Sets avoided by Brownian motion

Any fixed cylinder is hit almost surely by a 3-dimensional Brownian motion, but is there a random cylinder that is in the complement? We answer this for cylinders, and then replacing a cylinder with a more general set

Quasi integral of motion for axisymmetric potentials

We present an estimate of the third integral of motion for axisymmetric three-dimensional potentials. This estimate is based on a Staeckel approximation and is explicitly written as a function of the potential. We tested this scheme for the Besancon Galactic model and two other disc-halo models and find that orbits of disc stars have an accurately conserved third quasi integral. The accuracy ranges from of 0.1% to 1% for heights varying from z = 0~kpc to z= 6 kpc and Galactocentric radii R from 5 to 15kpc. We also tested the usefulness of this quasi integral in analytic distribution functions of disc stellar populations: we show that the distribution function remains approximately stationary and that it allows to recover the potential and forces by applying Jeans equations to its moments.Comment: 9 pages, 9 figures, accepted for publication in Astron. and Astrophy

Subradiance in a Large Cloud of Cold Atoms

Since Dicke's seminal paper on coherence in spontaneous radiation by atomic ensembles, superradiance has been extensively studied. Subradiance, on the contrary, has remained elusive, mainly because subradiant states are weakly coupled to the environment and are very sensitive to nonradiative decoherence processes.Here we report the experimental observation of subradiance in an extended and dilute cold-atom sample containing a large number of particles. We use a far detuned laser to avoid multiple scattering and observe the temporal decay after a sudden switch-off of the laser beam. After the fast decay of most of the fluorescence, we detect a very slow decay, with time constants as long as 100 times the natural lifetime of the excited state of individual atoms. This subradiant time constant scales linearly with the cooperativity parameter, corresponding to the on-resonance optical depth of the sample, and is independent of the laser detuning, as expected from a coupled-dipole model

Superradiance in a Large and Dilute Cloud of Cold Atoms in the Linear-Optics Regime

Superradiance has been extensively studied in the 1970s and 1980s in the regime of superfluores-cence, where a large number of atoms are initially excited. Cooperative scattering in the linear-optics regime, or "single-photon superradiance" , has been investigated much more recently, and superra-diant decay has also been predicted, even for a spherical sample of large extent and low density, where the distance between atoms is much larger than the wavelength. Here, we demonstrate this effect experimentally by directly measuring the decay rate of the off-axis fluorescence of a large and dilute cloud of cold rubidium atoms after the sudden switch-off of a low-intensity laser driving the atomic transition. We show that, at large detuning, the decay rate increases with the on-resonance optical depth. In contrast to forward scattering, the superradiant decay of off-axis fluorescence is suppressed near resonance due to attenuation and multiple-scattering effects

New surveys of UBV photometry and absolute proper motions at intermediate latitude

A photometric and proper motion survey has been obtained in 2 directions at intermediate latitude: ($l=167.5^\circ$, $b=47.4^\circ$; $\alpha_{2000}=9^h41^m26^s$,$\delta_{2000}=+49^\circ53'27''$) and ($l=278^\circ$, $b=47^\circ$; $\alpha_{2000}=11^h42^m56^s$, $\delta_{2000}=-12^\circ31'42''$). The survey covers 7.13 and 20.84 square degrees, respectively. The limiting magnitude is about 18.5 in V for both directions. We have derived the density laws for stars (M$_{V}$ $\ge$ 3.5) as a function of distance from the galactic plane. The density laws for stars follow a sum of two exponentials with scale heights of 240 pc (thin disk) and 790 pc (thick disk), respectively. The local density of thick disk is found to be 6.1$\pm$3 % relative to the thin disk. The kinematical distribution of stars has been probed to distances up to 3.5 kpc above the galactic plane. New estimates of the parameters of velocity ellipsoid have been derived for the thick disk of the Galaxy. A comparison of our data sets with the Besan\c con model star count predictions has been performed, giving a good agreement in the magnitude range V = 13 to 18.Comment: 13 pages, 8 PS figures, To appear in A&

Entanglement verification with finite data

Suppose an experimentalist wishes to verify that his apparatus produces entangled quantum states. A finite amount of data cannot conclusively demonstrate entanglement, so drawing conclusions from real-world data requires statistical reasoning. We propose a reliable method to quantify the weight of evidence for (or against) entanglement, based on a likelihood ratio test. Our method is universal in that it can be applied to any sort of measurements. We demonstrate the method by applying it to two simulated experiments on two qubits. The first measures a single entanglement witness, while the second performs a tomographically complete measurement.Comment: 4 pages, 3 pretty picture

Use Them or Lose Them: Inservice Teacher Perceptions Of the Usability and Sustainability of Facilitated Individual Education Program Meeting Training and Learned Techniques

Effective collaboration among family professional partnerships (FPPs) and work groups such as a multidisciplinary individualized education program (IEP) team has been identified as a critical characteristic in developing a specially designed program for students with a disability. Unfortunately, educators often do not feel prepared to interact and collaborate with colleagues, parents, and community partners due to limited instruction and practice during preservice coursework or in-service professional development workshops. Thus, there continues to be the need for guidance on how to prepare preservice and licensed educators to collaborate effectively within IEP team meetings. An emerging IEP meeting practice called facilitated IEP (FIEP), utilizes a trained facilitator to guide IEP teams through a collaborative meeting framework where all team members’ input is valued, heard, and considered in the creation of the student’s IEP. The purpose of this study was to investigate the experiences and perceptions of educators who attended the FIEP CPR training and identify associated outcomes experienced during a meeting once the trained educators implemented tools and techniques from the training. Using qualitative interview methodology, 11 educators described their experiences with learning and then applying the FIEP strategies. Participants identified four training characteristics used to maximize the participants learning potential creating an engaging learning environment, benefitting from experienced knowledgeable trainers, providing interactive opportunities to practice new skills, and encouraging interactive opportunities to collaborate. Additionally, the research identified effective procedural techniques used during FIEP meetings to increase team collaboration and construct a compliant IEP. Participants overwhelmingly agreed the FIEP improved the traditional IEP process through increased team preparation and participation, which in turn increased team members’ understanding of the IEP process and content of the IEP, and the strengths and challenges of the student. Finally, six common tools and techniques emerged as effective structural tools used to create an organized, collaborative discussion: (a) agenda, (b) outcomes, (c) parking lot, (d) norms, (e) group memory, (f) roles, and (g) facilitative language. The implications for practice resulting from this study fall into two main categories, training, and implementation. One strong theme that emerged from the data was the need for more structured opportunities to learn how to collaborate effectively within the school setting and in particular, during the IEP meeting. The information provided gives input to teacher preparation programs and in-service professional development leaders when planning coursework or workshops in critical need areas. To ensure the training opportunities honor the unique needs of the adult learner, suggestions for addressing these characteristics are also provided. Once the educators receive training, preservice programs and state and local districtlevel agencies would benefit from following a structured implementation process that ensures FIEP team members benefit from the merits of the facilitative structures and strategies and that the facilitators implement with fidelity. Specific recommendations are outlined in the Implications for Practice section. The study adds to the growing body of literature on the effectiveness of FIEP meetings used as a proactive IEP meeting framework. However, because the FIEP process is a relatively new practice, it is critical to explore perceptions from more diverse cultures and conditions. Additionally, gathering data from various stakeholders such as the family and the student will help to address common barriers known to limit stakeholder participation, and collaboration