scholarly journals Tubulin hooks as probes for microtubule polarity: an analysis of the method and an evaluation of data on microtubule polarity in the mitotic spindle.

1984 ◽  
Vol 98 (2) ◽  
pp. 525-533 ◽  
Author(s):  
J R McIntosh ◽  
U Euteneuer
Keyword(s):  
Cross Section ◽  
Mitotic Spindle ◽  
Reasonable Accuracy ◽  
Microtubule Orientation ◽  
Future Studies ◽  
Microtubule Polarity ◽  
Close Analysis ◽  
Evaluation Of Data ◽  
Hook Curvature

The structural polarity of cellular microtubules can be visualized in situ by lysing cells in special buffers containing tubulin. Under these conditions, the tubulin polymerizes to form curved sheets which attach to the walls of the endogenous microtubules. When such decorated microtubules are cut in cross section and viewed in the electron microscope, they appear to bear hooks curving clockwise or counter-clockwise. The direction of hook curvature is defined by the orientation of the decorated microtubule and thus serves as a probe for microtubule polarity. In this paper we describe a way to analyze the relative frequencies of hooks of different curvatures so as to measure the fidelity of the relation between hook curvature and microtubule polarity. The assumptions of the method are tested and found to be valid to a reasonable accuracy. The correlation between hook curvature and microtubule orientation is shown to be at least 0.98 for the spindles of PtK cells and Haemanthus endosperm at all stages of division and at all places in the spindle. The correlation is shown to be valid for each hook that forms, so the polarity of those microtubules that bear multiple hooks is specified with even better certainty than 0.98. This property of hook decoration is used to reinvestigate the possibility that some of the microtubules of the kinetochore fiber might be oriented with their plus ends distal to the kinetochore (opposite to the direction previously shown to predominate). Close analysis fails to identify such oppositely oriented microtubules. The scoring of tubules bearing multiple hooks also shows that individual interzone fibers at anaphase are constructed from clusters of antiparallel microtubules. The method for estimating the correlation between hook decoration and microtubule polarity is shown to be applicable to many structures and circumstances, but we find that the hook decoration assay for microtubule polarity is not uniformly accurate. We suggest that future studies using hook decorations should employ the method of data analysis presented here to assess the accuracy of the results obtained.

Structural Studies on Mitotic Spindle Fibres

1978 ◽  
Vol 36 (3) ◽  
pp. 615-626
Author(s):  
J.R. Mcintosh
Keyword(s):  
Chemical Composition ◽  
Mitotic Spindle ◽  
Structural Studies ◽  
Mitotic Apparatus ◽  
Chemical Studies ◽  
Medical Interest ◽  
Spindle Fibres

The mitotic apparatus is a structure of obvious biological and medical interest, but it has proved to be a difficult cellular machine to understand. The chemical composition of the spindle is only slightly elucidated, largely because of the difficulties in preparing useful isolates of the structure. Chemical studies of the mitotic spindle have been reviewed elsewhere (Mcintosh, 1977), and will not be discussed further here. One would think that structural studies on the mitotic apparatus (MA) in situ would be straightforward, but even with this approach there is some disagreement in the results obtained with various methods and by different investigators. In this paper I will review briefly the approaches which have been used in structural studies of the MA, pointing out the strengths and problems of each approach. I will summarize the principal findings of the different methods, and identify what seem to be fruitful avenues for further work.

In situ irradiation effects studies in medium- and high-voltage TEM

1995 ◽  
Vol 53 ◽  
pp. 234-235
Author(s):  
Charles W. Allen
Keyword(s):  
Cross Section ◽  
Particle Flux ◽  
Threshold Value ◽  
High Energy ◽  
Irradiation Damage ◽  
Defect Complexes ◽  
Lattice Position ◽  
Electrons And Ions ◽  
The Masses

With respect to structural consequences within a material, energetic electrons, above a threshold value of energy characteristic of a particular material, produce vacancy-interstial pairs (Frenkel pairs) by displacement of individual atoms, as illustrated for several materials in Table 1. Ion projectiles produce cascades of Frenkel pairs. Such displacement cascades result from high energy primary knock-on atoms which produce many secondary defects. These defects rearrange to form a variety of defect complexes on the time scale of tens of picoseconds following the primary displacement. A convenient measure of the extent of irradiation damage, both for electrons and ions, is the number of displacements per atom (dpa). 1 dpa means, on average, each atom in the irradiated region of material has been displaced once from its original lattice position. Displacement rate (dpa/s) is proportional to particle flux (cm-2s-1), the proportionality factor being the “displacement cross-section” σD (cm2). The cross-section σD depends mainly on the masses of target and projectile and on the kinetic energy of the projectile particle.

scholarly journals Ultraviolet Absorption Cross-Sections of Ammonia at Elevated Temperatures for Nonintrusive Quantitative Detection in Combustion Environments

2021 ◽  
pp. 000370282199044
Author(s):  
Wubin Weng ◽  
Shen Li ◽  
Marcus Aldén ◽  
Zhongshan Li
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Absorption Cross Section ◽  
Elevated Temperatures ◽  
Uv Absorption ◽  
Energy Utilization ◽  
Quantitative Detection ◽  
Absorption Cross ◽  
Hot Gas

Ammonia (NH3) is regarded as an important nitrogen oxides (NOx) precursor and also as an effective reductant for NOx removal in energy utilization through combustion, and it has recently become an attractive non-carbon alternative fuel. To have a better understanding of thermochemical properties of NH3, accurate in situ detection of NH3 in high temperature environments is desirable. Ultraviolet (UV) absorption spectroscopy is a feasible technique. To achieve quantitative measurements, spectrally resolved UV absorption cross-sections of NH3 in hot gas environments at different temperatures from 295 K to 590 K were experimentally measured for the first time. Based on the experimental results, vibrational constants of NH3 were determined and used for the calculation of the absorption cross-section of NH3 at high temperatures above 590 K using the PGOPHER software. The investigated UV spectra covered the range of wavelengths from 190 nm to 230 nm, where spectral structures of the [Formula: see text] transition of NH3 in the umbrella bending mode, v2, were recognized. The absorption cross-section was found to decrease at higher temperatures. For example, the absorption cross-section peak of the (6, 0) vibrational band of NH3 decreases from ∼2 × 10−17 to ∼0.5 × 10−17 cm2/molecule with the increase of temperature from 295 K to 1570 K. Using the obtained absorption cross-section, in situ nonintrusive quantification of NH3 in different hot gas environments was achieved with a detection limit varying from below 10 parts per million (ppm) to around 200 ppm as temperature increased from 295 K to 1570 K. The quantitative measurement was applied to an experimental investigation of NH3 combustion process. The concentrations of NH3 and nitric oxide (NO) in the post flame zone of NH3–methane (CH4)–air premixed flames at different equivalence ratios were measured.

The Effect of Water Injection on Sustained Combustion in a Porous Medium

1970 ◽  
Vol 10 (02) ◽  
pp. 145-163 ◽  
Author(s):  
H.L. Beckers ◽  
G.J. Harmsen
Keyword(s):  
Cross Section ◽  
Combustion Zone ◽  
Water Injection ◽  
Combustion Process ◽  
Physical Reality ◽  
Porous Matrix ◽  
Theoretical Description ◽  
Air Injection ◽  
Injection Ratio

Abstract This paper gives a theoretical description of the various semisteady states that may develop if in an in-situ combustion process water is injected together with the air. The investigation bas been restricted to cases of one-dimensional flow without heat losses, such as would occur in a narrow, perfectly insulated tube. perfectly insulated tube. Different types of behavior can be distinguished for specific ranges of the water/air injection ratio. At low values of this ratio the injected water evaporates before it reaches the combustion zone, while at high values it passes through the combustion zone without being completely evaporated, but without extinguishing combustion. At intermediate values and at sufficiently high fuel in which all water entering the combustion zone evaporates before leaving it. Formulas are presented that give the combustion zone velocity as a function of water/air injection ratio for each of the possible situations. Introduction In-situ combustion of part of the oil in an oil-bearing formation has become an established thermal-recovery technique, even though its economic prospects are limited by inherent technical drawbacks. The process has been extensively investigated both in the laboratory and in the field, while theoretical studies have also been made. The latter studies showed how performance was affected by various physical and chemical phenomena, such as conduction and convection of phenomena, such as conduction and convection of heat, reaction rate and phase changes. The degree of simplification determined whether these studies were of an analytical or a numerical nature. Recently an improvement of the process has been proposed. This modification involves the proposed. This modification involves the injection of water together with the air. The water serves to recuperate the heat stored in the burned-out sand, which would otherwise be wasted. This heat is now used to evaporate water. The steam thus formed condenses downstream of the combustion zone, where it displaces oil. At sufficiently high water-injection rates unevaporated water is bound to enter the combustion zone because more heat is required for complete evaporation than is available in the hot sand. Experiments showed that even under these conditions combustion is maintained. The improvement consists in a lower oxygen consumption per barrel of oil displaced and lower combustion-zone temperatures. This paper gives a theoretical description of this so-called wet-combustion process as described by Dietz and Weijdema. The prime object is to answer the basic question whether at any water/air injection ratio this process can be steady so that combustion does not die out. This objective justifies a number of assumptions that do not entirely correspond to physical reality, but that owe necessary for a physical reality, but that owe necessary for a tractable analytical treatment. This treatment is limited to the following idealized conditions.The process occurs in a perfectly insulated cylinder of unit cross-sectional area and infinite length.The Hudds are homogeneously distributed over the cross-section of the cylinder.Exchange of heat between the fluid phases and between fluids and matrix is instantaneous, so that in any cross-section the fluid phases are in equilibrium and the temperatures of fluids and porous matrix are the same. porous matrix are the same.Pressure chops over distances of interest are small compared with the pressure itself. (Pressure is taken to be constant.)Injection rates are constant, and a steady state has already been obtained. The second assumption implies that no segregation of liquid and gas occurs. Experimentally this might be achieved by using small-diameter tubes, where segregation is largely compensated by capillarity. SPEJ P. 145

Correlation Between LDA and Ultrasound Heart Catheter Measurements in a Stenosed Arterial Model

1995 ◽  
Vol 117 (1) ◽  
pp. 103-106 ◽  
Author(s):  
D. Liepsch ◽  
A. Poll ◽  
R. Blasini
Keyword(s):  
Cross Section ◽  
Laser Doppler Anemometry ◽  
Water Solution ◽  
Maximum Velocity ◽  
Symmetric Model ◽  
Axially Symmetric ◽  
Flow Conditions ◽  
Future Studies ◽  
Glycerine Water ◽  
Arterial Model

Ultrasound heart catheters are used to measure the velocity in coronary arteries. However, the act of introducing a catheter into the vessel disturbs the very flow being measured. We used laser Doppler anemometry to measure the velocity distribution in an axially symmetric model, both with and without a catheter inserted. The catheter reduced the center-line velocity by as much as 60 percent at a distance of 2 mm downstream from the catheter, and by as much as 25 percent at a distance of 10 mm. This means the velocity measured with an ultrasound catheter does not show the maximum velocity of the undisturbed flow in the tube center. In the constriction, however, the measured velocities with the LDA and ultrasound catheter are almost the same. Thus, catheter measurements in the stenosis achieve accurate results. The velocity profile in the stenosed areas is flattened over nearly the whole cross section. The velocity is extremely reduced only close to the wall. The measurements outside of the stenosis lead to large differences which need to be studied carefully in the future. The disturbed flow finally disappeared 15 mm downstream of the catheter. The measurements were done at steady flow using a glycerine water solution with a dynamic viscosity of 4.35m Pas. In future studies, these experiments will be repeated for pulsatile flow conditions using non-Newtonian blood-like fluids.

scholarly journals Autofluorescence Is a Common Trait in Different Oceanic Fungi

2021 ◽  
Vol 7 (9) ◽  
pp. 709
Author(s):  
Eva Breyer ◽  
Markus Böhm ◽  
Magdalena Reitbauer ◽  
Chie Amano ◽  
Marilena Heitger ◽  
...  
Keyword(s):  
Marine Fungi ◽  
Physiological State ◽  
Excitation Wavelength ◽  
Growth Stages ◽  
Future Studies ◽  
Different Types ◽  
Widespread Phenomenon ◽  
Ubiquitous Presence ◽  
Different Growth Stages

Natural autofluorescence is a widespread phenomenon observed in different types of tissues and organisms. Depending on the origin of the autofluorescence, its intensity can provide insights on the physiological state of an organism. Fungal autofluorescence has been reported in terrestrial and human-derived fungal samples. Yet, despite the recently reported ubiquitous presence and importance of marine fungi in the ocean, the autofluorescence of pelagic fungi has never been examined. Here, we investigated the existence and intensity of autofluorescence in five different pelagic fungal isolates. Preliminary experiments of fungal autofluorescence at different growth stages and nutrient conditions were conducted, reflecting contrasting physiological states of the fungi. In addition, we analysed the effect of natural autofluorescence on co-staining with DAPI. We found that all the marine pelagic fungi that were studied exhibited autofluorescence. The intensity of fungal autofluorescence changed depending on the species and the excitation wavelength used. Furthermore, fungal autofluorescence varied depending on the growth stage and on the concentration of available nutrients. Collectively, our results indicate that marine fungi can be auto-fluorescent, although its intensity depends on the species and growth condition. Hence, oceanic fungal autofluorescence should be considered in future studies when fungal samples are stained with fluorescent probes (i.e., fluorescence in situ hybridization) since this could lead to misinterpretation of results.

Estimating discharge in rivers through the combined use of dimensionless isovels and point velocity measurements

2017 ◽  
Vol 48 (3) ◽  
pp. 616-633 ◽  
Author(s):  
G. Farina ◽  
S. Alvisi ◽  
M. Franchini
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Accurate Estimation ◽  
Velocity Measurements ◽  
Combined Use ◽  
Point Velocity ◽  
New Formulation ◽  
The Relationship ◽  
River Cross Section

This paper presents a procedure for estimating discharge in a river cross-section based on the combined use of dimensionless isovels and point velocity measurements. Specifically, taking the Biot–Savart law on the magnetic field induced by an electric current in a wire as their basis as already done by other researchers, the authors propose a new formulation of the relationship characterizing the effect of the wetted perimeter on the range of velocities in a cross-section in order to take explicit account of roughness, expressed by means of Manning's coefficient. Once appropriately nondimensionalized, the isoeffect contours can be read as dimensionless isovels. Assuming in situ velocity measurements are available, discharge at a cross-section can be computed using two different methods. The proposed procedure was applied to six case studies characterized by river cross-sections which differed greatly from one another. The results show that the two methods proposed for estimating discharge lead to equivalent outcomes, and in all the cases the procedure as a whole enables a sufficiently accurate estimation of discharge, even when it is based on a limited number of velocity measurements or on the measurement of maximum surface-water velocity alone.

Coordinate amplification of metallothionein I and II genes in cadmium-resistant Chinese hamster cells: implications for mechanisms regulating metallothionein gene expression

1985 ◽  
Vol 5 (2) ◽  
pp. 320-329
Author(s):  
B D Crawford ◽  
M D Enger ◽  
B B Griffith ◽  
J K Griffith ◽  
J L Hanners ◽  
...  
Keyword(s):  
Gel Electrophoresis ◽  
Polyacrylamide Gel Electrophoresis ◽  
Chinese Hamster ◽  
Chinese Hamster Cell ◽  
Chinese Hamster Cells ◽  
Future Studies ◽  
Noncoding Regions ◽  
Genes Encoding ◽  
Chinese Hamster Cell Line

We describe here the derivation, characterization, and use of clonal cadmium-resistant (Cdr) strains of the Chinese hamster cell line CHO which differ in their metallothionein (MT) induction capacity. By nondenaturing polyacrylamide gel electrophoresis, we showed that the stable Cdr phenotype is correlated with the augmented expression of both isometallothioneins (MTI and MTII). In cells resistant to concentrations of CdCl2 exceeding 20 microM, coordinate amplification of genes encoding both isometallothioneins was demonstrated by using cDNA MT-coding sequence probes and probes specific for 3'-noncoding regions of Chinese hamster MTI and MTII genes. Molecular and in situ hybridization analyses supported close linkage of Chinese hamster MTI and MTII genes, which we have mapped previously to Chinese hamster chromosome 3. This suggests the existence of a functionally related MT gene cluster in this species. Amplified Cdr variants expressing abundant MT and their corresponding Cds parental CHO cells should be useful for future studies directed toward elucidating the mechanisms that regulate expression of the isometallothioneins.

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