Non fermi liquid ground states in strongly correlated f-electron materials

Experimental efforts to characterize and develop an understanding of non Fermi liquid (NFL) behavior at low temperature in f-electron materials are reviewed for three f-electron systems: M_1–xU_xPd₃ (M = Sc, Y), U_1–xTh_xPd₂Al₃, and UCu_5–xPd_x. The emerging systematics of NFL behavior in f-electron systems, based on the present sample of nearly ten f-electron systems, is updated. Many of the f-electron systems exhibit the following temperature dependences of the electrical resistivity p, specific heat C, and magnetic susceptibility for T T₀, where T_o is a characteristic temperature: P(T) 1 –aT/T ₀, where a < 0 or > 0, C(T)/T (-1/T _o) In (T/bT ₀), and (T) 1 –c(T/T_o)^1/2. In several of the f-electron systems, the characteristic temperature T_o can be identified with the Kondo temperature T_k.     

Hole pockets in the doped 2D Hubbard model

The electronic momentum distribution n(k) of the two dimensional Hubbard model is studied for different values of the coupling U/t, electronic density n , and temperature, using quantum Monte Carlo techniques. A detailed analysis of the data on 8 × 8 clusters shows that features consistent with hole pockets at momenta k=(±/2,±/2,) appear as the system is doped away from half-filling. Our results are consistent with recent experimental data for the cuprates discussed by Aebi et al. (Phys. Rev. Lett.72, 2757 (1994)). In the range of couplings studied, the depth of the pockets is maximum at n approximately 0.9, and it increases with decreasing temperature. The apparent absence of hole pockets in previous numerical studies of this model is explained.     

Bounded Rationality,Group Formation and the Emergence of Trust: An Agent-Based Economic Model

Computational Economics - It is possible to model trust as an investment game, where a player in order to receive a reward or a better outcome, accepts a certain risk of defection by another...     

Coupled temperature and moisture effects on the tensile behavior of strain hardening cementitious composites (SHCC) reinforced with PVA fibers

This paper reports the experimental findings on the tensile behavior of strain-hardening cement-based composites (SHCC). The composites were subjected to the combined effects of elevated temperatures and internal moisture condition. Uniaxial tensile tests on dumbbell-shaped SHCC specimens with in situ temperature control were performed at 22, 60 and 100 °C. In addition, the effect of the internal humidity of SHCC (95, 50, 20 and 0%) coupled to the elevated temperatures was investigated. It was shown that the tensile strength decreases and the strain capacity increases with an increase in temperature. The influence of the internal moisture conditions was more significant in high temperatures. The strain capacity reduced significantly with a decrease in the humidity level. The crack pattern of the SHCC specimens was determined. Furthermore, single fiber pullout tests were performed under the considered high temperatures condition. Finally, the results are discussed based on the thermogravimetry analysis of the PVA fiber, alterations on its microstructure and surface coating.     

Floral nectar phenolics as biochemical markers for the botanical origin of heather honey

In order to find out biochemical markers for the botanical origin of heather (Erica) honey, the phenolic metabolites present in heather floral nectar, collected from the honey-stomach of bees gathering nectar from these flowers, were analysed. The flavonoid fraction of nectar contained four main flavonoids. Two of them were quercetin and kaempferol 3-rhamnosides, and the other two were tentatively identified as myricetin 3-methyl ether and isorhamnetin 3-rhamnosides. Since the natural glycosides are hydrolysed by bee enzymes to render the corresponding aglycones, which are the metabolites detected in honey, acid hydrolysis of the nectar glycosides was achieved. The aglycones quercetin, myricetin 3-methyl ether, kaempferol and isorhamnetin were identified, as well as the gallic acid derivative ellagic acid. The analysis of Portuguese heather honey samples showed that ellagic acid was present in all the samples in significant amounts ranging between 100 g and 600 g per 100 g honey. The other nectar-derived flavonoids were also present, although some of them in very variable amounts. Ellagic acid and myricetin 3-methyl ether, which have not been detected in any of the monofloral honey samples investigated so far, with the only exception being a French honey sample of the botanically relatedCalluna (Ericaceae) which also contained ellagic acid, seem to be the most useful potential markers for the floral origin of heather honey. However, more detailed and extensive investigations are needed to prove the utility of these markers.     

Range of validity of the Rayleigh-Debye-Gans theory for optics of fractal aggregates

The range of validity of the Rayleigh-Debye-Gans approximation for the optical cross sections of fractal aggregates (RDG-FA) that are formed by uniform small particles was evaluated in comparison with the integral equation formulation for scattering (IEFS), which accounts for the effects of multiple scattering and self-interaction. Numerical simulations were performed to create aggregates that exhibit mass fractallike characteristics with a wide range of particle and aggregate sizes and morphologies, including x(p) = 0.01-1.0, ‖m - 1‖ = 0.1-2.0, N = 16-256, and D(f) = 1.0-3.0. The percent differences between both scattering theories were presented as error contour charts in the ‖m - 1‖x(p) domains for various size aggregates, emphasizing fractal properties representative of diffusion-limited cluster-cluster aggregation. These charts conveniently identified the regions in which the differences were less than 10%, between 10% and 30%, and more than 30% for easy to use general guidelines for suitability of the RDG-FA theory in any scattering applications of interest, such as laser-based particulate diagnostics. Various types of aggregate geometry ranging from straight chains (D(f) ≈ 1.0) to compact clusters (D(f) ≈ 3.0) were also considered for generalization of the findings. For the present computational conditions, the RDG-FA theory yielded accurate predictions to within 10% for ‖m - 1‖ to approximately 1 or more as long as the primary particles in aggregates were within the Rayleigh scattering limit (x(p) ≤ 0.3). Additionally, the effect of fractal dimension on the performance of the RDG-FA was generally found to be insignificant. The results suggested that the RDG-FA theory is a reasonable approximation for optics of a wide range of fractal aggregates, considerably extending its domain of applicability.     

Pulsed laser deposition of silicon nitride thin films by laser ablation of a Si target in low pressure ammonia

We report the deposition of Si-N films by multipulse excimer laser ( = 308 nm, _FWHM = 30 ns) ablation of Si wafers placed in a slow flow of NH₃ in the pressure range (1 bar-1 mbar). The films are deposited on to a Si collector placed parallel to the Si target. We succeeded in depositing pure amorphous Si₃N₄ films at a pressure of 1 mbar of NH₃. The deposition rate reached a maximum value of 0.2–0.3 nm per pulse. At lower pressures, the deposited films consist of a fine mixture of three amorphous phases (amorphous stoichiometric silicon nitride, amorphous non-stoichiometric silicon nitride and amorphous silicon). The amorphous silicon is prevalent in films deposited at a pressure of several to several tens of bars. Droplets of polycrystalline -Si are sometimes visible on the film surface. The experimental evidence, is analysed with a view to elucidating the participation in the chemical synthesis of the three main stages of the process: the substance expulsion from the target by laser ablation, the transition through the gas of the expulsed substance and it's final impact on the collector. We conclude that silicon nitride is mostly synthesized during the impact on the collector of the flow of the ablated substance.     

Some questions on the corrosion of steel in concrete—Part I: when,how and how much steel corrodes

It is widely accepted that concrete-embedded steel is in a passive state. However, there are some exceptional circumstances that induce corosion in an active state within concrete structures, thereby severely reducing their durability. This two-part paper analyses some major questions which, however elementary they may be, are still controversial in scientific, technical and economic terms. The first part provides answers to the following questions on the steel/concrete/environment system:

1. How does steel in concrete normally behave?
2. What are the initiating factors for depassivation?
3. What are the effects of corrosion?
4. What is the morphology of corrosion in the active state? and
5. What is the corrosion rate threshold above which the durability of reinforced concrete structures is impaired? The answers to these questions are provided in light of experimental results, most of which were obtained by the authors themselves.

     

Parallel programming for multimedia applications

Computing capabilities are continuing to increase with the availability of multi core and many core processors. The wide availability of multi core processors has made parallel programming possible for end user applications running on desktops, workstations, and mobile devices. While parallel hardware has become common, software that exploits parallel capabilities is just beginning to take hold. Multimedia applications, with their data parallel nature and large computing requirements will benefit significantly from parallel programming. In this paper an overview of parallel programming is presented and languages and tools for parallel programming such as OpenMP and CUDA are introduced within the scope of multimedia applications.