217 research outputs found
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Hotel Asset and Equity Risk Before, During, and After the Global Financial Crisis
In this paper, we use asset betas and equity betas over the period January 2000 through December 2015 to investigate the operating and financial risk of hotel industry REITs and C-Corps. We conclude that, on average over our sample period, the operating risk of C-Corps exceeds that of REITs. One interpretation of this result is that management contracts between REITs and C-Corps allocate more operating risk to C-Corps than to REITs. We also find that, on average, during our sample period, the equity betas of C-Corps exceed those of REITs. However, the difference between the average equity risk of the two sectors is much smaller than is the sectors’ difference in operating risk. Because equity betas capture both operating and financial risk, these results imply that REITs have significantly less operating risk than C-Corps and offset their lower business risk with higher financial leverage. During the global financial crisis, operating risk increases in both hotel industry subsectors, and the amount by which C-Corp asset betas exceed REIT asset betas is roughly proportionate to that observed in noncrisis periods. During the financial crisis, however, REITs experienced a greater increase in finan- cial leverage than did C-Corps, with the result being that the normal relation reverses, i.e., during the global financial crisis, REIT average equity betas significantly exceeded the average equity betas of C-Corps
Local atomic structure and discommensurations in the charge density wave of CeTe3
The local structure of CeTe3 in the incommensurate charge density wave
(IC-CDW) state has been obtained using atomic pair distribution function (PDF)
analysis of x-ray diffraction data. Local atomic distortions in the Te-nets due
to the CDW are larger than observed crystallographically, resulting in distinct
short and long Te-Te bonds. Observation of different distortion amplitudes in
the local and average structures are explained by the discommensurated nature
of the CDW since the PDF is sensitive to the local displacements within the
commensurate regions whereas the crystallographic result averages over many
discommensurated domains. The result is supported by STM data. This is the
first quantitative local structural study within the commensurate domains in an
IC-CDW system.Comment: 4 pages, 4 figure
Scanning-probe spectroscopy of semiconductor donor molecules
Semiconductor devices continue to press into the nanoscale regime, and new
applications have emerged for which the quantum properties of dopant atoms act
as the functional part of the device, underscoring the necessity to probe the
quantum structure of small numbers of dopant atoms in semiconductors[1-3].
Although dopant properties are well-understood with respect to bulk
semiconductors, new questions arise in nanosystems. For example, the quantum
energy levels of dopants will be affected by the proximity of nanometer-scale
electrodes. Moreover, because shallow donors and acceptors are analogous to
hydrogen atoms, experiments on small numbers of dopants have the potential to
be a testing ground for fundamental questions of atomic and molecular physics,
such as the maximum negative ionization of a molecule with a given number of
positive ions[4,5]. Electron tunneling spectroscopy through isolated dopants
has been observed in transport studies[6,7]. In addition, Geim and coworkers
identified resonances due to two closely spaced donors, effectively forming
donor molecules[8]. Here we present capacitance spectroscopy measurements of
silicon donors in a gallium-arsenide heterostructure using a scanning probe
technique[9,10]. In contrast to the work of Geim et al., our data show
discernible peaks attributed to successive electrons entering the molecules.
Hence this work represents the first addition spectrum measurement of dopant
molecules. More generally, to the best of our knowledge, this study is the
first example of single-electron capacitance spectroscopy performed directly
with a scanning probe tip[9].Comment: In press, Nature Physics. Original manuscript posted here; 16 pages,
3 figures, 5 supplementary figure
Direct observation of micron-scale ordered structure in a two-dimensional electron system
We have applied a novel scanned probe method to directly resolve the interior
structure of a GaAs/AlGaAs two-dimensional electron system in a tunneling
geometry. We find that the application of a perpendicular magnetic field can
induce surprising density modulations that are not static as a function of the
field. Near six and four filled Landau levels, stripe-like structures emerge
with a characteristic wave length ~2 microns. Present theories do not account
for ordered density modulations on this length scale.Comment: 5 pages, 4 figures. To appear in Phys. Rev.
Modifying the surface electronic properties of YBa2Cu3O7-delta with cryogenic scanning probe microscopy
We report the results of a cryogenic study of the modification of
YBa2Cu3O7-delta surface electronic properties with the probe of a scanning
tunneling microscope (STM). A negative voltage applied to the sample during STM
tunneling is found to modify locally the conductance of the native degraded
surface layer. When the degraded layer is removed by etching, the effect
disappears. An additional surface effect is identified using Scanning Kelvin
Probe Microscopy in combination with STM. We observe reversible surface
charging for both etched and unetched samples, indicating the presence of a
defect layer even on a surface never exposed to air.Comment: 6 pages, 4 figures. To appear in Superconductor Science and
Technolog
Chaos in Andreev Billiards
A new type of classical billiard - the Andreev billiard - is investigated
using the tangent map technique. Andreev billiards consist of a normal region
surrounded by a superconducting region. In contrast with previously studied
billiards, Andreev billiards are integrable in zero magnetic field, {\it
regardless of their shape}. A magnetic field renders chaotic motion in a
generically shaped billiard, which is demonstrated for the Bunimovich stadium
by examination of both Poincar\'e sections and Lyapunov exponents. The issue of
the feasibility of certain experimental realizations is addressed.Comment: ReVTeX3.0, 4 pages, 3 figures appended as postscript file (uuencoded
with uufiles
Modeling Subsurface Charge Accumulation Images of a Quantum Hall Liquid
Subsurface Charge Accumulation imaging is a cryogenic scanning probe
technique that has recently been used to spatially probe incompressible strips
formed in a two-dimensional electron system (2DES) at high magnetic fields. In
this paper, we present detailed numerical modeling of these data. At a basic
level, the method produces results that agree well with the predictions of
models based on simple circuit elements. Moreover, the modeling method is
sufficiently advanced to simulate the spatially resolved measurements. By
comparing directly the simulations to the experimentally measured data, we can
extract quantitatively local electronic features of the 2DES. In particular, we
deduce the electron density of states inside the incompressible strips and
electrical resistance across them.Comment: 11 pages, 3 figure
An Automated Coronary Artery Occlusion Device for Stimulating Collateral Development in Vivo
Introduction: Repetitive, brief coronary artery occlusions produce collateral development in experimental animals. This model causes coronary collateralization in a highly reproducible fashion, but the process is very labor intensive. We report the design and use of a fully automated hydraulic coronary occlusion device capable of producing repetitive coronary occlusions and enhancement of coronary collateral development in dogs.
Methods: The device consists of analog electronics that allow adjustment of occlusion number, frequency, pressure and duration, and mechanical components responsible for the coronary occlusion. The motor and piston of the device are coupled to a chronically implanted hydraulic vascular occluder placed around the left anterior descending coronary artery (LAD) of dogs instrumented for measurement of systemic and coronary hemodynamics. One group of dogs (n=6) underwent brief (2 min) LAD occlusions once per hour, eight times per day, 5 days/week for 3 weeks to stimulate collateral development (measured using radioactive microspheres). Another group of dogs (n=6) that did not receive repetitive occlusions served as controls.
Results: The device reproducibly produced repetitive LAD occlusions for the duration, frequency, and time interval initially programmed. A time-dependent increase in transmural collateral blood flow was observed in dogs undergoing repetitive occlusions using the device. Collateral blood flow was unchanged in dogs that did not undergo occlusions.
Discussion: The automated occluder device reliably produces repetitive coronary occlusions and may facilitate further study of coronary collateral development in response to chronic myocardial ischemia
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