Radial Velocity along the Voyager 1 Trajectory: The Effect of Solar Cycle

As Voyager 1 and Voyager 2 are approaching the heliopause (HP)—the boundary between the solar wind (SW) and the local interstellar medium (LISM)—we expect new, unknown features of the heliospheric interface to be revealed. A seeming puzzle reported recently by Krimigis et al. concerns the unusually low, even negative, radial velocity components derived from the energetic ion distribution. Steady-state plasma models of the inner heliosheath (IHS) show that the radial velocity should not be equal to zero even at the surface of the HP. Here we demonstrate that the velocity distributions observed by Voyager 1 are consistent with time-dependent simulations of the SW-LISM interaction. In this Letter, we analyze the results from a numerical model of the large-scale heliosphere that includes solar cycle effects. Our simulations show that prolonged periods of low to negative radial velocity can exist in the IHS at substantial distances from the HP. It is also shown that Voyager 1 was more likely to observe such regions than Voyager 2

Planning in action language BC while learning action costs for mobile robots

The action language BC provides an elegant way of formalizing dynamic domains which involve indirect effects of actions and recursively defined fluents. In complex robot task planning domains, it may be necessary for robots to plan with incomplete information, and reason about indirect or recursive action effects. In this paper, we demonstrate how BC can be used for robot task planning to solve these issues. Additionally, action costs are incorporated with planning to produce optimal plans, and we estimate these costs from experience making planning adaptive. This paper presents the first application of BC on a real robot in a realistic domain, which involves human-robot interaction for knowledge acquisition, optimal plan generation to minimize navigation time, and learning for adaptive planning

Formation of a "Cluster Molecule" (C20)2 and its thermal stability

The possible formation of a "cluster molecule" (C20)2 from two single C20 fullerenes is studied by the tight-binding method. Several (C20)2 isomers in which C20 fullerenes are bound by strong covalent forces and retain their identity are found; actually, these C20 fullerenes play the role of "atoms" in the "cluster molecule". The so-called open-[2+2] isomer has a minimum energy. Its formation path and thermal stability at T = 2000 - 4000 K are analyzed in detail. This isomer loses its molecular structure due to either the decay of one of C20 fullerenes or the coalescence of two C20 fullerenes into a C40 cluster. The energy barriers for the metastable open-[2+2] configuration are calculated to be U = 2 - 5 eV.Comment: 21 pages, 8 figure

The structure of self-gravitating clouds

To study the interaction of star-formation and turbulent molecular cloud structuring, we analyse numerical models and observations of self-gravitating clouds using the Delta-variance as statistical measure for structural characteristics. In the models we resolve the transition from purely hydrodynamic turbulence to gravitational collapse associated with the formation and mass growth of protostellar cores. We compare models of driven and freely decaying turbulence with and without magnetic fields. Self-gravitating supersonic turbulence always produces a density structure that contains most power on the smallest scales provided by collapsed cores as soon as local collapse sets in. This is in contrast to non-self-gravitating hydrodynamic turbulence where the Delta-variance is dominated by large scale structures. To detect this effect in star-forming regions observations have to resolve the high density contrast of protostellar cores with respect to their ambient molecular cloud. Using the 3mm continuum map of a star-forming cluster in Serpens we show that the dust emission traces the full density evolution. On the contrary, the density range accessible by molecular line observations is insufficient for this analysis. Only dust emission and dust extinction observations are able to to determine the structural parameters of star-forming clouds following the density evolution during the gravitational collapse.Comment: 12 pages, 9 figures, A&A in pres

Gravitational Constraint Combinations Generate a Lie Algebra

We find a first--order partial differential equation whose solutions are all ultralocal scalar combinations of gravitational constraints with Abelian Poisson brackets between themselves. This is a generalisation of the Kucha\v{r} idea of finding alternative constraints for canonical gravity. The new scalars may be used in place of the hamiltonian constraint of general relativity and, together with the usual momentum constraints, replace the Dirac algebra for pure gravity with a true Lie algebra: the semidirect product of the Abelian algebra of the new constraint combinations with the algebra of spatial diffeomorphisms.Comment: 10 pages, latex, submitted to Classical and Quantum Gravity. Section 3 is expanded and an additional solution provided, minor errors correcte

Theory of Systematic Computational Error in Free Energy Differences

Systematic inaccuracy is inherent in any computational estimate of a non-linear average, due to the availability of only a finite number of data values, N. Free energy differences (DF) between two states or systems are critically important examples of such averages in physical, chemical and biological settings. Previous work has demonstrated, empirically, that the ``finite-sampling error'' can be very large -- many times kT -- in DF estimates for simple molecular systems. Here, we present a theoretical description of the inaccuracy, including the exact solution of a sample problem, the precise asymptotic behavior in terms of 1/N for large N, the identification of universal law, and numerical illustrations. The theory relies on corrections to the central and other limit theorems, and thus a role is played by stable (Levy) probability distributions.Comment: 5 pages, 4 figure

Two simple systems with cold atoms: quantum chaos tests and nonequilibrium dynamics

This article is an attempt to provide a link between the quantum nonequilibrium dynamics of cold gases and fifty years of progress in the lowdimensional quantum chaos. We identify two atomic systems lying on the interface: two interacting atoms in a harmonic multimode waveguide and an interacting two-component Bose-Bose mixture in a double-well potential. In particular, we study the level spacing distribution, the wavefunction statistics, the eigenstate thermalization, and the ability to thermalize in a relaxation process as such.Comment: 18 pages, 9 figure

Polarization forces in water deduced from single molecule data

Intermolecular polarization interactions in water are determined using a minimal atomic multipole model constructed with distributed polarizabilities. Hydrogen bonding and other properties of water-water interactions are reproduced to fine detail by only three multipoles $\mu_H$, $\mu_O$, and $\theta_O$ and two polarizabilities $\alpha_O$ and $\alpha_H$, which characterize a single water molecule and are deduced from single molecule data.Comment: 4 revtex pages, 3 embedded color PS figure

Geometric phases and hidden local gauge symmetry

The analysis of geometric phases associated with level crossing is reduced to the familiar diagonalization of the Hamiltonian in the second quantized formulation. A hidden local gauge symmetry, which is associated with the arbitrariness of the phase choice of a complete orthonormal basis set, becomes explicit in this formulation (in particular, in the adiabatic approximation) and specifies physical observables. The choice of a basis set which specifies the coordinate in the functional space is arbitrary in the second quantization, and a sub-class of coordinate transformations, which keeps the form of the action invariant, is recognized as the gauge symmetry. We discuss the implications of this hidden local gauge symmetry in detail by analyzing geometric phases for cyclic and noncyclic evolutions. It is shown that the hidden local symmetry provides a basic concept alternative to the notion of holonomy to analyze geometric phases and that the analysis based on the hidden local gauge symmetry leads to results consistent with the general prescription of Pancharatnam. We however note an important difference between the geometric phases for cyclic and noncyclic evolutions. We also explain a basic difference between our hidden local gauge symmetry and a gauge symmetry (or equivalence class) used by Aharonov and Anandan in their definition of generalized geometric phases.Comment: 25 pages, 1 figure. Some typos have been corrected. To be published in Phys. Rev.