Focused Information Criterion for Locally Misspecified Vector Autoregressive Models

This paper investigates the focused information criterion and plug-in average for vector autoregressive models with local-to-zero misspecication. These methods have the advantage of focusing on a quantity of interest rather than aiming at overall model t. Any (suciently regular) function of the parameters can be used as a quantity of interest. We determine the asymptotic properties and elaborate on the role of the locally misspecied parameters. In particular, we show that the inability to consistently estimate locally misspecied parameters translates into suboptimal selection and averaging. We apply this framework to impulse response analysis. A Monte Carlo simulation study supports our claims

Generation of neutral atomic beams utilizing photodetachment by high power diode laser stacks

We demonstrate the use of high power diode laser stacks to photodetach fast hydrogen and carbon anions and produce ground term neutral atomic beams. We achieve photodetachment efficiencies of $\sim$7.4\% for H$^-$ at a beam energy of 10\,keV and $\sim$3.7\% for C$^-$ at 28\,keV. The diode laser systems used here operate at 975\,nm and 808\,nm, respectively, and provide high continuous power levels of up to 2\,kW, without the need of additional enhancements like optical cavities. The alignment of the beams is straightforward and operation at constant power levels is very stable, while maintenance is minimal. We present a dedicated photodetachment setup that is suitable to efficiently neutralize the majority of stable negative ions in the periodic table

Isotope effect for associative detachment: H(D)−+H(D)→H2(D2)+e

We report experimental and theoretical results for associative detachment (AD) of D−+D→D2+e−. We compare these data to our previously published results for H−+H→H2+e−. The measurements show no significant isotope effect in the total cross section. This is to be contrasted with previously published experimental and theoretical work which has found a significant isotope effect in diatomic systems for partial AD cross sections, i.e., as a function of the rotational and vibrational levels of the final molecule formed. Our work implies that though the rovibrational distribution of flux is different for AD of H− + H and D− + D, the total flux for these two systems is essentially the same when summed over all possible final channels

Supplemental material: Dynamics of the isotope exchange reaction of D with H3+, H2D+, and D2H+

No abstract has been provided for this article at this time

Static and Dynamic Properties of a Viscous Silica Melt Molecular Dynamics Computer Simulations

We present the results of a large scale molecular dynamics computer simulation in which we investigated the static and dynamic properties of a silica melt in the temperature range in which the viscosity of the system changes from O(10^-2) Poise to O(10^2) Poise. We show that even at temperatures as high as 4000 K the structure of this system is very similar to the random tetrahedral network found in silica at lower temperatures. The temperature dependence of the concentration of the defects in this network shows an Arrhenius law. From the partial structure factors we calculate the neutron scattering function and find that it agrees very well with experimental neutron scattering data. At low temperatures the temperature dependence of the diffusion constants $D$ shows an Arrhenius law with activation energies which are in very good agreement with the experimental values. With increasing temperature we find that this dependence shows a cross-over to one which can be described well by a power-law, D\propto (T-T_c)^gamma. The critical temperature T_c is 3330 K and the exponent gamma is close to 2.1. Since we find a similar cross-over in the viscosity we have evidence that the relaxation dynamics of the system changes from a flow-like motion of the particles, as described by the ideal version of mode-coupling theory, to a hopping like motion. We show that such a change of the transport mechanism is also observed in the product of the diffusion constant and the life time of a Si-O bond, or the space and time dependence of the van Hove correlation functions.Comment: 30 pages of Latex, 14 figure

High mortality associated with tapeworm parasitism in geladas (Theropithecus gelada) in the Simien Mountains National Park, Ethiopia

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/138266/1/ajp22684.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/138266/2/ajp22684_am.pd

Reaction Studies of Neutral Atomic C with H3+ using a Merged-beams Apparatus

We have investigated the chemistry of C + H_3^+ forming CH+, CH_2^+, and CH_3^+. These reactions are believed to be some of the key gas-phase astrochemical processes initiating the formation of organic molecules in molecular clouds. For this work, we have constructed a novel merged fast-beams apparatus which overlaps a beam of molecular ions onto a beam of ground-term neutral atoms. Here, we describe the apparatus in detail and present cross section data for forming CH+ and CH_2^+ at relative energies from ≈9 meV to ≈20 and 3 eV, respectively. Measurements were performed for statistically populated C (3P_J) in the ground term reacting with hot H_3^+ (at an internal temperature of ~2550 K). Using these data, we have derived rate coefficients for translational temperatures from ≈72 K to ~2.3 X 10^5 and 3.4 X 10^4 K, respectively. For the formation of CH_3^+, we are only able to place an upper limit on the rate coefficient. Our results for CH+ and CH_2^+ are in good agreement with the mass-scaled results from a previous ion trap study of C + D_3^+, at a translational temperature of ~1000 K. That work also used statistically populated C (3P_J) but internally cold D_3^+ (~77 K). The good agreement between the two experiments implies that the internal excitation of the H_3^+ is not significant so long as the reaction proceeds adiabatically. At 300 K, the C fine-structure levels are predicted to be essentially statistically populated, enabling us to compare our translational temperature results to thermal equilibrium calculations. At this temperature, our rate coefficient for forming CH+ lies a factor of ≈2.9 below the Langevin rate coefficient currently given in astrochemical databases, and a factor of ~1.8-3.3 below the published classical trajectory studies using quantum mechanical potential energy surfaces. Our results for CH_2^+ formation at 300 K are a factor of ≈26.7 above these semi-classical results. Astrochemical databases do not currently include this channel. We also present a method for converting our translational temperature results to thermal rate coefficients for temperatures below ~300 K. The results indicated that CH_2^+ formation dominates over that of CH+ at temperatures ~<50 K