38,173 research outputs found
The big Dehn surgery graph and the link of S^3
In a talk at the Cornell Topology Festival in 2005, W. Thurston discussed a
graph which we call "The Big Dehn Surgery Graph", B. Here we explore this
graph, particularly the link of S^3, and prove facts about the geometry and
topology of B. We also investigate some interesting subgraphs and pose what we
believe are important questions about B.Comment: 15 pages, 4 figures, 4 ancillary files. Reorganized and shortened
from previous versions, while correcting one error in the proof of Theorem
5.4. Also, ancillary files detailing our computations with the computer
program ORB have been provide
Enumeration of Hypermaps of a Given Genus
This paper addresses the enumeration of rooted and unrooted hypermaps of a
given genus. For rooted hypermaps the enumeration method consists of
considering the more general family of multirooted hypermaps, in which darts
other than the root dart are distinguished. We give functional equations for
the generating series counting multirooted hypermaps of a given genus by number
of darts, vertices, edges, faces and the degrees of the vertices containing the
distinguished darts. We solve these equations to get parametric expressions of
the generating functions of rooted hypermaps of low genus. We also count
unrooted hypermaps of given genus by number of darts, vertices, hyperedges and
faces.Comment: 42 page
New ammonia masers towards NGC6334I
We report the detection of new ammonia masers in the non-metastable (8,6) and
(11,9) transitions towards the massive star forming region NGC6334I.
Observations were made with the ATCA interferometer and the emitting region
appears unresolved in the 2.7" x 0.8" beam, with deconvolved sizes less than an
arcsecond. We estimate peak brightness temperatures of 7.8 x 10^5 and 1.2 x
10^5 K for the (8,6) and (11,9) transitions, respectively. The masers appear
coincident both spatially and in velocity with a previously detected ammonia
(6,6) maser. We also suggest that emission in the (10,9), (9,9) and (7,6)
transitions may also be masers, based on their narrow line widths and
overlapping velocity ranges with the above masers, as observed with the
single-dish Mopra radiotelescope
Using HINODE/Extreme-Ultraviolet Imaging Spectrometer to confirm a seismologically inferred coronal temperature
The Extreme-Ultraviolet Imaging Spectrometer on board the HINODE satellite is used to examine the loop system described in Marsh et al. (2009) by applying spectroscopic diagnostic methods. A simple isothermal mapping algorithm is applied to determine where the assumption of isothermal plasma may be valid, and the emission measure locii technique is used to determine the temperature profile along the base of the loop system. It is found that, along the base, the loop has a uniform temperature profile with a mean temperature of 0.89 +- 0.09 MK which is in agreement with the temperature determined seismologically in Marsh et al. (2009), using observations interpreted as the slow magnetoacoustic mode. The results further strengthen the slow mode interpretation, propagation at a uniform sound speed, and the analysis method applied in Marsh et al. (2009). It is found that it is not possible to discriminate between the slow mode phase speed and the sound speed within the precision of the present observations
The time resolved measurement of ultrashort THz-band electric fields without an ultrashort probe
The time-resolved detection of ultrashort pulsed THz-band electric field
temporal profiles without an ultrashort laser probe is demonstrated. A
non-linear interaction between a narrow-bandwidth optical probe and the THz
pulse transposes the THz spectral intensity and phase information to the
optical region, thereby generating an optical pulse whose temporal electric
field envelope replicates the temporal profile of the real THz electric field.
This optical envelope is characterised via an autocorrelation based FROG
measurement, hence revealing the THz temporal profile. The combination of a
narrow-bandwidth, long duration, optical probe and self-referenced FROG makes
the technique inherently immune to timing jitter between the optical probe and
THz pulse, and may find particular application where the THz field is not
initially generated via ultrashort laser methods, such as the measurement of
longitudinal electron bunch profiles in particle accelerators.Comment: 7 pages, 3 figures, submitted to AP
HeI in the central Giant HII Region of NGC 5253. A 2D observational approach to collisional and radiative transfer effects
ABRIDGED: NGC5253 is an ideal laboratory for detailed studies of starburst
galaxies. We present for the first time in a starburst galaxy a 2D study of the
spatial behavior of collisional and radiative transfer effects in He^+. The HeI
lines are analysed based on data obtained with FLAMES and GMOS. Collisional
effects are negligible for transitions in the singlet cascade while relatively
important for those in the triplet cascade. In particular, they can contribute
up to 20% of the flux in the HeIl7065 line. Radiative transfer effects are
important over an extended and circular area of 30pc in diameter centered at
the Super Star Clusters. HeI abundance, y^+, has been mapped using extinction
corrected fluxes of six HeI lines, realistic assumptions for T_e, n_e, and the
stellar absorption equivalent width as well as the most recent emissivities. We
found a mean of 10^3 y^+ ~80.3 over the mapped area. The relation between the
excitation and the total helium abundance, y_tot, is consistent with no
abundance gradient. Uncertainties in the derivation of He abundances are
dominated by the adopted assumptions. We illustrated the difficulty of
detecting a putative He enrichment due to the presence of Wolf-Rayet stars in
the main GHIIR. Data are marginally consistent with an excess in the N/He ratio
in the N enriched area of the order of both, the atmospheric N/He ratios in WR
stars and the uncertainties estimated for the N/He ratios.Comment: Accepted in Astronomy and Astrophysics; the emissivities presented in
the Corrigendum, Porter et al. 2013, arXiv:1303.5115, have been include
SOUTHERNMOST OCCURRENCE OF THE SUWANNEE COOTER, PSEUDEMYS CONCINNA SUWANNIENSIS (TESTUDINES: EMYDIDAE)
The Suwannee Cooter, Pseudemys concinna suwanniensis, the largest member of the speciose turtle family Emydidae, inhabits a small number of rivers that drain into the northeastern Gulf of Mexico along the northwest coast of Florida from just west of Tallahassee to just south of Tampa. The status of this state-protected subspecies in the southernmost of these rivers, the Alafia, is unknown and hence of conservation concern. We provide recent evidence confirming that a reproducing population still exists in this river, and review available specimens and both published and unpublished records documenting the southern limit of distribution. At least within the eastern United States, our observations also extend confirmed knowledge of the geographic occurrence of hatchling turtles overwintering in the nest southward by 285 km
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