1,116 research outputs found
Growth of the neo-aortic valve after the Ross procedure
Rovira Riera, AntoniPla general d'edifici, en un solar amb tres
façanes.
Fou construĂŻt al segle segle XIX, abans
de 1842.
Tot i que la seva autoria Ă©s encara dubtosa,
ha estat atribuĂŻt a Antoni Rovira Riera
User-Interface Modelling for Blind Users
The design of a user interface usable by blind people sets specific usability requirements that are unnecessary for sighted users. These requirements focus on task adequacy, dimensional trade-off, behaviour equivalence, semantic loss avoidance and device-independency. Consequently, the development of human-computer interfaces (HCI) that are based on task, domain, dialog, presentation, platform and user models has to be modified to take into account these requirements. This paper presents a user interface model for blind people, which incorporates these usability requirements into the above HCI models. A frame-work implementing the model has been developed and implemented in an electronic speaking bilingual software environment for blind or visually impaired people and in an educational system for children with special educational needs
Role of carbonates in the chemical evolution of sodium carbonate-activated slag binders
Multi-technique characterisation of sodium carbonate-activated blast furnace slag binders was conducted in order to determine the influence of the carbonate groups on the structural and chemical evolution of these materials. At early age (<4 days) there is a preferential reaction of Ca2+ with the CO3 2â from the activator, forming calcium carbonates and gaylussite, while the aluminosilicate component of the slag reacts separately with the sodium from the activator to form zeolite NaA. These phases do not give the high degree of cohesion necessary for development of high early mechanical strength, and the reaction is relatively gradual due to the slow dissolution of the slag under the moderate pH conditions introduced by the Na2CO3 as activator. Once the CO3 2â is exhausted, the activation reaction proceeds in similar way to an NaOH-activated slag binder, forming the typical binder phases calcium aluminium silicate hydrate and hydrotalcite, along with Ca-heulandite as a further (Ca,Al)-rich product. This is consistent with the significant gain in compressive strength and reduced porosity observed after 3 days of curing. The high mechanical strength and reduced permeability developed in these materials beyond 4 days of curing elucidate that Na2CO3-activated slag can develop desirable properties for use as a building material, although the slow early strength development is likely to be an issue in some applications. These results suggest that the inclusion of additions which could control the preferential consumption of Ca2+ by the CO3 2â might accelerate the reaction kinetics of Na2CO3-activated slag at early times of curing, enhancing the use of these materials in engineering applications
Collective Dynamics of One-Dimensional Charge Density Waves
The effect of disorder on the static and dynamic behaviour of one-dimensional
charge density waves at low temperatures is studied by analytical and numerical
approaches. In the low temperature region the spatial behaviour of the
phase-phase correlation function is dominated by disorder but the roughness
exponent remains the same as in the pure case. Contrary to high dimensional
systems the dependence of the creep velocity on the electric field is described
by an analytic function.Comment: 4 pages, 4 figure
Electromagnetic Dissociation of Nuclei in Heavy-Ion Collisions
Large discrepancies have been observed between measured Electromagnetic
Dissociation(ED) cross sections and the predictions of the semiclassical
Weiz\"acker-Williams-Fermi(WWF) method. In this paper, the validity of the
semiclassical approximation is examined. The total cross section for
electromagnetic excitation of a nuclear target by a spinless projectile is
calculated in first Born approximation, neglecting recoil. The final result is
expressed in terms of correlation functions and convoluted densities in
configuration space. The result agrees with the WWF approximation to leading
order(unretarded electric dipole approximation), but the method allows an
analytic evaluation of the cutoff, which is determined by the details of the
electric dipole transition charge density. Using the Goldhaber-Teller model of
that density, and uniform charge densities for both projectile and target, the
cutoff is determined for the total cross section in the nonrelativistic limit,
and found to be smaller than values currently used for ED calculations. In
addition, cross sections are calculated using a phenomenological momentum space
cutoff designed to model final state interactions. For moderate projectile
energies, the calculated ED cross section is found to be smaller than the
semiclassical result, in qualitative agreement with experiment.Comment: 28 page
A Proposed Test of the Einstein Theory of Gravitation by Means of an Unshielded Orbiting Gyro Using Passive Telemetry
Coordinated Science Laboratory was formerly known as Control Systems LaboratoryJoint Services Electronics Program / DAAB-07-67-C-0199National Aeronautics and Space Administration / NsG-44
Emission Spectrum of Fundamental Strings: An Algebraic Approach
We formulate a linear difference equation which yields averaged
semi-inclusive decay rates for arbitrary, not necessarily large, values of the
masses. We show that the rates for decays M \to m+\M' of typical heavy open
strings are independent of the masses and , and compute the ``mass
deffect''. For closed strings we find decay rates proportional to , where is the reduced mass of the decy products. Our
method yields exact interaction rates valid for all mass ranges and may provide
a fully microscopic basis, not limited to the long string approximation, for
the interactions in the Boltzmann equation approach to hot string gases.Comment: 35 pages, 3 figure
Nanostructural characterization of geopolymers by advanced beamline techniques
This paper presents the outcomes of a series of beamline-based studies, the results of which are combined to provide a more detailed multiscale understanding of the structure and chemistry of geopolymer binders.
The range of beamline-based characterization techniques which have been applied to the study of geopolymer binders is increasing rapidly; although no single technique can provide a holistic view of binder structure across all the length scales which are of importance in determining strength development and durability, the synergy achievable through the combination of multiple beamline techniques is leading to rapid advances in knowledge in this area. Studies based around beamline infrared and X-ray fluorescence microscopy, in situ and ex situ neutron pair distribution function analysis, and nano- and micro-tomography, are combined to provide an understanding of geopolymer gel chemistry, nano- and microstructure in two and three dimensions, and the influences of seeded nucleation and precursor chemistry in these key areas.
The application of advanced characterization methods in recent years has brought the understanding of geopolymer chemistry from a point, not more than a decade ago, when the analysis of the detailed chemistry of the aluminosilicate binder gel was considered intractable due to its disordered (âX-ray amorphousâ) nature, to the present day where the influence of key compositional parameters on nanostructure is well understood, and both gel structure and reaction kinetics can be manipulated through methods including seeding, temperature variation, and careful mix design.
This paper therefore provides a review outlining the value of nanotechnology â and particularly nanostructural characterization â in the development and optimization of a new class of environmentally beneficial cements and concretes. Key engineering parameters, in particularly strength development and permeability, are determined at a nanostructural level, and so it is essential that gel structures can be analyzed and manipulated at this level; beamline-based characterization techniques are critical in providing the ability to achieve this goal
Fluctuating Fuzzy Funnels
It is well known that a D-string ending on a D3, D5 or D7 brane is described
in terms of a non-commutative fuzzy funnel geometry. In this article, we give a
numerical study of the fluctuations about this leading geometry. This allows us
to investigate issues related to the stability and moduli space of these
solutions. We comment on the comparison to the linearized fluctuations in
supergravity.Comment: 24 pages, 3 figures; v2 references added and correcte
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