+publisher:"University of Southern California" +contributor:("Bickers, Gene")

University of Southern California

1. Yang, Shanling. Boundary layer and separation control on wings at low Reynolds numbers.

Degree: PhD, Aerospace Engineering, 2013, University of Southern California

URL: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/337675/rec/1157

► In the transitional chord-based Reynolds number regime for aeronautics, 10⁴ ≤ Re ≤ 10⁵, fluid flow over a surface is prone to separation followed by… (more)

▼ In the transitional chord-based Reynolds number regime for aeronautics, 10⁴ ≤ Re ≤ 10⁵, fluid flow over a surface is prone to separation followed by possible reattachment and transition to turbulence. The amplification of disturbances in the boundary layer promotes transition to turbulence, so boundary layer and separation control methods are especially favorable in this transitional Re regime. The use of sound to control flow separation at transitional and moderate Re for various smooth airfoils has been experimentally studied in the literature. Optimum excitation frequencies are reported to match the frequency or sub harmonics of the naturally occurring instabilities in the shear layer, and correlations between optimum frequencies for external acoustic forcing and tunnel anti-resonances have been observed. However, reported optimum frequency values based on the Strouhal number scaling St/Re^(1/2) are not in complete agreement among the different reported studies. Little attention has been given to distinguish the effects of standing waves from traveling sound waves. Mathematical and experimental studies of sound and boundary layer instability interactions have also yielded mixed results, suggesting that there still lacks a full understanding about the mechanism by which acoustic waves affect boundary layer flows. ❧ Results on boundary layer and separation control through acoustic excitation at low Re numbers are reported. The Eppler 387 profile is specifically chosen because of its pre-stall hysteresis and bi-stable state behavior in the transitional Re regime, which is a result of flow separation and reattachment. External acoustic forcing on the wing yields large improvements (more than 70%) in lift-to-drag ratio and flow reattachment at forcing frequencies that correlate with the measured anti-resonances in the wind tunnel. The optimum St/Re^(1/2) range for Re = 60,000 matches the proposed optimum range in the literature, but there is less agreement for Re = 40,000, which suggests that correct St scaling has not been determined. The correlation of aerodynamic improvements to wind tunnel resonances implies that external acoustic forcing is facility-dependent, which inhibits practical application. Therefore, internal acoustic excitation for the same wing profile is also pursued. ❧ Internal acoustic forcing is designed to be accomplished by embedding small speakers inside a custom-designed wing that contains many internal cavities and small holes in the suction surface. However, initial testing of this semi-porous wing model shows that the presence of the small holes in the suction surface completely transforms the aerodynamic performance by changing the mean chordwise separation location and causing an originally separated, low-lift state flow to reattach into a high-lift state. The aerodynamic improvements are not caused by the geometry of the small holes themselves, but rather by Helmholtz resonance that occurs in the cavities, which generate tones that closely match the intrinsic flow instabilities.… Advisors/Committee Members: Spedding, Geoffrey R. (Committee Chair), Redekopp, Larry G. (Committee Member), Eliasson, Veronica (Committee Member), Bickers, Gene (Committee Member), Radovich, Charles (Committee Member).

Subjects/Keywords: low Reynolds numbers; separation control; acoustic excitation; active separation control; passive separation control; boundary layers; fluid dynamics; aerodynamics; Helmholtz resonance; local acoustic forcing; external acoustic excitation; internal excitation; flow control

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APA (6^th Edition):

Yang, S. (2013). Boundary layer and separation control on wings at low Reynolds numbers. (Doctoral Dissertation). University of Southern California. Retrieved from http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/337675/rec/1157

Chicago Manual of Style (16^th Edition):

Yang, Shanling. “Boundary layer and separation control on wings at low Reynolds numbers.” 2013. Doctoral Dissertation, University of Southern California. Accessed January 18, 2021. http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/337675/rec/1157.

MLA Handbook (7^th Edition):

Yang, Shanling. “Boundary layer and separation control on wings at low Reynolds numbers.” 2013. Web. 18 Jan 2021.

Vancouver:

Yang S. Boundary layer and separation control on wings at low Reynolds numbers. [Internet] [Doctoral dissertation]. University of Southern California; 2013. [cited 2021 Jan 18]. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/337675/rec/1157.

Council of Science Editors:

Yang S. Boundary layer and separation control on wings at low Reynolds numbers. [Doctoral Dissertation]. University of Southern California; 2013. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/337675/rec/1157

University of Southern California

2. Kim, Jihyun. Experimental development and analysis of a continuous flow-through trace gas preconcentrator.

Degree: PhD, Aerospace Engineering, 2013, University of Southern California

URL: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/326099/rec/2627

► A new type of continuous flow-through trace gas preconcentrator for rarefied trace gas analysis, which has been proposed by Muntz et al. (Muntz et al.… (more)

▼ A new type of continuous flow-through trace gas preconcentrator for rarefied trace gas analysis, which has been proposed by Muntz et al. (Muntz et al. 2008, Muntz et al. 2004, Han et al. 2009) has been built and consists of a main flow channel, pumping chambers, and separation membranes between the main flow channel and the pumping chambers. In this case, preconcentration is not from stop, adsorption, and release; but is caused by the continuously changing cross section of the main flow channel until released through the detecting system such as gas chromatography, mass spectrometry, or optical diagnostics. This has the possibility of achieving concentration increase of various gases in a carrier gas by using relatively simple micro/mesoscale mass diffusion separation stages, without interrupting the gas flows, and is suitable for improving the time accuracy of analytical systems. The present study focused on the design and characterization of a new type of preconcentrator that enables use with various gas detection units. The research described here addressed for heavier molecules, at atmospheric pressure and room temperature optimized conditions and possibilities of the preconcentrator. ❧ The shape equation was introduced for the main flow channel and the concentration ratio of the trace gas was determined using a set of coefficients including; the fractional open area, the transmission probability, and the ratio of pressure between the main flow channel and pumping chambers. The fractional open area (porosity) and transmission probability were obtained from a pore diameter, thickness, and pore density of a membrane used. According to these equations and coefficients, it was possible to determine the shape and size of the main flow channel, and type of the separation membrane approximately. In order to fabricate a preconcentrator prototype, the variables were limited with reasonable boundary conditions, and could be predicted with available numerical data. Properties of the membrane were used as main factors to decide the type of the separation membranes. The pumping chambers located above and below the main flow channel maintained to maintain a constant gas flow speed in the main flow channel during the experiment, and were designed to create relatively lower pressure than that in the main flow channel. ❧ A series of experiments were conducted in an attempt to validate the available numerical data, such as the concentration and gas flow speed of the newly continuous preconcentration technology. This study involved experimental investigations using argon mixed with xenon to obtain a base-line comparison of the existing numerical predictions provided by the prototype preconcentrator. The concentration was calculated by pressure differences between the main flow channel and pumping chambers, and by mass flow rates obtained at exit of the main flow channel. ❧ The numerical models calculated an increase in concentration under the following conditions; 5cm/s for the helium gas flow speed, 4.2 × 10⁻⁵ for the porosity,… Advisors/Committee Members: Muntz, E. Phillip (Committee Chair), Shiflett, Geoffrey R. (Committee Member), Yang, Bingen (Ben) (Committee Member), Bickers, Gene (Committee Member).

Subjects/Keywords: preconcentrator; rarefied gas dynamics; mass flow rate; concentration of gas

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Kim, J. (2013). Experimental development and analysis of a continuous flow-through trace gas preconcentrator. (Doctoral Dissertation). University of Southern California. Retrieved from http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/326099/rec/2627

Chicago Manual of Style (16^th Edition):

Kim, Jihyun. “Experimental development and analysis of a continuous flow-through trace gas preconcentrator.” 2013. Doctoral Dissertation, University of Southern California. Accessed January 18, 2021. http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/326099/rec/2627.

MLA Handbook (7^th Edition):

Kim, Jihyun. “Experimental development and analysis of a continuous flow-through trace gas preconcentrator.” 2013. Web. 18 Jan 2021.

Vancouver:

Kim J. Experimental development and analysis of a continuous flow-through trace gas preconcentrator. [Internet] [Doctoral dissertation]. University of Southern California; 2013. [cited 2021 Jan 18]. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/326099/rec/2627.

Council of Science Editors:

Kim J. Experimental development and analysis of a continuous flow-through trace gas preconcentrator. [Doctoral Dissertation]. University of Southern California; 2013. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/326099/rec/2627

University of Southern California

3. Song, Kok Wee. Electronic correlation effects in multi-band systems.

Degree: PhD, Physics, 2014, University of Southern California

URL: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/376102/rec/2278

► The recent dominant trends in condensed matter physics research can be roughly summarized into three newly discovered materials: topological insulators, graphene, and iron‐based superconductors. All… (more)

▼ The recent dominant trends in condensed matter physics research can be roughly summarized into three newly discovered materials: topological insulators, graphene, and iron‐based superconductors. All these materials exhibit many intriguing properties which are fundamentally related to their electronic band structure. Therefore, this lead to many intense investigations on multi‐band electronic system to explore new physics. ❧ The physics of multi‐band electronic structure is fascinating in several aspects. Without many‐body effects, because of the gauge freedom of Bloch states, topological insulators can give rise a robust metallic behavior at its boundaries. In graphene, the touching between conduction and valence band at Fermi level yields a new criticality class which exhibit many unconventional electronic properties, especially its quasi‐relativistic behavior. Turning to the many‐body effects, for instance, the iron‐based superconductors can sustain an superconducting ground state despite of no attractive interactions in the system. Therefore, a deeper understanding for the conventional notions in condensed matter physics has put forward by many of these experimental observations. ❧ In this thesis, the many‐body effects in multi‐band systems are the main focus, especially the study of graphene and iron‐based superconductors which can be compared to experiments. These theoretical studies intend to understand how the underlying electronic bands degree of freedom can give rise to Fermi‐liquid instabilities, and how these effects can be related to intriguing physical properties. ❧ We first study the electrons correlation effects in bilayer graphene by a renormalization group technique. In this study, we build a microscopic model of bilayer graphene from a tight‐binding approach. In our finding, the peculiar Fermi surface configuration leads to critical behavior which is beyond the Fermi‐liquid paradigm. Furthermore, due to the electron‐electron interactions between different bands, excitonic instabilities are found in many different scattering channels. This analysis suggest a collection of competing orders in the system ground states. This result is consistent with the experimental observation that bilayer graphene is an insulator. ❧ Next, we study nematic order in the metallic phase of iron pnictides. In contrast to graphene, the density of states is finite at the Fermi surface. By careful investigating the scattering processes near these Fermi surface, and then identifying the most relevant collective modes from these processes, we find that a Pomeranchuk instability can be driven by magnetic fluctuations. This instability eventually leads to the break down of the isotropic metallic phase which electronic system exhibit broken crystalline rotational symmetry but preserve translation symmetry. As the experiment suggests, this can be a candidate for nematic order in the metallic phase. Advisors/Committee Members: Haas, Stephan W. (Committee Chair), Bickers, Gene (Committee Member), Dappen, Werner (Committee Member), Däppen, Werner (Committee Member), Daeppen, Werner (Committee Member), Haselwandter, Christoph (Committee Member), Jonckheere, Edmond A. (Committee Member).

Subjects/Keywords: excitonic instabilties; Fermi liquid; graphene; iron pnictides; nematic order; superconductivity

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Song, K. W. (2014). Electronic correlation effects in multi-band systems. (Doctoral Dissertation). University of Southern California. Retrieved from http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/376102/rec/2278

Chicago Manual of Style (16^th Edition):

Song, Kok Wee. “Electronic correlation effects in multi-band systems.” 2014. Doctoral Dissertation, University of Southern California. Accessed January 18, 2021. http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/376102/rec/2278.

MLA Handbook (7^th Edition):

Song, Kok Wee. “Electronic correlation effects in multi-band systems.” 2014. Web. 18 Jan 2021.

Vancouver:

Song KW. Electronic correlation effects in multi-band systems. [Internet] [Doctoral dissertation]. University of Southern California; 2014. [cited 2021 Jan 18]. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/376102/rec/2278.

Council of Science Editors:

Song KW. Electronic correlation effects in multi-band systems. [Doctoral Dissertation]. University of Southern California; 2014. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll3/id/376102/rec/2278

University of Southern California

4. Cai, Zizhe. Moment formation and pairing in the 2D Hubbard model.

Degree: PhD, Physics, 2007, University of Southern California

URL: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll127/id/539409/rec/4209

► The two-dimensional (2D) Hubbard model is solved in a new way. The zero-frequency components of the Hubbard interaction are separated out and solved to infinite… (more)

Subjects/Keywords: Hubbard model

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Cai, Z. (2007). Moment formation and pairing in the 2D Hubbard model. (Doctoral Dissertation). University of Southern California. Retrieved from http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll127/id/539409/rec/4209

Chicago Manual of Style (16^th Edition):

Cai, Zizhe. “Moment formation and pairing in the 2D Hubbard model.” 2007. Doctoral Dissertation, University of Southern California. Accessed January 18, 2021. http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll127/id/539409/rec/4209.

MLA Handbook (7^th Edition):

Cai, Zizhe. “Moment formation and pairing in the 2D Hubbard model.” 2007. Web. 18 Jan 2021.

Vancouver:

Cai Z. Moment formation and pairing in the 2D Hubbard model. [Internet] [Doctoral dissertation]. University of Southern California; 2007. [cited 2021 Jan 18]. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll127/id/539409/rec/4209.

Council of Science Editors:

Cai Z. Moment formation and pairing in the 2D Hubbard model. [Doctoral Dissertation]. University of Southern California; 2007. Available from: http://digitallibrary.usc.edu/cdm/compoundobject/collection/p15799coll127/id/539409/rec/4209

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