With climate warming and drying, fire activity is increasing in Cajander larch (Larix cajanderi Mayr.) forests underlain by continuous permafrost in northeastern Siberia, and initial post-fire tree demographic processes could unfold to determine long-term forest carbon (C) dynamics through impacts on tree density. Here, we evaluated above- and belowground C pools across 25 even-aged larch stands of varying tree densities that established following a wildfire in 1940 near Cherskiy, Russia. Total C pools increased with increased larch tree density, from 9,000 g C m−2 in low-density stands to 11,000 g C m−2 in high and very high-density stands, with increases most pronounced at tree densities < 1 stem m−2 and driven by increased above- and belowground (that is, coarse roots) and live and dead (that is, woody debris and snags) larch biomass. Total understory vegetation and non-larch coarse root C pools declined with increased tree density due to decreased shrub C pools, but these pools were relatively small compared to larch biomass. Fine root, soil organic matter (OM), and near surface (0–30 cm) mineral soil (MS) C pools varied little with tree density, although soil C pools held most (18–28

An ecosystem of a relic petrophytic steppe was studied in the Lower Kolyma River region. The soils of the steppe area significantly differed from those of the surrounding open larch forests in the following features: the presence of humus-accumulative horizons with a high content of roots; low moisture content; high heat supply; an extremely contrasting temperature regime; neutral reaction; decreased potential acidity; higher humification of organic matter; accumulation of exchangeable bases, soluble salts and organic nitrogen; and the presence of carbonate neoformations in the form of cutans on pebbly units. They also had a high microorganism saturation of the soil profile, a high share of actinomycetes in the microbial community, as is typical for arid soils, and a shift in the ratio of potential enzyme activities toward oxidoreductases, which reflects a deeper destruction of plant residues and more intensive humus formation. The petrophytic steppe had high bioproductivity. The growth rate of the aboveground phytomass (ANP) was closer to the true steppes of.entral Asia than to the zonal tundras of the Arctic and Subarctic; such communities can serve as models for paleoreconstructions and study of the Late Pleistocene cold steppes - mammoth fauna large grazing mammals habitats.

Along with rising air temperatures in the Arctic, ground temperatures in permafrost (i.e. perennially frozen ground) are rising globally (Biskaborn et al., 2019). The accelerated thaw of permafrost releases permafrost carbon (PF-C) that has been locked in permafrost soils since the last glacial period. The potential remineralisation of PF-C to greenhouse gases can contribute to further climate warming (Schuur et al., 2015). Dissolved organic carbon (DOC) mobilised from the old Yedoma outcrops on the banks of the Kolyma River is shown to be highly labile in aquatic systems (Mann et al., 2012; Vonk et al., 2013). Yet, vulnerability of particulate organic carbon (POC), released in much higher quantities from these Pleistocene deposits, to biodegradation is not known (Guo et al., 2007). The focus of this study is to quantify degradation of POC in the Kolyma River. Particulate organic carbon in the Kolyma River is older than DOC (Frey and McClelland, 2009; McClelland et al., 2016), especially in the summer months, thus serving as a good tracer for abrupt permafrost thaw (i.e. river bank erosion and thermokarst). We incubated whole-water samples collected in July 2018 in a constant turbulent flow to mimic the ambient river conditions (Richardson et al., 2013) and quantified the loss of POC over 10 to 14 days. The incubation was carried out in the dark and the room temperature was on average 16 oC, which is close to the surface water temperatures measured in the Kolyma River in July (12.5–15.9 oC).We used carbon isotopes (∆ 14 C,  13 C) to trace age and changes in POC composition during degradation. We also quantified DOC loss during the whole-water incubation, as well as in an additional pre-filtered (DOC only) incubation experiment that served as a control. To characterise compositional changes of DOC we analysed colored and fluorescent dissolved organic matter (CDOM and FDOM) and used parallel factor analysis (PARAFAC) to interpret the data (Murphy et al., 2013).

Observations and modelling show that the deep thermokarst lakes that formed in Siberia and Alaska when the permafrost warmed in the Holocene epoch changed from climate-warming methane sources to climate-cooling carbon sinks about 5,000 years ago.

High‐latitude northern rivers export globally significant quantities of dissolved organic carbon (DOC) to the Arctic Ocean. Climate change, and its associated impacts on hydrology and potential mobilization of ancient organic matter from permafrost, is likely to modify the flux, composition, and thus biogeochemical cycling and fate of exported DOC in the Arctic. This study examined DOC concentration and the composition of dissolved organic matter (DOM) across the hydrograph in Siberia's Kolyma River, with a particular focus on the spring freshet period when the majority of the annual DOC load is exported. The composition of DOM within the Kolyma basin was characterized using absorbance‐derived measurements (absorbance coefficienta330, specific UV absorbance (SUVA254), and spectral slope ratio SR) and fluorescence spectroscopy (fluorescence index and excitation‐emission matrices (EEMs)), including parallel factor analyses of EEMs. Increased surface runoff during the spring freshet led to DOM optical properties indicative of terrestrial soil inputs with high humic‐like fluorescence, SUVA254, and low SRand fluorescence index (FI). Under‐ice waters, in contrast, displayed opposing trends in optical properties representing less aromatic, lower molecular weight DOM. We demonstrate that substantial losses of DOC can occur via biological (∼30% over 28 days) and photochemical pathways (>29% over 14 days), particularly in samples collected during the spring freshet. The emerging view is therefore that of a more dynamic and labile carbon pool than previously thought, where DOM composition plays a fundamental role in controlling the fate and removal of DOC at a pan‐Arctic scale.

Optical emission spectra from plasma produced by a copper vacuum arc with argon and nitrogen have been investigated for the case when the plasma was guided by a straight solenoid. The spectra have been compared with those obtained from inductively coupled rf multicusp discharge in the 10−4–10−2 Torr argon and nitrogen pressure range and at an input power of up to 500 W. It has been found that the spectral line intensity distributions of neutral and ion species for arc and rf discharge were different. Also, the intensity evolutions of the lines have shown a different behavior between the arc current and rf power. Electron excitation temperature (Tex) for rf argon plasma at low pressure has been found to be approximately 2.5 eV which was about ten times higher than for Cu-argon arc discharge. Possible mechanisms of ionization-excitation of guest atoms/molecules in the case of metal vacuum arc discharge are discussed.

Optical emission spectroscopy in the range 200-800 nm was applied for investigation of the copper plasma produced by a metal vapour vacuum arc plasma source. The experiments were conducted for the cases when the plasma was guided by straight and Ω-shaped curved solenoids as well as without solenoids, and also for different vacuum conditions. It was found that, besides singly- and doubly-charged ions, a relatively high concentration of excited neutral copper atoms was present in the plasma. The relative fraction of excited atoms was much higher in the region close to the cathode surface than in the plasma column inside the solenoid. The concentration of excited neutral, singly- and doubly-ionized atoms increased proportionally when the arc current was increased to 400 A. Some weak lines were attributed to more highly ionized copper species and impurities in the cathode material.

A 150-kV, high-current, non-mass-analyzed ion implanter based on a modified duoplasmatron ion source and a completely computerized control has been developed for industrially applicable ion beam surface engineering at Chiang Mai University. High-current (∼mA) N-ion implantation in steels and alloys and other ion beam techniques such as single-ion-beam assisted deposition have been explored using the facility for modification of tribological properties. The ion implanter has been engaged in industrial service to local customers in implanting various practical objects. The ion implantation for both academic and applied purposes has proved to be successful in improving hardness and wear resistance as well as prolonging lifetime of the ion-beam-processed tools.

A metal vapor vacuum are (MEVVA) ion source has been constructed and installed at Chiang Mai University. The cathode-insulator-trigger electrode system and the cooling efficiency were found to be reliable during the source operation (without the cathode-insulator replacement), with total number of pulses of approximately 3 X 10(5) and with the repetition rate of up to 5.5 pps at 200 A are current. The main are and plasma ion current-voltage characteristics have been measured. The maximum plasma ion saturation current obtained at 3 cm distance from the cathode was approximately 6 A and the coefficient of transformation of the are current to the ion current was found to approach 3%. Preliminary experiments with copper film deposition on some dielectric substrates are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.

An ion beam center has been established at Chiang Mai University in Thailand with the recently completed construction of a self-developed, 150 kV, two-beam-line (non-analyzed and analyzed) ion implantation facility and a 20 kV, 3 mA, non-analyzed ion implanter based on a duoplasmatron ion source. Using these facilities, a program of heavy ion implantation in metals and alloys is being carried out. The present work is focused on various nitrogen ion implantations of steels for local industry. This paper reports our research results including data on the hardness and wear resistance of local stainless steels, carbon steels and mild steels as a function of ion doses, and data on the oxidation behavior and tribological properties of ion implanted steels. Also discussed are high current, high dose and low energy ion implantation, and implantation in practical objects. Experimental data on implantations beneficial to the mechanical and chemical properties of the steels are presented and provide baselines for industrial applications.

Structural distortions in high-T(c) 1-2-3 compounds under low temperature fast neutron irradiation are studied with neutron powder diffraction and compared with oxygen deficient samples. The results show the absence of essential charge transfer between the chains and planes for radiation-induced disorder and point to random defects to be responsible for the behavior of physical properties of high-T(c) superconductors.

Anisotropy of electrical resistivity, Hall effect and the upper critical field in high-Tc YBCO and NdCCO single crystals depending on disorder caused by fast neutron irradiation is investigated. To find out the features typical for HTSC's themselves we studied the same physical properties of other anisotropic single crystals. Though all the systems under study have some physical properties in common, the response of HTSC's to disorder evidences for unusual electronic states of these compounds.

Recent research suggests thermokarst lakes produce large amounts of methane due to active layer thawing of permafrost and increasing thaw bulb activity. In order to quantify the amount of methane generation potential and subsequent processing of labile carbon a basic understanding of elements is needed from permafrost. In this presentation we compare permafrost profiles from a watershed with continuous permafrost. Three profiles (upslope, adjacent to the lake, and near an alas adjacent to the lake) were obtained along a small subwatershed entering a thermokarst lake. One centimeter soil samples were collected once every five centimeters and analyzed for moisture and organic matter content using a drying oven and muffle furnace. Water soluble extracts were conducted on three sub-samples from each profile and tested for phosphorus (orthophosphate), nitrogen (ammonium and nitrate), and dissolved organic carbon. Soil moisture contents are highest in the alas (56-26%) and next to the lake (42-20%), and lower on the slope (21-12%). The organic matter content seems steady throughout the profiles (5-2.4%), except for spikes at shallower depths (28%) and slightly elevated levels in the alas and towards the bottom of the water table (7%). Soil organic matter content correlates with moisture content in that samples with higher organic matter contents also have higher water contents. Orthophosphate and dissolved organic carbon extract values correlate with the organic matter content in the soils. Higher organic content soils contained less water soluble amounts of phosphorus and dissolved organic carbon. Orthophosphate concentrations increased with depth for the alas and water table and decreased with depth for the slope. Orthophosphate was much higher for the slope (28.4-17.9 ug/L) compared with the other two profiles (22.2- 7.4 ug/L). Nitrate concentrations were highest in the alas (34.7-12.0 ug/L), while ammonium was low and decreased with depth on the slope (14.7-3.7 ug/L) and the alas