Adaptive Pilot Signaling in the Uplink of OFDM-Based Wireless Systems

Orthogonal frequency division multiplexing (OFDM) has been considered as one of key transmission technologies for high-speed wireless communication systems. For channel-adaptive transmission of OFDM signal, base stations transmit a common pilot signal in the downlink, but mobile stations transmit individual pilot signal in the uplink. As a consequence, the uplink may suffer from poorer channel estimation accuracy than the downlink. This problem can be alleviated by increasing the pilot signal density. But this reduces the time and frequency resources for the data transmission, deteriorating the actual transmission throughput. In this paper, we propose an adaptive pilot signaling scheme that adjusts the pilot density in response to the change of channel characteristics. Simulation results show that the proposed scheme can remarkably reduce the pilot overhead without performance degradation, compared to conventional schemes

Hepatitis B Virus X Protein Impairs Hepatic Insulin Signaling Through Degradation of IRS1 and Induction of SOCS3

Hepatitis B virus (HBV) is a major cause of chronic liver diseases, and frequently results in hepatitis, cirrhosis, and ultimately hepatocellular carcinoma. The role of HCV in associations with insulin signaling has been elucidated. However, the pathogenesis of HBV-associated insulin signaling remains to be clearly characterized. Therefore, we have attempted to determine the mechanisms underlying the HBV-associated impairment of insulin signaling.The expressions of insulin signaling components were investigated in HBx-transgenic mice, HBx-constitutive expressing cells, and transiently HBx-transfected cells. Protein and gene expression was examined by Western blot, immunohistochemistry, RT-PCR, and promoter assay. Protein-protein interaction was detected by coimmunoprecipitation.HBx induced a reduction in the expression of IRS1, and a potent proteasomal inhibitor blocked the downregulation of IRS1. Additionally, HBx enhanced the expression of SOCS3 and induced IRS1 ubiquitination. Also, C/EBPalpha and STAT3 were involved in the HBx-induced expression of SOCS3. HBx interfered with insulin signaling activation and recovered the insulin-mediated downregulation of gluconeogenic genes.These results provide direct experimental evidences for the contribution of HBx in the impairment of insulin signaling

Frequency Block Hopping in the Uplink of OFDM- based Wireless Systems

In this paper, we consider the use of frequency block hopping in the uplink of orthogonal frequency division multiplexing (OFDM) based wireless systems. The hopping block size influences the channel estimation accuracy and thus affects the effective signal-to-noise power ratio (SNR) of the receiver as well as the diversity gain. The hopping block size is optimally determined to minimize the average error probability which is associated with the SNR and diversity gain. Simulation results show that the analytic design is practically applicable to various channel coding schemes.Seoul R&BD Progra

모바일 와이맥스 시스템에서 인접 셀 간섭 완화를 위한 채널 추정

In orthogonal frequency division multiplexing based wireless system, a pilot signal is often employed to estimate channel state information (CSI). However, the received pilot signal is interfered by other cell interference in multi-cell environments. We consider the estimation of CSI by utilizing orthogonal preambles and channel correlation.Seoul R&BD Progra

Suppression of magnetic ordering in XXZ-type antiferromagnetic monolayer NiPS3

How a certain ground state of complex physical systems emerges, especially in two-dimensional materials, is a fundamental question in condensed-matter physics. A particularly interesting case is systems belonging to the class of XY Hamiltonian where the magnetic order parameter of conventional nature is unstable in two-dimensional materials leading to a Berezinskii-Kosterlitz-Thouless transition. Here, we report how the XXZ-type antiferromagnetic order of a magnetic van der Waals material, NiPS3, behaves upon reducing the thickness and ultimately becomes unstable in the monolayer limit. Our experimental data are consistent with the findings based on renormalization group theory that at low temperatures a two-dimensional XXZ system behaves like a two-dimensional XY one, which cannot have a long-range order at finite temperatures. This work provides experimental examination of the XY magnetism in the atomically thin limit and opens new opportunities of exploiting these fundamental theorems of magnetism using magnetic van der Waals materials.Comment: 57 pages, 24 figures (including Supplementary Information

Blood culture contamination in hospitalized pediatric patients: a single institution experience

PurposeBlood culture is the most important tool for detecting bacteremia in children with fever. However, blood culture contamination rates range from 0.6% to 6.0% in adults; rates for young children have been considered higher than these, although data are limited, especially in Korea. This study determined the contamination rate and risk factors in pediatric patients visiting the emergency room (ER) or being admitted to the ward.MethodsWe conducted a retrospective chart review of blood cultures obtained from children who visited Yonsei Severance Hospital, Korea between 2006 and 2010. Positive blood cultures were labeled as true bacteremia or contamination according to Centers for Disease Control and Prevention/National Healthcare Safety Network definitions for laboratory-confirmed bloodstream infection, after exclusion of cultures drawn from preexisting central lines only.ResultsAmong 40,542 blood cultures, 610 were positive, of which 479 were contaminations and 131 were true bacteremia (overall contamination rate, 1.18%). The contamination rate in the ER was significantly higher than in the ward (1.32% vs. 0.66%, P6 years, respectively).ConclusionOverall, contamination rates were higher in younger children than in older children, given the difficulty of performing blood sampling in younger children. The contamination rates from the ER were higher than those from the ward, not accounted for only by overcrowding and lack of experience among personnel collecting samples. Further study to investigate other factors affecting contamination should be required

Reperfusion Injury after Autologous Cranioplasty in a Patient with Sinking Skin Flap Syndrome

The sinking skin flap syndrome is a rare complication after a large craniectomy. It consists of a sunken skin above the bone defect with neurological symptoms such as severe headache, mental changes, focal deficits, or seizures. In patient with sinking skin flap syndrome, cerebral blood flow and cerebral metabolism are decreased by sinking skin flap syndrome, and it may cause the deterioration of autoregulation of brain. We report a case of a patient with sinking skin flap syndrome who suffered from reperfusion injury after cranioplasty with review of pertinent literature