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A 720 mm diameter 12-segment-bonded carbon-fiber-reinforced silicon carbide (C/SiC) composite mirror has been fabricated and tested at cryogenic temperatures. Interferometric measurements show significant cryogenic deformation of the C/SiC composite mirror, which is well reproduced by a model analysis with measured properties of the bonded segments. It is concluded that the deformation is due mostly to variation in coefficients of thermal expansion among segments. In parallel, a 4-degree-of-freedom ball-bearing support mechanism has been developed for cryogenic applications. The C/SiC composite mirror was mounted on an aluminum base plate with the support mechanism and tested again. Cryogenic deformation of the mirror attributed to thermal contraction of the aluminum base plate via the support mechanism is highly reduced by the support, confirming that the newly developed support mechanism is promising for its future application to large-aperture cooled space telescopes. OCIS codes: 120.6650, 220.4840, 230.4040, 350.1260.

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) have opposite actions on the gallbladder; PACAP induces contraction, whereas VIP induces relaxation. Here, we have attempted to identify key residues responsible for their interactions with PACAP ([PAC.sub.1]) and VIP (VPAC) receptors in the guinea pig gallbladder. We synthesized PACAP-27/VIP hybrid peptides and compared their actions on isolated guinea pig gallbladder smooth muscle strips using isotonic transducers. [[Ala.sup.4]]- and [[Val.sup.5]]PACAP-27 were more potent than PACAP-27 in stimulating the gallbladder. In contrast, [[Ala.sup.4], [Val.sup.5]]- and [[Ala.sup.4], [Val.sup.5], [Asn.sup.9]]PACAP-27 induced relaxation similarly to VIP. [[Asn.sup.9]]-, [[Thr.sup.11]]-, or [[Leu.sup.13]]PACAP-27 had 20-70% contractile activity of PACAP-27, whereas [[Asn.sup.24], [Ser.sup.25], [Ile.sup.26]]PACAP-27 showed no change in the activity. All VIP analogs, including [[Gly.sup.4], [Ile.sup.5], [Ser.sup.9]] VIP, induced relaxation. In the presence of a [PAC.sub.1] receptor antagonist, PACAP(6-38), the contractile response to PACAP-27 was inhibited and relaxation became evident. RT-PCR analysis revealed abundant expressions of [PAC.sub.1] receptor, 'hop' splice variant, and [VPAC.sub.1] and [VPAC.sub.2] receptor mRNAs in the guinea pig gallbladder. In conclusion, PACAP-27 induces contraction of the gallbladder via [PAC.sub.1]/hop receptors. [Gly.sup.4] and [Ile.sup.5] are the key N[H.sub.2]-terminal residues of PACAP-27 that distinguish [PAC.sub.1]/hop receptors from [VPAC.sub.1]/[VPAC.sub.2] receptors. However, both the N[H.sub.2]-terminal and [alpha]-helical regions of PACAP-27 are required for initiating gallbladder contraction. [PAC.sub.1] receptor; [VPAC.sub.1] receptor; [VPAC.sub.2] receptor; splice variant

The introduction of a porous structure into single-crystal Si causes variations in the photoelectronic properties of porous silicon (PS). Photoconductivity exhibits photosensitivity to visible light, high dark resistivity and an intrinsic bias voltage-dependent spectral response. An increase in band-gap width and luminescence properties of the PS layer results in variations in its photoelectronic properties.