Y.M. Sun

Photoluminescence from high-energy heavy ion irradiated C-doped SiO2 thin films

SiO2 thin films were implanted at room temperature (RT) with 120 keV carbon ions to a dose of 1.0 x 10(17) ions/cm(2) and then irradiated at RT with high-energy Kr-84 or Ar-40 ions to a fluence of 1.0 x 10(12) ions/cm(2). Using 320 nm monochromatic ultra-violet light for excitation, photoluminescence (PL) properties of these samples were examined and intense blue PL bands were observed. It was found that the blue PL peak intensity changes with electronic energy loss of the irradiation ion in the sample. With increasing the electronic energy loss level, the PL peak intensity decreases and the peak position shifts towards to the short-wavelength direction. Furthermore, the existence of C-dopants enhances the luminescence property of the irradiated samples

Effects of national ecological restoration projects on carbon sequestration in China from 2001 to 2010

Significance China has launched six key ecological restoration projects since the late 1970s, but the contribution of these projects to terrestrial C sequestration remains unknown. In this study we examined the ecosystem C sink in the project area (∼16% of the country’s land area) and evaluated the project-induced C sequestration. The total annual C sink in the project area between 2001 and 2010 was estimated to be 132 Tg C per y, over half of which (74 Tg C per y, 56%) was caused by the implementation of the six projects. This finding indicates that the implementation of the ecological restoration projects in China has significantly increased ecosystem C sequestration across the country. The long-term stressful utilization of forests and grasslands has led to ecosystem degradation and C loss. Since the late 1970s China has launched six key national ecological restoration projects to protect its environment and restore degraded ecosystems. Here, we conducted a large-scale field investigation and a literature survey of biomass and soil C in China’s forest, shrubland, and grassland ecosystems across the regions where the six projects were implemented (∼16% of the country’s land area). We investigated the changes in the C stocks of these ecosystems to evaluate the contributions of the projects to the country’s C sink between 2001 and 2010. Over this decade, we estimated that the total annual C sink in the project region was 132 Tg C per y (1 Tg = 1012 g), over half of which (74 Tg C per y, 56%) was attributed to the implementation of the projects. Our results demonstrate that these restoration projects have substantially contributed to CO2 mitigation in China.

Response of Pinus koraiensis seedling growth to different light conditions based on the assessment of photosynthesis in current and one-year-old needles

As one of the three major five-leaved pines in the northern hemisphere, Pinus koraiensis is the most important dominant tree species in the natural mixed-broadleaved Korean pine forests. However, the regeneration of P. koraiensis under the canopy of secondary forest stands is poor because of the light limitation. This study was conducted to understand how P. koraiensis seedlings adapt to different light intensities and what would be the optimum light level for their establishment and growth. Three repetition plots with four light intensities (15%, 30%, 60% and 100% of the natural incident irradiances, achieved by suspending layers of black nylon net above and surrounding the plots) were set up under natural climate conditions in a montane region in eastern Liaoning Province, Northeast China. A total of 80 P. koraiensis seedlings with similar height and root collar diameter were transplanted into four plots. After one year of acclimation to the specific light conditions, the seasonal variations of the photosynthetic variables and needle traits of the current and one-year-old needles, and the growth parameters were observed under four light intensities. The results indicated that: (1) The seedling at 60% treatment exhibited the greatest growth, which agreed with the response of the light-saturated photosynthetic rates (Amax) and the dark respiration rate (Rd) in the current and one-year-old needles, i.e., Rd at 60% treatment was significantly lower than that at 100% treatment, but Amax did not differ between the seedlings at 100% and 60% treatments. (2) The P. koraiensis seedlings have a certain photosynthetic plasticity to adapt the light conditions by adjusting their needle traits and regulating the physiological processes, because Amax, Rd, light saturation point and compensation point, the needle mass area, needle nitrogen and chlorophyll contents were significantly (p<0.05) correlated with the light intensities. Especially, Amax at 100% and 60% treatments was significantly higher (p<0.05) than that at 30% and 15% treatments for both current and one-year-old needles. (3) The needles of different ages played a commutative role during the growing season, i.e., the one-year-old needles played a major role for the photosynthesis in the early growing season; the current year needles did in the later growing season. This ensured the effective photosynthesis throughout the growing season. These findings suggest that P. koraiensis is the in-between heliophilous and shade-tolerant tree species at least for the seedlings up to 8 years.

Regeneration of a Coastal Pine (Pinus thunbergii Parl.) Forest 11 Years after Thinning, Niigata, Japan

To examine the effects of thinning intensity on wind vulnerability and regeneration in a coastal pine (Pinus thunbergii) forest, thinning with intensities of 20%, 30% and 50% was conducted in December 1997; there was an unthinned treatment as the control (total 8 stands). We re-measured the permanent sites to assess the regeneration characteristics 11 years after thinning. In the 50% thinned stand, seedlings aged from 2 to 10 years exhibited the highest pine seedling density and growth. The age composition ranged from 1–3 years with densities of 9.9 and 5.1 seedlings m−2 in 30% and 20% thinned stands; only 1-year-old seedlings with a density of 6.1 seedlings m−2 in the unthinned stand. Similar trends were found for the regeneration of broadleaved species such as Robinia pseudoacacia and Prunus serrulata. We speculate that the canopy openness and moss coverage contributed to the regeneration success in the 50% thinned stand, while the higher litter depth and lack of soil moisture induced the regeneration failure in the unthinned stand. The stands thinned at 20% or 30% were less favourable for pine regeneration than the stands thinned at 50%. Therefore, thinning with less than 30% canopy openness (20% and 30% thinned stands) should be avoided, and thinning at higher than 30% canopy openness (50% thinned stand, approximately 1500 stems ha−1 at ages 40–50 years) is suggested for increasing regeneration in the coastal pine forest. The implications of thinning-based silviculture in the coastal pine forest management are also discussed. The ongoing development of the broadleaved seedlings calls for further observations.

The impact of incident angle on multiple-bit upset in SRAMs

The effect of ion incident angle on multiple-bit upset (MBU) has been investigated for static random access memory IDT71256. The test pattern dependent MBU ratio can be as high as 70% when tested by either normal incident 136Xe ions or 36Ar ions incident at large angles. The increase of single event upset cross-section at large angles for light ions are mainly due to occurrence of high-ratio MBU. Charges collected through funnel effect play an important role in inducing MBU in NMOS IDT71256. The MBU ratio is in proportional to energy deposited in whole sensitive layer, but the ratios of more than 2-bit upset is decided by lateral distribution of charges.

Experimental studies of single-event effects induced by heavy ions

Abstract This paper presents the results of ground-based heavy ion test of single-event effect (SEE) vulnerability on microcircuits used in space. We observed the dependence of upset cross-sections on the incident angle of ions in Intel 8086 CPU. SEU cross-sections of various SRAMs did not depend on the stored pattern, but 0→1 and 1→0 transitions were completely different for different manufacturer products. Some SEE protection methods were verified in conditions of ground simulation experiments.

Blue-violet PL band formation in C : SiO2 films after swift heavy ion irradiation

Abstract One hundred and twenty keV C-ion doped SiO2 films were irradiated at RT with swift Ar, Kr, Xe or U ions and their photoluminescence (PL) properties were examined. From the obtained results, we found that an intense blue–violet PL band centred at ∼435±10 nm was formed in all ion irradiated samples and a weak ultraviolet PL band centred at ∼380 nm was formed only in the samples after Kr, Xe or U ion irradiations. The PL peak intensity of the blue–violet band (i) increases with the increase of the swift heavy ion irradiation fluence, (ii) decreases with the increase of electronic energy loss Se when Se 4.85 keV/nm. Furthermore, the peak central position of the blue–violet PL is shifted slightly to violet with increasing Se and some substructures appeared in the PL spectra of the samples irradiated with Xe or U ions. The appearance of these substructures is due to the high electronic energy loss. For the violet PL band, the intensity increases with Se. Possible origins and formation mechanism of light-emitters corresponding to the observed PL bands are discussed.

Swift heavy ion irradiation induced luminescence from C-doped SiO2 films

Abstract In the present work, a novel technique, “low energy ion implantation+high-energy heavy ion irradiation”, was used to synthesis light-emitting material. Experimentally, thermal-grown SiO 2 films were firstly implanted with 120 keV C + ions at room temperature (RT) to total doses in the range of (5.0×10 16 –1.0×10 18 ) ions/cm 2 . These C-doped SiO 2 films were then irradiated at RT with 335 and 855 MeV 40 Ar or 1.98 GeV 84 Kr ions to a fluence of 1.0×10 12 ions/cm 2 , or with 1.75 GeV 136 Xe ions to 1×10 11 , 5×10 11 or 1×10 12 ions/cm 2 , respectively. By measuring photoluminescence (PL) spectra of these samples excited by 320 nm light, the PL bands were investigated as functions of implantation ion dose, irradiation ion fluence and electronic energy loss S e . It was found that this technique is a useful tool to produce high quality light-emission structures, and that high-energy heavy ion irradiated C-doped SiO 2 films should be an efficient blue–violet emitting material. Furthermore, S e plays a dominant role in the formation of the PL bands, and proper C-dopant and suitable irradiation fluence will enhance the PL efficiency. Possible origins of the blue-violet PL bands formed in the ion irradiated C-doped SiO 2 films were discussed.

Growth and photosynthetic responses of Fraxinus mandshurica seedlings to various light environments

To determine light requirement and adaptability of Fraxinus mandshurica seedlings, the seasonal variations of photosynthetic variables were measured in 3-year-old seedlings grown under four light levels (100%, 60%, 30%, and 15% of full sunlight) with a LI-6400 portable photosynthesis system. The leaf chlorophyll content, special leaf weight, annual height and basal diameter increment of seedlings were also observed. The maximum and minimum values of net photosynthetic rate, maximum rate of carboxylation, and maximum rate of electron transport of F. mandshurica seedlings were detected with 60% and 15% of full sunlight treatments, respectively. With the decrease of light level, both light saturation point and special leaf weight significantly declined (p < 0.05), but leaf chlorophyll content significantly increased (p <0.05). Annual height and basal diameter increments of seedlings grown under 60% of full sunlight treatment were significantly greater than those of seedlings under other treatments (p < 0.05). It was concluded that F. mandshurica seedlings can adapt to a wide range of light environments from 15% to 100% of full sunlight by adjusting light saturation point, leaf chlorophyll content and special leaf weight. According to the maximum of relative growth, 60% of full sunlight treatment is the optimum light level for the growth of 3-year-old F. mandshurica seedlings.