Search

Diversity and similarity of butterfly communities were assessed in five different habitat types (from natural closed forest to agricultural lands) in the mountains of Tam Dao National Park, Vietnam for 3 years from 2002 to 2004. The line transect count was used to record species richness and abundance of butterfly communities in the different habitat types. For each habitat, the number of species and individuals, and indices of species richness, evenness and diversity of butterfly communities were calculated. The results indicated that species richness and abundance of butterfly communities were low in the natural closed forest, higher in the disturbed forest, highest in the forest edge, lower in the shrub habitat and lowest in the agricultural lands. The indices of species richness, evenness and diversity of butterfly communities were low in agricultural lands and natural closed forest but highest in the forest edge and shrub habitats. The families Satyridae and Amathusiidae have the greatest species richness and abundance in the natural closed forest, with a reduction in their species richness and abundance from the natural closed forest to the agricultural lands. Species composition of butterfly communities was different among five different habitat types (40%), was similar in habitats outside the forest (68%) and was similar in habitats inside the forest (63%). Diversity and abundance of butterfly communities are not different between the natural closed forest and the agriculture lands, but species composition changed greatly between these habitat types. A positive correlation between the size of species geographical distribution range and increasing habitat disturbance was found. The most characteristic natural closed forest species have the smallest geographical distribution range.

Magnetic Properties and Magnetic Viscosity of Pr4Fe76Co10B6Nb3Cu1 Nanocomposite Magnet N. D. The, N. H. Hai, H. D. Anh, V. V. Hiep, L. V. Vu, C. X. Huu and N. Chau Center for Materials Science, Hanoi University of Science, 334 Nguyen Trai Road, Hanoi, Vietnam (Received 15 July 2007) The nanocomposite magnet Pr4Fe76Co10B6Nb3Cu1 has been obtained by nanocrystallization of a rapidly-quenched amorphous ake. The in uence of the annealing process on the structural and the magnetic properties are investigated. High magnetic hardness was reached with of large coercivity of Hc = 3.65 kOe, a remanent induction of Mr = 12.0 kG, Mr=Ms = 0.79 and maximum energy product (BH)max = 17.6 MGOe at optimal annealing conditions. The multiphase structures of Fe3B as soft phases and of Pr2Fe14B as hard phase were con rmed by X-ray di raction data. The magnetic viscosity as a function of the reverse eld was evaluated for all specimen. The results show that the magnetic viscosity coe cient peaks at a critical nucleation eld, at which the magnetization reversal of the specimens becomes irreversible. PACS numbers: 75.50.Vv, 75.50.Ww, 75.75.+a, 75.60.Lr

Nanocomposite hard magnetic materials (Nd,Dy)4.5Fe77.5B18 (No. 1) and (Nd,Dy)4.5Fe76B18Nb1.2Cu0.3 (No. 2) have been prepared by crystallizing amorphous ribbons, fabricated by single roll melt-spinning. The evolution of a multiphase structure was monitored by an x-ray diffractometer and by thermomagnetic measurement. We observed that, at annealing temperatures below 670??C, there is crystallization of soft phase Fe3B and a small amount of hard phase Nd2Fe14B. At annealing temperatures above 670??C, crystallization of ?-Fe and probably Dy2Fe14B phases with large magnetocrystalline anisotropy led to a drastic enhancement in the hard magnetic properties of the materials. The maximum value of HC is found to be 4.2?kOe for sample No. 1. For sample No. 2, with co-doping of Nb and Cu, nanostructure refinement yields a strong enhancement in exchange coupling between the component phases. Thereby, we obtained high reduced-remanence of 0.78, high remanence of 1.15 and a high (BH)max value up to 16.2?MGOe.

An approach to obtain both large magnetostriction and large magnetostrictive susceptibility is developed. It is applied to sputtered {Tb(Fe0.55Co0.45)1.5∕(YxFe1−x)} (x=0, 0.1 and 0.2) multilayers. In the as-deposited samples, the TbFeCo layers are in the amorphous state, but the microstructure of the YxFe1−x layers is not the same: A crystalline state is observed in pure Fe layers (x=0), whereas body-centered-cubic-Fe nanocrystals coexist within an YFe amorphous matrix in Y0.1Fe0.9 layers. A parallel magnetostrictive susceptibility χλ‖ as large as 29.4×10−2T−1, which is almost half of that (79.6×10−2T−1) of the Metglas 2605SC was obtained for x=0.1. This is attributed to the exchange coupling between sandwiched TbFeCo layers and nanostructured YFe layers.

The photoinjector test facility at DESY, Zeuthen site (PITZ), was built to develop and optimize photoelectron sources for superconducting linacs for high-brilliance, short-wavelength free-electron laser (FEL) applications like the free-electron laser in Hamburg (FLASH) and the European x-ray free-electron laser (XFEL). In this paper, the detailed characterization of two laser-driven rf guns with different operating conditions is described. One experimental optimization of the beam parameters was performed at an accelerating gradient of about 43 MV/m at the photocathode and the other at about 60 MV/m. In both cases, electron beams with very high phase-space density have been demonstrated at a bunch charge of 1 nC and are compared with corresponding simulations. The rf gun optimized for the lower gradient has surpassed all the FLASH requirements on beam quality and rf parameters (gradient, rf pulse length, repetition rate) and serves as a spare gun for this facility. The rf gun studied with increased accelerating gradient at the cathode produced beams with even higher brightness, yielding the first demonstration of the beam quality required for driving the European XFEL: The geometric mean of the normalized projected rms emittance in the two transverse directions was measured to be 1.26±0.13 mm mrad for a 1-nC electron bunch. When a 10% charge cut is applied excluding electrons from those phase-space regions where the measured phase-space density is below a certain level and which are not expected to contribute to the lasing process, the normalized projected rms emittance is about 0.9 mm mrad.

At the Free Electron Laser Hamburg the laser beam is diverted towards 5 different test sites by massive silicon mirrors, which are mounted into vacuum vessels. One of these vessels is operated in permanent switching mode. The pursued switching frequency is 5 Hz. The initial motion concept is characterized by the motion of the entire vessel perpendicular to the laser beam by a linear drive. The initial vessel with a steel body allowed a switching at 2.5 Hz at the demanded precision. By substituting the steel body with one made of titanium, the frequency could be increased to 3.125 Hz. Further increase should be possible with a new motion concept, leaving the vessel stationary, which is not yet implemented. Another concept which is currently examined is the exclusive motion of the mirror inside the vacuum with piezo motors. Although the motors meet the requirements concerning the accuracy and driving speed, a steady motion under ultra-high vacuum conditions is not yet possible since the cooling of the motors is still insufficient.