176 research outputs found
Review of a frugal cooling mattress to induce therapeutic hypothermia for treatment of hypoxic-ischaemic encephalopathy in the UK NHS
Hypoxic ischaemic encephalopathy (HIE) is a major cause of neonatal mortality and disability in the United Kingdom (UK) and has significant human and financial costs. Therapeutic hypothermia (TH), which consists of cooling down the newborn’s body temperature, is the current standard of treatment for moderate or severe cases of HIE. Timely initiation of treatment is critical to reduce risk of mortality and disability associated with HIE. Very expensive servo-controlled devices are currently used in high-income settings to induce TH, whereas low-income settings rely on the use of low-tech devices such as water bottles, ice packs or fans. Cooling mattresses made with phase change materials (PCMs) were recently developed as a safe, efficient, and affordable alternative to induce TH in low-income settings. This frugal innovation has the potential to become a reverse innovation for the National Health Service (NHS) by providing a simple, efficient, and cost-saving solution to initiate TH in geographically remote areas of the UK where cooling equipment might not be readily available, ensuring timely initiation of treatment while waiting for neonatal transport to the nearest cooling centre. The adoption of PCM cooling mattresses by the NHS may reduce geographical disparity in the availability of treatment for HIE in the UK, and it could benefit from improvements in coordination across all levels of neonatal care given challenges currently experienced by the NHS in terms of constraints on funding and shortage of staff. Trials evaluating the effectiveness and safety of PCM cooling mattresses in the NHS context are needed in support of the adoption of this frugal innovation. These findings may be relevant to other high-income settings that experience challenges with the provision of TH in geographically remote areas. The use of promising frugal innovations such as PCM cooling mattresses in high-income settings may also contribute to challenge the dominant narrative that often favours innovation from North America and Western Europe, and consequently fight bias against research and development from low-income settings, promoting a more equitable global innovation landscape
Coherent ultrafast spin-dynamics probed in three dimensional topological insulators
Topological insulators are candidates to open up a novel route in spin based
electronics. Different to traditional ferromagnetic materials, where the
carrier spin-polarization and magnetization are based on the exchange
interaction, the spin properties in topological insulators are based on the
coupling of spin- and orbit interaction connected to its momentum. Specific
ways to control the spin-polarization with light have been demonstrated: the
energy momentum landscape of the Dirac cone provides spin-momentum locking of
the charge current and its spin. The directionality of spin and momentum, as
well as control with light has been demonstrated. Here we demonstrate a
coherent femtosecond control of spin-polarization for states in the valence
band at around the Dirac cone.Comment: 14 pages, 4 figure
Valence and magnetic ordering in intermediate valence compounds : TmSe versus SmB6
The intermediate valent systems TmSe and SmB6 have been investigated up to 16
and 18 GPa by ac microcalorimetry with a pressure (p) tuning realized in situ
at low temperature. For TmSe, the transition from an antiferromagnetic
insulator for p<3 GPa to an antiferromagnetic metal at higher pressure has been
confirmed. A drastic change in the p variation of the Neel temperature (Tn) is
observed at 3 GPa. In the metallic phase (p>3 GPa), Tn is found to increase
linearly with p. A similar linear p increase of Tn is observed for the
quasitrivalent compound TmS which is at ambiant pressure equivalent to TmSe at
p=7 GPa. In the case of SmB6 long range magnetism has been detected above p=8
GPa, i.e. at a pressure slightly higher than the pressure of the insulator to
metal transition. However a homogeneous magnetic phase occurs only above 10
GPa. The magnetic and electronic properties are related to the renormalization
of the 4f wavefunction either to the divalent or the trivalent configurations.
As observed in SmS, long range magnetism in SmB6 occurs already far below the
pressure where a trivalent Sm3+ state will be reached. It seems possible, to
describe roughly the physical properties of the intermediate valence
equilibrium by assuming formulas for the Kondo lattice temperature depending on
the valence configuration. Comparison is also made with the appearance of long
range magnetism in cerium and ytterbium heavy fermion compounds.Comment: 22 pages including figure
Multiconfigurational nature of 5f orbitals in uranium and plutonium intermetallics
Uranium and plutonium's 5f electrons are tenuously poised between strongly
bonding with ligand spd-states and residing close to the nucleus. The unusual
properties of these elements and their compounds (eg. the six different
allotropes of elemental plutonium) are widely believed to depend on the related
attributes of f-orbital occupancy and delocalization, for which a quantitative
measure is lacking. By employing resonant x-ray emission spectroscopy (RXES)
and x-ray absorption near-edge structure (XANES) spectroscopy and making
comparisons to specific heat measurements, we demonstrate the presence of
multiconfigurational f-orbital states in the actinide elements U and Pu, and in
a wide range of uranium and plutonium intermetallic compounds. These results
provide a robust experimental basis for a new framework for understanding the
strongly-correlated behavior of actinide materials.Comment: 30 pages, concatenated article and supporting information, 10 figure
Ultrafast carrier dynamics in tetrahedral amorphous carbon: carrier trapping versus electron–hole recombination
We report the investigation of the ultrafast carrier dynamics in thin tetrahedral amorphous carbon films by means of femtosecond time-resolved reflectivity. We estimated the electronphonon relaxation time of a few hundred femtoseconds and we observed that under low optical excitation photo-generated carriers decay according to two distinct mechanisms attributed to trapping by defect states and direct electronhole recombination. With high excitation, when photo-carrier and trap densities are comparable, a unique temporal evolution develops, as the time dependence of the trapping process becomes degenerate with the electronhole recombination. This experimental evidence highlights the role of defects in the ultrafast electronic dynamics and is not specific to this particular form of carbon, but has general validity for amorphous and disordered semiconductors. peerReviewe
Strain induced phase separation in La0.7Sr0.3MnO3 thin films.
La0.7Sr0.3MnO3 thin films having different thicknesses were grown by pulsed laser deposition with in situ
reflection high energy electron diffraction diagnostics on LaAlO3 substrates. The mismatch between film and
substrate gives rise to an in-plane compressive biaxial strain, which partially relaxes in films thicker than
30 unit cells. Accordingly, the ratio between the out-of-plane and the in-plane lattice parameter c/a varies
between 1.06 fully strained and 1.03 partially relaxed. In-plane compressive strain favors the stabilization of
the 3z2−r2 orbitals chain-type antiferromagnetic phase, thus giving rise to a sizeable x-ray absorption linear
dichroism signal. The shape of the linear dichroism depends weakly on the c/a ratio, while its intensity
strongly increases with c/a. At the same time, the metal-insulator transition temperature shifts from about
360 K towards lower temperatures with decreasing thickness, eventually reaching an insulating state for the
30 unit cells film. Low-temperature nuclear magnetic resonance spectra show a decrease of the MnDE doubleexchange
metallic contribution with decreasing the thickness, which becomes negligible in the 30 unit cells
thick film. The experimental results demonstrate a strain driven competition between two stable phases: the
orbital ordered chain-type insulating antiferromagnetic and the orbital disordered metallic ferromagnetic. For
intermediate values of the epitaxial strain the local minimum state of the system lies in a gap region between
the two stable phases. Such a region has glassy characteristics with coexisting clusters of the two phases. The
strain is used as a driving force to span the glassy region
Evidence for suppressed metallicity on the surface of La2-xSrxCuO4 and Nd2-xCexCuO4
Hard X-ray Photoemission spectroscopy (PES) of copper core electronic states,
with a probing depth of 60 \AA, is used to show that the Zhang-Rice
singlet feature is present in LaCuO but is absent in NdCuO.
Hole- and electron doping in LaSrCuO (LSCO) and
NdCeCuO (NCCO) result in new well-screened features which are
missing in soft X-ray PES. Impurity Anderson model calculations establish
metallic screening as its origin, which is strongly suppressed within 15
of the surface. Complemented with X-ray absorption spectroscopy,
the small chemical-potential shift in core levels ( eV) are shown to
be consistent with modifications of valence and conduction band states spanning
the band gap ( eV) upon hole- and electron-doping in LSCO and NCCO.Comment: 4 pages, 4 figure
A determination of the pairing interaction in the high Tc cuprate superconductor Tl2Ba2CaCu2O8 (Tl2212)
We have measured the near-normal reflectance of Tl2Ba2CaCu2O8 (Tl2212) for
energies from 0.1 to 4.0 eV at room temperature and used a Kramers-Kronig
analysis to find the complex, frequency dependent dielectric function, from
which the optical conductivity was determined. Using
Thermal-Difference-Reflectance (TDR) Spectroscopy the reflectance of the sample
in the normal state just above the superconducting transition, and in the
superconducting state were then obtained. From these data we determined the
ratio of the superconducting- to normal-state optical conductivities. Mattis
and Bardeen had calculated this function within the BCS theory, where the gap
is a fixed energy-independent quantity. Taking into account the retarded nature
of the electron-phonon coupling results in a complex, energy dependent gap
causing deviations from the Mattis-Bardeen plot at energies where the phonon
coupling function is large. We find a typical deviation near the phonon
energies in Tl2212, and in addition, at 1.2 and 1.7eV. The phonon, and these
electronic terms can each be described by a coupling constant. None of which by
itself gives rise to a high transition temperature, but the combination does.
Using Resonant Inelastic X-Ray Scattering (RIXS) we find that the d-to-d
excitations of the cuprate ion in Tl2212 fall at the same energies as the dips
in the Mattis-Bardeen plot. We conclude that the high superconducting
transition temperature of the cuprates is due to the sum of the phonon
interaction, and interactions with the Cu-ion d-shell.Comment: Preprint submitted to Physica C. Paper presented at M2S-HTSC-VIII,
Dresden, Germany, July 9-14,200
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