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Recent documents in Faculty Worken-usFri, 24 Apr 2020 15:43:30 PDT3600Controlling the ratchet effect for cold atoms
https://digitalcommons.carleton.edu/phys_faculty/17
https://digitalcommons.carleton.edu/phys_faculty/17Wed, 05 Dec 2018 06:37:42 PST
Low-order quantum resonances manifested by directed currents have been realized with cold atoms. Here we show that by increasing the strength of an experimentally achievable delta-kicking ratchet potential, quantum resonances of a very high order may naturally emerge and can induce larger ratchet currents than low-order resonances, with the underlying classical limit being fully chaotic. The results offer a means of controlling quantum transport of cold atoms.
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Anatole Kenfack et al.Nonmonotonicity in the quantum-classical transition: chaos induced by quantum effects
https://digitalcommons.carleton.edu/phys_faculty/16
https://digitalcommons.carleton.edu/phys_faculty/16Wed, 05 Dec 2018 06:37:28 PST
The classical-quantum transition for chaotic systems is understood to be accompanied by the suppression of chaotic effects as the relative h is increased. We show evidence to the contrary in the behavior of the quantum trajectory dynamics of a dissipative quantum chaotic system, the double-well Duffing oscillator. The classical limit in the case considered has regular behavior, but as the effective h is increased we see chaotic behavior. This chaos then disappears deeper into the quantum regime, which means that the quantum-classical transition in this case is nonmonotonic in h.
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Arie Kapulkin et al.A simple model for pulse profiles from precessing pulsars, with special application to relativistic binary PSR B1913+16
https://digitalcommons.carleton.edu/phys_faculty/15
https://digitalcommons.carleton.edu/phys_faculty/15Wed, 05 Dec 2018 06:37:15 PST
We study the observable pulse profiles that can be generated from precessing pulsars. A novel coordinate system is defined to aid visualization of the observing geometry. Using this system we explore the different families of profiles that can be generated by simple, circularly symmetric beam shapes. An attempt is then made to fit our model to the observations of relativistic binary PSR B1913+16. It is found that while qualitatively similar pulse profiles can be produced, this minimal model is insufficient for an accurate match to the observational data. Consequently, we confirm that the emission beam of PSR B1913+16 must deviate from circular symmetry, as first reported by Weisberg & Taylor (2002). However, the approximate fits obtained suggest that it may be sufficient to consider only minimal deviations from a circular beam in order to explain the data. We also comment on the applicability of our analysis technique to other precessing pulsars, both binary and isolated.
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Timothy Clifton et al.Arecibo HI absorption measurements of pulsars and the electron density at intermediate longitudes in the first galactic quadrant
https://digitalcommons.carleton.edu/phys_faculty/14
https://digitalcommons.carleton.edu/phys_faculty/14Wed, 05 Dec 2018 06:37:00 PST
We have used the Arecibo telescope to measure the H i absorption spectra of eight pulsars. We show how kinematic distance measurements depend on the values of the Galactic constants R0 and 0, and we select our preferred current values from the literature. We then derive kinematic distances for the low-latitude pulsars in our sample and electron densities along their lines of sight. We combine these measurements with all others in the inner Galactic plane visible from Arecibo to study the electron density in this region.
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J. M. Weisberg et al.Beating the spin-down limit on gravitational wave emission from the Crab pulsar
https://digitalcommons.carleton.edu/phys_faculty/13
https://digitalcommons.carleton.edu/phys_faculty/13Wed, 05 Dec 2018 06:36:46 PST
We present direct upper limits on gravitational wave emission from the Crab pulsar using data from the first nine months of the fifth science run of the Laser Interferometer Gravitational-wave Observatory (LIGO). These limits are based on two searches. In the first we assume that the gravitational wave emission follows the observed radio timing, giving an upper limit on gravitational wave emission that beats indirect limits inferred from the spin-down and braking index of the pulsar and the energetics of the nebula. In the second we allow for a small mismatch between the gravitational and radio signal frequencies and interpret our results in the context of two possible gravitational wave emission mechanisms
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LIGO Scientific Collaboration et al.Persistent patterns and multifractality in fluid mixing
https://digitalcommons.carleton.edu/phys_faculty/12
https://digitalcommons.carleton.edu/phys_faculty/12Wed, 05 Dec 2018 06:36:32 PST
Persistent patterns in periodically driven dynamics have been reported in a wide variety of contexts ranging from table-top and ocean-scale fluid mixing systems to the weak quantum-classical transition in open Hamiltonian systems. We illustrate a common framework for the emergence of these patterns by considering a simple measure of structure maintenance provided by the average radius of the scalar distribution in transform space. Within this framework, scaling laws related to both the formation and persistence of patterns in phase space are presented. Further, preliminary results linking the scaling exponents associated with the persistent patterns to the multifractal nature of the advective phase-space geometry are shown.
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Bala Sundaram et al.Teaching general relativity to undergraduates
https://digitalcommons.carleton.edu/phys_faculty/11
https://digitalcommons.carleton.edu/phys_faculty/11Wed, 05 Dec 2018 06:36:18 PSTNelson Christensen et al.First upper limits from LIGO on gravitational wave bursts
https://digitalcommons.carleton.edu/phys_faculty/10
https://digitalcommons.carleton.edu/phys_faculty/10Mon, 03 Dec 2018 21:07:29 PST
We report on a search for gravitational wave bursts using data from the first science run of the Laser Interferometer Gravitational Wave Observatory ~LIGO! detectors. Our search focuses on bursts with durations ranging from 4 to 100 ms, and with significant power in the LIGO sensitivity band of 150 to 3000 Hz. We bound the rate for such detected bursts at less than 1.6 events per day at a 90% confidence level. This result is interpreted in terms of the detection efficiency for ad hoc waveforms ~Gaussians and sine Gaussians! as a function of their root-sum-square strain hrss ; typical sensitivities lie in the range hrss ;10219–10217 strain/AHz, depending on the waveform. We discuss improvements in the search method that will be applied to future science data from LIGO and other gravitational wave detectors.
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LIGO Scientific Collaboration et al.Low-temperature glassy response of ultrathin La0.8ca0.2Mn03 films to electric and magnetic fields
https://digitalcommons.carleton.edu/phys_faculty/9
https://digitalcommons.carleton.edu/phys_faculty/9Mon, 03 Dec 2018 21:07:16 PST
The glassy response of ultrathin films of La0.8Ca0.2MnO3 in the mixed phase to external magnetic and gated electro-static fields have been studied at low temperatures. The response of the resistance to external fields provides direct evidence for a hierarchical energy landscape, with strong cross-couplings between spin and charge. Magnetic coercivity measurements indicate that strong magnetic disorder accompanies the mixed phase in these films. This magnetic disorder, and the resultant coercivity, can be decreased by cooling in a large magnetic field or by electrostatic gating.
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A. Bhattacharya et al.Coarse-grained entropy decrease and phase-space focusing in Hamiltonian dynamics
https://digitalcommons.carleton.edu/phys_faculty/8
https://digitalcommons.carleton.edu/phys_faculty/8Mon, 03 Dec 2018 21:07:02 PST
We analyze the behavior of the coarse-grained entropy for classical probabilities in nonlinear Hamiltonians. We focus on the result that if the trajectory dynamics are integrable, the probability ensemble shows transient increases in the coherence, corresponding to an increase in localization of the ensemble and hence the phasespace density of the ensemble. We discuss the connection of these dynamics to the problem of cooling in atomic ensembles. We show how these dynamics can be understood in terms of the behavior of individual trajectories, allowing us to manipulate ensembles to create “cold” dense final ensembles. We illustrate these results with an analysis of the behavior of particular nonlinear integrable systems, including discussions of the spin-echo effect and the seeming violation of Liouville’s theorem
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Arjendu K. Pattanayak et al.Discovery of pulsed OH emission stimulated by a pulsar
https://digitalcommons.carleton.edu/phys_faculty/7
https://digitalcommons.carleton.edu/phys_faculty/7Mon, 03 Dec 2018 21:06:48 PST
Curium lies at the center of the actinide series and has a half-filled shell with seven 5f electrons spatially residing inside its radon core. As a function of pressure, curium exhibits five different crystallographic phases up to 100 gigapascals, of which all but one are also found in the preceding element, americium. We describe here a structure in curium, Cm III, with monoclinic symmetry, space group C2/c, found at intermediate pressures (between 37 and 56 gigapascals). Ab initio electronic structure calculations agree with the observed sequence of structures and establish that it is the spin polarization of curium’s 5f electrons that stabilizes Cm III. The results reveal that curium is one of a few elements that has a lattice structure stabilized by magnetism.
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Joel M. Weisberg et al.Evidence for Alignment of the Rotation and Velocity Vectors in Pulsars
https://digitalcommons.carleton.edu/phys_faculty/6
https://digitalcommons.carleton.edu/phys_faculty/6Mon, 03 Dec 2018 21:06:34 PST
We review our case for strong observational evidence for a relationship between the direction of a pulsar’s motion and its rotation axis. The information comes from calibrated polarization data for 20 pulsars which display linearly polarized emission from the pulse longitude at closest approach to the magnetic pole. Of these 20 pulsars, 10 show an offset in the angle between the velocity vector and the polarisation position angle which is either less than 10◦ or more than 80◦ , a fraction which is very unlikely by random chance. We believe that the bimodal nature of the distribution arises from the presence of orthogonal polarisation modes in the pulsar radio emission. In some cases this orthogonal ambiguity is resolved by observations at other wavelengths so that we conclude that the velocity vector and the rotation axis are aligned at birth. Strengthening the case is the fact that 4 of the 5 pulsars with ages less than 3 Myr show this relationship, including the Vela pulsar.
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Simon Johnston et al.Pulsar Studies of Tiny-Scale Structure in the Neutral ISM
https://digitalcommons.carleton.edu/phys_faculty/5
https://digitalcommons.carleton.edu/phys_faculty/5Mon, 03 Dec 2018 21:06:20 PST
We describe the use of pulsars to study small-scale neutral structure in the interstellar medium (ISM). Because pulsars are high velocity objects, the pulsarEarth line of sight sweeps rapidly across the ISM. Multiepoch measurements of pulsar interstellar spectral line spectra therefore probe ISM structures on AU scales. We review pulsar measurements of small scale structure in HI and OH and compare these results with those obtained through other techniques.
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Joel M. Weisberg et al.Kinetic Model for Sintering of Supported Metal Particles with Improved Size-Dependent Energetics and Applications to Au on TiO2(110)
https://digitalcommons.carleton.edu/phys_faculty/4
https://digitalcommons.carleton.edu/phys_faculty/4Mon, 03 Dec 2018 21:06:06 PSTStephen C. Parker et al.Coherent Bayesian Inference on Compact Binary Inspirals Using a Network of Interferometric Gravitational Wave Detectors
https://digitalcommons.carleton.edu/phys_faculty/3
https://digitalcommons.carleton.edu/phys_faculty/3Mon, 03 Dec 2018 21:05:53 PST
Presented in this paper is the description of a Markov chain Monte Carlo (MCMC) routine for conducting coherent parameter estimation for interferometric gravitational wave observations of an inspiral of binary compact objects using multiple detectors. Data from several interferometers are processed, and all nine parameters (ignoring spin) associated with the binary system are inferred, including the distance to the source, the masses, and the location on the sky. The data is matched with time-domain inspiral templates that are 2.5 post-Newtonian (PN) in phase and 2.0 PN in amplitude. We designed and tuned an MCMC sampler so that it is able to efficiently find the posterior mode(s) in the parameter space and perform the stochastic integration necessary for inference within a Bayesian framework. Our routine could be implemented as part of an inspiral detection pipeline for a world wide network of detectors. Examples are given for simulated signals and data as seen by the LIGO and Virgo detectors operating at their design sensitivity.
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Christian R¨over et al.Reactivity and Sintering Kinetics of Au/TiO2(110) Model Catalysts: Particle Size Effects
https://digitalcommons.carleton.edu/phys_faculty/2
https://digitalcommons.carleton.edu/phys_faculty/2Mon, 03 Dec 2018 21:05:40 PST
We review here our studies of the reactivity and sintering kinetics of model catalysts consisting of gold nanoparticles dispersed on TiO2(110). First, the nucleation and growth of vapor-deposited gold on this surface was experimentally examined using x-ray photoelectron spectroscopy and low energy ion scattering. Gold initially grows as two-dimensional islands up to a critical coverage, hcr, after which 3D gold nanoparticles grow. The results at different temperatures are fitted well with a kinetic model, which includes various energetic parameters for Au adatom migration. Oxygen was dosed onto the resulting gold nanoparticles using a hot filament technique. The desorption energy of Oa was examined using temperature programmed desorption (TPD). The Oa is bonded ~40% more strongly to smaller (thinner) Au islands. Gaseous CO reacts rapidly with this Oa to make CO2, probably via adsorbed CO. The reactivity of Oa with CO increases with increasing particle size, as expected based on Brønsted relations. Propene adsorption leads to TPD peaks for three different molecularly adsorbed states on Au/TiO2(110), corresponding to propene adsorbed on gold islands, to Ti sites on the substrate, and to the perimeter of gold islands, with adsorption energies of 40, 52 and 73 kJ/mol, respectively. Thermal sintering of the gold nanoparticles was explored using temperature-programmed low-energy ion scattering. These sintering rates for a range of Au loadings at temperatures from 200 to 700 K were well fitted by a theoretical model which takes into consideration the dramatic effect of particle size on metal chemical potential using a modified bond additivity model. When extrapolated to simulate isothermal sintering at 700 K for 1 year, the resulting particle size distribution becomes very narrow. These results question claims that the shape of particle size distributions reveal their sintering mechanisms. They also suggest why the growth of colloidal nanoparticles in liquid solutions can result in very narrow particle size distributions.
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Stephen C. Parker et al.PSR J1829+2456: a relativistic binary pulsar
https://digitalcommons.carleton.edu/phys_faculty/1
https://digitalcommons.carleton.edu/phys_faculty/1Mon, 03 Dec 2018 05:11:46 PST
We report the discovery of a new binary pulsar, PSR J1829+2456, found during a mid-latitude drift-scan survey with the Arecibo telescope. Our initial timing observations show the 41-ms pulsar to be in a 28-hr, slightly eccentric, binary orbit. The advance of periastron ˙ω = 0 .28 ± 0 .01 deg yr − 1 is derived from our timing observations spanning 200 days. Assuming that the advance of periastron is purely relativistic and a reasonable range of neutron star masses for PSR J1829+2456 we constrain the companion mass to be between 1.22 M ⊙ and 1.38 M ⊙, making it likely to be another neutron star. We also place a firm upper limit on the pulsar mass of 1.38 M ⊙. The expected coalescence time due to gravitational-wave emission is long ( ∼ 60 Gyr) and this system will not significantly impact upon calculations of merger rates that are relevant to upcoming instruments such as LIGO.
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D. J. Champion et al.