The onset of vortex instability in laminar forced convection flow through a horizontal porous channel

The onset of convective instability in a fluid-saturated porous layer between the two horizontal plates heated isothermally from below has been analyzed theoretically by using propagation theory. In the analysis the thermal dispersion coefficient is assumed to be proportional to the streamwise velocity. The results show that both inertia and thermal dispersion stabilize the system.     

Two-fluid large-eddy simulation approach for particle-laden turbulent flows

In this paper, effects of particles on the subgrid scales of turbulence are properly accounted for during the modeling of subgrid scale stresses in the large-eddy simulation (LES) of fluid phase. In doing so, we propose closed filtered kinetic equations for phase space density of the particle. The various moments of these equations give the `fluid' equations which can be considered as the LES equations for the particle phase. The influence of subgrid scales motion on the particles is included in these `fluid' equations.     

FLOCCULATION OF ASPHALTENES AT HIGH PRESSURE. II. CALCULATION OF THE ONSET OF FLOCCULATION

The influence of pressure on the onset of flocculation of asphaltenes was calculated in the region from 1 to 300 bar and from 50 to 100°C. These calculations are the counterpart to our experimental data which, recently, have been reported in part 1 of an equally titled article [9]. As gas component methane and as precipitant i-octane were used. The asphaltene flocculation was considered to be a liquid-liquid equilibrium. For modelling the van der Waals equation of state (vdW-EOS) in the framework of continuous thermodynamics was applied. The composition of the crude oil was described by a continuous distribution function with respect to the solubility parameter δ of the Scatchard-Hildebrand theory. Within the distribution the asphaltenes represent the species with the highest δ-values. For oils with a very low content of asphaltenes the model developed describes the experimental flocculation data reasonably. In accordance to the experimental data the model predicts that, in the considered pressure range, without addition of i-octane asphaltene flocculation does not occur. However, on contrary to the experimental results, the model predicts the asphaltenes to show a higher flocculation tendency with increasing asphaltene content of the crude oil. For very high asphaltene contents the model even completely fails. Probably, the reason of this lack is the disregarding of asphaltene association.     

Yield Stress and Microstructure of Set Yogurt Made from High Hydrostatic Pressure-Treated Full Fat Milk

ABSTRACT: Set yogurts were prepared from fortified milk subjected to the following processes: (a) Thermal process (85C,°C,35 min), (b) High hydrostatic pressure process (193 or 676 MPa for 5 or 30 min), and (c) Nonprocessed milk (control). Yogurts from milk treated with 676 MPa for 30 min exhibited similar yield stress and water-holding capacity (WHC) to yogurts from heated milk. Transmission Electron Microscopy (TEM) micrographs exhibited small round casein micelle aggregates without appendages in yogurts from heated milk. Yogurts from milk treated with 193 MPa and untreated milk exhibited low yield stress, low WHC, and large clusters of coalesced micelles. Mechanisms for gel formation are discussed.     

Physical Aging of Amorphous Fructose

ABSTRACT: Physical aging of amorphous anhydrous fructose at temperature 5 °C and at 22 °C was studied using differential scanning calorimetry (DSC). The dynamic glass transition temperature, T_g0 for unaged samples was 16 °C and 13.3 °C for heating rate of 10 °C/min and 1 °C/min, respectively. The fictive temperature, T_f0 for unaged samples calculated by Richardson and Savill method was 12 °C, which is close to the dynamic value obtained from the lower DSC heating rate. The fictive temperature T_f of the aged fructose glasses at temperatures both below and above the transition region was fitted well by a non-exponential decay function (Williams-Watts form). Aging above the transition region (22 °C) for 18 d increased both the dynamic glass transition temperature T_g and the fictive temperature T_f. However, aging below the transition region (5 °C) for 1 d increased the dynamic glass transition temperature T_g but decreased the fictive temperature T_f.     

Comparison of the GFFF and LALLS Methods for the Measurement of Starch Granule Size Distribution in Spring Barley Caryopses

A newly developed method GFFF (Gravitational Field‐Flow Fractionation) and the well known method LALLS (Low Angle Laser Light Scattering) were used to assess starch granule size distribution of ten varieties of spring barley. As a distribution criterion, the ratio of starch granule content larger than 8 μm (type A) and smaller than 8 μm (type B) was chosen. Both methods divided the observed set in a similar way. Varieties Akcent, Forum and Atribut formed a variety set with the highest ratio of large and small starch granules. Varieties Scarlet and Kompakt had intermediate ratios. The remaining five varieties Amulet, Novum, Olbram, Tolar and Krona had the lowest ratios of large and small starch granules. Statistical analysis showed that there was a highly significant correlation between the GFFF and LALLS methods.     

On the application of adaptive antennas to microcellularenvironments: radio channel characteristics and system performance

The possible application of adaptive antennas in microcellular operational environments is studied in this paper with the help of a site-specific ray-tracing propagation model. First are examined the statistics of propagation parameters that play an important role for the performance of adaptive antennas. Particular emphasis is put on the spatial characteristics of the radio channel under line-of-sight (LOS) and non-LOS conditions. For this reason, area statistics are produced for a typical small-cell environment for parameters such as the number of multipath clusters, number of rays, angular size, and excess delay of each impulse response, as well as the number of rays, angular size and power of the multipath clusters. Results show that contrary to the common belief for such environments, the signal is not "almost" uniformly distributed in the spatial domain, instead is contained in a few narrow clusters. Then the effect of the microcellular environment on the uplink performance of some well-known techniques like conventional beamforming, maximum entropy, switched beams, maximum ratio and optimum combining, and beam-space optimum combining is examined . The results show that for typical time-division multiple-access (TDMA) scenarios with one and two users, the beam space optimum combining (strongest eigenvalue version) and the switched beams methods, offer the best performance     

Portable system for data acquisition and transmission based on handheld PC technology

A portable system is developed to monitor physical activity by acquiring and storing data from body-mounted sensors; a handheld PC is used for managing data acquisition and storage, including radio-transmission to a remote host. An application related to the use of a gyro-accelerometric sensor for determining walking distance is discussed.     

Electronic properties of Fibonacci quasi-periodic heterostructures

We study the electronic states of different GaAs-AlAs Fibonacci quasi-perodic heterostructures grown along the (001) direction. We employ an empirical tight-binding Hamiltonian including spin-orbit coupling together with the surface Green function matching method. We present results for the eighth Fibonacci generation formed from different building blocks. We compare these results with those of the constituent quantum wells and with those of heterostructures containing the same number of GaAs and AlAs slabs after periodic repetition of the building blocks. No Fibonacci spectrum is found in the energy regions near the conduction and valence band edges of GaAs. A selective localization of the local density of states in the GaAs layers is found for many electronic states.