Estimation of the detection probability for Yangtze finless porpoises (Neophocaena phocaenoides asiaeorientalis) with a passive acoustic method

Yangtze finless porpoises were surveyed by using simultaneous visual and acoustical methods from 6 November to 13 December 2006. Two research vessels towed stereo acoustic data loggers, which were used to store the intensity and sound source direction of the high frequency sonar signals produced by finless porpoises at detection ranges up to 300 m on each side of the vessel. Simple stereo beam forming allowed the separation of distinct biosonar sound source, which enabled us to count the number of vocalizing porpoises. Acoustically, 204 porpoises were detected from one vessel and 199 from the other vessel in the same section of the Yangtze River. Visually, 163 and 162 porpoises were detected from two vessels within 300 m of the vessel track. The calculated detection probability using acoustic method was approximately twice that for visual detection for each vessel. The difference in detection probabilities between the two methods was caused by the large number of single individuals that were missed by visual observers. However, the sizes of large groups were underestimated by using the acoustic methods. Acoustic and visual observations complemented each other in the accurate detection of porpoises. The use of simple, relatively inexpensive acoustic monitoring systems should enhance population surveys of free-ranging, echolocating odontocetes. (C) 2008 Acoustical Society of America.

Investigation on the Interaction of Laser Beam and Metal Powders Conveyed by Coaxial Powder Feeder

In order to investigate the transient thermal stress field in wall-shape metal part during laser direct forming, a FEM model basing on ANSYS is established, and its algorithm is also dealt with. Calculation results show that while the wall-shape metal part is being deposited, in X direction, the thermal stress in the top layer of the wall-shape metal part is tensile stress and in the inner of the wall-shape metal part is compressive stress. The reason causing above-mentioned thermal stress status in the wall-shape metal part is illustrated, and the influence of the time and the processing parameters on the thermal stress field in wall-shape metal part is also studied. The calculation results are consistent with experimental results in tendency.

beam-shaping microstructure optical fiber

Microstructure optical fiber with uniform intensity distribution of the fundamental mode is proposed. The design guide line and characteristics of this kind fiber are demonstrated. The relationship between refractive index profile and structure parameters is investigated. The mechanism of forming uniform fundamental mode in these fibers is analyzed.

Structural study of YSi1.7 layers formed by channeled ion beam synthesis

High quality YSi1.7 layers (chi(min) of Y is 3.5%) have been formed by 60 keV Y ion implantation in Si (111) substrates to a dose of 1.0 x 10(17)/cm(2) at 450 degrees C using channeled ion beam synthesis (CIBS). It shows that, compared to the conventional nonchanneled ion beam synthesis, CIBS is beneficial in forming YSi1.7 layers with better quality due to the lower defect density created in the implanted layer. Rutherford backscattering/channeling and x-ray diffraction have been used to study the structure and the strain of the YSi1.7 layers. The perpendicular and parallel elastic strains of the YSi1.7 epilayer are e(perpendicular to) = -0.67% +/- 0.02% and e(parallel to) = +1.04% +/- 0.08%. The phenomenon that a nearly zero mismatch of the YSi1.7/Si (111) system results in a nonpseudomorphic epilayer with a rather large parallel strain relative to the Si substrate (epsilon(parallel to) = +1.09%) is explained, and the model is further used to explain the elastic strain of epitaxial ErSi1.7 and GdSi1.7 rare-earth silicides. (C) 1998 American Vacuum Society.

Sulfur forming an isoelectronic center in zinc telluride thin films

ZnTe1-xSx epitaxial layers grown on GaAs by molecular-beam epitaxy were studied by photoluminescence (PL) as a function of temperatures, excitation powers, and hydrostatic pressures. A sulfur-related emission peak, labeled as P-2, is identified as a deep-level emission by hydrostatic-pressure PL measurement. This indicates that sulfur atoms form isoelectronic centers in a ZnTe matrix. The results qualitatively agree with the theoretical prediction and show experimental evidence of isoelectronic S in ZnTe. A model is proposed to explain the emission mechanisms in the ZnTe1-xSx system with small x values.

Study of He-induced nano-cavities as sinks of oxygen for forming silicon-on-insulator

In the present work, a Cz-Silicon wafer is implanted with helium ions to produce a buried porous layer, and then thermally annealed in a dry oxygen atmosphere to make oxygen transport into the cavities. The formation of the buried oxide layer in the case of internal oxidation (ITOX) of the buried porous layer of cavities in the silicon sample is studied by positron beam annihilation (PBA). The cavities are formed by 15 keV He implantation at a fluence of 2 x 10(16) cm(-2) and followed by thermal annealing at 673 K for 30 min in vacuum. The internal oxidation is carried out at temperatures ranging from 1073 to 1473 K for 2 h in a dry oxygen atmosphere. The layered structures evolved in the silicon are detected by using the PBA and the thicknesses of their layers and nature are also investigated. It is found that rather high temperatures must be chosen to establish a sufficient flux of oxygen into the cavity layer. On the other hand high temperatures lead to coarsening the cavities and removing the cavity layer finally.

Microstructure and Magnetic Properties of Nd60Al10Fe20Co10 Glass-forming Alloy

The microstructural variations of the Nd60Al10Fe20CO10 melt-spun ribbons and the as-cast rod were studied by high resolution transmission electron microscopy (HRTEM), x-ray diffraction (XRD) and differential scanning calorimetry. Nano-clusters in glassy m

Electron Beam Surface Treatment. Part I: Surface Hardening of AISI D3 Tool Steel

The effects of electron beam surface hardening treatment on the microstructure and hardness of AISI D3 tool steel have been investigated in this paper. The results showed that the microstructure of the hardened layer consisted of martensite, a dispersion

Metallographic Sample Prepared by Ion Beam Etching

Ion beam etching technique was used to reveal the metallograhpic microstructure and interface morphology of electroplating chromium coating, in particular, whose substrate surface layer was treated in advance by laser quenching. Chemical etchings were, also conducted for comparison. The reveal microstructures were observed and analyzed by scanning electron microscopy. The results show that ion beam etching can reveal well the whole microstructures of composite coating-substrate materials.

A Study of Composite Beam with Shape Memory Alloy Arbitrarily Embedded under Thermal and Mechanical Loadings

The constitutive relations and kinematic assumptions on the composite beam with shape memory alloy (SMA) arbitrarily embedded are discussed and the results related to the different kinematic assumptions are compared. As the approach of mechanics of materials is to study the composite beam with the SMA layer embedded, the kinematic assumption is vital. In this paper, we systematically study the kinematic assumptions influence on the composite beam deflection and vibration characteristics. Based on the different kinematic assumptions, the equations of equilibrium/motion are different. Here three widely used kinematic assumptions are presented and the equations of equilibrium/motion are derived accordingly. As the three kinematic assumptions change from the simple to the complex one, the governing equations evolve from the linear to the nonlinear ones. For the nonlinear equations of equilibrium, the numerical solution is obtained by using Galerkin discretization method and Newton-Rhapson iteration method. The analysis on the numerical difficulty of using Galerkin method on the post-buckling analysis is presented. For the post-buckling analysis, finite element method is applied to avoid the difficulty due to the singularity occurred in Galerkin method. The natural frequencies of the composite beam with the nonlinear governing equation, which are obtained by directly linearizing the equations and locally linearizing the equations around each equilibrium, are compared. The influences of the SMA layer thickness and the shift from neutral axis on the deflection, buckling and post-buckling are also investigated. This paper presents a very general way to treat thermo-mechanical properties of the composite beam with SMA arbitrarily embedded. The governing equations for each kinematic assumption consist of a third order and a fourth order differential equation with a total of seven boundary conditions. Some previous studies on the SMA layer either ignore the thermal constraint effect or implicitly assume that the SMA is symmetrically embedded. The composite beam with the SMA layer asymmetrically embedded is studied here, in which symmetric embedding is a special case. Based on the different kinematic assumptions, the results are different depending on the deflection magnitude because of the nonlinear hardening effect due to the (large) deflection. And this difference is systematically compared for both the deflection and the natural frequencies. For simple kinematic assumption, the governing equations are linear and analytical solution is available. But as the deflection increases to the large magnitude, the simple kinematic assumption does not really reflect the structural deflection and the complex one must be used. During the systematic comparison of computational results due to the different kinematic assumptions, the application range of the simple kinematic assumption is also evaluated. Besides the equilibrium study of the composite laminate with SMA embedded, the buckling, post-buckling, free and forced vibrations of the composite beam with the different configurations are also studied and compared.

Effect of Nb Content on the Microstructure and Mechanical Properties of Zr-Cu-Ni-Al-Nb Glass Forming Alloys

(Zr65Al10Ni10Cu15)(100-x) Nb-x glass forming alloys with Nb contents ranging from 0 to 15 at.% were prepared by water-cooled copper mould cast. The alloys with different Nb contents exhibited different microstructures and mechanical properties. Unlike the monolithic Zr65Al10Ni10Cu15 bulk metallic glass, only a few primary bee beta-Ti phase dendrites were found to distribute in the glassy matrix of the alloys with x = 5. For alloys with x = 10, more beta-phase dendrites forms, together with quasicrystalline particles densely distributed in the matrix of the alloys. For alloys with x = 15, the microstructure of the alloy is dominated by a high density of fully developed P-phase dendrites and the volume fraction of quasicrystalline particles significantly decreases. Room temperature compression tests showed that the alloys with x = 5 failed at 1793 MPa and exhibited an obvious plastic strain of 3.05%, while the other samples all failed in a brittle manner. The ultimate fracture strengths are 1793, 1975 and 1572 MPa for the alloys with x = 0, 10 and 15 at.% Nb, respectively.

Gal(1-x)Mn(1-x)Sb Grown on GaSb with Mass-Analyzed Low-Energy Dual Ion Beam Deposition

The Ga1-xMnxSb samples were fabricated by the implantation of Mn ions into GaSb (1 0 0) substrate with mass-analyzed low-energy dual ion beam deposition system, and post-annealing. Auger electron spectroscopy depth profile of the Ga1-xMnxSb samples showed

Magnetic properties and magnetic domain structure of bulk glass forming Nd60Al10Fe20Co10 alloy

The transition from hard to soft magnetic behaviour with increasing quenching rate is shown for Nd60WAl10Fe20Co10 melt-spun ribbons with different thickness. Microstructure and magnetic domain structure of ribbons were studied by magnetic force microscopy (MFM). Particle sizes < 5 nm decreasing gradually with increasing quenching rate were deduced from topographic images which differ from large-scale magnetic domains with a periodicity of about 350 nm in all ribbons irrespective the coercivity. This indicates that the magnetic properties of the alloy are governed by interaction of small magnetic particles. It is concluded that the presence of short-range-ordered structures with a local ordering similar to the Al metastable Nd-Fe binary phase is responsible for the hard magnetic properties in samples subjected to relatively low quenching rate.

Electron Beam Surface Remelting of AISI D2 Cold-Worked Die Steel

Electron beam surface remelting has been carried out on AISI D2 cold-worked die steel. The microstructure and hardening behavior of the electron beam surface remelted AISI D2 cold-worked die steel have been studied by means of optical microscopy and Vickers hardness testing. It was found that AISI D2 steel can be successfully surface hardened by electron beam surface remelting. This surface hardening effect can be attributed to microstructural refinement following electron beam surface remelting. (C) 2002 Elsevier Science B.V. All rights reserved.