Emission characteristics of three final continuum electrons produced in low-energy double ionization of helium

The double ionization of helium by electron impact for 106 eV incident energy was studied in a kinematically complete experiment by using a reaction microscope. The pattern of the angular correlation of the three emitted electrons was analyzed by selecting different values of the recoil ion longitudinal momentum. The Wannier predicted geometry appears when the recoil ion carries the full initial projectile momentum. It was found that at this low impact energy, the outgoing electrons still remember the initial-state collision information.

Microstructure and mechanical properties at TiCp/Ni-alloy interfaces in laser-synthesized coatings

Titanium carbide particle (TiCp) reinforced Ni alloy composite coatings were synthesized by laser cladding using a cw 3 kW CO2 laser. Two kinds of coatings were present in terms of TiCp origins, i.e. undissolved and in situ reacted TiCp, respectively. The former came from the TiCp pre-coated on the sample, whereas the latter from in situ reaction between titanium and graphite in the molten pool during laser irradiation. Conventional and high-resolution transmission electron microscope observations showed the epitaxial growth of TiC, the precipitation of CrB, and the chemical reaction between Ti and B elements around phase interfaces of undissolved TiCp. The hardness, H, and elastic modulus, E, were measured by nanoindentation of the matrix near the TiCp interface. For undissolved TiCp, the loading curve revealed pop-in phenomena caused by the plastic deformation of the crack formation or debounding of TiCp from the matrix. As for in situ generated TiCp, no pop-in mark appears. On the other hand, in situ reacted TiCp led to much higher hardness and modulus than that in the case of undissolved TiCp. The coating reinforced by in situ generated TiCp displayed the highest impact wear resistance at both low and high impact conditions, as compared with coatings with undissolved TiCp and without TiCp. The impact wear resistance of the coating reinforced by undissolved TiCp increases at a low impact work but decreases at a high impact work, as compared with the single Ni alloy coating. The degree of wear for the composite coating depends primarily on the debonding removal of TiCp.

Detection and Characterization of Long-Pulse Low-Velocity Impact Damage in Plastic Bonded Explosives

Damage not only degrades the mechanical properties of explosives, but also influences the shock sensitivity, combustion and even detonation behavior of explosives. The study of impact damage is crucial in the vulnerability evaluation of explosives. A long-pulse low-velocity gas gun with a gas buffer was developed and used to induce impact damage in a hot pressed plastic bonded explosive. Various methods were used to detect and characterize the impact damage of the explosive. The microstructure was examined by use of polarized light microscopy. Fractal analysis of the micrographs was conducted by use of box counting method. The correlation between the fractal dimensions and microstructures was analyzed. Ultrasonic testing was conducted using a pulse through-transmission method to obtain the ultrasonic velocity and ultrasonic attenuation. Spectra analyses were carried out for recorded ultrasonic signals using fast Fourier transform. The correlations between the impact damage and ultrasonic parameters including ultrasonic velocities and attenuation coefficients were also analyzed. To quantitatively assess the impact induced explosive crystal fractures, particle size distribution analyses of explosive crystals were conducted by using a thorough etching technique, in which the explosives samples were soaked in a solution for enough time that the binder was totally removed. Impact induces a large extent of explosive crystal fractures and a large number of microcracks. The ultrasonic velocity decreases and attenuation coefficients increase with the presence of impact damage. Both ultrasonic parameters and fractal dimension can be used to quantitatively assess the impact damage of plastic bonded explosives.

Morphology, structure, and properties of in situ compatibilized linear low-density polyethylene/polystyrene and linear low-density polyethylene/high-impact polystyrene blends

Blends of linear low-density polyethylene (LLDPE) with polystyrene (PS) and blends of LLDPE with high-impact polystyrene (HIPS) were prepared through a reactive extrusion method. For increased compatibility of the two blending components, a Lewis acid catalyst, aluminum chloride (AlCl3), was adopted to initiate the Friedel-Crafts alkylation reaction between the blending components. Spectra data from Raman spectra of the LLDPE/PS/AlCl3 blends extracted with tetrahydrofuran verified that LLDPE segments were grafted to the para position of the benzene rings of PS, and this confirmed the graft structure of the Friedel-Crafts reaction between the polyolefin and PS. Because the in situ generated LLDPE-g-PS and LLDPE-g-HIPS copolymers acted as compatibilizers in the relative blending systems, the mechanical properties of the LLDPE/PS and LLDPE/HIPS blending systems were greatly improved. For example, after compatibilization, the Izod impact strength of an LLDPE/PS blend (80/20 w/w) was increased from 88.5 to 401.6 J/m, and its elongation at break increased from 370 to 790%. For an LLDPE/HIPS (60/40 w/w) blend, its Charpy impact strength was increased from 284.2 to 495.8 kJ/m(2). Scanning electron microscopy micrographs showed that the size of the domains decreased from 4-5 to less than 1 mum, depending on the content of added AlCl3.

Plume Parameters and Thruster Properties of a Low Power Arcjet

Abstract. A low power arcjet-thruster of 1 kW-class with gas mixture of H2-N2 or pure argon as the propellant is fired at a chamber pressure about 10 Pa. The nozzle temperature is detected with an infrared pyrometer; a plate set perpendicular to the plume axis and connected to a force sensor is used to measure the thrust; a probe with a tapered head is used for measuring the impact pressure in the plume flow; and a double-electrostatic probe system is applied to evaluate the electron temperature. Results indicate that the high nozzle temperature could adversely affect the conversion from enthalpy to kinetic energy. The plume flow deviates evidently from the LTE condition, and the rarefied-gas dynamic effect should be considered under the high temperature and low-pressure condition in analyzing the experimental phenomena.

Impact of organic contamination on laser-induced damage threshold of high reflectance coatings in vacuum

The influence of organic contamination in vacuum on the laser-induced damage threshold (LIDT) of coatings is studied. TiO2/SiO2 dielectric mirrors with high reflection at 1064 nm are deposited by the electron beam evaporation method. The LIDTs of mirrors are measured in vacuum and atmosphere, respectively. It is found that the contamination in vacuum is easily attracted to optical surfaces because of the low pressure and becomes the source of damage. LIDTs of mirrors have a little change in vacuum compared with in atmosphere when the organic contamination is wiped off. The results indicate that organic contamination is a significant reason to decrease the LIDT. N-2 molecules in vacuum can reduce the influence of the organic contaminations and prtectect high reflectance coatings. (C) 2008 Elsevier B.V. All rights reserved.

Impact of environmental and innate factors on the food habit of Chinese perch Siniperca chuatsi (Basilewsky) (Percichthyidae)

Laboratory and field investigations were conducted to study the food habit of Chinese perch Siniperca chuatsi (Basilewsky) from first feeding through adult stage. Only fish larvae were consumed by Chinese perch larvae (2-21 days from hatching), and the presence of zooplankton did not have any significant effect on their survival rate. The ability of Chinese perch to feed on zooplankton is clearly limited by some innate factor. Instead of gill rakers, Chinese perch larvae have well-developed sharp teeth at the first feeding stage, and are well adapted to the piscivorous feeding habit unique to the larvae of Chinese perch, e.g. they bite and ingest the tails of other fish larvae. At the first feeding stage (2 days from hatching), daily rations were both very low, either in light or complete darkness. Although early-staged Chinese perch larvae (7-17 days from hatching) could feed in complete darkness, their daily rations were always significantly higher in light than in complete darkness. Late-staged Chinese perch larvae (21 days from hatching) were able to feed in complete darkness as well as in light, similar to the case of Chinese perch yearlings. Chinese perch yearlings (total length, 14-16 cm) consumed prey fish only and refused shrimp when visual cues were available (in light), but they consumed both prey when visual cues were not available (in complete darkness), suggesting that prey consumption by Chinese perch yearlings is affected by their sensory modality in predation. Both prey were found in the stomachs of similar-sized Chinese perch (total length, 14-32 cm) from their natural habitat, suggesting that shrimp are consumed by Chinese perch at night. Prey selection of Chinese perch with a length >38 cm, which consumed only fish in the field, appears to be based upon prey size instead of prey type. These results suggest that although environmental factors (e.g. light intensity) affect prey detection by Chinese perch, this fish is anatomically and behaviourally predisposed to prey on live fish from first feeding. This makes it a difficult fish to cultivate using conventional feeds.

Impact of eutrophication on biodiversity of the macrozoobenthos community in a Chinese shallow lake

Comparative studies on community structure and biodiversity of macrozoobenthos were carried out in three lake areas with different states of eutrophication (mesotrophic, eutrophic and hypereutrophic) in a shallow subtropic lake (Lake Donghu) in the middle basin of the Yangtze River of China. Thirty-three taxa (including six Mollusca, five Oligochaeta, 15 Chironomidae and seven other zoobenthos) were found during February 1998 to April 1999. The results show that the more eutrophic the lake water, the lower the macrozoobenthos species diversity (measured as species number, diversity index, and K-dominant curves). Abundance of the oligochaete Limnodrilus hoffmeisteri was positively correlated with the degree of eutrophication, which was due mainly to its ability to tolerate low dissolved oxygen. The chironomid Tanypus chinensis also thrived in the hypereutrophic environment; however, it was less endurable to eutrophication than L. hoffmeisteri.

Growth of Potamageton maackianus under low-light stress in eutrophic water

Decline of submersed macrophytes in Lake Donghu of China with the progress of eutrophication is assumedly due to low light stress by algae blooming. I conducted a laboratory experiment to study the impact of low-light stress on the growth of Potamogeton maackianus A. Been, a dominant submersed macrophyte of the lake before the 1970s. Plants were grown for six weeks in aquaria with Lake Donghu sediment and enriched water. Light delivered to aquaria was adjusted to simulate the typical Lake Donghu light intensities that exist at several water depths from 0.6m to 1.7m. Biomass growth of the plant was inversely related to light intensity at the simulated depths of greater than or equal to 1.0m (r = 0.96, p < 0.05, n=6) and was negative at the depths of greater than or equal to 1.4m. These results indicate that photosynthetic light saturation and compensation points of the plant in Lake Donghu should be ca. 0,9m and ca. 1.5m depths, respectively. Chlorophyll content, growth of main shoot, total shoot lengths and density of the plant all peaked at 1.2-1.3m simulated depths. These results indicate that P. maackianus responds to low light stress primarily by elongation of shoots, and increase of density. Its biomass growth and nutrient uptake rate did not correlate with the accelerated shoot growth. Below the light intensities of water deeper than 1.2-1.3m, shoot growth rate decreased. The flexible tolerant strategy of P. maackianus to low-light stress suggests that the disappearance of this plant from the lake was not mainly due to eutrophication-induced low-light stress.

Long-term toxic impact of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the reproduction, sexual differentiation, and development of different life stages of Gobiocypris rarus and Daphnia magna

The sexual ratio of Gobiocypris rarus exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and 17 beta -estradiol from embryo to sexually mature revealed feminization and overdevelopment of connective tissue in male fish gonad in 2-30 pg/L TCDD concentration range. Daphnia magna was not sensitive to the high dose of TCDD (0.1-1000 ng/ml), but the reproduction of D. magna treated with TCDD decreased after the 8th day. 7-Ethoxyresorufin-O-deethylase (EROD) activities in newly fertilized eggs of G. rarus exposed to TCDD dosage groups (1000-100,000 pg/L) were significantly induced and increased with TCDD concentrations at the early life stage, while no difference was found between low TCDD dosage groups (<100 pg/L), but a good relationship between the EROD activity and the TCDD concentration was observed during a long-term developmental stage. There was a pericardial edema formed in a 2-week yolk-sac at the concentration of 1000 pg/L TCDD. But in the exposure group (2 pg/L TCDD for 120 days), the cell nuclei of hepatocytes was far from the center and packed toward the cell membrane; the cristae of most mitochondria in the cell dropped and collapsed; the rough endoplasmic reticulum broke into fragments; and numerous lipid droplets formed in the cell. (C) 2001 Academic Press.

Impact of diode facet reflectivity on the fiber grating external cavity semiconductor laser

The scattering matrix method is used to analyze the multiple reflection effect between the laser diode facet and the fiber grating facet by considering the fiber grating external cavity laser diode (FGECL) as a four-mirror cavity laser. When neglecting other important parameters such as butt-coupling distance between the diode and the fiber facets, coupling efficiency, external cavity length, it is shown that low reflectivity is not a crucial factor for the laser characteristics such as SMSR. Experimentally high SMSR fiber grating external cavity laser is fabricated with a relatively large residual facet reflectivity (about 1%), which is coincident with our simulation results.

Theoretical Study on Inner Shell Electron Impact Excitation of Lithium

Cross sections for electron impact excitation of lithium from the ground state 1s(2)2s to the excited states 1s2s(2), 1s2p(2), 1s2snp (n = 2-5), 1s2sns (n = 3-5), 1s2pns (n = 3-5), and 1s2pnp (n = 3-5) are calculated by using a full relativistic distorted wave method. The latest experimental electron energy loss spectra for inner-shell electron excitations of lithium at a given incident electron energy of 2500 eV [Chin. Phys. Lett. 25 (2008) 3649] have been reproduced by the present theoretical investigation excellently. At the same time, the structures of electron energy loss spectra of lithium at low incident electron energy are also predicted theoretically, it is found that the electron energy loss spectra in the energy region of 55-57 eV show two-peak structures.

Electron impact excitation of xenon from the metastable state to the excited states

The electron impact excitation cross sections from the lowest metastable state 5p(5)6sJ = 2 to the six lowest excited states of the 5p(5)6p configuration of xenon are calculated systematically by using the fully relativistic distorted wave method. In order to discuss the effects of target state descriptions on the electron impact excitation cross sections, two correlation models are used to describe the target states based on the multiconfiguration Dirac-Fock (MCDF) method. It is found that the correlation effects play a very important role in low energy impact. For high energy impact, however, the cross sections are not sensitive to the description of the target states, but many more partial waves must be included.

Protective effects of melatonin against low- and high-LET irradiation

To investigate the protective effects of melatonin against high-LET ionizing radiation, V79 Chinese hamster cells were irradiated with 100 keV/mu m carbon beam. Parallel experiments were performed with 200 kV X-rays. To avoid the impact from extra solvents, melatonin was dissolved directly in culture medium. Cells were cultured in melatonin medium for 1 hr before irradiation. Cell inactivation was measured with conventional colony forming assay, medium containing 6-thioguanine was used for the selection of mutants at hprt locus, and the cell cycle was monitored by flow cytometry. Both carbon beam and X-rays induced cell inactivation, hprt gene mutation and cell cycle G2 block dose-dependently. But carbon beam showed stronger effects as indicated by all three endpoints and the relative biological effectiveness (RBE) was 3.5 for cell killing (at 10% survival level) and 2.9 for mutation induction (at 5 x 10(-5) mutants/ cell level). Melatonin showed protective effects against ionizing radiation in a dose-dependent manner. In terms of cell killing, melatonin only increased the survival level of those samples exposed to 8Gy or larger of X-rays or 6 Gy or larger of carbon beam. In the induction of hprt mutation and G2 block, melatonin reduced such effects induced by carbon beam but not by X-rays. The results suggest that melatonin reduces the direct interaction of particles with cells rather than an indirect interaction. Further studies are required to disclose the underlying mechanisms.

Evidence of strong projectile-target-core interaction in single ionization of neon by electron impact

The momentum distributions of recoil ions were measured in the single ionization of neon by electron impact at incident energies between 80 and 2300 eV. It was found that there are a noticeable number of recoil ions carrying large momenta, and the relative contributions of these ions becomes more pronounced with the further decrease of incident electron energy. These observed behaviors indicate that there is a strong projectile-target-core interaction in the single-ionization reaction. By comparing our results with those of electron-neon elastic scattering, we concluded that the elastic scattering of the projectile electron on the target core plays an important role at low and intermediate collision energies.