10,912 research outputs found
Paradoxical popups: Why are they hard to catch?
Even professional baseball players occasionally find it difficult to
gracefully approach seemingly routine pop-ups. This paper describes a set of
towering pop-ups with trajectories that exhibit cusps and loops near the apex.
For a normal fly ball, the horizontal velocity is continuously decreasing due
to drag caused by air resistance. But for pop-ups, the Magnus force (the force
due to the ball spinning in a moving airflow) is larger than the drag force. In
these cases the horizontal velocity decreases in the beginning, like a normal
fly ball, but after the apex, the Magnus force accelerates the horizontal
motion. We refer to this class of pop-ups as paradoxical because they appear to
misinform the typically robust optical control strategies used by fielders and
lead to systematic vacillation in running paths, especially when a trajectory
terminates near the fielder. In short, some of the dancing around when
infielders pursue pop-ups can be well explained as a combination of bizarre
trajectories and misguidance by the normally reliable optical control strategy,
rather than apparent fielder error. Former major league infielders confirm that
our model agrees with their experiences.Comment: 28 pages, 10 figures, sumitted to American Journal of Physic
The Trials and Tribulations of Applied Triangulation: Weighing Different Data Sources
Researchers employ triangulation to increase the validity of inference in qualitative and quantitative research. Leuffen, Shikano, and Walter have presented guidance as to which strategies to use when triangulating data sources. In this article, I explore how their findings can be translated for practical research purposes. I offer an illustrative application concentrating on the political power of traditional political authorities in Uganda and Tanzania. I analyze the status quo of political power and the preferred political power of traditional leaders. To triangulate, I use three sources: (1) constitutional-legal texts, (2) the Afrobarometer survey, and (3) in-depth interviews. I shed light on possible problems and analytical strategies for triangulation in practice, with a specific focus on convergence and divergence of sources
Competition Between Fractional Quantum Hall Liquid, Bubble and Wigner Crystal Phases in the Third Landau Level
Magnetotransport measurements were performed in a ultra-high mobility
GaAs/AlGaAs quantum well of density . The
temperature dependence of the magnetoresistance was studied in detail
in the vicinity of . In particular, we discovered new minima in
at filling factor and , but only at
intermediate temperatures mK. We interpret these as
evidence for a fractional quantum Hall liquid forming in the N=2 Landau level
and competing with bubble and Wigner crystal phases favored at lower
temperatures. Our data suggest that a magnetically driven insulator-insulator
quantum phase transition occurs between the bubble and Wigner crystal phases at
T=0.Comment: Phys. Rev. Lett.93 266804 (2004
Comparing juvenile catch rates among conventional fish traps and traps designed to reduce fishing mortality on juvenile reef fishes; Camparacion de tasas de captura entre trampas de peces convencionales y trampas disenadas para reducir la mortalidad de peces juveniles
The Indian Ocean humpback dolphin <i>Sousa plumbea</i> (G.Cuvier, 1829). A status report for the Arabian region. Scientific Committee document SC/54/SM6, International Whaling Commission, 26 April-10 May 2002, Shimonoseki, Japan
Available data on the genus Sousa are reviewed for the Arabian region. Nominal usage of Sousa plumbea (G. Cuvier 1828) is retained as a pragmatic measure, based on geographic and morphologic affiliation. Distribution is described for the region to include much of the Arabian (Persian) Gulf, Arabian Sea, Gulf of Aden and Red Sea, but notably excludes the Gulf of Oman. This discontinuous distribution suggests the possible presence of discreet populations within the region. Most available information on Sousa plumbea in the region originates from the Sultanate of Oman, where this species is among the most commonly recorded cetacean. However, there is no absolute measure of abundance here or elsewhere in the region and the status of the species is unknown. Beach cast individuals represent nearly two-thirds of all records (n=269) of this species in Oman. Live sightings indicate unusually large group sizes (up to 100 individuals) in the Arabian Sea and Arabian Gulf. Occasional association with Tursiops sp. and Delphinus sp. is documented. Mating behaviour and the presence of calves are recorded in the months of April and May and calves are additionally reported in October and December. Little is known about the ecology of this species in the region.Threats to Indian Ocean humpback dolphins in the Arabian region include incidental capture in fishing nets, general coastal and offshore development (e.g. land reclamation, dredging, port and harbor construction), pollution, boat traffic, oil and gas exploration (including seismic surveying), military exercises and toxins associated with red tide events. Evidence for historic and current directed catches of Sousa plumbea is presented.Intraspecific variation in cranial measurements is presented for cranially adult skulls originating from the Arabian Sea coast of Oman and initial comparison with limited data from the Saudi Arabian Gulf coast are drawn. Cranial abnormalities in skull specimens from Oman are discussed. Curated specimens from the Arabian region are listed
Evidence for Skyrmion crystallization from NMR relaxation experiments
A resistively detected NMR technique was used to probe the two-dimensional
electron gas in a GaAs/AlGaAs quantum well. The spin-lattice relaxation rate
was extracted at near complete filling of the first Landau level by
electrons. The nuclear spin of As is found to relax much more
efficiently with and when a well developed quantum Hall state with
occurs. The data show a remarkable correlation between the
nuclear spin relaxation and localization. This suggests that the magnetic
ground state near complete filling of the first Landau level may contain a
lattice of topological spin texture, i.e. a Skyrmion crystal
Localization Transition in a Ballistic Quantum Wire
The many-body wave-function of an interacting one-dimensional electron system
is probed, focusing on the low-density, strong interaction regime. The
properties of the wave-function are determined using tunneling between two
long, clean, parallel quantum wires in a GaAs/AlGaAs heterostructure, allowing
for gate-controlled electron density. As electron density is lowered to a
critical value the many-body state abruptly changes from an extended state with
a well-defined momentum to a localized state with a wide range of momentum
components. The signature of the localized states appears as discrete tunneling
features at resonant gate-voltages, corresponding to the depletion of single
electrons and showing Coulomb-blockade behavior. Typically 5-10 such features
appear, where the one-electron state has a single-lobed momentum distribution,
and the few-electron states have double-lobed distributions with peaks at . A theoretical model suggests that for a small number of particles (N<6),
the observed state is a mixture of ground and thermally excited spin states.Comment: 10 pages, 4 figures, 1 tabl
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