6,693 research outputs found
Carbon Trading: Theory and Practice
We present a summary of current initiatives to climate change management including a review of existing carbon trading schemes and the economic arguments supporting those schemes. We also outline conditions under which the existing carbon market structures are optimal as well as those under which improvements upon the current schemes can be made
The jet of Markarian 501 from millions of Schwarzschild radii down to a few hundreds
Aims: The TeV BL Lac object Markarian 501 is a complex, core dominated radio
source, with a one sided, twisting jet on parsec scales. In the present work,
we attempt to extend our understanding of the source physics to regions of the
radio jet which have not been accessed before.
Methods: We present new observations of Mrk 501 at 1.4 and 86 GHz. The 1.4
GHz data were obtained using the Very Large Array (VLA) and High Sensitivity
Array (HSA) in November 2004, in full polarization, with a final r.m.s. noise
of 25 microJy/beam in the HSA total intensity image; the 86 GHz observations
were performed in October 2005 with the Global Millimeter VLBI Array (GMVA),
providing an angular resolution as good as 110 x 40 microarcseconds.
Results: The sensitivity and resolution provided by the HSA make it possible
to detect the jet up to ~700 milliarcseconds (corresponding to a projected
linear size of ~500 pc) from its base, while the superior resolution of the 86
GHz GMVA observations probes the innermost regions of the jet down to ~200
Schwarzschild radii. The brightness temperature at the jet base is in excess of
6e10 K. We find evidence of limb brightening on physical scales from <1 pc to
~40 pc. Polarization images and fits to the trend of jet width and brightness
vs. distance from the core reveal a magnetic field parallel to the jet axis.Comment: 10 pages, accepted by A&
VLBI Observations of a Complete Sample of Radio Galaxies V. 3C346 and 4C31.04: two Unusual CSS Sources
We present observations at 1.7 and 8.4 GHz of two Compact Steep Spectrum
(CSS) sources from a complete sample of low-intermediate power radio galaxies.
3C346 shows an asymmetric structure with a one-sided ``jet'' and ``hot spot''.
Present observations suggest that the classification of this source as a CSS is
inappropriate, and that it is a common radio galaxy at a small angle to the
line of sight. Its properties are in agreement with the predictions of unified
schemes models. 4C31.04 shows more complex structure with the possibility of a
centrally located flat spectrum core in between two close lobes. We suggest
that this source could be a low redshift Compact Symmetric Object.Comment: 15 pages, LATEX, uuenconde ps figures To be published in the
Astrophysical Journal, October 20th issu
Magnetoelectric birefringence revisited
Electromagnetic wave propagation inside isotropic material media
characterized by dielectric coefficients and
is examined. The regime of the eikonal approximation is
considered. The Hadamard method of field disturbances is used and the
dispersion relations are obtained by solving the Fresnel equation. Some
applications of the formalism are presented. Particularly, birefringence
phenomena induced by applied external fields are derived and discussed. It is
shown that magnetoelectric birefringence effect can occur even without the
presence of Kerr and Cotton-Mouton effects, provided the physical system
satisfies certain conditions.Comment: 9 pages, 1 figure, LaTe
Induction of Parturition in Beef Cattle With Dexamethasone
In recent years many reports have shown that synthetic glucocorticoids such as dexamethasone (DXMS) and flumethasone will induce parturition in cattle when injected intramuscularly during various stages of gestation. A study was conducted at South Dakota State University to determine, under field conditions, the effectiveness of DXMS coupled with estradiol on the precision of parturition induction, the incidence of retained placentas and subsequent reproductive performance of beef cows
A geometrical approach to the dynamics of spinor condensates I: Hydrodynamics
In this work, we derive the equations of motion governing the hydrodynamics
of spin-F spinor condensates. We pursue a description based on standard
physical variables (total density and superfluid velocity), alongside 2F
`spin-nodes': unit vectors that describe the spin F state, and also exhibit the
point-group symmetry of a spinor condensate's mean-field ground state. The
hydrodynamic equations of motion consist of a mass continuity equation, 2F
Landau-Lifshitz equations for the spin-nodes, and a modified Euler equation. In
particular, we provide a generalization of the Mermin-Ho relation to spin one,
and find an analytic solution for the skyrmion texture in the incompressible
regime of a spin-half condensate. These results exhibit a beautiful geometrical
structure that underlies the dynamics of spinor condensates.Comment: 12 pages. First paper in two-part serie
Interaction of a CO molecule with a Pt monatomic wire: electronic structure and ballistic conductance
We carry out a first-principles density functional study of the interaction
between a monatomic Pt wire and a CO molecule, comparing the energy of
different adsorption configurations (bridge, on top, substitutional, and tilted
bridge) and discussing the effects of spin-orbit (SO) coupling on the
electronic structure and on the ballistic conductance of two of these systems
(bridge and substitutional). We find that, when the wire is unstrained, the
bridge configuration is energetically favored, while the substitutional
geometry becomes possible only after the breaking of the Pt-Pt bond next to CO.
The interaction can be described by a donation/back-donation process similar to
that occurring when CO adsorbs on transition-metal surfaces, a picture which
remains valid also in presence of SO coupling. The ballistic conductance of the
(tipless) nanowire is not much reduced by the adsorption of the molecule on the
bridge and on-top sites, but shows a significant drop in the substitutional
case. The differences in the electronic structure due to the SO coupling
influence the transmission only at energies far away from the Fermi level so
that fully- and scalar-relativistic conductances do not differ significantly.Comment: 12 pages, 12 figures; figure misplacement and minor syntax issues
fixed, some references updated and correcte
The Bologna Complete Sample of Nearby Radio Sources
We present a new, complete, sample of 95 radio sources selected from the B2
and 3CR catalogues, with z < 0.1. Since no selection effect on the core radio
power, jet velocity, or source orientation is present, this sample is well
suited for statistical studies. In this first paper we present the
observational status of all sources on the parsec (mas) and kiloparsec (arcsec)
scale; we give new parsec-scale data for 28 sources and discuss their
parsec-scale properties. Combining these data with those in the literature,
information on the parsec-scale morphology is available for a total of 53 radio
sources with different radio power and kpc-scale morphology. We investigate
their properties. We find a dramatically higher fraction of two-sided sources
in comparison to previous flux limited VLBI surveys.Comment: 29 pages, 21 figures - ApJ in press (10 Jan 2005 issue
Experimental verification of a self-consistent theory of the first-, second-, and third-order (non)linear optical response
We show that a combination of linear absorption spectroscopy, hyper-Rayleigh
scattering, and a theoretical analysis using sum rules to reduce the size of
the parameter space leads to a prediction of the two-photon absorption
cross-section of the dye AF455 that agrees with two-photon absorption
spectroscopy. Our procedure, which demands self-consistency between several
measurement techniques and does not use adjustable parameters, provides a means
for determining transition moments between the dominant excited states based
strictly on experimental characterization. This is made possible by our new
approach that uses sum rules and molecular symmetry to rigorously reduce the
number of required physical quantities.Comment: 10 pages, 9 figure
- …