NO adsorption and dissociation on Rh(111): PM-IRAS study.

We have used in situ polarization-modulation infrared reflection absorption spectroscopy to study the adsorption/dissociation of NO on Rh(111). While these studies have not been conclusive regarding the detailed surface structures formed during adsorption, they have provided important new information on the dissociation of NO on Rh(111). At moderate pressures (< or =10(-6) Torr) and temperatures (<275 K), a transition from 3-fold hollow to atop bonding is apparent. Data indicate that this transition is not due to the migration of the 3-fold hollow NO but rather to the adsorption of gas-phase NO that is directed toward the atop position due to the presence of NO decomposition products, particularly chemisorbed atomic O species at the hollow sites. These results indicate that NO dissociation occurs at temperatures well below the temperature previously reported. Additionally, high pressure (1 Torr) NO exposure at 300 K results in only atop NO, calling into question the surface structures previously proposed at these adsorption conditions consisting of atop and 3-fold hollow sites.

Clostridial antibody response from injection-site lesions in beef cattle, long-term response to single or multiple doses, and response in newborn beef calves.

Experiments were conducted to compare clostridial antibody response of beef heifers that do and do not develop injection-site lesions, evaluate long-term antibody response of a single- and multiple-dose toxoid, and evaluate the ability of a clostridial toxoid to elicit an active antibody response in newborn calves. In Exp. 1, 37 weaned heifers were vaccinated (d 0) with a clostridial vaccine (Alpha-7, 2 mL, s.c.). Serum samples were collected on d 0, 28, 56, 84, and 112 to determine clostridial antibody titers. On d 28, heifers were visually inspected and palpated for injection-site lesions. The percentage of heifers that developed lesions was 64.9%. Lesioned heifers had elevated antibody titers for Clostridium chauvoei (CC) on d 28 (P < 0.08) and 84 (P < 0.07) compared with non-lesioned heifers. Clostridium sordellii (CS) and perfringens type D (CPD) antibody titers were greater in lesioned heifers than in non-lesioned heifers on d 28 and 56. In Exp. 2, long-term antibody response of Alpha-7 (A7) and Ultrabac 7 (UB7) was investigated in stocker heifers. The A7 heifers (n = 15) received one 2-mL vaccination (d 0), and the UB7 heifers (n = 15) received a 5-mL vaccination on d 0 and 28. Blood samples were collected on d 0, 28, 56, 84, 112, 140, and 180. Clostridium chauvoei, CPD, and Cl. novyi (CN) antibody titers from the A7 heifers were greater than those from the UB7 heifers on d 28. Due to the second UB7 injection, CC, CS, CN, and Cl. perfringens type C (CPC) antibody titers were greater in UB7 heifers than in A7 heifers on d 56. By d 112, titers were not different, and by d 140 all antibody titers were below detectable levels. In Exp. 3, 58 pregnant, mature, crossbred cows were vaccinated with A7 before calving. At birth, calves were carefully observed to ensure consumption of colostrum. Calves were blocked according to parturition date, and calves in each block were randomly allocated to receive A7 (s.c. at 3 +/- 3 d of age) or remain unvaccinated controls. Calves were bled at the time of vaccination (d 0) and on d 28, 56, 84, and 112. Antibody titers for CC, CPC, and CPD were elevated on d 0 and decreased throughout the experimental period (P < 0.01), but no titer differences (P > 0.10) were detected between treatment groups on any of the days sampled. These data indicated that antibody titers against clostridial diseases are enhanced when injection-site lesions develop. One injection of Alpha-7 seemed to provide the same length of protection as two injections of Ultrabac 7.

Clostridial vaccination efficacy on stimulating and maintaining an immune response in beef cows and calves.

Experiments were conducted to determine the efficacy in stimulating and maintaining an immune response in the presence of maternal antibodies, compare the extent of the anamnestic responses to revaccination, and compare the maternal antibody response of 2- or 5-mL clostridial vaccination. In Exp. 1, 118 nursing calves were randomly assigned to receive a 2-mL (Alpha-7, A7) or a 5-mL clostridial vaccine (Ultrabac 7; UB7) at 50.4 +/- 15.30 (X +/- SD) d of age (d 0 = date of calving). Calves were revaccinated with the same treatment on d 170. Blood samples were collected from 10 calves of each treatment group on d 50, 170, and 191 to determine antitoxin units for Clostridium perfringens type C (PC) and D (PD) and agglutination titers for Cl. chauvoei (CC). The A7-treated calves tended (P < .10) to have higher PC units on d 170, an increased rate of change in PD units from d 170 to d 191 (P < .06), and a tendency (P < .10) for enhanced CC titers on d 191 compared with UB7-treated calves. In Exp. 2, 109 pregnant cows and 83 pregnant heifers were randomly assigned within a 2 x 2 x 2 factorial design. The main effects were dam age (cow or heifer), dam treatment (A7 or UB7), and calf treatment (A7 or UB7). Dams were vaccinated with A7 or UB7 d 124 prepartum (d -124) and d 53 after birth. At d 53.4 +/- 12.88, calves were vaccinated with A7 or UB7 (d 53). Calves were revaccinated with the same treatment on d 173. Blood samples were collected from 10 dams per treatment group on d -124, 53, and 173 and from their calves on d 53, 173, and 194. Cows had higher antitoxin levels for PC (P < .01) and PD (P < .05) than heifers. The A7-treated dams had higher (P < .01) PD units on d 53 and d 173 and CC on d 173 than did UB7-treated dams. Calves from A7-treated cows had higher (P < .03) PD units on d 53 than calves from UB7-treated cows. The A7-treated calves had higher titers for CC (P < .01) on d 173 than did UB7-treated calves, and this enhanced level seemed to continue to d 194 (P < .08). In conclusion, titers for clostridial diseases in 50- to 53-d-old calves can be enhanced if dams are vaccinated approximately 4 mo before calving, and 120 d between clostridial vaccinations seems to be too long for adequate protection.

Brightness of luminance distributions with gradual changes.

The perception of gradually changing luminance distributions was investigated. Luminance changed across the radius of a disk by a linear, quadratic, or cubic function with varying magnitudes. Subjects selected matching luminances for the inner and outer edges of each stimulus. The threshold for reporting that the inner and outer matches were different occurred at approximately 20% contrast between those regions. This threshold did not vary with the particular function which described the luminance distribution. Further, as the magnitude of luminance change across the stimulus increased, subjects judged the inner and outer edges to differ more in brightness. Matching luminances also depended upon the background configuration with greater differences perceived across the disk radius when the surround and center dot of the stimulus were of opposite, rather than the same, luminance. These results indicate that models of brightness must consider all luminance changes in the stimulus, not just changes of a particular type such as second differences or changes at a luminance step.