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PubMed1988

A computer graphics program system for protein structure representation.

We have developed a computer graphics program system for the schematic representation of several protein secondary structure analysis algorithms. The programs calculate the probability of occurrence of alpha-helix, beta-sheet and beta-turns by the method of Chou and Fasman and assign unique predicted structure to each residue using a novel conflict resolution algorithm based on maximum likelihood. A detailed structure map containing secondary structure, hydrophobicity, sequence identity, sequence numbering and the location of putative N-linked glycosylation sites is then produced. In addition, helical wheel diagrams and hydrophobic moment calculations can be performed to further analyze the properties of selected regions of the sequence. As they require only structure specification as input, the graphics programs can easily be adapted for use with other secondary structure prediction schemes. The use of these programs to analyze protein structure-function relationships is described and evaluated.

Algorithms↗
PubMed1993

A mathematical model of the intracerebral steal phenomenon in regional and focal ischaemia.

The objective of the present work was to mathematically estimate the extent and dynamics of intracerebral steal which may occur in response to cerebral vasodilation in regional and focal cerebral ischaemia. To this end, a spatially distributed mathematical model of regional cerebral blood flow (rCBF) was developed. The model contained a parallel system of intracerebral vascular resistances which were connected in series to a lumped extracerebral artery resistance and, for the focal ischaemia model, also a lumped pial collateral resistance. The rCBF was measured at 30 min of ischaemia in the following models: (1) bilateral carotid occlusion in spontaneously hypertensive rats (SHR), and (2) occlusion of the middle cerebral artery (MCA) in normotensive rats. The measured 3-dimensional rCBF data were used to set up the initial values of intracerebral resistance components. Cerebral vasodilation induced by inhalation of CO2 was simulated in the model by decreasing the values of both intracerebral and collateral resistance. Vascular responsiveness was specified to decrease with the ischaemic rCBF. In addition, a long term change in rCBF and resistance distribution was introduced to account for: (1) gradual rise in intracerebral resistance due to ischaemic oedema, and (2) adaptive decrease in collateral resistance. The following were predicted by the mathematical model. (1) At 60% maximum intracerebral dilatation a small intracerebral steal (5-10%) occurs at flow levels below 30-50 ml/100 g/min in both ischaemic models. (2) In focal ischaemia, the steal can be compensated by the 5% to 20% decrease in the collateral vascular resistance. (3) The rate of collateral adaptation overcomes the rate of intracerebral resistance rise and, therefore, eliminates the intracerebral steal after an adequately long period of time (on the order of a few hours). (4) An inverse steal effect can be demonstrated at the end of vasodilatation, provided that the time constant of collateral adaptation selected is longer (about 5:1) than the time constant of the intracerebral resistance rise. We conclude that the prediction of rCBF response to vasodilatation in cerebral ischaemia requires a knowledge of resting rCBF and of the response characteristics of both intracerebral and pial arterial segments.

Animals↗
PubMed2004

Generation of QSAR sets with a self-organizing map.

A Kohonen self-organizing map (SOM) is used to classify a data set consisting of dihydrofolate reductase inhibitors with the help of an external set of Dragon descriptors. The resultant classification is used to generate training, cross-validation (CV) and prediction sets for QSAR modeling using the ADAPT methodology. The results are compared to those of QSAR models generated using sets created by activity binning and a sphere exclusion method. The results indicate that the SOM is able to generate QSAR sets that are representative of the composition of the overall data set in terms of similarity. The resulting QSAR models are half the size of those published and have comparable RMS errors. Furthermore, the RMS errors of the QSAR sets are consistent, indicating good predictive capabilities as well as generalizability.

Algorithms↗
PubMed1997

ALATOP-RIA in the screening of atopy in a non Caucasian population.

UNLABELLED: ALATOP is an "in vitro" radioimmunoassay screening test for atopy, previously validated in a caucasian population. The aim of the study was to assess the usefulness of a screening test of atopy in a non caucasian population. We select a non caucasian population (n = 208), from hospital immunoallergy consultations, Cape Verde Republic (Africa). It was determined the sensitivity, specificity and predictive values comparing with skin prick tests (SPT) results for the 208 patients, and with clinical data (Clin) in 115 patients. It was also determined the levels of total IgE, done by IRMA. RESULTS: Using different corrections factors, 0.85 gives the best results: ALATOP/SPT-Sensitivity-88.5% +/- 4.34; Specificity-73.8% +/- 8.41; Positive predictive value-66.9%; Negative predictive value-91.4%; Efficiency of the test-79.3%. ALATOP/CLIN-Sensitivity-95.2% +/- 3.89; Specificity-71.2% +/- 12.07; Positive predictive value-65.6%; Negative predictive value-96.2%; Efficiency of the test-80.0%. The mean values of total IgE were-406 IU/ml. CONCLUSIONS: The mean value of total IgE was significantly increased even in the ALATOP-/SPT-not saw in caucasian populations. The use of a different correction factor (0.85) for ALATOP, optimize the test, showing a good negative predictive value, but raises the question of adapted compositions of screening tests for different populations.

Adolescent↗
PubMed1993

Adaptive orthogonalization of opponent-color signals.

This paper concerns the processing of the outputs of the two opponent-color mechanisms in the human visual system. We present experimental evidence that opponent-color signals interact after joint modulation even though they are essentially independent under neutral steady adaptation and after exclusive modulation of each mechanism. In addition, prolonged modulation linearizes the response function of each mechanism. The changes in interaction serve to orthogonalize opponent signals with respect to the adapting modulation, and the changes in response functions serve to equalize the relative frequencies of different levels of response to the adapting modulation. Adaptive orthogonalization reduces sensitivity to the adapting color direction, improves sensitivity to the orthogonal direction, and predicts shifts in color appearance. Response equalization enhances effective contrast and explains the difference between the effects of adaptation to uniform versus temporally or spatially modulated stimuli.

Adaptation, Ocular↗
PubMed1997

Predicting adolescent mothers' transition to adulthood.

This study investigates the relation among prenatal maternal resources (including intellectual ability, cognitive readiness for parenting, personal adjustment and social support), maternal perceptions about parenting and children's temperament when children were 6 months of age, and individual differences in the adaptation of 90 adolescent mothers 3 years after the birth of their first child. It was hypothesized that adolescent mothers¿ pre-existing resources and emerging perceptions about parenting determine not only their children's but also their own later adaptation to critical life events. Maternal resources uniquely predicted later maternal cognitive functioning, personal adjustment, and child abuse potential, whereas maternal perceptions uniquely predicted maternal demographic status 3 years after childbirth. Moreover, maternal perceptions were found to mediate the influence of maternal resources on parent-child interactional styles. The unique roles that maternal resources and perceptions played in determining later maternal functioning are discussed.

Adolescent↗
PubMed1983

Normal and pathological grief.

Physicians are often called on to care for patients and members of patients' families during the period of bereavement. The grief process serves a psychologically adaptive function and usually progresses in a predictable manner. Under certain unusual circumstances, however, the grieving process may become pathologically delayed or distorted, with serious consequences for the survivor's emotional and physical health. There are three phases of the normal grief process and particular guidelines for physician recognition and management of pathological grief reactions.

Adaptation, Psychological↗
PubMed2004

Comparing alternative definitions of the contemporary group effect in Avilena Negra Iberica beef cattle using classical and Bayesian criteria.

Data on weaning weight from 12,740 animals were used to compare different definitions of contemporary groups (CG) for the genetic evaluation of the Avilena Negra Iberica beef cattle breed. Six alternative definitions for the CG effect were considered: herd-year-season of calving (HYS), with seasons defined according to the four natural seasons; herd-year-month of calving (HYM); herd clusters of 30 d (HC30-30) or 90 d (HC90-90); and adaptive herd clusters with two time limits, 30 and 90 d (HC30-90), and 30 and 180 d (HC30-180). A minimum of five observations in each CG class was required. This rendered substantial differences in loss of information, ranging from 0.7% of the total number of records for HC30-180 to 14% for HYM. Several classical statistics and Bayesian criteria for statistical model comparison were used. The use of classical criteria, such as the between- and within-CG variation and the accuracy of prediction, can be controversial because of their dependency on the unknown variance components. Residual variance decreased with the decrease in time span associated with the definition of CG. This was expected in this population because environmental conditions are highly variable throughout the year. However, estimates of the additive genetic variance for direct effects, which should not be affected by the definition of CG, were substantially larger for definitions involving larger time periods (HYS, HC90-90). When parameters used in the current evaluation procedure were used with all data sets, CG involving 30 d (HYM and HC30-30) were optimal in terms of providing the lowest/largest within-/between-CG variation. On the other hand, CG involving 90 d (HYS and HC90-90) yielded the poorest within-/between CG variation, with only a slight improvement of accuracy of prediction of direct genetic values over the other definitions. Bayes factors and cross-validation predictive densities allowed for improved discrimination among models. Models including CG spanning 30 d were more plausible and showed better predicting ability than models spanning 90 d. Adaptive CG showed intermediate results. Overall, it seems that average time span rendered by the different definitions had a major effect on the ranking of models. However, from the breeder's point of view, the loss of information associated with definitions involving shorter periods of time, such as HYM or HC30-30, might be unacceptable.

Animals↗
PubMed1997

Stomatopod photoreceptor spectral tuning as an adaptation for colour constancy in water.

Where colour is used in communication absolute judgement of signalling spectra is important, and failures of colour constancy may limit performance. Stomatopod crustaceans have unusual eyes in which the midband contains ten or more classes of photoreceptor. For constancy based on receptor adaptation to a fixed background, elementary theory predicts and we confirm by modelling, that stomatopods' narrow-band receptors outperform more broadly tuned receptors. Similar considerations could account for the small spectral separation of receptors in each midband row. Thus, stomatopods seem to trade-off sensitivity and signal-to-noise ratio for increased colour constancy.

Adaptation, Ocular↗
PubMed1982

Oculomotor response to rapid head oscillation (0.5-5.0 Hz) after prolonged adaptation to vision-reversal. "Simple" and "complex" effects.

This study examined long-term (up to 27 days) effects of maintained vision reversal on (i) smooth visual tracking with head still, (ii) oculomotor response to actively, generated head oscillation and (iii) "spontaneous" saccades. Dove prism goggles produced horizontal, but not vertical (sagittal plane), vision reversal. Eye movements were recorded by EOG; head movements by an electro-magnetic search coil. Both visual tracking and saccade dynamics remained unchanged throughout. In contrast, both the ocular response to active head oscillations (goggles off and subject looking at a stationary target) and associated retinal image blur showed substantial and retained adaptive changes, akin to those previously found in the vestibulo-ocular reflex as tested in darkness at 0.17 Hz. However, several addition unexpected results emerged. First, in the fully adapted state smooth eye movements tended to be of reversed phase in the range 0.5-1.0 Hz (in spite of normal vision during tests), but of normal phase from about 2 Hz and above (in spite of negligible visual tracking in this upper range). Second, after permanent removal of the inverting goggles, this peculiar frequency response of the fully adapted state quickly (36 h) reverted to a dynamically simpler condition manifest as retained (2-3 weeks) attenuation of gain (eye vel./head vel.) which, as in control conditions, was monotonically related to frequency. From these two findings it is inferred that the fully adapted state may have comprised two separate components: (i) A "simple element of monotonic and long-lasting gain attenuation and (ii) a "complex", frequency labile, element which could be quickly rejected. Dynamic characteristics of the putative "complex" element were estimated by vectorial subtraction of the "simple" one from that of the fully adapted condition. The outcome suggests that the inferred "complex" condition might represent a predictive element. Two further findings are reported: (i) Substantially different vectors of the adapted response were obtained with normal and reversed vision at 3.0 Hz head oscillation, indicating a novel visual tracking. (ii) During head oscillation in the vesicle sagittal plane (in which vision was not reversed) there was never any image blur, indicating high geometric specificity in the adaptive process.

Acoustic Stimulation↗
PubMed2000

Plasticity to light cues and resources in Arabidopsis thaliana: testing for adaptive value and costs.

Plants shaded by neighbors or overhead foliage experience both a reduction in the ratio of red to far red light (R:FR), a specific cue perceived by phytochrome, and reduced photosynthetically active radiation (PAR), an essential resource. We tested the adaptive value of plasticity to crowding and to the cue and resource components of foliage shade in the annual plant Arabidopsis thaliana by exposing 36 inbred families from four natural populations to four experimental treatments: (1) high density, full sun; (2) low density, full sun; (3) low density, neutral shade; and (4) low density, low R:FR-simulated foliage shade. Genotypic selection analysis within each treatment revealed strong environmental differences in selection on plastic life-history traits. We used specific contrasts to measure plasticity to density and foliage shade, to partition responses to foliage shade into phytochrome-mediated responses to the R:FR cue and responses to PAR, and to test whether plasticity was adaptive (i.e., in the same direction as selection in each environment). Contrary to expectation, we found no evidence for adaptive plasticity to density. However, we observed both adaptive and maladaptive responses to foliage shade. In general, phytochrome-mediated plasticity to the R:FR cue of foliage shade was adaptive and counteracted maladaptive growth responses to reduced PAR. These results support the prediction that active developmental responses to environmental cues are more likely to be adaptive than are passive resource-mediated responses. Multiple regression analysis detected a few costs of adaptive plasticity and adaptive homeostasis, but such costs were infrequent and their expression depended on the environment. Thus, costs of plasticity may occasionally constrain the evolution of adaptive responses to foliage shade in Arabidopsis, but this constraint may differ among environments and is far from ubiquitous.

Adaptation, Physiological↗
PubMed2005

The stress process perspective and adaptation of people with schizophrenia--an exploratory study.

BACKGROUND: Adaptation of people suffering from schizophrenia still raises numerous questions left unanswered by correlational studies and predictive models. A theoretical framework likely to bring new answers is the stress process perspective. Using the transactional model of coping, to which psychological and social variables have been added, this exploratory research studies the adaptation of 101 people with schizophrenia. METHOD: The research design is correlational with only one crosswise measure. RESULTS: The model predicts 60.7% of variance of adaptation and gives support that the transactional model of coping contributes to this variance. Five variables show a significant effect and account for 48% of the variance, and three interaction effects (two two-way and one three-way) add another 12.7% to the explained variance. CONCLUSION: Results give support to the significant impact of the variables education, age and negative symptoms on adaptation. They highlight the importance of accommodation, a cognitive strategy used by people with schizophrenia to increase their adaptation. They also challenge the broadly accepted assumption of a negative influence of life events on adaptation. Finally, the interaction effects allow us to better understand the mutual effects of variables on adaptation and confirm their relevance.

Adaptation, Psychological↗
PubMed2004

Chromatic induction in humans: how are the cone signals combined to provide opponent processing?

We investigated the effect of 16 isoluminant chromatic surrounds on the perceived colour of an enclosed grey test-field at photopic (43 cd/m2) conditions. Stimuli were shown on a grey background identical to the test-field. Use of these stimuli implies that activations of receptoral (cS, cM, and cL) and postreceptoral (cM-cL, cS-(cM+cL)) mechanisms by surround colours are known quantitatively. This allows to predict shifts in colour of the test-field in terms of receptoral (adaptation) as well as postreceptoral (contrast) mechanisms assuming a standard two-stage model. Predictions are tested using matching and hue compensation procedures. Both procedures yield comparable results that are consistent with the assumption that postreceptoral mechanisms explain the observed shifts in perceived colour.

Adaptation, Physiological↗
PubMedDate not supplied

Visual cortical simple cells: who inhibits whom.

Simple cells display a specific adaptation aftereffect when tested with drifting gratings. The onset of the response to each cycle of the grating is delayed after adapting, but the offset is unaffected. Testing with stationary bars whose luminance was modulated in time revealed that aftereffects occur only at certain points in both space and time. The aftereffects seen with moving stimuli were predicted from those seen with stationary stimuli. These adaptation experiments suggest a model that consists of mutually inhibitory simple cells that are in spatiotemporal quadrature. The inhibition is appropriately localized in space and time to create the observed aftereffects. In this model, inhibition onto direction-selective simple cells arises from simple cells with the same preferred direction.

Adaptation, Physiological↗
PubMed2005

Modelling the fate of sulphur-35 in crops. 2. Development and validation of the CROPS-35 model.

Gas-cooled nuclear power plants in the UK release sulphur-35 during their routine operation, which can be readily assimilated by vegetation. It is therefore necessary to be able to model the uptake of such releases in order to quantify any potential contamination of the food chain. A model is described which predicts the concentration of (35)S in crop components following an aerial gaseous release. Following deposition the allocation to crop components is determined by an export function from a labile pool, the leaves, to those components growing most actively post exposure. The growth rates are determined by crop growth data, which is also used to determine the concentration. The loss of activity is controlled by radioactive decay only. The paper describes the calibration and the validation of the model. To improve the model, further experimental work is required particularly on the export kinetics of (35)S. It may be possible to adapt such a modelling approach to the prediction of crop content for gaseous releases of (3)H and (14)C from nuclear facilities.

Calibration↗
PubMed1997

Dynamic model of visual recognition predicts neural response properties in the visual cortex.

The responses of visual cortical neurons during fixation tasks can be significantly modulated by stimuli from beyond the classical receptive field. Modulatory effects in neural responses have also been recently reported in a task where a monkey freely views a natural scene. In this article, we describe a hierarchical network model of visual recognition that explains these experimental observations by using a form of the extended Kalman filter as given by the minimum description length (MDL) principle. The model dynamically combines input-driven bottom-up signals with expectation-driven top-down signals to predict current recognition state. Synaptic weights in the model are adapted in a Hebbian manner according to a learning rule also derived from the MDL principle. The resulting prediction-learning scheme can be viewed as implementing a form of expectation-maximization (EM) algorithm. The architecture of the model posits an active computational role of the reciprocal connections between adjoining visual cortical areas in determining neural response properties. In particular, the model demonstrates the possible role of feedback from higher cortical areas in mediating neurophysiological effects due to stimuli from beyond the classical receptive field. Simulations of the model are provided that help explain the experimental observations regarding neural responses in both free viewing and fixation conditions.

Animals↗
PubMed1990

Mueller-Lyer decrement: practice or prolonged inspection?

Noting the similarity between the illusion decrement and selective adaptation paradigms, Long has challenged the view that illusion decrement effects reflect a strategic--as opposed to a structural--underlying mechanism, and has called for further research on this issue. To investigate the confound between prolonged free inspection and repeated trials in the standard decrement procedure, the effects of three inspection conditions (continuous, intermittent, and immediate) on the magnitude of the overestimation Mueller-Lyer illusion have been assessed under two levels of trials (a total of two or six judgments). Significant illusion decline was found only under conditions of repeated trials, with either continuous or intermittent inspection. These findings do not support the predictions of purely structural theories (including neural adaptation and efferent readiness theories), according to which degree of decrement should be determined solely by viewing time. Instead, the data demonstrate that illusion decrement is a product of practice, providing converging evidence for the view of decrement as involving a cognitive 'recalibration' or learning process.

Adult↗
PubMed2006

Creativity enhancement: possibilities for successful aging.

Successful aging is of growing importance in the U.S. Many researchers have explored the phenomenon using various approaches, yet we are still lacking practical guidelines on how to promote successful aging in older adults. The Roy Adaptation Model supports the promotion of adaptation to chronic health problems at a time when one's overall health may be declining and is a useful guide for understanding successful aging. Current literature also suggests that functional performance and creativity are important in order to age successfully. This study examined the relationships between functional performance, creativity, and successful aging within the context of the Roy Adaptation Model. Although creativity was not significantly predictive of successful aging, functional performance was a statistically significant predictor of a successful aging indicator, purpose in life. The study was a pretest-posttest experimental design investigating the effects of a creativity enhancement intervention in older adults. Although the intervention did not appear to increase creativity or successful aging, there were some statistically significant results and valuable findings about the possibilities for creativity enhancement.

Activities of Daily Living↗