4,076 research outputs found
Coupled-channel analysis of the possible , and molecular states
We perform a coupled-channel study of the possible deuteron-like molecules
with two heavy flavor quarks, including the systems of with
double charm, with double bottom and
with both charm and bottom, within the
one-boson-exchange model. In our study, we take into account the S-D mixing
which plays an important role in the formation of the loosely bound deuteron,
and particularly, the coupled-channel effect in the flavor space. According to
our calculation, the states and
with double charm, the states
,
and
with double bottom, and
the states and
with both charm and bottom are good
molecule candidates. However, the existence of the states
with double charm and
with both charm and bottom is ruled out.Comment: 1 figure added, published in Physical Review
Gear optimization
The use of formal numerical optimization methods for the design of gears is investigated. To achieve this, computer codes were developed for the analysis of spur gears and spiral bevel gears. These codes calculate the life, dynamic load, bending strength, surface durability, gear weight and size, and various geometric parameters. It is necessary to calculate all such important responses because they all represent competing requirements in the design process. The codes developed here were written in subroutine form and coupled to the COPES/ADS general purpose optimization program. This code allows the user to define the optimization problem at the time of program execution. Typical design variables include face width, number of teeth and diametral pitch. The user is free to choose any calculated response as the design objective to minimize or maximize and may impose lower and upper bounds on any calculated responses. Typical examples include life maximization with limits on dynamic load, stress, weight, etc. or minimization of weight subject to limits on life, dynamic load, etc. The research codes were written in modular form for easy expansion and so that they could be combined to create a multiple reduction optimization capability in future
Medical Image Segmentation Based on Multi-Modal Convolutional Neural Network: Study on Image Fusion Schemes
Image analysis using more than one modality (i.e. multi-modal) has been
increasingly applied in the field of biomedical imaging. One of the challenges
in performing the multimodal analysis is that there exist multiple schemes for
fusing the information from different modalities, where such schemes are
application-dependent and lack a unified framework to guide their designs. In
this work we firstly propose a conceptual architecture for the image fusion
schemes in supervised biomedical image analysis: fusing at the feature level,
fusing at the classifier level, and fusing at the decision-making level.
Further, motivated by the recent success in applying deep learning for natural
image analysis, we implement the three image fusion schemes above based on the
Convolutional Neural Network (CNN) with varied structures, and combined into a
single framework. The proposed image segmentation framework is capable of
analyzing the multi-modality images using different fusing schemes
simultaneously. The framework is applied to detect the presence of soft tissue
sarcoma from the combination of Magnetic Resonance Imaging (MRI), Computed
Tomography (CT) and Positron Emission Tomography (PET) images. It is found from
the results that while all the fusion schemes outperform the single-modality
schemes, fusing at the feature level can generally achieve the best performance
in terms of both accuracy and computational cost, but also suffers from the
decreased robustness in the presence of large errors in any image modalities.Comment: Zhe Guo and Xiang Li contribute equally to this wor
Maritime coverage enhancement using UAVs coordinated with hybrid satellite-terrestrial networks
Due to the agile maneuverability, unmanned aerial vehicles (UAVs) have shown great promise for on-demand communications. In practice, UAV-aided aerial base stations are not separate. Instead, they rely on existing satellites/terrestrial systems for spectrum sharing and efficient backhaul. In this case, how to coordinate satellites, UAVs and terrestrial systems is still an open issue. In this paper, we deploy UAVs for coverage enhancement of a hybrid satellite-terrestrial maritime communication network. Using a typical composite channel model including both large-scale and small-scale fading, the UAV trajectory and in-flight transmit power are jointly optimized, subject to constraints on UAV kinematics, tolerable interference, backhaul, and the total energy of the UAV for communications. Different from existing studies, only the location-dependent large-scale channel state information (CSI) is assumed available, because it is difficult to obtain the small-scale CSI before takeoff in practice and the ship positions can be obtained via the dedicated maritime Automatic Identification System. The optimization problem is non-convex. We solve it by using problem decomposition, successive convex optimization and bisection searching tools. Simulation results demonstrate that the UAV fits well with existing satellite and terrestrial systems, using the proposed optimization framework
Optimal Beamforming for Hybrid Satellite Terrestrial Networks with Nonlinear PA and Imperfect CSIT
In hybrid satellite-terrestrial networks (HSTNs), spectrum sharing is crucial
to alleviate the "spectrum scarcity" problem. Therein, the transmit beams
should be carefully designed to mitigate the inter-satellite-terrestrial
interference. Different from previous studies, this work considers the impact
of both nonlinear power amplifier (PA) and large-scale channel state
information at the transmitter (CSIT) on beamforming. These phenomena are
usually inevitable in a practical HSTN. Based on the Saleh model of PA
nonlinearity and the large-scale multi-beam satellite channel parameters, we
formulate a beamforming optimization problem to maximize the achievable rate of
the satellite system while ensuring that the inter-satellite-terrestrial
interference is below a given threshold. The optimal amplitude and phase of
desired beams are derived in a decoupled manner. Simulation results demonstrate
the superiority of the proposed beamforming scheme.Comment: 5 pages, 5 figures, journa
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