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rss_1.0 Recursos de colección

Caltech Authors (92,131 recursos)
Repository of works by Caltech published authors.

Type = Article

Mostrando recursos 1 - 20 de 35,868

1. Exploring the Geometry of the Space of Shells - Heeren, B.; Rumpf, M.; Schröder, P.; Wardetzky, M.; Wirth, B.
We prove both in the smooth and discrete setting that the Hessian of an elastic deformation energy results in a proper Riemannian metric on the space of shells (modulo rigid body motions). Based on this foundation we develop a time- and space-discrete geodesic calculus. In particular we show how to shoot geodesics with prescribed initial data, and we give a construction for parallel transport in shell space. This enables, for example, natural extrapolation of paths in shell space and transfer of large nonlinear deformations from one shell to another with applications in animation, geometric, and physical modeling. Finally, we examine...

2. Observations of large-scale fluid transport by laser-guided plankton aggregations - Wilhelmus, Monica M.; Dabiri, John O.
Diel vertical migration of plankton has been proposed to affect global ocean circulation to a degree comparable to winds and tides. This biomixing process has never been directly observed, however, due to the inability to predict its occurrence in situ or to reproduce it in a laboratory setting. Furthermore, it has been argued that the energy imparted to the ocean by plankton migrations occurs at the scale of individual organisms, which is too small to impact ocean mixing. We describe the development of a multi-laser guidance system that leverages the phototactic abilities of plankton to achieve controllable vertical migrations concurrently...

3. How calcium affects oxygen formation - Lionetti, Davide; Agapie, Theodor
Calcium is an essential component of the catalyst that forms oxygen from water during photosynthesis. It seems that part of calcium's job is to enable the release of oxygen from this catalyst.

4. Timescales and mechanisms of formation of amorphous silica coatings on fresh basalts at Kilauea Volcano, Hawai’i - Chemtob, Steven M.; Rossman, George R.
Young basalts from Kilauea Volcano, Hawai'i, frequently feature opaque surface coatings, 1–80 μm thick, composed of amorphous silica and Fe-Ti oxides. These coatings are the product of interaction of the basaltic surface with volcanically-derived acidic fluids. Previous workers have identified these coatings in a variety of contexts on Hawai'i, but the timescales of coating development, coating growth rates, and factors controlling lateral coating heterogeneity were largely unconstrained. We sampled and analyzed young lava flows (of varying ages, from hours to ~ 40 years) along Kilauea's southwest and east rift zones to characterize variation in silica coating properties across the landscape....

5. Investigation of the effect of a bumpy base on granular segregation and transport properties under vertical vibration - Liao, C. C.; Hunt, M. L.; Hsiau, S. S.; Lu, S. H.
This study experimentally investigates the effect of a bumpy base on the Brazil-nut phenomenon in a vertically vibrated granular bed. The rise dynamics of an intruder is determined by the particle tracking method. The results indicate that the rise time increases with an increase in the base roughness, and the variation of the rise time with different base factors is more pronounced with smaller vibration acceleration and higher vibration frequency. A theoretical model is employed to measure the penetration length of the intruder and the drag force between the intruder and the immersed beads. The penetration length is reduced and...

6. Rapidly evaluating the compact-binary likelihood function via interpolation - Smith, R. J. E.; Hanna, C.; Mandel, I.; Vecchio, A.
Bayesian parameter estimation on gravitational waves from compact-binary coalescences (CBCs) typically requires millions of template waveform computations at different values of the parameters describing the binary. Sampling techniques such as Markov chain Monte Carlo and nested sampling evaluate likelihoods and, hence, compute template waveforms, serially; thus, the total computational time of the analysis scales linearly with that of template generation. Here we address the issue of rapidly computing the likelihood function of CBC sources with nonspinning components. We show how to efficiently compute the continuous likelihood function on the three-dimensional subspace of parameters on which it has a nontrivial dependence—the...

7. Impact of dissolution on the sedimentary record of the Paleocene–Eocene thermal maximum - Bralower, Timothy J.; Kelly, D. Clay; Gibbs, Samantha; Farley, Kenneth; Eccles, Laurie; Lindemann, T. Logan; Smith, Gregory J.
The input of massive amounts of carbon to the atmosphere and ocean at the Paleocene–Eocene Thermal Maximum (PETM; ∼55.53 Ma) resulted in pervasive carbonate dissolution at the seafloor. At many sites this dissolution also penetrated into the underlying sediment column. The magnitude of dissolution at and below the seafloor, a process known as chemical erosion, and its effect on the stratigraphy of the PETM, are notoriously difficult to constrain. Here, we illuminate the impact of dissolution by analyzing the complete spectrum of sedimentological grain sizes across the PETM at three deep-sea sites characterized by a range of bottom water dissolution...

8. Unsteady high-pressure flow experiments with applications to explosive volcanic eruptions - Orescanin, M. M.; Austin, J. M.; Kieffer, S. W.
Motivated by the hypothesis that volcanic blasts can have supersonic regions, we investigate the role of unsteady flow in jets from a high-pressure finite reservoir. We examine the processes for formation of far-field features, such as Mach disk shocks, by using a shock tube facility and numerical experiments to investigate phenomena to previously unobtained pressure ratios of 250:1. The Mach disk shock initially forms at the edges of the vent and moves toward the centerline. The shock is established within a few vent diameters and propagates downstream toward the equilibrium location as the jet develops. The start-up process is characterized...

9. 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...

10. Direct measurement of neon production rates by (α,n) reactions in minerals - Cox, Stephen E.; Farley, Kenneth A.; Cherniak, Daniele J.
The production of nucleogenic neon from alpha particle capture by ^(18)O and ^(19)F offers a potential chronometer sensitive to temperatures higher than the more widely used (U-Th)/He chronometer. The accuracy depends on the cross sections and the calculated stopping power for alpha particles in the mineral being studied. Published ^(18)O(α,n)^(21)Ne production rates are in poor agreement and were calculated from contradictory cross sections, and therefore demand experimental verification. Similarly, the stopping powers for alpha particles are calculated from SRIM (Stopping Range of Ions in Matter software) based on a limited experimental dataset. To address these issues we used a particle...

11. Mitochondrial genomes of Trichinella species and genotypes – a basis for diagnosis, and systematic and epidemiological explorations - Mohandas, Namitha; Pozio, Edoardo; La Rosa, Giuseppe; Korhonen, Pasi K.; Young, Neil D.; Koehler, Anson V.; Hall, Ross S.; Sternberg, Paul W.; Boag, Peter R.; Jex, Aaron R.; Chang, Bill; Gasser, Robin B.
In the present study we sequenced or re-sequenced, assembled and annotated 15 mitochondrial genomes representing the 12 currently recognised taxa of Trichinella using a deep sequencing-coupled approach. We then defined and compared the gene order in individual mitochondrial genomes (∼14 to 17.7 kb), evaluated genetic differences among species/genotypes and re-assessed the relationships among these taxa using the mitochondrial nucleic acid or amino acid sequence data sets. In addition, a rich source of mitochondrial genetic markers was defined that could be used in future systematic, epidemiological and population genetic studies of Trichinella. The sequencing-bioinformatic approach employed herein should be applicable to...

12. 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...

13. 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...

14. 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...

15. 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...

16. 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...

17. R3 receptor tyrosine phosphatases: Conserved regulators of receptor tyrosine kinase signaling and tubular organ development - Jeon, Mili; Zinn, Kai
R3 receptor tyrosine phosphatases (RPTPs) are characterized by extracellular domains composed solely of long chains of fibronectin type III repeats, and by the presence of a single phosphatase domain. There are five proteins in mammals with this structure, two in Drosophila and one in Caenorhabditis elegans. R3 RPTPs are selective regulators of receptor tyrosine kinase (RTK) signaling, and a number of different RTKs have been shown to be direct targets for their phosphatase activities. Genetic studies in both invertebrate model systems and in mammals have shown that R3 RPTPs are essential for tubular organ development. They also have important functions...

18. 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...

19. 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...

20. 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...

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