14,290 research outputs found
Spatiotemporal Calibration of Atmospheric Nitrogen Dioxide Concentration Estimates From an Air Quality Model for Connecticut
A spatiotemporal calibration and resolution refinement model was fitted to
calibrate nitrogen dioxide (NO) concentration estimates from the Community
Multiscale Air Quality (CMAQ) model, using two sources of observed data on
NO that differed in their spatial and temporal resolutions. To refine the
spatial resolution of the CMAQ model estimates, we leveraged information using
additional local covariates including total traffic volume within 2 km,
population density, elevation, and land use characteristics. Predictions from
this model greatly improved the bias in the CMAQ estimates, as observed by the
much lower mean squared error (MSE) at the NO monitor sites. The final
model was used to predict the daily concentration of ambient NO over the
entire state of Connecticut on a grid with pixels of size 300 x 300 m. A
comparison of the prediction map with a similar map for the CMAQ estimates
showed marked improvement in the spatial resolution. The effect of local
covariates was evident in the finer spatial resolution map, where the
contribution of traffic on major highways to ambient NO concentration
stands out. An animation was also provided to show the change in the
concentration of ambient NO over space and time for 1994 and 1995.Comment: 23 pages, 8 figures, supplementary materia
Vertical Structure of Stationary Accretion Disks with a Large-Scale Magnetic Field
In earlier works we pointed out that the disk's surface layers are
non-turbulent and thus highly conducting (or non-diffusive) because the
hydrodynamic and/or magnetorotational (MRI) instabilities are suppressed high
in the disk where the magnetic and radiation pressures are larger than the
plasma thermal pressure. Here, we calculate the vertical profiles of the {\it
stationary} accretion flows (with radial and azimuthal components), and the
profiles of the large-scale, magnetic field taking into account the turbulent
viscosity and diffusivity and the fact that the turbulence vanishes at the
surface of the disk.
Also, here we require that the radial accretion speed be zero at the disk's
surface and we assume that the ratio of the turbulent viscosity to the
turbulent magnetic diffusivity is of order unity. Thus at the disk's surface
there are three boundary conditions. As a result, for a fixed dimensionless
viscosity -value, we find that there is a definite relation between the
ratio of the accretion power going into magnetic disk winds to the
viscous power dissipation and the midplane plasma-, which is the ratio
of the plasma to magnetic pressure in the disk. For a specific disk model with
of order unity we find that the critical value required for a
stationary solution is , where the disk's
half thickness. For weaker magnetic fields, , we argue that
the poloidal field will advect outward while for it will
advect inward. Alternatively, if the disk wind is negligible (), there are stationary solutions with .Comment: 5 pages, 3 figure
Integrable variant of the one-dimensional Hubbard model
A new integrable model which is a variant of the one-dimensional Hubbard
model is proposed. The integrability of the model is verified by presenting the
associated quantum R-matrix which satisfies the Yang-Baxter equation. We argue
that the new model possesses the SO(4) algebra symmetry, which contains a
representation of the -pairing SU(2) algebra and a spin SU(2) algebra.
Additionally, the algebraic Bethe ansatz is studied by means of the quantum
inverse scattering method. The spectrum of the Hamiltonian, eigenvectors, as
well as the Bethe ansatz equations, are discussed
Thickness-dependent spontaneous dewetting morphology of ultrathin Ag films
We show here that the morphological pathway of spontaneous dewetting of
ultrathin Ag films on SiO2 under nanosecond laser melting is found to be film
thickness dependent. For films with thickness h between 2 <= h <= 9.5 nm, the
morphology during the intermediate stages of dewetting consisted of
bicontinuous structures. For films 11.5 <= h <= 20 nm, the intermediate stages
consisted of regularly-sized holes. Measurement of the characteristic length
scales for different stages of dewetting as a function of film thickness showed
a systematic increase, which is consistent with the spinodal dewetting
instability over the entire thickness range investigated. This change in
morphology with thickness is consistent with observations made previously for
polymer films [A. Sharma et al, Phys. Rev. Lett., v81, pp3463 (1998); R.
Seemann et al, J. Phys. Cond. Matt., v13, pp4925, (2001)]. Based on the
behavior of free energy curvature that incorporates intermolecular forces, we
have estimated the morphological transition thickness for the intermolecular
forces for Ag on SiO2 . The theory predictions agree well with observations for
Ag. These results show that it is possible to form a variety of complex Ag
nanomorphologies in a consistent manner, which could be useful in optical
applications of Ag surfaces, such as in surface enhanced Raman sensing.Comment: 20 pages, 5 figure
Standard random walks and trapping on the Koch network with scale-free behavior and small-world effect
A vast variety of real-life networks display the ubiquitous presence of
scale-free phenomenon and small-world effect, both of which play a significant
role in the dynamical processes running on networks. Although various dynamical
processes have been investigated in scale-free small-world networks, analytical
research about random walks on such networks is much less. In this paper, we
will study analytically the scaling of the mean first-passage time (MFPT) for
random walks on scale-free small-world networks. To this end, we first map the
classical Koch fractal to a network, called Koch network. According to this
proposed mapping, we present an iterative algorithm for generating the Koch
network, based on which we derive closed-form expressions for the relevant
topological features, such as degree distribution, clustering coefficient,
average path length, and degree correlations. The obtained solutions show that
the Koch network exhibits scale-free behavior and small-world effect. Then, we
investigate the standard random walks and trapping issue on the Koch network.
Through the recurrence relations derived from the structure of the Koch
network, we obtain the exact scaling for the MFPT. We show that in the infinite
network order limit, the MFPT grows linearly with the number of all nodes in
the network. The obtained analytical results are corroborated by direct
extensive numerical calculations. In addition, we also determine the scaling
efficiency exponents characterizing random walks on the Koch network.Comment: 12 pages, 8 figures. Definitive version published in Physical Review
Determining the Elemental and Isotopic Composition of the preSolar Nebula from Genesis Data Analysis: The Case of Oxygen
We compare element and isotopic fractionations measured in solar wind samples
collected by NASA's Genesis mission with those predicted from models
incorporating both the ponderomotive force in the chromosphere and conservation
of the first adiabatic invariant in the low corona. Generally good agreement is
found, suggesting that these factors are consistent with the process of solar
wind fractionation. Based on bulk wind measurements, we also consider in more
detail the isotopic and elemental abundances of O. We find mild support for an
O abundance in the range 8.75 - 8.83, with a value as low as 8.69 disfavored. A
stronger conclusion must await solar wind regime specific measurements from the
Genesis samples.Comment: 6 pages, accepted by Astrophysical Journal Letter
On the equivalence of Eulerian and Lagrangian variables for the two-component Camassa-Holm system
The Camassa-Holm equation and its two-component Camassa-Holm system
generalization both experience wave breaking in finite time. To analyze this,
and to obtain solutions past wave breaking, it is common to reformulate the
original equation given in Eulerian coordinates, into a system of ordinary
differential equations in Lagrangian coordinates. It is of considerable
interest to study the stability of solutions and how this is manifested in
Eulerian and Lagrangian variables. We identify criteria of convergence, such
that convergence in Eulerian coordinates is equivalent to convergence in
Lagrangian coordinates. In addition, we show how one can approximate global
conservative solutions of the scalar Camassa-Holm equation by smooth solutions
of the two-component Camassa-Holm system that do not experience wave breaking
Jordan-Wigner fermionization for the one-dimensional Bariev model of three coupled XY chains
The Jordan-Wigner fermionization for the one-dimensional Bariev model of
three coupled XY chains is formulated. The Lax operator in terms of fermion
operators and the quantum R-matrix are presented explicitly. Furthermore, the
graded reflection equations and their solutions are discussed.Comment: 10 pages, no figur
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