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Purpose The purpose of this paper is to introduce a low-cost quadrotor that can be used for educational purposes and investigate the applicability of a low-cost MEMS laser sensor for accurate altitude control. Design/methodology/approach A single printed circuit board is designed to form the structure of the quadrotor. A low-cost MEMS motion sensor, a microcontroller and four small motors are mounted on the board. A separate laser sensor module measures the altitude. A remote controller is designed to control the quadrotor’s motion. The remote controller communicates with the quadrotor via wireless connection. Roll and pitch attitude stabilization is achieved using the proportional and derivative control algorithm. The applicability of an MEMS laser sensor for altitude control is also studied. Findings The low-cost quadrotor works well even though its body structure is made using a printed circuit board. Low pass and Kalman filters work well for attitude estimation and control application. The laser sensor is very accurate and good for altitude feedback; however, it has a relatively short measurement range and its sampling rate is relatively slow, which limits its applications. The vertical velocity obtained by differentiating the laser altitude has delay and inhibits suitable damping. Using the vertical velocity obtained by integrating the vertical accelerometer’s output, the damping performance is improved. Originality/value Developing a low-cost quadrotor that can be used for educational purposes and successfully implementing altitude control using a laser sensor and accelerometer.

A microstructure-based integrated crystal plasticity (CP) and continuum damage mechanics (CDM) model is proposed for simulating rolling contact fatigue (RCF). The damage process through the formation of the dark etching region (DER) under RCF is implemented, i.e., a DER-CPCDM approach. A hierarchical microstructure of lath martensite is virtually generated by the Voronoi tessellation technique and the theoretical Kurdjumov-Sachs orientation relationship between the prior austenite grains and substructures of lath martensite. Moreover, the micro-plasticity calculated from the polycrystal finite element is coupled with dislocation-assisted carbon migration theory, which enables accurate predictions of the deformation inhomogeneity and the DER/damage distribution at the subsurface. The RCF lifespan of AISI 52100 bearing steel can be predicted within reasonable accuracy, in terms of Weibull probability analysis, when the jump-in-cycles approach is implemented in the DER-CPCDM model. The predicted representative lifespan of the Weibull plot is within an error of 13% when compared with reported experimental data. Process factors, including contact pressure, rotational speed, temperature, carbon concentration, and grain size, are analyzed in a numerical sensitivity study, which can be utilized for potential optimization of the RCF process for improving the performance of materials and parts.

A Crimp Force Monitor (CFM) is equipment for detecting crimp errors by analyzing crimp signals obtained from force and strain sensors. The analysis is commonly performed by aligning a measured crimp signal with a reference signal and comparing their difference. Current analysis methods often suffer from wrong alignments that result in false negative detections. This paper presents a new crimp signal analysis method in CFM. First, a falling edge alignment is proposed that matches falling edges of the measured and the reference signals by minimizing the absolute difference summation. Second, a signal parameter error is introduced to evaluate the crimp quality difference between the measured signal and the reference. For calculating the signal parameter error, part of a signal is identified and divided into several regions to maximize the signal parameter errors. Experiments showed that the proposed method can improve the signal alignment and accurately detect bad crimps especially with the strain sensor.

For next generation global navigation satellite systems, new carrier frequencies in Ku/V band are expected to emerge as a promising alternative to the current frequency windows in L band as they get severely congestive. In the case of higher frequency bands, signal attenuation phenomenon through the atmosphere is significantly different from the L band signal propagation. In this paper, a fundamental investigation is carried out to explore the Ku/V band as a candidate frequency band for a new global satellite navigation carrier signal, wherein specific attention is given to the effects of the dominant attenuation factors through the tropospheric propagation path. For a specific application, a candidate orbit preliminarily designed for the Korean regional satellite navigation system is adapted. Simulation results summarize that the Ku band can provide a promising satellite navigation implementation considering the present satellite’s power budget, while the V band still requires technical advances in satellite transceiver system implementations.

We propose a Multi-Satellite Data Model (MSDM) for the efcient database management of multi-satellite ground control systems; the paper also explains a satellite control data management method using MSDM. The MSDM can manipulate various data attributes without modifying the entity structure by adding tuples instead of new attributes to tables when a new data attribute is required for a specic satellite. Data for retired satellites are only used for analysis purposes. We propose a backup method that selects data for retired satellites by using SQL and backs them up in an analyzable table. In addition, we propose an SQL statement for nding candidate attributes that should be added or deleted according to continuous satellite launches and retirements. For the metadata specication in the attribute table, XML schema is dened and the semantics and characteristic information of the extended data are described using XML tag information.

Purpose – The purpose of this paper was to present the process of building hardware and software for a collision avoidance system of a quadrotor capable of an indoor autonomous flight. Design/methodology/approach – The system development was carried out in two steps. First, the quadrotor system was designed to mount mission equipments for an indoor flight. The prediction error minimization (PEM) method was used for system identification of the quadrotor, and the linear quadratic regulator (LQR) control method was used for the attitude control. Second, a collision detection system was realized by using a Kinect sensor, an embedded board and a ground control system (GCS). A Kinect sensor with embedded board can send the 3D depth information to GCS and then the GCS displays the 3D depth information with a warning message. Findings – As the controller design requires a linear model, the PEM method was used in system identification. The LQR was used in controller design. It was found that the use of the PEM me...

Electrospray and electrohydrodynamic (EHD) jet have been paid much attention to produce fine droplets or particles. However, although applying a constant voltage, meniscus fluctuation may occur because of the variation in electric field. There are various reasons for the change in electric field such as distance between a nozzle to a substrate, wetting condition, pressure drop, and liquid vaporization. The fluctuation of the meniscus during jetting may cause unstable jetting and spray, which results in non-uniform patterning or coating. To tackle this problem, this paper introduces an advanced control of applied voltage that keeps the meniscus stable. An image processing method called meniscus characterization is used to provide information about the meniscus shape to a controller as a feedback signal. In addition, this meniscus information is also used to evaluate an optimal voltage that is applied to the nozzle to improve the startup time in the spray and EHD ejection. The experiment results show that the shape of meniscus is stably maintained, the jetting and the electrospray also become stable and the jet startup time is reduced.

Recently, many unmanned aerial vehicle (UAV) studies have focused on small UAVs, because they are cost effective and suitable in dangerous indoor environments where human entry is limited. Map building through distance measurement is a key technology for the autonomous flight of small UAVs. In many researches for unmanned systems, distance could be measured by using laser range finders or stereo vision sensors. Even though a laser range finder provides accurate distance measurements, it has a disadvantage of high cost. Calculating the distance using a stereo vision sensor is straightforward. However, the sensor is large and heavy, which is not suitable for small UAVs with limited payload. This paper suggests a low-cost distance measurement system using a laser pointer and a monocular vision sensor. A method to measure distance using the suggested system is explained and some experiments on map building are conducted with these distance measurements. The experimental results are compared to the actual data and the reliability of the suggested system is verified.

Vision-based unmanned aerial vehicle (UAV) control is a core technology in global positioning system (GPS)-denied environments. However, small UAVs have difficulty processing image data in real time because of their limited payload capacity and relatively weak processor. Development of an image-processing system that is suitable for small UAVs is therefore needed. In this paper, an approach for a vision-based simultaneous localization and mapping (SLAM) system for small UAVs is suggested. For real-time localization, a method wherein Kanade-Lucas-Tomasi-based localization and tracking are performed within small UAVs in real time is adopted. At the same time, scale-invariant feature transform–based mapping and more accurate localization are performed at the ground-control station. A vision-based three-dimensional map-building method for small UAVs using a monocular camera is also proposed. The proposed method first extracts straight-line information from images and calculates their equations in thre...

PurposeThe purpose of this paper is to propose that the three‐dimensional information of obstacles should be identified to allow unmanned aerial vehicles (UAVs) to detect and avoid obstacles existing in their flight path.Design/methodology/approachFirst, the approximate outline of obstacles was detected using multi‐scale‐oriented patches (MOPS). At the same time, the spatial coordinates of feature points that exist in the internal outline of the obstacles were calculated through the scale‐invariant feature transform (SIFT) algorithm. Finally, the results from MOPS and the results from the SIFT algorithm were merged to show the three‐dimensional information of the obstacles.FindingsAs the method proposed in this paper reconstructs only the approximate outline of obstacles, a quick calculation can be done. Moreover, as the outline information is combined through SIFT feature points, detailed three‐dimensional information pertaining to the obstacles can be obtained.Practical implicationsThe proposed approach can be used efficiently in GPS‐denied environments such as certain indoor environments.Originality/valueFor the autonomous flight of small UAVs having a payload limit, this paper suggests a means of forming three‐dimensional information about obstacles with images obtained from a monocular camera.

In this paper, a closed-loop system constructed with a linear plant and nonlinearity in the feedback connection is considered to argue against its planar orbital stability. Through a state space approach, a main result that presents a sufficient stability criterion of the limit cycle predicted by solving the harmonic balance equation is given. Preliminarily, the harmonic balance of the nonlinear feedback loop is assumed to have a solution that determines the characteristics of the limit cycle. Using a state-space approach, the nonlinear loop equation is reformulated into a linear perturbed model through the introduction of a residual operator. By considering a series of transformations, such as a modified eigenstructure decomposition, periodic averaging, change of variables, and coordinate transformation, the stability of the limit cycle can be simply tested via a scalar function and matrix. Finally, the stability criterion is addressed by constructing a composite Lyapunov function of the transformed system.

Small unmanned aerial vehicles are cost-effective and easy to operate, and especially suitable in dangerous indoor environments. However, because GPS is not available in an indoor environment, indoor localization is a crucial problem in developing small unmanned aerial vehicles (UAVs). This paper suggests vision-based indoor localization for UAVs in GPS-denied environments. Our approach is based on image matching by applying the scale invariant feature transform algorithm.

In developing network-enabled embedded systems, developers are often forced to spend a great deal of time and effort analyzing and solving network performance problems. In this paper, we address one such problem: TCP performance interference on an asymmetric link. The upload or download throughput abruptly degrades if there is simultaneously upload and download TCP traffic on the link. While the problem has been addressed by many researchers, their solutions are incomplete as they only improve throughput in one direction, require TCP protocol modifications in end-user devices or are effective for a limited range of network configurations. In order to overcome such limitations, we propose ACKs-first variable-size queuing (AFVQ) for a gateway. In doing so, we have derived an analytic model of the steady-state TCP performance with bidirectional traffic to clearly identify the two sources of the problem: the excessive queuing delay of ACK packets and the excessive number of ACK packets in the queue. Our AFVQ mechanism is designed to directly eliminate the two causes. Specifically, we have based AFVQ on two policies. First, ACKs-first scheduling is used to shorten the queuing delay of ACK packets. Second, the queue size for ACK packets is dynamically adjusted depending on the number of data packets queued in the gateway so that the number of ACK packets is reduced when packets are congested in the gateway. By applying the two policies simultaneously at the uplink and downlink output queue in the gateway, AFVQ achieves balanced TCP throughput improvements in both directions. In this way, it breaks circular dependencies between upload and download traffic. We have implemented AFVQ in our ADSL-based residential gateway using the traffic control module of the Linux kernel. Our gateway yields 95.2% and 93.8% of the maximum download and upload bandwidth, respectively. We have also evaluated the proposed mechanism using the ns-2 simulator over a wide range of network configurations and have shown that AFVQ achieves better upload and download throughput than other representative gateway-based mechanisms such as ACQ, ACKs-first scheduling and ACK Filtering.

This study was conducted to evaluate the interaction between cryo-damage and ART outcome after cryopreservation of mouse ovarian tissues with different methods. Either a vitrification or a slow freezing was employed for the cryopreservation of B6CBAF1 mouse ovaries and follicle growth and the preimplantation development of intrafollicular oocytes following parthenogenesis or IVF were monitored. Both cryopreservation protocols caused significant damage to follicle components, including vacuole formation and mitochondrial deformities. Regardless of the cryopreservation protocols employed, a sharp (P < 0.0001) decrease in follicle viability and post-thaw growth was detected. When IVF program was employed, significant (P < 0.05) decrease in cleavage and blastocyst formation was notable in both modes of cryopreservation. However, such retardation was not found when oocytes were parthenogenetically activated. In the IVF oocytes, slow freezing led to better development than vitrification. In conclusion, a close relationship between cryopreservation and ART methods should be considered for the selection of cryopreservation program.

In implementing an INS/SLAM integrated navigation system based on the vision sensor, a suboptimal nonlinear filter is used to figure out the nonlinear characteristics in measurement and noise model. When a conventional centralized filter is used, however, the entire state vectors need to be reconfigured in every necessary cycle as the number of feature points changes, which is hard to isolate potential faults. Furthermore, any change in the number of feature points and a subsequent increase in the dimension of state variables may result in an exponential growth in computation quantities. In order to address these issues, this paper presents a distributed particle filter approach for implementing a vision sensor based INS/SLAM system. The proposed system has several local filters which are subject to change flexibly by the number of feature points, and separates state vectors into sub-states for vehicle dynamics and feature points so that minimum state vectors can be estimated in the master filter. Simulation results show that the distributed particle filter performs competitively as with the centralized particle filter and is capable of improving computation quantities.

An efficient Multidisciplinary Design and Optimization (MDO) framework for an aerospace engineering system should use and integrate distributed resources such as various analysis codes, optimization codes, Computer Aided Design (CAD) tools, Data Base Management Systems (DBMS), etc. in a heterogeneous environment, and need to provide user-friendly graphical user interfaces. In this paper, we propose a systematic approach for determining a reference MDO framework and for evaluating MDO frameworks. The proposed approach incorporates two well-known methods, Analytic Hierarchy Process (AHP) and Quality Function Deployment (QFD), in order to provide a quantitative analysis of the qualitative criteria of MDO frameworks. Identification and hierarchy of the framework requirements and the corresponding solutions for the reference MDO frameworks, the general one and the aircraft oriented one were carefully investigated. The reference frameworks were also quantitatively identified using AHP and QFD. An assessment of three in-house frameworks was then performed. The results produced clear and useful guidelines for improvement of the in-house MDO frameworks and showed the feasibility of the proposed approach for evaluating an MDO framework without a human interference.

In this paper, it is presented a novel approach for the self-sustained resonant accelerometer design, which takes advantages of an automatic gain control in achieving stabilized oscillation dynamics. Through the proposed system modeling and loop transformation, the feedback controller is designed to maintain uniform oscillation amplitude under dynamic input accelerations. The fabrication process for the mechanical structure is illustrated in brief. Computer simulation and experimental results show the feasibility of the proposed accelerometer design, which is applicable to a control grade inertial sense system.

Multiple ZnO nanorod device detecting gas was fabricated by sol-gel growth method and gas response characteristics were measured as a chemical gas sensor. The device is mainly composed of sensing electrode and sensing nano material. To acquire high sensitivity of the device for gas it was heated by a heat chuck up to The sensing part was easily made using the CMOS compatible process, for example, the large area and low temperature nano material growth process, etc. The sensors were successfully demonstrated and showed high sensitive response for gas sensing.

Delay analysis for superconductive Single Flux Quantum (SFQ) logic is performed for Self-Timing-Aligned Clock Synchronization Technique (STAC). With its pipelined-structure, the SFQ generates and propagates pulses that are to be processed sequentially through serial-connected functional logic blocks, and thus it is critical to acquire a ultra-high-speed and exactly synchronized clock/control signals with a few pico-second resolution. Both passive and Josephson-Junction circuits are investigated for the delay control. These delays, being connected in parallel with input line, and to the clocked-power/control node, produce a self-timing-aligned synchronization. Ways to achieve precision delays are seek by using Mo resistors along with junction inherent capacitors. Both current margins for the bias and critical timing information for the maximum throughput are also investigated. Layouts for the test SFQ circuits, such as D- and RS-flip-flops are done with XIC, and verifications are done through WRSpice with Hypres process parameters.

Multiple endocrine neoplasia type 1 (MEN1) is a familial cancer syndrome characterized by the combined occurrence of tumours of the parathyroid glands, pancreatic islet cells and anterior pituitary gland. Mutation analysis of the MEN1 gene has enabled the genetic diagnosis of patients with MEN1. Two MEN1-related disorders - familial isolated hyperparathyroidism (FIHP) and familial pituitary adenoma - are considered to be variants of MEN1, or at least to be incompletely expressed variants. Germline mutations of the MEN1 gene have been reported in some with FIHP, but familial pituitary adenoma usually lacks the MEN1 mutation and has been described as a genetically distinct disorder. In this work, we investigated five Korean families with MEN1, one family with FIHP and one family with familial pituitary adenoma. Polymerase chain reaction (PCR)-based single-strand conformation polymorphism (PCR-SSCP) analysis, denaturing high-performance liquid chromatography (DHPLC) and sequencing were used to detect the MEN1 mutations. Screening of the genetic variations of the MEN1 gene revealed four germline mutations in five typical MEN1 families. All four germline mutations led to truncated proteins or a change in the amino acids of the functional domains. In this study, we identified three novel MEN1 germline mutations (969C >A, 973G >C and 1213C >T) and one previously reported mutation (200-201insAGCCC). The frequency of the MEN1 germline mutation in Korean MEN1 families (four of five; 80%) was similar to those reported previously. In accordance with previous studies, no MEN1 germline mutation was detected in two families with FIHP or familial pituitary adenoma.

Juvenile polyposis (JP) is characterized by the development of multiple hamartomatous polyps and is inherited as an autosomal dominant trait. Germline mutations of the SMAD4 gene have been reported in JP. We have previously identified three SMAD4 germline mutations in five Korean JP patients. Recently, germline mutations of the BMPR1A (ALK3) gene were reported in JP cases without SMAD4 mutations. In order to determine whether BMPR1A could be involved in the development of JP, we screened all five patients using denaturing high-performance liquid chromatography (DHPLC) analysis. We found that one patient had a BMPR1A germline mutation without a SMAD4 mutation. This patient harbored a novel missense mutation (M470T) in exon 10. After close clinico-pathological examination, one patient who was previously diagnosed to have JP was excluded from the JP group. In total, all four Korean JP patients had either the SMAD4 or the BMPR1A mutation, with three having SMAD4 germline mutations and one carrying a BMPR1A germline mutation.

Discretely synchronized, distributed real-time systems may suffer from a time discontinuity problem in that local clocks observe the disappearance or reappearance of time intervals. This problem occurs since traditional discrete clock synchronization algorithms adjust local clocks instantaneously. Such time discontinuities may lead to runtime faults due to the loss or gain of critical time points such as task release times and deadlines. In this paper, we propose a dynamic constraint transformation technique we call a constraint transformation for equi-continuity (CTEC) to correctly enforce timing requirements in a distributed real-time system possessing periodically synchronized distributed local clocks. While continuous clock synchronization is generally suggested to avoid the time discontinuity problem, it incurs too much runtime overhead to be implemented in software. The proposed CTEC technique can solve the time discontinuity problem without modifying discrete clock synchronization algorithms. The CTEC, working as an added component of discrete clock synchronization, moves timing constraints out of discontinuous time intervals. In doing so, it makes use of a mapping derived from continuous clock synchronization in order to exploit its continuity property. We formally prove the correctness of CTEC by showing that the CTEC with discrete clock synchronization generates the same task schedule as continuous clock synchronization. In order to show the effectiveness of CTEC, we have implemented it on a distributed platform based on the CAN bus and performed extensive experiments. The experimental results indicate that time discontinuities present a consistency problem to real-world systems. They also show that CTEC is an effective solution to the problem while incurring little run-tine overhead.