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Papers by Kenneth Christensen
37th AIAA Fluid Dynamics Conference and Exhibit, 2007
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37th AIAA Fluid Dynamics Conference and Exhibit, 2007
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Volume 1, 2004
ABSTRACT
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37th AIAA Fluid Dynamics Conference and Exhibit, 2007
ABSTRACT
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45th AIAA Aerospace Sciences Meeting and Exhibit, 2007
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46th AIAA Aerospace Sciences Meeting and Exhibit, 2008
ABSTRACT
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International Journal of Heat and Fluid Flow, 2014
ABSTRACT The existence of meandering superstructures in a turbulent boundary layer overlying irre... more ABSTRACT The existence of meandering superstructures in a turbulent boundary layer overlying irregular roughness is explored with high-frame-rate particle-image velocimetry measurements within the roughness sublayer at moderate Reynolds number. Elongated streamwise fields of view reconstructed from this data using a Taylor’s hypothesis approach revealed spanwise-meandering regions of low-streamwise-momentum fluid that extended several boundary-layer thicknesses in the streamwise direction. Such signatures are consistent with previous observations of superstructures in smooth-wall turbulence. Counter-rotating wall-normal vortex cores were found to reside along the spanwise boundaries of these superstructure patterns, consistent with the spatial characteristics of hairpin vortex packets.
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41st AIAA Fluid Dynamics Conference and Exhibit, 2011
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40th Fluid Dynamics Conference and Exhibit, 2010
ABSTRACT The combined impact of irregular surface roughness and moderate favorable-pressure-gradi... more ABSTRACT The combined impact of irregular surface roughness and moderate favorable-pressure-gradient (FPG) conditions (K 2.5 x10-7) on the structure of a turbulent boundary layer is assessed using two-dimensional particle image velocimetry (PIV) measurements in the streamwise--wall-normal plane. The roughness under consideration is replicated from a turbine blade damaged by deposition of foreign materials and contains a broad range of topographical scales. These measurements are compared to measurements of smooth-wall flow under both identical FPG conditions as well as zero-pressure-gradient (ZPG) conditions in order to reveal the synergistic impact of roughness and FPG conditions on the underlying structure of the flow. While vortex organization is found to persist under both smooth- and rough-wall FPG conditions, its characteristics are altered compared to smooth-wall ZPG flow. Inspection of instantaneous velocity fields reveals this organization to be focused closer to the wall in the smooth- wall FPG case, with a shallower inclination angle noted as well as an elongated streamwise extent. In contrast, the rough-wall FPG results reveal packet structures more consistent with the smooth-wall ZPG case, indicating that roughness mitigates the FPG-induced focusing of these structural attributes toward the wall. Two-point correlations of streamwise velocity support these instantaneous observations.
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Biochemistry, Jan 25, 2005
The action of anthrax toxin begins when the protective antigen (PA(83), 83 kDa) moiety binds to a... more The action of anthrax toxin begins when the protective antigen (PA(83), 83 kDa) moiety binds to a mammalian cell-surface receptor and is cleaved by a furin-family protease into two fragments: PA(20) (20 kDa) and PA(63) (63 kDa). After PA(20) dissociates, receptor-bound PA(63) spontaneously oligomerizes to form a heptameric species, which is able to bind the two enzymatic components of the toxin and transport them to the cytosol. Treatment of PA(83) with trypsin yielded PA(63) and a form of PA(20) lacking unstructured regions at the N- and C-termini. We labeled these fragments with dyes capable of fluorescence resonance energy transfer to quantify their association in solution. We kinetically determined that the equilibrium dissociation constant is 190 nM with a dissociation rate constant, k(off), of 3.3 x 10(-)(2) s(-)(1) (t(1/2) of 21 s). A two-step association process was observed using stopped-flow: a fast bimolecular step (k(on) = 1.4 x 10(5) M(-)(1) s(-)(1)) was followed by a s...
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Aggregation of suspended yeast cells in a small-scale ultrasonic standing wave field has been mon... more Aggregation of suspended yeast cells in a small-scale ultrasonic standing wave field has been monitored and quan- tified. The aggregation effect is based on the acoustic radiation force, which concentrates the cells in clumps. The ultrasonic chamber employed (1.9 MHz, one wavelength pathlength) had a sonication volume of 60 µl. The aggreg- ation process was observed from above the transducer
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Physical review. B, Condensed matter, Jan 15, 1993
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Microfluidics and Nanofluidics, 2015
ABSTRACT The development of an experimental protocol to investigate the flow field produced by th... more ABSTRACT The development of an experimental protocol to investigate the flow field produced by the interaction of two immiscible liquids flowing through a porous network is reported. The experimental protocol allows simultaneous quantification of the velocity distribution in a multi-liquid system based on the microscopic particle image velocimetry technique. The experimental challenges associated with this unique application are discussed, including two-liquid imaging and interface tracking, and solutions that couple refractive index matching and fluorescent signal separation are described. The technique was applied to both single- and two-liquid flows in a two-dimensional pore network comprising a staggered array of circular pillars wherein the flow was driven by a steady pressure gradient. Both drainage and imbibition were considered herein with a focus on fluid–fluid front migration and effects owing to the passage of the interface. The velocity distribution obtained for these two-liquid-phase flow scenarios revealed several peculiarities when compared to the reference case of single-liquid-phase flow. In particular, the instabilities associated with the interfacial processes propagate downstream and perturb the flow field, resulting in dramatic differences from the regular and periodic flow paths typical of steady-state, single-phase flow. Additionally, the passage of the interface does not restore previous flow patterns, but instead yields complex preferential flow paths that mutually interact with residual trapped pockets of fluid. Such dynamical events must be quantified in order to properly model the pore-scale physics central to fully understanding the wealth of practical applications represented by this model flow system.
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Tony Perry, et al. (J. Fluid Mech., v. 439, 2001) have recently contributed to the discussion con... more Tony Perry, et al. (J. Fluid Mech., v. 439, 2001) have recently contributed to the discussion concerning the reasons for systematic deviations with Re's (Reynolds numbers) in the Princeton ``Super-Pipe'' data. Perry et al. demonstrate that the deviation of the constant within the ``log-law'' is compatible with the ``Colebrook formula'' for transitionally rough pipes. Since the experiments were completed, Lex
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ABSTRACT
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ABSTRACT
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37th AIAA Fluid Dynamics Conference and Exhibit, 2007
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37th AIAA Fluid Dynamics Conference and Exhibit, 2007
Bookmarks Related papers MentionsView impact
Volume 1, 2004
ABSTRACT
Bookmarks Related papers MentionsView impact
37th AIAA Fluid Dynamics Conference and Exhibit, 2007
ABSTRACT
Bookmarks Related papers MentionsView impact
45th AIAA Aerospace Sciences Meeting and Exhibit, 2007
Bookmarks Related papers MentionsView impact
46th AIAA Aerospace Sciences Meeting and Exhibit, 2008
ABSTRACT
Bookmarks Related papers MentionsView impact
International Journal of Heat and Fluid Flow, 2014
ABSTRACT The existence of meandering superstructures in a turbulent boundary layer overlying irre... more ABSTRACT The existence of meandering superstructures in a turbulent boundary layer overlying irregular roughness is explored with high-frame-rate particle-image velocimetry measurements within the roughness sublayer at moderate Reynolds number. Elongated streamwise fields of view reconstructed from this data using a Taylor’s hypothesis approach revealed spanwise-meandering regions of low-streamwise-momentum fluid that extended several boundary-layer thicknesses in the streamwise direction. Such signatures are consistent with previous observations of superstructures in smooth-wall turbulence. Counter-rotating wall-normal vortex cores were found to reside along the spanwise boundaries of these superstructure patterns, consistent with the spatial characteristics of hairpin vortex packets.
Bookmarks Related papers MentionsView impact
41st AIAA Fluid Dynamics Conference and Exhibit, 2011
Bookmarks Related papers MentionsView impact
40th Fluid Dynamics Conference and Exhibit, 2010
ABSTRACT The combined impact of irregular surface roughness and moderate favorable-pressure-gradi... more ABSTRACT The combined impact of irregular surface roughness and moderate favorable-pressure-gradient (FPG) conditions (K 2.5 x10-7) on the structure of a turbulent boundary layer is assessed using two-dimensional particle image velocimetry (PIV) measurements in the streamwise--wall-normal plane. The roughness under consideration is replicated from a turbine blade damaged by deposition of foreign materials and contains a broad range of topographical scales. These measurements are compared to measurements of smooth-wall flow under both identical FPG conditions as well as zero-pressure-gradient (ZPG) conditions in order to reveal the synergistic impact of roughness and FPG conditions on the underlying structure of the flow. While vortex organization is found to persist under both smooth- and rough-wall FPG conditions, its characteristics are altered compared to smooth-wall ZPG flow. Inspection of instantaneous velocity fields reveals this organization to be focused closer to the wall in the smooth- wall FPG case, with a shallower inclination angle noted as well as an elongated streamwise extent. In contrast, the rough-wall FPG results reveal packet structures more consistent with the smooth-wall ZPG case, indicating that roughness mitigates the FPG-induced focusing of these structural attributes toward the wall. Two-point correlations of streamwise velocity support these instantaneous observations.
Bookmarks Related papers MentionsView impact
Biochemistry, Jan 25, 2005
The action of anthrax toxin begins when the protective antigen (PA(83), 83 kDa) moiety binds to a... more The action of anthrax toxin begins when the protective antigen (PA(83), 83 kDa) moiety binds to a mammalian cell-surface receptor and is cleaved by a furin-family protease into two fragments: PA(20) (20 kDa) and PA(63) (63 kDa). After PA(20) dissociates, receptor-bound PA(63) spontaneously oligomerizes to form a heptameric species, which is able to bind the two enzymatic components of the toxin and transport them to the cytosol. Treatment of PA(83) with trypsin yielded PA(63) and a form of PA(20) lacking unstructured regions at the N- and C-termini. We labeled these fragments with dyes capable of fluorescence resonance energy transfer to quantify their association in solution. We kinetically determined that the equilibrium dissociation constant is 190 nM with a dissociation rate constant, k(off), of 3.3 x 10(-)(2) s(-)(1) (t(1/2) of 21 s). A two-step association process was observed using stopped-flow: a fast bimolecular step (k(on) = 1.4 x 10(5) M(-)(1) s(-)(1)) was followed by a s...
Bookmarks Related papers MentionsView impact
Aggregation of suspended yeast cells in a small-scale ultrasonic standing wave field has been mon... more Aggregation of suspended yeast cells in a small-scale ultrasonic standing wave field has been monitored and quan- tified. The aggregation effect is based on the acoustic radiation force, which concentrates the cells in clumps. The ultrasonic chamber employed (1.9 MHz, one wavelength pathlength) had a sonication volume of 60 µl. The aggreg- ation process was observed from above the transducer
Bookmarks Related papers MentionsView impact
Physical review. B, Condensed matter, Jan 15, 1993
Bookmarks Related papers MentionsView impact
Microfluidics and Nanofluidics, 2015
ABSTRACT The development of an experimental protocol to investigate the flow field produced by th... more ABSTRACT The development of an experimental protocol to investigate the flow field produced by the interaction of two immiscible liquids flowing through a porous network is reported. The experimental protocol allows simultaneous quantification of the velocity distribution in a multi-liquid system based on the microscopic particle image velocimetry technique. The experimental challenges associated with this unique application are discussed, including two-liquid imaging and interface tracking, and solutions that couple refractive index matching and fluorescent signal separation are described. The technique was applied to both single- and two-liquid flows in a two-dimensional pore network comprising a staggered array of circular pillars wherein the flow was driven by a steady pressure gradient. Both drainage and imbibition were considered herein with a focus on fluid–fluid front migration and effects owing to the passage of the interface. The velocity distribution obtained for these two-liquid-phase flow scenarios revealed several peculiarities when compared to the reference case of single-liquid-phase flow. In particular, the instabilities associated with the interfacial processes propagate downstream and perturb the flow field, resulting in dramatic differences from the regular and periodic flow paths typical of steady-state, single-phase flow. Additionally, the passage of the interface does not restore previous flow patterns, but instead yields complex preferential flow paths that mutually interact with residual trapped pockets of fluid. Such dynamical events must be quantified in order to properly model the pore-scale physics central to fully understanding the wealth of practical applications represented by this model flow system.
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
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Tony Perry, et al. (J. Fluid Mech., v. 439, 2001) have recently contributed to the discussion con... more Tony Perry, et al. (J. Fluid Mech., v. 439, 2001) have recently contributed to the discussion concerning the reasons for systematic deviations with Re's (Reynolds numbers) in the Princeton ``Super-Pipe'' data. Perry et al. demonstrate that the deviation of the constant within the ``log-law'' is compatible with the ``Colebrook formula'' for transitionally rough pipes. Since the experiments were completed, Lex
Bookmarks Related papers MentionsView impact
ABSTRACT
Bookmarks Related papers MentionsView impact
ABSTRACT
Bookmarks Related papers MentionsView impact