1,721,016 research outputs found
Thermodynamic Properties of Alkali Metals
No full textAbstract - We have calculated the equation of state at O K for the various alkali metals starting from a theoretical description of the volume dependence of their dynamical matrix. We also obtain a detailed knowledge of the individual Grueneisen parameters which also allow us to calculate temperature effects like the thermal pressure and the thermal expansion coefficient. The agreement with the experimental data is satisfactory and it can be considered as a test of validity of the quasi-harmonic approximation
In vitro validation of a passive left ventricular assist device
No full textCardiogenic shock, represents a dangerous consequence of myocardial infarction, severe cardiomyopathy, or mechanical obstruction or compression of the heart. The mismatch between the elastances of the failed left ventricle and the normal aorta limits the energy transfer between the pump and the arterial load worsening the just critical condition.. Since it is not possible to increase the ventricular elastance, a possible intervention to recover a better mechanical coupling is to decrease the aortic one, by inserting a dumper in aorta.
We tested this proposal by inserting an intra-aortic balloon filled with helium in a previously validated simulator of the cardiovascular system. Different conditions of mismatch between ventricle and aorta and different filling pressures of the balloon were simulated. Aortic pressures and flows were measured with a polygraphic system (EP-12, Esaote, Italy) and an AD converter (Light System, Sparkbio, Italy).
Results show that increasing step by step the helium pressure in the balloon, the shape of arterial pressure pulse changes both for systolic and diastolic values, with an overall increasing of the mean pressure. The maximum positive effect is obtained with a balloon pressure slightly higher than the mean aortic one.
This “pure passive biomechanical approach” seems to be useful and easy to apply. To evaluate the net benefit in clinical conditions an “in vivo” protocol is in progress and preliminary results support our in-vitro findings
Synthesis of alkaline-earth hexaborides, MB6 (M = Ca, Ba, Sr), by a solid state metathesis (SSM) reaction
No full textA new synthetic pathway for alkaline-earth hexaborides has been developed. This method involves a solid state metathesis between an alkaline-earth (Ca, Ba, Sr) salt and MgB2, which can be performed at relatively low temperatures, without any catalyst and with no hazardous side products. The proposed protocol shows a good reproducibility and a much lower energy consumption (and, consequently, lower costs) than any known traditional synthesis. In view of the possibility of using alkaline-earth hexaborides as overdopants in MgB2 superconductors in order to enhance its transport properties in magnetic field, several MgB2 + MB6 bulk composites were obtained with the “Reactive Liquid Mg Infiltration” (Mg-RLI) technique, and characterized by X-ray Powder Diffraction (XRPD) and Scanning Electron Microscopy (SEM) methods
MgB2: A superconductor produced and densified bu novel solid-liquid reactions of Mg and B
No full textAnalysis of the minority crystalline phases in bulk superconducting MgB2 obtained by reactive liquid Mg infiltration
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Experimental and Numerical Investigation of the Levitation Force Between Bulk Permanent Magnet and MgB2 disk
No full textThe experimental investigation of the levitation force between a PM and MgB2 disk prepared by means of the Reactive Mg Liquid Infiltration is presented. Both FC and ZFC levitation in the temperature range form 21 K to 37 K are considered. The long term behaviour of the levitation force is also investigated. A numerical model is developed in order to investigate the electrodynamics of levitation. The hysteretic behaviour of the levitation force is related to the dynamic of current penetration inside the MgB2 disk by means of the numerical model
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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