Repository of works by Caltech published authors.
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Communication: Predictive partial linearized path integral simulation of condensed phase electron transfer dynamics - Huo, Pengfei; Miller, Thomas F., III; Coker, David F.
A partial linearized path integral approach is used to calculate the condensed phase electron transfer (ET) rate by directly evaluating the flux-flux/flux-side quantum time correlation functions. We demonstrate for a simple ET model that this approach can reliably capture the transition between non-adiabatic and adiabatic regimes as the electronic coupling is varied, while other commonly used semi-classical methods are less accurate over the broad range of electronic couplings considered. Further, we show that the approach reliably recovers the Marcus turnover as a function of thermodynamic driving force, giving highly accurate rates over four orders of magnitude from the normal to...
Hydrogen Isotope Ratios of Mouse Tissues are Influenced by a Variety of Factors Other than Diet - DeNiro, Michael J.; Epstein, Samuel; Estep, Marilyn F.
In a recent report, Estep and Dabrowski (I) presented data which they claimed defined the relationship between the stable hydrogen isotopic ratios of an animal's tissues and those of its food and water sources. On the basis of their interpretation of these data, they suggested that the isotopic composition of animal hydrogen records information about an animal's diet. We wish to comment on their report.
Demonstration of surface electron rejection with interleaved germanium detectors for dark matter searches - Agnese, R.; Cornell, B.; Golwala, S. R.; Moore, D. C.; Nelson, R. H.
The SuperCDMS experiment in the Soudan Underground Laboratory searches for dark matter with a 9-kg array of cryogenic germanium detectors. Symmetric sensors on opposite sides measure both charge and phonons from each particle interaction, providing excellent discrimination between electron and nuclear recoils, and between surface and interior events. Surface event rejection capabilities were tested with two ^(210)Pb sources producing ∼130 beta decays/hr. In ∼800 live hours, no events leaked into the 8–115 keV signal region, giving upper limit leakage fraction 1.7 × 10^(−5) at 90% C.L., corresponding to < 0.6 surface event background in the future 200-kg SuperCDMS SNOLAB experiment.
Compositional Diversity in the Atmospheres of Hot Neptunes, with Application to GJ 436b - Moses, J. I.; Line, M. R.; Visscher, C.; Richardson, M. R.; Nettelmann, N.; Fortney, J. J.; Barman, T. S.; Stevenson, K. B.; Madhusudhan, N
Neptune-sized extrasolar planets that orbit relatively close to their host stars—often called "hot Neptunes"—are common within the known population of exoplanets and planetary candidates. Similar to our own Uranus and Neptune, inefficient accretion of nebular gas is expected produce hot Neptunes whose masses are dominated by elements heavier than hydrogen and helium. At high atmospheric metallicities of 10-10,000 times solar, hot Neptunes will exhibit an interesting continuum of atmospheric compositions, ranging from more Neptune-like, H_2-dominated atmospheres to more Venus-like, CO_2-dominated atmospheres. We explore the predicted equilibrium and disequilibrium chemistry of generic hot Neptunes and find that the atmospheric composition varies...
Lack of vascular endothelial growth factor receptor-2/Flk1 signaling does not affect substantia nigra development - Hermann, Andreas; Loewenbrück, Kai F.; Boldt, Änne; Fiedler, Christiane; Maisel, Martina; Kalucka, Joanna; Schwarz, Johannes; Breier, Georg; Storch, Alexander
Oxygen tension is critical for proliferation of human and murine midbrain-derived neural precursor cells (mNPCs). Lack of hypoxia-inducible factor-1α (HIF1α) impairs midbrain dopaminergic neurogenesis which could be rescued by vascular endothelial growth factor (VEGF) via VEGFR-2 signaling. Here, we conditionally inactivated the VEGFR-2, encoded by the fetal liver kinase 1 (Flk1) gene, in murine NPCs to determine its role in proliferation and survival in vitro as well as survival of dopaminergic neurons in vivo. Flk1 conditional knock-out (Flk1 CKO) mice showed no general brain phenotype. There was no midbrain-specific impairment of NPC proliferation as seen in HIF1α CKO mice. In...
Keck and VLT AO observations and models of the uranian rings during the 2007 ring plane crossings - de Pater, Imke; Dunn, David E.; Stam, Daphne M.; Showalter, Mark R.; Hammel, Heidi B.; Min, Michiel; Hartung, Markus; Gibbard, Seran G.; van Dam, Marcos A.; Matthews, Keith
We present observations of the uranian ring system at a wavelength of 2.2 μm, taken between 2003 and 2008 with NIRC2 on the W.M. Keck telescope in Hawaii, and on 15–17 August 2007 with NaCo on the Very Large Telescope (VLT) in Chile. Of particular interest are the data taken around the time of the uranian ring plane crossing with Earth on 16 August 2007, and with the Sun (equinox) on 7 December 2007. We model the data at the different viewing aspects with a Monte Carlo model to determine: (1) the normal optical depth τ_0, the location, and the...
Some Interior Problems of Hydromagnetics - Cole, J. D.; Huth, J. H.
The static boundary problems of line currents and dipoles immersed in a perfectly conducting static fluid are considered first. The perturbing effect of moving fluid on the magnetostatic boundary about an isolated line current is then investigated. In this case, the initial circular boundary is distorted into an ellipse with major axis transverse to the direction of flow.
Nonhydrostatic effects and the determination of icy satellites’ moment of inertia - Gao, Peter; Stevenson, David J.
We compare the moment of inertia (MOI) of a simple hydrostatic, two layer body as determined by the Radau–Darwin Approximation (RDA) to its exact hydrostatic MOI calculated to first order in the parameter q = Ω^2R^3/GM, where Ω, R, and M are the spin angular velocity, radius, and mass of the body, and G is the gravitational constant. We show that the RDA is in error by less than 1% for many configurations of core sizes and layer densities congruent with those of solid bodies in the Solar System. We then determine the error in the MOI of icy satellites...
Stimulated Brillouin Scattering Suppression With a Chirped Laser Seed: Comparison of Dynamical Model to Experimental Data - Petersen, Eliot; Yang, Zhi Yi; Satyan, Naresh; Vasilyev, Arseny; Rakuljic, George; Yariv, Amnon; White, Jeffrey O.
A numerical model is developed to simulate stimulated Brillouin scattering (SBS) in high power single-mode fiber amplifiers. The time dependent model incorporates both laser and Stokes wave amplification and initiates the Brillouin scattering from thermal phonons. A frequency chirped laser is used as the seed to suppress SBS. Experiments with Yb-doped fiber amplifiers show good agreement with the modeling. Using experimentally determined parameters, the model is used to predict chirp requirements for multi-kilowatt amplifiers with tens of meters of delivery fiber. A comparison is made between a chirped seed source and random phase modulation for SBS suppression.
Dynamical supersymmetry breaking in theories without Lagrangians - Maruyoshi, Kazunobu; Tachikawa, Yuji; Yan, Wenbin; Yonekura, Kazuya
We demonstrate that the supersymmetry can be dynamically broken even in theories without a Lagrangian. The example we study is the four-dimensional SU(N) gauge theory coupled to a strongly coupled superconformal theory, called T_N, which does not have a Lagrangian description at present. Such a theory without Lagrangians can be analyzed due to the supersymmetry and duality. The model is a direct generalization of the model of supersymmetry breaking on deformed moduli space in supersymmetric QCD with an SU(2) gauge group.
Millisecond pulsars cannot account for the inner Galaxy’s GeV excess - Hooper, Dan; Cholis, Ilias; Linden, Tim; Siegal-Gaskins, Jennifer M.; Slatyer, Tracy R.
Using data from the Fermi Gamma-Ray Space Telescope, a spatially extended component of gamma rays has been identified from the direction of the Galactic center, peaking at energies of ∼2–3 GeV. More recently, it has been shown that this signal is not confined to the innermost hundreds of parsecs of the Galaxy, but instead extends to at least ∼3 kpc from the Galactic center. While the spectrum, intensity, and angular distribution of this signal is in good agreement with predictions from annihilating dark matter, it has also been suggested that a population of unresolved millisecond pulsars could be responsible for this excess...
Model-based scaling of the streamwise energy density in high-Reynolds-number turbulent channels - Moarref, Rashad; Sharma, Ati S.; Tropp, Joel A.; McKeon, Beverley J.
We study the Reynolds-number scaling and the geometric self-similarity of a gainbased,
low-rank approximation to turbulent channel flows, determined by the resolvent
formulation of McKeon & Sharma (J. Fluid Mech., vol. 658, 2010, pp. 336–382),
in order to obtain a description of the streamwise turbulence intensity from direct
consideration of the Navier–Stokes equations. Under this formulation, the velocity
field is decomposed into propagating waves (with single streamwise and spanwise
wavelengths and wave speed) whose wall-normal shapes are determined from the
principal singular function of the corresponding resolvent operator. Using the accepted
scalings of the mean velocity in wall-bounded turbulent flows, we establish that the
resolvent operator admits three classes...
Accurate Mg/Ca, Sr/Ca, and Ba/Ca ratio measurements in carbonates by SIMS and NanoSIMS and an assessment of heterogeneity in common calcium carbonate standards - Gabitov, R. I.; Gagnon, A. C.; Guan, Y.; Eiler, J. M.; Adkins, J. F.
As archives of past climate variability, the micron and sub-micron scales of element:calcium (Me/Ca) variability in both biogenic and inorganic carbonates contain important geochemical information. Ideally working at smaller and smaller scales leads to higher temporal resolution of past changes, but more often it has revealed the strong overprint of other processes on the climate signal. Therefore, the role of SIMS and NanoSIMS techniques in studying paleoenvironmental proxies continues to increase. We evaluate the accuracy and precision of the CAMECA ims 7F-GEO and NanoSIMS-50L ion probes for measurements of Sr/Ca, Mg/Ca, and Ba/Ca ratios in carbonate minerals. Nine carbonate reference...
Autoregulatory Feedback Controls Sequential Action of cis-Regulatory Modules at the brinker Locus - Dunipace, Leslie; Saunders, Abbie; Ashe, Hilary L.; Stathopoulos, Angelike
cis-regulatory modules (CRMs) act sequentially to regulate temporal expression of genes, but how the switch from one to the next is accomplished is not well understood. To provide insight, here we investigate the cis-regulatory system controlling brinker (brk) expression in the Drosophila embryo. Two distally located CRMs support expression at different times, while a promoter-proximal element (PPE) is required to support their action. In the absence of Brk protein itself or upon mutagenesis of Brk binding sites within the PPE, the late-acting CRM, specifically, is delayed. This block to late-acting CRM function appears to be removed when the early-acting CRM...
Coupled motion of microscale and nanoscale elastic objects in a viscous fluid - Paul, M. R.; Clark, M. T.; Cross, M. C.
We study the coupled dynamics of two closely spaced micron or nanoscale elastic objects immersed in a viscous fluid. The dynamics of the elastic objects are coupled through the motion of the surrounding viscous fluid. We consider two cases: (i) one object is driven externally by an imposed harmonic actuation force and the second object is passive and (ii) both objects are driven by a Brownian force to yield stochastic dynamics. Using a harmonic oscillator approximation for the elastic objects and the unsteady Stokes equations to describe the fluid dynamics, we develop analytical expressions for the amplitude and phase of...
Mixing in gravity currents - Fragoso, A. T.; Patterson, M. D.; Wettlaufer, J. S.
We study entrainment in lock-release gravity currents using highly spatially resolved
optical transmission experiments and quantitative analysis of the available potential
energy of the flow. The principal results provide a resolution to the debate regarding
the mechanism and degree of mixing in the head of a gravity current during the
slumping phase. The nature of the complex internal mixing structure changes as a
bore propagates from the tail to the head of the current during the slumping phase
and overtakes its leading edge. We use quantitative methods to identify the connection
between dynamics and entrainment and show that its manifestation as examined using
different methodologies is the cause...
Local Generation and Propagation of Ripples along the Septotemporal Axis of the Hippocampus - Patel, Jagdish; Schomburg, Erik W.; Berényi, Antal; Fujisawa, Shigeyoshi; Buzsáki, György
A topographical relationship exists between the septotemporal segments of the hippocampus and their entorhinal–neocortical targets, but the physiological organization of activity along the septotemporal axis is poorly understood. We recorded sharp-wave ripple patterns in rats during sleep from the entire septotemporal axis of the CA1 pyramidal layer. Qualitatively similar ripples emerged at all levels. From the local seed, ripples traveled septally or temporally at a speed of ∼0.35 m/s, and the spatial spread depended on ripple magnitude. Ripples propagated smoothly across the septal and intermediate segments of the hippocampus, but ripples in the temporal segment often remained isolated. These findings...
Nd and Sr Isotopic Study of the Bay of Islands Ophiolite Complex and the Evolution of the Source of Midocean Ridge Basalts - Jacobsen, Stein B.; Wasserburg, G. J.
Two Sm-Nd internal isochrons for pyroxene gabbros of the Bay of Islands Ophiolite Complex give well-defined ages of 508 ± 6 m.y. and 501 ± 13 m.y. with initial ^(143)Nd/^(144)Nd of ε_(Nd) = +7.7 ∓ 0.1 and ε_(Nd) = +7.5 ∓ 0.2, respectively. Total rock samples from pillow basalts, sheeted dikes, trondhjemites, hornblende gabbros, pyroxene gabbros, and an orthopyroxenite layer from the harzburgite give initial ε_(Nd) in the range from +6.5 to +8.1 with an average value of +7.6. The initial ^(87)Sr/^(86)Sr obtained on a pyroxenegabbro is ε_(Sr) = −19.3 ± 0.3, which is typical of oceanic samples. However, the...
Isotopic Constraints for the Early Evolution of the Moon - Oberli, F.; Huneke, J. C.; McCulloch, M. T.; Papanastassiou, D. A.; Wasserburg, G. J.
A synthesis of the early evolution of the moon and of the lunar highland crust is made on the basis of U-Th-Pb, Rb-Sr, K-Ar and Sm-Nd isotopic data from lunar highland breccias.
Measurements of Cyclotron Features and Pulse Periods in the High-mass X-Ray Binaries 4U 1538–522 and 4U 1907+09 with the International Gamma-Ray Astrophysics Laboratory - Hemphill, Paul B.; Rothschild, Richard E.; Caballero, Isabel; Pottschmidt, Katja; Kühnel, Matthias; Fürst, Felix; Wilms, Jörn
We present a spectral and timing analysis of International Gamma-Ray Astrophysics Laboratory (INTEGRAL)
observations of two high-mass X-ray binaries, 4U 1538−522 and 4U 1907+09. Our timing measurements for 4U
1538−522 find the pulse period to have exhibited a spin-up trend until approximately 2009, after which there is
evidence for a torque reversal, with the source beginning to spin down to the most recently measured period of
525.407 ± 0.001 s. The most recent INTEGRAL observations of 4U 1907+09 are not found to yield statistically
significant pulse periods due to the significantly lower flux from the source compared with 4U 1538−522. A
spectral model consisting of a...