34,381 research outputs found
PDF turbulence modeling and DNS
The problem of time discontinuity (or jump condition) in the coalescence/dispersion (C/D) mixing model is addressed in probability density function (pdf). A C/D mixing model continuous in time is introduced. With the continuous mixing model, the process of chemical reaction can be fully coupled with mixing. In the case of homogeneous turbulence decay, the new model predicts a pdf very close to a Gaussian distribution, with finite higher moments also close to that of a Gaussian distribution. Results from the continuous mixing model are compared with both experimental data and numerical results from conventional C/D models. The effect of Coriolis forces on compressible homogeneous turbulence is studied using direct numerical simulation (DNS). The numerical method used in this study is an eight order compact difference scheme. Contrary to the conclusions reached by previous DNS studies on incompressible isotropic turbulence, the present results show that the Coriolis force increases the dissipation rate of turbulent kinetic energy, and that anisotropy develops as the Coriolis force increases. The Taylor-Proudman theory does apply since the derivatives in the direction of the rotation axis vanishes rapidly. A closer analysis reveals that the dissipation rate of the incompressible component of the turbulent kinetic energy indeed decreases with a higher rotation rate, consistent with incompressible flow simulations (Bardina), while the dissipation rate of the compressible part increases; the net gain is positive. Inertial waves are observed in the simulation results
Light weight fire resistant graphite composites
Composite structures with a honeycomb core and characterized by lightweight and excellent fire resistance are provided. These sandwich structures employ facesheets made up of bismaleimide-vinyl styrylpyridine copolymers with fiber reinforcement such as carbon fiber reinforcement. In preferred embodiments the facesheets are over layered with a decorative film. The properties of these composites make them attractive materials of construction aircraft and spacecraft
Fluctuation Effects in High Sheet Resistance Superconducting Films
As the normal state sheet resistance, , of a thin film superconductor
increases, its superconducting properties degrade. For
superconductivity disappears and a transition to a nonsuperconducting state
occurs. We present electron tunneling and transport measurements on ultrathin,
homogeneously disordered superconducting films in the vicinity of this
transition. The data provide strong evidence that fluctuations in the amplitude
of the superconducting order parameter dominate the tunneling density of states
and the resistive transitions in this regime. We briefly discuss possible
sources of these amplitude fluctuation effects. We also describe how the data
suggest a novel picture of the superconductor to nonsuperconductor transition
in homogeneous 2D systems.Comment: 11 pages, 5 figure
Sagnac Interferometer Enhanced Particle Tracking in Optical Tweezers
A setup is proposed to enhance tracking of very small particles, by using
optical tweezers embedded within a Sagnac interferometer. The achievable
signal-to-noise ratio is shown to be enhanced over that for a standard optical
tweezers setup. The enhancement factor increases asymptotically as the
interferometer visibility approaches 100%, but is capped at a maximum given by
the ratio of the trapping field intensity to the detector saturation threshold.
For an achievable visibility of 99%, the signal-to-noise ratio is enhanced by a
factor of 200, and the minimum trackable particle size is 2.4 times smaller
than without the interferometer
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Short-Term Precipitation Forecast Based on the PERSIANN System and LSTM Recurrent Neural Networks
Short-term Quantitative Precipitation Forecasting is important for flood forecasting, early flood warning, and natural hazard management. This study proposes a precipitation forecast model by extrapolating Cloud-Top Brightness Temperature (CTBT) using advanced Deep Neural Networks, and applying the forecasted CTBT into an effective rainfall retrieval algorithm to obtain the Short-term Quantitative Precipitation Forecasting (0–6 hr). To achieve such tasks, we propose a Long Short-Term Memory (LSTM) and the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN), respectively. The precipitation forecasts obtained from our proposed framework, (i.e., LSTM combined with PERSIANN) are compared with a Recurrent Neural Network (RNN), Persistency method, and Farneback optical flow each combined with PERSIANN algorithm and the numerical model results from the first version of Rapid Refresh (RAPv1.0) over three regions in the United States, including the states of Oregon, Oklahoma, and Florida. Our experiments indicate better statistics, such as correlation coefficient and root-mean-square error, for the CTBT forecasts from the proposed LSTM compared to the RNN, Persistency, and the Farneback method. The precipitation forecasts from the proposed LSTM and PERSIANN framework has demonstrated better statistics compared to the RAPv1.0 numerical forecasts and PERSIANN estimations from RNN, Persistency, and Farneback projections in terms of Probability of Detection, False Alarm Ratio, Critical Success Index, correlation coefficient, and root-mean-square error, especially in predicting the convective rainfalls. The proposed method shows superior capabilities in short-term forecasting over compared methods, and has the potential to be implemented globally as an alternative short-term forecast product
Experimental study of ion heating and acceleration during magnetic reconnection
Ion heating and acceleration has been studied in the well-characterized reconnection layer of the Magnetic Reconnection Experiment [M. Yamada , Phys. Plasmas 4, 1936 (1997)]. Ion temperature in the layer rises substantially during null-helicity reconnection in which reconnecting field lines are anti-parallel. The plasma outflow is sub-Alfvenic due to a downstream back pressure. An ion energy balance calculation based on the data and including classical viscous heating indicates that ions are heated largely via nonclassical mechanisms. The T-i rise is much smaller during co-helicity reconnection in which field lines reconnect obliquely. This is consistent with a slower reconnection rate and a smaller resistivity enhancement over the Spitzer value. These observations show that nonclassical dissipation mechanisms can play an important role both in heating the ions and in facilitating the reconnection process
An Interpretable Deep Hierarchical Semantic Convolutional Neural Network for Lung Nodule Malignancy Classification
While deep learning methods are increasingly being applied to tasks such as
computer-aided diagnosis, these models are difficult to interpret, do not
incorporate prior domain knowledge, and are often considered as a "black-box."
The lack of model interpretability hinders them from being fully understood by
target users such as radiologists. In this paper, we present a novel
interpretable deep hierarchical semantic convolutional neural network (HSCNN)
to predict whether a given pulmonary nodule observed on a computed tomography
(CT) scan is malignant. Our network provides two levels of output: 1) low-level
radiologist semantic features, and 2) a high-level malignancy prediction score.
The low-level semantic outputs quantify the diagnostic features used by
radiologists and serve to explain how the model interprets the images in an
expert-driven manner. The information from these low-level tasks, along with
the representations learned by the convolutional layers, are then combined and
used to infer the high-level task of predicting nodule malignancy. This unified
architecture is trained by optimizing a global loss function including both
low- and high-level tasks, thereby learning all the parameters within a joint
framework. Our experimental results using the Lung Image Database Consortium
(LIDC) show that the proposed method not only produces interpretable lung
cancer predictions but also achieves significantly better results compared to
common 3D CNN approaches
Erratum : Squeezing and entanglement delay using slow light
An inconsistency was found in the equations used to calculate the variance of
the quadrature fluctuations of a field propagating through a medium
demonstrating electromagnetically induced transparency (EIT). The decoherence
term used in our original paper introduces inconsistency under weak probe
approximation. In this erratum we give the Bloch equations with the correct
dephasing terms. The conclusions of the original paper remain the same. Both
entanglement and squeezing can be delayed and preserved using EIT without
adding noise when the decoherence rate is small.Comment: 1 page, no figur
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