70 research outputs found
A user-friendly and accurate machine learning tool for the evaluation of the worldwide yearly photovoltaic electricity production
While traditional methods for modelling the thermal and electrical behaviour of photovoltaic (PV) modules rely on analytical and empirical techniques, machine learning is gaining interest as a way to reduce the time, expertise, and tools required by designers or experts while maintaining high accuracy and reliability. This research presents a data-driven machine learning tool based on artificial neural networks (ANNs) that can forecast yearly PV electricity directly at the optimal PV inclination angle without geographic restrictions and is valid for a wide range of electrical characteristics of PV modules. Additionally, empirical correlations were developed to easily determine the optimal PV inclination angle worldwide. The ANN algorithm, developed in Matlab, systematically and quantitatively summarizes the behaviour of eight PV modules in 48 worldwide climatic conditions. The algorithm's applicability and robustness were proven by considering two different PV modules in the same 48 locations. Yearly climatic variables and electrical/thermal PV module parameters serve as input training data. The yearly PV electricity is derived using dynamic simulations in the TRNSYS environment, which is a simulation program primarily and extensively used in the fields of renewable energy engineering and building simulation for passive as well as active solar design. Multiple performance metrics validate that the ANN-based machine learning tool demonstrates high reliability and accuracy in the PV energy production forecasting for all weather conditions and PV module characteristics. In particular, by using 20 neurons, the highest value of R-square of 0.9797 and the lowest values of the root mean square error and coefficient of variance of 14.67 kWh and 3.8%, respectively, were obtained in the training phase. This high accuracy was confirmed in the ANN validation phase considering other PV modules. An R-square of 0.9218 and values of the root mean square error and coefficient of variance of 31.95 kWh and 7.8%, respectively, were obtained. The results demonstrate the algorithm's vast potential to enhance the worldwide diffusion and economic growth of solar energy, aligned with the seventh sustainable development goal
Isotropic Loop Quantum Cosmology with Matter
A free massless scalar field is coupled to homogeneous and isotropic loop
quantum cosmology. The coupled model is investigated in the vicinity of the
classical singularity, where discreteness is essential and where the quantum
model is non-singular, as well as in the regime of large volumes, where it
displays the expected semiclassical features. The particular matter content
(massless, free scalar) is chosen to illustrate how the discrete structure
regulates pathological behavior caused by kinetic terms of matter Hamiltonians
(which in standard quantum cosmology lead to wave functions with an infinite
number of oscillations near the classical singularity). Due to this
modification of the small volume behavior the dynamical initial conditions of
loop quantum cosmology are seen to provide a meaningful generalization of
DeWitt's initial condition.Comment: 18 pages, 4 figure
Loop Quantum Cosmology, Boundary Proposals, and Inflation
Loop quantum cosmology of the closed isotropic model is studied with a
special emphasis on a comparison with traditional results obtained in the
Wheeler-DeWitt approach. This includes the relation of the dynamical initial
conditions with boundary conditions such as the no-boundary or the tunneling
proposal and a discussion of inflation from quantum cosmology.Comment: 20 pages, 6 figure
Dynamical Initial Conditions in Quantum Cosmology
Loop quantum cosmology is shown to provide both the dynamical law and initial
conditions for the wave function of a universe by one discrete evolution
equation. Accompanied by the condition that semiclassical behavior is obtained
at large volume, a unique wave function is predicted.Comment: 4 pages, 1 figur
Spatially coordinated conservation auctions: a framed field experiment focusing on farmland wildlife conservation in China
How best to incentivize land managers to achieve conservation goals in an economically and ecologically effective manner is a key policy question that has gained increased relevance from the setting of ambitious new global targets for biodiversity conservation. Conservation (reverse) auctions are a policy tool for improving the environmental performance of agriculture, which has become well-established in the academic literature and in policy making in the US and Australia. However, little is known about the likely response of farmers to incentives within such an auction to (1) increase spatial connectivity and (2) encourage collective participation. This paper presents the first framed field experiment with farmers as participants that examines the effects of two features of conservation policy design: joint (collective) participation by farmers and the incentivization of spatial connectivity. The experiment employs farmers in China, a country making increasing use of payments for ecosystem services to achieve a range of environmental objectives. We investigate whether auction performanceâboth economic and ecologicalâcan be improved by the introduction of agglomeration bonus and joint bidding bonus mechanisms. Our empirical results suggest that, compared to a baseline spatially coordinated conservation auction, the performance of an auction with an agglomeration bonus, a joint bidding bonus, or both, is inferior on two key metricsâthe environmental benefits generated and cost effectiveness realized
Operator ordering and consistency of the wavefunction of the Universe
We demonstrate in the context of the minisuperspace model consisting of a
closed Friedmann-Robertson-Walker universe coupled to a scalar field that
Vilenkin's tunneling wavefunction can only be consistently defined for
particular choices of operator ordering in the Wheeler-DeWitt equation. The
requirement of regularity of the wavefunction has the particular consequence
that the probability amplitude, which has been used previously in the
literature in discussions of issues such as the prediction of inflation, is
likewise ill-defined for certain choices of operator ordering with Vilenkin's
boundary condition. By contrast, the Hartle-Hawking no-boundary wavefunction
can be consistently defined within these models, independently of operator
ordering. The significance of this result is discussed within the context of
the debate about the predictions of semiclassical quantum cosmology. In
particular, it is argued that inflation cannot be confidently regarded as a
"prediction" of the tunneling wavefunction, for reasons similar to those
previously invoked in the case of the no-boundary wavefunction. A synthesis of
the no-boundary and tunneling approaches is argued for.Comment: 9 pages, epsf, revTeX-3.1, 1 figure. In revised version (v2) a new
section etc with additional arguments increases the length of paper by 3
pages of Physical Review; several references added. v3: small typos fixe
Bosonic field equations from an exact uncertainty principle
A Hamiltonian formalism is used to describe ensembles of fields in terms of
two canonically conjugate functionals (one being the field probability
density). The postulate that a classical ensemble is subject to nonclassical
fluctuations of the field momentum density, of a strength determined solely by
the field uncertainty, is shown to lead to a unique modification of the
ensemble Hamiltonian. The modified equations of motion are equivalent to the
quantum equations for a bosonic field, and thus this exact uncertainty
principle provides a new approach to deriving and interpreting the properties
of quantum ensembles. The examples of electromagnetic and gravitational fields
are discussed. In the latter case the exact uncertainty approach specifies a
unique operator ordering for the Wheeler-DeWitt and Ashtekar-Wheeler-DeWitt
equations.Comment: 24 pages, extended version of part (B) of hep-th/0206235, to appear
in J. Phys.
Wave functions for arbitrary operator ordering in the de Sitter minisuperspace approximation
We derive exact series solutions for the Wheeler-DeWitt equation
corresponding to a spatially closed Friedmann-Robertson-Walker universe with
cosmological constant for arbitrary operator ordering of the scale factor of
the universe. The resulting wave functions are those relevant to the
approximation which has been widely used in two-dimensional minisuperspace
models with an inflationary scalar field for the purpose of predicting the
period of inflation which results from competing boundary condition proposals
for the wave function of the universe. The problem that Vilenkin's tunneling
wave function is not normalizable for general operator orderings, is shown to
persist for other values of the spatial curvature, and when additional matter
degrees of freedom such as radiation are included.Comment: 12 pages, revTeX-3.
Quantum Cosmology and Open Universes
Quantum creation of Universes with compact spacelike sections that have
curvature either closed, flat or open, i.e. are studied. In the
flat and open cases, the superpotential of the Wheeler De Witt equation is
significantly modified, and as a result the qualitative behaviour of a typical
wavefunction differs from the traditional closed case. Using regularity
arguments, it is shown that the only consistent state for the wavefunction is
the Tunneling one. By computing the quantum probabilities for the curvature of
the sections, it is shown that quantum cosmology actually favours that the
Universe be open, . In all cases sufficient inflation
e-foldings is predicted: this is an improvement over classical measures that
generally are ambiguous as to whether inflation is certain to occur.Comment: 11 pages, Revtex, 7 figures. Accepted for publication in PRD. New
material and important corrections added in response to referee's repor
The Warden Attitude: An investigation of the value of interaction with everyday wildlife
Using a discrete choice experiment, we elicit valuations of engagement with âeveryday wildlifeâ through feeding garden birds. We find that bird-feeding is primarily but not exclusively motivated by the direct consumption value of interaction with wildlife. The implicit valuations given to different species suggest that people prefer birds that have aesthetic appeal and that evoke human feelings of protectiveness. These findings suggest that people derive wellbeing by adopting a warden-like role towards âtheirâ wildlife. We test for external validity by conducting a hedonic analysis of sales of bird food. We discuss some policy implications of the existence of warden attitudes
- âŠ