4,563 research outputs found
Fundamental Performance of a Dispersed Fixed Delay Interferometer In Searching For Planets Around M Dwarfs
We present a new method to calculate fundamental Doppler measurement limits
with a dispersed fixed-delay interferometer (DFDI) in the near infrared
wavelength region for searching for exoplanets around M dwarfs in the coming
decade. It is based on calculating the Q factor, a measure of flux-normalized
Doppler sensitivity in the fringing spectra created with DFDI. We calculate the
Q factor as a function of spectral resolution R, stellar projected rotational
velocity V sini, stellar effective temperature T_eff and optical path
difference (OPD) of the interferometer. We also compare the DFDI Q factor to
that for the popular cross-dispersed echelle spectrograph method (the direct
echelle (DE) method). Given the IR Doppler measurement is likely to be
detector-limited for a while, we introduce new merit functions, which is
directly related to photon-limited RV uncertainty, to evaluate Doppler
performance with the DFDI and DE methods. We find that DFDI has strength in
wavelength coverage and multi-object capability over the DE for a limited
detector resource. We simulate the performance of the InfraRed Exoplanet
Tracker (IRET) based on the DFDI design, being considered for the next
generation IR Doppler measurements. The predicted photon-limited RV uncertainty
suggests that IRET is capable of detecting Earth-like exoplanets in habitable
zone around nearby bright M dwarfs if they exist. A new method is developed to
quantitatively estimate the influence of telluric lines on RV uncertainty. Our
study shows that photon-limited RV uncertainty can be reached if 99% of the
strength of telluric lines can be removed from the measured stellar spectra. At
low to moderate levels of telluric line strength removal (50% to 90%), the
optimal RV uncertainty is typically a factor of 2-3 times larger than
photon-limited RV uncertainty.Comment: 43 pages, 20 figures, 6 tables. Accepted by Ap
THE FAUST PHYSICAL MODELING LIBRARY: A MODULAR PLAYGROUND FOR THE DIGITAL LUTHIER
International audienceThis paper introduces the FAUST Physical Modeling Library, an environment to create physical models of musical instruments in a modular way in the FAUST programming language. Low and high level elements can be combined to implement existing or completely novel instruments. Various examples of physical models are provided. The combined use of mesh2faust, a tool to generate FAUST physical models from 3D drawings, and of the FAUST Physical Modeling Library is also demonstrated through the implementation of a marimba physical model
The cosmic microwave background radiation temperature at z = 3.025 toward QSO 0347--3819
From the analysis of the CII fine-structure population ratio in the damped
Ly_alpha system at z = 3.025 toward the quasar Q0347--3819 we derive an upper
bound of 14.6 (+/- 0.2) K on the cosmic microwave background temperature
regardless the presence of other different excitation mechanisms. The analysis
of the ground state rotational level populations of H_2 detected in the system
reveals a Galactic-type UV radiation field ruling out UV pumping as an
important excitation mechanism for CII. The low dust content estimated from the
Cr/Zn ratio indicates that the IR dust emission can also be neglected. When the
collisional excitation is considered, we measure a temperature for the cosmic
background radiation of T = 12.1 (+1.7, -3.2) K. The results are in agreement
with the T = 10.968 (+/-) 0.004 K predicted by the hot Big Bang cosmology at z
= 3.025.Comment: Accepte
Design of U-PPC-Type II for nonlinear systems
In this study, a new U-PPC-Type II (U-model Pole Placement Control Type II) control system design procedure is proposed based on the U-model principle. The objective of a U-PPC-Type II design is to determine a linear controller Gc from a specified closed loop linear transfer function Gcls . The study also compares the new design procedure with a U-PPC-Type I based design procedure. For demonstration of the effectiveness of the proposed new procedure, U-PPC-Type II is designed for both a linear dynamic model and a Hammerstein (nonlinear dynamic) model. The simulation results are presented with discussions and graphical illustrations
ROX Index to Guide Management of COVID-19 Pneumonia
Coronavirus disease 2019 (COVID-19) caused by novel severe acute respiratory syndrome
coronavirus 2 (SARS-CoV-2) emerged from China in December 2019 leading to a global
pandemic (1). Approximately 17% of patients admitted to hospital require critical care, the
majority of whom undergo mechanical ventilation (MV) for pneumonia complicated by
hypoxaemia (2)
Wittgensteinian Anti-Scepticism and Epistemic Vertigo
status: publishe
Deep Markov Random Field for Image Modeling
Markov Random Fields (MRFs), a formulation widely used in generative image
modeling, have long been plagued by the lack of expressive power. This issue is
primarily due to the fact that conventional MRFs formulations tend to use
simplistic factors to capture local patterns. In this paper, we move beyond
such limitations, and propose a novel MRF model that uses fully-connected
neurons to express the complex interactions among pixels. Through theoretical
analysis, we reveal an inherent connection between this model and recurrent
neural networks, and thereon derive an approximated feed-forward network that
couples multiple RNNs along opposite directions. This formulation combines the
expressive power of deep neural networks and the cyclic dependency structure of
MRF in a unified model, bringing the modeling capability to a new level. The
feed-forward approximation also allows it to be efficiently learned from data.
Experimental results on a variety of low-level vision tasks show notable
improvement over state-of-the-arts.Comment: Accepted at ECCV 201
Using item response theory to explore the psychometric properties of extended matching questions examination in undergraduate medical education
BACKGROUND:
As assessment has been shown to direct learning, it is critical that the examinations developed to test clinical competence in medical undergraduates are valid and reliable. The use of extended matching questions (EMQ) has been advocated to overcome some of the criticisms of using multiple-choice questions to test factual and applied knowledge.
METHODS:
We analysed the results from the Extended Matching Questions Examination taken by 4th year undergraduate medical students in the academic year 2001 to 2002. Rasch analysis was used to examine whether the set of questions used in the examination mapped on to a unidimensional scale, the degree of difficulty of questions within and between the various medical and surgical specialties and the pattern of responses within individual questions to assess the impact of the distractor options.
RESULTS:
Analysis of a subset of items and of the full examination demonstrated internal construct validity and the absence of bias on the majority of questions. Three main patterns of response selection were identified.
CONCLUSION:
Modern psychometric methods based upon the work of Rasch provide a useful approach to the calibration and analysis of EMQ undergraduate medical assessments. The approach allows for a formal test of the unidimensionality of the questions and thus the validity of the summed score. Given the metric calibration which follows fit to the model, it also allows for the establishment of items banks to facilitate continuity and equity in exam standards
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