115 research outputs found
Candidate Quantum Spin Liquid in the Ce\textsuperscript{3+} Pyrochlore Stannate CeSnO
We report the low temperature magnetic properties of CeSnO, a
rare-earth pyrochlore. Our susceptibility and magnetization measurements show
that due to the thermal isolation of a Kramers doublet ground state,
CeSnO has Ising-like magnetic moments of
. The magnetic moments are confined to the local trigonal axes,
as in a spin ice, but the exchange interactions are antiferromagnetic. Below 1
K the system enters a regime with antiferromagnetic correlations. In contrast
to predictions for classical -Ising spins on the
pyrochlore lattice, there is no sign of long-range ordering down to 0.02 K. Our
results suggest that CeSnO features an antiferromagnetic liquid
ground state with strong quantum fluctuations.Comment: 6 pages, 4 figure
Cement, CCS and CO2 Uptake, Including an Update on the EU LEILAC Project
Portland cement manufacture is responsible for around 7% of anthropogenic CO2 emissions, a percentage which is rising. The majority of direct emissions come from the calcination of limestone to form calcium oxide and calcium silicates, the main constituent of Portland cement. However, after cement is hydrated to make concrete, it can react with carbon dioxide in the air to re-form calcium carbonate, completing a cycle. This carbonation mechanism can be measured and the rate at which the global inventory of concrete absorbs CO2 can be estimated – the results of such an exercise will be shown in this presentation. That said, concrete carbonation only counterbalances a small fraction of emissions from concrete production, the majority of which come from cement manufacture. Incremental improvements in composition and efficiency are not sufficient to reduce CO2 emissions by the extent necessary to hit a 1.5–2 °C temperature rise target – CCS is the only practical technology to achieve this ambition. The technological options for the cement-CCS will be presented. Three options – calcium looping, an oxy-fueled kiln, and direct capture – will be described and discussed in depth, including discussion of the effects of various highly integrated processes on the strength and other properties of the cement produced; for calcium looping and oxyfueled kilns, it will be shown that there are negligible effects on the quality of the cement produced. Direct Capture will be presented and discussed in detail, as part of a recently funded project in the process of producing results. This process is being developed as part of Leilac (Low Emissions Intensity Lime and Cement), a EU Horizon 2020 research and innovation project. This €21m project has received €12m from the EU (H2020 No 654465), with the balance provided by the consortium partners. It runs for five years from 2016 to 2020 and the project team includes industrial, technology and research & development partners. The objective is to pilot a breakthrough carbon capture technology that can capture the process emissions from the calcination of limestone, without imposing a significant energy or capital penalty. The pilot plant will be hosted by Heidelberg Cement at Lixhe in Belgium. Imperial College is carrying out research on the kinetics of calcination under the conditions of interest, suitability of product for destination industries, defining reference technologies for modelling and modelling of the radiative heat transfer in the reactor. Here, we shall present an overview of the project and the current status
Candidate quantum spin ice in the pyrochlore PrHfO
We report the low temperature magnetic properties of the pyrochlore
PrHfO. Polycrystalline and single-crystal samples are investigated
using time-of-flight neutron spectroscopy and macroscopic measurements,
respectively. The crystal-field splitting produces a non-Kramers doublet ground
state for Pr, with Ising-like anisotropy. Below 0.5 K ferromagnetic
correlations develop, which suggests that the system enters a spin ice-like
state associated with the metamagnetic behavior observed at
~T. In this regime, the development of a discrete inelastic
excitation in the neutron spectra indicates the appearance of spin dynamics
which are likely related to cooperative quantum fluctuations.Comment: 7 pages, 5 figures, 1 tabl
Topological Sector Fluctuations and Curie Law Crossover in Spin Ice
At low temperatures, a spin ice enters a Coulomb phase - a state with
algebraic correlations and topologically constrained spin configurations. In
Ho2Ti2O7, we have observed experimentally that this process is accompanied by a
non-standard temperature evolution of the wave vector dependent magnetic
susceptibility, as measured by neutron scattering. Analytical and numerical
approaches reveal signatures of a crossover between two Curie laws, one
characterizing the high temperature paramagnetic regime, and the other the low
temperature topologically constrained regime, which we call the spin liquid
Curie law. The theory is shown to be in excellent agreement with neutron
scattering experiments. On a more general footing, i) the existence of two
Curie laws appears to be a general property of the emergent gauge field for a
classical spin liquid, and ii) sheds light on the experimental difficulty of
measuring a precise Curie-Weiss temperature in frustrated materials; iii) the
mapping between gauge and spin degrees of freedom means that the susceptibility
at finite wave vector can be used as a local probe of fluctuations among
topological sectors.Comment: 10 pages, 5 figure
Experimental Proof of a Magnetic Coulomb Phase
Spin ice materials are magnetic substances in which the spin directions map
onto hydrogen positions in water ice. Recently this analogy has been elevated
to an electromagnetic equivalence, indicating that the spin ice state is a
Coulomb phase, with magnetic monopole excitations analogous to ice's mobile
ionic defects. No Coulomb phase has yet been proved in a real magnetic
material, as the key experimental signature is difficult to resolve in most
systems. Here we measure the scattering of polarised neutrons from the
prototypical spin ice Ho2Ti2O7. This enables us to separate different
contributions to the magnetic correlations to clearly demonstrate the existence
of an almost perfect Coulomb phase in this material. The temperature dependence
of the scattering is consistent with the existence of deconfined magnetic
monopoles connected by Dirac strings of divergent length.Comment: 18 pages, 4 fig
CONFIRM: a double-blind, placebo controlled phase III clinical trial investigating the effect of nivolumab in patients with relapsed mesothelioma: study protocol for a randomised controlled trial
Background: Mesothelioma is an incurable, apoptosis-resistant cancer caused in most cases by previous exposure
to asbestos and is increasing in incidence. It represents a growing health burden but remains under-researched,
with limited treatment options. Early promising signals of activity relating to both PD-L1- and PD-1-targeted
treatment in mesothelioma implicate a dependency of mesothelioma on this immune checkpoint. There is a need
to evaluate checkpoint inhibitors in patients with relapsed mesothelioma where treatment options are limited.
Methods: The addition of 12 months of nivolumab (anti-PD1 antibody) to standard practice will be conducted in
the UK using a randomised, placebo-controlled phase III trial (the Cancer Research UK CONFIRM trial). A total of 336
patients with pleural or peritoneal mesothelioma who have received at least two prior lines of therapy will be
recruited from UK secondary care sites. Patients will be randomised 2:1 (nivolumab:placebo), stratified according to
epithelioid/non-epithelioid, to receive either 240 mg nivolumab monotherapy or saline placebo as a 30-min
intravenous infusion. Treatment will be for up to 12 months. We will determine whether the use of nivolumab
increases overall survival (the primary efficacy endpoint). Secondary endpoints will include progression-free
survival, objective response rate, toxicity, quality of life and cost-effectiveness. Analysis will be performed
according to the intention-to-treat principle using a Cox regression analysis for the primary endpoint (and
for other time-to-event endpoints).
Discussion: The outcome of this trial will provide evidence of the potential benefit of the use of nivolumab
in the treatment of relapsed mesothelioma. If found to be clinically effective, safe and cost-effective it is likely
to become the new standard of care in the UK
Spiral spin-liquid and the emergence of a vortex-like state in MnScS
Spirals and helices are common motifs of long-range order in magnetic solids,
and they may also be organized into more complex emergent structures such as
magnetic skyrmions and vortices. A new type of spiral state, the spiral
spin-liquid, in which spins fluctuate collectively as spirals, has recently
been predicted to exist. Here, using neutron scattering techniques, we
experimentally prove the existence of a spiral spin-liquid in MnScS by
directly observing the 'spiral surface' - a continuous surface of spiral
propagation vectors in reciprocal space. We elucidate the multi-step ordering
behavior of the spiral spin-liquid, and discover a vortex-like triple-q phase
on application of a magnetic field. Our results prove the effectiveness of the
- Hamiltonian on the diamond lattice as a model for the spiral
spin-liquid state in MnScS, and also demonstrate a new way to realize a
magnetic vortex lattice.Comment: 10 pages, 11 figure
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