The RENO experiment has observed the disappearance of reactor electron antineutrinos, consistent with neutrino oscillations, with a significance of 4.9 standard deviations. Antineutrinos from six 2.8  GW(th) reactors at the Yonggwang Nuclear Power Plant in Korea, are detected by two identical detectors located at 294 and 1383 m, respectively, from the reactor array center. In the 229 d data-taking period between 11 August 2011 and 26 March 2012, the far (near) detector observed 17102 (154088) electron antineutrino candidate events with a background fraction of 5.5% (2.7%). The ratio of observed to expected numbers of antineutrinos in the far detector is 0.920±0.009(stat)±0.014(syst). From this deficit, we determine sin(2)2θ(13)=0.113±0.013(stat)±0.019(syst) based on a rate-only analysis.

A new class of epoxy nanocomposites with completely defined organic/inorganic phases was prepared by reacting octakis(glycidyldimethylsiloxy)octasilsesquioxane [(glydicylMe(2)SiOSiO(1.5))(8)] (OG) with diaminodiphenylmethane (DDM) at various compositional ratios. The effects of reaction curing conditions on nanostructural organization and mechanical properties were explored. A commercial epoxy resin based on the diglycidyl ether of bisphenol A (DGEBA) was used as a reference material throughout these studies. FTIR was used to follow the curing process and to demonstrate that the silsesquioxane structure is preserved during processing. OG/DDM composites possess comparable tensile moduli (E) and fracture toughness (K(IC)) to, and better thermal stabilities than, DGEBA/DDM cured under similar conditions. Dynamic mechanical analysis and model reaction studies suggest that the maximum cross-link density is obtained at N = 0.5 (NH(2):epoxy groups = 0.5) whereas the mechanical properties are maximized at N = 1.0. Digestion of the inorganic core with HF followed by GPC analysis of the resulting organic tether fragments when combined with the model reaction studies confirms that, at N = 0.5, each organic tether connects four cubes, while, at N = 1.0, linear tethers connecting two cubes dominate the network structure. Thus, well-defined nanocomposites with controlled variation of the organic tether architecture can be made and their properties assessed.

Scaffolding plays pivotal role in tissue engineering. In this work, a novel processing technique has been developed to create three-dimensional biodegradable polymer scaffolds with well-controlled interconnected spherical pores. Paraffin spheres were fabricated with a dispersion method, and were bonded together through a heat treatment to form a three-dimensional assembly in a mold. Biodegradable polymers such as PLLA and PLGA were dissolved in a solvent and cast onto the paraffin sphere assembly. After dissolving the paraffin, a porous polymer scaffold was formed. The fabrication parameters were studied in relation to the pore shape, interpore connectivity, pore wall morphology, and mechanical properties of the polymer scaffolds. The compressive modulus of the scaffolds decreased with increasing porosity. Longer heat treatment time of the paraffin spheres resulted in larger openings between the pores of the scaffolds. Foams of smaller pore size (100-200 microm) resulted in significantly lower compressive modulus than that of larger pore sizes (250-350 or 420-500 microm). The PLLA foams had a skeletal structure consisting of small platelets, whereas PLGA foams had homogeneous skeletal structure. The new processing technique can tailor the polymer scaffolds for a variety of potential tissue engineering applications because of the well-controlled architecture, interpore connectivity, and mechanical properties.

The RENO experiment has analyzed about 500 live days of data to observe an energy dependent disappearance of reactor νe by comparison of their prompt signal spectra measured in two identical near and far detectors. In the period between August 2011 and January 2013, the far (near) detector observed 31541 (290775) electron antineutrino candidate events with a background fraction of 4.9% (2.8%). The measured prompt spectra show an excess of reactor νe around 5 MeV relative to the prediction from a most commonly used model. A clear energy and baseline dependent disappearance of reactor νe is observed in the deficit of the observed number of νe. Based on the measured far-to-near ratio of prompt spectra, we obtain sin 2 2θ13 = 0. The reactor ν e disappearance has been firmly observed to determine the smallest neutrino mixing angle θ 13 [1-3]. All of the three mixing angles in the Pontecorvo-MakiNakagawa-Sakata matrix [4,5] have been measured to provide a comprehensive picture of neutrino transformation. The successful measurement of a rather large θ 13 value opens the possibility of searching for CP violation in the leptonic sector and determining the neutrino mass ordering. Appearance of ν e from an accelerator ν µ beam is also observed by the T2K [6] and NOνA [7] experiments.Using the ν e survival probability P [8], reactor experiments with a baseline distance of ∼1 km can determine the mixing angle θ 13 and an effective squared-massdifference ∆m where ∆ ij ≡ 1.267∆m 2 ij L/E, E is the ν e energy in MeV, and L is the distance between the reactor and detector in meters.The first measurement of θ 13 by RENO was based on the rate-only analysis of deficit found in ∼220 live days of data [1]. The oscillation frequency |∆m 2 ee | in the measurement was approximated by the measured value |∆m 2 31 | assuming the normal ordering in the ν µ disappearance [10]. In this Letter, we present a more precisely measured value of θ 13 and our first determination of |∆m 2 ee |, based on the rate, spectral and baseline information (rate+spectrum analysis) of reactor ν e disappearance using ∼500 live days of data. The Daya Bay collaboration has also reported spectral measurements [11].The RENO uses identical near and far ν e detectors located at 294 m and 1383 m, respectively, from the center of six reactor cores of the Hanbit (known as Yonggwang) Nulcear Power Plant. The far (near) detector is under a 450 m (120 m) of water equivalent overburden. Six pressurized water reactors, each with maximum thermal output of 2.8 GW th , are situated in a linear array spanning 1.3 km with equal spacings. The reactor flux-weighted baseline is 410.6 m for the near detector and 1445.7 m for the far detector.The reactor ν e is detected through the inverse beta decay (IBD) interaction, ν e + p → e + + n, with free protons in hydrocarbon liquid scintillator (LS) with 0.1% Gadolinium (Gd) as a target. The coincidence of a prompt positron signal and a mean time of ∼28 µs delayed signal from neutron capture by Gd (n-Gd) provides the distinctive IBD signatur...