Description of Placoneis mologaensis, a new diatom from the Rybinsk reservoir on the Volga River, European Russia

Phytotaxa ◽  
2020 ◽  
Vol 464 (3) ◽  
pp. 217-226
Author(s):  
VASILY S. VISHNYAKOV
Keyword(s):  
Rybinsk Reservoir ◽  
Central Area ◽  
Morphological Observation ◽  
Regulated Rivers ◽  
Volga River ◽  
Radial Pattern ◽  
Unknown Species ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
The Rybinsk Reservoir

A survey of surficial bottom sediments of the Rybinsk reservoir on the Volga, one of the largest and highly regulated rivers in Europe, revealed unknown species of the genus Placoneis. Detailed morphological observation using light and scanning electron microscopes allowed to describe this as P. mologaensis sp. nov. The species is characterized by linear-elliptical valves with slightly pronounced poles and conspicuous combination of other features, such as radial pattern of coarsely punctate uniseriate striae, bowtie-shaped central area without of isolated stigma, and raphe branches with heteromorphous terminal fissures. Ultrastructurally, P. mologaensis shows external areolar openings placed in depressions, which vary markedly in shape from round to slit-like. The new species is compared with similar and misidentified species and distributional data are provided based on confirmed records from the Pleistocene of the Boreal regions of Europe.

scholarly journals Sarcophagodes duodecima sp. nov., a new small araphid fossil diatom (Bacillariophyceae) from Lower to Middle Pleistocene sediments of Japan

Phytotaxa ◽  
2021 ◽  
Vol 505 (1) ◽  
pp. 85-96
Author(s):  
TOMONORI NAYA ◽  
KIYOHIDE MIZUNO
Keyword(s):  
New Species ◽  
Central Area ◽  
Early Pleistocene ◽  
Morphological Observation ◽  
Middle Pleistocene ◽  
Fossil Species ◽  
Habitat Differences ◽  
Western Japan ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes

A new fossil diatom species, Sarcophagodes duodecima, is described from the Lower to Middle Pleistocene Karato Formation of Himeshima Island, western Japan, based on detailed morphological observation of valves using light and scanning electron microscopes. This new species is characterized by a smaller valve length range, a wide lanceolate central area, shorter striae on the valve face, and longer striae on the mantle than other members of the genus. The new species was also found in the Lower Pleistocene Bushi Formation, central Japan, suggesting that S. duodecima sp. nov. was widely distributed in Japan during Early Pleistocene time. The species composition in the sample chosen as type suggests that the new fossil species occupied a brackish-water habitat. Differences in morphological features from closely related taxa are discussed.

scholarly journals In MemoriamTamara L. Poddubnaya (1930–2011)—Oligochaetologist

Zoosymposia ◽  
2014 ◽  
Vol 9 (1) ◽  
pp. 6-9
Author(s):  
TARMO TIMM ◽  
MARK J. WETZEL
Keyword(s):  
Rybinsk Reservoir ◽  
Large City ◽  
Inland Waters ◽  
Volga River ◽  
Limnodrilus Hoffmeisteri ◽  
Don River ◽  
Southern Russia ◽  
In Memoriam ◽  
Northern Russia ◽  
The Rybinsk Reservoir

Dr. Tamara Leont'evna Poddubnaya (nee Protopopova) was born 18 February 1930 in Rostov-na-Donu, a large city on the Don River in Southern Russia. After graduating the Rostov University in 1953 she joined the Biological Station in Borok, which later became the Institute for Biology of Inland Waters at Rybinsk Reservoir, located on the Upper Volga River in Northern Russia. Here she spent the remaining 57 years of her lifetime, working in the same research institute. In 1962, she received her Cand. Biol. Sci. (= Ph.D.) degree in Moscow; her thesis (in Russian) was entitled, "Studies on the biology of mass species of tubificids (Limnodrilus newaensis Mich. and Limnodrilus hoffmeisteri Clap.) of the Rybinsk Reservoir”.

Morphology of some fossil lacustrine centric species from the western United States assigned to the genus Cyclotella (Bacillariophyta), including four described as new

Phytotaxa ◽  
2013 ◽  
Vol 127 (1) ◽  
pp. 81 ◽  
Author(s):  
J. P. KOCIOLEK ◽  
G. K. KHURSEVICH
Keyword(s):  
United States ◽  
New Species ◽  
Central Area ◽  
Morphological Features ◽  
Western United States ◽  
Fossil Species ◽  
Centric Diatoms ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

During consideration of fossil centric diatoms from a variety of non-marine localities in the western USA, we encountered four new species and two previously known taxa that should be assigned to the genus Cyclotella (F.T. Kützing) A. de Brébisson. We detail the morphological features of these species, and discuss their relevance to other members of the Cyclotella. These fossil species are studied in light and scanning electron microscopes, and can be assigned to several morphological groups with respect mainly to the structure of alveolae as well as positon(s) of rimoportula(e) and marginal fultoportulae. Presence of loculate areolae with internal domed cribra and external foramina, or both areolae and valve face fultoportulae in the central area are characteristics found in all of these Cyclotella taxa.

Toward High-Resolution Low-Voltage SEM

1988 ◽  
Vol 46 ◽  
pp. 218-219
Author(s):  
Zhifeng Shao
Keyword(s):  
Low Voltage ◽  
Spherical Aberration ◽  
Chromatic Aberration ◽  
Limiting Factor ◽  
Operating Voltage ◽  
Probe Radius ◽  
Non Local ◽  
Electron Microscopes ◽  
Image Position ◽  
Scanning Electron Microscopes

Recently, low voltage (≤5kV) scanning electron microscopes have become popular because of their unprecedented advantages, such as minimized charging effects and smaller specimen damage, etc. Perhaps the most important advantage of LVSEM is that they may be able to provide ultrahigh resolution since the interaction volume decreases when electron energy is reduced. It is obvious that no matter how low the operating voltage is, the resolution is always poorer than the probe radius. To achieve 10Å resolution at 5kV (including non-local effects), we would require a probe radius of 5∽6 Å. At low voltages, we can no longer ignore the effects of chromatic aberration because of the increased ratio δV/V. The 3rd order spherical aberration is another major limiting factor. The optimized aperture should be calculated as

Current State of Biological High-Resolution Scanning Electron Microscopy

1988 ◽  
Vol 46 ◽  
pp. 180-181 ◽  
Author(s):  
Klaus-Ruediger Peters
Keyword(s):  
High Performance ◽  
Low Voltage ◽  
Backscattered Electrons ◽  
Lens Position ◽  
Low Voltage Operation ◽  
Signal Collection ◽  
Probe Size ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

A new generation of high performance field emission scanning electron microscopes (FSEM) is now commercially available (JEOL 890, Hitachi S 900, ISI OS 130-F) characterized by an "in lens" position of the specimen where probe diameters are reduced and signal collection improved. Additionally, low voltage operation is extended to 1 kV. Compared to the first generation of FSEM (JE0L JSM 30, Hitachi S 800), which utilized a specimen position below the final lens, specimen size had to be reduced but useful magnification could be impressively increased in both low (1-4 kV) and high (5-40 kV) voltage operation, i.e. from 50,000 to 200,000 and 250,000 to 1,000,000 x respectively.At high accelerating voltage and magnification, contrasts on biological specimens are well characterized1 and are produced by the entering probe electrons in the outmost surface layer within -vl nm depth. Backscattered electrons produce only a background signal. Under these conditions (FIG. 1) image quality is similar to conventional TEM (FIG. 2) and only limited at magnifications >1,000,000 x by probe size (0.5 nm) or non-localization effects (%0.5 nm).

Chromatic aberration and low-voltage SEM

1987 ◽  
Vol 45 ◽  
pp. 546-547
Author(s):  
Zhifeng Shao ◽  
A.V. Crewe
Keyword(s):  
Electron Energy ◽  
Low Voltage ◽  
Spherical Aberration ◽  
Chromatic Aberration ◽  
Primary Electron ◽  
Probe Size ◽  
Non Local ◽  
Optical Treatment ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes

For scanning electron microscopes, it is plausible that by lowering the primary electron energy, one can decrease the volume of interaction and improve resolution. As shown by Crewe /1/, at V0 =5kV a 10Å resolution (including non-local effects) is possible. To achieve this, we would need a probe size about 5Å. However, at low voltages, the chromatic aberration becomes the major concern even for field emission sources. In this case, δV/V = 0.1 V/5kV = 2x10-5. As a rough estimate, it has been shown that /2/ the chromatic aberration δC should be less than ⅓ of δ0 the probe size determined by diffraction and spherical aberration in order to neglect its effect. But this did not take into account the distribution of electron energy. We will show that by using a wave optical treatment, the tolerance on the chromatic aberration is much larger than we expected.

High-resolution observation of sintered alumina (Al2O3) using the specimen-heated and electron-beam-induced conductivity method in a UHR-SEM

1994 ◽  
Vol 52 ◽  
pp. 1046-1047
Author(s):  
K. Ogura ◽  
T. Suzuki ◽  
C. Nielsen
Keyword(s):  
Electron Beam ◽  
High Resolution ◽  
Specimen Preparation ◽  
Conductivity Method ◽  
Fine Grain ◽  
Grain Structures ◽  
Resolution Observation ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Charging Effect

In spite of the complicated specimen preparation, Transmission Electron Microscopes (TEM) have traditionally been used for the investigation of the fine grain structures of sintered ceramics. Scanning Electron Microscopes (SEM) have not been used much for the same purpose as TEM because of poor results caused by the specimen charging effect, and also the lack of sufficient resolution. Here, we are presenting a successful result of high resolution imaging of sintered alumina (pure Al2O3) using the Specimen Heated and Electron Beam Induced Conductivity (SHEBIC) method, which we recently reported, in an ultrahigh resolution SEM (UHR-SEM). The JSM-6000F, equipped with a Field Emission Gun (FEG) and an in-lens specimen position, was used for this application.After sintered Al2O3 was sliced into a piece approximately 0.5 mm in thickness, one side was mechanically polished to get a shiny plane for the observation. When the observation was started at 20 kV, an enormous charging effect occured, and it was impossible to obtain a clear Secondary Electron (SE) image (Fig.1).

High resolution at low voltage: A new approach

1989 ◽  
Vol 47 ◽  
pp. 76-77
Author(s):  
Arthur V. Jones
Keyword(s):  
Low Voltage ◽  
Emission Sources ◽  
New Approach ◽  
Design Concepts ◽  
Probe Diameter ◽  
Low Voltage Operation ◽  
Sufficient Intensity ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Immersion Type

With the introduction of field-emission sources and “immersion-type” objective lenses, the resolution obtainable with modern scanning electron microscopes is approaching that obtainable in STEM and TEM-but only with specific types of specimens. Bulk specimens still suffer from the restrictions imposed by internal scattering and the need to be conducting. Advances in coating techniques have largely overcome these problems but for a sizeable body of specimens, the restrictions imposed by coating are unacceptable.For such specimens, low voltage operation, with its low beam penetration and freedom from charging artifacts, is the method of choice.Unfortunately the technical dificulties in producing an electron beam sufficiently small and of sufficient intensity are considerably greater at low beam energies — so much so that a radical reevaluation of convential design concepts is needed.The probe diameter is usually given by

Observation of GaAs/AlAs Superlattice Structures in both Secondary and Backscattcred Electron Imaging Modes with an Ultrahigh Resolution Scanning Electron Microscope

1990 ◽  
Vol 48 (1) ◽  
pp. 404-405
Author(s):  
K. Ogura ◽  
A. Ono ◽  
S. Franchi ◽  
P.G. Merli ◽  
A. Migliori
Keyword(s):  
Gaas Layer ◽  
Objective Lens ◽  
Superlattice Structure ◽  
Backscattered Electron ◽  
Instrumental Resolution ◽  
Electron Microscopes ◽  
Superlattice Structures ◽  
Electron Imaging ◽  
Scanning Electron Microscopes ◽  
Scanning Electron

In the last few years the development of Scanning Electron Microscopes (SEM), equipped with a Field Emission Gun (FEG) and using in-lens specimen position, has allowed a significant improvement of the instrumental resolution . This is a result of the fine and bright probe provided by the FEG and by the reduced aberration coefficients of the strongly excited objective lens. The smaller specimen size required by in-lens instruments (about 1 cm, in comparison to 15 or 20 cm of a conventional SEM) doesn’t represent a serious limitation in the evaluation of semiconductor process techniques, where the demand of high resolution is continuosly increasing. In this field one of the more interesting applications, already described (1), is the observation of superlattice structures.In this note we report a comparison between secondary electron (SE) and backscattered electron (BSE) images of a GaAs / AlAs superlattice structure, whose cross section is reported in fig. 1. The structure consist of a 3 nm GaAs layer and 10 pairs of 7 nm GaAs / 15 nm AlAs layers grown on GaAs substrate. Fig. 2, 3 and 4 are SE images of this structure made with a JEOL JSM 890 SEM operating at an accelerating voltage of 3, 15 and 25 kV respectively. Fig. 5 is a 25 kV BSE image of the same specimen. It can be noticed that the 3nm layer is always visible and that the 3 kV SE image, in spite of the poorer resolution, shows the same contrast of the BSE image. In the SE mode, an increase of the accelerating voltage produces a contrast inversion. On the contrary, when observed with BSE, the layers of GaAs are always brighter than the AlAs ones , independently of the beam energy.

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