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Articles 1 - 30 of 30
Full-Text Articles in Physics
New Far-Infrared Laser Frequencies Generated By Ch3cn, Cd3cn, 13ch3i, Cd3i, And 13cd3i, Michael Jackson
New Far-Infrared Laser Frequencies Generated By Ch3cn, Cd3cn, 13ch3i, Cd3i, And 13cd3i, Michael Jackson
All Faculty Scholarship for the College of the Sciences
Heterodyne techniques have been used to experimentally determine, for the first time, the frequencies for nineteen laser emissions ranging from 264 to 984 GHz. These laser emissions were generated by optically pumping either CH3CN, CD3CN, 13CH3, CD3I, or 13CD3I with a CO2 laser. This includes the newly discovered 566.325-μ m laser emission from optically pumped 13CD3I. The fractional uncertainties with which these frequencies were experimentally determined, up to ± 5 × 10− 7, were of sufficient accuracy to confirm or revise …
Nasa Student Launch - Payload, Eli Kirk
Nasa Student Launch - Payload, Eli Kirk
All Undergraduate Projects
A team of mechanical engineering, physics, and computer science students from Central Washington University have constructed a fully functional subscale model rocket to be flown at the NASA Student Launch competition. The rocket’s payload was designed to open the nose cone and take a photo of the rocket’s surroundings after descending from the launch. Smaller parts were constructed through machining and 3D printing that will be added to the purchased major component, the linear actuator, in order to perform the required tasks. These tasks are signaled by an attached electronics board, which will receive an RF command remotely, execute code, …
Design Of Broadband Helmholtz Resonator Arrays Using The Radiation Impedance Method, Vidhya Rajendran, Andy Piacsek, Tomás Méndez Echenagucia
Design Of Broadband Helmholtz Resonator Arrays Using The Radiation Impedance Method, Vidhya Rajendran, Andy Piacsek, Tomás Méndez Echenagucia
All Faculty Scholarship for the College of the Sciences
This paper describes the design process of a low-frequency sound absorptive panel composed of differently tuned Helmholtz resonators (HRs), considering size and fabrication constraints relevant for applications in the building sector. The paper focuses on cylindrical and spiral resonators with embedded necks that are thin and can achieve high absorption. the mutual interaction between the resonators was modeled based on the radiation impedance method and it plays a key component in enhancing the absorption performance of the array. The differential evolution search algorithm was used to design the resonators and modify their mutual interaction to derive the absorption performance of …
Herschel Gould Belt Survey Observations Of Dense Cores In The Cepheus Flare Clouds, James Di Francesco, Jared Keown, Cassandra Fallscheer, Philippe André, Bilal Ladjelate, Vera Könyves, Alexander Men'shchikov, Shaun Stephens-Whale, Quang Nguyen-Luong, Peter Martin, Sarah Sadavoy, Stefano Pezzuto, Eleonora Fiorellino, Milena Benedettini, Nicola Schneider, Sylvain Bontemps, Doris Arzoumanian, Pedro Palmeirim, Jason M. Kirk, Derek Ward-Thompson
Herschel Gould Belt Survey Observations Of Dense Cores In The Cepheus Flare Clouds, James Di Francesco, Jared Keown, Cassandra Fallscheer, Philippe André, Bilal Ladjelate, Vera Könyves, Alexander Men'shchikov, Shaun Stephens-Whale, Quang Nguyen-Luong, Peter Martin, Sarah Sadavoy, Stefano Pezzuto, Eleonora Fiorellino, Milena Benedettini, Nicola Schneider, Sylvain Bontemps, Doris Arzoumanian, Pedro Palmeirim, Jason M. Kirk, Derek Ward-Thompson
All Faculty Scholarship for the College of the Sciences
We present Herschel SPIRE and PACS maps of the Cepheus Flare clouds L1157, L1172, L1228, L1241, and L1251, observed by the Herschel Gould Belt Survey of nearby star-forming molecular clouds. Through modified blackbody fits to the SPIRE and PACS data, we determine typical cloud column densities of (0.5–1.0) × 1021 cm−2 and typical cloud temperatures of 14–15 K. Using the getsources identification algorithm, we extract 832 dense cores from the SPIRE and PACS data at 160–500 μm. From placement in a mass versus size diagram, we consider 303 to be candidate prestellar cores, and 178 of these …
Contact In The Unitary Fermi Gas Across The Superfluid Phase Transition, S. Jensen, Christopher N. Gilbreth, Y. Alhassid
Contact In The Unitary Fermi Gas Across The Superfluid Phase Transition, S. Jensen, Christopher N. Gilbreth, Y. Alhassid
All Faculty Scholarship for the College of the Sciences
A quantity known as the contact is a fundamental thermodynamic property of quantum many-body systems with short-range interactions. Determination of the temperature dependence of the contact for the unitary Fermi gas of infinite scattering length has been a major challenge, with different calculations yielding qualitatively different results. Here we use finite-temperature auxiliary-field quantum Monte Carlo (AFMC) methods on the lattice within the canonical ensemble to calculate the temperature dependence of the contact for the homogeneous spin-balanced unitary Fermi gas. We extrapolate to the continuum limit for 40, 66, and 114 particles, eliminating systematic errors due to finite-range effects. We observe …
Dual-Axis Solar Tracker, Bryan Kennedy
Dual-Axis Solar Tracker, Bryan Kennedy
All Undergraduate Projects
Renewable energies, and fuels that are not fossil fuel-based, are one of the prolific topics of debate in modern society. With climate change now becoming a primary focus for scientists and innovators of today, one of the areas for the largest amount of potential and growth is that of the capturing and utilization of Solar Energy. This method involves using a mechanical system to track the progression of the sun as it traverses the sky throughout the day. A dual-axis solar tracker such as the one designed and built for this project, can follow the sun both azimuthally and in …
Magnetocaloric Effect Near Room Temperature In Quintenary And Sextenary Heusler Alloys, Benjamin D. White, R. I. Barabash, O. M. Barabash, I. Jeon, M. B. Maple
Magnetocaloric Effect Near Room Temperature In Quintenary And Sextenary Heusler Alloys, Benjamin D. White, R. I. Barabash, O. M. Barabash, I. Jeon, M. B. Maple
All Faculty Scholarship for the College of the Sciences
An inverse magnetocaloric effect is studied in Ni2Mn1+xX1-x-type Heusler alloys. Principally known for their shape-memory properties, these alloys also exhibit significant entropy and temperature changes (ΔS and ΔTAd, respectively) under adiabatic conditions when a modest magnetic field is applied. We investigated the impact on magnetocaloric properties of introducing substantial chemical disorder on the X-site (X = Si, Ga, In), of replacing Ni with nonmagnetic Ag, and of replacing a small amount of Mn with Gd. While a reduction in ΔS is observed in the first two cases, we observe a significant enhancement …
Phase Transitions In A Symmetry-Conserving Framework, Yoram Alhassid, G. F. Bertsch, Christopher N. Gilbreth, Mika T. Mustonen
Phase Transitions In A Symmetry-Conserving Framework, Yoram Alhassid, G. F. Bertsch, Christopher N. Gilbreth, Mika T. Mustonen
All Faculty Scholarship for the College of the Sciences
Phase transitions are often associated with the breaking of a symmetry in the low-temperature phase described by non-vanishing values of certain order parameters. However, in finite-size systems the correlated equilibrium configuration preserves the symmetries of the underlying Hamiltonian. We discuss a method to calculate the statistical distribution of the order parameters without breaking the corresponding symmetries. The maxima of these statistical distributions mimic the phase transitions that are found in a mean-field approximation. We demonstrate the method for the case of shape transitions in atomic nuclei.
Tuning The Magnetic Ground State Of Ce1−Xybxrhin5 By Yb Valence Fluctuations, S. Jang, N. Pouse, T. Keiber, Benjamin White, S. M. Dissler, J. W. Lynn, J. C. Collini, M. Janoschek, F. Bridges, M. Brian Maple
Tuning The Magnetic Ground State Of Ce1−Xybxrhin5 By Yb Valence Fluctuations, S. Jang, N. Pouse, T. Keiber, Benjamin White, S. M. Dissler, J. W. Lynn, J. C. Collini, M. Janoschek, F. Bridges, M. Brian Maple
All Faculty Scholarship for the College of the Sciences
We characterize the properties of Ce1−xYbxRhIn5 single crystals with 0 ⩽ x ⩽ 1 using measurements of powder x-ray diffraction, energy dispersive x-ray spectroscopy, electrical resistivity, magnetic susceptibility, specific heat, x-ray absorption near edge structure (XANES), and neutron diffraction. The Yb valence vYb, calculated from the magnetic susceptibility and measured using XANES, decreases from 3+ at x = 0 to ∼2.1+ at xact = 0.2, where xact is the measured Yb concentration. A transition from incommensurate to commensurate antiferromagnetism is observed in neutron diffraction measurements …
Model For Coordination Of Microtubule And Actin Dynamics In Growth Cone Turning, Erin M. Craig
Model For Coordination Of Microtubule And Actin Dynamics In Growth Cone Turning, Erin M. Craig
All Faculty Scholarship for the College of the Sciences
In the developing nervous system, axons are guided to their synaptic targets by motile structures at the axon tip called growth cones, which reorganize their cytoskeleton in order to steer in response to chemotactic cues. Growth cone motility is mediated by an actin-adhesion “clutch” mechanism, in which mechanical attachment to a substrate, coupled with polarized actin growth, produces leading-edge protrusion. Several studies suggest that dynamic microtubules (MTs) in the growth cone periphery play an essential role in growth cone steering. It is not yet well-understood how the MT cytoskeleton and the dynamic actin-adhesion clutch system are coordinated to promote growth …
Polarity Sorting Of Axonal Microtubules: A Computational Study, Erin M. Craig, Howard T. Yeung, Anand N. Rao, Peter W. Baas
Polarity Sorting Of Axonal Microtubules: A Computational Study, Erin M. Craig, Howard T. Yeung, Anand N. Rao, Peter W. Baas
All Faculty Scholarship for the College of the Sciences
We present a computational model to test a “polarity sorting” mechanism for microtubule (MT) organization in developing axons. We simulate the motor-based axonal transport of short MTs to test the hypothesis that immobilized cytoplasmic dynein motors transport short MTs with their plus ends leading, so “mal-oriented” MTs with minus-end-out are transported toward the cell body while “correctly” oriented MTs are transported in the anterograde direction away from the soma. We find that dynein-based transport of short MTs can explain the predominately plus-end-out polarity pattern of axonal MTs but that transient attachments of plus-end-directed motor proteins and nonmotile cross-linker proteins are …
Polarity Sorting Of Axonal Microtubules: A Computational Study, Erin M. Craig, Howard T. Yeung, Anand N. Rao, Peter W. Baas
Polarity Sorting Of Axonal Microtubules: A Computational Study, Erin M. Craig, Howard T. Yeung, Anand N. Rao, Peter W. Baas
All Faculty Scholarship for the College of the Sciences
We present a computational model to test a “polarity sorting” mechanism for microtubule (MT) organization in developing axons. We simulate the motor-based axonal transport of short MTs to test the hypothesis that immobilized cytoplasmic dynein motors transport short MTs with their plus ends leading, so “mal-oriented” MTs with minus-end-out are transported toward the cell body while “correctly” oriented MTs are transported in the anterograde direction away from the soma. We find that dynein-based transport of short MTs can explain the predominately plus-end-out polarity pattern of axonal MTs but that transient attachments of plus-end-directed motor proteins and nonmotile cross-linker proteins are …
Cytoplasmic Dynein Transports Axonal Microtubules In A Polarity-Sorting Manner, Anand N. Rao, Ankita Patil, Mark M. Black, Erin M. Craig, Kennith A. Myers, Howard T. Yeung, Peter W. Bass
Cytoplasmic Dynein Transports Axonal Microtubules In A Polarity-Sorting Manner, Anand N. Rao, Ankita Patil, Mark M. Black, Erin M. Craig, Kennith A. Myers, Howard T. Yeung, Peter W. Bass
All Faculty Scholarship for the College of the Sciences
Axonal microtubules are predominantly organized into a plus-end-out pattern. Here, we tested both experimentally and with computational modeling whether a motor-based polarity-sorting mechanism can explain this microtubule pattern. The posited mechanism centers on cytoplasmic dynein transporting plus-end-out and minus-end-out microtubules into and out of the axon, respectively. When cytoplasmic dynein was acutely inhibited, the bidirectional transport of microtubules in the axon was disrupted in both directions, after which minus-end-out microtubules accumulated in the axon over time. Computational modeling revealed that dynein-mediated transport of microtubules can establish and preserve a predominantly plus-end-out microtubule pattern as per the details of the experimental …
Superconducting And Normal State Properties Of The Systems La1−Xmxpt4ge12 (M=Ce,Th), K. Huang, D. Yazici, Benjamin D. White, I. Jeon, A. J. Breindel, N. Pouse, M. B. Maple
Superconducting And Normal State Properties Of The Systems La1−Xmxpt4ge12 (M=Ce,Th), K. Huang, D. Yazici, Benjamin D. White, I. Jeon, A. J. Breindel, N. Pouse, M. B. Maple
All Faculty Scholarship for the College of the Sciences
Electrical resistivity, magnetization, and specific heat measurements were performed on polycrystalline samples of the filled-skutterudite systems La1−xMxPt4Ge12 (M = Ce and Th). Superconductivity in LaPt4Ge12 was quickly suppressed with Ce substitution and no evidence for superconductivity was found down to 1.1 K for x > 0.2. Temperature-dependent specific heat data at low temperatures for La1−xCexPt4Ge12 show a change from powerlaw to exponential behavior, which may be an indication for multiband superconductivity in LaPt4Ge12. …
Investigation Of Superconducting And Normal-State Properties Of The Filled-Skutterudite System Prpt4ge12−Xsbx, I. Jeon, K. Huang, D. Yazici, N. Kanchanavatee, Benjamin D. White, P.-C. Ho, S. Jang, N. Pouse, M. B. Maple
Investigation Of Superconducting And Normal-State Properties Of The Filled-Skutterudite System Prpt4ge12−Xsbx, I. Jeon, K. Huang, D. Yazici, N. Kanchanavatee, Benjamin D. White, P.-C. Ho, S. Jang, N. Pouse, M. B. Maple
All Faculty Scholarship for the College of the Sciences
We report a study of the superconducting and normal-state properties of the filled-skutterudite system PrPt4Ge12−xSbx . Polycrystalline samples with Sb concentrations up to x = 5 were synthesized and investigated by means of x-ray diffraction, electrical resistivity, magnetic susceptibility, and specific heat measurements. We observed a suppression of superconductivity with increasing Sb substitution up to x = 4, above which no signature of superconductivity was observed down to 140 mK. The Sommerfeld coefficient, γ , of superconducting specimens decreases with increasing x up to x = 3, suggesting that superconductivity may depend on the …
Characterizing Far-Infrared Laser Emissions And The Measurement Of Their Frequencies, Michael Jackson, Lyndon R. Zink
Characterizing Far-Infrared Laser Emissions And The Measurement Of Their Frequencies, Michael Jackson, Lyndon R. Zink
All Faculty Scholarship for the College of the Sciences
The generation and subsequent measurement of far-infrared radiation has found numerous applications in high-resolution spectroscopy, radioastronomy, and Terahertz imaging. For about 45 years, the generation of coherent, far-infrared radiation has been accomplished using the optically pumped molecular laser. Once far-infrared laser radiation is detected, the frequencies of these laser emissions are measured using a three-laser heterodyne technique. With this technique, the unknown frequency from the optically pumped molecular laser is mixed with the difference frequency between two stabilized, infrared reference frequencies. These reference frequencies are generated by independent carbon dioxide lasers, each stabilized using the fluorescence signal from an external, …
Measured Laser Frequencies From The Optically Pumped Methanol Isotopologue 13cd3od, Benjamin Freeman
Measured Laser Frequencies From The Optically Pumped Methanol Isotopologue 13cd3od, Benjamin Freeman
Symposium Of University Research and Creative Expression (SOURCE)
The far-infrared region of the electromagnetic spectrum, informally defined as the wavelength region between 0.025 mm and 2.00 mm, is an area that has been investigated using laser radiation for more than 50 years. Research with far infrared lasers has a range of applications including terahertz imaging, a form of noninvasive imaging. Creating a catalog of far-infrared laser emissions is also beneficial for their use in high-resolution spectroscopic investigations of stable molecules and short-lived free radicals. The purpose of this research was to measure the frequencies of known far-infrared laser emissions generated by 13CD3OD, an isotopic form of methanol. This …
Nonlinear Progressive Wave Equation For Stratified Atmospheres, B. Edward Mcdonald, Andrew A. Piacsek
Nonlinear Progressive Wave Equation For Stratified Atmospheres, B. Edward Mcdonald, Andrew A. Piacsek
All Faculty Scholarship for the College of the Sciences
The nonlinear progressive wave equation (NPE) [McDonald and Kuperman, J. Acoust. Soc. Am. 81, 1406–1417 (1987)] is expressed in a form to accommodate changes in the ambient atmospheric density, pressure, and sound speed as the time-stepping computational window moves along a path possibly traversing significant altitude differences (in pressure scale heights). The modification is accomplished by the addition of a stratification term related to that derived in the 1970s for linear range-stepping calculations and later adopted into Khokhlov-Zabolotskaya-Kuznetsov-type nonlinear models. The modified NPE is shown to preserve acoustic energy in a ray tube and yields analytic similarity solutions for …
The Rotational Spectrum Of The Fed Radical In Its X4Δ State, Measured By Far-Infrared Laser Magnetic Resonance, Michael Jackson, Lyndon R. Zink, Jonathan P. Towle, Neil Riley, John M. Brown
The Rotational Spectrum Of The Fed Radical In Its X4Δ State, Measured By Far-Infrared Laser Magnetic Resonance, Michael Jackson, Lyndon R. Zink, Jonathan P. Towle, Neil Riley, John M. Brown
All Faculty Scholarship for the College of the Sciences
Transitions between the spin-rotational levels of the FeD radical in the v = 0level of the X 4Δ ground state have been detected by the technique of laser magnetic resonance at far-infrared wavelengths. Pure-rotational transitions have been observed for the three lowest spin components. Lambda-type doubling is resolved on all the observed transitions; nuclear hyperfine structure is not observed. The energy levels of FeD are strongly affected by the breakdown of the Born–Oppenheimer approximation and cannot be modeled accurately by an effective Hamiltonian. The data are therefore fitted to an empirical formula to yield term values and g-factors for …
Carrier Dynamics In Α‐Fe2o3 (0001) Thin Films And Single Crystals Probed By Femtosecond Transient Absorption And Reflectivity, Alan G. Joly, Joshua R. Williams, Scott A. Chambers, Gang Xiong, Wayne P. Hess, David M. Laman
Carrier Dynamics In Α‐Fe2o3 (0001) Thin Films And Single Crystals Probed By Femtosecond Transient Absorption And Reflectivity, Alan G. Joly, Joshua R. Williams, Scott A. Chambers, Gang Xiong, Wayne P. Hess, David M. Laman
All Faculty Scholarship for the College of the Sciences
Femtosecond transient reflectivity and absorption are used to measure the carrier lifetimes in α‐Fe2O3 thin films and single crystals. The results from the thin films show that initially excited hot electrons relax to the band edge within 300 fs and then recombine with holes or trap within 5 ps. The trapped electrons have a lifetime of hundreds of picoseconds. Transient reflectivity measurements from hematite (α‐Fe2O3)single crystals show similar but slightly faster dynamics leading to the conclusion that the short carrier lifetimes in these materials are due primarily to trapping to Fe d- …
The Structures Of Fluorene– (H2o)1,2 Determined By Rotational Coherence Spectroscopy, David M. Laman, Alan G. Joly, Douglas Ray
The Structures Of Fluorene– (H2o)1,2 Determined By Rotational Coherence Spectroscopy, David M. Laman, Alan G. Joly, Douglas Ray
All Faculty Scholarship for the College of the Sciences
Rotational coherence spectroscopy ~RCS!, via time-correlated single photon counting, and two-color resonant two-photon ionization ~R2PI! time-of-flight mass spectrometry, have been used to characterize fluorene–(water)1,2[FL– (H2O)1,2] van der Waals clusters generated in supersonic jets. Rotational coherence traces have been obtained at excitation energies corresponding to several resonant features in the S1<-S0 R2PI spectra of FL– (H2O)1,2 . RCS simulations and diagonalization of the moment of inertia tensor have been used to obtain S1 excited state rotational constants and structures of FL– (H2O)1,2 that are consistent with …
Atmospheric Turbulence Conditions Leading To Focused And Folded Sonic Boom Wave Fronts, Andrew A. Piacsek
Atmospheric Turbulence Conditions Leading To Focused And Folded Sonic Boom Wave Fronts, Andrew A. Piacsek
All Faculty Scholarship for the College of the Sciences
The propagation and subsequent distortion of sonic booms with rippled wave fronts are investigated theoretically using a nonlinear time-domain finite-difference scheme. This work seeks to validate the rippled wave front approach as a method for explaining the significant effects of turbulence on sonic booms [A. S. Pierce and D. J. Maglieri, J. Acoust. Soc. Am. 51, 702–721 (1971)]. A very simple description of turbulence is employed in which velocity perturbations within a shallow layer of the atmosphere form strings of vortices characterized by their size and speed. Passage of a steady-state plane shock front through such a vortex layer …
Pion-Induced Transport Of Π Mesons In Nuclei, S. G. Mashnik, R. J. Peterson, A. J. Sierk, Michael R. Braunstein
Pion-Induced Transport Of Π Mesons In Nuclei, S. G. Mashnik, R. J. Peterson, A. J. Sierk, Michael R. Braunstein
All Faculty Scholarship for the College of the Sciences
A large body of data for pion-induced neutral pion continuum spectra spanning outgoing energies near 180 MeV shows no dip there that might be ascribed to internal strong absorption processes involving the formation of Δ’s. This is the same observation previously made for the charged pion continuum spectra. Calculations in an intranuclear cascade model or a cascade exciton model with free-space parameters predict such a dip for both neutral and charged pions. We explore several medium modifications to the interactions of pions with internal nucleons that are able to reproduce the data for nuclei from 7Li through Bi.
Metastable States In Classical And Quantum Systems, Mark Makela, Samantha Parmley, Roger Yu
Metastable States In Classical And Quantum Systems, Mark Makela, Samantha Parmley, Roger Yu
All Faculty Scholarship for the College of the Sciences
The classical vibrational metastable states in a one-dimensional two-mass system are investigated experimentally and theoretically via the transmission of a coherent wave packet propagating through the system. The Fourier transform of the vibrational signal recorded in between the masses reveals resonant excitations by the coherent wave packet. The time-resolved spectrum indicates that the lifetime of a metastable state of higher frequency is longer than that of lower frequency, which is in contrast with the quantum mechanical double-barrier system. This study, which is easily accessible to physics majors, also demonstrates quantum resonant tunneling in a very simple classical way.
Phononic Band Structure In A Mass Chain, Samantha Parmley, Tom Zobrist, Terry Clough, Anthony Perez-Miller, Mark Makela, Roger Yu
Phononic Band Structure In A Mass Chain, Samantha Parmley, Tom Zobrist, Terry Clough, Anthony Perez-Miller, Mark Makela, Roger Yu
All Faculty Scholarship for the College of the Sciences
The vibrational properties of a finite one‐dimensional string‐mass chain are studied experimentally and theoretically. In the experiment both normal mode analysis and pulse analysis are used to obtain the eigenfrequencies of the string‐mass chain. The theoretical predictions are made based upon the numerical solution to the wave equation. The phononic band structure for a periodically massed string as well as Anderson localized gap modes for a disordered system are found. The theoretical and experimental results match satisfactorily well.
Vibrational Properties Of A Loaded String, Samantha Parmley, Tom Zobrist, Terry Clough, Anthony Perez-Miller, Mark Makela
Vibrational Properties Of A Loaded String, Samantha Parmley, Tom Zobrist, Terry Clough, Anthony Perez-Miller, Mark Makela
All Faculty Scholarship for the College of the Sciences
In this paper we discuss our study of a string–mass chain and its anology to quantum mechanical systems. Theoretical predictions are made based upon the numerical solution to the wave equation. These predictions are tested experimentally using both normal mode analysis and pulse analysis. The frequency band structures for periodic and disordered string mass chains are studied as well as their corresponding eigenfunctions. The theoretical and experimental results are in accord. This experiment, suitable for advanced physics majors, demonstrates many important features of quantum mechanics: eigenvalues, superposition principle, band structure, gap modes, and Anderson localization.
Wannier-Stark Localization In Modulation-Doped Multiple-Quantum-Well Structures, Roger H. Yu
Wannier-Stark Localization In Modulation-Doped Multiple-Quantum-Well Structures, Roger H. Yu
All Faculty Scholarship for the College of the Sciences
The external-electric-field effect and the doping effect on a modulation-doped finite-length GaAs/AlxGa1−xAs superlattice have been studied by solving the Schrödinger-Kohn-Sham equation and the Poisson equation self-consistently. In the heavy-doping case, the external electric field makes electrons sequentially tunnel through several potential barriers, and accumulates electrons near one side of the finite-length superlattice. The collective motion of the electrons results in high- and low-field domains in the superlattice. We have found that Wannier-Stark localization exists only in the high-field domain, and that the electronic states are not evenly spaced. The electric-field-induced (doping induced) depopulation (population) of subbands …
Self-Consistent Determination Of Electronic Structure And Elementary Excitations Of Finite Modulation-Doped Superlattices, Roger H. Yu
All Faculty Scholarship for the College of the Sciences
A self-consistent framework for the study of the electronic level structure of finite superlattices has been proposed. One of the surface states (Tamm states) found in our calculation crosses the Fermi energy in the energy gap when the depletion effect near the surface increases. We have shown the existence of low-energy Tamm states in our calculation when the surface barrier is lower than that of the interior. The electronic excitations of the superlattice have been studied via the electron-energy-loss function within the random-phase approximation. Two plasmon modes (well above the phonon response frequency) due to the Tamm states have also …
Tamm States In Finite Semiconductor Superlattices: Influence Of Accumulation And Depletion Layers, Roger H. Yu
Tamm States In Finite Semiconductor Superlattices: Influence Of Accumulation And Depletion Layers, Roger H. Yu
All Faculty Scholarship for the College of the Sciences
We discuss the electronic-level structure of finite semiconductor superlattices and the influence of accumulation and depletion regions on the surface localized states (Tamm states). Exact solutions of the Poisson and Schrödinger equations are obtained self-consistently, through use of a nonuniform jellium model. Both high-energy and low-energy Tamm states are found.
Asymptotic Behavior Of Fluid Jets, Ronald Walter Godfrey
Asymptotic Behavior Of Fluid Jets, Ronald Walter Godfrey
All Master's Theses
In this paper we shall consider the steady-state, two dimensional, irrotational flow of an inviscid, incompressible fluid under gravity.