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At least 433 records · Page 24Linked to original sources
PubMed1989

Are Drosophila melanogaster populations under a stable geographical differentiation due to the presence of P elements?

In order to simulate the outcome of the P-M status of Eurasian populations of Drosophila melanogaster, the evolution of experimental mixed-strains was monitored for up to 50 generations. The results were compared with the evolution in natura of European populations sampled in 1981-83 and 1986-87 over a similar period of time. Different combinations of P and M' strains, Q and M' strains, M' and M' strains and M and M' strains were set up at 25 degrees C and duplicated at 13 degrees C night-21 degrees C day. The possibility of a change towards a P type only appeared with the introduction of the strong P strain Harwich into Eurasian strains. Strains with strength similar to that of Harwich are not currently found in wild populations. With the introduction of weak P and Q strains of the strength presently observed in western Europe, experimental populations evolved slowly towards a Q state or a weak M' state. M'-M' mixed populations resulted in strong M' strains, as was the case for M-M' populations. In these cases. P sequences were not eliminated. In wild populations both genetic and molecular analyses showed no significant differences, over a five year period, for GD sterility potentials, for total P copy number or for distribution of the full-sized and KP elements. Changes in Eurasian populations are probably taking place at a very low rate and may even have stopped, leading to a quasi-stable differentiation over the continent. During the different steps of progressive invasion of P transposable elements, several deleted elements developed and natural selection may have acted on them. The possibility of the selection of different types of regulatory mechanisms according to the presence of different kinds of derivative elements, leading to a world-wide differentiation between P-Q and M' strains is discussed.

Animals↗
PubMed2005

Experimental implementation of local adiabatic evolution algorithms by an NMR quantum information processor.

Quantum adiabatic algorithm is a method of solving computational problems by evolving the ground state of a slowly varying Hamiltonian. The technique uses evolution of the ground state of a slowly varying Hamiltonian to reach the required output state. In some cases, such as the adiabatic versions of Grover's search algorithm and Deutsch-Jozsa algorithm, applying the global adiabatic evolution yields a complexity similar to their classical algorithms. However, using the local adiabatic evolution, the algorithms given by J. Roland and N.J. Cerf for Grover's search [J. Roland, N.J. Cerf, Quantum search by local adiabatic evolution, Phys. Rev. A 65 (2002) 042308] and by Saurya Das, Randy Kobes, and Gabor Kunstatter for the Deutsch-Jozsa algorithm [S. Das, R. Kobes, G. Kunstatter, Adiabatic quantum computation and Deutsh's algorithm, Phys. Rev. A 65 (2002) 062301], yield a complexity of order N (where N=2(n) and n is the number of qubits). In this paper, we report the experimental implementation of these local adiabatic evolution algorithms on a 2-qubit quantum information processor, by Nuclear Magnetic Resonance.

Journal Article↗
PubMed2002

Excitation fronts in a spatially modulated light-sensitive Belousov-Zhabotinsky system.

The evolution of excitation wave fronts in a spatially modulated light-sensitive Belousov-Zhabotinsky system is investigated experimentally and theoretically. The excitation wave propagates in a thin, quasi-two-dimensional reaction layer, which is illuminated through a periodical gray level mask. The light-induced differences in excitability and velocity give rise to a temporal and spatial modulation of the initially flat fronts. The experimental front evolution is described in the framework of a kinematical theory as developed earlier for nonuniformly curved systems.

Journal Article↗
PubMed2000

Evolution of drug resistance in experimental populations of Candida albicans.

Adaptation to inhibitory concentrations of the antifungal agent fluconazole was monitored in replicated experimental populations founded from a single, drug-sensitive cell of the yeast Candida albicans and reared over 330 generations. The concentration of fluconazole was maintained at twice the MIC in six populations; no fluconazole was added to another six populations. All six replicate populations grown with fluconazole adapted to the presence of drug as indicated by an increase in MIC; none of the six populations grown without fluconazole showed any change in MIC. In all populations evolved with drug, increased fluconazole resistance was accompanied by increased resistance to ketoconazole and itraconazole; these populations contained ergosterol in their cell membranes and were amphotericin sensitive. The increase in fluconazole MIC in the six populations evolved with drug followed different trajectories, and these populations achieved different levels of resistance, with distinct overexpression patterns of four genes involved in azole resistance: the ATP-binding cassette transporter genes, CDR1 and CDR2; the gene encoding the target enzyme of the azoles in the ergosterol biosynthetic pathway, ERG11; and the major facilitator gene, MDR1. Selective sweeps in these populations were accompanied by additional genomic changes with no known relationship to drug resistance: loss of heterozygosity in two of the five marker genes assayed and alterations in DNA fingerprints and electrophoretic karyotypes. These results show that chance, in the form of mutations that confer an adaptive advantage, is a determinant in the evolution of azole drug resistance in experimental populations of C. albicans.

AIDS-Related Opportunistic Infections↗
PubMedDate not supplied

Experimentally contaminated reabsorbable meshes: their evolution in abdominal wall defects.

Contamination by septic materials may represent an important handicap in evaluating the tolerance of reabsorbable prostheses, increasing the possible onset of abdominal fistulae. This is also the case when these materials are used in the treatment of abdominal wall defects. Nevertheless, reabsorbable meshes exist that allow visceroprosthetic contact without risk, thus making it possible to use them in spite of the presence of infection. We have performed this experimental study with the aim of evaluating the behaviour and evolution of polyglycolic acid reabsorbable meshes contaminated by septic materials in the treatment of abdominal wall defects. For this purpose, 40 Wistar rats were operated and distributed into two series of 20 animals each. Massive mesh contamination by fecaloid material did not jeopardise the fact that prostheses were well tolerated in experimental animals throughout the reabsorption process, without increasing the incidence of infection.

Abdominal Muscles↗
PubMed2001

Mass on a spring map for the dripping faucet at low flow rates.

An improved discrete map for the mass-on-a-spring model for the dripping faucet is used to reproduce the evolution of experimental dripping spectra at low flow rates. If an inverse dependence of drop mass on flow rate is supposed, a repeated evolution from period 1 to chaos is obtained. A comparison between discrete relaxation oscillator attractors and dissipative type-web map attractors is carried out. It is found that a dissipative web map accounts for some characteristics of the relaxation oscillator map, thus giving further tools for investigation.

Journal Article↗
PubMed1998

Experimental radiotherapy: a brief history.

Studies of the effects of ionizing radiation on tumors and normal tissues began within weeks of Roentgen's discovery of X rays, and are continuing today. The evolution of these studies reflects both the changing philosophy and sociology of science and the continuing application of new technologies and new knowledge from a diverse range of scientific fields to address the important problem of improving the treatment of cancer. This brief history reviews the evolution of "experimental radiotherapy" over the past century and describes how the development of new technologies and new experimental models influenced this field of study. In addition, it describes critical points at which studies in radiation biology and cancer biology had an impact on research throughout the biomedical sciences.

Animals↗
PubMed1999

Experimental approaches to vocal fold alteration: introduction to the minithyrotomy.

Treatment of challenging laryngeal disorders, such as lamina propria loss or neuromuscular dysfunction, may require novel approaches and techniques. This paper discusses an evolution of experimental techniques for treatment of lamina propria loss and use of the minithyrotomy. These techniques have been used for surgical access for lamina propria substitution, as well as placement of stimulating electrodes. The minithyrotomy is tolerated well by patients, provides access for microscopic instruments with the surgeon's hand close to the tissue of interest, avoids intralaryngeal mucosal incisions, and lines up the direction of dissection in an anterior-to-posterior orientation. This orientation is favorable for particular situations herein discussed. We present anatomic and physiologic concepts relevant to the surgical treatment of lamina propria dysfunction, as well as presenting our clinical experience. This paper is not intended to state how these difficult problems should be handled, but rather, to present our experience in techniques that may prove useful through further development.

Adipose Tissue↗
PubMed2001

Directed evolution of ampicillin-resistant activity from a functionally unrelated DNA fragment: A laboratory model of molecular evolution.

To establish an experimental system to directly observe molecular evolution, a DNA fragment that confers ampicillin resistance on Escherichia coli was cloned from an archaeal genomic DNA. The activity of this clone was enhanced by 50 rounds of directed evolution by using DNA shuffling. Analysis of the evolved DNA fragments shows that two genetic regions have coevolved: One region, which has no obvious ORF, is essential for the activity, whereas the other, which appears to encode a protein, is not essential but enhances the activity of the former region. Analysis of the evolutionary intermediates shows that negative mutations are effectively removed while beneficial mutations accumulate and illustrates how a protein has evolved over the course of the evolution experiments. Although the mechanism of the activity remains unclear, the evolved DNA fragments also confer resistance to other drugs that inhibit bacterial cell-wall synthesis. The present system would serve as an experimental model to study evolutionary dynamics in the laboratory and provide the concept of screening natural libraries to obtain starting materials for directed evolution.

Ampicillin↗
PubMed1998

[Morphometric correlation at the experimental level of renogram with renal arterial stenosis].

RATIONALE: A reduction of the renal size seen with the nephrogram (intravenous urography) has been described in renal artery stenosis. Such reduction, however, has not been quantified and the evolution is unknown in terms of duration of stenosis evolution. METHODS: Experimental study in rats which underwent controlled stenosis of a renal artery, with evaluation, using planimetry of the area and perimeter of the nephrogram, of the consequences such stenosis had at different observation intervals (30, 90 and 180 days). The effects of the stenosis relative to the duration of the experiment is also evaluated. RESULTS: The area and perimeter of the nephrogram become reduced in kidneys with artery stenosis. Besides, this reduction increases over time. CONCLUSION: The area and perimeter of the nephrogram are a useful method to study renal artery stenosis in rats.

Analysis of Variance↗
PubMed1997

Molecular evolution of RNA in vitro.

Experimental studies of RNA evolution in vitro are reviewed in the context of Eigen's 1971 theory and its subsequent extensions. Current research activity and future prospects for using automated molecular biology techniques for in vitro evolution experiments are surveyed.

Evolution, Molecular↗
PubMed1992

[Submicroscopic features of cecal cells in experimental Escherichia infection].

Ultrastructural changes of the caecum cells were studied for the period from 15 minutes to 2 weeks after inoculation using the model of experimental escherichiosis. Evolution processes in relation to different caecum cell populations were followed up submicroscopically. Ultrastructural changes observed evidence derangement of protein and water-salt cell metabolism, immune trends of experimental escherichiosis.

Animals↗
PubMed1997

Evaluation of a murine model of experimental trichomoniasis.

By using a reference strain of Trichomonas vaginalis and the intraperitoneal route for infecting animals, the influence of the strain of mice, the time observation and the inoculation doses were followed in order to standardize the optimal conditions for the evolution of experimental trichomoniasis. Our results suggest that the inoculation of BALB/c mice with 10(7) trichomonads and the semiquantitative assessment at day 15 postinfection of the gross-pathologic changes in the abdominal cavity--peritoneum, spleen, pancreas, stomach and liver--as well as the presence of ascitic fluid and mortality, maybe a suitable laboratory model of trichomoniasis.

Adult↗
PubMed1990

The subtelomeric Y' repeat family in Saccharomyces cerevisiae: an experimental system for repeated sequence evolution.

The subtelomeric Y' repeated sequence families in two divergent strains of the yeast Saccharomyces cerevisiae have been characterized in terms of copy number, location and restriction site differences. The strain YP1 has 26 to 30 Y's that fall into two previously described, long (6.7 kb) and short (5.2 kb), size classes. These Y's reside at 19 of the 32 chromosome ends and are concentrated in the higher molecular weight chromosomes. Five ends contain tandem arrays, each of which has only one size class of Y's. There is restriction site homogeneity among the Y's of YP1 even between size classes. The Y's of strain Y55 contrast sharply with the Y's of YP1 in terms of copy number, location and sequence differences. There are 14 to 16 Y's, both long and short, most of which are found at different chromosome ends than those of YP1. None of these are tandemly arrayed. Four to six of the Y's appear degenerate in that they have homology with a telomere distal end Y' probe but no homology with sequences at the telomere proximal end. The majority of the Y55 Y's have the same restriction sites as in YP1. Despite the conservation of restriction sites among Y's, a great deal of restriction fragment length heterogeneity between the strains is observed. The characterized Y' repeated sequence families provide an experimental system in which repeated sequence interactions and subsequent evolution can be studied.

Biological Evolution↗
PubMed1999

Complex patterns predicted in an in vitro experimental model system for the evolution of molecular cooperation.

An isothermal biochemical in vitro amplification system with two trans-cooperatively coupled amplifying DNA molecules was investigated homogeneously using a hierarchy of kinetic models and as a simplified reaction-diffusion system. In our model of this recently developed experimental system, no reaction mechanism higher than second order occurs, yet numerical simulations show a variety of complex spatiotemporal patterns which arise in response to finite amplitude perturbations in a flow reactor. In a certain domain of the kinetic parameters the system shows self-replicating spots. These spots can stabilize the cooperative amplification in such evolving systems against emerging parasites. The results are of high relevance for experimental studies on these functional in vitro ecosystems in spatially resolved microstructured reactors.

Journal Article↗
PubMed1994

[Expired ethane as a non-invasive marker of the course of experimental multiple organ dysfunction syndrome (MODS)].

UNLABELLED: BACKGROUND AND WORK HYPOTHESIS: The mechanisms of organ damage in MODS are unclear. Given that lipid peroxidation induced by oxygen radicals may play a key role in organ damage, expired ethane, a marker of lipid peroxidation, could be correlated to the entity and evolution of experimental MODS. STUDY DESIGN AND METHODS: Forty wistar male rats (250 +/- 15 g body weight) were intraperitoneally injected with 10 ml of Zymosan mineral oil suspension (2.5%) to provoke MODS. Survival and symptoms were noted daily. On the 2nd, 7th and 14th day the animals underwent thorax CT scanning. CT images were processed to evaluate the relative density of lung parenchima. Expired ethane was measured using mass spectrometer and percentual changes were noted. Relative organ weight (liver and lung) were measured in 2nd, 7th and 14th day. STATISTICAL ANALYSIS: Pearson's linear correlation. RESULTS: The results show that maximal lung damage took place at the same moments as ethane concentrations peaked. A strict correlation (r = 0.93; p < 0.0001) was found between lung density and expired ethane. Strict correlation was found between organ weight, symptoms, survival and ethane production. CONCLUSIONS: Lipid peroxidation, as expressed by ethane production, might be an important cause of organ damage in MODS.

Animals↗