158 research outputs found
OMG: How Much Should I Pay Bob in Truthful Online Mobile Crowdsourced Sensing?
Mobile crowdsourced sensing (MCS) is a new paradigm which takes advantage of
the pervasive smartphones to efficiently collect data, enabling numerous novel
applications. To achieve good service quality for a MCS application, incentive
mechanisms are necessary to attract more user participation. Most of existing
mechanisms apply only for the offline scenario where all users' information are
known a priori. On the contrary, we focus on a more real scenario where users
arrive one by one online in a random order. We model the problem as an online
auction in which the users submit their private types to the crowdsourcer over
time, and the crowdsourcer aims to select a subset of users before a specified
deadline for maximizing the total value of the services provided by selected
users under a budget constraint. We design two online mechanisms, OMZ and OMG,
satisfying the computational efficiency, individual rationality, budget
feasibility, truthfulness, consumer sovereignty and constant competitiveness
under the zero arrival-departure interval case and a more general case,
respectively. Through extensive simulations, we evaluate the performance and
validate the theoretical properties of our online mechanisms.Comment: 14 pages, 8 figure
Tether-cutting Reconnection between Two Solar Filaments Triggering Outflows and a Coronal Mass Ejection
Triggering mechanisms of solar eruptions have long been a challenge. A few
previous case studies have indicated that preceding gentle filament merging via
magnetic reconnection may launch following intense eruption, according with the
tether-cutting (TC) model. However, detailed process of TC reconnection between
filaments has not been exhibited yet. In this work, we report the high
resolution observations from the Interface Region Imaging Spectrometer (IRIS)
of TC reconnection between two sheared filaments in NOAA active region 12146.
The TC reconnection commenced since 15:35 UT on 2014 August 29 and triggered an
eruptive GOES C4.3-class flare 8 minutes later. An associated coronal mass
ejection appeared in the field of view of SOHO/LASCO C2 about 40 minutes later.
Thanks to the high spatial resolution of IRIS data, bright plasma outflows
generated by the TC reconnection are clearly observed, which moved along the
subarcsecond fine-scale flux tube structures in the erupting filament. Based on
the imaging and spectral observations, the mean plane-of-sky and line-of-sight
velocities of the TC reconnection outflows are separately measured to be 79 and
86 km/s, which derives an average real speed of 120 km/s. In addition, it is
found that spectral features, such as peak intensities, Doppler shifts, and
line widths in the TC reconnection region evidently enhanced compared with
those in the nearby region just before the flare.Comment: Accepted for publication in ApJLette
PVSS: A Progressive Vehicle Search System for Video Surveillance Networks
This paper is focused on the task of searching for a specific vehicle that
appeared in the surveillance networks. Existing methods usually assume the
vehicle images are well cropped from the surveillance videos, then use visual
attributes, like colors and types, or license plate numbers to match the target
vehicle in the image set. However, a complete vehicle search system should
consider the problems of vehicle detection, representation, indexing, storage,
matching, and so on. Besides, attribute-based search cannot accurately find the
same vehicle due to intra-instance changes in different cameras and the
extremely uncertain environment. Moreover, the license plates may be
misrecognized in surveillance scenes due to the low resolution and noise. In
this paper, a Progressive Vehicle Search System, named as PVSS, is designed to
solve the above problems. PVSS is constituted of three modules: the crawler,
the indexer, and the searcher. The vehicle crawler aims to detect and track
vehicles in surveillance videos and transfer the captured vehicle images,
metadata and contextual information to the server or cloud. Then multi-grained
attributes, such as the visual features and license plate fingerprints, are
extracted and indexed by the vehicle indexer. At last, a query triplet with an
input vehicle image, the time range, and the spatial scope is taken as the
input by the vehicle searcher. The target vehicle will be searched in the
database by a progressive process. Extensive experiments on the public dataset
from a real surveillance network validate the effectiveness of the PVSS
Two Successive Type II Radio Bursts Associated with B-class Flares and Slow CMEs
From 2018 Oct 12 to 13, three successive solar eruptions (E1--E3) with
B-class flares and poor white light coronal mass ejections (CMEs) occurred from
the same active region NOAA AR 12724. Interestingly, the first two eruptions
are associated with Type II radio bursts but the third is not. Using the soft
X-ray flux data, radio dynamic spectra and dual perspective EUV intensity
images, we comparatively investigate the three events. Our results show that
their relevant flares are weak (B2.1, B7.9 and B2.3) and short-lived (13, 9 and
14 minutes). The main eruption directions of E1 and E2 are along
45 north of their radial directions, while E3 primarily
propagated along the radial direction. In the EUV channels, the early speeds of
the first two CMEs have apparent speeds of 320 km s and 380
km s, which could exceed their respective local Alfvn speeds
of 300 km s and 350 km s. However, the CME in the
third eruption possesses a much lower speed of 160 km s. These
results suggest that the observed Type II radio bursts in the eruptions E1 and
E2 are likely triggered by their associated CMEs and the direction of eruption
and the ambient plasma and magnetic environments may take an important place in
producing Type II radio burst or shock as well.Comment: 9 figures and 1 tabl
KTAN: Knowledge Transfer Adversarial Network
To reduce the large computation and storage cost of a deep convolutional
neural network, the knowledge distillation based methods have pioneered to
transfer the generalization ability of a large (teacher) deep network to a
light-weight (student) network. However, these methods mostly focus on
transferring the probability distribution of the softmax layer in a teacher
network and thus neglect the intermediate representations. In this paper, we
propose a knowledge transfer adversarial network to better train a student
network. Our technique holistically considers both intermediate representations
and probability distributions of a teacher network. To transfer the knowledge
of intermediate representations, we set high-level teacher feature maps as a
target, toward which the student feature maps are trained. Specifically, we
arrange a Teacher-to-Student layer for enabling our framework suitable for
various student structures. The intermediate representation helps the student
network better understand the transferred generalization as compared to the
probability distribution only. Furthermore, we infuse an adversarial learning
process by employing a discriminator network, which can fully exploit the
spatial correlation of feature maps in training a student network. The
experimental results demonstrate that the proposed method can significantly
improve the performance of a student network on both image classification and
object detection tasks.Comment: 8 pages, 2 figure
Generalized Zero-Shot Learning for Action Recognition with Web-Scale Video Data
Action recognition in surveillance video makes our life safer by detecting
the criminal events or predicting violent emergencies. However, efficient
action recognition is not free of difficulty. First, there are so many action
classes in daily life that we cannot pre-define all possible action classes
beforehand. Moreover, it is very hard to collect real-word videos for certain
particular actions such as steal and street fight due to legal restrictions and
privacy protection. These challenges make existing data-driven recognition
methods insufficient to attain desired performance. Zero-shot learning is
potential to be applied to solve these issues since it can perform
classification without positive example. Nevertheless, current zero-shot
learning algorithms have been studied under the unreasonable setting where seen
classes are absent during the testing phase. Motivated by this, we study the
task of action recognition in surveillance video under a more realistic
\emph{generalized zero-shot setting}, where testing data contains both seen and
unseen classes. To our best knowledge, this is the first work to study video
action recognition under the generalized zero-shot setting. We firstly perform
extensive empirical studies on several existing zero-shot leaning approaches
under this new setting on a web-scale video data. Our experimental results
demonstrate that, under the generalize setting, typical zero-shot learning
methods are no longer effective for the dataset we applied. Then, we propose a
method for action recognition by deploying generalized zero-shot learning,
which transfers the knowledge of web video to detect the anomalous actions in
surveillance videos. To verify the effectiveness of our proposed method, we
further construct a new surveillance video dataset consisting of nine action
classes related to the public safety situation
Multi-Granularity Reasoning for Social Relation Recognition from Images
Discovering social relations in images can make machines better interpret the
behavior of human beings. However, automatically recognizing social relations
in images is a challenging task due to the significant gap between the domains
of visual content and social relation. Existing studies separately process
various features such as faces expressions, body appearance, and contextual
objects, thus they cannot comprehensively capture the multi-granularity
semantics, such as scenes, regional cues of persons, and interactions among
persons and objects. To bridge the domain gap, we propose a Multi-Granularity
Reasoning framework for social relation recognition from images. The global
knowledge and mid-level details are learned from the whole scene and the
regions of persons and objects, respectively. Most importantly, we explore the
fine-granularity pose keypoints of persons to discover the interactions among
persons and objects. Specifically, the pose-guided Person-Object Graph and
Person-Pose Graph are proposed to model the actions from persons to object and
the interactions between paired persons, respectively. Based on the graphs,
social relation reasoning is performed by graph convolutional networks.
Finally, the global features and reasoned knowledge are integrated as a
comprehensive representation for social relation recognition. Extensive
experiments on two public datasets show the effectiveness of the proposed
framework
Untwisting and Disintegration of a Solar Filament Associated with Photospheric Flux Cancellation
Using the high-resolution observations from New Vacuum Solar Telescope (NVST)
jointly with the Solar Dynamics Observatory data, we investigate two successive
confined eruptions (Erup1 and Erup2) of a small filament in a decaying active
region on 2017 November 10. During the process of Erup1, the overlying magnetic
arcade is observed to inflate with the rising filament at beginning and then
stop the ongoing of the explosion. In the hot EUV channel, a coronal sigmoidal
structure appears during the first eruption and fade away after the second one.
The untwisting rotation and disintegration of the filament in Erup2 are clearly
revealed by the NVST H_alpha intensity data, hinting at a pre-existing twisted
configuration of the filament. By tracking two rotating features in the
filament, the average rotational angular velocity of the unwinding filament is
found to be ~10.5 degree/min. A total twist of ~1.3 pi is estimated to be
stored in the filament before the eruption, which is far below the criteria for
kink instability. In the course of several hours prior to the event, some
photospheric flux activities, including the flux convergence and cancellation,
are detected around the northern end of the filament, where some small-scale
EUV brightenings are also captured. Moreover, strongly-sheared transverse
fields are found in the cancelling magnetic features from the vector
magnetograms. Our observational results support the flux cancellation model, in
which the interaction between the converging and sheared opposite-polarity
fluxes destabilizes the filament and triggers the ensuing ejection.Comment: Accepted to be published in the Ap
Generalized Lottery Trees: Budget-Consistent Incentive Tree Mechanisms for Crowdsourcing
Incentive mechanism design has aroused extensive attention for crowdsourcing
applications in recent years. Most research assumes that participants are
already in the system and aware of the existence of crowdsourcing tasks.
Whereas in real life scenarios without this assumption, it is a more effective
way to leverage incentive tree mechanisms that incentivize both users' direct
contributions and solicitations to other users. Although some such mechanisms
have been investigated, we are the first to propose budget-consistent incentive
tree mechanisms, called generalized lottrees, which require the total payout to
all participants to be consistent with the announced budget, while guaranteeing
several other desirable properties including continuing contribution incentive,
continuing solicitation incentive, value proportional to contribution,
unprofitable solicitor bypassing, and unprofitable sybil attack. Moreover, we
present three types of generalized lottree mechanisms, 1-Pachira, K-Pachira,
and Sharing-Pachira, which support more diversified requirements. A solid
theoretical guidance to the mechanism selection is provided as well based on
the Cumulative Prospect Theory. Both extensive simulations and realistic
experiments with 82 users have been conducted to confirm our theoretical
analysis.Comment: 14 pages, 22 figure
Language Guided Networks for Cross-modal Moment Retrieval
We address the challenging task of cross-modal moment retrieval, which aims
to localize a temporal segment from an untrimmed video described by a natural
language query. It poses great challenges over the proper semantic alignment
between vision and linguistic domains. Existing methods independently extract
the features of videos and sentences and purely utilize the sentence embedding
in the multi-modal fusion stage, which do not make full use of the potential of
language. In this paper, we present Language Guided Networks (LGN), a new
framework that leverages the sentence embedding to guide the whole process of
moment retrieval. In the first feature extraction stage, we propose to jointly
learn visual and language features to capture the powerful visual information
which can cover the complex semantics in the sentence query. Specifically, the
early modulation unit is designed to modulate the visual feature extractor's
feature maps by a linguistic embedding. Then we adopt a multi-modal fusion
module in the second fusion stage. Finally, to get a precise localizer, the
sentence information is utilized to guide the process of predicting temporal
positions. Specifically, the late guidance module is developed to linearly
transform the output of localization networks via the channel attention
mechanism. The experimental results on two popular datasets demonstrate the
superior performance of our proposed method on moment retrieval (improving by
5.8\% in terms of [email protected] on Charades-STA and 5.2\% on TACoS). The source
code for the complete system will be publicly available
- …