112 research outputs found
Uncertainty Quantification in Synthetic Controls with Staggered Treatment Adoption
We propose principled prediction intervals to quantify the uncertainty of a
large class of synthetic control predictions (or estimators) in settings with
staggered treatment adoption, offering precise non-asymptotic coverage
probability guarantees. From a methodological perspective, we provide a
detailed discussion of different causal quantities to be predicted, which we
call `causal predictands', allowing for multiple treated units with treatment
adoption at possibly different points in time. From a theoretical perspective,
our uncertainty quantification methods improve on prior literature by (i)
covering a large class of causal predictands in staggered adoption settings,
(ii) allowing for synthetic control methods with possibly nonlinear
constraints, (iii) proposing scalable robust conic optimization methods and
principled data-driven tuning parameter selection, and (iv) offering valid
uniform inference across post-treatment periods. We illustrate our methodology
with an empirical application studying the effects of economic liberalization
in the 1990s on GDP for emerging European countries. Companion general-purpose
software packages are provided in Python, R and Stata
Character of the invasive margin in colorectal cancer: does it improve prognostic information of Dukes staging?
Lymph node recovery from colorectal tumor specimens: recommendation for a minimum number of lymph nodes to be examined.
Tumor angiogenesis in lymph node-negative rectal cancer: correlation with clinicopathological parameters and prognosis.
Temperature Dependence of Electrical Resistance in Graphite Films Deposited on Glass and Low-Density Polyethylene by Spray Technology
Graphite lacquer was simply sprayed on glass and low-density polyethylene (LDPE) substrates to obtain large area films. Scanning Electron Microscopy (SEM) images, Raman spectra, X Ray Diffraction (XRD) spectra and current-voltage characteristics show that at room temperature, the as-deposited films on different substrates have similar morphological, structural and electrical properties. The morphological characterization reveals that the films are made of overlapped graphite platelets (GP), each composed of nanoplatelets with average sizes of a few tens of nanometers and about forty graphene layers. The thermoresistive properties of the GP films deposited on the different substrates and investigated in the temperature range from 20 to 120 °C show very different behaviors. For glass substrate, the resistance of the film decreases monotonically as a function of temperature by 7%; for LDPE substrate, the film resistance firstly increases more than one order of magnitude in the 20–100 °C range, then suddenly decreases to a temperature between 105 and 115 °C. These trends are related to the thermal expansion properties of the substrates and, for LDPE, also to the phase transitions occurring in the investigated temperature range, as evidenced by differential scanning calorimetry measurements
Variations in the amount of water ice on Ceres' surface suggest a seasonal water cycle.
The dwarf planet Ceres is known to host a considerable amount of water in its interior, and areas of water ice were detected by the Dawn spacecraft on its surface. Moreover, sporadic water and hydroxyl emissions have been observed from space telescopes. We report the detection of water ice in a mid-latitude crater and its unexpected variation with time. The Dawn spectrometer data show a change of water ice signatures over a period of 6 months, which is well modeled as ~2-km2 increase of water ice. The observed increase, coupled with Ceres' orbital parameters, points to an ongoing process that seems correlated with solar flux. The reported variation on Ceres' surface indicates that this body is chemically and physically active at the present time
Detection of Crystalline and Fine-grained Calcic Plagioclases on Vesta
Plagioclase feldspars are among the most prevalent minerals in the solar system, and are present in many chondritic and achondritic meteorite families. Nevertheless, spectral features of plagioclases have never been unambiguously and directly observed in remote observations of asteroids. We report here the detection of an absorption band at 12.2 μm on Vesta spectra provided by ground-based spectral observations at the Subaru Telescope. This signature represents the first direct evidence of a widespread presence of crystalline Ca-rich plagioclase on Vesta and reveals that its regolith is comminuted to a very fine grain size, smaller than a few tens of microns, indicating that the mechanical brecciation process has been very effective. The crystalline nature of plagioclase strongly suggests that impacts alone cannot be the sole mechanism for regolith formation on Vesta and a milder process, such as thermal fatigue, should be invoked as an important and concomitant process Thermal fatigue should be considered a very effective process in regolith production and rejuvenation not only for near-Earth asteroids but even for large asteroids located in the main belt
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