4,311 research outputs found
From collective periodic running states to completely chaotic synchronised states in coupled particle dynamics
We consider the damped and driven dynamics of two interacting particles
evolving in a symmetric and spatially periodic potential. The latter is exerted
to a time-periodic modulation of its inclination. Our interest is twofold:
Firstly we deal with the issue of chaotic motion in the higher-dimensional
phase space. To this end a homoclinic Melnikov analysis is utilised assuring
the presence of transverse homoclinic orbits and homoclinic bifurcations for
weak coupling allowing also for the emergence of hyperchaos. In contrast, we
also prove that the time evolution of the two coupled particles attains a
completely synchronised (chaotic) state for strong enough coupling between
them. The resulting `freezing of dimensionality' rules out the occurrence of
hyperchaos. Secondly we address coherent collective particle transport provided
by regular periodic motion. A subharmonic Melnikov analysis is utilised to
investigate persistence of periodic orbits. For directed particle transport
mediated by rotating periodic motion we present exact results regarding the
collective character of the running solutions entailing the emergence of a
current. We show that coordinated energy exchange between the particles takes
place in such a manner that they are enabled to overcome - one particle
followed by the other - consecutive barriers of the periodic potential
resulting in collective directed motion
Clock and Trigger Synchronization between Several Chassis of Digital Data Acquisition Modules
In applications with segmented high purity Ge detectors or other detector
arrays with tens or hundreds of channels, where the high development cost and
limited flexibility of application specific integrated circuits outweigh their
benefits of low power and small size, the readout electronics typically consist
of multi-channel data acquisition modules in a common chassis for power, clock
and trigger distribution, and data readout. As arrays become larger and reach
several hundred channels, the readout electronics have to be divided over
several chassis, but still must maintain precise synchronization of clocks and
trigger signals across all channels. This division becomes necessary not only
because of limits given by the instrumentation standards on module size and
chassis slot numbers, but also because data readout times increase when more
modules share the same data bus and because power requirements approach the
limits of readily available power supplies. In this paper, we present a method
for distributing clocks and triggers between 4 PXI chassis containing DGF
Pixie-16 modules with up to 226 acquisition channels per chassis in a data
acquisition system intended to instrument the over 600 channels of the SeGA
detector array at the National Superconducting Cyclotron Laboratory. Our
solution is designed to achieve synchronous acquisition of detector waveforms
from all channels with a jitter of less then 1 ns, and can be extended to a
larger number of chassis if desired.Comment: CAARI 200
Non-existence of stationary two-black-hole configurations
We resume former discussions of the question, whether the spin-spin repulsion
and the gravitational attraction of two aligned black holes can balance each
other. To answer the question we formulate a boundary value problem for two
separate (Killing-) horizons and apply the inverse (scattering) method to solve
it. Making use of results of Manko, Ruiz and Sanabria-G\'omez and a novel black
hole criterion, we prove the non-existence of the equilibrium situation in
question.Comment: 15 pages, 3 figures; Contribution to Juergen Ehlers Memorial Issue
(GeRG journal
Multi-site H-bridge breathers in a DNA--shaped double strand
We investigate the formation process of nonlinear vibrational modes
representing broad H-bridge multi--site breathers in a DNA--shaped double
strand.
Within a network model of the double helix we take individual motions of the
bases within the base pair plane into account. The resulting H-bridge
deformations may be asymmetric with respect to the helix axis. Furthermore the
covalent bonds may be deformed distinctly in the two backbone strands.
Unlike other authors that add different extra terms we limit the interaction
to the hydrogen bonds within each base pair and the covalent bonds along each
strand. In this way we intend to make apparent the effect of the characteristic
helicoidal structure of DNA. We study the energy exchange processes related
with the relaxation dynamics from a non-equilibrium conformation. It is
demonstrated that the twist-opening relaxation dynamics of a radially distorted
double helix attains an equilibrium regime characterized by a multi-site
H-bridge breather.Comment: 27 pages and 10 figure
Import of cytochrome c into mitochondria
The import of cytochrome c into mitochondria can be resolved into a number of discrete steps. Here we report on the covalent attachment of heme to apocytochrome c by the enzyme cytochrome c heme lyase in mitochondria from Neurospora crassa.
A new method was developed to measure directly the linkage of heme to apocytochrome c. This method is independent of conformational changes in the protein accompanying heme attachment. Tryptic peptides of [35S]cysteine-labelled apocytochrome c, and of enzymatically formed holocytochrome c, were resolved by reverse-phase HPLC. The cysteine-containing peptide to which heme was attached eluted later than the corresponding peptide from apocytochrome c and could be quantified by counting 35S radioactivity as a measure of holocytochrome c formation. Using this procedure, the covalent attachment of heme to apocytochrome c, which is dependent on the enzyme cytochrome c heme lyase, could be measured. Activity required heme (as hemin) and could be reversibly inhibited by the analogue deuterohemin. Holocytochrome c formation was stimulated 5–10-fold by NADH > NADPH > glutathione and was independent of a potential across the inner mitochondrial membrane. NADH was not required for the binding of apocytochrome c to mitochondria and was not involved in the reduction of the cysteine thiols prior to heme attachment. Holocytochrome c formation was also dependent on a cytosolic factor that was necessary for the heme attaching step of cytochrome c import. The factor was a heat-stable, protease-insensitive, low-molecular-mass component of unknown function.
Cytochrome c heme lyase appeared to be a soluble protein located in the mitochondrial intermembrane space and was distinct from the previously identified apocytochrome c binding protein having a similar location. A model is presented in which the covalent attachment of heme by cytochrome c heme lyase also plays an essential role in the import pathway of cytochrome c
Cognitive Organization, Perceptions of Parenting and Depression Symptoms in Early Adolescence
Despite its strong relation to depression and theorized development across childhood and adolescence, cognitive schema organization has not been explored in early adolescence, a sensitive developmental period for first depression onset. Schema organization is theorized to derive from childhood cognitive internalizations of caregiving relationships, such as critical parenting experiences (e.g., Young et al. in Schema therapy: a practitioner’s guide. Guilford Press, New York, 2003). Thus, the current investigation considers the organization of positive and negative schemas with youth’s perceptions of parental warmth and psychological control and self-reported emotional functioning. Participants were 198 boys and girls aged 9–14 years who completed the Psychological Distance Scaling Task, measures of perceptions of parenting behaviors, anxiety symptoms and depression symptoms. Consistent with hypotheses, higher depression, but not anxiety symptoms were associated with a loosely-interconnected positive schema organization and a tightly-interconnected negative schema organization. Parental responsiveness emerged as the strongest predictor of negative schema structure. Implications for cognitive-developmental theories of depression and early identification of depression risk are discussed
The decay of quadrupole-octupole states in Ca and Ce
Background: Two-phonon excitations originating from the coupling of two
collective one-phonon states are of great interest in nuclear structure
physics. One possibility to generate low-lying excitations is the coupling
of quadrupole and octupole phonons.
Purpose: In this work, the -decay behavior of candidates for the
state in the doubly-magic nucleus Ca and in
the heavier and semi-magic nucleus Ce is investigated.
Methods: experiments have been carried out at the
High Intensity -ray Source (HIS) facility in combination with
the high-efficiency -ray spectroscopy setup consisting of
HPGe and LaBr detectors. The setup enables the acquisition of
- coincidence data and, hence, the detection of direct decay
paths.
Results: In addition to the known ground-state decays, for Ca the
decay into the state was observed, while for Ce the direct
decays into the and the state were detected. The experimentally
deduced transition strengths and excitation energies are compared to
theoretical calculations in the framework of EDF theory plus QPM approach and
systematically analyzed for isotones. In addition, negative parities for
two states in Ca were deduced simultaneously.
Conclusions: The experimental findings together with the theoretical
calculations support the two-phonon character of the excitation in the
light-to-medium-mass nucleus Ca as well as in the stable even-even
nuclei.Comment: 11 pages, 6 figures, as accepted in Phys. Rev.
Sialic acid-specific affinity chromatography for the separation of erythropoietin glycoforms using serotonin as a ligand
AbstractRecombinant human erythropoietin (rhEPO) is an important CHO cell-derived glycoprotein and the degree of sialylation of this hormone is crucial for its in vivo bioactivity. In order to improve the purification process serotonin as a potential affinity ligand was tested for preparative chromatographic separation of rhEPO glycoforms into fractions of different degrees of sialylation. Therefore, two chromatographic matrices were prepared by immobilizing serotonin on CNBr- and NHS-Sepharoseâ„¢. First it was shown both matrices bind rhEPO only in its sialylated form. Results indicate that binding is pH independent between pH 3.5 to 8 suggesting it is not only based on electrostatic interactions. Second, after optimal binding conditions were identified, semi-purified rhEPO was loaded onto both matrices and eluted using a stepwise elution gradient of sodium chloride. For comparison same affinity purification experiments were performed using wheat germ agglutinin-coupled agarose, a lectin known for its affinity towards sialylated glycoproteins. To monitor changes in N-glycan fingerprint, eluate fractions were analyzed by multiplexed capillary gel electrophoresis coupled to laser-induced fluorescence (xCGE-LIF). For the serotonin matrices an increasing degree of sialylation was observed from the first to the third elution fraction while purity of rhEPO could be increased at the same time. The late elution fractions of serotonin-coupled CNBr- and NHS-Sepharoseâ„¢ also showed an overall sialylation degree exceeding that of the starting material. In contrast, for rhEPO bound to wheat germ agglutinin-coupled agarose, no distinct change in the degree of sialylation could be observed after elution. Overall, these encouraging results highlight the potential of serotonin as a chromatographic ligand for the improvement of pharmaceutical purification processes of rhEPO
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