Transport measurements, solids

Fig. 6. The magnetic field dependence of the high- and low-temperature MR, respeetively the solid lines are caleulated. The inset shows a sehematic of the eontact eonfiguration for the transport measurements.

In a recent study of the transport of solids by liquid in a 38 mm diameter pipe. 30 the following variables were measured ... 

This relation applies from the initial expansion of the bed until transport of solids takes place. There may be some discrepancy between the calculated and measured minimum velocities for fluidisation. This may be attributable to channelling, as a result of which the drag force acting on the bed is reduced, to the action of electrostatic forces in case of gaseous fluidisation—particularly important in the case of sands—to agglomeration which is often considerable with small particles, or to friction between the fluid and the walls of the containing vessel. This last factor is of greatest importance with beds of small diameters. Leva et al.<4 introduced a term, (GF — GE)/ GF, which is a fluidisation efficiency, in which GF is the minimum flowrate required to produce fluidisation and G / is the rate required to produce the initial expansion of the bed. 

It has been established from conductivity measurements that thermally activated and field-assisted hole hopping is responsible for the charge transport in solid polysilanes [48,49]. The mobility of the hole is as high as 10 m /V sec, while the mobility of the electron is a few orders of magnitude lower. In this section, we will show the reason why only the hole is mobile in polysilanes and how we can construct electron-conductive polysilanes. 

The experiments in the solid state are based on several techniques, including imaging, spectroscopy, and electrical transport measurements that reveal the electric current flux through the molecule under an external field. The results pertain to single molecules (or bundles) and can be remeasured many times. The roles of the donor and of the acceptor are in this case played either by the metal leads, or by the substrate and a metal tip. The interpretation is generally given in terms of conductivity, determined by the electronic energy levels (if the molecular structure supports the existence of localized... 

Fig. 9. Magnetic field dependence of the magnetization at selected temperatures for a 150-nm thick Ga xMn As film with a Mn composition x = 0.03S. The magnetic field is applied parallel to the sample surface (direction of magnetic easy axis) except for the closed circles at 5 K taken in perpendicular geometry. The solid line for S K shows the magnetization determined from transport measurements. The upper left inset shows a magnified view of the magnetization in the parallel field at 5 K. The lower right inset shows the temperature dependence of the remanent magnetization (Ohno et al. 1996a).

The solid line in fig. 9 shows M determined by the transport measurements, where the Hall resistance is almost proportional to the perpendicular component of M, as described in the next section. The good agreement between M determined by SQUID and transport measurements indicates that one can correctly determine M of (Ga,Mn)As by magnetotransport measurements. 

While electrochemical experiments provide useful information regarding electron transport through these molecular monolayers, construction of real devices requires formation of a top contact so that solid-state transport measurements can be made. The fabrication of contacts to molecular layers has been the major obstacle to the development of molecular electronic devices, whether based on thiol-based SAMs on gold or covalently attached molecules on silicon. The most popular approach to making contacts involves evaporation of metals onto the molecular layer, which is likely to result in at least partial penetration of the monolayer, and may possibly damage the molecules in the layer. 

Solid Liquid Electrophoresis Electric field Electrophoretic mobility via mass transport measurement, microscope or Doppler effect... 

It would be interesting if in a solid metal both the electro-self-trans-port and the electro-isotope-transport could be measured. Lodding has tried to do this by subjecting In at 137°C. to a direct current of 5000 amps./cm. for about eight months. He preliminarily reported a self-transport and a transport of the light isotope towards the cathode (45) meanwhile in more elaborate measurements he found the reverse direction for the self-transport in solid indium (46). It remains a question in which direction the isotope migration in solid indium goes, because the isotope effect reported in Reference 45 was at the limit of measurability. 

Earlier experiments have shown the utility of excitation transport measurements in providing relative information regarding coll size in pol)rmer blends (18). Here, we will summarize the results of recent experiments (28) which demonstrate that monitoring excitation transport on isolated colls in solid blends through time-resolved fluorescence depolarization techniques provides a quantitative measure of for the guest pol3mier. 

A very wide range of techniques can be used to probe atomic transport in solids, and these have been detailed in various books [204—208] and reviews [21, 209-212[ (see also Chapters 13, 8, 11 and 12). The most commonly used are tracer methods, ionic conductivity, and NMR measurements. Less commonly used (but more specialized) techniques include creep, quasi-elastic neutron scattering (QENS), and Mbssbauer spectroscopy (M S). An elegant survey ofthe methods that have been used on nanoionic materials has been made by Heitjans and Indris [210]. The principles, procedures, and limitations of the more common techniques are outlined in the following sections. 

An electron in a solid behaves as if its mass [CGS units are used in this review the exception is for the tabulation of effective masses, which are scaled by the mass of an electron (m0), and lattice constants and radii associated with trapped charges, which are expressed in angstroms (1A = 10 8 cm)] were different from that of an electron in free space (m0). This effective mass is determined by the band structure. The concept of an effective mass comes from electrical transport measurements in solids. If an electron s motion is fast compared to the lattice vibrations or relaxation, then the important quantity is the band effective mass (mb[eff]). If the electron moves more slowly (most cases of interest) and carries with it lattice distortions, then the (Frohlich) polaron effective mass (tnp[eff]) is appropriate [11]. The known band effective and polaron effective masses for electrons in the silver halides are listed in Table 1. The polaron and band effective masses are related to a... 

Pneumatic transportation of solids is important to many industrial processes, for example transporting coal and powder particles. To an operator of such a pneumatic conveyor, the mass flow rate of the solids is the primary process parameter to be measured accurately. A solid/gas flow is very difficult to control because it behaves quite differently from solid/liquid flows. A recent review (Yan, 1996) discussed several variables that may affect the performance of a flow instrument. The distribution of solids in a pneumatic pipeline can be highly inhomogeneous consequently, the particle velocity distribution over the pipe cross section can be widespread. Figure 6.28 shows examples in which the roping type flow is particularly difficult to understand and monitor. 

Wall Sampling from Vertical Slurry Pipelines. Moujaes (44) used wall sampling to measure solids concentration in upward vertical slurry flows. He found the sample concentration to be consistently lower than the true values in the pipe. Torrest and Savage (45) studied collection of particles in small branches. The sampling transport efficiency, E, defined as the ratio of the solids flow rate in the branch to that in the main pipe, was found to be a function of the single particle settling velocity (W0) and the upstream bulk velocity (Ub) as follows ... 

Mechanical transport of solids by the stream, as suspended or bed load, removes additional material. Direct measurement of suspended load yields a figure of 0.28 metric tons, or 0.0027 metric tons per acre for the... 

Permeabilities apply mainly to molecular transport in solid polymers, particularly polymer films. Also, diffusivities are usually obtained in conjunction with permeability measurements. Although such behavior is obviously important in many applications, it relates only indirectly to processing that occurs mainly with molten or thermally softened polymers. The principal role of processing with respect to permeabilities and diffusivities in solid polymers is development of the material s structural characteristics which, in turn, affect properties. As such, consideration of permeability will be deferred to Chapter 12, which deals with the effect of processing or structural parameters. 

Oxygen Anion Transport in Solid Oxides, Fig. 8 Projection of the observed nuclear density map of Lao.5Sro.5Coo.8Feo.203 5 measured at 800 °C, p02 = 10 atm. Note the cross-shaped displacement of the 0-atoms [28]... 

It is noteworthy that LOV-based techniques have not only been extensively employed in homogeneous solution-based assays, but have also shown promise in heterogeneous assays because flexible fluid manipulation is also suitable for delivering beads in flow-based manifolds, i.e. precise fluid manipulation by the LOV system and the channel configuration also make it a powerful platform for Bl [22,23]. In combination with the renewable surface concept, Bl has been widely exploited for separation and preconcentration of analytes in the presence of complex matrix components. Most importantly, the automated transport of solid materials in such a system allows their automatic renewal at will and thus provides measurement, packing and perfusion of beads with samples and... 

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