R=100,000 Spectroscopy of Photodissociation Regions: H2 Rotational Lines in the Orion Bar

Ground state rotational lines of H2 are good temperature probes of moderately hot (200-1000 K) gas. The low A-values of these lines result in low critical densities while ensuring that the lines are optically thin. ISO observations of H2 rotational lines in PDRs reveal large quantities of warm gas that are difficult to explain via current models, but the spatial resolution of ISO does not resolve the temperature structure of the warm gas. We present and discuss high spatial resolution observations of H2 rotational line emission from the Orion Bar.Comment: 4 pages, 1 figure, Proceedings of the ESO Workshop on High Resolution Infrared Spectroscop

Ultracold Chemistry and its Reaction Kinetics

We study the reaction kinetics of chemical processes occurring in the ultracold regime and systematically investigate their dynamics. Quantum entanglement is found to play a key role in driving an ultracold reaction towards a dynamical equilibrium. In case of multiple concurrent reactions Hamiltonian chaos dominates the phase space dynamics in the mean field approximation.Comment: 15 pages, 5 figure

The Rule: Modernizing the Potent, But Overlooked, Rule of Witness Sequestration

Starting with its illustration in the Apocrypha and continuing into the modern day both in courtrooms and in ubiquitous criminal procedurals, one evidence rule has proven so powerful that it has become known as “THE” Rule of Evidence. The rule of witness sequestration demands that multiple witnesses to the same events be examined separately from one another to prevent them from, consciously or subconsciously, tailoring their testimony to ensure that it remains consistent. Witness sequestration is conceptually simplistic and famously mighty. Yet, this bedrock protection against inaccurate trial testimony is imperiled by conflicting interpretations of Federal Rule of Evidence 615, the Rule that provides sequestration protection in federal court. In some circuits, the Rule is narrowly construed in accordance with its plain language to prohibit witnesses only from remaining physically present in the courtroom during testimony. Under this view, the Rule offers no protection against testimonial tailoring outside the courtroom. Yet, remaining physically present during the testimony of other witnesses is not the only means by which a prospective witness might adapt her testimony to match that of other witnesses. Although extra-tribunal witness coordination has always been possible, the explosion in technology and the recent specter of COVID-19 have multiplied exponentially options for testimonial tailoring beyond the courtroom doors. For this reason, some circuits construe terse “Rule 615” orders broadly to prohibit witness collaboration and access to testimony beyond the trial setting. Although these circuits afford the full complement of sequestration protection, their expansive construction of succinct “Rule 615” orders generates fairness concerns about inadequate notice of proscribed witness behavior. This Article details the competing interpretations of Rule 615 orders adopted by the federal courts and examines the merits and demerits of each approach. It further elucidates the philosophical divide reflected in the circuit split, exposing the textualist and purposive theories of rule construction animating the opposing views. The Article ultimately proposes detailed alternatives for revising Rule 615, offering draft language that could be adopted to memorialize either of the federal approaches to witness sequestration in amended rule text

Ne II Observations of Gas Motions in Compact and Ultracompact H II Regions

We present high spatial and spectral resolution observations of 16 Galactic compact and ultracompact H II regions in the [Ne II] 12.8 mu m fine-structure line. The small thermal width of the neon line and the high dynamic range of the maps provide an unprecedented view of the kinematics of compact and ultracompact H II regions. These observations solidify an emerging picture of the structure of ultracompact H II regions suggested in our earlier studies of G29.96-0.02 and Mon R2 IRS 1; systematic surface flows, rather than turbulence or bulk expansion, dominate the gas motions in the H II regions. The observations show that almost all of the sources have significant (5-20 km s(-1)) velocity gradients and that most of the sources are limb-brightened. In many cases, the velocity pattern implies tangential flow along a dense shell of ionized gas. None of the observed sources clearly fits into the categories of filled expanding spheres, expanding shells, filled blister flows, or cometary H II regions formed by rapidly moving stars. Instead, the kinematics and morphologies of most of the sources lead to a picture of H II regions confined to the edges of cavities created by stellar wind ram pressure and flowing along the cavity surfaces. In sources where the radio continuum and [Ne II] morphologies agree, the majority of the ionic emission is blueshifted relative to nearby molecular gas. This is consistent with sources lying on the near side of their natal clouds being less affected by extinction and with gas motions being predominantly outward, as is expected for pressure-driven flows.NSF AST-0607312, NSF-0708074SOFIA USRA8500-98-008NYSTAR Faculty Development ProgramNASA NNG 04-GG92G, CAN-NCC5-679Lunar and Planetary InstituteAstronom

Boom and Bust Carbon-Nitrogen Dynamics during Reforestation

Legacies of historical land use strongly shape contemporary ecosystem dynamics. In old-field secondary forests, tree growth embodies a legacy of soil changes affected by previous cultivation. Three patterns of biomass accumulation during reforestation have been hypothesized previously, including monotonic to steady state, non-monotonic with a single peak then decay to steady state, and multiple oscillations around the steady state. In this paper, the conditions leading to the emergence of these patterns is analyzed. Using observations and models, we demonstrate that divergent reforestation patterns can be explained by contrasting time-scales in ecosystem carbon-nitrogen cycles that are influenced by land use legacies. Model analyses characterize non-monotonic plant-soil trajectories as either single peaks or multiple oscillations during an initial transient phase controlled by soil carbon-nitrogen conditions at the time of planting. Oscillations in plant and soil pools appear in modeled systems with rapid tree growth and low initial soil nitrogen, which stimulate nitrogen competition between trees and decomposers and lead the forest into a state of acute nitrogen deficiency. High initial soil nitrogen dampens oscillations, but enhances the magnitude of the tree biomass peak. These model results are supported by data derived from the long-running Calhoun Long-Term Soil-Ecosystem Experiment from 1957 to 2007. Observed carbon and nitrogen pools reveal distinct tree growth and decay phases, coincident with soil nitrogen depletion and partial re-accumulation. Further, contemporary tree biomass loss decreases with the legacy soil C:N ratio. These results support the idea that non-monotonic reforestation trajectories may result from initial transients in the plant-soil system affected by initial conditions derived from soil changes associated with land-use history

The density of states of chaotic Andreev billiards

Quantum cavities or dots have markedly different properties depending on whether their classical counterparts are chaotic or not. Connecting a superconductor to such a cavity leads to notable proximity effects, particularly the appearance, predicted by random matrix theory, of a hard gap in the excitation spectrum of quantum chaotic systems. Andreev billiards are interesting examples of such structures built with superconductors connected to a ballistic normal metal billiard since each time an electron hits the superconducting part it is retroreflected as a hole (and vice-versa). Using a semiclassical framework for systems with chaotic dynamics, we show how this reflection, along with the interference due to subtle correlations between the classical paths of electrons and holes inside the system, are ultimately responsible for the gap formation. The treatment can be extended to include the effects of a symmetry breaking magnetic field in the normal part of the billiard or an Andreev billiard connected to two phase shifted superconductors. Therefore we are able to see how these effects can remold and eventually suppress the gap. Furthermore the semiclassical framework is able to cover the effect of a finite Ehrenfest time which also causes the gap to shrink. However for intermediate values this leads to the appearance of a second hard gap - a clear signature of the Ehrenfest time.Comment: Refereed version. 23 pages, 19 figure

Signatures of Galaxy-Cluster Interactions: Tully-Fisher Observations at z~0.1

We have obtained new optical imaging and spectroscopic observations of 78 galaxies in the fields of the rich clusters Abell 1413 (z = 0.14), Abell 2218 (z = 0.18) and Abell 2670 (z = 0.08). We have detected line emission from 25 cluster galaxies plus an additional six galaxies in the foreground and background, a much lower success rate than what was found (65%) for a sample of 52 lower-richness Abell clusters in the range 0.02 < z < 0.08. We have combined these data with our previous observations of Abell 2029 and Abell 2295 (both at z = 0.08), which yields a sample of 156 galaxies. We evaluate several parameters as a function of cluster environment: Tully-Fisher residuals, H-alpha equivalent width, and rotation curve asymmetry, shape and extent. Although H-alpha is more easily detectable in galaxies that are located further from the cluster cores, we fail to detect a correlation between H-alpha extent and galaxy location in those where it is detected, again in contrast with what is found in the clusters of lesser richness. We fail to detect any statistically significant trends for the other parameters in this study. The zero-point in the z~0.1 Tully-Fisher relation is marginally fainter (by 1.5 sigma) than that found in nearby clusters, but the scatter is essentially unchanged.Comment: 27 pages including 5 figures; accepted for publication in the Astronomical Journa

TEXES Observations of Pure Rotational H_2 Emission from AB Aurigae

We present observations of pure rotational molecular hydrogen emission from the Herbig Ae star, AB Aur. Our observations were made using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility and the Gemini North Observatory. We searched for H_2 emission in the S(1), S(2), and S(4) lines at high spectral resolution and detected all three. By fitting a simple model for the emission in the three transitions, we derive T = 670 ± 40 K and M = 0.52 ± 0.15 M_⊙ for the emitting gas. On the basis of the 8.5 km s^(-1) FWHM of the S(2) line, assuming the emission comes from the circumstellar disk, and with an inclination estimate of the AB Aur system taken from the literature, we place the location for the emission near 18 AU. Comparison of our derived temperature to a disk structure model suggests that UV and X-ray heating are important in heating the disk atmosphere

Semiactive Virtual Control Method for Robots with Regenerative Energy-Storing Joints

A framework for modeling and control is introduced for robotic manipulators with a number of energetically self-contained semiactive joints. The control approach consists of three steps. First, a virtual control design is conducted by any suitable means, assuming a fully-actuated system. Then, virtual control inputs are matched by a parameter modulation law. Finally, the storage dynamics are shaped using design parameters. Storage dynamics coincide with the system\u27s internal dynamics under exact virtual control matching. An internal energy balance equation and associated self-powered operation condition are given for the semiactive joints. This condition is a structural characteristic of the system and independent of the control law. Moreover, the internal energy balance equation is independent of the energy storage parameter (capacitance), which adds flexibility to the approach. An external energy balance equation is also given that can be used to calculate the work required from the active joints. A simulation example using a 3-dof prosthesis test robot illustrates the concepts

Optimal Mixed Tracking/Impedance Control With Application to Transfemoral Prostheses With Energy Regeneration

We design an optimal passivitybased tracking/impedance control system for a robotic manipulator with energy regenerative electronics, where the manipulator has both actively and semi-actively controlled joints. The semi-active joints are driven by a regenerative actuator that includes an energy-storing element. Method: External forces can have a large influence on energy regeneration characteristics. Impedance control is used to impose a desired relationship between external forces and deviation from reference trajectories. Multi-objective optimization (MOO) is used to obtain optimal impedance parameters and control gains to compromise between the two conflicting objectives of trajectory tracking and energy regeneration. We solve the MOO problem under two different scenarios: 1) constant impedance; and 2) timevarying impedance. Results: The methods are applied to a transfemoral prosthesis simulation with a semi-active knee joint. Normalized hypervolume and relative coverage are used to compare Pareto fronts, and these two metrics show that time-varying impedance provides better performance than constant impedance. The solution with time-varying impedance with minimum tracking error (0.0008 rad) fails to regenerate energy (loses 9.53 J), while a solution with degradation in tracking (0.0452 rad) regenerates energy (gains 270.3 J). A tradeoff solution results in fair tracking (0.0178 rad) and fair energy regeneration (131.2 J). Conclusion: Our experimental results support the possibility of net energy regeneration at the semi-active knee joint with human-like tracking performance. Significance: The results indicate that advanced control and optimization of ultracapacitor-based systems can significantly reduce power requirements in transfemoral prostheses