12,272 research outputs found
A Normalization Model for Analyzing Multi-Tier Millimeter Wave Cellular Networks
Based on the distinguishing features of multi-tier millimeter wave (mmWave)
networks such as different transmit powers, different directivity gains from
directional beamforming alignment and path loss laws for line-of-sight (LOS)
and non-line-of-sight (NLOS) links, we introduce a normalization model to
simplify the analysis of multi-tier mmWave cellular networks. The highlight of
the model is that we convert a multi-tier mmWave cellular network into a
single-tier mmWave network, where all the base stations (BSs) have the same
normalized transmit power 1 and the densities of BSs scaled by LOS or NLOS
scaling factors respectively follow piecewise constant function which has
multiple demarcation points. On this basis, expressions for computing the
coverage probability are obtained in general case with beamforming alignment
errors and the special case with perfect beamforming alignment in the
communication. According to corresponding numerical exploration, we conclude
that the normalization model for multi-tier mmWave cellular networks fully
meets requirements of network performance analysis, and it is simpler and
clearer than the untransformed model. Besides, an unexpected but sensible
finding is that there is an optimal beam width that maximizes coverage
probability in the case with beamforming alignment errors.Comment: 7 pages, 4 figure
Methyl eucomate
The crystal structure of the title compound [systematic name: methyl 3-carboxy-3-hydroxy-3-(4-hydroxybenzyl)propanoate], C12H14O6, is stabilized by intermolecular O—H⋯O and C—H⋯O hydrogen bonds. The molecules are arranged in layers, parallel to (001), which are interconnected by the O—H⋯O hydrogen bonds
Recommended from our members
Hypericin enhances β-lactam antibiotics activity by inhibiting sarA expression in methicillin-resistant Staphylococcus aureus.
Bacteremia is a life-threating syndrome often caused by methicillin-resistant Staphylococcus aureus (MRSA). Thus, there is an urgent need to develop novel approaches to successfully treat this infection. Staphylococcal accessory regulator A (SarA), a global virulence regulator, plays a critical role in pathogenesis and β-lactam antibiotic resistance in Staphylococcus aureus. Hypericin is believed to act as an antibiotic, antidepressant, antiviral and non-specific kinase inhibitor. In the current study, we investigated the impact of hypericin on β-lactam antibiotics susceptibility and mechanism(s) of its activity. We demonstrated that hypericin significantly decreased the minimum inhibitory concentrations of β-lactam antibiotics (e.g., oxacillin, cefazolin and nafcillin), biofilm formation and fibronectin binding in MRSA strain JE2. In addition, hypericin significantly reduced sarA expression, and subsequently decreased mecA, and virulence-related regulators (e.g., agr RNAⅢ) and genes (e.g., fnbA and hla) expression in the studied MRSA strain. Importantly, the in vitro synergistic effect of hypericin with β-lactam antibiotic (e.g., oxacillin) translated into in vivo therapeutic outcome in a murine MRSA bacteremia model. These findings suggest that hypericin plays an important role in abrogation of β-lactam resistance against MRSA through sarA inhibition, and may allow us to repurpose the use of β-lactam antibiotics, which are normally ineffective in the treatment of MRSA infections (e.g., oxacillin)
TiC: Exploring Vision Transformer in Convolution
While models derived from Vision Transformers (ViTs) have been phonemically
surging, pre-trained models cannot seamlessly adapt to arbitrary resolution
images without altering the architecture and configuration, such as sampling
the positional encoding, limiting their flexibility for various vision tasks.
For instance, the Segment Anything Model (SAM) based on ViT-Huge requires all
input images to be resized to 10241024. To overcome this limitation, we
propose the Multi-Head Self-Attention Convolution (MSA-Conv) that incorporates
Self-Attention within generalized convolutions, including standard, dilated,
and depthwise ones. Enabling transformers to handle images of varying sizes
without retraining or rescaling, the use of MSA-Conv further reduces
computational costs compared to global attention in ViT, which grows costly as
image size increases. Later, we present the Vision Transformer in Convolution
(TiC) as a proof of concept for image classification with MSA-Conv, where two
capacity enhancing strategies, namely Multi-Directional Cyclic Shifted
Mechanism and Inter-Pooling Mechanism, have been proposed, through establishing
long-distance connections between tokens and enlarging the effective receptive
field. Extensive experiments have been carried out to validate the overall
effectiveness of TiC. Additionally, ablation studies confirm the performance
improvement made by MSA-Conv and the two capacity enhancing strategies
separately. Note that our proposal aims at studying an alternative to the
global attention used in ViT, while MSA-Conv meets our goal by making TiC
comparable to state-of-the-art on ImageNet-1K. Code will be released at
https://github.com/zs670980918/MSA-Conv
3D Model-free Visual Localization System from Essential Matrix under Local Planar Motion
Visual localization plays a critical role in the functionality of low-cost
autonomous mobile robots. Current state-of-the-art approaches for achieving
accurate visual localization are 3D scene-specific, requiring additional
computational and storage resources to construct a 3D scene model when facing a
new environment. An alternative approach of directly using a database of 2D
images for visual localization offers more flexibility. However, such methods
currently suffer from limited localization accuracy. In this paper, we propose
an accurate and robust multiple checking-based 3D model-free visual
localization system to address the aforementioned issues. To ensure high
accuracy, our focus is on estimating the pose of a query image relative to the
retrieved database images using 2D-2D feature matches. Theoretically, by
incorporating the local planar motion constraint into both the estimation of
the essential matrix and the triangulation stages, we reduce the minimum
required feature matches for absolute pose estimation, thereby enhancing the
robustness of outlier rejection. Additionally, we introduce a multiple-checking
mechanism to ensure the correctness of the solution throughout the solving
process. For validation, qualitative and quantitative experiments are performed
on both simulation and two real-world datasets and the experimental results
demonstrate a significant enhancement in both accuracy and robustness afforded
by the proposed 3D model-free visual localization system
A novel fractional-order extended Kalman filtering method for on-line joint state estimation and parameter identification of the high power li-ion batteries.
To ensure the reliability and sustainability of the energy storage system, it is important to accurately estimate the state of charge of the battery management system. The Li-ion battery is established based on fractional-order model, and the model parameters are identified online using particle swarm optimization combined with the forgetting factor recursive least square method. On this basis, a novel fractional-order extended Kalman filter method for on-line joint state estimation and parameter identification is proposed. This method can update the parameter model of Li-ion battery in real-time, which not only improves the accuracy of the battery model but also improves the accuracy of SOC estimation. Finally, to verify the accuracy and superiority of the method, the integral order extended Kalman filter, fractional-order extended Kalman filter are compared with the proposed method under the BBDST test schedule. Experimental results show that the algorithm has the highest SOC estimation accuracy and the smallest estimation error (1.5 %.). The results indicate that the fractional-order model can better describe the dynamic characteristics of Li-ion battery, and the adaptive scheme can significantly suppress noise measurement errors and battery model errors. The algorithm realizes online parameter identification and can be used in engineering applications
- …