413 research outputs found
Magneto-structural phase transitions and two-dimensional spin waves in graphite
We have previously found experimental evidence for several quantum phenomena
in oxygen-ion implanted of hydrogenated graphite: ferromagnetism,
antiferromagnetism, paramagentism, triplet superconductivity, Andreev states,
Little-Parks oscillations, Lamb shift, Casimir effect, colossal
magnetoresistance, and topologically-protected flat-energy bands [1-6]. Triplet
superconductivity results in the formation of Josephson junctions, thus with
potential of being used for spintronics applications in the critical area of
quantum computing. In this paper, we are showing new experimental evidence for
the formation of two-dimensional (2D) spin waves in oxygen-ion enriched and in
hydrogenated highly oriented pyrolytic graphite. The temperature evolution of
the remanent magnetization Mrem(T) data confirms the formation of spin waves
that follow the 2D Heisenberg model with a weak uniaxial anisotropy. In
addition, the step-like features also found in the temperature dependence of
the electrical resistivity between insulating and metallic states suggest
several outstanding possibilities, such as a structural transition, triplet
superconductivity, and chiral properties.Comment: 8 pages,7 figures, accepted by the Conference Editors for the
CEC-ICMC 2023 Conference for publication in the IOP Conference Series:
Materials Science and Engineering, Advances in Cryogenic Engineerin
Flat-band energy analysis of the temperature-dependent superconducting gap for hydrogenated graphite fibers found from nonlocal electrical conductance experimental data
Experimental evidence of novel phenomena in hydrogenated graphite fibers is
found. An indirect excitonic mechanism is likely leading to a SC state below
the temperature Tc = 50 K, where the gap is divergent. Analysis of the gap
within the framework provided by the Bardeen-Cooper-Schrieffer (BCS) theory of
superconductivity shows that this is a multigap system. The energy gap data can
be better explained within the framework of topologically protected flat bands
applied to systems in which superconductivity occurs on the surface or at the
internal interfaces of the samples. The temperature dependence of the SC gap is
linear above 50 K. We use nonlocal differential conductance Gdiff(V) = dI(V)/dV
experimental data to show clear evidence of topological phenomena such as
interference of chiral asymmetric Andreev edge states and crossed Andreev
conversion. Gdiff(V) has a negative part that results from the nonlocal
coherence between electron and holes in the Andreev edge states. We conclude
that hydrogenated graphite bears the marks of an unconventional
high-temperature superconductor (HTSC).Comment: 5 pages, 7 figures. arXiv admin note: substantial text overlap with
arXiv:2005.0587
Application of a new Structural Joint Inversion Approach to Teleseismic and Gravity Data from Mt.Vesuvius, Italy
A 3-D joint inversion of seismic and gravimetric data is performed to re-investigate the subsurface structure of Mt. Vesuvius (Italy) utilizing an improved joint inversion method. The aim is to derive models of the 3D distribution of velocity and density perturbations that are consistent with both data sets and with local velocity models. Mt. Vesuvius is a strato volcano located within a graben (Campania Plain) formed in Plio-Pleistocene. Campania Plain is bordered by mostly Mesozoic carbonaceous rocks. Mt. Vesuvius is the southernmost and the youngest of a group of Pleistocene volcanoes, three of which (Ischia, Campi Flegrei and Mt. Vesuvius) have erupted in historical times. The most recent eruption of Mt. Vesuvius occurred in 1944 and since then the volcanic activity has been characterized by moderate low magnitude seismicity and low temperature fumaroles at the summit crater. We modified the coupling mechanism between velocity and density models in the JI-3D optimized joint inversion method (Jordan and Achauer, 1999). This method was designed to provide stable and high resolution results and involves iterative optimized parameterization, 3D ray tracing, and the incorporation of a priori information. The coupling of the velocity and density models, vital to the joint inversion, is based on a cross-gradient approach (e.g. Gallardo and Meju, 2004), which has been proven to work very well in a variety of cases involving seismic, magnetic, CSEM, MT and gravity data sets. We implemented the cross-gradient coupling for our 3-D irregular adaptive grid parameterization. In contrast to conventional joint inversion methods this approach encourages structural similarities in the models and does not rely on predefined relationships between velocity and density parameters. As a consequence, the resulting velocity-density relations are not contaminated by a priori assumptions and can be utilized to derive rock physical parameters. We apply this method to data from the TomoVes project (Gasparini et al. 1998), combining seismics and Bouguer gravity and local high resolution velocity models as a priori information. The starting models for the joint inversion are derived by separate inversions of the individual data sets. We show 3D distributions of velocity perturbations and density variations from the joint inversion of teleseismic relative traveltimes and Bouguer anomaly data with the aim of extracting further information about the physical status of the volcano- tectonic system
Interrater reliability of surveillance for ventilator-associated events and pneumonia
OBJECTIVETo compare interrater reliabilities for ventilator-associated event (VAE) surveillance, traditional ventilator-associated pneumonia (VAP) surveillance, and clinical diagnosis of VAP by intensivists.DESIGNA retrospective study nested within a prospective multicenter quality improvement study.SETTINGIntensive care units (ICUs) within 5 hospitals of the Centers for Disease Control and Prevention Epicenters.PATIENTSPatients who underwent mechanical ventilation.METHODSWe selected 150 charts for review, including all VAEs and traditionally defined VAPs identified during the primary study and randomly selected charts of patients without VAEs or VAPs. Each chart was independently reviewed by 2 research assistants (RAs) for VAEs, 2 hospital infection preventionists (IPs) for traditionally defined VAP, and 2 intensivists for any episodes of pulmonary deterioration. We calculated interrater agreement using Îș estimates.RESULTSThe 150 selected episodes spanned 2,500 ventilator days. In total, 93â96 VAEs were identified by RAs; 31â49 VAPs were identified by IPs, and 29â35 VAPs were diagnosed by intensivists. Interrater reliability between RAs for VAEs was high (Îș, 0.71; 95% CI, 0.59â0.81). Agreement between IPs using traditional VAP criteria was slight (Îș, 0.12; 95% CI, â0.05â0.29). Agreement between intensivists was slight regarding episodes of pulmonary deterioration (Îș 0.22; 95% CI, 0.05â0.39) and was fair regarding whether episodes of deterioration were attributable to clinically defined VAP (Îș, 0.34; 95% CI, 0.17â0.51). The clinical correlation between VAE surveillance and intensivistsâ clinical assessments was poor.CONCLUSIONSProspective surveillance using VAE criteria is more reliable than traditional VAP surveillance and clinical VAP diagnosis; the correlation between VAEs and clinically recognized pulmonary deterioration is poor.Infect Control Hosp Epidemiol 2017;38:172â178</jats:sec
Lithospheric structure of the Western Pyrenees- Cantabrian Mountains based on 3D modelling of gravity anomalies and geoid undulations: preliminary results
Moho depths of Antarctica: comparison of seismic, gravity, and isostatic results
The lithospheric structure of Antarctica is still underâexplored. Moho depth estimate studies are in disagreement by more than 10 km in several regions, including for example the hinterland of the Transantarctic Mountains. Taking account the sparseness of seismological stations and the nonâuniqueness of potential field methods, inversions of Moho depth are performed here based on satellite gravity data in combination with currently available seismically constrained Moho depth estimates. Our results confirm that a lower density contrast at the Moho is present under East Antarctica than beneath West Antarctica. A comparison between the Moho depth derived from our inversion and an Airyâisostatic Moho model also reveals a spatially variable buoyancy contribution from the lithospheric mantle beneath contrasting sectors of East Antarctica. Finally, to test the plausibility of different Moho depths scenarios for the Transantarctic MountainsâWilkes Subglacial Basin system, we present 2âD lithospheric models along the TAMSEIS/GAMSEIS seismic profile. Our models show that if a moderately depleted lithospheric mantle of inferred Proterozoic age underlies the region, then a shallower Moho is more likely beneath the Wilkes Subglacial Basin. If however, reâfertilisation processes occurred in the upper mantle, for example in response to Rossâage subduction, then a deeper Moho scenario is preferred. We conclude that 3D lithospheric modeling, coupled with the availability of new seismic information in the hinterland of the Transantarctic Mountains is required to help resolve this controversy, thereby also reducing the ambiguities in geothermal heat flux estimation beneath this key part of the East Antarctic Ice Sheet
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