513 research outputs found

    Possible observation of parametrically amplified coherent phasons in K0.3MoO3 using time-resolved extreme-ultraviolet ARPES

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    We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) in the Extreme Ultraviolet (EUV) to measure the time- and momentum-dependent electronic structure of photo-excited K0.3MoO3. Prompt depletion of the Charge Density Wave (CDW) condensate launches coherent oscillations of the amplitude mode, observed as a 1.7-THz-frequency modulation of the bonding band position. In contrast, the anti-bonding band oscillates at about half this frequency. We attribute these oscillations to coherent excitation of phasons via parametric amplification of phase fluctuations.Comment: 4 figure

    Comparing extrapolations of the coronal magnetic field structure at 2.5 solar radii with multi-viewpoint coronagraphic observations

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    The magnetic field shapes the structure of the solar corona but we still know little about the interrelationships between the coronal magnetic field configurations and the resulting quasi-stationary structures observed in coronagraphic images (as streamers, plumes, coronal holes). One way to obtain information on the large-scale structure of the coronal magnetic field is to extrapolate it from photospheric data and compare the results with coronagraphic images. Our aim is to verify if this comparison can be a fast method to check systematically the reliability of the many methods available to reconstruct the coronal magnetic field. Coronal fields are usually extrapolated from photospheric measurements typically in a region close to the central meridian on the solar disk and then compared with coronagraphic images at the limbs, acquired at least 7 days before or after to account for solar rotation, implicitly assuming that no significant changes occurred in the corona during that period. In this work, we combine images from three coronagraphs (SOHO/LASCO-C2 and the two STEREO/SECCHI-COR1) observing the Sun from different viewing angles to build Carrington maps covering the entire corona to reduce the effect of temporal evolution to ~ 5 days. We then compare the position of the observed streamers in these Carrington maps with that of the neutral lines obtained from four different magnetic field extrapolations, to evaluate the performances of the latter in the solar corona. Our results show that the location of coronal streamers can provide important indications to discriminate between different magnetic field extrapolations.Comment: Accepted by A&A the 20th of May, 201

    Chemical stabilization of dentin extracellular matrix detected by FEISEM and EDS

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    Dentin collagen degradation represents an important limit to the stability of the resin-dentin interface in conservative dentistry. In vitro application of 1-ethyl-3-(3- dimethylaminopropyl)-carbodiimide hydrochloride (EDC), an imide-based zerolength cross-linking agent, showed [1] the capability to inactivate the endogenous dentin matrix metalloproteinases and to increase the mechanical properties of the organic dentin extracellular matrix. In the present study, a correlative high resolution SEM (FEISEM) with an Energy Dispersive Spectroscopy (EDS) analysis was performed to characterize the fine structure and the chemical modifications of EDCstabilized human dentin, after compressive mechanical stress (Chewing Simulation - CS). Demineralized human dentin disks were assigned to four groups: (1) artificial saliva at 37°C for 30 days; (2) pre-treatment with 0.5M EDC for 60 s, then as in Group 1; (3) CS challenge for 30 days; (4) 0.5M EDC as in Group 2 and CS challenge as in Group 3. The FEISEM analysis revealed that the EDC-pretreatment made the collagen fibrillar network more compact, in comparison to controls and this effect was particularly evident on the surface of not stressed samples. Along with the increased compactness of the collagen complex, the EDS analysis showed a significant semi-quantitative increase of sulfur. The presence of chlorine in EDC treated samples was also detectable. The increase of sulfur, not present in EDC composition, suggests a possible implication of sulfate glycosaminoglycans containing proteoglycans during the extracellular matrix stabilization, as also suggested by the concurrent increase of the amorphous matrix. The presence of chlorine in EDC treated samples induces to conclude that the activity of the cross-linking agent is stable even after the experimental time intervals

    Metabolic and physiologic improvements from consuming a paleolithic, hunter-gatherer type diet

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    Background: The contemporary American diet figures centrally in the pathogenesis of numerous chronic diseases-'diseases of civilization'. We investigated in humans whether a diet similar to that consumed by our preagricultural hunter-gatherer ancestors (that is, a paleolithic type diet) confers health benefits. Methods: We performed an outpatient, metabolically controlled study, in nine nonobese sedentary healthy volunteers, ensuring no weight loss by daily weight. We compared the findings when the participants consumed their usual diet with those when they consumed a paleolithic type diet. The participants consumed their usual diet for 3 days, three ramp-up diets of increasing potassium and fiber for 7 days, then a paleolithic type diet comprising lean meat, fruits, vegetables and nuts, and excluding nonpaleolithic type foods, such as cereal grains, dairy or legumes, for 10 days. Outcomes included arterial blood pressure (BP); 24-h urine sodium and potassium excretion; plasma glucose and insulin areas under the curve (AUC) during a 2 h oral glucose tolerance test (OGTT); insulin sensitivity; plasma lipid concentrations; and brachial artery reactivity in response to ischemia. Results: Compared with the baseline (usual) diet, we observed (a) significant reductions in BP associated with improved arterial distensibility (À3.1±2.9, P ¼ 0.01 and þ 0.19±0.23, P ¼ 0.05);(b) significant reduction in plasma insulin vs time AUC, during the OGTT (P ¼ 0.006); and (c) large significant reductions in total cholesterol, low-density lipoproteins (LDL) and triglycerides (À0.8±0.6 (P ¼ 0.007), À0.7±0.5 (P ¼ 0.003) and À0.3±0.3 (P ¼ 0.01) mmol/l respectively). In all these measured variables, either eight or all nine participants had identical directional responses when switched to paleolithic type diet, that is, near consistently improved status of circulatory, carbohydrate and lipid metabolism/physiology. Conclusions: Even short-term consumption of a paleolithic type diet improves BP and glucose tolerance, decreases insulin secretion, increases insulin sensitivity and improves lipid profiles without weight loss in healthy sedentary humans
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