1,679 research outputs found
Sea Ice Versus Storms: What Controls Sea Salt in Arctic Ice Cores?
The sea ice surface is thought to be a major source of sea salt aerosol, suggesting that sodium records of polar ice cores may trace past sea ice extent. Here we test this possibility for the Arctic, using a chemical transport model to simulate aerosol emission, transport and deposition in the satellite era. Our simulations suggest that sodium records from inland Greenland ice cores are strongly influenced by the impact of meteorology on aerosol transport and deposition. In contrast, sodium in coastal Arctic cores is predominantly sourced from the sea ice surface and the strength of these aerosol emissions controls the ice core sodium variability. Such ice cores may therefore record decadal to centennial scale Holocene sea ice changes. However, any relationship between ice core sodium and sea ice change may depend on how sea ice seasonality impacts sea salt emissions. Field-based observations are urgently required to constrain this.European Union Horizon 2020 Marie Sklodowska-Curie Individual Fellowship (658120, SEADOG) awarded to RHR.
EWW acknowledges support from the Royal Society (RP 120096)
XY acknowledges funding from NERC (NE/J023051/1)
Effect of Temperature on the Deformation Behavior of B2 Austenite in a Polycrystalline Ni49.9Ti50.1 (at.Percent) Shape Memory Alloy
Superelasticity in austenitic B2-NiTi is of great technical interest and has been studied in the past by several researchers [1]. However, investigation of temperature dependent deformation in B2-NiTi is equally important since competing mechanisms of stress-induced martensite (SIM), retained martensite, plastic and deformation twinning can lead to unusual mechanical behaviors. Identification of the role of various mechanisms contributing to the overall deformation response of B2-NiTi is imperative to understanding and maturing SMA-enabled technologies. Thus, the objective of this work was to study the deformation of polycrystalline Ni49.9Ti50.1 (at. %) above A(sub f) (105 C) in the B2 state at temperatures between 165-440 C, and generate a B2 deformation map showing active deformation mechanisms in different temperature-stress regimes
Modulational instability in periodic quadratic nonlinear materials
We investigate the modulational instability of plane waves in quadratic
nonlinear materials with linear and nonlinear quasi-phase-matching gratings.
Exact Floquet calculations, confirmed by numerical simulations, show that the
periodicity can drastically alter the gain spectrum but never completely
removes the instability. The low-frequency part of the gain spectrum is
accurately predicted by an averaged theory and disappears for certain gratings.
The high-frequency part is related to the inherent gain of the homogeneous
non-phase-matched material and is a consistent spectral feature.Comment: 4 pages, 7 figures corrected minor misprint
Absolute dimensions of the unevolved B-type eclipsing binary GG Orionis
We present photometric observations in B and V as well as spectroscopic
observations of the detached, eccentric 6.6-day double-lined eclipsing binary
GG Ori, a member of the Orion OB1 association. Absolute dimensions of the
components, which are virtually identical, are determined to high accuracy
(better than 1% in the masses and better than 2% in the radii) for the purpose
of testing various aspects of theoretical modeling. We obtain M(A) = 2.342 +/-
0.016 solar masses and R(A) = 1.852 +/- 0.025 solar radii for the primary, and
M(B) = 2.338 +/- 0.017 solar masses and R(B) = 1.830 +/- 0.025 solar radii for
the secondary. The effective temperature of both stars is 9950 +/- 200 K,
corresponding to a spectral type of B9.5. GG Ori is very close to the ZAMS, and
comparison with current stellar evolution models gives ages of 65-82 Myr or 7.7
Myr depending on whether the system is considered to be burning hydrogen on the
main sequence or still in the final stages of pre-main sequence contraction. We
have detected apsidal motion in the binary at a rate of dw/dt = 0.00061 +/-
0.00025 degrees per cycle, corresponding to an apsidal period of U = 10700 +/-
4500 yr. A substantial fraction of this (approximately 70%) is due to the
contribution from General Relativity.Comment: To appear in The Astronomical Journal, December 200
Polychromatic solitons in a quadratic medium
We introduce the simplest model to describe parametric interactions in a
quadratically nonlinear optical medium with the fundamental harmonic containing
two components with (slightly) different carrier frequencies [which is a direct
analog of wavelength-division multiplexed (WDM) models, well known in media
with cubic nonlinearity]. The model takes a closed form with three different
second-harmonic components, and it is formulated in the spatial domain. We
demonstrate that the model supports both polychromatic solitons (PCSs), with
all the components present in them, and two types of mutually orthogonal simple
solitons, both types being stable in a broad parametric region. An essential
peculiarity of PCS is that its power is much smaller than that of a simple
(usual) soliton (taken at the same values of control parameters), which may be
an advantage for experimental generation of PCSs. Collisions between the
orthogonal simple solitons are simulated in detail, leading to the conclusion
that the collisions are strongly inelastic, converting the simple solitons into
polychromatic ones, and generating one or two additional PCSs. A collision
velocity at which the inelastic effects are strongest is identified, and it is
demonstrated that the collision may be used as a basis to design a simple
all-optical XOR logic gate.Comment: 9 pages, 8 figures, accepted to Phys. Rev.
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