Oxidation of GaN: An ab initio thermodynamic approach

GaN is a wide-bandgap semiconductor used in high-efficiency LEDs and solar cells. The solid is produced industrially at high chemical purities by deposition from a vapour phase, and oxygen may be included at this stage. Oxidation represents a potential path for tuning its properties without introducing more exotic elements or extreme processing conditions. In this work, ab initio computational methods are used to examine the energy potentials and electronic properties of different extents of oxidation in GaN. Solid-state vibrational properties of Ga, GaN, Ga2O3 and a single substitutional oxygen defect have been studied using the harmonic approximation with supercells. A thermodynamic model is outlined which combines the results of ab initio calculations with data from experimental literature. This model allows free energies to be predicted for arbitrary reaction conditions within a wide process envelope. It is shown that complete oxidation is favourable for all industrially-relevant conditions, while the formation of defects can be opposed by the use of high temperatures and a high N2:O2 ratio

A universal chemical potential for sulfur vapours

The unusual chemistry of sulfur is illustrated by the tendency for catenation. Sulfur forms a range of open and closed S$_n$ species in the gas phase, which has led to speculation on the composition of sulfur vapours as a function of temperature and pressure for over a century. Unlike elemental gases such as O$_2$ and N$_2$, there is no widely accepted thermodynamic potential for sulfur. Here we combine a first-principles global structure search for the low energy clusters from S$_2$ to S$_8$ with a thermodynamic model for the mixed-allotrope system, including the Gibbs free energy for all gas-phase sulfur on an atomic basis. A strongly pressure-dependent transition from a mixture dominant in S$_2$ to S$_8$ is identified. A universal chemical potential function, $\mu_{\mathrm{S}}(T,P)$, is proposed with wide utility in modelling sulfurisation processes including the formation of metal chalcogenide semiconductors.Comment: 12 pages, 9 figures. Supporting code and data is available at https://github.com/WMD-Bath/sulfur-model [snapshot DOI: 10.5281/zenodo.28536]. Further data will be available from DOI:10.6084/m9.figshare.1513736 and DOI:10.6084/m9.figshare.1513833 following peer-revie

Osteoarthritis severely decreases the elasticity and hardness of knee joint cartilage: A nanoindentation study

The nanoindentation method was applied to determine the elastic modulus and hardness of knee articular cartilage. Cartilage samples from both high weight bearing (HWB) and low weight bearing (LWB) femoral condyles were collected from patients diagnosed with osteoarthritis (OA). The mean elastic modulus of HWB cartilage was 4.46 ± 4.44 MPa in comparison to that of the LWB region (9.81 ± 8.88 MPa, p < 0.001). Similarly, the hardness was significantly lower in HWB tissue (0.317 ± 0.397 MPa) than in LWB cartilage (0.455 ± 0.434 MPa, p < 0.001). When adjusted to patients’ ages, the mean elastic modulus and hardness were both significantly lower in the age group over 70 years (p < 0.001). A statistically significant difference in mechanical parameters was also found in grade 3 and 4 OA. This study provides an insight into the nanomechanical properties of the knee articular cartilage and provides a starting point for personalized cartilage grafts that are compatible with the mechanical properties of the native tissue

Flugten til Sverige - en dokumentarfilm

Selskabet for Dansk Jødisk Historie gik sammen med Mosaisk Troessamfund, Carolineskolen og Det Jødiske Nationalfond (KKL) om at udskrive en konkurrence for unge jøder. Hensigten var at opfordre de unge til at tale med ældre familiemedlemmer om deres oplevelser under flugten samt at reflektere over, hvilken betydning begivenhederne har for dem selv i dag.Adam Aron Edelsten vandt 3. pladsen for sin film om farfar Leopold Edelstens flugt til Sverige

Preventing a Thought from Coming to Mind Elicits Increased Right Frontal Beta Just as Stopping Action Does.

In the stop-signal task, an electrophysiological signature of action-stopping is increased early right frontal beta band power for successful vs. failed stop trials. Here we tested whether the requirement to stop an unwanted thought from coming to mind also elicits this signature. We recorded scalp EEG during a Think/No-Think task and a subsequent stop signal task in 42 participants. In the Think/No-Think task, participants first learned word pairs. In a second phase, they received the left-hand word as a reminder and were cued either to retrieve the associated right-hand word ("Think") or to stop retrieval ("No-Think"). At the end of each trial, participants reported whether they had experienced an intrusion of the associated memory. Finally, they received the left-hand reminder word and were asked to recall its associated target. Behaviorally, there was worse final recall for items in the No-Think condition, and decreased intrusions with practice for No-Think trials. For EEG, we reproduced increased early right frontal beta power for successful vs. failed action stopping. Critically, No-Think trials also elicited increased early right frontal beta power and this was stronger for trials without intrusion. These results suggest that preventing a thought from coming to mind also recruits fast prefrontal stopping

Bioevaluation of superparamagnetic iron oxide nanoparticles (SPIONs) functionalized with dihexadecyl phosphate (DHP)

Superparamagnetic iron oxide nanoparticles (SPIONs) have been investigated for wide variety of applications. Their unique properties render them highly applicable as MRI contrast agents, in magnetic hyperthermia or targeted drug delivery. SPIONs surface properties affect a whole array of parameters such as: solubility, toxicity, stability, biodistribution etc. Therefore, progress in the field of SPIONs surface functionalization is crucial for further development of therapeutic or diagnostic agents. In this study, SPIONs were synthesized by thermal decomposition of iron (III) acetylacetonate Fe(acac) 3 and functionalized with dihexadecyl phosphate (DHP) via phase transfer. Bioactivity of the SPION-DHP was assessed on SW1353 and TCam-2 cancer derived cell lines. The following test were conducted: cytotoxicity and proliferation assay, reactive oxygen species (ROS) assay, SPIONs uptake (via Iron Staining and ICP-MS), expression analysis of the following genes: alkaline phosphatase (ALPL); ferritin light chain (FTL); serine/threonine protein phosphatase 2A (PP2A); protein tyrosine phosphatase non-receptor type 11 (PTPN11); transferrin receptor 1 (TFRC) via RT-qPCR. SPION-DHP nanoparticles were successfully obtained and did not reveal significant cytotoxicity in the range of tested concentrations. ROS generation was elevated, however not correlated with the concentrations. Gene expression profile was slightly altered only in SW1353 cells