Field Masks

The first and most obvious question is whether or not a narrower velocity distribution leads to narrower collisional resonances. In Fig. 14.14 we show the Na 26s + Na 26s — Na 26p + Na 25p resonances obtained under three different experimental conditions.20 In Fig. 14.14(a) the atoms are in a thermal 670 K beam. In Figs. 14.14(b) and (c) the beam is velocity selected using the approach shown in Fig. 14.13 to collision velocities of 7.5 X 103 and 3.8 X 103 cm/s, respectively. The dramatic reduction in the linewidths of the collisional resonances is evident. The calculated linewidths are 400, 28, and 10 MHz, and the widths of the collisional resonances shown in Figs. 14.14(a)-(c) are 350,40, and 23 MHz respectively. The widths decrease approximately as l/v3/2 until Fig. 14.14(c), at which point the inhomogeneities of the electric field mask the intrinsic linewidth of the collisional resonance. 

The etching procedure using a negative photoresist is identical except that the lithographic mask must be opaque in the regions where metal is to be removed — this is known as a dark-field mask. Exposure of negative resist to UV light makes it insoluble in its developer. 

FIGURE 20.1 Pressure-flow relationships of a U.S. Army M40 field mask. (From Musa, S.R., Banderet, L.E., Cadarette, B. Textbook of Military Medicine Medical Aspects of Harsh Environments, Volume 2, K.B. Pandolf and R.E. Burr, eds. Office of the Surgeon General, Department of the Army, United States of America, Falls Church, VA, 2002.)... 

The blended natural rubber faceblank of the M17A2 Chemical-Biological Field Mask protects the wearer s face, eyes, and respiratory tract, while the... 

Fig. 16-7. The M40 Chemical-Biological Field Mask. Reprinted from Brletich NR, Tracy MF, Dashiell TR. Worldwide NBC Mask Handbook. Edgewood, Md Chemical Warfare/ Chemical and Biological Defense Information Center September 1992 385.

The M42 Chemical-Biological Field Mask is the same series as the M40. The materials of construction and the basic features are identical, but the M42 protective mask is used by combat vehicle crews (Figure 16-8). 

Some eye protectors and helmets may interfere with the peripheral visual field. Masks and breathing apparatus interfere with olfactory senses. 

The first step involving the preparation of master is spin coating of silicon wafer with SU-8 negative resist. Subsequently, UV exposure is carried out with a clear field mask. This is followed by the development of SU-8 master. Glass posts are placed on SU-8 master to define the inlets and reservoirs. PDMS is mixed with prepolymers having weight ratio of the base and... 

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