Kam-Yiu Lam

Kam-Yiu Lam
City University of Hong Kong | CityU · Department of Computer Science

Ph.D.

About

217
Publications
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1,991
Citations

Publications

Publications (217)
Article
Full-text available
In this paper, we study how to denoise medical ultrasound images and improve the performance of instance segmentation using deep learning technology. Since medical ultrasound images usually contain a lot of noises, we first propose a novel unsupervised learning approach called Dual Image (DI) for denoising of medical ultrasound images. DI consists...
Article
Full-text available
Background: Medication nonadherence represents a major burden on national health systems. According to the World Health Organization, increasing medication adherence may have a greater impact on public health than any improvement in specific medical treatments. More research is needed to better predict populations at risk of medication nonadherenc...
Article
Linguistic intelligence and the ability to converse with human are important and indispensable parts of humanoid robots. One of the most challenging tasks in knowledge-grounded task-oriented dialog systems (KTDS) is the knowledge selection task, which aims to find the proper knowledge snippets to respond to user dialog requests. In this paper, we f...
Article
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Background: From Ebola, Zika, to the latest COVID-19 pandemic, outbreaks of highly infectious diseases continue to reveal severe consequences of social and health inequalities. People from low socioeconomic and educational backgrounds as well as low health literacy tend to be affected by the uncertainty, complexity, volatility, and progressiveness...
Article
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Neural machine translation technologies are having increasing applications in clinical and healthcare settings. In multicultural countries, automatic translation tools provide critical support to medical and health professionals in their interaction and exchange of health messages with migrant patients with limited or non-English proficiency. While...
Article
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Background: Due to its convenience, wide availability, low usage cost, neural machine translation (NMT) has increasing applications in diverse clinical settings and web-based self-diagnosis of diseases. Given the developing nature of NMT tools, this can pose safety risks to multicultural communities with limited bilingual skills, low education, and...
Article
Although LSM-trees are commonly adopted in many NoSQLs as they can significantly improve the write performance in updating a database, most of the proposed LSM-trees are concentrated on storing single version of data. On the other hand, in many IoT applications, it is important to maintain the old versions of data in addition to the latest version....
Article
In this paper, we study the problem of fast constructions of source-wise round-trip spanners in weighted directed graphs. For a source vertex set S⊆V in a graph G(V,E), an S-sourcewise round-trip spanner of G of stretch k is a subgraph H of G such that for every pair of vertices u,v∈S×V, their round-trip distance in H is at most k times of their ro...
Preprint
In this paper, we study the problem of efficiently constructing source-wise round-trip spanners in weighted directed graphs. For a source vertex set $S\subseteq V$ in a digraph $G(V,E)$, an $S$-source-wise round-trip spanner of $G$ of stretch $k$ is a subgraph $H$ of $G$ such that for every $u\in S,v\in V$, the round-trip distance between $u$ and $...
Article
Passive indoor localization for mobile Wi-Fi devices, e.g., smartphones, has attracted increasing attention from research communities recently. Existing passive localization techniques leverage received signal strength (RSS) of packets transmitted by target Wi-Fi devices and do not require a dedicated software installed on the devices. However, RSS...
Article
When a shingle magnetic recording (SMR) drive has been widely applied to modern computer systems (e.g., archive file systems, big data computing systems, and large-scale database systems), storage system developers should thoroughly review whether current designs (e.g., index schemes and data placements) are appropriate for an SMR drive because of...
Article
We consider the problem of clustering graph nodes over large-scale dynamic graphs, such as citation networks, images and web networks, when graph updates such as node/edge insertions/deletions are observed distributively. We propose communication-efficient algorithms for two well-established communication models namely the message passing and the b...
Article
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Data dissemination in vehicular ad hoc networks (VANETs) has attracted researchers’ attention in recent years. However, due to high vehicle density in urban areas and increasing data volume, wireless interference seriously impairs data dissemination performance of a VANET. To alleviate the interference problem, we propose a cross-layer design to ex...
Article
Graph sparsification has been used to improve the computational cost of learning over graphs, e.g., Laplacian-regularized estimation, graph semisupervised learning (SSL) and spectral clustering (SC). However, when graphs vary over time, repeated sparsification requires polynomial order computational cost per update. We propose a new type of graph s...
Article
The VC-dimension, which has wide uses in learning theory, has been used in the analysis and design of graph algorithms recently. In this paper, we study the problem of bounding the VC-dimension of unique round-trip shortest path set systems (URTSP), which are set systems induced by sets of vertices in unique round-trip shortest paths in directed gr...
Article
Received signal strength (RSS)/channel state information (CSI) fingerprinting techniques have been widely adopted for wireless local area network (WLAN)-based indoor localization. However, in most of the RSS/CSI fingerprinting techniques, an application/software has to be installed on the target for uploading RSS/CSI information to the localization...
Preprint
We consider the problem of clustering graph nodes over large-scale dynamic graphs, such as citation networks, images and web networks, when graph updates such as node/edge insertions/deletions are observed distributively. We propose communication-efficient algorithms for two well-established communication models namely the message passing and the b...
Article
The world is experiencing an unprecedented, enduring, and pervasive aging process. With more people who need walking assistance, the demand for lower-extremity gait rehabilitation has increased rapidly over the years. The current clinical gait rehabilitative training requires heavy involvement of both medical doctors and physical therapists and thu...
Article
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In most process control systems nowadays, process measurements are periodically collected and archived in historians. Analytics applications process the data, and provide results offline or in a time period that is considerably slow in comparison to the performance of the manufacturing process. Along with the proliferation of Internet-of-Things (Io...
Article
In this paper, we study the deterministic construction of round-trip spanners for weighted directed graphs. We propose a deterministic algorithm which constructs, for any n-vertex graph G(V,E), a round-trip spanner H(V,E′⊆E) of stretch 2k+ϵ and size O((k/ϵ)⋅n1+1/klog⁡(nw)), where w is the maximum edge weight of G. Notably, this is the first determi...
Article
Although various air-indices, e.g., Next Region (NR), have been proposed to support shortest path and distance queries at mobile clients on a road network, how to minimize the energy cost, which is dominated by the cost for obtaining traffic data from data broadcast, is still one of the most important performance objectives. Inspired by various pre...
Article
Previous fingerprinting techniques proposed for sensor-based indoor localization assume that the fingerprint database is constructed by the measurement of received signal strength (RSS) at a fixed transmit power of the transmitter sensors (TSs). In order to improve the performance of the fingerprinting technique, we consider using the measurement o...
Article
In this paper, we study a new type of graph spanners, called source-wise round-trip spanners. Given any source vertex set in a directed graph , such a spanner (with stretch k) has the property that the round-trip shortest path distance from any vertex to any vertex is at most k times of their round-trip distance in G. We present an algorithm to con...
Article
Full-text available
In this paper, by applying motion detection and machine learning technologies, we have designed and developed an activity tracking and monitoring system, called SmartMind, to help Alzheimer’s Disease (AD) patients to live independently within their living rooms while providing emergency assistances and supports when necessary. Allowing AD patients...
Article
In this article, we study the indexing problem of using PCM as the storage medium for embedded multiversion databases in cyber-physical systems (CPSs). Although the multiversion B⁺-tree (MVBT) index has been shown to be efficient in managing multiple versions of data items in a database, MVBT is designed for databases residing in traditional block-...
Article
In this paper, by exploring the application characteristics of cyber-physical systems (CPS) and the performance characteristics of PCM, we propose a new B-tree index structure, called Linked Block-based Multi-Version B-Tree (LBMVBT), for indexing multi-version data in an embedded multi-version database for CPS. In LBMVBT, to reduce the number of wr...
Article
Although various efficient indexing techniques have been proposed to improve the performance in distributing road data to mobile clients to perform shortest path searches on road networks, how to minimize the tune-in and path searching costs are still important performance goals since the clients usually have limited processing capability and energ...
Article
Various efficient indexing techniques have been proposed for formulating broadcast index to minimize the tune-in cost at mobile clients to support shortest path search in a road network. However, none of them is designed for shortest path continuous queries (SPCQ). Due to frequent updates of traffic data, an SPCQ has to be invoked periodically whil...
Article
Full-text available
In this paper, we propose a novel pervasive business model for sales promotion in retail chain stores utilizing WLAN localization and near field communication (NFC) technologies. The objectives of the model are to increase the customers’ flow of the stores and their incentives in purchasing. In the proposed model, the NFC technology is used as the...
Article
In this paper, we propose a novel multi-version B$^+$ -tree index structure, called block-based multi-version B$^+$ -tree ( BbMVBT), for indexing multi-versions of data items in an embedded multi-version database (EMVDB ) on flash memory. An EMVDB needs to support streams of update transactions and version-range queries to access different versions...
Article
This paper describes SmartMood, a mood tracking and analysis system designed for patients with mania. By analyzing the voice data captured from a smartphone while the user is having a conversation, statistics are generated for each behavioral factor to quantitatively describe his/her mood status. By comparing the newly generated statistics with tho...
Article
Maintaining the freshness of real-time data is one of the crucial design issues in cyber-physical systems (CPS). Past studies have focused on designing update algorithms to minimize the workload imposed by a fixed set of update tasks while ensuring the temporal validity of data. In this paper, we revisit this problem in dynamic cyber-physical syste...
Chapter
Two of the major considerations in helping patients with Alzheimer's disease are: (1) the monitoring of activities to minimize the risk in their daily lives and (2) to reduce the worsening rate of the symptoms of Alzheimer's disease. By introducing our tracking and monitoring system, SmartMind, the authors demonstrate how the latest pervasive and s...
Chapter
Two of the major considerations in helping patients with Alzheimer’s disease are: (1) the monitoring of patients’ activities to minimize the risk in their daily lives and (2) to reduce the worsening rate of the symptoms of Alzheimer’s disease. By introducing our tracking and monitoring system, SmartMind, the authors demonstrate how the latest perva...
Article
Maintaining a multi-version index on flash memory could generate a lot of updates and invalid pages. It is important to have an efficient garbage collection mechanism to ensure the flash memory has sufficient number of free blocks for storing new data versions and their index structures. In this paper, we study the important performance issues in u...
Article
Many mission-critical and safety-critical applications in networked wireless sensing and control systems have stringent reliability requirements and timing constraints on end-to-end (E2E) packet delivery. Late arrivals of packets could severely degrade overall system performance and cause serious problems in system operation. In this paper, we stud...
Article
Recently, flash-based embedded databases have gained their momentum in various control and monitoring systems, such as cyber-physical systems (CPSes). To support the functionality to access the historical data, a multiversion index is adopted to simultaneously maintain multiple versions of data items, as well as their index information. However, ma...
Article
Embedded database systems are widely adopted in various control and motoring systems, e.g., cyber-physical systems (CPSes). To support the functionality to access the historical data, a multiversion index is adopted to maintain multiple versions of data items and their index information. However, CPSes are usually battery-powered embedded systems t...
Conference Paper
In this paper, we study how mobile computing and wireless technologies can be explored to provide effective ubiquitous healthcare services. Instead of reinventing the wheels, we make use of smartphones, off-the-shelf components, and existing technologies in ubiquitous computing (i.e. wireless and mobile positioning technologies, and data acquisitio...
Article
Full-text available
Although the deferrable scheduling algorithm for fixed priority transactions ( DS-FP) has been shown to provide a better performance compared with the More-Less (ML) method, there is still a lack of any comprehensive studies on the necessary and sufficient conditions for the schedulability of DS-FP. In this paper, we first analyze the necessary and...
Conference Paper
In this paper, we study the important performance issues in using the purging-range query to reclaim old data versions to be free blocks in a flash-based multi-version database. To reduce the overheads for using the purging-range query in garbage collection, the physical block labeling (PBL) scheme is proposed to provide a better estimation on the...
Article
Localization is an essential function for location-dependent services. Although various efficient localization methods have been proposed, many of them have not tested with practical applications. Different location-dependent applications may have very different performance and operation requirements such as the accuracy in localization and frequen...
Article
An important function of many cyber-physical systems (CPS) is to provide a close monitoring of the operation environment to be able to adapt to changing situations effectively. One of the commonly applied techniques for that is to invoke time-constrained periodic application transactions to check the status of the operation environment. The status...
Article
Maintaining sensor data validity while exercising timely control is crucial in real-time sensing and control systems. The goal of scheduling algorithms deployed in such systems is to maintain the validity of real-time sensor data so as to maximize the schedulability of update transactions with minimum update workload so that control actions occur o...
Article
Although in a multi-threaded processor, the processor may execute more than one process simultaneously to maximize the overall throughput of the system, the executing processes may compete with each other in using shared caches of the processor. This can seriously affect the average performance of the processes as the probability of cache hit for e...
Conference Paper
Although wireless local area networks (WLAN) have been shown to be an effective technique for localization of moving objects, their potential for business applications still have a lot of rooms for exploration. In this paper, we propose a novel business model for sales promotion in retail chain stores with the use of WLAN localization and near fiel...
Conference Paper
Advances in mobile technologies have continuously improved the capability and data access of mobile devices. High resolution camera, large multi-touch screen and improving data rate make video communication more ready to replace voice communication on mobile phones. However, connectivity and data rate are not guaranteed in mobile networks which mak...
Conference Paper
In typical location-based services (LBS), moving objects (e.g., GPS-enabled mobile phones) report their locations through a wireless network. An LBS server can use the location information to answer various types of continuous queries. Due to hardware limitations, location data reported by the moving objects are often uncertain. In this paper, we s...
Article
In this paper, we study the co-scheduling problem of periodic application transactions and update transactions in real-time database systems for surveillance of critical events. To perform the surveillance functions effectively, it is important to meet the deadlines of the application transactions and maintain the quality of the real-time data obje...
Article
Previous works on maintaining temporal consistency of real-time data objects mainly focuses on real-time database systems in which the transmission delays (jitters) of update jobs are simply ignored. However, this assumption does not hold in distributed real-time systems where the jitters of the update jobs can be large and change unpredictably wit...
Article
Full-text available
In a real-time database system for detection of critical events, meeting the deadlines of the application transactions and maintaining the quality of the real-time data objects are two critical issues in ensuring the effectiveness of performing the real-time monitoring tasks. Unfortunately, these two goals conflict with each other and are difficult...
Article
Full-text available
Although data broadcast has been shown to be an efficient method for disseminating data items in a mobile computing system with large number of clients, the issue on how to ensure the data consistency observed by mobile transactions, which are generated by mobile clients, has been largely ignored by researchers in the area. While data items are bei...
Article
Typical real-time sensing and control systems consist of a set of update tasks for installing sensor measurements from the operation environment and a set of control tasks to access to these measurements for making control decisions. Although configuring the sensors with higher sampling rates could improve the accuracy of the measurements and contr...
Article
Full-text available
Although the deferrable scheduling algorithm for fixed priority transactions (DS-FP) has been shown to be a very effective approach for minimizing real-time update transaction workload, it suffers from its on-line scheduling overhead. In this work, we propose two extensions of DS-FP to minimize the on-line scheduling overhead. The proposed algorith...
Article
Full-text available
The periodic update transaction model has been used to maintain freshness (or temporal validity) of real-time data. Period and deadline assignment has been the main focus in the past studies such as the More-Less scheme [25] in which update transactions are guaranteed by the Deadline Monotonic scheduling algorithm [16] to complete by their deadline...
Article
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In this paper, we propose integrated methods for concurrency control in mixed soft real-time database systems (MSRTDBS), which consist of both non-real-time and soft real-time transactions. The protocols should support the real-time processing of soft real-time transactions and, at the same time, to minimize the mean response time of non-real-time...
Chapter
Many applications use sensors extensively to capture and monitor the status of physical entities. In a habitat-monitoring system, for example, the temperature values of birds nests are investigated through the use of wireless sensor networks (Deshpande 2004). Sensors are also installed in different parts of the building, so that the temperature off...
Article
In a moving-object database system that supports continuous queries (CQ), an important problem is to keep the location data consistent with the actual locations of the entities being monitored, in order to produce correct query results. This goal is often difficult to achieve due to limited network resources. However, if an object is not required b...
Article
Full-text available
In this paper, we study the important issues in the design of an efficient wireless real-time visual surveillance system (WISES). Two important considerations are to minimize: (1) the video workload on the wireless network; and (2) the processing workload at the front-end video capturing unit. To achieve the first objective, we propose a cooperativ...
Article
In this paper, we study the bandwidth allocation problem for serving video requests in a mobile real-time video player system. One of the main issues to maintain the quality of services (QoS) in mobile video playback is to ensure sufficient number of video frames available at the client side while a video is being played. However, due to the limite...
Article
Full-text available
A common approach to improve the reliability of query results based on error-prone sensors is to introduce redundant sensors. However, using multiple sensors to generate the value for a data item can be expensive, especially in wireless environments where continuous queries are executed. Moreover, some sensors may not be working properly and their...
Chapter
Full-text available
Research in the concurrency control of real-time data access over mobile networks is receiving growing attention. With possibly lengthy transmission delay and frequent disconnection, traditional concurrency control mechanisms may become very costly and time-consuming in mobile distributed real-time database systems (MDRTDBS). Due to limited bandwid...
Article
Full-text available
The percentages of blocking and forced termination rates as parameters representing quality of services (QoS) requirements are presented. The relation between the connection statistics of mobile users in a cell and the handoff number and new call number in next duration in each cell is explored. Based on the relation, statistic reservation tactics...