2,701 research outputs found
From stripe to checkerboard order on the square lattice in the presence of quenched disorder
We discuss the effects of quenched disorder on a model of charge density wave
(CDW) ordering on the square lattice. Our model may be applicable to the
cuprate superconductors, where a random electrostatic potential exists in the
CuO2 planes as a result of the presence of charged dopants. We argue that the
presence of a random potential can affect the unidirectionality of the CDW
order, characterized by an Ising order parameter. Coupling to a unidirectional
CDW, the random potential can lead to the formation of domains with 90 degree
relative orientation, thus tending to restore the rotational symmetry of the
underlying lattice. We find that the correlation length of the Ising order can
be significantly larger than the CDW correlation length. For a checkerboard CDW
on the other hand, disorder generates spatial anisotropies on short length
scales and thus some degree of unidirectionality. We quantify these disorder
effects and suggest new techniques for analyzing the local density of states
(LDOS) data measured in scanning tunneling microscopy experiments.Comment: 10 pages, 11 figures; added referenc
Cu(I)-Catalyzed Alkynylation of Quinolones
[Image: see text] Herein we report the first alkynylation of quinolones with terminal alkynes under mild reaction conditions. The reaction is catalyzed by Cu(I) salts in the presence of a Lewis acid, which is essential for the reactivity of the system. The enantioselective version of this transformation has also been explored, and the methodology has been applied in the synthesis of the enantioenriched tetrahydroquinoline alkaloid cuspareine
Evidence for gapped spin-wave excitations in the frustrated Gd2Sn2O7 pyrochlore antiferromagnet from low-temperature specific heat measurements
We have measured the low-temperature specific heat of the geometrically
frustrated pyrochlore Heisenberg antiferromagnet Gd2Sn2O7 in zero magnetic
field. The specific heat is found to drop exponentially below approximately 350
mK. This provides evidence for a gapped spin-wave spectrum due to an anisotropy
resulting from single ion effects and long-range dipolar interactions. The data
are well fitted by linear spin-wave theory, ruling out unconventional low
energy magnetic excitations in this system, and allowing a determination of the
pertinent exchange interactions in this material
Analysis of photovoltaic self-consumption systems
Components and installation prices could make the self-consumption of solar photovoltaic (PV) systems competitive. In this paper, we explore different self-consumption options, off-grid PV systems (with back-up generator and/or batteries), and grid-connected PV systems under net-metering policies. The calculation of the net present cost (NPC) reveals that the grid-connected PV-only case (for the net-metering scheme) is the most attractive from the technical and financial points of view, with a levelised cost of energy less than 0.1 €/kWh. Off-grid PV + Diesel + Batteries has a higher cost, around two or three times the grid-connected PV-only under net metering. Additionally, the off-grid PV + Diesel is less attractive from a financial point of view, which has a cost of around 10 times the PV-only under net metering. In addition, the values of life cycle CO2 emissions in each of the cases studied have been compared, and we have concluded that although the off-grid PV + Diesel + Batteries system presents lower CO2 emissions than the PV-only system, the existence of batteries does not allow one to affirm that the PV + Diesel + Batteries system is the best from an environmental point of view
The Physical Parameters of the Retired A Star HD185351
We report here an analysis of the physical stellar parameters of the giant
star HD185351 using Kepler short-cadence photometry, optical and near infrared
interferometry from CHARA, and high-resolution spectroscopy. Asteroseismic
oscillations detected in the Kepler short-cadence photometry combined with an
effective temperature calculated from the interferometric angular diameter and
bolometric flux yield a mean density, rho_star = 0.0130 +- 0.0003 rho_sun and
surface gravity, logg = 3.280 +- 0.011. Combining the gravity and density we
find Rstar = 5.35 +- 0.20 Rsun and Mstar = 1.99 +- 0.23 Msun. The trigonometric
parallax and CHARA angular diameter give a radius Rstar = 4.97 +- 0.07 Rsun.
This smaller radius,when combined with the mean stellar density, corresponds to
a stellar mass Mstar = 1.60 +- 0.08 Msun, which is smaller than the
asteroseismic mass by 1.6-sigma. We find that a larger mass is supported by the
observation of mixed modes in our high-precision photometry, the spacing of
which is consistent only for Mstar =~ 1.8 Msun. Our various and independent
mass measurements can be compared to the mass measured from interpolating the
spectroscopic parameters onto stellar evolution models, which yields a
model-based mass M_star = 1.87 +- 0.07 Msun. This mass agrees well with the
asteroseismic value,but is 2.6-sigma higher than the mass from the combination
of asteroseismology and interferometry. The discrepancy motivates future
studies with a larger sample of giant stars. However, all of our mass
measurements are consistent with HD185351 having a mass in excess of 1.5 Msun.Comment: ApJ accepte
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