1,669 research outputs found
Transfer of spectral weight across the gap of Sr2IrO4 induced by La doping
We study with Angle Resolved PhotoElectron Spectroscopy (ARPES) the evolution
of the electronic structure of Sr2IrO4, when holes or electrons are introduced,
through Rh or La substitutions. At low dopings, the added carriers occupy the
first available states, at bottom or top of the gap, revealing an anisotropic
gap of 0.7eV in good agreement with STM measurements. At further doping, we
observe a reduction of the gap and a transfer of spectral weight across the
gap, although the quasiparticle weight remains very small. We discuss the
origin of the in-gap spectral weight as a local distribution of gap values
Short small-polaron lifetime in the mixed-valence perovskite CsAuI from high-pressure pump-probe experiments
We study the ultrafast phonon response of mixed-valence perovskite
CsAuI using pump-probe spectroscopy under high-pressure in a
diamond anvil cell. We observed a remarkable softening and broadening of the Au
- I stretching phonon mode with both applied pressure and photoexcitation.
Using a double-pump scheme we measured a lifetime of the charge transfer
excitation into single valence Au of less than 4 ps, which is an
indication of the local character of the Au excitation. Furthermore, the
strong similarity between the pressure and fluence dependence of the phonon
softening shows that the inter-valence charge transfer plays an important role
in the structural transition.Comment: 4 pages, 4 figure
Characterizing Polytobacco Use Trajectories and Their Associations With Substance Use and Mental Health Across Mid-Adolescence.
Background:Polytobacco product use is suspected to be common, dynamic across time, and increase risk for adverse behavioral outcomes. We statistically modeled characteristic types of polytobacco use trajectories during mid-adolescence and tested their prospective association with substance use and mental health problems. Methods:Adolescents (N = 3393) in Los Angeles, CA, were surveyed semiannually from 9th to 11th grade. Past 6-month combustible cigarette, e-cigarette, or hookah use (yes/no) over four assessments were analyzed using parallel growth mixture modeling to identify a parsimonious set of polytobacco use trajectories. A tobacco product use trajectory group was used to predict substance use and mental health at the fifth assessment. Results:Three profiles were identified: (1) tobacco nonusers (N = 2291, 67.5%) with the lowest use prevalence (<3%) of all products across all timepoints; (2) polyproduct users (N = 920, 27.1%) with moderate use prevalence of each product (8-35%) that escalated for combustible cigarettes but decreased for e-cigarettes and hookah across time; and (3) chronic polyproduct users (N = 182, 5.4%) with high prevalence of each product use (38-86%) that escalated for combustible cigarettes and e-cigarettes. Nonusers, polyproduct users, and chronic polyproduct users reported successively higher alcohol, marijuana, and illicit drug use and ADHD at the final follow-up, respectively. Both tobacco using groups (vs. nonusers) reported greater odds of depression and anxiety at the final follow-up but did not differ from each other. Conclusions:Adolescent polytobacco use may involve a common moderate risk trajectory and a less common high-risk chronic trajectory. Both trajectories predict substance use and mental health symptomology. Implications:Variation in use and co-use of combustible cigarette, e-cigarette, and hookah use in mid-adolescence can be parsimoniously characterized by a small set common trajectory profiles in which polyproduct use are predominant patterns of tobacco product use, which predict adverse behavioral outcomes. Prevention and policy addressing polytobacco use (relative to single product use) may be optimal tobacco control strategies for youth, which may in turn prevent other forms of substance use and mental health problems
Structure and Magnetic Properties of the Pyrochlore Iridate Y2Ir2O7
Neutron powder diffraction and inelastic measurements were performed
examining the 5d pyrochlore YIrO. Temperature dependent
measurements were performed between 3.4 K and 290 K, spanning the magnetic
transition at 155 K. No sign of any structural or disorder induced phase
transition was observed over the entire temperature range. In addition, no sign
of magnetic long-range order was observed to within the sensitivity of the
instrumentation. These measurements do not rule out long range magnetic order,
but the neutron powder diffraction structural refinements do put an upper bound
for the ordered iridium moment of 0.2 Ir (for a magnetic
structure with wave vector ) or 0.5 Ir (for Q = 0).Comment: 5 pages, 8 figure
A proposed prioritization system for the management of invasive alien plants in South Africa
Every country has weed species whose presence conflicts in some way with human management objectives and needs. Resources for research and control are limited, so priority should be given to species that are the biggest problem. The prioritization system described in this article was designed to assess objectively research and control priorities of invasive alien plants at a national scale in South Africa. The evaluation consists of seventeen criteria, grouped into five modules, that assess invasiveness, spatial characteristics, potential impact, potential for control, and conflicts of interest for each plant species under consideration. Total prioritization scores, calculated from criterion and module scores, were used to assess a species' priority. Prioritization scores were calculated by combining independent assessments provided by several experts, thus increasing the reliability of the rankings. The total confidence score, a separate index, indicates the reliability and availability of data used to make an assessment. Candidate species for evaluation were identified and assessed by several experts using the prioritization system. The final ranking was made by combining two separate indices, the total prioritization score and the total confidence score. This approach integrates the plant's perceived priority with an index of data reliability. Of the 61 species assessed, those with the highest ranks (Lantana camara, Chromolaena odorata and Opuntia ficus-indica) had high prioritization and high confidence scores, and are thus of most concern. Those species with the lowest ranks, for example, Harrisia martinii, Opuntia spinulifera and Opuntia exaltata, had low prioritization scores and high confidence scores, and thus are of least concern. Our approach to ranking weeds offers several advantages over existing systems because it is designed for multiple assessors based on the Delphi decision-making technique, the criteria contribute equally to the total score, and the system can accommodate incomplete data on a species. Although the choice of criteria may be criticized and the system has certain limitations, it appears to have delivered credible results
A proposed prioritization system for the management of invasive alien plants in South Africa
Every country has weed species whose presence conflicts in some way with human management objectives and needs. Resources for research and control are limited, so priority should be given to species that are the biggest problem. The prioritization system described in this article was designed to assess objectively research and control priorities of invasive alien plants at a national scale in South Africa. The evaluation consists of seventeen criteria, grouped into five modules, that assess invasiveness, spatial characteristics, potential impact, potential for control, and conflicts of interest for each plant species under consideration. Total prioritization scores, calculated from criterion and module scores, were used to assess a species' priority. Prioritization scores were calculated by combining independent assessments provided by several experts, thus increasing the reliability of the rankings. The total confidence score, a separate index, indicates the reliability and availability of data used to make an assessment. Candidate species for evaluation were identified and assessed by several experts using the prioritization system. The final ranking was made by combining two separate indices, the total prioritization score and the total confidence score. This approach integrates the plant's perceived priority with an index of data reliability. Of the 61 species assessed, those with the highest ranks (Lantana camara, Chromolaena odorata and Opuntia ficus-indica) had high prioritization and high confidence scores, and are thus of most concern. Those species with the lowest ranks, for example, Harrisia martinii, Opuntia spinulifera and Opuntia exaltata, had low prioritization scores and high confidence scores, and thus are of least concern. Our approach to ranking weeds offers several advantages over existing systems because it is designed for multiple assessors based on the Delphi decision-making technique, the criteria contribute equally to the total score, and the system can accommodate incomplete data on a species. Although the choice of criteria may be criticized and the system has certain limitations, it appears to have delivered credible results
Skyrmion Quantization and the Decay of the Delta
We present the complete solution to the so-called ``Yukawa problem'' of the
Skyrme model. This refers to the perceived difficulty of reproducing---purely
from soliton physics---the usual pseudovector pion-nucleon coupling, echoed by
pion coupling to the higher spin/isospin baryons in a manner fixed by large- group theory. The solution involves
surprisingly elegant interplay between the classical and quantum properties of
a new configuration, the ``new improved skyrmion''. This is the near-hedgehog
obtained by minimizing the usual skyrmion mass functional augmented by an
all-important isorotational kinetic term. The numerics are pleasing: a
decay width within a few MeV of its measured value, and furthermore, the
higher-spin baryons with widths so large ()
that these undesirable large- artifacts effectively drop out of the
spectrum, and pose no phenomenological problem. Beyond these specific results,
we ground the Skyrme model in the Feynman Path Integral, and set up a
transparent collective coordinate formalism that makes maximal use of the
expansion. This approach elucidates the connection between skyrmions on
the one hand, and Feynman diagrams in an effective field theory on the other.Comment: This TeX file inputs the macropackage harvmac.tex . Choose the ``b''
(big) option or equations will overrun
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