Large force fluctuations in a flowing granular medium

We study fluctuations in the force at the boundary of a 2D granular flow. The forces are mainly impulsive at all flow rates. The probability distribution of impulses decays exponentially at large impulses, as do the forces in a static granular medium. At small impulses, the distribution evolves continuously with flow rate with no indication of the transition from collisional flow to intermittently jamming flows. However, the distribution of the time interval between collisions tends to a power law, P(tau) - tau(-3/2), showing a clear dynamical signature of the approach to jamming.     

Electrical and optical properties of vacuum deposited MnPc thin films

Sandwich and planar structures were fabricated using manganese phthalocyanine (MnPc) as active layer and gold (Au) as electrodes by thermal evaporation method. The permittivity ε of MnPc was determined from the dependence of capacitance on film thickness. J-V characteristics of Au/MnPc/Au structure at room temperature were performed. Thermally generated hole concentration p₀, hole mobility μ_p, total trap concentration N_t and depth of the trap level were estimated. The activation energies of MnPc films were determined from the Arrhenius plots of ln σ versus 1000/T. The absorption and reflectance spectra of MnPc thin film deposited at room temperature were recorded in the spectral range 300–900 nm. The optical band gap of MnPc thin film was determined from the α² versus hν graph. The optical constants n and k were found. The real and imaginary parts of the optical dielectric constant ε₁ and ε₂ were calculated.     

Electrical properties of hybrid phthalocyanines thin films using gold and lead electrodes

The electrical properties of mixed copper phthalocyanine (CuPc) and nickel phthalocyanine (NiPc) thin films devices with gold and lead electrodes have been investigated. The two phthalocyanines were co-evaporated and deposited on to a pre-cleaned glass substrate by thermal evaporation technique at room temperature. By the co-sublimation technique an integrated phthalocyanine sample was prepared. At low voltages the film showed an ohmic conduction whereas at higher voltage levels the conduction mechanisms were dominated by space charged limited conduction (SCLC). The value of mobility of holes were calculated as μ= 3.1×10^-8 m² V^-1 s^-1 which is lower for the mixed phthalocyanines whereas the trap concentrations N_t(e) = 8.06 ×10²⁵ m^-3 have increased in the SCLC region. Further the reverse conduction mechanisms have also been investigated. From the current limitations in the reverse condition a strong rectifying behaviour was evident.     

Pyridine-catalyzed addition of diaryl-1,2-diones to dimethyl butynedioate leading to the formation of 1,2-diaroyl dimethyl maleates via an unprecedented rearrangement

[reaction: see text] Pyridine catalyzes the reaction of 1,2-diaryl diones with dimethyl butynedioate to afford diaroyl maleates. This unprecedented rearrangement involves a unique benzoyl migration and proceeds with complete stereoselectivity.     

Generalized diffusion solution for light scattering from anisotropic sources

The traditional diffusion theory, often used for isotropic sources, becomes inaccurate at short source-detector spacings and cannot be applied to media with large absorption or with small scattering strengths. We show that for any type of source anisotropy, a Green's-function-based procedure can remove these limitations. The accuracy of the new approach is examined through a comparison with the numerical solution to the radiative transfer equation.     

Fluidized granular medium as an instance of the fluctuation theorem

We study the statistics of the power flux into a collection of inelastic beads maintained in a fluidized steady state by external mechanical driving. The power shows large fluctuations, including frequent large negative fluctuations, about its average value. The relative probabilities of positive and negative fluctuations in the power flux are in close accord with the fluctuation theorem of Gallavotti and Cohen, even at time scales shorter than those required by the theorem. We also compare an effective temperature that emerges from this analysis to the kinetic granular temperature.     

Noise properties of a NMR transceiver coil array

The use of multiple radiofrequency (RF) surface coil elements has applications in both fast parallel imaging and conventional imaging techniques. Through implementation of a simple magnetic decoupling network, 50 Omega matching can be achieved in both the transmitter and receiver chains, enabling the use of conventional RF power amplifiers and preamplifiers for transceive applications. Unlike phased array coil arrangements using low impedance preamplifiers for decoupling, the noise correlation between 50 Omega coils decoupled with discrete components has not been characterized. We have measured the dependence of coil quality factor (Q-factor) and noise correlation on coil separation and shown these quantities to be consistent with theoretical arguments, at least at 4 T (170 MHz). Our results suggest that a coil system for transmission and reception of NMR signals with 50 Omega coils can be built to take advantage of all the benefits of conventional array coils and with the added advantages of using conventional amplifiers.     

Degradation of inter-atomic bonds during structural phase change in intermediate Ni-clusters (Ni39-Ni49)

Results based on a symmetry- and spin-unrestricted tight-binding molecular-dynamics study are presented for the ground-state geometries of intermediate Ni(n), n in [39,49], clusters. A structural phase change is found to take place around n=43 during which a structural transition from fcc/hcp structure to icosahedral one is observed. This is in good agreement with recent experimental findings. This structural transition is found to be associated with a degradation of the inter-atomic bond energy which indicates that the inter-atomic bond does not only depend on the coordination number of each atom but also on its point group symmetry.     

Magnetic properties of C60 polymers

Magnetic properties of various C60 polymers are calculated using tight-binding molecular-dynamics and ab initio methods. Our results suggest a mechanism involving an interplay between structural defects and sp(3) hybridization to be responsible for the origin of this magnetism. The onset of magnetism is found to occur much more readily for the Rh-C60 polymeric phase with defects than for any of the other polymers, in agreement with the recent experiment. Our estimate of the magnetic moment is also in very good agreement with the value observed in experiment.