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At least 1,225 records · Page 68Linked to original sources
PubMed2004

Character of order-disorder and displacive components in barium titanate.

Reconciling the apparently contradictory results of NMR and x-ray absorption fine structure measurements on the ferroelectric perovskite BaTiO3 gives insight into the character of the displacive and order-disorder components of the phase transitions of this material. The order-disorder component in the transition consists of local atomic displacements from cubic symmetry of constant magnitude that partially lose long-range order, while the displacive component consists of reorientation of these displacements.

Journal Article↗
PubMed2004

Positron annihilation studies of the f-electron character in actinides.

Measurement of the angular correlation of the electron-positron annihilation radiation complemented with ab initio calculations can provide decisive information about the character of f electrons in actinide compounds. Our studies of the antiferromagnet UGa3 in the paramagnetic phase produce substantial evidence that an unconstrained f-electron itinerant description applies.

Journal Article↗
PubMed2006

Experimental evidence of the local character of vibrations constituting the Boson peak in amorphous solids.

We report the first measurement of the density of states of low-energy vibrational excitations in a disordered solid via single-molecule (SM) spectroscopy. Optical spectra of many single tetra-tert-butylterrylene (TBT) molecules embedded to amorphous polyisobutylene (PIB) as spectral probes were recorded at low temperatures. The T dependences of SM spectral linewidths showed the broad distribution of local frequencies of vibrations under study. The obtained distribution was compared with the "Boson peak" in pure PIB measured in [R. Inoue, J. Chem. Phys. 95, 5332 (1991)] by neutron scattering. We found that embedding of a small amount of TBT into PIB does not influence markedly on the observed vibrational dynamics. These results prove the local character of low-energy vibrational excitations in glasses and the existence of relationship between these excitations and the Boson peak.

Journal Article↗
PubMed2004

Iterative multimodel subimage binarization for handwritten character segmentation.

Existing binarization methods are categorized as either global or local. In this paper, we present a new category, where the image is considered a collection of subimages. Each subimage provides a statistical model for the handwritten characters that can be used to optimize the binarization of other subimages based on gray-level and stroke-run features. The proposed method uses these multimodels to iteratively arrive at the optimal threshold for each subimage. It can be applied to different types of documents where prior knowledge about the noisiness of the subimages is not available. Experimental results showed significant improvement in the binarization quality in comparison with other well-established algorithms.

Algorithms↗
PubMed2004

Mining pinyin-to-character conversion rules from large-scale corpus: a rough set approach.

This paper introduces a rough set technique for solving the problem of mining Pinyin-to-character (PTC) conversion rules. It first presents a text-structuring method by constructing a language information table from a corpus for each pinyin, which it will then apply to a free-form textual corpus. Data generalization and rule extraction algorithms can then be used to eliminate redundant information and extract consistent PTC conversion rules. The design of our model also addresses a number of important issues such as the long-distance dependency problem, the storage requirements of the rule base, and the consistency of the extracted rules, while the performance of the extracted rules as well as the effects of different model parameters are evaluated experimentally. These results show that by the smoothing method, high precision conversion (0.947) and recall rates (0.84) can be achieved even for rules represented directly by pinyin rather than words. A comparison with the baseline tri-gram model also shows good complement between our method and the tri-gram language model.

Journal Article↗
PubMed2023

A plurality of morphological characters need not equate with phylogenetic accuracy: A rare genomic change refutes the placement of Solifugae and Pseudoscorpiones in Haplocnemata.

Recent advances in higher-level invertebrate phylogeny have leveraged shared features of genomic architecture to resolve contentious nodes across the tree of life. Yet, the interordinal relationships within Chelicerata have remained recalcitrant given competing topologies in recent molecular analyses. As such, relationships between topologically unstable orders remain supported primarily by morphological cladistic analyses. Solifugae, one such unstable chelicerate order, has long been thought to be the sister group of Pseudoscorpiones, forming the clade Haplocnemata, on the basis of eight putative morphological synapomorphies. The discovery, however, of a shared whole genome duplication placing Pseudoscorpiones in Arachnopulmonata provides the opportunity for a simple litmus test evaluating the validity of Haplocnemata. Here, we present the first developmental transcriptome of a solifuge (Titanopuga salinarum) and survey copy numbers of the homeobox genes for evidence of systemic duplication. We find that over 70% of the identified homeobox genes in T. salinarum are retained in a single copy, while representatives of the arachnopulmonates retain orthologs of those genes as two or more copies. Our results refute the placement of Solifugae in Haplocnemata. Subsequent reevaluation of putative interordinal morphological synapomorphies among chelicerates reveals a high incidence of homoplasy, reversals, and inaccurate coding within Haplocnemata and other small clades, as well as Arachnida more broadly, suggesting existing morphological character matrices are insufficient to resolve chelicerate phylogeny.

Animals↗
PubMed2000

Reproductive character displacement and speciation in periodical cicadas, with description of new species, 13-year Magicicada neotredecem.

Acoustic mate-attracting signals of related sympatric, synchronic species are always distinguishable, but those of related allopatric species sometimes are not, thus suggesting that such signals may evolve to "reinforce" premating species isolation when similar species become sympatric. This hypothesis predicts divergences restricted to regions of sympatry in partially overlapping species, but such "reproductive character displacement" has rarely been confirmed. We report such a case in the acoustic signals of a previously unrecognized 13-year periodical cicada species, Magicicada neotredecim, described here as a new species (see Appendix). Where M. neotredecim overlaps M. tredecim in the central United States, the dominant male call pitch (frequency) of M. neotredecim increases from approximately 1.4 kHz to 1.7 kHz, whereas that of M. tredecim remains comparatively stable. The average preferences of female M. neotredecim for call pitch show a similar geographic pattern, changing with the call pitch of conspecific males. Magicicada neotredecim differs from 13-year M. tredecim in abdomen coloration, mitochondrial DNA, and call pitch, but is not consistently distinguishable from 17-year M. septendecim; thus, like other Magicicada species, M. neotredecim appears most closely related to a geographically adjacent counterpart with the alternative life cycle. Speciation in Magicicada may be facilitated by life-cycle changes that create temporal isolation, and reinforcement could play a role by fostering divergence in premating signals prior to speciation. We present two theories of Magicicada speciation by life-cycle evolution: "nurse-brood facilitation" and "life-cycle canalization."

Acoustic Stimulation↗
PubMed2003

Detecting correlation between characters in a comparative analysis with uncertain phylogeny.

The importance of accommodating the phylogenetic history of a group when performing a comparative analysis is now widely recognized. The typical approaches either assume the tree is known without error, or they base inferences on a collection of well-supported trees or on a collection of trees generated under a stochastic model of cladogenesis. However, these approaches do not adequately account for the uncertainty of phylogenetic trees in a comparative analysis, especially when data relevant to the phylogeny of a group are available. Here, we develop a method for performing comparative analyses that is based on an extension of Felsenstein's independent contrasts method. Uncertainties in the phylogeny, branch lengths, and other parameters are accommodated by averaging over all possible trees, weighting each by the probability that the tree is correct. We do this in a Bayesian framework and use Markov chain Monte Carlo to perform the high-dimensional summations and integrations required by the analysis. We illustrate the method using comparative characters sampled from Anolis lizards.

Animals↗
PubMed1985

Associations between marker genotypes, halothane reaction, creatine kinase activity and meat quality characters in a sample of German Landrace pigs.

Routine blood typing of German Landrace pedigree populations and an earlier study revealed very low frequencies of the favourable alleles at the marker loci Phi, Pgd and H. The hypothesis was that in this population the whole linkage group of favourable alleles at the halothane and neighbouring marker loci may have been lost as a consequence of intense selection for leanness and type. The present study of 1050 German Landrace pigs at the Relliehausen experimental station, where some effort has been made to maintain a higher frequency of the favourable alleles PhiA (0.48), H- (0.43) and PgdA (0.70) gave quite different results. The frequency of halothane-positive pigs found by using a severe test was only 30%. Only 5.4%, 8.8%, 13.4% and 13.9% of animals with PhiA/A, H-/-, PgdA/A and PhiA/B genotypes respecitively were halothane-positive. Forty to sixty per cent of pigs with these marker genotypes could therefore be expected to be homozygous halothane-negative (N/N) animals. Creatine kinase activity and three selected meat quality characters showed highly significant differences between the A/A and the B/B genotypes for the marker loci Phi and Pgd, with the heterozygotes being intermediate. These differences are greater than those observed between halothane-negative and halothane-positive phenotypes. The only other consistently superior marker genotype in this population was the H blood group genotype H-/-. In contrast to findings from Sweden and Switzerland, the postalbumin locus Po2 and the suppressor locus S for the A-O blood groups did not exhibit useful marker qualities.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗
PubMed1983

Consistency and variability in the character of thyrotrophin receptor antibodies in Graves' disease.

At diagnosis there was no correlation between the uptake of pertechnetate by the thyroid and thyrotrophin receptor antibodies (TRAb) measured as TSH binding inhibitory immunoglobulins in a series of 27 patients with Graves' disease. TRAb were detectable initially in 19 patients, in 11 of these there was a significant positive correlation (P less than 0.05) between serial measurements of pertechnetate uptake and TRAb made during 2 years following diagnosis. In five patients pertechnetate uptake fell with time whilst TRAb levels were maintained or fluctuated. In the remaining three of the 19 patients both measurements were low and did not change during treatment. We conclude that TRAb in any individual patient are a mixture of immunoglobulins of variable effectiveness as thyroid stimulators. In a majority of patients the composition of this mixture remains constant during the course of the illness and the clinical state reflects the levels of TRAb in the blood. In a minority, however, the character of these antibodies may alter with time or there is a change in the responsiveness of the thyroid gland. The general lack of correlation between measurements of thyroid stimulating activity and TSH binding inhibitory immunoglobulins in groups of patients is due to differences between patients in the composition of TRAb.

Female↗
PubMed2005

Co-evolution of male and female reproductive characters across the Scathophagidae (Diptera).

Sperm morphometry is extremely variable across species, but a general adaptive explanation for this diversity is lacking. As sperm must function within the female, variation in sperm form may be associated with variation in female reproductive tract morphology. We investigated this and other potential evolutionary associations between male and female reproductive characters across the Scathophagidae. Sperm length was positively associated with the length of the spermathecal (sperm store) ducts, indicating correlated evolution between the two. No association was found between sperm length and spermathecal size. However, the size of the spermathecae was positively associated with testis size indicating co-evolution between male investment in sperm production and female sperm storage capacity. Furthermore, species with a higher degree of polyandry (larger testes) had longer spermathecal ducts. However, no associations between sperm length or length variation and testis size were found which suggests greater sperm competition sensu stricto does not select for longer sperm.

Animals↗
PubMed1995

Abomasal displacement in the bovine--a review on character, occurrence, aetiology and pathogenesis.

Literature on the subject of character, history, occurrence, causes and pathogenesis of abomasal displacement in the bovine is listed and summarized. The chapter on occurrence is subdivided according to heritibility, sex, age, season, husbandry, milk yield and concomitant diseases. In the chapter on causes special consideration is given to feeding. The chapter on pathogenesis is subdivided according to mechanical influences, disturbances of the abomasal motor activity, collection of gas and dilatation of the abomasum and artificial displacement of the abomasum. Displacement of the abomasum is seen predominantly in the spring in herds with above-average milk yield in dairy cows between the age of 4 and 7 years which have calved within the last month and have ketosis. The etiology and pathogenesis of abomasal displacement are unclear.

Abomasum↗
PubMed1993

Endogenous event-related potentials in obsessive character.

Fifteen healthy subjects with obsessive character (OC) and 15 control subjects were tested for endogenous event-related potentials using the auditory odd ball paradigm. A difference was found in the peak amplitude of the P200 component in response to both stimuli; the subjects with OC had smaller amplitudes than the controls, and the mean amplitude for the 120 to 200 ms latency range was smaller (negative shift) for the OC subjects. In the OC subjects, NA appears to be markedly induced to both rare and frequent stimuli; moreover, the OC subjects may show excessive reactions to selective attention as well as to the process of pattern recognition.

Acoustic Stimulation↗
PubMed1980

Cytological characters, transformation, and ontogenesis of dermal histiocytes and fibroblasts of rats.

Cell morphology of histiocytes and fibroblasts was observed light- and electron microscopically in the subcutaneous connective tissue of unstimulated adult rats. Striking ultrastructural differences between them were noted in the cell surface characters, extent and development of endoplasmic reticula, especially of rough-surfaced ones, and volumes of lysosomal components. Rosetting assays revealed that histiocytes were positive for EA- and EAC-rosette formation and capable of engaging in immunophagocytosis. However, fibroblasts were negative for both rosettings. In the experiments of vital staining with lithium carmine, Fesin phagocytosis, carrageenin granuloma formation, in vivo culture by intraperitoneal implantation of diffusion chambers, and subculture, cytological changes of histiocytes or macrophages and fibroblasts, as well as their transformation, were investigated. Although fibroblasts often simulated histiocytes under certain stimulated conditions, no transformation of fibroblasts into histiocytes was confirmed. Ontogenetically, histiocytes already existed in the subepidermal mesenchyme of rat fetuses before differentiation of undifferentiated mesenchymal cells into fibroblasts and showed no relationship to the fibroblasts. Ultrastructural cell morphology and cultural characteristics of the fetal histiocytes were presented and their possible origin was discussed briefly.

Animals↗
PubMed1975

A non-parametric test for linkage with a quantitative character.

A non-parametric test for the detection of linkage between a quantitative and a mendelian character is described. It can be applied to families of three, two or one generations. The limitations, advantages and disadvantages of this test are discussed.

Alleles↗
PubMed1976

On the method of Penrose of estimating the number of effective factors contributing to a character.

Penrose (1969) presented a method of estimating the number of effective factors contributing to a quantitative character. The method uses samples of parent-child and sib-sib phenotypic values. More detailed mathematical analysis shows that his assertions regarding the method are correct under the assumptions which he made, provided that his phrase 'the same quantitative effect' is interpreted to mean 'makes an equal contribution to the variance'.

Alleles↗
PubMed1978

Search for heterozygosis in quantitative characters.

A method is described of searching for heterozygotes in a quantitative character, based on the idea that heterozygotes have more variable children than homozygotes. The variability in a set of sibs is therefore partitioned into components from the mother and father, using a least squares technique; a large component indicates a probably heterozygous parent. The method is tried out on dermatoglyphic data.

Dermatoglyphics↗