263 research outputs found
Towards greener horizontal-axis wind turbines: Analysis of carbon emissions, energy and costs at the early design stage
This paper describes the development of a quantitative analysis system as a platform for rapidly estimate energy, costs and carbon emission to facilitate the comparison of different wind turbine concept designs. This system aimed specifically at wind turbine manufacturing processes due to the fact that a large proportion of the environmental, costs and energy impacts would occur at this stage. The proposed method supports an initial assessment of multiple design concepts which allows the selection and development of a “greener” wind turbine. The developed system enables concept design of commercial wind turbine towers of hub heights between 44 and 135 m. The method supports an accurate estimation in regards to the dimension, energy consumed, maximum power output, costs and carbon emission in the early design phases of a wind turbine. As a result of the development, the proposed approach could potentially be used to minimise the carbon footprints of major engineering projects such as wind farms
Quantum Critical Point of Itinerant Antiferromagnet in the Heavy Fermion Ce(Ru_{1-x}Rh_x)_2Si_2
A focus of recent experimental and theoretical studies on heavy fermion
systems close to antiferromagnetic (AFM) quantum critical points (QCP) is
directed toward revealing the nature of the fixed point, i.e., whether it is an
itinerant antiferromagnet [spin density wave (SDW)] type or a locally-critical
fixed point. The relevance of the local QCP was proposed to explain the
E/T-scaling with an anomalous exponent observed for the AFM QCP of
CeCu_{5.9}Au_{0.1}. In this work, we have investigated an AFM QCP of another
archetypal heavy fermion system Ce(Ru_{1-x}Rh_x)_2Si_2 with x = 0 and 0.03 (sim
x_c) using single-crystalline neutron scattering. Accurate measurements of the
dynamical susceptibility Im[chi(Q,E)] at the AFM wave vector Q = 0.35 c^* have
shown that Im[chi(Q,E)] is well described by a Lorentzian and its energy width
Gamma(Q), i.e., the inverse correlation time depends on temperature as Gamma(Q)
= c_1 + c_2 T^{3/2 +- 0.1}, where c_1 and c_2 are x dependent constants, in low
temperature ranges.This critical exponent 3/2 proves that the QCP is controlled
by the SDW QCP in three space dimensions studied by the renormalization group
and self-consistent renormalization theories.Comment: 4 pages, 4 figures, LT24 (Aug. 2005, Orlando
Quantum Critical Point of Itinerant Antiferromagnet in Heavy Fermion
A quantum critical point (QCP) of the heavy fermion Ce(Ru_{1-x}Rh_x)_2Si_2 (x
= 0, 0.03) has been studied by single-crystalline neutron scattering. By
accurately measuring the dynamical susceptibility at the antiferromagnetic wave
vector k_3 = 0.35 c^*, we have shown that the energy width Gamma(k_3), i.e.,
inverse correlation time, depends on temperature as Gamma(k_3) = c_1 + c_2
T^{3/2 +- 0.1}, where c_1 and c_2 are x dependent constants, in a low
temperature range. This critical exponent 3/2 +- 0.1 proves that the QCP is
controlled by that of the itinerant antiferromagnet.Comment: 4 pages, 3 figure
Competition and/or Coexistence of Antiferromagnetism and Superconductivity in CeRhIn and CeCoIn
The Ce compounds CeCoIn and CeRhIn are ideal model systems to study
the competition of antiferromagnetism (AF) and superconductivity (SC). Here we
discuss the pressure--temperature and magnetic field phase diagrams of both
compounds. In CeRhIn the interesting observation is that in zero magnetic
field a coexistence AF+SC phase exist inside the AF phase below the critical
pressure GPa. Above AF is
suppressed in zero field but can be re-induced by applying a magnetic field.
The collapse of AF under pressure coincides with the abrupt change of the Fermi
surface.
In CeCoIn a new phase appears at low temperatures and high magnetic field
(LTHF) which vanishes at the upper critical field . In both
compounds the paramagnetic pair breaking effect dominates at low temperature.
We discuss the evolution of the upper critical field under high pressure of
both compounds and propose a simple picture of the glue of reentrant magnetism
to the upper critical field in order to explain the interplay of
antiferromagnetic order and superconductivity.Comment: 6 pages, 7 figures, Manuscript for Proceedings of the International
Conference on Quantum Criticality and Novel Phases (QCNP09, Dresden); to
appear in pss(b
Magnetic Quantum Phase Transitions in Kondo Lattices
The identification of magnetic quantum critical points in heavy fermion
metals has provided an ideal setting for experimentally studying quantum
criticality. Motivated by these experiments, considerable theoretical efforts
have recently been devoted to reexamine the interplay between Kondo screening
and magnetic interactions in Kondo lattice systems. A local quantum critical
picture has emerged, in which magnetic interactions suppress Kondo screening
precisely at the magnetic quantum critical point (QCP). The Fermi surface
undergoes a large reconstruction across the QCP and the coherence scale of the
Kondo lattice vanishes at the QCP. The dynamical spin susceptibility exhibits
scaling and non-trivial exponents describe the temperature and
frequency dependence of various physical quantities. These properties are to be
contrasted with the conventional spin-density-wave (SDW) picture, in which the
Kondo screening is not suppressed at the QCP and the Fermi surface evolves
smoothly across the phase transition. In this article we discuss recent
microscopic studies of Kondo lattices within an extended dynamical mean field
theory (EDMFT). We summarize the earlier work based on an analytical
-expansion renormalization group method, and expand on the more
recent numerical results. We also discuss the issues that have been raised
concerning the magnetic phase diagram. We show that the zero-temperature
magnetic transition is second order when double counting of the RKKY
interactions is avoided in EDMFT.Comment: 10 pages, 4 figures; references added; as published in JPCM in early
September, except for the correction to the legend for Figure
Antiferromagnetism and Superconductivity in CeRhIn
We discuss recent results on the heavy fermion superconductor CeRhIn
which presents ideal conditions to study the strong coupling between the
suppression of antiferromagnetic order and the appearance of unconventional
superconductivity. The appearance of superconductivity as function of pressure
is strongly connected to the suppression of the magnetic order. Under magnetic
field, the re-entrance of magnetic order inside the superconducting state shows
that antiferromagnetism nucleates in the vortex cores. The suppression of
antiferromagnetism in CeRhIn by Sn doping is compared to that under
hydrostatic pressure.Comment: 6 pages, 8 figures, to be published in Proc. Int. Conf. Heavy
Electrons (ICHE2010) J. Phys. Soc. Jpn. 80 (2011
Antiferromagnetism and Superconductivity in Cerium based Heavy Fermion Compounds
The study of competing ground states is a central issue in condensed matter
physic. In this article we will discuss the interplay of antiferromagnetic
order and unconventional superconductivity in Ce based heavy-fermion compounds.
In all discussed examples superconductivity appears at the border of magnetic
order. Special focus is given on the pressure-temperature-magnetic field phase
diagram of CeRhIn5 and CeCoIn5 which allows to discuss microscopic coexistence
of magnetic order and superconductivity in detail. A striking point is the
similarity of the phase diagram of different classes of strongly correlated
systems which is discussed briefly. The recently discovered non-centrosymmetric
superconductors will open a new access with the possible mixing of odd and even
parity pairing.Comment: 38 pages, 22 figures, to be published in Comptes rendues - Physiqu
First LIGO search for gravitational wave bursts from cosmic (super)strings
We report on a matched-filter search for gravitational wave bursts from
cosmic string cusps using LIGO data from the fourth science run (S4) which took
place in February and March 2005. No gravitational waves were detected in 14.9
days of data from times when all three LIGO detectors were operating. We
interpret the result in terms of a frequentist upper limit on the rate of
gravitational wave bursts and use the limits on the rate to constrain the
parameter space (string tension, reconnection probability, and loop sizes) of
cosmic string models.Comment: 11 pages, 3 figures. Replaced with version submitted to PR
Stacked Search for Gravitational Waves from the 2006 SGR 1900+14 Storm
We present the results of a LIGO search for short-duration gravitational
waves (GWs) associated with the 2006 March 29 SGR 1900+14 storm. A new search
method is used, "stacking'' the GW data around the times of individual
soft-gamma bursts in the storm to enhance sensitivity for models in which
multiple bursts are accompanied by GW emission. We assume that variation in the
time difference between burst electromagnetic emission and potential burst GW
emission is small relative to the GW signal duration, and we time-align GW
excess power time-frequency tilings containing individual burst triggers to
their corresponding electromagnetic emissions. We use two GW emission models in
our search: a fluence-weighted model and a flat (unweighted) model for the most
electromagnetically energetic bursts. We find no evidence of GWs associated
with either model. Model-dependent GW strain, isotropic GW emission energy
E_GW, and \gamma = E_GW / E_EM upper limits are estimated using a variety of
assumed waveforms. The stacking method allows us to set the most stringent
model-dependent limits on transient GW strain published to date. We find E_GW
upper limit estimates (at a nominal distance of 10 kpc) of between 2x10^45 erg
and 6x10^50 erg depending on waveform type. These limits are an order of
magnitude lower than upper limits published previously for this storm and
overlap with the range of electromagnetic energies emitted in SGR giant flares.Comment: 7 pages, 3 figure
Sensitivity to Gravitational Waves from Compact Binary Coalescences Achieved during LIGO's Fifth and Virgo's First Science Run
We summarize the sensitivity achieved by the LIGO and Virgo gravitational
wave detectors for compact binary coalescence (CBC) searches during LIGO's
fifth science run and Virgo's first science run. We present noise spectral
density curves for each of the four detectors that operated during these
science runs which are representative of the typical performance achieved by
the detectors for CBC searches. These spectra are intended for release to the
public as a summary of detector performance for CBC searches during these
science runs.Comment: 12 pages, 5 figure
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