21,306 research outputs found
Copernicus observations of Betelgeuse and Antares
Copernicus observations of the M-supergiants, alpha Ori and alpha Sco, are presented. The MgII h and k resonance lines are strongly in emission in both stars. The k line is highly asymmetric in both stars but the h line is symmetric. Upper limits for several other resonance lines are given for alpha Ori. The possibility is explored that the k line asymmetry is caused by overlying resonance lines of MnI and FeI formed in the cool circumstellar gas shells around these stars. Observations of the MnI 4030-4033 A lines are used to show that circumstellar shell absorption is too weak to explain the asymmetry. It is suggested that the absorption occurs in a cool turbulent region between the base of the circumstellar shell and the top of the chromosphere
Procyon-A and Eta-Bootis: Observational Frequencies Analyzed by the Local-Wave Formalism
In the present analysis of Procyon-A and Eta-Bootis, we use the local-wave
formalism which, despite its lack of precision inherent to any semi-analytical
method, uses directly the model profile without any modification when
calculating the acoustic mode eigenfrequencies. These two solar-like stars
present steep variations toward the center due to the convective core
stratification, and toward the surface due to the very thin convective zone.
Based on different boundary conditions, the frequencies obtained with this
formalism are different from that of the classical numerical calculation. We
point out that (1) the frequencies calculated with the local-wave formalism
seem to agree better with observational ones. All the frequencies detected with
a good confident level including those classified as 'noise' find an
identification, (2) some frequencies can be clearly identified here as
indications of the core limit.Comment: SOHO 18 / GONG 2006 / HELAS I Meetin
Picosecond excitation of jet-cooled hydrogen-bonded systems: Dispersed fluorescence and time-resolved studies of methyl salicylatea
Long progressions involving frequency intervals of 180 cm^(−1) are observed in the fluoresence of MS for 3327.5 Å excitation. (AIP
Observation of intracavity absorption of molecules in supersonic beams
Intracavity absorption studies of DMT and I2 are reported at rotational and vibrational temperatures of <0.1 K and 16 K, respectively
Quasiparticle interference from different impurities on the surface of pyrochlore iridates: signatures of the Weyl phase
Weyl semimetals are gapless three-dimensional topological materials where two
bands touch at an even number of points in the bulk Brillouin zone. These
semimetals exhibit topologically protected surface Fermi arcs, which pairwise
connect the projected bulk band touchings in the surface Brillouin zone. Here,
we analyze the quasiparticle interference patterns of the Weyl phase when
time-reversal symmetry is explicitly broken. We use a multi-band -electron
Hubbard Hamiltonian on a pyrochlore lattice, relevant for the pyrochlore
iridate RIrO (where R is a rare earth). Using exact
diagonalization, we compute the surface spectrum and quasiparticle interference
(QPI) patterns for various surface terminations and impurities. We show that
the spin and orbital texture of the surface states can be inferred from the
absence of certain backscattering processes and from the symmetries of the QPI
features for non-magnetic and magnetic impurities. Furthermore, we show that
the QPI patterns of the Weyl phase in pyrochlore iridates may exhibit
additional interesting features that go beyond those found previously in TaAs.Comment: 15 pages, 16 figure
Redistribution Through the Income Tax: The Vertical and Horizontal Effects of Noncompliance and Tax Evasion
This paper uses the unique Taxpayer Compliance Measurement Program (TCMP) micro data to study the equity effects of noncompliance. We access four years of TCMP data, 1979,1982,1985, and 1988. The TCMP data allows us to observe income and taxes before and after a tax audit. In order to generate a range of scalar estimates of the redistributive impact of more complete compliance we employ the family of extended Gini and concentration coefficients. We find that the vertical equity effects are very small of negative; however, there is a considerable amount of horizontal inequity generated by noncompliance and in this sense more complete auditing of tax returns could improve the fairness of the tax system
Peculiar Nature of Snake States in Graphene
We study the dynamics of the electrons in a non-uniform magnetic field
applied perpendicular to a graphene sheet in the low energy limit when the
excitation states can be described by a Dirac type Hamiltonian. We show that as
compared to the two-dimensional electron gas (2DEG) snake states in graphene
exibit peculiar properties related to the underlying dynamics of the Dirac
fermions. The current carried by snake states is locally uncompensated even if
the Fermi energy lies between the first non-zero energy Landau levels of the
conduction and valence bands. The nature of these states is studied by
calculating the current density distribution. It is shown that besides the
snake states in finite samples surface states also exist.Comment: 4 pages, 5 figure
Suppression of Giant Magnetoresistance by a superconducting contact
We predict that current perpendicular to the plane (CPP) giant
magnetoresistance (GMR) in a phase-coherent magnetic multilayer is suppressed
when one of the contacts is superconducting. This is a consequence of a
superconductivity-induced magneto-resistive (SMR) effect, whereby the
conductance of the ferromagnetically aligned state is drastically reduced by
superconductivity. To demonstrate this effect, we compute the GMR ratio of
clean (Cu/Co)_nCu and (Cu/Co)_nPb multilayers, described by an ab-initio spd
tight binding Hamiltonian. By analyzing a simpler model with two orbitals per
site, we also show that the suppression survives in the presence of elastic
scattering by impurities.Comment: 5 pages, 4 figures. Submitted to PR
Generalised BPS conditions
We write down two E11 invariant conditions which at low levels reproduce the
known half BPS conditions for type II theories. These new conditions contain,
in addition to the familiar central charges, an infinite number of further
charges which are required in an underlying theory of strings and branes. We
comment on the application of this work to higher derivative string
corrections
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