Aleix Ciudad

Polytechnic University of Catalonia, Barcino, Catalonia, Spain

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Publications (12)22.5 Total impact

  • Aleix Ciudad, Laia Haurie, A. M. Lacasta
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    ABSTRACT: SUMMARY In a fire scenario, huge amounts of heat are generated and high temperatures rapidly achieved in such a way that the integrity of structural materials becomes compromised. One of the aims of passive fire protection is the use of building materials that are able to absorb at least part of that heat and maintain the structural materials under critical temperatures for longer times in order to gain evacuation time. Gypsum panels are commonly used in building walls, but they only absorb heat at temperatures around 110 °C. We use three inorganic fillers, Mg(OH)2, Ca(OH)2 and CaCO3, which undergo endothermic transitions at high temperatures to obtain an improved panel with a richer heat-absorbing profile. With this formulation, the time to reach temperatures of the order of 500 °C, critical for steel and reinforced concrete, is significantly increased. In this work, we focus on the kinetics of the endothermic fillers as an essential ingredient for further spatially extended simulations that include macroscopic heat and mass transfer phenomena or sample heterogeneities. However, kinetics may be affected as well by heat transfer effects that occur at molecular levels. Copyright © 2014 John Wiley & Sons, Ltd.
    Fire and Materials 01/2014; · 1.07 Impact Factor
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    ABSTRACT: Export Date: 11 July 2013, Source: Scopus, CODEN: CBUME, :doi 10.1016/j.conbuildmat.2012.12.012, Language of Original Document: English, Correspondence Address: Haurie, L.; UPC-EPSEB, Av Dr. Marañon 44-50, 08028 Barcelona, Spain; email: laia.haurie@upc.edu, References: Biron, M., Thermosets and composites: Technical information for plastics users (2003) Elsevier Ltd.;
    Construction and Building Materials 01/2013; 42:266-270. · 2.29 Impact Factor
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    ABSTRACT: Passive Fire Protection is currently a field of active interest in building technology. One of the different approaches to obtain a material that provides this protection is to add substances to the initial formulation that are capable to absorb heat when the temperature of the material is increased. This is achieved by means of endothermic reactions that these substances undergo at specified temperatures. In the case of a fire scenario huge amounts of heat are released and such heat absorbing reactions delay the achievement of temperatures that can be critical for structural stability. In this work we specifically analyze the behavior of gypsum, which is commonly used in buildings. In order to enrich its endothermic profile we add magnesium hydroxide, calcium hydroxide and calcium carbonate to the sample. These three alkaline earth components have their heat absorbing peaks located along the temperature domain in a way that the temperature rising is reasonably damped. In this work we find, as the main result, that when these three fillers are added to gypsum, the protection offered by the new combination of materials is significantly improved with respect to the behavior of gypsum alone. Under external heating, the component is able to keep itself under critical temperatures for a longer period. For the theoretical description, we first use non isothermal thermogravimetry (TG) to analyze and characterize the kinetic response of each component of the mixture. We propose a conversion function which is based on the correlation between consecutive reactions in neighboring molecules. The heating rate is included in the model as an analytical variable. Later we perform high temperature tests in a tubular furnace and their corresponding numerical simulations where heat transfer is explicitly carried and mass transfer effects are discussed.
    Applied Thermal Engineering 01/2011; 31:3971-3978. · 2.13 Impact Factor
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    ABSTRACT: We model proteins as continuous electrostatic media immersed in water to investigate charge mediated processes in their interior. We use a Green's function formalism and find analytical expressions for the electrostatic energy in the vicinity of the protein surfaces. We find that due to image charges generated by the protein dielectric medium embedded in water, the effective electrostatic interaction between the two charges in the interior of the protein has an energy larger than the thermal energy. We focus specifically on kinesin to asses the strength of the electrostatic interaction between ATP and ADP molecules. It is known experimentally that ADP expulsion is correlated to ATP kinesin binding while both processes are essential for the kinesin walk. We estimate that the Bjerrum length in the interior of the kinesin dimer protein is of the order of 4 nm and that the pure electrostatic ATP–ADP interaction is of the order of 3–5 kBT.
    International Journal of Quantum Chemistry 01/2010; 110:233-241. · 1.17 Impact Factor
  • Aleix Ciudad, J M Sancho
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    ABSTRACT: Kinesin-1 motion on a microtubule (MT) is still receiving a great attention due to its relevance in understanding molecular motion triggered by adenosine triphosphate (ATP) hydrolysis. Recent experimental data on kinesin-tubulin-nucleotide interactions have clarified some of the conformational details involved in the hydrolysis process [T. Mori et al., Nature (London) 450, 750 (2007)]. Specifically, fluorescence resonance energy transfer was used to measure the affinity of motor domains to tubulin heterodimers. Our work is directly devoted to understand and reproduce the main output of these experiments as well as to go beyond and give a global dynamical picture of the whole hydrolysis cycle. We predict that phosphate groups have the ability to confine to the tubulin domains in order to explain the delay between ATP hydrolysis and head detaching, which seems crucial for the achievement of processivity. In our approach me make use of chemical kinetics complemented with stochastic molecular simulations of the elements involved.
    The Journal of Chemical Physics 08/2009; 131(1):015104. · 3.12 Impact Factor
  • Aleix Ciudad, J M Sancho
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    ABSTRACT: We present a unified phenomenological kinetic framework to analyze the experimental data of several motor proteins (either linear or rotatory). This formalism allows us to discriminate the characteristic times of most relevant subprocesses. Explicitly, internal mechanical as well as chemical times are taken into account and joined together in a full-cycle time where effusion, diffusion and chemical rates, viscoelastic friction, and overdamped motion are considered. This approach clarifies the most relevant mechanisms in a particular motor by using the available experimental data of velocity versus external load and substrate concentration. We apply our analysis to three real molecular motors for which enough experimental data are available: the bacterial flagellar motor [Yoshiyuki et al., J. Mol. Biol. 377, 1043 (2003)], conventional kinesin (kinesin-1) [Block et al., Proc. Natl. Acad. Sci. U.S.A. 100, 2351 (2003)], and a RAN polymerase [Abbondanzieril, Nature (London) 438, 460 (2003)]. Moreover, the mechanism of stalling a motor is revised and split into two different concepts (mechanical and chemical stalling) that shed light to the understanding of backstepping in kinesin-1.
    The Journal of Chemical Physics 07/2008; 128(22):225107. · 3.12 Impact Factor
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    ABSTRACT: Kinesin and related motor proteins utilize ATP fuel to propel themselves along the external surface of microtubules in a processive and directional fashion. We show that the observed step-like motion is possible through time varying charge distributions furnished by the ATP hydrolysis circle while the static charge configuration on the microtuble provides the guide for motion. Thus, while the chemical hydrolysis energy induces appropriate local conformational changes, the motor translational energy is fundamentally electrostatic. Numerical simulations of the mechanical equations of motion show that processivity and directionality are direct consequences of the ATP-dependent electrostatic interaction between the different charge distributions of kinesin and microtubule. Treating proterins as continuous dielectric media and using a Green's function formalism we find analytical expressions for the electrostatic energy in the vicinity of the protein surfaces. We calculate the Bjerrum length in the interior of the protein and analyze its dependence on the charge proximity to the protein interface. We apply these results to kinesin and estimate the pure electrostatic ATP-ADP interaction to be larger than 2k T.
    03/2008;
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    ABSTRACT: Kinesin and related motor proteins utilize ATP fuel to propel themselves along the external surface of microtubules in a processive and directional fashion. We show that the observed step-like motion is possible through time-varying charge distributions furnished by the ATP hydrolysis cycle while the static charge configuration on the microtubule provides the guide for motion. Thus, while the chemical hydrolysis energy induces appropriate local conformational changes, the motor translational energy is fundamentally electrostatic. Numerical simulations of the mechanical equations of motion show that processivity and directionality are direct consequences of the ATP-dependent electrostatic interaction between the different charge distributions of kinesin and the microtubule.
    Journal of Biological Physics 12/2006; 32(5):455-63. · 0.95 Impact Factor
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    ABSTRACT: An inchworm processive mechanism is proposed to explain the motion of dimeric molecular motors such as kinesin.We present here preliminary results for this mechanism focusing on observables like mean velocity, coupling ratio and efficiency versus ATP concentration and the external load F.
    Physica A: Statistical Mechanics and its Applications 02/2006; · 1.68 Impact Factor
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    A Ciudad, A M Lacasta, J M Sancho
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    ABSTRACT: We present a model that allows for the derivation of the experimentally accessible observables: spatial steps, mean velocity, stall force, useful power, efficiency and randomness, etc. as a function of the [adenosine triphosphate] concentration and an external load F. The model presents a minimum of adjustable parameters and the theoretical predictions compare well with the available experimental results.
    Physical Review E 10/2005; 72(3 Pt 1):031918. · 2.31 Impact Factor
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    Aleix Ciudad, José María Sancho
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    ABSTRACT: We analysed published force-velocity data for kinesin using classical Michaelis-Menten kinetic theory and found that the effect of force on the stepping rate of kinesin is analogous to the effect of a mixed inhibitor in classical inhibition theory. We derived an analytical expression for the velocity of kinesin (the stepping rate, equal to the ATP turnover rate) as a function of ATP concentration and force, and showed that it accurately predicts the observed single molecule stepping rate of kinesin under a variety of conditions.
    Biochemical Journal 09/2005; 390(Pt 1):345-9. · 4.65 Impact Factor
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    ABSTRACT: Substances undergoing endothermic reactions are of wide interest in the de- velopment of materials oriented to fire passive protection. These components can be used as aggregates in usual building materials in order to improve the response under high temperature scenarios. The mechanism of action is based on the absorption of part of the generated heat of combustion by the corre- sponding endothermic reactions. The materials can be formulated in order to spread the position of absorbing peaks along the overall temperature domain. In order to achieve the mentioned goal it is necessary to perform an exhaustive characterization of the different chemical substances. Specifically we analyze the underlying kinetic behavior under different heating rates as an essential ingredi- ent to model heat transfer phenomena in spatially extended systems. On the one hand we perform a series of experiments with different formulations, aggregate sizes and heating rates. On the other hand we carry out numerical simulations in order to compare the results with the experimental data.