Lithium related deep and shallow acceptors in Li-doped ZnO nanocrystals

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Journal of Applied Physics 107, 024311 (2010) and may be found at https://doi.org/10.1063/1.3275889.We study the existence of Li-related shallow and deep acceptor levels in Li-doped ZnO nanocrystals using electron paramagnetic resonance (EPR) and photoluminescence (PL) spectroscopy. ZnO nanocrystals with adjustable Li concentrations between 0% and 12% have been prepared using organometallic precursors and show a significant lowering of the Fermi energy upon doping. The deep Li acceptor with an acceptor energy of 800 meV could be identified in both EPR and PL measurements and is responsible for the yellow luminescence at 2.2 eV. Additionally, a shallow acceptor state at 150 meV above the valence band maximum is made responsible for the observed donor-acceptor pair and free electron-acceptor transitions at 3.235 and 3.301 eV, possibly stemming from the formation of Li-related defect complexes acting as acceptors.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement

Effects of hospital facilities on patient outcomes after cancer surgery: an international, prospective, observational study

Background Early death after cancer surgery is higher in low-income and middle-income countries (LMICs) compared with in high-income countries, yet the impact of facility characteristics on early postoperative outcomes is unknown. The aim of this study was to examine the association between hospital infrastructure, resource availability, and processes on early outcomes after cancer surgery worldwide.Methods A multimethods analysis was performed as part of the GlobalSurg 3 study-a multicentre, international, prospective cohort study of patients who had surgery for breast, colorectal, or gastric cancer. The primary outcomes were 30-day mortality and 30-day major complication rates. Potentially beneficial hospital facilities were identified by variable selection to select those associated with 30-day mortality. Adjusted outcomes were determined using generalised estimating equations to account for patient characteristics and country-income group, with population stratification by hospital.Findings Between April 1, 2018, and April 23, 2019, facility-level data were collected for 9685 patients across 238 hospitals in 66 countries (91 hospitals in 20 high-income countries; 57 hospitals in 19 upper-middle-income countries; and 90 hospitals in 27 low-income to lower-middle-income countries). The availability of five hospital facilities was inversely associated with mortality: ultrasound, CT scanner, critical care unit, opioid analgesia, and oncologist. After adjustment for case-mix and country income group, hospitals with three or fewer of these facilities (62 hospitals, 1294 patients) had higher mortality compared with those with four or five (adjusted odds ratio [OR] 3.85 [95% CI 2.58-5.75]; p<0.0001), with excess mortality predominantly explained by a limited capacity to rescue following the development of major complications (63.0% vs 82.7%; OR 0.35 [0.23-0.53]; p<0.0001). Across LMICs, improvements in hospital facilities would prevent one to three deaths for every 100 patients undergoing surgery for cancer.Interpretation Hospitals with higher levels of infrastructure and resources have better outcomes after cancer surgery, independent of country income. Without urgent strengthening of hospital infrastructure and resources, the reductions in cancer-associated mortality associated with improved access will not be realised

Elektronspinresonanz-Untersuchungen an organischen Spinketten und zweidimensionalen organischen Leitern

In this work, detailed electron spin resonance and SQUID investigations on single crystals of the organic spin chain compounds (TMTTF)2X (X = SbF6, AsF6, BF4 and SCN) were performed to explore the spin and the charge ordered states in these materials. Furthermore, the transport and ESR measurements of the quasi-two dimensional organic superconductor Theta-(BEDT-TTF)2I3, its tempered phase (Theta)T-(BEDT-TTF)2I3, and the new synthesized organic conductor (BEDT-TTF)2(B12H12)(CH2Cl2) are presented and discussed. The temperature dependence of the spin susceptibility at constant volume (χs)v for T>100K of the investigated (TMTTF)2X (X = SbF6, AsF6, BF4 and SCN) salts can be modeled using the EAT (Eggert, Affleck and Takahashi) model for a S = 1/2 antiferromagnetic spin chain. The obtained values of the antiferromagnetic exchange constant |J| are 400 K, 410 K, 430 K and 460 K for (TMTTF)2X with X=SbF6, AsF6, BF4 and SCN, respectively. The linewidth decreases more slowly for (TMTTF)2SbF6 and (TMTTF)2AsF6 and increases by decreasing the temperature for (TMTTF)2SCN below the charge ordering transition temperature TCO. Also the anisotropy of the linewidth changes below TCO. These observations are attributed to the loss of the inversion symmetry between the TMTTF molecules along the stacking direction below TCO. Doubling in the periodicity in the orientation dependence of the linewidth along the ab'-plane is observed in the (TMTTF)2SbF6 and (TMTTF)2AsF6 salts in the charge order region. The linewidth have a minimum along the a-axis and the b'-axis and maximum at 45 degree and 135 degree between the two axes. The doubling of the periodicity in the orientation pattern can be due to the coexistence of two inequivalent magnetic TMTTF sites in the CO region. The spin Peierls transition in (TMTTF)2AsF6 (TSP = 13K) and the anion ordering transition in (TMTTF)2BF4 (TAO=41 K) were studied. Below the transition temperature of these spin-singlet ground states, the spin susceptibility decreases rapidly by lowering the temperature down to lowest temperatures. The spin susceptibility in this region for both salts can be described by the Bulaevskii's model for alternating spin chains. Using Bulaevskii's model we get for (TMTTF)2AsF6, the alternation parameter gama=0.94, the intradimer AFM exchange constant |J1|=423K and the interdimer AFM exchange constant |J2|=397K. The singlet triplet energy gap in the T=0 limit is 34.8K. For (TMTTF)2BF4, we obtained the parameters gama =0.90, |J1|=452.6K, |J2|=407.4K and The singlet triplet energy gap is 52.0K. The resistivity of Theta-(BEDT-TTF)2I3, crystals show a metallic behaviour from room temperature down to the superconducting transition temperature (Tc = 3.6 K) where the resistivity drops sharply. About 30% of the investigated crystals show the superconducting transition. The superconducting transition was confirmed to be a bulk property by the observation of the shielding signal for the superconducting samples. The ESR linewidth decreases monotonically from 82 Oe and 62 Oe at room temperature when the static magnetic field is applied perpendicular and parallel to the conduction plane, respectively to 9 Oe and 6 Oe at 20 K along the same orientations. Along both orientations the linewidth increases with decreasing temperature below 20 K. The g-value along both directions is temperature independent at high temperatures and decrease with decreasing the temperature below about 20 K. The tempered crystals (Theta)T-(BEDT-TTF)2I3 were obtained by annealing single crystals of Theta-(BEDT-TTF)2I3, at 60-70 oC for two to three hours. By tempering the crystal, the ESR linewidth changes from (81-62) Oe in Theta-phase to (26.7-24.5) Oe in (Theta)T-phase depending on the crystal orientation. All (Theta)T-(BEDT-TTF)2I3 crystals investigated show metallic behaviour down to 4 K where they show a bulk superconducting transition. This means that by tempering Theta-(BEDT-TTF)2I3,crystals the superconductivity is observed in all tempered crystals instead of 30% of the crystals in the Theta-phase.In dieser Arbeit wird eine detaillierte ESR- und SQUID-Studie vorgestellt, die an Einkristallen der (TMTTF)2X-Salze durchgeführt wurde und deren Schwerpunkt auf der Untersuchung der Spin- und Ladungsordnung liegt. Ebenso werden die Transport- und die magnetischen Eigenschaften des quasi-zweidimensionalen organischen Supraleiters Theta-(BEDT-TTF)2I3 und des neu synthetisierten organische Leiter (BEDT-TTF)2(B12H12)(CH2Cl2) vorgestellt und diskutiert. Diese wurden durch X-Band ESR-, SQUID- und Gleichstromwiderstands-Messungen im temperatur bereich zwischen 4 und 300 K ermittelt. Die Spinsuszeptibilitäten der vier untersuchten (TMTTF)2X-Salze können für Temperaturen T >100K mit den Modellen von Bonner und Fisher bzw. Eggert, Affleck und Takahashi (EAT) für eine antiferromagnetische (AFM) S=1/2 Heisenberg-Spinkette beschrieben werden. Die Spinsuszeptibilität von (TMTTF)2AsF6 fällt unterhalb des Spin-Peierls-Übergangs bei TSP = 13K exponentiell ab. In diesem Temperaturbereich kann die Spinsuszeptibilität mit dem Bulaevskii-Modell für alternierende Spinketten beschrieben werden und der Alternierungsparameter gama=J2/J1, die antiferromagnetischen Austauschkonstanten J1 und J2 sowie die Singulett-Triplett-Energielücke berechnet werden. Unterhalb der Anionenordnung in (TMTTF)2BF4 (TAO = 41 K) tritt zunächst ein sprungartigen Abfall und dann eine exponentielle Abnahme der Spinsuszeptibilität mit fallender Temperatur auf, die wiederum mit dem Bulaevskii-Modell für alternierende Spinketten angepasst werden kann. Im paramagnetischen Bereich bei höheren Temperaturen wurde festgestellt, dass die g-Faktoren und die ESR Linienbreiten delta H aller untersuchten (TMTTF)2X-Salze eine charakteristische Anisotropie aufweisen. Die Anisotropie der g-Faktoren wird durch die Anisotropie der Spin-Bahn-Kopplung hervorgerufen. Aufgrund der Symmetrie¬beschränkung dieser Materialien weisen die Linienbreiten dasselbe anisotrope Verhalten wie die g-Faktoren auf. Die ESR-Linienbreiten nehmen bei den TMTTF-Salzen im paramagnetischen Bereich linear mit der Temperatur ab, während die g-Faktoren temperaturunabhängig sind. Die Linienbreiten nehmen in (TMTTF)2AsF6 und (TMTTF)2SbF6 unterhalb der Ladungsordnungstemperatur TCO langsamer ab, und nehmen in (TMTTF)2SCN unterhalb von TCO sogar zu. Ebenso ändert sich unterhalb TCO die Anisotropie der Linienbreiten, wobei es Unterschiede zwischen den Salzen mit punktsymmetrischen Anionen (AsF6, SbF6) und dem nicht-punktsymmetrischen Anion SCN gibt: Im ersten Fall gilt delta Hc* > delta Hb' > delta Ha, für SCN jedoch delta Hc* ~ delta Hb' > delta Ha. Dieses Verhalten wird dem Verlust der Punktsymmetrie unterhalb TCO zugeschrieben, wie bereits mit Kernspinresonanzexperimenten (NMR) und durch Messungen der dielektrischen Permittivität gezeigt wurde. Es wurde festgestellt, dass die Linienverbreiterung durch Ladungsträgerordnung in (TMTTF)2SbF6 eine größere Rolle spielt als in (TMTTF)2AsF6, was auf einen höheren Grad an Ladungs-Ungleichverteilung im Fall von (TMTTF)2SbF6 hindeutet. An mehreren Kristallen des organischen Supraleiters Theta-(BEDT-TTF)2I3 wurde der Gleichstromwiderstand in einem Temperaturbereich von Raumtemperatur bis hinab zu 1,6 K gemessen. Der spezifische Widerstand lag bei Raumtemperatur typischerweise bei 0,04 Ohm.cm entlang der leitenden Ebene, bei 4K lag er bei 0,04 Ohm.cm. Der spezifische Widerstand nimmt bei Temperaturerniedrigung von Raumtemperatur an bis zur Übergangstemperatur zur Supraleitung Tc=3,6K stetig ab. Bei hohen Temperaturen ist die Spinsuszeptibilität temperaturunabhängig, wie dies für die Pauli-Spinsuszeptibilität von Metallen zu erwarten ist. Das es sich bei der Supraleitung um eine Volumenerscheinung handelt, wurde mit der Beobachtung des Abschirmungs¬signals durch das Herausdrängen des magnetischen Flusses im supraleitenden Zustand nachgewiesen. Die Winkelabhängigkeit der Peak-to-Peak-ESR-Linienbreite (delta Hpp) von Theta-(BEDT-TTF)2I3 bei Raumtemperatur (RT) verhält sich qualitativ so wie die g-Faktoren: hier tritt ein Maximum von 81 Oe entlang der c-Achse auf während der Wert innerhalb der ab-Ebene bei 61 Oe liegt. Die Linienbreite nimmt monoton von 82 bzw. 61Oe bei Raumtemperatur auf 9 bzw. 6 Oe bei 20 K ab. Durch 3 stündiges tempern der Theta-(BEDT-TTF)2I3 Einkristalle bei 60-70 oC wurden die getemperten (Theta)T-(BEDT-TTF)2I3-Kristalle hergestellt. Dadurch änderte sich die ESR-Linienbreite von (81-62) Oe in der Theta-Phase zu (26,7-24,5) Oe in der (Theta)T -Phase, abhängig von der Orientierung. Alle vermessenen Kristalle zeigen metallisches Verhalten und einen scharfen Abfall des spezifischen Widerstandes bei ungefähr 5 K. Durch den Abschirmungseffekt in der Suszeptibilitätsmessung konnte nachgewiesen werden, dass unterhalb von 4K das gesamte Volumen supraleitend war

Physiochemical properties of a bioceramic-based root canal sealer reinforced with multi-walled carbon nanotubes, titanium carbide and boron nitride biomaterials

AIM Bioceramic-containing root canal sealers are the most recently introduced sealers in endodontics. The present work reported experiments on a bioceramic-based root canal sealer with the objective of improving its physiochemical properties via reinforcement with each one of the three different nanomaterials: multi-walled carbon nanotubes (MWCNTS), titanium carbide (TC) or boron nitride (BN) in two weight percentages (1 wt% and 2 wt%). METHODOLOGY Each nanomaterial was added to a definite weight of BioRoot root canal sealer (BioRoot™ RCS, Septodont, Saint-Maur-des-Fossés, France). Three composite groups of each weight percentage were prepared for evaluation: BioRoot/MWCNTS, BioRoot/TC and BioRoot/BN. The initial and final setting times, solubility, elution and pH values of the freshly-mixed and set samples were evaluated and compared to pristine BioRoot™ RCS. Setting times were evaluated using Gilmore needles. Solubility and elution were determined after immersion in water for 24 h. Scanning electron microscopy was used to examine the microstructure of the composite materials. RESULTS The 1-wt. % composites possessed significantly shorter initial and final setting times compared with the pristine BioRoot™ RCS (p < 0.05). The 2-wt.% composites exhibited longer initial setting times but significantly shorter final setting times than BioRoot RCS (p < 0.05). Most of the composites had relatively lower solubility and elution profiles, with BioRoot/1-wt.% TC and BioRoot/1-wt.% BN being the lowest (p < 0.05). BioRoot™ RCS and all composites exhibited an alkaline pH profile over a period of 4 weeks and a significantly higher alkaline pH (p < 0.05) was recorded for BioRoot/1-wt.% and Bioroot/2-wt.% TC. CONCLUSIONS A bioceramic-containing root canal sealer (BioRootTM RCS) with a shorter setting time, an alkaline pH profile, and a relatively lower solubility may be developed by incorporation of nanomaterials

Domain walls at the spin density wave endpoint of the organic superconductor (TMTSF)2PF6 under pressure

5 pagesWe report the first comprehensive investigation of the organic superconductor (TMTSF)2PF6 in the vicinity of the endpoint of the spin density wave - metal phase transition where phase coexistence occurs. At low temperature, the transition of metallic domains towards superconductivity is used to reveal the various textures. In particular, we demonstrate experimentally the existence of 1D and 2D metallic domains with a cross-over from a filamentary superconductivity mostly along the c⋆-axis to a 2D superconductivity in the b′c-plane perpendicular to the most conducting direction. The formation of these domain walls may be related to the proposal of a soliton phase in the vicinity of the critical pressure of the (TMTSF)2PF6 phase diagram

Reconstruction of the anterior cruciate- and anterolateral ligament deficient knee with a modified iliotibial graft reduces instability more than with an intra-articular hamstring graft

PURPOSE: To compare knee kinematics before and after anterior cruciate ligament ACL reconstruction (ACL-R) using hamstring graft (HG) and a double-stranded iliotibial tract graft attached to Gerdy's tubercle (providing an extra-articular anterolateral tenodesis) (named the modified iliotibial tract graft = MIT). METHOD: Eighteen cadaveric knees were tested in a 6 degree of freedom kinematics rig. An optical tracking system recorded kinematics of the knee from 0 to 80 degrees of flexion applying no load, internal/external rotation (IR/ER), valgus/varus rotation (VGR/VRR), simulated pivot shift (SPS), anterior translation (AT) and posterior translation loads. The knee was tested before and after resection of the ACL and the anterolateral ligament (ALL), respectively; then after HG-ACL-R and MIT-ACL-R. Grafts were fixed at 20° of flexion. Results were compared to the intact knee. RESULTS: ACL resection resulted in a significant increase in AT (p < 0.05) over the entire range of motion, peaking at 20° of flexion, mean difference 6.6 ± 2.25 mm (p = 0.0007). ACL-R with HG-ACL and MIT-ACL restored AT. Resection of the ALL increased IR in the fully extended knee, mean difference 2.4 ± 2.1° (p = 0.024). When compared to the intact knee and the knee after HG-ACL-R, MIT-ACL-R knee reduced IR/SPS significantly (p < 0.05) in deep flexion angles (60°-80°), peaking at 80° of flexion. The MIT-ACL-R caused significantly less VRR at 80° flexion (p = 0.02). CONCLUSION: MIT-ACL-R restored AT equally to the HG-ACL-R. The MIT-ACL-R reduced IR and SPS in deep flexion, resulting in overconstraint. MIT-ACL-R can be used as an alternative to standard reconstruction methods

Global variation in postoperative mortality and complications after cancer surgery: a multicentre, prospective cohort study in 82 countries

Background: 80% of individuals with cancer will require a surgical procedure, yet little comparative data exist on early outcomes in low-income and middle-income countries (LMICs). We compared postoperative outcomes in breast, colorectal, and gastric cancer surgery in hospitals worldwide, focusing on the effect of disease stage and complications on postoperative mortality. Methods: This was a multicentre, international prospective cohort study of consecutive adult patients undergoing surgery for primary breast, colorectal, or gastric cancer requiring a skin incision done under general or neuraxial anaesthesia. The primary outcome was death or major complication within 30 days of surgery. Multilevel logistic regression determined relationships within three-level nested models of patients within hospitals and countries. Hospital-level infrastructure effects were explored with three-way mediation analyses. This study was registered with ClinicalTrials.gov, NCT03471494. Findings: Between April 1, 2018, and Jan 31, 2019, we enrolled 15 958 patients from 428 hospitals in 82 countries (high income 9106 patients, 31 countries; upper-middle income 2721 patients, 23 countries; or lower-middle income 4131 patients, 28 countries). Patients in LMICs presented with more advanced disease compared with patients in high-income countries. 30-day mortality was higher for gastric cancer in low-income or lower-middle-income countries (adjusted odds ratio 3·72, 95% CI 1·70–8·16) and for colorectal cancer in low-income or lower-middle-income countries (4·59, 2·39–8·80) and upper-middle-income countries (2·06, 1·11–3·83). No difference in 30-day mortality was seen in breast cancer. The proportion of patients who died after a major complication was greatest in low-income or lower-middle-income countries (6·15, 3·26–11·59) and upper-middle-income countries (3·89, 2·08–7·29). Postoperative death after complications was partly explained by patient factors (60%) and partly by hospital or country (40%). The absence of consistently available postoperative care facilities was associated with seven to 10 more deaths per 100 major complications in LMICs. Cancer stage alone explained little of the early variation in mortality or postoperative complications. Interpretation: Higher levels of mortality after cancer surgery in LMICs was not fully explained by later presentation of disease. The capacity to rescue patients from surgical complications is a tangible opportunity for meaningful intervention. Early death after cancer surgery might be reduced by policies focusing on strengthening perioperative care systems to detect and intervene in common complications. Funding: National Institute for Health Research Global Health Research Unit