3,713 research outputs found
Non-Fermi liquid angle resolved photoemission lineshapes of Li0.9Mo6O17
A recent letter by Xue et al. (PRL v.83, 1235 ('99)) reports a Fermi-Liquid
(FL) angle resolved photoemission (ARPES) lineshape for quasi one-dimensional
Li0.9Mo6O17, contradicting our report (PRL v.82, 2540 ('99)) of a non-FL
lineshape in this material. Xue et al. attributed the difference to the
improved angle resolution. In this comment, we point out that this reasoning is
flawed. Rather, we find that their data have fundamental differences from other
ARPES results and also band theory.Comment: To be published as a PRL Commen
New Luttinger liquid physics from photoemission on LiMoO
Temperature dependent high resolution photoemission spectra of quasi-1
dimensional LiMoO evince a strong renormalization of its
Luttinger liquid density-of-states anomalous exponent. We trace this new effect
to interacting charge neutral critical modes that emerge naturally from the
two-band nature of the material. LiMoO is shown thereby to
be a paradigm material that is capable of revealing new Luttinger physics.Comment: 4 pages, 3 figures. Accepted for publication by Phys. Rev. Let
Luttinger liquid ARPES spectra from samples of LiMoO grown by the temperature gradient flux technique
Angle resolved photoemission spectroscopy line shapes measured for
quasi-one-dimensional LiMoO samples grown by a temperature
gradient flux technique are found to show Luttinger liquid behavior, consistent
with all previous data by us and other workers obtained from samples grown by
the electrolyte reduction technique. This result eliminates the sample growth
method as a possible origin of considerable differences in photoemission data
reported in previous studies of LiMoO.Comment: Some text adde
Non-fermi-liquid single particle lineshape of the quasi-one-dimensional non-CDW metal Li_{0.9}Mo_{6}O_{17} : comparison to the Luttinger liquid
We report the detailed non-Fermi liquid (NFL) lineshape of the dispersing
excitation which defines the Fermi surface (FS) for quasi-one-dimensional
Li_{0.9}Mo_{6}O_{17}. The properties of Li_{0.9}Mo_{6}O_{17} strongly suggest
that the NFL behavior has a purely electronic origin. Relative to the
theoretical Luttinger liquid lineshape, we identify significant similarities,
but also important differences.Comment: 5 pages, 3 eps figure
ARPES Line Shapes in FL and non-FL Quasi-Low-Dimensional Inorganic Metals
Quasi-low-dimensional (quasi-low-D) inorganic materials are not only ideally
suited for angle resolved photoemission spectroscopy (ARPES) but also they
offer a rich ground for studying key concepts for the emerging paradigm of
non-Fermi liquid (non-FL) physics. In this article, we discuss the ARPES
technique applied to three quasi-low-D inorganic metals: a paradigm Fermi
liquid (FL) material TiTe, a well-known quasi-1D charge density wave
(CDW) material KMoO and a quasi-1D non-CDW material
LiMoO. With TiTe, we establish that a many body
theoretical interpretation of the ARPES line shape is possible. We also address
the fundamental question of how to accurately determine the {\bf k} value
from ARPES. Both KMoO and LiMoO show
quasi-1D electronic structures with non-FL line shapes. A CDW gap opening is
observed for KMoO, whereas no gap is observed for
LiMoO. We show, however, that the standard CDW theory,
even with strong fluctuations, is not sufficient to describe the non-FL line
shapes of KMoO. We argue that a Luttinger liquid (LL) model is
relevant for both bronzes, but also point out difficulties encountered in
comparing data with theory. We interpret this situation to mean that a more
complete and realistic theory is necessary to understand these data.Comment: 23 pages, including 21 figures; to appear in a special issue of J.
Elec. Spectr. Rel. Pheno
Dynamics of the Electro-Optic response of Blue Bronze
We have studied the charge density wave (CDW) repolarization dynamics in blue
bronze by applying square-wave voltages of different frequencies to the sample
and measuring the changes in infrared transmittance, proportional to CDW
strain. The frequency dependence of the electro-transmittance was fit to a
modified harmonic oscillator response and the evolution of the parameters as
functions of voltage, position, and temperature are discussed. Resonant
frequencies decrease with distance from the current contacts, indicating that
the resulting delays are intrinsic to the CDW with the strain effectively
flowing from the contact. For a fixed position, the average relaxation time has
a voltage dependence given by tau_0~V^-p, with 1<p<2. The temperature
dependence of the fitting parameters shows that the dynamics are governed by
both the force on the CDW and the CDW current: for a given force and position,
both the relaxation and delay times are inversely proportional to the CDW
current as temperature is varied. The long relaxation and delay times (~ 1 ms)
suggest that the strain response involves the motion of macroscopic objects,
presumably CDW phase dislocation lines.Comment: 36 pages, including 12 figures, submitted to Phys. Rev.
Efficacy and safety of ipratropium bromide/albuterol compared with albuterol in patients with moderate-to-severe asthma: a randomized controlled trial
Abstract Background Many patients with asthma require frequent rescue medication for acute symptoms despite appropriate controller therapies. Thus, determining the most effective relief regimen is important in the management of more severe asthma. This study’s objective was to evaluate whether ipratropium bromide/albuterol metered-dose inhaler (CVT-MDI) provides more effective acute relief of bronchospasm in moderate-to-severe asthma than albuterol hydrofluoroalkaline (ALB-HFA) alone after 4 weeks. Methods In this double-blind, crossover study, patients who had been diagnosed with asthma for ≥1 year were randomized to two sequences of study medication “as needed” for symptom relief (1–7 day washout before second 4-week treatment period): CVT-MDI/ALB-HFA or ALB-HFA/CVT-MDI. On days 1 and 29 of each sequence, 6-hour serial spirometry was performed after administration of the study drug. Co-primary endpoints were FEV 1 area under the curve (AUC 0–6 ) and peak (post-dose) forced expiratory volume in 1 s (FEV 1 ) response (change from test day baseline) after 4 weeks. The effects of “as needed” treatment with ALB-HFA/CVT-MDI were analyzed using mixed effect model repeated measures (MMRM). Results A total of 226 patients, ≥18 years old, with inadequately controlled, moderate-to-severe asthma were randomized. The study met both co-primary endpoints demonstrating a statistically significant treatment benefit of CVT-MDI versus ALB-HFA. FEV 1 AUC 0-6h response was 167 ml for ALB-HFA, 252 ml for CVT-MDI (p <0.0001); peak FEV 1 response was 357 ml for ALB-HFA, 434 ml for CVT-MDI (p <0.0001). Adverse events were comparable across groups. Conclusions CVT-MDI significantly improved acute bronchodilation over ALB-HFA alone after 4 weeks of “as-needed” use for symptom relief, with a similar safety profile. This suggests additive bronchodilator effects of β 2 -agonist and anticholinergic treatment in moderate-to-severe, symptomatic asthma. Trial registration ClinicalTrials.gov No.: NCT00818454; Registered November 16, 2009
Exchange Anisotropy in Epitaxial and Polycrystalline NiO/NiFe Bilayers
(001) oriented NiO/NiFe bilayers were grown on single crystal MgO (001)
substrates by ion beam sputtering in order to determine the effect that the
crystalline orientation of the NiO antiferromagnetic layer has on the
magnetization curve of the NiFe ferromagnetic layer. Simple models predict no
exchange anisotropy for the (001)-oriented surface, which in its bulk
termination is magnetically compensated. Nonetheless exchange anisotropy is
present in the epitaxial films, although it is approximately half as large as
in polycrystalline films that were grown simultaneously. Experiments show that
differences in exchange field and coercivity between polycrystalline and
epitaxial NiFe/NiO bilayers couples arise due to variations in induced surface
anisotropy and not from differences in the degree of compensation of the
terminating NiO plane. Implications of these observations for models of induced
exchange anisotropy in NiO/NiFe bilayer couples will be discussed.Comment: 23 pages in RevTex format, submitted to Phys Rev B
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Consistent negative response of US crops to high temperatures in observations and crop models
High temperatures are detrimental to crop yields and could lead to global warming-driven reductions in agricultural productivity. To assess future threats, the majority of studies used process-based crop models, but their ability to represent effects of high temperature has been questioned. Here we show that an ensemble of nine crop models reproduces the observed average temperature responses of US maize, soybean and wheat yields. Each day >30 °C diminishes maize and soybean yields by up to 6% under rainfed conditions. Declines observed in irrigated areas, or simulated assuming full irrigation, are weak. This supports the hypothesis that water stress induced by high temperatures causes the decline. For wheat a negative response to high temperature is neither observed nor simulated under historical conditions, since critical temperatures are rarely exceeded during the growing season. In the future, yields are modelled to decline for all three crops at temperatures >30 °C. Elevated CO 2 can only weakly reduce these yield losses, in contrast to irrigation
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