Showing papers by "Pusan National University published in 2011"

A gravitational wave observatory operating beyond the quantum shot-noise limit

Abstract: Around the globe several observatories are seeking the first direct detection of gravitational waves (GWs). These waves are predicted by Einstein’s general theory of relativity1 and are generated, for example, by black-hole binary systems2. Present GW detectors are Michelson-type kilometre-scale laser interferometers measuring the distance changes between mirrors suspended in vacuum. The sensitivity of these detectors at frequencies above several hundred hertz is limited by the vacuum (zero-point) fluctuations of the electromagnetic field. A quantum technology—the injection of squeezed light3—offers a solution to this problem. Here we demonstrate the squeezed-light enhancement of GEO 600, which will be the GW observatory operated by the LIGO Scientific Collaboration in its search for GWs for the next 3–4 years. GEO 600 now operates with its best ever sensitivity, which proves the usefulness of quantum entanglement and the qualification of squeezed light as a key technology for future GW astronomy4.

Centrality Dependence of the Charged-Particle Multiplicity Density at Midrapidity in Pb-Pb Collisions at root s(NN)=2.76 TeV

Abstract: The centrality dependence of the charged-particle multiplicity density at midrapidity in Pb-Pb collisions at root s(NN) = 2: 76 TeV is presented. The charged-particle density normalized per participating nucleon pair increases by about a factor of 2 from peripheral (70%-80%) to central (0%-5%) collisions. The centrality dependence is found to be similar to that observed at lower collision energies. The data are compared with models based on different mechanisms for particle production in nuclear collisions.

Higher harmonic anisotropic flow measurements of charged particles in Pb-Pb collisions at root s(NN)=2.76 TeV

Abstract: We report on the first measurement of the triangular nu(3), quadrangular nu(4), and pentagonal nu(5) charged particle flow in Pb-Pb collisions at root s(NN) = 2.76 TeV measured with the ALICE detector at the CERN Large Hadron Collider. We show that the triangular flow can be described in terms of the initial spatial anisotropy and its fluctuations, which provides strong constraints on its origin. In the most central events, where the elliptic flow nu(2) and nu(3) have similar magnitude, a double peaked structure in the two-particle azimuthal correlations is observed, which is often interpreted as a Mach cone response to fast partons. We show that this structure can be naturally explained from the measured anisotropic flow Fourier coefficients.

A High-Speed Sliding-Mode Observer for the Sensorless Speed Control of a PMSM

Abstract: This paper proposes a sensorless speed control strategy for a permanent-magnet synchronous motor (PMSM) based on a new sliding-mode observer (SMO), which substitutes a sigmoid function for the signum function with a variable boundary layer. In order to apply a sensorless PMSM control which is robust against parameter fluctuations and disturbances, a high-speed SMO is proposed, which estimates the rotor position and the angular velocity from the back EMF. In the conventional SMO, a low-pass filter and an additional position compensation of the rotor are used to reduce the chattering problem that is commonly found in the SMO using the signum function. In order to overcome the time delay caused by the low-pass filter, in this research, a sigmoid function is used for the switching function instead of the signum function. Also, the variation in the stator resistance is estimated to improve the steady-state performance of the SMO. The stability of the proposed SMO was verified using the Lyapunov second method to determine the observer gain. The validity of the proposed high-speed PMSM sensorless velocity control has been demonstrated with simulations and real experiments.

Intravenous delivery of a multi-mechanistic cancer-targeted oncolytic poxvirus in humans

Abstract: Oncolytic viruses, either natural or engineered, preferentially infect and lyse tumour cells. David Kirn and colleagues now report a phase I clinical trial in which they demonstrate systemic delivery of the engineered oncolytic virus JX-594 selectively to tumour tissue after a single injection. Tumour biopsies indicate that the virus replicates in cancer but not in adjacent normal tissue. JX-594 is engineered to replicate in a broad spectrum of cancer cells harbouring activation of the epidermal growth factor receptor/Ras pathway. Although the trial was not designed to demonstrate clinical efficacy, the results suggest that JX-594 may elicit a clinical response in some patients. The efficacy and safety of biological molecules in cancer therapy, such as peptides and small interfering RNAs (siRNAs), could be markedly increased if high concentrations could be achieved and amplified selectively in tumour tissues versus normal tissues after intravenous administration. This has not been achievable so far in humans. We hypothesized that a poxvirus, which evolved for blood-borne systemic spread in mammals, could be engineered for cancer-selective replication and used as a vehicle for the intravenous delivery and expression of transgenes in tumours. JX-594 is an oncolytic poxvirus engineered for replication, transgene expression and amplification in cancer cells harbouring activation of the epidermal growth factor receptor (EGFR)/Ras pathway, followed by cell lysis and anticancer immunity1. Here we show in a clinical trial that JX-594 selectively infects, replicates and expresses transgene products in cancer tissue after intravenous infusion, in a dose-related fashion. Normal tissues were not affected clinically. This platform technology opens up the possibility of multifunctional products that selectively express high concentrations of several complementary therapeutic and imaging molecules in metastatic solid tumours in humans.

Synthesis and Drug-Delivery Behavior of Chitosan-Functionalized Graphene Oxide Hybrid Nanosheets

Abstract: Chitosan-functionalized graphene oxides (FGOCs) were successfully synthesized. FGOCs were found to significantly improve the solubility of the GO in aqueous acidic media. The presence of organic groups was confirmed by means of XPS and TGA. Restoration of the sp2 carbon network and exfoliation of graphene sheets were confirmed by Raman spectroscopy, UV-visible spectroscopy and WAXD. The SEM and AFM investigations of the resultant FGOCs showed that most of the graphene sheets were individual and few were layered. Controlled release behavior of Ibuprofen and 5-fluorouracil was then investigated. We found that FGOCs are a promising new material for biological and medical applications.

Stretchable, Transparent Graphene Interconnects for Arrays of Microscale Inorganic Light Emitting Diodes on Rubber Substrates

Abstract: This paper describes the fabrication and design principles for using transparent graphene interconnects in stretchable arrays of microscale inorganic light emitting diodes (LEDs) on rubber substrates. We demonstrate several appealing properties of graphene for this purpose, including its ability to spontaneously conform to significant surface topography, in a manner that yields effective contacts even to deep, recessed device regions. Mechanics modeling reveals the fundamental aspects of this process, as well as the use of the same layers of graphene for interconnects designed to accommodate strains of 100% or more, in a completely reversible fashion. These attributes are compatible with conventional thin film processing and can yield high-performance devices in transparent layouts. Graphene interconnects possess attractive features for both existing and emerging applications of LEDs in information display, biomedical systems, and other environments.

Parkin is transcriptionally regulated by ATF4: evidence for an interconnection between mitochondrial stress and ER stress.

Abstract: Loss of parkin function is responsible for the majority of autosomal recessive parkinsonism. Here, we show that parkin is not only a stress-protective, but also a stress-inducible protein. Both mitochondrial and endoplasmic reticulum (ER) stress induce an increase in parkin-specific mRNA and protein levels. The stress-induced upregulation of parkin is mediated by ATF4, a transcription factor of the unfolded protein response (UPR) that binds to a specific CREB/ATF site within the parkin promoter. Interestingly, c-Jun can bind to the same site, but acts as a transcriptional repressor of parkin gene expression. We also present evidence that mitochondrial damage can induce ER stress, leading to the activation of the UPR, and thereby to an upregulation of parkin expression. Vice versa, ER stress results in mitochondrial damage, which can be prevented by parkin. Notably, the activity of parkin to protect cells from stress-induced cell death is independent of the proteasome, indicating that proteasomal degradation of parkin substrates cannot explain the cytoprotective activity of parkin. Our study supports the notion that parkin has a role in the interorganellar crosstalk between the ER and mitochondria to promote cell survival under stress, suggesting that both ER and mitochondrial stress can contribute to the pathogenesis of Parkinson's disease.

Genome-wide association study identifies FCGR2A as a susceptibility locus for Kawasaki disease.

Abstract: Kawasaki disease is a systemic vasculitis of unknown etiology, with clinical observations suggesting a substantial genetic contribution to disease susceptibility. We conducted a genome-wide association study and replication analysis in 2,173 individuals with Kawasaki disease and 9,383 controls from five independent sample collections. Two loci exceeded the formal threshold for genome-wide significance. The first locus is a functional polymorphism in the IgG receptor gene FCGR2A (encoding an H131R substitution) (rs1801274; P = 7.35 × 10(-11), odds ratio (OR) = 1.32), with the A allele (coding for histadine) conferring elevated disease risk. The second locus is at 19q13, (P = 2.51 × 10(-9), OR = 1.42 for the rs2233152 SNP near MIA and RAB4B; P = 1.68 × 10(-12), OR = 1.52 for rs28493229 in ITPKC), which confirms previous findings(1). The involvement of the FCGR2A locus may have implications for understanding immune activation in Kawasaki disease pathogenesis and the mechanism of response to intravenous immunoglobulin, the only proven therapy for this disease.

Using marine macroalgae for carbon sequestration: a critical appraisal

Abstract: There has been a good deal of interest in the potential of marine vegetation as a sink for anthropogenic C emissions (“Blue Carbon”). Marine primary producers contribute at least 50% of the world’s carbon fixation and may account for as much as 71% of all carbon storage. In this paper, we analyse the current rate of harvesting of both commercially grown and wild-grown macroalgae, as well as their capacity for photosynthetically driven CO2 assimilation and growth. We suggest that CO2 acquisition by marine macroalgae can represent a considerable sink for anthropogenic CO2 emissions and that harvesting and appropriate use of macroalgal primary production could play a significant role in C sequestration and amelioration of greenhouse gas emissions.

Production of pions, kaons and protons in pp collisions at root s=900 GeV with ALICE at the LHC

Abstract: The production of π+, π−, K+, K−, p, and \(\overline{\mathrm{p}}\) at mid-rapidity has been measured in proton-proton collisions at \(\sqrt{s} = 900~\mathrm{GeV}\) with the ALICE detector. Particle identification is performed using the specific energy loss in the inner tracking silicon detector and the time projection chamber. In addition, time-of-flight information is used to identify hadrons at higher momenta. Finally, the distinctive kink topology of the weak decay of charged kaons is used for an alternative measurement of the kaon transverse momentum (pt) spectra. Since these various particle identification tools give the best separation capabilities over different momentum ranges, the results are combined to extract spectra from pt=100 MeV/c to 2.5 GeV/c. The measured spectra are further compared with QCD-inspired models which yield a poor description. The total yields and the mean pt are compared with previous measurements, and the trends as a function of collision energy are discussed.

A smart polysaccharide/drug conjugate for photodynamic therapy.

Abstract: Recent improvements in drug-carrier design for photodynamic therapy (PDT) have brought about significant advances for treating skin, breast, and lung tumors. The local high-dose strategy of PDT suggests beneficial therapeutic efficacy with high selectivity when using photosensitizing drugs for the target site, as well as reduced side effects for normal tissues. A variety of drug-carrying vehicles, such as nanoparticles, drug conjugates, and polymeric micelles have frequently exhibited characteristics that may make possible the successful delivery of photosensitizing drugs, thus improving cell entry and residence in tumor sites. However, these approaches have, thus far, achieved rather limited success, owing primarily to the practical obstacles inherent to natural in vivo conditions. In this study, we describe a novel molecular “Trojan horse” system that quickly switches into an aggressive molecule for tumor destruction within the environment of the tumor. Advances in functionality have enabled our system to exhibit an intelligent switch from a threedimensional supramolecular assembly (i.e., self-quenched state of photosensitizing drugs) into extended random molecules (i.e., dequenched state for singlet-oxygen production), which corresponds to a change in surface charge (Figure 1). This system may be more significant than any known photosensitizing drug conjugate thus far developed.

Graphite Oxides as Effective Fire Retardants of Epoxy Resin

Abstract: Graphite oxides (GOs) at various oxidation states were examined as fire retardants of epoxy resin. Excessive oxidation is detrimental to the fire retardant effect of GO because it generated a weak GO with reduced intumescent ability. GO manifested optimum fire retardant properties when it was properly oxidized due to the effective intumescence, demonstrating that intumescent GO needs to be strong enough to effectively push the epoxy resin matrix apart to cause efficient intumescence and generate a solid remnant char that acts as an efficient barrier. The fire retardant effect of GO was also reduced when a dispersion of GO in the epoxy resin was enhanced by sonication. This shows that the fine dispersion and disordering of layered structure of GO by the intercalation of epoxy molecules into the gallery of GO also reduced the intumescent ability, and the fire retardant effects of GO.

A role for interleukin-2 trans -presentation in dendritic cell–mediated T cell activation in humans, as revealed by daclizumab therapy

Abstract: Dendritic cells produce interleukin-2 (IL-2) and express the IL-2 receptor subunit CD25. Bibiana Bielekova and her colleagues show that dendritic cells, upon interacting with cognate T cells, secrete IL-2 into the immune synapse and use their CD25 to trans-present IL-2 to T cells, facilitating early IL-2 signaling in T cells. Inhibition of CD25 by the monoclonal antibody daclizumab prevents T cell activation and may partly account for the therapeutic effects of daclizumab in patients with multiple sclerosis.

Active Synchronizing Control of a Microgrid

Abstract: A microgrid is an aggregation of multiple distributed generators (DGs), such as renewable energy sources, conventional generators, and energy storage systems that provide both electric power and thermal energy. Typically, a microgrid operates in parallel with the main grid. However, there are cases in which a microgrid operates in an islanded mode, or in a disconnected state. Islanded microgrid can change its operational mode to grid-connected operation by reconnection to the grid, which is referred to as synchronization. Generally, a single machine simply synchronizes with the grid using a synchronizer. However, the synchronization of microgrids that operate with multiple DGs and loads cannot be controlled by a traditional synchronizer. It is needed to control multiple generators and energy storage systems in a coordinated way for the microgrid synchronization. This is not a simple problem, considering that a microgrid consists of various power electronics-based DGs as well as alternator-based generators that produce power together. This paper proposes an active synchronizing control scheme that adopts the network-based coordinated control of multiple DGs. From the simulation results using Simulink dynamic models, it is shown that the scheme provides the microgrid with a deterministic and reliable reconnection to the grid. The proposed method is verified by using the test cases with the experimental setup of a practical microgrid pilot plant.