38 research outputs found
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Note on Graphite Oxidation by Oxygen and Moisture
Simplified equations of graphite oxidation are reviewed for semi-infinite slab, finite slab, and cylinder geometries, using the principal assumptions of linearized oxidation kinetics and quasi-steady state oxidation profile. All equations are coupled to a general surface mass transfer boundary condition. The equations include those for oxidant concentration distribution, surface oxidation rate, burnoff profile, and oxidation efficiency. This review also covers some areas that may not be well recognized. The key role of the effective diffusivity is highlighted, with a brief review of measured values. The temperature-dependence of the surface oxidation rate is shown to be more complex than usually shown for the diffusion-affected zone. Assumption of linear kinetics permits ready estimation of equilibration time for development of the quasi-steady burnoff profile. In addition, approximations for the time-steady hydrogen concentration profiles are developed for the case of oxidation by H2O. All cited methods can be readily evaluated by spreadsheet calculation
Asenjonamides AâC, antibacterial metabolites isolated from Streptomyces asenjonii strain KNN 42.f from an extreme-hyper arid Atacama Desert soil
Bio-guided fractionation of the culture broth extract of Streptomyces asenjonii strain KNN 42.f recovered from an extreme hyper-arid Atacama Desert soil in northern Chile led to the isolation of three new bioactive ?-diketones; asenjonamides AâC (1â3) in addition to the known N-(2-(1H-indol-3-yl)-2-oxoethyl)acetamide (4), a series of bioactive acylated 4-aminoheptosyl-?-N-glycosides; spicamycins AâE (5â9), and seven known diketopiperazines (10â16). All isolated compounds were characterized by HRESIMS and NMR analyses and tested for their antibacterial effect against a panel of bacteria
Hunting for cultivable Micromonospora strains in soils of the Atacama Desert
Innovative procedures were used to selectively isolate small numbers of Micromonospora strains from extreme hyper-arid and high altitude Atacama Desert soils. Micromonosporae were recognised on isolation plates by their ability to produce filamentous microcolonies that were strongly attached to the agar. Most of the isolates formed characteristic orange colonies that lacked aerial hyphae and turned black on spore formation, whereas those from the high altitude soil were dry, blue-green and covered by white aerial hyphae. The isolates were assigned to seven multi- and eleven single-membered groups based on BOX-PCR profiles. Representatives of the groups were assigned to either multi-membered clades that also contained marker strains or formed distinct phyletic lines in the Micromonospora 16S rRNA gene tree; many of the isolates were considered to be putatively novel species of Micromonospora. Most of the isolates from the high altitude soils showed activity against wild type strains of Bacillus subtilis and Pseudomonas fluorescens while those from the rhizosphere of Parastrephia quadrangulares and from the Lomas Bayas hyper-arid soil showed resistance to UV radiation
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Conversion of laser phase noise to amplitude noise in a Lummer-Gehrcke interferometer and in oxygen gas
In order to observe laser phase noise, this noise must be converted to
amplitude noise, which can be achieved using either an interferometer or an
absorption resonance in an atomic/molecular vapor or gas. When phase noise is
converted to amplitude noise, it is manifested as a heterodyne signal in the
output of an optical square-law detector. Thus, phase noise is measured by
optical heterodyne spectroscopy, or, equivalently, laser phase noise
spectroscopy.
In recent work on diode laser noise spectroscopy of rubidium and oxygen, the
observed spectroscopic lineshapes were not in total agreement with theoretical
predictions. We have repeated the previous work on the oxygen A-band
transitions, and we now find qualitative agreement with theory.
In addition, we have measured the diode laser noise spectrum of a Lummer-
Gehrcke interferometer (LGI), comparing the heterodyne lineshape of a LGI
transmission spectrum with a qualitative theory that we develop in this thesis.
A theory, from other workers, predicts the intensity fluctuations from a
Doppler-broadened, two-level atomic/molecular system driven with a phase-diffusing
laser field. We show that a simplified version of this theory, which
ignores Doppler effects of the system, is a useful approximation to the complete
theory, by comparing computer-generated heterodyne lineshapes of each, for a
rubidium transition. We apply this approximate theory to an oxygen A-band
transition, and compare these results with our experimental measurements.
For the experimental arrangement used in the present work, diode laser noise
spectroscopy may also include effects of selective reflection, which is dealt with
experimentally and theoretically.
Diode laser phase noise has practical importance in optical communications
and atomic clocks
Dysregulated development of IL-17-and IL-21-expressing follicular helper T cells and increased germinal center formation in the absence of RORÎłt
Interleukin 17-producing helper T (Th17) cells have been widely defined by the lineage transcription factor retinoid-related orphan receptor (ROR)gammat. Pathophysiologically, these cells play a crucial role in autoimmune diseases and have been linked to dysregulated germinal center (GC) reactions and autoantibody production. In this study, we used gene expression and flow cytometric analyses for the characterization of Rorgammat-/- and Rorgammat-/-Il21RFP/+ mice to demonstrate a previously unknown transcriptional flexibility in the development of IL-17-producing Th-cell subsets. We found an accumulation of follicular Th (Tfh) cells by 5.2-fold, spontaneous 13-fold higher GC formation, decreased frequency of follicular Foxp3+ T-regulatory (Treg) cells (50%), and a 3.4-fold increase in the number of proliferating follicular B cells in RORgammat-deficient vs. wild-type mice. Dysregulated B-cell responses were associated with enhanced production of IL-17 (6.4-fold), IL-21 (2.2-fold), and B-cell-activating factor (BAFF) (2-fold) and were partially rescued by adoptive transfer of Treg cells. In an unexpected finding, we detected RORgammat-independent IL-17 expression in ICOS+CXCR5+Tfh and in ICOS+CXCR5-Th cells. Based on the observed high Irf4 and Batf gene expression, we suggest that CD4+ T-cell transcription factors other than RORgammat can cooperatively induce differentiation of IL-17-producing Th cells, including Th17-like Tfh-cell subsets. We conclude that the occurrence of aberrant Tfh and follicular Treg cells support spontaneous GC formation and dysregulated B-cell responses in RORgammat-deficient mice