311 research outputs found
A comparison of low carbon investment needs between China and Europe in stringent climate policy scenarios
The radical change in recent global climate governance calls for China and Europe to ramp up their efforts in leading the world to reach the long-term climate goals. By analyzing the results from the state-of-the-art global integrated assessment model, MESSAGEix-GLOBIOM, this paper aims to understand the future levels of financial investment needed for building and maintaining energy-related infrastructure in the two regions for fulfilling stringent targets consistent with 'well below 2 °C'. The results indicate that a rapid upscaling and structural change of these investments towards decarbonization are necessitated by the climate stringent scenarios. China and Europe need to increase their low carbon investments by 65% and 38% in a scenario reaching the 2° target relative to their respective reference scenarios which assume no such target from 2016–2050. In a more stringent climate policy scenario of the 1.5° target, these investment needs will increase by 149% and 79% for China and Europe respectively. Among all the energy sectors, energy efficiency, renewable electricity generation and electricity transmission and distribution are the three largest investing targets for the two regions. However, those investments will not likely be realized without strong policy incentives. Implications for green finance and multilateral cooperation initiatives are discussed in the context of the scenario results
Generalizing with perceptrons in case of structured phase- and pattern-spaces
We investigate the influence of different kinds of structure on the learning
behaviour of a perceptron performing a classification task defined by a teacher
rule. The underlying pattern distribution is permitted to have spatial
correlations. The prior distribution for the teacher coupling vectors itself is
assumed to be nonuniform. Thus classification tasks of quite different
difficulty are included. As learning algorithms we discuss Hebbian learning,
Gibbs learning, and Bayesian learning with different priors, using methods from
statistics and the replica formalism. We find that the Hebb rule is quite
sensitive to the structure of the actual learning problem, failing
asymptotically in most cases. Contrarily, the behaviour of the more
sophisticated methods of Gibbs and Bayes learning is influenced by the spatial
correlations only in an intermediate regime of , where
specifies the size of the training set. Concerning the Bayesian case we show,
how enhanced prior knowledge improves the performance.Comment: LaTeX, 32 pages with eps-figs, accepted by J Phys
A Transport and Microwave Study of Superconducting and Magnetic RuSr2EuCu2O8
We have performed susceptibility, thermopower, dc resistance and microwave
measurements on RuSr2EuCu2O8. This compound has recently been shown to display
the coexistence of both superconducting and magnetic order. We find clear
evidence of changes in the dc and microwave resistance near the magnetic
ordering temperature (132 K). The intergranular effects were separated from the
intragranular effects by performing microwave measurements on a sintered
ceramic sample as well as on a powder sample dispersed in an epoxy resin. We
show that the data can be interpreted in terms of the normal-state resistivity
being dominated by the CuO2 layers with exchange coupling to the Ru moments in
the RuO2 layers. Furthermore, most of the normal-state semiconductor-like
upturn in the microwave resistance is found to arise from intergranular
transport. The data in the superconducting state can be consistently
interpreted in terms of intergranular weak-links and an intragranular
spontaneous vortex phase due to the ferromagnetic component of the
magnetization arising from the RuO2 planes.Comment: 20 pages including 6 figures in pdf format. To be published in Phys.
Rev.
Absence of Meissner State and Robust Ferromagnetism in the Superconducting State of UCoGe: Possible Evidence of Spontaneous Vortex State
We report ac magnetic susceptibility and dc magnetization measurements on the
superconducting ferromagnet UCoGe (with superconducting and Curie temperatures
of ~K and ~K, respectively).
In the normal, ferromagnetic state (), the
magnetization curve exhibits a hysteresis loop similar to that of a regular
itinerant ferromagnet. Upon lowering the temperature below , the
spontaneous magnetization is unchanged, but the hysteresis is markedly
enhanced. Even deeply inside the superconducting state, ferromagnetism is not
completely shielded, and there is no Meissner region, a magnetic field region
of (a lower critical field). From these results, we suggest
that UCoGe is the first material in which ferromagnetism robustly survives in
the superconducting state and a spontaneous vortex state without the Meissner
state is realized.Comment: 5 pages, 4 figures, to be published in J. Phys. Soc. Jp
Gas hydrates: Entrance to a methane age or climate threat?
Methane hydrates, ice-like compounds in which methane is held in crystalline cages formed by water molecules, are widespread in areas of permafrost such as the Arctic and in sediments on the continental margins. They are a potentially vast fossil fuel energy source but, at the same time, could be destabilized by changing pressure-temperature conditions due to climate change, potentially leading to strong positive carbon-climate feedbacks. To enhance our understanding of both the vulnerability of and the opportunity provided by methane hydrates, it is necessary (i) to conduct basic research that improves the highly uncertain estimates of hydrate occurrences and their response to changing environmental conditions, and (ii) to integrate the agendas of energy security and climate change which can provide an opportunity for methane hydrates -- in particular if combined with carbon capture and storage -- to be used as a 'bridge fuel' between carbon-intensive fossil energies and zero-emission energies. Taken one step further, exploitation of dissociating methane hydrates could even mitigate against escape of methane to the atmosphere. Despite these opportunities, so far, methane hydrates have been largely absent from energy and climate discussions, including global hydrocarbon assessments and the Fourth Assessment Report of the Intergovernmental Panel on Climate Change
Hysteresis, Avalanches, and Disorder Induced Critical Scaling: A Renormalization Group Approach
We study the zero temperature random field Ising model as a model for noise
and avalanches in hysteretic systems. Tuning the amount of disorder in the
system, we find an ordinary critical point with avalanches on all length
scales. Using a mapping to the pure Ising model, we Borel sum the
expansion to for the correlation length exponent. We sketch a
new method for directly calculating avalanche exponents, which we perform to
. Numerical exponents in 3, 4, and 5 dimensions are in good
agreement with the analytical predictions.Comment: 134 pages in REVTEX, plus 21 figures. The first two figures can be
obtained from the references quoted in their respective figure captions, the
remaining 19 figures are supplied separately in uuencoded forma
Inhomogeneous Superconductivity in Condensed Matter and QCD
Inhomogeneous superconductivity arises when the species participating in the
pairing phenomenon have different Fermi surfaces with a large enough
separation. In these conditions it could be more favorable for each of the
pairing fermions to stay close to its Fermi surface and, differently from the
usual BCS state, for the Cooper pair to have a non zero total momentum. For
this reason in this state the gap varies in space, the ground state is
inhomogeneous and a crystalline structure might be formed. This situation was
considered for the first time by Fulde, Ferrell, Larkin and Ovchinnikov, and
the corresponding state is called LOFF. The spontaneous breaking of the space
symmetries in the vacuum state is a characteristic feature of this phase and is
associated to the presence of long wave-length excitations of zero mass. The
situation described here is of interest both in solid state and in elementary
particle physics, in particular in Quantum Chromo-Dynamics at high density and
small temperature. In this review we present the theoretical approach to the
LOFF state and its phenomenological applications using the language of the
effective field theories.Comment: RevTex, 83 pages, 26 figures. Submitted to Review of Modern Physic
Spintronics: Fundamentals and applications
Spintronics, or spin electronics, involves the study of active control and
manipulation of spin degrees of freedom in solid-state systems. This article
reviews the current status of this subject, including both recent advances and
well-established results. The primary focus is on the basic physical principles
underlying the generation of carrier spin polarization, spin dynamics, and
spin-polarized transport in semiconductors and metals. Spin transport differs
from charge transport in that spin is a nonconserved quantity in solids due to
spin-orbit and hyperfine coupling. The authors discuss in detail spin
decoherence mechanisms in metals and semiconductors. Various theories of spin
injection and spin-polarized transport are applied to hybrid structures
relevant to spin-based devices and fundamental studies of materials properties.
Experimental work is reviewed with the emphasis on projected applications, in
which external electric and magnetic fields and illumination by light will be
used to control spin and charge dynamics to create new functionalities not
feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes
from the published versio
Decarbonization pathways and energy investment needs for developing Asia in line with 'well below' 2 °C
Exploring potential future pathways for developing Asia’s energy consumption, CO2 emissions and infrastructure investment needs is essential to understanding how the countries of this rapidly growing region may contribute to the global climate targets set out in the 2015 Paris Agreement. To this end, this study employs the state-of-the-art global integrated assessment model MESSAGEix-GLOBIOM to investigate mid-century decarbonization strategies for developing Asia to 2050. Our results indicate that a radical change in the energy portfolio is required to reach the target of ‘well below’ 2°C. Specifically, our scenarios point to a rapid reduction of fossil fuel utilization, enhancement of low-carbon energy supply, and boosting of energy efficiency efforts. Such a transformation leads to a deep cut in CO2 emissions by 78% and 93% by 2050 in scenarios consistent with the 2°C and 1.5°C targets, respectively. Electricity generation and final energy consumption become dominated by low-carbon energy by 2050 in these scenarios. In terms of investment needs beyond a baseline scenario, the 2°C and 1.5°C pathways imply that the scale of low-carbon investment may need to double and triple, respectively. These increases would be partially offset by disinvestment in coal, oil and natural gas extraction and conversion infrastructure. Decarbonizing the energy system also impacts the capital needed for making progress on other sustainable development goals (SDGs), such as air pollution, clean water and food security
Guiding superconducting vortices by magnetic domain walls
We demonstrate a unique prospect for inducing anisotropic vortex pinning and
manipulating the directional motion of vortices using the stripe domain
patterns of a uniaxial magnetic film in a the superconducting/ferromagnetic
hybrid. Our observations can be described by a model, which considers
interactions between magnetic charges of vortices and surface magnetic charges
of domains resulting in the enhanced pinning of vortices on domain walls.Comment: 12 pages, 6 figure
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