6,180 research outputs found
Channeled propagation of solar particles
Bartley (1966) and McCracken and Ness (1966) identified bundles of interplanetary magnetic field (IMF) lines that differed in direction from the interplanetary field lines in which they were imbedded. These bundles, called filaments differed in direction by as much as several tens of degrees from the surrounding field. The filaments werre first noticed due to the large and sudden change in flow direction of highly anisotropic solar flare protons in the energy range 1 to 13 MeV. Passage of the filaments over the spacecraft required a few hours, implying a diameter for the filaments of approximately 3 x 10 to the 6th power km at a distance of 1 AU from the Sun. In 1968, Jakipii and Parker used Leighton's hypothesis of random walk of magnetic field lines associated with granules and supergranules (1964) to develop a picture of an interplanetary medium composed of a tangle of field lines frozen into the solar wind, but whose feet were carried about by the random motions at the solar surface. Jakipii and Parker noted that using a correlation length of 15,000 km - about the radius of a supergranule - the magnetic structure would be 3 x 10 to the 6th power km in size of the filaments as determined by Bartley and McCracken and Ness. These workers did not find changes in the solar particle intensity, anisotropy ratio or energy spectrum as the spacecraft entered the filament
Particle propagation channels in the solar wind
The intensities of low energy solar-interplanetary electrons and ions at 1 AU occasionally change in a square wave manner. The changes may be increases or decreases and they typically have durations of from one hour to a few hours. In some cases these channels are bounded by discontinuities in the interplanetary field and the plasma properties differ from the surrounding solar wind. In one case solar flare particles were confined to a channel of width 3 x 10 to the 6th km at Earth. At the Sun this dimension extrapolates to about 12,000 km, a size comparable to small flares
Subunit Stoichiometry of a Heteromultimeric G protein-coupled Inward-rectifier K^+ Channel
We investigated the stoichiometry of the heteromultimeric G protein-coupled inward-recitfier K^+ channel (GIRK) formed from GIRK1 and GIRK4 subunits. Multimeric GIRK constructs with several concatenated channel subunits were expressed in Xenopus oocytes. Coexpression of various trimeric constructs with different monomers clearly showed that the functional channel has stoichiometry (GIRK1)_2(GIRK4)_2. Efforts to establish a preferred arrangement of subunits around the channel pore suggest that more than one arrangement may be viable
General Scheme for Perfect Quantum Network Coding with Free Classical Communication
This paper considers the problem of efficiently transmitting quantum states
through a network. It has been known for some time that without additional
assumptions it is impossible to achieve this task perfectly in general --
indeed, it is impossible even for the simple butterfly network. As additional
resource we allow free classical communication between any pair of network
nodes. It is shown that perfect quantum network coding is achievable in this
model whenever classical network coding is possible over the same network when
replacing all quantum capacities by classical capacities. More precisely, it is
proved that perfect quantum network coding using free classical communication
is possible over a network with source-target pairs if there exists a
classical linear (or even vector linear) coding scheme over a finite ring. Our
proof is constructive in that we give explicit quantum coding operations for
each network node. This paper also gives an upper bound on the number of
classical communication required in terms of , the maximal fan-in of any
network node, and the size of the network.Comment: 12 pages, 2 figures, generalizes some of the results in
arXiv:0902.1299 to the k-pair problem and codes over rings. Appeared in the
Proceedings of the 36th International Colloquium on Automata, Languages and
Programming (ICALP'09), LNCS 5555, pp. 622-633, 200
Of the sky above you must beware : Airspace and airpower in twentieth century literature
This project interrogates the tension between the military discourse of air war in the twentieth century and the literature that challenged that discourse. Situated within the broader study of war literature, the project moves beyond traditional studies of soldiers fighting ground wars, to explore instead the dynamics of war in the skies above. I examine the paradoxical representation of aerial warfare that has allowed airpower advocates to propose, and conduct, massive airstrikes on cities and civilians, while promising a cleaner method of waging war. Suggested in the writings of military theorists Giulio Douhet, Billy Mitchell, and B.H. Liddell Hart, this notion of a clean air war---one that would save lives through its speed and precision---proved seductive throughout the century to politicians, military leaders, aircrews, and the general public. I argue that writers of the twentieth century, and beyond, challenge the assumptions that support this discourse, showing aerial warfare that is messy, prolonged, and imprecise, and that saves lives of privileged populations only by sacrificing those of marginalized peoples.
The air war is perceived as clean, I suggest, when we see neither the aviator nor the targeted populations in this dynamic. Strong forces of spatial and discursive distancing, produced by the verticality of the air war and the rhetoric of chivalry, machine war, or patriotism, combine to hide the aviators\u27 damaged bodies and psyches. Targeted populations also disappear, cloaked in misrepresentation, displaced by precision discourse, or lost in the unreliability of the aerial perspective. The writers in this study challenge this rhetorical disappearance through poetry, fiction, reportage, and memoir, sketching credible counternarratives by making visible both aviators and targeted populations. The primarily, though not exclusively, American writers examined here aim to expose the complexities of the air war to an audience that may never otherwise see it somewhere over there. By depicting both aviators and target populations, and the rhetorical devices used to obscure them, these writers present powerful counternarratives to a discourse of airpower as a cleaner and more desirable method of waging war
Saturn's Exploration Beyond Cassini-Huygens
For its beautiful rings, active atmosphere and mysterious magnetic field,
Saturn is a fascinating planet. It also holds some of the keys to understanding
the formation of our Solar System and the evolution of giant planets in
general. While the exploration by the Cassini-Huygens mission has led to great
advances in our understanding of the planet and its moons, it has left us with
puzzling questions: What is the bulk composition of the planet? Does it have a
helium core? Is it enriched in noble gases like Jupiter? What powers and
controls its gigantic storms? We have learned that we can measure an outer
magnetic field that is filtered from its non-axisymmetric components, but what
is Saturn's inner magnetic field? What are the rings made of and when were they
formed? These questions are crucial in several ways: a detailed comparison of
the compositions of Jupiter and Saturn is necessary to understand processes at
work during the formation of these two planets and of the Solar System. This
calls for the continued exploration of the second largest planet in our Solar
System, with a variety of means including remote observations and space
missions. Measurements of gravity and magnetic fields very close to the
planet's cloud tops would be extremely valuable. Very high spatial resolution
images of the rings would provide details on their structure and the material
that form them. Last but not least, one or several probes sent into the
atmosphere of the planet would provide the critical measurements that would
allow a detailed comparison with the same measurements at Jupiter. [abridged
abstract
The role of cosmic rays and Alfven waves in the structure of the galactic halo
The effect that cosmic rays and the Alfven waves they generate have on the structure of the plasma distribution perpendicular to the galactic disk is examined. It is shown that the plasma distribution exhibits two length scales and the predicted values of gas density far from the galactic plane indicate that models involving hydrostatic equilibrium should be replaced by those allowing for a galactic wind
Probing the role of the cation–π interaction in the binding sites of GPCRs using unnatural amino acids
We describe a general application of the nonsense suppression methodology for unnatural amino acid incorporation to probe drug–receptor interactions in functional G protein-coupled receptors (GPCRs), evaluating the binding sites of both the M2 muscarinic acetylcholine receptor and the D2 dopamine receptor. Receptors were expressed in Xenopus oocytes, and activation of a G protein-coupled, inward-rectifying K^+ channel (GIRK) provided, after optimization of conditions, a quantitative readout of receptor function. A number of aromatic amino acids thought to be near the agonist-binding site were evaluated. Incorporation of a series of fluorinated tryptophan derivatives at W6.48 of the D2 receptor establishes a cation–π interaction between the agonist dopamine and W6.48, suggesting a reorientation of W6.48 on agonist binding, consistent with proposed “rotamer switch” models. Interestingly, no comparable cation–π interaction was found at the aligning residue in the M2 receptor
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