Ribbon-Substrate adhesion dynamics in chill block melt-spinning processes

Rapidly quenched ribbons made directly from the melt by chill block melt-spinning exhibit a variable ribbon-substrate adhesion distance, especially during the start of a run. The present work reports on experimental parameters which affect the ribbon-substrate adhesion dynamics. Frame-by-frame measurements of ribbon-substrate adhesion distance in high speed movies were taken for a variety of melt-spin process conditions. The results are interpreted in terms of interfacial temperature, compositional compatibility, and stresses between the melt or ribbon and the substrate. Calculated interfacial thermal profiles are used to visualize adhesion dynamics qualitatively. It is shown that the interface thermal and compositional factors considered in the present investigation are a key to the nature of ribbon-substrate adhesion dynamics in chill block melt-spinning processes.     

On the temporal dynamics of digit comparison processes.

The authors studied the temporal dynamics of digit comparison processes by presenting the digits with a stimulus onset asynchrony (SOA) of 0, 70, 140, or 210 ms. Experiment 1 used the standard complete paired comparison design that confounds numerical and probabilistic information in the digit presented first. The results showed large effects of SOA that differed characteristically for different digit pairs. These results changed considerably in Experiment 2, using a design that removed any probabilistic contingencies. Experiment 3 examined a form of congruity effect related to the temporal order of the digits. The authors formulated and compared to the data 2 models that differed in their assumptions about the loci of digit-specific and SOA-specific effects: Either the participants use partial numerical advance information to prepare for the suggested response, or they start to process numerical information only after both digits are presented. When probabilistic contingencies were removed, the data favored the latter model. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Statistical issues in biological radiation dosimetry for risk assessment using stable chromosome aberrations

Biological dosimeters are useful for epidemiologic risk assessment in populations exposed to catastrophic nuclear events and as a means of validating physical dosimetry in radiation workers. Application requires knowledge of the magnitude of uncertainty in the biological dose estimates and an understanding of potential statistical pitfalls arising from their use. This paper describes the statistical aspects of biological dosimetry in general and presents a detailed analysis in the specific case of dosimetry for risk assessment using stable chromosome aberration frequency. Biological dose estimates may be obtained from a dose-response curve, but negative estimates can result and adjustment must be made for regression bias due to imprecise estimation when the estimates are used in regression analyses. Posterior-mean estimates, derived as the mean of the distribution of true doses compatible with a given value of the biological endpoint, have several desirable properties: they are nonnegative, less sensitive to extreme skewness in the true dose distribution, and implicitly adjusted to avoid regression bias. The methods necessitate approximating the true-dose distribution in the population in which biological dosimetry is being applied, which calls for careful consideration of this distribution through other information. An important question addressed here is to what extent the methods are robust to misspecification of this distribution, because in many applications of biological dosimetry it cannot be characterized well. The findings suggest that dosimetry based solely on stable chromosome aberration frequency may be useful for population-based risk assessment.     

Simulations of stable crack propagation based on cavity growth by coupled diffusional and creep processes

A model based on cavity growth by coupled diffusional and creep processes has been developed to describe the stable crack growth behavior that has been observed experimentally in pure copper and Cu + 1 wt% Sb. Favorable comparisons of the predictions with experimental data for different possible stress distributions suggest that cavity growth and coalescence on transverse grain boundaries limit the rate of crack growth once cavitation has become extensive. These comparisons also indicate that stable crack growth can occur in the presence of a gradual, nonsingular stress distribution once a stable cavity size gradient exists ahead of the crack tip.     

The dynamics of cognition and action: Mental processes inferred from speed-accuracy decomposition.

The interpretation of reaction time (RT) data requires strong assumptions about how Ss trade accuracy for speed of performance and about whether there is a discrete or continuous transmission of information from one component process to the next. Conventional RT and speed–accuracy trade-off procedures are not, by themselves, sufficiently powerful to test these assumptions. However, the deficiency can be remedied in part through a new speed–accuracy decomposition technique. The technique uses a hybrid mixture of (a) conventional RT trials in which Ss must process a given test stimulus with high accuracy and (b) peremptory response-signal trials in which Ss must make prompted guesses before stimulus processing has been finished. Data from this "titrated RT procedure" are then analyzed in terms of a parallel sophistication-guessing model, under which normal mental processes and guessing processes are assumed to race against each other in producing overt responses. With the model, the amount of partial information that Ss have accumulated about a test stimulus can be estimated at each intermediate moment during a reaction time trial. An application of speed–accuracy decomposition to 5 studies of word recognition illustrates the potential power of the technique. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A 'landscape' model of reading comprehension: Inferential processes and the construction of a stable memory representation.

The theoretical model of reading proposed in this paper captures the processes that take place during reading and specifies how these processes result in a stable memory representation of the text. The model is based on the premise that, during reading, the ideas and concepts associated with the text fluctuate in their activation. The result is a dynamically shifting landscape of activations. Two factors contribute to the shape of this landscape: readers' limited attentional resources and their attempts to maintain standards for coherence. As a result, at any point during reading the following concepts are most likely to be activated: information described in or associated to the current sentence, information retained from the prior reading cycle, and information that is reinstated from prior text or drawn from background knowledge in order to maintain coherence. Readers' standards for coherence vary between as well as within individuals (e.g., as a function of reading goal), but here the focus is on two types of coherence that seem to be employed by the modal reader: anaphoric/referential and causal coherence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Molecular dynamics simulation of cytochrome c3: studying the reduction processes using free energy calculations

The tetraheme cytochrome c3 from Desulfovibrio vulgaris Hildenborough is studied using molecular dynamics simulation studies in explicit solvent. The high heme content of the protein, which has its core almost entirely made up of c-type heme, presents specific problems in the simulation. Instability in the structure is observed in long simulations above 1 ns, something that does not occur in a monoheme cytochrome, suggesting problems in heme parametrization. Given these stability problems, a partially restrained model, which avoids destruction of the structure, was created with the objective of performing free energy calculations of heme reduction, studies that require long simulations. With this model, the free energy of reduction of each individual heme was calculated. A correction in the long-range electrostatic interactions of charge groups belonging to the redox centers had to be made in order to make the system physically meaningful. Correlation is obtained between the calculated free energies and the experimental data for three of four hemes. However, the relative scale of the calculated energies is different from the scale of the experimental free energies. Reasons for this are discussed. In addition to the free energy calculations, this model allows the study of conformational changes upon reduction. Even if the precise details of the structural changes that take place in this system upon individual heme reduction are probably out of the reach of this study, it appears that these structural changes are small, similarly to what is observed for other redox proteins. This does not mean that their effect is minor, and one example is the conformational change observed in propionate D from heme I when heme II becomes reduced. A motion of this kind could be the basis of the experimentally observed cooperativity effects between heme reduction, namely positive cooperativity.     

Phase- and density-dependent population dynamics in Norwegian lemmings: interaction between deterministic and stochastic processes

We analysed two 26-year long (1970-1995) time-series on annual population growth rates of Norwegian lemmings (Lemmus lemmus) from Finse, south Norway, using a threshold autoregressive (TAR) approach. We demonstrate that the population dynamics is both phase- and density-dependent. The phase-dependence accounts for the observed nonlinearity. We used the deduced stochastic model structure as a basis for evaluating the dynamic properties of this system. The dynamics is characterized either by limit cycles or chaos (the latter with a strong semi-periodic component). Stochasticity is seen to play an important role in the determination of the periodicity. The ecological implications of these statistical and mathematical results are discussed.     

Dimensional and mechanical dynamics of active and stable edges in motile fibroblasts investigated by using atomic force microscopy

The atomic force microscope (AFM) was employed to investigate the extension and retraction dynamics of protruding and stable edges of motile 3T3 fibroblasts in culture. Such dynamics closely paralleled the results of earlier studies employing video microscopy that indicated that the AFM force-mapping technique does not appreciably perturb these dynamics. Force scans permitted height determinations of active and stable edges. Whereas the profiles of active edges are flat with average heights of 0.4-0.8 micrometer, stable edges smoothly ascend to 2-3 micrometers within about 6 micrometers of the edge. In the region of the leading edge, the height fluctuates up to 50% (SD) of the mean value, much more than the stable edge; this fluctuation presumably reflects differences in underlying cytoskeletal activity. In addition, force mapping yields an estimate of the local Young's modulus or modulus of elasticity (E, the cortical stiffness). This stiffness will be related to "cortical tension," can be accurately calculated for the stable edges, and is approximately 12 kPa in this case. The thinness of the leading edge precludes accurate estimation of the E values, but within 4 micrometers of the margin it is considerably smaller than that for stable edges, which have an upper limit of 3-5 kPa. Although blebbing cannot absolutely be ruled out as a mechanism of extension, the data are consistent with an actin polymerization and/or myosin motor mechanism in which the average material properties of the extending margin would be nearly constant to the edge. Because the leading edge is softer than the stable edge, these data also are consistent with the notion that extension preferentially occurs in regions of lower cortical tension.