Atomic oxygen beam source for erosion simulation

A device for the production of low energy (3 to 10 eV) neutral atomic beams for surface modification studies is described that reproduces the flux of atomic oxygen in low Earth orbit. The beam is produced by the acceleration of plasma ions onto a negatively biased plate of high-Z metal; the ions are neutralized and reflected by the surface, retaining some fraction of their incident kinetic energy, forming a beam of atoms. The plasma is generated by a coaxial RF exciter which produces a magnetically-confined (4 kG) plasma column. At the end of the column, ions fall through the sheath to the plate, whose bias relative to the plasma can be varied to adjust the beam energy. The source provides a neutral flux approximately equal to 5 x 10(exp 16)/sq cm at a distance of 9 cm and a fluence approximately equal to 10(exp 20)/sq cm in five hours. The composition and energy of inert gas beams was diagnosed using a mass spectometer/energy analyzer. The energy spectra of the beams demonstrate energies in the range 5 to 15 eV, and qualitatively show expected dependences upon incident and reflecting atom species and potential drop. Samples of carbon film, carbon-based paint, Kapton, mylar, and teflon exposed to atomic O beams show erosion quite similar to that observed in orbit on the space shuttle

Characterization of a 5-eV neutral atomic oxygen beam facility

An experimental effort to characterize an existing 5-eV neutral atomic oxygen beam facility being developed at Princeton Plasma Physics Laboratory is described. This characterization effort includes atomic oxygen flux and flux distribution measurements using a catalytic probe, energy determination using a commercially designed quadrupole mass spectrometer (QMS), and the exposure of oxygen-sensitive materials in this beam facility. Also, comparisons were drawn between the reaction efficiencies of materials exposed in plasma ashers, and the reaction efficiencies previously estimated from space flight experiments. The results of this study show that the beam facility is capable of producing a directional beam of neutral atomic oxygen atoms with the needed flux and energy to simulate low Earth orbit (LEO) conditions for real time accelerated testing. The flux distribution in this facility is uniform to +/- 6 percent of the peak flux over a beam diameter of 6 cm

Evidence of immunometabolic dysregulation and airway dysbiosis in athletes susceptible to respiratory illness

Background Respiratory tract infection (RTI) is a leading cause of training and in-competition time-loss in athlete health. The immune factors associated with RTI susceptibility remain unclear. In this study, we prospectively characterise host immune factors in elite athletes exhibiting RTI susceptibility. Methods Peripheral blood lymphocyte flow cytometry phenotyping and 16S rRNA microbial sequencing of oropharyngeal swabs was performed in a prospective elite athlete cohort study (n = 121). Mass cytometry, peripheral blood mononuclear cell (PBMC) stimulation and plasma metabolic profiling was performed in age-matched highly-susceptible (HS) athletes (≥4RTI in last 18 months) (n = 22) compared to non-susceptible (NS) (≤1RTI in last 18 months) (n = 23) athletes. Findings were compared to non-athletic healthy controls (HC) (n = 19). Findings Athletes (n = 121) had a reduced peripheral blood memory T regulatory cell compartment compared to HC (p = 0.02 (95%CI:0.1,1.0)) and reduced upper airway bacterial biomass compared to HC (p = 0.032, effect size r = 0.19). HS athletes (n = 22) had lower circulating memory T regulatory cells compared to NS (n = 23) athletes (p = 0.005 (95%CI:-1.5,-0.15)) and HC (p = 0.002 (95%CI:-1.9,-0.3) with PBMC microbial stimulation assays revealing a T-helper 2 skewed immune response compared to HC. Plasma metabolomic profiling showed differences in sphingolipid pathway metabolites (a class of lipids important in infection and inflammation regulation) in HS compared to NS athletes and HC, with sphingomyelin predictive of RTI infection susceptibility (p = 0.005). Interpretation Athletes susceptible to RTI have reduced circulating memory T regulatory cells, metabolic dysregulation of the sphingolipid pathway and evidence of upper airway bacterial dysbiosis. Funding This study was funded by the English Institute of Sport (UK)

Burnout in the ICU : potential consequences for staff and patient well-being

Peer reviewedAuthor versio

The direct arylation of allylic sp3 C–H bonds via organic and photoredox catalysis

The direct functionalization of unactivated sp3 C–H bonds is still one of the most challenging problems facing synthetic organic chemists. The appeal of such transformations derives from their capacity to facilitate the construction of complex organic molecules via the coupling of simple and otherwise inert building blocks, without introducing extraneous functional groups. Despite notable recent efforts1, the establishment of general and mild strategies for the engagement of sp3 C–H bonds in C–C bond forming reactions has proved difficult. Within this context, the discovery of chemical transformations that are able to directly functionalize allylic methyl, methylene and methine carbons in a catalytic manner is a priority. Although protocols for direct oxidation and amination of allylic C–H bonds (that is, C–H bonds where an adjacent carbon is involved in a C = C bond) have become widely established2,3, the engagement of allylic substrates in C–C bond forming reactions has thus far required the use of pre-functionalized coupling partners4. In particular, the direct arylation of non-functionalized allylic systems would enable access to a series of known pharmacophores (molecular features responsible for a drug’s action), though a general solution to this long-standing challenge remains elusive. Here we report the use of both photoredox and organic catalysis to accomplish a mild, broadly effective direct allylic C–H arylation. This C–C bond forming reaction readily accommodates a broad range of alkene and electron-deficient arene reactants, and has been used in the direct arylation of benzylic C–H bonds

Comparison of the airway microbiota in children with chronic suppurative lung disease

Rationale: The airway microbiota is important in chronic suppurative lung diseases (CSLD), such as primary ciliary dyskinesia (PCD) and cystic fibrosis (CF). This comparison has not previously been described but is important because difference between the two diseases may relate to the differing prognoses and lead to pathological insights and potentially, new treatments. Objectives: To compare the longitudinal development of the airway microbiota in children with PCD to that of CF and relate this to age and clinical status. Methods: Sixty-two age-matched children (age range 0.5–17 years) with PCD or CF (n=31 in each group) were recruited prospectively and followed for 1.1 years. Throat swabs or sputum as well as clinical information were collected at routine clinical appointments. 16S rRNA gene sequencing was performed. Measurements and Main Results: The microbiota was highly individual and more diverse in PCD and differed in community composition when compared with CF. Whilst Streptococcus was the most abundant genus in both conditions, Pseudomonas was more abundant in CF with Haemophilus more abundant in PCD (Padj=0.0005). In PCD only, an inverse relationship was seen in the relative abundance of Streptococcus and Haemophilus with age. Conclusions: Bacterial community composition differs between children with PCD and those with CF. Pseudomonas is more prevalent in CF and Haemophilus in PCD, at least until infection with Pseudomonas supervenes. Interactions between organisms, particularly members of Haemophilus, Streptococcus, and Pseudomonas genera appear important. Study of the interactions between these organisms may lead to new therapies or risk stratification

Disruption Studies in DIII-D

Characteristics of disruptions in the DIII-D tokamak including the current decay rate, halo current magnitude and toroidal asymmetry, and heat pulse to the divertor are described. Neon and argon pellet injection is shown to be an effective method for mitigating the halo currents and the heat pulse with a 50% reduction in both quantities achieved. The injection of these impurity pellets frequently gives rise to runaway electrons