18,586 research outputs found
Chromatin proteins and RNA are associated with DNA during all phases of mitosis.
Mitosis brings about major changes to chromosome and nuclear structure. We used recently developed proximity ligation assay-based techniques to investigate the association with DNA of chromatin-associated proteins and RNAs in Drosophila embryos during mitosis. All groups of tested proteins, histone-modifying and chromatin-remodeling proteins and methylated histones remained in close proximity to DNA during all phases of mitosis. We also found that RNA transcripts are associated with DNA during all stages of mitosis. Reduction of H3K27me3 levels or elimination of RNAs had no effect on the association of the components of PcG and TrxG complexes to DNA. Using a combination of proximity ligation assay-based techniques and super-resolution microscopy, we found that the number of protein-DNA and RNA-DNA foci undergoes significant reduction during mitosis, suggesting that mitosis may be accompanied by structural re-arrangement or compaction of specific chromatin domains
New nickel-base wrought superalloy with applications up to 1253 K (1800 F)
Alloy possesses combination of high tensile strength at low and intermediate temperatures to 1033 K with good rupture strength at high temperatures to 1255 K. Alloy has promise for turbine disk application in future gas turbine engines and for wrought integrally bladed turbine wheel; thickness and weight of disk portion of wheel could be reduced
Winter wheat: A model for the simulation of growth and yield in winter wheat
The basic ideas and constructs for a general physical/physiological process level winter wheat simulation model are documented. It is a materials balance model which calculates daily increments of photosynthate production and respiratory losses in the crop canopy. The partitioning of the resulting dry matter to the active growing tissues in the plant each day, transpiration and the uptake of nitrogen from the soil profile are simulated. It incorporates the RHIZOS model which simulates, in two dimensions, the movement of water, roots, and soluble nutrients through the soil profile. It records the time of initiation of each of the plant organs. These phenological events are calculated from temperature functions with delays resulting from physiological stress. Stress is defined mathematically as an imbalance in the metabolite supply; demand ratio. Physiological stress is also the basis for the calculation of rates of tiller and floret abortion. Thus, tillering and head differentiation are modeled as the resulants of the two processes, morphogenesis and abortion, which may be occurring simulaneously
Cognitive Information Processing
Contains reports on four research projects.National Science Foundation (Grant G-16526)National Institutes of Health (Grant MH-04737-03)National Aeronautics and Space Administration (Grant NsG-496
Low-frequency noise as a source of dephasing of a qubit
With the growing efforts in isolating solid-state qubits from external
decoherence sources, the material-inherent sources of noise start to play
crucial role. One representative example is electron traps in the device
material or substrate. Electrons can tunnel or hop between a charged and an
empty trap, or between a trap and a gate electrode. A single trap typically
produces telegraph noise and can hence be modeled as a bistable fluctuator.
Since the distribution of hopping rates is exponentially broad, many traps
produce flicker-noise with spectrum close to 1/f. Here we develop a theory of
decoherence of a qubit in the environment consisting of two-state fluctuators,
which experience transitions between their states induced by interaction with
thermal bath. Due to interaction with the qubit the fluctuators produce
1/f-noise in the qubit's eigenfrequency. We calculate the results of qubit
manipulations - free induction and echo signals - in such environment. The main
problem is that in many important cases the relevant random process is both
non-Markovian and non-Gaussian. Consequently the results in general cannot be
represented by pair correlation function of the qubit eigenfrequency
fluctuations. Our calculations are based on analysis of the density matrix of
the qubit using methods developed for stochastic differential equations. The
proper generating functional is then averaged over different fluctuators using
the so-called Holtsmark procedure. The analytical results are compared with
simulations allowing checking accuracy of the averaging procedure and
evaluating mesoscopic fluctuations. The results allow understanding some
observed features of the echo decay in Josephson qubits.Comment: 18 pages, 8 figures, Proc. of NATO/Euresco Conf. "Fundamental
Problems of Mesoscopic Physics: Interactions and Decoherence", Granada,
Spain, Sept.200
Low- and high-frequency noise from coherent two-level systems
Recent experiments indicate a connection between the low- and high-frequency
noise affecting superconducting quantum systems. We explore the possibilities
that both noises can be produced by one ensemble of microscopic modes, made up,
e.g., by sufficiently coherent two-level systems (TLS). This implies a relation
between the noise power in different frequency domains, which depends on the
distribution of the parameters of the TLSs. We show that a distribution,
natural for tunneling TLSs, with a log-uniform distribution in the tunnel
splitting and linear distribution in the bias, accounts for experimental
observations.Comment: minor corrections, references adde
Comparison of manual and semi-automated delineation of regions of interest for radioligand PET imaging analysis
BACKGROUND
As imaging centers produce higher resolution research scans, the number of man-hours required to process regional data has become a major concern. Comparison of automated vs. manual methodology has not been reported for functional imaging. We explored validation of using automation to delineate regions of interest on positron emission tomography (PET) scans. The purpose of this study was to ascertain improvements in image processing time and reproducibility of a semi-automated brain region extraction (SABRE) method over manual delineation of regions of interest (ROIs).
METHODS
We compared 2 sets of partial volume corrected serotonin 1a receptor binding potentials (BPs) resulting from manual vs. semi-automated methods. BPs were obtained from subjects meeting consensus criteria for frontotemporal degeneration and from age- and gender-matched healthy controls. Two trained raters provided each set of data to conduct comparisons of inter-rater mean image processing time, rank order of BPs for 9 PET scans, intra- and inter-rater intraclass correlation coefficients (ICC), repeatability coefficients (RC), percentages of the average parameter value (RM%), and effect sizes of either method.
RESULTS
SABRE saved approximately 3 hours of processing time per PET subject over manual delineation (p 0.8) for both methods. RC and RM% were lower for the manual method across all ROIs, indicating less intra-rater variance across PET subjects' BPs.
CONCLUSION
SABRE demonstrated significant time savings and no significant difference in reproducibility over manual methods, justifying the use of SABRE in serotonin 1a receptor radioligand PET imaging analysis. This implies that semi-automated ROI delineation is a valid methodology for future PET imaging analysis
Should HIV be a notifiable disease? Old questions with some new arguments
KMHIV notification enters national debate regularly, often introduced by politicians and supported by many individual healthcare workers. We argue that its proponents advance confused or poorly informed rationales for making HIV notifiable. We present reasons why making HIV notifiable would be inappropriate in South Africa, why the public health benefits of a notification programme are not even likely, and why there are risks of public health and human rights harms
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