Transition from decelerated to accelerated cosmic expansion in braneworld universes

Braneworld theory provides a natural setting to treat, at a classical level, the cosmological effects of vacuum energy. Non-static extra dimensions can generally lead to a variable vacuum energy, which in turn may explain the present accelerated cosmic expansion. We concentrate our attention in models where the vacuum energy decreases as an inverse power law of the scale factor. These models agree with the observed accelerating universe, while fitting simultaneously the observational data for the density and deceleration parameter. The redshift at which the vacuum energy can start to dominate depends on the mass density of ordinary matter. For _m = 0.3, the transition from decelerated to accelerated cosmic expansion occurs at z _T ≈ 0.48 ± 0.20, which is compatible with SNe data. We set a lower bound on the deceleration parameter today, namely > − 1 + 3 _m /2, i.e., > − 0.55 for _m = 0.3. The future evolution of the universe crucially depends on the time when vacuum starts to dominate over ordinary matter. If it dominates only recently, at an epoch z < 0.64, then the universe is accelerating today and will continue that way forever. If vacuum dominates earlier, at z > 0.64, then the deceleration comes back and the universe recollapses at some point in the distant future. In the first case, quintessence and Cardassian expansion can be formally interpreted as the low energy limit of our model, although they are entirely different in philosophy. In the second case there is no correspondence between these models and ours.     

Reflection and transmission at normal incidence onto air-saturated porous materials and direct measurements based on parametric demodulated ultrasonic waves

The present work is related to the characterization of air-saturated porous media by using parametric demodulated ultrasonic waves. One uses two different powerful ultrasonic emitters working either at 47 kHz or at 162 kHz which are electronically amplitude modulated over the 200 Hz-4 kHz or 2 kHz-40 kHz bandwidths respectively. The demodulation process takes place in air, due to its nonlinearity enabling to generate audio range acoustical waves or alternatively low frequency ultrasonic waves which can be used to characterize porous materials in the reflection configuration at normal incidence. Some appropriate theoretical calculations are introduced for three configurations of interest, i.e. a porous slab, a porous layer mounted onto a rigid plate, and a porous half space, in the case of the equivalent-fluid model. Comparisons between theoretical modeling and experimental data are provided and prospective industrial applications are discussed.     

Carbon monoxide dissociation on Rh nanopyramids

CO dissociation on rhomboidal faceted nanopyramids, produced on Rh(110) by fine-tuning of ion irradiation conditions, has been studied by high resolution core-level spectroscopy. We find that this morphology presents a large efficiency towards CO dissociation, a process which is inhibited on flat (110) terraces. We also measured the reactivity of nanostructures bound by different artificial step distributions identifying the sites responsible for the molecular bond disruption in the undercoordinated (n=6) edges running along the [11[over ]2] equivalent directions, with CO sitting in on-top configuration.     

直升机声测设备探测距离估计方法

直升机声测设备用于探测低空飞行的直升机,探测距离是其关键性能。为了精确测定探测距离,可以运用探测结果与机载数据综合分析的方法。此种方法需要较多人员和其它设备,包括机载设备,在设备研制的初期较繁琐。本文提出了一种简便的直升机声测设备探测距离估计方法,此方法不需要使用机载设备,对直升机飞行基本无约束,通过对大量实测数据处理,针对某直升机声测设备该方法的平均误差在7%以内。     

Electrical and microscopic characterization of ZnO films on p-SiC substrates

ZnO/p- SiC heterojunctions were fabricated by thermal evaporation from ZnO high quality powder (99.99%) onto 4H and 6H p-SiC polytypes. We find that, despite the low cost technique employed for the deposition of the ZnO film, the devices exhibited breakdown voltages in excess of 100 V, high rectification ratio (forward to reverse current ratio, I_F/I_R) and low leakage current, respectively, 2×10⁵ and 4.5×10⁻⁷ A/cm² (for the 4H p-SiC based device) and 5×10⁴ and 5×10⁻⁷ A/cm² (for the 6H p-SiC based device). The current-voltage (I×V) characteristics were also measured at the nanometer scale by means of conductive atomic force microscopy. A simple Schottky diode model and conductance divided by current versus conductance plots (G/I×G plots) was used to analyze device characteristics. This analysis shows that, when probing at the nanometric scale, fluctuations of the effective barrier height and/or surface states across individual grains or grain boundaries cause deviations from linear G/I×G plots. These fluctuations are smeared out when probing at the macroscale and thus it becomes possible to obtain linear plots and extract diode parameters.     

A nonextensive approach to the dynamics of financial observables

We present results about financial market observables, specifically returns and traded volumes. They are obtained within the current nonextensive statistical mechanical framework based on the entropy . More precisely, we present stochastic dynamical mechanisms which mimic probability density functions empirically observed. These mechanisms provide possible interpretations for the emergence of the entropic indices q in the time evolution of the corresponding observables. In addition to this, through multi-fractal analysis of return time series, we verify that the dual relation q_stat+q_sens=2 is numerically satisfied, q_stat and q_sens being associated to the probability density function and to the sensitivity to initial conditions respectively. This type of simple relation, whose understanding remains ellusive, has been empirically verified in various other systems.     

Beam-helicity asymmetry in photon and pion electroproduction in the Δ(1232)-resonance region at Q2 = 0.35(GeV/c)2

The beam-helicity asymmetry has been measured simultaneously for the reactions p→epγ and p→epπ ⁰ in the Δ(1232)-resonance region at Q ² = 0.35(GeV/c)². The experiment was performed at MAMI with a longitudinally polarized beam and an out-of-plane detection of the proton. The results are compared with calculations based on dispersion relations for virtual Compton scattering and with the MAID model for pion electroproduction. There is an overall good agreement between experiment and theoretical calculations. The remaining discrepancies may be ascribed to an imperfect parametrization of some γ ^(*) N→πN multipoles, mainly contributing to the non-resonant background. The beam-helicity asymmetry in both channels (γ and π ⁰) shows a good sensitivity to these multipoles and should allow future improvement in their parametrization.     

Can MRI Contribute to the Understanding and Therapy of Mental Diseases?

The nowadays most accepted hypothesis of the origin of mental diseases is an impaired connectivity between various brain areas. Magnetic resonance tractography reveals structural connectivities through neuronal fibers and resting state functional imaging allows one to visualize functional connectivities. The detection of the small signal changes needs the highest sensitivity and the magnetic resonance imaging scans must be repeated as fast as possible. Statistical evaluation and cross correlation of the signals in all voxels show synchrony of signal-level fluctuations even in remote brain areas. This makes it possible to establish brain networks. The most important of them are the default mode network, the salience network, and the central executive network. Applications to schizophrenia and depression will be discussed. In deep brain stimulation, the excitation, currently used for therapy of Parkinson’s disease, is now introduced for therapy of major depressive disorder and can be taylored to the necessary brain location.     

"Safe" Coulomb excitation of 30Mg

We report on the first radioactive beam experiment performed at the recently commissioned REX-ISOLDE facility at CERN in conjunction with the highly efficient gamma spectrometer MINIBALL. Using 30Mg ions accelerated to an energy of 2.25 MeV/u together with a thin (nat)Ni target, Coulomb excitation of the first excited 2+ states of the projectile and target nuclei well below the Coulomb barrier was observed. From the measured relative deexcitation gamma-ray yields the B(E2;0(+)gs-->2(+)1) value of 30Mg was determined to be 241(31)e2 fm4. Our result is lower than values obtained at projectile fragmentation facilities using the intermediate-energy Coulomb excitation method, and confirms the theoretical conjecture that the neutron-rich magnesium isotope 30Mg resides outside the "island of inversion."