Contrast dependence

Ogawa, S., Lee, T. M., Kay, A. R. etal. Brain magnetic resonance imaging with contrast dependent on blood oxygenation. Proc. Natl Acad. Sci. U.S.A. 87 9868-9872, 1990. 

As pointed out by C. Moonen (National Institutes of Health), For discrimination of healthy and diseased tissues, adequate contrast is essential. Such contrast depends not only on differences in water concentration, but also on the NMR relaxations, which, in turn, are related to local mobilities and interactions. ... 

Lately one has been able to encounter experimental studies more frequently denoted Chemical Force Microscopy , CMF. This includes various attempts to observe tip-surface interactions which are specific to the chemical constitution of the surface. Mostly, CFM involves modification of the tip by a surface layer with molecules which contain particular functional groups, i.e. hydrophilic or hydro-phobic moieties, hydrogen bonding groups, ionic substituents and molecular units which can undergo electron-donor-acceptor interactions. However, sometimes the term Chemical Force Microscopy is just used for any method which can provide a material specific contrast. Depending on the specificity, CFM provides valuable information on the nanoscale composition complementary to other surface characterisation methods which are sensitive to the chemical con-... 

In contrast, depending on their stoichiometry, the higher bromosiloxenes do form bridges, as indicated by the fluorescence spectra. 

Fig. 12.6. The laser contrast dependence of a the X-ray spectrum and b the mean ion energy measured at an intensity of 3 x 1018 W/cm2 and a pulse duration of 30 fs...

The reported influence of humic substances or DOM on organic pollutants phototransformation is one of contrasts. Depending on the pollutant structure, inhibiting or enhancing effects were found. 

Science is primarily a scholarly endeavor the practice of medicine is primarily a practical trade. Scientists try to find out more and more about the world, even if doing so is time-consuming. Medicine, in contrast, depends more on what is usefiil than on what is true. That includes the specialties of neurology and psychiatry. The important information for medicine is that which enables medical practicioners to decide how best to try to help individual sick people. Generally those decisions must be made within a limited amount of time in order to be useful. Even the decision to do nothing is a decision that affects patient welfare. When possible, medical decisions are based on scientific information, but where the science is lacking the decisions still have to be made. 

The the well-known contrast dependence of R on the real contrast assumes a more general form in the case of complex contrast... 

These sources of redox contrast would have been limited. The hydrothermal contrasts depend on local thermally driven juxtaposition (e.g., in vent fluids) of chemical species from differing environments. From the vents would come H2, H2S, and probably CH4. The size and activity of the hydrothermal biosphere, and hence its impact, would have been considerable, as early Archean volcanism was probably much more common than today, with a higher heat flow out of the Earth. Nevertheless, the total potential productivity of an early hydrothermal biosphere would have been small on a global scale compared to the modem photosynthetically driven biosphere. Moreover, modem biota at hydrothermal vents depend on the supply of sulfate, oxidized in the photosynthetic biosphere before photosynthesis, the sulfate supply may have been limited. Thus, as a first guess, with a planetary heat flow higher than today... 

Next, the pattern is developed by dissolving the exposed parts of the pattern in the correct solvent. The quality of the pattern (contrast) depends on both the exposure and the development time, both of which must be experimentally determined for different resist systems and substrates. Once the pattern has been exposed and developed, the actual catalytically active metal(s) or oxide(s) is vapor deposited both within the holes in the pol3mier and on top of the polymer (step 5). This metal (or oxide) film should be discontinuous at the pattern boundaries in order to make possible the liftoff the remaining resist. This requires that the resist layer is thicker than the deposited film, and that the developed resist features have an undercut or negative profile... 

AM methods, in contrast, depend on the modulation of the enzyme signal by competition of the test molecule for the same immunoreactant. Contrary to AA methods, the sensitivity of AM assays increases with lower immunoreactant concentrations since at low concentrations a variation in the amount of competing molecules has a larger impact on the interaction with the labeled species. According to the law of mass action, the low antigen and antibody concentrations reduce considerably the rate of complex formation. Moreover, at very low concentrations the accuracy tends to be poor. 

The use of polarized light to generate contrast between bone components provides information on the spatial distribution of bone components and their orientation. Kazanci et al. used Raman polarized imaging to examine the distribution of mineral and matrix constituents around osteons, and showed that the POi Vi and amide I bands are highly orientation-dependent, whereas the amide III and POi V2 and V4 are less orientation-dependent [35]. Orientation effects are nicely illustrated in Figure 4.2 [36]. The POi Vj amide I ratio coincides with the orientation of the lamellae the same lamellae have different contrasts, depending on the polarization of the excitation light and the orientation of the specimen. 

The hazards of any battery system increase with size (as mentioned above), but in contrast, depending on the type, a smaller lithium system may be much more reactive than a larger lithium system of a different type. 

Following exposure, poly(olefin sulfones) can be developed by two main methods by solvent development or by thermal development. The exposed areas of the resist simply evaporate on heating, or in some cases during exposure, in a phenomenon termed self-development, which negatively impacts the vacuum of the exposure tool s electron column. The liquid development method is not without its drawbacks, as it requires a careful choice of solvent, since the development contrast depends only on molecular weight. ... 

Fourier transformation of the excess scattering density p(r)-ps gives the amplitude A(Q) and this has the same contrast dependence as above ... 

In the case of inhomogeneous particles, contrast variation techniques can be used to separate the shape and density fluctuation terms. D r) is now proportional to the number of pairs of scattering lengths separated by the distance r in the volume elements p and q, where each value of r is weighted by the product fp -f. Depending on the solvent scattering density, some volume elements can make a negative contribution to 7>(r). As previously, the contrast dependence of 7)(r) is readily derived in terms of three basic functions ... 

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