143 research outputs found
The knowledge-based software assistant
Where the Knowledge Based Software Assistant (KBSA) is now, four years after the initial report, is discussed. Also described is what the Rome Air Development Center expects at the end of the first contract iteration. What the second and third contract iterations will look like are characterized
Influence of Blue-Green Algae on the pH and Buffer Capacity of Culture Media
Three strains of the blue-green algae Anabaena cylindrica, Anacystis nidulans and Nostoc muscorum are able to adjust the pH of culture medium from stress levels (pH 4-6) to levels favorable for growth (pH 7-10). Over a period of one week, these strains increased the buffer capacity of their media with time. The pH of maximum buffer capacity after one week was very close to the pK2 of phosphoric acid. Algae grown in a medium initially buffered with Na2CO3 shifted the pH of maximum buffer capacity from the pK of carbonic acid to that of phosphoric acid
Spin dynamics and spin freezing behavior in the two-dimensional antiferromagnet NiGaS revealed by Ga-NMR, NQR and SR measurements
We have performed Ga nuclear magnetic resonance (NMR) and nuclear
quadrupole resonance (NQR) and muon spin rotation/resonance on the quasi
two-dimensional antiferromagnet (AFM) NiGaS, in order to investigate
its spin dynamics and magnetic state at low temperatures. Although there exists
only one crystallographic site for Ga in NiGaS, we found two distinct
Ga signals by NMR and NQR. The origin of the two Ga signals is not fully
understood, but possibly due to stacking faults along the c axis which induce
additional broad Ga NMR and NQR signals with different local symmetries. We
found the novel spin freezing occurring at , at which the specific
heat shows a maximum, from a clear divergent behavior of the nuclear
spin-lattice relaxation rate and nuclear spin-spin relaxation rate
measured by Ga-NQR as well as the muon spin relaxation rate
. The main sharp NQR peaks exhibit a stronger tendency of divergence,
compared with the weak broader spectral peaks, indicating that the spin
freezing is intrinsic in NiGaS. The behavior of these relaxation rates
strongly suggests that the Ni spin fluctuations slow down towards ,
and the temperature range of the divergence is anomalously wider than that in a
conventional magnetic ordering. A broad structureless spectrum and
multi-component were observed below 2 K, indicating that a static
magnetic state with incommensurate magnetic correlations or inhomogeneously
distributed moments is realized at low temperatures. However, the wide
temperature region between 2 K and , where the NQR signal was not
observed, suggests that the Ni spins do not freeze immediately below , but keep fluctuating down to 2 K with the MHz frequency range.Comment: 14 pages, 14 figures. To appear in Phys. Rev.
Functional Memory B Cells and Long-Lived Plasma Cells Are Generated after a Single Plasmodium chabaudi Infection in Mice
Antibodies have long been shown to play a critical role in naturally acquired immunity to malaria, but it has been suggested that Plasmodium-specific antibodies in humans may not be long lived. The cellular mechanisms underlying B cell and antibody responses are difficult to study in human infections; therefore, we have investigated the kinetics, duration and characteristics of the Plasmodium-specific memory B cell response in an infection of P. chabaudi in mice. Memory B cells and plasma cells specific for the C-terminal region of Merozoite Surface Protein 1 were detectable for more than eight months following primary infection. Furthermore, a classical memory response comprised predominantly of the T-cell dependent isotypes IgG2c, IgG2b and IgG1 was elicited upon rechallenge with the homologous parasite, confirming the generation of functional memory B cells. Using cyclophosphamide treatment to discriminate between long-lived and short-lived plasma cells, we demonstrated long-lived cells secreting Plasmodium-specific IgG in both bone marrow and in spleens of infected mice. The presence of these long-lived cells was independent of the presence of chronic infection, as removal of parasites with anti-malarial drugs had no impact on their numbers. Thus, in this model of malaria, both functional Plasmodium-specific memory B cells and long-lived plasma cells can be generated, suggesting that defects in generating these cell populations may not be the reason for generating short-lived antibody responses
Toward Automatic Label-Free Whispering Gallery Modes Biodetection with a Quantum Dot-Coated Microsphere Population
We explore a new calibration-free approach to biodetection based on whispering gallery modes (WGMs) without a reference measure and relative shifts. Thus, the requirement to keep track of the sensor position is removed, and a freely moving population of fluorophore-doped polystyrene microspheres can now fulfill this role of sensing resonator. Breaking free from fixed surface-based biosensing promotes adhesion between the microsphere sensors and the analytes since both can now be thoroughly mixed. The 70-nm-wide spectrum of green fluorescent microbeads allows us to monitor over 20 WGMs simultaneously without needing evanescent light coupling into the microspheres, hence enabling remote sensing. Since the exact radius of each microsphere is unknown a priori, it requires algorithmic analyses to obtain a reliable result for the refractive index of a solution. We first test our approach with different solutions of alcohol in water obtaining 3 × 10−4 precision on the refractive index at lower concentrations. Then, the solutions of bacterial spores in water yield clear evidence of biodetection in the statistical analysis of WGMs from 50 microspheres. To extend the fluorescence spectral range of our WGM sensors, we present preliminary results on coating microspheres with CdSe/ZnS quantum dots
How external and internal resources influence user action: the case of infusion devices
Human error can have potentially devastating consequences in contexts such as healthcare, but there is a rarely a simple dichotomy between errors and correct behaviour. Furthermore, there has been little consideration of how the activities of users (erroneous and otherwise) relate to the conceptual fit between user and device, despite the fact that healthcare technologies are becoming increasingly prevalent and complex. In this article, we present a study in which nurses’ conceptions of infusion device practice were elicited to identify misfits. By focusing on key concepts that users work with when setting up infusions and the extent to which the system supports them, our analysis highlights how actions are influenced by the different resources available to users including: the device itself; supporting artefacts; the conceptual understanding of the user; and the community of practice the user is part of. The findings reveal the ways in which users are resourceful in their day-to-day activities and also suggest potential vulnerabilities within the wider system that could threaten patient safety. Our approach is able to make previously under-explored aspects of practice visible, thus enabling insight into how users act and why
Non-Redfield carbon and nitrogen cycling in the Arctic: Effects of ecosystem structure and dynamics
The C:N ratio is a critical parameter used in both global ocean carbon models and field studies to understand carbon and nutrient cycling as well as to estimate exported carbon from the euphotic zone. The so-called Redfield ratio (C:N = 6.6 by atoms) [Redfield et al., 1963] is widely used for such calculations. Here we present data from the NE Greenland continental shelf that show that most of the C:N ratios for particulate (autotrophic and heterotrophic) and dissolved pools and rates of transformation among them exceed Redfield proportions from June to August, owing to species composition, size, and biological interactions. The ecosystem components that likely comprised sinking particles and had relatively high C:N ratios (geometric means) included (1) the particulate organic matter (C:N = 8.9) dominated by nutrient-deficient diatoms, resulting from low initial nitrate concentrations (approximately 4 μM) in Arctic surface waters; (2) the dominant zooplankton, herbivorous copepods (C:N = 9.6), having lipid storage typical of Arctic copepods; and (3) copepod fecal pellets (C:N = 33.2). Relatively high dissolved organic carbon concentrations (median 105 μM) were approximately 25 to 45 μM higher than reported for other systems and may be broadly characteristic of Arctic waters. A carbon-rich dissolved organic carbon pool also was generated during summer. Since the magnitude of carbon and nitrogen uncoupling in the surface mixed layer appeared to be greater than in other regions and occurred throughout the productive season, the C:N ratio of particulate organic matter may be a better conversion factor than the Redfield ratio to estimate carbon export for broad application in northern high-latitude systems
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