11,912 research outputs found
Is the partner of in the nonet?
Based on a mass matrix, the mixing angle of the axial vector
states and is determined to be , and the
theoretical results about the decay and production of the two states are
presented. The theoretical results are in good agreement with the present
experimental results, which suggests that can be assigned as the
partner of in the nonet. We also suggest that
the existence of needs further experimental confirmation.Comment: Latex, 6 pages, to be published in Chin. Phys. let
Global-mean Vertical Tracer Mixing in Planetary Atmospheres II: Tidally Locked Planets
In Zhang Showman (2018, hereafter Paper I), we developed an analytical
theory of 1D eddy diffusivity for global-mean vertical tracer
transport in a 3D atmosphere. We also presented 2D numerical simulations on
fast-rotating planets to validate our theory. On a slowly rotating planet such
as Venus or a tidally locked planet (not necessarily a slow-rotator) such as a
hot Jupiter, the tracer distribution could exhibit significant longitudinal
inhomogeneity and tracer transport is intrinsically 3D. Here we study the
global-mean vertical tracer transport on tidally locked planets using 3D
tracer-transport simulations. We find that our analytical theory in
Paper I is validated on tidally locked planets over a wide parameter space.
strongly depends on the large-scale circulation strength, horizontal
mixing due to eddies and waves and local tracer sources and sinks due to
chemistry and microphysics. As our analytical theory predicted, on
tidally locked planets also exhibit three regimes In Regime I where the
chemical and microphysical processes are uniformly distributed across the
globe, different chemical species should be transported via different eddy
diffusivity. In Regime II where the chemical and microphysical processes are
non-uniform---for example, photochemistry or cloud formation that exhibits
strong day-night contrast---the global-mean vertical tracer mixing does not
always behave diffusively. In the third regime where the tracer is long-lived,
non-diffusive effects are significant. Using species-dependent eddy
diffusivity, we provide a new analytical theory of the dynamical quench points
for disequilibrium tracers on tidally locked planets from first principles.Comment: Accepted at ApJ, 16 pages, 12 figures. This is the part II. Part I is
"Global-mean Vertical Tracer Mixing in Planetary Atmospheres I: Theory and
Fast-rotating Planets
Effects of Bulk Composition on The Atmospheric Dynamics on Close-in Exoplanets
Super Earths and mini Neptunes likely have a wide range of atmospheric
compositions, ranging from low-molecular mass atmospheres of H2 to higher
molecular atmospheres of water, CO2, N2, or other species. Here, we
systematically investigate the effects of atmospheric bulk compositions on
temperature and wind distributions for tidally locked sub-Jupiter-sized
planets, using an idealized 3D general circulation model (GCM). The bulk
composition effects are characterized in the framework of two independent
variables: molecular weight and molar heat capacity. The effect of molecular
weight dominates. As the molecular weight increases, the atmosphere tends to
have a larger day-night temperature contrast, a smaller eastward phase shift in
the thermal phase curve and a smaller zonal wind speed. The width of the
equatorial super-rotating jet also becomes narrower and the "jet core" region,
where the zonal-mean jet speed maximizes, moves to a greater pressure level.
The zonal-mean zonal wind is more prone to exhibit a latitudinally alternating
pattern in a higher-molecular-weight atmosphere. We also present analytical
theories that quantitatively explain the above trends and shed light on the
underlying dynamical mechanisms. Those trends might be used to indirectly
determine the atmospheric compositions on tidally locked sub-Jupiter-sized
planets. The effects of the molar heat capacity are generally small. But if the
vertical temperature profile is close to adiabatic, molar heat capacity will
play a significant role in controlling the transition from a divergent flow in
the upper atmosphere to a jet-dominated flow in the lower atmosphere.Comment: 25 pages, 22 figure
Retrieving the Size of Deep-subwavelength Objects via Tunable Optical Spin-Orbit Coupling
We propose a scheme to retrieve the size parameters of a nano-particle on a
glass substrate at a scale much smaller than the wavelength. This is achieved
by illuminating the particle using two plane waves to create rich and
non-trivial local polarization distributions, and observing the far-field
scattering pattern into the substrate. A simple dipole model which exploits
tunneling effect of evanescent field into regions beyond the critical angle, as
well as directional scattering due to spin-orbit coupling is developed, to
relate the particle's shape, size and position to the far-field scattering with
remarkable sensitivity. Our method brings about a far-field super-resolution
imaging scheme based on the interaction of vectorial light with nanoparticles
Atmospheric Circulation of Brown Dwarfs: Jets, Vortices, and Time Variability
A variety of observational evidence demonstrates that brown dwarfs exhibit
active atmospheric circulations. In this study we use a shallow-water model to
investigate the global atmospheric dynamics in the stratified layer overlying
the convective zone on these rapidly rotating objects. We show that the
existence and properties of the atmospheric circulation crucially depend on key
parameters including the energy injection rate and radiative timescale. Under
conditions of strong internal heat flux and weak radiative dissipation, a
banded flow pattern comprising east-west jet streams spontaneously emerges from
the interaction of atmospheric turbulence with the planetary rotation. In
contrast, when the internal heat flux is weak and/or radiative dissipation is
strong, turbulence injected into the atmosphere damps before it can
self-organize into jets, leading to a flow dominated by transient eddies and
isotropic turbulence instead. The simulation results are not very sensitive to
the form of the forcing. Based on the location of the transition between
jet-dominated and eddy-dominated regimes, we suggest that many brown dwarfs may
exhibit atmospheric circulations dominated by eddies and turbulence (rather
than jets) due to the strong radiative damping on these worlds, but a jet
structure is also possible under some realistic conditions. Our simulated light
curves capture important features from observed infrared lightcurves of brown
dwarfs, including amplitude variations of a few percent and shapes that
fluctuate between single-peak and multi-peak structures. More broadly, our work
shows that the shallow-water system provides a useful tool to illuminate
fundamental aspects of the dynamics on these worlds
Non-negligible magnetic dipole scattering from metallic nanowire for ultrasensitive deflection sensing
It is generally believed that when a single metallic nanowire is sufficiently
small, it scatters like a point electric dipole. We show theoretically when a
metallic nanowire is placed inside specially designed beams, the non-negligible
magnetic dipole contribution along with the electric dipole resonance can lead
to unidirectional scattering in the far-field, fulfilling Kerker's condition.
Remarkably, this far-field unidirectional scattering encodes information that
is highly dependent on the nanowire's deflection at a scale much smaller than
the wavelength. The special role of small but non-negligible magnetic response
and plasmonic resonance are highlighted for this extreme sensitivity as
compared with the dielectric counterpart. Effects such as scattering efficiency
and shape of the nanowire's cross section are also discussed.Comment: 5 pages, 3 figures. Comments are welcom
Atmospheric Circulation of Brown Dwarfs and Jupiter and Saturn-like Planets: Zonal Jets, Long-term Variability, and QBO-type Oscillations
Brown dwarfs and directly imaged giant planets exhibit significant evidence
for active atmospheric circulation, which induces a large-scale patchiness in
the cloud structure that evolves significantly over time, as evidenced by
infrared light curves and Doppler maps. These observations raise critical
questions about the fundamental nature of the circulation, its time
variability, and the overall relationship to the circulation on Jupiter and
Saturn. Jupiter and Saturn themselves exhibit numerous robust zonal (east-west)
jet streams at the cloud level; moreover, both planets exhibit long-term
stratospheric oscillations involving perturbations of zonal wind and
temperature that propagate downward over time on timescales of ~4 years
(Jupiter) and ~15 years (Saturn). These oscillations, dubbed the Quasi
Quadrennial Oscillation (QQO) for Jupiter and the Semi-Annual Oscillation (SAO)
on Saturn, are thought to be analogous to the Quasi-Biennial Oscillation (QBO)
on Earth, which is driven by upward propagation of equatorial waves from the
troposphere. To investigate these issues, we here present global,
three-dimensional, high-resolution numerical simulations of the flow in the
stratified atmosphere--overlying the convective interior--of brown dwarfs and
Jupiter-like planets. The effect of interior convection is parameterized by
inducing small-scale, randomly varying perturbations in the
radiative-convective boundary at the base of the model. In the simulations, the
convective perturbations generate atmospheric waves and turbulence that
interact with the rotation to produce numerous zonal jets. Moreover, the
equatorial stratosphere exhibits stacked eastward and westward jets that
migrate downward over time, exactly as occurs in the terrestrial QBO, Jovian
QQO, and Saturnian SAO. This is the first demonstration of a QBO-like
phenomenon in 3D numerical simulations of a giant planet.Comment: 27 pages, 15 figures, in press at ApJ; this is the revised (accepted)
version, which includes a major new section providing detailed analysis of
the types of wave modes present in the model, and characterizing the
wave-mean-flow interactions by which they generate the QBO-like oscillation
Astrophysical constraints on the proton-to-electron mass ratio with FAST
That the laws of physics are the same at all times and places throughout the
Universe is one of the basic assumptions of physics. Astronomical observations
provide the only means to test this basic assumption on cosmological time and
distance scales. The possibility of variations in the dimensionless physical
constant {\mu} - the proton-to-electron mass ratio, can be tested by comparing
astronomical measurements of the rest frequency of certain spectral lines at
radio wavelengths with laboratory determinations. Different types of molecular
transitions have different dependencies on {\mu} and so observations of two or
more spectral lines towards the same astronomical source can be used to test
whether there is any evidence for either temporal or spatial changes in the
physical fundamental constants. {\mu} will change if the relative strength of
the strong nuclear force compared to the electromagnetic force varies.
Theoretical studies have shown that the rotational transitions of some
molecules which have transitions in the frequency range that will be covered by
FAST (e.g., CH3OH, OH and CH) are sensitive to changes in {\mu}. A number of
studies looking for possible variations in {\mu} have been undertaken with
existing telescopes, however, the greater sensitivity of FAST means it will
open new opportunities to significantly improve upon measurements made to date.
In this paper, we discuss which molecular transitions and sources (both in the
Galaxy and external galaxies) are likely targets for providing improved
constraints on {\mu} with FAST
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