Omnidirectional

The plasma source implantation system does not use the extraction and acceleration scheme found in traditional mass-analy2ing implanters, but rather the sample to be implanted is placed inside a plasma (Fig. 4). This ion implantation scheme evolved from work on controlled fusion devices. The sample is repetitively pulsed at high negative voltages (around 100 kV) to envelope the surface with a flux of energetic plasma ions. Because the plasma surrounds the sample, and because the ions are accelerated normal to the sample surface, plasma-source implantation occurs over the entire surface, thereby eliminating the need to manipulate nonplanar samples in front of the ion beam. In this article, ion implantation systems that implant all surfaces simultaneously are referred to as omnidirectional systems. 

The capture velocity of a hood is defined as the air velocity created by the hood at the point of contaminant generation. The hood must generate a capture velocity sufficient to overcome opposing air currents and transport the contaminant to the hood. For enclosing hoods, capture velocity is the velocity at the hood opening. In this case, the velocity must be sufficient to keep the contaminant in the hood. In practice, hood shape and the influence of crossdrafts on the measured capture velocity have to be considered. All three velocity components should be measured and used to calculate the magnitude and direction of the total velocity. Other methods used, not as good as the previous one, are to measure the velocity with a directional velocity sensor towards the hood or to measure the net velocity by an omnidirectional velocity sensor. In the last method the main airflow direction should be viewed and evaluated by means of a smoke test (see Sections 10.2.1 and 10.2.2.1). 

Usually this type of anemometer does not provide information on the flow direction. Vice versa, the. sensors are made as independent of the flow direction as possible—omnidirectional. This is an advantage for free-space ventilation measurements, as the flow direction varies constantly and a direction-sensitive anemometer would be difficult to use. Naturally, no sensor is fully omnidirectional, but satisfactory constructions are available. Due to the high sensor thermal inertia, this type of anemometer is unsuitable for high-frequency flow fluctuation measurement. They can be used to monitor low-frequency turbulence up to a given cut-off frequency, which depends on the dynamic properties of the instrument. 

A calibration facility must produce the desired velocity range for the meter to be calibrated. The air temperature should be kept constant over the test to ensure constant density. For thermal anemometers, velocity calibration only is not sufficient. They should also be checked for temperature compensation. In the case of omnidirectional probes, sensitivity to flow direction should be tested. In the case of low-speed (thermal) anemometers, their self-convection error should be measured, and, for instruments measuring flow fluctuation (turbulence), dynamic characteristics testing should be carried out as well. ... 

The immensity of this figure suggests that emissions may not in fact be omnidirectional. The total energy output can be substantially reduced by assuming... 

The performance of a head-mounted two-microphone adaptive noise-cancellation system was investigated by Weiss [Weiss, 1987] and Schwander and Levitt [Schwander and Levitt, 1987]. In this system, an omnidirectional microphone was used for the speech signal and a rear-facing hypercardioid microphone mounted directly above the speech microphone was used for the noise reference. In a room having a reverberation time of 0.4 sec, this system improved the speech recognition score to 74 percent from 34 percent correct for the unprocessed condition for normal-hearing listeners given... 

Fig. 4 Schematic photonic bandgap HWG cross section of a honeycomb-type structures, where light is confined to the central defect hole, and b omnidirectional guide, where light is confined by cylindrical photonic crystal layers...

The omnidirectional guide is most useful for sensing applications owing to the open hollow core. In honeycomb-type structures [31,32], light is confined to the small central air hole, which is difficult to fill with analyte gas for sensing owing to considerable back-pressure building up in the hollow structure. 

While C-H activations are often relatively fast, C-C activations are commonly slow. This is usually ascribed to the omnidirectional character of the H(ls) orbital allowing it to form strong bonds in the ttansition state, as well as to the lesser steric hindrance in the C-H case. 

Data Reliability. In Cases II-VII of Table II, the data have been subdivided to examine possible aerosol sampling bias due to forward ship motion and/or relative wind direction. In Cases II and III, the wind data do have a bias toward lower speeds while on station compared to underway. This bias is to be expected because stations were not taken in rough weather conditions. Overall, the similarity in the regression analysis and Gaussian parameters for Cases I, II, IV, V, and VII reaffirms the omnidirectional sampling capability of the ARCAS, as well as minimal ship effect under the conditions encountered during this cruise. 

Figure 2. June 3, 1982, solar neutron event (a) Count rate enhancement of the Jungfraujoch 18-IGY neutron monitor, (b) Simulated omnidirectional spectra of secondary particles at 700 g cm-2 induced by 1068 MeV solar neutrons at onset time [Moser et al., 2003].

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