To send content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about sending content to .
To send content items to your Kindle, first ensure firstname.lastname@example.org
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about sending to your Kindle.
Note you can select to send to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be sent to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
The average power of diode-pumped fiber lasers has been developed deeply into the kW regime in the past years. However, stimulated Raman scattering (SRS) is still a major factor limiting the further power scaling. Here, we have demonstrated the mitigation of SRS in kilowatt-level diode-pumped fiber amplifiers using a chirped and tilted fiber Bragg grating (CTFBG) for the first time. The CTFBG is designed and inscribed in large-mode-area (LMA) fibers, matching with the operating wavelength of the fiber amplifier. With the CTFBG inserted between the seed laser and the amplifier stage, an SRS suppression ratio of
is achieved in spectrum at the maximum output laser power of 2.35 kW, and there is no reduction in laser slope efficiency and degradation in beam quality. This work proves the feasibility and practicability of CTFBGs for SRS suppression in high-power fiber lasers, which is very useful for the further power scaling.
Stimulated Raman scattering (SRS) effect is considered to be one of the main obstacles for power scaling in general-type fiber lasers. Different from previous techniques that aim at suppressing SRS, nonlinear fiber amplifier (NFA), which manipulates and employs the SRS for power scaling in rare-earth-doped fiber, is under intensive research in recent years. In this paper, the authors will present an all-round study on this new kind of high-power fiber amplifier. A theoretical model is proposed based on the rate equation and amplified spontaneous emission (ASE), with random noise taken into account. By numerical solving of the theoretical model, the power scaling potential, heat analysis and advantages in suppressing the undesired backscattering light are quantificationally analyzed for the first time. Then two different types of high-power NFAs are demonstrated individually. Firstly, a laser diode pumped NFA has reached kilowatt output power, and the results agree well with theoretical predictions. Secondly, a tandem-pumped NFA is proposed for the first time and validated experimentally, in which 1.5 kW output power has been achieved. The authors also briefly discuss several new issues relating to the complex nonlinear dynamics that occur in high-power NFAs, which might be interesting topics for future endeavors.
Glacial lake outburst flood hazards in the Himalayan region have received considerable attention in recent years. Accurate volume estimation for glacial lakes is important for calculating outburst flood peak discharge and simulating flood evolution. Longbasaba lake, a potentially dangerous moraine-dammed lake, is located on the north side of the Himalaya. Its depth was surveyed using the SyQwest Hydrobox™ high-resolution echo sounder, and 6916 measurements were collected in September 2009. The maximum and average depths of the lake were 102 ± 2 and 48 ± 2 m, respectively. The morphology of the lake basin was modeled by constructing a triangulated irregular network, and the lake was found to have a storage capacity of 0.064 ± 0.002 km3. Multi-source remote-sensing images from Landsat MSS, Landsat TM/ETM+ and Terra ASTER and a topographic map were digitized to delineate the outlines of the lake between 1977 and 2009. The results indicate that the length and area of the lake have increased during the past 32 years, with a drastic expansion occurring since 2000. Based on volume and area data of Longbasaba lake in different periods, we deduced an empirical equation of the lake volume-area relationship that can be used to calculate the storage capacity of similar moraine-dammed lakes in the Himalayan region.
The Tibetan Plateau interior area (TPIA), often termed the Qangtang Plateau, is distinguished by many dome-like mountains higher than 6000 ma.s.l. These mountains provide favourable conditions for the development of ice caps and glaciers of extreme continental/subpolar type. According to historical topographic maps (1959–80) and recent Landsat images (2004–11), continuous retreat was observed and the glacierized part of this area decreased by 9.5% (0.27% a–1) with respect to the total glacier area of 8036.4 km2 in the 1970s. Glaciers in the Zhari Namco basin have experienced the highest area shrinkage, with a reduction rate of 0.72% a–1, while the smallest reduction occurred in Bangong Co (0.12% a–1) and Dogai Coying basins (0.11% a–1). A regional gradient of area loss was found, with a larger decrease in the south and a smaller decrease in the north of the plateau. Comparisons indicate glaciers have experienced smaller shrinkage in the TPIA than in surrounding regions. Glacier shrinkage in the TPIA is mainly attributed to an increase in air temperature, while precipitation, glacier size and positive difference of glaciation also played an important role.
We use remote-sensing and GIS technologies to monitor glacier changes in the Koshi River basin, central Himalaya. The results indicate that in 2009 there were 2061 glaciers in this region, with a total area of 3225 ±90.3 km2. This glacier population is divided into 1290 glaciers, with a total area of 1961 ±54.9 km2, on the north side of the Himalaya (NSH), and 771 glaciers, with a total area of 1264 ± 35.4 km2, on the south side of the Himalaya (SSH). From 1976 to 2009, glacier area in the basin decreased by about 19±5.6% (0.59±0.17%a–1). Glacier reduction was slightly faster on SSH (20.3 ±5.6%) than on NSH (18.8±5.6%). The maximum contribution to glacier area loss came from glaciers within the 1-5 km2 area interval, which accounted for 32% of total area loss between 1976 and 2009. The number of glaciers in the Koshi River catchment decreased by 145 between 1976 and 2009. Glacier area on SSH decreased at a rate of 6.2 ±3.2% (0.68 ±0.36% a–1), faster than on NSH, where the rate was 2.5 ±3.2% (0.27±0.36% a–1) during 2000-09. Based on records from Tingri weather station, we infer that temperature increase and precipitation decrease were the main causes of glacier thinning and retreat during the 1976-2000 period. Glacier retreat during the 2000-09 period appears to be controlled by temperature increase, since precipitation increase over this period did not offset ice losses to surface melting.
The second Chinese glacier inventory was compiled based on 218 Landsat TM/ETM+ scenes acquired mainly during 2006–10. The widely used band ratio segmentation method was applied as the first step in delineating glacier outlines, and then intensive manual improvements were performed. The Shuttle Radar Topography Mission digital elevation model was used to derive altitudinal attributes of glaciers. The boundaries of some glaciers measured by real-time kinematic differential GPS or digitized from high-resolution images were used as references to validate the accuracy of the methods used to delineate glaciers, which resulted in positioning errors of ±10 m for manually improved clean-ice outlines and ±30 m for manually digitized outlines of debris-covered parts. The glacier area error of the compiled inventory, evaluated using these two positioning accuracies, was ±3.2%. The compiled parts of the new inventory have a total area of 43 087 km2, in which 1723 glaciers were covered by debris, with a total debris-covered area of 1494 km2. The area of uncompiled glaciers from the digitized first Chinese glacier inventory is ∼8753 km2, mainly distributed in the southeastern Tibetan Plateau, where no images of acceptable quality for glacier outline delineation can be found during 2006–10.
This work was to evaluate the differences of soil and plant analysis development (SPAD) and normalized difference vegetation index (NDVI) readings and their relationship with leaf nitrogen accumulation (LNA). The study explored new indices to diagnose nitrogen (N) status. These indices were obtained by multiplying SPAD readings and leaf area index (LAI). Linear regression relationships between Chlorophyll values and N indicators showed the SPAD readings (Chl: LNA=0.0546×Chl-0.479, R2=0.94***, P<0.001). The projected results suggested that Chl values could play an important role for improving N status diagnosis from stem elongation to heading stages in paddy rice.
The ice cap on Nelson Island in the South Shetland Islands, West Antarctica, was studied between 1985 and 1989. The ice cap has an average thickness of 120 m. it is temperate, exists under the sub-Antarctic maritime climate and almost completely covers the island. Owing to intense percolation of meltwater (and, to some extent, liquid precipitation), the snow-firn layer is in the soaked facies, with a firn-ice transition at a depth of 25-26 m at the summit. A force-balance model suggests that the ice is almost linearly viscous but has a high viscosity. The model further suggests that basal sliding makes a larger contribution to the ice movement than does ice deformation. From 1970 to 1988. the average accumulation rate was 120 kg m−2a−1 at the centre, and between 1985 and 1989 the equilibrium-line elevation averaged 110m a.s.l. Analysis of chemical impurities in the surface snow suggests that the precipitation source is mainly local marine air masses and that human activity has already exerted a detectable influence on the local environment.
Mountain systems are often recognised as biodiversity hotspots; however, most montane forests are human-modified. Understanding the conservation value of human-modified forests is essential to mountain biodiversity conservation. In this study, mist-nets and point-counts were used to compare the bird communities of primary forests on ridges in the Ailao Mountains of Yunnan, China, and secondary forests, firewood forests, and pine plantations in nearby lower elevation zones. We found that community turnover among habitats was very high using both methods. Although the percentage of forest interior species and insectivores in each habitat was higher in the primary forests than in the human-modified forests, relatively high percentages of forest interior species and insectivores were recorded in the human-modified forests. Moreover, many bird species, forest interior species, insectivores and babblers were only recorded in the human-modified forests. Our study indicated that the primary forests are important for sustaining mountain bird diversity. However, given that primary forests are restricted to ridges, secondary forests, firewood forests, and pine plantations at lower elevations also play important roles in bird conservation in mountainous regions by increasing landscape diversity and partially offsetting species loss from primary forests. Therefore, conservation efforts should also be concentrated on human-modified forests at lower elevations in mountainous regions in south-west China.
This study was conducted to investigate the effect of in ovo feeding (IOF) of folic acid on the folate metabolism, immune function and the involved epigenetic modification of broilers. A total of 400 (Cobb) hatching eggs were randomly divided into four groups (0, 50, 100 and 150 µg injection of folic acid at embryonic age 11 d), and chicks hatched from each treatment were randomly divided into six replicates with 12 broilers/replicate after incubation. The results indicated that, in ovo, 100- and 150-µg folic acid injections improved the hatchability. The average daily gain and feed conversion ratio increased in the 150-µg group during the late growth stage. Simultaneously, in the 100- and 150-µg groups, an increase was observed in hepatic folate content and the expression of methylenetetrahydrofolate reductase (d1 and 42) and methionine synthase reductase (d21). IgG and IgM concentrations, as well as plasma lysozyme activity of broilers, showed a marked increase along with increasing folic acid levels. The splenic expression levels of IL-2 and IL-4 were up-regulated, whereas that of IL-6 was down-regulated, in the 100- and 150-µg folic acid treatment groups. In addition, histone methylation in IL-2 and IL-4 promoters exhibited an enrichment of H3K4m2 but a loss of H3K9me2 with the increased amount of folic acid additive. In contrast, a decrease in H3K4m2 and an increase in H3K9me2 were observed in the IL-6 promoter in folic acid treatments. Furthermore, in ovo, the 150-µg folic acid injection improved the chromatin tightness of the IL-2 and IL-4 promoter regions. Our findings suggest that IOF of 150 µg of folic acid can improve the growth performance and folate metabolism of broilers, and enhance the relationship between immune function and epigenetic regulation of immune genes, which are involved with the alterations in chromatin conformation and histone methylation in their promoters.
We designed and fabricated a class of self-assembling peptides into nanofiber scaffolds. KLDL-12 has been shown to be a permissible nanofiber scaffold for chondrocytes in cartilage 3-D cell cultures. However, the biochemical, structural, and biophysical properties of KLDL- 12 remain unclear. We show that KLDL-12 peptides form stable β-sheet structures at different pH values and that KLDL-12 and RIDI-12 self-assemble into nanofibers. The nanofiber length, though, is sensitive to pH changes. These results not only suggest the importance of electrostatic attraction or repulsion affecting the fiber lengths but also provide us with useful information for rational design and fabrication of peptide scaffolds.
The decomposition mechanism of block copolymer templates inside as-synthesized mesostructured solids has been systematically studied using solid-state 1H magic angle spinning nuclear magnetic resonance spectroscopy, thermogravimetric analysis, and high-vacuum Fourier transform infrared spectrometry. It is shown that there exists hydrogen-bonding interaction between silanols and block copolymers at the inorganic–organic interface in the self-assembled as-synthesized mesostructured solids, which plays an important role in protecting the surfactants against decomposition during the high-temperature hydrothermal treatment process. Increasing silanol concentration can enhance the hydrogen-bonding interaction and thus shows better “protection” effect. Moreover, the thermal decomposition of the block copolymer in as-synthesized mesostructured solids in air commences at higher temperatures compared with that in acidic solution or in air, providing further evidence in support of the silanol protection mechanism.
Multispectral analysis combined with the Periodic Acid-Schiff method was used to investigate cytological features of insoluble polysaccharides and changes in total insoluble polysaccharide content (TPC) during pollen development in rice, including four cytoplasmic male sterility lines (MSLs) and their corresponding fertility-maintaining lines (FMLs). The multispectral curves of the relative transmittance value (RTV) and the images of developing pollen cells were obtained across a range of successive wavelengths (400–720 nm). A minimum RTV was found near 550 nm indicating an absorption peak of the TPC. Thus, the TPC was measured using the RTV of 550 nm. In the four FMLs, the minimum TPC of developing pollen cells occurred at the late microspore stage, while the maximum TPC occurred at the mature pollen grain stage. The TPC levels of pollen cells were significantly higher in the four FMLs than in their corresponding MSLs during and after pollen abortion. Notably, a steep decrease of multispectral curves at 420 nm appeared before the occurrence of abortion, implying a marker associated with pollen abortion in rice. Our results will be helpful for exploring the changes in TPC during pollen ontogenesis in rice and provide a novel method for the study of bio-macromolecules.
A major obstacle to the positional cloning of quantitative trait loci (QTLs) lies in resolving genetic
factors whose allelic effects are blurred by environmental and background genetic variation. We
investigate a fine-mapping approach that combines the use of an interval-specific congenic strain
with progeny testing of recombinants for markers flanking a QTL. We apply the approach to map
a murine QTL with an approximately 20% effect on growth rate by progeny testing 39
recombinants in a 12 cM region of the X chromosome. We use a likelihood analysis in an attempt
to maximize the information on QTL map location and effect. The major X-linked effect is
mapped to an approximately 2 cM region flanked by markers about 5 cM apart, outside which
LOD support for the QTL drops extremely steeply by about 80. Nearly unambiguous assignment
of the QTL genotypic state is obtained for each recombinant. The resolution of individual
recombinants in the region is therefore sufficiently high to facilitate the positional cloning of the
locus, although progress has been hampered because the genomic region containing the QTL
shows an exceptionally low level of polymorphism in comparison with recent studies.
The research of particle beam fusion and its related problems at The Institute of Atomic Energy in Beijing is evolving along the following five directions: 1. Pulsed power technology. An 80 GW intense electron beam accelerator has been built. Switch research is ongoing. 2. Diode research. The experimental research and theoretical simulation of electron pinch in the diode have been carried out. The pinch process has been investigated by measuring the area collapsing velocity of the pinching electron ring on the anode surface. Expanding velocities of the cathode and anode plasmas have been observed. The diode with large area cathode of 38 × 5 cm2 can produce a 46 kA electron beam current with a beam cross-section of 36 × 4 cm2 and good uniformity for pumping of a KrF laser. 3. Energy deposition of the electron beam on the targets has been studied by means of measurements of the intensity of soft X-rays, the energy spectrum of blow-off ions, the visible light spectra and the rear surface velocity of the target. These experiments show that the results are in agreement with the classical interaction mechanism for high Z targets, but it is several times higher than the classical result for low Z targets. 4. Electron beam propagation in neutral gases with various pressures space-and current-neutralization processes have been investigated. 5. The production of a KrF laser pumped by an electron beam. A laser beam with an energy of 13 J and pulse duration of 70 ns has been obtained.
Email your librarian or administrator to recommend adding this to your organisation's collection.