Collective dynamics of liquid sulphur across the polymerisation transition temperature probed by inelastic x-ray scattering.

Inelastic x-ray scattering (IXS) experiments on liquid sulphur were carried out below (140◦C) and above (180◦C) the polymerisation temperature Tλ of about 159◦C to investigate changes in the collective dynamics of this unique liquid, that exhibits a liquid‒liquid transition. As reported earlier, broad longitudinal acoustic excitation signals were observed at both temperatures, and only the width of the quasielastic peaks slightly decreased when the temperature crossed the transition temperature. A model analysis was performed using a generalised Langevin formalism with a memory function having one thermal and two viscoelastic decay channels with the help of simple sparse modelling, and large positive deviations from the hydrodynamic sound velocity by 51‒54% were observed. The fast viscoelastic relaxation time τµis close to the correlation times of intermolecular stretching and bending motions of local sulphur connections in both ring and chain structures, and is similar to those of other molecular liquids. The small contrasts in the IXS spectra across the λ transition result in large changes in only the slow viscoelastic decay time τα of the memory function. The τα value at 140◦C matches the mixed internal/external torsional modes of S8 molecules well, whereas that at 180◦C has no corresponding molecular motion mode. The kinematic viscosity values at thesmaller than the minimum values of macroscopic shear viscosity, in⃗dicating that largeQ 0 limit are much changes in relaxation dynamics are expected with Q in the GHz and MHz excitation regimes. .

Phonon dispersion curves in the type-I crystalline and molten clathrate compound Eu8Ga16Ge30.

The dynamic structure factorS(Q,E), whereQandEare momentum and energy transfer, respectively, has been measured for liquid Eu8Ga16Ge30(EGG), using inelastic x-ray scattering. The excitation energy of the longitudinal acoustic mode in the liquid was scaled to that in liquid Ba8Ga16Sn30(BGS) with the effective mass. This result means that the local structure in both liquids are similar. The longitudinal acoustic excitation energy of type-I clathrate compound EGG disperses faster than that in the liquid, suggesting that the interatomic force is weakened on melting. The lower energy excitation was observed in both liquid EGG and liquid BGS. In comparison with the longitudinal phonon dispersion in crystalline clathrate compound EGG obtained by density functional theory-based calculations, the lower energy in the liquid was found to be near the optical mode energy. The result indicates that the lower energy mode arises from the relative motion between Eu and (Ga, Ge) atoms.

Effects of molecular shape and flexibility on fast sound of organic liquids.

Inelastic x-ray scattering spectra of four organic liquids, n-hexane, cyclohexane, ethylene glycol dimethyl ether, and 1,4-dioxane, were measured, and the sound velocity in the nm-1 wavenumber and meV energy regimes was determined. Compared with the corresponding values in the hydrodynamic limit, the sound velocity in the nm-1 regime was faster, and the positive dispersion of the longitudinal modulus was stronger in liquids composed of ring structures (cyclohexane and 1,4-dioxane) than in those of linear chain structures (n-hexane and ethylene glycol dimethyl ether). Molecular dynamics simulation of n-hexane and cyclohexane was also performed. The difference in the positive dispersion of the longitudinal modulus was reproduced by simulation, and it was elucidated by the difference in the longitudinal modulus in the q = 0 limit and the THz frequency regime. The excess part of the longitudinal modulus from the hydrodynamic limit was further divided into various contributions, and the smaller excess modulus of n-hexane was mainly ascribed to two reasons. The first one is that the shear modulus of n-hexane is smaller in the THz regime, and the second one is that the positive dispersion of the bulk modulus due to the vibrational energy relaxation is weaker. The second mechanism was further interpreted in terms of the fast vibrational energy relaxation of intramolecular modes associated with the chain deformation of n-hexane.

A cryostat designed for x-ray fluorescence holography experiments down to 4 K.

A cryostat was designed for x-ray fluorescence holography (XFH) experiments at low temperatures down to 4 K, where many functional materials show characteristic transitions, such as high-temperature superconducting, magnetic, dielectric, and valence transitions. For XFH measurements, changes in two angles of samples with respect to the incident synchrotron x-ray beam, i.e., incident angle θ and azimuthal angle ϕ, are necessary. A low-temperature specialized small piezoelectric motor is installed at the cryostat head for ϕ, and the cryostat itself is rotated by a stepping motor for θ. The heat from the piezoelectric motor for ϕ and the cryostat power determining the total cryostat mass were optimized for the limited working spaces and beamtimes of synchrotron experiments. Some examples of the XFH results at low temperatures, such as a Pb crystal and an YbInCu4 valence transition material, are presented to show the feasibility of this low-temperature equipment.

The use of diversity indices for local assessment of marine sediment quality.

Diversity indices are commonly used to measure changes in marine benthic communities. However, the reliability (and therefore suitability) of these indices for detecting environmental change is often unclear because of small sample size and the inappropriate choice of communities for analysis. This study explored uncertainties in taxonomic density and two indices of community structure in our target region, Japan, and in two local areas within this region, and explored potential solutions. Our analysis of the Japanese regional dataset showed a decrease in family density and a dominance of a few species as sediment conditions become degraded. Local case studies showed that species density is affected by sediment degradation at sites where multiple communities coexist. However, two indices of community structure could become insensitive because of masking by community variability, and small sample size sometimes caused misleading or inaccurate estimates of these indices. We conclude that species density is a sensitive indicator of change in marine benthic communities, and emphasise that indices of community structure should only be used when the community structure of the target community is distinguishable from other coexisting communities and there is sufficient sample size.

Potential impacts of marine urbanization on benthic macrofaunal diversity.

Urbanization and associated human activities have caused numerous changes to natural environments, including the loss of natural habitats and replacement with artificial structures. How these changes impact coastal marine biodiversity and ecosystem functioning is not well known. In this study, we examined the potential impacts of habitat changes by comparing species commonality and community structure (i.e., species richness, abundance, and functional composition) among artificial (a breakwater wall) and natural habitats (eelgrass bed, intertidal flat, and subtidal bottom) within a semi-enclosed coastal sea impacted by marine urbanization. We found considerable species overlap (i.e., high species sharing) among the eelgrass bed, intertidal flat, and subtidal bottom habitats. By contrast, the breakwater wall was a distinctive habitat with little overlap in species and functional groups with the other habitats, and was therefore a poor substitute for natural habitats. Our study suggests that marine urbanization degrades redundancy and inhibits the maintenance of biodiversity in coastal marine zones.

Local- and Intermediate-Range Structures on Ordinary and Exotic Phase-Change Materials by Anomalous X-ray Scattering.

Local- and intermediate-range atomic structures were investigated on amorphous phases of an ordinary phase-change material, Ge2Sb2Te5 (GST), and an exotic one, Cu2GeTe3 (CGT), by using anomalous X-ray scattering close to K absorption edges of each element to find a fast amorphous-crystalline phase-change mechanism. The obtained data were analyzed by using reverse Monte Carlo modeling to obtain partial structure factors, partial pair distribution functions, and three-dimensional atomic configurations. Ring statistics were carefully examined to clarify the similarity and difference compared with the corresponding crystal structures, and it was found that amorphous GST has a number of four-membered rings indicating fragments of crystal structure, and amorphous CGT has a remarkable number of three-membered rings showing a collapse of crystal structures composed of purely six-membered rings. A persistent homology analysis was carried out and long-range ring structures of the constituent elements were observed in the amorphous phase, which may originate from fragments of crystal structures with a long-range periodicity.

Multiple-wavelength neutron holography with pulsed neutrons.

Local structures around impurities in solids provide important information for understanding the mechanisms of material functions, because most of them are controlled by dopants. For this purpose, the x-ray absorption fine structure method, which provides radial distribution functions around specific elements, is most widely used. However, a similar method using neutron techniques has not yet been developed. If one can establish a method of local structural analysis with neutrons, then a new frontier of materials science can be explored owing to the specific nature of neutron scattering-that is, its high sensitivity to light elements and magnetic moments. Multiple-wavelength neutron holography using the time-of-flight technique with pulsed neutrons has great potential to realize this. We demonstrated multiple-wavelength neutron holography using a Eu-doped CaF2 single crystal and obtained a clear three-dimensional atomic image around trivalent Eu substituted for divalent Ca, revealing an interesting feature of the local structure that allows it to maintain charge neutrality. The new holography technique is expected to provide new information on local structures using the neutron technique.

Accumulation of Trace Metal Elements (Cu, Zn, Cd, and Pb) in Surface Sediment via Decomposed Seagrass Leaves: A Mesocosm Experiment Using Zostera marina L.

Accumulation of Cu, Zn, Cd, and Pb in the sediment of seagrass ecosystems was examined using mesocosm experiments containing Zostera marina (eelgrass) and reference pools. Lead was approximately 20-fold higher in the surface sediment in the eelgrass pool than in eelgrass leaves and epiphytes on the eelgrass leaves, whereas zinc and cadmium were significantly lower in the surface sediment than in the leaves, with intermediate concentrations in epiphytes. Copper concentrations were similar in both the surface sediment and leaves but significantly lower in epiphytes. Carbon and nitrogen contents increased significantly with increasing δ13C in surface sediments of both the eelgrass and reference pools. Copper, Zn, Cd, and Pb also increased significantly with increasing δ13C in the surface sediment in the eelgrass pool but not in the reference pool. By decomposition of eelgrass leaves with epiphytes, which was examined in the eelgrass pool, copper and lead concentrations increased more than 2-fold and approximately a 10-fold, whereas zinc and cadmium concentrations decreased. The high copper and lead concentrations in the surface sediment result from accumulation in decomposed, shed leaves, whereas zinc and cadmium remobilized from decomposed shed leaves but may remain at higher concentrations in the leaves than in the original sediments. The results of our mesocosm study demonstrate that whether the accumulation or remobilization of trace metals during the decomposition of seagrass leaves is trace metal dependent, and that the decomposed seagrass leaves can cause copper and lead accumulation in sediments in seagrass ecosystems.

Net uptake of atmospheric CO2 by coastal submerged aquatic vegetation.

'Blue Carbon', which is carbon captured by marine living organisms, has recently been highlighted as a new option for climate change mitigation initiatives. In particular, coastal ecosystems have been recognized as significant carbon stocks because of their high burial rates and long-term sequestration of carbon. However, the direct contribution of Blue Carbon to the uptake of atmospheric CO2 through air-sea gas exchange remains unclear. We performed in situ measurements of carbon flows, including air-sea CO2 fluxes, dissolved inorganic carbon changes, net ecosystem production, and carbon burial rates in the boreal (Furen), temperate (Kurihama), and subtropical (Fukido) seagrass meadows of Japan from 2010 to 2013. In particular, the air-sea CO2 flux was measured using three methods: the bulk formula method, the floating chamber method, and the eddy covariance method. Our empirical results show that submerged autotrophic vegetation in shallow coastal waters can be functionally a sink for atmospheric CO2. This finding is contrary to the conventional perception that most near-shore ecosystems are sources of atmospheric CO2. The key factor determining whether or not coastal ecosystems directly decrease the concentration of atmospheric CO2 may be net ecosystem production. This study thus identifies a new ecosystem function of coastal vegetated systems; they are direct sinks of atmospheric CO2.

An evaluation of leaf biomass : length ratio as a tool for nondestructive assessment in eelgrass (Zostera marina L.).

The characterization of biomass and its dynamics provides valuable information for the assessment of natural and transplanted eelgrass populations. The need for simple, nondestructive assessments has led to the use of the leaf biomass-to-length ratio for converting leaf-length measurements, which can be easily obtained, to leaf growth rates through the plastochrone method. Using data on leaf biomass and length collected in three natural eelgrass populations and a mesocosm, we evaluated the suitability of a leaf weight-to-length ratio for nondestructive assessments. For the data sets considered, the isometric scaling that sustains the weight-to-length proxy always produced inconsistent fittings, and for leaf-lengths greater than a threshold value, the conversion of leaf length to biomass generated biased estimations. In contrast, an allometric scaling of leaf biomass and length was highly consistent in all the cases considered. And these nondestructive assessments generated reliable levels of reproducibility in leaf biomass for all the ranges of variability in leaf lengths. We argue that the use of allometric scaling for the representation of leaf biomass in terms of length provides a more reliable approach for estimating eelgrass biomass.

Variable and complex food web structures revealed by exploring missing trophic links between birds and biofilm.

Food webs are comprised of a network of trophic interactions and are essential to elucidating ecosystem processes and functions. However, the presence of unknown, but critical networks hampers understanding of complex and dynamic food webs in nature. Here, we empirically demonstrate a missing link, both critical and variable, by revealing that direct predator-prey relationships between shorebirds and biofilm are widespread and mediated by multiple ecological and evolutionary determinants. Food source mixing models and energy budget estimates indicate that the strength of the missing linkage is dependent on predator traits (body mass and foraging action rate) and the environment that determines food density. Morphological analyses, showing that smaller bodied species possess more developed feeding apparatus to consume biofilm, suggest that the linkage is also phylogenetically dependent and affords a compelling re-interpretation of niche differentiation. We contend that exploring missing links is a necessity for revealing true network structure and dynamics.

X-ray fluorescence holography.

X-ray fluorescence holography (XFH) is a method of atomic resolution holography which utilizes fluorescing atoms as a wave source or a monitor of the interference field within a crystal sample. It provides three-dimensional atomic images around a specified element and has a range of up to a few nm in real space. Because of this feature, XFH is expected to be used for medium-range local structural analysis, which cannot be performed by x-ray diffraction or x-ray absorption fine structure analysis. In this article, we explain the theory of XFH including solutions to the twin-image problem, an advanced measuring system, and data processing for the reconstruction of atomic images. Then, we briefly introduce our recent applications of this technique to the analysis of local lattice distortions in mixed crystals and nanometer-size clusters appearing in the low-temperature phase of a shape-memory alloy.

Collective dynamics of hydrated ß-lactoglobulin by inelastic x-ray scattering.

Inelastic x-ray scattering measurements of hydrated ß-lactoglobulin (ß-lg) were performed to investigate the collective dynamics of hydration water and hydrated protein on a picosecond time scale. Samples with different hydration levels h [=mass of water (g)/mass of protein (g)] of 0 (dry), 0.5, and 1.0 were measured at ambient temperature. The observed dynamical structure factor S(Q,ω)/S(Q) was analyzed by a model composed of a Lorentzian for the central peak and a damped harmonic oscillator (DHO) for the side peak. The dispersion relation between the excitation energy in the DHO model and the momentum transfer Q was obtained for the hydrated ß-lg at both hydration levels, but no DHO excitation was found for the dry ß-lg. The high-frequency sound velocity was similar to that previously observed in pure water. The ratio of the high-frequency sound velocity of hydrated ß-lg to the adiabatic one of hydrated lysozyme (h=0.41) was estimated as ∼1.6 for h=0.5. The value is significantly smaller than that (∼2) of pure water that has the tetrahedral network structure. The present finding thus suggests that the tetrahedral network structure of water around the ß-lg is partially disrupted by the perturbation from protein surface. These results are consistent with those reported from Brillouin neutron spectroscopy and molecular dynamics simulation studies of hydrated ribonuclease A.