scholarly journals DIFFERENTIAL SENSITIVITY OF PROPHASE POLLEN TUBE CHROMOSOMES TO X-RAYS AND ULTRAVIOLET RADIATION

1943 ◽  
Vol 26 (5) ◽  
pp. 485-494 ◽  
Author(s):  
C. P. Swanson
Keyword(s):  
Nucleic Acid ◽  
Pollen Tube ◽  
Differential Sensitivity ◽  
X Rays ◽  
Relative Importance ◽  
Generative Nucleus ◽  
Acid Cycle ◽  
X Ray ◽  
Total Absence ◽  
The Matrix

1. Through use of the pollen tube technique it has been possible to study the sensitivity of prophase stages to x-rays and ultraviolet, and to correlate the varying sensitivity with changes in the generative nucleus of Tradescantia. 2. Sensitivity to ultraviolet decreases from the 2 hour stage until at 11 hours after germination there is no further production of breaks. The 0 and 1 hour stages show a decreased sensitivity over the 2 hour stage but it has been suggested that this is not due to a decreased sensitivity but to shielding by the pollen wall. 3. Sensitivity to x-rays rises to a peak at the 4 hour stage, but then subsides until no breaks are realized (at a dose of 370.8 r) after the 10 hour stage. In this respect the effects of x-rays and ultraviolet are similar. Each type of x-ray break shows its own individual trend. 4. Correlation of x-ray breaks with changes in the generative nucleus indicates that the important events determining the sensitivity of the chromosomes to breakage are the uptake of water at the time of germination and the movement involved in spiralization. The total absence of breaks after the 11 hour stage is not understood. 5. The changing sensitivity to ultraviolet may depend on any one or all of three factors: (a) the nucleic acid cycle, (b) changes in the matrix, and (c) the number of subdivisions in the chromosome. These are discussed although their relative importance is not known.

Improving x-ray map resolution with image restoration techniques

1996 ◽  
Vol 54 ◽  
pp. 598-599
Author(s):  
Richard B. Mott ◽  
John J. Friel ◽  
Charles G. Waldman
Keyword(s):  
Image Restoration ◽  
Hubble Space Telescope ◽  
Extensive Literature ◽  
Small Object ◽  
X Rays ◽  
X Ray ◽  
Mapping Parameters ◽  
The Matrix ◽  
The 1960S ◽  
Map Resolution

X-rays are emitted from a relatively large volume in bulk samples, limiting the smallest features which are visible in X-ray maps. Beam spreading also hampers attempts to make geometric measurements of features based on their boundaries in X-ray maps. This has prompted recent interest in using low voltages, and consequently mapping L or M lines, in order to minimize the blurring of the maps.An alternative strategy draws on the extensive work in image restoration (deblurring) developed in space science and astronomy since the 1960s. A recent example is the restoration of images from the Hubble Space Telescope prior to its new optics. Extensive literature exists on the theory of image restoration. The simplest case and its correspondence with X-ray mapping parameters is shown in Figures 1 and 2.Using pixels much smaller than the X-ray volume, a small object of differing composition from the matrix generates a broad, low response. This shape corresponds to the point spread function (PSF). The observed X-ray map can be modeled as an “ideal” map, with an X-ray volume of zero, convolved with the PSF. Figure 2a shows the 1-dimensional case of a line profile across a thin layer. Figure 2b shows an idealized noise-free profile which is then convolved with the PSF to give the blurred profile of Figure 2c.

Mobile digital x-ray and portable cartridge based nucleic acid amplification test machines for point-of-care diagnosis of TB in rural India

2020 ◽  
Author(s):  
Bornali Datta ◽  
David Ford ◽  
Pinky Goyal ◽  
Ashish Prakash ◽  
Jaya Prasad Tripathy ◽  
...  
Keyword(s):  
Nucleic Acid ◽  
Point Of Care ◽  
Nucleic Acid Amplification Test ◽  
Clinical Suspicion ◽  
Nucleic Acid Amplification ◽  
Rural India ◽  
X Rays ◽  
X Ray ◽  
Microbiological Confirmation ◽  
Good Success Rate

Abstract Background There is no experience of point-of-care (POC) microbiological confirmation for TB in India in field settings. Methods Under the TB-Free Haryana project, a mobile van-mounted digital x-ray and portable GeneXpert system screened all presumptive TB patients with strong clinic-radiological suspicion for TB. Results Of 1673 x-rays, 215 (13%) had findings suggestive of TB, 109 had strong clinical suspicion and were eligible for POC GeneXpert, in whom a test was performed in 82 (75%) cases; 59 (72%) tested positive and were initiated on treatment within 24 h. Conclusions A mobile van equipped with digital x-ray and POC GeneXpert is feasible and has a good success rate with potential for replication.

X-ray Fluorescence Analysis of Gold Ore

1996 ◽  
Vol 50 (5) ◽  
pp. 572-575 ◽  
Author(s):  
Benito De Celis
Keyword(s):  
Analytical Techniques ◽  
Fluorescence Analysis ◽  
High Sensitivity ◽  
X Rays ◽  
Nondestructive Analysis ◽  
X Ray ◽  
Gold Ore ◽  
Large Samples ◽  
Radioisotope Source ◽  
The Matrix

A method to obtain high sensitivity and accuracy for nondestructive analysis of gold ore is proposed. The applied technique is energy-dispersive X-ray fluorescence, using a Co-57 radioisotope source to excite gold K X-rays in the sample, and a high-purity Ge (HPGe) detector with a range of energies from 1 keV to 4 MeV. The use of radioisotope sources and K X-rays gives some advantages in comparison with other analytical techniques and the usual tube excitation L X-ray analysis: the high sensitivity to concentrations of 1 ppm, the absence of interferences from other elements present in the matrix, and the possibility of performing fast and economical nondestructive analyses of large samples.

X-ray spatial resolution in electron microbeam analysis

1991 ◽  
Vol 49 ◽  
pp. 462-463
Author(s):  
John T. Armstrong ◽  
Paul K. Carpenter
Keyword(s):  
Spatial Resolution ◽  
X Rays ◽  
X Ray ◽  
Excitation Potential ◽  
Sample Density ◽  
The Matrix ◽  
Backscattered Electron ◽  
X Ray Absorption ◽  
Critical Excitation ◽  
Secondary Fluorescence

The spatial resolution of characteristic x-ray production from electron bombardment in thick specimens is dependent upon the rate of energy loss of the primary electrons, the degree of electron scattering, the degree of x-ray absorption by the matrix, and the extent of secondary fluorescence of the x-rays by higher energy characteristic and continuum x-rays. The x-ray spatial resolution in thick specimens is much coarser than the secondary or backscattered electron resolution, typically being of the order of a fraction of a μm to several μm when secondary fluorescence is not significant, or as much as 100 to 200 μm when it is. The size of the excited volume of x-ray production is dependent upon the accelerating potential of the electron beam, the critical excitation potential, and the sample density. The size of the excited volumes of different elements’ x-ray lines can be considerably different in the same matrix, due to differences in critical excitation potential; the emitting volumes can vary even more, due to differences in mass absorption.

Quantitative Evaluation of Degree of Internal Standardization in X-ray Fluorescence Analysis Using Scattered X-rays

1973 ◽  
Vol 27 (5) ◽  
pp. 352-355 ◽  
Author(s):  
D. L. Taylor ◽  
G. Andermann
Keyword(s):  
Experimental Data ◽  
Aqueous Solutions ◽  
Quantitative Evaluation ◽  
Scattered Radiation ◽  
Matrix Effects ◽  
Fluorescence Analysis ◽  
X Rays ◽  
X Ray ◽  
The Matrix ◽  
Internal Standardization

The “degree of internal standardization” for the scattered radiation method of compensation for matrix effects in x-ray fluorescence analysis is defined as the closeness of agreement between the results of analyses of specimens containing identical concentrations of analyte but with differing over-all elemental constituencies. The definition is derived in mathematical terms and is applied to experimental data of analyses of calcium in aqueous solutions containing different dissolved substances as matrix variants. The matrix compensation effectiveness of various wavelengths of scattered radiation can be clearly indicated. Interpretation of the results in terms of basic spectroscopic parameters is offered.

Mechanism of montmorillonite structure degradation by percussive grinding

Clay Minerals ◽  
1981 ◽  
Vol 16 (2) ◽  
pp. 151-162 ◽  
Author(s):  
Blahoslav Číčel ◽  
Günther Kranz
Keyword(s):  
Degradation Process ◽  
Exchangeable Cations ◽  
Hydroxyl Groups ◽  
Relative Importance ◽  
Chemical Bonds ◽  
Coordination Polyhedra ◽  
X Ray ◽  
Structure Degradation ◽  
The Matrix ◽  
Complete Breakdown

AbstractThe processes taking place during decomposition of montmorillonite by percussive grinding have been studied by IR, X-ray and DTA methods. Destruction can be described as a series of parallel changes in the montmorillonite structure which proceed at various rates. The fastest is a change in status of the exchangeable cations followed by that of the hydroxyl groups. The slowest degradation process is the separation of tetrahedral and octahedral sheets. Degradation of the structure proceeds by delamination of particles, breaking of layers, crushing of layers by shocks perpendicular to the ab-direction, rearrangement of coordination polyhedra and transfer of protons within the structure. The relative importance of each of these processes is evaluated. It is assumed that the matrix resulting from complete breakdown of the montmorillonite structure consists mainly of the residue of tetrahedral sheets and deformed incomplete tetrahedra and octahedra, or of individual atoms held together in clumps either by Van der Waals forces or possibly, in some cases, by newly formed chemical bonds.

White-Light Coronal Structures: Streamers and CMEs

1994 ◽  
Vol 144 ◽  
pp. 82
Author(s):  
E. Hildner
Keyword(s):  
Emission Line ◽  
Electron Density ◽  
White Light ◽  
Coronal Mass Ejections ◽  
X Rays ◽  
Solar Cycles ◽  
Temperature Function ◽  
X Ray ◽  
Eclipse Observations ◽  
Coronal Structures

AbstractOver the last twenty years, orbiting coronagraphs have vastly increased the amount of observational material for the whitelight corona. Spanning almost two solar cycles, and augmented by ground-based K-coronameter, emission-line, and eclipse observations, these data allow us to assess,inter alia: the typical and atypical behavior of the corona; how the corona evolves on time scales from minutes to a decade; and (in some respects) the relation between photospheric, coronal, and interplanetary features. This talk will review recent results on these three topics. A remark or two will attempt to relate the whitelight corona between 1.5 and 6 R⊙to the corona seen at lower altitudes in soft X-rays (e.g., with Yohkoh). The whitelight emission depends only on integrated electron density independent of temperature, whereas the soft X-ray emission depends upon the integral of electron density squared times a temperature function. The properties of coronal mass ejections (CMEs) will be reviewed briefly and their relationships to other solar and interplanetary phenomena will be noted.

Chemical Species Identification in an SEM by Changes in Emitted X-Ray Energies

1974 ◽  
Vol 32 ◽  
pp. 570-571
Author(s):  
R. H. Duff
Keyword(s):  
Species Identification ◽  
Valence Electron ◽  
Chemical Species ◽  
X Rays ◽  
Chemical Bonds ◽  
Small Shift ◽  
X Ray ◽  
Electron Transitions ◽  
Peak Energy ◽  
Chemical Combination

A material irradiated with electrons emits x-rays having energies characteristic of the elements present. Chemical combination between elements results in a small shift of the peak energies of these characteristic x-rays because chemical bonds between different elements have different energies. The energy differences of the characteristic x-rays resulting from valence electron transitions can be used to identify the chemical species present and to obtain information about the chemical bond itself. Although these peak-energy shifts have been well known for a number of years, their use for chemical-species identification in small volumes of material was not realized until the development of the electron microprobe.

Influence of X-Ray Induced Fluorescence on Energy Dispersive X-Ray Analysis of Thin Foils

1977 ◽  
Vol 35 ◽  
pp. 328-329
Author(s):  
E. A. Kenik ◽  
J. Bentley
Keyword(s):  
Thin Foil ◽  
Electron Excitation ◽  
Simple Approach ◽  
Foil Thickness ◽  
X Rays ◽  
X Ray ◽  
Hole Spectrum ◽  
Illumination System ◽  
Thin Foils ◽  
Intensity Ratios

Cliff and Lorimer (1) have proposed a simple approach to thin foil x-ray analy sis based on the ratio of x-ray peak intensities. However, there are several experimental pitfalls which must be recognized in obtaining the desired x-ray intensities. Undesirable x-ray induced fluorescence of the specimen can result from various mechanisms and leads to x-ray intensities not characteristic of electron excitation and further results in incorrect intensity ratios.In measuring the x-ray intensity ratio for NiAl as a function of foil thickness, Zaluzec and Fraser (2) found the ratio was not constant for thicknesses where absorption could be neglected. They demonstrated that this effect originated from x-ray induced fluorescence by blocking the beam with lead foil. The primary x-rays arise in the illumination system and result in varying intensity ratios and a finite x-ray spectrum even when the specimen is not intercepting the electron beam, an ‘in-hole’ spectrum. We have developed a second technique for detecting x-ray induced fluorescence based on the magnitude of the ‘in-hole’ spectrum with different filament emission currents and condenser apertures.

Lateral resolution of the electron microbeam analysis

1978 ◽  
Vol 36 (1) ◽  
pp. 542-543
Author(s):  
H.J. Dudek
Keyword(s):  
Quantitative Analysis ◽  
Depth Resolution ◽  
Lateral Resolution ◽  
Cylindrical Particle ◽  
Correction Procedure ◽  
X Ray ◽  
Element Concentrations ◽  
Microbeam Analysis ◽  
The Matrix

The chemical inhomogenities in modern materials such as fibers, phases and inclusions, often have diameters in the region of one micrometer. Using electron microbeam analysis for the determination of the element concentrations one has to know the smallest possible diameter of such regions for a given accuracy of the quantitative analysis.In th is paper the correction procedure for the quantitative electron microbeam analysis is extended to a spacial problem to determine the smallest possible measurements of a cylindrical particle P of high D (depth resolution) and diameter L (lateral resolution) embeded in a matrix M and which has to be analysed quantitative with the accuracy q. The mathematical accounts lead to the following form of the characteristic x-ray intens ity of the element i of a particle P embeded in the matrix M in relation to the intensity of a standard S

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