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The 318-m-thick sediment record from Lake El'gygytgyn provides unique opportunities for a detailed examination of environmental changes during the Réunion Subchron polarity reversal event (2.1384–2.1216 Myr BP) in the northeastern Russian Arctic. The paper describes vegetation and climate fluctuations between ~ 2.15 and 2.10 Myr BP as inferred from palynological data. Biome reconstructions indicate that throughout this interval the tundra (TUND) biome generally has higher affinity scores as compared to cold steppe (STEP) or cold deciduous forest (CLDE). An exception is the climatic optimum between ~ 2.139 and 2.131 Myr BP, coinciding with Marine Isotope Stage 81 (approximately the Réunion Subchron), when the CLDE biome has the highest scores. Landscape-openness indices suggest that more closed vegetation characterized most of the interval between 2.146 and 2.127 Myr BP, when deciduous forest and shrubs expanded in the regional vegetation and climate was relatively warm and wet. Peaks in green algal colonies ( Botryococcus ) and Zygnema -type spores ~ 2.150–2.146, ~ 2.131–2.123, and ~ 2.112–2.102 Myr BP indicate expansions of shallow-water habitats and lowered lake levels. Comparisons with biome reconstructions from other interglacial intervals at Lake El'gygytgyn suggest that precession-related summer insolation intensity and obliquity-related duration of summer daylight are major controls on the onset of interglaciations, whereas obliquity probably plays a more significant role on vegetation succession at northern high latitudes during the Pleistocene. [ABSTRACT FROM AUTHOR]

Abstract: A gas cluster ion accelerator with energies up to 20 keV is described. Parameters of the main components of the equipment were determined. It was demonstrated that a pulse regime of the accelerator can be realized with a relatively low (500 l/sec) pumping speed of the cluster ion source. Conditions for stable cluster beam generation were found. In pulse mode ion clusters appear in the accelerated beam in the first stages of ion beam evolution. A model describing the behavior of the ion beam in the pulse regime is suggested. To analyze the beam mass composition two systems were constructed: a magnetic mass-separation system and a time-of-flight system. Cluster ions Ar n + with number of atoms/charge n ≥ 500 were detected in the beam by using deflection in a homogeneous magnetic field. Clusters up to 3000 atoms/charge were detected by using time-of-flight measurements. [Copyright &y& Elsevier]

Abstract: Pollen, palynomorphs, and rhizopods were studied from several <1 m thick, peaty and silty sediment sections on southwestern October Revolution Island, Severnaya Zemlya. Six AMS radiocarbon ages from the sections show that peat accumulation started at ca. 11,500 and stopped after 9500 cal. yr BP, consistent with several previously reported 14C ages. Open steppe-like vegetation existed on the island during the late Glacial, shortly before the Pleistocene/Holocene transition. Environmental conditions on the island were most favourable for local biota during the early Holocene, ca. 11,500–9500 cal. yr BP, when tundra-like sedge-grass communities dominated the vegetation. Low shrub tundra associations with dwarf birch and willow grew in more wind-sheltered localities. The temperatures during the growing season were at least 4 °C higher than today. The Vavilov Ice Cap was at or behind its present margins. Environmental conditions in the region changed significantly ca. 9400 cal. yr BP as a result of colder and drier conditions, when vegetation became similar to the modern, sparse lichen–moss–grass cover. [Copyright &y& Elsevier]

The results of experimental measurement and analytical estimation of the coefficient of backward reflection from targets made of various materials upon their irradiation by a picosecond laser pulse having the intensity of (0.8–4) × 1018 W/cm2 are presented. It is shown that the induced surface instability leads to the formation of a profile backscattering the incident radiation. The coefficient of backward reflection achieves a few percent and has an intensity optimum depending on the target material. [ABSTRACT FROM AUTHOR]

Abstract: The erosion behavior of W–Pd bimetallic systems has been investigated for both hydrogen-saturated (H/Pd∼0.65) and unsaturated states during impact of a steady-state nitrogen plasma from a mirror Penning discharge. An essential decrease by factors of about 2–5 in the erosion rate of W was observed for hydrogen-saturated W–Pd samples in the nitrogen ion energy range from 0.8 to 1.6keV. Possible reasons for this erosion behavior are discussed. Isotherms and isobars of hydrogen permeability through W–Pd systems were measured in the temperature range of 573–973K and hydrogen pressure range of 1.33×102 to 105 Pa. It is shown that the limiting stage of permeation process is, most likely, the diffusion in the W film. The activation energy of hydrogen permeability was determined to be ∼12kJ/mol, this being much lower than the literature data for bulk tungsten at molecular hydrogen-driven permeation. Possible mechanisms are suggested and analyzed to explain the observed decrease in the activation energy of hydrogen penetration through W–Pd systems. [Copyright &y& Elsevier]

A continuous lacustrine sequence from the western part of Lama Lake (69°32′N, 90°12′E), complemented by a peat sequence from the lake catchment provides the first detailed environmental reconstruction for the Late Glacial and Holocene on the Taymyr Peninsula. Scarce steppe-like communities with Artemisia, Poaceae, and Cyperaceae dominated during the Late Glacial. Tundra-like communities with Betula nana, Dryas, and Salix grew on more mesic sites. There are distinct climatic signals, which may be correlated with the Bølling and Allerød warming and Middle and Younger Dryas cooling. The Late Glacial/Preboreal transition, at about 10,000 14C yr BP, was characterized by changes from predominantly open herb communities to shrub tundra ones. Larch forest might have been established as early as 9700–9600 14C yr BP, whilst shrub alder came to the area ca 9500–9400 14C yr BP, and spruce did not reach area before ca 9200 14C yr BP. Spruce-larch forests with shrub alder and tree birch dominated the vegetation around the Lama Lake from ca 9000 14C yr BP. Dwarf birch communities were also broadly distributed. The role of spruce in the forest gradually decreased after 4500 14C yr BP. The vegetation cover in the Lama Lake area became similar to the modern larch-spruce forest ca 2500 14C yr BP. A pollen-based biome reconstruction supports a quantitative interpretation of the pollen spectra. Climate reconstructions obtained with information-statistical and plan-functional-type methods show very similar trends in reconstructed July temperature since ca 12,300 14C yr BP, while precipitation anomalies are less coherent, especially during the Late Glacial–Holocene transition. [Copyright &y& Elsevier]

The invention of high-power, ultra-short-pulse lasers has opened the way to investigations aimed at the creation of a new type of bright X-ray source for various uses including material science applications and time-resolved X-ray diffraction for biology. The efficiency with which laser energy incident on a solid target is converted into an X-ray emission depends on many factors, including the temporal profile of the laser pulse. Here we report the results of our theoretical and experimental investigations of the line X-ray emission from layered solid targets irradiated by ultra-short laser pulses. The laser prepulse parameters and target thickness are optimized to convert the maximum laser energy into an emission in the selected X-ray line. Multilayer foils are proposed to increase the energy of the Kα-line emission from laser plasma while simultaneously keeping the X-ray pulse duration at a hundred femtoseconds. The emission is studied both experimentally and theoretically by means of an analytical model and numerical simulations. [ABSTRACT FROM AUTHOR]

Abstract. Soft-X-radiation in the "water-window" region (23.3-43.6 Angstrom) mainly from carbon laser plasmas generated by subpicosecond (700 fs) 0.248-mu m laser pulses is studied as a function of angle of incidence and intensity (up to 10[sup 18] W/cm[sup 2]) for p-polarized laser light. Furthermore, comparison is made between plasmas generated from massive and toil targets. Numerical calculations are performed using a hydrocode coupled to X-ray line and continuum emission calculations including radiation transport. The optimized conditions to achieve maximum water-window X-ray emissivity and, in particular, carbon Lyman-alpha line emission are investigated. In addition, analytical scalings are presented. These theoretical results are essentially confirmed by previous experiments. It is found that at optimized conditions, picosecond or subpicosecond laser plasma X-ray sources with a power of the order of 1-10 GW in a spectral window of 1 Angstrom could be developed. [ABSTRACT FROM AUTHOR]

This Letter presents a selective and efficient one-pot synthesis of tetraalkynylstannanes via direct interaction of terminal alkynes with tin tetrachloride in the presence of zinc chloride and amines. The influence of the nature and amount of Lewis acid and amine on the course of this transformation has been investigated. The proposed approach has the advantages of readily available reactants, high yields and atom economy. It is also applicable to a wide range of substrates with base-, and nucleophile-sensitive groups. [ABSTRACT FROM AUTHOR]

A sediment sequence was taken from a closed, high altitude lake (informal name Olive-backed Lake) in the central mountain range of Kamchatka, in the Russian Far East. The sequence was dated by radiocarbon and tephrochronology and used for multi-proxy analyses (chironomids, pollen, diatoms). Although the evolution of Beringian climate through the Holocene is primarily driven by global forcing mechanisms, regional controls, such as volcanic activity or vegetation dynamics, lead to a spatial heterogeneous response. This study aims to reconstruct past changes in the aquatic and terrestrial ecosystems and to separate the climate-driven response from a response to regional or localised environmental change. Radiocarbon dates from plant macrophytes gave a basal date of 7800 cal yr BP. Coring terminated in a tephra layer, so sedimentation at the lake started prior to this date, possibly in the early Holocene following local glacier retreat. Initially the catchment vegetation was dominated by Betula and Alnus woodland with a mosaic of open, wet, aquatic and semi-aquatic habitats. Between 7800 and 6000 cal yr BP the diatom-inferred lake water was pH 4.4–5.3 and chironomid and diatom assemblages in the lake were initially dominated by a small number of acidophilic/acid tolerant taxa. The frequency of Pinus pumila (Siberian dwarf pine) pollen increased from 5000 cal yr BP and threshold analysis indicates that P . pumila arrived in the catchment between 4200 and 3000 cal yr BP. Its range expansion was probably mediated by strengthening of the Aleutian Low pressure system and increased winter snowfall. The diatom-inferred pH reconstructions show that after an initial period of low pH, pH gradually increased from 5500 cal yr BP to pH 5.8 at 1500 cal yr BP. This trend of increasing pH through the Holocene is unusual in lake records, but the initially low pH may have resulted directly or indirectly from intense regional volcanic activity during the mid-Holocene. The chironomid-inferred July temperature reconstruction suggests cool periods between 3200–2800 cal yr BP and 1100–700 cal yr BP and a warmer period between 2800 and 1100 cal yr BP. Chironomid and diatom DCA scores decline from ca. 6000 cal yr BP, indicating compositional changes in these aquatic assemblages. In comparison declines in pollen PCA scores are delayed, starting ca. 5100 cal yr BP. The results suggest that while catchment vegetation was responding primarily to climate change, the biota within the lake and lake water chemistry were responding to localised environmental conditions. [ABSTRACT FROM AUTHOR]

High resolution palaeoenvironmental records in Far-Eastern Russia are rare, and the Kamchatka Peninsula is among the least studied areas of the region. This paper describes a record spanning the last ca. 11,000 yr, obtained from a bog in the southern part of Kamchatka. The radiocarbon dated core was analysed for pollen, testate amoebae, charcoal and loss-on-ignition (LOI). The vegetation during the early Holocene was dominated by grasses (Poaceae), birch ( Betula ) and heath (Ericaceae p. p.). Around 10,300 cal yr BP there was a substantial change in the vegetation cover to shrub alder ( Alnus viridis s.l.) stands with sedges and ferns (Polypodiophyta) as well as herbs such as meadow rue ( Thalictrum ) in the understory. In the surroundings of Utka peatlands started to form. The variations in the vegetation cover were most probably caused by climatic changes. At the beginning of sediment accumulation, before 10,300 cal yr BP, the composition of the vegetation points to cooler summers and/or decreased annual precipitation. Around 10,300 cal yr BP, changes in vegetation occurred due to rising temperatures and/or changed water regimes. Increased abundancies of dry indicating testate amoebae after 9100 cal yr BP point to intermediate to dry soil conditions. Between 8600 and 7700 cal yr BP tree alder ( Alnus incana ) was widely spread at the site which probably indicates optimal environmental conditions. The tephra layer at 381–384.5 cm (ca. 8500 cal yr BP) produces a strong impact on the testate amoebae assemblages. At 7700 cal yr BP there was a sudden drop of A. incana in the local vegetation. From this time on, A. incana and also A. viridis decrease continuously whereas Betula gradually increases. The upper part of the sequence (after 6300 cal yr BP) shows higher abundancies of meadowsweet ( Filipendula ) and sweet gale ( Myrica ) pollen. After 6300 cal yr BP, changes in testate amoebae demonstrate variable soil moisture conditions at the site. Between 3700 and 1800 cal yr BP, wet conditions dominate as dry indicating testate amoebae decrease. After 1800 cal yr BP soil conditions become more variable again but this time with dry dominating testate amoebae. In contrast to surrounding regions, there is no evidence of trees such as spruce or larch growing in the surroundings of the site even though those trees are characteristic of many eastern Siberian sites. This difference might be because of the maritime influence of the Okhotsk Sea. Even dwarf pine ( Pinus pumila ), which is currently widely dispersed in northern Kamchatka, became part of the local vegetation only during the last 700 yr. [ABSTRACT FROM AUTHOR]

A radiocarbon and tephra-dated sediment core from Lifebuoy Lake, located on the north-east coast of Kamchatka Peninsula, was analysed for pollen, spores, diatoms, chironomids and tephra in order to uncover regional environmental history. The 6500-year environmental history of Lifebuoy Lake correlates with the broad regional patterns of vegetation development and climate dynamics with both diatoms and chironomids showing near-synchronous changes. Between ca. 6300 and 3900 cal yr BP, the lake ecosystem was naturally enriched, with several Stephanodiscus species dominating the diatom plankton. This natural eutrophication state is likely to be due to a combination of the base-rich catchment geology, the fertilisation effect of several fires in the catchment, silica input from tephra layers and, possibly, nitrogen input from seabirds. The substantial tephra deposit at about 3850 cal yr BP might have stopped sedimentary phosphorus from entering the lake water thus decreasing the trophic state of the lake and facilitating the shift in diatom composition to a benthic Fragiliariaceae complex. Both diatoms and chironomids showed simultaneous compositional changes, which are also reflected by statistically significant changes in their rates of change 300–400 years after the arrival of Pinus pumila in the lake catchment. The rapid increase in both total diatom concentration and the percentage abundance of the large heavy species, Aulacoseira subarctica might be a response to the change in timing and intensity of lake spring turn-over due to the changes in the patterns of North Pacific atmospheric circulation, most notably westward shift of the Aleutian Low. The two highest peaks in A. subarctica abundance at Lifebouy Lake occurred during opposite summer temperature inferences: the earlier peak (3500–2900 cal yr BP) coincided with warm summers and the latter peak (300 cal yr BP–present) occurred during the cold summer period. These imply that A. subarctica shows no direct response to the changes of summer air temperature. Instead, it appears to thrive during the periods of increased winter precipitation, thicker ice and late spring turn-over periods, i.e., shows indirect response to climate. The clearest effect of tephra deposition on the lake ecosystem is above 908 cm (ca. 3800 cal yr BP) where the tephra deposit might have caused the shift from Stephanodiscus -dominated planktonic assemblages to the Fragilariaceae complex of benthic species. Tephra deposits might have also contributed towards the development of eutrophic plankton from about 6300 cal yr BP. It is not certain if several tephra deposits influenced diatom and chironomid changes during the last 300 years. [ABSTRACT FROM AUTHOR]

Abstract: A suppression of transverse proton divergence by a localization of high-energy electron bunch generated by an interaction between an intense laser and a foil target is investigated in this paper. When an intense laser illuminates a foil target, electrons are accelerated longitudinally by the ponderomotive force and produce a strong magnetic field. The electrons are confined by the magnetic field and an electric field is generated locally. Protons are extracted and mainly accelerated longitudinally by the local electric field. Consequently, the transverse divergence of high-energy protons is successfully suppressed. [Copyright &y& Elsevier]

Abstract: A pollen record from the core sediments collected in the northern part of Lake Baikal represents the latest stage of the Taz (Saale) Glaciation, Kazantsevo (Eemian) Interglacial (namely the Last Interglacial), and the earliest stage of the Zyryanka (Weichselian) Glaciation. According to the palaeomagnetic-based age model applied to the core, the Last Interglacial in the Lake Baikal record lasted about 10.6 ky from 128 to 117.4 ky BP, being more or less synchronous with the Marine Isotope Stage 5e. The reconstructed changes in the south Siberian vegetation and climate are summarised as follows: a major spread of shrub alder (Alnus fruticosa) and shrub birches (Betula sect. Nanae/Fruticosae) in the study area was a characteristic feature during the late glacial phase of the Taz Glaciation. Boreal trees e.g. spruce (Picea obovata) and birch (Betula sect. Albae) started to play an important role in the regional vegetation with the onset of the interglacial conditions. Optimal conditions for Abies sibirica–P. obovata taiga development occurred ca. 126.3 ky BP. The maximum spread of birch forest-steppe communities took place at the low altitudes ca. 126.5–125.5 ky BP and Pinus sylvestris started to form forests in the northern Baikal area after ca. 124.4 ky BP. Re-expansion of the steppe communities, as well as shrubby alder and willow communities and the disappearance of forest vegetation occurred at about 117.4 ky BP, suggesting the end of the interglacial succession. The changes in the pollen assemblages recorded in the sediments from northern Baikal point to a certain instability of the interglacial climate. Three phases of climate deterioration have been distinguished: 126–125.5, 121.5–120, and 119.5–119 ky BP. The penultimate cooling signal may be correlated with the cool oscillation recorded in European pollen records. However, such far distant correlation requires more careful investigation. [Copyright &y& Elsevier]

Spectra of intraband absorption of polarized mid-IR light were investigated in undoped, p-, and n-doped InAs/GaAs quantum dots (QDs) covered with an InGaAs layer. Optical matrix elements for intraband electron and hole transitions in QD5 have been calculated for different polarizations of light, and a good agreement with the experimental data is obtained. It is shown that the intraband absorption of light by electrons strongly exceeds the absorption by holes. Photoluminescence spectra and TEM images of structures with artificial molecules formed by pairs of QDs were studied. [ABSTRACT FROM AUTHOR]

Abstract: The luminescence due to rare earth ions in Al and Ga nitride thin layers can be increased by proper structural tailoring. In this contribution, we report on the photoluminescence of the rare earth ion Tb3+ that is contained in films prepared by DC magnetron co-sputtering of Ga or Al targets with additional Tb pellets in a nitrogen atmosphere. These results are typical also for other rare earth ions, such as Eu3+, Sm3+, Tm3+ and Ce3+. Thermal annealing of the samples results in significant improvement of the photoluminescence by factors up to several tens in intensity. Interestingly enough, optimum intensity is achieved with annealing temperatures in a window between approximately 500 and 750°C in all cases. This finding indicates similar excitation and emission processes based on structural properties of the layers. [Copyright &y& Elsevier]