Raman spectroscopy as a probe of molecular order,orientation, and stacking of fluorinated copper‐phthalocyanine (F16CuPc) thin films

We report Raman scattering measurements on azimuthally ordered thin films of F₁₆CuPc, prepared by organic molecular beam deposition on A‐plane sapphire substrates. The observed peak frequencies have been compared both to the results of a model calculation for the vibrational modes of the free molecule and to those reported by other authors in related materials. This analysis provides a plausible identification of the modes responsible for the strongest spectral features. Detailed evaluation of the spectra reveals that some observed modes, which correspond to vibrations of the macrocycle inner ring, largely retain the intramolecular character and their polarisation properties can be used to study the orientation and stacking configuration of the molecules. We provide structural parameters deduced either in molecular or crystal symmetry considering the simpler possibilities, i.e. a single column molecular stacking and a herringbone‐like structure. The results suggest that the thicker and most ordered film is structurally close to the recently reported crystal organisation of bulk ribbon samples of this compound. The crystalline quality of the ordered films is mainly reflected in some other Raman peaks which are related to the motion of peripheral atoms and dominate the high wavenumber part of the spectra. These modes are affected by intermolecular interactions inducing Davydov splittings that are unequivocally identified by the observed Raman selection rules. The performed analysis also provides quantitative estimates of the degree of in‐plane ordering. Copyright © 2013 John Wiley & Sons, Ltd.     

Search for scalar bottom quark pair production with the ATLAS detector in pp collisions at sqrt[s]=7 TeV

The results of a search for pair production of the scalar partners of bottom quarks in 2.05 fb(-1) of pp collisions at sqrt[s]=7 TeV using the ATLAS experiment are reported. Scalar bottom quarks are searched for in events with large missing transverse momentum and two jets in the final state, where both jets are identified as originating from a bottom quark. In an R-parity conserving minimal supersymmetric scenario, assuming that the scalar bottom quark decays exclusively into a bottom quark and a neutralino, 95% confidence-level upper limits are obtained in the b(1) - χ(1)(0) mass plane such that for neutralino masses below 60 GeV scalar bottom masses up to 390 GeV are excluded.     

Search for a standard model Higgs boson in the H→ZZ→ℓ(+)ℓ(-)νν decay channel with the ATLAS detector

A search for a heavy standard model Higgs boson decaying via H→ZZ→→?(+)?(-)νν, where ?=e, μ, is presented. It is based on proton-proton collision data at √s=7 TeV, collected by the ATLAS experiment at the LHC in the first half of 2011 and corresponding to an integrated luminosity of 1.04 fb(-1). The data are compared to the expected standard model backgrounds. The data and the background expectations are found to be in agreement and upper limits are placed on the Higgs boson production cross section over the entire mass window considered; in particular, the production of a standard model Higgs boson is excluded in the region 340相似文献   

Distributional and Classical Solutions to the Cauchy Boltzmann Problem for Soft Potentials with Integrable Angular Cross Section

This paper focuses on the study of existence and uniqueness of distributional and classical solutions to the Cauchy Boltzmann problem for the soft potential case assuming S ^n?1 integrability of the angular part of the collision kernel (Grad cut-off assumption). For this purpose we revisit the Kaniel–Shinbrot iteration technique to present an elementary proof of existence and uniqueness results that includes the large data near local Maxwellian regime with possibly infinite initial mass. We study the propagation of regularity using a recent estimate for the positive collision operator given in (Alonso et al. in Convolution inequalities for the Boltzmann collision operator. arXiv:0902.0507 [math.AP]) , by E. Carneiro and the authors, that allows us to show such propagation without additional conditions on the collision kernel. Finally, an L ^p -stability result (with 1≤p≤∞) is presented assuming the aforementioned condition.     

On different implementations of spatial evolutionary games

Evolutionary spatial 2×2 games between unconditional agents are analysed introducing several variants of cellular automata (CA).     

Detection and characterization of the spatial inhibition potential in electroperforated sheet materials

The spatial distribution of tiny holes in sheet materials generated by means of electrical discharges is investigated using spatial statistics techniques. It is shown that whereas the holes appear to be randomly distributed according to a Poisson point pattern, there is in fact a small region around each hole in which the generation of a new one is statistically inhibited as a consequence of the lower impedance path offered by the already made hole. The resulting pattern is known in spatial statistics as a point process with a soft-core inhibition potential, which can be characterized using the pair correlation function.     

Evidence for nearby supernova explosions

Supernova (SN) explosions are one of the most energetic---and potentially lethal---phenomena in the Universe. We show that the Scorpius-Centaurus OB association, a group of young stars currently located at approximately 130 pc from the Sun, has generated 20 SN explosions during the last 11 Myr, some of them probably as close as 40 pc to our planet. The deposition on Earth of (60)Fe atoms produced by these explosions can explain the recent measurements of an excess of this isotope in deep ocean crust samples. We propose that approximately 2 Myr ago, one of the SNe exploded close enough to Earth to seriously damage the ozone layer, provoking or contributing to the Pliocene-Pleistocene boundary marine extinction.     

Nuclear Spin Alignment of 12,13B Produced in Heavy Ion Collisions

The nuclear spin alignments of the β-emitting fragments ¹²B(I ^π=1⁺, T _1/2=20.2 ms) and ¹³B(I ^π=3/2⁻, T _1/2=17.4 ms) produced in the 100A-MeV ¹³C, ¹⁵N + ⁹Be collisions respectively have been observed for the first time detecting asymmetric β-ray emission from these nuclei. By means of the spin manipulation technique based on the hyperfine interaction of B isotopes in TiO₂, both the polarization P and the alignment A were determined reliably. The obtained P and A were significantly smaller than the expectation from the kinematical model. From the fact that the quenching factors for P and A are almost the same, there may be some depolarization mechanism in the collision process itself. This revised version was published online in September 2006 with corrections to the Cover Date.     

Radial electric fields and confinement in the TJ-II stellarator

Radial plasma potential profiles have been obtained in the TJ-II by the Heavy Ion Beam Probing (HIBP) diagnostics. Results show that the potential increases up to 1 kV near the magnetic axis in ECRH low-density plasmas. The secondary ion current profiles, which directly reflect the plasma density, are hollow. In low-density ECRH operation, radial electric fields are found to be positive in the plasma core, however, a reduction in these fields is observed with increasing density. Radial plasma potential profiles show evidence of structures in configurations with low-order rational surfaces. In particular, HIBP measurements have permitted characterization of the plasma potential profile during e-ITB formation. Experiments in TJ-II have shown that it is possible to modify the global confinement and edge plasma parameters with limiter biasing, illustrating the direct impact of radial electric fields on confinement properties. Plasma potential measurements by the HIBP diagnostic show a strong impact of heating method (ECRH versus NBI) on radial electric fields.Presented at the Workshop Electric Fields Structures and Relaxation in Edge Plasmas, Nice, France, October 26–27, 2004.