Electronic and optical properties of pure and Ce3+-doped CaS single crystals: a first-principles prediction

This paper investigates the electronic and optical properties for pure and Ce³⁺-doped CaS crystals by using the first-principles total energy calculations. The results show that CaS:Ce has a direct band gap of 2.16 eV, and the top of the valence band is determined by S 3p states and the bottom of the conduction band is determined by Ce 4f states, respectively. Our results validate that the yellow emission from CaS:Ce is produced by doped cerium and the green emission quenches at 12.5% cerium concentration. The Ce-S bond shows more covalent character than the Ca-S bond.     

N掺杂SnO2材料光电性质的第一性原理研究

采用全电势线性缀加平面波(full potential linearized augmented plane wave method,简记为FP-LAPW)方法,基于密度泛函理论第一性原理计算分析N掺杂SnO₂材料,研究了在N替代O原子和N替代Sn原子情况下的电子态密度、电荷密度分布以及光学性质.研究表明N掺杂替代Sn较之N掺杂替代O原子的带隙要宽,都宽于SnO₂的本征带隙,且两种情况下N分别处于负氧化态和正氧化态,其介电函数谱也与带隙对应发生蓝移,从理论上指出     

Temporal electronic structure of non-resonant Raman excited virtual state of P-nitroaniline by 514 nm excitation via bond polarisabilities

We have studied the temporal bond polarisabilities of para-nitroaniline from the Raman intensities by the algorithm proposed by Wu et al. in 1987 (Tian B, Wu G, Liu G 1987 J. Chem. Phys. 87 7300). The bond polarisabilities provide much information concerning the electronic structure of the non-resonant Raman excited virtual state. At the initial moment by the 514.5 nm excitation, the tendency of the excited electrons (mapped out by the bond polarisabilities) is to spread to the molecular periphery, and the electronic structure of the Raman virtual state is close to the pseudo-quinonoidic state. When the final stage of relaxation is approached, the bond polarisabilities of those peripheral bonds relax faster than those closer to the molecular core, the phenyl ring. The molecule is in the benzenoidic form as demonstrated by the bond polarisabilities after relaxation.     

各向异性光子晶体中二能级原子和自发辐射场间的纠缠

应用 Von Neumann熵 和 Schmidt number K两种纠缠度量讨论了各向异性光子晶体中二能级原子和自发辐射场间纠缠度的演化性质. 研究发现,原子-光场纠缠度的演化与原子上能级和光子晶体能带带边的相对位置有关,当原子上能级处于光子晶体禁带内,原子-光场纠缠度将保持稳定,当原子上能级处于光子晶体能带中,原子-光场纠缠度先增大后衰减到零. 纠缠度的大小还与原子的初态有关. 可以通过控制原子的初态和原子上能级与带边的相对位置来控制原子-光场纠缠度的演化特性.     

厚壳贻贝(Mytilus coruscus)中抗生素耐受细菌多样性研究

抗生素的滥用是当前水产养殖业发展及食品安全面临的重大威胁。贻贝体内含有丰富的附生菌群,但目前尚不清楚贻贝附生菌群在抗生素残留背景下的动态变化和耐受性特征。为此进行了厚壳贻贝中抗生素耐受细菌多样性研究。将厚壳贻贝暴露于含有青霉素、链霉素和卡那霉素的养殖水体中,之后采用超声法获取含贻贝软体部组织表面附着菌群的超声液,经Zobell 2216E液体培养基培养后,将组织超声液和培养液一并经16S rDNA高通量测序来分析厚壳贻贝微生物的群落组成。结果表明,超声处理后获得的微生物主要为拟杆菌门(Bacteroidetes)、变形菌门(Proteobacteria)和疣微菌门(Verrucomicrobia)。多重抗生素的处理可以显著下降贻贝体内微生物的OTU数,对微生物群落结构有明显影响。经264h恢复养殖后,在门水平上观察到贻贝体内微生物群落可以恢复重建,表明其具有一定的韧性。研究结果将为今后进一步探索宿主相关微生物群落构建机制及特殊抗性微生物奠定基础。     

Fabrication of suspended graphene devices and their electronic properties

Suspended graphene devices are successfully fabricated by using a novel PMMA/MMA/PMMA tri-layer resist technique. The gap between graphene and dielectric substrate can be easily controlled by the thickness of the bottom PMMA layer, and no wet-etching with hazardous hydrofluoric acid is involved in our fabrication process. Electrical characterizations on suspended graphene devices are performed in vacuum when in-situ current annealing directly leads to a significant improvement on transport properties of graphene, i.e., the increase of carrier mobility with the reduction of width of Dirac peak. Our results make a new opportunity to study intrinsic properties of graphene.     

Inertial and tidal shear variability above Reykjanes Ridge

Yearlong 75 kHz acoustic Doppler current profiler (ADCP) data were obtained well above Reykjanes Ridge (northern extension of the Mid-Atlantic Ridge (MAR)). The area is characterized by relatively large semidiurnal tidal (‘D₂’) currents that have (at lunar M₂) more than half a decade larger variance than inertial (f) currents. However, despite the relatively weak near-inertial kinetic energy, its vertical current shear shows larger magnitudes than at M₂ in an otherwise flat f−D₂ band limited between frequencies 0.74 and 1.35f, which equals the inertio-gravity wave bounds [σ_min, σ_max](N=f). N represents the buoyancy frequency. The shear in this band dominates all shear computed at 20 m effective vertical scale. As the kinetic energy spectrum peaks at M₂, but not (significantly) at S₂ and N₂, a difference in tidal (and inertial) scales and hence sources is observed. M₂-tides contribute mostly to large-scale coherent motions. The dominant incoherent f−D₂ shear is highly variable in time (∼2-day periodicity). Furthermore, inertial and tidal shear are more or less completely separated in space and time, each occurring in different layers in the vertical. The thin shear layers reflect the rapidly varying short vertical scale N_s profile, to within the ∼20 m limitation of ADCP data, rather than the large-scale smooth N_L. In each of large-N_s layers Ri≈1, probably. The yearlong smoothed shear magnitude follows N_L, but only as stable Ri≈5. The shear polarization is more circular than rectilinear, albeit varying with time, and highly symmetric around f. During transitions, e.g., between stratified and homogeneous layers and between waves from varying sources, near-circular motions can generate near-rectilinear shear in the direction of wave propagation (in the direction of the minor axis of the current ellipse). This contrasts with the possibility of near-rectilinear barotropic oscillatory motions generating near-circular shear under viscosity in shallow seas.     

Structural and thermodynamic signatures of marine microlayer surfactant films

Natural surface film experiments in inland waters and shallow offshore regions of the Baltic and Mediterranean Seas were carried out in the time period 1990–1999 under calm sea conditions using a novel device for sampling and force-area studies. The sampler-Langmuir trough-Wilhelmy filter paper plate system ‘cuts out’ an undisturbed film-covered sea area to perform π-A studies without any initial physico-chemical sample processing. The limiting specific area A_lim (2.68–31.57 nm²/molecule) and mean molecular mass M_w (0.65–9.7 kDa) of microlayer surfactants were determined from the 2D virial equation of state applied to the isotherms. Enthalpy ΔH and entropy ΔS_t of the 2D first-order phase transitions were evaluated using the Clausius-Clapeyron equation applied to the isotherms. Miscibility of film components and film structure evolution is expressed by the scaling exponent y adopting the 2D polymer film scaling theory. The stress-relaxation measurements revealed a two-step relaxation process at the interface with characteristic times τ₁=1.1–2.8 and τ₂=5.6–25.6 seconds suggesting the presence of diffusion-controlled and structural organisation relaxation phenomena. The obtained results suggest that natural films are a complex mixture of biomolecules covering a wide range of solubilities, surface activity and molecular masses with an apparent structural organisation exhibiting a spatial and temporal variability.     

中国黄渤海真江蓠(Agarophyton vermiculophyllum)群体遗传多样性研究

真江蓠是原产于西北太平洋的重要经济红藻。我们利用10对微卫星引物检测中国黄渤海地区真江蓠的群体遗传多样性和结构。10个微卫星位点在12个群体中共检测到65个等位基因,每个位点的等位基因（N_a）为1~28,有效等位基因（N_e）为1.0~9.6。每个群体的平均等位基因（N_a）、平均有效等位基因（N_e）、平均香浓指数（I）、平均观察杂合度（H_o）和平均预期杂合度（H_e）分别为2.4、1.6、0.419、0.133和0.227,显示较低的群体遗传多样性。中国黄渤海12个真江蓠群体间遗传分化较大（F_st=0.398 7）,基因流有限（N_m=0.377 1）,近交系数为正（F_is=0.391 3,F_it=0.634 0）,表明可能存在近交和杂合子缺失现象。Structure和UPGMA系统进化分析一致将12个群体分为两个遗传组,并在黑石礁群体（HS）和石岛群体（SD）中发现明显的遗传混杂现象。AMOVA分析显示遗传变异主要来自于群体内（73.27%）。该研究可为黄渤海地区真江蓠自然资源保护和管理提供科学依据。     

Nonlinear tidal waves in a kind of estuary with gradually varying cross-section

-Nonlinear tidal waves in a kind of estuary are studied in the paper using one-dimensional nonlinear hydrody-namic equations with friction. The estuary has exponentially varying width B=B0 e-bx and uniform depth h. The one-dimensional hydrodynamic equations are solved by perturbation method. It was found that our solution included two special cases, Pelisenpeki's solution and Airy's solution. The former can be got by letting b=0 in our solutions, and the latter by setting 6 = 0 and f= 0 (f is linear frictional coefficient). In terms of the second-order solution, the physical mechanism of nonlinear tidal waves in estuaries with gradually varying cross-section is explored. It is shown that, under the assumption of linear friction coefficient, shallow water constituent waves consist of two parts, one is produced by shallow water nonlinear effect outside the estuary, the other is generated by shallow water nonlinear effect inside estuary. In addition, the physical mechanism of the residual tidal current and     

Great Japan earthquake of March 11, 2011: Tectonic and seismological aspects

The tectonic and seismological aspects of the Great Japan Earthquake, which occurred on March 11, 2011 (M _w = 9.0), at the Pacific margin of the northeastern part of Honshu Island, are discussed. The structure and seismotectonic data, seismicity, and the reccurence rate of the great (M ≥ 7.6) earthquakes throughout history and in modern times are represented. It is shown that the reccurence rate of the great events is about 40 years, and that of megaearthquakes is 1000 years or more. A seismic gap of about 800 km in length is found in the region under study, located to the south of latitude 39° N and full of aftershocks to the megaearthquake of March 11, 2011. This event is probably connected with the deep thrust along the Benioff zone and its structural front (Oyashio nappe at the middle Pacific continental slope). The aftershock sequences of this megaearthquake and the Sumatra-Andaman (2004) megaearthquake are compared. It is found that several of their key characteristics (the number of aftershocks, the magnitude of the strongest aftershock, and the time of its occurrence) for 25 days are comparable for both cases with a significant difference in the energies of aftershock processes. A probable scenario for the origination of a repeated shock with M ∼ 8.0 in the Japan Trench is discussed.     

Effects of bed perturbation and velocity asymmetry on ripple initiation: wave-flume experiments

Laboratory experiments using a wave flume were designed to examine the threshold condition for ripple formation under asymmetrical oscillatory flows on an artificially roughened bed. Three types of sand beds were prepared in the experiments: they were flat, notched, and notch-mounded beds with bed roughness increasing in this order. The beds were constructed with three kinds of well-sorted sand with similar density, but different diameters. Data analyses were made using the two dimensionless parameters: the mobility number, M, a simplified form of the Shields number, and the Ursell number, U, a surrogate for asymmetry of flow field. The result confirmed that the threshold for ripple initiation is decreased with increasing bed perturbation and that as the bed perturbation increases, the dependency of this threshold on the flow asymmetry becomes less and finally null for the notch-mounded bed. This relationship is quantified by the following equations: M=17−14.5e^−0.03U on the flat bed, M=5.0−2.5e^−0.1U for the notched bed, and M=2.5 for the notch-mounded bed. A comparison between the previous field data and the present laboratory findings indicates that the threshold in the notch-mounded bed experiment, M=2.5, seems to provide a critical condition for rippling in the natural environment.     

Monitoring of position of the Kuroshio axis in the Tokara Strait using sea level data

Properties of the index of position of the Kuroshio axis in the Tokara Strait, named the Kuroshio position index (KPI), were examined using sea-level data during 1984–92. The index is KPI=(X+M _x )/(Y+M _y whereX(Y) is the anomaly of sea-level difference of Nakanoshima (Naze) minus Nishinoomote from the 1984–92 meanM _x (M _y ). The correlation with the latitude of the Kuroshio axis in the Tokara Strait concluded that the KPI withM _x /M _y =0.83 and realisticM _y (100±40 cm) best indicates the position of the Kuroshio axis in the strait. The KPI withM _x =83 cm andM _y =100 cm was newly called the KPI as the best index. Using daily values of this KPI, the relation between the position of the Kuroshio in the strait and the large meander of the Kuroshio shown by Kawabe (1995) was confirmed and studied in detail. A large meander forms (ends) 3.3 (5.1) months after a northward (southward) shift of the Kuroshio in the Tokara Strait. Yet, a temporary southward shift with a duration of ten to twenty days does not finish the large-meander (LM) path. At the LM formation, a small meander southeast of Kyushu begins to move eastward associated with the northward shift. The processes of LM formation and decay are started by the meridional move of the Kuroshio axis in the Tokara Strait. The Kuroshio axis at the FES line during the LM path is located farther north by 7 latitude than that during the non-large-meander (NLM) path. The latitude during the LM formation (decay) stage is a little higher (lower) than that during the LM (NLM) period, though the Kuroshio still takes an NLM (LM) path.     

Investigation on Effects of Mooring Line Fractures and Connector Failures for A Hybrid Modular Floating Structure System

The present work reports a Hybrid Modular Floating Structure (HMFS) system with typical malfunction conditions. The effects of both fractured mooring lines and failed connectors on main hydrodynamic responses (mooring line tensions, module motions, connector loads and wave power production) of the HMFS system under typical sea conditions are comparatively investigated. The results indicate that the mooring tension distribution, certain module motions (surge, sway and yaw) and connector loads (M_z) are significantly influenced by mooring line fractures. The adjacent mooring line of the fractured line on the upstream side suffers the largest tension among the remaining mooring lines, and the case with two fractured mooring lines in the same group on the upstream side is the most dangerous among all cases of two-line failures in view of mooring line tensions, module motions and connector loads. Therefore, one emergency strategy with appropriate relaxation of a proper mooring line has been proposed and proved effective to reduce the risk of more progressive mooring line fractures. In addition, connector failures substantially affect certain module motions (heave and pitch), certain connector loads (F_z and M_y) and wave power production. The present work can be helpful and instructive for studies on malfunction conditions of modular floating structure (MFS) systems.

     

Sources and threats of chronic tissue loss on coral reefs in the Lakshadweep Islands,Indian Ocean

Tissue degradation and resulting mortality are major threats to coral reefs around the world. Information on interactions of the major environmental factors that mediate tissue loss and mortality in coral reefs is of great importance. It is essential to understand the prevailing reef health conditions and to develop appropriate management actions. In the present study, a series of benthic surveys conducted in the Lakshadweep Islands revealed the interaction of major biological factors in causing tissue loss and mortality. Hierarchical regression analysis revealed interactions of various environmental scenarios. Tissue loss was prevalent in islands with high cover of massive corals (m = 20.91) and low in islands dominated by branching corals (m = 0.61). Hierarchical regression analysis revealed black band disease (β = .59; p < .001) and algal interactions (β = .48; p < .001) to be major factors responsible for coral mortality caused by tissue loss in the region.     

Changes in vertical distribution and aggregative behaviour in response to population density for larval sea urchins (Strongylocentrotus droebachiensis) and sea stars (Asterias rubens)

We examined the effects of the presence of larval conspecifics on larval vertical distribution of four‐arm and six‐arm plutei of Strongylocentrotus droebachiensis and bipinnaria of Asterias rubens, in laboratory experiments, by manipulating population density. Larvae were introduced to experimental columns (10 × 10 × 30 cm) at one of two or three population densities (S. droebachiensis: 0.1 and 10 larvae·ml^?1; A. rubens: 0.1, 1 and 10 larvae·ml^?1). Subsequent changes in vertical distribution were determined from images of the larvae in the columns illuminated by a 532‐nm laser and captured by a high‐resolution camera. Larvae of both species were found higher in the water column in the high than in the low and intermediate population densities. The relationship between vertical swimming velocity and nearest neighbour distance (NND) was measured for four‐arm plutei of S. droebachiensis, and used to determine a range in distances among individuals that may affect potential interactions. The variation in swimming velocity decreased with increasing proximity below a threshold distance among individuals of 10 mm, which was greater than the estimated distance in the high population density. We suggest that the increased larval aggregation near the water surface under high population density is the result of a behavioural response to conspecifics.     

Non-linear interaction between tidal and subinertial barotropic flows in the Strait of Gibraltar

The present work establishes clear relationships of the amplitude and phase variation of the barotropic M₂ signal in the velocity of the current with the barotropic subinertial flow in the Strait of Gibraltar. The analytical procedure is applied on data from Gibraltar Experiment in order to obtain barotropic subinertial series and the amplitude and phase variation of the M₂ signal series involves harmonic analysis, empirical orthogonal function analysis and complex demodulation. In addition, cross-spectral analysis has been applied to study these relationships, concerning which non-linear interaction between M₂ and the subinertial oscillation is proposed as the responsible physical mechanism. An analytical solution characterizing this type of non-linear interaction is offered in explanation of the experimental results.     

Structural, electronic and optical properties of orthorhombic distorted perovskite TbMnO3

This paper calculates the structural parameters, electronic and optical properties of orthorhombic distorted perovskite-type TbMnO₃ by first principles using density functional theory within the generalised gradient approximation. The calculated equilibrium lattice constants are in a reasonable agreement with theoretical and experimental data. The energy band structure, density of states and partial density of states of elements are obtained. Band structures show that TbMnO₃ is an indirect band gap between the O 2p states and Mn 3d states, and the band gap is of 0.48 eV agreeing with experimental result. Furthermore, the optical properties, including the dielectric function, absorption coefficient, optical reflectivity, refractive index and energy loss spectrum are calculated and analysed, showing that the TbMnO₃ is a promising dielectric material.     

长牡蛎(Crassostrea gigas)野生与选育群体的微卫星遗传多样性分析

为了评估长牡蛎(Crassostrea gigas) 2个壳长性状(掌心形)快速生长选育群体(LY2-K4、LY2-K7)、1个壳高性状(速生型)快速生长选育群体(LY2-K11)和6个野生群体(QHD、LS、HD、ZH、WD、KTD)的遗传多样性和遗传结构, 用21对多态性丰富的微卫星引物对9个长牡蛎群体的269个个体进行了遗传分析。结果显示: 21个微卫星位点共检测出了460个等位基因(N_a),平均等位基因数为21.905; 21个微卫星位点的多态信息含量(PIC)均大于0.5, 具有高度遗传多态性; 选育群体LY2-K11的遗传多样性最低(N_a=13, I=2.128,H_e=0.831, PIC=0.825), 野生群体KTD的遗传多样性最高(N_a=29,I=3.112, H_e=0.941, PIC=0. 938); 189个群体位点组合有66%偏离哈代-温伯格平衡, 表明这些群体存在一定程度的杂合子缺失; 9个群体间的遗传分化指数(F_st)为0.012~0.064, 处于较低的遗传分化水平; AMOVA分析显示遗传变异主要来自于个体内; PCoA分析结果与UPGMA聚类树一致, LY2-K11群体单独聚为一类, QHD和HD群体聚为一类, 其他6个群体聚为一类。综上所述, 长牡蛎3个选育群体和6个野生群体遗传多样性均较高, 遗传分化水平较低; 选育群体LY2-K11多样性略有下降, 选育过程中应保证亲本的数量及质量, 防止因近交衰退造成遗传多样性降低, 苗种抗逆性变差。该结果将为长牡蛎新品种的选育和野生种质资源的保护提供科学指导。     

Correlations between CPT and FVT Results for Busan Clay

In this study, CPT and FVT tests are carried out on young, normally consolidated clay (Busan clay, which is an unusually thick deposit) at several locations in the Nakdong River deltaic plane in Busan, Korea. Two correlation techniques are applied for estimating the cone factors for which the uncorrected and corrected field vane strengths are used as the reference strength. First, due to the scattered data over the entire depth, a direct correlation between the tested results (a method generally used in practice), is applied for each depositional environment (facies) that is detected from the CPT profiles and the geological analysis. Secondly, a special attempt is made to determine the cone factors based on the fact that the ratios of the field vane strength and the (q _t  ? σ _v0) and (u ₂ ? u ₀) values to the effective overburden pressure respectively, are approximately constant for each facies (the indirect correlation). It appears that the values obtained from the two techniques are almost identical. However, the direct correlation is sensitively affected by the fabric effects especially in some of the uppermost and lowermost layers of the clay and hence the arithmetic average values of each facies sometimes result in lower correlation coefficients. It is therefore inferred that the indirect correlation is more proficient for estimating the cone factors at each facies and can be used for practical applications. From the results of the indirect correlation, the cone factors of Busan clay are N _kt  = 7.13–13.06, N _kt,corr  = 9.45–17.07, N _Δu  = 6.10–9.88 and N _Δu,corr  = 8.41–12.24, the corrected values of which are considerably smaller or larger than the general ranges recommended by Lunne et al. (1997a). However, good correlations between N _kt and I _P , and between N _Δu (or N _kt ) and B _q , are not found for the clay.