Large-Area Scintillator Hodoscope with 50 ps Timing Resolution Onboard BESS

We describe the design and performance of a large-area scintillator hodoscope onboard the BESS rigidity spectrometer; an instrument with an acceptance of 0.3 m^{2}sr. The hodoscope is configured such that 10 and 12 counters are respectively situated in upper and lower layers. Each counter is viewed from its ends by 2.5 inch fine-mesh photomultiplier tubes placed in a stray magnetic field of 0.2 Tesla. Various beam-test data are presented. Use of cosmic-ray muons at ground-level confirmed 50 ps timing resolution for each layer, giving an overall time-of-flight resolution of 70 ps rms using a pure Gaussian resolution function. Comparison with previous measurements on a similar scintillator hodoscope indicates good agreement with the scaling law that timing resolution is proportional to 1/$\sqrt{N_{\rm pe}}$, where $N_{\rm pe}$ is the effective number of photoelectrons.Comment: 16 pages, 14 figure

Short-range Charge and Spin Superstructures in Doped Layered Co Perovskites

We have investigated cobaltite relatives of the layered perovskite cuprates and nickelates, Pr$_{2-x}$Ca$_x$CoO$_4$ ($0.39 \leq x \leq 0.73$) and La$_{2-x}$Sr$_x$CoO$_4$ ($x = 0.61$), using elastic neutron scattering. We have discovered doping-dependent incommensurate short-range ordering of charges and magnetic moments, which in cobaltites occur in the range of heavy doping, $0.5 \lesssim x \lesssim 0.75$. The charge order exists already at room temperature and shows no change on cooling. The incommensurability of its propagation vector, ${\bf Q}_c = (\epsilon_c,0,l)$, roughly scales with the concentration of Co$^{2+}$ ions, $\epsilon_c \sim (1-x)$. Magnetic order is only established at low T$\lesssim 40$ K and has twice larger periodicity, indicating a dominant antiferromagnetic correlation between the nearest Co$^{2+}$ spins.Comment: 4 pages 4 figure

Site-specific biotinylation of RNA molecules by transcription using unnatural base pairs

Direct site-specific biotinylation of RNA molecules was achieved by specific transcription mediated by unnatural base pairs. Unnatural base pairs between 2-amino-6-(2-thienyl)purine (denoted by s) and 2-oxo(1H)pyridine (denoted by y), or 2-amino-6-(2-thiazolyl)purine (denoted as v) and y specifically function in T7 transcription. Using these unnatural base pairs, the substrate of biotinylated-y (Bio-yTP) was selectively incorporated into RNA, opposite s or v in the DNA templates, by T7 RNA polymerase. This method was applied to the immobilization of an RNA aptamer on sensor chips, and the aptamer accurately recognized its target protein. This direct site-specific biotinylation will provide a tool for RNA-based biotechnologies

Nonchaotic Stagnant Motion in a Marginal Quasiperiodic Gradient System

A one-dimensional dynamical system with a marginal quasiperiodic gradient is presented as a mathematical extension of a nonuniform oscillator. The system exhibits a nonchaotic stagnant motion, which is reminiscent of intermittent chaos. In fact, the density function of residence times near stagnation points obeys an inverse-square law, due to a mechanism similar to type-I intermittency. However, unlike intermittent chaos, in which the alternation between long stagnant phases and rapid moving phases occurs in a random manner, here the alternation occurs in a quasiperiodic manner. In particular, in case of a gradient with the golden ratio, the renewal of the largest residence time occurs at positions corresponding to the Fibonacci sequence. Finally, the asymptotic long-time behavior, in the form of a nested logarithm, is theoretically derived. Compared with the Pomeau-Manneville intermittency, a significant difference in the relaxation property of the long-time average of the dynamical variable is found.Comment: 11pages, 5figure

Dilution and clustering of Fe in the rutile phases of TiO2 and SnO2

ABSTRACT: Dilute magnetic semiconductors of Fe-doped SnO2 and TiO2 with the structure of rutile were prepared in forms of powder and thin films using the techniques of sol gel and pulsed-laser deposition. We present the results of measurement of vibrational density of states of Fe impurity dopants in these oxides and demonstrate the cases of dilution and clustering. The oxygen pressure during the film deposition was varied between 10−1 and 10−8 Torr. In TiO2 films made at 10−1 Torr, Fe is diluted, however, in films made at 10−8 Torr Fe is clustered. The case of true Fe dilution in SnO2 is also shown. In spite of larger mass defect for Fe in SnO2 than that for Fe in TiO2 the dilute Fe species probe the phonon states in SnO2 more faithfully than in TiO2. This result is understood in terms of the combined effect of mass defect and nearest-neighbor force-constant changes. The impurity modes are more pronounced in TiO2 than in SnO2 due to ca. 10% difference of the lattice cell volumes between these two rutile oxides

Extra dimensions and invisible decay of orthopositronium

We point out that some models with infinite additional dimension(s) of Randall-Sundrum type predict the disappearance of orthopositronium (o-Ps) into additional dimension(s). The experimental signature of this effect is the o-Ps -> invisible decay of orthopositronium which may occur at a rate within three orders of magnitude of the present experimental upper limit. This result enhances existing motivations for a more sensitive search for this decay mode and suggests additional directions for testing extra dimensions in non accelerator experiments.Comment: 3 pages, to appear in Phys. Rev.

Analytical method for parameterizing the random profile components of nanosurfaces imaged by atomic force microscopy

The functional properties of many technological surfaces in biotechnology, electronics, and mechanical engineering depend to a large degree on the individual features of their nanoscale surface texture, which in turn are a function of the surface manufacturing process. Among these features, the surface irregularities and self-similarity structures at different spatial scales, especially in the range of 1 to 100 nm, are of high importance because they greatly affect the surface interaction forces acting at a nanoscale distance. An analytical method for parameterizing the surface irregularities and their correlations in nanosurfaces imaged by atomic force microscopy (AFM) is proposed. In this method, flicker noise spectroscopy - a statistical physics approach - is used to develop six nanometrological parameters characterizing the high-frequency contributions of jump- and spike-like irregularities into the surface texture. These contributions reflect the stochastic processes of anomalous diffusion and inertial effects, respectively, in the process of surface manufacturing. The AFM images of the texture of corrosion-resistant magnetite coatings formed on low-carbon steel in hot nitrate solutions with coating growth promoters at different temperatures are analyzed. It is shown that the parameters characterizing surface spikiness are able to quantify the effect of process temperature on the corrosion resistance of the coatings. It is suggested that these parameters can be used for predicting and characterizing the corrosion-resistant properties of magnetite coatings.Comment: 7 pages, 3 figures, 2 tables; to be published in Analys

Measurement of the double-\beta decay half-life of ^{136}Xe with the KamLAND-Zen experiment

We present results from the KamLAND-Zen double-beta decay experiment based on an exposure of 77.6 days with 129 kg of $^{136}$Xe. The measured two-neutrino double-beta decay half-life of $^{136}$Xe is $T_{1/2}^{2\nu} = 2.38 \pm 0.02(stat) \pm 0.14(syst) \times 10^{21}$ yr, consistent with a recent measurement by EXO-200. We also obtain a lower limit for the neutrinoless double-beta decay half-life, $T_{1/2}^{0\nu} > 5.7 \times 10^{24}$ yr at 90% confidence level (C.L.), which corresponds to almost a five-fold improvement over previous limits.Comment: 6 pages, 4 figures. Version as published in PR

Precision Measurement of Cosmic-Ray Antiproton Spectrum

The energy spectrum of cosmic-ray antiprotons has been measured in the range 0.18 to 3.56 GeV, based on 458 antiprotons collected by BESS in recent solar-minimum period. We have detected for the first time a distinctive peak at 2 GeV of antiprotons originating from cosmic-ray interactions with the interstellar gas. The peak spectrum is reproduced by theoretical calculations, implying that the propagation models are basically correct and that different cosmic-ray species undergo a universal propagation. Future BESS flights toward the solar maximum will help us to study the solar modulation and the propagation in detail and to search for primary antiproton components.Comment: REVTeX, 4 pages including 4 eps figure