Internal impedance

Tuning the probe assures that the resonant frequency of the probe coil is the same as the RF frequency you will be using and matching the probe matches the probe coil as a load to the impedance (internal electrical resistance) of the amplifiers. This gives maximum efficiency of transfer of RF power from the amplifiers to your sample nuclei and maximum sensitivity in detecting the FID. Each sample modifies the resonant frequency and matching of the probe, so these have to be reoptimized with each new sample. Tuning the probe is not necessary for routine XH spectra, but for advanced experiments it is important if you wish to use standard values for pulse widths without the need to calibrate for each sample. 

In membrane separation of the olefin/paraffin mixture, the predominant selective separation of the olefin is evident. First, the olefin molecule is smaller in size compared to the respective paraffin. Specifically, C—C distance in paraffins is 0.1534 nm, whereas the C=C distance in olefins is 0.1337 nm. Atoms of carbon in paraffins feature sp hybridization and free rotation around C—C bonds. Atoms of olefins feature sp hybridization. The rigid C=C bond impedes internal rotation in the olefin molecule and makes it flat. It is therefore clear why olefin molecules are smaller in size compared to paraffin and why the diffusion coefficients of olefins in polymers would be higher than those of paraffins. Second, the presence of unsaturated bonds in olefin molecules makes them capable of specific interactions with the membrane matrix. Efforts to take advantage of these capabilities resulted in the development of an important field of research facilitated transport. 

In passing, we note that this device can be made into a power divider/combiner merely by terminating the A port and having the rf input at B. Alternatively, an out-of-phase power divider/combiner can be made by putting the terminating impedance on B and the input at A. In fact, power dividers are made in exactly this way with the terminating impedance internal to the package. 

In 1939 Frank-Kamenetskii considered circumstances where Newtonian cooling was only an empirical approximation, and where the escape of heat was impeded internally by the thermal properties of the medium. (This will always be the case for a large enough system.) An internal temperature-distribution with a maximum at the middle results. For stability, this central temperature may not exceed a critical value. For a sphere with its surface at T the relationship is ... 

Takao Nakamura and Yoshitake Yamamoto (2001) Evaluation System of Physical Exercise Ability using Bio-electrical Impedance, International Symposium on Industrial Electronics Proc., Pusan, Korea, 2001, pp 2053-2058... 

Solar cells have been used extensively and successfully to power sateUites in space since the late 1950s, where their high power-to-weight ratio and demonstrated rehabiUty are especially desirable characteristics. On earth, where electrical systems typically provide large amounts of power at reasonable costs, three principal technical limitations have thus far impeded the widespread use of photovoltaic products solar cells are expensive, sunlight has a relatively low power density, and commercially available solar cells convert sunlight to electricity with limited efficiency. Clearly, terrestrial solar cells must be reasonably efficient, affordable, and durable. International efforts are dedicated to obtaining such devices, and a number of these activities have been reviewed (1). 

Internal resistance or impedance is the resistance or impedance that a battery or cell offers to current flow. 

Fig. 7. (a) Simple battery circuit diagram where represents the capacitance of the electrical double layer at the electrode—solution interface, W depicts the Warburg impedance for diffusion processes, and R is internal resistance and (b) the corresponding Argand diagram of the behavior of impedance with frequency, for an idealized battery system, where the characteristic behavior of A, ohmic B, activation and C, diffusion or concentration (Warburg... 

Through laults which may be much higher than at F2 but outside the CTs 2one Internal fault being fed by two sources although limited by the equipment impedance... 

V = theoretical maximum CTsecondary voltage across the relay circuit at the maximtim internal fault current. (The maximum internal fault current is the level of fault of the machine or the system tinder protection.) This must also take into account any other supply sources that may also feed the fault, such as more than one supply bus, as shown in Section 13.4.1 (5) and Figure 13.18, and illustrated in Figure 15.30. If the cumrilative fault current is /scc> hen the maximum CT secondary voltage will be k m = Ascc impedance of the relay circuit. 

External events are accident initiators that do not fit well into the central PSA structure used for "internal events." Some "external events" such as fire due to ignition of electrical wires, or flood from a ruptured service water pipe occur inside the plant. Others, such as earthquakes and tornados, occur outside of the plant. Either may cause failures in a plant like internal events. External initiators may cause multiple failures of independent equipment thereby preventing action of presumably redundant protection systems. For example, severe offsite flooding may fli 1 the pump room and disable cooling systems. An earthquake may impede evacuation of the nearby populace. These multiple effects must be considered in the analysis of the effects of external events. 

The impedance of the transducer is important if it provides an output signal to an electronic device (an amplifier, for example) and the impedance of the two must be matched for accurate measurement. Some transducers (thermocouples, for example) generate their output by internal mechanisms (i.e. they are self-excited). Others such as resistance thermometers need an external source and an appropriate type must be available. Transducers used in the measurement of the more common physical quantities are discussed below. 

Tests for quality of sealing of anodic coatings have become internationally standardised. They include dye spot tests with prior acid treatment of the surface (ISO 2143 1981 and BS 6161 Part 5 1982), measurement of admittance or impedance (ISO 2931 1983 and BS 6161 Part 6 1984), or measurement of weight loss after acid immersion (ISO 3210 1983 and BS 6161 Part 3 1984, and ISO 2932 1981 and BS 6161 Part 4 1981). Of these the chromic-phosphoric acid immersion test (ISO 3210) has become the generally accepted reference test. 

Amalgamated zinc powder has been used as the negative material to prevent zinc corrosion and zinc passivation. Recently, from the viewpoint of environmental problems, mercury-free alkaline-manganese batteries were developed by using zinc powder with indium, bismuth and other additives [2-4]. Adding indium to zinc powder is the most effective way to improve the characteristics of the cells [3]. Figure 3 shows the variation in the internal impedance of the cells according to the additive content of the zinc powder. 

Cell voltage / V Internal cell Impedance / m 0 Cell voltage / V... 

Figure 3. Variation of internal impedance of alkaline-manganese cells with the additives content of the zinc powder o, Hg additive , In additive.

Underwriters Laboratories (UL) requires that consumer batteries pass a number of safety tests [3]. UL requires that a battery withstand a short circuit without fire or explosion. A positive temperature coefficient (PTC) device [4] is used for external short-circuit protection. The resistance of a PTC placed in series with the cell increases by orders of magnitude at high currents and resulting high temperatures. However, in the case of an internal short, e.g., if the positive tab comes lose and contacts the interior of the negative metal can, the separator could act as a fuse. That is, the impedance of the separator increases by two to three orders of magnitude due to an increase in cell temperature. 

As reviewed there is much to consider. Examples include cooling as the product sets up results in different shrinkage rates for thicker versus thinner sections in the different processes. This results in either external waviness or sink marks, or warpage and internal voids, as the product contracts. Flat surfaces are difficult to maintain but not impossible to attain using certain processes. High speed of flow to fill the cavity of the mold is impeded going around square corners, so provision for radii and fillets are important. 

The effects of total flow rate of fuels (CO2/CH4 = 1) on the impedance in the internal reforming of CH4 by C02 0ver ESC (NiO-YSZ- Ce02 I YSZ I (LaSr)Mn03) of SOFC system are represoited in Figure 6. It was comsidaed fliat the total resistance was dependent on the total flow rate because the conva sions of CO2 and CH4 over ESC were affected by contact time in the internal reforming system. 

Most of the difficulties occur when reference materials cross national borders and, as a result of specific national or international regulations, are in some way impeded. Generally the impediments include questions involving tariff numbers and customs duty coupled with environmental and health and shipping regulations. Many times, these questions arise because reference materials are shipped in small quantities and not used directly in commerce. 

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