23,574 research outputs found
Long-term variation in the Sun's activity caused by magnetic Rossby waves in the tachocline
Long-term records of sunspot number and concentrations of cosmogenic
radionuclides (10Be and 14C) on the Earth reveal the variation of the Sun's
magnetic activity over hundreds and thousands of years. We identify several
clear periods in sunspot, 10Be, and 14C data as 1000, 500, 350, 200 and 100
years. We found that the periods of the first five spherical harmonics of the
slow magnetic Rossby mode in the presence of a steady toroidal magnetic field
of 1200-1300 G in the lower tachocline are in perfect agreement with the time
scales of observed variations. The steady toroidal magnetic field can be
generated in the lower tachocline either due to the steady dynamo magnetic
field for low magnetic diffusivity or due to the action of the latitudinal
differential rotation on the weak poloidal primordial magnetic field, which
penetrates from the radiative interior. The slow magnetic Rossby waves lead to
variations of the steady toroidal magnetic field in the lower tachocline, which
modulate the dynamo magnetic field and consequently the solar cycle strength.
This result constitutes a key point for long-term prediction of the cycle
strength. According to our model, the next deep minimum in solar activity is
expected during the first half of this century.Comment: 4 pages, 4 figures, accepted in ApJ
Photophoretic Structuring of Circumstellar Dust Disks
We study dust accumulation by photophoresis in optically thin gas disks.
Using formulae of the photophoretic force that are applicable for the free
molecular regime and for the slip-flow regime, we calculate dust accumulation
distances as a function of the particle size. It is found that photophoresis
pushes particles (smaller than 10 cm) outward. For a Sun-like star, these
particles are transported to 0.1-100 AU, depending on the particle size, and
forms an inner disk. Radiation pressure pushes out small particles (< 1 mm)
further and forms an extended outer disk. Consequently, an inner hole opens
inside ~0.1 AU. The radius of the inner hole is determined by the condition
that the mean free path of the gas molecules equals the maximum size of the
particles that photophoresis effectively works on (100 micron - 10 cm,
depending on the dust property). The dust disk structure formed by
photophoresis can be distinguished from the structure of gas-free dust disk
models, because the particle sizes of the outer disks are larger, and the inner
hole radius depends on the gas density.Comment: 15 pages, 9 figures, Accepted by ApJ; corrected a typo in the author
nam
Entanglement transfer from electron spins to photons in spin light-emitting diodes containing quantum dots
We show that electron recombination using positively charged excitons in
single quantum dots provides an efficient method to transfer entanglement from
electron spins onto photon polarizations. We propose a scheme for the
production of entangled four-photon states of GHZ type. From the GHZ state, two
fully entangled photons can be obtained by a measurement of two photons in the
linear polarization basis, even for quantum dots with observable fine structure
splitting for neutral excitons and significant exciton spin decoherence.
Because of the interplay of quantum mechanical selection rules and
interference, maximally entangled electron pairs are converted into maximally
entangled photon pairs with unity fidelity for a continuous set of observation
directions. We describe the dynamics of the conversion process using a
master-equation approach and show that the implementation of our scheme is
feasible with current experimental techniques.Comment: 5 pages, 2 figures. v2: Extended scheme, revised version. v3: Minor
additions and extended title, published versio
Ultra-Low-Power Superconductor Logic
We have developed a new superconducting digital technology, Reciprocal
Quantum Logic, that uses AC power carried on a transmission line, which also
serves as a clock. Using simple experiments we have demonstrated zero static
power dissipation, thermally limited dynamic power dissipation, high clock
stability, high operating margins and low BER. These features indicate that the
technology is scalable to far more complex circuits at a significant level of
integration. On the system level, Reciprocal Quantum Logic combines the high
speed and low-power signal levels of Single-Flux- Quantum signals with the
design methodology of CMOS, including low static power dissipation, low latency
combinational logic, and efficient device count.Comment: 7 pages, 5 figure
Twisting moduli for GL(2)
We prove various converse theorems for automorphic forms on \Gamma_0(N), each assuming fewer twisted functional equations than the last. We show that no twisting at all is needed for holomorphic modular forms in the case that N\in{18,20,24} - these integers are the smallest multiples of 4 or 9 not covered by earlier work of Conrey–Farmer. This development is a consequence of finding generating sets for \Gamma_0(N) such that each generator can be written as a product of special matrices. As for real-analytic Maass forms of even (resp. odd) weight we prove the analogous statement for 1\leq N\leq 12, 14\leq N\leq18 and N\in{16,18} (resp. 1\leq N\leq 12, 14\leq N\leq 18 and N\in{20,23,24})
Multiple forms of tyrosine aminotransferase in rat liver and their hormonal induction in the neonate
Lift-up, Kelvin-Helmholtz and Orr mechanisms in turbulent jets
Three amplification mechanisms present in turbulent jets, namely lift-up, Kelvin–Helmholtz and Orr, are characterized via global resolvent analysis and spectral proper orthogonal decomposition (SPOD) over a range of Mach numbers. The lift-up mechanism was recently identified in turbulent jets via local analysis by Nogueira et al. (J. Fluid Mech., vol. 873, 2019, pp. 211–237) at low Strouhal number ( St ) and non-zero azimuthal wavenumbers ( m ). In these limits, a global SPOD analysis of data from high-fidelity simulations reveals streamwise vortices and streaks similar to those found in turbulent wall-bounded flows. These structures are in qualitative agreement with the global resolvent analysis, which shows that they are a response to upstream forcing of streamwise vorticity near the nozzle exit. Analysis of mode shapes, component-wise amplitudes and sensitivity analysis distinguishes the three mechanisms and the regions of frequency–wavenumber space where each dominates, finding lift-up to be dominant as St/m→0 . Finally, SPOD and resolvent analyses of localized regions show that the lift-up mechanism is present throughout the jet, with a dominant azimuthal wavenumber inversely proportional to streamwise distance from the nozzle, with streaks of azimuthal wavenumber exceeding five near the nozzle, and wavenumbers one and two most energetic far downstream of the potential core
B-Meson Distribution Amplitudes of Geometric Twist vs. Dynamical Twist
Two- and three-particle distribution amplitudes of heavy pseudoscalar mesons
of well-defined geometric twist are introduced. They are obtained from
appropriately parametrized vacuum-to-meson matrix elements by applying those
twist projectors which determine the enclosed light-cone operators of definite
geometric twist and, in addition, observing the heavy quark constraint.
Comparing these distribution amplitudes with the conventional ones of dynamical
twist we derive relations between them, partially being of Wandzura-Wilczek
type; also sum rules of Burkhardt-Cottingham type are derived.The derivation is
performed for the (double) Mellin moments and then re-summed to the non-local
distribution amplitudes. Furthermore, a parametrization of vacuum-to-meson
matrix elements for non-local operators off the light-cone in terms of
distribution amplitudes accompanying independent kinematical structures is
derived.Comment: 18 pages, Latex 2e, no figure
Explicit solution of the linearized Einstein equations in TT gauge for all multipoles
We write out the explicit form of the metric for a linearized gravitational
wave in the transverse-traceless gauge for any multipole, thus generalizing the
well-known quadrupole solution of Teukolsky. The solution is derived using the
generalized Regge-Wheeler-Zerilli formalism developed by Sarbach and Tiglio.Comment: 9 pages. Minor corrections, updated references. Final version to
appear in Class. Quantum Gra
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