370 research outputs found
The star cluster mass--galactocentric radius relation: Implications for cluster formation
Whether or not the initial star cluster mass function is established through
a universal, galactocentric-distance-independent stochastic process, on the
scales of individual galaxies, remains an unsolved problem. This debate has
recently gained new impetus through the publication of a study that concluded
that the maximum cluster mass in a given population is not solely determined by
size-of-sample effects. Here, we revisit the evidence in favor and against
stochastic cluster formation by examining the young ( a few yr-old) star cluster mass--galactocentric radius relation in M33, M51,
M83, and the Large Magellanic Cloud. To eliminate size-of-sample effects, we
first adopt radial bin sizes containing constant numbers of clusters, which we
use to quantify the radial distribution of the first- to fifth-ranked most
massive clusters using ordinary least-squares fitting. We supplement this
analysis with an application of quantile regression, a binless approach to
rank-based regression taking an absolute-value-distance penalty. Both methods
yield, within the to uncertainties, near-zero slopes in the
diagnostic plane, largely irrespective of the maximum age or minimum mass
imposed on our sample selection, or of the radial bin size adopted. We conclude
that, at least in our four well-studied sample galaxies, star cluster formation
does not necessarily require an environment-dependent cluster formation
scenario, which thus supports the notion of stochastic star cluster formation
as the dominant star cluster-formation process within a given galaxy.Comment: ApJ, in press, 39 pages in AAS preprint format, 10 multi-panel
figures (some reduced in size to match arXiv compilation routines
Solving the Pose Ambiguity via a Simple Concentric Circle Constraint
Estimating the pose of objects with circle feature from images is a basic and important question in computer vision community. This paper is focused on the ambiguity problem in pose estimation of circle feature, and a new method is proposed based on the concentric circle constraint. The pose of a single circle feature, in general, can be determined from its projection in the image plane with a pre-calibrated camera. However, there are generally two possible sets of pose parameters. By introducing the concentric circle constraint, interference from the false solution can be excluded. On the basis of element at infinity in projective geometry and the Euclidean distance invariant, cases that concentric circles are coplanar and non-coplanar are discussed respectively. Experiments on these two cases are performed to validate the proposed method
Herding Effect based Attention for Personalized Time-Sync Video Recommendation
Time-sync comment (TSC) is a new form of user-interaction review associated
with real-time video contents, which contains a user's preferences for videos
and therefore well suited as the data source for video recommendations.
However, existing review-based recommendation methods ignore the
context-dependent (generated by user-interaction), real-time, and
time-sensitive properties of TSC data. To bridge the above gaps, in this paper,
we use video images and users' TSCs to design an Image-Text Fusion model with a
novel Herding Effect Attention mechanism (called ITF-HEA), which can predict
users' favorite videos with model-based collaborative filtering. Specifically,
in the HEA mechanism, we weight the context information based on the semantic
similarities and time intervals between each TSC and its context, thereby
considering influences of the herding effect in the model. Experiments show
that ITF-HEA is on average 3.78\% higher than the state-of-the-art method upon
F1-score in baselines.Comment: ACCEPTED for ORAL presentation at IEEE ICME 201
CALD : surviving various application-layer DDoS attacks that mimic flash crowd
Distributed denial of service (DDoS) attack is a continuous critical threat to the Internet. Derived from the low layers, new application-layer-based DDoS attacks utilizing legitimate HTTP requests to overwhelm victim resources are more undetectable. The case may be more serious when suchattacks mimic or occur during the flash crowd event of a popular Website. In this paper, we present the design and implementation of CALD, an architectural extension to protect Web servers against various DDoS attacks that masquerade as flash crowds. CALD provides real-time detection using mess tests but is different from other systems that use resembling methods. First, CALD uses a front-end sensor to monitor thetraffic that may contain various DDoS attacks or flash crowds. Intense pulse in the traffic means possible existence of anomalies because this is the basic property of DDoS attacks and flash crowds. Once abnormal traffic is identified, the sensor sends ATTENTION signal to activate the attack detection module. Second, CALD dynamically records the average frequency of each source IP and check the total mess extent. Theoretically, the mess extent of DDoS attacks is larger than the one of flash crowds. Thus, with some parameters from the attack detection module, the filter is capable of letting the legitimate requests through but the attack traffic stopped. Third, CALD may divide the security modules away from the Web servers. As a result, it keeps maximum performance on the kernel web services, regardless of the harassment from DDoS. In the experiments, the records from www.sina.com and www.taobao.com have proved the value of CALD
Data-Free Quantization with Accurate Activation Clipping and Adaptive Batch Normalization
Data-free quantization is a task that compresses the neural network to low
bit-width without access to original training data. Most existing data-free
quantization methods cause severe performance degradation due to inaccurate
activation clipping range and quantization error, especially for low bit-width.
In this paper, we present a simple yet effective data-free quantization method
with accurate activation clipping and adaptive batch normalization. Accurate
activation clipping (AAC) improves the model accuracy by exploiting accurate
activation information from the full-precision model. Adaptive batch
normalization firstly proposes to address the quantization error from
distribution changes by updating the batch normalization layer adaptively.
Extensive experiments demonstrate that the proposed data-free quantization
method can yield surprisingly performance, achieving 64.33% top-1 accuracy of
ResNet18 on ImageNet dataset, with 3.7% absolute improvement outperforming the
existing state-of-the-art methods.Comment: submitted to ICML202
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