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Articles 1 - 30 of 69
Full-Text Articles in Astrophysics and Astronomy
The X-Ray Variability Of Seyfert Galaxies, Kevin Marshall
The X-Ray Variability Of Seyfert Galaxies, Kevin Marshall
Physics and Astronomy Dissertations
Strong and variable X-ray emission has long been known to be a universal property of active galaxies. However, despite years of study, the exact nature of the variability remains relatively unknown. We present here results of a multi-year monitoring campaign of a sample of Seyfert galaxies (3C 120, Mkn 509, 3C 390.3, and Akn 120), carried out using the Rossi X-ray Timing Explorer (RXTE). For Mkn 509, we also present results of optical monitoring. Mkn 509 shows a strong correlation between X-ray and optical variations, with the optical leading the X-ray by 25 days. We also investigate the rms-flux relationship …
Threshold Extension Of Gallium Arsenide/Aluminum Gallium Arsenide Terahertz Detectors And Switching In Heterostructures, Mohamed Buhary Rinzan
Threshold Extension Of Gallium Arsenide/Aluminum Gallium Arsenide Terahertz Detectors And Switching In Heterostructures, Mohamed Buhary Rinzan
Physics and Astronomy Dissertations
In this work, homojunction interfacial workfunction internal photoemission (HIWIP) detectors based on GaAs, and heterojunction interfacial workfunction internal photoemission (HEIWIP) detectors based mainly on the Gallium Arsenide/Aluminum Gallium Arsenide material system are presented. Design principles of HIWIP and HEIWIP detectors, such as free carrier absorption, photocarrier generation, photoemission, and responsivity, are discussed in detail. Results of p-type HIWIPs based on GaAs material are presented. Homojunction detectors based on p-type GaAs were found to limit their operating wavelength range. This is mainly due to band depletion arising through carrier transitions from the heavy/light hole bands to the split off band. Designing …
Optical Variability Of The Three Brightest Nearby Quasars, C. Martin Gaskell, Andrew J. Benker, Jeffrey S. Campbell, Thomas A. George, Cecilia H. Hedrick, Mary E. Hiller, Elizabeth S. Klimek, Joseph P. Leonard, Shoji Masatoshi, Bradley W. Peterson, Kelly S. Peterson, Kelly M. Sanders
Optical Variability Of The Three Brightest Nearby Quasars, C. Martin Gaskell, Andrew J. Benker, Jeffrey S. Campbell, Thomas A. George, Cecilia H. Hedrick, Mary E. Hiller, Elizabeth S. Klimek, Joseph P. Leonard, Shoji Masatoshi, Bradley W. Peterson, Kelly S. Peterson, Kelly M. Sanders
C. Martin Gaskell Publications
We report on the relative optical variability of the three brightest nearby quasars, 3C 273, PDS 456, and PHL 1811. All three have comparable absolute magnitudes, but PDS 456 and PHL 1811 are radio quiet. PDS 456 is a broadline object, but PHL 1811 could be classified as a high-luminosity Narrow-Line Seyfert 1 (NLS1). Both of the radio-quiet quasars show significant variability on a timescale of a few days. The seasonal rms V-band variability amplitudes of 3C 273 and PDS 456 are indistinguishable, and the seasonal rms variability amplitude of PHL 1811 was only exceeded by 3C 273 once in …
Computationally Modeling The Effects Of Surface Roughness On Soft X-Ray Multilayer Reflectors, Jedediah Edward Jensen Johnson
Computationally Modeling The Effects Of Surface Roughness On Soft X-Ray Multilayer Reflectors, Jedediah Edward Jensen Johnson
Theses and Dissertations
Electromagnetic scattering from a rough two dimensional homogeneous scatterer has been computationally modeled. The scatterer is intended to simulate reflection from a two interface multilayer. The rough scatterer was created from Gaussian random points centered about an ideal interface. The points were connected with a third order spline interpolant which accounts for correlation between neighboring surface atoms. The scalar electric field integral equation (EFIE) and magnetic field integral equation (MFIE) were solved using the Nystrom method to obtain the reflected intensity as a function of observation angle. Verification of the accuracy of the code was obtained by means of comparison …
Gravitation In Vectorial Relativity, Jorge A. Franco
Gravitation In Vectorial Relativity, Jorge A. Franco
Jorge A Franco
It is known that Kepler’s Laws can be derived from the Newton’s Law of Universal Gravitation. For doing this, mass is considered as an invariable parameter. Although this consideration works wonderfully to solve most of problems in astronomy calculations, as in all physics, when body’s speeds are so high and very precise measurements are required, the referred Kepler Laws do not cope enough what is expected. That’s why the General Theory of Relativity materialized. As it was indirectly pointed out by Einstein in 1905, Newton and Kepler Laws do not consider the relativistic variation of mass with its velocity. In …
Ordering Tendencies In The Binary Alloys Of Rh, Pd, Ir, And Pt: Density Functional Calculations, Gus L. W. Hart, Brian Kolb, Stefan Müller, David B. Botts
Ordering Tendencies In The Binary Alloys Of Rh, Pd, Ir, And Pt: Density Functional Calculations, Gus L. W. Hart, Brian Kolb, Stefan Müller, David B. Botts
Faculty Publications
The binary alloys of Rh, Pd, Ir, and Pt are important because of their high catalytic potential. We report in this paper that the Rh1-xIrx and Rh1-xPtx systems, long thought to phase separate at low temperatures, actually exhibit miscibility over the entire concentration and temperature range. We find low critical ordering temperatures, indicating that long-range order is unlikely to be observed experimentally. These results are compared with previous theoretical predications for the other binary alloys of Rh, Pd, Ir, and Pt and with calculations performed here on the Pt1-xIrx and Pd1-xIrx systems. We discuss these results and investigate the mechanisms …
Casimir Forces And Non-Newtonian Gravitation, Roberto Onofrio
Casimir Forces And Non-Newtonian Gravitation, Roberto Onofrio
Dartmouth Scholarship
The search for non-relativistic deviations from Newtonian gravitation can lead to new phenomena signalling the unification of gravity with the other fundamental interactions. Various recent theoretical frameworks indicate a possible window for non-Newtonian forces with gravitational coupling strength in the micrometre range. The major expected background in the same range is attributable to the Casimir force or variants of it if dielectric materials, rather than conducting ones, are considered. Here we review the measurements of the Casimir force performed so far in the micrometre range and how they determine constraints on non-Newtonian gravitation, also discussing the dominant sources of false …
Cross Sections Fall 2006, Department Of Physics And Astronomy
Cross Sections Fall 2006, Department Of Physics And Astronomy
Cross Sections
No abstract provided.
Energy Levels And Transition Probabilities For Boron-Like Fe Xxii, V. Jonauskas, P. Bogdanovich, F. P. Keenan, R. Kisielius, M. E. Foord, R. F. Heeter, S. J. Rose, Gary J. Ferland, P. H. Norrington
Energy Levels And Transition Probabilities For Boron-Like Fe Xxii, V. Jonauskas, P. Bogdanovich, F. P. Keenan, R. Kisielius, M. E. Foord, R. F. Heeter, S. J. Rose, Gary J. Ferland, P. H. Norrington
Physics and Astronomy Faculty Publications
The Multiconfiguration Dirac-Fock method is used to calculate the energies of the 407 lowest levels in FeXXII. These results are cross-checked using a suite of codes which employ the configuration interaction method on the basis set of transformed radial orbitals with variable parameters, and takes into account relativistic corrections in the Breit-Pauli approximation. Transition probabilities, oscillator and line strengths are presented for electric dipole (E1), electric quadrupole (E2) and magnetic dipole (M1) transitions among these levels. The total radiative transition probabilities, as well as the five largest values from each level be it of E1, M1, E2, M2, or E3 …
Comparison Of Tropospheric Ozone Columns Calculated From Mls, Omi, And Ozonesonde Data, Gary A. Morris, Bojan Bojkov, Mark R. Schoeberl, Amy Wozniak, Jerry Ziemke, Sushil Chandra, Jack Fishman, Ivanka Stajner
Comparison Of Tropospheric Ozone Columns Calculated From Mls, Omi, And Ozonesonde Data, Gary A. Morris, Bojan Bojkov, Mark R. Schoeberl, Amy Wozniak, Jerry Ziemke, Sushil Chandra, Jack Fishman, Ivanka Stajner
Physics and Astronomy Faculty Presentations
This poster shows a comparison of three derived tropospheric ozone residual (TOR) products with integrated tropospheric ozone columns from ozonesonde profile: (1) the method of Ziemke et al. (2006), (2) a modified version of Fishman et al. (2003), and (3) a trajectory mapping approach. In each case, MLS ozone profiles are integrated to the tropopause and subtracted from OMI (TOMS retrieval) total column ozone. The effectiveness of each of these techniques is examined as a function of latitude, time, and geographic region. In general, we find good agreement between the derived products and the ozonesondes, with the Fishman et al. …
Comparison Of Tropospheric Ozone Columns Calculated From Mls, Omi, And Ozonesonde Data, Gary A. Morris, Bojan Bojkov, Mark R. Schoeberl, Amy Wozniak, Jerry Ziemke, Sushil Chandra, Jack Fishman, Ivanka Stajner
Comparison Of Tropospheric Ozone Columns Calculated From Mls, Omi, And Ozonesonde Data, Gary A. Morris, Bojan Bojkov, Mark R. Schoeberl, Amy Wozniak, Jerry Ziemke, Sushil Chandra, Jack Fishman, Ivanka Stajner
Gary A. Morris
This poster shows a comparison of three derived tropospheric ozone residual (TOR) products with integrated tropospheric ozone columns from ozonesonde profile: (1) the method of Ziemke et al. (2006), (2) a modified version of Fishman et al. (2003), and (3) a trajectory mapping approach. In each case, MLS ozone profiles are integrated to the tropopause and subtracted from OMI (TOMS retrieval) total column ozone. The effectiveness of each of these techniques is examined as a function of latitude, time, and geographic region. In general, we find good agreement between the derived products and the ozonesondes, with the Fishman et al. …
Detection Of A Far-Infrared Bow Shock Nebula Around R Hya: The First Miriad Results, T. Ueta, A. K. Speck, R. E. Stencel, F. Herwig, R. D. Gehrz, R. Szczerba, H. Izumiura, A. A. Zijlstra, W. B. Latter, M. Matsuura, M. Meixner, M. Steffen, Moshe Elitzur
Detection Of A Far-Infrared Bow Shock Nebula Around R Hya: The First Miriad Results, T. Ueta, A. K. Speck, R. E. Stencel, F. Herwig, R. D. Gehrz, R. Szczerba, H. Izumiura, A. A. Zijlstra, W. B. Latter, M. Matsuura, M. Meixner, M. Steffen, Moshe Elitzur
Physics and Astronomy Faculty Publications
We present the first results of the MIRIAD (MIPS InfraRed Imaging of AGB Dust shells) project using the Spitzer Space Telescope. The primary aim of the project is to probe the material distribution in the extended circumstellar envelopes (CSEs) of evolved stars and recover the fossil record of their mass-loss history. Hence, we must map the whole of the CSEs plus the surrounding sky for background subtraction while avoiding the central star that is brighter than the detector saturation limit. With our unique mapping strategy, we have achieved better than 1 MJy sr-1 sensitivity in 3 hr of …
Fourier Spectroscopy Of Ultrashort Laser Pulses, Scott D. Bergeson, Justin Peatross
Fourier Spectroscopy Of Ultrashort Laser Pulses, Scott D. Bergeson, Justin Peatross
Faculty Publications
We describe a Fourier-transform spectrometer appropriate for use in an undergraduate optics laboratory. The modular design, which uses off-the-shelf equipment, is suitable for determining the spectra of ultrashort pulsed and continuous light sources. The spectrometer does not require equal step sizes for the motion of the mirror. An algorithm interpolates the phase of both a reference and an unknown light beam at equal intervals before performing the Fourier transform. The interferometer scan and the phase and spectral analysis are performed in a few seconds, making the apparatus a useful tool for teaching concepts of temporal coherence and Fourier spectroscopy.
Sound Absorption And Sound Power Measurements In Reverberation Chambers Using Energy Density Methods, David B. Nutter
Sound Absorption And Sound Power Measurements In Reverberation Chambers Using Energy Density Methods, David B. Nutter
Theses and Dissertations
Measurements in a reverberation chamber use spatially averaged squared pressure to calculate sound absorption, sound power, and other sound measurements. While a reverberation chamber provides an approximation of a diffuse sound field, variations in the measurements introduce uncertainty in measurement results. Room qualification procedures require a sufficient number of source-receiver locations to obtain suitable measurements. The total acoustic energy density provides greater spatial uniformity than squared pressure, which requires fewer source-receiver positions to produce similar or better accuracy in measurement results. This paper explores the possibility of using energy density in place of squared pressure, using methods outlined in current …
Spinning-Black-Hole Binaries: The Orbital Hang-Up, Manuela Campanelli, Carlos O. Lousto, Y. Zlochower
Spinning-Black-Hole Binaries: The Orbital Hang-Up, Manuela Campanelli, Carlos O. Lousto, Y. Zlochower
Physics and Astronomy Faculty Publications and Presentations
We present the first fully-nonlinear numerical study of the dynamics of highly-spinning-black-hole binaries. We evolve binaries from quasicircular orbits (as inferred from post-Newtonian theory), and find that the last stages of the orbital motion of black-hole binaries are profoundly affected by their individual spins. In order to cleanly display its effects, we consider two equal-mass holes with individual spin parameters S/m2=0.757, both aligned and antialigned with the orbital angular momentum (and compare with the spinless case), and with an initial orbital period of 125M. We find that the aligned case completes three orbits and merges significantly after the antialigned case, …
Feedback Applications In Active Noise Control For Small Axial Cooling Fans, Matthew J. Green
Feedback Applications In Active Noise Control For Small Axial Cooling Fans, Matthew J. Green
Theses and Dissertations
Feedback active noise control (ANC) has been applied as a means of attenuating broadband noise from a small axial cooling fan. Such fans are used to maintain thermal stability inside of computers, projectors, and other office equipment and home appliances. The type of low-level noise radiated from axial cooling fans has been classified as harmful to productivity and human well being. Previous research has successfully implemented feed-forward ANC, targeting specific narrow-band fan noise content related to the blade passage frequency (BPF) of the fan. The reference signal required for a feed-forward algorithm limits its ability to attenuate much of the …
Mesoscopic Domain Average Engineering Simulations Of Ferroelectric Perovskites Compared With Multidomain Group Theoretical Predictions, Brandon J. Keith, Dorian M. Hatch
Mesoscopic Domain Average Engineering Simulations Of Ferroelectric Perovskites Compared With Multidomain Group Theoretical Predictions, Brandon J. Keith, Dorian M. Hatch
Faculty Publications
Engineered, multidomain ferroelectrics are of current interest for mechatronic and optical applications. Previously [D. M. Hatch et al., J. Appl. Phys. 94, 5220 (2003)], we presented a set of tables/symmetry rules showing all possible domain average engineered multidomain structures arising from [100]-, [110]-, and [111]-ordering ferroelectric transitions from a Pm[overline 3]m perovskite structure. In this work we test those predictions against three-dimensional mesoscopic fast quench simulations under various electric/stress field combinations and find excellent agreement with multidomain group theory. These simulations use a Langevin strain-displacement/polarization evolution strategy and are important to developing processing conditions for materials with precise domain structures.
Understanding Dc-Bias Sputtered Thorium Oxide Thin Films Useful In Euv Optics, William R. Evans, Sarah C. Barton, Michael Clemens, David D. Allred
Understanding Dc-Bias Sputtered Thorium Oxide Thin Films Useful In Euv Optics, William R. Evans, Sarah C. Barton, Michael Clemens, David D. Allred
Faculty Publications
We use spectroscopic ellipsometry to determine the optical constants of seven thin-film ThO2 samples deposited by radio-frequency sputtering, thickness ranging between 24 and 578 nm, for the spectral range of 1.2 to 6.5. We used a hollow-cathode light source and vacuum monochromator to measure constants at 10.2 eV. None of the deposition parameters studied including DC-bias voltages successfully increased the n of (that is, densify) thoria films. The value of n at 3.0 eV is 1.86 ± 0.04. We find compelling evidence to conclude that the direct bad gap is at ~5.9 eV, clarifying the results of others, some of …
Determining The H+ Region / Pdr Equation Of State In Star-Forming Regions, N. P. Abel, Gary J. Ferland
Determining The H+ Region / Pdr Equation Of State In Star-Forming Regions, N. P. Abel, Gary J. Ferland
Physics and Astronomy Faculty Publications
The emission-line regions of starburst galaxies and active nuclei reveal a wealth of spectroscopic information. A unified picture of the relationship among ionized, atomic, and molecular gas makes it possible to better understand these observations. We performed a series of calculations designed to determine the equation of state-the relationship among density, temperature, and pressure-through emission-line diagnostic ratios that form in the H+ region and the photodissociation region (PDR). We consider a wide range of physical conditions in the H+ region. We connect the H+ region to the PDR by considering two constant pressure cases: one with no …
Modeling The Power Evolution Of Classical Double Radio Galaxies Over Cosmological Scales, Paramita Barai
Modeling The Power Evolution Of Classical Double Radio Galaxies Over Cosmological Scales, Paramita Barai
Physics and Astronomy Dissertations
During the quasar era (redshifts between 1 and 3) Radio Galaxies (RGs) have been claimed to have substantially influenced the growth and evolution of large scale structures in the universe. In this dissertation I test the robustness of these exciting claims. In order to probe the impacts in more detail, good theoretical models for such RG systems are required. With this motivation, I seek to develop an essentially analytical model for the evolution of Fanaroff-Riley Class II radio galaxies both as they age individually and as their numbers vary with cosmological epoch. To do so, I first compare three sophisticated …
Kinematics Of The Narrow-Line Regions In The Seyfert Galaxies Ngc 4151 And Ngc 1068, Varendra Das
Kinematics Of The Narrow-Line Regions In The Seyfert Galaxies Ngc 4151 And Ngc 1068, Varendra Das
Physics and Astronomy Dissertations
We present a study of high-resolution long-slit spectra of the Narrow-Line Regions (NLRs) of NGC 4151 (a Seyfert 1 galaxy) and NGC 1068 (a Seyfert 2 galaxy) obtained with the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope (HST). The spectra were retrieved from the Multimission Archive at Space Telescope (MAST) and were obtained from five and seven orbits of HST time resulting in five and seven parallel slit configurations at position angles of 52 degrees and 38 degrees for NGC 4151 and NGC 1068 respectively. The spectra have a spatial resolution of 0.2 arcsecond across and 0.1 …
Optimization Of Active Noise Control For Small Axial Cooling Fans, Brian B. Monson
Optimization Of Active Noise Control For Small Axial Cooling Fans, Brian B. Monson
Theses and Dissertations
Previous work has shown that active noise control is a feasible solution to attenuate tonal noise radiated by small axial cooling fans, such as those found in desktop computers. One such control system reduced noise levels of a baffled 80-mm fan in the free field with four small loudspeakers surrounding the fan. Due to industry specified spatial constraints, a smaller fan and speaker configuration was desirable. The smaller configuration maintains similar control performance, further facilitating practical implementation of the control system. The smaller control system employs a smaller fan running at a higher speed. Different loudspeaker configurations for control exist …
A Search For Low-Amplitude Variability Among Population I Main Sequence Stars, Michael Benjamin Rose
A Search For Low-Amplitude Variability Among Population I Main Sequence Stars, Michael Benjamin Rose
Theses and Dissertations
The detection of variable stars in open clusters is an essential component of testing stellar structure and evolution theories. The ability to detect low-amplitude variability among cluster members is directly related to the quality of the photometric results. Point Spread Function (PSF) fitting is the best method available for measuring accurate magnitudes within crowded fields of stars, while high-precision differential photometry is the preferred technique for removing the effects of atmospheric extinction and variable seeing. In the search for new variable stars among hundreds or thousands of stars, the Robust Median Statistic (RoMS) is proven more effective for finding low-amplitude …
Physical Conditions In Orion's Veil. Ii. A Multicomponent Study Of The Line Of Sight Toward The Trapezium, N. P. Abel, Gary J. Ferland, C. R. O'Dell, G. Shaw, Thomas H. Troland
Physical Conditions In Orion's Veil. Ii. A Multicomponent Study Of The Line Of Sight Toward The Trapezium, N. P. Abel, Gary J. Ferland, C. R. O'Dell, G. Shaw, Thomas H. Troland
Physics and Astronomy Faculty Publications
Orion's Veil is an absorbing screen that lies along the line of sight to the Orion H II region. It consists of two or more layers of gas that must lie within a few parsecs of the Trapezium cluster. Our previous work considered the Veil as a whole and found that the magnetic field dominates the energetics of the gas in at least one component. Here we use high-resolution STIS UV spectra that resolve the two velocity components in absorption and determine the conditions in each. We derive a volume hydrogen density, 21 cm spin temperature, turbulent velocity, and kinetic …
Mechanisms Of The Wurtzite To Rock Salt Phase Transitions In Galium Nitride, Jesse Z. Gunter
Mechanisms Of The Wurtzite To Rock Salt Phase Transitions In Galium Nitride, Jesse Z. Gunter
Theses and Dissertations
We studied the wurtzite to rock salt phase transition in gallium nitride ( GaN ). Using the mapping algorithm of COMSUBS we found 435 possible mechanisms for this transition. We then used FIREBALL to do density functional theory calculations and found enthalpy barrier heights for the transition pathway. We used this to determine the mechanisms that are the most favorable for GaN. The most favorable mechanisms for GaN are those that break no bonds during the phase transition. The bond-preserving mechanisms involve bilayer sliding of (010) hexagonal plane in the plus or minus [100] hexagonal direction.
[Accepted Article Manuscript Version (Postprint)] Testing The Inverse-Compton Catastrophe Scenario In The Intra-Day Variable Blazar S5 0716+71. I. Simultaneous Broadband Observations During November 2003, Bruce Wilking, L. Ostorero, S Wagner, J. Gracia, E. Ferrero, T Krichbaum, S. Britzen, A. Witzel, K. Nilsson, M. Villata, U. Bach, D. Barnaby, S. Bernhart, M Carini, C Chen, W. Chen, S. Ciprini, S. Crapanzano, V. Doroshenko, N Efimova, D. Emmanoulopoulos, L. Fuhrmann, K Gabanyi, A. Giltinan, V. Hagen-Thorn, M. Hauser, J. Heidt, A Hojaev, T. Hovatta, F. Hroch, M. Ibrahimov, V. Impellizzeri, R Ivanidze, D. Kachel, A. Kraus, O. Kurtanidze, A. Lähteenmäki, L. Lanteri, V. Larionov, Z Lin, E. Lindfors, F. Munz, M. Nikolashvili, G. Nucciarelli, A. O’Connor, J. Ohlert, M. Pasanen, C. Pullen, C. Raiteri, T Rector, R. Robb, L. Sigua, A. Sillanpää, L. Sixtova, N. Smith, P. Strub, S. Takahashi, L. Takalo, C. Tapken, J. Tartar, M. Tornikoski, G. Tosti, M. Tröller, R. Walters, W. Wills, I. Agudo, H. Aller, M. Aller, E. Angelakis, J. Klare, E. Körding, R Strom, H. Teräsranta, H. Ungerechts, B. Vila-Vilaró
[Accepted Article Manuscript Version (Postprint)] Testing The Inverse-Compton Catastrophe Scenario In The Intra-Day Variable Blazar S5 0716+71. I. Simultaneous Broadband Observations During November 2003, Bruce Wilking, L. Ostorero, S Wagner, J. Gracia, E. Ferrero, T Krichbaum, S. Britzen, A. Witzel, K. Nilsson, M. Villata, U. Bach, D. Barnaby, S. Bernhart, M Carini, C Chen, W. Chen, S. Ciprini, S. Crapanzano, V. Doroshenko, N Efimova, D. Emmanoulopoulos, L. Fuhrmann, K Gabanyi, A. Giltinan, V. Hagen-Thorn, M. Hauser, J. Heidt, A Hojaev, T. Hovatta, F. Hroch, M. Ibrahimov, V. Impellizzeri, R Ivanidze, D. Kachel, A. Kraus, O. Kurtanidze, A. Lähteenmäki, L. Lanteri, V. Larionov, Z Lin, E. Lindfors, F. Munz, M. Nikolashvili, G. Nucciarelli, A. O’Connor, J. Ohlert, M. Pasanen, C. Pullen, C. Raiteri, T Rector, R. Robb, L. Sigua, A. Sillanpää, L. Sixtova, N. Smith, P. Strub, S. Takahashi, L. Takalo, C. Tapken, J. Tartar, M. Tornikoski, G. Tosti, M. Tröller, R. Walters, W. Wills, I. Agudo, H. Aller, M. Aller, E. Angelakis, J. Klare, E. Körding, R Strom, H. Teräsranta, H. Ungerechts, B. Vila-Vilaró
Physics Faculty Works
Context. Some intra-day variable, compact extra-galactic radio sources show brightness temperatures severely exceeding 1012 K, the limit set by catastrophic inverse-Compton (IC) cooling in sources of incoherent synchrotron radiation. The violation of the IC limit, actually possible under non-stationary conditions, would lead to IC avalanches in the soft-γ-ray energy band during transient periods.Aims. For the first time, broadband signatures of possible IC catastrophes were searched for in a prototypical source, S5 0716+71.Methods. A multifrequency observing campaign targetting S5 0716+71 was carried out during November 06-20, 2003. The observations, organized under the framework of the European Network for the Investigation of …
High Pressure Chemical Vapor Deposition: A Novel Approach For The Growth Of Inn, Vincent Timothy Woods
High Pressure Chemical Vapor Deposition: A Novel Approach For The Growth Of Inn, Vincent Timothy Woods
Physics and Astronomy Dissertations
The development of next generation devices for high speed switching, high efficiency energy conversion, spintronic devices require the development of advanced material systems. While conventional group IV, group II-VI and group III-V based materials systems have served as a base material in many modern device structures, they posses fundamental materials properties that limit their suitability in next generation device structures. The group III-N material system is very promising for the development of advanced device structures. GaN is currently widely used in high efficiency lighting applications. However, the development of this material system has been limited to material systems with limited …
X-Irradiation Of Dna Components In The Solid State: Experimental And Computational Studies Of Stabilized Radicals In Guanine Derivatives, Nayana Kumudini Jayatilaka
X-Irradiation Of Dna Components In The Solid State: Experimental And Computational Studies Of Stabilized Radicals In Guanine Derivatives, Nayana Kumudini Jayatilaka
Physics and Astronomy Dissertations
Single crystals of sodium salt of guanosine dihydrate and 9 Ethyl Guanine were X-irradiated with the objective of identifying the radical products. Study with K-band EPR, ENDOR, and ENDOR-Induced EPR techniques indicated at least four radical species to appear in both crystals in the temperature range of 6K to room temperature. Three of these radicals (Radicals R1, R2, and R3) were present immediately after irradiation at 6K. Computational chemistry and EPR spectrum simulation methods were also used to assist in radical identifications. Radical R1, the product of net hydrogen addition to N7, and Radical R2, the product of electron loss …
Development And Comparison Of Highly Directional Loudspeakers, Gordon Robert Dix
Development And Comparison Of Highly Directional Loudspeakers, Gordon Robert Dix
Theses and Dissertations
Highly directive loudspeakers have long been important tools for sound system designers, experimental acousticians, and many other professionals in the audio industry. They allow sound engineers to more easily manipulate the radiation pattern of their loudspeakers to accommodate the purpose of the venue. Many commercially available products, while exhibiting good directivity at mid and high frequencies, generally lack control in the low frequency range. A new method for controlling the radiation pattern of a loudspeaker at low frequencies has been developed and modeled extensively. Prototypes have been built and tested in an anechoic chamber. Results from computer modeling and experimental …
Direct Observation Of Laser Filamentation In High-Order Harmonic Generation, John Charles Painter
Direct Observation Of Laser Filamentation In High-Order Harmonic Generation, John Charles Painter
Theses and Dissertations
We investigate the spatial evolution of an intense laser pulse as it generates high-order harmonics in a long gas cell, filled with 80 torr of helium. A thin foil separates the gas-filled region of the cell from a subsequent evacuated region. The exit plane of the gas cell can be scanned along the laser axis so that the evolution of the laser throughout the focus can be observed (full scanning range of 9 cm). We constructed an apparatus that images the laser radial energy profile as it exits the cell. The high harmonics, odd orders ranging from 45 to 91, …