1,976 research outputs found
Speckle Control with a remapped-pupil PIAA-coronagraph
The PIAA is a now well demonstrated high contrast technique that uses an
intermediate remapping of the pupil for high contrast coronagraphy
(apodization), before restoring it to recover classical imaging capabilities.
This paper presents the first demonstration of complete speckle control loop
with one such PIAA coronagraph. We show the presence of a complete set of
remapping optics (the so-called PIAA and matching inverse PIAA) is transparent
to the wavefront control algorithm. Simple focal plane based wavefront control
algorithms can thus be employed, without the need to model remapping effects.
Using the Subaru Coronagraphic Extreme AO (SCExAO) instrument built for the
Subaru Telescope, we show that a complete PIAA-coronagraph is compatible with a
simple implementation of a speckle nulling technique, and demonstrate the
benefit of the PIAA for high contrast imaging at small angular separation.Comment: 6 figures, submitted to PAS
Identifying and improving green spaces on a college campus: A photovoice study
; Ecopsychology is available online at: http://online.liebertpub.com. Abstract: Research suggests that a large percent of college students experience stress due to the demands of college life. Campus health professionals use a wide range of interventions to reduce student stress; however, the ability of green spaces on campuses to alleviate stress is often lacking in college health programs and related research. In this study, photovoice methodology was used to conduct a community-based participatory research project in order to identify and improve campus green spaces that students frequent for stress relief. Participants included 45 undergraduate students enrolled in an emotional health course. Students were instructed to take photos that addressed two open-ended questions: (1) What green spaces on campus do you visit to alleviate stress? (2) How could the green spaces on campus be improved for alleviating stress? Afterward, students analyzed and placed their photos into distinct themes. Results showed that students enjoyed green spaces that featured both man-made structures (e.g., swings, fountains, benches) and exclusively natural areas (e.g., magnolia trees, campus parks). Students indicated that campus areas in need of improvement for alleviating stress included trash cans, areas lacking landscaping, piles of cigarette butts, and a dilapidated campus tower. Spaces that helped alleviate stress and spaces that needed improvement were both reflective of Attention Restoration Theory. At the culmination of the project, the students shared their findings with the campus community at a photo exhibit. During the exhibit, students' voices were heard by campus administrators in positions of authority (e.g., chancellor, director of Facilities Operations, grounds crew supervisor)
Direct Photons at RHIC
The PHENIX experiment has measured direct photons in
GeV Au+Au collisions and p+p collisions. The fraction of photons due to direct
production in Au+Au collisions is shown as a function of and centrality.
This measurement is compared with expectation from pQCD calculations. Other
possible sources of direct photons are discussed.Comment: 7 pages, 5 figures, presented at Hot Quarks 2004, Taos, N
Inherent-Structure Dynamics and Diffusion in Liquids
The self-diffusion constant D is expressed in terms of transitions among the
local minima of the potential (inherent structure, IS) and their correlations.
The formulae are evaluated and tested against simulation in the supercooled,
unit-density Lennard-Jones liquid. The approximation of uncorrelated
IS-transition (IST) vectors, D_{0}, greatly exceeds D in the upper temperature
range, but merges with simulation at reduced T ~ 0.50. Since uncorrelated IST
are associated with a hopping mechanism, the condition D ~ D_{0} provides a new
way to identify the crossover to hopping. The results suggest that theories of
diffusion in deeply supercooled liquids may be based on weakly correlated IST.Comment: submitted to PR
The Vector Probe in Heavy-Ion Reactions
We review essential elements in using the channel as a probe for
hot and dense matter as produced in (ultra-) relativistic collisions of heavy
nuclei. The uniqueness of the vector channel resides in the fact that it
directly couples to photons, both real and virtual (dileptons), enabling the
study of thermal radiation and in-medium effects on both light () and heavy () vector mesons. We emphasize the importance
of interrelations between photons and dileptons, and characterize relevant
energy/mass regimes through connections to Quark-Gluon-Plasma emission and
chiral symmetry restoration. Based on critical analysis of our current
understanding of data from fixed-target energies, we identify open key
questions to be addressed.Comment: Invited Talk at the Hot Quarks 2004 Workshop, July 18-24, 2004 (Taos
Valley, NM, USA), 15 pages latex incl 14 figs and iop style files, to appear
in the proceeding
The Potential Energy Landscape and Mechanisms of Diffusion in Liquids
The mechanism of diffusion in supercooled liquids is investigated from the
potential energy landscape point of view, with emphasis on the crossover from
high- to low-T dynamics. Molecular dynamics simulations with a time dependent
mapping to the associated local mininum or inherent structure (IS) are
performed on unit-density Lennard-Jones (LJ). New dynamical quantities
introduced include r2_{is}(t), the mean-square displacement (MSD) within a
basin of attraction of an IS, R2(t), the MSD of the IS itself, and g_{loc}(t)
the mean waiting time in a cooperative region. At intermediate T, r2_{is}(t)
posesses an interval of linear t-dependence allowing calculation of an
intrabasin diffusion constant D_{is}. Near T_{c} diffusion is intrabasin
dominated with D = D_{is}. Below T_{c} the local waiting time tau_{loc} exceeds
the time, tau_{pl}, needed for the system to explore the basin, indicating the
action of barriers. The distinction between motion among the IS below T_{c} and
saddle, or border dynamics above T_{c} is discussed.Comment: submitted to pr
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