4,841 research outputs found
Low-energy magnetic radiation: deviations from GOE
A pronounced spike at low energy in the strength function for magnetic
radiation (LEMAR) is found by means of Shell Model calculations, which explains
the experimentally observed enhancement of the dipole strength. LEMAR
originates from statistical low-energy M1-transitions between many excited
complex states. Re-coupling of the proton and neutron high-j orbitals generates
the strong magnetic radiation. LEMAR is closely related to Magnetic Rotation.
LEMAR is predicted for nuclides participating in the r-process of element
synthesis and is expected to change the reaction rates. An exponential decrease
of the strength function and a power law for the size distribution of the
values are found, which strongly deviate from the ones of the GOE of
random matrices, which is commonly used to represent complex compound states.Comment: Proceedings of the conference on Nuclei and Mesoscopic Physics 2014,
MSU, to be published AIP Conference Proceeding
Electronic position indicator for latching solenoid valves
Electronic circuit connected to solenoid valve coils visually indicates the position of the valve stem. Transient suppression is provided to prevent damaging voltage spikes
Robustness of edge states in graphene quantum dots
We analyze the single particle states at the edges of disordered graphene
quantum dots. We show that generic graphene quantum dots support a number of
edge states proportional to circumference of the dot over the lattice constant.
Our analytical theory agrees well with numerical simulations. Perturbations
breaking electron-hole symmetry like next-nearest neighbor hopping or edge
impurities shift the edge states away from zero energy but do not change their
total amount. We discuss the possibility of detecting the edge states in an
antidot array and provide an upper bound on the magnetic moment of a graphene
dot.Comment: Added figure 6, extended discussion (version as accepted by Physical
Review B
An elliptic expansion of the potential field source surface model
Context. The potential field source surface model is frequently used as a
basis for further scientific investigations where a comprehensive coronal
magnetic field is of importance. Its parameters, especially the position and
shape of the source surface, are crucial for the interpretation of the state of
the interplanetary medium. Improvements have been suggested that introduce one
or more additional free parameters to the model, for example, the current sheet
source surface (CSSS) model.
Aims. Relaxing the spherical constraint of the source surface and allowing it
to be elliptical gives modelers the option of deforming it to more accurately
match the physical environment of the specific period or location to be
analyzed.
Methods. A numerical solver is presented that solves Laplace's equation on a
three-dimensional grid using finite differences. The solver is capable of
working on structured spherical grids that can be deformed to create elliptical
source surfaces.
Results. The configurations of the coronal magnetic field are presented using
this new solver. Three-dimensional renderings are complemented by
Carrington-like synoptic maps of the magnetic configuration at different
heights in the solar corona. Differences in the magnetic configuration computed
by the spherical and elliptical models are illustrated.Comment: 11 pages, 7 figure
One-loop surface tensions of (supersymmetric) kink domain walls from dimensional regularization
We consider domain walls obtained by embedding the 1+1-dimensional
-kink in higher dimensions. We show that a suitably adapted dimensional
regularization method avoids the intricacies found in other regularization
schemes in both supersymmetric and non-supersymmetric theories. This method
allows us to calculate the one-loop quantum mass of kinks and surface tensions
of kink domain walls in a very simple manner, yielding a compact d-dimensional
formula which reproduces many of the previous results in the literature. Among
the new results is the nontrivial one-loop correction to the surface tension of
a 2+1 dimensional N=1 supersymmetric kink domain wall with chiral domain-wall
fermions.Comment: 23 pages, LATeX; v2: 25 pages, 2 references added, extended
discussion of renormalization schemes which dispels apparent contradiction
with previous result
Tauroursodeoxycholic acid exerts anticholestatic effects by a cooperative cPKC alpha-/PKA-dependent mechanism in rat liver.
Objective: Ursodeoxycholic acid (UDCA) exerts anticholestatic effects in part by protein kinase C (PKC)-dependent mechanisms. Its taurine conjugate, TUDCA, is a cPKCa agonist. We tested whether protein kinase A (PKA) might contribute to the anticholestatic action of TUDCA via cooperative cPKCa-/PKA-dependent mechanisms
in taurolithocholic acid (TLCA)-induced cholestasis.
Methods: In perfused rat liver, bile flow was determined gravimetrically, organic anion secretion spectrophotometrically,
lactate dehydrogenase (LDH) release enzymatically, cAMP response-element binding protein (CREB) phosphorylation by immunoblotting, and cAMP by immunoassay. PKC/PKA inhibitors were tested radiochemically. In vitro phosphorylation of the conjugate export pump, Mrp2/Abcc2, was studied in rat hepatocytes and human Hep-G2 hepatoma cells.
Results: In livers treated with TLCA (10 mmol/l)+TUDCA (25 mmol/l), combined inhibition of cPKC by the cPKCselective
inhibitor Go¨6976 (100 nmol/l) or the nonselective PKC inhibitor staurosporine (10 nmol/l) and of PKA by H89 (100 nmol/l) reduced bile flow by 36% (p,0.05) and 48% (p,0.01), and secretion of the Mrp2/
Abcc2 substrate, 2,4-dinitrophenyl-S-glutathione, by 31% (p,0.05) and 41% (p,0.01), respectively; bile flow was
unaffected in control livers or livers treated with TUDCA only or TLCA+taurocholic acid. Inhibition of cPKC or PKA alone did not affect the anticholestatic action of TUDCA. Hepatic cAMP levels and CREB phosphorylation as readout of PKA activity were unaffected by the bile acids
tested, suggesting a permissive effect of PKA for the anticholestatic action of TUDCA. Rat and human hepatocellular Mrp2 were phosphorylated by phorbol ester pretreatment and recombinant cPKCa, nPKCe, and PKA, respectively, in a staurosporine-sensitive manner.
Conclusion: UDCA conjugates exert their anticholestatic action in bile acid-induced cholestasis in part via cooperative post-translational cPKCa-/PKA-dependent
mechanisms. Hepatocellular Mrp2 may be one target of bile acid-induced kinase activation
Interfaces Within Graphene Nanoribbons
We study the conductance through two types of graphene nanostructures:
nanoribbon junctions in which the width changes from wide to narrow, and curved
nanoribbons. In the wide-narrow structures, substantial reflection occurs from
the wide-narrow interface, in contrast to the behavior of the much studied
electron gas waveguides. In the curved nanoribbons, the conductance is very
sensitive to details such as whether regions of a semiconducting armchair
nanoribbon are included in the curved structure -- such regions strongly
suppress the conductance. Surprisingly, this suppression is not due to the band
gap of the semiconducting nanoribbon, but is linked to the valley degree of
freedom. Though we study these effects in the simplest contexts, they can be
expected to occur for more complicated structures, and we show results for
rings as well. We conclude that experience from electron gas waveguides does
not carry over to graphene nanostructures. The interior interfaces causing
extra scattering result from the extra effective degrees of freedom of the
graphene structure, namely the valley and sublattice pseudospins.Comment: 19 pages, published version, several references added, small changes
to conclusion
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