ALBERT

Notes: The rotational-, spin-, and lambda doublet-state distributions for nitric oxide (NO) formed in the CO2 laser multiphoton dissociation of methyl nitrite, CH3ONO, in a pulsed molecular beam are reported. Upon methyl nitrite photolysis by temporal square wave infrared laser pulses at 983 cm−1 of 50 ns duration and 800 MW/cm2 intensity, the low-lying rotational levels of the nitric oxide fragments formed in the 2Π1/2 (F1) and 2Π3/2 (F2) spin-orbit states exhibited Boltzmann-like population distributions, characterizable by the rotational temperatures TR (F1)=400±10 K and TR (F2)=530±100 K; the integrated populations for J〈30.5 of the two spin components were in the ratio F1/F2=2.7 : 1. For those highly rotationally excited levels with J(approximately-greater-than)24.5 there is no measurable spin preference, the level population depending solely on total internal energy Eint. There is no apparent preference for formation of either lambda doublet component and there is no observable fragment alignment, the nascent NO species exhibiting an isotropic distribution of angular momentum vectors.

Notes: The rotational level distribution of the NO fragments formed as a result of the predissociation of the vibrationally excited NO–C2H4 (ν7) van der Waals molecule was measured by laser excited fluorescence techniques. The distribution was found to be Boltzmann in character, described by the rotational temperature 75±15 K. An average kinetic energy release of ≈105 cm−1 per fragment, in an isotropic flux distribution, was determined from Doppler profiles of the NO fragments in selected rotational levels.

Notes: Picosecond infrared transmission spectroscopy was used to directly measure the vibrational energy relaxation time T1 of hydroxyl groups chemisorbed on the surface of colloidal silica (SiO2). T1 was obtained for OH(νstretch=1) in the strongly bound "isolated sites'' of fumed silica particles in vacuum and dispersed in several liquids at T=293 K. At the SiO2/vacuum interface, T1=204±20 ps. When the SiO2 particles are surrounded by solvents, the relaxation time of the surface OH(v=1) groups decreases: for the liquids CCl4, CF2Br2, CH2Cl2, and C6H6, T1(ps)=159±16, 140±30, 102±20, and 87±30, respectively. T1 does not depend on the size of the SiO2 particles for the range 70 A(ring)≤ diameter ≤150 A(ring), or on the surface OH coverage up to an average density of 4 OH/100 A(ring)2. Significant amounts of physisorbed water (5 H2O/100 A(ring)2) decreased T1 for the isolated OH(v=1) to T1=56±10 ps. For comparison to the surface hydroxyls, the vibrational deactivation time for OH(v=1) groups in the bulk of fused silica (OH/SiO2≈130 ppm by weight) was determined to be T1=109±11 ps. These observations are discussed in terms of the possible mechanisms of vibrational energy flow in these systems. The observed T1 values demonstrate that the spectral linewidths (e.g., IR and Raman) observed for these surface vibrations are too large (by factors of 200–2000) to be caused solely by T1 uncertainty broadening. The slow transfer of vibrational energy between surface and lattice vibrations may have important implications for surface chemistry.

Notes: The rat CT antigens are a system of medial histocompatibility antigens linked to RT1, the rat major histocompatibility complex (MHC). They have aroused interest firstly because, despite their extreme serological weakness, they are targets for ‘unrestricted’ cytotoxic T lymphocytes (CTL); and secondly because they have appeared to represent a complex genetic system in terms both of the number of genetic loci involved and the number of distinguishable antigenic specificities expressed. The CT system was originally defined by the reactions of LEW anti-F344 (RT1l anti-RT1lvl) secondary in vitro CTL. These CTL reacted strongly on DA(RT1avl) targets, but much more weakly on AUG or PVG (RT1c) targets. We have used the recently derived RT1 recombinant rat strains PVG.R19 (RT1.AavlIavlCc) and PVG.R20 (RT1.AcIcCavl) to investigate the genetic control of this system. Contrary to previous interpretations, the results are consistent with a model in which CT is a single locus, which maps to the RTI.C region. In addition, our results demonstrate that there is cross-reactivity of anti-RT1C CTLs on RT1A products, and we suggest that the earlier placement of a CT locus in the RT1.A region was probably incorrect and a consequence of this cross-reactivity.

Notes: A recent study on low-alloy, nonoriented, semiprocessed electrical steels indicated that at 60 Hz and 15 and 17 kG the anomalous loss per cycle Wa increased linearly with t2/ρ, i.e., Wa=Wao+kt2/ρ, where t is sheet thickness, ρ is resistivity, and Wao and k are empirical constants. The present study explores the above relationship over inductions B of 5 to 17 kG and frequencies f of 20 to 200 Hz. A separation of hysteresis loss Wh into synchronous and asynchronous components is also considered. Six laboratory heats with Si+Al〈1.1 wt. % were hot and cold rolled to 0.035, 0.07, and 0.11 cm. The sheets were annealed, critically strained, and decarburized. Longitudinal strips were tested with dc as well as ac current in a 25-cm Epstein frame. The above linear equation was generally valid. At each combination of B and f, the intercepts Wao were always positive, but the slopes k were negative at 5 and 10 kG and positive at 15 and 17 kG. Furthermore, a fifth of the Wa values were negative. The negative Wa and k were associated with lack of flux penetration. Wh, but not Wa, increased with increasing oxygen and decreasing grain size, and these effects resided in the B1.6 component of Wh.

Notes: Abstract Occultations and eclipses from ancient times down to the present are analysed to determine changes in the length of the day. By subtracting the expected tidal contribution from the observed changes, the non-tidal variations are obtained. The non-tidal varations are shown to occur on time-scales of decades and millennia.

Notes: Summary 1. Photoreceptors ofMusca were superfused with solutions containing either fluoride (F−), vanadate (VO 3 − ), or one of the GTP analogs GPPNHP and GTPγS. These agents have been reported to generate discrete voltage fluctuations (bumps) when injected intoLimulus photoreceptors. All four agents produced noisy depolarizations inMusca photoreceptors when added to the perfusate. 2. The effects of all four agents were reversible. GPPNHP induced dark noise only after exposure to light, whereas VO 3 − and F− did not require light for their effect. 3. Although individual bumps were too small to be resolved, the power spectra of voltage noise induced by these agents resembled closely those of light-induced noise. 4. F−-induced noise was reduced by adaptation following strong illumination. As F−-induced depolarization increased beyond 6 mV the voltage noise diminished, probably due in part to adaptation. With increasing F−-induced depolarization the power spectrum of F− noise changed shape slightly. Part of this change was probably due to adaptation, and it was similar to but smaller than corresponding changes in the spectrum of light-induced noise. 5. Analysis of F−-induced noise indicated that it was composed of bumps which, though similar in time course, were not identical to light-induced bumps. At small depolarizations, the F−-induced bumps were calculated to be 3–5 times smaller than light bumps and were less strongly affected by adaptation. Although the calculated duration of light-induced bumps diminished as intensity increased, the duration of F−-induced bumps showed no such dependence on depolarization, and was equal to that of light bumps in moderately dim light. Moreover light- and F-induced noise did not summate in the manner expected if they were indistinguishable to the photoreceptor. 6. In addition to noise, we saw other effects as well. The earliest effect of VO 3 − was a smooth depolarization which may have been due to this ion's role as a Na/K pump inhibitor. In experiments with some of these agents strong light caused a wave of afterdepolarization with no increase in noise. This effect occurred under a variety of conditions, however, and was not specific to the agents used. 7. F−, VO 3 − GPPNHP and GTPγS appear to generate noise inMusca photoreceptors through a common effect on the pathway of phototransduction. In the case of F− in particular, chemically induced bumps are smaller and less affected by adaptation than those produced by light. We discuss possible mechanisms of action consistent with these findings.