常用鱼药漂白粉和氯杀宁对背角无齿蚌的毒性影响

试验以洱海流域的背角无齿蚌为研究对象,确定常用鱼药:漂白粉、氯杀宁对湖泊大型底柄动物背角无齿蚌的毒性影响.试验得出漂白粉作用下,背角无齿蚌24 h、48 h、72 h、96 h、120 h、144 h、168 h的半致死率;氯杀宁作用下,背角无齿蚌24 h、48 h、72 h、96 h的半致死率;漂白粉有效氯安全浓度95.25～108.86 mg/L;氯杀宁有效氯安全浓度3.32～3.55 mg/L.通过显微镜观察,漂白粉和氯杀宁的主要作用部位为背角无齿蚌的呼吸系统,在其鳃上可见明显病变.

罗氏沼虾卵子在授精时的变化(英文)

<正> The freshwater giant prawn, Macrobrachium rosenbergii is of great economic importance in many coun-tries. It's farmed production is recorded globally. We examine the fertilization cytology in the hope that theymay serve to augment the previous reports

Extraordinarily thick-boned fish linked to the aridification of the Qaidam Basin (northern Tibetan Plateau)

Scattered with numerous salt lakes and approximate to 2,700-3,200 m above sea level, the giant Qaidam inland basin on the northern Tibetan Plateau has experienced continuing aridification since the beginning of the Late Cenozoic as a result of the India-Asia plate collision and associated uplift of the Tibetan Plateau. Previous evidence of aridification comes mainly from evaporite deposits and salinity-tolerant invertebrate fossils. Vertebrate fossils were rare until recent discoveries of abundant fish. Here, we report an unusual cyprinid fish, Hsianwenia wui, gen. et sp. nov., from Pliocene lake deposits of the Qaidam Basin, characterized by an extraordinarily thick skeleton that occupied almost the entire body. Such enormous skeletal thickening, apparently leaving little room for muscles, is unknown among extant fish. However, an almost identical condition occurs in the much smaller cyprinodontid Aphanius crassicaudus (Cyprinodonyiformes), collected from evaporites exposed along the northern margins of the Mediterranean Sea during the Messinian desiccation period. H. wui and A. crassicaudus both occur in similar deposits rich in carbonates (CaCO3) and sulfates (CaSO4), indicating that both were adapted to the extreme conditions resulting from the ariclification in the two areas. The overall skeletal thickening was most likely formed through deposition of the oversaturated calcium and was apparently a normal feature of the biology and growth of these fish.

Uniaxial Strain Effects on Optical Properties of c-plane Wurtzite GaN

We investigate the uniaxial strain effect in the c-plane on optical properties of wurtzite GaN based on k center dot p theory, the spin-orbit interactions are also taken into account. The energy dispersions show that the uniaxial strain in the c-plane gives an anisotropic energy splitting in the k(x) - k(y) plane, which can reduce the density of states. The uniaxial strain also results in giant in-plane optical polarization anisotropy, hence causes the threshold carrier density reduced. We clarify the relations between the uniaxial strain and the optical polarization properties. As a result, it is suggested that the compressive uniaxial strain perpendicular to the laser cavity direction in the c-plane is one of the preferable approaches for the effcient improvement of GaN-based laser performance.

Strain Effects on the Optical Polarization Properties of R-Plane Wurtzite GaN

Using the effective-mass Hamiltonian for an arbitrary direction wurtzite semiconductor on the basis of k.p theory, we investigate the strain effects on the transition energies and optical properties in the R-plane ([1012]-oriented plane) GaN. The results show that (1) the transition energies decrease with the biaxial strains changing from -0.5 to 0.5%; and (2) giant optical anisotropy appears in the R-plane which is significantly affected by the biaxial strains. We clarify the relation between the strains and the polarization properties. Finally, we discuss the application of these properties to the R-plane GaN based devices. (c) 2009 The Japan Society of Applied Physics

Ballistic electron transport in hybrid ferromagnet/two-dimensional electron gas sandwich nanostructure: Spin polarization and magnetoresistance effect

We have theoretically investigated ballistic electron transport through a combination of magnetic-electric barrier based on a vertical ferromagnet/two-dimensional electron gas/ferromagnet sandwich structure, which can be experimentally realized by depositing asymmetric metallic magnetic stripes both on top and bottom of modulation-doped semiconductor heterostructures. Our numerical results have confirmed the existence of finite spin polarization even though only antisymmetric stray field B-z is considered. By switching the relative magnetization of ferromagnetic layers, the device in discussion shows evident magnetoconductance. In particular, both spin polarization and magnetoconductance can be efficiently enhanced by proper electrostatic barrier up to the optimal value relying on the specific magnetic-electric modulation. (C) 2009 American Institute of Physics. [DOI 10.1063/1.3041477]

Interlayer segregation in magnetic multilayers and its influence on exchange coupling

Experimental results show that the exchange coupling field (H-ex) of NiFe/FeMn for Ta/NiFe/FeMn/Ta multilayers is higher than that for spin-valve multilayers Ta/NiFe/Cu/NiFe/FeMn/Ta. X-ray photoelectron spectroscopy shows that Cu atoms segregate to the NiFe/FeMn interface for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers. While studying Ta/X(X=Bi,Pb,Ag,In)/NiFe/FeMn multilayers, we also find that X atoms segregate to the NiFe/FeMn interface, which results in a decrease of the H-ex. However, a small amount of Bi, Pb, etc. deposited between Cu and pinned NiFe layer for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers can increase H-ex. (C) 2003 American Institute of Physics.

Interlayer segregation of Cu atoms in Ta/NiFe/Cu/NiFe/FeMn/Ta spin-valve multilayers and its influence on magnetic properties

Experimental results show that the exchange coupling field (H-ex) of NiFe/FeMn for Ta/NiFe/FeMn/Ta multilayers is higher than that for spin-valve multilayers Ta/NiFe/Cu/NiFe/FeMn/Ta. In order to find out the reason, the composition and chemical states at the surface of Ta(12 nm)/NiFe(7 nm), Ta(12 nm)/NiFe(7 nm)/Cu(4 nm), and Ta(12 nm)/NiFe(7 nm)/Cu(3 nm)/NiFe(5 nm) were studied using x-ray photoelectron spectroscopy. The results show that no elements from lower layers float out or segregate to the surface in the first and second samples. However, Cu atoms segregate to the surface of Ta(12 nm)/NiFe(7 nm)/Cu(3 nm)/NiFe(5 nm) multilayers, i.e., Cu atoms segregate to the NiFe/FeMn interface for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers. We believe that the presence of Cu atoms at the interface of NiFe/FeMn is one of the important factors which causes the exchange coupling field (H-ex) of Ta/NiFe/Cu/NiFe/FeMn/Ta to be weaker than that of Ta/NiFe/FeMn/Ta. (C) 2002 American Institute of Physics.

Determination of the values of hole-mixing coefficients due to interface and electric field in GaAs/AlxGa1-xAs superlattices

Numerical calculations within the envelope function framework have been performed to analyze the relations between the magnitude of in-plane optical anisotropy and the values of the additional hole-mixing coefficients due to interface and electric field in (001) symmetric GaAs/AlxGa1-xAs superlattices for light propagating along the [001] direction. It is found that the heavy- and light-hole states are mixed independently by interface and electric field. The numeric results demonstrate that the line shape of the in-plane anisotropic spectrum is determined by the ratio of the two hole-mixing coefficients. Theoretical analysis shows that with the help of simple calculation of the anisotropy at k=0, reliable values of the hole-mixing coefficients can be determined by reflectance-difference spectroscopy (IDS) technique, demanding no tedious fitting of experimental curves. The in-plane optical anisotropy measured by RDS provides a new method of getting the information on buried interfaces through the Value of the hole-mixing coefficient due to interface.

Influence of Fe3+ on perovskite oxides: La2/3Ca1/3Mn1-xFexO3

The structure and magnetoresistance properties in sintered samples of La-2/3 Ca-1/3 Mn1-x FexO3 (0 less than or equal to x less than or equal to 0.84) are studied by using Mossbauer spectroscopy, XRD and magnetic measurement. There are antiferromagnetic interactions between Fe and its nearest neighbors (Fe, Mn) when 0 less than or equal to x less than or equal to 0.67, which are important factors influencing the double-exchange between Mn3+ and Mn4+, Curie temperature, magnetic moment and GMR. It is suggested that the Mn3+(Fe3+)/Mn4+ system also consists of magnetic clusters with different sizes.

Analysis of the interfaces of [NiFe/Mo](30) and [Fe/Mo](30) multilayers

The interface states of [NiFe/Mo](30) and [Fe/Mo](30) multilayers have been investigated by x-ray small angle reflection and diffuse scattering. Significant interface roughness correlation was observed in both ultrathin [NiFe/Mo](30) and [Fe/Mo](30) multilayers. An uncorrelated roughness of about 27-3.1 Angstrom was revealed in the [NiPe/Mo](30) multilayers, which is explained as originating from a transition layer between the NiFe and the Mo layers. By the technique of diffuse scattering, it is clearly indicated that the interfacial roughness of NiFe/Mo is much smaller than that of Fe/Mo although the lattice mismatch is the same in both multilayers.

Simultaneous multiwavelength observations of sagittarius A

We observed Sgr A* using the Very Large Array (VLA) and the Giant Metrewave Radio Telescope (GMRT) at multiple centimeter and millimeter wavelengths on 2003 June 17. The measured flux densities of Sgr A*, together with those obtained from the Submillimeter Array (SMA) and the Keck II 10 m telescope on the same date, are used to construct a simultaneous spectrum of Sgr A* from 90 cm to 3.8 mu m. The simultaneous spectrum shows a spectral break at about 3.6 cm, a possible signature of synchrotron self-absorption of the strong radio outburst that occurred near epoch 2003 July 17. At 90 cm, the flux density of Sgr A* is 0.22 +/- 0.06 Jy, suggesting a sharp decrease in flux density at wavelengths longer than 47 cm. The spectrum at long cm wavelengths appears to be consistent with free-free absorption by a screen of ionized gas with a cutoff similar to 100 cm. This cutoff wavelength appears to be three times longer than that of similar to 30 cm suggested by Davies, Walsh, & Booth based on observations in 1974 and 1975. Our analysis suggests that the flux densities of Sgr A* at wavelengths longer than 30 cm could be attenuated and modulated by stellar winds from massive stars close to Sgr A*.

Electron tunneling through double magnetic barriers on the surface of a topological insulator

We study electron tunneling through a planar magnetic and electric barrier on the surface of a three-dimensional topological insulator. For the double barrier structures, we find (i) a directional-dependent tunneling which is sensitive to the magnetic field configuration and the electric gate voltage, (ii) a spin rotation controlled by the magnetic field and the gate voltage, (iii) many Fabry-Perot resonances in the transmission determined by the distance between the two barriers, and (iv) the electrostatic potential can enhance the difference in the transmission between the two magnetization configurations, and consequently lead to a giant magnetoresistance. Points (i), (iii), and (iv) are alike with that in graphene stemming from the same linear-dispersion relations.