30,004 research outputs found
On the Geometric Principles of Surface Growth
We introduce a new equation describing epitaxial growth processes. This
equation is derived from a simple variational geometric principle and it has a
straightforward interpretation in terms of continuum and microscopic physics.
It is also able to reproduce the critical behavior already observed, mound
formation and mass conservation, but however does not fit a divergence form as
the most commonly spread models of conserved surface growth. This formulation
allows us to connect the results of the dynamic renormalization group analysis
with intuitive geometric principles, whose generic character may well allow
them to describe surface growth and other phenomena in different areas of
physics
On the spectrum of nonrelativistic AdS/CFT
We develop a Hamiltonian picture for a family of models of nonrelativistic
AdS/CFT duality. The Schrodinger group is realized via the conformal quantum
mechanics of De Alfaro, Fubini and Furlan in the holographic direction. We show
that most physical requirements, including the introduction of harmonic traps,
can be realized with exact AdS metrics, but without any need for exotic matter
sectors in the bulk dynamics. This Hamiltonian picture can be used to compare
directly with many-body spectra of fermions at unitarity on harmonic traps,
thereby providing a direct physical interpretation of the holographic radial
coordinate for these systems. Finally, we add some speculations on the
dynamical generation of mass gaps in the AdS description, the resulting
quasiparticle spectra, and the analog of `deconfining' phase transitions that
may occur.Comment: 20 pages and 1 figure; typos corrected, references added; references
added, minor changes matching published versio
Geometrical approach to tumor growth
Tumor growth has a number of features in common with a physical process known
as molecular beam epitaxy. Both growth processes are characterized by the
constraint of growth development to the body border, and surface diffusion of
cells/particles at the growing edge. However, tumor growth implies an
approximate spherical symmetry that makes necessary a geometrical treatment of
the growth equations. The basic model was introduced in a former article [C.
Escudero, Phys. Rev. E 73, 020902(R) (2006)], and in the present work we extend
our analysis and try to shed light on the possible geometrical principles that
drive tumor growth. We present two-dimensional models that reproduce the
experimental observations, and analyse the unexplored three-dimensional case,
for which new conclusions on tumor growth are derived
World trends in fertilizer use and projections to 2020
Fertilizers have played an important role in increased crop production, especially in cereal yields, and will continue to be a cornerstone of the science-based agriculture required to feed the expanding world population. Fertilizers replenish the nutrients removed from soils by harvested crops, encourage adoption of high-yielding varieties, and increase biomass in the nutrient-poor soils of the tropics. Bumb and Baanante trace fertilizer use until the 1990s as well as production and price trends. Finally they propose projected trends in use, requirements, and production. The authors conclude that, overall, a conducive and stable policy environment, including macroeconomic stability, price incentives, credit availability, efficient organizational arrangements, research and extension support, regulatory frameworks, and environmental monitoring, will be essential to promote environmentally friendly growth in fertilizer use and supply to 2020.Fertilizers. ,Crops Economic aspects. ,Cereal crops. ,Environmental protection. ,
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