Showing papers by "Korea Institute of Science and Technology Information published in 2012"

A single-atom transistor

Abstract: The ability to control matter at the atomic scale and build devices with atomic precision is central to nanotechnology. The scanning tunnelling microscope can manipulate individual atoms and molecules on surfaces, but the manipulation of silicon to make atomic-scale logic circuits has been hampered by the covalent nature of its bonds. Resist-based strategies have allowed the formation of atomic-scale structures on silicon surfaces, but the fabrication of working devices-such as transistors with extremely short gate lengths, spin-based quantum computers and solitary dopant optoelectronic devices-requires the ability to position individual atoms in a silicon crystal with atomic precision. Here, we use a combination of scanning tunnelling microscopy and hydrogen-resist lithography to demonstrate a single-atom transistor in which an individual phosphorus dopant atom has been deterministically placed within an epitaxial silicon device architecture with a spatial accuracy of one lattice site. The transistor operates at liquid helium temperatures, and millikelvin electron transport measurements confirm the presence of discrete quantum levels in the energy spectrum of the phosphorus atom. We find a charging energy that is close to the bulk value, previously only observed by optical spectroscopy.

Observation of two charged bottomoniumlike resonances in Υ(5S) decays.

Abstract: We report the observation of two narrow structures in the mass spectra of the pi(+/-) Y(nS) (n = 1, 2, 3) and pi(+/-) h(b)(mP) (m = 1, 2) pairs that are produced in association with a single charged pion in Y(5S) decays The measured masses and widths of the two structures averaged over the five final states are M-1 = (10 6072 +/- 20) MeV/c(2), Gamma(1) =(184 +/- 24) MeV, and M-2 = (10 6522 +/- 15) MeV/c(2), Gamma(2) = (115 +/- 22) MeV The results are obtained with a 1214 fb(-1) data sample collected with the Belle detector in the vicinity of the Y(5S) resonance at the KEKB asymmetric-energy e(+)e(-) collider

Flavonoid-mediated inhibition of SARS coronavirus 3C-like protease expressed in Pichia pastoris

Abstract: The 3C-like protease (3CLpro) of severe acute respiratory syndrome associated coronavirus (SARS-CoV) is vital for SARS-CoV replication and is a promising drug target. Recombinant 3CLpro was expressed in Pichia pastoris GS115 as a 42 kDa protein that displayed a K m of 15 ± 2 μM with Dabcyl-KTSAVLQSGFRKME-Edans as substrate. Purified 3CLpro was used for inhibition and kinetic assays with seven flavonoid compounds. The IC50 of six flavonoid compounds were 47–381 μM. Quercetin, epigallocatechin gallate and gallocatechin gallate (GCG) displayed good inhibition toward 3CLpro with IC50 values of 73, 73 and 47 μM, respectively. GCG showed a competitive inhibition pattern with K i value of 25 ± 1.7 μM. In molecular docking experiments, GCG displayed a binding energy of −14 kcal mol−1 to the active site of 3CLpro and the galloyl moiety at 3-OH position was required for 3CLpro inhibition activity.

J/psi Suppression at Forward Rapidity in Pb-Pb Collisions at root s(NN)=2.76 TeV

Abstract: The ALICE experiment has measured the inclusive J/psi production in Pb-Pb collisions at root s(NN) = 2.76 TeV down to zero transverse momentum in the rapidity range 2.5 < y < 4. A suppression of the inclusive J/psi yield in Pb-Pb is observed with respect to the one measured in pp collisions scaled by the number of binary nucleon-nucleon collisions. The nuclear modification factor, integrated over the 0%-80% most central collisions, is 0.545 +/- 0.032(stat) +/- 0.083dsyst_ and does not exhibit a significant dependence on the collision centrality. These features appear significantly different from measurements at lower collision energies. Models including J/psi production from charm quarks in a deconfined partonic phase can describe our data.

Search for gravitational waves from low mass compact binary coalescence in LIGO's sixth science run and Virgo's science runs 2 and 3

Abstract: We report on a search for gravitational waves from coalescing compact binaries using LIGO and Virgo observations between July 7, 2009, and October 20, 2010. We searched for signals from binaries with total mass between 2 and 25M(circle dot); this includes binary neutron stars, binary black holes, and binaries consisting of a black hole and neutron star. The detectors were sensitive to systems up to 40 Mpc distant for binary neutron stars, and further for higher mass systems. No gravitational-wave signals were detected. We report upper limits on the rate of compact binary coalescence as a function of total mass, including the results from previous LIGO and Virgo observations. The cumulative 90% confidence rate upper limits of the binary coalescence of binary neutron star, neutron star-black hole, and binary black hole systems are 1.3 x 10(-4), 3.1 x 10(-5), and 6.4 x 10(-6) Mpc(-3) yr(-1), respectively. These upper limits are up to a factor 1.4 lower than previously derived limits. We also report on results from a blind injection challenge.

Measurement of γγ *→π0 transition form factor at Belle

Abstract: We report a measurement of the process gamma gamma* -> pi(0) with a 759 fb(-1) data sample recorded with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. The pion transition form factor, F(Q(2)), is measured for the kinematical region 4 GeV2 <= Q(2) <= 40 GeV2, where -Q(2) is the invariant-mass squared of a virtual photon. The measured values of Q(2)vertical bar F(Q(2))vertical bar agree well with the previous measurements below Q(2) similar or equal to 9 GeV2 but do not exhibit the rapid growth in the higher Q(2) region seen in another recent measurement, which exceeds the asymptotic QCD expectation by as much as 50%.

Combination of the top-quark mass measurements from the Tevatron collider

Abstract: We thank the Fermilab staff and technical staffs of the participating institutions for their vital contributions and acknowledge support from the DOE and NSF (USA), ARC (Australia), CNPq, FAPERJ, FAPESP, and FUNDUNESP (Brazil), NSERC (Canada), NSC, CAS, and CNSF (China), Colciencias (Colombia), MSMT and GACR (Czech Republic), the Academy of Finland, CEA, and CNRS/IN2P3 (France), BMBF and DFG (Germany), DAE and DST (India), SFI (Ireland), INFN (Italy), MEXT (Japan), the Korean World Class University Program and NRF (Korea), CONACyT (Mexico), FOM (Netherlands), MON, NRC KI, and RFBR (Russia), the Slovak R&D Agency, the Ministerio de Ciencia e Innovacio´n, and Programa Consolider-Ingenio 2010 (Spain), The Swedish Research Council (Sweden), SNSF (Switzerland), STFC and the Royal Society (United Kingdom), and the A. P. Sloan Foundation (USA).

Measurement of charm production at central rapidity in proton-proton collisions at √s = 2.76 TeV

Abstract: The p t-differential production cross sections of the prompt (B feed-down subtracted) charmed mesons D0, D+, and D*+ in the rapidity range |y| < 0.5, and for transverse momentum 1 < p t < 12 GeV/c, were measured in proton-proton collisions at $ \sqrt {s} = 2.76\;{\text{TeV}} $ with the ALICE detector at the Large Hadron Collider. The analysis exploited the hadronic decays D0 → K−π+, D+ → K−π+π+, D*+ → D0π+, and their charge conjugates, and was performed on a $ {\mathcal{L}_{{{\rm int} }}} = 1.1\;{\text{n}}{{\text{b}}^{{ - 1}}} $ event sample collected in 2011 with a minimum-bias trigger. The total charm production cross section at $ \sqrt {s} = 2.76\;{\text{TeV}} $ and at 7 TeV was evaluated by extrapolating to the full phase space the p t-differential production cross sections at $ \sqrt {s} = 2.76\;{\text{TeV}} $ and our previous measurements at $ \sqrt {s} = 7\;{\text{TeV}} $ . The results were compared to existing measurements and to perturbative-QCD calculations. The fraction of $ {\text{c}}\overline {\text{d}} $ D mesons produced in a vector state was also determined.

Search for gravitational waves associated with gamma-ray bursts during LIGO science run 6 and Virgo science runs 2 and 3

Abstract: We present the results of a search for gravitational waves associated with 154 gamma-ray bursts (GRBs) that were detected by satellite-based gamma-ray experiments in 2009-2010, during the sixth LIGO science run and the second and third Virgo science runs. We perform two distinct searches: a modeled search for coalescences of either two neutron stars or a neutron star and black hole, and a search for generic, unmodeled gravitational-wave bursts. We find no evidence for gravitational-wave counterparts, either with any individual GRB in this sample or with the population as a whole. For all GRBs we place lower bounds on the distance to the progenitor, under the optimistic assumption of a gravitational-wave emission energy of 10–2 M ☉ c 2 at 150 Hz, with a median limit of 17 Mpc. For short-hard GRBs we place exclusion distances on binary neutron star and neutron-star-black-hole progenitors, using astrophysically motivated priors on the source parameters, with median values of 16 Mpc and 28 Mpc, respectively. These distance limits, while significantly larger than for a search that is not aided by GRB satellite observations, are not large enough to expect a coincidence with a GRB. However, projecting these exclusions to the sensitivities of Advanced LIGO and Virgo, which should begin operation in 2015, we find that the detection of gravitational waves associated with GRBs will become quite possible.

First observation of the P-wave spin-singlet bottomonium states h b(1P) and h b(2P)

Abstract: We report the first observations of the spin-singlet bottomonium states h(b)(1P) and h(b)(2P). The states are produced in the reaction e(+)e(-) --> h(b)(nP)pi(+)pi(-) using a 121.4 fb(-1) data sample collected at energies near the Y(5S) resonance with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. We determine M[h(b)(1P)] = (9898.2(-1.0-1.1)(+1.1+1.0)) MeV/c(2) and M[h(b)(2P)] = (10 259.8 +/- 0.6(-1.0)(+1.4)) MeV/c(2), which correspond to P-wave hyperfine splittings Delta M-HF = (+1.7 +/- 1.5) and (+0.5(-1.2)(+1.6)) MeV/c(2), respectively. The significances of the h(b)(1P) and h(b)(2P) are 5.5 sigma and 11.2 sigma, respectively. We find that the production of the h(b)(1P) and h(b)(2P) is not suppressed relative to the production of the Y(1S), Y(2S), and Y(3S).

Roles of Four Arabidopsis U-Box E3 Ubiquitin Ligases in Negative Regulation of Abscisic Acid-Mediated Drought Stress Responses

Abstract: AtPUB18 and AtPUB19 are homologous U-box E3 ubiquitin ligases in Arabidopsis (Arabidopsis thaliana). AtPUB19 is a negative regulator of abscisic acid (ABA)-mediated drought responses, whereas the role of AtPUB18 in drought responses is unknown. Here, loss-of-function and overexpression tests identified AtPUB18 as a negative regulator in ABA-mediated stomatal closure and water stress responses. The atpub18-2atpub19-3 double mutant line displayed more sensitivity to ABA and enhanced drought tolerance than each single mutant plant; therefore, AtPUB18 and AtPUB19 are agonistic. Stomatal closure of the atpub18-2atpub19-3 mutant was hypersensitive to hydrogen peroxide (H2O2) but not to calcium, suggesting that AtPUB18 and AtPUB19 exert negative effects on the ABA signaling pathway downstream of H2O2 and upstream of calcium. AtPUB22 and AtPUB23 are other U-box E3 negative regulators of drought responses. Although atpub22atpub23 was more tolerant to drought stress relative to wild-type plants, its ABA-mediated stomatal movements were highly similar to those of wild-type plants. The atpub18-2atpub19-3atpub22atpub23 quadruple mutant exhibited enhanced tolerance to drought stress as compared with each atpub18-2atpub19-3 and atpub22atpub23 double mutant progeny; however, its stomatal behavior was almost identical to the atpub18-2atpub19-3 double mutant in the presence of ABA, H2O2, and calcium. Overexpression of AtPUB18 and AtPUB19 in atpub22atpub23 effectively hindered ABA-dependent stomatal closure, but overexpression of AtPUB22 and AtPUB23 in atpub18-2atpub19-3 did not inhibit ABA-enhanced stomatal closure, highlighting their ABA-independent roles. Overall, these results suggest that AtPUB18 has a linked function with AtPUB19, but is independent from AtPUB22 and AtPUB23, in negative regulation of ABA-mediated drought stress responses.

Implementation and testing of the first prompt search for gravitational wave transients with electromagnetic counterparts

Abstract: Aims. A transient astrophysical event observed in both gravitational wave (GW) and electromagnetic (EM) channels would yield rich scientific rewards. A first program initiating EM follow-ups to possible transient GW events has been developed and exercised by the LIGO and Virgo community in association with several partners. In this paper, we describe and evaluate the methods used to promptly identify and localize GW event candidates and to request images of targeted sky locations. Methods. During two observing periods (Dec. 17, 2009 to Jan. 8, 2010 and Sep. 2 to Oct. 20, 2010), a low-latency analysis pipeline was used to identify GW event candidates and to reconstruct maps of possible sky locations. A catalog of nearby galaxies and Milky Way globular clusters was used to select the most promising sky positions to be imaged, and this directional information was delivered to EM observatories with time lags of about thirty minutes. A Monte Carlo simulation has been used to evaluate the low-latency GW pipeline's ability to reconstruct source positions correctly. Results. For signals near the detection threshold, our low-latency algorithms often localized simulated GW burst signals to tens of square degrees, while neutron star/neutron star inspirals and neutron star/black hole inspirals were localized to a few hundred square degrees. Localization precision improves for moderately stronger signals. The correct sky location of signals well above threshold and originating from nearby galaxies may be observed with similar to 50% or better probability with a few pointings of wide-field telescopes.

Production of muons from heavy flavor decays at forward rapidity in pp and Pb-Pb collisions at root s(NN)=2.76 TeV

Abstract: The ALICE Collaboration has measured the inclusive production of muons from heavy-flavor decays at forward rapidity, 2.5 < y < 4, in pp and Pb-Pb collisions at root s(NN) = 2.76 TeV. The p(t)-differential inclusive cross section of muons from heavy-flavor decays in pp collisions is compared to perturbative QCD calculations. The nuclear modification factor is studied as a function of p(t) and collision centrality. A weak suppression is measured in peripheral collisions. In the most central collisions, a suppression of a factor of about 3-4 is observed in 6 < p(t) < 10 GeV/c. The suppression shows no significant p(t) dependence.

All-sky search for gravitational-wave bursts in the second joint LIGO-Virgo run

Abstract: We present results from a search for gravitational-wave bursts in the data collected by the LIGO and Virgo detectors between July 7, 2009 and October 20, 2010: data are analyzed when at least two of the three LIGO-Virgo detectors are in coincident operation, with a total observation time of 207 days. The analysis searches for transients of duration less than or similar to 1 s over the frequency band 64-5000 Hz, without other assumptions on the signal waveform, polarization, direction or occurrence time. All identified events are consistent with the expected accidental background. We set frequentist upper limits on the rate of gravitational-wave bursts by combining this search with the previous LIGO-Virgo search on the data collected between November 2005 and October 2007. The upper limit on the rate of strong gravitational-wave bursts at the Earth is 1.3 events per year at 90% confidence. We also present upper limits on source rate density per year and Mpc(3) for sample populations of standard-candle sources. As in the previous joint run, typical sensitivities of the search in terms of the root-sum-squared strain amplitude for these waveforms lie in the range similar to 5 x 10(-22) Hz(-1/2) to similar to 1 x 10(-20) Hz(-1/2). The combination of the two joint runs entails the most sensitive all-sky search for generic gravitational-wave bursts and synthesizes the results achieved by the initial generation of interferometric detectors.

Precise measurement of the CP violation parameter sin21 in B0→(cc̄)K0 decays

Abstract: We present a precise measurement of the CP violation parameter sin2 phi(1) and the direct CP violation parameter A(f) using the final data sample of 772 x 10(6) B (B) over bar pairs collected at the gamma(4S) resonance with the Belle detector at the KEKB asymmetric-energy e(+) e(-) collider. One neutral B meson is reconstructed in a J/psi K-S(0), psi(2S)K-S(0), chi K-c1(S)0, or J/psi K-L(0) CP eigenstate an(its flavor is identified from the decay products of the accompanying B meson. From the distribution of proper-time intervals between the two B decays, we obtain the following CP violation parameters: sin2 phi(1) 0.667 +/- 0.023(stat) +/- 0.012(syst) and A(f) = 0.006 +/- 0.016(stat) +/- 0.012(syst).

First low-latency LIGO+Virgo search for binary inspirals and their electromagnetic counterparts

Abstract: Aims: The detection and measurement of gravitational-waves from coalescing neutron-star binary systems is an important science goal for ground-based gravitational-wave detectors. In addition to emitting gravitational-waves at frequencies that span the most sensitive bands of the LIGO and Virgo detectors, these sources are also amongst the most likely to produce an electromagnetic counterpart to the gravitational-wave emission. A joint detection of the gravitational-wave and electromagnetic signals would provide a powerful new probe for astronomy. Methods: During the period between September 19 and October 20, 2010, the first low-latency search for gravitational-waves from binary inspirals in LIGO and Virgo data was conducted. The resulting triggers were sent to electromagnetic observatories for followup. We describe the generation and processing of the low-latency gravitational-wave triggers. The results of the electromagnetic image analysis will be described elsewhere. Results: Over the course of the science run, three gravitational-wave triggers passed all of the low-latency selection cuts. Of these, one was followed up by several of our observational partners. Analysis of the gravitational-wave data leads to an estimated false alarm rate of once every 6.4 days, falling far short of the requirement for a detection based solely on gravitational-wave data.

The characterization of Virgo data and its impact on gravitational-wave searches

Abstract: Between 2007 and 2010 Virgo collected data in coincidence with the LIGO and GEO gravitational-wave (GW) detectors. These data have been searched for GWs emitted by cataclysmic phenomena in the universe, by non-axisymmetric rotating neutron stars or from a stochastic background in the frequency band of the detectors. The sensitivity of GW searches is limited by noise produced by the detector or its environment. It is therefore crucial to characterize the various noise sources in a GW detector. This paper reviews the Virgo detector noise sources, noise propagation, and conversion mechanisms which were identified in the three first Virgo observing runs. In many cases, these investigations allowed us to mitigate noise sources in the detector, or to selectively flag noise events and discard them from the data. We present examples from the joint LIGO-GEO-Virgo GW searches to show how well noise transients and narrow spectral lines have been identified and excluded from the Virgo data. We also discuss how detector characterization can improve the astrophysical reach of GW searches.

Measurement of event background fluctuations for charged particle jet reconstruction in Pb-Pb collisions at root s (NN= 2.76 TeV

Abstract: The effect of event background fluctuations on charged particle jet reconstruction in Pb-Pb collisions at root s(NN) = 2.76 TeV has been measured with the ALICE experiment. The main sources of non-statistical fluctuations are characterized based purely on experimental data with an unbiased method, as well as by using single high p(t) particles and simulated jets embedded into real Pb-Pb events and reconstructed with the anti-k(t) jet finder. The influence of a low transverse momentum cut-off on particles used in the jet reconstruction is quantified by varying the minimum track p(t) between 0.15 GeV/c and 2 GeV/c. For embedded jets reconstructed from charged particles with p(t) > 0.15 GeV/c, the uncertainty in the reconstructed jet transverse momentum due to the heavy-ion background is measured to be 11.3 GeV/c (standard deviation) for the 10% most central Pb-Pb collisions, slightly larger than the value of 11.0 GeV/c measured using the unbiased method. For a higher particle transverse momentum threshold of 2 GeV/c, which will generate a stronger bias towards hard fragmentation in the jet finding process, the standard deviation of the fluctuations in the reconstructed jet transverse momentum is reduced to 4.8-5.0 GeV/c for the 10% most central events. A non-Gaussian tail of the momentum uncertainty is observed and its impact on the reconstructed jet spectrum is evaluated for varying particle momentum thresholds, by folding the measured fluctuations with steeply falling spectra.

Ring polymers as model bacterial chromosomes: confinement, chain topology, single chain statistics, and how they interact

Abstract: Chromosomes in living cells are strongly confined but show a high level of spatial organization. Similarly, confined polymers display intriguing organizational and segregational properties. Here, we discuss how ring topology influences self-avoiding polymers confined in a cylindrical space, i.e. individual polymers as well as the way they interact. Our molecular dynamics simulations suggest that a ring polymer can be viewed as a “parallel connection” of two linear subchains, each trapped in a narrower imaginary tube. As a consequence, ring topology “stiffens” individual chains about fivefold and enhances their segregation appreciably, as if it induces extra linear ordering. Using a “renormalized” Flory approach, we show how ring topology influences individual chains in the long chain limit. Our polymer model quantitatively explains the long-standing observations of chromosome organization and segregation in E. coli.

Measurement of the Cross Section for Electromagnetic Dissociation with Neutron Emission in Pb-Pb Collisions at root s(NN)=2.76 TeV

Abstract: The first measurement of neutron emission in electromagnetic dissociation of Pb-208 nuclei at the LHC is presented. The measurement is performed using the neutron zero degree calorimeters of the ALICE experiment, which detect neutral particles close to beam rapidity. The measured cross sections of single and mutual electromagnetic dissociation of Pb nuclei at root s(NN) = 2.76 TeV with neutron emission are sigma(singleEMD) = 187.4 +/- 0.2(stat)(-11.2)(+13.2) (syst) b and sigma(mutualEMD) = 5. 7 +/- 0.1(stat) +/- 0.4(syst) b, respectively. The experimental results are compared to the predictions from a relativistic electromagnetic dissociation model. DOI: 10.1103/PhysRevLett.109.252302

Underlying Event measurements in pp collisions at \( \sqrt {s} = 0.9 \) and 7 TeV with the ALICE experiment at the LHC

Abstract: We present measurements of Underlying Event observables in pp collisions at sqrt(s) = 0.9 and 7 TeV. The analysis is performed as a function of the highest charged-particle transverse momentum pT,LT in the event. Different regions are defined with respect to the azimuthal direction of the leading (highest transverse momentum) track: Toward, Transverse and Away. The Toward and Away regions collect the fragmentation products of the hardest partonic interaction. The Transverse region is expected to be most sensitive to the Underlying Event activity. The study is performed with charged particles above three different pT thresholds: 0.15, 0.5 and 1.0 GeV/c. In the Transverse region we observe an increase in the multiplicity of a factor 2-3 between the lower and higher collision energies, depending on the track pT threshold considered. Data are compared to Pythia 6.4, Pythia 8.1 and Phojet. On average, all models considered underestimate the multiplicity and summed pT in the Transverse region by about 10-30%.

Electric Field Effects on the Adsorption of CO on a Graphene Nanodot and the Healing Mechanism of a Vacancy in a Graphene Nanodot

Abstract: It is well known that the external electric field can effectively modify the electronic structures and transport properties of low-dimensional systems. However, to our knowledge, the corresponding ...