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Articles 1 - 9 of 9
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Multiband Detectors And Application Of Nanostructured Anti-Reflection Coatings For Improved Efficiency, J. A. Ranga C. Jayasinghe
Multiband Detectors And Application Of Nanostructured Anti-Reflection Coatings For Improved Efficiency, J. A. Ranga C. Jayasinghe
Physics and Astronomy Dissertations
This work describes multiband photon detection techniques based on novel semiconductor device concepts and detector designs with simultaneous detection of dierent wavelength radiation such as UV and IR. One aim of this investigation is to examine UV and IR detection concepts with a view to resolve some of the issues of existing IR detectors such as high dark current, non uniformity, and low operating temperature and to avoid having additional optical components such as filters in multiband detection. Structures were fabricated to demonstrate the UV and IR detection concepts and determine detector parameters: (i) UV/IR detection based on GaN/AlGaN heterostructures, …
Optical And Structural Properties Of Indium Nitride Epilayers Grown By High-Pressure Chemical Vapor Deposition And Vibrational Studies Of Zgp Single Crystal, Ramazan Atalay
Physics and Astronomy Dissertations
The objective of this dissertation is to shed light on the physical properties of InN epilayers grown by High-Pressure Chemical Vapor Deposition (HPCVD) for optical device applications. Physical properties of HPCVD grown InN layers were investigated by X-ray diffraction, Raman scattering, infrared reflection spectroscopies, and atomic force microscopy. The dependencies of physical properties as well as surface morphologies of InN layers grown either directly on sapphire substrates or on GaN/sapphire templates on varied growth conditions were studied. The effect of crucial growth parameters such as growth pressure, V/III molar ratio, precursor pulse separation, substrate material, and mass transport along the …
J Psi Measurement In Au+Au Collisions At Sqrt (Snn) = 39 And 62.4 Gev, Abhisek Sen
J Psi Measurement In Au+Au Collisions At Sqrt (Snn) = 39 And 62.4 Gev, Abhisek Sen
Physics and Astronomy Dissertations
J/psi production is considered a very important probes for studying the properties of quark-gluon plasma (QGP). At the PHENIX experiment at Brookhaven National Laboratory, a large suppression of J/psi production in Au+Au collisions at 200 GeV center of mass energy as compared to the binary collision scaled p+p collisions was observed. The level of suppression is similar to that observed at other energies at CERN's SPS and LHC experiments. This work addresses the PHENIX J/psi measurements at sqrt{s_{NN}}= 39 and 62 GeV Au+Au collisions. These allow for the energy dependent J/psi suppression measurements in order to disentangle the important contributing …
A Tale Of Two Telescopes: Taking A Closer Look At The Multiplicity Properties Of Massive Stars In Cygnus, Saida M. Caballero
A Tale Of Two Telescopes: Taking A Closer Look At The Multiplicity Properties Of Massive Stars In Cygnus, Saida M. Caballero
Physics and Astronomy Dissertations
Massive stars profoundly influence the evolution of the Universe, from Galactic dynamics and structure to star formation. They are often found with bound companions. However, our knowledge of O-type multiple systems with periods in the range from years to thousands of years is incomplete due their great distances. We present results from a high angular resolution survey to find angularly resolved companions using the Fine Guidance Sensor (FGS) on the Hubble Space Telescope and using ground-based adaptive optics at Gemini North. We observed 75 O- and early B-type stars in Cyg OB2 and determined that 42% of the sample have …
Magnetotransport In Two Dimensional Electron Systems Under Microwave Excitation And In Highly Oriented Pyrolytic Graphite, Aruna N. Ramanayaka
Magnetotransport In Two Dimensional Electron Systems Under Microwave Excitation And In Highly Oriented Pyrolytic Graphite, Aruna N. Ramanayaka
Physics and Astronomy Dissertations
This thesis consists of two parts. The first part considers the effect of microwave radiation on magnetotransport in high quality GaAs/AlGaAs heterostructure two dimensional electron systems. The effect of microwave (MW) radiation on electron temperature was studied by investigating the amplitude of the Shubnikov de Haas (SdH) oscillations in a regime where the cyclotron frequency $\omega_{c}$ and the MW angular frequency $\omega$ satisfy $2\omega \leq \omega_{c} \leq 3.5\omega$. The results indicate negligible electron heating under modest MW photoexcitation, in agreement with theoretical predictions. Next, the effect of the polarization direction of the linearly polarized MWs on the MW induced magnetoresistance …
Hiding In Plain Sight, Adric Richard Riedel
Hiding In Plain Sight, Adric Richard Riedel
Physics and Astronomy Dissertations
Since the first successful measurements of stellar trigonometric parallax in the 1830s, the study of nearby stars has focused on the highest proper motion stars (mu > 0.18"/yr). Those high proper motion stars have formed the backbone of the last 150 years of study of the Solar Neighborhood and the composition of the Galaxy. Statistically speaking, though, there is a population of stars that will have low proper motions when their space motions have been projected onto the sky. At the same time, over the last twenty years, populations of relatively young stars (less than ~100 Myr), most of them with …
Determining Inclinations Of Active Galactic Nuclei Via Their Narrow-Line Region Kinematics, Travis C. Fischer
Determining Inclinations Of Active Galactic Nuclei Via Their Narrow-Line Region Kinematics, Travis C. Fischer
Physics and Astronomy Dissertations
Active Galactic Nuclei (AGN) are axisymmetric systems to first order; their observed properties are likely strong functions of inclination with respect to our line of sight. However, except for a few special cases, the specific inclinations of individual AGN are unknown. We have developed a promising technique for determining the inclinations of nearby AGN by mapping the kinematics of their narrow-line regions (NLRs), which are easily resolved with Hubble Space Telescope (HST) [O III] imaging and long-slit spectra from the Space Telescope Imaging Spectrograph (STIS). Our studies indicate that NLR kinematics dominated by radial outflow can be fit with simple …
Spectroscopy And Interferometry Of The Winds Of Luminous Blue Variables, Noel D. Richardson
Spectroscopy And Interferometry Of The Winds Of Luminous Blue Variables, Noel D. Richardson
Physics and Astronomy Dissertations
Massive stars are rare, but emit most of the light we observe in the Universe and create many of the heavy elements. New observational approaches and long time-series are utilized in order to examine the basic observable properties of the stars and the mass lost during their lifetimes. In order to study the winds and the long-term changes of the stars, hot stars with some of the strongest winds (the luminous blue variables) were studied in detail with optical spectroscopy and photometry. A 25-year survey on the prototype P Cygni is presented, where the long-term changes are documented for many …
Circumstellar Disks Around Rapidly Rotating Be-Type Stars, Yamina Touhami
Circumstellar Disks Around Rapidly Rotating Be-Type Stars, Yamina Touhami
Physics and Astronomy Dissertations
Be stars are rapidly rotating B-type stars that eject large amounts of material into a circumstellar disk. Evidence of the presence of a disk is found through hydrogen emission lines in their spectra, IR excess flux, and linear intrinsic polarization. In this dissertation, we report the first simultaneous interferometric and spectroscopic observations of circumstellar disks around 24 bright Be stars made using the techniques of long baseline interferometry and moderate resolution spectroscopy in the near infrared. The goal of the project is to characterize the fundamental geometrical and physical properties of the emitting regions that are responsible for the IR …