Zhengzhong Jin

Control of filamentation induced by femtosecond laser pulses propagating in air

Filamentation formed by self-focusing of intense laser pulses propagating in air is investigated. It is found that the position of filamentation can be controlled continuously by changing the laser power and divergence angle of the laser beam. An analytical model for the process is given.

Characteristics of the soil microbial population in forest land irrigated with saline water in the desert area

The study of soil microbial populations and diversity is an important way to understanding the soil energy process.In this study we analyzed the characteristics of soil microbial populations of the Tarim Desert Highway shelter-forest,by identifying microbial fatty acids and using methods of conventional cul-tivation.The results illustrated that the amount of soil microbial activity and the diversity of soil microbial fatty acid increased significantly with the plantation age of the shelter-forest;the soil microbial population was dominated by bacteria.The fatty acids of C14︰0,C15︰0,C16︰0,C17︰0,C18︰1ω9,C18︰0,C18︰2ω6 and C21︰0 were found to be dominant soil microbial fatty acids in the shelter-forest soil.Prin-cipal analysis and regression analysis showed that(1) concentrations of fatty acids of C14︰0,C16︰0 and C18︰0 could be used as indicators of total soil microbial population;(2) soil bacteria and actinomycetes populations were closely correlated with the amount of fatty acids of C15︰0 and C17︰0;and(3) soil fungi were closely correlated with the amount of fatty acids of C18︰1ω9 and C18︰2ω6.

Soft X-ray spectroscopy of highly charged silicon ions in dense plasmas

Rich soft X-ray emission lines of highly charged silicon ions (Si VI-Si XII) were observed by irradiating an ultraintense laser pulse with width of 200 fs and energy of ~90 mJ on the solid silicon target. The high-resolution spectra of highly charged silicon ions with full width at half-maximum (FWHM) of ~0.3-0.4 A is analyzed in the wavelength range of 40-90 A. The wavelengths of 53 prominent lines are determined with statistical uncertainties of up to 0.005 A. Collisional-radiative models were constructed for Si VI-Si XII ions, which satisfactorily reproduce the experimental spectra and help in the line identification. Calculations at different electron densities reveal that the spectra of dense plasmas are more complicated than the spectra of thin plasmas. A comparison with the Kelly database reveals a good agreement for most peak intensities and differences for a few emission lines.

Soil microbial diversity, site conditions, shelter forest land, saline water drip-irrigation, drift desert

Soil microbes in forest land are crucial to soil development in extreme areas. In this study, methods of conventional culture, PLFA and PCR‐DGGE were utilized to analyze soil microbial quantity, fatty acids and microbial DNA segments of soils subjected to different site conditions in the Tarim Desert Highway forest land. The main results were as follows: the soil microbial amount, diversity indexes of fatty acid and DNA segment differed significantly among sites with different conditions (F < F0.05). Specifically, the values were higher in the middle and base of dunes than the top part of dunes and hardened flat sand, but all values for dunes were higher than for drift sand. Bacteria was dominant in the soil microbial community (>84%), followed by actinomycetes and then fungi (<0.05%). Vertical differences in the soil microbial diversity were insignificant at 0–35 cm. Correlation analysis indicated that the forest trees grew better as the soil microbial diversity index increased. Therefore, construction of the Tarim Desert Highway shelter‐forest promoted soil biological development; however, for enhancing sand control efficiency and promoting sand development, we should consider the effects of site condition in the construction and regeneration of shelter‐forest ecological projects.

Correlations of Soil Nutrients, Microbial Mass and Enzyme Activity in the Hinterland of the Taklimakan Desert, a Case Study

We explored the unique environmental conditions and management model of the Tarim Desert Highway shelter forest as well as the important roles of such shelter forest in development of the socio-economy of South Xinjiang. Experiments were conducted in the shelter forest lands drip-irrigated with underground saline water. Our results indicated that there are canonical correlations among soil nutrients, microbial amount and enzyme activity. The correlation between soil nutrients and soil microbial biomass was mainly attributed to total nitrogen, organic matter, total phosphate of nutrient factors, and amount of actinomycetes, carbon and phosphate content in microbe. The correlation between soil nutrients and soil enzyme activity was due to organic carbon, available potassium in soil and soil enzyme activities such as catalase activity and phosphatase activity. The correlation between soil microbial mass and activities of soil enzymes was due to phosphate and nitrogen contents in microbe and soil enzymes invertase and phosphatase activities. In addition to the correlations of soil nutrients and soil bio-activities, there is a vertical difference between these three factors in soil. We concluded that irrigation with saline groundwater had major effects on soil mineralization process. The release of soil nutrients in the process supported microbial mass colonization and soil enzyme activities in the Tarim Desert Highway shelter forest land. However, high level of salt in ground water adversely affected soil nutrient accumulation and microbe survival.

Relation between Surface Properties of Photosynthetic Organs of 10 Species of Shrubs and Their Dust-Retaining Capabilities in the Hinterland of Taklimakan Desert

In this paper, photosynthetic organs stained with dusts on the whole plant of ten kinds of shrubs planted in Tazhong Botanical Garden, near the Tazhong Si Oilfield, in the hinterland of the Taklimkan Desert, were sampled, and their dust-retaining capabilities of photosynthetic organs were analyzed in mass subtraction method. The results showed that: (1) The order of photosynthetic organ dust-retaining capability of 10 species of shrub evalued in index of dust-retaining capacities of unit fresh weight photosynthetic organs is Tamarix androssowii>; Tamarix hohenakeri>; Tamarix hispida.>; Tamarix ramosissma>; Tamarix elongata >; Tamarix austromongolica >; Tamarix juniperina>; Tamarix taklamakanensis >; Haloxylon ammodendron>; Calligonum caput-medusae. (2) Dust-retaining capability of photosynthetic organs of 10 species of shrub are closely related to its surface properties. Haloxylon ammodendro with higher dust-retaining capabilities of photosynthetic organ than Calligonum caput-medusae is determined by its assimilating branches with shorter knot spacing and more leaves. Though leaves of Tamarix plants are also extremely degraded, they have excellent dust-retaining capability by their photosynthetic organs, higher than Haloxylon ammodendron and Calligonum caput-medusae, due to their photosynthetic organs surface characteristics (such as relatively bigger leaf size, abundant tomenta, salt-secrecting gland), a mass of leaves, greater photosynthetic organs density of crown. Therefore the dust-retaining capability of these Tamarix plants mentioned in this paper differs greatly from each other. These results may provide a scientific basis for tree species selection and allocation in landscaping and shelterbelt constructions and its dust-retaining effect evaluation, also can offer a reference for the studying correlation between plants and soils in arid regions.

Effect of target shape on fast electron emission

Fast electrons emission from the interaction of femtosecond laser pulses with shaped solid targets has been studied. It is found that the angular distributions of the forward fast electrons are closely dependent upon the target shape. The important role played by the electrostatic fields built up near the target surfaces in the confinement of fast electrons is identified. Our two-dimensional particle-in-cell simulations can reproduce the main observations.

Relativistic Laser Acceleration Of Electrons Along Solid Surfaces

Recent experimental and theoretical studies on surface electron emission will be presented. A collimated fast electron beam was observed along the target surface irradiated by intense laser pulses up to 20TW when the laser is incident with large angles such as over 45 degree. Numerical simulations suggest that such an electron beam is formed due to the confinement of the surface quasistatic electric and magnetic fields. Meanwhile, an acceleration process similar to the inverse‐free‐electron‐laser is found to occur and is responsible for the generation of the most energetic electrons. A general formula for electron angular distributions accounting for the quasistatic electric and magnetic fields is given. In certain conditions, quasi‐monoenergetic electron beams are also produced. These results are of interest for potential applications of laser‐produced electron beams and helpful to the undersanding of the cone‐target physics in the fast ignition related experiments.