7,660 research outputs found
Genetic differentiation and phylogenetic relationships among six Abies species from European and Turkish areas
The phylogenetic relationships of the Abies species in European and Turkish regions have frequently been an object of controversial conclusions. Therefore, we compared the genetic structures of 21 populations belonging to six Abies species which are native to  entral, eastern and south-eastern European regions and  different areas in the Turkey (Asia minor). We used the allele frequency distribution of five isozyme gene locialready showing a high discriminatory power to assess the genetic differentiation among the Abies populations. The UPGMA-dendrogram based on genetic distances showed a clear discrimination between the Turkish Abies species and A. alba from Europe. The particular allele frequency distributions at the isozyme loci PGI-A and 6PGDH-Aconfirmed a great genetic dissimilarity between A. alba and the Turkish Abies species.These results contradict the phylogenetic relationships of the Abies species postulated inother studies
On reference frames in spacetime and gravitational energy in freely falling frames
We consider the interpretation of tetrad fields as reference frames in
spacetime. Reference frames may be characterized by an antisymmetric
acceleration tensor, whose components are identified as the inertial
accelerations of the frame (the translational acceleration and the frequency of
rotation of the frame). This tensor is closely related to
gravitoelectromagnetic field quantities. We construct the set of tetrad fields
adapted to observers that are in free fall in the Schwarzschild spacetime, and
show that the gravitational energy-momentum constructed out of this set of
tetrad fields, in the framework of the teleparallel equivalent of general
relatrivity, vanishes. This result is in agreement with the principle of
equivalence, and may be taken as a condition for a viable definition of
gravitational energy.Comment: 19 pages, no figures, accepted by Classical and Quantum Gravit
GPS observables in general relativity
I present a complete set of gauge invariant observables, in the context of
general relativity coupled with a minimal amount of realistic matter (four
particles). These observables have a straightforward and realistic physical
interpretation. In fact, the technology to measure them is realized by the
Global Positioning System: they are defined by the physical reference system
determined by GPS readings. The components of the metric tensor in this
physical reference system are gauge invariant quantities and, remarkably, their
evolution equations are local.Comment: 6 pages, 1 figure, references adde
A New Superwind Wolf-Rayet Galaxy Mrk 1259
We report the discovery of a starburst-driven wind (superwind) from the
starburst nucleus galaxy Mrk 1259. The estimated number ratio of Wolf-Rayet
(WR) to O stars amounts to ~0.09. While the nuclear emission-line region is due
to usual photoionization by massive stars, the circumnuclear emission-line
regions show anomalous line ratios that can be due to cooling shocks. Since the
host galaxy seems to be a face-on disk galaxy and the excitation conditions of
the circumnuclear emission-line regions show the spatial symmetry, we consider
that we are seeing the superwind nearly from a pole-on view. Cooling shock
models may explain the observed emission line ratios of the circumnuclear
regions although a factor of 2 overabundance of nitrogen is necessary. All
these suggest that the high-mass enhanced starburst occurred ~5X10^6 years ago
in the nuclear region of Mrk 1259.Comment: To be published in the Astrophysical Journal Letters, 15 pages, 4
figure
Temperature-controlled interlayer exchange coupling in strong/weak ferromagnetic multilayers: a thermo-magnetic Curie-switch
We investigate a novel type of interlayer exchange coupling based on driving
a strong/weak/strong ferromagnetic tri-layer through the Curie point of the
weakly ferromagnetic spacer, with the exchange coupling between the strongly
ferromagnetic outer layers that can be switched, on and off, or varied
continuously in magnitude by controlling the temperature of the material. We
use Ni-Cu alloy of varied composition as the spacer material and model the
effects of proximity-induced magnetism and the interlayer exchange coupling
through the spacer from first principles, taking into account not only thermal
spin-disorder but also the dependence of the atomic moment of Ni on the
nearest-neighbor concentration of the non-magnetic Cu. We propose and
demonstrate a gradient-composition spacer, with a lower Ni-concentration at the
interfaces, for greatly improved effective-exchange uniformity and
significantly improved thermo-magnetic switching in the structure. The reported
magnetic multilayer materials can form the base for a variety of novel magnetic
devices, such as sensors, oscillators, and memory elements based on
thermo-magnetic Curie-switching in the device.Comment: 15 pages, 5 figure
Modelling the [Fe II] λ1.644 μm outflow and comparison with H₂ and H+ kinematics in the inner 200 pc of NGC 1068
We map the kinematics of the inner (200 pc) narrow-line region (NLR) of the Seyfert 2 galaxy NGC 1068 using the instrument Near-infrared Integral Field Spectrograph and adaptive optics at the Gemini North telescope. Channel maps and position–velocity diagrams are presented at a spatial resolution of ≅8 pc and spectral resolution ∼5300 in the emission lines [Fe II] λ1.644 μm, H₂ λ2.122 μm and Brγ. The [Fe II] emission line provides a better coverage of the NLR outflow than the previously used [O III] λ5007 emission line, extending beyond the area of the bipolar cone observed in Brγ and [O III]. This is mainly due to the contribution of the redshifted channels to the north-east of the nucleus, supporting its origin in a partial ionized zone with additional contribution from shocks of the outflowing gas with the galactic disc. We modelled the kinematics and geometry of the [Fe II] emitting gas finding good agreement with the data for outflow models with conical and lemniscate (or hourglass) geometry. We calculate a mass outflow rate of 1.9⁺²ˍ₁ M⊙ yr⁻¹ but a power for the outflow of only 0.08 per cent LBol. The molecular (H₂) gas kinematics is completely distinct from that of [Fe II] and Brγ, showing radial expansion in an off-centred ∼100 pc radius ring in the galaxy plane. The expansion velocity decelerates from ≈200 km s−1 in the inner border of the ring to approximately zero at the outer border where our previous studies found a 10 Myr stellar population
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