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At least 1,171 records · Page 65Linked to original sources
PubMed1996

Intention, history, and artifact concepts.

What determines our intuitions as to which objects are members of specific artifact kinds? Prior research suggests that factors such as physical appearance, current use, and intended function are not at the core of concepts such as chair, clock and pawn. The theory presented here, based on Levinson's (1993) intentional-historical theory of our concept of art, is that we determine that something is a member of a given artifact kind by inferring that it was successfully created with the intention to belong to that kind. This theory can explain why some properties (such as shape) are more important than others (such as color) when we determine kind membership and can account for why certain objects are judged to be members of artifact kinds even though they are highly dissimilar from other members of the kinds. It can also provide a framework for explaining the conditions under which broken objects cease to be members of their kinds and new artifacts can come into existence. This account of our understanding of artifact concepts is argued to be consistent with more general "essentialist" theories of our understanding of concepts corresponding to proper names and natural kind terms.

Art↗
PubMed1994

Increased incidence of high-order and singleton conceptions after ovulation induction in winter.

The possible relationship between the season of conception after ovulation induction and high-order multifetal pregnancies, was investigated. From 1975 to 1989, 111 high-order multiple births after ovulation induction were recorded at the Chaim Sheba Medical Center. This group was compared with 142 singleton pregnancies that resulted from induction of ovulation during 1989. Composite monthly cohorts of high-order multifetal pregnancies were constructed for each month of the year, and the probability of such pregnancies was estimated. The period of ovulation induction and the day of presumed conception were noted. A statistically-significant increase in the probability of high-order and singleton conceptions occurred during the winter. Our observation indicates a seasonal pattern in high order and singleton conceptions after ovulation induction.

Adolescent↗
PubMed1987

Seasonal influences on conception efficiency in Minnesota dairy herds.

This study was undertaken to investigate the influence of climatological factors on the conception efficiency of cows in 23 Minnesota dairy herds between March 1982 and March 1985. It was found that year of insemination (P < 0.005), herd (P < 0.005), linear and quadratic terms of days open (P < 0.05), and linear and quadratic terms of minimum temperature (MNT), maximum temperature (MXT) and temperature humidity index (THI) were similarly related to observed monthly variations in first service conception rates. The year of insemination (P < 0.005), herd (P < 0.005), and linear and quadratic terms of MNT, MXT and THI were also related to the variation in overall conception rate. Conception rate declined from April to August and increased from August to January. There was an 11% difference between the month of lowest fertility (August) and the month of highest fertility (November). It can be concluded that climatological factors appear to depress herd fertility in the northern United States as well as in the warmer southern areas. Thus, consideration should be given to strategies which will minimize the impact of the observed fertility depression due to these climatic factors.

Journal Article↗
PubMed1991

Effect of heat stress on conception in a dairy herd model under South African conditions.

Three regression models are proposed for predicting reproduction in a model dairy herd under South African conditions. Conception rate (CR%) was related to mean monthly temperature-humidity index (THI) by; CR% = 31.15 THI - 0.25 THI(2) - 890.2, and first service conception rate (FSCR%) to THI by; FSCR% = 173.45 - 1.79 THI. Conception rate was related to numerical month of the year (M) by; CR% = 11.86 M - 0.82 M(2) + 26.36. The relation between mean monthly THI values and the conception rate of dairy cattle is significant. Further investigations to test the proposed regression models under various dairy herd conditions and to improve reproduction in South African dairy herds are needed.

Journal Article↗
PubMed1991

Factors affecting response of groups of dairy cows managed for different calving-conception intervals.

Factors which positively or adversely affect the response of cow groups to different planned conception periods were analyzed and quantified. Cows were randomly assigned to groups for breeding at postpartum intervals of 35 to 59, 60 to 90 and 120 to 150 days in a research herd, or 60 to 90 and 120 to 150 days in a cooperating commercial herd, with a planned preceding dry period of 60 days in both herds. Breeding at 35 to 59 and 60 to 90 days post partum resulted in a lower conception rate among multiparous cows but had no effect on primiparous cows. Genital disorders such as metritis, retained placenta, vulva inflammation and vaginitis, did not affect the start of luteal activity or length of the subsequent cycles, but caused a significant delay of the first behavioral estrus and, consequently, a delay of the first insemination in the earlier breeding groups. About 30% of the cows in the different categories were inseminated three or more times and were considered to be repeat breeders. Response rates (number of cows conceiving on time/number assigned) in the later breeding group improved due to higher submission rates (number of cows submitted on time/number assigned), and the conception rates were higher (number of cows conceiving on time/number submitted). The rates in all groups were adversely affected by repeat breeding and genital disorders. The latter delayed the first insemination and the conception rate.

Journal Article↗
PubMed1992

Cumulative conception and livebirth rates after in-vitro fertilisation.

Cumulative conception and livebirth rates related to age and cause of infertility provide the most useful estimate of success after in-vitro fertilisation (IVF), but limited data are available. It is also uncertain whether the probability of pregnancy, livebirth, and pregnancy failure changes with repeated treatment cycles. To assess the effects of patients' age and cause of infertility on these outcomes, we studied the results of 5055 consecutive IVF cycles (773 clinical pregnancies, 518 livebirths) undertaken on 2735 patients in a single IVF unit. Cumulative conception and livebirth rates were analysed by the life-table approach and differences in rates between age-groups and between causes of infertility were measured by the log-rank test and logistic regression modelling. Both conception and livebirth rates per cycle declined with age (p less than 0.001), and cumulative conception and livebirth rates after five treatment cycles were about 54% and 45%, respectively, at 20-34 years, compared with 38.7% and 28.9% at 35-39 years and 20.2% and 14.4% at greater than or equal to 40 years. The two rates were significantly different between causal groups (p less than 0.001 and p = 0.02, respectively) and were lowest in patients with male infertility or multiple infertility factors. The pregnancy failure rate was higher (p = 0.006) in women over the age of 34 years and there was a significant decline in the chances of pregnancy and livebirth per cycle with successive treatment cycles.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

A constructivist approach to concept attainment.

A teaching strategy for concept attainment based upon a constructivist model is described and evaluated. The constructivist model is outlined, which suggests that students must construct their own knowledge, using their existing knowledge to do so. Transmission methods of teaching run the risk of concepts being altered to fit students' existing conceptions. A constructivist strategy for concept learning is exemplified drawing on the transcript of an experimental session conducted with a peer group of student teachers studying for the Certificate in Education.

Education, Nursing↗
PubMed1987

The viability of the concept of a primary health care team in developing countries.

The concept of a team approach in primary health care (PHC) is an integral part of the overall PHC strategy and is advocated at many occasions. Its theoretical advantages are multiple, even though very few sound studies exist on the effectiveness of PHC team. The viability of the concept of PHC teams is affected by two groups of factors. The first group is related to (health) manpower problems in developing countries with its underlying economic causes. The second group of factors is associated with the viability of the PHC concept in general. This pertains to decentralization, intersectoral collaboration and community participation which all affect the viability of the concept of PHC teams.

Africa↗
PubMed1985

Learning and coding of concepts in neural networks.

Our environment consists of virtually an infinite number of scenarios in which we have to function. In order to respond properly to an incoming stimulus, the brain has first to analyze it, and to find out the basic familiar elements that are part of it. In other words, by using a library which contains a relatively small number of basic concepts, the brain analyzes the multitude of incoming events. Some of those basic concepts are innate, but many of them must be learned, in order to accommodate for the arbitrary environment around us. A classifying box is defined as the neural network that finds out the familiar concepts that are present in an incoming stimulus. Models for classifying boxes are introduced, and possible mechanisms by which they may establish their libraries of concepts are suggested, and then compared and evaluated by computer simulations.

Classification↗
PubMed1993

A case that biomedicine is unduly negative to radical hypotheses and to theorizing--evidence based on cardiology's reaction to the spasm of resistance vessel concept and on the nature of scientific research.

This communication will attempt to make a case that biomedicine is unduly negative to radical hypotheses and to theorizing. Evidence will be based on a proposed undue negativity by cardiology to a radical hypothesis I first described two and a half decades ago--the spasm of resistance vessel (S-RV) concept of ischemic heart disease (IHD). The theory is regarded as an alternate paradigm and deals with basic pathogenetic mechanisms of IHD, the most significant disorder of Western civilization. The concept, if valid, might help in reducing the impact of this disorder, and I believe that the evidence for the theory and the importance of IHD support a more open minded attitude toward the idea. Cardiology's negativity is attributed to the nature of research; the most important factor is considered to be the Kuhnian negativity of scientific communities to hypotheses which are destructive of conventional wisdom, and a second factor is the special nature of biomedical research. Biomedicine is regarded as special because a low level of specific information about complex biomedical processes has fostered an essentially total study-based approach. Such an approach is assumed to have resulted in biomedicine's use of induction as 'the' method of scientific inquiry, and prompted negativity towards the hypothetico-deductive method used to develop and test the theory. Also, the study-based nature of biomedicine appears to have fostered an intuitive reliance on only newly performed studies to test hypotheses, which led to ignoring evidence for the concept derived from known information about IHD. Biomedicine is also regarded as special because its infrequent use of paradigm-change has resulted in unfamiliarity with this method, and because the practical method of training in biomedical research has worsened the general unfamiliarity of scientists with theoretical aspects of science. Because of these factors, the S-RV concept has not yet been properly evaluated--a quarter of a century after it was first created.

Cardiology↗
PubMed1990

Upper limits of brain blood flow autoregulation in stable infants of various conceptional age.

In healthy adults cerebral blood flow is autoregulated and kept constant over a wide range of mean arterial blood pressures (MAP) between 60 and 150 mmHg. In 27 stable infants with different conceptional ages ranging from 33 to 50 weeks, Doppler measurements of mean flow velocity at the anterior cerebral artery have been recorded simultaneously with mean arterial blood pressures (MAP) during a period of 6 h. The range of autoregulation and its upper limit could thus be determined. The upper limit was found to increase with advancing age. In the infants with conceptional ages between 33 and 35 weeks, the upper limit of autoregulation varied between 45 and 60 mmHg, while the upper limit shifted to a MAP of 100 mmHg at 47 weeks conceptional age. A significant positive linear relationship existed between the upper limit of autoregulation and conceptional age.

Aging↗
PubMed1982

Basic concepts for nuclear magnetic resonance imaging.

The basic concepts necessary to understand the physical basis of NMR imaging are presented in this didactic article. It is intended as a starting point for the radiologist or medical physicist who is addressing the topic of NMR for the first time. The basic of the NMR phenomena is described with introduction of the concepts of magnetic moment, magnetic fields, magnetic resonance, net magnetic moment of a sample, NMR excitation and NMR emission. The equipment necessary to observe these NMR properties of matter is summarized as well as the procedures for basic pulsed NMR experiments. The physical concepts for spatial localization of NMR emissions are introduced with physical analogies to stringed musical instruments. Several alternative imaging modalities are compared with greatest emphasis on the inversion recovery technique which yields images weighted by tissue T values. The six subsystems of an NMR imaging device (primary magnet, computer, radio equipment, magnetic gradient, data storage and display subsystems) are described in an overview fashion. The paper is followed by a series of study questions to test the reader's comprehension of basic NMR imaging concepts.

Humans↗
PubMed1993

The personality of the patient: going beyond the trait concept.

The concept of dominance is a key concept in reversal theory and distinguishes the theory from traditional trait theories in personality psychology. By dominance is meant the individual's tendency to spend more time in one rather than another of the pairs of opposite emotional or motivational states identified in the theory. This is in many ways a more sophisticated concept than that of trait. Some psychometric scales that have been developed to measure different kinds of dominance are reviewed: the Telic Dominance Scale, the Nijmegen Telic Dominance Scale, the Paratelic Dominance Scale, the Negativism Dominance Scale and the Personal Orientation Profile. The relevance of the dominance concept is discussed in relation to patient management.

Adult↗
PubMed1996

Hierarchical Concept Formation in Associative Memory Composed of Neuro-window Elements.

In the present letter, the authors propose a model of hierarchical concept formation in auto-associative memory composed of neuro-window elements. When hierarchically correlated patterns are memorized, each center of the correlated memory patterns can be defined as a concept pattern which represents those similar patterns. It is shown that the concept patterns are formed under a Hebbian learning rule in the neural network where all the neuro-window elements are just mutually connected, and that the memory patterns and the concept patterns in each level of hierarchy can be retrieved selectively by adjusting the parameters of the neuro-window elements. Copyright 1996 Elsevier Science Ltd

Journal Article↗
PubMed1994

Learning and discovery from a clinical database: an incremental concept formation approach.

The main interest of this research is to discover clinical implications from a large PTCA (Percutaneous Transluminal Coronary Angioplasty) database. A case-based concept formation model D-UNIMEM, a modified version of Lebowitz's UNIMEM, is proposed for this purpose. In this model, we integrated two kinds of class memberships: the feature-disjunction class membership and the index-conjunction class membership. The former is a polythetic clustering approach and serves at the early stage of concept formation. The latter allows only relevant instances to be placed in the same cluster and serves as the later stage of concept formation. D-UNIMEM could extract interesting correlations among features from the learned concept hierarchy.

Abstracting and Indexing↗
PubMed1995

Durations of adolescent sexual relationships before and after conception.

PURPOSE: To explore durations of young couples' relationships between meeting and first intercourse, before first conception and for two years following conception and the associations between these durations; to describe the association between these durations and the young women's perceptions of the nature of these relationships. METHODS: Three hundred and seven adolescent women were enrolled in a prospective study while presenting for pregnancy tests (the index event); they were followed for two years in three groups--those with negative tests, those who terminated the pregnancy and those who bore a child. Retrospective information about durations of relationships with first partners and partners at the index event was obtained at baseline; follow-up data was obtained on continuing relationships with the index partner. RESULTS: Durations of relationships between adolescent females and their partners in this sample, both before and after conception, are rarely brief; the median duration of a girl's prior relationship with a partner with whom she conceives is almost two years. Similarly, almost half of the sample is still in a relationship at two years following the index event, a proportion that rises to two-thirds among those who bore a child together. CONCLUSIONS: Contrary to common belief or practice, there may be sufficient time and commitment to include many male partners in intervention programs before, and in parenting programs after, a first conception--a practice which could have positive implications for both adolescent partners and, potentially, for their child.

Adolescent↗
PubMed2006

Neurotoxicity of reactive aldehydes: the concept of "aldehyde load" as demonstrated by neuroprotection with hydroxylamines.

The concept of "oxidative stress" has become a mainstay in the field of neurodegeneration but has failed to differentiate critical events from epiphenomena and sequalae. Furthermore, the translation of current concepts of neurodegenerative mechanisms into effective therapeutics for neurodegenerative diseases has been meager and disappointing. A corollary of current concepts of "oxidative stress" is that of "aldehyde load". This relates to the production of reactive aldehydes that covalently modify proteins, nucleic acids, lipids and carbohydrates and activate apoptotic pathways. However, reactive aldehydes can also be generated by mechanisms other than "oxidative stress". We therefore hypothesized that agents that can chemically neutralize reactive aldehydes should demonstrate superior neuroprotective actions to those of free radical scavengers. To this end, we evaluated hydroxylamines as aldehyde-trapping agents in an in vitro model of neurodegeneration induced by the reactive aldehyde, 3-aminopropanal (3-AP), a product of polyamine oxidase metabolism of spermine and spermidine. In this model, the hydroxylamines N-benzylhydroxylamine, cyclohexylhydroxylamine and t-butylhydroxylamine were shown to protect, in a concentration-dependent manner, against 3-AP neurotoxicity. Additionally, a therapeutic window of 3 h was demonstrated for delayed administration of the hydroxylamines. In contrast, the free radical scavengers TEMPO and TEMPONE and the anti-oxidant ascorbic acid were ineffective in this model. Extending these tissue culture findings in vivo, we examined the actions of N-benzylhydroxylamine in the trimethyltin (TMT) rat model of hippocampal CA3 neurodegeneration. This model involves augmented polyamine metabolism resulting in the generation of reactive aldehydes that compromise mitochondrial integrity. In the rat TMT model, NBHA (50 mg/kg, sc, daily) provided 100% protection against neurodegeneration, as reflected by measurements of KCl-evoked glutamate release from hippocampal brain slices and septal high affinity glutamate uptake. In contrast, ascorbic acid (100 mg/kg, sc, daily) failed to protect CA3 neurons from TMT toxicity. In summary, our data support further evaluation of the concept of "aldehyde load" in neurodegeneration and the potential clinical investigation of agents that are effective traps for reactive aldehydes.

Aldehydes↗
PubMed2004

Pursuing the leadlikeness concept in pharmaceutical research.

Lipinski and others, through concepts such as drug-likeness, re-focussed drug discovery back to the principles of medicinal chemistry in the high-throughput era as key to reducing attrition. More recently, the need to go further in defining what makes a good lead has been recognised with the concept of leadlikeness. Leadlikeness implies cut-off values in the physico-chemical profile of chemical libraries such that they have reduced complexity (e.g. MW below <400) and other more restricted properties. We examine these concepts in the context of Virtual (theoretically possible), Tangible (chemically feasible) and Real (physically available) worlds of molecules. In a thought experiment, we take the HTS concept to the extreme: screening an estimated 60 million 'Global Collection' on 5000 targets and realising that perhaps millions of drug candidates might be found that could not possibly be handled in reality. Sampling of the Virtual and Tangible worlds is therefore a necessity. We show that the world of Reals is significantly under-sampled as the MW of compounds increases. This supports the design and screening of 'reduced complexity' (leadlike) compound libraries, preferably with synthetic handles available for rapid chemical iteration and detected as interesting by careful screening or biophysical assays.

Carboxylic Acids↗