41 research outputs found
Influence of Rotation on Pulsar Radiation Characteristics
We present a relativistic model for pulsar radio emission by including the
effect of rotation on coherent curvature radiation by bunches. We find that
rotation broadens the width of leading component compared to the width of
trailing component. We estimate the component widths in the average pulse
profiles of about 24 pulsars, and find that 19 of them have a broader leading
component. We explain this difference in the component widths by using the
nested cone emission geometry.
We estimate the effect of pulsar spin on the Stokes parameters, and find that
the inclination between the rotation and magnetic axes can introduce an
asymmetry in the circular polarization of the conal components. We analyze the
single pulse polarization data of PSR B0329+54 at 606 MHz, and find that in its
conal components, one sense of circular polarization dominates in the leading
component while the other sense dominates in the trailing component. Our
simulation shows that changing the sign of the impact parameter changes the
sense of circular polarization as well as the swing of polarization angle.Comment: 20 pages, 4 Postscript figures, uses aastex.cls. Accepted for
Publication in ApJ 200
Radio Emission by Particles due to Pulsar Spin
We present a relativistic model for the motion of charged particles in
rotating magnetic field lines projected on to a plane perpendicular to the
rotation axis. By making an approximation that the projected field lines are
straight, an analytical expression is obtained for the particle trajectory. The
motive behind developing this model is to elucidate some of the effects of
rotation in pulsar profiles. There is a significant contribution to the
curvature of particle trajectory due to the rotation of pulsar, which is in
addition to the inherent curvature of the field lines. The asymmetry in the
observed pulse shapes can be explained by considering the
aberration-retardation effects. The single sign circular polarization that has
been observed in many pulsars, might be due to the relative orientation of
sight line with respect to the particle trajectory plane.Comment: 19 pages, 6 figues. Submitted to Astronomy and Astrophysic
Combined histamine H_1/H_2 receptor antagonists: Part II. Pharmacological hybrids with pheniramine- and tiotidine-like substructures,
Hybrid molecules combining the crucial structural features of both pheniramine-type histamine H1 receptor antagonists and guanidinothiazole-type H2 receptor antagonists have been synthesized and tested for in vitro pharmacological activity at the isolated ileum and the spontaneously beating right atrium of the guinea-pig. In the title compounds the basic side chain nitrogen of the H1 antagonist and the so-called âpolar group' (cyanoguanidine, urea, or nitroethenediamine) of the H2 antagonist moiety have been linked by a polymethylene spacer. The new substances displayed high affinities to both histamine receptor subtypes and a dual type of antagonism (surmountable/insurmountable) characterized by a shift of the concentration response curves to the right accompanied by a depression of the maximal response to the agonist if the antagonist concentration was â„100 nM. Highest combined histamine antagonist activities were found in the nitroethenediamine series with pKB values ranging from 8.16 to 9.04 in the ileum (H1) and 7.0â8.08 in the atrium (H2
Dissociations in the effects of beta2-adrenergic receptor agonists on cAMP formation and superoxide production in human neutrophils: Support for the concept of functional selectivity
In neutrophils, activation of the beta2-adrenergic receptor (beta2AR), a Gs-coupled receptor,
inhibits inflammatory responses, which could be therapeutically exploited. The aim of this study was to
evaluate the effects of various beta2AR ligands on adenosine-3',5'-cyclic monophosphate (cAMP)
accumulation and N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP)-induced superoxide anion
(O2*-) production in human neutrophils and to probe the concept of ligand-specific receptor
conformations (also referred to as functional selectivity or biased signaling) in a native cell system.
cAMP concentration was determined by HPLC/tandem mass spectrometry, and O2*- formation was
assessed by superoxide dismutase-inhibitable reduction of ferricytochrome c. beta2AR agonists were
generally more potent in inhibiting fMLP-induced O2*- production than in stimulating cAMP
accumulation. (-)-Ephedrine and dichloroisoproterenol were devoid of any agonistic activity in the
cAMP assay, but partially inhibited fMLP-induced O2*- production. Moreover, (-)-adrenaline was equiefficacious
in both assays whereas the efficacy of salbutamol was more than two-fold higher in the O2*-
assay. In contrast to the agonists, the effects of beta2AR antagonists were comparable between the two
parameters on neutrophils. Differences between the data from neutrophils and recombinant test
systems were observed for the beta2AR agonists as well as for the beta2AR antagonists. Lastly, we
obtained no evidence for an involvement of protein kinase A in the inhibition of fMLP-induced O2*-
production after beta2AR-stimulation, although, in principle, cAMP-increasing substances can inhibit
O2*- production. Taken together, our data corroborate the concept of ligand-specific receptor
conformations with unique signaling capabilities and suggest that the beta2AR inhibits O2*-
production in a cAMP-independent manner