SEARCH · PubMed Health
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
A biological context for understanding human pathogens and parasites emanates from evolutionary studies among tapeworms of the genus Taenia. Human taeniasis and cysticercosis represent archaic associations and remain significant challenges for socioeconomic development, public health and food safety, and a continuing threat to animal production on a global basis.
Domain is a protein architecture in a subunit. It might be defined as a basic unit for structure, function, folding, evolution and design. Different combinations of domains lead to the formation of various tertiary structures with various functions for proteins. The delineation of domains for a protein is important both conceptually and practically, which remains up to date a challenging and unsolved problem. Based on the above definition, a method was previously proposed based on refolding free energy to define continuous domains in proteins. By constructing a residue-residue contact matrix, using correspondence analysis, and then selecting optimal partition function of a protein according to refolding free energy and some empirical scoring functions, a new computer program, PDOM, was developed, which was applicable to both continuous and discontinuous domains. When compared with the manual partition results reported by crystallographers, PDOM has achieved an accuracy of 76% on a test data set including 55 protein structures frequently used. The differences in 13 proteins between PDOM, literature as well as SCOP have been discussed extensively.
A seven-membered microbial community capable of utilising the herbicide Dalapon has been isolated by continuous-flow enrichment culture. The composition of this community has remained remarkably stable over thousands of hours in a Dalapon-limited chemostat. During this period, however, one member of the community, Pseudomonas putida, acquired the ability to grow on Dalapon through the evolution of an extant dehalogenase.
This paper presents the first theoretical study of spatial genetic structure within nonuniformly distributed continuous plant populations. A novel individual-based model of isolation by distance was constructed to simulate genetic evolution within such populations. We found larger values of spatial genetic autocorrelations in highly clumped populations than in uniformly distributed populations. Most of this difference was caused by differences in mean dispersal distances, but aggregation probably also produced a slight increase in spatial genetic structure. Using an appropriate level of approximation of the continuous distribution of individuals in space, we assessed the potential effects of density, seed and pollen dispersal, generation overlapping, and overdominance selection at an independent locus, on fine-scale genetic structure, by varying them separately in a few particular cases with extreme clumping. When selfing was allowed, all these input variables influenced both aggregation and spatial genetic structure. Most variations in spatial genetic structure were closely linked to variations in clumping and/or local density. When selfing was not allowed, spatial genetic structure was lower in most cases.
The mechanisms of innate immunity in vertebrates show certain overall resemblances to immune mechanisms of insects. Two hypotheses have been proposed to explain these resemblances. (1) According to the evolutionary continuity hypothesis, innate immune mechanisms evolved in the common ancestor of vertebrates and insects and have been conserved since that time. (2) In the independent-evolution hypothesis, the mechanisms of innate immunity in vertebrates evolved independently from invertebrate immune mechanisms. Phylogenetic analysis of five gene families (Pelle, Rel, IkappaB, Toll, and TRAF) whose members are involved in NF-kappaB signaling in vertebrates and insects were used to decide between these hypotheses. The phylogenies of the Rel and TRAF families strongly supported independent evolution of immune functions in vertebrates and invertebrates, and, except for a possible case in the Pelle family, orthologous molecules having immune functions in both vertebrates and invertebrates were not found. The results suggest that NF-kappaB represents an ancient, generalized signaling system that has been co-opted for immune system roles independently in vertebrate and insect lineages.
Concerning a discrete-time quantum walk X(t)(d) with a symmetric distribution on the line, whose evolution is described by the Hadamard transformation, it was proved by the author that the following weak limit theorem holds: X(t)(d)/t -->dx/pi(1-x2) square root of (1-2x2) as t --> infinity. The present paper shows that a similar type of weak limit theorem is satisfied for a continuous-time quantum walk X((c) )(t ) on the line as follows: X(t)(c)/t --> dx/pi square root of (1-x2) as t --> infinity. These results for quantum walks form a striking contrast to the central limit theorem for symmetric discrete- and continuous-time classical random walks: Y(t)/square root of (t) --> e(-x2/2)dx/square root of (2pi) as t --> infinity. The work deals also with the issue of the relationship between discrete and continuous-time quantum walks. This topic, subject of a long debate in the previous literature, is treated within the formalism of matrix representation and the limit distributions are exhaustively compared in the two cases.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
Explore the source record for details and available documents.
In complex traffic systems, driving risk often evolves in a continuous and progressive manner prior to crash occurrence. How to effectively represent and analyze such latent risk states remains a central challenge in traffic safety research. In recent years, risk field-based approaches have introduced spatial and spatiotemporal continuous modeling paradigms, providing new perspectives for characterizing the distribution of traffic risk and its dynamic evolution. Motivated by the rapid growth of this research area and the lack of a systematic synthesis, this paper presents a comprehensive review of studies applying risk field theory to driving safety and traffic risk analysis. Following the PRISMA guidelines, relevant literature was collected through multi-database searches and analyzed using a combination of bibliometric analysis and qualitative review. The review systematically summarizes the theoretical foundations, modeling elements, data sources, analytical methods, and application domains of risk field-related research. Particular attention is given to studies that conceptualize traffic risk as a continuous field, complemented by a broader review of traffic risk factor literature to identify key elements and analytical dimensions involved in risk field modeling. On this basis, the paper synthesizes research progress in major application areas, including traffic safety state representation, driving behavior analysis, traffic conflict assessment, and autonomous driving and human-machine cooperative systems. Differences and commonalities among existing studies are compared in terms of modeling strategies, data support, and application scenarios. Through this systematic review, the paper clarifies the main research themes and methodological trends of risk field-based studies, providing a structured framework for understanding the evolution and application of this approach and offering methodological insights for risk perception modeling and safety-oriented decision support in intelligent transportation systems (ITS).
Darwin believed that sexual selection accounts for the evolution of exaggerated male ornaments, such as the sword-like caudal fin extensions of male fishes of the genus Xiphophorus, that appear detrimental to survival. Swordtails continue to feature prominently in empirical work and theories of sexual selection; the pre-existing bias hypothesis has been offered as an explanation for the evolution of swords in these fishes. Based upon a largely morphological phylogeny, this hypothesis suggests that female preference to mate with sworded males arose in ancestrally swordless species, thus pre-dating the origin of the sword itself and directly driving its evolution. Here we present a molecular phylogeny (based on mitochondrial and nuclear DNA sequences) of Xiphophorus which differs from the traditional one: it indicates that the sword originated and was lost repeatedly. Our phylogeny suggests that the ancestor of the genus is more likely to have possessed a sword than not, thus questioning the applicability of the pre-existing bias hypothesis as an explanation for the evolution of this sexually selected trait.
HIV-1 continually replicates in spite of long-term highly active anti-retroviral therapy (HAART) and therefore, it is conceivable that the low level, persistent viral activity could continue to stimulate the hosts immune system despite remaining below the detection limit of the current assays. In this study, we performed a longitudinal analysis of the CD8+ T-cell receptor Vbeta repertoire in HAART-treated and untreated HIV patients. HAART-mediated control of viremia, for up to 18 months, did not prevent similar perturbations within the CD8+ Vbeta repertoire in both study groups as defined by CDR3 spectratyping. Oligoclonal Vbeta expansions, with new dominant CDR3 lengths, were observed throughout the study period. Our findings are compatible with antigen-driven CD8+ immune responses to bursts of replication from a continuously changing viral reservoir, regardless of HAART-mediated suppression of HIV-1 viremia.
Radiation Protection has evolved and will continue to evolve as new information becomes available, as the result of changes in public perception and concern and, perhaps in the future, as a result of enormous expenditures on reducing small risks. In the early part of the last century it was a sense of real danger among medical Practitioners that prompted the first set of exposure limiting suggestions. Addressing medical concerns continued to be the basis of guidance until after the Second World War. An array of new sources and applications led to new approaches, which modified many of the technical issues but didn't result in substantial changes in the dose limits. Fallout from the first generation of thermonuclear weapons in the 1950's resulted in focusing attention on genetic effects, which continued until the middle 1970's. Data from the Japanese Survivor Studies provided the information for risk based recommendations beginning in 1977 and continue to do so today. Both the ICRP and the NCRP are heavily criticized by both those groups of individuals which believe the risk estimates are underestimated and by those which believe the risks are greatly overestimated. Perhaps both organizations can take some comfort in Saint Thomas Aquinas' suggestion, "In medio virtus."
The Wilms' tumor gene, WT1, is a tumor marker for leukemic blast cells. The WT1 expression levels were examined for 57 patients with myelodysplastic syndromes (MDS) (refractory anemia (RA), 35; RA with excess of blasts (RAEB) 14; RAEB in transformation (RAEB-t), six; and MDS with fibrosis, two) and 12 patients with acute myeloid leukemia (AML) evolved from MDS. These levels significantly increased in proportion to the disease progression of MDS from RA to overt AML via RAEB and RAEB-t in both bone marrow (BM) and peripheral blood (PB). WT1 expression levels in PB significantly correlated with the evolution of RAEB or RAEB-t to overt AML within 6 months. Therefore, WT1 expression levels in PB were superior to those in BM for early prediction of the evolution to AML by means of quantitation of the WT1 expression levels. Furthermore, WT1 expression in PB of patients with overt AML evolved from MDS was significantly decreased by effective chemotherapy or allogeneic stem cell transplantation and became undetectable in long-term survivors. These results clearly showed that WT1 expression levels are a tumor marker for preleukemic or leukemic blast cells of MDS and thus reflect the disease progression of MDS. Therefore, monitoring of WT1 expression levels has made continuous assessment of the disease progression of MDS possible, as well as the prediction of the evolution of RAEB or RAEB-t to overt AML within 6 months. The results also showed that quantitation of WT1 expression levels is useful for diagnosis of minimal residual disease of MDS with high sensitivity, thus making it possible to evaluate the efficacy of treatment for MDS.
Previous studies have defined a novel cell culture system in which a modified RNA genome of hepatitis delta virus (HDV) is able to maintain a low level of continuous replication for at least 1 year, using a separate and limited DNA-directed source of mRNA for the essential small delta protein. This mode of replication is analogous to that used by plant viroids. An examination was made of the nucleotide changes that accumulated on the HDV RNA during 1 year of replication. The length of the RNA genome was maintained, except for some single-nucleotide deletions and insertions. There was an abundance of single-nucleotide substitutions, with a 22-fold excess of these being base transitions rather than transversions. Of the detected transitions, at least 70% were consistent with being the consequences of posttranscriptional RNA editing by an adenosine deaminase acting on RNA. The remainder of the changes, including the single-nucleotide insertions and deletions, are likely to be the consequence of misincorporation during transcription. In addition, an intermolecular competition assay was used to show that the majority of the genomes present after 1 year of replication were essentially as competent in replication as the original single HDV RNA sequence that was used to initiate the genome replication. A model is provided to explain how, in this experimental system, the observed single-nucleotide changes were essentially neutral in terms of their effect on the ability of the HDV genome to carry out continued rounds of replication.
Progress in biology has been extremely fast in the second half of the twentieth century in terms of numbers and quality of data. However less attention has been paid to the revision of existing theories on living beings structure and dynamics in development and evolution. Within this frame, the discussion on the very definition of life is lagging in the sometimes ideological debate between mechanistic and holistic views often without serious trials to integrate the overwhelming amount of new data into the different theoretical frameworks. The aim of this short review is to try to define a series of parameters specific of the living state of matter on the basis of existing evidence. The analysis starts from mathematical, physical and experimental studies on DNA constraints in nucleotide distributions and the interactions with proteins in some basic processes of life. The data discussed seem to show that short and long range correlations in DNA, particularly significant in non coding regions and increasing during evolution may have been fixed because of the need of structural landscapes complementarity for DNA-protein recognition and complex dynamics. The need for highly efficient and frequent recognition between the molecules has been extended to gene expression, protein-protein, protein-ligand complex formation and to signal transduction pointing out to the relevance of plasticity on one hand, complementarity on the other. Compartmentalisation and individuality are then taken as critical conditions favouring such processes in the hierarchical networks of all levels, from the cell to organisms, populations, ecosystems, the biosphere. Finally the specific meaning in life of useful (correlated) and disruptive noise is discussed along with the dynamics of evolutionary change in terms of homeorrhetic, plastic maintenance of flexible equilibria continuously challenged by internal and external signals.
Today, Belarus still has to deal with many problems that resulted owing to the extensive contamination of its territory after the Chernobyl accident. These problems remain omnipresent in everyday life of the affected population and have a continuous impact on the economic well being of the country. This paper describes the major changes that have been carried out in the rehabilitation strategies in Belarus since the Chernobyl accident. The evolution of the legal and administrative framework for rehabilitation and actions taken in this context over the past two decades are summarized. The continuing challenges faced by the population in the affected areas are discussed and the key principles underlying rehabilitation strategies (that are both practicable and accepted) are identified. The latter include openness, voluntary participation, collective decision-making and empowerment of local population and professionals. These principles have underpinned the development of recent national and international initiatives that are described.