538 research outputs found
Quench cooling under reduced gravity
We report the quench cooling experiments performed with liquid O2 under
different levels of gravity simulated with the magnetic gravity compensation. A
copper disk is quenched from 270K to 90K. It is found that the cooling time in
microgravity is very long in comparison with any other gravity level. This
phenomenon is explained by the isolation effect of the gas surrounding the
disk. The liquid subcooling is shown to drastically improuve the heat exchange
thus reducing the cooling time (about 20 times). The effect of subcooling on
the heat transfer is analyzed at different gravity levels. It is shown that
such type of experiments cannot be used for the analysis of the critical heat
flux (CHF) of the boiling crisis. The minimum heat flux (MHF) of boiling is
analyzed instead
Manifestation of interface anisotropy in CdTe quantum wells
Photoluminescence and polarized reflection spectra of quantum well structures
with symmetric CdZnTe/CdTe/CdZnTe and
asymmetric CdZnTe/CdTe/CdMgTe barriers were
studied. The Stokes parameters of the reflected light from these structures
were measured. In the structures with symmetric barriers, exciton resonances
were found in the reflection spectra and were not present in the
photoluminescence spectra. In structures with asymmetric barriers, in the
region of exciton resonances, the phenomenon of light birefringence was
detected, caused by a lower symmetry of the interfaces compared to the symmetry
of bulk crystals. A discussion of both phenomena was given
Phase diagrams of magnetopolariton gases
The magnetic field effect on phase transitions in electrically neutral
bosonic systems is much less studied than those in fermionic systems, such as
superconducting or ferromagnetic phase transitions. Nevertheless, composite
bosons are strongly sensitive to magnetic fields: both their internal structure
and motion as whole particles may be affected. A joint effort of ten
laboratories has been focused on studies of polariton lasers, where
non-equilibrium Bose-Einstein condensates of bosonic quasiparticles,
exciton-polaritons, may appear or disappear under an effect of applied magnetic
fields. Polariton lasers based on pillar or planar microcavities were excited
both optically and electrically. In all cases a pronounced dependence of the
onset to lasing on the magnetic field has been observed. For the sake of
comparison, photon lasing (lasing by an electron-hole plasma) in the presence
of a magnetic field has been studied on the same samples as polariton lasing.
The threshold to photon lasing is essentially governed by the excitonic Mott
transition which appears to be sensitive to magnetic fields too. All the
observed experimental features are qualitatively described within a uniform
model based on coupled diffusion equations for electrons, holes and excitons
and the Gross-Pitaevskii equation for exciton-polariton condensates. Our
research sheds more light on the physics of non-equilibrium Bose-Einstein
condensates and the results manifest high potentiality of polariton lasers for
spin-based quantum logic applications.Comment: 21 pages, 11 figure
Applied investigation of person-specific and context-specific factors on postoperative recovery and clinical outcomes of patients undergoing gastrointestinal cancer surgery: multicentre European study
INTRODUCTION: Cancer treatments have greatly advanced over the past two decades causing survival improvements and reduced complications from cancer surgery. However, the cancer diagnosis and the effects of treatment modalities pose a major risk to patients' psychological well-being. Given current interest and emerging evidence about the importance of psychological and social factors on cancer survival and coping with cancer treatments, this study will build and expand research in order to identify key modifiable psychosocial variables that contribute to better physical and mental health following gastrointestinal cancer (GIC) surgery. OBJECTIVES: To elucidate the incidence of postoperative psychiatric morbidity within 6 months following GIC surgery. To identify key measurable modifiable preoperative psychological factors that can significantly affect postoperative psychiatric morbidity in patients undergoing surgery for GIC. To clarify the changes seen in a patient's psychological well-being during their treatment pathway for GIC. METHODS AND ANALYSIS: This multicentre study has an observational longitudinal study design. In total, 1000 patients will be screened with a multicomponent psychological questionnaire at four different time points: at diagnosis, preoperatively, 1 and 6 months after surgery. Data from this questionnaire will be linked to postoperative complications including psychiatric morbidity, length of hospital stay and recovery to normal activity. ETHICS AND DISSEMINATION: NHS Health Research Authority approval was gained on (REC reference 15.LO/1847) for the completion of this study. Multiple platforms will be used for the dissemination of the research data, including international clinical and patient group presentations and publication of research outputs in a high impact clinical journal
Correlation of plasma metabolites with glucose and lipid fluxes in human insulin resistance
Objective: Insulin resistance develops prior to the onset of overt type 2 diabetes, making its early detection vital. Direct accurate evaluation is currently only possible with complex examinations like the stable isotope-based hyperinsulinemic euglycemic clamp (HIEC). Metabolomic profiling enables the detection of thousands of plasma metabolites, providing a tool to identify novel biomarkers in human obesity. Design: Liquid chromatography mass spectrometry–based untargeted plasma metabolomics was applied in 60 participants with obesity with a large range of peripheral insulin sensitivity as determined via a two-step HIEC with stable isotopes [6,6-2H2]glucose and [1,1,2,3,3-2H5]glycerol. This additionally enabled measuring insulin-regulated lipolysis, which combined with metabolomics, to the knowledge of this research group, has not been reported on before. Results: Several plasma metabolites were identified that significantly correlated with glucose and lipid fluxes, led by plasma (gamma-glutamyl)citrulline, followed by betaine, beta-cryptoxanthin, fructosyllysine, octanylcarnitine, sphingomyelin (d18:0/18:0, d19:0/17:0) and thyroxine. Subsequent machine learning analysis showed that a panel of these metabolites derived from a number of metabolic pathways may be used to predict insulin resistance, dominated by non-essential amino acid citrulline and its metabolite gamma-glutamylcitrulline. Conclusion: This approach revealed a number of plasma metabolites that correlated reasonably well with glycemic and lipolytic flux parameters, measured using gold standard techniques. These metabolites may be used to predict the rate of glucose disposal in humans with obesity to a similar extend as HOMA, thus providing potential novel biomarkers for insulin resistance
Rhodium catalyzed hydroformylation of kaurane derivatives: A route to new diterpenes with potential bioactivity
Kaurenic and grandiflorenic acids are naturally occurring diterpenes whose biological activity has been described. Both acids contain an exocyclic methylenic double bond that allows further functionalization on their structure. In an attempt to expand the number of derivatives of these two natural products, we have undertaken a study on the hydroformylation of the methyl esters of the two acids and the trimethylsilyl ether of kaurenol. These substrates have been hydroformylated by using unmodified Rh catalysts, as well as Rh/PPh3 and Rh/tris-(o-t-butylphenyl)phosphite catalytic systems at 100 °C and 20 bar of CO/H2 (1:1). For the three substrates, the two Rh catalysts modified with P-donor ligands, produced high conversions and chemo- and regioselectivities in the diastereoisomeric pair of linear aldehydes. In all cases, the stereoselectivity observed is strongly dependent of the system used, being the most diastereoselective the least hindered unmodified Rh/CO catalyst. A correlation between the higher diastereoselectivity and the faster [beta]-elimination of the metal-alkyl intermediate observed in the unmodified system is discussed.http://www.sciencedirect.com/science/article/B6TF5-4RVMXFD-3/1/d27e671ad9e0b7fc325dfd0bdf413c7
The ability of synovitis to predict structural damage in rheumatoid arthritis: A comparative study between clinical examination and ultrasound
Objectives: To evaluate synovitis (clinical vs ultrasound (US)) to predict structural progression in rheumatoid arthritis (RA). Methods: Patients with RA. Study design: Prospective, 2-year follow-up. Data collected: Synovitis (32 joints (2 wrists, 10 metacarpophalangeal, 10 proximal interphalangeal, 10 metatarsophalangeal)) at baseline and after 4 months of therapy by clinical, US grey scale (GS-US) and power doppler (PD-US); x-rays at baseline and at year 2. Analysis: Measures of association (OR) were tested between structural deterioration and the presence of baseline synovitis, or its persistence, after 4 months of therapy using generalised estimating equation analysis. Results: Structural deterioration was observed in 9% of the 1888 evaluated joints in 59 patients. Baseline synovitis increased the risk of structural progression: OR=2.01 (1.36-2.98) p<0.001 versus 1.61 (1.06-2.45) p=0.026 versus 1.75 (1.18-2.58) p=0.005 for the clinical versus US-GS versus US-PD evaluation, respectively. In the joints with normal baseline examination (clinical or US), an increased probability for structural progression in the presence of synovitis for the other modality was also observed (OR=2.16 (1.16-4.02) p=0.015 and 3.50 (1.77-6.95) p<0.001 for US-GS and US-PD and 2.79 (1.35-5.76) p=0.002) for clinical examination. Persistent (vs disappearance) synovitis after 4 months of therapy was also predictive of subsequent structural progression. Conclusions: This study confi rms the validity of synovitis for predicting subsequent structural deterioration irrespective of the modality of examination of joints, but also suggests that both clinical and ultrasonographic examinations may be relevant to optimally evaluate the risk of subsequent structural deterioration
- …