Quasi-chemical study of Be2+^{2+}(aq) speciation

Be$^{2+}$(aq) hydrolysis can to lead to the formation of multi-beryllium clusters, but the thermodynamics of this process has not been resolved theoretically. We study the hydration state of an isolated Be$^{2+}$ ion using both the quasi-chemical theory of solutions and ab initio molecular dynamics. These studies confirm that Be$^{2+}$(aq) is tetra-hydrated. The quasi-chemical approach is then applied to then the deprotonation of Be(H_2O)_4^{2+}} to give BeOH(H_2O)_3{}^{+}}. The calculated pK$_a$ of 3.8 is in good agreement with the experimentally suggested value around 3.5. The calculated energetics for the formation of BeOHBe$^{3+}$ are then obtained in fair agreement with experiments.Comment: 11 pages, 3 figure

Analysis of the energy performance of a ground source heat pump system after five years of operation

[EN] GeoCool plant was the result of a EU project whose main purpose was to adapt ground coupled heat pump technology to coolingdominatedareas. The executionofthis experimentalplant was completedatthe end of year 2004, starting on February 2005 the regular operation of the air conditioning system. Since then, GeoCool facility has been monitored by a network of sensors characterizing its most relevant parameters. Several aspects of the performance and behaviour of the system during its first operational year were presented on a previous paper. This paper presents the energy performance measurements of GeoCool ground coupled heat pump system acquired during five years of operation as well as the evolution of the return water temperature from the ground as a representative of the ground temperature. The analysis of the experimental results shows that the system energy performance is maintained through the years with no appreciable impact on ground thermal responseThis work has been supported by FP7 project "Advanced ground source heat pump systems for heating and cooling in Mediterranean climate" (GROUND-MED).Montagud Montalvá, CI.; Corberán Salvador, JM.; Montero Reguera, ÁE.; Urchueguía Schölzel, JF. (2011). Analysis of the energy performance of a ground source heat pump system after five years of operation. Energy and Buildings. 43(12):3618-3626. https://doi.org/10.1016/j.enbuild.2011.09.036S36183626431

Efficiency improvement of a ground coupled heat pump system from energy management

The installed capacity of an air conditioning system is usually higher than the average cooling or heating demand along the year. So, most of the time, the system is working under its actual capacity. In this contribution, we study the way to improve the efficiency of a ground coupled heat pump air conditioning system by adapting its produced thermal energy to the actual thermal demand. For this purpose, an air conditioning system composed by a ground coupled heat pump and a central fan coil linked to an office located in a cooling dominated area was simulated, and a new management strategy aiming to diminish electrical consumption was developed under the basic constraint that comfort requirements are kept. This strategy takes advantage of the possibility of managing the air flow in the fan, the water mass flows in the internal and external hydraulic systems, and the set point temperature in the heat pump to achieve this objective. The electrical consumption of the system is calculated for the new management strategy and compared with the results obtained for a conventional one, resulting in estimated energy savings around 30%This work has been supported by the Spanish Government under projects "Modelado y simulacion de sistemas energeticos complejos" (2005 Ramon y Cajal program), "Modelado, simulacion y validacion experimental de la transferencia de calor en el entorno de la edificacion" (ENE2008-0059/CON). A. Sala is grateful to the financial support of grants DPI2008-06731-c02-01 (Spanish Government), and Generalitat Valenciana Prometeo/2008/088.Pardo García, N.; Montero Reguera, ÁE.; Sala Piqueras, A.; Martos Torres, J.; Urchueguía Schölzel, JF. (2011). Efficiency improvement of a ground coupled heat pump system from energy management. Applied Thermal Engineering. 31(2):391-398. https://doi.org/10.1016/j.applthermaleng.2010.09.016S39139831

Reasoning about discrete and continuous noisy sensors and effectors in dynamical systems

Among the many approaches for reasoning about degrees of belief in the presence of noisy sensing and acting, the logical account proposed by Bacchus, Halpern, and Levesque is perhaps the most expressive. While their formalism is quite general, it is restricted to fluents whose values are drawn from discrete finite domains, as opposed to the continuous domains seen in many robotic applications. In this work, we show how this limitation in that approach can be lifted. By dealing seamlessly with both discrete distributions and continuous densities within a rich theory of action, we provide a very general logical specification of how belief should change after acting and sensing in complex noisy domains.Comment: To appear in Artificial Intelligence 201

Crystal structure and mechanism of human lysine-specific demethylase-1

The reversible methylation of specific lysine residues in histone tails is crucial in epigenetic gene regulation. LSD1, the first known lysine-specific demethylase, selectively removes monomethyl and dimethyl, but not trimethyl modifications of Lys4 or Lys9 of histone-3. Here, we present the crystal structure of LSD1 at 2.9-Å resolution. LSD1 forms a highly asymmetric, closely packed domain structure from which a long helical 'tower' domain protrudes. The active site cavity is spacious enough to accommodate several residues of the histone tail substrate, but does not appear capable of recognizing the different methylation states of the substrate lysine. This supports the hypothesis that trimethylated lysine is chemically rather than sterically discriminated. We present a biochemical analysis of LSD1 mutants that identifies crucial residues in the active site cavity and shows the importance of the SWIRM and tower domains for catalysis

Structure Collisions between Interacting Proteins

Protein-protein interactions take place at defined binding interfaces. One protein may bind two or more proteins at different interfaces at the same time. So far it has been commonly accepted that non-overlapping interfaces allow a given protein to bind other proteins simultaneously while no collisions occur between the binding protein structures. To test this assumption, we performed a comprehensive analysis of structural protein interactions to detect potential collisions. Our results did not indicate cases of biologically relevant collisions in the Protein Data Bank of protein structures. However, we discovered a number of collisions that originate from alternative protein conformations or quaternary structures due to different experimental conditions