Single particles, measurement

Figure 12. Schematic representation of the setup for single particle measurements by electrostatic trapping (ET). Pt denotes two freestanding Pt electrodes (dashed region). A ligand-stabilized Pd cluster is polarized by the applied voltage and attracted to the gap between the Pt electrodes. (Reprinted with permission from Ref. [29], 1997, American Institute of Physics.)...

In Eq. (4.11) the variable DPRT is a very small number, since it is the diameter of a single particle measured in feet. As a particle is, say, 100 to 500 pm, and since 1 in = 25,400 pm, it becomes obvious that the Eq. (4.11) calculation will always have a very small answer, usually 2 to 4 places or more to the right of the decimal point. This fact is supported... 

Electrophoresis is always accompanied by Brownian motion that is, the mobility of a single particle measured at given time point is not necessarily representative of that particle or of the entire population. Brownian motion is responsible for... 

Figure 5.35 Schematic representation of the set-up for single particle measurements. Pt denotes two freestanding Ptelectrodes (dashed region). A ligand-stabilized Pd cluster is...

As a unit of the single particle measurement software on-line calculation of all interesting statistic parameters was integrated. 

A wide variety of measurements can now be made on single molecules, including electrical (e.g. scanning tunnelling microscopy), magnetic (e.g. spin resonance), force (e.g. atomic force microscopy), optical (e.g. near-field and far-field fluorescence microscopies) and hybrid teclmiques. This contribution addresses only Arose teclmiques tliat are at least partially optical. Single-particle electrical and force measurements are discussed in tire sections on scanning probe microscopies (B1.19) and surface forces apparatus (B1.20). 

Measurement of single particle settling velocity in a turbulent field is not easy. However, it is known to be a function of free settling velocity which for spherical particles can be estimated from the following ... 

Phase Doppler particle analyzers are essentially single-particle counters because they measure one particle at a time within a small sampling volume. This volume must be kept small to minimize the probabiUty of having more than one droplet in the volume at any given instant. This probabiUty increases as the concentration of droplets becomes greater, and there is more risk of measurement errors. 

Because a FIXE spectrum represents the int al of all the X rays created along the particle s path, a single FIXE measurement does not provide any depth profile information. All attempts to obtain general depth profiles using FIXE have involved multiple measurements that varied either the beam energy or the angle between the beam and the target, and have compared the results to those calculated for assumed elemental distributions. Frofiles measured in a few special cases surest that the depth resolution by nondestructive FIXE is only about 100 nm and that the absolute concentration values can have errors of 10-50%. 

This is our principal result for the rate of desorption from an adsorbate that remains in quasi-equihbrium throughout desorption. Noteworthy is the clear separation into a dynamic factor, the sticking coefficient S 6, T), and a thermodynamic factor involving single-particle partition functions and the chemical potential of the adsorbate. The sticking coefficient is a measure of the efficiency of energy transfer in adsorption. Since energy supply from the... 

Parker [55] studied the IN properties of MEH-PPV sandwiched between various low-and high work-function materials. He proposed a model for such photodiodes, where the charge carriers are transported in a rigid band model. Electrons and holes can tunnel into or leave the polymer when the applied field tilts the polymer bands so that the tunnel barriers can be overcome. It must be noted that a rigid band model is only appropriate for very low intrinsic carrier concentrations in MEH-PPV. Capacitance-voltage measurements for these devices indicated an upper limit for the dark carrier concentration of 1014 cm"3. Further measurements of the built in fields of MEH-PPV sandwiched between metal electrodes are in agreement with the results found by Parker. Electro absorption measurements [56, 57] showed that various metals did not introduce interface states in the single-particle gap of the polymer that pins the Schottky contact. Of course this does not imply that the metal and the polymer do not interact [58, 59] but these interactions do not pin the Schottky barrier. 

According to Schack(55), a single particle of soot transmits approximately 95 per cent of the incident radiation and a cloud must contain a very large number of particles before an appreciable emission can occur. If the concentration of particles is K, then the product of K and the thickness of the layer L is equivalent to the product PgLe in the radiation of gases. For a known or measured emissivity of the flame ey, the heat transfer rate per unit time to a wall is given by. 

Diffusion through a product layer can be treated like a film resistance. The surface concentration is measured inside the ash layer at the unbumed surface of the particle. If the ash thickness is constant and as 0, then the rate has the form of Equation (11.48). The ash thickness will probably increase with time, and this will cause the rate constant applicable to a single particle to gradually decline with time. 

To measure the strength of the forces exerted on particles, various analytical techniques have been developed [6, 7]. Unfortunately, since most of these techniques are based on hydrodynamics, assumption of the potential profiles is required and the viscosities of the fiuid and the particle sizes must be precisely determined in separate experiments, for example, using the viscous flow technique [8,9] and power spectrum analysis of position fluctuation [10]. Furthermore, these methods provide information on ensemble averages for a mass of many particles. The sizes, shapes, and physical and chemical properties of individual particles may be different from each other, which will result in a variety of force strengths. Thus, single-particle... 

Trimborn et al. (2000) describe a four-week field campaign to characterise an aerosol in a particular area, where the LAMPAS 2 instrument was continuously analysing the size and composition of individual particles in five size ranges between 0.2 pm and 1.5 pm. Some 10,000 single particle spectra were recorded during the measuring period, and one example of these is shown in Figure 3.13. 

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