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rss_1.0 Recursos de colección

Caltech Authors (92,099 recursos)
Repository of works by Caltech published authors.

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Mostrando recursos 1 - 20 de 40,705

1. Effect of Concave Wall Geometry on Heat Transfer in Hypersonic Boundary Layers - Flaherty, W.; Austin, J. M.
Heat transfer measurements are made to investigate the effects of concave surface curvature on a high-stagnation enthalpy boundary layer in a Mach 5.1 flow. Experiments are carried out using two curved models with 16 and 25 degree turning angles, and baseline planar models (at plate and linear ramp) for comparative study. Streamwise and spanwise cross-sections are obtained. Significant destabilization of the boundary layer is observed over the adverse pressure gradient geometries. For the curved surfaces, the heat flux distribution appears to exhibit a quadratic dependence with streamwise distance, in contrast with the linear dependence observed on the linear ramp.

2. Exhaust of Underexpanded Jets from Finite Reservoirs - Orescanin, M. M.; Prisco, D.; Austin, J. M.
We examine the response of an underexpanded jet to a depleting, finite reservoir with experiments and simulations. An open-ended shock tube facility with variable reservoir length is used to obtain images of nitrogen and helium jet structures at successive instances during the blowdown from initial pressure ratios of up to 250. The reservoir and ambient pressures are simultaneously measured to obtain the instantaneous pressure ratio. We estimate the time-scales for jet formation and reservoir depletion as a function of the specific heat ratio of the gas and the initial pressure ratio. The jet structure formation time-scale is found to become approximately independent of pressure ratio for ratios...

3. The Calibration of the WISE W1 and W2 Tully-Fisher Relation - Neill, J. D.; Seibert, Mark; Tully, R. Brent; Courtois, Hélène; Sorce, Jenny G.; Jarrett, T. H.; Scowcroft, Victoria; Masci, Frank J.
In order to explore local large-scale structures and velocity fields, accurate galaxy distance measures are needed. We now extend the well-tested recipe for calibrating the correlation between galaxy rotation rates and luminosities—capable of providing such distance measures—to the all-sky, space-based imaging data from the Wide-field Infrared Survey Explorer (WISE) W1 (3.4 μm) and W2 (4.6 μm) filters. We find a correlation of line width to absolute magnitude (known as the Tully-Fisher relation, TFR) of M^(b,i,k,ɑ)_(W1) = -20.35 - 9.56(log W^i_(mx) - 2.5) (0.54 mag rms) and M^(b,i,k,ɑ)_(W2) = -19.76 - 9.74 (log W^i_(mx)-2.5)(0.56 mag rms) from 310 galaxies in 13...

4. Evaluation of Hypervelocity Carbon Dioxide Blunt Body Experiments in an Expansion Tube Facility - Sharma, M.; Swantek, A. B.; Flaherty, W.; Austin, J. M.; Doraiswamy, S.; Candler, G. V.
This work represents efforts to study high-enthalpy carbon dioxide flows in anticipation of the upcoming Mars Science Laboratory (MSL) and future missions. The current study extends the previous presentation of experimental results by the comparison now with axisymmetric simulations incorporating detailed thermochemical modeling. The work is motivated by observed anomalies between experimental and numerical studies in hypervelocity impulse facilities. In this work, experiments are conducted in the Hypervelocity Expansion Tube (HET) which, by virtue of its flow acceleration process, exhibits minimal freestream dissociation in comparison to reflected shock tunnels. This simplifies the comparison with computational result as freestream dissociation and considerable thermochemical excitation can be neglected. Shock shapes of the...

5. Reflected Shock Bifurcation in a Square Channel - Khokhlov, A. M.; Austin, J. M.; Bacon, C.; Aithal, S.; Riley, K.
We examine the bifurcation of a reflected shock in a three-dimensional, square channel through numerical simulations using a distributed memory parallel adaptive mesh refinement, Navier-Stokes solver with multicomponent equation of state and microscopic transport. The three-dimensional, rather than axisymmetric, geometry introduces considerable complexity into the flow structures, particularly in the vicinity of the corners. Spanwise cross-sections show the boundary layer growth is significantly reduced in the corner regions, where the shape of the turbulent jet and recirculation regions are modified. This appears to be consistent with existing experimental studies which report the boundary layer in the corner region is deformed and the propagation velocity is reduced. A pair...

6. Application of Fast Pressure Sensitive Paint in Hypervelocity Flow - Flaherty, W.; Crafton, J.; Elliott, G. S.; Austin, J. M.
The development of fast responding pressure sensitive paints for measurements in high-enthalpy, hypersonic flows is reported. Data are obtained for at plate boundary layers in an impulse facility with typical test gas times on the order of hundreds of microseconds. The fast pressure sensitive paint is found to have the required response time and sufficient signal level to visualize vortical boundary layer structures in a Mach 5.12 freestream. The flow behind protuberance strips with different geometries is evaluated with measurements of the vortex frequency and diameter, as well as breakdown distance. Comparisons with static pressure measurements made using pressure taps show differences of up to a...

7. Converging cylindrical shocks in ideal magnetohydrodynamics - Pullin, D. I.; Mostert, W.; Wheatley, V.; Samtaney, R.
We consider a cylindrically symmetrical shock converging onto an axis within the framework of ideal, compressible-gas non-dissipative magnetohydrodynamics (MHD). In cylindrical polar co-ordinates we restrict attention to either constant axial magnetic field or to the azimuthal but singular magnetic field produced by a line current on the axis. Under the constraint of zero normal magnetic field and zero tangential fluid speed at the shock, a set of restricted shock-jump conditions are obtained as functions of the shock Mach number, defined as the ratio of the local shock speed to the unique magnetohydrodynamic wave speed ahead of the shock, and also...

8. Design and initial characterization of a compact, ultra high vacuum compatible, low frequency, tilt accelerometer - O'Toole, A.; Peña Arellano, F. E.; Rodionov, A. V.; Shaner, M.; Sobacchi, E.; Dergachev, V.; DeSalvo, R.; Asadoor, M.; Bhawal, A.; Gong, P.; Kim, C.; Lottarini, A.; Minenkov, Y.; Murphy, C.
A compact tilt accelerometer with high sensitivity at low frequency was designed to provide low frequency corrections for the feedback signal of the Advanced Laser Interferometer Gravitational Wave Observatory active seismic attenuation system. It has been developed using a Tungsten Carbide ceramic knife-edge hinge designed to avoid the mechanical 1/f noise believed to be intrinsic in polycrystalline metallic flexures. Design and construction details are presented; prototype data acquisition and control limitations are discussed. The instrument's characterization reported here shows that the hinge is compatible with being metal-hysteresis-free, and therefore also free of the 1/f noise generated by the dislocation Self-Organized...

9. Ignition and chemical kinetics of acrolein–oxygen–argon mixtures behind reflected shock waves - Chatelain, K.; Mével, R.; Menon, S.; Blanquart, G.; Shepherd, J. E.
In order to address increasing greenhouse gas emissions, the future fossil fuel shortage and increasingly stringent pollutant emission regulations, a variety of biofuels are being progressively incorporated into conventional transportation fuels. Despite the beneficial impact of biofuels on most regulated pollutants, their combustion induces the increase of a variety of aldehydes that are being considered for specific regulations due to their high toxicity. One of the most hazardous aldehyde compounds is acrolein, C_2H_3CHO. Despite its high toxicity and increased formation during bioalcohol and biodiesel combustion, no experimental data are available for acrolein combustion. In the present study, we have investigated...

10. Replication stress by Py–Im polyamides induces a non-canonical ATR-dependent checkpoint response - Martínez, Thomas F.; Philips, John W.; Karanja, Kenneth K.; Polaczek, Piotr; Wang, Chieh-Mei; Li, Benjamin C.; Campbell, Judith L.; Dervan, Peter B.
Pyrrole–imidazole polyamides targeted to the androgen response element were cytotoxic in multiple cell lines, independent of intact androgen receptor signaling. Polyamide treatment induced accumulation of S-phase cells and of PCNA replication/repair foci. Activation of a cell cycle checkpoint response was evidenced by autophosphorylation of ATR, the S-phase checkpoint kinase, and by recruitment of ATR and the ATR activators RPA, 9-1-1, and Rad17 to chromatin. Surprisingly, ATR activation was accompanied by only a slight increase in single-stranded DNA, and the ATR targets RPA2 and Chk1, a cell cycle checkpoint kinase, were not phosphorylated. However, ATR activation resulted in phosphorylation of the...

11. Allosteric response and substrate sensitivity in peptide binding of the signal recognition particle - Wang, Connie Y.; Miller, Thomas F., III
We characterize the conformational dynamics and substrate selectivity of the signal recognition particle (SRP) using a thermodynamic free energy cycle approach and microsecond-timescale molecular dynamics simulations. The SRP is a central component of the co-translational protein targeting machinery that binds to the N-terminal signal peptide (SP) of nascent proteins. We determined the shift in relative conformational stability of the SRP upon substrate binding to quantify allosteric coupling between SRP domains. In particular, for dipeptidyl aminopeptidase, an SP that is recognized by the SRP for co-translational targeting, it is found that substrate binding induces substantial changes in the SRP towards configurations...

12. An Unusual Ligand Coordination Gives Rise to a New Family of Rhodium Metalloinsertors with Improved Selectivity and Potency - Komor, Alexis C.; Barton, Jacqueline K.
Rhodium metalloinsertors are octahedral complexes that bind DNA mismatches with high affinity and specificity and exhibit unique cell-selective cytotoxicity, targeting mismatch repair (MMR)-deficient cells over MMR-proficient cells. Here we describe a new generation of metalloinsertors with enhanced biological potency and selectivity, in which the complexes show Rh–O coordination. In particular, it has been found that both Δ- and Λ-[Rh(chrysi)(phen)(DPE)]2+ (where chrysi =5,6 chrysenequinone diimmine, phen =1,10-phenanthroline, and DPE = 1,1-di(pyridine-2-yl)ethan-1-ol) bind to DNA containing a single CC mismatch with similar affinities and without racemization. This is in direct contrast with previous metalloinsertors and suggests a possible different binding disposition for...

13. Measurement of jet fragmentation in PbPb and pp collisions at √sNN = 2.76 TeV - Chatrchyan, S.; Apresyan, A.; Bornheim, A.; Bunn, J.; Chen, Y.; Di Marco, E.; Duarte, J.; Kcira, D.; Mott, A.; Newman, H. B.; Pena, C.; Rogan, C.; Spiropulu, M.; Timciuc, V.; Wilkinson, R.; Xie, S.; Zhu, R. Y.; Dias, F. A.
The jet fragmentation function of inclusive jets with transverse momentum p_T above 100GeV/c in PbPb collisions has been measured using reconstructed charged particles with p_T above 1GeV/c in a cone of radius 0.3 around the jet axis. A data sample of PbPb collisions collected in 2011 at a nucleon-nucleon center-of-mass energy of √sNN = 2.76 TeV corresponding to an integrated luminosity of 150μb^(−1) is used. The results for PbPb collisions as a function of collision centrality and jet transverse momentum are compared to reference distributions based on pp data collected at the same center-of-mass energy in 2013, with an integrated...

14. Thermoelectric Transport in Cu_7PSe_6 with High Copper Ionic Mobility - Weldert, Kai S.; Zeier, Wolfgang G.; Day, Tristan W.; Panthöfer, Martin; Snyder, G. Jeffrey; Tremel, Wolfgang
Building on the good thermoelectric performances of binary superionic compounds like Cu_2Se, Ag_2Se and Cu_2S, a better and more detailed understanding of phonon-liquid electron-crystal (PLEC) thermoelectric materials is desirable. In this work we present the thermoelectric transport properties of the compound Cu_7PSe_6 as the first representative of the class of argyrodite-type ion conducting thermoelectrics. With a huge variety of possible compositions and high ionic conductivity even at room temperature, the argyrodites represent a very good model system to study structure–property relationships for PLEC thermoelectric materials. We particularly highlight the extraordinary low thermal conductivity of Cu_7PSe_6 below the glass limit, which...

15. On network coding and routing in dynamic wireless multicast networks - Ho, Tracey; Jin, Jia-Qi
We compare multicast network coding and routing for a time-varying wireless network model with interference- determined link capacities. We use dynamic back pressure algorithms that are optimal for intra-session network coding and routing respectively. Our results suggest that under such conditions, the gap in multicast capacity between network coding and routing can decrease relative to a collision-based wireless model with fixed link capacities.

16. Investigation of Cavity Flow Using Fast-Response Pressure Sensitive Paint - Flaherty, W.; Reedy, Todd M.; Elliott, Gregory S.; Austin, J. M.; Schmit, Ryan F.; Crafton, J.
An experimental study was conducted to investigate the pressure fluctuations on the entire side wall of a rectangular cavity with an L/D of 5.67 using fast-response pressure sensitive paint. Additionally, the performance of four different passive flow-control devices was quantified. Experiments were conducted in the Trisonic Gasdynamics Facility at the Air Force Research Laboratory at Mach 0.7 and 1.5. The frequency spectrum (including Rossiter tones) and sound pressure levels (SPLs) obtained from the pressure sensitive paint (PSP) measurements are validated against data taken with conventional dynamic pressure sensors. The complex flow phenomena over the cavity wall were visualized, and full wall pressure spectra were calculated. The rod in...

17. Irreversible Phenomena: Ignitions, Combustion and Detonation Waves [Book Review] - Austin, Joanna M.
A broad range of combustion phenomena occur that exhibit inherently stochastic behavior, producing fascinating observations but also significant challenges in experiments, simulations, and predictive models. Although the turbulence and turbulent combustion literature is rich in statistical modeling approaches (for example, texts by Pope [1] or Peters [2], among many others), the stochastic nature of ignition processes, shock-induced combustion, and detonation waves has been much less comprehensively addressed. This book is focused on the latter applications and offers a rather unique viewpoint in comparison with the existing combustion literature.

18. Experimental simulations of the May 18, 1980 directed blast at Mount St. Helens, WA - Orescanin, Mara M.; Austin, Joanna M.; Kieffer, Susan W.
The 1980 directed blast at Mount St. Helens erupted from a high-pressure magma chamber into atmospheric conditions at a pressure ratio of ~150:1, producing a high-velocity dusty gas flow. Decompression from even modestly high pressure ratios (>2:1) produces supersonic flow and thus, this event was modeled as a supersonic underexpanded jet by Kieffer (1981). Steady-state underexpanded jets have a complex geometrical structure in which there is an abrupt, stationary, normal shock wave, called the Mach disk shock. For steady flow, a log-linear relationship between pressure ratio and Mach disk standoff distance, known as the Ashkenas-Sherman relation, is valid for pressure...

19. Design and Demonstration of a New Small-Scale Jet Noise Experiment - Fontaine, Ryan A.; Bobbitt, Brock; Elliott, Gregory S.; Austin, Joanna M.; Freund, Jonathan B.
A facility capable of acoustic and velocity field measurements of high-speed jets has recently been built and tested. The anechoic chamber that houses the jet has a 2.1 m × 2.3 m × 2.5 m wedge tip to wedge tip working volume. We aim to demonstrate that useful experiments can be performed in such a relatively small facility for a substantially lower cost than in larger facility. Rapid prototyping allows for quick manufacturing of both simple and complex geometry nozzles. Sideline and 30° downstream acoustic measurements between 400 Hz and 100 kHz agree well with accepted results. Likewise, nozzle exit-plane data obtained using particle image velocimetry are...

20. Heat Transfer on a Double Wedge Geometry in Hypervelocity Air and Nitrogen Flows - Swantek, A. B.; Austin, J. M.
We investigate shock wave/boundary-layer interaction and resulting heat transfer in hypervelocity double wedge flows. An expansion tube is used to generate air and nitrogen flows with stagnation enthalpies ranging from 2.1-8.0 MJ/kg and Mach numbers from 4-7. The range of free stream conditions were selected to investigate the impact of thermochemical effects by i) systematically varying the chemical composition from nitrogen to air while maintaining constant the stagnation enthalpy or the Mach number, and ii) varying the stagnation enthalpy. Flow features are visualized with schlieren photography, and heat transfer is measured using fast response coaxial thermocouples. Data are presented for both nitrogen and air test...

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