Spatial patterns and environmental drivers of benthic infaunal community structure and ecosystem function on the New Zealand continental margin

To investigate regional drivers of spatial patterns in macro- and meio-faunal community structure (abundance, biomass and taxonomic diversity) and ecosystem function (sediment community oxygen consumption [SCOC]), we sampled two regions in close proximity on New Zealand's continental margin—the Chatham Rise and the Challenger Plateau. Sites (n = 15) were selected in water depths ranging from 266–1212 m to generate a gradient in sedimentary properties and, in particular, surface pelagic productivity. Both macro- and meio-fauna abundance and biomass was 2–3.5 times higher on the Chatham Rise than on the Challenger Plateau, reflecting regional differences in pelagic primary production. We also found significant inter- and intra-regional differences in macro-fauna taxonomic diversity with two distinctive site groupings in each region. Univariate and multivariate measures of macro-fauna community attributes were most strongly correlated with sediment photosynthetic pigment (explaining 24%–59% of the variation). Sediment pigment content was as equally important in explaining meio-fauna community structure (36%–7%). Unlike community structure, SCOC was most strongly correlated with depth (44%), most likely reflecting temperature effects on benthic metabolism. Our results highlight the importance of a benthic labile food supply in structuring infaunal communities on continental margins and emphasise a tight coupling between pelagic and benthic habitats.     

The influence of multivariate analysis methods and target grain size on the accuracy of remote quantitative chemical analysis of rocks using laser induced breakdown spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was used to quantitatively analyze 195 rock slab samples with known bulk chemical compositions, 90 pressed-powder samples derived from a subset of those rocks, and 31 pressed-powder geostandards under conditions that simulate the ChemCam instrument on the Mars Science Laboratory Rover (MSL), Curiosity. The low-volatile (<2 wt.%) silicate samples (90 rock slabs, corresponding powders, and 22 geostandards) were split into training, validation, and test sets. The LIBS spectra and chemical compositions of the training set were used with three multivariate methods to predict the chemical compositions of the test set. The methods were partial least squares (PLS), multilayer perceptron artificial neural networks (MLP ANNs) and cascade correlation (CC) ANNs. Both the full LIBS spectrum and the intensity at five pre-selected spectral channels per major element (feature selection) were used as input data for the multivariate calculations. The training spectra were supplied to the algorithms without averaging (i.e. five spectra per target) and with averaging (i.e. all spectra from the same target averaged and treated as one spectrum). In most cases neural networks did not perform better than PLS for our samples. PLS2 without spectral averaging outperformed all other procedures on the basis of lowest quadrature root mean squared error (RMSE) for both the full test set and the igneous rocks test set. The RMSE for PLS2 using the igneous rock slab test set is: 3.07 wt.% SiO₂, 0.87 wt.% TiO₂, 2.36 wt.% Al₂O₃, 2.20 wt.% Fe₂O₃, 0.08 wt.% MnO, 1.74 wt.% MgO, 1.14 wt.% CaO, 0.85 wt.% Na₂O, 0.81 wt.% K₂O. PLS1 with feature selection and averaging had a higher quadrature RMSE than PLS2, but merits further investigation as a method of reducing data volume and computation time and potentially improving prediction accuracy, particularly for samples that differ significantly from the training set. Precision and accuracy were influenced by the ratio of laser beam diameter (∼490 μm) to grain size, with coarse-grained rocks often resulting in lower accuracy and precision than analyses of fine-grained rocks and powders. The number of analysis spots that were normally required to produce a chemical analysis within one standard deviation of the true bulk composition ranged from ∼10 for fine-grained rocks to >20 for some coarse-grained rocks.     

Reconstruction of propagating Kelvin–Helmholtz vortices at Mercury's magnetopause

A series of quasi-periodic magnetopause crossings were recorded by the MESSENGER spacecraft during its third flyby of Mercury on 29 September 2009, likely caused by a train of propagating Kelvin–Helmholtz (KH) vortices. We here revisit the observations to study the internal structure of the waves. Exploiting MESSENGER's rapid traversal of the magnetopause, we show that the observations permit a reconstruction of the structure of a rolled-up KH vortex directly from the spacecraft's magnetic field measurements. The derived geometry is consistent with all large-scale fluctuations in the magnetic field data, establishes the non-linear nature of the waves, and shows their vortex-like structure. In several of the wave passages, a reduction in magnetic field strength is observed in the middle of the wave, which is characteristic of rolled-up vortices and is related to the increase in magnetic pressure required to balance the centrifugal force on the plasma in the outer regions of a vortex, previously reported in computer simulations. As the KH wave starts to roll up, the reconstructed geometry suggests that the vortices develop two gradual transition regions in the magnetic field, possibly related to the mixing of magnetosheath and magnetospheric plasma, situated at the leading edges from the perspectives of both the magnetosphere and the magnetosheath.     

层结流体中具有纬向基本剪切流的Rossby波振幅的mKdV方程

In this paper,modified Korteweg-de Vries (mKdV) equations for the amplitude of solitary Rossby waves in stratified fluids with a zonal shear flow are derived by using a weakly nonlinear method.It is found that the coefficients of mKdV equations depend not only on the β effect and the Visl-Brunt frequency,but also on the basic shear flow.     

Creator应用于虚拟城市三维建模的关键技术与实践

分析了将Creator应用于虚拟城市三维建模的技术路线,讨论了建模过程中的三个关键技术,解决了虚拟城市三维建模中精细程度和数据量之间的矛盾,并结合实践加以应用.     

Shallow ocean overturning and the heat and carbon content of the Glacial Tropical Ocean

Mechanisms affecting the heat and carbon content of the Glacial Tropical Ocean (21,000 years BP) remain controversial. Exchange with the deep ocean via vertical mixing and the overturning circulation is one aspect that is clearly relevant to greenhouse gas concentrations and future climate change. We examined evidence of the possible role of the shallow overturning contribution on the Glacial Tropical Ocean temperature and carbonate ion concentration. Compared to the present, we find that the Glacial tropical upper ocean (0–1000 m) had enhanced vertical gradients in temperature and carbonate ion concentration, reduced turbulent diffusivity (vertical mixing rate) (by 20% or more), and weakened Ekman pumping in middle-latitudes, all consistent with reduced shallow overturning. The weakened property exchanges between the tropical upper ocean and the ocean below (cold with high total dissolved carbon-dioxide concentration) provide a unified explanation for both the unexpectedly-small sea surface cooling and the lower carbon-dioxide content in the Glacial tropical upper ocean and the atmosphere.     

Current assessment of the Red Rectangle band problem

In this paper we discuss our insights into several key problems in the identification of the Red Rectangle Bands (RRBs). We have combined three independent sets of observations in order to try to define the constraints guiding the bands. We provide a summary of the general behavior of the bands and review the evidence for a molecular origin of the bands. The extent, composition, and possible absorption effects of the bands are discussed. Comparison spectra of the strongest band obtained at three different spectral resolutions suggests that an intrinsic line width of individual rotational lines can be deduced. Spectroscopic models of several relatively simple molecules were examined in order to investigate where the current data are weak. Suggestions are made for future studies to enhance our understanding of these enigmatic bands.     

Temperature Dependence of Single-Crystal Spinel (MgAl2O4) Elastic Constants from 293 to 423°K Measured by Light-Sound Scattering in the Raman-Nath Region

Summary. The temperature dependence of single-crystal elastic constants of synthetic stoichiometric MgAl₂O₄ spinel has been measured by the light-sound scattering technique in the Raman-Nath region. The crystal is set into forced vibration by a single crystal LiNbO₃ transducer coupled to one crystal face. A He-Ne Laser beam is diffracted by the stress-induced birefringence inside the crystal. The diffraction angle is determined from the distance between two spots exposed on a photographic plate by the first order diffracted beams as measured by a microdensitometer. The sound wavelength inside the crystal is then inferred from the laser diffraction angle. Combining the sound wavelength with the measured transducer frequency, the velocity inside the crystal is determined typically to a precision of 0·05 per cent. In this method, the measurement of velocity is not dependent on either the determination of sample length or on phase shifts at sample-transducer interface. Velocities of four pure modes, L //[001], T //[001], L //[110], and T //[110]( P //[1 1 0] are measured in the temperature range between 293 and 423 °K. A linear temperature dependence is fit to the data by a least square method. Values obtained at 25 °C from this linear fit are
The temperature dependence of the adiabatic elastic constants and bulk and shear (VRH average) moduli is computed using the density and literature value of thermal expansion coefficient. Values obtained are:
A comparison with previous measurements by pulse superposition and ultrasonic interferometry methods is made. Disagreement, when present, is discussed in terms of the separate measuring techniques. Finally, the present method, with its possibility for further improvement, is evaluated as a new method to measure temperature and pressure dependence of elastic constants.