Learning to integrate reactivity and deliberation in uncertain planning and scheduling problems

This paper describes an approach to planning and scheduling in uncertain domains. In this approach, a system divides a task on a goal by goal basis into reactive and deliberative components. Initially, a task is handled entirely reactively. When failures occur, the system changes the reactive/deliverative goal division by moving goals into the deliberative component. Because our approach attempts to minimize the number of deliberative goals, we call our approach Minimal Deliberation (MD). Because MD allows goals to be treated reactively, it gains some of the advantages of reactive systems: computational efficiency, the ability to deal with noise and non-deterministic effects, and the ability to take advantage of unforseen opportunities. However, because MD can fall back upon deliberation, it can also provide some of the guarantees of classical planning, such as the ability to deal with complex goal interactions. This paper describes the Minimal Deliberation approach to integrating reactivity and deliberation and describe an ongoing application of the approach to an uncertain planning and scheduling domain

Neutron transition strengths of 21+2^+_1 states in the neutron rich Oxygen isotopes determined from inelastic proton scattering

A coupled-channel analysis of the $^{18,20,22}$O$(p,p')$ data has been performed to determine the neutron transition strengths of 2$^+_1$ states in Oxygen targets, using the microscopic optical potential and inelastic form factor calculated in the folding model. A complex density- and \emph{isospin} dependent version of the CDM3Y6 interaction was constructed, based on the Brueckner-Hatree-Fock calculation of nuclear matter, for the folding model input. Given an accurate isovector density dependence of the CDM3Y6 interaction, the isoscalar ($\delta_0$) and isovector ($\delta_1$) deformation lengths of 2$^+_1$ states in $^{18,20,22}$O have been extracted from the folding model analysis of the $(p,p')$ data. A specific $N$-dependence of $\delta_0$ and $\delta_1$ has been established which can be linked to the neutron shell closure occurring at $N$ approaching 16. The strongest isovector deformation was found for 2$^+_1$ state in $^{20}$O, with $\delta_1$ about 2.5 times larger than $\delta_0$, which indicates a strong core polarization by the valence neutrons in $^{20}$O. The ratios of the neutron/proton transition matrix elements ($M_n/M_p$) determined for 2$^+_1$ states in $^{18,20}$O have been compared to those deduced from the mirror symmetry, using the measured $B(E2)$ values of 2$^+_1$ states in the proton rich $^{18}$Ne and $^{20}$Mg nuclei, to discuss the isospin impurity in the $2^+_1$ excitation of the $A=18,T=1$ and $A=20,T=2$ isobars.Comment: Version accepted for publication in Physical Review

Anisotropic magnetoresistance of spin-orbit coupled carriers scattered from polarized magnetic impurities

Anisotropic magnetoresistance (AMR) is a relativistic magnetotransport phenomenon arising from combined effects of spin-orbit coupling and broken symmetry of a ferromagnetically ordered state of the system. In this work we focus on one realization of the AMR in which spin-orbit coupling enters via specific spin-textures on the carrier Fermi surfaces and ferromagnetism via elastic scattering of carriers from polarized magnetic impurities. We report detailed heuristic examination, using model spin-orbit coupled systems, of the emergence of positive AMR (maximum resistivity for magnetization along current), negative AMR (minimum resistivity for magnetization along current), and of the crystalline AMR (resistivity depends on the absolute orientation of the magnetization and current vectors with respect to the crystal axes) components. We emphasize potential qualitative differences between pure magnetic and combined electro-magnetic impurity potentials, between short-range and long-range impurities, and between spin-1/2 and higher spin-state carriers. Conclusions based on our heuristic analysis are supported by exact solutions to the integral form of the Boltzmann transport equation in archetypical two-dimensional electron systems with Rashba and Dresselhaus spin-orbit interactions and in the three-dimensional spherical Kohn-Littinger model. We include comments on the relation of our microscopic calculations to standard phenomenology of the full angular dependence of the AMR, and on the relevance of our study to realistic, two-dimensional conduction-band carrier systems and to anisotropic transport in the valence band of diluted magnetic semiconductors.Comment: 15 pages, Kohn-Littinger model adde

Proximity effects and triplet correlations in Ferromagnet/Ferromagnet/Superconductor nanostructures

We report the results of a study of superconducting proximity effects in clean Ferromagnet/Ferromagnet/Superconductor (${\rm F_1F_2S}$) heterostructures, where the pairing state in S is a conventional singlet s-wave. We numerically find the self-consistent solutions of the Bogoliubov-de Gennes (BdG) equations and use these solutions to calculate the relevant physical quantities. By linearizing the BdG equations, we obtain the superconducting transition temperatures $T_c$ as a function of the angle $\alpha$ between the exchange fields in $\rm F_1$ and $\rm F_2$. We find that the results for $T_c(\alpha)$ in ${\rm F_1F_2S}$ systems are clearly different from those in ${\rm F_1 S F_2}$ systems, where $T_c$ monotonically increases with $\alpha$ and is highest for antiparallel magnetizations. Here, $T_c(\alpha)$ is in general a non-monotonic function, and often has a minimum near $\alpha \approx 80^{\circ}$. For certain values of the exchange field and layer thicknesses, the system exhibits reentrant superconductivity with $\alpha$: it transitions from superconducting to normal, and then returns to a superconducting state again with increasing $\alpha$. This phenomenon is substantiated by a calculation of the condensation energy. We compute, in addition to the ordinary singlet pair amplitude, the induced odd triplet pairing amplitudes. The results indicate a connection between equal-spin triplet pairing and the singlet pairing state that characterizes $T_c$. We find also that the induced triplet amplitudes can be very long-ranged in both the S and F sides and characterize their range. We discuss the average density of states for both the magnetic and the S regions, and its relation to the pairing amplitudes and $T_c$. The local magnetization vector, which exhibits reverse proximity effects, is also investigated.Comment: 14 pages including 11 figure

Antisymmetric magnetoresistance in magnetic multilayers with perpendicular anisotropy

While magnetoresistance (MR) has generally been found to be symmetric in applied field in non-magnetic or magnetic metals, we have observed antisymmetric MR in Co/Pt multilayers. Simultaneous domain imaging and transport measurements show that the antisymmetric MR is due to the appearance of domain walls that run perpendicular to both the magnetization and the current, a geometry existing only in materials with perpendicular magnetic anisotropy. As a result, the extraordinary Hall effect (EHE) gives rise to circulating currents in the vicinity of the domain walls that contributes to the MR. The antisymmetric MR and EHE have been quantitatively accounted for by a theoretical model.Comment: 17 pages, 4 figure

Angular dependence of superconductivity in superconductor / spin valve heterostructures

We report measurements of the superconducting transition temperature, $T_c$, in CoO/Co/Cu/Co/Nb multilayers as a function of the angle $\alpha$ between the magnetic moments of the Co layers. Our measurements reveal that $T_c(\alpha)$ is a nonmonotonic function, with a minimum near $\alpha={\pi}/{2}$. Numerical self-consistent solutions of the Bogoliubov - de Gennes equations quantitatively and accurately describe the behavior of $T_c$ as a function of $\alpha$ and layer thicknesses in these superconductor / spin-valve heterostructures. We show that experimental data and theoretical evidence agree in relating $T_c(\alpha)$ to enhanced penetration of the triplet component of the condensate into the Co/Cu/Co spin valve in the maximally noncollinear magnetic configuration.Comment: 9 pages, 9 figure

Massive Star Cluster Formation and Destruction in Luminous Infrared Galaxies in GOALS

We present the results of a {\it Hubble Space Telescope} ACS/HRC FUV, ACS/WFC optical study into the cluster populations of a sample of 22 Luminous Infrared Galaxies in the Great Observatories All-Sky LIRG Survey. Through integrated broadband photometry we have derived ages and masses for a total of 484 star clusters contained within these systems. This allows us to examine the properties of star clusters found in the extreme environments of LIRGs relative to lower luminosity star-forming galaxies in the local Universe. We find that by adopting a Bruzual \& Charlot simple stellar population (SSP) model and Salpeter initial mass function, the age distribution of clusters declines as $dN/d\tau = \tau^{-0.9 +/- 0.3}$, consistent with the age distribution derived for the Antennae Galaxies, and interpreted as evidence for rapid cluster disruption occuring in the strong tidal fields of merging galaxies. The large number of $10^{6} M_{\odot}$ young clusters identified in the sample also suggests that LIRGs are capable of producing more high-mass clusters than what is observed to date in any lower luminosity star-forming galaxy in the local Universe. The observed cluster mass distribution of $dN/dM = M^{-1.95 +/- 0.11}$ is consistent with the canonical -2 power law used to describe the underlying initial cluster mass function (ICMF) for a wide range of galactic environments. We interpret this as evidence against mass-dependent cluster disruption, which would flatten the observed CMF relative to the underlying ICMF distribution.Comment: 63 pages, 58 Figures, 56 Tables, Accepted for publication in Ap