7,982 research outputs found
Fermilab Collider Run II: Accelerator Status and Upgrades
Fermilab will continue to maintain its pre-eminent position in the world of
High Energy Physics, with a unique opportunity to make unprecedented studies of
the top quark and major discoveries, until the Large Hadron collider (LHC) at
CERN becomes operational near the end of the decade. Run II is well underway
with major accelerator and detector upgrades since Run I. A program of further
upgrades to the accelerator complex will result in an integrated luminosity of
4-8 fb-1 per experiment, by the year 2009.Comment: 12 pages, 6 figures. To be published in the Proceedings of the 15th
Topical Conference on Hadron Collider Physics, HCP2004, Michigan State
University, East Lansing, MI, June 14-18, 2004 (American Institute of
Physics, NY, 2004
Resonant Removal of Exomoons During Planetary Migration
Jupiter and Saturn play host to an impressive array of satellites, making it
reasonable to suspect that similar systems of moons might exist around giant
extrasolar planets. Furthermore, a significant population of such planets is
known to reside at distances of several Astronomical Units (AU), leading to
speculation that some moons thereof might support liquid water on their
surfaces. However, giant planets are thought to undergo inward migration within
their natal protoplanetary disks, suggesting that gas giants currently
occupying their host star's habitable zone formed further out. Here we show
that when a moon-hosting planet undergoes inward migration, dynamical
interactions may naturally destroy the moon through capture into a so-called
"evection resonance." Within this resonance, the lunar orbit's eccentricity
grows until the moon eventually collides with the planet. Our work suggests
that moons orbiting within about 10 planetary radii are susceptible to this
mechanism, with the exact number dependent upon the planetary mass, oblateness
and physical size. Whether moons survive or not is critically related to where
the planet began its inward migration as well as the character of inter-lunar
perturbations. For example, a Jupiter-like planet currently residing at 1AU
could lose moons if it formed beyond 5AU. Cumulatively, we suggest that an
observational census of exomoons could potentially inform us on the extent of
inward planetary migration, for which no reliable observational proxy currently
exists.Comment: 6 Figures, Accepted for Publication in The Astrophysical Journa
Mechanical Evidence of the Orbital Angular Momentum to Energy Ratio of Vortex Beams
We measure, in a single experiment, both the radiation pressure and the torque due to a wide variety of
propagating acoustic vortex beams. The results validate, for the first time directly, the theoretically
predicted ratio of the orbital angular momentum to linear momentum in a propagating beam. We
experimentally determine this ratio using simultaneous measurements of both the levitation force and
the torque on an acoustic absorber exerted by a broad range of helical ultrasonic beams produced by a
1000-element matrix transducer array. In general, beams with helical phase fronts have been shown to
contain orbital angular momentum as the result of the azimuthal component of the Poynting vector around
the propagation axis. Theory predicts that for both optical and acoustic helical beams the ratio of the
angular momentum current of the beam to the power should be given by the ratio of the beam’s
topological charge to its angular frequency. This direct experimental observation that the ratio of the
torque to power does convincingly match the expected value (given by the topological charge to angular
frequency ratio of the beam) is a fundamental result
Factors affecting breeding status of wading birds in the Everglades.
This goals of this research and monitoring effort are to document nesting effort
and roughly categorize success of nesting by wading birds in the central Everglades of
Florida, and to investigate the causes of nonbreeding in a high proportion of the adult
wading birds in the ecosystem The latter goal has focused on breeding of White Ibises
(Eudocimus albus) and has been approached through 1) understanding the nutritional,
behavioral, and hormonal aspects of normal breeding in a captive colony ofScarlet Ibises
(considered conspecific to White Ibises) in central Florida, and 2) comparing breeding and
nonbreeding wild White Ibises in the Everglades, in their physiology, nutritional state,
breeding phenology, contaminant load, and hormonal status. This report covers work on
this project between January and November, 2000. (81 page docoument
Studies In Mesoscopics And Quantum Microscopies
This thesis begins with a foundational section on quantum optics. The single-photon detectors used in the first chapter were obtained through the Advanced Laboratory Physics Association (ALPhA), which brokered reduced cost for educational use, and the aim of the single-photon work presented in Chapter 1 is to develop modules for use in Illinois Wesleyan\u27s instructional labs beyond the first year of university. Along with the American Association of Physics Teachers, ALPhA encourages capstone-level work, such as Chapter 1 of this honors thesis, which is explicitly designed to play the role of passing on, to a next generation of physics majors, materials that can play a central role in their curriculum. Thus, although such work had previously been done at other institutions, the value added by this work has to do with the impact upon the local curriculum, and the utility of the collation o of these materials into one single, easily accessible form.
Beyond its first chapter, this thesis extends into my research projects, each of which, in the long term, carries a motivation that connects back to questions raised in the studies described in Chapter 1. While the first chapter describes ways in which we can experimentally study the ``spin\u27\u27 polarization state of a single photon, the second deals extends the discussion of how information may be encoded into the angular momentum of light, and some of its potential long-term consequences, e.g., for experiments involving optical traps that may someday test for the (controversial) hypothesized existence of a boundary between the microscopic (quantum) and macroscopic (classical) domains. Here, too, the work presented builds upon a body of work in the recent research literature. The final chapter deals with the creation of meso-scale systems for use in advanced optical traps studies. Each of these last two chapters points towards opportunities in physics research that are tentative in nature and, as such, constitute research that is very much aspirational. The citations provided, while not exhaustive, point both towards some of the more useful resources discovered during this work, and to some ongoing controversies in the field. At the same time, these chapters also aim to delineate concrete, specific steps that we have taken, which we believe are of immediate interest in their own rights
Twisted [(R3P)PdX] groups above dicarbaborane ligands: 4-dimethylsulfido-3-iodo-3-triphenylphosphine-closo-3-pallada-1,2-dicarbadodecaborane and 3-dimethylphenylphosphine-3-chloro-4-dimethylsulfido-closo-3-pallada-1,2-dicarbadodecaborane
The structural analyses of [3-(PPh₃)-3-I-4-(SMe₂)-closo-3,1,2-PdC₂B₉H₁₀] or [Pd(C₄H₁₆B₉S)I(C₁₈H₁₅P)], (I), and [3-(PPhMe₂)-3-Cl-4-(SMe₂)-closo-3,1,2-PdC₂B₉H₁₀] or [Pd(C₄H₁₆B₉S)Cl(C₈H₁₁P)], (II), show that in comparison with [3-(PR₃)2-closo-3,1,2-PdC₂B₉H₁₁] the presence of the 4-SMe₂ group causes the [PdX(PR₃)] unit (X = halogen) to twist about an axis passing through the Pd atom and the directly opposite B atom of the carbaborane ligand. The halogen atoms are located almost directly above a C atom in the C₂B₃ face, and the conformations of the [PdX(PR₃)] units above the C₂B₃ faces are not those predicted from molecular orbital calculations of the closo-3,1,2-PdC₂B₉ system. The fact that the variation from the predicted conformation is greater in the case of (I) than in (II) may be ascribed to the greater steric interactions induced by the I atom in (I) compared with the Cl atom in (II)
Alignment of Protostars and Circumstellar Disks During the Embedded Phase
Star formation proceeds via the collapse of a molecular cloud core over
multiple dynamical timescales. Turbulence within cores results in a spatially
non-uniform angular momentum of the cloud, causing a stochastic variation in
orientation of the disk forming from the collapsing material. In the absence of
star-disk angular momentum coupling, such disk-tilting would provide a natural
mechanism for production of primordial spin-orbit misalignments in the
resulting planetary systems. However, owing to high accretion rates in the
embedded phase of star formation, the inner edge of the circumstellar disk
extends down to the stellar surface, resulting in efficient gravitational and
accretional angular momentum transfer between the star and the disk. Here, we
demonstrate that the resulting gravitational coupling is sufficient to suppress
any significant star-disk misalignment, with accretion playing a secondary
role. The joint tilting of the star-disk system leads to a stochastic wandering
of star-aligned bipolar outflows. Such wandering widens the effective opening
angle of stellar outflows, allowing for more efficient clearing of the
remainder of the protostar's gaseous envelope. Accordingly, the processes
described in this work provide an additional mechanism responsible for
sculpting the stellar Initial Mass Function (IMF).Comment: 6 pages, 3 Figures, Accepted for publication in The Astrophysical
Journal Letter
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