ALBERT

Notes: Abstract  Stocks of eastern oysters, Crassostrea virginica (Gmelin), in mesohaline Chesapeake Bay, USA, exhibit a high degree of inter-annual and spatial variability in recruitment. We found that cumulative oyster spatfall on off-bottom collector plates, measured throughout the summer in 14 years over a span of three decades, was highly positively correlated (r 2 = 0.8) with juvenile oyster recruitment on adjacent oyster bars. Total abundances of juvenile oysters on these bars were, however, generally 99.7% lower than predicted from cumulative seasonal larval settlement on collector plates. We propose that although the number of larvae metamorphosing was the key factor in determining the gross annual pattern of recruitment to these mesohaline oyster bars, the actual magnitude of recruitment was governed by post-settlement processes, such as competition for limited resources and predation. We tested the hypothesis that predation may be partly responsible for high post-settlement juvenile oyster mortality. We performed a series of 3-d field investigations over two summers (1989, 1990) at a mesohaline site, employing cages of various mesh sizes (400, 800, 1500 μm) to protect hatchery-reared spat of 0.5 to 4.0 mm shell height. Mortality rates for spat held for 3 d in the estuary (17.8%) were significantly higher (P = 0.0001) for the smallest spat (0.5 to 2.0 mm) compared with those of 2.01 to 4.0 mm (4.2%). In 1990, but not in 1989, enclosure within 400 and 800 μm mesh cages significantly (P = 0.004) increased survival during 3-d deployments (9.4 and 10.1%, respectively) compared with spat unprotected by mesh cages (21.9%). In a series of laboratory predation studies that used the entire community of invertebrates that could penetrate the cages, microscopic juvenile polyclad flatworms, Stylochus ellipticus, were the only organisms that we observed crawling into living oysters and feeding on oyster tissue. Large flatworms (50 to 200 mm2) are known to be important predators on oysters, but this ability of flatworms that were so small (〈ca. 5 mm2) and translucent as to be almost invisible without magnification to feed on immediate post-metamorphic oysters has not been documented previously. Our results suggest that the rate of mortality due to predation in mesohaline Chesapeake Bay is much reduced once spat survive for 2 to 3 weeks post-metamorphosis. Thus, it is likely that predation in the 1 to 2 week period immediately after settlement may be a crucial factor in the structuring of eastern oyster populations.

Notes: Rotationally resolved experiments on the NO/Pt(111) system explore the mechanisms of inelastic scattering and trapping/desorption. The rotational dynamics associated with these two regimes are markedly different. A neat supersonic NO beam is scattered at normal incidence from a Pt(111) crystal at 375–475 K. The non-Boltzmann rotational population distribution of the scattered species exhibits considerable rotational excitation beyond the energy available from the incident beam. Thus, a surface vibration to rotational energy transfer mechanism must be operative. The accompanying rotational alignment data reveal that highly excited rotational states exhibit predominantly "cartwheel'' motion. In contrast, rotationally excited molecules that desorb from a 553 K Pt(111) surface show a preference for "helicopter'' motion. The opposite preferences for rotational alignment in the two dynamical regimes provide insight into the anisotropy of molecule–surface interactions.

Notes: A model is presented to describe the dynamical processes of trapping/desorption as well as direct and indirect inelastic scattering on single-crystal surfaces. Newton's equations of motion are integrated for a system consisting of a rigid rotor interacting with a slab of 19 surface atoms. The surface atom which is closest to the center of mass of the molecule is permitted to translate only along the surface normal. In turn, this mobile surface atom is harmonically coupled to a microcanonical heat bath consisting of three subsurface atoms. This method is much less computationally intensive than the typical generalized Langevin equation (GLE) approach. Direct comparison is made between the predictions of this model and experiment for the NO/Pt(111) system. In the case of trapping/desorption, the model accurately describes the observed dependence of rotational alignment on rotational quantum number. For the inelastic scattering regime, the model successfully reproduces the degree of rotational excitation and qualitatively accounts for the observed rotational alignment. In addition, the model predicts correlations between final state velocity and final state rotational angular momentum (both direction and magnitude), as well as the effect of molecular orientation and surface impact parameter on the overall trapping probability.

Notes: An empirical observation is made of an apparent universal shift in the consolute point (Xc=critical composition, Tc=critical temperature) of binary fluid mixtures when the system identity is perturbed. The shift in a "pure'' system's critical point (Xco, Tco) when perturbed becomes (Xc,Tc) which seems to obey (Tc−Tco)/Tco= (Xc−Xco)/Xco. This relation has been observed to hold in a wide range of systems including closed-loop coexistence curves (guaiacol–glycerol–water, or tertiary butyl alcohol in secondary butyl alcohol and water), deuterated systems (methanol–cyclohexane, or isobutyric acid–water), impurities added to methanol–cyclohexane, the molecular weight dependence in polystyrene–methylcyclohexane, and the pressure dependence of methanol–cyclohexane.

Notes: The refractive index in each phase of the binary fluid mixture isobutyric acid and water was measured at temperatures below the system's upper consolute point. This data was combined with existing density data to test the Lorentz–Lorenz relation in a near-critical binary fluid mixture. The Lorentz–Lorenz relation is verified within experimental error (0.5%) when the volume change on mixing the components is taken into account. The density coexistence curve data is reanalyzed to determine the critical exponent β and amplitude B. By allowing the order parameter to be a definition of the volume fraction that includes volume loss on mixing, a very symmetric coexistence curve is obtained which can be described by simple scaling with β=0.326±0.003 and B=1.565±0.021. This exponent agrees with theoretical predictions while the amplitude, when combined with existing turbidity data, confirms two-scale-factor universality. The amplitude obtained by analyzing the coexistence curve when the refractive index is the order parameter also combines with turbidity data to confirm two-scale-factor universality, but does not require knowledge of the volume loss on mixing or the composition dependence of the refractive index.