4,749 research outputs found
Chiral Symmetry and Hyperfine Quark-Antiquark Splittings
We briefly review theoretical calculations for the pseudoscalar-vector meson
hyperfine splitting with no open flavor and also report a many body field
theoretical effort to assess the impact of chiral symmetry in the choice of
effective potentials for relativistic quark models. Our calculations predict
the missing eta_b meson to have mass near 9400 . The radial excitation
is in agreement with the measurements of the BELLE and most
recently BABAR collaborations.Comment: European HEP conference proceedings (Aachen, July 2003). A few
typographical errors correcte
Entangled spinning particles in charged and rotating black holes
Spin precession for an EPR pair of spin-1/2 particles in equatorial orbits
around a Kerr-Newman black hole is studied. Hovering observers are introduced
to ensure fixed reference frames in order to perform the Wigner rotation. These
observers also guarantee a reliable direction to compare spin states in
rotating black holes. The velocity of the particle due frame-dragging is
explicitly incorporated by addition of velocities with respect the hovering
observers and the corresponding spin precession angle is computed. The
spin-singlet state is observed to be mixed with the spin-triplet by dynamical
and gravity effects, thus it is found that a perfect anti-correlation of
entangled states for these observers is deteriorated. Finally, an analysis
concerning the different limit cases of parameters of spin precession including
the frame-dragging effects is carried out.Comment: 25+1 pages, 7 eps figures. Major changes were made through all the
manuscript. Clarifications regarding modifications were introduced through
the draft. Figures were changed and reduced in number. arXiv admin note: text
overlap with arXiv:quant-ph/030711
Evolution of Cluster Ellipticals at 0.2 < z < 1.2 from Hubble Space Telescope Imaging
Two-dimensional surface photometry derived from Hubble Space Telescope
imaging is presented for a sample of 225 early-type galaxies (assumed to be
cluster members) in the fields of 9 clusters at redshifts .
The 94 luminous ellipticals (; selected by morphology alone with
no reference to color) form tight sequences in the size-luminosity plane. The
position of these sequences shifts, on average, with redshift so that an object
of a given size at z=0.55 is brighter by mag than
its counterpart (measured with the same techniques) in nearby clusters. At
z=0.9 the shift is mag. If the relation between
size and luminosity is universal so that the local cluster galaxies represent
the evolutionary endpoints of those at high redshift, and if the
size-luminosity relation is not modified by dynamical processes then this
population of galaxies has undergone significant luminosity evolution since z=1
consistent with expectations based on models of passively evolving, old stellar
populations.Comment: 7 pages, 3 figures, and 1 Tabl
Hybrid confinement of optical and mechanical modes in a bullseye optomechanical resonator
Optomechanical cavities have proven to be an exceptional tool to explore
fundamental and technological aspects of the interaction between mechanical and
optical waves. Such interactions strongly benefit from cavities with large
optomechanical coupling, high mechanical and optical quality factors, and
mechanical frequencies larger than the optical mode linewidth, the so called
resolved sideband limit. Here we demonstrate a novel optomechanical cavity
based on a disk with a radial mechanical bandgap. This design confines light
and mechanical waves through distinct physical mechanisms which allows for
independent control of the mechanical and optical properties. Our device design
is not limited by unique material properties and could be easily adapted to
allow large optomechanical coupling and high mechanical quality factors with
other promising materials. Finally, our demonstration is based on devices
fabricated on a commercial silicon photonics facility, demonstrating that our
approach can be easily scalable.Comment: 16 pages, 11 figure
Signatures of the impact of flare ejected plasma on the photosphere of a sunspot light-bridge
We investigate the properties of a sunspot light-bridge, focusing on the
changes produced by the impact of a plasma blob ejected from a C-class flare.
We observed a sunspot in active region NOAA 12544 using spectropolarimetric
raster maps of the four Fe I lines around 15655 \AA\ with the GREGOR Infrared
Spectrograph (GRIS), narrow-band intensity images sampling the Fe I 6173 \AA\
line with the GREGOR Fabry-P\'erot Interferometer (GFPI), and intensity broad
band images in G-band and Ca II H band with the High-resolution Fast Imager
(HiFI). All these instruments are located at the GREGOR telescope at the
Observatorio del Teide, Tenerife, Spain. The data cover the time before,
during, and after the flare event. The analysis is complemented with
Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI)
data from the Solar Dynamics Observatory (SDO). The physical parameters of the
atmosphere at differents heights were inferred using spectral-line inversion
techniques. We identify photospheric and chromospheric brightenings, heating
events, and changes in the Stokes profiles associated to the flare eruption and
the subsequent arrival of the plasma blob to the light bridge, after traveling
along an active region loop. The measurements suggest that these phenomena are
the result of reconnection events driven by the interaction of the plasma blob
with the magnetic field topology of the light bridge.Comment: Accepted for publication in A&
Impact of two different dual tasks on obstacle crossing in elderly
O desempenho de uma dupla tarefa pode aumentar o risco de quedas durante a marcha em idosos. O impacto de uma dupla tarefa pode depender de sua complexidade em relação ao processamento de informação. Diferentes configurações de duplas tarefas deduzem diferentes demandas para o processamento de informação. Neste estudo investigamos se diferentes configurações de duplas tarefas podem afetar o desempenho da transposição de obstáculo na marcha de idosos. Dez idosos independentes foram avaliados durante a marcha cruzando um obstáculo vertical enquanto desempenhando duas duplas tarefas: (a) com input auditório (variação da tarefa de Stroop), e (b) sem imput auditório (falar os dias da semana em ordem reversa). Nós hipotetizamos que um efeito da dupla tarefa seria relacionado com o tipo de seu input, e o input auditório requereria maior processamento de informação; portanto, poderia ter maior impacto na marcha. Nós encontramos que o desempanho de transpor obstáculo foi similar nas duas condições de dupla tarefa. Sendo assim, ambas duplas tarefas testadas afetam a transposição de obstáculo na mesma medida em idosos.El desempeño de una doble tarea puede aumentar el riesgo de caídas durante la marcha en personas mayores. El impacto de una doble tarea puede depender de su complejidad en cuanto al procesamiento de información. Las distintas configuraciones de dobles tareas infieren distintas demandas para dicho procesamiento. En este estudio se investigó si las distintas configuraciones de dobles tareas pueden afectar el rendimiento de la transposición de obstáculo en la marcha de personas mayores. Han participado diez personas mayores independientes y evaluadas durante la marcha cruzando un obstáculo vertical mientras hacían dos dobles tareas: (a) con input auditorio (variación de la tarea de Stroop) y (b) sin input auditorio (hablar los días de semana en orden reverso). Se dedujo que el rendimiento de la doble tarea estaría relacionado con el tipo de su input, y el input auditorio exigía un mayor procesamiento de información; por lo tanto, podría tener un mayor impacto en la marcha. Se encontró que el rendimiento en la superación de obstáculos fue semejante en las dos condiciones de doble tarea evaluadas. Así, ambas afectan a la superación del obstáculo en igual medida en personas mayores.The performance of a dual task increases risk of falling during walking in the elderly. Such impact of a dual task may depend on its complexity regarding information processing. Therefore, different dual task configurations may elicit different demands for information processing. We investigated whether different dual task configurations can differently affect the performance of obstacle crossing in the gait of elderly. Ten independent elderly performed vertical obstacle crossing while performing two dual tasks during walking: (a) with auditory input (variation of Stroop task), and (b) without auditory input (report the days of the week in reverse sequence). We hypothesized that a dual task effect would be related with the type of dual task input, and the auditory input would require further information processing and therefore could have larger impact on gait. We found that performance of obstacle crossing was similar regardless of the dual task configuration. Both dual task conditions affect the obstacle crossing in the same extent in the elderly
Ion pairing in model electrolytes: A study via three particle correlation functions
A novel integral equations approach is applied for studying ion pairing in
the restricted primitive model (RPM) electrolyte, i. e., the three point
extension (TPE) to the Ornstein-Zernike integral equations. In the TPE
approach, the three-particle correlation functions are obtained. The TPE results are compared to molecular
dynamics (MD) simulations and other theories. Good agreement between TPE and MD
is observed for a wide range of parameters, particularly where standard
integral equations theories fail, i. e., low salt concentration and high ionic
valence. Our results support the formation of ion pairs and aligned ion
complexes.Comment: 43 pages (including 18 EPS figs) - RevTeX 4 - J. Chem. Phys. (in
press
Numerical simulations of conversion to Alfven waves in sunspots
We study the conversion of fast magneto-acoustic waves to Alfven waves by
means of 2.5D numerical simulations in a sunspot-like magnetic configuration. A
fast, essentially acoustic, wave of a given frequency and wave number is
generated below the surface and propagates upward though the Alfven/acoustic
equipartition layer where it splits into upgoing slow (acoustic) and fast
(magnetic) waves. The fast wave quickly reflects off the steep Alfven speed
gradient, but around and above this reflection height it partially converts to
Alfven waves, depending on the local relative inclinations of the background
magnetic field and the wavevector. To measure the efficiency of this conversion
to Alfven waves we calculate acoustic and magnetic energy fluxes. The
particular amplitude and phase relations between the magnetic field and
velocity oscillations help us to demonstrate that the waves produced are indeed
Alfven waves. We find that the conversion to Alfven waves is particularly
important for strongly inclined fields like those existing in sunspot
penumbrae. Equally important is the magnetic field orientation with respect to
the vertical plane of wave propagation, which we refer to as "field azimuth".
For field azimuth less than 90 degrees the generated Alfven waves continue
upwards, but above 90 degrees downgoing Alfven waves are preferentially
produced. This yields negative Alfven energy flux for azimuths between 90 and
180 degrees. Alfven energy fluxes may be comparable to or exceed acoustic
fluxes, depending upon geometry, though computational exigencies limit their
magnitude in our simulations.Comment: Accepted for publication in Ap
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