Toward a situation model in a cognitive architecture

The ability to coherently represent information that is situationally relevant is vitally important to perform any complex task, especially when that task involves coordinating with team members. This paper introduces an approach to dynamically represent situation information within the ACT-R cognitive architecture in the context of a synthetic teammate project. The situation model represents the synthetic teammate’s mental model of the objects, events, actions, and relationships encountered in a complex task simulation. The situation model grounds textual information from the language analysis component into knowledge usable by the agent-environment interaction component. The situation model is a key component of the synthetic teammate as it provides the primary interface between arguably distinct cognitive processes modeled within the synthetic teammate (e.g., language processing and interactions with the task environment). This work has provided some evidence that reasoning about complex situations requires more than simple mental representations and requires mental processes involving multiple steps. Additionally, the work has revealed an initial method for reasoning across the various dimensions of situations. One purpose of the research is to demonstrate that this approach to implementing a situation model provides a robust capability to handle tasks in which an agent must construct a mental model from textual information, reason about complex relationships between objects, events, and actions in its environment, and appropriately communicate with task participants using natural language. In this paper we describe an approach for modeling situationally relevant information, provide a detailed example, discuss challenges faced, and present research plans for the situation model.     

Similarity decay of enstrophy in an electron fluid

A similarity decay law is proposed for enstrophy of a one-signed-vorticity fluid in a circular free-slip domain. It excludes the metastable equilibrium enstrophy which cannot drive turbulence, and approaches Batchelor's t(-2) law for strong turbulence. Measurements of the decay of a turbulent electron fluid agree well with the predictions of the decay law for a variety of initial conditions.     

Distance measurements in the borderline region of applicability of CW EPR and DEER: a model study on a homologous series of spin-labelled peptides

Inter-spin distances between 1 nm and 4.5 nm are measured by continuous wave (CW) and pulsed electron paramagnetic resonance (EPR) methods for a series of nitroxide-spin-labelled peptides. The upper distance limit for measuring dipolar coupling by the broadening of the CW spectrum and the lower distance limit for the present optimally-adjusted double electron electron resonance (DEER) set-up are determined and found to be both around 1.6-1.9 nm. The methods for determining distances and corresponding distributions from CW spectral line broadening are reviewed and further developed. Also, the work shows that a correction factor is required for the analysis of inter-spin distances below approximately 2 nm for DEER measurements and this is calculated using the density matrix formalism.     

The gas-phase kinetics of the reaction of 1,1-difluoroiodoethane with hydrogen iodide: The C–I bond dissociation energy in 1,1-difluoroiodoethane

The kinetics of gas-phase reaction of CH₃CF₂I with HI were studied from 496 to 549K and have been shown to be consistent with the following mechanism: A least squares treatment of the data gave where θ = 2.303 RT kcal/mole. The observed activation energy E₁ was combined with E₂ = 0 ± 1 kcal/mole to yield The result, combined with data for several C? I bond dissociation energies, leads us to conclude that the C(sp³)? I bond is relatively insensitive to F for H substitution and that the C(sp²)–I bond has considerable double-bond character.     

Parallel branch and bound algorithms for quadratic zero–one programs on the hypercube architecture

We present a parallel branch and bound algorithm for unconstrained quadratic zero-one programs on the hypercube architecture. Subproblems parallelize well without the need of a shared data structure to store expanded nodes of the search tree. Load balancing is achieved by demand splitting of neighboring subproblems. Computational results on a variety of large-scale problems are reported on an iPSC/1 32-node hypercube and an iPSC/2 16-node hypercube.     

A numerical study of the hierarchical Ising model: High-temperature versus epsilon expansion

We study numerically the magnetic susceptibility of the hierarchical model with Ising spins (=±1) above the critical temperature and for two values of the epsilon parameter. The integrations are performed exactly using recursive methods which exploit the symmetries of the model. Lattices with up to 2¹⁸ sites have been used. Surprisingly, the numerical data can be fitted very well with a simple power law of the form (1-/ ₀)^g for thewhole temperature range considered. This approximate law implies a simple approximate formula for the coefficients of the high-temperature expansion, and, more importantly, approximate relations among the coefficients themselves. We found that some of these approximate relations hold with errors less then 2%. On the other hand,g differs significantly from the critical exponent calculated with the epsilon expansion, even when the fit is restricted to intervals closer to ^c. We discuss this discrepancy in the context the renormalization group analysis of the hierarchical model.     

OH rotational quantum state distributions and relaxation efficiencies for the reaction system O(1D) + H2O → 2OH

The OH rotational distribution from O(¹D) + H₂O → 2OH is presented. The v' = 0 distribution corresponds to two Boltzmann distributions. ≈500 K (k = 1–6) and ≈2500 K (k ? 6). Rotational relaxation efficiencies for N₂, He, O₂ were ?0.1, ?0.1, ?0.4. More limited data are presented for the v' = 1 and 2 levels.     

Structural, electronic, and vibrational characterization of Fe-HNO porphyrinates by density functional theory

A recent report of the structural and vibrational properties of heme-bound HNO in myoglobin, MbHNO, revealed a long Fe-N(HNO) bond with the hydrogen atom bonded to the coordinated N atom. The Fe-N(H)-O moiety was reported to exhibit an unusually high Fe-N(HNO) stretching frequency relative to those of the corresponding [FeNO]6 and [FeNO]7 porphyrinates, despite the Fe-N(HNO) bond being longer than either of its Fe-N(NO) counterparts. Herein, we present results from density functional theory calculations of an active site model of MbHNO that support the previous assignment and clarify this seemingly contradictory result. The results are consistent with the experimental evidence for a ground-state Fe-N(H)-O structure having a long Fe-N(HNO) bond and a uniquely high nu(Fe)(-)(N(HNO)) frequency. This high frequency is the result of the correspondingly low reduced mass of the normal mode, which is largely attributable to significant motion of the N-bound hydrogen atom. Additionally, the calculations show the Fe-N(H)O bonding in this complex to be remarkably insensitive to whether the HNO and ImH ligand planes are parallel or perpendicular. This is attributed to insensitivities of the Fe-L(axial) characters of molecular orbitals to the relative HNO and ImH orientation in both the parallel and perpendicular conformers.     

Micellar-mediated shifts of ionization constants of amino acids and peptides

The acid-base dissociation constants, K_a, of amino acids and small peptides were determined in both aqueous and micellar solutions of sodium dodecyl sulfate and cetyltrimethylammonium bromide by potentiometric and chromatographic means. The observed differences in pK_a values between micellar media and aqueous solutions ranged between 0.23 and 2.21 units. The micellar-mediated pK_a shifts can be attributed to different solute-micelle interactions, mainly hydrophobic and electrostatic forces. The implications of the change in acid-base behavior on separation selectivity in micellar liquid chromatography and micellar electrokinetic capillary chromatography are discussed.