7,814 research outputs found
Quantizing the line element field
A metric with signature (-+++) can be constructed from a metric with
signature (++++) and a double-sided vector field called the line element field.
Some of the classical and quantum properties of this vector field are studied.Comment: 9 page
Conservative-dissipative approximation schemes for a generalized Kramers equation
We propose three new discrete variational schemes that capture the
conservative-dissipative structure of a generalized Kramers equation. The first
two schemes are single-step minimization schemes while the third one combines a
streaming and a minimization step. The cost functionals in the schemes are
inspired by the rate functional in the Freidlin-Wentzell theory of large
deviations for the underlying stochastic system. We prove that all three
schemes converge to the solution of the generalized Kramers equation
Unexpected contraction of a zeolite framework upon isomorphous substitution of Si by Al
Isomorphous substitution of Si by Al in the framework of sodalites synthesized in ethylene glycol causes an unexpected contraction of the zeolite framework
Synthesis of titanium-containing ZSM-48
Titanium-containing ZSM-48 is synthesized with silicon to titanium ratios of 26 or larger; changes in unit cell volume and IR data show that titanium is incorporated into framework positions
Aluminophosphate molecular sieves comprised of hydrated triple crankshaft chains
We report the first synthesis of pure aluminophosphate hydrate H2 (AlPO4-H2) and its structure; AlPO4-H2 is constructed exclusively from a hydrated chain building unit that also builds the 18-ring VPI-5 structure and has one-dimensional channels circumscribed by highly elliptical rings consisting often oxygen atoms, implications from the existence of this building unit for the synthesis of novel aluminophosphate molecular sieves and for the synthesis of aluminosilicate and silicate analogues of AlPO4-H2 and VPI-5 are discussed
Galactic outflows and the kinematics of damped Lyman alpha absorbers
The kinematics of damped Lyman alpha absorbers (DLAs) are difficult to
reproduce in hierarchical galaxy formation models, particularly the
preponderance of wide systems. We investigate DLA kinematics at z=3 using
high-resolution cosmological hydrodynamical simulations that include a
heuristic model for galactic outflows. Without outflows, our simulations fail
to yield enough wide DLAs, as in previous studies. With outflows, predicted DLA
kinematics are in much better agreement with observations. Comparing two
outflow models, we find that a model based on momentum-driven wind scalings
provides the best match to the observed DLA kinematic statistics of Prochaska &
Wolfe. In this model, DLAs typically arise a few kpc away from galaxies that
would be identified in emission. Narrow DLAs can arise from any halo and galaxy
mass, but wide ones only arise in halos with mass >10^11 Mo, from either large
central or small satellite galaxies. This implies that the success of this
outflow model originates from being most efficient at pushing gas out from
small satellite galaxies living in larger halos. This increases the
cross-section for large halos relative to smaller ones, thereby yielding wider
kinematics. Our simulations do not include radiative transfer effects or
detailed metal tracking, and outflows are modeled heuristically, but they
strongly suggest that galactic outflows are central to understanding DLA
kinematics. An interesting consequence is that DLA kinematics may place
constraints on the nature and efficiency of gas ejection from high-z galaxies.Comment: submitted to MNRA
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