2,184 research outputs found
Socioeconomic impact of photovoltaic power at Schuchuli, Arizona
The social and economic impact of photovoltaic power on a small, remote native American village is studied. Village history, group life, energy use in general, and the use of photovoltaic-powered appliances are discussed. No significant impacts due to the photovoltaic power system were observed
Conserved quantities in isotropic loop quantum cosmology
We develop an action principle for those models arising from isotropic loop
quantum cosmology, and show that there is a natural conserved quantity for
the discrete difference equation arising from the Hamiltonian constraint. This
quantity relates the semi-classical limit of the wavefunction at large
values of the spatial volume, but opposite triad orientations. Moreover, there
is a similar quantity for generic difference equations of one parameter arising
from a self-adjoint operator.Comment: 6 pages, to be published in Europhysics Letter
Significant contribution to total mass from very small glaciers
A single large glacier can contain tens of millions of times the mass of a small glacier. Nevertheless, very small glaciers (with area &le;1 km<sup>2</sup>) are so numerous that their contribution to the world's total ice volume is significant and may be a notable source of error if excluded. With current glacier inventories, total global volume errors on the order of 10% are possible. However, to reduce errors to below 1% requires the inclusion of glaciers that are smaller than those recorded in most inventories. At the global scale, 1% accuracy requires a list of all glaciers and ice caps (GIC, exclusive of the ice sheets) larger than 1 km<sup>2</sup>, and for regional estimates requires a complete list of all glaciers down to the smallest possible size. For this reason, sea-level rise estimates and other total mass and total volume analyses should not omit the world's smallest glaciers. In particular, upscaling GIC inventories has been common practice in sea level estimates, but downscaling may also be necessary to include the smallest glaciers
Social and Economic Impact of Solar Electricity at Schuchuli Village
Schuchuli, a small remote village on the Papago Indian Reservation in southwest Arizona, is 27 kilometers (17 miles) from the nearest available utility power. Its lack of conventional power is due to the prohibitive cost of supplying a small electrical load with a long-distance distribution line. Furthermore, alternate energy sources are expensive and place a burden on the resources of the villagers. On December 16, 1978, as part of a federally funded project, a solar cell power system was put into operation at Schuchuli. The system powers the village water pump, lighting for homes and other village buildings, family refrigerators and a communal washing machine and sewing machine
From the discrete to the continuous - towards a cylindrically consistent dynamics
Discrete models usually represent approximations to continuum physics.
Cylindrical consistency provides a framework in which discretizations mirror
exactly the continuum limit. Being a standard tool for the kinematics of loop
quantum gravity we propose a coarse graining procedure that aims at
constructing a cylindrically consistent dynamics in the form of transition
amplitudes and Hamilton's principal functions. The coarse graining procedure,
which is motivated by tensor network renormalization methods, provides a
systematic approximation scheme towards this end. A crucial role in this coarse
graining scheme is played by embedding maps that allow the interpretation of
discrete boundary data as continuum configurations. These embedding maps should
be selected according to the dynamics of the system, as a choice of embedding
maps will determine a truncation of the renormalization flow.Comment: 22 page
On the Expansions in Spin Foam Cosmology
We discuss the expansions used in spin foam cosmology. We point out that
already at the one vertex level arbitrarily complicated amplitudes contribute,
and discuss the geometric asymptotics of the five simplest ones. We discuss
what type of consistency conditions would be required to control the expansion.
We show that the factorisation of the amplitude originally considered is best
interpreted in topological terms. We then consider the next higher term in the
graph expansion. We demonstrate the tension between the truncation to small
graphs and going to the homogeneous sector, and conclude that it is necessary
to truncate the dynamics as well.Comment: 17 pages, 4 figures, published versio
Towards computational insights into the large-scale structure of spin foams
Understanding the large-scale physics is crucial for the spin foam approach
to quantum gravity. We tackle this challenge from a statistical physics
perspective using simplified, yet feature-rich models. In particular, this
allows us to explicitly answer whether broken symmetries will be restored by
renormalization: We observe a weak phase transition in both Migdal-Kadanoff and
tensor network renormalization. In this work we give a concise presentation of
the concepts, results and promises of this new direction of research.Comment: 10 pages, 9 figures, to be published in proceedings of the Loops'11
Madrid international conference on quantum gravit
Towards computational insights into the large-scale structure of spin foams
Understanding the large-scale physics is crucial for the spin foam approach
to quantum gravity. We tackle this challenge from a statistical physics
perspective using simplified, yet feature-rich models. In particular, this
allows us to explicitly answer whether broken symmetries will be restored by
renormalization: We observe a weak phase transition in both Migdal-Kadanoff and
tensor network renormalization. In this work we give a concise presentation of
the concepts, results and promises of this new direction of research.Comment: 10 pages, 9 figures, to be published in proceedings of the Loops'11
Madrid international conference on quantum gravit
Towards computational insights into the large-scale structure of spin foams
Understanding the large-scale physics is crucial for the spin foam approach
to quantum gravity. We tackle this challenge from a statistical physics
perspective using simplified, yet feature-rich models. In particular, this
allows us to explicitly answer whether broken symmetries will be restored by
renormalization: We observe a weak phase transition in both Migdal-Kadanoff and
tensor network renormalization. In this work we give a concise presentation of
the concepts, results and promises of this new direction of research.Comment: 10 pages, 9 figures, to be published in proceedings of the Loops'11
Madrid international conference on quantum gravit
Regge calculus from a new angle
In Regge calculus space time is usually approximated by a triangulation with
flat simplices. We present a formulation using simplices with constant
sectional curvature adjusted to the presence of a cosmological constant. As we
will show such a formulation allows to replace the length variables by 3d or 4d
dihedral angles as basic variables. Moreover we will introduce a first order
formulation, which in contrast to using flat simplices, does not require any
constraints. These considerations could be useful for the construction of
quantum gravity models with a cosmological constant.Comment: 8 page
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