778 research outputs found
Doping dependence of the coupling of electrons to bosonic modes in the single-layer high-temperature Bi2Sr2CuO6 superconductor
A recent highlight in the study of high-Tc superconductors is the observation
of band renormalization / self-energy effects on the quasiparticles. This is
seen in the form of kinks in the quasiparticle dispersions as measured by
photoemission and interpreted as signatures of collective bosonic modes
coupling to the electrons. Here we compare for the first time the self-energies
in an optimally doped and strongly overdoped, non-superconducting single-layer
Bi-cuprate (Bi2Sr2CuO6). Besides the appearance of a strong overall weakening,
we also find that weight of the self-energy in the overdoped system shifts to
higher energies. We present evidence that this is related to a change in the
coupling to c-axis phonons due to the rapid change of the c-axis screening in
this doping range.Comment: 4 pages, 3 figure
Quantitative analysis of Sr2RuO4 ARPES spectra: Many-body interactions in a model Fermi liquid
ARPES spectra hold a wealth of information about the many-body interactions
in a correlated material. However, the quantitative analysis of ARPES spectra
to extract the various coupling parameters in a consistent manner is extremely
challenging, even for a model Fermi liquid system. We propose a fitting
procedure which allows quantitative access to the intrinsic lineshape,
deconvolved of energy and momentum resolution effects, of the correlated
2-dimensional material Sr2RuO4. For the first time in correlated 2-dimensional
materials, we find an ARPES linewidth that is narrower than its binding energy,
a key property of quasiparticles within Fermi liquid theory. We also find that
when the electron-electron scattering component is separated from the
electron-phonon and impurity scattering terms it decreases with a functional
form compatible with Fermi liquid theory as the Fermi energy is approached. In
combination with the previously determined Fermi surface, these results give
the first complete picture of a Fermi liquid system via ARPES. Furthermore, we
show that the magnitude of the extracted imaginary part of the self-energy is
in remarkable agreement with DC transport measurements.Comment: 10 pages, 5 figure
Policy Brief MIX AND MATCH: WHAT PRINCIPALS REALLY LOOK FOR WHEN HIRING TEACHERS
Abstract The vast majority of research and policy related to teacher quality focuses on the supply of teachers and ignores teacher demand. In particular, the important role of school principals in hiring teachers is rarely considered. Using interviews of school principals in a midsized Florida school district, we provide an exploratory mixed methods analysis of the teacher characteristics principals prefer. Our findings contradict the conventional wisdom that principals undervalue content knowledge and intelligence. Principals in our study ranked content knowledge third among a list of twelve characteristics. Intelligence does appear less important at first glance, but this is apparently because principals believe all applicants who meet certification requirements meet a minimum threshold on intelligence and because some intelligent teachers have difficulty connecting with students. More generally, we find that principals prefer an "individual mix" of personal and professional qualities. They also create an "organizational mix," hiring teachers who differ from those already in the school in terms of race, gender, experience, and skills, and an "organizational match," in which teachers have similar work habits and a high propensity to remain with the school over time. Because of tenure rules, many principals also prefer less experienced (untenured) teachers, even though research suggests that they are less effective
Ultraviolet photochemistry of ethane: implications for the atmospheric chemistry of the gas giants
Chemical processing in the stratospheres of the gas giants is driven by incident vacuum ultraviolet (VUV) light. Ethane is an important constituent in the atmospheres of the gas giants in our solar system. The present work describes translational spectroscopy studies of the VUV photochemistry of ethane using tuneable radiation in the wavelength range 112 ≤ λ ≤ 126 nm from a free electron laser and event-triggered, fast-framing, multi-mass imaging detection methods. Contributions from at least five primary photofragmentation pathways yielding CH_{2}, CH_{3} and/or H atom products are demonstrated and interpreted in terms of unimolecular decay following rapid non-adiabatic coupling to the ground state potential energy surface. These data serve to highlight parallels with methane photochemistry and limitations in contemporary models of the photoinduced stratospheric chemistry of the gas giants. The work identifies additional photochemical reactions that require incorporation into next generation extraterrestrial atmospheric chemistry models which should help rationalise hitherto unexplained aspects of the atmospheric ethane/acetylene ratios revealed by the Cassini–Huygens fly-by of Jupiter
Geometric Realizations of Bi-Hamiltonian Completely Integrable Systems
In this paper we present an overview of the connection between completely
integrable systems and the background geometry of the flow. This relation is
better seen when using a group-based concept of moving frame introduced by Fels
and Olver in [Acta Appl. Math. 51 (1998), 161-213; 55 (1999), 127-208]. The
paper discusses the close connection between different types of geometries and
the type of equations they realize. In particular, we describe the direct
relation between symmetric spaces and equations of KdV-type, and the possible
geometric origins of this connection.Comment: This is a contribution to the Proc. of the Seventh International
Conference ''Symmetry in Nonlinear Mathematical Physics'' (June 24-30, 2007,
Kyiv, Ukraine), published in SIGMA (Symmetry, Integrability and Geometry:
Methods and Applications) at http://www.emis.de/journals/SIGMA
Structural origin of apparent Fermi surface pockets in angle-resolved photoemission of BiSrLaCuO
We observe apparent hole pockets in the Fermi surfaces of single-layer
Bi-based cuprate superconductors from angle-resolved photoemission (ARPES).
From detailed low-energy electron diffraction measurements and an analysis of
the ARPES polarization-dependence, we show that these pockets are not
intrinsic, but arise from multiple overlapping superstructure replicas of the
main and shadow bands. We further demonstrate that the hole pockets reported
recently from ARPES [Meng et al, Nature 462, 335 (2009)] have a similar
structural origin, and are inconsistent with an intrinsic hole pocket
associated with the electronic structure of a doped CuO plane. The nature
of the Fermi surface topology in the enigmatic pseudogap phase therefore
remains an open question.Comment: 5 pages, 4 figure
Insights into enterotoxigenic Escherichia coli diversity in Bangladesh utilizing genomic epidemiology
Estrogens and their precursors in postmenopausal women with early breast cancer receiving anastrozole
PURPOSE: We determined hormone concentrations (estradiol [E2], estrone [E1], estrone conjugates [E1-C], androstenedione [A], testosterone [T]) before and on anastrozole therapy where we also determined plasma concentrations of anastrozole and its metabolites.
EXPERIMENTAL: Postmenopausal women who were to receive adjuvant anastrozole for resected early breast cancer were studied. Pretreatment, blood samples were obtained for the acquisition of DNA and for plasma hormone measurements (E2, E1, E1-C, A, and T). A second blood draw was obtained at least 4 weeks after starting anastrozole for hormone, anastrozole and metabolite measurements. For hormone assays, a validated bioanalytical method using gas chromatography negative ionization tandem mass spectrometry was used. Anastrozole and metabolite assays involved extraction of plasma followed by LC/MS/MS assays.
RESULTS: 649 patients were evaluable. Pretreatment and during anastrozole, there was large inter-individual variability in E2, E1, and E1-C as well as anastrozole and anastrozole metabolite concentrations. E2 and E1 concentrations were below the lower limits of quantitation in 79% and 70%, respectively, of patients on anastrozole therapy, but those with reliable concentrations had a broad range (0.627-234.0 pg/mL, 1.562-183.2 pg/mL, respectively). Considering E2, 8.9% had the same or higher concentration relative to baseline while on anastrozole, documented by the presence of drug.
CONCLUSIONS: We demonstrated large inter-individual variability in anastrozole and anastrozole metabolite concentrations as well as E1, E2, E1-C, A, and T concentrations before and while on anastrozole. These findings suggest that the standard 1mg daily dose of anastrozole is not optimal for a substantial proportion of women with breast cancer
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