3,773 research outputs found
Optical properties of quinolinium tetracyanoquinodimethanide, [Qn(TCNQ)2] and (N-methylphenazinium)x(phenazine)1-x (tetracyanoquinodimethane) [(NMP)x(Phen)1-x(TCNQ)]
Journal ArticleWe present here optical-absorption data of quinolinium ditetracyanoquinodimethanide [Qn(TCNQ)2] and (N-methylphenazinium)x(phenazine)1-x(tetracyanoquinodimethanide) [(NMP)x(Phen)1-x(TCNQ)] for 0.5 <_x<_ 0.6. These materials span the range of electronic structure from commensurate, to commensurate with confined soliton-antisoliton pairs (bipolarons), to incommensurate. The data show that these materials are semiconductors up to 300 K. The semiconducting gap, due mostly to a Peierls distortion, is weakly temperature dependent, decaying slowly as the temperature increases. This behavior, determined by the observation of the totally symmetric a, vibrational modes of the TCNQ molecule, is similar for all compositions studied and is suggested to be due to the effects of an external cation potential or to Coulomb effects, which vary little with composition. Substantial in-gap absorption is observed and is suggested to be due to the presence of quantum-nucleated and thermally generated bipolarons. The variation of higher-energy electronic transitions with composition corresponds to a crossover from commensurate to incommensurate electronic structure
Optical properties of the 1:2 compound of dimethylferrocenium with tetracyanoquinodimethanide: [(Me2Fc)(TCNQ)2]
Journal ArticleWe present the results of a study of the room-temperature polarized reflectance of (1:2) 1,1'-dimethylferrocenium ditetracyanoquinodimethanide [(Me2Fc)(TCNQ)2] over the range between the far infrared and the near ultraviolet. Kramers-Kronig analysis of the reflectance is used to determine the optical properties of the compound. Vibrational features are evident at low frequencies whereas electronic excitations, including charge transfer between TCNQ molecules, are observed at higher frequencies
The Interstellar Medium of IRAS 08572+3915 NW: H3+ and Warm High Velocity CO
We confirm the first detection of the molecular ion H3+ in an extragalactic
object, the highly obscured ultraluminous galaxy IRAS 08572+3915 NW. We also
have detected absorption lines of the fundamental band of CO in this galaxy.
The CO absorption consists of a cold component close to the systemic velocity
and warm, highly blueshifted and redshifted components. The warm blueshifted
component is remarkably strong and broad and extends at least to -350 km/s.
Some analogies can be drawn between the H3+ and cold CO in IRAS08572+3915 NW
and the same species seen toward the Galactic center. The profiles of the warm
CO components are not those expected from a dusty torus of the type thought to
obscure active galactic nuclei. They are probably formed close to the dust
continuum surface near the buried and active nucleus and are probably
associated with an unusual and energetic event there.Comment: 21 pages, 4 postscript figures, accepted by Ap
Modelling storm response on gravel beaches using XBeach-G
EPRSC New Understanding and Prediction of Storm Impacts on Gravel beaches (NUPSIG; EP/H040056/1) and Adaptation and Resilience of Coastal Energy Supply (ARCEoS; EP/IO35390/1). The full text is under embargo until 01.12.15. Published by ICE Publishin
Observations of rotationally resolved C3 in translucent sight lines
The rotationally resolved spectrum of the A ^1Pi_u <- X ^1Sigma^+_g 000-000
transition of C3, centered at 4051.6A, has been observed along 10 translucent
lines of sight. To interpret these spectra, a new method for the determination
of column densities and analysis of excitation profiles involving the
simulation and fitting of observed spectra has been developed. The populations
of lower rotational levels (J<14) in C3 are best fit by thermal distributions
that are consistent with the kinetic temperatures determined from the
excitation profile of C2. Just as in the case of C2, higher rotational levels
(J>14) of C3 show increased nonthermal population distributions in clouds which
have been determined to have total gas densities below ~500 cm-3.Comment: 12 pages, 4 figures, accepted for publication in The Astrophysical
Journa
Four Poynting Theorems
The Poynting vector is an invaluable tool for analysing electromagnetic
problems. However, even a rigorous stress-energy tensor approach can still
leave us with the question: is it best defined as \Vec{E} \cross \Vec{H} or
as \Vec{D} \cross \Vec{B}? Typical electromagnetic treatments provide yet
another perspective: they regard \Vec{E} \cross \Vec{B} as the appropriate
definition, because \Vec{E} and \Vec{B} are taken to be the fundamental
electromagnetic fields. The astute reader will even notice the fourth possible
combination of fields: i.e. \Vec{D} \cross \Vec{H}. Faced with this diverse
selection, we have decided to treat each possible flux vector on its merits,
deriving its associated energy continuity equation but applying minimal
restrictions to the allowed host media. We then discuss each form, and how it
represents the response of the medium. Finally, we derive a propagation
equation for each flux vector using a directional fields approach; a useful
result which enables further interpretation of each flux and its interaction
with the medium.Comment: 8 pages. Updated slightly from EJP versio
Introduction to RISC-KIT: Resilience-increasing strategies for coasts
Recent and historic low-frequency, high-impact events have demonstrated the flood risks faced by exposed coastal areas in Europe and beyond. These coastal zone risks are likely to increase in the future which requires a re-evaluation of coastal disaster risk reduction (DRR) strategies and a new mix of PMP (prevention, e.g., dike protection; mitigation, e.g., limiting construction in flood-prone areas and eco-system based solutions; and preparedness, e.g., Early Warning Systems, EWS) measures.
In response to these challenges, the RISC-KIT project has delivered a set of open-source and openaccess methods, tools and management approaches to reduce risk and increase resilience to lowfrequency, high-impact hydro-meteorological events in the coastal zone (the “RISC-toolKIT”). These products enhance forecasting, prediction and early warning capabilities, improve the assessment of long-term coastal risk and optimise the mix of PMP-measures.
In this paper an introduction is provided to the objectives, products, applications and lessonslearned of the RISC-KIT project, which are the subjects of this Special Issue. Subsequent papers provide details on the tools and their application on 10 case study sites in Europe
Spectropolarimetry of the Type IIb Supernova 2001ig
We present spectropolarimetric observations of the Type IIb SN 2001ig in NGC
7424; conducted with the ESO VLT FORS1 on 2001 Dec 16, 2002 Jan 3 and 2002 Aug
16 or 13, 31 and 256 days post-explosion. These observations are at three
different stages of the SN evolution: (1) The hydrogen-rich photospheric phase,
(2) the Type II to Type Ib transitional phase and (3) the nebular phase. At
each of these stages, the observations show remarkably different polarization
properties as a function of wavelength. We show that the degree of interstellar
polarization is 0.17%. The low intrinsic polarization (~0.2%) at the first
epoch is consistent with an almost spherical (<10% deviation from spherical
symmetry) hydrogen dominated ejecta. Similar to SN 1987A and to Type IIP SNe, a
sharp increase in the degree of the polarization (~1%) is observed when the
outer hydrogen layer becomes optically thin by day 31; only at this epoch is
the polarization well described by a ``dominant axis.'' The polarization angle
of the data shows a rotation through ~40 degrees between the first and second
epochs, indicating that the asymmetries of the first epoch were not directly
coupled with those observed at the second epoch. For the most polarized lines,
we observe wavelength-dependent loop structures in addition to the dominant
axis on the Q-U plane. We show that the polarization properties of Type IIb SNe
are roughly similar to one another, but with significant differences arising
due to line blending effects especially with the high velocities observed for
SN 2001ig. This suggests that the geometry of SN 2001ig is related to SN 1993J
and that these events may have arisen from a similar binary progenitor system.Comment: 42 pages, 12 figures (figs. 11 and 12 are both composed of four
subpanels, figs. 6,7,8,11 and 12 are in color, fig. 1 is low res and a high
res version is available at http://www.as.utexas.edu/~jrm/), ApJ Accepte
Magnetization and Magnetotransport of LnBaCo2O5.5 (Ln=Gd, Eu) Single Crystals
The magnetization, resistivity and magnetoresistance (MR) of single crystals
of GdBaCo2O5.5 and EuBaCo2O5.5 are measured over a wide range of dc magnetic
fields (up to 30 T) and temperature. In LnBaCo2O5.5 (Ln=Gd, Eu), the Co-ions
are trivalent and can exist in three spin states, namely, the S=0 low spin
state (LS), the S= 1 intermediate spin state (IS) and the S=2 high spin state
(HS). We confirm that GdBaCo2O5.5 and EuBaCo2O5.5 have a metal-insulator
transition accompanied by a spin-state transition at TMI >> 365 and 335 K,
respectively. The data suggest an equal ratio of LS (S=0) and IS (S=1) Co3+
ions below TMI, with no indication of additional spin state transitions. The
low field magnetization shows a transition to a highly anisotropic
ferromagnetic phase at 270 K, followed by another magnetic transition to an
antiferromagnetic phase at a slightly lower temperature. The magnetization data
are suggestive of weak correlations between the Gd-spins but no clear signature
of ordering is seen for T > 2 K. Significant anisotropy between the a-b plane
and c axis was observed in magnetic and magnetotransport properties for both
compounds. For GdBaCo2O5.5, the resistivity and MR data imply a strong
correlation between the spin-order and charge carriers. For EuBaCo2O5.5, the
magnetic phase diagram is very similar to its Gd counterpart, but the low-T MR
with current flow in the ab plane is positive rather than negative as for Gd.
The magnitude and the hysteresis of the MR for EuBaCo2O5.5 decrease with
increasing temperature, and at higher T the MR changes sign and becomes
negative. The difference in the behavior of both compounds may arise from a
small valence admixture in the nonmagnetic Eu ions, i.e. a valence slightly
less than 3+.Comment: Accepted for publication in PR
- …