Reactive Desorption of CO Hydrogenation Products under Cold Pre-stellar Core Conditions

The astronomical gas-phase detection of simple species and small organic molecules in cold pre-stellar cores, with abundances as high as $\sim$$10^{-8}-10^{-9}$ n$_\text{H}$, contradicts the generally accepted idea that at $10$ K, such species should be fully frozen out on grain surfaces. A physical or chemical mechanism that results in a net transfer from solid-state species into the gas phase offers a possible explanation. Reactive desorption, i.e., desorption following the exothermic formation of a species, is one of the options that has been proposed. In astronomical models, the fraction of molecules desorbed through this process is handled as a free parameter, as experimental studies quantifying the impact of exothermicity on desorption efficiencies are largely lacking. In this work, we present a detailed laboratory study with the goal of deriving an upper limit for the reactive desorption efficiency of species involved in the CO-H$_2$CO-CH$_3$OH solid-state hydrogenation reaction chain. The limit for the overall reactive desorption fraction is derived by precisely investigating the solid-state elemental carbon budget, using reflection absorption infrared spectroscopy and the calibrated solid-state band-strength values for CO, H$_2$CO and CH$_3$OH. We find that for temperatures in the range of $10$ to $14$ K, an upper limit of $0.24\pm 0.02$ for the overall elemental carbon loss upon CO conversion into CH$_3$OH. This corresponds with an effective reaction desorption fraction of $\leq$$0.07$ per hydrogenation step, or $\leq$$0.02$ per H-atom induced reaction, assuming that H-atom addition and abstraction reactions equally contribute to the overall reactive desorption fraction along the hydrogenation sequence. The astronomical relevance of this finding is discussed.Comment: 9 pages, 7 figure

The impact of surgical delay on resectability of colorectal cancer: An international prospective cohort study

AIM: The SARS-CoV-2 pandemic has provided a unique opportunity to explore the impact of surgical delays on cancer resectability. This study aimed to compare resectability for colorectal cancer patients undergoing delayed versus non-delayed surgery. METHODS: This was an international prospective cohort study of consecutive colorectal cancer patients with a decision for curative surgery (January-April 2020). Surgical delay was defined as an operation taking place more than 4 weeks after treatment decision, in a patient who did not receive neoadjuvant therapy. A subgroup analysis explored the effects of delay in elective patients only. The impact of longer delays was explored in a sensitivity analysis. The primary outcome was complete resection, defined as curative resection with an R0 margin. RESULTS: Overall, 5453 patients from 304 hospitals in 47 countries were included, of whom 6.6% (358/5453) did not receive their planned operation. Of the 4304 operated patients without neoadjuvant therapy, 40.5% (1744/4304) were delayed beyond 4 weeks. Delayed patients were more likely to be older, men, more comorbid, have higher body mass index and have rectal cancer and early stage disease. Delayed patients had higher unadjusted rates of complete resection (93.7% vs. 91.9%, P = 0.032) and lower rates of emergency surgery (4.5% vs. 22.5%, P < 0.001). After adjustment, delay was not associated with a lower rate of complete resection (OR 1.18, 95% CI 0.90-1.55, P = 0.224), which was consistent in elective patients only (OR 0.94, 95% CI 0.69-1.27, P = 0.672). Longer delays were not associated with poorer outcomes. CONCLUSION: One in 15 colorectal cancer patients did not receive their planned operation during the first wave of COVID-19. Surgical delay did not appear to compromise resectability, raising the hypothesis that any reduction in long-term survival attributable to delays is likely to be due to micro-metastatic disease

A computed tomography study of the fibula: morphology, morphometry, intramedullary anatomy, application prospects on intramedullary nailing

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Flexibility of molecular films as determined by deuterium solid state NMR

A new technique is proposed for the measurement of the bilayer bending modulus $\kappa$, in the lamellar phase L$_{\alpha}$ of lyotropic systems. It resides in the measurement of quadrupolar splittings by deuterium solid state NMR. By separating the different motional contributions accounting for the reorientation of the C-D bond with respect to the magnetic field, we have calculated within a simple Gaussian theory the effect of thermal fluctuations of the film upon the recorded quadrupolar splitting. This has been applied to the study of the effects of membrane composition on the mean bending modulus $\kappa$ in ternary and pseudo ternary systems of water-(salt)-sodium dodecyl sulfate-alcohol. It is found that $\kappa$ is sensitive both to the amount of alcohol in the membrane and to the alcohol chain length, with typical values increasing between 1.3 $k_{\rm B} \, T$ and 13.0 $k_{\rm B} \, T$ from bexanol to decanol systems. Our results allow to attribute the reduction in $\kappa$ obtained by replacing surfactant by alcohol to the thinning of the membrane and to the increase of the area occupied by the surfactant at the interface