Chankil Lee

Surface-enhanced Raman scattering aptasensor for ultrasensitive trace analysis of bisphenol A.

Surface-enhanced Raman scattering (SERS)-based aptasensor platform, using double strand DNA-embedded Au/Ag core-shell nanoparticles, has been developed for the ultrasensitive detection of bisphenol A (BPA) in water. By combining optimally controlled Au/Ag core-shell nanoparticles with the selective BPA binding characteristics of DNA aptamers, a highly sensitive limit of detection (LOD) of 10 fM could be achieved for BPA-spiked tap water over a wide concentration range from 100 nM to 10 fM. This LOD is two or three orders of magnitude lower than that reported for other BPA sensing techniques, and also yields a detection limit that is 100-1000 times lower than the US EPA-defined Predicted No Effect Concentration (PNEC) values in potable water. Total detection time is estimated to be about 40 min including the reaction between aptamer and BPA (30 min) and detection (10 min). This sensing platform is also suitable for field applications since measurement can be performed under aqueous colloidal conditions.

Highly sensitive SERS-based immunoassay of aflatoxin B1 using silica-encapsulated hollow gold nanoparticles

Aflatoxin B1 (AFB1) is a well-known carcinogenic contaminant in foods. It is classified as an extremely hazardous compound because of its potential toxicity to the human nervous system. AFB1 has also been extensively used as a biochemical marker to evaluate the degree of food spoilage. In this study, a novel surface-enhanced Raman scattering (SERS)-based immunoassay platform using silica-encapsulated hollow gold nanoparticles (SEHGNs) and magnetic beads was developed for highly sensitive detection of AFB1. SEHGNs were used as highly stable SERS-encoding nano tags, and magnetic beads were used as supporting substrates for the high-density loading of immunocomplexes. Quantitative analysis of AFB1 was performed by monitoring the intensity change of the characteristic peaks of Raman reporter molecules. The limit of detection (LOD) of AFB1, determined by this SERS-based immunoassay, was determined to be 0.1 ng/mL. This method has some advantages over other analytical methods with respect to rapid analysis (less than 30 min), good selectivity, and reproducibility. The proposed method is expected to be a new analytical tool for the trace analysis of various mycotoxins.

Implementation of ZigBee-GSM based home security monitoring and remote control system

Home security and control is one of the basic needs of mankind from early days. But today it has to be updated with the rapidly changing technology to ensure vast coverage, remote control, reliability, and real time operation. Deploying wireless technologies for security and control in home automation systems offers attractive benefits along with user friendly interface. In this paper, implementation of a novel security and control system for home automation is presented. The proposed system consists of a control console interfaced with different sensors using ZigBee. Suspected activities are conveyed to remote user through SMS (Short Message Service) or Call using GSM (Global System for Mobile communication) technology. Upon reply, the remote user can control his premises again through GSM-ZigBee combination. Besides, traditional burglar alarm enhances security in case of no acknowledgment from remote user. This system offers a low cost, low power consumption and user friendly way of a reliable portable monitoring and control of the secured environment. Using the concept of serial communication and mobile phone AT-commands (Attention Telephone/Terminal commands), the software is programmed using C-language. The design has been implemented in the hardware using ZigBee EM357 module, Atmega128 MCU (microcontroller unit) and Sony Ericsson T290i mobile phone set.

Energy-Efficient Intelligent Street Lighting System Using Traffic-Adaptive Control

Lighting, both indoor and outdoor, consumes a substantial amount of energy, making improved efficiency a significant challenge. A promising approach to address outdoor lighting is the smart control of public lighting. Smart lighting using electronically controlled light-emitting diode (LED) lights for adaptable illumination and monitoring is being used to achieve an energy efficient system. However, the traffic engineering integrated with smart control for energy optimization has not been widely used. In this paper, a novel concept of traffic-flow-based smart (LED) street lighting for energy optimization is proposed. The developed smart grid architecture-based system uses low power ZigBee mesh network to provide maximum energy efficiency in response to adaptive traffic on the road. Moreover, the scalable wireless network of smart LED lights offers improved reliability, reduced cost, and more user satisfaction. In order to validate the performance, the proposed system was implemented and tested in a real environment inside a university campus. Experimental results show that in comparison with the replaced conventional metal halide lighting, our system is capable of 68%-82% energy savings depending on the variations in daylight hours between summer and winter. A significant reduction in greenhouse gases, improved overall system reliability, and reduced maintenance due to smart control suggests promising results for future wide-area deployment.

A fast moment method algorithm using spectral domain wavelet concepts

A multiresolution wavelet algorithm is developed for the fast solution of electromagnetic scattering problems. A multiscale feature of the spectral domain Greens function is observed in the joint spectral-spatial representation. Owing to the multiscale nature of the electrodynamic Greens function in the spectral domain, wavelet application in the spectral domain (KDWT) is more appropriate in representing the Greens function than the wavelet transform applied in the space domain (SDWT). Using the KDWT, a sparse moment impedance matrix, which is a discretized form of the Greens function, is obtained and a fast multiresolution moment method algorithm is developed in conjunction with the conjugate gradient solver. For a square cylinder the sparsity of the moment method matrix and the resulting time performance are compared with those from the conventional moment method. It is found that the KDWT algorithm leads to a matrix-vector multiplication which scales with an order less than N2.

Smart and Energy Efficient LED Street Light Control System Using ZigBee Network

The world is converging towards wireless as a communication channel and at the same time facing energy and environmental problems. The solution is by mingling the information technology (IT) and power. Streetlights are among a citys most important and expensive assets usually costs one third of the electricity bill. The proposed smart light control system outclasses the previous systems because it integrates the low power communication protocol Zig Bee with the LED lights. The system reduces the power of the LED lights according to outside conditions of light intensity as it has the ability to dim the lights. The initial experimental results show that it saves remarkable power as compared to conventional systems. This efficiency increases even two fold by considering the advantage of remotely monitoring and controlling the lights through the centralized point. Thus the proposed system is the cost effective and efficient system satisfying the needs of the modern users.

Energy Efficient Outdoor Light Monitoring and Control Architecture Using Embedded System

In this letter, we propose an energy efficient ZigBee-based outdoor light monitoring and control system that can monitor and handle outdoor lights more efficiently as compared to the conventional systems. The proposed system uses the ZigBee-based wireless devices which allow more efficient lamps management. The designed system uses sensors to control and guarantee the optimal system parameters. To realize effectiveness of the proposed system, the prototype has been installed inside the University, where the experimental results proved that the proposed system saves around 70.8% energy for the outdoor street environment because of using sensors, LED lamps, and ZigBee based communication network.

Maximizing throughput with wireless spectrum sensing network assisted cognitive radios

In a cognitive radio network (CRN), secondary users (SUs) utilize primary users (PUs) licensed spectrum in an opportunistic manner. Spectrum sensing is of the utmost importance in CRN to find and use the available spectrum without harmful interference to the PUs. Conventionally, to implement spectrum utilization, SUs are required to sense the primary spectrum first and then transmit data on the available spectrum. In this paper, we propose a dedicated wireless spectrum sensing network (WSSN), eliminating sensing overhead from SUs with the aim of improving achievable throughput. With WSSN assistance, we eliminate sensing time from the SUs frame, hence increasing the transmission time, which maximizes the achievable throughput. Additionally, the sensing duration is increased by deploying a dedicated WSSN, decreasing the probability of false alarm and achieving a targeted high probability of detection. A low probability of false alarm increases the spectrum utilization, improving the achievable throughput, while a high detection probability ensures PUs protection. Moreover, the proposed technique also addresses hidden and exposed terminal problems along with smooth spectrum mobility. Finally, we provide simulation results to demonstrate the proposed techniques, effectiveness. In the results, we have compared the achievable throughput of the proposed scheme with that of conventional CRN.

Macrocells-User Protected Interference-Aware Transmit Power Control for LTE-A Heterogeneous Networks

In Long Term Evolution-Advanced (LTE-A) heterogeneous networks (HetNets), small cells are deployed within the coverage area of macrocells having 1 : 1 frequency reuse. The coexistence of small cells and a macrocell in the same frequency band poses cross-tier interference which causes outage for macrocells users and/or small cell users. To address this problem, in this paper, we propose two algorithms that consider the received interference level at the evolved NodeB (eNB) while allocating transmit power to the users. In the proposed algorithm, the transmit power of all users is updated according to the target and instantaneous signal-to-noise-plus-interference ratio (SINR) condition as long as the effective received interference at the serving eNB is below the given threshold. Otherwise, if the effective received interference at the eNB is greater than the threshold, the transmit power of small cell users is gradually reduced in order to guarantee the target SINR for all macrocells users, aiming for zero-outage for macrocells users at the cost of an increased outage ratio for small cell users. Further, in the second algorithm, the transmit power of all users is additionally controlled by the power headroom report that considers the current channel condition while updating the transmit power which results in the outage ratio decreasing for small cell users. The extensive system-level simulations show significant improvements in the average throughput and outage ratio when compared with the conventional transmit power control technique.

Research on low-latency MAC protocols for wireless sensor networks

Energy-efficient should not be the only design goal in MAC protocols for wireless sensor networks, which involve the use of battery-operated computing and sensing devices. Low-latency operation becomes the same important as energy-efficient in the case that the traffic load is very heavy or the real-time constrain is used in applications like tracking or locating. This paper introduces some causes of traditional time delays which are inherent in a multi-hops network using existing WSN MAC protocols, illuminates the importance of low-latency MAC design for wireless sensor networks, and presents three MACs as examples of low-latency protocols designed specially for sleep delay, wait delay and wakeup delay in wireless sensor networks, respectively. The paper also discusses design trade-offs with emphasis on low-latency and points out their advantages and disadvantages, together with some design considerations and suggestions for MAC protocols for future applications and researches.