[Show abstract][Hide abstract] ABSTRACT: In this work we have studied the effect of different flame retardants on the fire behavior and mechanical properties of epoxy mortars. Flame retardants acting under different mechanisms of action have been compared: phosphate flame retardants as well as magnesium hydroxides and carbonates. Besides the commercial flame retardants we have also used a magnesium basic carbonate obtained from an industrial by-product. The use of an alternative based on an industrial by-product combines an economic and sustainable solution. Different formulations of flame retarded epoxy mortars have been prepared and characterized. The obtained results prove the effectiveness of the tested flame retardants on the improvement of the fire properties of the epoxy mortars without a significant decrease on their mechanical properties.
Full-text · Article · May 2013 · Construction and Building Materials
[Show abstract][Hide abstract] 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.
No preview · Article · Dec 2011 · Applied Thermal Engineering
[Show abstract][Hide abstract] 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.
No preview · Article · Jan 2010 · International Journal of Quantum Chemistry
[Show abstract][Hide abstract] 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.
No preview · Article · Aug 2009 · The Journal of Chemical Physics
[Show abstract][Hide abstract] 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.
No preview · Article · Jul 2008 · The Journal of Chemical Physics
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.
Full-text · Article · Dec 2006 · Journal of Biological Physics
[Show abstract][Hide abstract] 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.
Full-text · Article · Feb 2006 · Physica A: Statistical Mechanics and its Applications
[Show abstract][Hide abstract] 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.
Full-text · Article · Oct 2005 · Physical Review E
[Show abstract][Hide abstract] 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.
[Show abstract][Hide abstract] 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.