Tuberculosis of the Craniocervical Junction: A Case Report
In: Central European neurosurgery: Zentralblatt für Neurochirurgie, Band 66, Heft 2, S. 95-97
ISSN: 1868-4912, 1438-9746
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In: Central European neurosurgery: Zentralblatt für Neurochirurgie, Band 66, Heft 2, S. 95-97
ISSN: 1868-4912, 1438-9746
In: Minimally invasive neurosurgery, Band 50, Heft 1, S. 7-11
ISSN: 1439-2291
The origin of the modified optical properties of InAs/GaAs quantum dots (QD) capped with a thin GaAs 1-xSb x layer is analyzed in terms of the band structure. To do so, the size, shape, and composition of the QDs and capping layer are determined through cross-sectional scanning tunnelling microscopy and used as input parameters in an 8 × 8 k·p model. As the Sb content is increased, there are two competing effects determining carrier confinement and the oscillator strength: the increased QD height and reduced strain on one side and the reduced QD-capping layer valence band offset on the other. Nevertheless, the observed evolution of the photoluminescence (PL) intensity with Sb cannot be explained in terms of the oscillator strength between ground states, which decreases dramatically for Sb > 16%, where the band alignment becomes type II with the hole wavefunction localized outside the QD in the capping layer. Contrary to this behaviour, the PL intensity in the type II QDs is similar (at 15 K) or even larger (at room temperature) than in the type I Sb-free reference QDs. This indicates that the PL efficiency is dominated by carrier dynamics, which is altered by the presence of the GaAsSb capping layer. In particular, the presence of Sb leads to an enhanced PL thermal stability. From the comparison between the activation energies for thermal quenching of the PL and the modelled band structure, the main carrier escape mechanisms are suggested. In standard GaAs-capped QDs, escape of both electrons and holes to the GaAs barrier is the main PL quenching mechanism. For small-moderate Sb (16) for which the type I band alignment is kept, electrons escape to the GaAs barrier and holes escape to the GaAsSb capping layer, where redistribution and retraping processes can take place. For Sb contents above 16% (type-II region), holes remain in the GaAsSb layer and the escape of electrons from the QD to the GaAs barrier is most likely the dominant PL quenching mechanism. This means that electrons and holes behave dynamically as uncorrelated pairs in both the type-I and type-II structures. © 2012 American Institute of Physics. ; This work has been supported by the Comunidad de Madrid through the project "Q&C Light" (P2009/ESP-1503) and "Nanophotonic devices for optical communications" (CCG10-UPM/TIC-4932), by the European Union through the SANDiE Network of Excellence (Contract No. NMP4-CT-2004-500101), by STW-VICI Grant No. 6631 and by contracts TEC2008-06756-C03-01 and TEC2011-29120-C05-04. J. M. Ulloa would like to thank the support of the Spanish "Ministerio de Ciencia e Innovación" through the "Ramón y Cajal" program. ; Peer Reviewed
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Background: Surgery is the main modality of cure for solid cancers and was prioritised to continue during COVID-19 outbreaks. This study aimed to identify immediate areas for system strengthening by comparing the delivery of elective cancer surgery during the COVID-19 pandemic in periods of lockdown versus light restriction. Methods: This international, prospective, cohort study enrolled 20 006 adult (≥18 years) patients from 466 hospitals in 61 countries with 15 cancer types, who had a decision for curative surgery during the COVID-19 pandemic and were followed up until the point of surgery or cessation of follow-up (Aug 31, 2020). Average national Oxford COVID-19 Stringency Index scores were calculated to define the government response to COVID-19 for each patient for the period they awaited surgery, and classified into light restrictions (index 60). The primary outcome was the non-operation rate (defined as the proportion of patients who did not undergo planned surgery). Cox proportional-hazards regression models were used to explore the associations between lockdowns and non-operation. Intervals from diagnosis to surgery were compared across COVID-19 government response index groups. This study was registered at ClinicalTrials.gov, NCT04384926. Findings: Of eligible patients awaiting surgery, 2003 (10·0%) of 20 006 did not receive surgery after a median follow-up of 23 weeks (IQR 16-30), all of whom had a COVID-19-related reason given for non-operation. Light restrictions were associated with a 0·6% non-operation rate (26 of 4521), moderate lockdowns with a 5·5% rate (201 of 3646; adjusted hazard ratio [HR] 0·81, 95% CI 0·77-0·84; p<0·0001), and full lockdowns with a 15·0% rate (1775 of 11 827; HR 0·51, 0·50-0·53; p<0·0001). In sensitivity analyses, including adjustment for SARS-CoV-2 case notification rates, moderate lockdowns (HR 0·84, 95% CI 0·80-0·88; p<0·001), and full lockdowns (0·57, 0·54-0·60; p<0·001), remained independently associated with non-operation. Surgery beyond 12 weeks from diagnosis in patients without neoadjuvant therapy increased during lockdowns (374 [9·1%] of 4521 in light restrictions, 317 [10·4%] of 3646 in moderate lockdowns, 2001 [23·8%] of 11 827 in full lockdowns), although there were no differences in resectability rates observed with longer delays. Interpretation: Cancer surgery systems worldwide were fragile to lockdowns, with one in seven patients who were in regions with full lockdowns not undergoing planned surgery and experiencing longer preoperative delays. Although short-term oncological outcomes were not compromised in those selected for surgery, delays and non-operations might lead to long-term reductions in survival. During current and future periods of societal restriction, the resilience of elective surgery systems requires strengthening, which might include protected elective surgical pathways and long-term investment in surge capacity for acute care during public health emergencies to protect elective staff and services.
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