35 research outputs found
First direct observation of a nearly ideal graphene band structure
Angle-resolved photoemission and X-ray diffraction experiments show that
multilayer epitaxial graphene grown on the SiC(000-1) surface is a new form of
carbon that is composed of effectively isolated graphene sheets. The unique
rotational stacking of these films cause adjacent graphene layers to
electronically decouple leading to a set of nearly independent linearly
dispersing bands (Dirac cones) at the graphene K-point. Each cone corresponds
to an individual macro-scale graphene sheet in a multilayer stack where
AB-stacked sheets can be considered as low density faults.Comment: 5 pages, 4 figure
Interface properties and built-in potential profile of a LaCrO/SrTiO superlattice determined by standing-wave excited photoemission spectroscopy
LaCrO (LCO) / SrTiO (STO) heterojunctions are intriguing due to a
polar discontinuity along (001), two distinct and controllable interface
structures [(LaO)/(TiO) and (SrO)/(CrO)], and
interface-induced polarization. In this study, we have used soft- and hard
x-ray standing-wave excited photoemission spectroscopy (SW-XPS) to generate a
quantitative determination of the elemental depth profiles and interface
properties, band alignments, and the depth distribution of the
interface-induced built-in potentials in the two constituent oxides. We observe
an alternating charged interface configuration: a positively charged
(LaO)/(TiO) intermediate layer at the
LCO/STO interface and a negatively charged
(SrO)/(CrO) intermediate layer at the
STO/LCO interface. Using core-level SW data,
we have determined the depth distribution of species, including through the
interfaces, and these results are in excellent agreement with scanning
transmission electron microscopy and electron energy loss spectroscopy
(STEM-EELS) mapping of local structure and composition. SW-XPS also enabled
deconvolution of the LCO-contributed and STO- contributed
matrix-element-weighted density of states (MEWDOSs) from the valence band (VB)
spectra for the LCO/STO superlattice (SL). Monitoring the VB edges of the
deconvoluted MEWDOS shifts with a change in probing profile, the alternating
charge- induced built-in potentials are observed in both constituent oxides.
Finally, using a two-step simulation approach involving first core-level
binding energy shifts and then valence-band modeling, the built-in potential
gradients across the SL are resolved in detail and represented by the depth
distribution of VB edges.Comment: Main text: 29 pages, 5 figures; Supplementary Information: 20 pages,
10 figure
Simulating rewetting events in intermittent rivers and ephemeral streams: A global analysis of leached nutrients and organic matter
Climate change and human pressures are changing the global distribution and the exâ
tent of intermittent rivers and ephemeral streams (IRES), which comprise half of the
global river network area. IRES are characterized by periods of flow cessation, during
which channel substrates accumulate and undergo physicoâchemical changes (preconâ
ditioning), and periods of flow resumption, when these substrates are rewetted and
release pulses of dissolved nutrients and organic matter (OM). However, there are no
estimates of the amounts and quality of leached substances, nor is there information
on the underlying environmental constraints operating at the global scale. We experiâ
mentally simulated, under standard laboratory conditions, rewetting of leaves, riverâ
bed sediments, and epilithic biofilms collected during the dry phase across 205 IRES
from five major climate zones. We determined the amounts and qualitative characterâ
istics of the leached nutrients and OM, and estimated their areal fluxes from riverbeds.
In addition, we evaluated the variance in leachate characteristics in relation to selected
environmental variables and substrate characteristics. We found that sediments, due
to their large quantities within riverbeds, contribute most to the overall flux of disâ
solved substances during rewetting events (56%â98%), and that flux rates distinctly
differ among climate zones. Dissolved organic carbon, phenolics, and nitrate contribâ
uted most to the areal fluxes. The largest amounts of leached substances were found
in the continental climate zone, coinciding with the lowest potential bioavailability of
the leached OM. The opposite pattern was found in the arid zone. Environmental variâ
ables expected to be modified under climate change (i.e. potential evapotranspiration,
aridity, dry period duration, land use) were correlated with the amount of leached subâ
stances, with the strongest relationship found for sediments. These results show that
the role of IRES should be accounted for in global biogeochemical cycles, especially
because prevalence of IRES will increase due to increasing severity of drying event
Simulating rewetting events in intermittent rivers and ephemeral streams: a global analysis of leached nutrients and organic matter
Climate change and human pressures are changing the global distribution and extent of intermittent rivers and ephemeral streams (IRES), which comprise half of the global river network area. IRES are characterized by periods of flow cessation, during which channel substrates accumulate and undergo physicoâchemical changes (preconditioning), and periods of flow resumption, when these substrates are rewetted and release pulses of dissolved nutrients and organic matter (OM). However, there are no estimates of the amounts and quality of leached substances, nor is there information on the underlying environmental constraints operating at the global scale. We experimentally simulated, under standard laboratory conditions, rewetting of leaves, riverbed sediments, and epilithic biofilms collected during the dry phase across 205 IRES from five major climate zones. We determined the amounts and qualitative characteristics of the leached nutrients and OM, and estimated their areal fluxes from riverbeds. In addition, we evaluated the variance in leachate characteristics in relation to selected environmental variables and substrate characteristics. We found that sediments, due to their large quantities within riverbeds, contribute most to the overall flux of dissolved substances during rewetting events (56â98%), and that flux rates distinctly differ among climate zones. Dissolved organic carbon, phenolics, and nitrate contributed most to the areal fluxes. The largest amounts of leached substances were found in the continental climate zone, coinciding with the lowest potential bioavailability of the leached organic matter. The opposite pattern was found in the arid zone. Environmental variables expected to be modified under climate change (i.e. potential evapotranspiration, aridity, dry period duration, land use) were correlated with the amount of leached substances, with the strongest relationship found for sediments. These results show that the role of IRES should be accounted for in global biogeochemical cycles, especially because prevalence of IRES will increase due to increasing severity of drying events
Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries
Abstract
Background
Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres.
Methods
This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and lowâmiddle-income countries.
Results
In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of âsingle-useâ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for lowâmiddle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia.
Conclusion
This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both highâ and lowâmiddleâincome countries
COVID-19 symptoms at hospital admission vary with age and sex: results from the ISARIC prospective multinational observational study
Background:
The ISARIC prospective multinational observational study is the largest cohort of hospitalized patients with COVID-19. We present relationships of age, sex, and nationality to presenting symptoms.
Methods:
International, prospective observational study of 60â109 hospitalized symptomatic patients with laboratory-confirmed COVID-19 recruited from 43 countries between 30 January and 3 August 2020. Logistic regression was performed to evaluate relationships of age and sex to published COVID-19 case definitions and the most commonly reported symptoms.
Results:
âTypicalâ symptoms of fever (69%), cough (68%) and shortness of breath (66%) were the most commonly reported. 92% of patients experienced at least one of these. Prevalence of typical symptoms was greatest in 30- to 60-year-olds (respectively 80, 79, 69%; at least one 95%). They were reported less frequently in children (â€â18 years: 69, 48, 23; 85%), older adults (â„â70 years: 61, 62, 65; 90%), and women (66, 66, 64; 90%; vs. men 71, 70, 67; 93%, each Pâ<â0.001). The most common atypical presentations under 60 years of age were nausea and vomiting and abdominal pain, and over 60 years was confusion. Regression models showed significant differences in symptoms with sex, age and country.
Interpretation:
This international collaboration has allowed us to report reliable symptom data from the largest cohort of patients admitted to hospital with COVID-19. Adults over 60 and children admitted to hospital with COVID-19 are less likely to present with typical symptoms. Nausea and vomiting are common atypical presentations under 30 years. Confusion is a frequent atypical presentation of COVID-19 in adults over 60 years. Women are less likely to experience typical symptoms than men