38,386 research outputs found
Understanding Nanopore Window Distortions in the Reversible Molecular Valve Zeolite RHO
Molecular valves are becoming popular for potential biomedical applications.
However, little is known concerning their performance in energy and
environmental areas. Zeolite RHO shows unique pore deformations upon changes in
hydration, cation siting, cation type, or temperature-pressure conditions. By
varying the level of distortion of double eight-rings, it is possible to
control the adsorption properties, which confer a molecular valve behavior to
this material. We have employed interatomic potentials-based simulations to
obtain a detailed atomistic view of the structural distortion mechanisms of
zeolite RHO, in contrast with the averaged and space group restricted
information provided by diffraction studies. We have modeled four
aluminosilicate structures, containing Li, Na, K, Ca, and
Sr cations. The distortions of the three different zeolite rings are
coupled, and the six- and eight-membered rings are largely flexible. A large
dependence on the polarizing power of the extra-framework cations and with the
loading of water has been found for the minimum aperture of the eight-membered
rings that control the nanovalve effect. The calculated energy barriers for
moving the cations across the eight-membered rings are very high, which
explains the experimentally observed slow kinetics of the phase transition as
well as the appearance of metastable phases
Enabling Disaster Resilient 4G Mobile Communication Networks
The 4G Long Term Evolution (LTE) is the cellular technology expected to
outperform the previous generations and to some extent revolutionize the
experience of the users by taking advantage of the most advanced radio access
techniques (i.e. OFDMA, SC-FDMA, MIMO). However, the strong dependencies
between user equipments (UEs), base stations (eNBs) and the Evolved Packet Core
(EPC) limit the flexibility, manageability and resiliency in such networks. In
case the communication links between UEs-eNB or eNB-EPC are disrupted, UEs are
in fact unable to communicate. In this article, we reshape the 4G mobile
network to move towards more virtual and distributed architectures for
improving disaster resilience, drastically reducing the dependency between UEs,
eNBs and EPC. The contribution of this work is twofold. We firstly present the
Flexible Management Entity (FME), a distributed entity which leverages on
virtualized EPC functionalities in 4G cellular systems. Second, we introduce a
simple and novel device-todevice (D2D) communication scheme allowing the UEs in
physical proximity to communicate directly without resorting to the
coordination with an eNB.Comment: Submitted to IEEE Communications Magazin
Modeling, Simulation and Emulation of Intelligent Domotic Environments
Intelligent Domotic Environments are a promising approach, based on semantic models and commercially off-the-shelf domotic technologies, to realize new intelligent buildings, but such complexity requires innovative design methodologies and tools for ensuring correctness. Suitable simulation and emulation approaches and tools must be adopted to allow designers to experiment with their ideas and to incrementally verify designed policies in a scenario where the environment is partly emulated and partly composed of real devices. This paper describes a framework, which exploits UML2.0 state diagrams for automatic generation of device simulators from ontology-based descriptions of domotic environments. The DogSim simulator may simulate a complete building automation system in software, or may be integrated in the Dog Gateway, allowing partial simulation of virtual devices alongside with real devices. Experiments on a real home show that the approach is feasible and can easily address both simulation and emulation requirement
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Simulating the mechanisms of serrated flow in interstitial alloys with atomic resolution over diffusive timescales.
The Portevin-Le Chatelier (PLC) effect is a phenomenon by which plastic slip in metallic materials becomes unstable, resulting in jerky flow and the onset of inhomogeneous deformation. The PLC effect is thought to be fundamentally caused by the dynamic interplay between dislocations and solute atoms. However, this interplay is almost always inaccessible experimentally due to the extremely fine length and time scales over which it occurs. In this paper, simulations of jerky flow in W-O interstitial solid solutions reveal three dynamic regimes emerging from the simulated strain rate-temperature space: one resembling standard solid solution strengthening, another one mimicking solute cloud formation, and a third one where dislocation/solute coevolution leads to jerky flow as a precursor of dynamic strain aging. The simulations are carried out in a stochastic framework that naturally captures rare events in a rigorous manner, providing atomistic resolution over diffusive time scales using no adjustable parameters
Ligand Binding, Protein Fluctuations, and Allosteric Free Energy
Although the importance of protein dynamics in protein function is generally
recognized, the role of protein fluctuations in allosteric effects scarcely has
been considered. To address this gap, the Kullback-Leibler divergence (Dx)
between protein conformational distributions before and after ligand binding
was proposed as a means of quantifying allosteric effects in proteins. Here,
previous applications of Dx to methods for analysis and simulation of proteins
are first reviewed, and their implications for understanding aspects of protein
function and protein evolution are discussed. Next, equations for Dx suggest
that k_{B}TDx should be interpreted as an allosteric free energy -- the free
energy associated with changing the ligand-free protein conformational
distribution to the ligand-bound conformational distribution. This
interpretation leads to a thermodynamic model of allosteric transitions that
unifies existing perspectives on the relation between ligand binding and
changes in protein conformational distributions. The definition of Dx is used
to explore some interesting mathematical relations among commonly recognized
thermodynamic and biophysical quantities, such as the total free energy change
upon ligand binding, and ligand-binding affinities for individual protein
conformations. These results represent the beginnings of a theoretical
framework for considering the full protein conformational distribution in
modeling allosteric transitions. Early applications of the framework have
produced results with implications both for methods for coarsed-grained
modeling of proteins, and for understanding the relation between ligand binding
and protein dynamics.Comment: 18 pages; 7 figures; Second International Congress of the
Biocomputing and Physics of Complex Systems Research Institute, Zaragoza,
Spain, 8-11 Feb 2006; increase breadth of review of methods for analysis of
allosteric mechanisms; Add AIP in press; fix missing kTs in equation
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