Hayoung Oh

An energy-efficient sensor routing scheme for home automation networks

In the emerging ubiquitous home, sensors are placed everywhere in the house and collect various physical data such as temperature, humidity, and light to provide information to consumer electronics devices. The devices are then automatically activated if necessary. For example, the ventilator works when the air is foul and the heating system performs according to the weather and the existence of people in the house. Because sensors have limited battery power, energy-efficient routing is important. In this paper, we present a new sensor routing scheme that provides energy-efficient data delivery from sensors to the home base station. The proposed scheme divides the home area into sectors and locates a manager node to each sector. The manager node receives collected data from sensors and delivers the data to the base station through the shortest path of the 2-dimensional (x, y) coordinates. Performance results show that the proposed scheme reduces energy consumption significantly compared with conventional sensor routing schemes.

A seamless handover scheme in IPv6-based mobile networks

With the rapid development of wireless technologies, the need to support moving hosts of IPv6-based mobile networks in ubiquitous is growing. Various well-known approaches to optimising the handover latency have been proposed in the literature: MIPv6, FMIPv6, HMIPv6 and F-HMIPv6. However, these approaches are inefficient in packet loss, out-of order problem, dependency of exact predictive information and a sudden disruption of the link. In this paper, we propose a seamless handover scheme with temporal reuse of Care of Addresses (CoAs) and Packet Buffering Point (PBP) in IPv6-Based mobile networks.

An Energy-Efficient Sensor Routing with low latency, scalability in Wireless Sensor Networks

Energy efficiency, low latency, scalability are important requirements for wireless sensor networks. Specially, because sensor nodes are usually battery powered, and highly resource constrained, energy- efficient routing sensor routing scheme with low latency, scalability in wireless sensor networks is very important. In this paper, we present a sensor routing scheme, EESR (energy-efficient sensor routing) that provides energy-efficient data delivery from sensors to the base station. The proposed scheme divides the area into sectors and locates a manager node to each sector. The manager node receives collected data from sensor devices in its corresponding sector and then transfers the data to the base station through the shortest path of the 2-dimensional (x, y) coordinates. In this process, we use relative direction based routing in the 2- dimensional (x, y) coordinates in wireless sensor networks. Via analysis and simulation, we show that the proposed scheme achieve significant energy savings and outperform idealized transitional schemes (e.g., broadcasting, directed diffusion, clustering) under the investigated scenarios.

Robust Sybil attack defense with information level in online Recommender Systems

As the major function of Recommender Systems (RSs) is recommending commercial items to potential consumers (i.e., system users), providing correct information of RS is crucial to both RS providers and system users. The influence of RS over Online Social Networks (OSNs) is expanding rapidly, whereas malicious users continuously try to attack the RSs with fake identities (i.e., Sybils) by manipulating the information in the RS adversely. In this paper, we propose a novel robust recommendation algorithm called RobuRec which exploits a distinctive feature, admission control. RobuRec provides highly trusted recommendation results since RobuRec predicts appropriate recommendations regardless of whether the ratings are given by honest users or by Sybils thanks to the power of admission control. To demonstrate the performance of RobuRec, we have conducted extensive experiments with various datasets as well as diverse attack scenarios. The evaluation results confirm that RobuRec outperforms the comparable schemes such as PCA and LTSMF significantly in terms of Prediction Shift (PS) and Hit Ratio (HR).

Increased risk of acute kidney injury associated with higher infusion rate of mannitol in patients with intracranial hemorrhage

OBJECT Mannitol, an osmotic agent used to decrease intracranial pressure, can cause acute kidney injury (AKI). The objectives of this study were to assess the impact of mannitol on the incidence and severity of AKI and to identify risk factors and outcome for AKI in patients with intracranial hemorrhage (ICH). METHODS The authors retrospectively evaluated 153 adult patients who received mannitol infusion after ICH between January 2005 and December 2009 in the neurosurgical intensive care unit. Multivariate analysis was used to evaluate the risk factors for AKI after ICH. Based on the odds ratio, weighted scores were assigned to predictors of AKI. RESULTS The overall incidence of AKI among study participants was 10.5% (n = 16). Acute kidney injury occurred more frequently in patients who received mannitol infusion at a rate ≥ 1.34 g/kg/day than it did in patients who received mannitol infusion at a rate < 1.34 g/kg/day. A higher mannitol infusion rate was associated with more severe AKI. Independent risk factors for AKI were mannitol infusion rate ≥ 1.34 g/kg/day, age ≥ 70 years, diastolic blood pressure (DBP) ≥ 110 mm Hg, and glomerular filtration rate < 60 ml/min/1.73 m(2). The authors developed a risk model for AKI, wherein patients with a higher risk score showed a graded association with a higher incidence of AKI. CONCLUSIONS The incidence of AKI following mannitol infusion in patients with ICH was 10.5%. A higher mannitol infusion rate was associated with more frequent and more severe AKI. Additionally, age ≥ 70 years, DBP ≥ 110 mm Hg, and established renal dysfunction before starting mannitol therapy were associated with development of AKI.

A Flow-Based Hybrid Mechanism to Improve Performance in NOX and Wireless OpenFlow Switch Networks

With the advantage of practical way to experiment with new network protocols in realistic settings, NOX and OpenFlow switch networks are becoming extremely popular. However, because of basic characteristics of NOX and OpenFlow switch based on the separation between control and data plane, every OpenFlow switch faces a long transmission and retransmission delay when it fails to transmit its data. Until now, the virtualized programmable networks only consider how to achieve the throughput for the direct link between OpenFlow switches. Since wireless channel experiences different conditions and NOX and OpenFlow switch networks supports the maximum flow size threshold, the aggregated flow size of a neighbor OpenFlow switch may be delivered faster than through the direct link if the neighbor link has higher RSS (Received Signal Strength). In this paper, we propose a flow-based hybrid mechanism to improve performance in NOX and wireless OpenFlow switch networks. The main idea of this scheme is that when the transmission of a OpenFlow switch fails, one of neighbor OpenFlow switches with better channel condition transmits the lost frame as well as the own data using flow aggregation scheme. To do so, every OpenFlow switch should manage overhear table to buffer the transmitted packets that is not yet acknowledged. We also present algorithms to retransmit lost packets, to maintain the overhear table and to compensate for the retransmission of packets of other OpenFlow switches. Simulation results show that the proposed flow-based hybrid mechanism can significantly improve the system throughput and the throughput gain.

PSD: Practical Sybil detection schemes using stickiness and persistence in online recommender systems

The main function of recommender systems (RSs) is to recommend user-customized information to customers or system users. Correct and useful information is crucial for both customers and service providers. The influence of RSs is expanding over the Internet. However, criminal users try to manipulate the results of RSs with fake identities (i.e., Sybils) for financial gain. Effective metrics are consequently required for defense against Sybil attack. In this paper, we first explore two metrics, stickiness and persistence, from the perspective of the RS security domain. We then propose practical detecting schemes, Dynamic Sybil Attack Monitoring on Recommender Systems (DySy-Rec) and Fuzzy rule-based DySy-Rec (FDySy-Rec), which apply stickiness and persistence in two real datasets from real movie RSs. To demonstrate the effectiveness and potential of DySy-Rec and FDySy-Rec, we conducted extensive experiments on the inclusion of more diverse and smart types of attacks. The experimental results show that the proposed schemes achieve substantial performance improvement compared with previous statistical approaches in terms of precision and recall. Finally, the results confirm the practical possibilities of exploiting stickiness and persistence in the fight against dynamic Sybil attacks in online RSs.

An Efficient Security Management in IPv6 Network via MCGA

IPv6 has appeared for solving the address exhaustion of IPv4 and for guaranteeing the problems of security and QoS. It occurs because of the unexpected new attacks of IPv6 as well as the existing attacks of IPv4 because of the increasing address space to 128 bits and the address hierarchies for efficient network management and additions of the new messages between nodes and routers like neighbor discovery and auto address configuration for the various comfortable services. For the successful transition from IPv4 to IPv6, we should get the secure compatibility between IPv4 hosts or routers working based on secure and systematic policy and IPv6. The network manager should design security technologies for efficient management in IPv4/IPv6 co-existence network and IPv6 network and security management framework designation. In this paper, we inspected the characteristics of IPv4 and IPv6, study the security requirement for efficient security management of various attacks, protocol, service in IPv4/IPv6 co-existence and IPv6 network, and finally suggest solution about security vulnerability of IPv6 network in considering MCGA (modified cryptographically generated address).

Risk Factors for Renal Functional Decline in Chronic Hepatitis B Patients Receiving Oral Antiviral Agents

AbstractRenal functional decline that is frequently seen during chronic hepatitis B (CHB) treatment can exert adverse effects on overall prognosis. It, however, is difficult to distinguish vulnerable patients who may experience renal dysfunction because most previous CHB studies were conducted in relatively healthy individuals. In this retrospective observational study, renal functional decline in CHB patients receiving oral antiviral agents for more than 6 months was analyzed and risk factors of chronic kidney disease (CKD) progression were determined.Renal functional decline was defined when the estimated glomerular filtration rate (eGFR) decreased by more than 25% from baseline and rapid CKD progression was defined as eGFR decreased by more than 5 mL/min/1.73 m2/y among patients who experienced renal functional decline.A total of 4178 patients were followed up for a median 23 months. Antiviral agents included lamivudine (17.0%), adefovir (3.7%), entecavir (70.4%), telbivudine (0.6%), tenofovir (4.0%), or clevudine (4.3%). Renal functional decline occurred in 706 (16.9%) patients. Based on multivariate Cox regression analysis, age, hypertension, diabetes, history of liver or kidney transplantation, underlying underlying CKD, and simultaneous administration of diuretics increased the hazard ratio for renal functional decline; however, clevudine reduced risk. The eGFR significantly increased over time in patients receiving telbivudine or clevudine compared with lamivudine. Among the 3175 patients followed up for more than 1 year, 407 (12.8%) patients experienced rapid CKD progression. Patients with rapid CKD progression showed lower serum albumin, higher total bilirubin, and prolonged prothrombin time compared with patients with stable renal function, but hepatitis B envelope antigen positivity and hepatitis B virus deoxyribonucleic acid level did not differ between the control and rapid CKD progression groups. Age, diabetes, kidney transplantation, underlying CKD, and simultaneous administration of diuretics were identified as risk factors for rapid CKD progression, and clevudine showed a beneficial effect.Age, hypertension, diabetes, liver or kidney transplantation, underlying CKD, and diuretics were identified as risk factors for renal functional decline. This study suggests that close monitoring of renal function and adequate management are required for CHB patients receiving antiviral agents with these risk factors.

Effect of losartan on proteinuria and urinary angiotensinogen excretion in non-diabetic patients with chronic kidney disease

Purpose Activation of the rennin–angiotensin system (RAS) is thought to contribute to hypertension and proteinuria, and eventually to the progression of chronic kidney disease (CKD). Recent evidence suggests that urinary angiotensinogen (UAGT) excretion reflects activation of the intrarenal RAS. This study was performed to determine the effect of losartan on proteinuria and UAGT excretion in non-diabetic patients with CKD with non-nephrotic-range proteinuria. Study design Thirty-two patients with non-nephrotic-range proteinuria (0.045–0.23 g/mmol creatinine) and normal renal function between April 2005 and April 2006 were randomised to a losartan (n=17) or a control (n=15) group. Patients in the losartan group received losartan 50 mg/day, and the doses were titrated up to 100 mg/day after 6 weeks. Serum and urinary angiotensinogen concentrations were measured by sandwich ELISA. The primary end point was the percentage change in proteinuria. The secondary end points were changes in estimated glomerular filtration rate and UAGT excretion. The follow-up period was 24 months. Results Baseline characteristics in the two groups were similar. After 24 months, losartan had reduced urinary protein excretion by 43% (from mean±SD 0.13±0.04 to 0.073±0.03 g/mmol, p<0.0001), but proteinuria had not changed in the control group. The percentage change in mean arterial pressure did not differ between the groups. Losartan decreased logarithmically converted UAGT excretion (from 1.58±0.47 to 1.00±0.52, p=0.001). Estimated glomerular filtration rate decreased significantly only in the control group. Conclusion Losartan significantly decreased proteinuria and UAGT excretion, and preserved renal function in non-diabetic patients with CKD.