of 419.6 ± 0.28 nm. Studies on drug to polymer ratio showed a linear relationship between concentration of drug and drug loading capacity. In vitro release kinetic study revealed that the release of drug from the nanospheres followed Fickian diffusion. In vivo studies showed that the nanosphere-bound drug produced a higher antifungal efficacy than the free drug. Conclusion: The formulated sodium alginate nanospheres containing amphotericin B was found to have better antifungal activity when compared to the free drug and also yielded sustained in vitro release. Keywords: Nanospheres, sodium alginate, amphotericin B, controlled gellification method, in vitro & in vivo release > Tropical Journal of Pharmaceutical Research Vol. 6 (1) 2007: pp. 653-65

Separating hyperfine from spin-orbit interactions in organic semiconductors by multi-octave magnetic resonance using coplanar waveguide microresonators

Separating the influence of hyperfine from spin-orbit interactions in spin-dependent carrier recombination and dissociation processes necessitates magnetic resonance spectroscopy over a wide range of frequencies. We have designed compact and versatile coplanar waveguide resonators for continuous-wave electrically detected magnetic resonance, and tested these on organic light-emitting diodes. By exploiting both the fundamental and higher-harmonic modes of the resonators we cover almost five octaves in resonance frequency within a single setup. The measurements with a common pi-conjugated polymer as the active material reveal small but non-negligible effects of spin-orbit interactions, which give rise to a broadening of the magnetic resonance spectrum with increasing frequency

Development and in-vitro Evaluation of a Topical Drug Delivery System Containing Betamethazone Loaded Ethyl Cellulose Nanospheres

Purpose: Lipid nanospheres are used for the passive targeting of cosmetic agents to skin, thereby achieving major benefits such as reduction of total dose and avoidance of systemic absorption. The present study was carried out to exploit the feasibility of using polymeric nanospheres as an alternative and cheaper carrier for targeting corticosteroids to the skin. Methods: Nanospheres were prepared from ethyl cellulose by a modified method of desolvation and cross linking. The drug betamethazone was incorporated into nanospheres and the drug: polymer ratio was evaluated to determine the carrier capacity of the polymer. In-vitro release studies of drug-loaded nanospheres were carried out by the centrifugal ultrafiltration method. The kinetics of release was determined and fitted to an empirical equation. The release of drug from drug-loaded nanospheres dispersing in a conventional cream was evaluated. A comparative in-vitro diffusion study was carried out between a commercial brand of cream and the cream incorporating nanospheres. Results: Formulation of nanospheres of betamethazone by a modified method produced discrete particles. Studies on drug:polymer ratio showed a linear relationship between drug concentration and percentage of loading. The in-vitro release of drug-loaded nanospheres was found to be first order. The comparative in-vitro diffusion study between the commercial cream and the formulated cream showed a marked reduction in release rate from nanospheres-bound cream. Conclusion: Formulated topical cream containing nanospheres of betamethazone was found to be a potential dermal delivery system for sustaining the release of the drug. Keywords: Nanospheres, desolvation and cross-linking method, ethyl cellulose, betamethazone, in-vitro diffusion studies.> Tropical Journal of Pharmaceutical Research Vol. 4 (2) 2005: pp. 495-50