Effects of high-pressure heat treatment on the solid-state phase transformation and microstructures of Cu61.13Zn33.94Al4.93 alloys

The phase transformation activation energy of the Cu_61.13Zn_33.94Al_4.93 alloys, which were treated at 4 GPa and 700 °C for 15 minutes, was calculated by means of differential scanning calorimetry curves obtained at various heating and cooling rates. Then, the effects of high-pressure heat treatments on the solid-state phase transformation and the microstructures of Cu_61.13Zn_33.94Al_4.93 alloys were investigated. The results show that high-pressure heat treatments can refine the grains and can change the preferred orientation from (111) to (200) of α phase. Compared with the as-cast alloy, the sample with high-pressure heat treatment has finer grains, lower β' → β and β → β ' transformation temperature and activation energy. Furthermore, we found that high cooling rate favours the formation of fine needle-like α phase in the range of 5--20 °C/min.     

Finite Larmor radius magnetohydrodynamic analysis of the ballooning modes in tokamaks

In this paper, the effect of finite Larmor radius (FLR) on high n ballooning modes is studied on the basis of FLR magnetohydrodynamic (FLR-MHD) theory. A linear FLR ballooning mode equation is derived in an `U+015D - α ' type equilibrium of circular-flux-surfaces, which is reduced to the ideal ballooning mode equation when the FLR effect is neglected. The present model reproduces some basic features of FLR effects on ballooning mode obtained previously by kinetic ballooning mode theories. That is, the FLR introduces a real frequency into ballooning mode and has a stabilising effect on ballooning modes (e.g., in the case of high magnetic shear U+015D ≥ 0.8). In particular, some new properties of FLR effects on ballooning mode are discovered in the present research. Here it is found that in a high magnetic shear region (U+015D ≥ 0.8) the critical pressure gradient (α_c,FLR ) of ballooning mode is larger than the ideal one (α_c,IMHD ) and becomes larger and larger with the increase of FLR parameter b₀ . However, in a low magnetic shear region, the FLR ballooning mode is more unstable than the ideal one, and the α_c,FLR is much lower than the α_c,IMHD . Moreover, the present results indicate that there exist some new weaker instabilities near the second stability boundary (obtained from ideal MHD theory), which means that the second stable region becomes narrow.     

Monitoring of coral communities in the inner Gulf of Thailand influenced by the elevated seawater temperature and flooding

There were two severe coral bleaching events at Ko Khang Khao, the inner Gulf of Thailand, occurred during the prolonged period of the elevated sea surface temperature (SST) in 2010 and low salinity as well as turbidity due to heavy flooding in 2011. The bleaching index (BI) and mortality index (MI) are calculated to compare the susceptibilities of coral species in the two bleaching events. The BI and MI vary significantly among the study sites and bleaching events. The most susceptible corals during both bleaching events are Acropora millepora, Pocillopora damicornis and Pavona decussate, while the most resistant species were Galaxea fascicularis, Fungia fungites, Pavona frondifera, Oulastrea crispate, and Symphyllia recta. The corals Favia favus, Goniopora columna, Platygyra pini, Symphyllia agaricia were relatively more tolerant to high SST but they are relatively more susceptible to low salinity. Coral bleaching is a phenomenon that the dissociation stress of the symbiotic relationship between zooxanthellae and their cnidarian host results in the reduction in photosynthetic pigment concentration. Among stressors, both prolonged exposure of high SST and low salinity, above and below their thresholds, respectively. The long-term resilience of coral communities at Ko Khang Khao and other coral communities close to the mouth of large rivers may depend on the frequency and duration of the exposure on the elevated SST due to atmospheric heating and low salinity due to river flooding.     

Influence of annealing conditions on impurity species in arsenic-doped HgCdTe grown by molecular beam epitaxy

Based on our previous work, the influence of annealing conditions on impurity species in in-situ arsenic (As)-doped Hg_1-xCd_xTe (x≈ 0.3) grown by molecular beam epitaxy has been systematically investigated by modulated photoluminescence spectra. The results show that (i) the doped-As acting as undesirable shallow/deep levels in as-grown can be optimized under proper annealing conditions and the physical mechanism of the disadvantage of high activation temperature, commonly assumed to be more favourable for As activation, has been discussed as compared with the reports in the As-implanted HgCdTe epilayers (x≈ 0.39), (ii) the density of V_textrmHg has an evident effect on the determination of bandgap (or composition) of epilayers and the excessive introduction of V_Hg will lead to a short-wavelength shift of epilayers, and (iii) the V_textrmHg prefers forming the V_Hg-As_Hg complex when the inactivated-As (As_Hg or related) coexists in a certain density, which makes it difficult to annihilate V_Hg in As-doped epilayers. As a result, the bandedge electronic structures of epilayers under different conditions have been drawn as a brief guideline for preparing extrinsic p-type epilayers or related devices.     

Numerical Study on Instantaneous Discharge of Unsorted Particle Cloud in Cross Flow

The mixing characteristics of particles such as dredged sediment of variable size discharged into cross flow are studied by a 3D numerical model, which is developed to model the particle-fluid two-phase flow. The Eulerian method with the modified k-ε parameterization of turbulence for the fluid phase is used to solve fluid phase, while a Lagrangian method for the solid phase (particles), both the processes are coupled through the momentum sources. In the model the wake turbulence induced by particles has been included as additional source term in the k-ε model; and the variable drift velocities of the particles are treated efficiently by the Lagrangian method in which the particles are tracked explicitly and the diffusion process is approximated by a random walk model. The hydrodynamic behavior of dumping a cloud of particles is governed by the total buoyancy of the cloud, the drag force on each particle and the velocity of cross-flow. The computed results show a roughly linear relationship between the displacement of the frontal position and the longitudinal width of the particle cloud. The particle size in the cloud and the velocity of cross flow dominate the flow behavior. The computed results are compared with the results of laboratory experiments and satisfactory agreement is obtained.     

Synthesis of large diamond crystals containing high-nitrogen concentration at high pressure and high temperature using Ni-based solvent by temperature gradient method

This paper reprots that with Ni-based catalyst/solvent and with a dopant of NaN₃, large green single crystal diamonds with perfect shape are successfully synthesized by temperature gradient method under high pressure and high temperature in a China-type cubic anvil high-pressure apparatus (SPD-6×1200), and the highest nitrogen concentration reaches approximately 1214-1257 ppm calculated by infrared absorption spectra. The synthesis conditions are about 5.5 GPa and 1240-1300 ℃. The growth behaviour of diamond with high-nitrogen concentration is investigated in detail. The results show that, with increasing the content of NaN₃ added in synthesis system, the width of synthesis temperature region for growth high-quality diamonds becomes narrower, and the morphology of diamond crystal is changed from cube-octahedral to octahedral at same temperature and pressure, the crystal growth rate is slowed down, nevertheless, the nitrogen concentration doped in synthetic diamond increases.     

Nonlinear waves in a fluid-filled thin viscoelastic tube

In the present paper the propagation property of nonlinear waves in a thin viscoelastic tube filled with incompressible inviscid fluid is studied. The tube is considered to be made of an incompressible isotropic viscoelastic material described by Kelvin--Voigt model. Using the mass conservation and the momentum theorem of the fluid and radial dynamic equilibrium of an element of the tube wall, a set of nonlinear partial differential equations governing the propagation of nonlinear pressure wave in the solid--liquid coupled system is obtained. In the long-wave approximation the nonlinear far-field equations can be derived employing the reductive perturbation technique (RPT). Selecting the exponent α of the perturbation parameter in Gardner--Morikawa transformation according to the order of viscous coefficient η, three kinds of evolution equations with soliton solution, i.e. Korteweg--de Vries (KdV)--Burgers, KdV and Burgers equations are deduced. By means of the method of traveling-wave solution and numerical calculation, the propagation properties of solitary waves corresponding with these evolution equations are analysed in detail. Finally, as a example of practical application, the propagation of pressure pulses in large blood vessels is discussed.     

Interference phase of mass neutrino in Reissner—Nordstr?m—de Sitter space—time

In Reissner--Nordstr?m--de Sitter space--time, we calculate the interference phase of mass neutrino along geodesic in the radial direction, and then investigate the effects of the cosmological constant La on the phase. Morever, the expression of the interference phase can be reduced to that in Reissner--Nordstr?m space--time when Λ approaches to zero.     

Numerical study on effect of tidal phase on storm surge in the South Yellow Sea

Because of the special topography and large tidal range in the South Yellow Sea,the dynamic process of tide and storm surge is very complicated.The shallow water circulation model Advanced Circulation(ADCIRC)was used to simulate the storm surge process during typhoon Winnie,Prapiroon,and Damrey,which represents three types of tracks attacking the South Yellow Sea,which are,moving northward after landing,no landing but active in offshore areas,and landing straightly to the coastline.Numerical experiments were carried out to investigate the effects of tidal phase on the tide-surge interaction as well as storm surge.The results show that the peak surge caused by Winnie and Prapiroon occurs 2-5 h before the high tide and its occurring time relative to high tide has little change with tidal phase variations.On the contrary,under the action of Damrey,the occurring time of the peak surge relative to high tide varies with tidal phase.The variation of tide-surge interaction is about 0.06-0.37 m,and the amplitude variations of interaction are smooth when tidal phase changes for Typhoon Winnie and Prapiroon.While the interaction is about 0.07-0.69 m,and great differences exists among the stations for Typhoon Damrey.It can be concluded that the tide-surge interaction of the former is dominated by the tidal phase modulation,and the time of surge peak is insensitive to the tidal phase variation.While the interaction of the latter is dominated by storm surge modulation due to the water depth varying with tide,the time of surge peak is significantly affected by tidal phase.Therefore,influence of tidal phase on storm surge is related to typhoon tracks which may provide very useful information at the design stage of coastal protection systems.     

A New model to forecast fishing ground of Scomber japonicus in the Yellow Sea and East China Sea

The pelagic species is closely related to the marine environmental factors, and establishment of forecasting model of fishing ground with high accuracy is an important content for pelagic fishery. The chub mackerel(Scomber japonicus) in the Yellow Sea and East China Sea is an important fishing target for Chinese lighting purse seine fishery. Based on the fishery data from China's mainland large-type lighting purse seine fishery for chub mackerel during the period of 2003 to 2010 and the environmental data including sea surface temperature(SST), gradient of the sea surface temperature(GSST), sea surface height(SSH) and geostrophic velocity(GV), we attempt to establish one new forecasting model of fishing ground based on boosted regression trees. In this study, the fishing areas with fishing effort is considered as one fishing ground, and the areas with no fishing ground are randomly selected from a background field, in which the fishing areas have no records in the logbooks. The performance of the forecasting model of fishing ground is evaluated with the testing data from the actual fishing data in 2011. The results show that the forecasting model of fishing ground has a high prediction performance, and the area under receiver operating curve(AUC) attains 0.897. The predicted fishing grounds are coincided with the actual fishing locations in 2011, and the movement route is also the same as the shift of fishing vessels, which indicates that this forecasting model based on the boosted regression trees can be used to effectively forecast the fishing ground of chub mackerel in the Yellow Sea and East China Sea.     

Two Improvements on Numerical Simulation of 2-DOF Vortex-Induced Vibration with Low Mass Ratio

Till now, there have been lots of researches on numerical simulation of vortex-induced vibration. Acceptable results have been obtained for fixed cylinders with low Reynolds number. However, for responses of 2-DOF vortex-induced vibration with low mass ratio, the accuracy is not satisfactory, especially for the maximum amplitudes. In Jauvtis and Williamson''s work, the maximum amplitude of the cylinder with low mass ratio m*=2.6 can reach as large as 1.5D to be called as the “super-upper branch”, but from current literatures, few simulation results can achieve such value, even fail to capture the upper branch. Besides, it is found that the amplitude decays too fast in the lower branch with the RANS-based turbulence model. The reason is likely to be the defects of the turbulence model itself in the prediction of unsteady separated flows as well as the unreasonable setting of the numerical simulation parameters. Aiming at above issues, a modified turbulence model is proposed in this paper, and the effect of the acceleration of flow field on the response of vortex-induced vibration is studied based on OpenFOAM. By analyzing the responses of amplitude, phase and trajectory, frequency and vortex mode, it is proved that the vortex-induced vibration can be predicted accurately with the modified turbulence model under appropriate flow field acceleration.     

Experimental Study on Cross-Flow Induced Vibrations in Heat Exchanger Tube Bundle

Vibration in heat exchangers is one of the main problems that the industry has faced over last few decades. Vibration phenomenon in heat exchangers is of major concern for designers and process engineers since it can lead to the tube damage, tube leakage, baffle damage, tube collision damage, fatigue, creep etc. In the present study, vibration response is analyzed on single tube located in the centre of the tube bundle having parallel triangular arrangement (60°) with P/D ratio of 1.44. The experiment is performed for two different flow conditions. This kind of experiment has not been reported in the literature. Under the first condition, the tube vibration response is analyzed when there is no internal flow in the tube and under the second condition, the response is analyzed when the internal tube flow is maintained at a constant value of 0.1 m/s. The free stream shell side velocity ranges from 0.8 m/s to 1.3 m/s, the reduced gap velocity varies from 1.80 to 2.66 and the Reynolds number varies from 44500 to 66000. It is observed that the internal tube flow results in larger vibration amplitudes for the tube than that without internal tube flow. It is also established that over the current range of shell side flow velocity, the turbulence is the dominant excitation mechanism for producing vibration in the tube since the amplitude varies directly with the increase in the shell side velocity. Damping has no significant effect on the vibration behavior of the tube for the current velocity range.     

The origin of the suspended particulate matter in the seagrass meadow of tropical waters, an evidence of the stable isotope signatures

Suspended particulate matter (SPM) has been known as an important variable in the organic matter flow of coastal ecosystem. Half of burial carbon in seagrass meadows is contributed by allochthonous sources that compose the SPM such as phytoplankton, seagrass detritus, marine snow aggregates and terrestrially derived particles. Each composition of the SPM contributes different roles and is important to be identified, for instance, the exact contribution of seagrass detritus will be useful for determination of carbon export through the detritus form in seagrass meadows. Here, the SPM of seagrass meadows is studied in Bintan Island and the Selayar Archipelago. The aim of this research is to determine the source origin of the SPM using a stable isotope signature. In order to fulfill this aim, the objectives are defined as: (1) to specify the stable isotope signature (δ¹³C and δ¹⁵N) of the SPM, and (2) to determine the proportional distribution of the SPM''s prospectus sources. The result shows that the possibility of the source origin of the SPM includes a seagrass fraction (Enhalus acoroides and Thalassia hemprichii), terrestrial C4 plant, macroalgae, and terrestrial C3 plant. The SPM lies between the marine- and terrigenous-end members. However, it seems that the SPM is more to be terrigenous-end and allochthonous. According to a Bayesian mixing model, the terrestrial C4 has the highest contribution of the SPM at all sites except Barugaia and Pasi Island in Selayar (i.e., the highest contribution of the SPM is from the detritus of E. acoroides). The second contribution has been contributed by either seagrass detritus (E. acoroides or Th. hemprichii) or terrestrial C3 plant. The finding of this study indicates that there is a strong influence of the terrigenous sources in the SPM of the seagrass meadows.     

EFFECT OF THE KUROSHIO VARIATION ON THE SUBTROPICAL HIGH PRESSURE

By using occanographic data (luring 1955-1978, we have analysed aspects of volume transport variation of the Kuroshio tor PN-linc in the East China Sea, and relationships between volume transport variation of the Kuroshio and the subtropical high pressure (SHP) of the Pacific. We have found that volume transport of the Kuroshio is closely related to the long-period oscillations of the subtropical high pressure for 8-9 years and 2-3 years, respectively. The subtropical high pressure has a phase lag behind compared with volume transport of the Kuroshio. In addition, the seasonal volume transport of the Kuroshio is closely related to the subtropical high pressure, too. The results show that volume transport variation of the Kuroshio has certain influence on future variation of the subtropical high pressure. Therefore, the volume transport of the Kuroshio may be an important parameter lor long-period forecasting of the subtropical high pressure.     

Experimental Study on Mean Overtopping of Sloping Seawall Under Oblique Irregular Waves

In this paper, domestic and abroad research progresses and related calculation formulae of the mean overtopping discharge are summarized. Through integral physical model experiments, the relation between the wave direction and the overtopping discharge on the top of the sloping dike is focused on and put into analysis and discussion; and a modified formula for mean overtopping discharges under oblique irregular waves is proposed. The study shows that the mean overtopping discharge generally goes down as the relative wave obliquity β increases for a fixed measurement point and the mean overtopping discharge generally increases as the wave steepness H/L decreases (the cycle increases) for a fixed relative wave obliquity.     

Studies on ecological characteristics variation and population dynamics of four lizardfishes in the southern Taiwan Straits

The ecological characteristics of four lizardfishes, Trachinocephalus myops, Saurida undosquamis, Saurida tumbil and Saurida elongata, were studied from specimens (910 T. myops, 454 S. un-dosquamis, 686 S. tumbil and 744 S. elongata) collected monthly in the southern Taiwan Straits from April 2005 to March 2006. The population dynamics of the four lizardfishes was also discussed by the comparison with the previous studies. All being composed of 7 a classes; the dominant group of T. myops and S. tumbil was 1-2 a, while S. undosquamis and S. elongate were 2-3 a. The total mortality coefficient Z and the fishing mortality F were at high as indicated by the exploitation ratio E(>0.5), and a large number of by-caught juvenile and young fishes showing that the stock of lizardfishes in this area was overexploited and the fishing gear was irrational. Compared with the previous studies, the maximum and mean fork length, body mass and age of the four lizard-fishes declined gradually, the lizardfishes populations were younger in age and smaller in size. The asymptotic fork length L_∞ decreased while increasing growth coefficient k, and age at the inflexion point of mass t_r was younger compared with the previous studies. The declining of older ones has moderated the feeding competition and the younger ones grew faster. The larger mortality param-eters Z,M and F have revealed higher fishing pressure. The smaller change of the first mature fork length of female T. myops and the change from K selection pattern to r selection pattern of S. tumbil have indicated a more vulnerable fishery ecosystem in this area. The changes of ecological characteristics and population dynamics may be caused by over-exploitation of demersal fishes such as the lizardfishes, especially a large number of juvenile and young fishes by-catch by the current fishing gears and methods. Therefore, in addition to the traditional fishery management approach such as the minimum length-limit, ecosystem approach to fisheries management (EAF) should be taken to improve the practical marine ecosystem management, including increased fishing intensity of the non-economic species especially the feeding competitors of the lizardfishes and the conser-vation of the pelagic fishery population in the fisheries ecosystem, in order to restore the fishery population and achieve the sustainable use of the fishery stocks.     

3D Effects on Vortex-Shedding Flow and Hydrodynamic Coefficients of A Vertically Oscillating Cylinder with A Bottom-Attached Disk

Vortex-shedding flow induced by the vertical oscillation of a cylinder with bottom-attached disks of different diameter ratio D_d/D_c and thickness ratio t_d/D_c is studied by a 3D (three-dimensional) numerical model developed in this paper, and compared with the results obtained through 2D (two-dimensional) numerical model. The high-order upwind scheme is applied to stabilize the computation, and convergence is accelerated by the multi-grid method. Qualitative and quantitative analyses of the differences between the 2D and 3D simulation results reveal the 3D effect on the flow field characteristics and hydrodynamic coefficients of the vertically oscillating cylinder with a bottom-attached disk. The 3D effect on the fluid field is mainly reflected in the significance of three vortex-shedding patterns: ω_x has a greater effect on the flow fields around the sharp edges relative to the vortices generated in the 2D simulation. In the slice along the axial orientation, the vortex effect of ω_y along the radial axis is smaller than that of ω_x along the circumferential direction, indicating the radial effect on the velocity more pronounced than the circumferential effect around the sharp edges of the disk. The rotational interaction ω_z of the fluid in the horizontal plane during the heave motion is insignificant. Based on the 2D and 3D simulation results, the turning points that separate the increasing regimes of the added mass coefficient and damping ratio are identified. The dependence of the turning point on the diameter ratio D_d/D_c and thickness ratio t_d/D_c are discussed in detail.     

Influence of Dzyaloshinskii-Moriya and Kaplan-Shekhtman-Entinwohlman-Aharony superexchange interactions on ground state properties of the one-dimensional spin-Peilers model in open chain

The effects of the Dzyaloshinskii--Moriya (DM) and the Kaplan--Shekhtman--Entinwohlman--Aharony (KSEA) superexchange interactions on the ground state properties of the one-dimensional spin-Peilers system in open chain are studied by using the Lanczos numerical method. The study concentrates mainly on the influence of systemic dimerisation in open chain. The results show that systemic ground state energy density varies with dimerisation parameter δ in different DM interactions, and there exists a special point δ_c where the DM interaction has no influence on the systemic dimerisation, no matter whether the DM interaction is relative or irrelative to systemic dimerisation (η = 1 or η = 0). The KSEA interaction has no fixed special point, but the points of intersection are dense relatively in a certain numberical value range, and sparse in other numberical value ranges. So we can conclude that the antisymmetric anisotropy DM interaction differs from the symmetric anisotropy KSEA interaction, but they are analogous in the sense of the influence of systemic dimerisation in open chain.     

Preliminary research on dissolved oxygen maximum of seawater in low latitude of China

-During the multi-disciplinary investigations on the waters of Nansa Islands for three cruises respectively in 1985. 1986. 1987. it is found that the dissolved oxygen maximum (DOmax) in its vertical distribution usually exists between 20m and 75m deep. The deep position of O2 maximum is near the thermocline below and above the deep chlorophyll maximum, as well as above the light-beam attenuation coefficient maximum. In the parts of O2 maximum occurring, the minimum of CO2 partial pressure and the maximum of pH value are also found at the same depth. It is still difficult to explain the features exactly by using the published research results about the oxygen maximum in its vertical distribution on the waters of middle and high latitude.In the present paper, the dissolved oxygen maximum in its vertical distribution on the waters of low latitude is described. It is made by an internal wave which holds eddy mixture. The feature appears to arise from the biological photosynthesis with stratification, from t     

Tension and Drag Forces of Flexible Risers Undergoing Vortex-Induced Vibration

This paper presents the results of an experimental investigation on the variation in the tension and the distribution of drag force coefficients along flexible risers under vortex-induced vibration (VIV) in a uniform flow for Reynolds numbers (Re) up to 2.2×10⁵. The results show that the mean tension is proportional to the square of the incoming current speed, and the tension coefficient of a flexible riser undergoing VIV can be up to 12. The mean drag force is uniformly and symmetrically distributed along the axes of the risers undergoing VIV. The corresponding drag coefficient can vary between 1.6 and 2.4 but is not a constant value of 1.2, as it is for a fixed cylinder in the absence of VIV. These experimental results are used to develop a new empirical prediction model to estimate the drag force coefficient for flexible risers undergoing VIV for Reynolds number on the order of 10⁵, which accounts for the effects of the incoming current speed, the VIV dominant modal number and the frequency.