6,178 research outputs found
Laser-Doppler gas-velocity instrument
Three-D instrument using a laser light source measures both turbulence and mean velocity of subsonic and supersonic gas flows. This instrument is based on the measurement of the Doppler frequency shift of light waves scattered by moving particles in the gas stream
Sulphur and Carbon Isotopes as Tracers of Past Sub-seafloor Microbial Activity
Microbial life below the seafloor has changed over geological time, but these changes are often not obvious, as they are not recorded in the sediment. Sulphur (S) isotope values in pyrite extracted from a Plio- to Holocene sequence of the Peru Margin (Ocean Drilling Program, ODP, Site 1229) show a down-core pattern that correlates with the pattern of carbon (C) isotopes in diagenetic dolomite. Early formation of the pyrite is indicated by the mineralogical composition of iron, showing a high degree of pyritization throughout the sedimentary sequence. Hence, the S-record could not have been substantially overprinted by later pyrite formation. The S- and C-isotope profiles show, thus, evidence for two episodes of enhanced microbial methane production with a very shallow sulphate-methane transition zone. The events of high activity are correlated with zones of elevated organic C content in the stratigraphic sequence. Our results demonstrate how isotopic signatures preserved in diagenetic mineral phases provide information on changes of past biogeochemical activity in a dynamic sub-seafloor biosphere
Laser Doppler velocity instrument
Laser Doppler velocity instrument for measuring turbulence and mean velocity in subsonic and supersonic gas flow
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An Engineered Calmodulin-Based Allosteric Switch for Peptide Biosensing
This work describes the development of a new platform for allosteric protein engineering that takes advantage of the ability of calmodulin to change conformation upon binding to peptide and protein ligands. The switch we have developed consists of a fusion protein in which calmodulin is genetically inserted into the sequence of TEM1 β-lactamase. In this approach, calmodulin acts as the input domain, whose ligand-dependent conformational changes control the activity of the β-lactamase output domain. The new allosteric enzyme exhibits up to 120 times higher catalytic activity in the activated (peptide bound) state compared to the inactive (no peptide bound) state in vitro. Activation of the enzyme is ligand-dependent-peptides with higher affinities for wild-type calmodulin exhibit increased switch activity. Calmodulin's ability to "turn on" the activity of β-lactamase makes this a potentially valuable scaffold for the directed evolution of highly specific biosensors for detecting toxins and other clinically relevant biomarkers.Chemistry and Chemical Biolog
Countering Social Engineering through Social Media: An Enterprise Security Perspective
The increasing threat of social engineers targeting social media channels to
advance their attack effectiveness on company data has seen many organizations
introducing initiatives to better understand these vulnerabilities. This paper
examines concerns of social engineering through social media within the
enterprise and explores countermeasures undertaken to stem ensuing risk. Also
included is an analysis of existing social media security policies and
guidelines within the public and private sectors.Comment: Proceedings of The 7th International Conference on Computational
Collective Intelligence Technologies and Applications (ICCCI 2015), LNAI,
Springer, Vol. 9330, pp. 54-6
A minimal model for spontaneous cell polarization and edge activity in oscillating, rotating and migrating cells
How the cells break symmetry and organize their edge activity to move
directionally is a fun- damental question in cell biology. Physical models of
cell motility commonly rely on gradients of regulatory factors and/or feedback
from the motion itself to describe polarization of edge activity. Theses
approaches, however, fail to explain cell behavior prior to the onset of
polarization. Our analysis using the model system of polarizing and moving fish
epidermal keratocytes suggests a novel and simple principle of
self-organization of cell activity in which local cell-edge dynamics depends on
the distance from the cell center, but not on the orientation with respect to
the front-back axis. We validate this principle with a stochastic model that
faithfully reproduces a range of cell-migration behaviors. Our findings
indicate that spontaneous polarization, persistent motion, and cell shape are
emergent properties of the local cell-edge dynamics controlled by the distance
from the cell center.Comment: 8 pages, 5 figure
Neuronal Encoding of Texture in the Whisker Sensory Pathway
A major challenge of sensory systems neuroscience is to quantify brain activity underlying perceptual experiences and to explain this activity as the outcome of elemental neuronal response properties. Rats make extremely fine discriminations of texture by “whisking” their vibrissae across an object's surface, yet the neuronal coding underlying texture sensations remains unknown. Measuring whisker vibrations during active whisking across surfaces, we found that each texture results in a unique “kinetic signature” defined by the temporal profile of whisker velocity. We presented these texture-induced vibrations as stimuli while recording responses of first-order sensory neurons and neurons in the whisker area of cerebral cortex. Each texture is encoded by a distinctive, temporally precise firing pattern. To look for the neuronal coding properties that give rise to texture-specific firing patterns, we delivered horizontal and vertical whisker movements that varied randomly in time (“white noise”) and found that the response probabilities of first-order neurons and cortical neurons vary systematically according to whisker speed and direction. We applied the velocity-tuned spike probabilities derived from white noise to the sequence of velocity features in the texture to construct a simulated texture response. The close match between the simulated and real responses indicates that texture coding originates in the selectivity of neurons to elemental kinetic events
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