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1.
Appl Opt ; 60(16): 4885-4891, 2021 Jun 01.
Artículo en Inglés | MEDLINE | ID: mdl-34143050

RESUMEN

High resolution luminosity product measurements of neutral beam emission in magnetized plasmas are severely limited by the artificial Doppler broadening inherent to the use of large diameter collection optics. In this paper, a broadening compensation method is developed for the spatial heterodyne spectroscopy interferometric technique. The compensation technique greatly reduces the artificial broadening, thereby enabling high resolution measurements at a significantly higher photon flux than previously available. Compensated and uncompensated measurements of emission generated by impact excitation of 61 keV deuterium neutrals in a tokamak plasma at the DIII-D National Fusion Facility are presented. The spectral width of the compensated measurement is ${\sim}0.13 \;{\rm{nm}}$, which is comparable to the instrument resolution. This width is ${\sim}4 \times$ smaller than the uncompensated width, which for the 20 cm diameter collection lens system utilized in this study is ${\sim}0.5 \;{\rm{nm}}$.

2.
Rev Sci Instrum ; 89(10): 10D114, 2018 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-30399811

RESUMEN

Measurement of electrostatic potential, or local electric field, turbulence is a critical missing component in validating nonlinear turbulence and transport simulations of fusion plasmas. A novel diagnostic is being developed for measuring local electric field fluctuations, E ̃ ( r , t ) , via high-speed measurements of the light emitted from a hydrogenic neutral beam. It exploits the proportionality of the spectral line splitting from the Motional Stark Effect to the total electric field experienced by the neutral atom at the excitation site. The measurement is localized by the usual cross-beam geometry of beam-spectroscopy measurements. The corner stone of the diagnostic is a high spectral resolution, high etendue spatial heterodyne spectrometer (SHS). A SHS design with high etendue (∼5 mm2 sr) and resolution (∼0.14 nm) meets the formidable spectrometer requirements. Field tests of the spectrometer at the DIII-D tokamak demonstrate that the beam emission spectrum produced by the SHS agrees with that of a traditional spectrometer and that the measured flux is adequate for turbulence studies.

3.
Sci Rep ; 7(1): 7332, 2017 08 04.
Artículo en Inglés | MEDLINE | ID: mdl-28779097

RESUMEN

Creep cavitation in an ex-service nuclear steam header Type 316 stainless steel sample is investigated through a multiscale tomography workflow spanning eight orders of magnitude, combining X-ray computed tomography (CT), plasma focused ion beam (FIB) scanning electron microscope (SEM) imaging and scanning transmission electron microscope (STEM) tomography. Guided by microscale X-ray CT, nanoscale X-ray CT is used to investigate the size and morphology of cavities at a triple point of grain boundaries. In order to understand the factors affecting the extent of cavitation, the orientation and crystallographic misorientation of each boundary is characterised using electron backscatter diffraction (EBSD). Additionally, in order to better understand boundary phase growth, the chemistry of a single boundary and its associated secondary phase precipitates is probed through STEM energy dispersive X-ray (EDX) tomography. The difference in cavitation of the three grain boundaries investigated suggests that the orientation of grain boundaries with respect to the direction of principal stress is important in the promotion of cavity formation.

4.
Phys Rev Lett ; 119(3): 035001, 2017 Jul 21.
Artículo en Inglés | MEDLINE | ID: mdl-28777627

RESUMEN

Access to and characterization of sustained, toroidally confined plasmas with a very high plasma-to-magnetic pressure ratio (ß_{t}), low internal inductance, high elongation, and nonsolenoidal current drive is a central goal of present tokamak plasma research. Stable access to this desirable parameter space is demonstrated in plasmas with ultralow aspect ratio and high elongation. Local helicity injection provides nonsolenoidal sustainment, low internal inductance, and ion heating. Equilibrium analyses indicate ß_{t} up to ∼100% with a minimum |B| well spanning up to ∼50% of the plasma volume.

5.
J Mater Sci ; 52(14): 8665-8680, 2017.
Artículo en Inglés | MEDLINE | ID: mdl-32103837

RESUMEN

The growth/coarsening kinetics of γ ″ ( Ni 3 Nb - D0 22 ) precipitates have been found by numerous researchers to show an apparent correspondence with the classical (Ostwald ripening) equation outlined by Lifshitz, Slyozov and (separately) Wagner for a diffusion controlled regime. Nevertheless, a significant disparity between the actual precipitate size distribution shape and that predicted by LSW is frequently observed in the interpretation of these results, the origin of which is unclear. Analysis of the literature indicates one likely cause for this deviation from LSW for γ ″ precipitates is the "encounter" phenomenon described by Davies et al. (Acta Metall 28(2):179-189, 1980) that is associated with secondary phases comprising a high volume fraction. Consequently, the distributions of both γ ″ precipitates described in the literature (Alloy 718) and measured in this research in Alloy 625 are analysed through employing the Lifshitz-Slyozov-Encounter-Modified (LSEM) formulation (created by Davies et al.). The results of the LSEM analysis show good far better agreement than LSW with experimental distributions after the application of a necessary correction for what is termed in this research as "directional encounter". Moreover, the activation energy for γ ″ coarsening in Alloy 625 shows conformity with literature data once the effect of heterogeneous (on dislocations) precipitate nucleation at higher temperatures is accounted for.

6.
Ultramicroscopy ; 176: 46-51, 2017 05.
Artículo en Inglés | MEDLINE | ID: mdl-27932032

RESUMEN

In situ analytical transmission electron microscopy (TEM) can provide a unique perspective on dynamic reactions in a variety of environments, including liquids and gases. In this study, in situ analytical TEM techniques have been applied to examine the localised oxidation reactions that occur in a Ni-Cr-Fe alloy, Alloy 600, using a gas environmental cell at elevated temperatures. The initial stages of preferential intergranular oxidation, shown to be an important precursor phenomenon for intergranular stress corrosion cracking in pressurized water reactors (PWRs), have been successfully identified using the in situ approach. Furthermore, the detailed observations correspond to the ex situ results obtained from bulk specimens tested in hydrogenated steam and in high temperature PWR primary water. The excellent agreement between the in situ and ex situ oxidation studies demonstrates that this approach can be used to investigate the initial stages of preferential intergranular oxidation relevant to nuclear power systems.

8.
Phys Rev Lett ; 116(17): 175001, 2016 Apr 29.
Artículo en Inglés | MEDLINE | ID: mdl-27176526

RESUMEN

Tokamak experiments at near-unity aspect ratio A≲1.2 offer new insights into the self-organized H-mode plasma confinement regime. In contrast to conventional A∼3 plasmas, the L-H power threshold P_{LH} is ∼15× higher than scaling predictions, and it is insensitive to magnetic topology, consistent with modeling. Edge localized mode (ELM) instabilities shift to lower toroidal mode numbers as A decreases. These ultralow-A operations enable heretofore inaccessible J_{edge}(R,t) measurements through an ELM that show a complex multimodal collapse and the ejection of a current-carrying filament.

9.
Ultramicroscopy ; 161: 119-129, 2016 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-26683814

RESUMEN

Ga(+) Focused Ion Beam-Scanning Electron Microscopes (FIB-SEM) have revolutionised the level of microstructural information that can be recovered in 3D by block face serial section tomography (SST), as well as enabling the site-specific removal of smaller regions for subsequent transmission electron microscope (TEM) examination. However, Ga(+) FIB material removal rates limit the volumes and depths that can be probed to dimensions in the tens of microns range. Emerging Xe(+) Plasma Focused Ion Beam-Scanning Electron Microscope (PFIB-SEM) systems promise faster removal rates. Here we examine the potential of the method for large volume serial section tomography as applied to bainitic steel and WC-Co hard metals. Our studies demonstrate that with careful control of milling parameters precise automated serial sectioning can be achieved with low levels of milling artefacts at removal rates some 60× faster. Volumes that are hundreds of microns in dimension have been collected using fully automated SST routines in feasible timescales (<24h) showing good grain orientation contrast and capturing microstructural features at the tens of nanometres to the tens of microns scale. Accompanying electron back scattered diffraction (EBSD) maps show high indexing rates suggesting low levels of surface damage. Further, under high current Ga(+) FIB milling WC-Co is prone to amorphisation of WC surface layers and phase transformation of the Co phase, neither of which have been observed at PFIB currents as high as 60nA at 30kV. Xe(+) PFIB dual beam microscopes promise to radically extend our capability for 3D tomography, 3D EDX, 3D EBSD as well as correlative tomography.

11.
Ultramicroscopy ; 144: 1-8, 2014 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-24814008

RESUMEN

Energy-dispersive X-ray (EDX) spectroscopy in the scanning transmission electron microscope (STEM) has been used to demonstrate the presence of size-dependent compositional variation for L12-structured Ni3Al-type gamma-prime (γ') precipitates within a commercial RR1000 Ni-based superalloy. This semi-quantitative elemental analysis has been achieved using electrochemical extraction of the γ' precipitates from the γ matrix. The applicability of this approach to size-dependent compositional analysis of precipitates was confirmed by a comparison of the size distribution for the extracted precipitates with those present in traditional electropolished foil specimens in the size range 20-250nm. By applying suitable thickness-dependent absorption-corrections we have demonstrated that the composition of γ' precipitates in our material depends on the size of the precipitate in the range of 5nm to 3µm. In particular, the Al content was observed to increase in smaller γ' precipitates while Ti and Ta contents are constant for all sizes of precipitate. Hf was observed to be present only in the largest precipitates. This type of local compositional information provides invaluable input to assess the accuracy of microstructural modelling for these complex alloys and provides new evidence supporting the importance of anti-site diffusion.

12.
Rev Sci Instrum ; 83(10): 10D516, 2012 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-23126858

RESUMEN

A passive ion temperature polychromator has been deployed on Pegasus to study power balance and non-thermal ion distributions that arise during point source helicity injection. Spectra are recorded from a 1 m F/8.6 Czerny-Turner polychromator whose output is recorded by an intensified high-speed camera. The use of high orders allows for a dispersion of 0.02 Å/mm in 4th order and a bandpass of 0.14 Å (~13 km/s) at 3131 Å in 4th order with 100 µm entrance slit. The instrument temperature of the spectrometer is 15 eV. Light from the output of an image intensifier in the spectrometer focal plane is coupled to a high-speed CMOS camera. The system can accommodate up to 20 spatial points recorded at 0.5 ms time resolution. During helicity injection, stochastic magnetic fields keep T(e) low (100 eV) and thus low ionization impurities penetrate to the core. Under these conditions, high core ion temperatures are measured (T(i) ≈ 1.2 keV, T(e) ≈ 0.1 keV) using spectral lines from carbon III, nitrogen III, and boron IV.

13.
Ultramicroscopy ; 111(6): 676-82, 2011 May.
Artículo en Inglés | MEDLINE | ID: mdl-21232865

RESUMEN

In this work, the importance of optimising experimental conditions for the analysis of reactor pressure vessel (RPV) steels using atom probe tomography is explored. The quality of the resultant atom probe data is assessed in terms of detection efficiency, noise levels and mass resolution. It is demonstrated that artefacts can exist even when experimental conditions have been optimised. In particular, it is shown that surface diffusion of some minority species, including P and Si, to major poles prior to field evaporation can be an issue. The effects were most noticeable during laser pulsing. The impact of surface migration on the characterisation of dislocations and grain boundaries is assessed. The importance of selecting appropriate regions of the reconstructed data for subsequent re-analysis is emphasised.

14.
Ultramicroscopy ; 109(5): 510-7, 2009 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-19081677

RESUMEN

Microstructural characterisation of neutron irradiated low alloy steels is important for developing mechanistic understanding of irradiation embrittlement. This work is focused on the early stages of irradiation-induced clustering in a low Cu (0.03wt%), high Ni ( approximately 1wt%) weld. The weld was irradiated at a very high dose rate and then examined by atom probe (energy-compensated position-sensitive atom probe (ECOPoSAP) and local electrode atom probe (LEAP)) with supporting microstructural information obtained by small angle neutron scattering (SANS) and positron annihilation (PALA). It was demonstrated that extreme care must be taken optimising parameters used to characterise the extent of clustering. This is particularly important during the early stages of irradiation-damage when the clusters are poorly defined and significant compositional variations are present in what is traditionally described as matrix. Analysis of the irradiated materials showed increasing clustering of Cu, Mn, Ni and Si with dose. In the low Cu steel the results showed that initially the irradiation damage results in clustering of Mn, Ni and Si, but at very high doses, at very high dose rates, redistribution of Si is significantly more advanced than that for Mn and Ni.

17.
J Biol Chem ; 269(39): 24090-4, 1994 Sep 30.
Artículo en Inglés | MEDLINE | ID: mdl-7929061

RESUMEN

The porcine uterus synthesizes a proteinase inhibitor (M(r) 14,000) under the influence of progesterone that is relatively specific for plasmin and trypsin, but that also has weak affinity for chymotrypsin. Several isoforms of this uterine plasmin/trypsin inhibitor were purified by a procedure whose final two steps involved affinity chromatography on immobilized chymotrypsin and cation exchange chromatography. Amino-terminal sequencing showed that at least three of the isoforms were closely related. An oligonucleotide probe based on the protein sequence was used to identify a cDNA that contained an open reading frame coding for a mature protein (M(r) 10,295) of 93 amino acids. The inhibitor had a well defined, but unique, Kunitz domain of 64 residues at its amino terminus that shared 67% sequence identity to bovine pancreatic trypsin inhibitor. Its P1 residue was arginine rather than lysine. Northern analysis showed the presence of a single mRNA species (700 bases) that in adult female pigs appeared to be confined to the uterus. During pregnancy, UPTI mRNA expression was high until Day 30 and decreased significantly thereafter. By contrast, uteroferrin mRNA reached maximal concentrations in late pregnancy. These data are consistent with an earlier hypothesis that the inhibitor serves to neutralize the activities of one or more serine proteinases generated by the proliferating trophoblast during the formation of the noninvasive placenta of the pig.


Asunto(s)
Péptidos , Proteínas de Plantas , Inhibidores de Tripsina/metabolismo , Útero/enzimología , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Cromatografía por Intercambio Iónico , Clonación Molecular , ADN Complementario , Femenino , Masculino , Datos de Secuencia Molecular , Embarazo , ARN Mensajero/genética , ARN Mensajero/metabolismo , Homología de Secuencia de Aminoácido , Porcinos , Inhibidores de Tripsina/genética , Útero/metabolismo
18.
Anim Genet ; 22(4): 343-52, 1991.
Artículo en Inglés | MEDLINE | ID: mdl-1952283

RESUMEN

A 1.2-kb bovine DR beta-like cDNA clone (BoLA-DRB3) was isolated from a peripheral blood lymphocyte cDNA library utilizing a human DR beta cDNA as a probe. BoLA-DRB3 was found to have a high degree of nucleotide sequence similarity (96.8%) with a previously sequenced bovine DR beta-like gene (A1). It is believed that BoLA-DRB3 and A1 represent distinct alleles of one of the three bovine DR beta-like loci. Sequence comparison of BoLA-DRB3 with genes representing the other two bovine DR beta-like loci resulted in moderate degrees of sequence similarities (83.1% and 86.3%, respectively). Comparison of the relative abundance of RNA transcripts of the three bovine DR beta-like loci by Northern analysis of lymphocyte RNA indicated that BoLA-DRB3 is the most actively transcribed of the three bovine DR beta-like genes. Based on these results we suggest that of the three DR beta-like loci thus far identified in the bovine, only one is actively transcribed.


Asunto(s)
Bovinos/genética , Genes MHC Clase II/genética , Homología de Secuencia de Ácido Nucleico , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Northern Blotting , Southern Blotting , Bovinos/inmunología , Clonación Molecular , Sondas de ADN/genética , Antígenos HLA-DR/genética , Datos de Secuencia Molecular
19.
Artículo en Inglés | MEDLINE | ID: mdl-18267632

RESUMEN

The growth of ferroelectric BaMgF(4) thin films on Si(100), sapphire, and other substrates under ultrahigh vacuum (UHV) conditions is reported. Microstructural characterization of the films using transmission electron microscopy (TEM) revealed that they were oriented crystalline films, although not epitaxial. Ferroelectric hysteresis measurements yielded spontaneous polarization and coercivity values of almost 1.0 muC/cm(2) and 160 kV/cm, respectively. The discrepancy with the bulk ferroelectric values were attributed to the electrical contacts, impurities in the film, and lack of polar axis orientation. Preliminary capacitance-voltage (C-V) hysteresis measurements on a 480-nm-thick BaMgF(4) film yielded a 10.8-V threshold shift (memory window) in response to a +/-10-V programming voltage for a MIS gate structure similar to that of the ferroelectric memory field-effect transistor (FEMFET).

20.
J Biol Chem ; 265(6): 3248-55, 1990 Feb 25.
Artículo en Inglés | MEDLINE | ID: mdl-2303448

RESUMEN

Two-dimensional polyacrylamide gel electrophoresis has revealed the presence of a group of relatively acidic proteins of molecular weight about 22,000 in the uterine flushings of pseudopregnant pigs. The proteins have been purified by a combination of gel filtration chromatography and high performance anion-exchange chromatography and shown to bind both [3H] retinol and [3H]retinoic acid. At least four protein peaks that bound retinoids could be detected in the uterine secretions of a single pig. The ion-exchange procedure also allowed the retinol-free apoproteins to be separated from the holoforms that had associated ligand. Amino acid sequencing of the NH2 termini of polypeptides within three of the peaks revealed the presence of proteins with some degree of sequence identity to serum retinol-binding proteins (RBP). The most basic polypeptides showed the least similarity (about 30% identity), while the most acidic isoform analyzed shared about 70% sequence identity with the NH2 terminus of human serum RBP. Western blotting procedures employing an antiserum raised against the most basic isoforms showed that the amount of retinol-binding protein in uterine secretions increased markedly in ovariectomized animals in response to long term progesterone treatment. These proteins appear to form part of the uterine histotroph thought to be essential for nourishment of the conceptuses during pregnancy. A simple three-step procedure for purifying retinol-binding protein from pig serum is also described. The NH2-terminal sequence of this RBP is similar to that of human RBP but different from those of the uterine forms. The study suggests that a family of RBP, distinct from the serum form, is secreted by the uterine endometrium of the pig in response to progesterone.


Asunto(s)
Endometrio/metabolismo , Progesterona/farmacología , Proteínas de Unión al Retinol/biosíntesis , Útero/metabolismo , Secuencia de Aminoácidos , Animales , Células Cultivadas , Cromatografía en Gel , Cromatografía Líquida de Alta Presión , Cromatografía por Intercambio Iónico , Electroforesis en Gel Bidimensional , Endometrio/efectos de los fármacos , Femenino , Humanos , Datos de Secuencia Molecular , Peso Molecular , Ovariectomía , Progesterona/sangre , Proteínas de Unión al Retinol/genética , Proteínas de Unión al Retinol/aislamiento & purificación , Homología de Secuencia de Ácido Nucleico , Porcinos , Útero/efectos de los fármacos , Vitamina A/metabolismo
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