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Qualitative Features (qualitative + feature)

Distribution by Scientific Domains

Life Sciences	40%
Chemistry	40%

Selected Abstracts

SEXUAL SELECTION AND THE EVOLUTION OF COSTLY FEMALE PREFERENCES: SPATIAL EFFECTS

EVOLUTION, Issue 3 2000
Troy Day
Abstract., Models of Fisher's runaway process show that if there is a cost to female preference, no preference or male trait exaggeration will evolve. Surprisingly, this is true no matter how small the cost, which reveals that these models of Fisher's process are structurally unstable (Bulmer 1989). Here a model of Fisher's runaway process is presented to demonstrate that costly female preference evolves very easily when space is explicitly included in the model. The only requirement is that the optimal male phenotype changes across the species' range. The model shows that the spatial average of the female preference and male trait reach an evolutionary equilibrium that is identical to those of nonspatial models, but that the preference and male trait can deviate greatly from these averages at any point in space. For example, if random mating results in the lowest cost to females, then at equilibrium the spatial average preference will be zero. Nevertheless, there will be some locations at which females prefer males with larger ornaments and others where they prefer males with smaller ornaments. Results also show that the structural instability of nonspatial models of Fisher's process is less of a problem in spatial models. In particular, many of the main qualitative features of cost-free spatial models of Fisher's process remain valid even when there are small costs of female preference. Finally, the model shows that abrupt changes in the optimal male phenotype across space can result in an amplification of this pattern when preference has a small cost, but it can also result in a pattern similar to reproductive character displacement. Which of these occurs depends on the magnitude of the cost of female preference. This suggests that some patterns of reproductive character displacement in nature might be explained simply by sexual selection rather than by hybrid dysgenesis and reinforcement. [source]

Cardioventilatory Coupling in Resting Human Subjects

EXPERIMENTAL PHYSIOLOGY, Issue 6 2003
Y. C. Tzeng
In 48 conscious resting subjects we examined the temporal coupling of heart beat timing and the onset of inspiration (cardioventilatory coupling), and the relationship between coupling and spectral indices of autonomic function. Using the proportional Shannon entropy (SH,) of the RI -1 interval (interval between inspiration and the preceding ECG R wave) as a measure of coupling we detected statistically significant coupling in 32 of the 48 subjects. This was confirmed by visual inspection of time series plots of RI intervals, in which coupling was evident as horizontal banding. Coupling resulted in a significant preference for whole number heart rate/respiratory frequency ratios. The strongest coupling was associated with low ventilatory frequency and high heart rate variability in the high (0.15-0.40 Hz) and low (0.04-0.15 Hz) frequency ranges, but was not related to blood pressure variability, or to a spectral measure of baroreflex sensitivity (,-index, low frequency range). There was no difference in coupling strength between males and females. We have previously described cardioventilatory coupling in spontaneously breathing anaesthetised subjects. The current study extends those observations by demonstrating that the qualitative features of coupling seen during anaesthesia are also observed in the conscious state. We conclude that the role of coupling in normal physiological respiratory control needs to be more widely explored. [source]

Enhanced hydrogenation in a reverse flow chromatographic reactor

AICHE JOURNAL, Issue 5 2006
Guillermo A. Viecco
Abstract An experimental study of the reverse flow chromatographic reactor is carried with the equilibrium limited hydrogenation of 1,3,5-trimethylbenzene (mesitylene, MES) to 1,3,5-trimethylcyclohexane. The reaction is pseudo first-order when carried out in excess hydrogen. A simple experimental setup is used to evaluate the effects of carrier flow, reactant feed concentration, and amount of catalyst on conversion. Conversions exceeding the thermodynamic equilibrium conversion are obtained for a wide variety of switching times, catalyst amounts, carrier flow rates, and reactant concentrations, showing the robustness of the system. While the qualitative features of the process can be predicted for a simple linear adsorption equilibrium model, the experimental results are best fitted by assuming a linear adsorption isotherm combined with an adjusted interfacial mass-transfer resistance. The experimental results are very similar to those reported in previous research of the same reaction in a simulated moving-bed chromatographic reactor. © 2006 American Institute of Chemical Engineers AIChE J, 2006 [source]

Image contrast in X-ray reflection interface microscopy: comparison of data with model calculations and simulations

JOURNAL OF SYNCHROTRON RADIATION, Issue 6 2008
P. Fenter
The contrast mechanism for imaging molecular-scale features on solid surfaces is described for X-ray reflection interface microscopy (XRIM) through comparison of experimental images with model calculations and simulated measurements. Images of elementary steps show that image contrast is controlled by changes in the incident angle of the X-ray beam with respect to the sample surface. Systematic changes in the magnitude and sign of image contrast are asymmetric for angular deviations of the sample from the specular reflection condition. No changes in image contrast are observed when defocusing the condenser or objective lenses. These data are explained with model structure-factor calculations that reproduce all of the qualitative features observed in the experimental data. These results provide new insights into the image contrast mechanism, including contrast reversal as a function of incident angle, the sensitivity of image contrast to step direction (i.e. up versus down), and the ability to maximize image contrast at almost any scattering condition defined by the vertical momentum transfer, Qz. The full surface topography can then, in principle, be recovered by a series of images as a function of incident angle at fixed momentum transfer. Inclusion of relevant experimental details shows that the image contrast magnitude is controlled by the intersection of the reciprocal-space resolution function (i.e. controlled by numerical aperture of the condenser and objective lenses) and the spatially resolved interfacial structure factor of the object being imaged. Together these factors reduce the nominal contrast for a step near the specular reflection condition to a value similar to that observed experimentally. This formalism demonstrates that the XRIM images derive from limited aperture contrast, and explains how non-zero image contrast can be obtained when imaging a pure phase object corresponding to the interfacial topography. [source]

Non-carious cervical lesions: a scanning electron microscopic study

AUSTRALIAN DENTAL JOURNAL, Issue 2 2010
JA Michael
Abstract Background:, Examining non-carious cervical lesions using scanning electron microscopy (SEM) provides an opportunity to clarify their complex aetiology. This study aimed to examine the morphological forms of non-carious cervical lesions found within a sample of extracted human permanent anterior teeth using scanning electron microscopy. Methods:, Five examples of non-carious cervical lesions from each of eight different morphologic categories were replicated and examined using scanning electron microscopy. Results:, In total, 40 non-carious cervical lesions were examined at magnifications ranging from 10× to 2605× magnification. Qualitative ultrastructural features evident in the lesions were described and classified according to their appearance. A total of 13 different qualitative features were observed throughout the sample of NCCLs. Conclusions:, SEM highlighted a broad range of microscopic features of NCCLs, providing valuable insights into their complex, multifactorial aetiology. [source]