Stellar Dynamics of Extreme-Mass-Ratio Inspirals

Inspiral of compact stellar remnants into massive black holes (MBHs) is accompanied by the emission of gravitational waves at frequencies that are potentially detectable by space-based interferometers. Event rates computed from statistical (Fokker-Planck, Monte-Carlo) approaches span a wide range due to uncertaintities about the rate coefficients. Here we present results from direct integration of the post-Newtonian N-body equations of motion descrbing dense clusters of compact stars around Schwarzschild MBHs. These simulations embody an essentially exact (at the post-Newtonian level) treatment of the interplay between stellar dynamical relaxation, relativistic precession, and gravitational-wave energy loss. The rate of capture of stars by the MBH is found to be greatly reduced by relativistic precession, which limits the ability of torques from the stellar potential to change orbital angular momenta. Penetration of this "Schwarzschild barrier" does occasionally occur, resulting in capture of stars onto orbits that gradually inspiral due to gravitational wave emission; we discuss two mechanisms for barrier penetration and find evidence for both in the simulations. We derive an approximate formula for the capture rate, which predicts that captures would be strongly disfavored from orbits with semi-major axes below a certain value; this prediction, as well as the predicted rate, are verified in the N-body integrations. We discuss the implications of our results for the detection of extreme-mass-ratio inspirals from galactic nuclei with a range of physical properties.Comment: 28 pages, 16 figures. Version 2 is significantly revised to reflect new insights into J and Q effects, to be published late

Charge transport across metal/molecular (alkyl) monolayer-Si junctions is dominated by the LUMO level

We compare the charge transport characteristics of heavy doped p- and n-Si-alkyl chain/Hg junctions. Photoelectron spectroscopy (UPS, IPES and XPS) results for the molecule-Si band alignment at equilibrium show the Fermi level to LUMO energy difference to be much smaller than the corresponding Fermi level to HOMO one. This result supports the conclusion we reach, based on negative differential resistance in an analogous semiconductor-inorganic insulator/metal junction, that for both p- and n-type junctions the energy difference between the Fermi level and LUMO, i.e., electron tunneling, controls charge transport. The Fermi level-LUMO energy difference, experimentally determined by IPES, agrees with the non-resonant tunneling barrier height deduced from the exponential length-attenuation of the current

iPTF13beo: The Double-Peaked Light Curve of a Type Ibn Supernova Discovered Shortly after Explosion

We present optical photometric and spectroscopic observations of the Type Ibn (SN 2006jc-like) supernova iPTF13beo. Detected by the intermediate Palomar Transient Factory ~3 hours after the estimated first light, iPTF13beo is the youngest and the most distant (~430 Mpc) Type Ibn event ever observed. The iPTF13beo light curve is consistent with light curves of other Type Ibn SNe and with light curves of fast Type Ic events, but with a slightly faster rise-time of two days. In addition, the iPTF13beo R-band light curve exhibits a double-peak structure separated by ~9 days, not observed before in any Type Ibn SN. A low-resolution spectrum taken during the iPTF13beo rising stage is featureless, while a late-time spectrum obtained during the declining stage exhibits narrow and intermediate-width He I and Si II features with FWHM ~ 2000-5000 km/s and is remarkably similar to the prototypical SN Ibn 2006jc spectrum. We suggest that our observations support a model of a massive star exploding in a dense He-rich circumstellar medium (CSM). A shock breakout in a CSM model requires an eruption releasing a total mass of ~0.1 Msun over a time scale of couple of weeks prior to the SN explosion.Comment: 8 pages, 5 figures, submitted to MNRA

Worth the risk? Terrorism-induced fear of flying

We conducted two bi-national experiments regarding emotional and behavioral responses to a terrorist plot against commercial flights, examining both feelings and projected action. The studies employed hypothetical scenarios in which terrorists attacked airplanes with shoulder-fired missiles as they were landing or taking off from an international airport. The scenarios were built around two factorially crossed manipulated variables, each with three levels: (1) government announcements or actions (2) social norm, expressed as variation in airline ticket sales. Each respondent read a questionnaire containing only one of the nine scenarios. Experiment 1 was conducted in Spain and California (n = 360, 50% female), Experiment 2 in Israel and California (n = 504, 50% female). In both studies, fear and flight plans were not differentially affected by governmental response or social norm. Women expressed more fear than men. Experiment 1 examined the purpose of the trip. Most respondents would not change a planned flight to attend a close friend’s wedding or important job interview, but a substantial number would postpone a vacation or drive to a different location. Experiment 2 featured escalating attacks. These yielded increased fear and more canceled trips. Within both studies, responses were similar across countries despite national differences in direct experience with terrorism

¿Vale la pena el riesgo? Miedo inducido por el terrorismo a volar

We conducted two bi-national experiments regarding emotional and behavioral responses to a terrorist plot against commercial flights, examining both feelings and projected action. The studies employed hypothetical scenarios in which terrorists attacked airplanes with shoulder-fired missiles as they were landing or taking off from an international airport. The scenarios were built around two factorially crossed manipulated variables, each with three levels: (1) government announcements or actions (2) social norm, expressed as variation in airline ticket sales. Each respondent read a questionnaire containing only one of the nine scenarios. Experiment 1 was conducted in Spain and California (n = 360, 50% female), Experiment 2 in Israel and California (n = 504, 50% female). In both studies, fear and flight plans were not differentially affected by governmental response or social norm. Women expressed more fear than men. Experiment 1 examined the purpose of the trip. Most respondents would not change a planned flight to attend a close friend’s wedding or important job interview, but a substantial number would postpone a vacation or drive to a different location. Experiment 2 featured escalating attacks. These yielded increased fear and more canceled trips. Within both studies, responses were similar across countries despite national differences in direct experience with terrorism.Se realizaron dos experimentos bi-nacionales con respecto a las respuestas emocionales y conductuales a un plan terrorista contra vuelos comerciales, examinando ambas cosas: sentimientos y proyectos de acción. Los estudios emplearon escenarios hipotéticos en los que los terroristas atacaron los aviones con misiles disparados desde el hombro, ya que estaban aterrizando o despegando desde un aeropuerto internacional. Los escenarios fueron construidos alrededor de dos variables factoriales cruzadas, cada uno con tres niveles: (1) los anuncios o acciones del gobierno (2) norma social, expresada como la variación en la venta de billetes de avión. Cada encuestado leyó un cuestionario que contenía sólo uno de los nueve escenarios. El experimento 1 se realizó en España y California (n = 360, 50% mujeres), el experimento 2 en Israel y California (n = 504, 50% mujeres). En ambos estudios, el miedo y los planes de vuelo no fueron diferencialmente afectados por la respuesta gubernamental o la norma social. Las mujeres expresaron más miedo que los hombres. El experimento 1 examinó el propósito del viaje. La mayoría de los encuestados no cambiarían un vuelo planeado para asistir a la boda de un amigo cercano o para una importante entrevista de trabajo, pero un número considerable de participantes podrían posponer unas vacaciones o ir en coche a un lugar diferente. El experimento 2 contó con la escalada de los ataques. Estas aumentaron el temor y la cantidad de viajes cancelados. En ambos estudios, las respuestas fueron similares en todos los países a pesar de las diferencias nacionales y la experiencia directa con el terrorismo.Depto. de Economía Aplicada, Estructura e HistoriaFac. de Ciencias Económicas y EmpresarialesTRUEpu

Robustness and Generalization

We derive generalization bounds for learning algorithms based on their robustness: the property that if a testing sample is "similar" to a training sample, then the testing error is close to the training error. This provides a novel approach, different from the complexity or stability arguments, to study generalization of learning algorithms. We further show that a weak notion of robustness is both sufficient and necessary for generalizability, which implies that robustness is a fundamental property for learning algorithms to work

Quantum Nonlocality without Entanglement

We exhibit an orthogonal set of product states of two three-state particles that nevertheless cannot be reliably distinguished by a pair of separated observers ignorant of which of the states has been presented to them, even if the observers are allowed any sequence of local operations and classical communication between the separate observers. It is proved that there is a finite gap between the mutual information obtainable by a joint measurement on these states and a measurement in which only local actions are permitted. This result implies the existence of separable superoperators that cannot be implemented locally. A set of states are found involving three two-state particles which also appear to be nonmeasurable locally. These and other multipartite states are classified according to the entropy and entanglement costs of preparing and measuring them by local operations.Comment: 27 pages, Latex, 6 ps figures. To be submitted to Phys. Rev. A. Version 2: 30 pages, many small revisions and extensions, author added. Version 3: Proof in Appendix D corrected, many small changes; final version for Phys. Rev. A Version 4: Report of Popescu conjecture modifie

U-Th dating of lake sediments: Lessons from the 700 ka sediment record of Lake Junín, Peru

Deep sediment cores from long-lived lake basins are fundamental records of paleoenvironmental history, but the power of these reconstructions has been often limited by poor age control. Uranium-thorium (U-Th) dating has the potential to fill a gap in current geochronological tools available for such sediment archives. We present our systematic approach to U-Th date carbonate-rich sediments from the ∼100 m drill core from Lake Junín, Peru. The results form the foundation of an age-depth model spanning ∼700 kyrs. High uranium concentrations (0.3–4 ppm) of these sediments allow us to date smaller amounts of material, giving us the opportunity to improve sample selection by avoiding detrital contamination, the greatest factor limiting the success of previous U-Th dating efforts in other lake basins. Despite this advantage, the dates from 174 analyses on 55 bulk carbonate samples reveal significant scatter that cannot be resolved with traditional isochrons, suggesting that at least some of the sediments have not remained closed systems. To understand the source of noise in the geochronological data, we first apply threshold criteria that screen samples by their U/Th ratio, reproducibility, and δ²³⁴U_(initial) value. We then compare these results with facies types, trace element concentrations, carbonate and total organic carbon content, color reflectance, mineralogy, and ostracode shell color to investigate the causes of open system behavior. Alongside simulations of the isotopic evolution of our samples, we find that the greatest impediment to U-Th dating of these sediments is not detrital contamination, but rather post-depositional remobilization of uranium. Examining U-Th data in these contexts, we identify samples that have likely experienced the least amount of alteration, and use dates from those samples as constraints for the age-depth model. Our work has several lessons for future attempts to U-Th date lake sediments, namely that geologic context is equally as important as the accuracy and precision of analytical measurements. In addition, we caution that significant geologic scatter may remain undetected if not for labor intensive tests of reproducibility achieved through replication. As a result of this work, the deep sediment core from Lake Junín is the only continuous record in the tropical Andes spanning multiple glacial cycles that is constrained entirely by independent radiometric dates