Theoretical and experimental investigations of flexural wave propagation in periodic grid structures designed with the idea of phononic crystals

The propagation characteristics of flexural waves in periodic grid structures designed with the idea of phononic crystals are investigated by combining the Bloch theorem with the finite element method. This combined analysis yields phase constant surfaces, which predict the location and the extension of band gaps, as well as the directions and the regions of wave propagation at assigned frequencies. The predictions are validated by computation and experimental analysis of the harmonic responses of a finite structure with 11 × 11 unit cells. The flexural wave is localized at the point of excitation in band gaps, while the directional behaviour occurs at particular frequencies in pass bands. These studies provide guidelines to designing periodic structures for vibration attenuation.

Hydrothermal Synthesis and Crystal Structure of a Square Grid Coordination Copper(II) Polymer from 1,4-Bis(imidazole-1-ylmethyl)benzene

The title compound [Cu（bix）2（NO3）z·H2P]n 1 （bix = 1,4-bis（imidazole-1-ylme-thyl） benzene） has been synthesized by hydrothermal method. Its crystal structure is of monoclinic, space group P1^- with a = 8.3075（13）, b = 9.4725（13）, c = 10.0192（13） A, α = 91.088（4）, β = 104.063（6）, γ = 101.88（1）, V = 746.5（3） A^3, Z = 1, C28H30N10O7Cu1, Mr = 682.16, Dc = 1.518 g/cm^3, μ = 0.796 mm^-1, F（000） = 353, the final R = 0.0535 and wR = 0.0996 for 2921 observed reflections with I 〉 2σ（I）. Each bix ligand binds two Cu（Ⅱ） ions to form a 2-D（4,4） square grid layer, which is connected by hydrogen bonds showing large channels occupied by solvated water molecules and nitrate anions.

Azimuthal distributions of final-state particles and fragments and transverse structure of emission source in high-energy nucleus-nucleus collisions

The azimuthal distributions of final-state particles and fragments produced in high-energy nucleus-nucleus collisions are described by a modified multisource ideal gas model which contains the expansions and movements of the emission sources. The transverse structures of the sources are given in the transverse plane by momentum components Px and Py, and described by parameters in the model. The results of the azimuthal distributions, calculated by the Monte Carlo method, are in good agreement with the experimental data in nucleus-nucleus collisions at high energies.

Determination of optimal grid opening width for herringbone water-sediment separation structures based on sediment separation efficiency

The herringbone water-sediment separation structure(HWSSS) was developed to prevent debris flows. This paper mainly focuses on evaluating the sediment separation efficiency of HWSSS in debris flow prevention and determining the grid opening width D, a crucial structure parameter for HWSSS design. Theoretical analysis on the total sediment separation rate Pt reveals that the efficiency of sediment separation is much related with sediment grain size distribution(GSD) and grid opening width. The lower limit of Pt is deduced from the perspective of safety consideration by transforming debris flow into sediment-laden flow. Hydraulic model tests were carried out. Based on the regression analysis of the experimental data, the quantitative relationships between Pt and D and GSD characteristic values were finally established. A procedure for determining optimal grid opening width is proposed based on these analyses. These results are of significance in evaluating sediment separation effect by HWSSS in debris flow prevention and contribute to a more explicit methodology for design of HWSSS.

Analysis of Reflection Characteristics for Foam Filled Grid Structure

The reflection characteristics of gird structures are calculated by the spatial network method in the case of normal incidence plane electromagnetic wave. The numerical result shows that the grid panels without electromagnetic wave absorbing foams are not ideal. However, the absorbing ability can be achieved as low as -25 dBsm from 8 GHz to 12 GHz when the grid cells are filled with foam absorbers. Also it is noted from computation that the foam filled grid structures with larger cell size, higher and thinner ribs will improve the absorbing abilities, which illustrates that they can be used as the effective light-weight stealth structures for aeronautical application.

Effects of landscape fragmentation of plantation forests on carbon storage in the Loess Plateau,China

Tree plantation and forest restoration are the major strategies for enhancing terrestrial carbon sequestration and mitigating climate change.The Grain for Green Project in China has positively impacted global carbon sequestration and the trend towards fragmentation of plantation forests.Limited studies have been conducted on changes in plantation biomass and stand structure caused by fragmentation,and the effect of fragmentation on the carbon storage of plantation forests remains unclear.This study evaluated the differences between carbon storage and stand structure in black locust forests in fragmented and continuous landscape in the Ansai District,China and discussed the effects of ecological significance of four landscape indices on carbon storage and tree density.We used structural equation modelling to explore the direct and indirect effects of fragmentation,edge,abiotic factors,and stand structure on above-ground carbon storage.Diameter at breast height(DBH)in fragmented forests was 53.3%thicker,tree density was 40.9%lower,and carbon storage was 49.8%higher than those in continuous forests;for all given DBH>10 cm,the trees in fragmented forests were shorter than those in continuous forests.The patch area had a negative impact on carbon storage,i.e.,the higher the degree of fragmentation,the lower the density of the tree;and fragmentation and distance to edge(DTE)directly increased canopy coverage.However,canopy coverage directly decreased carbon storage,and fragmentation directly increased carbon storage and tree density.In non-commercial forests,fragmentation reduces the carbon storage potential of plantation,and the influence of patch area,edge,and patchy connection on plantation should be considered when follow-up trees are planted and for the plantation management.Thus,expanding the area of plantation patches,repairing the edges of complex-shaped patches,enhancing the connectivity of similar patches,and applying nutrients to plantation forests at regular intervals are recommended in fragmented areas of the Loess Plateau.

Crystal Structure and Mass Spectrometric Fragmentation Behavior of Eprosartan

The crystal structure determination and mass spectrometric fragmentation analysis of the medicinal ingredient eprosartan （4-[2-butyl-5-（2-carboxy-3-thiophen-2-yl-propenyl）-imidazol-l-ylmethyl]-benzoic acid） are presented. The single-crystal X-ray diffraction shows that the colorless transparent crystal of eprosartan is of monoclinic system, space group P2/c with a = 16.1861（15）, b = 10.9813（12）, c = 28.610（3） A, β = 118.452（2）°, Z = 4, V= 4471.1（8） A3, Dc = 1.288 g/cm3,μ（MoKα） = 0.178 mm^-1 and F（000） = 1831. The independent part of the unit cell contains two eprosartan molecules and one unordered H2O molecule in the crystal structure which is fixed by inter- and intramolecular hydrogen bonds. The product ions in electrospray ionization tandem mass spectrometry （ESI-MSn） displays the protonated eprosartan dissociated in three competitive pathways and the fragmentation mechanism is proposed and supported by the FTICRMSn results.

Molecular and Crystal Structure of Hexacobalt Carbonyl Cluster Containg Twin Co_3S(CO)_7 Fragments Linked by a Novel Phosphido-Thiolato Ligand as Backbone

Reaction of dimers of (R) thionophosphine sulfide (R = P - C6H4OMe,SMe ) with Co, (CO), yields the novel hexacobalt cluster [Co'(μ3, -S)2, (CO) 14 (μ4 -μ4- and the trinuclear clusterPSCH,)J 2' In 1, tw0 Co3S(C0)7 units linked by a novel phosphido-thio1ato bifunc-tiona1 bridging p'-SPR ligand as backbone.

CRYSTAL STRUCTURE OF THE COMPLEX OF MUNG BEAN TRYPSIN INHIBITOR LYSINE ACTIVE FRAGMENT WITH BOVINE TRYPSIN AT 1.8 A RESOLUTION

The structure of the complex of mung bean trypsin inhibitor lysine active fragment with bovine trypsin has been determined at a resolution of 1.8 A by A-ray crystallographic analysis and the complex model refined by restrained least-squares minimization with the data between 10 and 1.8 resolution.The current conventional R factor is 17.3%,and the model con- tains 1648 protein atoms,219 inhibitor atoms and 126 water molecules.The most prominent feature of the inhibitor fragment is that it does not contain any alpha-helices.Most of the chain fold in an irregular fashion.The seven residues of the binding segment of the inhibitor lysine active frag- ment are in specific contact with bovine trypsin.The binding interaction and geometry around the reactive site are similar to that observed in other studies of trypsin-inhibitor complexes.

An Overset Grid Method for Fluid-Structure Interaction

An overset grid methodology is developed for the fully coupled analysis of fluid-structure interaction (FSI) problems. The overset grid approach alleviates some of the computational geometry difficulties traditionally associated with Arbitrary-Lagrangian-Eulerian (ALE) based, moving mesh methods for FSI. Our partitioned solution algorithm uses separate solvers for the fluid (finite volume method) and the structure (finite element method), with mesh motion computed only on a subset of component grids of our overset grid assembly. Our results indicate a significant reduction in computational cost for the mesh motion, and element quality is improved. Numerical studies of the benchmark test demonstrate the benefits of our overset mesh method over traditional approaches.

Influence of pore structure on thermal stress distribution inside coal particles during primary fragmentation

Thermal stress is an important reason of coal particle primary fragmentation,during which the role of pore structure is ambiguous.Thermal stress induced fragmentation experiments were conducted with low volatile coal/char particles,and the results show that the fragmentation severity enhances with increasing porosity.Various porous thermal stress models were developed with finite element method,and the influences of the pore shape,size,position and porosity on the thermal stress were discussed.The maximum thermal stress inside particle increases with pore curvature,the pore position affects the thermal stress more significantly at the particle center and surface.The expectation of the maximum tensile thermal stress linearly increases with porosity,making the particles with higher porosity easier to fragment,contrary to the conclusion deduced from the devolatilization theory.The obtained results are valuable for the analysis of different thermal processes concerning the thermal stresses of the solid feedstocks.

Solidification behavior and rheo-diecasting microstructure of A356 aluminum alloy prepared by self-inoculation method

Semisolid slurry of A356 aluminum alloy was prepared by self-inoculation method, and the microstructure and solidification behavior during rheo-diecasting process were investigated. The results indicate that the semisolid slurry of A356 aluminum alloy can be prepared by self-inoculation method at 600 °C. Primary α-Al particles with fine and spherical morphologies are uniformly distributed when the isothermal holding time of slurry is 3 min. Liquid phase segregation occurs during rheo-diecasting process of semisolid slurry and the primary particles(α1) show obvious plastic deformation in the area of high stress and low cooling rate. A small amount of dendrites resulting from the relatively low temperature of the shot chamber at the initial stage of secondary solidification are fragmented as they pass through the in-gate during the mould filling process. The amount of dendrite fragments decreases with the increase of filling distance. During the solidification process of the remaining liquid, the nucleation rate of secondary particles(α2) increases with the increase of cooling rate, and the content of Si in secondary particles(α2) are larger than primary particles(α1). With the increase of cooling rate, the content of Si in secondary particles(α2) gradually increases. The morphologies of eutectic Si in different parts of die casting are noticeably different. The low cooling rate in the first filling positions leads to coarse eutectic structures, while the high cooling rate in the post filling positions promotes small and compact eutectic structures.

PERTURBATIONAL FINITE VOLUME METHOD FOR THE SOLUTION OF 2-D NAVIER-STOKES EQUATIONS ON UNSTRUCTURED AND STRUCTURED COLOCATED MESHES

Based on the first-order upwind and second-order central type of finite volume (UFV and CFV) scheme, upwind and central type of perturbation finite volume (UPFV and CPFV) schemes of the Navier-Stokes equations were developed. In PFV method, the mass fluxes of across the cell faces of the control volume (CV) were expanded into power series of the grid spacing and the coefficients of the power series were determined by means of the conservation equation itself. The UPFV and CPFV scheme respectively uses the same nodes and expressions as those of the normal first-order upwind and second-order central scheme, which is apt to programming. The results of numerical experiments about the flow in a lid-driven cavity and the problem of transport of a scalar quantity in a known velocity field show that compared to the first-order UFV and second-order CFV schemes, upwind PFV scheme is higher accuracy and resolution, especially better robustness. The numerical computation to flow in a lid-driven cavity shows that the under-relaxation factor can be arbitrarily selected ranging from (0.3) to (0.8) and convergence perform excellent with Reynolds number variation from 10~2 to 10~4.

Atomic structure and collision dynamics with highly charged ions

The research progresses on the investigations of atomic structure and collision dynamics with highly charged ions based on the heavy ion storage rings and electron ion beam traps in recent 20 years are reviewed.The structure part covers test of quantum electrodynamics and electron correlation in strong Coulomb field studied through dielectronic recombi-nation spectroscopy and VUV/x-ray spectroscopy.The collision dynamics part includes charge exchange dynamics in ion-atom collisions mainly in Bohr velocity region,ion-induced fragmentation mechanisms of molecules,hydrogen-bound and van de Waals bound clusters,interference,and phase information observed in ion-atom/molecule collisions.With this achievements,two aspects of theoretical studies related to low energy and relativistic energy collisions are presented.The applications of data relevant to key atomic processes like dielectronic recombination and charge exchanges involving highly charged ions are discussed.At the end of this review,some future prospects of research related to highly charged ions are proposed.

Response of Box-Type Structures Under Internal-Blast Loading

The tests of box-type structures under internal-blast loading are carried out. Then a numerical analysis of the test structures is done using a fully coupled numerical finite element model. The break-up process of the structure is simulated. The failure modes of the simulated structure agree well with the experimental results. The effects of the size of the reinforcing bars and the detailing of connections among the rebars in the concrete on the throw velocity of the fragments are discussed.

Spatial Structure Adjustment Strategies of the Coal Resource-Based Cities during the Mature Period: A Case Study of Pingdingshan

Coal cities are the main part of the resource-based cities in China, and the benign development of coal cities' spatial structure has a direct impact on these cities' future economic and social development, as well as the urban residents' welfare. Land use fragmentation is the most typical morphological characteristic of the coal city's spatial structure development. In this paper, Pingdingshan City of Henan Province in China is taken as an example. Through empirical analysis, the urban spatial structure development processes of a typical coal resource-based city in its mature period are illustrated, and the formation reasons and potential mechanism behind coal city land use fragmentation are explored, and the measurement method of land use fragmentation degree of the coal city is put forward. On the above basis, the appropriate adjustment strategies and methods aimed at the coal city spatial structure are found out and given. This study is a good guideline and reference for the spatial structure planning and land use planning of the coal city during the mature and declining period, which is of great help to the sustainable development and industrial structure transformation of the coal city. It also has certain reference significance for the coal city in the growth period.

High levels of genetic diversity and an absence of genetic structure among breeding populations of the endangered Rufous-backed Bunting in Inner Mongolia,China:implications for conservation

Background:The Rufous-backed Bunting,Emberiza jankowskii,is an endangered species that is primarily distributed in Inner Mongolia,China.The main threats to the continued persistence of this species are habitat loss and degradation.However,the impact of population loss on genetic diversity remains unclear.To support future conservation and management efforts,we assessed the genetic diversity and population structure of E.jankowskii using mitochondrial DNA and microsatellites.Methods:Blood samples were collected from 7-8-day-old nestlings in Inner Mongolia,China between May and August of 2012 and 2013.Mitochondrial DNA sequences and microsatellite markers were used to assess the genetic diversity,genetic structure and inbreeding of E.jankowskii.The results of genetic diversity and inbreeding were compared to other avian species.Results:We found an unexpectedly high level of genetic diversity in terms of mitochondrial DNA and microsatellite compared to other avian species.However,there were high levels of gene flow and minimal genetic structuring,among the fragmented breeding populations of E.jankowskii in Inner Mongolia.These findings suggest that E.jankowskii in Inner Mongolia is a metapopulation.Despite the high genetic diversity of E.jankowskii,local populations in each small patch remain at risk of extinction due to habitat loss.In addition,the E.jankowskii population has a high risk of inbreeding.Conclusions:To minimize further loss of genetic diversity of this endangered species,we suggest that the E.jankowskii in Inner Mongolia should be considered as a protected species for management purposes.Conservation efforts should concentrate on E.jankowskii habitat management.This may be most effectively achieved by protecting the current breeding habitats and prohibiting over-grazing.

Research on buffer structure and flow field simulation of swash plate plunger type hydraulic transformer

In order to solve the problem of excessive noise and vibration during the operation of the hydraulic transformer,an optimization method of valve plate damping hole structure is proposed to alleviate the phenomenon of pressure shock.Firstly,the mathematical model of oil pressure gradient in the plunger cavity is established,and the incremental equation of pressure change is derived.Secondly,a kind of buffering structure is proposed,the corresponding relationship between the pressure change and the envelopment angle of the buffering hole and the aperture size is determined by analyzing the oil pressure change curve in the plunger cavity.Finally,the flow field models with buffering holes are established,and the transient simulation of the pressure change process under the optimal solution is carried out with ANSYS software and the flow field pressure distribution contours are obtained.Through the analysis of simulation results,it is concluded that the optimal envelope angle of the three buffer holes ofA-T-B-Ais 5°,and the optimal aperture is 1.8 mm,1.6 mm,and 1.7 mm,respectively.The buffer hole can achieve a better-buffering effect in the range of variable pressure angle[0°,101°].The buffer hole structure can effectively alleviate the pressure shock and reduce the noise level,which lays a foundation for the design and theoretical research of hydraulic transformers.

Impact of Crop Rotation on Pathotype and Genetic Structure of Phythophthora sojae in Fields

To estimate the impact of crop rotation on the pathotype and genetic structure of Phythophthora sojae in fields, 372 isolates of P. sojae were obtained from long-term localisation experimental fields in Heilongjiang Province of China. The hypocotyl inoculation method was used to characterize the virulence of P. sojae on 13 differential cultivars, and the amplified fragment length polymorphism（AFLP） technique was used to analyze difference in the genetic structure of P. sojae. The results indicated that an abundant diversity of genetic structures and pathotypes of P. sojae, a more uniform distribution of pathotypes and less dominance of pathotypes occurred in corn-soybean and wheat-soybean rotation fields than in a continuous soybean mono-cropping field. These findings suggested that P. sojae did not easily become the dominant race in rotation fields, which maintain disease resistance in soybean varieties. Therefore, the results of this study suggested that Phytophthora stem and root rot of soybeans could be effectively controlled by rotating soybeans with non-host crops of corn and wheat.