Density Fluctuations in an Electrolyte from Generalized Debye-Hueckel Theory

Near-critical thermodynamics in the hard-sphere (1,1) electrolyte is well described, at a classical level, by Debye-Hueckel (DH) theory with (+,-) ion pairing and dipolar-pair-ionic-fluid coupling. But DH-based theories do not address density fluctuations. Here density correlations are obtained by functional differentiation of DH theory generalized to {\it non}-uniform densities of various species. The correlation length $\xi$ diverges universally at low density $\rho$ as $(T\rho)^{-1/4}$ (correcting GMSA theory). When $\rho=\rho_c$ one has $\xi\approx\xi_0^+/t^{1/2}$ as $t\equiv(T-T_c)/T_c\to 0+$ where the amplitudes $\xi_0^+$ compare informatively with experimental data.Comment: 5 pages, REVTeX, 1 ps figure included with epsf. Minor changes, references added. Accepted for publication in Phys. Rev. Let

New insights into embayed beach rotation: The importance of wave exposure and cross-shore processes

Although embayed beach rotation has been viewed and modeled as an alongshore sediment transport process acting on a uniform beach profile, recent research suggests a more complex response whereby alongshore variability in cross-shore sediment fluxes may be more significant. This study utilizes 5 years of fully three-dimensional beach surveys at Narrabeen-Collaroy Beach (SE Australia) to quantify the control of alongshore nonuniform wave exposure and cross-shore processes on embayed beach rotation. Empirical orthogonal function analysis of the alongshore variability in subaerial beach volume/width and berm slope confirms that the dominant mode of subaerial beach variability is an onshore/offshore sediment exchange that is strongly controlled (R > 0.8) by the alongshore gradient in breaker wave height and coincides with a uniform flattening/steepening of the berm slope. A secondary rotation-like signal is observed in both the subaerial beach volume/width data and, significantly, the berm slope. This inverse flattening/steepening of the berm slope between beach extremities is most likely a proxy for differing cross-shore processes within the surf zone between the exposed and sheltered ends of the embayment, particularly with regards to dissipation of storm wave energy by offshore sandbars and beach recovery following storms. Analysis of the corresponding wave data reveals two distinct time scales of wave forcing characteristic of short-term erosion and longer-term recovery processes. A new conceptual model is presented of three differing modes of embayed beach rotation, with the newly identified beach rotation mode controlled by offshore sandbars considered of particular importance at embayments where headland sheltering of oblique waves is pronounced

A reevaluation of coastal embayment rotation: The dominance of cross-shore versus alongshore sediment transport processes, Collaroy-Narrabeen Beach, southeast Australia

Over 30 years of wave and beach survey data at Collaroy-Narrabeen Beach in southeast Australia are analyzed to investigate the extent to which shoreline variability within this coastal embayment is dominated by shoreline oscillations due to cross-shore sediment exchange or shoreline rotations due to alongshore exchange between the beachs extremities. Offshore wave data are derived from both buoy measurements and ERA-40 reanalysis data. EOF analysis of the monthly shoreline data suggests that the dominant mode of shoreline variability (60% of variability) is an onshore-offshore sediment exchange that is greater at the more exposed northern end of the beach than at the predominantly sheltered southern end. This mode is primarily associated with variability in wave energy/storms, which by the nature of the wave climate of this region chiefly occurs from the south-southeast. The secondary mode of shoreline variability (26% of variability) is a rotational signal between either end of the beach, which coincides with 24% of the offshore wave climate shifting between the south-southeast and east as well as changes in the wave period and wave energy/storms. A distinct annual cycle is identified in this rotation signal. It is concluded that alongshore sediment transport processes associated with embayment rotation is more subtle than previously thought and a refined conceptual model of coastal embayment variability in this region is presented highlighting the dominance of cross-shore sediment exchange processe

Conserved features of Y RNAs revealed by automated phylogenetic secondary structure analysis.

Item does not contain fulltextY RNAs are small 'cytoplasmic' RNAs which are components of the Ro ribonucleoprotein (RNP) complex. The core of this complex, which is found in the cell nuclei of higher eukaryotes as well as the cytoplasm, is composed of a complex between the 60 kDa Ro protein and Y RNAs. Human cells contain four distinct Y RNAs (Y1, Y3, Y4 and Y5), while other eukaryotes contain a variable number of Y RNA homologues. When detected in a particular species, the Ro RNP has been present in every cell type within that particular organism. This characteristic, along with its high conservation among vertebrates, suggests an important function for Ro RNP in cellular metabolism; however, this function has not yet been definitively elucidated. In order to identify conserved features of Y RNA sequences and structures which may be directly involved in Ro RNP function, a phylogenetic comparative analysis of Y RNAs has been performed. Sequences of Y RNA homologues from five vertebrate species have been obtained and, together with previously published Y RNA sequences, used to predict Y RNA secondary structures. A novel RNA secondary structure comparison algorithm, the suboptimal RNA analysis program, has been developed and used in conjunction with available algorithms to find phylogenetically conserved secondary structure models for YI, Y3 and Y4 RNAs. Short, conserved sequences within the Y RNAs have been identified and are invariant among vertebrates, consistent with a direct role for Y RNAs in Ro function. A subset of these are located wholly or partially in looped regions in the Y3 and Y4 RNA predicted model structures, in accord with the possibility that these Y RNAs base pair with other cellular nucleic acids or are sites of interaction between the Ro RNP and other macromolecules

Below the surface: Twenty-five years of seafloor litter monitoring in coastal seas of North West Europe (1992–2017)

Marine litter presents a global problem, with increasing quantities documented in recent decades. The distribution and abundance of marine litter on the seafloor off the United Kingdom's (UK) coasts were quantified during 39 independent scientific surveys conducted between 1992 and 2017. Widespread distribution of litter items, especially plastics, were found on the seabed of the North Sea, English Channel, Celtic Sea and Irish Sea. High variation in abundance of litter items, ranging from 0 to 1835 pieces km−2 of seafloor, was observed. Plastic tems such as bags, bottles and fishing related debris were commonly observed across all areas. Over the entire 25-year period (1992–2017), 63% of the 2461 trawls contained at least one plastic litter item. There was no significant temporal trend in the percentage of trawls containing any or total plastic litter items across the long-term datasets. Statistically significant trends, however, were observed in specific plastic litter categories only. These trends were all positive except for a negative trend in plastic bags in the Greater North Sea - suggesting that behavioural and legislative changes could reduce the problem of marine litter within decades