194 research outputs found
Recent Studies in Superconductivity at Extreme Pressures
Studies of the effect of high pressure on superconductivity began in 1925
with the seminal work of Sizoo and Onnes on Sn to 0.03 GPa and have continued
up to the present day to pressures in the 200 - 300 GPa range. Such enormous
pressures cause profound changes in all condensed matter properties, including
superconductivity. In high pressure experiments metallic elements, Tc values
have been elevated to temperatures as high as 20 K for Y at 115 GPa and 25 K
for Ca at 160 GPa. These pressures are sufficient to turn many insulators into
metals and magnetics into superconductors. The changes will be particularly
dramatic when the pressure is sufficient to break up one or more atomic shells.
Recent results in superconductivity to Mbar pressures wll be discussed which
exemplify the progress made in this field over the past 82 years.Comment: Proceedings of the 21st AIRAPT and 45th EHPRG International
Conference on High Pressure Science and Technology, Catania, Italy, Sept.
17-21, 200
Pressure-Induced Superconductivity in Sc to 74 GPa
Using a diamond anvil cell with nearly hydrostatic helium pressure medium we
have significantly extended the superconducting phase diagram Tc(P) of Sc, the
lightest of all transition metals. We find that superconductivity is induced in
Sc under pressure, Tc increasing monotonically to 8.2 K at 74.2 GPa. The Tc(P)
dependences of the trivalent d-electron metals Sc, Y, La, and Lu are compared
and discussed within a simple s-d charge transfer framework.Comment: to be published in Phys. Rev. B (Brief Reports
Structural transitions, octahedral rotations, and electronic properties of NiO rare-earth nickelates under high pressure
Motivated by the recent observation of superconductivity with K
in pressurized La3Ni2O7 [Nature 621, 493 (2023)], we explore the structural and
electronic properties in A3Ni2O7 bilayer nickelates (A=La-Lu, Y, Sc) as a
function of hydrostatic pressure (0-150 GPa) from first principles including a
Coulomb repulsion term. At GPa, we observe an
orthorhombic-to-tetragonal transition in LaNiO at variance with
recent x-ray diffraction data, which points to so-far unresolved complexities
at the onset of superconductivity, e.g., charge doping by variations in the
oxygen stoichiometry. We compile a structural phase diagram with particular
emphasis on the ratio, octahedral anisotropy, and octahedral rotations.
Intriguingly, chemical and external pressure emerge as two distinct and
counteracting control parameters. We find unexpected correlations between
and the in-plane Ni-O-Ni bond angles for LaNiO. Moreover, two novel
structural phases with significant octahedral rotations and in-plane bond
disproportionations are uncovered for A=Nd-Lu, Y, Sc that exhibit a surprising
pressure-driven electronic reconstruction in the Ni manifold. By
disentangling the involvement of basal versus apical oxygen states at the Fermi
surface, we identify TbNiO as an interesting candidate for
superconductivity at ambient pressure. These results suggest a profound
tunability of the structural and electronic phases in this novel materials
class and are key for a fundamental understanding of the superconductivity
mechanism.Comment: 12 pages, 5 figure
Studies on the Weak Itinerant Ferromagnet SrRuO3 under High Pressure to 34 GPa
The dependence of the Curie temperature Tc on nearly hydrostatic pressure has
been determined to 17.2 GPa for the weak itinerant ferromagnetic SrRuO3 in both
polycrystalline and single-crystalline form. Tc is found to decrease under
pressure from 162 K to 42.7 K at 17.2 GPa in nearly linear fashion at the rate
dTc/dP = -6.8 K/GPa. No superconductivity was found above 4 K in the pressure
range 17 to 34 GPa. Room-temperature X-ray diffraction studies to 25.3 GPa
reveal no structural phase transition but indicate that the average Ru-O-Ru
bond angle passes through a minimum near 15 GPa. The bulk modulus and its
pressure derivative were determined to be B =192(3) GPa and B' = 5.0(3),
respectively. Parallel ac susceptibility studies on polycrystalline CaRuO3 at 6
and 8 GPa pressure found no evidence for either ferromagnetism or
superconductivity above 4 K
Social Jetlag and Cardiometabolic Risk in Preadolescent Children.
Objective: Childhood cardiometabolic disease risk (CMD) has been associated with short sleep duration. Its relationship with other aspects of sleep should also be considered, including social jetlag (SJL) which represents the difference between a person's social rhythms and circadian clock. This study investigated whether childhood CMD risk is associated with sleep duration, sleep disturbances, and SJL. Study Design: The observational study included 332 children aged 8–10 years (48.5% female). The three independent variables were sleep duration, sleep disturbances, and SJL. SJL was calculated as the variation in hours between the midpoint of sleep during free (weekend) days and work/school days. Eleven cardiometabolic biomarkers were measured, including central blood pressure, lipids, glycated hemoglobin, arterial wave reflection, and glucose. Underlying CMD risk factors were identified using factor analysis. Results: Four underlying CMD risk factors were identified using factor analysis: blood pressure, cholesterol, vascular health, and carbohydrate metabolism. Neither sleep disturbances nor sleep duration were significantly associated with any of the four CMD factors following adjustments to potential confounders. However, SJL was significantly linked to vascular health (p = 0.027) and cholesterol (p = 0.025). Conclusion: These findings suggest that SJL may be a significant and measurable public health target for offsetting negative CMD trajectories in children. Further studies are required to determine biological plausibility
Comparison of the pressure dependences of Tc in the trivalent d-electron superconductors
Whereas dhcp La superconducts at ambient pressure with Tc = 5 K, the other
trivalent d-electron metals Sc, Y, and Lu only superconduct if high pressures
are applied. Earlier measurements of the pressure dependence of Tc for Sc and
Lu metal are here extended to much higher pressures. Whereas Tc for Lu
increases monotonically with pressure to 12.4 K at 174 GPa (1.74 Mbar). Tc for
Sc reaches 19.6 K at 107 GPa, the 2nd highest value observed for any elemental
superconductor. At higher pressures a phase transition occurs whereupon Tc
drops to 8.31 K at 111 GPa. The Tc(P) dependences for Sc and Lu are compared to
those of Y and La. An interesting correlation is pointed out between the value
of Tc and the fractional free volume available to the conduction electrons
outside the ion cores, a quantity which is directly related to the number of d
electrons in the conduction band
Physical Activity, Mental Health and Wellbeing during the First COVID-19 Containment in New Zealand: A Cross-Sectional Study
From MDPI via Jisc Publications RouterHistory: accepted 2021-11-11, pub-electronic 2021-11-16Publication status: PublishedStrategies implemented worldwide to contain COVID-19 outbreaks varied in severity across different countries, and established a new normal for work and school life (i.e., from home) for many people, reducing opportunities for physical activity. Positive relationships of physical activity with both mental and physical health are well recognised, and therefore the aim was to ascertain how New Zealand’s lockdown restrictions impacted physical activity, mental health and wellbeing. Participants (n = 4007; mean ± SD: age 46.5 ± 14.7 years, 72% female, 80.7% New Zealand European) completed (10–26 April 2020) an online amalgamated survey (Qualtrics): International Physical Activity Questionnaire: Short Form; Depression, Anxiety and Stress Scale-9; World Health Organisation-Five Well-Being Index; Stages of Change Scale. Positive dose–response relationships between physical activity levels and wellbeing scores were demonstrated for estimates that were unadjusted (moderate activity OR 3.79, CI 2.88–4.92; high activity OR 8.04, CI 6.07–10.7) and adjusted (confounding variables: age, gender, socioeconomic status, time sitting and co-morbidities) (moderate activity 1.57, CI 1.11–2.52; high activity 2.85, CI 1.97–4.14). The study results support previous research demonstrating beneficial effects of regular physical activity on mental health and wellbeing. Governments may use these results to promote meeting physical activity guidelines in order to protect mental health and wellbeing during the ongoing COVID-19 restrictions and future pandemics
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Asian outflow and trans-Pacific transport of carbon monoxide and ozone pollution: An integrated satellite, aircraft, and model perspective
Satellite observations of carbon monoxide (CO) from the Measurements of Pollution in the Troposphere (MOPITT) instrument are combined with measurements from the Transport and Chemical Evolution Over the Pacific (TRACE-P) aircraft mission over the northwest Pacific and with a global three-dimensional chemical transport model (GEOS-CHEM) to quantify Asian pollution outflow and its trans-Pacific transport during spring 2001. Global CO column distributions in MOPITT and GEOS-CHEM are highly correlated (R2 = 0.87), with no significant model bias. The largest regional bias is over Southeast Asia, where the model is 18% too high. A 60% decrease of regional biomass burning emissions in the model (to 39 Tg yr−1) would correct the discrepancy; this result is consistent with TRACE-P observations. MOPITT and TRACE-P also give consistent constraints on the Chinese source of CO from fuel combustion (181 Tg CO yr−1). Four major events of trans-Pacific transport of Asian pollution in spring 2001 were seen by MOPITT, in situ platforms, and GEOS-CHEM. One of them was sampled by TRACE-P (26–27 February) as a succession of pollution layers over the northeast Pacific. These layers all originated from one single event of Asian outflow that split into northern and southern plumes over the central Pacific. The northern plume (sampled at 6–8 km off California) had no ozone enhancement. The southern subsiding plume (sampled at 2–4 km west of Hawaii) contained a 8–17 ppbv ozone enhancement, driven by decomposition of peroxyacetylnitrate (PAN) to nitrogen oxides (NOx). This result suggests that PAN decomposition in trans-Pacific pollution plumes subsiding over the United States could lead to significant enhancements of surface ozone
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