Flaw Selection Strategies for Partial-Order Planning

Several recent studies have compared the relative efficiency of alternative flaw selection strategies for partial-order causal link (POCL) planning. We review this literature, and present new experimental results that generalize the earlier work and explain some of the discrepancies in it. In particular, we describe the Least-Cost Flaw Repair (LCFR) strategy developed and analyzed by Joslin and Pollack (1994), and compare it with other strategies, including Gerevini and Schubert's (1996) ZLIFO strategy. LCFR and ZLIFO make very different, and apparently conflicting claims about the most effective way to reduce search-space size in POCL planning. We resolve this conflict, arguing that much of the benefit that Gerevini and Schubert ascribe to the LIFO component of their ZLIFO strategy is better attributed to other causes. We show that for many problems, a strategy that combines least-cost flaw selection with the delay of separable threats will be effective in reducing search-space size, and will do so without excessive computational overhead. Although such a strategy thus provides a good default, we also show that certain domain characteristics may reduce its effectiveness.Comment: See http://www.jair.org/ for an online appendix and other files accompanying this articl

Demonstration of the Zero-Crossing Phasemeter with a LISA Test-bed Interferometer

The Laser Interferometer Space Antenna (LISA) is being designed to detect and study in detail gravitational waves from sources throughout the Universe such as massive black hole binaries. The conceptual formulation of the LISA space-borne gravitational wave detector is now well developed. The interferometric measurements between the sciencecraft remain one of the most important technological and scientific design areas for the mission. Our work has concentrated on developing the interferometric technologies to create a LISA-like optical signal and to measure the phase of that signal using commercially available instruments. One of the most important goals of this research is to demonstrate the LISA phase timing and phase reconstruction for a LISA-like fringe signal, in the case of a high fringe rate and a low signal level. We present current results of a test-bed interferometer designed to produce an optical LISA-like fringe signal previously discussed in the literature.Comment: find minor corrections in the CQG versio

Outgassing, Temperature Gradients and the Radiometer Effect in LISA: A Torsion Pendulum Investigation

Thermal modeling of the LISA gravitational reference sensor (GRS) includes such effects as outgassing from the proof mass and its housing and the radiometer effect. Experimental data in conditions emulating the LISA GRS are required to confidently predict the GRS performance. Outgassing and the radiometer effect are similar in characteristics and are difficult to decouple experimentally. The design of our torsion balance allows us to investigate differential radiation pressure, the radiometer effect, and outgassing on closely separated conducting surfaces with high sensitivity. A thermally controlled split copper plate is brought near a freely hanging plate-torsion pendulum.We have varied the temperature on each half of the copper plate and have measured the resulting forces on the pendulum. We have determined that to first order the current GRS model for the radiometer effect, outgassing, and radiation pressure are mostly consistent with our torsion balance measurements and therefore these thermal effects do not appear to be a large hindrance to the LISA noise budget. However, there remain discrepancies between the predicted dependence of these effects on the temperature of our apparatus.Comment: 6th International LISA Symposiu

Finite range corrections near a Feshbach resonance and their role in the Efimov effect

We have measured the binding energy of $^7$Li Feshbach molecules deep into the non-universal regime by associating free atoms in a Bose-Einstein condensate by modulating the magnetic field. We extract the scattering length from these measurements, correcting for non-universal short-range effects using several different methods. We find that field-dependent effective range corrections agree well with the data. With this more precise determination of the scattering length vs. field we reanalyze our previous data on the location of atom loss features produced by the Efimov effect \cite{PollackSci09} and investigate effective range corrections to universal theory.Comment: Accepted for publication in Phys. Rev.

Towards a Principled Representation of Discourse Plans

We argue that discourse plans must capture the intended causal and decompositional relations between communicative actions. We present a planning algorithm, DPOCL, that builds plan structures that properly capture these relations, and show how these structures are used to solve the problems that plagued previous discourse planners, and allow a system to participate effectively and flexibly in an ongoing dialogue.Comment: requires cogsci94.sty, psfig.st

Extending Foster Care to Age 21: Weighing the Costs to Government against the Benefits to Youth

The Fostering Connections to Success and Increasing Adoptions Act of 2008 allows states to claim federal reimbursement for the costs of caring for and supervising Title IV-E eligible foster youth until their 21st birthday. This issue brief provides preliminary estimates of what the potential costs to government and the benefits to young people would be if states extend foster care to age 21. The analysis focuses on the increase in postsecondary educational attainment associated with allowing foster youth to remain in care until they are 21 years old and the resulting increase in lifetime earnings associated with postsecondary education. Researchers estimate that lifetime earnings would increase an average of two dollars for every dollar spent on keeping foster youth in care beyond age 18

A Demonstration of LISA Laser Communication

Over the past few years questions have been raised concerning the use of laser communications links between sciencecraft to transmit phase information crucial to the reduction of laser frequency noise in the LISA science measurement. The concern is that applying medium frequency phase modulations to the laser carrier could compromise the phase stability of the LISA fringe signal. We have modified the table-top interferometer presented in a previous article by applying phase modulations to the laser beams in order to evaluate the effects of such modulations on the LISA science fringe signal. We have demonstrated that the phase resolution of the science signal is not degraded by the presence of medium frequency phase modulations.Comment: minor corrections found in the CQG versio

Universality in Three- and Four-Body Bound States of Ultracold Atoms

Under certain circumstances, three or more interacting particles may form bound states. While the general few-body problem is not analytically solvable, the so-called Efimov trimers appear for a system of three particles with resonant two-body interactions. The binding energies of these trimers are predicted to be universally connected to each other, independent of the microscopic details of the interaction. By exploiting a Feshbach resonance to widely tune the interactions between trapped ultracold lithium atoms, we find evidence for two universally connected Efimov trimers and their associated four-body bound states. A total of eleven precisely determined three- and four-body features are found in the inelastic loss spectrum. Their relative locations on either side of the resonance agree well with universal theory, while a systematic deviation from universality is found when comparing features across the resonance.Comment: 16 pages including figures and Supplementary Online Materia

Parallel Process: An Empirical Investigation

The purpose of the present study was to conduct an empirical investigation of parallel process. The study used a cross-sectional design in which 30 therapy relationships and the corresponding supervision relationships were studied. The therapist assessed the behavior manifested by the patient during a targeted therapy session. Following the subsequent supervision session, the supervisor assessed the behavior manifested by the supervisee during the supervision session. In addition, each of the triad participants (patient, therapist, supervisor) rated the level of anxiety they experienced during the targeted therapy and supervision sessions. Measures of interpersonal style for each of the subjects were also obtained. Correlations were computed between each therapy relationship and the corresponding supervision relationship. The correlations were formed by pairing the therapist\u27s rating of the patient\u27s behavior during the targeted therapy session with the supervisor\u27s rating of the supervisee\u27s behavior during the targeted supervision session. In 67 percent of the triads the Pearson product-moment correlations were significant. Across all triads, 20 percent of the variation in the patient\u27s behavior during the targeted therapy session could be accounted for by the variation in the supervisee\u27s behavior during the targeted supervision session. Regression analyses were used to investigate conditions which might facilitate the occurrence of parallel process. No relationship was found between the level of anxiety experienced by the subjects during the targeted sessions and the occurrence of parallel process. The level of complementarity, as derived by the pairings in interpersonal styles between the participants in each relationship, also failed to predict the occurrence of parallel process. The results of a two-way analysis of variance with repeated measures indicated that the behavioral profile obtained by patients was similar to the profile obtained by supervisees. The finding suggested that helpees, whether patients or supervisees, tended to manifest similar behaviors. It was concluded that the occurrence of parallel process may be due to the similarity in role relationship between the patient and therapist in therapy and the supervisee and supervisor in supervision