2,288 research outputs found
Evolution of photoemission spectral functions in doped transition metal oxides
We discuss the experimental photoemission and inverse photoemission of early
transition metal oxides, in the light of the dynamical mean field theory of
correlated electrons which becomes exact in the limit of infinite dimensions.
We argue that a comprehensive description of the experimental data requires
spatial inhomogeneities and present a calculation of the evolution of the
spectral function in an inhomogenous system with various degrees of
inhomogeneity. We also point out that comparaison of experimental results and
large d calculations require that the degree of correlation and disorder is
larger in the surface than in the bulk
Optimal operating conditions and characteristics of acetone/CaF_2 detector for inverse photoemission spectroscopy
Performance and characteristics of a band-pass photon detector using acetone
gas and CaF_2 window (acetone/CaF_2) have been studied and compared with an
ethanol/MgF_2 detector. The optimal operating conditions are found to be 4 mbar
acetone pressure and 745+/-20 V anode voltage. The count rate obtained by us is
about a factor of 3 higher than what has been reported earlier for the acetone
detector. Unlike other gas filled detectors, this detector works in the
proportional region with very small dead time (4 micro sec). A detector
band-pass of 0.48+/-0.01 eV FWHM is obtained.Comment: Review of Scientific Instruments 76, 066102 (2005
Spectral functions in doped transition metal oxides
We present experimental photoemission and inverse photoemission spectra of
SrTiO representing electron doped systems. Photoemission
spectra in presence of electron doping exhibit prominent features arising from
electron correlation effects, while the inverse photoemssion spectra are
dominated by spectral features explainable within single-particle approaches.
We show that such a spectral evolution in chemically doped correlated systems
is not compatible with expectations based on Hubbard or any other similar
model. We present a new theoretical approach taking into account the
inhomogeneity of the `real' system which gives qualitatively different results
compared to standard `homogeneous' models and is in quantitative agreement with
experiments.Comment: 10 pages; 1 tex file+4 postscript files (to appear in Europhysics
Letters
Discovery of a Very Young Field L Dwarf, 2MASS J01415823-4633574
While following up L dwarf candidates selected photometrically from the Two
Micron All Sky Survey, we uncovered an unusual object designated 2MASS
J01415823-4633574. Its optical spectrum exhibits very strong bands of vanadium
oxide but abnormally weak absorptions by titanium oxide, potassium, and sodium.
Morphologically such spectroscopic characteristics fall intermediate between
old, field early-L dwarfs (log(g)~5) and very late M giants (log(g)~0), leading
us to favor low gravity as the explanation for the unique spectral signatures
of this L dwarf. Such a low gravity can be explained only if this L dwarf is
much lower in mass than a typical old field L dwarf of similar temperature and
is still contracting to its final radius. These conditions imply a very young
age. Further evidence of youth is found in the near-infrared spectrum,
including a triangular-shaped H-band continuum reminiscent of young brown dwarf
candidates discovered in the Orion Nebula Cluster. Using the above information
along with comparisons to brown dwarf atmospheric and interior models, our
current best estimate is that this L dwarf has an age of 1-50 Myr and a mass of
6-25 M_Jupiter. The location of 2MASS 0141-4633 on the sky coupled with a
distance estimate of ~35 pc and the above age estimate suggests that this
object may be a brown dwarf member of either the 30-Myr-old Tucana/Horologium
Association or the ~12-Myr-old beta Pic Moving Group.Comment: Accepted for publication in the 10 March 2006 issue (volume 639) of
the Astrophysical Journa
Enhanced surface metallic density of states in icosahedral quasicrystals
Valence and core-level photoemission spectra show that cleaved i-Al-Pd-Mn quasicrystals have a pronounced metallic signature. Spectra from states above EF, populated by increasing the sample temperature, indicate the presence of a shallow pseudogap 0.09 eV above EF. The Al 2p line asymmetry, on the other hand, which indicates metallic behavior, decreases with increasing photoelectron escape depth. This implies a decreasing density of states at EF with increasing distance from the surface, consistent with indications that the density of states near EF in the bulk is reduced. Our results thus help to resolve the apparent contradiction between the theoretical predictions for a bulk pseudogap, and the clear metallic Fermi edges in photoemission
A Survey of Alkali Line Absorption in Exoplanetary Atmospheres
We obtained over 90 hours of spectroscopic observations of four exoplanetary
systems with the Hobby-Eberly Telescope (HET). Observations were taken in
transit and out of transit, and we analyzed the differenced spectra---i.e., the
transmission spectra---to inspect it for absorption at the wavelengths of the
neutral sodium (\ion{Na}{1}) doublet at and neutral
potassium (\ion{K}{1}) at . We used the transmission spectrum at
\ion{Ca}{1} ---which shows strong stellar absorption but is not an
alkali metal resonance line that we expect to show significant absorption in
these atmospheres---as a control line to examine our measurements for
systematic errors. We use an empirical Monte Carlo method to quantity these
systematic errors. In a reanalysis of the same dataset using a reduction and
analysis pipeline that was derived independently, we confirm the previously
seen \ion{Na}{1} absorption in HD 189733b at a level of
(the average value over a 12 \AA{} integration
band to be consistent with previous authors). Additionally, we tentatively
confirm the \ion{Na}{1} absorption seen in HD 209458b (independently by
multiple authors) at a level of , though the
interpretation is less clear. Furthermore, we find \ion{Na}{1} absorption of
at in HD 149026b; features apparent in
the transmission spectrum are consistent with real absorption and indicate this
may be a good target for future observations to confirm. No other results
(\ion{Na}{1} in HD 147506b and \ion{Ca}{1} and \ion{K}{1} in all four targets)
are significant to , although we observe some features that we
argue are primarily artifacts.Comment: 38 total pages (preprint format), 9 color figures, 4 tables, accepted
for publication in Ap
Hot-Jupiters and hot-Neptunes: a common origin?
We compare evolutionary models for close-in exoplanets coupling irradiation
and evaporation due respectively to the thermal and high energy flux of the
parent star with observations of recently discovered new transiting planets.
The models provide an overall good agreement with observations, although at the
very limit of the quoted error bars of OGLE-TR-10, depending on its age. Using
the same general theory, we show that the three recently detected hot-Neptune
planets (GJ436, Cancri, Ara) may originate from more massive gas
giants which have undergone significant evaporation. We thus suggest that
hot-Neptunes and hot-Jupiters may share the same origin and evolution history.
Our scenario provides testable predictions in terms of the mass-radius
relationships of these hot-Neptunes.Comment: 5 pages, 2 figures, accepted in A&A Lette
Rotational Velocities of Very Low Mass Binaries
We present rotational velocities for individual components of eleven very low mass (VLM) binaries with spectral types between M7.5 and L4. These results are based on observations taken with the near-infrared spectrograph, NIRSPEC, and the Keck II laser guide star adaptive optics (LGS AO) system. The binaries were targeted as part of a dynamical mass program, and their orbital inclinations are used to translate vsini into a rotational velocity for each component. We find that the observed sources tend to be rapid rotators (vsini > 10 km s^(-1)), consistent with previous measurements for ultracool objects. Five systems have component vsini's that are statistically different, with three binaries having velocity differences greater than 25 km s^(-1). To bring these discrepant rotational velocities into agreement would require their rotational axes to be inclined between 10 to 40° with respect to each other, and that at least one component has a significant inclination with respect to the orbital plane. Alternatively, each component could be rotating at a different rate, even though they have similar spectral types. Both differing rotational velocities and inclinations have interesting implications for binary star formation. Two of the binaries with large differences in rotational velocity are also known radio sources, LP 349-25AB and 2MASS 0746+20AB. LP 349-25B is rotating at ∼95 km s^(-1), within a factor of ∼3 of the break up speed, and is one of the most rapidly rotating VLM objects known
Cationic vacancy induced room-temperature ferromagnetism in transparent conducting anatase Ti_{1-x}Ta_xO_2 (x~0.05) thin films
We report room-temperature ferromagnetism in highly conducting transparent
anatase Ti1-xTaxO2 (x~0.05) thin films grown by pulsed laser deposition on
LaAlO3 substrates. Rutherford backscattering spectrometry (RBS), x-ray
diffraction (XRD), proton induced x-ray emission (PIXE), x-ray absorption
spectroscopy (XAS) and time-of-flight secondary ion mass spectrometry
(TOF-SIMS) indicated negligible magnetic contaminants in the films. The
presence of ferromagnetism with concomitant large carrier densities was
determined by a combination of superconducting quantum interference device
(SQUID) magnetometry, electrical transport measurements, soft x-ray magnetic
circular dichroism (SXMCD), XAS, and optical magnetic circular dichroism (OMCD)
and was supported by first-principle calculations. SXMCD and XAS measurements
revealed a 90% contribution to ferromagnetism from the Ti ions and a 10%
contribution from the O ions. RBS/channelling measurements show complete Ta
substitution in the Ti sites though carrier activation was only 50% at 5% Ta
concentration implying compensation by cationic defects. The role of Ti vacancy
and Ti3+ was studied via XAS and x-ray photoemission spectroscopy (XPS)
respectively. It was found that in films with strong ferromagnetism, the Ti
vacancy signal was strong while Ti3+ signal was absent. We propose (in the
absence of any obvious exchange mechanisms) that the localised magnetic
moments, Ti vacancy sites, are ferromagnetically ordered by itinerant carriers.
Cationic-defect-induced magnetism is an alternative route to ferromagnetism in
wide-band-gap semiconducting oxides without any magnetic elements.Comment: 21 pages, 10 figures, to appear in Philosophical Transaction - Royal
Soc.
Mental health status and perceived burden in caregiving spouses of persons with psychotic illness (a study from India)
Mental illness poses a great deal of burden on other family members, particularly the primary caregiver. In the Indian context for a married person with mental illness, the caregiving burden is usually experienced by the spouse, who is considered to be the ‘natural’ option. This quantitative study used survey methodology to assess caregiving burden in fifty spouses of persons diagnosed with a psychotic illness. Data was collected at a neuro-psychiatric facility in Tiruchirappalli, India. The Depression, Anxiety and Stress Scale and the Burden Assessment Schedule were the instruments administered to assess the mental health status of the spouse and their perceived burden. Findings revealed that the majority of spouses were classified as experiencing ‘severe’ and ‘extremely severe’ in terms of their depression, anxiety and stress levels and ‘high’ in terms of perceived burden. The specific ‘type’ of clinical diagnosis, however, did not differentiate the spouses on the key variables studied. The correlation of these key variables with other background variables has also been examined. The implications of the results of this study for psychosocial intervention have also been discussed in this article
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