Sedimentary and environmental characteristics of the Gilan-Mazenderan plain, northern Iran: Influence of long- and short-term Caspian water level fluctuations on geomorphology

The south-southwestern Caspian coastal lowland in Iran, or the Gilan-Mazenderan plain, is a relatively narrow but long, composite depositional area of late Quaternary age. The Sefid Rud delta, the Anzali Lake (connected to the Caspian Sea by a meandering outlet 3.5 km long) and storm-dominated beaches are its prominent sedimentary features. They are controlled by the present water level of the Caspian Sea at -26.36 m in 2000. The Late Pleistocene-Holocene deposits of the lowland, which are covered commonly by a modern loess-origin soil, mainly consist of alternations of marine and non-marine sediments. The marine units form coastal terraces at 19-20 m (I), 2-0 m (II) and –6/-8 m (III) corresponing to the Late Khvalinian and Neocaspian transgressions. The deposits of the youngest terrace (terrace III) that represents a prograding beach-ridge complex are a consequence of several medium-term, cyclic water level oscillations in Late Holocene. Just after the initiation of the beach-ridge complex, Lake Anzali formed by damming of rivers and then by progradation of the complex in time forced to form the outlet of the lake. The nearest medium-term cycle lasted c. 65 years between 1930-1995 and the records showed that it included a lot of short-term (c. 4-5 yrs) and very short-term (week to months) water level oscillations. During the last erratic rise of sea level (1977-1996), the area of Lake Anzali doubled; the delta and the coastal sands including modern beaches were eroded on c. 30-100 m. Overall, a step-like morphology, repetition of marine and non-marine facies and also water level records of the last 75 years indicate that the ancient and recent deposition on the coastal lowland has been controlled by long- medium- and short-term fluctuations of the Caspian Sea level

Mapping the Dirac point in gated bilayer graphene

We have performed low temperature scanning tunneling spectroscopy measurements on exfoliated bilayer graphene on SiO2. By varying the back gate voltage we observed a linear shift of the Dirac point and an opening of a band gap due to the perpendicular electric field. In addition to observing a shift in the Dirac point, we also measured its spatial dependence using spatially resolved scanning tunneling spectroscopy. The spatial variation of the Dirac point was not correlated with topographic features and therefore we attribute its shift to random charged impurities.Comment: 3 pages, 3 figure

Spatially resolved spectroscopy of monolayer graphene on SiO2

We have carried out scanning tunneling spectroscopy measurements on exfoliated monolayer graphene on SiO$_2$ to probe the correlation between its electronic and structural properties. Maps of the local density of states are characterized by electron and hole puddles that arise due to long range intravalley scattering from intrinsic ripples in graphene and random charged impurities. At low energy, we observe short range intervalley scattering which we attribute to lattice defects. Our results demonstrate that the electronic properties of graphene are influenced by intrinsic ripples, defects and the underlying SiO$_2$ substrate.Comment: 6 pages, 7 figures, extended versio

Performance of the SERT 2 spacecraft after 4 and one-half years in space

The SERT 2 satellite, launched in February, 1970, has recently been reactivated after being dormant for a year. The satellite orientation was changed to spin stabilization in 1973 and the satellite is now coning such that the active side of the solar arrays move into and out of the sun every 23 days. There is sufficient power to operate the ion thrusters for seven days of this cycle. The 2 ion thruster system was successfully operated; the electrical short in the accelerating grids had cleared during the year long dormant phase

Late Holocene erosion in NW Anatolia from sediments of Lake Manyas, Lake Ulubat and the southern shelf of the Marmara Sea, Turkey

This paper deals with modern and ancient sedimentation in fresh water lakes and the marine shelf of the southern Marmara region, NW Anatolia, Turkey. Most of the information has been obtained from monitoring of suspended load discharged into two lakes (Manyas and Ulubat) in the last 45 years and from 8-11 m thick lacustrine sediments, in addition to radiocarbon-dated shelf sediments. This allows a holistic approach to the drainage basin denudation over time. The results show that the sedimentation rates in the lakes were low 0. 22 cm.yr-1, from 4000-2000 yr BP and then they increased (0.29 cm.yr-1) up to sub-recent times and reached 0.44 cm.yr-1 in the last century. It is suggested that deforestation created high rates of sedimentation in the basins and/or strong denudation of the region during the Late Holocene. This study also shows that for shallow freshwater lakes the calculation of sedimentation rates must include fine particles lost by the outlets and coarse-grained bed load deposited on their shores. In addition, a high rate of sedimentation has been created by short, but repetitive intense depositions. During the last century particularly during the last 45 years the rate of sedimentation or denudation has increased dramatically in NW Turkey. The two World Wars and mismanagement of the land had important local effects by increasing deforestation and resulting in the present erosive conditions

Natural and anthropogenic forest fires recorded in the Holocene pollen record from a Jinchuan peat bog, northeastern China

Pollen and charcoal particles from a Jinchuan peat (northeastern China) were examined to investigate the fire origin and interaction between climate, vegetation, fire and human activity during the Holocene. Pollen results show that: (i) a broadleaved deciduous forest was dominant during the early Holocene; (ii) from ~5500 cal. yr B.P. there was a gradual increase in coniferous trees (mainly Pinus), and a decrease in broadleaved deciduous trees (e.g. Quercus, Juglans, and Ulmus–Zelkova); (iii) after ~4200 cal. yr B.P., the deciduous forest was replaced by a mixed forest of coniferous and deciduous trees; (iv) coniferous trees including Pinus, Abies and Picea further increased after ~2000 cal. yr B.P., reflecting a cooler and drier climate after ~5500–4200 cal. yr B.P. Two layers of abundant microfossil charcoal particles (250–10 μm) and the coexistence of macrofossil particles (N2 mm) suggest two local fires: fire event 1 (5120±66 cal. yr B.P.) and fire event 2 (1288±8 cal. yr B.P., AD 662±8). Charcoal layer 1, with a large amount of Monolete psilate spores, is superimposed on the long-term trend of vegetation changes, indicating a natural origin for fire event 1 that was probably facilitated by drying environmental conditions since the mid-Holocene. Cerealia-type pollen and a low percentage of Monolete psilate spores were observed in charcoal layer 2, indicating that fire event 2 was caused by clearing. We suggest that fire event 2 may be related to the spread of the Han farming culture accompanied by the territorial expansion of the Tang Dynasty to the studied area in AD 668

Structure and Substitutions in Fluorapatite

Fluorapatite, Ca<inf>10</inf>(PO<inf>4</inf>)<inf>6</inf>F<inf>2</inf>. is a widely spread form of calcium phosphate present particularly in biological material. Human hard tissues contain crystals structurally related to apatite. Fluoride can be found in various natural sources and is also used for its beneficial action in caries prevention. Fluorapatite belongs to the spatial group P6<inf>3/m</inf> (C<inf>6h</inf>²) and consists of 3 ions: F^-, Ca²⁺, PO<inf>4</inf>^3-. In the present paper, we have carried out a crystallographic study of the fluorapatite structure and of the changes induced by the substitutions. The fluorapatite structure and the presence of a large number of ionic bonds make fluorapatite a very suitable host for many substitutents, some of them harmless for the human organism, some not. According to the substitution site, we can describe four types of substitution. The F^- substitution, also called Type A substitution, is the main one, and the best known. Only the Ca²⁺ substitution implies changes in the crystal structure. However, some questions remain, in particular for the PO<inf>4</inf>^3- substitution, which is the main substitution present in the biological calcium phosphates