45,053 research outputs found
Search for acoustic signals from high energy cascades
High energy cosmic ray secondaries can be detected by means of the cascades they produce when they pass through matter. When the charged particles of these cascades ionize the matter they are traveling through, the heat produced and resulting thermal expansion causes a thermoacoustic wave. These sound waves travel at about one hundred-thousandth the speed of light, and should allow an array of acoustic transducers to resolve structure in the cascade to about 1 cm without high speed electronics or segmentation of the detector
Fossil trees, tree moulds and tree casts in the Palaeocene Mull Lava Field, NW Scotland: context, formation and implications for lava emplacement
Megafossils and macrofossils of terrestrial plants (trees, leaves, fruiting bodies, etc.) are found in sedimentary and pyroclastic units interbedded with lavas in many ancient lava fields worldwide, attesting to subaerial environments of eruption and the establishment of viable plant communities during periods of volcanic quiescence. Preservation within lava is relatively rare and generally confined to the more robust woody tissues of trees, which are then revealed in the form of charcoal, mineralised tissue or as trace fossil moulds (tree moulds) and casts of igneous rock (tree casts, s.s.).
In this contribution, we document several such fossil trees (s.l.), and the lavas with which they are associated, from the Palaeocene Mull Lava Field (MLF) on the Isle of Mull, NW Scotland. We present the first detailed geological account of a unique site within the Mull Plateau Lava Formation (MPLF) at Quinish in the north of the island and provide an appraisal of the famous upright fossil tree â MacCulloch's Tree â remotely located on the Ardmeanach Peninsula on the west coast of the island, and another large upright tree (the Carsaig Tree) near Malcolm's Point in the district of Brolass, SW Mull; both occurring within the earlier Staffa Lava Formation (SLF). The taphonomy of these megafossils, along with palynological and lithofacies assessments of associated strata, allows speculation of likely taxonomic affinity and the duration of hiatuses supporting the establishment of forest/woodland communities. The Ardmeanach and Carsaig specimens, because of their size and preservation as upright (? in situ) casts enveloped by spectacularly columnar-jointed basaltic lava, appear to be unique. The aspect of these trees, the thickness of the enveloping lavas and the arrangement of cooling joints adjacent to the trees, implies rapid emplacement, ponding and slow, static cooling of voluminous and highly fluid basaltic magma. The specimens from Quinish include two prostrate casts and several prostrate moulds that collectively have a preferred orientation, aligning approximately perpendicular to that of the regional Mull Dyke Swarm, the putative fissure source of the lavas, suggesting local palaeo-flow was directed towards the WSW. The Quinish Lava is an excellent example of a classic pÄhoehoe (compound-braided) type, preserving some of the best examples of surface and internal features so far noted from the Hebridean Igneous Province (HIP) lava fields.
These Mull megafossils are some of the oldest recorded examples, remarkably well preserved, and form a significant feature of the island's geotourism industry
Exact Equivalence of the D=4 Gauged Wess-Zumino-Witten Term and the D=5 Yang-Mills Chern-Simons Term
We derive the full Wess-Zumino-Witten term of a gauged chiral lagrangian in
D=4 by starting from a pure Yang-Mills theory of gauged quark flavor in a flat,
compactified D=5. The theory is compactified such that there exists a B_5 zero
mode, and supplemented with quarks that are ``chirally delocalized'' with q_L
(q_R) on the left (right) boundary (brane). The theory then necessarily
contains a Chern-Simons term (anomaly flux) to cancel the fermionic anomalies
on the boundaries. The constituent quark mass represents chiral symmetry
breaking and is a bilocal operator in D=5 of the form: \bar{q}_LWq_R+h.c, where
W is the Wilson line spanning the bulk, 0\leq x^5 \leq R and is interpreted as
a chiral meson field, W=\exp(2i\tilde{\pi}/f_\pi), where f_\pi \sim 1/R. The
quarks are integrated out, yielding a Dirac determinant which takes the form of
a ``boundary term'' (anomaly flux return), and is equivalent to Bardeen's
counterterm that connects consistent and covariant anomalies. The
Wess-Zumino-Witten term then emerges straightforwardly, from the Yang-Mills
Chern-Simons term, plus boundary term. The method is systematic and allows
generalization of the Wess-Zumino-Witten term to theories of extra dimensions,
and to express it in alternative and more compact forms. We give a novel form
appropriate to the case of (unintegrated) massless fermions.Comment: 25 pages, 1 figure; minor errors fixe
Cultivation and use of bryophytes as experimental material
Bryophytes can be grown successfully if keptmoist, supplied
with nutrients, and out of direct sunlight. They remain greener
on peat than on sand. However, difficulties were encountered when
attempting to grow mosses and liverworts in an unshaded
glasshouse, in spring and summer. Even spraying hourly with water
did not prevent scorching and desiccation.
Growth can be measured using a variety of techniques; height
measurement and shoot elongation from thread markers proved the
most reliabl
Particle acceleration and magnetic field amplification in the jets of 4C74.26
We model the multi-wavelength emission in the southern hotspot of the radio
quasar 4C74.26. The synchrotron radio emission is resolved near the shock with
the MERLIN radio-interferometer, and the rapid decay of this emission behind
the shock is interpreted as the decay of the amplified downstream magnetic
field as expected for small scale turbulence. Electrons are accelerated to only
0.3 TeV, consistent with a diffusion coefficient many orders of magnitude
greater than in the Bohm regime. If the same diffusion coefficient applies to
the protons, their maximum energy is only ~100 TeV.Comment: Accepted for publication in ApJ. 6 pages - 2 figures. Minor
correction
Not throwing out the baby with the bathwater: Bell's condition of local causality mathematically 'sharp and clean'
The starting point of the present paper is Bell's notion of local causality
and his own sharpening of it so as to provide for mathematical formalisation.
Starting with Norsen's (2007, 2009) analysis of this formalisation, it is
subjected to a critique that reveals two crucial aspects that have so far not
been properly taken into account. These are (i) the correct understanding of
the notions of sufficiency, completeness and redundancy involved; and (ii) the
fact that the apparatus settings and measurement outcomes have very different
theoretical roles in the candidate theories under study. Both aspects are not
adequately incorporated in the standard formalisation, and we will therefore do
so. The upshot of our analysis is a more detailed, sharp and clean mathematical
expression of the condition of local causality. A preliminary analysis of the
repercussions of our proposal shows that it is able to locate exactly where and
how the notions of locality and causality are involved in formalising Bell's
condition of local causality.Comment: 14 pages. To be published in PSE volume "Explanation, Prediction, and
Confirmation", edited by Dieks, et a
Evidence that particle acceleration in hotspots of FR II galaxies is not constrained by synchrotron cooling
We study the hotspots of powerful radiogalaxies, where electrons accelerated
at the jet termination shock emit synchrotron radiation. The turnover of the
synchrotron spectrum is typically observed between infrared and optical
frequencies, indicating that the maximum energy of non-thermal electrons
accelerated at the shock is ~TeV for a canonical magnetic field of ~100 micro
Gauss. We show that this maximum energy cannot be constrained by synchrotron
losses as usually assumed, unless the jet density is unreasonably large and
most of the jet upstream energy goes to non-thermal particles. We test this
result by considering a sample of hotspots observed at radio, infrared and
optical wavelengths.Comment: 7 pages, 2 figures. To be appear in the proceedings of the conference
"Cosmic ray origin - beyond the standard models" (San Vito di Cadore, Italy,
September 2016
Non-Bilocal Measurement via Entangled State
Two observers, who share a pair of particles in an entangled mixed state, can
use it to perform some non-bilocal measurement over another bipartite system.
In particular, one can construct a specific game played by the observers
against a coordinator, in which they can score better than a pair of observers
who only share a classical communication channel.Comment: 6 pages. minor change
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