Measured smearing

Step 11. At this point a computer program refines the atomic parameters of the atoms that were assigned labels. The atomic parameters consist of the three position parameters x,j, and for each atom. Also one or six atomic displacement parameters that describe how the atom is "smeared" (due to thermal motion or disorder) are refined for each atom. The atomic parameters are varied so that the calculated reflection intensities are made to be as nearly equal as possible to the observed intensities. During this process, estimated phase angles are obtained for all of the reflections whose intensities were measured. A new three-dimensional electron density map is calculated using these calculated phase angles and the observed intensities. There is less false detail in this map than in the first map. 

Neutron reflectivity measures the variation in concentration normal to the surface of the specimen. This concentration at any depth is averaged over the coherence length of the neutrons (on the order of 1 pm) parallel to the sur ce. Consequendy, no information can be obtained on concentration variadons parallel to the sample surface when measuring reflectivity under specular conditions. More imponantly, however, this mandates that the specimens be as smooth as possible to avoid smearing the concentration profiles. 

In practice once a desirable catalyst condition was achieved x-ray measurements often were taken at temperature and after quenching to 90 K In an attempt to minimize thermal smearing of the EXAFS data. 

A standard initial laboratory evaluation for anemia includes a complete blood count (evaluation of the serum hemoglobin and hematocrit concentration, white blood cell count, platelets), measurement of the red blood cell count and size, and review of peripheral smear. 

Iversen et al, in their study of crystalline beryllium [32], were the first to make use of NUP distributions calculated by superposition of thermally-smeared spherical atoms. More recently, a superposition of thermally-smeared spherical atoms was used as NUP in model studies on noise-free structure factor amplitudes for crystalline silicon and beryllium by de Vries et al. [38]. The artefacts present in the densities computed with a uniform prior-prejudice distributions have been shown to disappear upon introduction of the NUP. No quantitative measure of the residual errors were given. 

Analyses I.r. spectra were measured as smears on sodium chloride plates or as a solution in carbon tetrachloride using a Perkin-Elmer 567 grating spectrophotometer, while u.v. spectra were measured as a solution in hexane (spectroscopic grade) using a Unicam SP 1700 instrument. Fluorescence and phosphorescence spectra were recorded as described elsewhere (5, 6). 

Measurements show some variation depending upon the staining solution used and the method of application. In dried and fixed smears, the cell wall and slime layer do not stain with weakly staining dyes such as methylene blue but do stain with the intensely staining pararosaniline, new fuchsin, crystal violet, and methyl violet. The great majority of bacteria have been measured in fixed and stained preparations. In some instances dried, negatively stained smears have been used. Therefore, the method employed should be specified when measurements of bacteria are reported otherwise the results will be of doubtful v alue. 

Some bacteria measure as large as 80 p in length others as small as 0.2 ix. However, the majority of the commonly encountered bacteria, including the disease producers, measure about 0.5 n in diameter for the spherical cells and 0.5 by 2 to 3 p for the rod forms. Bacteria producing spores are generally larger than the nonspore-producing species. The sizes of some common species in dried and stained smears are as follows Escherichia coli, 0.5 by 1 to 3... 

Careful attention should be paid to sample preparation, however. The materials investigated may be changed by the preparation procedure (e.g., smearing during microtomy of soft materials at room temperature is avoided when using cryo-microtomy) or during the measurement (radiation damage, contact with ATR crystal, etc.). 

Smearing. Because scattering is emanating from every point of the irradiated volume, the recorded scattering pattern is smeared by the shape of the effective cross-section of the primary beam measured in the detector plane. In terms of mathematics this smearing is accomplished by convolution (Eq. (2.17)) with the primary beam profile. 

J (s) = Jl (s) dsi is the slit-smeared scattering intensity, P(t is the total primary beam intensity per slit-length element - a quantity determined by the moving slit device. R is the distance between sample and detector slit as measured on the optical axis of the camera. L is the (fixed and known) length of the detector slit in the registration plane. H is the (adjustable) height of the detector slit. exp(—jut) is the linear absorption factor of the sample19. 

In practice, either a pole figure has been measured in a texture-goniometer setup, or a 2D SAXS pattern with fiber symmetry has been recorded. In the first case we take the measured intensity g (pole figure. In the second case we can choose a reflection that is smeared on spherical arcs and project in radial direction over the range of the reflection. From the measured or extracted intensities I (orientation parameter by numerical integration and normalization... 

If the smeared image of a point-reflection on the meridian is unimodal, the orientation distribution g(texture measurement through the reflection, I((p,s = c) contains the information sought-after [256]... 

Sea cores offer a data base which should in principle allow deduction of the history of the local sea surface temperature immediately above the deposition site of the core, for there is enough organic material in sea cores to provide the necessary samples for isotope measurement at frequent intervals versus depth in the core, but the time resolution is far less accurate than in varves and tree rings because burrowing sea bottom animals smear the record of the layers. 

Macrocytic anemias are characterized by increased mean corpuscular volume (110 to 140 fL). One of the earliest and most specific indications of macrocytic anemia is hypersegmented polymorphonuclear leukocytes on the peripheral blood smear. Vitamin B12 and folate concentrations can be measured to differentiate between the two deficiency anemias. A vitamin B12 value of less than 150 pg/mL, together with appropriate peripheral smear and clinical symptoms, is diagnostic of vitamin B12-deficiency anemia. A decreased RBC folate concentration (less than 150 ng/mL) appears to be a better indicator of folate-deficiency anemia than a decreased serum folate concentration (less than 3 ng/mL). 

In order to obtain data with reduced temperature smearing, experiments were also carried out at 77 K. However, such experiments could not be carried out in. situ and the catalysts were thus exposed to air before the measurements. EXAFS data of three catalysts with Co/Mo atomic ratios of 0.0., 0.25, and 0.50 were obtained. The results show many similarities with the data recorded in situ and were fitted in a similar fashion using phase and amplitude functions of the well-crystallized model compound M0S2 recorded at 77 K. The results, which are given in Table III, show that the bond lengths for the first and second coordination shell are the same for all the catalysts and identical to the values obtained for the catalyst recorded in situ (Table II). The coordination numbers for both shells appear, however, to be somewhat smaller. Although coordination numbers determined by EXAFS cannot be expected to be determined with an accuracy better than + 20, the observed reduction... 

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