11,306 research outputs found
Isolation of Nuclei from Physarum flavicomum: Demonstration of Nuclear Cyclic Acid AMP Phosphodiesterase
Cyclic AMP phosphodiesterase activity in the nucleus of the myxomycete Physarum flavicomum was demonstrated by cytochemical staining utilizing electron microscopy and by enzymatic assays with tritiated cyclic AMP as the substrate. Cytochemical staining showed Physarum\u27s plasmodial phosphodiesterase activity to be located in the nucleus, along the plasma membrane, in vesicles, and free in the cytoplasm. Nuclear phosphodiesterase, which may be cell cycle dependent, was primarily located in the nucleolus. Nuclei from three to five day old microplasmodial cultures were isolated by the method of Henney and Yee. Whole cells were collected through centrifugation and washed. Pellets were homogenized in a medium composed of 0.01 MTris-HC1 (pH 7.2 at 4 °C), 0.25 M sucrose, 0.01% Triton X-100, and 5mM CaC1â. Nuclei were collected through double filtration and two 1.0 M sucrose density gradient centrifugations. After the nuclei were washed, microscopic examination revealed a purity of over 90%. Radioactive assays of the nuclear preparations demonstrated phosphodiesterase activity consistant with that indicated by cytochemical localization. The specific activity of the nuclear enzyme was 15 nMole of cyclic AMP hydrolyzed /min/mg. of protein
An Induced Natural Selection Heuristic for Finding Optimal Bayesian Experimental Designs
Bayesian optimal experimental design has immense potential to inform the
collection of data so as to subsequently enhance our understanding of a variety
of processes. However, a major impediment is the difficulty in evaluating
optimal designs for problems with large, or high-dimensional, design spaces. We
propose an efficient search heuristic suitable for general optimisation
problems, with a particular focus on optimal Bayesian experimental design
problems. The heuristic evaluates the objective (utility) function at an
initial, randomly generated set of input values. At each generation of the
algorithm, input values are "accepted" if their corresponding objective
(utility) function satisfies some acceptance criteria, and new inputs are
sampled about these accepted points. We demonstrate the new algorithm by
evaluating the optimal Bayesian experimental designs for the previously
considered death, pharmacokinetic and logistic regression models. Comparisons
to the current "gold-standard" method are given to demonstrate the proposed
algorithm as a computationally-efficient alternative for moderately-large
design problems (i.e., up to approximately 40-dimensions)
Field Induced Nodal Order Parameter in the Tunneling Spectrum of YBaCuO Superconductor
We report planar tunneling measurements on thin films of
YBaCuO at various doping levels under magnetic fields. By
choosing a special setup configuration, we have probed a field induced energy
scale that dominates in the vicinity of a node of the d-wave superconducting
order parameter. We found a high doping sensitivity for this energy scale. At
Optimum doping this energy scale is in agreement with an induced
order parameter. We found that it can be followed down to low fields at optimum
doping, but not away from it.Comment: 9 pages, 8 figures, accepted for publication in Phys. Rev.
Temporal evolution of long-period seismicity at Etna Volcano, Italy, and its relationships with the 2004â2005 eruption
Between December 2004 and August 2005, more than 50,000 long-period events (LP) accompanied by very-long period pulses (VLP) were recorded at Mt. Etna, encompassing the effusive eruption which started in September 2004. The observed activity can be explained by the injection of a gas slug formed within the magmatic column into an overlying cavity filled by either magmatic or hydrothermal fluids, thus triggering cavity resonance. Although a large number of LP events exhibit similar waveforms before the eruption, they change significantly during and after the eruption. We study the temporal evolution of the LP-VLP activity in terms of the source movement, change of the waveforms, temporal evolution of the dominant resonance frequencies and the source Q factor and changes in the polarization of the signal. The LP source locations before and after the eruption, respectively, do not move significantly, while a slight movement of the VLP source is found. The intensity of the LP events increases after the eruption as well as their dominant frequency and Q factor, while the polarization of the signals changes from predominantly transversal to pure radial motion. Although in previous studies a link between the observed LP activity and the eruption was not found, these observations suggest that such a link was established at the latter end of the eruptive sequence, most likely as a consequence of a reestablishment of the pressure balance in the plumbing system, after it was undermined due to the discharge of large amounts of resident magma during the eruption. Based on the polarization properties of the signal and geological setting of the area, a fluid-filled crack is proposed as the most likely source geometry. The spectral analysis based on the autoregressive-models (SOMPI) is applied to the signals in order to analyse the resonance frequencies and the source Q-factors. The results suggest water and basalt at low gas volume fraction as the most likely fluids involved in the source process. Using theoretical relations for the âslow wavesâ radiated from the fluid-filled crack, we also estimate the crack size for both fluids, respectively
Weak Lensing Effects on the Galaxy Three-Point Correlation Function
We study the corrections to the galaxy three-point correlation function
(3PCF) induced by weak lensing magnification due to the matter distribution
along the line of sight. We consistently derive all the correction terms
arising up to second order in perturbation theory and provide analytic
expressions as well as order of magnitude estimates for their relative
importance. The magnification contributions depend on the geometry of the
projected triangle on the sky plane, and scale with different powers of the
number count slope and redshift of the galaxy sample considered. We evaluate
all terms numerically and show that, depending on the triangle configuration as
well as the galaxy sample considered, weak lensing can in general significantly
contribute to and alter the three-point correlation function observed through
galaxy and quasar catalogs.Comment: 24 pages, 11 figures; version accepted for publication in Phys. Rev.
D; v2: typos corrected, figure caption clarifie
Photoemission Measurement of Equilibrium Segregation at GeSi Surfaces
Photoemission spectroscopy is used to demonstrate that Ge segregates to the first atomic layer of Ge0.5Si0.5(100)2Ă1 and that the second layer is predominantly Si. Comparison of the resolved signals from the dimer atoms of the reconstructed (100)2Ă1 surfaces of Ge, Si, and equiatomic GeâSi alloy shows that the surface layer of the alloy is extremely Ge rich and the second layer is occupied mainly by Si atoms. This result is in good agreement with theoretical predictions
Analysis of sustained long-period activity at Etna Volcano, Italy
Following the installation of a broadband network on Mt. Etna, sustained Long- Period (LP) activity was recorded
accompanying a period of total quiescence and the subsequent onset of the 2004â2005 effusive episode. From c. about 56000
events detected by an automatic classification procedure, we analyse a subset of about 3000 signals spanning the December 17th,
2003âSeptember 25th, 2004, time interval. LP spectra are characterised by several, unevenly-spaced narrow peaks spanning the
0.5â10 Hz frequency band. These peaks are common to all the recording sites of the network, and different from those associated
with tremor signals. Throughout the analysed time interval, LP spectra and waveforms maintain significant similarity, thus
indicating the involvement of a non-destructive source process that we interpret in terms of the resonance of a fluid-filled buried
cavity. Polarisation analysis indicates radiation from a non-isotropic source involving large amounts of shear. Concurrently with LP
signals, recordings from the summit station also depict Very-Long-Period (VLP) pulses whose rectilinear motion points to a region
located beneath the summit craters at depths ranging between 800 and 1100 m beneath the surface. Based on a refined repicking of
similar waveforms, we obtain robust locations for a selected subset of the most energetic LP events from probabilistic inversion of
travel-times calculated for a 3D heterogenous structure. LP sources cluster in a narrow volume located beneath the summit craters,
and extending to a maximum depth of â800 m beneath the surface. No causal relationships are observed between LP, VLP and
tremor activities and the onset of the 2004â2005 lava effusions, thus indicating that magmatic overpressure played a limited role in
triggering this eruption. These data represent the very first observation of LP and VLP activity at Etna during non-eruptive periods,
and open the way to the quantitative modelling of the geometry and dynamics of the shallow plumbing system
Vector magnetic hysteresis of hard superconductors
Critical state problems which incorporate more than one component for the
magnetization vector of hard superconductors are investigated. The theory is
based on the minimization of a cost functional
which weighs the changes of the magnetic field vector within the sample. We
show that Bean's simplest prescription of choosing the correct sign for the
critical current density in one dimensional problems is just a particular
case of finding the components of the vector . is
determined by minimizing under the constraint , with a bounded set. Upon the selection of
different sets we discuss existing crossed field measurements and
predict new observable features. It is shown that a complex behavior in the
magnetization curves may be controlled by a single external parameter, i.e.:
the maximum value of the applied magnetic field .Comment: 10 pages, 9 figures, accepted in Phys. Rev.
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