SEARCH · PubMed Health

Results for “Experimental evolution”

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.

At least 1,693 records · Page 94Linked to original sources

PubMed2002

Observation of solitary elastic surface pulses.

The formation of solitary elastic surface pulses from laser-generated pulselike initial conditions is reported. The nonlinearity of the medium is compensated by both normal dispersion and anomalous dispersion, which were realized by coating isotropic fused silica by a metal and titanium nitride film, respectively. As an anisotropic material, silicon covered with an oxide layer was studied. The experimental results agree with numerical simulations carried out with a nonlocal evolution equation, which describes nonlinear propagation of surface acoustic waves in a dispersive medium.

Journal Article↗

PubMed2004

Test by NMR of the phase coherence of electromagnetically induced transparency.

Electromagnetically induced transparency is an effect observed in atomic systems, originating from quantum interference, in which electromagnetic transitions to and from a certain quantum state become suppressed. This dark state is also characterized by a quantum phase, relative to other states, which theoretically should stop evolving, but remain phase coherent, during transparency. We test this theoretical prediction using techniques developed for liquid-state nuclear magnetic resonance quantum computation, applied to a spin-7/2 nuclear spin system. A sequence of quantum operations is applied to create the dark state, and during transparency its phase evolution is measured relative to a reference state using Ramsey interferometry. Experimental measurements of the fringe visibility are in excellent agreement with theoretical expectations, taking into account measured decoherence rates.

Journal Article↗

PubMed2004

Ultrafast molecular dissociation of water in ice.

Using x-ray emission and photoemission spectroscopies to measure the occupied valence levels in a thin crystalline ice film, we resolve the ionization-induced dissociation of water in ice on a femtosecond time scale. Isotope substitution confirms proton transfer during the core-hole lifetime in spite of the nonresonant excitation. Through ab initio molecular dynamics on the core-ionized state, the dissociation and spectrum evolution are followed at femtosecond intervals. The theoretical simulations confirm the experimental analysis and allow for a detailed study of the dissociative reaction path.

Biophysical Phenomena↗

PubMed1994

The Unsaturation of Membrane Lipids Stabilizes Photosynthesis against Heat Stress.

The effect of the unsaturation of glycerolipids of thylakoid membranes on the heat tolerance of the photosynthetic evolution of oxygen was studied in vivo by mutation and transformation of fatty-acid desaturases in the cyanobacterium Synechocystis PCC6803. The experimental results indicate that elimination of dienoic lipid molecules decreases, to a small but distinct extent, the heat tolerance of photosynthetic oxygen evolution, but that elimination of trienoic lipid molecules has no effect on the heat tolerance. This conclusion contrasts with the previous hypothesis that the heat tolerance of photosynthesis is enhanced upon an increase in the level of saturation of membrane lipids. It is also shown that light does not affect the nature of the effect of lipid unsaturation on the heat tolerance of photosynthesis.

Journal Article↗

PubMed2007

Three-dimensional spatial and temporal temperature imaging in gel phantoms using backscattered ultrasound.

Thermal therapies such as radio frequency, heated saline, and high-intensity focused ultrasound ablations are often performed suboptimally due to the inability to monitor the spatial and temporal distribution of delivered heat and the extent of tissue necrosis. Ultrasound-based temperature imaging recently was proposed as a means to measure noninvasively the deposition of heat by tracking the echo arrival time shifts in the ultrasound backscatter caused by changes in speed of sound and tissue thermal expansion. However, the clinical applicability of these techniques has been hampered by the two-dimensional (2-D) nature of traditional ultrasound imaging, and the complexity of the temperature dependence of sound speed for biological tissues. In this paper, we present methodology, results, and validation of a 3-D spatial and temporal ultrasound temperature estimation technique in an alginate-based gel phantom to track the evolution of heat deposition over a treatment volume. The technique was experimentally validated for temperature rises up to approximately 10 degrees C by comparison with measurements from thermocouples that were embedded in the gel. Good agreement (rms difference = 0.12 degrees C, maximum difference = 0.24 degrees C) was observed between the noninvasive ultrasound temperature estimates and thermocouple measurements. Based on the results obtained for the temperature range studied in this paper, the technique demonstrates potential for applicability in image guidance of thermal therapy for determining the location of the therapeutic focal spot and assessing the extent of the heated region at subablative intensities.

Algorithms↗

PubMed2001

Real-space imaging of nucleation and growth in colloidal crystallization.

Crystallization of concentrated colloidal suspensions was studied in real space with laser scanning confocal microscopy. Direct imaging in three dimensions allowed identification and observation of both nucleation and growth of crystalline regions, providing an experimental measure of properties of the nucleating crystallites. By following their evolution, we identified critical nuclei, determined nucleation rates, and measured the average surface tension of the crystal-liquid interface. The structure of the nuclei was the same as the bulk solid phase, random hexagonal close-packed, and their average shape was rather nonspherical, with rough rather than faceted surfaces.

Journal Article↗

PubMed1986

Time-of-flight MR flow imaging: selective saturation recovery with gradient refocusing.

A novel magnetic resonance flow-imaging technique is presented and its suitability evaluated for both qualitative and quantitative imaging of flow. The method is derived from a selective saturation-recovery scheme consisting of a tagging and detection pulse followed by a bipolar read gradient. The detrimental phase effects causing signal loss at fast flow are shown to be greatly reduced because of the absence of a 180 degrees pulse and its associated section-selection gradient. The second loss mechanism intrinsic to 180 degrees spin echoes, the washout of excited spins between excitation and detection pulse, likewise is not present with the discussed technique. Assuming a parabolic flow profile, the authors calculated the signal evolution curve and found it to be in agreement with the experimental washout curve. The technique is shown to provide high-intensity signals for arteries such as carotid and vertebral arteries. Arteries and veins can be differentiated by judiciously choosing interpulse intervals or by alternating selective and nonselective tagging pulses.

Blood Flow Velocity↗

PubMed1981

Cellophane perinephritic hypertension in the dog: some biochemical, hemodynamic and pathological characteristics.

Perinephritic hypertension was induced in mongrel dogs by cellophane encapsulation of one kidney and simultaneous contralateral nephrectomy. Systolic blood pressure began to rise before diastolic blood pressure and both reached maximal values 3 weeks after surgery, their levels becoming stable thereafter up to the end of the study (20 weeks). Cardiac contractility, measured by the index dp/dt/P40 (rate of rise of isovolumic left intraventricular pressure at a developed left ventricular pressure of 40 mm Hg) was not altered during the evolution of hypertension; heart weight and left ventricular thickness were increased. Plasma renin activity markedly decreased in the chronic phase and plasma urea and creatinine levels rised initially in a moderate but significant way, thereafter remaining stable. The structure of the wrapped kidney remained normal 20 weeks after surgery, when microscopic arterial lesions were seen in other organs. The comparison of the evolution of this hypertensive model with other more commonly used renal experimental hypertension types allows us to conclude that cellophane perinephritic hypertension in the dog must be considered as an individual entity.

Animals↗

PubMed1994

Synthetic fibronectin peptides suppress arthritis in rats by interrupting leukocyte adhesion and recruitment.

In an experimental model of arthritis, increased leukocyte adhesion is associated with the evolution of acute and chronic synovial inflammation. Whereas peripheral blood mononuclear cells (PBMC) from control animals bind minimally to fibronectin matrices, PBMC from animals receiving arthropathic doses of bacterial cell walls demonstrate increased integrin mRNA expression and enhanced adhesion. To determine whether this augmented adhesion was causal in the development of synovial pathology, peptides synthesized from several fibronectin domains which inhibited leukocyte adhesion in vitro were administered to arthritic animals either as free peptides or coupled to a carrier molecule. Not only were peptides containing either the RGD or CS-1 cell-binding domains inhibitory to chronic synovial pathology (articular index = 10.5 +/- 0.3 for untreated animals compared to 1.25 +/- 0.25 for RGD and 2.5 +/- 0.7 for CS-1), but three peptides synthesized from the carboxy-terminal 33-kD heparin-binding domain of fibronectin were also found to significantly inhibit leukocyte recruitment and the evolution of arthritis. Based on these data, which are the first to explore the therapeutic potential of heparin-binding fibronectin peptides in chronic inflammation, it appears that antagonism of cellular adhesion and recruitment by fibronectin peptides may provide an important mechanism for modulating the multi-step adhesion process and attenuating aberrant inflammatory responses.

Amino Acid Sequence↗

PubMed2004

FunnyBase: a systems level functional annotation of Fundulus ESTs for the analysis of gene expression.

BACKGROUND: While studies of non-model organisms are critical for many research areas, such as evolution, development, and environmental biology, they present particular challenges for both experimental and computational genomic level research. Resources such as mass-produced microarrays and the computational tools linking these data to functional annotation at the system and pathway level are rarely available for non-model species. This type of "systems-level" analysis is critical to the understanding of patterns of gene expression that underlie biological processes. RESULTS: We describe a bioinformatics pipeline known as FunnyBase that has been used to store, annotate, and analyze 40,363 expressed sequence tags (ESTs) from the heart and liver of the fish, Fundulus heteroclitus. Primary annotations based on sequence similarity are linked to networks of systematic annotation in Gene Ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) and can be queried and computationally utilized in downstream analyses. Steps are taken to ensure that the annotation is self-consistent and that the structure of GO is used to identify higher level functions that may not be annotated directly. An integrated framework for cDNA library production, sequencing, quality control, expression data generation, and systems-level analysis is presented and utilized. In a case study, a set of genes, that had statistically significant regression between gene expression levels and environmental temperature along the Atlantic Coast, shows a statistically significant (P < 0.001) enrichment in genes associated with amine metabolism. CONCLUSION: The methods described have application for functional genomics studies, particularly among non-model organisms. The web interface for FunnyBase can be accessed at http://genomics.rsmas.miami.edu/funnybase/super_craw4/. Data and source code are available by request at jpaschall@bioinfobase.umkc.edu.

Animals↗

PubMed2002

Long terminal repeat retrotransposons of Oryza sativa.

BACKGROUND: Long terminal repeat (LTR) retrotransposons constitute a major fraction of the genomes of higher plants. For example, retrotransposons comprise more than 50% of the maize genome and more than 90% of the wheat genome. LTR retrotransposons are believed to have contributed significantly to the evolution of genome structure and function. The genome sequencing of selected experimental and agriculturally important species is providing an unprecedented opportunity to view the patterns of variation existing among the entire complement of retrotransposons in complete genomes. RESULTS: Using a new data-mining program, LTR_STRUC, (LTR retrotransposon structure program), we have mined the GenBank rice (Oryza sativa) database as well as the more extensive (259 Mb) Monsanto rice dataset for LTR retrotransposons. Almost two-thirds (37) of the 59 families identified consist of copia-like elements, but gypsy-like elements outnumber copia-like elements by a ratio of approximately 2:1. At least 17% of the rice genome consists of LTR retrotransposons. In addition to the ubiquitous gypsy- and copia-like classes of LTR retrotransposons, the rice genome contains at least two novel families of unusually small, non-coding (non-autonomous) LTR retrotransposons. CONCLUSIONS: Each of the major clades of rice LTR retrotransposons is more closely related to elements present in other species than to the other clades of rice elements, suggesting that horizontal transfer may have occurred over the evolutionary history of rice LTR retrotransposons. Like LTR retrotransposons in other species with relatively small genomes, many rice LTR retrotransposons are relatively young, indicating a high rate of turnover.

Animals↗

PubMedDate not supplied

Indirect evidence for a very fast recovery kinetics of chlorophyll-aII in spinach chloroplasts.

The 690 nm absorption change reflecting the turnover of the system-II-reaction center chlorophyll, Chl-aII (often referred to as P 680), has been investigated under different experimental conditions in spinach chloroplasts. A comparison was made with oxygen evolution and with absorption changes of Chl-aI measured at 703 nm, both indicating the number of electrons produced by system II. It was found: 1. The dependency on actinic flash intensity of the initial amplitudes of the measured 690 nm absorption change, deltaalpha0(Chl-aII) in Tris-washed chloroplasts is similar to that for the total amplutude of the 703 nm absorption change, deltaalpha0(Chl-aI) in normal chloroplasts, and can be described by an exponential function. On the other hand, deltaalphao(chl-aII) in normal chloroplasts exhibits a more complex biphasic dependency and much higher flash intensities are required for saturation. 3. Unver repetitive flash group excitation and in the presence of an ADRY(= acceleration of the deactivation reactions of the water-splitting enzyme system Y)-reagent the initial amplitude of the 690 nm absorption change oscillates in the same characteristic pattern as the oxygen evolution. 4. The initial amplitude of the 690 nm absorption change, deltaalpha0(Chl-aII), IN Tris-washed chloroplasts becomes significantly smaller (more than 50%) by the addition of system-II-electron donors (benzidine, p-phenylendiamine, tetraphenylboron), whereas the total amplitude of the 703 nm absorption change, detalalpha0)Chl-aI) increases 3-4-fold. In order to explain these results, the existance of a very fast reduction kinetics of Chl-aII+ is postulated, which is not detectable by our measuring equipment. The half time of this reaction is less than or equal to mus. Reaction centers with the very gast "undetected" Chl-aII+-reduction are photochemically transformed into slower one by double hit processes with a comparatively low quantum yield. Furthermore, it is inferred, that the dark recovery kinetics of Chl-aII is dependent on be charge accumulation state of the watersplitting enzyme system Y. This phenomenon is shown to explain also the oscillation pattern of delayed fluorescence. On the basis of the present results two alternative reaction schemes for the functional organization of the electron transport on the donor side of system II are discussed.

Chlorophyll↗

PubMed2006

Immune pathogenesis of paroxysmal nocturnal hemoglobinuria.

Somatic mutation in the PIG-A gene is the initial event in the pathogenesis of paroxysmal nocturnal hemoglobinuria (PNH), but the pathophysiologic mechanisms leading to clonal expansion remain unclear. The intricate association of PNH with immune-mediated bone marrow failure syndromes, including aplastic anemia (AA), suggests an immunologic selection process for the glycosylphosphatidyl-inositol (GPI)-deficient hematopoietic clone. The mechanism for the growth advantage of PNH cells may be related to the nature of the antigens targeted by the immune response or to the function of immunomodulatory GPI-anchored proteins on the surface of the hematopoietic target cells. Alternative theories of PNH evolution may include intrinsic properties of the mutated cells, but the experimental evidence is largely lacking. Elucidation of the pathogenesis of PNH may provide key information about the causes of idiopathic AA and help understand the regulation of the hematopoietic stem cell compartment.

Anemia, Aplastic↗

PubMed1995

Purification and preliminary sequencing of Tc-45, an immunodominant Trypanosoma cruzi antigen: absence of homology with cruzipain, cruzain, and a 46-kilodalton protein.

In spite of being separated by more than 20 million years of evolution, the murine and human immune systems share extensive similarities. Thus, experimental results obtained with the murine model may have predictive value for human Chagas' disease. Challenge of the H-2 congenic mouse stains A.SW (H-2s) and A.CA (H-2f) with Trypanosoma cruzi yields different results. The A.CA animals die approximately 12 days postinfection, while A.SW mice survive indefinitely. A 45-kD protein (Tc45), an antigen differentially recognized by the A.SW strain, is present in cultured epimastigotes and blood trypomastigotes. We describe here its purification from epimastigotes. The presence of Tc45 was monitored and a single band was detected. Since the molecular weights of Tc45, cruzipain, cruzain, and a 46-kD parasite polypeptide are similar, it was important to determine if these molecules are related. A complete lack of homology was observed when the sequence of cruzain, cruzipain, and the 46-kD polypeptide were compared with the preliminary sequence of Tc45.

Amino Acid Sequence↗

PubMed1990

Liquid ventilation during early development: theory, physiologic processes and application.

Clinical statistics indicate that extrauterine viability becomes increasingly compromised at earlier gestational ages. It is generally accepted that this trend is largely due to the immaturity of the pulmonary system. Investigators have attributed the high degree of instability during the perinatal period of the preterm infant to incomplete biochemical development of the lung. Whereas disruption in biochemical development results in alveolar surfactant deficiency, elevated interfacial tension, alveolar instability, and inadequate pulmonary gas exchange, it is possible that incomplete development of other components within the pulmonary as well as other organ systems may also influence ultimate extrauterine viability of the preterm neonate. However, until recently, little was known in this regard as conventional gas ventilation techniques have been unsuccessful in supporting a stable animal preparation for controlled experimental investigation of physiologic processes before approximately 85% gestation. In the early 1970s, the concept of liquid ventilation was applied to the preterm and newborn animal. Since this time, technological advances in liquid delivery systems have established this experimental approach as a viable means to support the preterm infant during the transition from the liquid-filled intrauterine to gas-filled extrauterine environment. Reduction of surface tension, improvement in lung mechanics, effective pulmonary gas exchange, acid-base balance, improved distribution of pulmonary blood flow, and cardiovascular stability in the liquid ventilated preterm animal support the use of this alternative method of ventilation as a valuable experimental tool and potential clinical therapeutic modality during early development. The evolution of this approach is presented in this article.

Animals↗

PubMedDate not supplied

[Endothelial effects of radial keratotomy in a non-human primate].

The study of the endothelial repercussion of radial keratotomy has been done on 33 corneas of 21 non human primates, using Scanning Electronic Microscope. Various lesions has been observed; the relationship between these lesions and the surgery parameters have been studied. One can conclude that the lesions are constant; their severity is related to the number and the depth of the incisions; as for their evolution, they do not seem to worsen with time during the experimental study (1 hour to 18 months).

Animals↗

PubMed1977

Ultrastructural study of methionine sulfoximine-induced Alzheimer type II astrocytosis.

An ultrastructural study of cerebral cortex was performed in rats during the preictal period following the administration of the convulsant methionine sulfoximine (MSO). The morphologic changes were restricted to astrocytes and consisted of cytoplasmic enlargement, mitochondrial and rough endoplasmic reticulum proliferation, accumulation of glycogen, development of cisternal and saccular smooth endoplasmic reticulum, nuclear chromatin clumping, and hydropic degenerative changes. These findings resemble those seen in experimental ammonia encephalopathy, suggesting an important role of ammonia in the evolution of these morphologic changes. The findings, moreover, suggest that the primary effect of MSO is on astrocytes and that abnormalities in astrocytes may play a role in the development of MSO-induced seizures.

Alzheimer Disease↗

PubMed1978

Electroretinography in pigmented rats with tapeto-retinal degeneration.

We studied tapeto-retinal degeneration in the offspring of Royal College of Surgeons (RCS) and Wistar albino rats. Normal ERG values vary according to skin pigmentation: thresholds and implicit times are different. We believe the best experimental material is to be found in the affected pigmented offspring. Evolution of the degeneration over more than 9 months has been observed before extinction and the expressivity of the disease varies from one individual to another. This animal model closely resembles the ERG findings observed clinically in certain pigmentary degenerations of the retina.

Albinism↗