33,949 research outputs found
Mission oriented study of advanced nuclear system parameters, phase 6. Volume 1 - Summary technical report Final report
Summarized study tasks, analyses, and results of advanced nuclear propulsion parameters for Mars and Venus mission
A Selected Ion Flow Tube Study of the Reactions of Several Cations with the Group 6B Hexafluorides SF6, SeF6, and TeF6
The first investigation of the ion chemistry of SeF and TeF is presented. Using a selected ion flow tube, the thermal rate coefficients and ion product distributions have been determined at 300 K for the reactions of fourteen atomic and molecular cations, namely HO, CF, CF, CF, HO, NO, O, CO, CO, N, N, Ar, F and Ne (in order of increasing recombination energy), with SeF and TeF. The results are compared with those from the reactions of these ions with SF, for which the reactions with CF, CF, NO and F are reported for the first time. Several distinct processes are observed amongst the large number of reactions studied, including dissociative charge transfer, and F, F, F and F abstraction from the neutral reactant molecule to the reagent ion. The dissociative charge transfer channels are discussed in relation to vacuum ultraviolet photoelectron and threshold photoelectron-photoion coincidence spectra of XF (X = S, Se, and Te). For reagent ions whose recombination energies lie between the first dissociative ionisation limit, XF XF + F + e, and the onset of ionisation of the XF molecule, the results suggest that if dissociative charge transfer occurs, it proceeds via an intimate encounter. For those reagent ions whose recombination energies are greater than the onset of ionisation, long-range electron transfer may occur depending on whether certain physical factors apply, for example non-zero Franck-Condon overlap. From the reaction kinetics, limits for the heats of formation of SeF, SeF, TeF and TeF at 298 K have been obtained; H(SeF) < -369 kJ mol, H(SeF) < -621 kJ mol, H(TeF) > -570 kJ mol, and H(TeF) < -822 kJ mol
Star - Planet - Debris Disk Alignment in the HD 82943 system: Is planetary system coplanarity actually the norm?
Recent results suggest that the two planets in the HD 82943 system are
inclined to the sky plane by 20 +/- 4deg. Here, we show that the debris disk in
this system is inclined by 27 +/- 4deg, thus adding strength to the derived
planet inclinations and suggesting that the planets and debris disk are
consistent with being aligned at a level similar to the Solar System. Further,
the stellar equator is inferred to be inclined by 28 +/- 4deg, suggesting that
the entire star - planet - disk system is aligned, the first time such
alignment has been tested for radial velocity discovered planets on ~AU wide
orbits. We show that the planet-disk alignment is primordial, and not the
result of planetary secular perturbations to the disk inclination. In addition,
we note three other systems with planets at >10AU discovered by direct imaging
that already have good evidence of alignment, and suggest that empirical
evidence of system-wide star - planet - disk alignment is therefore emerging,
with the exception of systems that host hot Jupiters. While this alignment
needs to be tested in a larger number of systems, and is perhaps unsurprising,
it is a reminder that the system should be considered as a whole when
considering the orientation of planetary orbits.Comment: Accepted to MNRA
The effects of visual deprivation on adaptation to a rotating environment
Visual deprivation effects on adaptation to rotating environment - Motion sickness studie
Structuring Services and Facilities for Library Instruction
published or submitted for publicatio
Computing the Loewner driving process of random curves in the half plane
We simulate several models of random curves in the half plane and numerically
compute their stochastic driving process (as given by the Loewner equation).
Our models include models whose scaling limit is the Schramm-Loewner evolution
(SLE) and models for which it is not. We study several tests of whether the
driving process is Brownian motion. We find that just testing the normality of
the process at a fixed time is not effective at determining if the process is
Brownian motion. Tests that involve the independence of the increments of
Brownian motion are much more effective. We also study the zipper algorithm for
numerically computing the driving function of a simple curve. We give an
implementation of this algorithm which runs in a time O(N^1.35) rather than the
usual O(N^2), where N is the number of points on the curve.Comment: 20 pages, 4 figures. Changes to second version: added new paragraph
to conclusion section; improved figures cosmeticall
Stripe phases in the two-dimensional Falicov-Kimball model
The observation of charge stripe order in the doped nickelate and cuprate
materials has motivated much theoretical effort to understand the underlying
mechanism of the stripe phase. Numerical studies of the Hubbard model show two
possibilities: (i) stripe order arises from a tendency toward phase separation
and its competition with the long-range Coulomb interaction or (ii) stripe
order inherently arises as a compromise between itinerancy and magnetic
interactions. Here we determine the restricted phase diagrams of the
two-dimensional Falicov-Kimball model and see that it displays rich behavior
illustrating both possibilities in different regions of the phase diagram.Comment: (5 pages, 3 figures
A Fast Algorithm for Simulating the Chordal Schramm-Loewner Evolution
The Schramm-Loewner evolution (SLE) can be simulated by dividing the time
interval into N subintervals and approximating the random conformal map of the
SLE by the composition of N random, but relatively simple, conformal maps. In
the usual implementation the time required to compute a single point on the SLE
curve is O(N). We give an algorithm for which the time to compute a single
point is O(N^p) with p<1. Simulations with kappa=8/3 and kappa=6 both give a
value of p of approximately 0.4.Comment: 17 pages, 10 figures. Version 2 revisions: added a paragraph to
introduction, added 5 references and corrected a few typo
Structural model optimization using statistical evaluation
The results of research in applying statistical methods to the problem of structural dynamic system identification are presented. The study is in three parts: a review of previous approaches by other researchers, a development of various linear estimators which might find application, and the design and development of a computer program which uses a Bayesian estimator. The method is tried on two models and is successful where the predicted stiffness matrix is a proper model, e.g., a bending beam is represented by a bending model. Difficulties are encountered when the model concept varies. There is also evidence that nonlinearity must be handled properly to speed the convergence
The motivating operation and negatively reinforced problem behavior. A systematic review.
The concept of motivational operations exerts an increasing influence on the understanding and assessment of problem behavior in people with intellectual and developmental disability. In this systematic review of 59 methodologically robust studies of the influence of motivational operations in negative reinforcement paradigms in this population, we identify themes related to situational and biological variables that have implications for assessment, intervention, and further research. There is now good evidence that motivational operations of differing origins influence negatively reinforced problem behavior, and that these might be subject to manipulation to facilitate favorable outcomes. There is also good evidence that some biological variables warrant consideration in assessment procedures as they predispose the person's behavior to be influenced by specific motivational operations. The implications for assessment and intervention are made explicit with reference to variables that are open to manipulation or that require further research and conceptualization within causal models
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