626 research outputs found
Environmental protection of titanium alloys in centrifugal compressors at 500°C in saline atmosphere
The use of the titanium alloy Ti-6246 (Ti–6Al–2Sn–4Zr–6Mo, wt-%) for gas turbine compressors allows an increase in working temperature and stress level. Under severe service conditions, the material experiences combined high temperature and high mechanical stress and, in saline atmospheres, stress corrosion cracking (SCC) can occur, leading to catastrophic mechanical failure. The present study was performed to evaluate the potential of several surface treatments to protect Ti-6246 alloy, after salt deposit, from hot salt SCC at temperatures ?500°C and 500 MPa static mechanical stress conditions. Shot peening, thermal oxidation and metal–ceramic coatings were investigated. Experimental results confirm the existence of brittle stress corrosion phenomena marked by a low residual elongation of test samples and the presence of oxides on the fracture surfaces. Both shot peening and metal–ceramic coatings increase the hot salt SCC resistance of the alloy. Times to rupture were improved by a factor of 3 for shot peening and by a factor of 10 for metal–ceramic coatings. Inversely, the time to rupture of preoxidised alloys has been halved compared with uncoated alloys. As well as these interesting quantitative results, structural studies of metal–ceramic coatings showed that they are mechanically and chemically compatible with the titanium alloy substructure and should work under severe thermomechanical stresses and aggressive atmospheres
Novel antimicrobial secondary metabolites from a Penicillium sp. isolated from Brazilian cerrado soil
The morphological features of a Penicillium , isolated from Brazilian
cerrado soil, were characterized and showed to be distinctly different
from all well-defined Penicillium species. Chemical and biological
investigation on the ethyl acetate extract of this Penicillium isolate
resulted in the isolation of three new naphthalenoids: a major
metabolite, methyl
6-acetyl-4-methoxy-5,7,8-trihydroxynaphthalene-2-carboxylate and two
minor ones, methyl
6-acetyl-4-methoxy-7,8-dihydroxynaphthalene-2-carboxylate and methyl
6-acetyl-4-methoxy-5,8-dihydroxynaphthalene-2-carboxylate. Their
structures were determined based on their mono and bidimensional
nuclear magnetic resonance data. Acetyl, allyl and methoxyl derivatives
of the major metabolite were prepared in order to establish
structure-activity relation. Antimicrobial activity of the major
natural product and its semi-synthetic derivatives was screened by
macro dilution methodology and the corresponding minimum inhibitory
concentrations were determined. Natural secondary metabolite methyl
6-acetyl-4-methoxy-5,7,8-trihydroxynaphthalene-2-carboxylate, isolated
in a very high yield (0.3175 mg.L-1) showed to be the most active
compound, possessing expressive activity against Candida albicans
(minimum inhibitory concentration (MIC) 32 \ub5g/mL), Listeria
monocitogenes and Bacillus cereus (MIC 64 \ub5g/mL for both)
Ultracold molecules for quantum simulation: rotational coherence in CaF and RbCs
Polar molecules offer a new platform for quantum simulation of systems with long-range interactions, based on the electrostatic interaction between their electric dipole moments. Here, we report the development of coherent quantum state control using microwave fields in CaF and RbCs molecules, a crucial ingredient for many quantum simulation applications. We perform Ramsey interferometry measurements with fringe spacings of and investigate the dephasing time of a superposition of and rotational states when the molecules are confined. For both molecules, we show that a judicious choice of molecular hyperfine states minimises the impact of spatially varying transition-frequency shifts across the trap. For magnetically trapped CaF we use a magnetically insensitive transition and observe a coherence time of 0.61(3)~ms. For optically trapped RbCs we exploit an avoided crossing in the AC Stark shifts and observe a maximum coherence time of 0.75(6)~ms
Cardiolipin provides an essential activating platform for caspase-8 on mitochondria
Cardiolipin is a mitochondria-specific phospholipid known to be intimately involved with apoptosis. However, the lack of appropriate cellular models to date restricted analysis of its role in cell death. The maturation of cardiolipin requires the transacylase tafazzin, which is mutated in the human disorder Barth syndrome. Using Barth syndrome patient-derived cells and HeLa cells in which tafazzin was knocked down, we show that cardiolipin is required for apoptosis in the type II mitochondria-dependent response to Fas stimulation. Cardiolipin provides an anchor and activating platform for caspase-8 translocation to, and embedding in, the mitochondrial membrane, where it oligomerizes and is further activated, steps that are necessary for an efficient type II apoptotic response
An optimal acquisition and post-processing pipeline for hybrid IVIM-DKI in head and neck
Purpose: To optimize the diffusion-weighting b values and postprocessing pipeline for hybrid intravoxel incoherent motion diffusion kurtosis imaging in the head and neck region. Methods: Optimized diffusion-weighting b value sets ranging between 5 and 30 b values were constructed by optimizing the Cramér-Rao lower bound of the hybrid intravoxel incoherent motion diffusion kurtosis imaging model. With this model, the perfusion fraction, pseudodiffusion coefficient, diffusion coefficient, and kurtosis were estimated. Sixteen volunteers were scanned with a reference b value set and 3 repeats of the optimized sets, of which 1 with volunteers swallowing on purpose. The effects of (1) b value optim
Magnetic detection of sentinel lymph node in papillary thyroid carcinoma: The MAGIC-PAT study results
Introduction: Despite the controversy concerning sentinel lymph node biopsy (SLNB) in papillary thyroid carcinoma (PTC), successful detection rates can be achieved by radioguidance and vital dyeing. However, the drawbacks in both techniques are notable. Magnetic-guided SLNB (mSLNB) using superparamagnetic iron oxide (SPIO) nanoparticles is appealing as an alternative procedure.
Materials and Methods: mSLNB using the Sentimag-Sienna System ® , total thyroidectomy and central compartment dissection (CCD) were performed on all PTC patients. Lymph node involvement was assessed by postoperative pathological examination.
Results: From 2014 to 2016, 33 consecutive patients with PTC were enrolled in the study. A total of 20 patients met the eligibility. mSLNB succeeded in 16 patients, with a detection rate of 80%. A median of two SLN per patient were detected. A median of 10.5 non-sentinel lymph nodes (NSLN) from CCD were examined. Among the patients, 56.25% (9/16) had no metastatic nodes, while 12.5% (2/16) had exclusively SLN involvement. No false negative cases were found. The agreement between SLN and NSLN status was 87.5%. The prediction of NSLN involvement by SLN status showed 100% sensitivity, 81.8% specificity, 71.4% PPV and 100% NPV. Subsequently, mSLNB and the final pathological analysis would discriminate 43.75% (7/16) of patients who would certainly benefit from CCD whilst 56.25% of the total would confirm an unnecessary lymphadenectomy and avoid morbidity.
Conclusion: mSLNB showed satisfactory performance in PTC with clinical-negative nodes. We have shown mSLNB to be a good predictor of central compartment status that can improve the staging and management of PTC patients
4f-spin dynamics in La(2-x-y)Sr(x)Nd(y)CuO(4)
We have performed inelastic magnetic neutron scattering experiments on
La(2-x-y)Sr(x)Nd(y)CuO(4) in order to study the Nd 4f-spin dynamics at low
energies. In all samples we find at high temperatures a quasielastic line
(Lorentzian) with a line width which decreases on lowering the temperature. The
temperature dependence of the quasielastic line width Gamma/2(T) can be
explained with an Orbach-process, i.e. a relaxation via the coupling between
crystal field excitations and phonons. At low temperatures the Nd-4f magnetic
response S(Q,omega) correlates with the electronic properties of the
CuO(2)-layers. In the insulator La(2-y)Nd(y)CuO(4) the quasielastic line
vanishes below 80 K and an inelastic excitation occurs. This directly indicates
the splitting of the Nd3+ ground state Kramers doublet due to the static
antiferromagnetic order of the Cu moments. In La(1.7-x)Sr(x)Nd(0.3)CuO(4) with
x = 0.12, 0.15 and La(1.4-x)Sr(x)Nd(0.6)CuO(4) with x = 0.1, 0.12, 0.15, 0.18
superconductivity is strongly suppressed. In these compounds we observe a
temperature independent broad quasielastic line of Gaussian shape below T about
30 K. This suggests a distribution of various internal fields on different Nd
sites and is interpreted in the frame of the stripe model. In
La(1.8-y)Sr(0.2)Nd(y)CuO(4) (y = 0.3, 0.6) such a quasielastic broadening is
not observed even at lowest temperature.Comment: 8 pages, 10 figures included, to appear in Phys. Rev.
Atmospheric Heating and Wind Acceleration: Results for Cool Evolved Stars based on Proposed Processes
A chromosphere is a universal attribute of stars of spectral type later than
~F5. Evolved (K and M) giants and supergiants (including the zeta Aurigae
binaries) show extended and highly turbulent chromospheres, which develop into
slow massive winds. The associated continuous mass loss has a significant
impact on stellar evolution, and thence on the chemical evolution of galaxies.
Yet despite the fundamental importance of those winds in astrophysics, the
question of their origin(s) remains unsolved. What sources heat a chromosphere?
What is the role of the chromosphere in the formation of stellar winds? This
chapter provides a review of the observational requirements and theoretical
approaches for modeling chromospheric heating and the acceleration of winds in
single cool, evolved stars and in eclipsing binary stars, including physical
models that have recently been proposed. It describes the successes that have
been achieved so far by invoking acoustic and MHD waves to provide a physical
description of plasma heating and wind acceleration, and discusses the
challenges that still remain.Comment: 46 pages, 9 figures, 1 table; modified and unedited manuscript;
accepted version to appear in: Giants of Eclipse, eds. E. Griffin and T. Ake
(Berlin: Springer
Dispersion of Ordered Stripe Phases in the Cuprates
A phase separation model is presented for the stripe phase of the cuprates,
which allows the doping dependence of the photoemission spectra to be
calculated. The idealized limit of a well-ordered array of magnetic and charged
stripes is analyzed, including effects of long-range Coulomb repulsion.
Remarkably, down to the limit of two-cell wide stripes, the dispersion can be
interpreted as essentially a superposition of the two end-phase dispersions,
with superposed minigaps associated with the lattice periodicity. The largest
minigap falls near the Fermi level; it can be enhanced by proximity to a (bulk)
Van Hove singularity. The calculated spectra are dominated by two features --
this charge stripe minigap plus the magnetic stripe Hubbard gap. There is a
strong correlation between these two features and the experimental
photoemission results of a two-peak dispersion in LaSrCuO, and
the peak-dip-hump spectra in BiSrCaCuO. The
differences are suggestive of the role of increasing stripe fluctuations. The
1/8 anomaly is associated with a quantum critical point, here expressed as a
percolation-like crossover. A model is proposed for the limiting minority
magnetic phase as an isolated two-leg ladder.Comment: 24 pages, 26 PS figure
Magnetic Field Generation in Stars
Enormous progress has been made on observing stellar magnetism in stars from
the main sequence through to compact objects. Recent data have thrown into
sharper relief the vexed question of the origin of stellar magnetic fields,
which remains one of the main unanswered questions in astrophysics. In this
chapter we review recent work in this area of research. In particular, we look
at the fossil field hypothesis which links magnetism in compact stars to
magnetism in main sequence and pre-main sequence stars and we consider why its
feasibility has now been questioned particularly in the context of highly
magnetic white dwarfs. We also review the fossil versus dynamo debate in the
context of neutron stars and the roles played by key physical processes such as
buoyancy, helicity, and superfluid turbulence,in the generation and stability
of neutron star fields.
Independent information on the internal magnetic field of neutron stars will
come from future gravitational wave detections. Thus we maybe at the dawn of a
new era of exciting discoveries in compact star magnetism driven by the opening
of a new, non-electromagnetic observational window.
We also review recent advances in the theory and computation of
magnetohydrodynamic turbulence as it applies to stellar magnetism and dynamo
theory. These advances offer insight into the action of stellar dynamos as well
as processes whichcontrol the diffusive magnetic flux transport in stars.Comment: 41 pages, 7 figures. Invited review chapter on on magnetic field
generation in stars to appear in Space Science Reviews, Springe
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